Paavai Institutions Department of IT

Paavai Institutions Department of IT

UNIT-1 1. 1

UNIT 1

INTRODUCTION

www.Vidyarthiplus.com



UNIT-1 1. 2

CONTENTS

1.1Mobile Communication

1.1.1 Guided Transmission

1.1.2 Unguided Wireless Transmission

1.1.3 Antennae

1.1.4 Modulation of wireless signals:

1.1.5 Multiplexing

1.1.6 Introduction to 2G and 3G Data Communication Standards

1.1.7 Introduction to WPANs and WLANs

1.2 Mobile computing

1.2.1 Ubiquitous computing

1.2.2 Pervasive Computing

1.2.3 Limitations to mobile computing

1.3 Mobile Computing Architecture

1.3.1 Functions of Operating System

1.3.2 Middleware for Mobile Systems

1.3.3 Mobile Computing Architectural Layer

1.3.4 Protocols

1.3.5 Mobile Computing system Layers

1.4 Mobile Devices

1.5 Mobile System Networks

1.6 Data Dissemination

1.6.1 Data Synchronization Example

1.7 Mo bility Management

1.8 Security

1.8.1 Cryptography

1.9 Introduction to Cellular systems

1.9.1 Cellular systems: technologies & subscribers




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1.10 GSM: Global System for Mobile Communication

1.10.1 GSM Architecture

1.10.2 GSM Services

1.10.3 GSM: Radio Technology

1.11 GPRS: General Packet Radio Service

1.11.1 GPRS – Architecture

1.11.2 GPRS: Channel Coding and Multiplexing

1.11.3 GPRS architecture and interfaces

1.11.4 GPRS Core Network Functions

1.11.5 GPRS: Protocol Stack

1.11.6 GPRS: Obtaining IP Connectivity

1.12 Question Bank




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TECHNICAL TERMS

1. Mobile Communication entails transmission of data to and from handheld devices. Two

or more communicating devices at least one is handheld or mobile. Location of the

device can vary either locally or globally.

2. Antennae are devices that transmit and receive electromagnetic signals.

3. Attenuation is the gradual loss in intensity of any kind of flux through a medium.

4. Co-channel Interference is, if two transmissions overlap in time.

5. Frequency division multiplexing (FDM) describes schemes to subdivide the frequency

dimension into several non-overlapping frequency bands

6. Guard Space is the space between the interference ranges.

7. Modulation is the process of varying one signal, called carrier, according to the pattern

provided by another signal

8. Multiplexing describes how several users can share a medium with minimum or no

interference.

9. Signals from a system transmit through a fiber, wire, or wireless medium. According to

defined regulations, recommended standards and protocols.

10. Code division multiple Access (CDMA) is an access method in which multiple users are

allotted different codes to access the same spread spectrum (set of frequencies) for

transmitting the symbols.




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1. INTRODUCTION

1.1 Mobile Communication Communication is a two-way transmission and reception of data streams. Signals for

Voice, data, or multimedia streams are transmitted. Signals are received by a receiver.

Signals from a system transmit through a fiber, wire, or wireless medium, according to

defined regulations, recommended standards and protocols.

Mobile Communication entails transmission of data to and from handheld devices. Two

or more communicating devices at least one is handheld or mobile. Location of the device can

vary either locally or globally. Communication takes place through a wireless, distributed, or

diversified network.

1.1.1 Guided Transmission

Metal wires and optical fibers are guided or wired transmission of data. Guided

transmission of electrical signals takes place using four types of cables are

1. Optical fiber for pulses of wavelength 1.35–1.5 µm

2. Coaxial cable for electrical signals of frequencies up to 500 MHz and up to a range of

about 40 m.

3. Twisted wire pairs ─ for conventional (without coding) electrical signals of up to 100

KHz and up to a range of 2 km, or for coded signals of frequencies up to 200 MHz and

a range of about 100 m.

4. Power lines, a relatively recent advent in communication technology─ used for long

range transmission of frequencies between 10 kHz and 525 kHz.

Guided Transmission Advantages

Here the transmission is along a directed path from one point to another. There is

practically no interference in transmission from any external source or path. Using multiplexing

and coding, a large number of signal-sources simultaneously transmitted along an optical fiber, a

coaxial cable, or a twisted-pair cable.




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Guided Transmission Disadvantages

Signal transmitter and receiver are fixed (immobile). Hence there is no mobility of

transmission and reception points. The number of transmitter and receiver systems limits the

total number of interconnections possible.

1.1.2 Unguided─ Wireless Transmission

Electrical signals transmitted by converting them into electromagnetic radiation.

Radiation transmitted via antennae that radiate electromagnetic signals. The electromagnetic

radiation are related by the classical formula

f = c/λ = (300/ λ) MHz [λ in meter].

The frequencies and wavelengths of transmitters for various ranges are as follows:

Long-wavelength radio, very low frequency (LW): 30 kHz to 1 MHz (10,000 to 300m)

Medium-wavelength radio, medium frequency (MW): 0.5 to 2 MHz (600 to 150m)

Short-wavelength radio, high frequency (SW): 6 to 30 MHz (50 to 10m)

FM Radio band frequency (FM): 87.5 to 108 MHz (3.4 to 2.8m)

Very high frequency (VHF): 50 to 250 MHz (6 to 1.2m)

Ultra high frequency (UHF): 200 to ~2000MHz (1.5 to 0.15m)

Super high microwave frequency (SHF): 2 to 40 GHz (~15 to 0.75cm)

Extreme High frequency (EHF): Above 40 GHz to 1014 Hz (0.75cm to 3 µm)

Far Infrared: Optical wavelengths between 1.0 µm to 2.0 µm and [(1.5 to 3) X 1014 Hz

(0.15-0.3 THz)]

Infrared: 0.90 µm to 0.85 µm in wavelength and ~(3.3 to 3.5) X 1014Hz [350 to 330

THz].

Visible Light: 0.70 µm to 0.40 µm in wavelength and ~ (4.3 to 7.5) X 1014 Hz (~430 to

750 THZ).

Ultraviolet: <0.40 µm in wavelength (>750 THz).

1.1.2.1 Advantages and Disadvantages of VHF and UHF

The Advantages and Disadvantages of VHF and UHF are listed below.




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1.1.3 Antennae

Antennae are devices that transmit and receive electromagnetic signals. Most function

efficiently for relatively narrow frequency ranges. If not properly tuned to the frequency band in

which the transmitting system connected to it operates, the transmitted or received signals may

be impaired. The forms of antennae are chiefly determined by the frequency ranges they operate

in and can vary from a single piece of wire to a parabolic dish.




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1.1.3.1 Radiation Pattern of Antenna:

The important feature of an antenna is

Signal amplitude at an instant is identical along the pattern.

Circular pattern means that radiated energy, and thus signal strength, is equally

distributed in all directions in the plane.

A pattern in which the signal strength is directed along a specific direction in the

plane.

/2 Dipole Antenna /4 Dipole Antenna

/4 Radiation pattern in y-z and x-z planes Directed Transmission Antenna Radiation

pattern in z-y and z-z planes

Same Antenna Radiation pattern in x-y Planes

Figure 1.1 Antenna Radiation Pattern in Planes




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1.1.3.2 Propagation of signals

The Wireless propagation of signals faces many complications. Mobile

communication renders reliable wireless transmission much more difficult than

communication between fixed antennae. The antenna height and size at mobile terminals

are generally quite small. The obstacles in the vicinity of the antenna have a significant

influence on the propagated signal. The propagation properties vary with place and, for a

mobile terminal, with time. Attenuation is the gradual loss in intensity of any kind of

flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are

attenuated by lead, and light and sound are attenuated by water.

1.1.3.2.1 Ranges for transmission, detection, and interference of signals

Transmission range:

Within a certain radius of the sender transmission is possible, i.e., a receiver

receives the signals with an error rate low enough to be able to communicate and can also

act as sender.

Detection range:

Within a second radius, detection of the transmission is possible, i.e., the

transmitted power is large enough to differ from background noise. However, the error

rate is too high to establish communication.

Interference range:

Within a third even larger radius, the sender may interfere with other transmission

by adding to the background noise. A receiver will not be able to detect the signals, but

the signals may disturb other signals.

Figure 1.2 Ranges for transmission, detection, and interference of signals




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The Signal strength

1. Decrease due to attenuation

2. When obstacles in the path of the signal greater in size than the wavelength of the

signal.

The propagation of signals is

Line of Sight is the transmission of signals without refraction, diffraction, or scattering in

between the transmitter and receiver.

Shadowing

Reflection at large obstacles

Refraction depending on the density of a medium

Scattering at small obstacles

Diffraction at edges

Figure 1.3 Propagation of signals

1.1.3.2.2 Multi-path Propagation

Signal can take many different paths between sender and receiver due to Reflection,

scattering, and diffraction

Time dispersion: signal is dispersed over time

Interference with “neighbor” symbols, Inter Symbol Interference (ISI)

The signal reaches a receiver directly and phase shifted

Distorted signal depending on the phases of the different parts




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Figure 1.3 Multi-path Propagation

1.1.4 Modulation of wireless signals:

The Sizes of antennae required for wireless transmission inversely proportional to the

frequencies. Voice signals frequencies between 0.1 kHz to 8 kHz and Music-signal frequencies

lie between 0.1 kHz to 16 kHz. These ranges are unsuitable for any kind of wireless

transmission. This is due to the requirement of abnormally large sized antennae as well as much

less radiated energy. Moreover, due to the signal properties medium (air or vacuum) such that

ultra low frequency signals cannot be transmitted across long distances.

Modulation:

The process of varying one signal, called carrier, according to the pattern provided by

another signal (modulating signal)

The carrier usually an analog signal selected to match the characteristics of a particular

transmission system.

The amplitude, frequency, or phase angle of a carrier wave is varied in proportion to the

variation in the amplitude variation of the modulating wave (message signal).

Makes wireless transmission practical

Increases the compatibility of transmitted signal and transmission medium

Equation for signal amplitude at an instant t, s(t)

s(t)=s0 sin [( ] where

s0 is the peak amplitude (amplitude varies between s0 and –s0)

is phase angle of the signal at t = 0 (a reference point with respect to

t is considered)

f is the signal frequency




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The Modulation of the voice or data signal is a technique by which fc or a set of carrier

frequencies used for wireless transmission such that peak amplitude, sc0, frequency, fc, Phase

angle varies with t in proportion to the peak amplitude of the modulating signal s(t). The

modulation is called Amplitude modulation (AM) if amplitude of carrier varied or Frequency

modulation (FM) if frequency varied or Phase modulation if phase angle varied.

Figure 1.4 Modulation in a transmitter

1.1.5 Multiplexing

Multiplexing is not only a fundamental mechanism in communication systems but also

in everyday life. Multiplexing describes how several users can share a medium with minimum or

no interference. One example is highways with several lanes. Many users (car drivers) use the

same medium (the highways) with hopefully no interference (i.e., accidents). This is possible due

to the provision of several lanes (space division multiplexing) separating the traffic.

1.1.5.1 Space division multiplexing

For wireless communication, multiplexing can be carried out in four dimensions: space,

time, frequency, and code. In this field, the task of multiplexing is to assign space, time,

frequency, and code to each communication channel with a minimum of interference and a

maximum of medium utilization. The term communication channel here only refers to an

association of sender(s) and receiver(s) who want to exchange data.

The figure 1.5 shows six channels ki and introduces a three dimensional coordinates

system. This system shows the dimensions of code c, time t and frequency f. For this first type of

multiplexing, space division multiplexing (SDM), the (three dimensional) space si is also

shown. Here space is represented via circles indicating the interference range as introduced in

figure 1.5.




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Figure 1.5 Space division multiplexing (SDM)

How is the separation of the different channels achieved? The channels k1 to k3 can

be mapped onto the three ‘spaces’ s1 to s3 which clearly separate the channels and prevent the

interference ranges from overlapping. The space between the interference ranges is sometimes

called guard space. Such a guard space is needed in all four multiplexing schemes presented.

For the remaining channels (k4 to k6) three additional spaces would be needed. In our

highway example this would imply that each driver had his or her own lane. Although this

procedure clearly represents a waste of space, this is exactly the principle used by the old analog

telephone system: each subscriber is given a separate pair of copper wires to the local exchange.

1.1.5.2 Frequency division multiplexing

Frequency division multiplexing (FDM) describes schemes to subdivide the frequency

dimension into several non-overlapping frequency bands as shown in figure 1.6. Each channel ki

is now allotted its own frequency band as indicated. Senders using a certain frequency band can

use this band continuously. Again, guard spaces are needed to avoid frequency band

overlapping (also called adjacent channel interference). This scheme is used for radio stations

within the same region, where each radio station has its own frequency. This very simple

multiplexing scheme does not need complex coordination between sender and receiver: the

receiver only has to tune in to the specific sender.




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Figure 1.6 Frequency division multiplexing (FDM)

However, this scheme also has disadvantages. While radio stations broadcast 24 hours a

day, mobile communication typically takes place for only a few minutes at a time. Assigning a

separate frequency for each possible communication scenario would be a tremendous waste of

(scarce) frequency resources. Additionally, the fixed assignment of a frequency to a sender

makes the scheme very inflexible and limits the number of senders.

1.1.5.3 Time division multiplexing

A more flexible multiplexing scheme for typical mobile communications is time division

multiplexing (TDM). Here a channel ki is given the whole bandwidth for a certain amount of

time, i.e., all senders use the same frequency but at different points in time (see figure 1.7).

Again, guard spaces, which now represent time gaps, have to separate the different periods

when the senders use the medium. In our highway example, this would refer to the gap between

two cars. If two transmissions overlap in time, this is called co-channel interference.

To avoid this type of interference, precise synchronization between different senders is

necessary. This is clearly a disadvantage, as all senders need precise clocks or, alternatively, a

way has to be found to distribute a synchronization signal to all senders. For a receiver tuning in

to a sender this does not just involve adjusting the frequency, but involves listening at exactly the

right point in time. However, this scheme is quite flexible as one can assign more sending time to

senders with a heavy load and less to those with a light load.




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Figure 1.7 Time division multiplexing (TDM)

Frequency and time division multiplexing can be combined, i.e., a channel ki can use a

certain frequency band for a certain amount of time as shown in figure 1.8. Now guard spaces

are needed both in the time and in the frequency dimension. This scheme is more robust against

frequency selective interference, i.e., interference in a certain small frequency band.

A channel may use this band only for a short period of time. Additionally, this scheme

provides some (weak) protection against tapping, as in this case the sequence of frequencies a

sender must be known to listen in to a channel. The mobile phone standard GSM uses this

combination of frequency and time division multiplexing for transmission between a mobile

phone and a so-called base station.

Figure 1.8 Frequency and time division multiplexing combined

A disadvantage of this scheme is again the necessary coordination between different

senders. One has to control the sequence of frequencies and the time of changing to another

frequency. Two senders will interfere as soon as they select the same frequency at the same time.




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However, if the frequency change (also called frequency hopping) is fast enough, the periods of

interference may be so small that, depending on the coding of data into signals, a receiver can

still recover the original data.

1.1.5.4 Code division multiplexing (CDM)

Code division multiplexing is by using a wide range of frequencies, called spread

spectrum. Spread spectrum has distinct set of equally separated frequencies. Different source

transmitting signals along identical path in the same time slices transmits using spread spectrum

frequencies using distinct codes.

Figure 1.9 Code division multiplexing (CDM)

Figure 1.9 shows how all channels ki use the same frequency at the same time for

transmission. Separation is now achieved by assigning each channel its own ‘code’, guard

spaces are realized by using codes with the necessary ‘distance’ in code space, e.g., orthogonal

codes. The typical everyday example of CDM is a party with many participants from different

countries around the world, who establish communication channels, i.e., they talk to each other,

using the same frequency range at the same time. If everybody speaks the same language, SDM

is needed to be able to communicate. But as soon as another code, i.e., another language, is used,

one can tune in to this language and clearly separate communication in this language from all the

other languages.




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The main advantage of CDM for wireless transmission is that it gives good protection

against interference and tapping. Different codes have to be assigned, but code space is huge

compared to the frequency space.

The main disadvantage of this scheme is the relatively high complexity of the receiver.

A receiver has to know the code and must separate the channel with user data from the

background noise composed of other signals and environmental noise. Additionally, a receiver

must be precisely synchronized with the transmitter to apply the decoding correctly. The voice

example also gives a hint to another problem of CDM receivers. All signals should reach a

receiver with almost equal strength; otherwise some signals could drain others.

1.1.6 Introduction to 2G and 3G Data Communication Standards

First generation wireless devices only voice signals

Second generation (2G) devices communicate voice as well as data signals have

data rates of up to 14.4 kbps

The 2.5G and 2.5G+ are enhancements of the second generation and sport data

rates up to 100 kbps

Third generation (3G) mobile devices communication.

Higher data rates than 2G and support voice, data, and multimedia streams.

Facilitates data rates of 2 Mbps.

Higher for short distances.

384 kbps for long distance transmissions.

Enable transfer of video clips and faster multimedia communication

1.1.6.1 GSM and CDMA based Standards

The GSM and CDMA based Standards are mentioned in the below figure.




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Figure 1.10 GSM and CDMA based Standards

1.1.6.2 GSM standards

A set of standards and protocols for mobile telecommunication.

A global system for mobile (GSM) was developed by the Groupe Spéciale Mobile

(GSM)

Founded in Europe in 1982

Support cellular networks

1.1.6.3 GSM 900

GMSK modulation

FDMA for 124 up channels and 124 down channels

890-915 MHz for uplink and 935-960MHz

Channel of bandwidth 200 kHz

8 radio-carrier analog-signals TDMA for user access in each deployed channel

Users time-slices of 577 µs each

Data rates are up to 14.4 kbps

1.1.6.4 EGSM (Extended Global System for Mobile communication)

An additional spectrum of 10 MHz on both uplink and downlink channels




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1.1.6.5 EGSM 900/1800/1900 MHz tri-band

An additional spectrum of 10 MHz on both uplink and downlink channels

GSM 1800 1710–1785 MHz for uplink and 1805–1880 MHz for downlink

GSM 1900 1850–1910 MHz for uplink and 1930–1990 MHz for downlink

1.1.6.6 GPRS (General Packet Radio Service) ─GSM 2G+ (2.5G)

Packet-oriented service for data communication of mobile devices

Utilizes the unused channels in the TDMA mode in a GSM network

1.1.6.7 EDGE (Enhanced Data rates for GSM Evolution)

An enhancement GSM Phase 2.5G+]

8 PSK communication to achieve higher rates of up to 48 kbps per 200 kHz channel

High compares to up to 14.4 kbps in GSM.

Using coding techniques the rate can be enhanced to 384 kbps for the same 200 kHz

channel.

1.1.6.8 EGPRS and HSCSD

EGPRS is enhanced general packet radio service is an extension of GPRS using 8PSK

(phase shift keying) modulation

Enhances the data rate EGPRS based on EDGE

Used for HSCSD (high speed circuit switched data)

1.1.6.9 CDMA

Evolution of CDMA from 2.5G in 1991 as CDMAOne (IS-95)

CDMA supports high data rates in 3G.

Voice as well as data and multimedia streams.

CDMA 2000, IMT-2000, WCDMA and UMTS and support cellular networks

1.1.6.10 CDMAOne

Founded in 1991,QUALCOM, USA

Belongs to 2G+IS-95 (interim standards 95) and operates at 824–849 MHz and 869–

894MHz.

CDMA channel transmits analog signals from multiple sources and users




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1.1.6.11 WCDMA

Supports asynchronous operations

10 ms frame length with 15 slices.

Smaller end-to-end delay in the 10 ms frame as compared to 20, 40, or 80 ms frames

Each frame length is modulated by QPSK both for uplink and downlink

1.1.6.12 WCDMA

DSSS CDMA

Supports a 3.84 Mbps chipping rate

Both short and long scrambling codes are supported, but for uplink only

3G partnership project (3GPP)

1.1.6.13 CDMA2000 and CDMA 2000 1x (3GPP2)

For voice communication, Circuit as well as packet switched communication.

Packet transmission uses Internet protocol (IP) for transmitting Multimedia and real time

multimedia applications

1.1.6.14 UMTS (Universal Mobile Telecommunication System)

Supports both 3GPP (3G partnership project) and 3GPP2

Communicates at data rates of 100 kbps to 2 Mbps

1.1.6.15 CDMA2000 and CDMA 2000 1x

Chipping rates are in multiples of fs = 1.2288 Mbps

3G IMT 2000 carrier frequency fc0 = 2GHz

Included in UMTS

CDMA 2000 1x fs = 1.2288 Mbps

Also backward compatible to 2.5G CDMAOne IS-95

1.1.7 Introduction to WPANs and WLANs

Wireless personal area network using Bluetooth, ZigBee, or IrDA protocols




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Figure 1.11 WPAN

1.1.7.1 Bluetooth IEEE 802.15.1

WPAN standard operates at a frequency of 2.4 GHz radio spectrum which is identical to

that of the IEEE 802.11b WLAN standard.

Bluetooth provides short distance (1 m to 100 m range as per the radio spectrum) mobile

communication

Data rates between the wireless electronic devices are up to 1 Mbps.

Works between the mobile phone handset and headset for hands-free talking

Works between the computer and printer, or Computer and mobile phone handset.

Enables user mobility in a short space with other Bluetooth enabled devices or computers

in the vicinity

Uses FHSS (frequency hopping spread spectrum)

Facilitates object exchanges

Object can be a file, address book, or presentation

1.1.7.2 ZigBee WPAN standard IEEE 802.15.4

Lower stack size (28 KB) in the protocol

Lower network-joining latency when compared to Bluetooth (250 KB).

For Low transmitting power systems

Interoperable standard based on RF wireless communication

Expected to provide large-scale automation and the remote controls up to a range of 70 m

Data rates of 250 kbps, 40 kbps, and 20 kbps at the spectra of 2.4 GHz, 902 MHz to 928

MHz, and 868 MHz to 870 MHz, respectively




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Uses DSSS

Designed for robotic control, industrial, home, and monitoring applications.

Some of the Applications are

ZigBee enabled electric meter communicates electricity consumption data to the

mobile meter reader

A ZigBee enabled home security system alerts the mobile user of any security

breach at the home.

1.1.7.3 IrDA (infrared Data Association) 1.0

Protocol for data rates up to 115 kbps

IrDA 1.1 supports data rates of 1.152 Mbps to 4 Mbps

1.1.7.4 WLAN and Internet Access

IEEE 802.11a, 802.11b, and 802.11g standards

WLAN also called Wi-Fi (Wireless Fidelity).

Mobile communication using an 802.11 WLAN standard

Figure 1.12 WLAN

1.1.7.4.1 IEEE 802.11 based standards for WLANs

802.11a─ MAC layer operations such that multiple physical layers in 5 GHz (infrared,

two 2.4 GHz physical layers)

Infrastructure based architecture as well as Mobile ad hoc network (MANET) based

architecture.

Modulation is OFDM at data rates of 6 Mbps, 9 Mbps.

Data rates supported are from 54 kbps to a few Mbps.




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In 802.11a, MAC layer operations such that multiple physical layers in 5 GHz (infrared,

two 2.4 GHz physical layers)

Infrastructure based architecture as well as Mobile ad hoc network (MANET) based

architecture.

802.11a

o OFDM at data rates of 6 Mbps, 9 Mbps

o Data rates supported are from 54 kbps to a few Mbps

802.11b

o 54 Mbps and at 2.4 GHz.

o Modulation DSSS /FHSS

o Supports short-distance wireless networks using Bluetooth (IEEE 802.15.1) based

applications and the HIPERLAN2 (HIPERformance LAN 2)

o OFDMA physical layer

o Provides protected Wi-Fi access.

o The data rates are 1 Mbps (Bluetooth), 2Mbps, 5.5 Mbps, 11 Mbps, and 54 Mbps

(HIPERLAN 2).

802.11g

o Operates at 54 Mbps and at 2.4 GHz

o Used for many new Bluetooth applications

o Compatible to 802.11b

o Uses DSSS in place of OFDMA

802.11i

o Provides the AES and DES security standards

WiMax (worldwide interoperability for microwave access) IEEE 802.16

o New generation innovative technology

o Delivers high-speed, broadband, fixed, and mobile services wirelessly to large

areas with much less infrastructure.

WAP (wireless application protocol)

o Provides the web contents to small-area display devices in mobile phones




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o Service providers format contents in the WAP format

I-Mode (internet in mobile mode)

o Developed by NTT Do Como, Japan

o Very popular wireless Internet service for mobile phones

1.2 Mobile computing The process of computation on a mobile device

In mobile computing, a set of distributed computing systems or service provider servers

participate, connect, and synchronize through mobile communication protocols.

Mobile computing as a generic term describing ability to use the technology to wirelessly

connect to and use centrally located information and/or application software through the

application of small, portable, and wireless computing and communication devices.

Provides decentralized (distributed) computations on diversified devices, systems, and

networks, which are mobile, synchronized, and interconnected via mobile communication

standards and protocols.

Mobile device does not restrict itself to just one application, such as, voice

communication.

Offers mobility with computing power.

Facilitates a large number of applications on a single device

1.2.1 Ubiquitous computing

Refers to the blending of computing devices with environmental objects

A term that describes integration of computers into practically all objects in our everyday

environment, endowing them with computing abilities

Based on pervasive computing

1.2.2 Pervasive Computing

Pervasive means ‘existing in all parts of a place or thing’.




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Pervasive computing─ The next generation of computing which takes into account the

environment in which information and communication technology is used everywhere,

by everyone, and at all times.

Assumes information and communication technology to be an integrated part of all facets

of our environment, such as toys, computers, cars, homes, factories, and work-areas

Takes into account the use of the integrated processors, sensors, and actuators connected

through high-speed networks and combined with new devices for viewing and display.

Mobile Computing is also called pervasive computing when a set of computing devices,

systems, or networks have the characteristics of transparency, application-aware

adaptation, and have an environment sensing ability

Pervasive computing devices are not PCs, are handheld, very tiny, or even invisible

devices which are either mobile or embedded in almost any type of object.

1.2.3 Limitations to mobile computing

Resource constraints: Battery

Interference: the quality of service (QoS)

Bandwidth: connection latency

Dynamic changes in communication environment: variations in signal power within a

region, thus link delays and connection losses

Network Issues: discovery of the connection-service to destination and connection

stability

Interoperability issues: the varying protocol standards

Security constraints: Protocols conserving privacy of communication

1.3 Mobile Computing Architecture Programming languages used for mobile system software. Operating system functions to

run the software components onto the hardware. Middleware components deployment Layered

structure arrangement of mobile computing components. Protocols and layers used for

transmission and reception.




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Some of the Programming Languages are Java, J2SE, J2ME (Java2 Micro edition), Java

Card (Java for smart card. The Java enterprise edition (J2EE) used for web and enterprise server

based applications of mobile services C and C++, Visual C++, Visual Basic.

1.3.1 Functions of Operating System

Operating Systems are Symbian OS, Window CE, Mac OS. It offers the user to run an

application without considering the hardware specifications and functionalities. It provides

functions which are used for scheduling the multiple tasks in a system. It provides the functions

required for the synchronization of multiple tasks in the system and multiple threads

synchronization and priority allocation.

Management functions (such as creation, activation, deletion, suspension, and delay) for

tasks and memory. It provides Interfaces for communication between software components at the

application layer, middleware layers, and hardware devices. It facilitates execution of software

components on diversified hardware. It provides Configurable libraries for the GUI (graphic user

interface) in the device. It Provides User application’s GUIs, VUI (voice user interface)

components, and phone API.

1.3.2 Middleware for Mobile Systems

Middleware are the software components that link the application components with the

network-distributed components.

Examples of Middleware Applications are:

To discover the nearby device such as Bluetooth

To discover the nearby hot spot.

To achieving device synchronization with the server or an enterprise server

For retrieving data (which may be in Oracle or DB2) from a network database

For service discovery at network

For adaptation of the application to the platform and service availability

1.3.3 Mobile Computing Architectural Layer

The Mobile Computing Architectural Layer is illustrated in the figure below.




UNIT-1 1. 27

Figure 1.13 Mobile Computing Architectural Layer

1.3.4 Protocols

Some of the protocols are WAP, GSM 900, GSM900/1800/1900, UMTS, and I-Mode.

Some of the WPAN protocols are Bluetooth, IrDA, and Zigbee. Some of the WLAN protocols

802.11a and 802.11b.

1.3.5 Mobile Computing system Layers

1. Physical for sending and receiving signals (for example, TDMA or CDMA coding)

2. Data-link (for example, multiplexing)

3. Networking (for linking to the destination)

4. Wireless transport layer security (for establishing end-to-end connectivity)

5. Wireless transaction protocol

6. Wireless session protocol

7. Wireless application environment (Running a web application, for e.g., mobile e-

business).




UNIT-1 1. 28

1.5 Mobile Devices

A mobile device (also known as a handheld device, handheld computer or simply

handheld) is a small, hand-held computing device, typically having a display screen with touch

input and/or a miniature keyboard and weighing less than 2 pounds (0.91 kg). Apple, HTC, LG,

Motorola, Research in Motion (RIM), and Samsung are just a few examples of the many

manufacturers that produce these types of devices.

A handheld computing device has an operating system (OS), and can run various types of

application software, known as apps. Most hand held devices can also be equipped with WI-FI,

Bluetooth and GPS capabilities that can allow connections to the Internet and other Bluetooth

capable devices such as an automobile or a microphone headset. A camera or media player

feature for video or music files can also be typically found on these devices along with a stable

battery power source such as a lithium battery.

Early pocket sized ones were joined in the late 2000s by larger but otherwise similar

tablet computers. As in a personal digital assistant (PDA), the input and output are often

combined into a touch-screen interface.

Smart phones and PDAs are popular amongst those who wish to use some of the powers

of a conventional computer in environments where carrying one would not be practical.

Enterprise digital assistants can further extend the available functionality for the business user by

offering integrated data capture devices like barcode, RFID and smart card readers

1.5 Mobile System Networks • Cellular networks

A cell is the coverage area of a base station, connected to other stations via wire

or fiber or wirelessly through switching centers. Each cell base station functions as an

access point for the mobile service. Each mobile device connects to the base station of the

cell which covers the current location of the device. All the mobile devices within the

range of a given base station communicate with each other through that base station only.




UNIT-1 1. 29

Figure 1.14 Cellular Networks

• WLAN networks and Mobile IP:

For connectivity between the Internets, two LANs, mobile devices, and computers

are needed. Mobile device connects to an access point, called a hot spot. The access

point, in turn, connects to a host LAN which links up to the Internet through a router.

Mobile IP is an open standard based on the IP (internet protocol). Mobile IP network

provides the mobile IP service using home agents and foreign agents.

Figure 1.15 Communication between mobile devices using a WLAN network through hot-

spots.




UNIT-1 1. 30

• Ad Hoc Networks:

The nodes, mobile nodes, and sensor nodes communicate among themselves

using a base station. The base stations function as gateways. The ad hoc networks

deployed for routing, target detection, service discovery, and other needs in a mobile

environment.

Figure 1.16 Communication of mobile nodes and Sensor nodes using a base station as a

gateway.

1.6 Data Dissemination Mobile phone also acts as a data access device for obtaining information from the service

provider’s server. Smart phones in enterprise networks work as enterprise data access devices.

An enterprise server disseminating the data to the enterprise mobile device iPhone is a data

access device for accessing music or video. The data links up to download files which can then

be saved and played. Students also use the iPhone for replaying faculty lectures and retrieving e-

learning material disseminated from University server.




UNIT-1 1. 31

Figure 1.17 Data dissemination by servers through base stations and access points

1.6.1 Data Synchronization Example

A new popular ringtone added to one of the servers of a mobile service provider. Data

synchronization means that all the servers of the service provider get identical sets of ringtones.

All the devices connected to the server should be updated about the availability of any new data.

Ringtone databases available to all the mobile phones include a copy of the title of that tone.

Some of the Data Synchronization is One to One Synchronization, One to Many

Synchronization, Many to Many Synchronization. Data synchronization paths in a mobile

network in illustrated in the figure 1.18.

1.7 Mobility Management Mobility Management means maintaining uninterrupted (seamless) signal connectivity

when a mobile device changes location from within a cell Ci or network Ni to a cell Cj or

network Nj in figure 1.19. The Infrastructure management for installation and maintenance of the

infrastructure that connects cell Ci to Cj or network Ni to Nj. Location management and

registration management by handoff for cell transfer when a mobile device’s connection with the

ith cell is transferred.




UNIT-1 1. 32

Figure 1.18 Data synchronization paths in a mobile network

Figure 1.19 Mobility Management

1.8 Security Security is important for maintaining privacy and for mobile e-business transactions.

Wireless security mechanisms for providing security of the data transmitted from one end point

to another. It provides for wire-equivalent privacy and non-repudiation when some data sent to

an end-point. No denial of service to authenticated object(s). A serving station authenticated

before it can provide service to mobile devices.




UNIT-1 1. 33

Figure 1.20 Authentication method of security in case of GSM

1.8.1 Cryptography

Cryptography is to keep private information from getting into the hands of unauthorized

agents. Encryption is the transformation of data into coded formats. Encrypted data decrypted

(transformed back to an intelligible form) at its destination.

1.8.1.1 Cryptography Algorithms

It is used for encryption and decryption of transmitted data. It enables the receiver and the

sender to authenticate data. Discover if data security has been compromised during transmission

Use a secret key, to encrypt data into secret codes for transmission. RSA (Rivest, Shamir, and

Adleman) algorithm is a cryptography algorithm used for private key generation. Cryptography

Algorithms is classified into two categories; symmetric and asymmetric. It is used to create a

hash of the message or a MAC (message authentication).

1.8.1.2 Hash function

Hash function is used to create a small digital fingerprint of the data to be transmitted.

Fingerprint is called the hash value, hash sum, or, simply, hash. Hash of the message is a set of

bits obtained after applying the hash algorithm (or function). This set of bits alters in case the

data is modifies during transmission code) Message authentication codes (MAC). It is also used

to authenticate messages during transmission.

The MAC of a message created using a cryptographic MAC function which is similar to

the hash function but has different security requirements. The receiver reviews the hash or the

MAC of the received message and returns it to the sender. Exchange enables the sender and the




UNIT-1 1. 34

receiver to find out if the message has been tampered with and thus helps verify message

integrity and authenticity.

1.8.1.3 Data encryption standard (DES)

DES uses 56-bits for a key plus 8 bits for parity. Block length 64 bit. [Maximum block

size = 264 bits

1.8.1.4 Triple DES

Triple DES an enhance version of DES. Multiple encryptions or encryption-decryption-

encryption steps in the cryptic message are a different key at each step for cryptic message

creation.

1.8.1.5 Advanced encryption standard (AES)

There are nine possible combinations of key lengths and block lengths. The key-length

can be 128, 192, or 256 bits. The block lengths can also be 128, 192, or 256 bits. Block length of

128 bits means maximum block length = 2128 bits.

1.8.1.6 RSA─ The Asymmetric key based standard

The RSA (Rivest, Shamir, Alderman) algorithm uses 128, 256, 512, or 1024 bit prime

numbers for encryption

1.8.1.7 DSA (digital signature algorithm)

DSA is used to sign a record before transmitting. DSA provides for a variable key length

of maximum 512 or 1024 bits

1.8.1.8 DSS (digital signature standard)

DSS is based on the DSA. Signature enables identification of the sender, identifies the

origin of the message, and checks the message integrity.

1.8.1.9 Digital certificate

An electronic certificate used to establish the credentials of a data set. Issued by a

certification authority and contains the certificate holder's name, a copy of the certificate holder's

public key, a serial number, and expiration dates. It includes the digital signature of the

certificate-issuing authority for verification of the authenticity of the certificate. The certification

authority distributes a digital certificate, which binds a public key to a specific sender.




UNIT-1 1. 35

1.9 Introduction to Cellular systems: Geographic region is subdivided in radio cells. Base Station provides radio connectivity

to Mobile Station within cell. Handover to neighboring base station when necessary. Base

Stations connected by some networking infrastructure.

Figure 1.21 Cellular Networks

1.9.1 Cellular systems: technologies & subscribers

The usage of cellular systems is represented in graph as shown below.

Figure 1.22 Cellular systems: technologies & subscribers

1.10 GSM: Global System for Mobile Communication GSM is a set of standards and protocols for mobile telecommunication. A global system for

mobile (GSM) was developed by the Groupe Spéciale Mobile (GSM) and it was founded in

Europe in 1982. It supports cellular networks.




UNIT-1 1. 36

History:

• 2nd Generation of Mobile Telephony Networks

• 1982: Groupe Spèciale Mobile (GSM) founded

• 1987: First Standards defined

• 1991: Global System for Mobile Communication, Standardization by ETSI (European

Telecommunications Standardization Institute) - First European Standard

• 1995: Fully in Operation

Today:

• Deployed in more than 184 countries in Asia, Africa, Europe, Australia, America)

• More than 747 million subscribers

• More than 70% of all digital mobile phones use GSM

• Over 10 billion SMS per month in Germany, > 360 billion/year worldwide

1.10.1 GSM Architecture:

Components:

• BTS: Base Transceiver Station

• BSC: Base Station Controller

• MSC: Mobile Switching Center

• HLR/VLR: Home/Visitor Location Register

• AuC: Authentication Center

• EIR: Equipment Identity Register

• OMC: Operation and Maintenance Center

Transmission:

• Circuit switched transfer

• Radio link capacity: 9.6 kb/s (FDMA/TDMA)

• Duration based charging




UNIT-1 1. 37

Figure 1.23 GSM Architecture

1.10.2 GSM Services

‘Traditional’ voice services

voice telephony:

The primary goal of GSM was to enable mobile telephony offering the traditional

bandwidth of 3.1 kHz

Emergency number:

Common number throughout Europe (112); mandatory for all service providers;

free of charge; connection with the highest priority (preemption of other connections

possible)

Multi-numbering:

Several ISDN phone numbers per user possible

Voice mailbox (implemented in the fixed network supporting the mobile terminals)

Supplementary services, e.g.: identification, call forwarding, number suppression,

conferencing

‘Non-Voice’ Services (examples)

• Fax Transmissions




UNIT-1 1. 38

• Electronic mail (MHS, Message Handling System, implemented in the fixed network)

• Short Message Service (SMS):

Alphanumeric data transmission to/from the mobile terminal using the signaling

channel, thus allowing simultaneous use of basic services and SMS.

1.10.3 GSM: Radio Technology

Cellular Concept:

The segmentation of geographical area into divided cells. Cell sizes vary from some 100

m up to 35 km depending on user density, geography, transceiver power etc. The hexagonal

shape of cells is idealized (cells overlap, shapes depend on geography). The use of several carrier

frequencies avoids same frequency in adjoining cells. If a mobile user changes cells, handover of

the connection to the neighbor cell takes place.

1.11 GPRS: General Packet Radio Service GRS is Packet Switched Extension of GSM. In 1996, new standard developed by ETSI

Components are integrated in GSM architecture.

Some of the Improvements are:

Packet-switched transmission

Higher transmission rates on radio link (multiple time-slots)

Volume based charging ‚Always ON‘ mode possible

Operation started in 2001 (Germany)

1.11.1 GPRS – Architecture

Components:

• CCU: Channel Coding Unit

• PCU: Packet Control Unit

• SGSN: Serving GPRS Support Node

• GGSN: Gateway GPRS Support Node

• GR: GPRS Register




UNIT-1 1. 39

Transmission:

• Packet Based Transmission

• Radio link:

Radio transmission identical to GSM

Different coding schemes (CS1-4)

Use of Multiple Time Slots

On-demand allocation of time-slots

• Volume Based Charging

Figure 1.24 GPRS – Architecture

1.11.2 GPRS: Channel Coding and Multiplexing

Figure 1.25 GPRS: Channel Coding and Multiplexing




UNIT-1 1. 40

1.11.3 GPRS architecture and interfaces

Figure 1.26 GPRS architecture and interfaces

1.11.4 GPRS Core Network Functions

The GPRS Core Network Functions are shown in the figure below.

Figure 1.27 GPRS Core Network Functions




UNIT-1 1. 41

1.11.5 GPRS: Protocol Stack

The Protocol Stack of GRRS is illustrated below.

Figure 1.28 GPRS: Protocol Stack

1.11.6 GPRS: Obtaining IP Connectivity

The IP Connectivity process in GPRS is shown in the below diagram.

Figure 1.29 GPRS: Obtaining IP Connectivity




UNIT-1 1. 42

1.12 QUESTION BANK PART – A (2MARKS)

1 .What is the 3 fundamental propagation behaviors depending on their frequency?

2. What is multipath propagation?

3. What is guard space?

4. What are all the different basic schemes in analog modulation?

5. What is the use of Phase Lock Loop (PLL)?

6. What is hopping sequence?

7. What is dwell time?

8. What are the advantages of cellular systems?

9. What is browsing channel allocation and fixed channel allocation?

10. What are the disadvantages of cellular systems?

11. What is digital sense multiple access?

12. What is Network and Switching subsystem?

13. What is authentication centre?

14. What is called burst and normal burst?

15. What are the basic groups of logical channels?

16. Define traffic multiframe and control multiframe?

17. What is OVSF?

18. Specify the steps perform during the search for a cell after power on?

19. Explain about transparent mode?

20. What are the basic classes of handovers?




UNIT-1 1. 43

PART – B (16 MARKS)

1. Discuss briefly the multiplexing techniques.

2. Explain about the signal propagation.

3. Discuss about the cellular system.

4. List the difference between S/T/F/CDMA.

5. What is spread spectrum with its types.

6. Explain about the TDMA.

7. Why CDMA is needed and explain it with an example?

8. Why do MAC scheme in wired network fail in wireless networks and how does the multiple

access with collision avoidance (MACA) scheme work.

9. Define modulation and explain the method for analog modulation techniques in details.

10. Discuss briefly the code division multiplexing techniques.

11. Discuss briefly the advanced phase shift keying.




UNIT-2 2. 1

UNIT 2

WIRELESS MEDIUM ACCESS CONTROL




UNIT-2 2. 2

CONTENTS

2.1 Interference in cellular system

2.2 Frequency management

2.3 Channel Assignment

2.4 Location management in cellular networks

2.4.1 Mobility Management

2.5 Medium Access Control (MAC)

2.5.1 Preamble

2.5.2 Header

2.5.3 CRC

2.5.4 Inter Frame Gap

2.5.5 Byte Order

2.5.6 CSMA /CD

2.5.7 Receiver Processing Algorithm

2.5.8 Runt Frame

2.5.9 Giant Frame

2.5.10 Jumbo Frame

2.5.11 Misaligned Frame

2.5.12 Other Issues

2.6 Introduction to CDMA based systems

2.6.1 Spread Spectrum in CDMA systems

2.6.2 Three Types of Spread Spectrum Communications

2.6.3 Direct Sequence Spread Spectrum

2.7 Coding Methods in CDMA

2.7.1 Input data

2.7.2 Generating Pseudo-Random Codes

2.7.3 Pseudo-Noise Spreading

2.7.4 Transmitting Data

2.7.5 Working with Complex Data




UNIT-2 2. 3

2.7.6 Summing Many Channels Together

2.7.7 Receiving Data

2.8 Question Bank




UNIT-2 2. 4

TECHNICAL TERMS

1. Cellular System: In a Cellular System, a cell is the coverage area of a base station,

connected to other stations via wire or fiber or wirelessly through switching centers.

2. Interference is anything which alters, modifies, or disrupts a signal as it travels along a

channel between a source and a receiver.

3. Interface is a tool and concept that refers to a point of interaction between components,

and is applicable at the level of both hardware and software.

4. Beacon contains a timestamp and other management information used for power

management and roaming. e.g., identification of the base station subsystem (BSS)

5. Frequency Management The requesting, recording, deconfliction of and issuance of

authorization to use frequencies (operate electromagnetic spectrum dependent systems)

coupled with monitoring and interference resolution processes.

6. Mobile terminals (MT) are platforms that allow the broadcasting of television programs

with their multimedia content and for the digital transmission of data and communication

based on Internet Protocol. These include cellular phones, portable digital players,

computer tablets, wireless game consoles, etc. They are by definition digital since they

are used to send and receive data

7. Location Management locates MTs with the main purposes to deliver incoming calls to

them at a reasonable cost.

8. Handover: The term handover or handoff refers to the process of transferring an ongoing

call or data session from one channel connected to the core network to another.

9. Handoff or Handover Management transfers ongoing calls to adjacent cells as a MT

moves from one access point in the network to another

10. Medium Access Control (MAC): data communication protocol is a sub layer of the data

link layer, which itself is layer 2. The MAC sub layer provides addressing and channel

access control mechanisms that make it possible for several terminals or network nodes

to communicate within a multiple access network that incorporates a shared medium,

e.g. Ethernet. It is also referred to as a medium access controller.




UNIT-2 2. 5

11. Polling Cycle is the process which is done by the network when a call arrives to a MT,

The network send Polling signal to target cell in the Residing area and wait for response.

12. Spread Spectrum has distinct set of equally separated frequencies.

13. Subscriber is the term used to refer to a person that has an account with a mobile

network carrier. They are called such because they subscribe to the carrier's mobile phone

services.




UNIT-2 2. 6

2. WIRELESS MEDIUM ACCESS CONTROL

2.1 Interference in cellular system As wireless systems proliferate worldwide, the number one enemy of wireless systems

designers and service providers is signal interference. Interference hampers coverage and

capacity, and limits the effectiveness of both new and existing systems. It is an unavoidable fact

that wireless communications systems must coexist in extremely complicated signal

environments. These environments are comprised of multiple operating wireless networks

ranging from mobile communication services to specialized mobile radio and paging/broadcast

systems. At the same time, wireless local area networks (WLANs) and digital video broadcasting

are introducing new technologies and signal sources that further threaten to disrupt wireless

communications service.

Compounding the problem are regulatory and environmental restrictions which have

effectively limited the number of suitable new base station transceiver sites that can be put in

place. Hence, many wireless service providers are now faced with co-location issues further

contributing to the potential for signal interference as more antennae are placed on individual cell

towers. This application note presents the subject of interference and its degrading effects on the

performance of wireless networks. It provides a brief theory of operation of communications

receivers and antennae, as well as instructions on how to locate and identify an interfering signal.

It also reviews the operating principles of the Anritsu Spectrum Master MS2711B and some of

its functional routines which make it an ideal interference troubleshooting tool.

Interference:

Interference is, anything which alters, modifies, or disrupts a message as it travels along a channel

Electromagnetic interference (EMI)

Co-channel interference (CCI), also known as crosstalk

Adjacent-channel interference (ACI), interference caused by extraneous power from a signal

in an adjacent channel




UNIT-2 2. 7

Intersymbol interference (ISI), distortion of a signal in which one symbol interferes with

subsequent symbols

Inter-carrier interference (ICI), caused by doppler shift in OFDM modulation

2.2 Frequency management Unlike a traditional client-server network, a mobile computing environment has a

very limited bandwidth in a wireless link.

Thus, one design goal of caching management in a mobile computing

environment is to reduce the use of wireless links.

Quota data and private data mechanisms are used in our design so that an MU

user is able to query and update data from the local DBMS without cache

coherence problems.

The effect of the two mechanisms is to increase the hit ratio. An agent on an MU

along with a program on a base station are used to handle the caching

management, including prefetching/hoarding, cache use, cache replacement, and

cache-miss handling.

The simulation results clearly indicate that our approaches are improvements to

the previous research.

2.3 Channel Assignment

Frequency allocation should be carefully planned to avoid degradation caused by

co-channel interference

Fixed channel assignment, dynamic channel assignment, and hybrid channel

assignment are the types of channel assignment.

Classification of channel assignment are

1. Fixed Channel Assignment

2. Dynamic Channel Assignment

3. Hybrid Channel Assignment

4. FCA with Borrowing




UNIT-2 2. 8

5. Directed Retry

6. Load Sharing

Figure 2.1 Interference among cells

Figure 2.2 Interference of neighboring radio channels.

2.4 Location management in cellular networks 2.4.1 Mobility Management

In wireless networks, efficient management of mobility is a crucial issue to support

mobile users. The Mobile Internet Protocol (MIP) has been proposed to support global mobility

in IP networks. Several mobility management strategies have been proposed which aim reducing

the signaling traffic related to the Mobile Terminals (MTs) registration with the Home Agents

(HAs) whenever their Care-of-Addresses (CoAs) change. They use different Foreign Agents

(FAs) and Gateway FAs (GFAs) hierarchies to concentrate the registration processes.

For high-mobility MTs, the Hierarchical MIP (HMIP) and Dynamic HMIP (DHMIP)

strategies localize the registration in FAs and GFAs, yielding to high-mobility signaling. The




UNIT-2 2. 9

Multicast HMIP strategy limits the registration processes in the GFAs. For high-mobility MTs, it

provides lowest mobility signaling delay compared to the HMIP and DHMIP approaches.

However, it is resource consuming strategy unless for frequent MT mobility.

Mobility Management allows locating roaming MTs at any time to deliver its services

and to maintain connections as the MT moves from one service area to another. Mobility

management consists of two components.

Location Management:

It locates MTs with the main purposes to deliver incoming calls to them at a

reasonable cost.

Handoff or Handover Management:

It transfers ongoing calls to adjacent cells as a MT moves from one access point

in the network to another

Figure 2.3 Location Management




UNIT-2 2. 10

Figure 2.4 Hand off or Handover Management

Location Update schemes

Location Update (LU) schemes are classified in two main groups:

Static or global schemes:

LU is triggered based on the topology of the network.

Dynamic or local schemes:

An MT sends a LU message according to the time elapsed (time-based method), the

number of cells visited (movement-based method), or the distance -in terms of cells-

travelled (distance-based method) to the node in the cellular network.

Movement Based LU Schemes

In Movement Based Schemes:

Each MT only keeps a counter of the number of cells visited

A location update is performed when this counter exceeds a predefined threshold

value

Center Cell is the cell where the last location update occurred

Residing Area of the MT is the area in which the mobile can be located and this area is

within a maximum distance of d - 1 from the center cell




UNIT-2 2. 11

Figure 2.5 Location Update schemes

Polling Cycle

The process which is done by the network when a call arrives to a MT, The

network send Polling signal to target cell in the residing area and wait for

response

Movement Based Location Update

The movement based LU is performed by a mobile terminal when the number of

cell boundary crossings since the last location registration equals a threshold

value.

2.5 Medium Access Control (MAC) MAC is a data communication protocol. It is a sub layer of the data link layer, which

itself is layer 2. The MAC sub layer provides addressing and channel access control mechanisms

that make it possible for several terminals or network nodes to communicate within a multiple




UNIT-2 2. 12

access network that incorporates a shared medium, e.g. Ethernet. It is also referred to as

a medium access controller. 2.5.1 Preamble

The purpose of the idle time before transmission starts is to allow a small time interval

for the receiver electronics in each of the nodes to settle after completion of the previous frame.

A node starts transmission by sending an 8 byte (64 bit) preamble sequence. This consists of 62

alternating 1's and 0's followed by the pattern 11. Strictly speaking the last byte which finished

with the '11' is known as the "Start of Frame Delimiter". When encoded using Manchester

encoding, at 10 Mbps, the 62 alternating bits produce a 10 MHz square wave (one complete

cycle each bit period).

Figure 2.6 Preamble in Medium Access Control

The purpose of the preamble is to allow time for the receiver in each node to achieve lock

of the receiver digital phase lock loop which is used to synchronize the receiver data clock to the

transmitter data clock. At the point when the first bit of the preamble is received, each receiver

may be in an arbitrary state (i.e. have an arbitrary phase for its local clock).

During the course of the preamble it learns the correct phase, but in so doing it may miss

(or gain) a number of bits. A special pattern (11) is therefore used to mark the last two bits of the

preamble. When this is received, the ethernet receiver interface starts collecting the bits into

bytes for processing by the MAC layer. It also confirms the polarity of the transition representing

a '1' bit to the receiver (as a check in case this has been inverted).




UNIT-2 2. 13

2.5.2 Header

Figure 2.7 MAC encapsulation of a packet of data

The header consists of three parts:

A 6-byte destination address, which specifies either a single recipient node (unicast

mode), a group of recipient nodes (multicast mode), or the set of all recipient nodes

(broadcast mode).

A 6-byte source address, which is set to the sender's globally unique node address.

This may be used by the network layer protocol to identify the sender, but usually other

mechanisms are used (e.g. ARP).

Its main function is to allow address learning which may be used to configure the filter

tables in a bridge.

A 2-byte type field, which provides a Service Access Point (SAP) to identify the type of

protocol being carried (e.g. the values 0x0800 is used to identify the IP network protocol,

other values are used to indicate other network layer protocols).

In the case of IEEE 802.3 LLC, this may also be used to indicate the length of the data

part.

The type field is also be used to indicate when a tag field is added to a frame.

2.5.3 CRC

The final field in an ethernet MAC frame is called a Cyclic Redundancy Check

(sometimes also known as a Frame Check Sequence). A 32-bit CRC provides error detection in

the case where line errors (or transmission collisions in Ethernet) result in corruption of the

MAC frame. Any frame with an invalid CRC is discarded by the MAC receiver without further

processing. The MAC protocol does not provide any indication that a frame has been discarded

due to an invalid CRC.

The link layer CRC therefore protects the frame from corruption while being transmitted

over the physical medium (cable). A new CRC is added if the packet is forwarded by the router

on another ethernet link. While the packet is being processed by the router the packet data is not




UNIT-2 2. 14

protected by the CRC. Router processing errors must be detected by network or transport-layer

checksums.

2.5.4 Inter Frame Gap

After transmission of each frame, a transmitter must wait for a period of 9.6

microseconds (at 10 Mbps) to allow the signal to propagate through the receiver electronics at

the destination. This period of time is known as the Inter-Frame Gap (IFG). While every

transmitter must wait for this time between sending frames, receivers do not necessarily see a

"silent" period of 9.6 microseconds. The way in which repeaters operate is such that they may

reduce the IFG between the frames which they regenerate.

2.5.5 Byte Order

It is important to realize that nearly all serial communications systems transmit the least

significant bit of each byte first at the physical layer. Ethernet supports broadcast, unicast, and

multicast addresses. The appearance of a multicast address on the cable (in this case an IP

multicast address, with group set to the bit pattern 0xxx xxxx xxxx xxxx xxxx xxxx) is therefore

as shown below (bits transmitted from left to right):

0 23 IP Multicast Address Group 47

| | <--------------------------->|

1000 0000 0000 0000 0111 1010 xxxx xxx0 xxxx xxxx xxxx xxxx

| |

Multicast Bit 0 = Internet Multicast 1 = Assigned for other uses

When the same frame is stored in the memory of a computer, the bits are ordered such

that the least significant bit of each byte is stored in the right most position (the bits are

transmitted right-to-left within bytes, bytes transmitted left-to-right):

0 23 47

| | |

0000 0001 0000 0000 0101 1110 0xxx xxxx xxxx xxxx xxxx xxxx

| <--------------------------->

Multicast Bit IP Multicast Address Group




UNIT-2 2. 15

2.5.6 CSMA /CD

The Carrier Sense Multiple Access (CSMA) with Collision Detection (CD) protocol is

used to control access to the shared ethernet medium. A switched network (e.g. Fast Ethernet)

may use a full duplex mode giving access to the full link speed when used between directly

connected two NICs, Switch to NIC cables, or Switch to Switch cables.

2.5.7 Receiver Processing Algorithm

The receiver processing algorithm is illustrated below

Figure 2.8 Receiver Processing Algorithm

2.5.8 Runt Frame

Any frame which is received and which is less than 64 bytes is illegal, and is called a

"runt". In most cases, such frames arise from a collision, and while they indicate an illegal

reception, they may be observed on correctly functioning networks. A receiver must discard all

runt frames.

2.5.9 Giant Frame

Any frame which is received and which is greater than the maximum frame size is called

a "giant". In theory, the jabber control circuit in the transceiver should prevent any node from

generating such a frame, but certain failures in the physical layer may also give rise to over-sized

Ethernet frames. Like runts, giants are discarded by an ethernet receiver.




UNIT-2 2. 16

2.5.10 Jumbo Frame

Some modern Gigabit Ethernet NICs support frames that are larger than the traditional

1500 bytes specified by the IEEE. This new mode requires support by both ends of the link to

support Jumbo Frames. Path MTU Discovery is required for a router to utilize this feature, since

there is no other way for a router to determine that all systems on the end-to-end path will

support these larger sized frames.

2.5.11 Misaligned Frame

Any frame which does not contain an integral number of received bytes (bytes) is also

illegal. A receiver has no way of knowing which bits are legal, and how to compute the CRC-32

of the frame. Such frames are therefore also discarded by the ethernet receiver.

2.5.12 Other Issues

The ethernet standard dictates a minimum size of frame, which requires at least 46 bytes

of data to be present in every MAC frame. If the network layer wishes to send less than 46 bytes

of data the MAC protocol adds sufficient number of zero bytes (0x00, is also known as null

padding characters) to satisfy this requirement. The maximum size of data which may be carried

in a MAC frame using Ethernet is 1500 bytes (this is known as the MTU in IP).

2.6 Introduction to CDMA based systems 2.6.1 Spread Spectrum in CDMA systems

CDMA is a form of Direct Sequence Spread Spectrum communications. In general,

Spread Spectrum communications is distinguished by three key elements:

1. The signal occupies a bandwidth much greater than that which is necessary to send the

information.

2. This results in many benefits, such as immunity to interference and jamming and multi-

user access, which we’ll discuss later on.

3. The bandwidth is spread by means of a code which is independent of the data.

4. The independence of the code distinguishes this from standard modulation schemes in

which the data modulation will always spread the spectrum.

5. The receiver synchronizes to the code to recover the data.




UNIT-2 2. 17

6. The use of an independent code and synchronous reception allows multiple users to

access the same frequency band at the same time.

Figure 2.9 Direct Sequence Spread Spectrum System

In order to protect the signal, the code used is pseudo-random. It appears random, but is

actually deterministic, so that the receiver can reconstruct the code for synchronous detection.

This pseudo-random code is also called pseudo-noise (PN).

2.6.2 Three Types of Spread Spectrum Communications

There are three ways to spread the bandwidth of the signal:

Frequency hopping. The signal is rapidly switched between different frequencies within

the hopping bandwidth pseudo-randomly, and the receiver knows beforehand where to

find the signal at any given time.

Time hopping. The signal is transmitted in short bursts pseudo-randomly, and the

receiver knows beforehand when to expect the burst.

Direct sequence. The digital data is directly coded at a much higher frequency.




UNIT-2 2. 18

The code is generated pseudo-randomly, the receiver knows how to generate the same

code, and correlates the received signal with that code to extract the data.

2.6.3 Direct Sequence Spread Spectrum

CDMA is a Direct Sequence Spread Spectrum system. The CDMA system works directly

on 64 kb/sec digital signals. These signals can be digitized voice, ISDN channels, modem data,

etc. Figure 2.9 shows a simplified Direct Sequence Spread Spectrum system. For clarity, the

figure shows one channel operating in one direction only.

Signal transmission consists of the following steps:

1. A pseudo-random code is generated, different for each channel and each successive

connection.

2. The Information data modulates the pseudo-random code (the Information data is

“spread”).

3. The resulting signal modulates a carrier.

4. The modulated carrier is amplified and broadcast.

Signal reception consists of the following steps:

The carrier is received and amplified.

The received signal is mixed with a local carrier to recover the spread digital signal.

A pseudo-random code is generated, matching the anticipated signal.

The receiver acquires the received code and phase locks its own code to it.

The received signal is correlated with the generated code, extracting the information data.

2.7 Coding Methods in CDMA The following sections describe how a system might implement the steps illustrated in

figure 2.9

2.7.1 Input data

CDMA works on information data from several possible sources, such as digitized voice

or ISDN channels. Data rates can vary, here are some examples:




UNIT-2 2. 19

Data Source Data Rate

Voice Pulse Code Modulation (PCM) 64 kBits/sec

Adaptive Differential Pulse Code Modulation (ADPCM) 32 kBits/sec

Low Delay Code Excited Linear Prediction (LD-CELP) 16 kBits/sec

ISDN Bearer Channel (B-Channel) 64 kBits/sec

Data Channel (D-Channel) 16 kBits/sec

The system works with 64 kBits/sec data, but can accept input rates of 8, 16, 32, or 64

kBits/sec. Inputs of less than 64 kBits/sec are padded with extra bits to bring them up to 64

kBits/sec. For inputs of 8, 16, 32, or 64 kBits/sec, the system applies Forward Error Correction

(FEC) coding, which doubles the bit rate, up to 128 kbits/sec. The complex modulation scheme

(which we’ll discuss in more detail later), transmits two bits at a time, in two bit symbols. For

inputs of less than 64 kbits/sec, each symbol is repeated to bring the transmission rate up to 64

kilosymbols/sec. Each component of the complex signal carries one bit of the two bit symbol, at

64 kBits/sec, as shown below.

Figure 2.10 Complex Signal carries one bit of the two bit symbol

2.7.2 Generating Pseudo-Random Codes

For each channel the base station generates a unique code that changes for every

connection. The base station adds together all the coded transmissions for every subscriber. The




UNIT-2 2. 20

subscriber unit correctly generates its own matching code and uses it to extract the appropriate

signals. Note that each subscriber uses several independent channels.

In order for all this to occur, the pseudo-random code must have the following properties:

1. It must be deterministic. The subscriber station must be able to independently generate

the code that matches the base station code.

2. It must appear random to a listener without prior knowledge of the code (i.e. it has the

statistical properties of sampled white noise).

3. The cross-correlation between any two codes must be small (see below for more

information on code correlation).

4. The code must have a long period (i.e. a long time before the code repeats itself).

Code Correlation

In this context, correlation has a specific mathematical meaning. In general the correlation

function has these properties:

It equals 1 if the two codes are identical

It equals 0 of the two codes have nothing in common

Intermediate values indicate how much the codes have in common. The more they have in

common, the harder it is for the receiver to extract the appropriate signal.

There are two correlation functions:

Cross-Correlation: The correlation of two different codes. As we’ve said, this should be

as small as possible.

Auto-Correlation: The correlation of a code with a time-delayed version of itself. In order

to reject multi-path interference, this function should equal 0 for any time delay other

than zero.

The receiver uses cross-correlation to separate the appropriate signal from signals meant for

other receivers, and auto-correlation to reject multi-path interference.




UNIT-2 2. 21

Figure 2.11 Pseudo-Noise Spreading

Figure 2.12 Frequency Spreading

2.7.3 Pseudo-Noise (PN) Spreading

The Forward Error Correction (FEC) coded information data modulates the pseudo-random

code, as shown in figure 2.11. Some terminology related to the pseudo-random code:

Chipping Frequency (fc): the bit rate of the PN code.

Information rate (fi): the bit rate of the digital data.

Chip: One bit of the PN code.

Epoch: The length of time before the code starts repeating itself with PN (the period of

the code). The epoch must be longer than the round trip propagation delay (The epoch is

on the order of several seconds).




UNIT-2 2. 22

Figure 2.12 shows the process of frequency spreading. In general, the bandwidth of a digital

signal is twice its bit rate. The bandwidths of the information data (fi) and the PN code are shown

together. The bandwidth is the combination of the two for fc>fi and fc<fi and it can be

approximated by the bandwidth of the PN code.

Processing Gain

An important concept relating to the bandwidth is the processing gain (Gp). This is a

theoretical system gain that reflects the relative advantage that frequency spreading provides.

The processing gain is equal to the ratio of the chipping frequency to the data frequency:

i

cp f

fG

There are two major benefits from high processing gain:

Interference rejection: the ability of the system to reject interference is directly

proportional to Gp.

System capacity: the capacity of the system is directly proportional to Gp.

So higher the PN code bit rate (the wider the CDMA bandwidth), better the system

performance.

Figure 2.13 Complex Modulator




UNIT-2 2. 23

Figure 2.14 Complex Modulation

2.7.4 Transmitting Data

The resultant coded signal next modulates an RF carrier for transmission using

Quadrature Phase Shift Keying (QPSK). QPSK uses four different states to encode each symbol.

The four states are phase shifts of the carrier spaced 90 degrees apart. By convention, the phase

shifts are 45, 135, 225, and 315 degrees. Since there are four possible states used to encode

binary information, each state represents two bits. This two bit “word” is called a symbol.

Complex modulation in general, applying it to a single channel with no PN-coding. Then

we’ll discuss how we apply it to a multi-channel, PN-coded, system. Algebraically, a carrier

wave with an applied phase shift, A (t), can be expressed as a sum of two components, a cosine

wave and a sine wave, as:

I(t) is called the real, or In-phase, component of the data, and Q(t) is called the imaginary,

or quadrature-phase, component of the data. We end up with two Binary PSK waves

superimposed. These are easier to modulate and later demodulate.

This is not only an algebraic identity, but also forms the basis for the actual

modulation/demodulation scheme. The transmitter generates two carrier waves of the same




UNIT-2 2. 24

frequency, a sine and cosine. I(t) and Q(t) are binary, modulating each component by phase

shifting it either 0 or 180 degrees. Both components are then summed together. Since I(t) and

Q(t) are binary, we’ll refer to them as simply I and Q.

The receiver generates the two reference waves, and demodulates each component. It is

easier to detect 180 degrees phase shifts than 90 degrees phase shifts. The following table

summarizes this modulation scheme. Note that I and Q are normalized to 1.

Symbol I Q Phase shift

00 +1 +1 45

01 +1 -1 315

10 -1 +1 135

11 -1 -1 225

For Digital Signal Processing, the two-bit symbols are considered to be complex

numbers, I +jQ.

2.7.5 Working with Complex Data

In order to make full use of the efficiency of digital signal processing, the conversion of

the information data into complex symbols occurs before the modulation. The system generates

complex PN codes made up of 2 independent components, PNi +jPNq. To spread the

Information data the system performs complex multiplication between the complex PN codes

and the complex data.

2.7.6 Summing Many Channels Together

Many channels are added together and transmitted simultaneously. This addition happens

digitally at the chip rate. Remember, there are millions of chips in each symbol. For clarity, let’s

say each chip is represented by an 8 bit word (it’s slightly more complicated than that, but those

details are beyond the scope of this discussion).

At the Chip Rate

Information data is converted to two bit symbols.

The first bit of the symbol is placed in the I data stream, the second bit is placed in the Q

data stream.




UNIT-2 2. 25

The complex PN code is generated. The complex PN code has two independently

generated components, an I component and a Q component.

The complex Information data and complex PN code are multiplied together.

For each component (I or Q):

Each chip is represented by an 8 bit word. However, since one chip is either a one or a

zero, the 8 bit word equals either 1 or -1.

When many channels are added together, the 8-bit word, as the sum of all the chips, can

take on values from between -128 to +128.

The 8-bit word then goes through a Digital to Analog Converter, resulting in an analog

level proportional to the value of the 8-bit word.

This value then modulates the amplitude of the carrier (the I component modulates the

Cosine, the Q component modulates the Sine)

The modulated carriers are added together.

2.7.7 Receiving Data

The receiver performs the following steps to extract the Information:

Demodulation

Code acquisition and lock

Correlation of code with signal

Decoding of Information data

Demodulation

The receiver generates two reference waves, a cosine wave and a sine wave. Separately

mixing each with the received carrier, the receiver extracts I(t) and Q(t). Analog to Digital

converters restore the 8-bit words representing the I and Q chips.

Code Acquisition and Lock

The receiver, as described earlier, generates its own complex PN code that matches the

code generated by the transmitter. However, the local code must be phase-locked to the encoded

data. The RCS and FSU each have different ways of acquiring and locking onto the other’s

transmitted code. Each method will be covered in more detail in later sections.




UNIT-2 2. 26

Correlation and Data Despreading

Once the PN code is phase-locked to the pilot, the received signal is sent to a correlator

that multiplies it with the complex PN code, extracting the I and Q data meant for that receiver.

The receiver reconstructs the information data from the I and Q data.

Automatic Power Control

The RCS gets bombarded by signals from many FSUs. Some of these FSUs are close and

their signals are much stronger than FSUs farther away. This results in the Near/Far problem

inherent in CDMA communications. System Capacity is also dependant on signal power. For

these reasons, both the RCS and FSU measure the received power and send signals to control the

others transmit power.

Near/Far Problem

The near-far problem is a condition in which a receiver captures a strong signal and

thereby makes it impossible for the receiver to detect a weaker signal.

Interference Rejection

CDMA technology is inherently resistant to interference and jamming. A common

problem with urban communications is multi-path interference. Multi-path interference is caused

by the broadcast signal traveling over different paths to reach the receiver. The receiver then has

to recover the signal combined with echoes of varying amplitude and phase. This results in two

types of interference:

Inter-chip interference: The reflected signals are delayed long enough that successive bits

(or chips, in this case) in the demodulated signals overlap, creating uncertainty in the

data.

Selective fading: The reflected signals are delayed long enough that they are randomly

out of phase, and add destructively to the desired signal, causing it to fade.




UNIT-2 2. 27

Figure 2.15 Multi-Path Interference Rejection

Combating Interference

Two methods are commonly used to combat multi-path interference:

Rake filter: Correlators are set up at appropriate time intervals to extract all the echoes.

The relative amplitude and phase of each echo is measured, and each echo signal is phase

corrected and added to the signal.

Adaptive Matched Filter: This filter is “matched” to the transfer function (i.e. the

propagation characteristics) of the signal path. It phase shifts the echo signals and adds

them to maximize the received signal.




UNIT-2 2. 28

System Operation

The following sections describe a hypothetical implementation of CDMA technology. A

connection can be one of many types of data, but for simplicity we will refer to any connection

as a “call”.

These sections cover the following system states:

System Idle: System operation when there is no call in progress.

Call Setup: The steps to setup a connection.

Call Processing: The processing and transmission of the digital data once a connection is

established.

Call Teardown: The steps taken once a call is finished to free system resources.

But first, in order to understand system operation, you must understand the Pilot codes and

communication channels the system uses.

Pilot Codes

At each phase of operation, the system broadcasts pilot signals. These pilot signals are the

unmodulated PN codes associated with each channel, used to synchronize and track the locally

generated PN codes for despreading. The system uses the following pilot signals.

Global Pilot: Broadcast by the RCS. All FSUs use the Global Pilot for all received

channels.

Short Access Pilot: Broadcast by FSU. Monitored by the RCS for an incoming access

attempt by an FSU. Alerts the RCS that an FSU is requesting access.

Long Access Pilot: Broadcast by the FSU. Allows the RCS to synchronize to the FSU to

setup a call.

Assigned Pilot: Broadcast by FSU. Unmodulated PN code of the assigned channel.

Allows RCS to synchronize to and track the PN codes of the FSU assigned channels for

despreading.

Communication Channels

In order to understand system operation, we need to introduce the system communication

channels. The system has the following channel groups:

The Broadcast Channel group: Channels continuously broadcasted by the RCS.




UNIT-2 2. 29

Call Setup Channel group: Channels used to setup a call. There are four sets of these

channels; up to 4 FSUs can request access at one time.

Assigned Channel group: Channels used for the call.

Each logical channel in each group is realized by assigning a unique PN code to it.

Table 2.1 Channel group and Name description

Channel

Group

Channel

Name

Direction Number of

Channels

Description

Broadcast Global Pilot F One An unmodulated PN code that the FSU can

synchronize to.

Fast

Broadcast

Channel

F One A single message indicating which services

and access channels are available. This

information may change rapidly.

Slow

Broadcast

Channel

F One Paging messages and other system

information that does not need to be

updated rapidly.

Call Setup Short Pilot R Four Alerts the RCS that an FSU is requesting

access.

Long Pilot Four Allows the RCS to synchronize to the FSU

to setup a call.

Access

Channel

R Four Used by the FSUs to access an RCS and

get assigned channels.

Control

Channel

F Four Used by the RCS to reply to access

attempts from FSUs.

Control

Channel APC

F Four Controls FSU power during initial access.

Assigned Assigned R One per FSU An unmodulated PN code that the RCS can




UNIT-2 2. 30

Pilot synchronize to.

APC Channel F One per FSU Controls FSU power during call.

R Controls RCS power of assigned FSU

channels.

Traffic

Channels

F Up to 3 per

FSU

Signal data from RCS to FSU.

R Signal data from FSU to RCS.

Order wire F One per FSU Control signals: CDMA and Telco

messages.

R

Note on Direction: F - Forward - From RCS to FSU

R - Reverse - From FSU to RCS

Pilot Ramp Up

When the FSU transmits its Short and Long Access Pilots, it ramps the power up to

determine what power level it should transmit. When the RCS detects the Short Access Pilot, it

acknowledges over the Fast Broadcast Channel. The FSU then knows that it is being received,

and switches to the Long Access Pilot code. The Long Access Pilot code ramps up more slowly,

until the RCS locks and starts transmitting Automatic Power Control signals.

System Idle

On startup, the RCS places one of its modems in broadcast mode, in which state it broadcasts

the following Global Channels continuously:

Global Pilot

Slow Broadcast Channel

Fast Broadcast Channel




UNIT-2 2. 31

Paging Groups and Sleep Cycles

The RCS divides all the FSUs associated with it into paging groups. The RCS assigns

each paging group a particular time slot on its Slow Broadcast Channel (the first time slot is

reserved for general Slow Broadcast information).

The Slow Broadcast Channel cycles through all the paging groups. The cycle takes

approximately one second to complete. When the Slow Broadcast Channel reaches the time slot

of the FSU’s paging group, the FSU powers up, synchronizes to the Global Pilot, and checks for

its address in the paging group.

Figure 2.16 Call Setup




UNIT-2 2. 32

Call Setup

Two events can initiate a call:

The FSU receives a page from the RCS. This is called a terminating call.

The FSU generates an off-hook signal in response to subscriber equipment.

The FSU locks on to the Global Pilot. This is called an originating call.

Once either of these events occurs, call setup proceeds as follows:

1. FSU requests access.

FSU transmits Short Access Pilot Code.

RCS detects transmission and acknowledges. Flags Call Setup Channel as busy.

FSU transmits Long Access Pilot Code.

RCS synchronizes to the FSU and confirms sync over Control Channel.

RCS measures received power and starts transmitting APC signal on APC Control

Channel.

RCS and FSU exchange messages on Access and Control Channels.

Type of service and types of traffic channels are specified.

2. RCS assigns channel group to FSU.

RCS designates assigned code on Control Channel

FSU generates complex PN codes for all channels in its assigned group.

Both FSU and RCS synchronously switch to the assigned channel groups.

The call is connected.

The RCS flags the Call Setup Channel as available, and assigns it to the next available

modem.

Note that the RCS now tracks the Assigned Pilot; the FSU continues to track the Global Pilot.

Call Processing

Call processing puts together everything we’ve covered so far. There are slight

differences in the way the RCS and FSU process calls, so we will cover both the Forward link

(RCS to FSU) and Reverse link (FSU to RCS). Note that the system uses Frequency Division

Duplexing for the Forward and Reverse links: they transmit over different frequencies.

In the forward direction, the RCS:




UNIT-2 2. 33

1. Generates CDMA data signal for each traffic channel:

FEC codes the Information data, and converts the data to two-bit symbols.

Converts the symbols to I and Q data, and pads each data stream to 64 kbits/sec.

Generates the Complex PN code for each channel.

Multiplies the Complex Information data and the Complex PN code together.

Reads APC data from FSU, digitally scales channels accordingly.

2. Generates other signal channels:

Calculates APC signal

Converts it to I data only

Multiplies it with its own Complex PN code

3. Adds all signals together:

Traffic channels

APC channel

Order Wire channel

Global Pilot

4. Adds together the signals for all currently active FSUs.

5. Modulates and transmits carriers

I and Q data modulate Cosine and Sine carriers.

Carriers are combined, amplified, and broadcast.

The FSU:

1. Extracts the I and Q data:

Receives and amplifies the modulated carriers.

Demodulates the signal and extracts the I and Q data.

2. Filters the I and Q data:

Extracts multi-path information from the Pilot Rake filter and supplies it to the Adaptive

Matched Filter.

Removes multi-path interference from I and Q data using the Adaptive Matched Filter.

Performs Automatic Gain Control on received signal

3. Extracts the CDMA data signal for each traffic channel:




UNIT-2 2. 34


Multiplies the Complex signal and the Complex PN code together.

Converts the I and Q data to symbols.

Decodes the symbols for error correction.

Extracts the signal data.

In the reverse direction, the FSU:

1. Generates CDMA data signal for each traffic channel:

FEC codes the Information data, and converts the data to two-bit symbols.

Converts the symbols to I and Q data, and pads each data stream to 64 kbits/sec.



Reads APC data from FSU, digitally scales channels accordingly.

2. Generates other signal channels:

Calculates APC signal

Converts it to I data only

Multiplies it with its own Complex PN code

3. Adds all signals together:

Traffic channels

APC channel

Order Wire channel

Global Pilot

4. Passes the signal through a pulse shaping digital filter.

5. Modulates and transmits carriers

I and Q data modulate Cosine and Sine carriers.

Carriers are combined, amplified, and broadcast.

The RCS:

1. Extracts the I and Q data:

Receives and amplifies the modulated carriers and demodulates the signal and extracts

the I and Q data.




UNIT-2 2. 35

2. Filters the I and Q data:

Extracts multi-path information from the Pilot Rake filter and supplies it to the Adaptive

Matched Filter and removes multi-path interference from I and Q data using the Adaptive

Matched Filter. It Performs Automatic Gain Control on the received signal

3. Extracts the CDMA data signal for each traffic channel, for each subscriber connection:



Converts the I and Q data to symbols and decodes the symbols for error correction.

Extracts the Information data.

Call Teardown

An on-hook signal causes the RCS to release the resources, and the FSU returns to its idle

state.




UNIT-2 2. 36

2.8 QUESTION BANK

PART-A

1. What is meant by cellular system?

2. What is meant by Frequency management?

3. What is the interference in cellular system?

4. What is Interference in Cellular Systems?

5. What is Channel Assignment?

6. What is Location management in cellular networks?

7. Define Medium Access Control.

8. Define CDMA based systems.

9. What is Spread Spectrum in CDMA systems?

10. Define Coding Methods.


12. What are the categories of Mobile services?


14. What are the disadvantages of cellular systems?

15. What are subsystems in GSM system?

16. What are the control channel groups in GSM?

17. What are the four types of handover available in GSM?

18. What are types of Handover?

19. What are the services provided by supplementary services?

20. What is authentication centre (AuC)?




UNIT-2 2. 37

PART-B (16 Marks)

1. Explain with diagram the Hidden terminal and exposed terminal problem in CSMA.

2. Explain with diagram the Near-Far terminal problem in CSMA.

3. Explain Location Management in cellular network?

4. Explain Channel Assignment in cellular network?

5. Explain in detail about Coding Methods

6. Explain in detail about Spectrum in CDMA systems.

7. Explain the different types of transport modes and the channel used to carry packets in

Digital Audio Broadcasting.

8. Explain in detail about Digital Audio Broadcasting.

9. Explain in detail about Digital Video Broadcasting.

10. What are different interleaving and repetition schemes applied by DAB to objects and

segments?




UNIT-3 3. 1

UNIT 3

MOBILE IP NETWORK LAYER




UNIT-3 3. 2

CONTENTS

3.1 Mobile IP Protocol Overview

3.1.1 Requirements for the evolution of the new mobile IP protocol

3.1.2 Need for upgrading capacity of Routers, and Data-link and Physical layers

3.1.3 Security Needs

3.1.4 Need for Non-Transparency from higher layers

3.1.5 Reestablishment problems due to Non-Transparency from higher layers

3.1.6 Need of Non-Transparency from higher layers

3.1.7 Examples of Non-Transparency from higher layers

3.1.8 Routing table problems

3.1.9 Reestablishment Problems

3.1.10 Working of Mobile IP

3.1.11Use of HAs and FAs

3.1.12 Mobile IP network employing home and foreign agents

3.1.13 Switching Center home agent (HA)

3.1.14 Paging area

3.1.15 Switching centre foreign agent for a foreign network of visiting MNs

3.1.16 Different paging areas interconnected through gateway routers

3.2 Route optimization

3.2.1 CN (MNk) corresponding with visiting MNI

3.2.2 Mobile IP network employing home and foreign agents FAk and FAj

3.3 Mobility support for IPV6

3.3.1 IP micro-mobility support

3.3.2 Cellular IP

3.4 Connectivity with 3G Networks

3.5 Packet Delivery and Handover Management

3.6 Location Management

3.6.1 Handover Management protocols

3.6.2 Location Management Protocols




UNIT-3 3. 3

3.6.3 Agent Discovery

3.6.4 Agent advertisements

3.6.5 Header extension

3.6.6 Co-located COA

3.6.7 Flags

3.6.8 Agent solicitation

3.7 Registration

3.7.1 Function of HA after registration

3.7.2 Registration steps

3.7.3 Registration

3.7.4 Registration Request

3.7.5 8 flag bits

3.7.6 Registration Reply

3.7.7 New database entry fields after registration at the HA

3.8 Tunneling and Encapsulation

3.8.1Tunneling

3.8.2 IP header-in-IP header Method of encapsulation

3.8.3 Format of Encapsulated data

3.8.4 IP header-in-IP header encapsulation Format of Encapsulated data

3.8.5 Redundancy in IP header-in-IP header method

3.8.6 Minimum Encapsulation (ME) method by IP header of an IP Packet

3.8.7 Deficiencies in the IP header-in-IP header and ME methods

3.8.8 Generic Routing Encapsulation (GRE) by IP header of an IP Packet

3.8.9 Tunnel characteristics

3.8.10 GRE by IP header of an IP Packet

3.8.11 GRE (GRE) Header(s)

3.8.12 IP Header and IP Packet data

3.8.13 Source routing




UNIT-3 3. 4

3.9 Route Optimization

3.9.1 Triangular route

3.9.2 Optimization of route for the triangular routing example

3.9.3 Mobility binding Steps in the calling network

3.9.4 Warning sent to HAl of MNl

3.9.5 Smooth handover in Mobile IP protocol method of optimization

3.9.6 Reverse Tunnel

3.9.7 Advantage of reverse tunneling

3.9.8 Time-to-live for forward and reverse tunneling

3.9.9 Reverse tunneling

3.10 Dynamic Host Configuration Protocol

3.11 Question Bank




UNIT-3 3. 5

TECHNICAL TERMS

1. Home Agent (HA) is a host in the home network of the MN, typically a router. It

registers the location of the MN, tunnels IP packets to the COA

2. Mobility Binding: The Mobile Node sends its registration request to the Home Agent.

The HA sets up a mobility binding containing the mobile node’s home IP address and the

current COA.

3. Tunnel establishes a virtual pipe for data packets between a tunnel entry and a tunnel

endpoint. Packets entering a tunnel are forwarded inside the tunnel and leave the tunnel

unchanged.

4. Encapsulation is the mechanism of taking a packet consisting of packet header and data

putting it into the data part of a new packet.

5. De capsulation is the reverse operation, taking a packet out of the data part of another

packet

6. Cellular IP provides local handovers without renewed registration by installing a single

cellular IP gateway for each domain, which acts to the outside world as a foreign agent.

7. Routing table is maintained and regularly updated by the router

8. Broadcasting is the Message or packet transmits to all the IP addresses which are set for

listening

9. Mobile Node (MN) is node that moves across networks without changing its IP address

10. Correspondent Node (CN) is a host with which MN is “corresponding” (TCP)

11. Foreign Agent (FA) is a host in the current foreign network of the MN, typically a

router. It forwards tunneled packets to the MN, typically the default router for MN

12. Care-of Address (COA) is a address of the current tunnel end-point for the MN (at FA

or MN). The actual location of the MN from an IP point of view

13. Tunneling is an encapsulating IP packet including a path and an original IP packet.




UNIT-3 3. 6

3. MOBILE IP NETWORK LAYER

3.1 Mobile IP Protocol Overview Defined by the Internet Engineering Task Force (IETF)

Described in the IETF RFC 3344

A protocol developed to allow internetwork mobility for wireless nodes without them

having to change their IP addresses by the Internet Engineering Task Force (IETF)

3.1.1 Requirements for the evolution of the new mobile IP protocol

Need for Enhancing IP Network capacity─ Use of the existing IP protocol by large

number of Mobile nodes (MNs) will lead to a decrease in the network.

3.1.2 Need for upgrading capacity of Routers, and Data-link and Physical layers

IP network protocols support 48-bit MAC addresses

But when the number of MNs is large, then other interfaces and lower level protocols

are required

For mobile nodes to move from one place to another while using the existing IP protocol,

new protocols are required at the data-link and physical layer.

3.1.3 Security Needs

The mobility of the called MN must be hidden from the calling MN

When a new IP address allocates at the new hosting subnet of the existing IP based

infrastructure, the identity of the mobile node is not hidden from another host

The MN exposes and lacks security when using the existing IP protocol.

3.1.4 Need for Non-Transparency from higher layers

The transport layer establishes a connection between a given port at a given IP address

(called socket) with a another port at another IP address

The connection, once established by the transport layers between the sockets, is broken as

soon as the new address is assigned.

3.1.5 Reestablishment problems due to Non-Transparency from higher layers

(a) Reestablishment of the connection takes time which means loss of data during that

interval




UNIT-3 3. 7

(b) Reestablishment process has to share the same network and the given transmission rate.

3.1.6 Need of Non-Transparency from higher layers

Any movement of the MN will be transparent to the TCP and to L7 in case the TCP layer

re-establishes the connection when the IP protocol used by the MN

There is, therefore, a need for non-transparency of the MN to distant ports.

3.1.7 Examples of Non-Transparency from higher layers

Assume a distant router is sending data packets for an IP address, presently assigned to a

mobile terminal using another router

When the terminal moves from one service area to another, the routing tables on the route

need to be updated

Till this is done the packets will not reach their new destination.

3.1.8 Routing table problems

The reconfiguration messages for updating the routing tables have to share the same

network and the given transmission rate.

3.1.9 Reestablishment Problems

Reestablishment of the connection takes time and this means loss of data during that

interval

Any movement on the part of the MN transparent and, thus, not secure from the distant

hosts on the network of distant routers.

3.1.10 Working of Mobile IP

A router has a home agent (HA) for a set of home networked MNs, as well as a foreign

agent (FA) for the visiting MNs

An agent ─ software employed at a router or the host serviced by a router.

An MN can access Internet services using the mobile IP protocol

The MN can change its service router when visiting another location (which is serviced

by a different router)

The HA and the FA play a location management role similar to that of the HLR and the

VLR in a GSM system.




UNIT-3 3. 8

3.1.11 Use of HAs and FAs

The same software can function as both the HA and the FA at different instants of time

An MN can also have software which functions as an FA instead of the FA at the router.

3.1.12 Mobile IP network employing home and foreign agents

The Mobile IP network employing home and foreign agents are shown in the figure

below.

Figure 3.1 Mobile IP network employing home and foreign agents

3.1.13 Switching Center Home Agent (HA)

Provides services to an MN at the registered home network including transmitting and

receiving packets from the Internet

A home agent assigns MNs to routers which support the MNs

A home network is a mobile radio subsystems network within an area, called paging area

The home network is like a subnet

Just like a subnet has a number of IP hosts, a home network has the MNs




UNIT-3 3. 9

3.1.14 Paging area

Area in which the MNs of home as well as foreign networks can be approached through a

single MSC or a set of MSCs

Routing of packets through the routers performed when an MN moves within one paging

area

3.1.15 Switching centre foreign agent for a foreign network of visiting MNs

Foreign network─ another mobile radio subsystem network which the MNs of home

network visit within the paging area

Foreign agent─ a provider of the IP address and services, including transmitting and

receiving packets from the Internet, for MNs on visit to a foreign network

Foreign agent─ assigns MNs to a router, which supports the MNs of other home

networks

3.1.16 Different paging areas interconnected through gateway routers

Form a backbone network

Rerouting of the packets done through the gateway routers when an MN moves from one

paging area to another

3.2 Route optimization 3.2.1 CN (MNk) corresponding with visiting MNI

The route optimization is explained with CN (MNk) corresponding with visiting MNI

below in figure 3.2.

3.2.2 Mobile IP network employing home and foreign agents FAk and FAj

Packet delivers to and from the MNk at a foreign network with FAk and MNI at the

foreign network with FAj

Example

Assume that MNI visiting a foreign network which happens to be the home network of

CN2 is very close to CNI




UNIT-3 3. 10

Figure 3.2 CN (MNk) corresponding with visiting MNI

Triangular route

Triangular route without mobility binding between COAj and CNk

Also possible that FAk and FAj are identical

Optimization of route for the triangular routing example

Optimization of route for the triangular routing can be made in case the MN1 opts to

make its mobility known




UNIT-3 3. 11

Figure 3.3 Packets make a triangular trip to reach from CN2 to MNI

3.3 Mobility support for IPV6 While mobile IP was originally designed for IP version 4, IP version 6 (Deering, 1998)

makes life much easier. Several mechanisms that had to be specified separately for mobility

support come free in IPv6 (Perkins, 1996d), (Johnson, 2002b). One issue is security with regard

to authentication, which is now a required feature for all IPv6 nodes. No special mechanisms as

add-ons are needed for securing mobile IP registration. Every IPv6 node masters address auto-

configuration – the mechanisms for acquiring a COA are already built in.

Neighbor discovery as a mechanism mandatory for every node is also included in the

specification; special foreign agents are no longer needed to advertise services. Combining the

features of auto-configuration and neighbor discovery means that every mobile node is able to

create or obtain a topologically correct address for the current point of attachment. Every IPv6

node can send binding updates to another node, so the MN can send its current COA directly to

the CN and HA. These mechanisms are an integral part of IPv6. A soft handover is possible with




UNIT-3 3. 12

IPv6. The MN sends its new COA to the old router servicing the MN at the old COA, and the old

router encapsulates all incoming packets for the MN and forwards them to the new COA.

Altogether, mobile IP in IPv6 networks requires very few additional mechanisms of a

CN, MN, and HA. The FA is not needed any more. A CN only has to be able to process binding

updates, i.e., to create or to update an entry in the routing cache. The MN itself has to be able to

decapsulate packets, to detect when it needs a new COA, and to determine when to send binding

updates to the HA and CN. A HA must be able to encapsulate packets.

3.3.1 IP micro-mobility support

Mobile IP exhibits several problems regarding the duration of handover and the

scalability of the registration procedure. Assuming a large number of mobile devices changing

networks quite frequently, a high load on the home agents as well as on the networks is

generated by registration and binding update messages. IP micro-mobility protocols can

complement mobile IP by offering fast and almost seamless handover control in limited

geographical areas.

Consider a client arriving with his or her laptop at the customer’s premises. The home

agent only has to know an entry point to the customer’s network, not the details within this

network. The entry point acts as the current location. Changes in the location within the

customer’s network should be handled locally to minimize network traffic and to speed-up local

handover.

The basic underlying idea is the same for all micro-mobility protocols: Keep the frequent

updates generated by local changes of the points of attachment away from the home network and

only inform the home agent about major changes, i.e., changes of a region. In some sense all

micro-mobility protocols establish a hierarchy. However, the debate is still going on if micro-

mobility aspects should really be handled on the IP layer or if layer 2 is the better place for it.

Layer 2 mobility support would comprise, e.g., the inter access point protocol (IAPP) of 802.11

WLANs or the mobility support mechanisms of mobile phone systems.

The following presents three of the most prominent approaches, which should be seen

neither as standards nor as final solutions of the micro-mobility problems. Campbell (2002)

presents a comparison of the three approaches.




UNIT-3 3. 13

3.3.2 Cellular IP

Cellular IP (Valko, 1999), (Campbell, 2000) provides local handovers without renewed

registration by installing a single cellular IP gateway (CIPGW) for each domain, which acts to

the outside world as a foreign agent. Inside the cellular IP domain, all nodes collect routing

information for accessing MNs based on the origin of packets sent by the MNs towards the

CIPGW. Soft handovers are achieved by allowing simultaneous forwarding of packets destined

for a mobile node along multiple paths. A mobile node moving between adjacent cells will

temporarily be able to receive packets via both old and new base stations (BS) if this is

supported by the lower protocol layers.

Concerning the manageability of cellular IP, it has to be noted that the approach has a

simple and elegant architecture and is mostly self-configuring. However, mobile IP tunnels could

be controlled more easily if the CIPGW was integrated into a firewall, but there are no detailed

specifications in (Campbell, 2000) regarding such integration. Cellular IP requires changes to the

basic mobile IP protocol and is not transparent to existing systems. The foreign network’s

routing tables are changed based on messages sent by mobile nodes. These should not be trusted

blindly even if they have been authenticated. This could be exploited by systems in the foreign

network for wiretapping packets.

Figure 3.5 Basic architecture of cellular IP




UNIT-3 3. 14

Advantage

● Manageability: Cellular IP is mostly self-configuring, and integration of the CIPGW

into a firewall would facilitate administration of mobility-related functionality. This is, however,

not explicitly specified in (Campbell, 2000).

Disadvantages

● Efficiency: Additional network load is induced by forwarding packets on multiple

paths.

● Transparency: Changes to MNs are required.

● Security: Routing tables are changed based on messages sent by mobile nodes.

Additionally, all systems in the network can easily obtain a copy of all packets destined

for an MN by sending packets with the MN’s source address to the CIPGW.

HAWAII (Handoff-Aware Wireless Access Internet Infrastructure, Ramjee, 1999) and

Hierarchical mobile IPv6 (HMIPv6) supports IPv6.

3.4 Connectivity with 3G Networks 3G or 3rd generation mobile telecommunications is a generation of standards for

mobile phones and mobile telecommunication services fulfilling the International Mobile

Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication

Union. Application services include wide-area wireless voice telephone, mobile Internet access,

video calls and mobile TV, all in a mobile environment.

Several telecommunications companies market wireless mobile Internet services as 3G,

indicating that the advertised service is provided over a 3G wireless network. Services advertised

as 3G are required to meet IMT-2000 technical standards, including standards for reliability and

speed (data transfer rates). To meet the IMT-2000 standards, a system is required to provide peak

data rates of at least 200 kbit/s (about 0.2 Mbit/s).




UNIT-3 3. 15

Figure 3.4 Route optimization and path 1, 2, 3, 4, 5 after mobility binding of MN1 at COAj

with CNk

However, many services advertised as 3G provide higher speed than the minimum

technical requirements for a 3G service. Recent 3G releases, often denoted 3.5G and 3.75G, also

provide mobile broadband access of several Mbit/s to smartphones and mobile modems in laptop

computers. The following standards are typically branded 3G:

The UMTS system, first offered in 2001, standardized by 3GPP, used primarily in

Europe, Japan, China (however with a different radio interface) and other regions

predominated by GSM 2G system infrastructure. The cell phones are typically UMTS

and GSM hybrids. Several radio interfaces are offered, sharing the same infrastructure:

o The original and most widespread radio interface is called W-CDMA.

o The TD-SCDMA radio interface was commercialized in 2009 and is only offered

in China.




UNIT-3 3. 16

o The latest UMTS release, HSPA+, can provide peak data rates up to 56 Mbit/s in

the downlink in theory (28 Mbit/s in existing services) and 22 Mbit/s in the

uplink.

The CDMA2000 system, first offered in 2002, standardized by 3GPP2, used especially in

North America and South Korea, sharing infrastructure with the IS-95 2G standard. The

cell phones are typically CDMA2000 and IS-95 hybrids. The latest release EVDO Rev B

offers peak rates of 14.7 Mbit/s downstream.

The above systems and radio interfaces are based on spread spectrum radio transmission

technology. While the GSM EDGE standard ("2.9G"), DECT cordless phones and Mobile

WiMAX standards formally also fulfill the IMT-2000 requirements and are approved as 3G

standards by ITU, these are typically not branded 3G, and are based on completely different

technologies.

A new generation of cellular standards has appeared approximately every tenth year since 1G

systems were introduced in 1981/1982. Each generation is characterized by new frequency

bands, higher data rates and non backwards compatible transmission technology. The first

release of the 3GPP Long Term Evolution (LTE) standard does not completely fulfill the ITU 4G

requirements called IMT-Advanced. First release LTE is not backwards compatible with 3G, but

is a pre-4G or 3.9G technology, however sometimes branded "4G" by the service providers. Its

evolution LTE Advanced is a 4G technology. WiMAX is another technology verging on or

marketed as 4G.

Applications of 3G

The bandwidth and location information available to 3G devices gives rise to applications not

previously available to mobile phone users. Some of the applications are:

Mobile TV

Video on demand

Videoconferencing

Telemedicine

Location-based services




UNIT-3 3. 17

3.5 Packet Delivery and Handover Management Correspondent node (CN) is an MN or a fixed IP host linked to a router, which

communicates IP packets to another MN in a home or foreign network (when on visit).

Case 1: CN a fixed node and MNl at the home network

• CN message transmits for connection establishment or a packet using the IP protocol

• HAl (the home agent for MNl) receives the message or packet and, using the information that

the destined MNl is at the home network itself, it delivers the message or packet to MNl

• Receives the response message or packet from MNl

• Delivers it to the CN using the IP protocol

Case 2: CN an MNk and MNl both at home networks with agents HAk and HAl

• MNk message for connection establishment or a packet using the IP protocol transmits through

HAk.

• Same way as in case 1

• The packet delivers to HAl and then to MNl

• MNl response like in case 1

• HAk and HAl deliver the packets from one end to another and vice versa by just forwarding the

packets to their respective MNs using the IP protocol

Case 3: CN a fixed node and MNl is at a foreign network

• CN transmits a message for connection establishment or a packet using the IP protocol

• As in case 1

• HAl receives the packets and uses the information that the destined mobile node MNl is not at

the home network and is presently visiting a foreign network and is reachable via a foreign agent

FAj.

• HAl encapsulates the received IP packet using a new header

• Care-of address (COA) at the new header over the IP packet sent by HAl

• Handover─ Packet encapsulated with the new header with COA transmits to FAj by tunneling




UNIT-3 3. 18

3.6 Location Management 3.6.1 Handover Management protocols

• Mobile node (MN) moves

• Visits foreign networks often

• Handover management─ managing the transfer of service availability to the new

location network

3.6.2 Location Management Protocols

• By the network for management of the MNs location

• Preparing for the services (packet receiving and packet transmitting) at the new network

• Agent discovery through agent advertisement

• Agent discovery and agent solicitation

Figure 3.5 FA discoveries by MN by receiving COA during advertisement

3.6.3 Agent Discovery

• MN must discover (find) a foreign agent (FA) when visiting a foreign network

• Agent discovery by a mobile node MNl─receiving the COA (care-of-address)

• COA enables FA to get messages for MNl

• Home agent (HA) of MNl transfers the messages from sender

• Uses COA




UNIT-3 3. 19

Steps 1 and 2 in the protocol for discovering an agent

1. Listen to an advertisement (ICMP message) from an agent

2. Proceed to step 3 if the advertisement is found, else solicit the agent from the routers

•If agent found, then proceed to step 3, else repeat the step Steps 3 and 4 in the

protocol for discovering an agent

3. If the COA discovered from the message is found to be the same as the previous COA,

go back to step 1, else proceed to step 4

4. If the discovered COA is the same as the home network, deregister at this network and

go back to step 1, else if the current COA is a new COA then register with the new COA

3.6.4 Agent advertisements

• Agent advertisements─ essentially ICMP messages

• Sent to a number of addresses ICMP message options and words

• Added mobility extension fields in the ICMP header

3.6.5 Header extension

• One 32-bit word format ─ First byte 00010000

• Second byte for length

• Length = 2 words + number of COAs specified in the extension to which the ICMP

message is to be sent + two bytes for the 16-bit sequence number (for the ICMP message

advertised

• Two-byte lifetime in second plus 8 bits for flags

• Remaining byte is not used ─ reserved for any future requirements of modifications or

specification expansion in ICMP

• Lifetime─ during which the MN can register with the new COA (step 4 in agent

discovery)

• For the COA addresses for the MN at that agent

3.6.6 Co-located COA

• COA when the MN acquires temporarily an additional IP address while on visit to a

new network

• Else the COA is the same IP address for that MN while on visit and when at home FA.




UNIT-3 3. 20

• Obtains the co-located COA using the dynamic host configuration protocol (DHCP)

3.6.7 Flags

• Flag1─ whether the COA is a co-located COA

• Flag2─ whether the advertising agent is the HA

• Flag3─ whether the advertising agent is an FA

• Flag4─ specifies whether there is reverse tunneling support by the FA for encapsulation

and sending packets by tunneling to the HA

• Flag5─ specifies whether the encapsulation method is generic

• Flag6─ specifies whether the encapsulation method is a minimal mandatory method

• Flag7─specifies if the agent is busy and cannot register the visiting MN

3.6.8 Agent solicitation

• A method by which an MN visiting a network discovers the FA and the COA in case

COA not found from advertisements

• If an advertisement is not listened to, solicitation can be done three times at 1 s intervals

• Later this interval can be increased

3.7 Registration Registration after an MN discovering FA for service and finding a COA

• Needed for the service of receiving and transmitting of IP packets with the new agent

FA

• For creating a tunnel between HAl and FAj

3.7.1 Function of HA after registration

• To encapsulate the IP packets and transmit them to the discovered FA (through

tunneling), whenever a CN (corresponding node) communicates with the MN

Deregistration for the receiving and transmitting of IP packets

• Also needed with the HA (step 4 of agent discovery in the protocol)




UNIT-3 3. 21

3.7.2 Registration steps

• Requests and replies are made by the MN, FA, and HA using a UDP datagram • Let us

assume that the MN has IP address of the HA • If not, then the MN broadcasts the

registration request to a paging area

• The HAs then send the registration replies

• The MN requests one of the HAs (out of those which reply) for registration

Step 1 for registration at an agent

1. The MN sends a registration request to FA

• FA sends that request to the HA

• When the COA is a co-located COA, then the request sent directly to the HA


2. The HA binds itself for mobility (binds itself for encapsulating and tunneling

the packets to the MN through a new FA)

• The binding period equals the lifetime of the COA


3. The MN registers again before the binding period expires

• When it moves to another foreign network

• When it returns back to the home network


4. The HA sends a registration reply to the FA and the FA to the MN

• The MN checks whether the reply shows successful registration

3.7.3 Registration

• Success─ mobility binding now exists from the HA to FA

• Failure ─ when there are too many tunnels created at the HA and the HA does not have

the resources to handle new requests or there is an authentication failure or the HA not

reachable to the FA




UNIT-3 3. 22

Figure 3.6 MNk after discovery of FAj seeking registration for creating tunnel between

HAl and FAj

3.7.4 Registration Request

• Next 32-bit word for the home agent IP address of the MN

• Next 32-bit word for the COA of the MN at the new agent

• Next 32-bit word for the identification of the MN

• Next─ A set of words for extensions MNk after discovery of FAj seeking registration

for creating tunnel between HAl and FAj

3.7.5 8 flag bits

• Flag1─ specifies whether the COA is a collocated COA

• Flag2─ whether the advertising agent is the HA 8 flag bits

• Flag3─ whether the advertising agent is the FA

• Flag4─specifies whether the MN requests previous mobility binding to be retained.

This permits both—the new and previous mobility bindings 8 flag bits

• Flag5─ specifies whether the encapsulation method is generic.




UNIT-3 3. 23

• Flag6─ specifies whether the encapsulation method is a minimal mandatory method 8

flag bits

• Flag7─ specifies whether the MN wishes to receive broadcast (multicast) messages,

which the HA receives for tunneling to the new FA. If not, then the broadcast messages

are filtered at the HA

• Flag8─ specify if there is reverse tunneling support from the FA Words after UDP

header in the

3.7.6 Registration Reply

• 32-bit word with first byte = 00000011, 8 bits for a code specifying the result of

registration, and two bytes for the lifetime (in seconds)

• Next 32-bit word for the home IP address of the MN Words after UDP header in the

• Next 32-bit word for the home agent IP address of the MN

• Next 32-bit word for identification of the MN

• Next a set of words for extensions

3.7.7 New database entry fields after registration at the HA

1. ID for identification of MN

2. COA of the MN

3. Lifetime of binding to tunnel the packets to the MN’s COA

When the binding life expires the tunnel is not forwarding from the HA to the FA using

the COA. Database Entries in the fields at the FA after registration at the HA

(a) MN identification field

(b) Home IP address of the MN

(c) IP address of the HA

(d) MN link layer address for sending and receiving packets and messages to and from

the MN

(e) UDP source port of the registration request

(f) Received identification of the MN

(g) COA of the MN and lifetime of binding to tunnel the packets to the MN’s COA

(h) Remaining lifetime




UNIT-3 3. 24

3.8 Tunneling and Encapsulation FA has the COA (care-of address) of the MN

• The FA receives the IP packets, that were received at the home agent (HA) through a

tunnel from the HA to the FA─ from HA IP address to the COA IP address at the FA

• Packets received at the HA─ transmitted through the tunnel after encapsulation

3.8.1Tunneling

• Establishing of a pipe

• Pipe─ a data stream between two connected ends

• The data stream─ inserted from one end

• FIFO (first in first out) words from the other end.

Figure 3.7 Three ways of encapsulation

3.8.2 IP header-in-IP header Method of encapsulation

• Over the IP packet received at the HA

• Maximum 216-byte IP packet

• New IP header─ the IP address of the HA as the source and the IP address of the FA as

the destination.

• The three ways of encapsulation in the figure 3.7




UNIT-3 3. 25

Figure 3.8 Two tunnels Tlj and Tkk

Figure 3.9 A tunnel between the HA and FA to carry the encapsulated packet

3.8.3 Format of Encapsulated data

• First 32-bit word to specify the IP version (IPv4 or IPv6 for Internet or broadband

Internet), length of header (= 5 words), precedence of the packet, and total packet-length

(which is now 5 words more than that of IP packet received at the HA)

• Second 32-bit word, to specify the ID for the packet, flags, and fragment offset for the

same packet ID




UNIT-3 3. 26

• Third 32-bit word, to specify the time-to live (number of attempts to hop before expiry

of packets at the network), type of protocol, checksum of the header (for finding

transmission errors, if any)

• Fourth 32-bit word (four decimal numbers separated by dots and each less than 256) to

specify the IP address of the home agent

• Fifth 32-bit word (four decimal numbers separated by dots and each less than 256) to

specify the IP address of the destination COA (care-of address)

• sixth to tenth words are the IP header of 5 words with the fourth word as the IP address

of the correspondent node (CN), and the fifth word as the IP address of the MN

3.8.4 IP header-in-IP header encapsulation Format of Encapsulated data

IP Packet data received from the transport layer at the correspondent node, each

packet has a maximum of 216 bytes

3.8.5 Redundancy in IP header-in-IP header method

• First words in the new IP header (of five words) and the IP packet header (of five

words) are the same and are duplicating in case of IP-in-IP encapsulation

3.8.6 Minimum Encapsulation (ME) method by IP header of an IP Packet

• Combines header of 10 words specified into 7 or 8 words

• The 6th and 7th words in the 6th item of the new IP header are not present in ME as

both words are mere repetitions in ME method by IP header to an IP Packet

• The 8th word in the 6th item─ changed and now specifies the type of protocol, a one bit

flag, seven reserved bits, and a 16- bit checksum of the modified three-word IP header

(from the original five) for finding transmission error, if any.

• The 9th word in the 6th item─ changed and now specifies (instead of the CN IP

address) the MN IP address (which was earlier specified by the 10th word).

• The 10th word in the 6th item─ changed and now specifies (instead of the MN IP

address) the CN IP address in case the flag bit is set to 1 and the 10th word in the 6th

item is removed in case the flag bit is set to 0. Action by FA in case of ME method

• Reads the first five words in ME

• Transmits the packet to the MN using the COA




UNIT-3 3. 27

• The MN IP address is specified by the 7th or the 8th word, depending upon the flag bit.

3.8.7 Deficiencies in the IP header-in-IP header and ME methods

(a) Routing information for tunneling not given

(b) No provision for recursive encapsulations

• Recursive encapsulations needed when the tunnel transmits multiple pieces of

information for the MN and each piece of information encapsulates in one

protocol

(c) No provision for a key that can be used for authentication or encryption

3.8.8 Generic Routing Encapsulation (GRE) by IP header of an IP Packet

• One or more GRE headers depending on the number of recursions required to send

multiple pieces of information

3.8.9 Tunnel characteristics

• The tunnel does not need an extra hop (attempt) so time-to-live can be set to 1 • Tunnel

does not get blocked like routers due to external IP address transmissions

• Has fixed source and destination endpoints

3.8.10 GRE by IP header of an IP Packet

• Same as the 1st to 5th words in the 1st to 5th items of the new IP header

• Time-to-live is however set as 1

• Results in once-only forwarding to the FA by the HA

3.8.11 GRE (GRE) Header(s)

• The 6th 32-bit word in encapsulation and the 1st word of the first GRE header

• 16-bit flags─ bits to define the number of recursions, reserve bits, and version bits

• Next 16 bits─ specify the protocol for encapsulating the information sent with the GRE

header

• The 7th word─ specifies a 16-bit checksum and a 16-bit offset Both are optional as

indicated by the flag bits used to define these options

• The 8th word─ a 32-bit key

• Optional as indicated by the flag bit to used define the key-option

• The key at the GRE header─ enables authentication or encryption at the FA




UNIT-3 3. 28

• The 9th word─ specifies 32-bit sequence number information

• Optional as indicated by the flag bit used to define the sequencing-option

• Sequencing at the GRE header enables the FA to rearrange the packets sent by the HA

• The 10th word─ specifies 32-bit routing information

• Optional as indicated by the flag bit used to define the routing-option

• Routing at the GRE header enables use of routing information at the FA

• 11th word onwards─ , if number of recursions are defined in the first word of the GRE

header, then the next GRE header is inserted before the IP header and IP data sent by the

HA

• If number of recursions specified in the 11th word in the GRE header is two, then the

next two GRE headers are also inserted before the IP header and IP data sent by the HA

3.8.12 IP Header and IP Packet data

• This part remains the same as that in the un-encapsulated IP header and the data

received from the CN (correspondent node) IP packet at the HA. The first word has 5 flag

bits and three recursion-number-defining bits

• The five flag bits are—checksum option flag, sequence number field option flag, key-

option flag, and source-routing option flag

3.8.13 Source routing

• Source of a packet provides the route information

• Router uses the routing information word for routing a packet

3.9 Route Optimization Mobile IP network employing home and foreign agents FAk and FAj

• Packet delivers to and from the MNk at a foreign network with FAk and MN1 at

the foreign network with FAj is shown in figure 3.10.

Example

• Assume that MNl visiting a foreign network which happens to be the home

network of CN2 as shown in figure 3.11. CN2 is very close to CN.




UNIT-3 3. 29

Figure 3.10 CN (MNk) corresponding with visiting MNl

3.9.1 Triangular route

• Triangular route without mobility binding between COAj and CNk

• Also possible that FAk and FAj are identical

3.9.2 Optimization of route for the triangular routing example

Route optimization and path 1, 2, 3, 4, 5 after mobility binding of MN1 at COAj with

CNk can be made in case the MNl opts to make its mobility known as shown in the figure 3.12.

3.9.3 Mobility binding Steps in the calling network

1. CNk (fixed) or MNk (mobile) network sends a mobility-binding request to HAl

2. HAl detects whether MNl (for which binding request is made) has blocked external

mobility binding requests

• If not, then HAl sends the update for the mobility-binding message to the CNk

network

• External─ does not include the visiting network FA

3. Mobility binding message has the IP address of MN1 and the present COA (COAj) of

MNl when on visit to a foreign network and registered with FAj




UNIT-3 3. 30

4. CNk issues an acknowledgement to HAl on receiving the binding message.

5. CN2 network decapsulates the IP packet (this decapsulation would have been

performed by FAj through HA1 if MN1 had blocked external binding requests) and sends

a warning for binding

Figure 3.11 Packets make a triangular trip to reach from CNk to MNl

3.9.4 Warning sent to HAl of MNl

• Serves a purpose─ HAl sending the binding update to CNk when MNl moves to visit

another foreign network or when it returns to the home network Warning for binding

• A message to the effect that the new IP addresses of MNl and CN2 will decapsulate the

encapsulated IP packets (from the moment that the warning is aired) instead of FAj




UNIT-3 3. 31

Figure 3.12 Route optimization and path 1, 2, 3, 4, 5 after mobility binding of MN1 at

COAj with CNk

3.9.5 Smooth handover in Mobile IP protocol method of optimization

• FAj sends a binding warning to CNk when MN1 deregisters with it

• Lets CNk initiate another binding request to HAl of MNl

• CNk gets the new binding and COAm address from HAl in the binding cache

3.9.6 Reverse Tunnel

• If a reverse tunnel is formed then another tunnel is present through the paths from 10 to

3 and reverse tunneling is from FA to HA

3.9.7 Advantage of reverse tunneling

• Multicasting needs bi-directional tunneling

• Reverse tunneling is required when a firewall is employed

3.9.8 Time-to-live for forward and reverse tunneling

• Time-to-live defines the number of attempts to hop before expiry of packets at the

network




UNIT-3 3. 32

• GRE header encapsulation during tunneling sets time-to-live = 1, so the packets are

forwarded only once

• The tunnel does not need extra hops, has fixed endpoints

• Results in once-only forwarding through the tunnel from the home agent (HA) to the

foreign agent (FA) when the mobile node (MN) visits a foreign network

• The tunnel does not need extra hops

• It has fixed endpoints Time-to-live for MNl on visit sending to CNk

• At the foreign agent, the time-to-live setting might be too low

• Therefore, when the MNl sends the response to the correspondent network (CNk), then

the time-to-live set at the FA may not be sufficient

• When the COA is used to send the response to the CN without reverse tunneling, then a

very low setting of timeto- live blocks the packets after a very small number of hops

(attempts) to the CN

3.9.8.1 Time-to-live for reverse tunneling

• Sets the time-to-live equal to 1 because IP packets need to be sent only once

• The tunnel does not need extra hop

• It has fixed source and destination endpoints

3.9.9 Reverse tunneling

• Facilitates guaranteed transmission of the IP packet responses through the tunnel to the

HA

• Now, the HA transmits the response to the CN

• A low value of time-to-live at the FA does not lead to packet expiries

3.10 Dynamic Host Configuration Protocol The dynamic host configuration protocol (DHCP, RFC 2131, Drohms, 1997) is mainly

used to simplify the installation and maintenance of networked computers. If a new computer is

connected to a network, DHCP can provide it with all the necessary information for full system

integration into the network, e.g., addresses of a DNS server and the default router, the subnet

mask, the domain name, and an IP address. Providing an IP address makes DHCP very attractive




UNIT-3 3. 33

for mobile IP as a source of care-of-addresses. While the basic DHCP mechanisms are quite

simple, many options are available as described in RFC 2132 (Alexander, 1997).

DHCP is based on a client/server model as shown in figure 3.13. DHCPclients send a

request to a server (DHCPDISCOVER in the example) to which the server responds. A client

sends requests using MAC broadcasts to reach all devices in the LAN. A DHCP relay might be

needed to forward requests across inter-working units to a DHCP server

Figure 3.13 Basic DHCP Configuration

Figure 3.14 Client initialization via DHCP

A typical initialization of a DHCP client is shown in figure. The figure shows one client

and two servers. As described above, the client broadcasts a DHCP DISCOVER into the subnet.

There might be a relay to forward this broadcast.




UNIT-3 3. 34

In the case shown, two servers receive this broadcast and determine the configuration

they can offer to the client. One example for this could be the checking of available IP addresses

and choosing one for the client. Servers reply to the client’s request with DHCPOFFER and offer

a list of configuration parameters.

The client can now choose one of the configurations offered. The client in turn replies to

the servers, accepting one of the configurations and rejecting the others using DHCPREQUEST.

If a server receives a DHCPREQUEST with a rejection, it can free the reserved configuration for

other possible clients. The server with the configuration accepted by the client now confirms the

configuration with DHCPACK. This completes the initialization phase.

If a client leaves a subnet, it should release the configuration received by the server using

DHCPRELEASE. Now the server can free the context stored for the client and offer the

configuration again. The configuration a client gets from a server is only leased for a certain

amount of time, it has to be reconfirmed from time to time. Otherwise the server will free the

configuration. This timeout of configuration helps in the case of crashed nodes or nodes moved

away without releasing the context.

DHCP is a good candidate for supporting the acquisition of care-of addresses for mobile

nodes. The same holds for all other parameters needed, such as addresses of the default router,

DNS servers, the timeserver etc. A DHCP server should be located in the subnet of the access

point of the mobile node, or at least a DHCP relay should provide forwarding of the messages.

RFC 3118 specifies authentication for DHCP messages which is needed to protect mobile nodes

from malicious DHCP servers. Without authentication, the mobile node cannot trust a DHCP

server, and the DHCP server cannot trust the mobile node.




UNIT-3 3. 35

3.11 Question Bank PART – A (2 MARKS)

1. What are the requirements of mobile IP?

2. Mention the different entities in a mobile IP.

3. What do you mean by mobility binding?

4. Define a tunnel.

5. What is encapsulation?

6. What is decapsulation?

7. Define an outer header

8. Define an inner header.

9. What is meant by generic routing encapsulation?

10. What is the use of network address translation?

11. Define triangular routing.

12. What is meant by a binding cache?

13. Define binding request.

14. What is known as Binding update?

15. Explain binding acknowledgement.

16. Define binding warning.

17. Explain cellular IP.

18. What are the advantages of cellular IP?

19. What is known as mobility anchor point?

20. Explain destination sequence distance vector routing.

21. What are the two things added to the distance vector algorithm?

22. How the dynamic source routing does divide the task of routing into two separate problems?




UNIT-3 3. 36

PART – B (16 Marks)

1. What are the requirements of a mobile IP?

2. Describe Dynamic host configuration protocol.

3. Discuss the routing algorithm in ad-hoc network

4. What are the entities in mobile IP?

5. Discuss how optimization in achieved in mobile IP

6. Explain tunneling and encapsulation in mobile IP.

7. Explain how dynamic source routing protocols handles routing with an example.

8. How can DHCP be used for mobility and support of mobile IP?




UNIT-4 4. 1

UNIT 4

MOBILE TRANSPORT LAYER




UNIT-4 4. 2

CONTENTS 4.1 Classical TCP Improvements

4.2 Indirect TCP

4.3 Snooping TCP

4.4 Mobile TCP

4.5 Fast Retransmit/Fast Recovery

4.6 Transmission/Time-Out Freezing

4.7 Selective Retransmission

4.8 Transaction-Oriented TCP

4.9 Mobile Operating Systems

4.10 Palm OS

4.11 Windows CE

4.12 Symbion OS

4.13 Linux for Mobile Devices

4.14 Question Bank




UNIT-4 4. 3

TECHNICAL TERMS

1. TCP is Transmission Control Protocol. It provides reliable, ordered delivery of a stream

of bytes from a program on one computer to another program on another

computer.(Connection oriented)

2. Internet Protocol (IP) is the principal communications protocol used for

relaying datagram across an internetwork using the Internet Protocol Suite.

3. IP Addressing refers to how end hosts are assigned IP addresses and how sub networks

of IP host addresses are divided and grouped.

4. IP routing is performed by all hosts, but most importantly by routers, which typically use

either interior gateway protocols (IGPs) or external gateway protocols (EGPs) to decide

how to move datagram’s among networks.

5. Packets are the IP works by exchanging pieces of information called packets

6. UDP (User Datagram Protocol) is a communications protocol that offers a limited

amount of service when messages are exchanged between computers in a network that

uses the Internet Protocol (IP). (Connectionless protocol)

7. Snooping is unauthorized access to another person's or company's data.

8. Eavesdropping is the unauthorized real-time interception of a private communication,

such as a phone call, instant message, video conference or fax transmission.

9. Datagram is a basic transfer unit associated with a packet-switched network in which the

delivery, arrival time, and order of arrival are not guaranteed by the network service.

10. An operating system (OS) is a set of software that manages computer

hardware resources and provides common services for computer programs. The operating

system is a vital component of the system software in a computer system. Application

programs require an operating system to function.

11. Palm OS (also known as Garnet OS) is a mobile operating system initially developed

by Palm, Inc., for personal digital assistants (PDAs) in 1996. Palm OS is designed for

ease of use with a touch screen-based graphical user interface. It is provided with a suite

of basic applications for personal information management.




UNIT-4 4. 4

4. MOBILE TRANSPORT LAYER

4.1 Conventional TCP/IP protocols Together with the introduction of WLANs in the mid-nineties several research projects

were started with the goal to increase TCP’s performance in wireless and mobile environments.

4.2 Indirect TCP

Two competing insights led to the development of indirect TCP (I-TCP) (Bakre, 1995).

One is that TCP performs poorly together with wireless links; the other is that TCP within the

fixed network cannot be changed. I-TCP segments a TCP connection into a fixed part and a

wireless part. Figure 4.1 shows an example with a mobile host connected via a wireless link and

an access point to the ‘wired’ internet where the correspondent host resides. The correspondent

node could also use wireless access. The following would then also be applied to the access link

of the correspondent host.

Standard TCP is used between the fixed computer and the access point. No computer in

the internet recognizes any changes to TCP. Instead of the mobile host, the access point now

terminates the standard TCP connection, acting as a proxy. This means that the access point is

now seen as the mobile host for the fixed host and as the fixed host for the mobile host. Between

the access point and the mobile host a special TCP, adapted to wireless links, is used. However,

changing TCP for the wireless link is not a requirement. Even an unchanged TCP can benefit

from the much shorter round trip time, starting retransmission much faster.

A good place for segmenting the connection between mobile host and correspondent host

is at the foreign agent of mobile IP. The foreign agent controls the mobility of the mobile host

anyway and can also hand over the connection to the next foreign agent when the mobile host

moves on.




UNIT-4 4. 5

Figure 4.1 Indirect TCP segments a TCP connection into two parts

The correspondent host in the fixed network does not notice the wireless link or the

segmentation of the connection. The foreign agent acts as a proxy and relays all data in both

directions. If the correspondent host sends a packet, the foreign agent acknowledges this packet

and tries to forward the packet to the mobile host. If the mobile host receives the packet, it

acknowledges the packet. However, this acknowledgement is only used by the foreign agent. If a

packet is lost on the wireless link due to a transmission error, the correspondent host would not

notice this. In this case, the foreign agent tries to retransmit this packet locally to maintain

reliable data transport.

Similarly, if the mobile host sends a packet, the foreign agent acknowledges this packet

and tries to forward it to the correspondent host. If the packet is lost on the wireless link, the

mobile hosts notice this much faster due to the lower round trip time and can directly retransmit

the packet. Packet loss in the wired network is now handled by the foreign agent.

Figure 4.2 Socket and state migration after handover of a mobile host




UNIT-4 4. 6

There are several advantages with I-TCP:

I-TCP does not require any changes in the TCP protocol as used by the hosts in the fixed

network or other hosts in a wireless network that do not use this optimization. All current

optimizations for TCP still work between the foreign agent and the correspondent host.

Due to the strict partitioning into two connections, transmission errors on the wireless

link, i.e., lost packets, cannot propagate into the fixed network. Without partitioning,

retransmission of lost packets would take place between mobile host and correspondent host

across the whole network. Now only packets in sequence, without gaps leave the foreign agent.

It is always dangerous to introduce new mechanisms into a huge network such as the

internet without knowing exactly how they will behave. However, new mechanisms are needed

to improve TCP performance (e.g., disabling slow start under certain circumstances), but with I-

TCP only between the mobile host and the foreign agent. Different solutions can be tested or

used at the same time without jeopardizing the stability of the internet. Furthermore, optimizing

of these new mechanisms is quite simple because they only cover one single hop.

Assume that the short delay between the mobile host and foreign agent could be

determined and was independent of other traffic streams. An optimized TCP could use precise

time-outs to guarantee retransmission as fast as possible. Even standard TCP could benefit from

the short round trip time, so recovering faster from packet loss. Delay is much higher in a typical

wide area wireless network than in wired networks due to FEC and MAC. GSM has a delay of

up to 100 ms circuit switched, 200 ms and more packet switched (depending on packet size and

current traffic). This is even higher than the delay on transatlantic links.

Partitioning into two connections also allows the use of a different transport layer

protocol between the foreign agent and the mobile host or the use of compressed headers etc.

The foreign agent can now act as a gateway to translate between the different protocols.

But the idea of segmentation in I-TCP also comes with some disadvantages:

The loss of the end-to-end semantics of TCP might cause problems if the foreign agent

partitioning the TCP connection crashes. If a sender receives an acknowledgement, it assumes

that the receiver got the packet. Receiving an acknowledgement now only means (for the mobile




UNIT-4 4. 7

host and a correspondent host) that the foreign agent received the packet. The correspondent

node does not know anything about the partitioning, so a crashing access node may also crash

applications running on the correspondent node assuming reliable end-to-end delivery.

In practical use, increased handover latency may be much more problematic. All packets

sent by the correspondent host are buffered by the foreign agent besides forwarding them to the

mobile host (if the TCP connection is split at the foreign agent). The foreign agent removes a

packet from the buffer as soon as the appropriate acknowledgement arrives. If the mobile host

now performs a handover to another foreign agent, it takes a while before the old foreign agent

can forward the buffered data to the new foreign agent. During this time more packets may

arrive. All these packets have to be forwarded to the new foreign agent first, before it can start

forwarding the new packets redirected to it.

The foreign agent must be a trusted entity because the TCP connections end at this point.

If users apply end-to-end encryption, e.g., according to RFC 2401 (Kent, 1998a), the foreign

agent has to be integrated into all security mechanisms.

4.3 Snooping TCP One of the drawbacks of I-TCP is the segmentation of the single TCP connection into

two TCP connections. This loses the original end-to-end TCP semantic. The following TCP

enhancement works completely transparently and leaves the TCP end-to-end connection intact.

The main function of the enhancement is to buffer data close to the mobile host to perform fast

local retransmission in case of packet loss. A good place for the enhancement of TCP could be

the foreign agent in the Mobile IP context.

In this approach, the foreign agent buffers all packets with destination mobile host and

additionally ‘snoops’ the packet flow in both directions to recognize acknowledgements

(Balakrishnan, 1995), (Brewer, 1998). The reason for buffering packets toward the mobile node

is to enable the foreign agent to performa local retransmission in case of packet loss on the

wireless link. The foreign agent buffers every packet until it receives an acknowledgement from

the mobile host.




UNIT-4 4. 8

If the foreign agent does not receive an acknowledgement from the mobile host within a

certain amount of time, either the packet or the acknowledgement has been lost. Alternatively,

the foreign agent could receive a duplicate ACK which also shows the loss of a packet. Now the

foreign agent retransmits the packet directly from the buffer, performing a much faster

retransmission compared to the correspondent host. The time out for acknowledgements can be

much shorter, because it reflects only the delay of one hop plus processing time.

Figure 4.3 Snooping TCP as a transparent TCP extension

To remain transparent, the foreign agent must not acknowledge data to the correspondent

host. This would make the correspondent host believe that the mobile host had received the data

and would violate the end-to-end semantic in case of a foreign agent failure. However, the

foreign agent can filter the duplicate acknowledgements to avoid unnecessary retransmissions of

data from the correspondent host. If the foreign agent now crashes, the time-out of the

correspondent host still works and triggers a retransmission. The foreign agent may discard

duplicates of packets already retransmitted locally and acknowledged by the mobile host. This

avoids unnecessary traffic on the wireless link.

Data transfer from the mobile host with destination correspondent host works as

follows. The foreign agent snoops into the packet stream to detect gaps in the sequence numbers

of TCP. As soon as the foreign agent detects a missing packet, it returns a negative

acknowledgement (NACK) to the mobile host. The mobile host can now retransmit the missing

packet immediately. Reordering of packets is done automatically at the correspondent host by

TCP. Extending the functions of a foreign agent with a ‘snooping’ TCP has several advantages:




UNIT-4 4. 9

The end-to-end TCP semantic is preserved. No matter at what time the foreign agent

crashes (if this is the location of the buffering and snooping mechanisms), neither the

correspondent host nor the mobile host have an inconsistent view of the TCP connection

as is possible with I-TCP. The approach automatically falls back to standard TCP if the

enhancements stop working.

The correspondent host does not need to be changed; most of the enhancements are in the

foreign agent. Supporting only the packet stream from the correspondent host to the

mobile host does not even require changes in the mobile host.

It does not need a handover of state as soon as the mobile host moves to another foreign

agent. Assume there might still be data in the buffer not transferred to the next foreign

agent. All that happens is a time-out at the correspondent host and retransmission of the

packets, possibly already to the new care-of address.

It does not matter if the next foreign agent uses the enhancement or not. If not, the

approach automatically falls back to the standard solution. This is one of the problems of

I-TCP, since the old foreign agent may have already signaled the correct receipt of data

via acknowledgements to the correspondent host and now has to transfer these packets to

the mobile host via the new foreign agent.

The simplicity of the scheme also results in some disadvantages:

Snooping TCP does not isolate the behavior of the wireless link as well as ITCP.

Assume, for example, that it takes some time until the foreign agent can successfully retransmit a

packet from its buffer due to problems on the wireless link (congestion, interference). Although

the time-out in the foreign agent may be much shorter than the one of the correspondent host,

after a while the time-out in the correspondent host triggers a retransmission.

The problems on the wireless link are now also visible for the correspondent host and not

fully isolated. The quality of the isolation, which snooping TCP offers, strongly depends on the

quality of the wireless link, time-out values, and further traffic characteristics. It is problematic

that the wireless link exhibits very high delays compared to the wired link due to error correction




UNIT-4 4. 10

on layer 2 (factor 10 and more higher). This is similar to ITCP. If this is the case, the timers in

the foreign agent and the correspondent host are almost equal and the approach is almost

ineffective.

Using negative acknowledgements between the foreign agent and the mobile host

assumes additional mechanisms on the mobile host. This approach is no longer transparent for

arbitrary mobile hosts.

All efforts for snooping and buffering data may be useless if certain encryption schemes

are applied end-to-end between the correspondent host and mobile host. Using IP encapsulation

security payload (RFC 2406, (Kent, 1998b)) the TCP protocol header will be encrypted –

snooping on the sequence numbers will no longer work. Retransmitting data from the foreign

agent may not work because many security schemes prevent replay attacks – retransmitting data

from the foreign agent may be misinterpreted as replay. Encrypting end-to-end is the way many

applications work so it is not clear how t his scheme could be used in the future. If encryption is

used above the transport layer (e.g., SSL/TLS) snooping TCP can be used.

4.4 Mobile TCP Dropping packets due to a handover or higher bit error rates is not the only phenomenon

of wireless links and mobility – the occurrence of lengthy and/or frequent disconnections is

another problem. Quite often mobile users cannot connect at all. One example is islands of

wireless LANs inside buildings but no coverage of the whole campus.

What happens to standard TCP in the case of disconnection?

A TCP sender tries to retransmit data controlled by a retransmission timer that

doubles with each unsuccessful retransmission attempt, up to a maximum of one minute

(the initial value depends on the round trip time). This means that the sender tries to

retransmit an unacknowledged packet every minute and will give up after 12

retransmissions.




UNIT-4 4. 11

What happens if connectivity is back ear-lier than this?

No data is successfully transmitted for a period of one minute. The

retransmission time-out is still valid and the sender has to wait. The sender also goes into

slow-start because it assumes congestion.

What happens in the case of I-TCP if the mobile is disconnected?

The proxy has to buffer more and more data, so the longer the period of

disconnection, the more buffer is needed. If a handover follows the disconnection, which

is typical, even more state has to be transferred to the new proxy. The snooping approach

also suffers from being disconnected. The mobile will not be able to send ACKs so,

snooping cannot help in this situation.

The M-TCP (mobile TCP) approach has the same goals as I-TCP and snooping TCP: to

prevent the sender window from shrinking if bit errors or disconnection but not congestion cause

current problems. M-TCP wants to improve overall throughput, to lower the delay, to maintain

end-to-end semantics of TCP, and to provide a more efficient handover. Additionally, M-TCP is

especially adapted to the problems arising from lengthy or frequent disconnections.

M-TCP splits the TCP connection into two parts as I-TCP does. An unmodified TCP is

used on the standard host-supervisory host (SH) connection, while an optimized TCP is used on

the SH-MH connection. The supervisory host is responsible for exchanging data between both

parts similar to the proxy in). The M-TCP approach assumes a relatively low bit error rate on the

wireless link. Therefore, it does not perform caching/retransmission of data via the SH. If a

packet is lost on the wireless link, it has to be retransmitted by the original sender. This

maintains the TCP end-to-end semantics.

The SH monitors all packets sent to the Mobile Host (MH) and ACKs returned from the

MH. If the SH does not receive an ACK for some time, it assumes that the MH is disconnected.

It then chokes the sender by setting the sender’s window size to 0. Setting the window size to 0

forces the sender to go into persistent mode, i.e., the state of the sender will not change no

matter how long the receiver is disconnected. This means that the sender will not try to




UNIT-4 4. 12

retransmit data. As soon as the SH (either the old SH or a new SH) detects connectivity again, it

reopens the window of the sender to the old value. The sender can continue sending at full speed.

This mechanism does not require changes to the sender’s TCP.

The wireless side uses an adapted TCP that can recover from packet loss much faster.

This modified TCP does not use slow start, thus, M-TCP needs a bandwidth manager to

implement fair sharing over the wireless link.

The advantages of M-TCP are

It maintains the TCP end-to-end semantics. The SH does not send any ACK itself but

forwards the ACKs from the MH.

If the MH is disconnected, it avoids useless retransmissions, slow starts or breaking

connections by simply shrinking the sender’s window to 0.1 The reader should be aware

that mobile TCP does not have the same status as mobile IP, which is an internet RFC.

Since it does not buffer data in the SH as I-TCP does, it is not necessary to forward

buffers to a new SH. Lost packets will be automatically retransmitted to the new SH.

The lack of buffers and changing TCP on the wireless part also has some disadvantages:

As the SH does not act as proxy as in I-TCP, packet loss on the wireless link due to bit

errors is propagated to the sender. M-TCP assumes low bit error rates, which is not

always a valid assumption.

A modified TCP on the wireless link not only requires modifications to the MH protocol

software but also new network elements like the bandwidth manager.

4.5 Fast Retransmit/Fast Recovery

TCP concludes congestion and goes into slow start, although there is no congestion. The

mechanisms of fast recovery/fast retransmit a host can use after receiving duplicate

acknowledgements, thus concluding a packet loss without congestion.

The idea presented by Caceres (1995) is to artificially force the fast retransmit behavior

on the mobile host and correspondent host side. As soon as the mobile host registers at a new




UNIT-4 4. 13

foreign agent using mobile IP, it starts sending duplicated acknowledgements to correspondent

hosts. The proposal is to send three duplicates. This forces the corresponding host to go into fast

retransmit mode and not to start slow start, i.e., the correspondent host continues to send with the

same rate it did before the mobile host moved to another foreign agent.

As the mobile host may also go into slow start after moving to a new foreign agent, this

approach additionally puts the mobile host into fast retransmit. The mobile host retransmits all

unacknowledged packets using the current congestion window size without going into slow start.

The advantage of this approach is its simplicity. Only minor changes in the mobile

host’s software already result in a performance increase. No foreign agent or correspondent host

has to be changed.

The main disadvantage of this scheme is the insufficient isolation of packet losses.

Forcing fast retransmission increases the efficiency, but retransmitted packets still have to cross

the whole network between correspondent host and mobile host. If the handover from one

foreign agent to another takes a longer time, the correspondent host will have already started

retransmission. The approach focuses on loss due to handover: packet loss due to problems on

the wireless link is not considered. This approach requires more cooperation between the mobile

IP and TCP layer making it harder to change one without influencing the other.

4.6 Transmission/Time-Out Freezing

While the approaches presented so far can handle short interruptions of the connection,

either due to handover or transmission errors on the wireless link, some were designed for longer

interruptions of transmission. Examples are the use of mobile hosts in a car driving into a tunnel,

which loses its connection to, e.g., a satellite (however, many tunnels and subways provide

connectivity via a mobile phone), or a user moving into a cell with no capacity left over. In this

case, the mobile phone system will interrupt the connection. The reaction of TCP, even with the

enhancements of above, would be a disconnection after a time out.

Quite often, the MAC layer has already noticed connection problems, before the

connection is actually interrupted from a TCP point of view. Additionally, the MAC layer knows

the real reason for the interruption and does not assume congestion, as TCP would. The MAC




UNIT-4 4. 14

layer can inform the TCP layer of an upcoming loss of connection or that the current interruption

is not caused by congestion. TCP can now stop sending and ‘freezes’ the current state of its

congestion window and further timers. If the MAC layer notices the upcoming interruption early

enough, both the mobile and correspondent host can be informed. With a fast interruption of the

wireless link, additional mechanisms in the access point are needed to inform the correspondent

host of the reason for interruption. Otherwise, the correspondent host goes into slow start

assuming congestion and finally breaks the connection.

As soon as the MAC layer detects connectivity again, it signals TCP that it can resume

operation at exactly the same point where it had been forced to stop. For TCP time simply does

not advance, so no timers expire.

The advantage of this approach is that it offers a way to resume TCP connections even

after longer interruptions of the connection. It is independent of any other TCP mechanism, such

as acknowledgements or sequence numbers, so it can be used together with encrypted data.

However, this scheme has some severe disadvantages. Not only does the software on the mobile

host have to be changed, to be more effective the correspondent host cannot remain unchanged.

All mechanisms rely on the capability of the MAC layer to detect future interruptions. Freezing

the state of TCP does not help in case of some encryption schemes that use time-dependent

random numbers. These schemes need resynchronization after interruption.

4.7 Selective Retransmission A very useful extension of TCP is the use of selective retransmission. TCP

acknowledgements are cumulative, i.e., they acknowledge in-order receipt of packets up to a

certain packet. If a single packet is lost, the sender has to retransmit everything starting from the

lost packet (go-back-n retransmission). This obviously wastes bandwidth, not just in the case of a

mobile network, but for any network (particularly those with a high path capacity, i.e.,

bandwidth delay- product).

Using RFC 2018 (Mathis, 1996), TCP can indirectly request a selective retransmission of

packets. The receiver can acknowledge single packets, not only trains of in-sequence packets.

The sender can now determine precisely which packet is needed and can retransmit it.




UNIT-4 4. 15

The advantage of this approach is obvious: a sender retransmits only the lost packets.

This lowers bandwidth requirements and is extremely helpful in slow wireless links. The gain in

efficiency is not restricted to wireless links and mobile environments. Using selective

retransmission is also beneficial in all other networks. However, there might be the minor

disadvantage of more complex software on the receiver side, because now more buffer is

necessary to resequence data and to wait for gaps to be filled. But while memory sizes and CPU

performance permanently increase, the bandwidth of the air interface remains almost the same.

Therefore, the higher complexity is no real disadvantage any longer as it was in the early days of

TCP.

4.8 Transaction-Oriented TCP Assume an application running on the mobile host that sends a short request to a server

from time to time, which responds with a short message. If the application requires reliable

transport of the packets, it may use TCP.

Using TCP now requires several packets over the wireless link. First, TCP uses a three-

way handshake to establish the connection. At least one additional packet is usually needed for

transmission of the request, and requires three more packets to close the connection via a three-

way handshake. Assuming connections with a lot of traffic or with a long duration, this overhead

is minimal. But in an example of only one data packet, TCP may need seven packets altogether.

Web services are based on HTTP which requires a reliable transport system. In the internet, TCP

is used for this purpose. HTTP request can be transmitted the TCP connection has to be

established. This already requires three messages. If GPRS is used as wide area transport system,

one-way delays of 500 ms and more are quite common. The setup of a TCP connection already

takes far more than a second.

This led to the development of a transaction-oriented TCP (T/TCP, RFC 1644 (Braden,

1994)). T/TCP can combine packets for connection establishment and connection release with

user data packets. This can reduce the number of packets down to two instead of seven. Similar

considerations led to the development of a transaction service in WAP.




UNIT-4 4. 16

Figure 4.4 Example TCP connection setup overhead

The obvious advantage for certain applications is the reduction in the overhead which

standard TCP has connection setup and connection release. However, T/TCP is not the original

TCP anymore, so it requires changes in the mobile host and all correspondent hosts, which is a

major disadvantage. This solution no longer hides mobility. Furthermore, T/TCP exhibits

several security problems. The table 4.1 shows the overview of classical enhancements to TCP

for mobility.

4.9 Mobile Operating Systems i) Operating system (OS):

The master control program.

Manages all software and hardware resources.

Controls, allocates, frees, and modifies the memory by increasing or decreasing it

Also manages files, disks, and security, provides device drivers and GUIs for desktop

or mobile computer, other functions, and applications.

Enables the assignment of priorities for requests to the system and controls IO

devices and network.




UNIT-4 4. 17

Table 4.1 Overview of classical enhancements to TCP for mobility

ii) Device driver :

• As software component which enables the use of a device, port, or network by

configuring (for open, close, connect, or specifying a buffer size, mode, or control word)

and sends output or receives input

• Driver Functions─ create, delete, open, close, read, write, io_control, connect, bind,

listen and accept

• Has the utility programs, for example, file manager and configuration of OS (memory

and resource allocation and enabling and disabling the use of specific resources and

functions)




UNIT-4 4. 18

• Can be accompanied by a specific suite of applications, for example, Internet Explorer

and MS Office

iii) Process:

• A program unit which runs when scheduled to do so by OS and each state of which

is controlled by OS

• Can call a function (method) but cannot call another process directly.

States of a process :

• Can be in any of the states—

1. Created

2. Active

3. Running

4. Suspended

5. Pending for a specified time interval

Pending state of a process for a specific communication from other process

• Signal

• Semaphore

• Mailbox-message

• Queue-message

• Socket

iv) Task:

• An application process which runs according to its schedule set by the OS

• Each state of which is controlled by OS

• Can be a real-time task which has time constraints or maximum defined latency within

which it must run or finish.

v) Thread:

• An application process or a process subunit (when a process or task has multiple

threads)

• Runs as scheduled by the OS




UNIT-4 4. 19

• Each state controlled by OS

• Runs as a light-weight process

Light-weight:

• Does not depend on certain system resources, for example, memory management unit

(MMU), GUI functions provided by the OS, or the functions which need running of other

processes or threads for their implementation.

vi) Interrupt service routine (ISR) :

• A program unit (function, method, or subroutine) which runs when a hardware or

software event occurs.

• Running of which can be masked and can be prioritized by assigning a priority

• Higher priority than any other process or task or thread

vii) Interrupt service thread (IST):

• A special type of ISR or ISR unit (function, method, or subroutine) which initiates and

runs on an event or message from an high priority ISR

• ISTs can be prioritized by assigning a priority

• The type of IST depends on the specific OS

viii) Page :

• A unit of memory which can load from a program stored in a hard drive or from any

other storage device to the program memory, RAM, before the execution of a program

• A contiguous memory address block of 4 kB (in x86 processors), 2 kB, or 1 kB

ix) Page table :

• For address mapping

• Provides the mapping of fragmented physical memory pages with the pages of the

virtual addresses which are the memory addresses




UNIT-4 4. 20

• Pages of memory are spread over the memory-address space leading to fragmentation of

codes and data in physical memory space

x) MMU :

• Creates and maintains the page table and hence performs address mapping and

translation

• Program during execution first translates the accessed address (virtual address) into a

physical address using the page table at the MMU and then accesses the physical address

and fetches the code or data

xi) Priority inversion :

• Takes place when a process or thread which is to provide a waiting object to a higher

priority process or thread gets preempted by a middle priority process or thread and thus

the middle priority process or thread starts running on obtaining the object for which it

was waiting and higher priority process or thread keeps waiting for wait object.

xii) Pipe :

• A virtual device which sends the bytes from a thread to another thread.

Hardware events for interrupts

• Time-out of a timer (clock tick)

• Division by zero

• Overflow

• Underflow detection by hardware during computation

• Finishing of DMA (direct memory access by a peripheral) transfer

• Data abort

• External FIQ (fast interrupt request through a pin input)

• External IRQ (interrupt request through a pin input)

• A memory buffer becoming full




UNIT-4 4. 21

• Port, transmitter, receiver, or device buffer─ becoming half filled, buffer with at

least one memory address filled, and buffer becoming empty

• Buffer─ associated with the memory addresses for the LCD, printer, serial or USB port,

keypad, or modem.

Software related events for interrupts

• Exception─ software instruction for interrupt on detection of a certain condition during

computations or error while logging in

• Illegal operation code provided to CPU

4.10 PALM OS • An OS for handheld devices

• Designed for highly efficient running of small productivity programs for devices with a

few application tasks

• Offers high performance due to a special feature that it supports only one process which

controls all computations by the event handlers

PalmOS Features

• Single process (no multi-processing and multi-threading)

• Compiled for a specific set of hardware, performance very finely tuned

• Memory space partitioned into program memory and multiple storage heaps for data

and applications

• A file in format of a database

• IP-based network connectivity and Wi-Fi (in later version only)

• Integration to cellular GSM/CDMA phone

PalmOS

• No multi-processing or multi-tasking

• Simplifies the kernel of the OS─ there is an infinite waiting loop in the only process

that kernel runs

• The loop polls for an event




UNIT-4 4. 22

Polling for events at specific intervals

• Each polled event─ sends interrupt signal

• Handled by an event handler

• Functioning as non-maskable nonprioritized ISR

Example: Polling for the events

• For a request to run an application or sub-application

• For a search program request to process a query

• Notifications (like time-out alarm)

• GUI actions (such as touching or tapping the screen with stylus)

PalmOS Hardware Support

• Compiles for a specific set of hardware, its performance is very finely tuned

• Optimized to support a very specific range of hardware, CPU, controller chips, and

smaller screens of Palm OSbased devices

Display Screen Support

• Generally wide screen

• 160 × 160 pixels

• Optimized layout of desktop programs displayed on screen

• 256 colour touch screen

• Higher resolution support in new versions

PalmOS Memory Support

• 16 MB memory

• 256 MB internal flash (non-volatile ROM)

• 256 MB card consisting of flash memory which the user inserts into the device

PalmOS Memory Space Partitions

• Program memory dynamic heap─ for process stacks and global variables

• Multiple storage heaps─ for data and applications

PalmOS File Format

• Format of a database

• Multiple records




UNIT-4 4. 23

• Information fields about the file.

• Name, attributes, and version of the database for the application

PalmOS Connectivity

• IP-based network connectivity

• WiFi (in later version only)

• Wireless communication protocols


PalmOS APIs

• Simple APIs compared to Windows CE

• Simple APIs for developing the GUIs ─ buttons, menus, scroll bar, dialogs, forms, and

tables

• Using HTML markup language

PalmOS Desktop and Desktop Programs

• Desktop for Windows and Mac both and other essential software

• SMS, Address, Card-Info, HotSync, To- Do-List, SMS, Security, Date Book/Calendar,

Calc, Welcome, and Clock

PalmOS PIM

• Address book

• Data book for task-to-do and organization

• Memo pad

• SMTP (simple mail transfer protocol) email download

PalmOS PIM

• Offline creation and sending of POP3 (post office protocol 3) email

• Internet browsing functions using Blazer (a browser for handhelds)

• Windows organizer

• PDA (personal digital assistant)

PalmOS Query Development Platform

• Query development support platform Palm query applications (PQA) written using

HTML and ported at Palm device




UNIT-4 4. 24

PalmOS Client side Applications

• GUI development support on C/C++ platform using Palm SDK

• For Java application using J2ME and advanced tools, for example, Metrowerk

CodeWarrior

• Multimedia applications such as playing music (Palm Tungsten)

PalmOS Ports

• Serial and infrared ports for communication with mobile phones and external modems

• Synchroniszing a PC personal area computer using HotSync after resolving the conflicts

in different versions of files during data exchange

Port Protocols

• IrDA or serial device

• System mounted on a cradle

• Connects to computer PCs through IR or serial port

• A cradle is an attachment on which the handheld device can rest near a PC and connects

to the PC via a USB or infrared

Device handling

• Assumed as a new flash drive of a PC

• HotSync facilitates drag and drop of files from device to PC and vice versa

Cards

• MMC (multimedia card)

• SD (secure digital) memory card

• SDIO (secure digital input/output) memory card

Third Party applications support

• Examples are games, travel and flight planner, calculator, graphic drawings, preparing

slide shows.




UNIT-4 4. 25

Application layer in architectural layers of PalmOS:

The OS and hardware layer in architectural layers of PalmOS is shown below.

Figure 4.5 Application layer in architectural layers of PalmOS

Lowest level layer in OS

• Kernel

• Directly interfaces the assembler, firmware (software installed in the hardware

devices in the system), and hardware

• PalmOS has a micro-kernel

PalmOS 4.x

• Adds improved security

• Improved GUIs,VUIs, telephony libraries

• Standard interfaces for access to the external SD cards for the files




UNIT-4 4. 26

PalmOS 5.x

• Supports

(i) a standardized API for high resolution screen

(ii) dynamic input areas

(iii) Instead of persistent battery-backed RAM, a non-volatile file system using flash

memory─ saves the files and data in case the battery charge is draining out

(iv) ARM, the processor─ providing efficient code and an energy-efficient architecture

Advanced PalmOS Handheld

• Merged PDA and smart phones

• Feature to double as a hard drive using USB cable to PC

• Enables the drag and drop of files between the Palm and PC in a manner similar to the

drag and drop functions in a PC between C: and D: drives

Recent Developments

• Integration in Wndows CE

• A few Windows mobile handheld devices in use are Palm look-alikes

• But these do not deploy PalmOS platform but Windows CE

PalmOS Deficiencies

1. Instead of multi-tasking, PalmOS provides for running a sub-application from within

an application

2. Not an ideal platform for running multimedia applications because due to PalmOS is

not for designing real-time systems

3. Does not offer much expandability

4. Inability to adapt to different sorts of hardware may also be considered a limitation for

this operating system


• Assumes that there is a 256 MB memorycard(s)

• The card─ RAM, ROM, and flash memories

• A memory card ─ logical hexadecimal addresses from 00000h to 3FFFFh




UNIT-4 4. 27


• RAM─ for stacks of processes and for the global variables in the running processes of

the application(s)

• ROM or flash─ for permanent resident application programs and OS

• Flash─ used for storage of non-volatile data

Memory

• A dynamic heap (within 96 kB for PalmOS 3.x) of application process stacks (3kB)

• TCP/IP stack (32 kB)

• OS functions stack, applications and OS functions dynamic-memory spaces, system

global variables (2.5 kB

• Application global variables

Direct memory address spaces in card

• Used instead of allocated dynamic memory buffers for the I/O port devices (e.g., LCD

display, keypad input, and modem I/Os)

Execute-in-place system

• PalmOS 3.x and 4.x (not 5.x)

• Static allocation of the memory addresses for the application-installed programs and

data storage

File manager

• Manages each file as a database which has multiple records and information fields

• Each record attributes protected record, deleted record (similar to deleted file), locked

ecord (in use by application process or OS), and updated record • Deleted record attribute

helps in data recovery by a recovery program

The info fields of each record

• Record ID and record attributes

• Info fields about the file have (i) name, (ii) file attributes, (iii) version of application

database, (iv) modification number (number of times modified) and access counter for

number of times accessed), and (v) file local ID




UNIT-4 4. 28

File Local ID

• In place of several characters─ requiring several bytes

• The file local ID─ a number used to identify the file locally when an application is

running

File ID

• A local file sorting table uses the file local ID to sort the file in the required order

• For example, the ordering may also be based on the time and date of the last

modification made in the file

Communication APIs

• For serial, IrDA, and TCP/IP communication • Serial communication uses a cradle

Protocols

• Connection management (CM) protocol

• Modem manager (MM)

• Serial link protocol (SLP) interacts with SM to transmit the data to PC

• A device receives the data from the other end through serial manager and SLP, MM, or

CM

Communication Protocols

• MM for deploying a dial up-modem

• CM carries out exchanges for establishing connection, baud rate selection, and finding

version number

• SLP for packet communication on serial line

• A desktop link protocol (DLP) transmits data to PADP when serial device is sending

data to PC and receives data from PADP when serial device is receiving data from the PC

IrDA

• Asynchronous serial (115 kbps)

• Synchronous serial communication (1.152 or 4 Mbps)

• Exchange manager as session layer and IrDA library functions (for IrDA protocol

layers) at lower level




UNIT-4 4. 29

Exchange manager

• Enables data interchange directly without HotSync

• Exchange manager and application use a set of launch codes to generate appropriate

events

Network library functions

• TCP/IP network library functions (for UDP and TCP) to send stack to a net protocol

stack (NPS) and provides a socket API

• Berkeley Socket APIs also supported

• Uses HTTP/HTTPS net library for Internet connectivity

Application Development Method

• Corresponding to each event, there is an event handler

• Application development means defining additional events and coding for the

corresponding handlers

Application Development Method

• An application can be assumed to be divisible into sub-applications am to an−1 along

with the existing event handlers a0 to am−1

• Assume that ai runs on the events ei

• An event ei polled at a sleep interval of ti−1 in an infinite while loop

Application

• SMS

• Address

• Card-Info

• HotSync

• To-Do-List

• Security

• Date Book/Calendar

• Calc, Welcome, and Clock




UNIT-4 4. 30

Application Development Packages

• Supports development packages Palm SDK (software development kit) and CDK

(conduit development kit)

• A conduit is a path

4.11 Windows CE • A 32 bit OS from Microsoft

• Customized for each specific hardware and processor in order to fine-tune the

performance

• Compatible with a variety of processor architectures

• Compiled for a specific set of hardware, its performance is very finely tuned

• User─ personal-computer-like feel and Windows-like GUIs

• Large number of Windows-based applications available at the device

Windows CE 4.x

• Adds improved security, GUIs, VUIs, telephony libraries, and standard interfaces for

access to the external SD cards for the files

Windows CE 5.x

• Supports a non-volatile file system using flash memory

• Flash nowadays used instead of persistent battery-backed RAM

• Windows CE supports a new file system that supports larger file sizes, removable media

encryption, and larger storage media

• The flash file system saves the files and data in case the battery charge is draining out

Windows Embedded CE 6.0

• Open, scalable, 32-bit operating system (OS) with small-footprint and advanced

Windows technologies

• Provides hard real-time capabilities, with a redesigned kernel and embedded specific

development tools




UNIT-4 4. 31

Windows Embedded CE 6.0 devices

• For home as well as work places

• Provisions for media and shared presentations

• Connectivity to cellular networks

Windows Mobile 6 platform

• For mobile devices such as Pocket PC

• for managing Visual C# and Visual Basic .NET codes

• Based on Windows CE and hardware such as personal digital assistants (PDAs) and

smart phones

• Microsoft Visual Studio 2005

• Windows Mobile SDK for creating software for the platform

• The code developed in Visual C++

Thread

• Basic unit of computation

• A process─ any number of threads

• Threads run concurrently

Windows Mobile

• Deployed in (i) Smart phone, (ii) handheld Pocket PC which features the digitizer in the

human computer interface (HCI), and (iii) portable media player • PDA with Microsoft

Smartphone phone device, touch screen, touchpad, or directional pad Pocket PC

• Has digitization software which converts (i) analog signals to digital ones to enable

scanning of photos and video recordings for storage or transmission (ii) audio analog

sources into digital form to enable speech processing, voice, or music for creating records

and files which are stored or transmitted

Windows CE

• Kernel divided into two sub layers

• One sub layer consists of large part of the OS

• Then the OS is adjusted according to the device hardware by adding the remaining part

of the OS




UNIT-4 4. 32

• Second sub layer called hardware abstraction layer

• Shared source licensed with controlled access to full or limited parts of the source code

for a product

• Windows CE 5.x developers have the freedom to modify down to the kernel level

without the need to share their changes with Microsoft or competitors

• A component-based, embedded, real-time operating system with deterministic interrupt

latency

• Can be configured as a real-time operating system for handheld Smart phone, Pocket

PC, computers, and embedded systems

• Modular/componentized to provide the foundation of several classes of devices and

supports addition of features of other components for Windows, DCOM, and COM

• Data format─ database or object file

• File automatically compresses when stored and decompresses when loaded

• Visual C/C++ platform integrates use of web

• .NET XML parsing (trimmed version)

GUIs development support

• Using markup language as well as C/C++ language

• Embedded complex APIs

• Gives the user a PC-like feel and Windows-like GUIs (window resizing not provided)

VUIs development support

• Built-in microphone for voice recording

Display

• High resolution colour/ display

• Touch screen

• Stylus keypad with Windows layout of desktop programs displayed on colored touch

screen

Software

• Desktop for Windows

• Other essential software




UNIT-4 4. 33

• PIM

• Contacts

• Task-to-do

• Smart phone

• Multimedia applications such as playing music

Desktop Programs

• Owner

• Number of messages not read

• Tasks

• Present hour subject

• Button and tool bar for task start menu

• Today calendar, contacts, Internet explorer, messages, phone, pocket MSN, album,

MSN messenger, camera, programs, settings, and help], phone mode indicator (on/off),

signal strength status, speaker status (on/off), and time

Ports

• USB and infrared port support for communication of a device with mobile phones and

for synchronizing a PC using ActiveSync after resolving the conflicts due to different

versions of object files during data exchange.

• Bluetooth

• TCP/IP

• WiFi or Ethernet LAN interface . 30 ActiveSync

• Synchronization of mobile device data with PC using a USB, Bluetooth, and PC

infrared port Connectivity to other devices

• A cradle connects to PC

• USB 2.0 in Windows CE 5.0 PocketPC conform as the USB mass storage class, the

storage on device can be accessed, and drag and drop menu can be used from any USB

port of PC, which considers the handheld device just another flash drive

Window CE device three states

(i) ON with clock frequency lowered in idle state




UNIT-4 4. 34

(ii) Suspend with power to unused system units and port peripherals disconnected,

memory data persistent, CPU idle till next interrupt, and clock running

(iii) dead with power disconnected

Windows CE deficiencies

• Cooperative running of multi-threading does not support simultaneous multimodal user

interfaces (data by multiple modes, for example, text as well as speech) Poor Adaptability

• Adapts to different sorts of hardware limits mainly because of two reasons (i)

compiled for a specific set of hardware for very fine-tuned Windows CE performance,

(ii) large parts of OS offered in the form of source code first and then adjusted to the

hardware by the manufacturer

Figure 4.6 OS layer in Windows CE




UNIT-4 4. 35

Windows CE Memory Management

• Assumes 4 GB virtual memory

• RAM, ROM, and flash memories

• A memory has logical hexadecimal addresses from 000000000h to FFFFFFFFh


• A ROM image─ the footprint of OS, data, and the applications at the permanently

installed ROM (or flash memory)

• An OS configured and customized for an embedded application(s)─ footprint is the

ROM image

• The customization reduces the OS footprint


• Windows CE needs a minimum footprint of 350 kB

• Device applications optimized so that the devices need minimal storage below 1 MB

with no disk storage

• Windows CE footprint burned in ROM and configured as it does not allow end-user

extension

Memory manager

• Assigns contagious pages in virtual address space to one of the 32 memory slots

• Each slot of 32 MB

• Allocates a distinct slot to a distinct process among the maximum 32 concurrently

running processes

Memory manager

• Allocation of memory slots reduces fragmentation of pages to a significant extent as

pages of processes are at the contagious addresses in the slot. Fragmentation occurs only

when the memory needed by the process code and data is more than 32 MB

Dynamic heap in the program memory

• The Application process stacks, TCP/IP stack, OS functions stack, applications and OS

functions dynamic-memory spaces, system and application global variables, Bluetooth

stack, and WiFi stack




UNIT-4 4. 36

ROM and RAM

• OS and system functions in ROM

• An automotive PC with Windows CE 8 MB ROM and RAM each

• The Pocket PC 2–8 MB ROM and 8–32 MB RAM in storage memory

File manager

• Manages data as a database or object file

• A file system─ a root directory with which the file folders associate in a tree-like

structure

• Division of all files and folders into volumes

• A volume ─ unit which can be loaded from the device to the computer or can be stored

on the device from the computer

File Volume

• Each volume has a root directory which has directories and file folders • Each directory

can have further divisions into subdirectories and file folders

• Each subdirectory can have further divisions into files and subdirectories till the leaf

node which has a single file folder

Communication, Network, Device, and Peripheral Drivers

• Communication and network APIs for serial, IrDA, TCP/IP, Bluetooth stack, and WiFi

stack

• IP-based connectivity to the network and WiFi-based connectivity in later versions

• Window CE integrates Microsoft Smart phone software

• Enables the application of Windows CE device as cellular GSM/CDMA phone

Serial communication

• Uses a cradle

• A serial manager (SM) provides interface to the device on cradle with the RS232C

COM port of the PC

• Connection management (CM) by using the serial link interface protocol (SLIP) and

point to- point (PPP) protocol




UNIT-4 4. 37

• IrDA asynchronous serial (115 kbps) or synchronous serial communication (1.152 or 4

Mbps) uses ActiveSync

Network connectivity

• By radio transceiver and LAN adapter

• A NDIS (network driver interface specification) used for the drivers other than the

driver loaded at the hardware

Windows CE device drivers

• Device driver and peripheral driver functions for low-level drivers at the kernel

Windows CE

• USB connectivity provided for the peripherals

Event

• Sends interrupt signal which is checked for source, that is, whether the source is a

hardware event, software exception, user action- based event, or kernel event (e.g., a

kernel command, WM_HIBERNATE)

Event handler

• Separate for each event • Asynchronous events

• Event handler calls interrupt service thread (IST) in Windows CE device

Application Development tools

• Visual basic and Visual C++

• Platform Builder─ for developing a Windows CE application by carrying out OS image

creation and integration

• Platform Builder provides an integrated environment for customized operating system

designs based on Windows CE

4.12 SYMBION OS • OS for handheld Smart phones and mobile handhelds with phone and multi-modal

communication features

• Multi-modal means usage of different modes—text, image, video, or audio

• Multi-modal communication integrates and




UNIT-4 4. 38

Synchronizes multimedia (Video with text, audio with text …)

Symbian OS─ C/C++ as well as Java Support

• Supports application development in C/C++ as well as Java and many communication

protocols

• Java Phone

Symbian application architecture

• GUIs and VUIs─ APIs for the buttons, menus, advanced voice features such as a hands-

free speakerphone, and conference calling capability

• Application view

• Application engine

• Powerful development platforms and GUIs

Application development tools

• Personal Java and Symbian Everywhere

• Symbian C++ Software development kit (SDK)

• Symbian emulator for application development using Windows Metrowerk,

CodeWarrior

Synchronization

• SyncML synchronization

• Can also deploy C/C++-based synchronization software

Symbian OS

• Low boot time

• OS supports multi-processing or multitasking

• Multithreading

• Internet connectivity for Web browsing, IP-based network connectivity, and WiFi (in

later version only).


Memory Support

• Large storage memory

• Includes 80 MB of built-in memory in a Multimedia Card (MMC)




UNIT-4 4. 39

• MMC (multimedia card), SD (secure digital) memory card, and SDIO (secure digital

input/output) memory card.

Software

• Desktop both for Lotus and Windows programs

• Push-to-talk

• Graphics support including support for 3D rendering

• Simple APIs as compared to Windows CE, PIM, Java Phone

• Telephony standard interfaces

• MIDP (mobile information device profile)

• Contacts

• SyncML

• Office

• address book

• Spreadsheet

• Calendar

• Agenda

• Word processor

• Text-to-speech converter

• Browsing

• Messaging (SMS, MMS, email, and IMAP4)

• WAP push Microsoft Office formats (MS Office 97 onwards)

• Slide shows

• email download, offline creation and sending of POP3 (post office protocol 3) email

• Internet browsing

• GUI development support on C/C++ and Java platform

• Java application using J2ME

• multimedia applications such as playing music (Palm Tungsten)

• Wireless communications Support for WLAN

• Adobe Reader for accessing PDF files




UNIT-4 4. 40

• Symantec Client Security 3.0

• IBM Web Sphere Everyplace Access

• BlackBerry Connect

• Oracle Collaboration Suite

• Secure mobile connections via VPN Client

Ports

• Serial

• USB

• Infrared

• Telephony

• Bluetooth for communication with mobile phones and external modems

Third Party Support

• Extensive

• Games

• Travel and flight planner

• Enterprise solutions

• Calculator

• Graphic drawings

• Preparing slide shows

OS and Hardware layers of Symbian

The OS and Hardware layers of Symbian OS is shown in the below figure.




UNIT-4 4. 41

Figure 4.7 OS and Hardware layers of Symbian OS

Communication APIs

• WAP

• WiFi

• CDMA

• GPRS

• GSM Telephony

Network APIs

• Serial

• Bluetooth

• IrDA




UNIT-4 4. 42

• TCP/IP, communication APIs for HTTP, TCP/IP, DNS, SSL, WAP, PPP

4.13 LINUX FOR MOBILE DEVICES Linux

• Embedded Linux Consortium (ELC) standards for Linux for designing user interfaces,

managing power consumption in devices, and real-time operation

• Also considered to be more secure than most other operating system. Several

international mobile phone manufacturers use Linux for their OS requirements.

Example of Linux OS – Mobile

• An open source OS

• Enables the user to customize their device to suit their specific needs

• Provides ease to suit different sorts of hardware and software applications




UNIT-4 4. 43

4.14 Question Bank PART – A (2 MARKS)

1. What is slow start?

2. What is the use of congestion threshold?

3. What led to the development of Indirect TCP?

4. What is the goal of M-TCP?

5. What do you mean by persistent mode?

6. What are the characteristics of 2.5G/3.5G wireless networks?

7. What are the configuration parameters to adapt TCP to wireless environments?

8. What are the requirements of mobile IP?

9. Mention the different entities in a mobile IP.

10. Define Mobile node

11. Define Cellular IP

12. What do you mean by mobility binding?

13. Define COA.

14. Define a tunnel.

15. What is encapsulation?

16. What is decapsulation?

17. Define an outer header

18. Define an inner header

19. What is the use of network address translation?

20. Define triangular routing.




UNIT-4 4. 44

PART – B (16 MARKS)

1. Explain traditional TCP in details.

2. Explain classical TCP improvements and snooping TCP.

3. Explain the function of the components of the WAP architecture.

4. Explain the concept of wireless markup language.

5. Explain wireless application protocols with its version WAP 2.0 in detail.

6. Describe the operation of the window flow control mechanism.

7. Explain in detail about tunneling

8. Explain in detail about Cellular IP.

9. Explain in detail about binding concept.




UNIT-5 5. 1

UNIT 5

MOBILE MIDDLEWARE




UNIT-5 5. 2

CONTENTS

5.1 Mobile Middleware

5.2 Middleware for application development

5.3 Adaptation

5.4 Mobile Agent

5.4.1 Reputation and Trust

5.4.2 Differences between trust and reputation systems

5.5 Service discovery

5.6 Services

5.7 Garbage Collection

5.8 Eventing

5.9 Security

5.10 Interoperability

5.11 Adhoc and Sensor Networks

5.11.1 Mobile Sensor Networks Overview

5.11.2 Mobile Ad-Hoc Networks – MANET Overview

5.12 Properties of MANETs

5.13Unique features of sensor networks

5.14Applications

5.15 Challenges

5.16 Constrained Resources

5.17 Security

5.18 Mobility

5.19 Protocols

5.20 Auto Configuration

5.21 Energy Efficient Communication

5.22 Mobility requirements

5.23 Question Bank




UNIT-5 5. 3

TECHNICAL TERMS

1. Mobile middleware is, as the name implies, middleware used in the context of mobile-

computing devices. Mobile middleware offers various transparencies that hide the

complexities of mobile environments.

2. Middleware is the "glue" between software components or between software and the

network or it is the slash in Client/Server.

3. Adaptation middleware assists applications in providing the best quality of service

possible to users, given the widely fluctuating resource levels that may exist in mobile

environments.

4. Mobile agents provide an alternative to static client/server systems for designing

interesting mobile applications that access remote data and computational services.

5. Service discovery is an adaptable middleware in a device (or a mobile computing

system) that dynamically discovers services. Bluetooth Service discovery protocol, JINI,

SLP (service location protocol), UPnP (Universal Plug and Play) service discovery

functions

6. Location management enables the wireless network to discover the current point of

attachment of the MS and deliver calls.

7. Split multipath routing (SMR) is an on-demand routing protocol that constructs

maximally disjoint paths between a given source destination.

8. Caching and multipath routing protocol (CHAMP) makes use of temporal locality in

dropped packets and targets at reducing packet loss due to a route breakdown.

9. Neighbor-table-based multipath routing (NTBMR) is a mixed multipath routing

protocol that deals with regular topology changes in mobile ad hoc networks.

10. Adhoc on-demand distance vector–backing routing (AODV–BR) is a multipath

routing protocol which constructs routes on demand and uses alternate paths only when

the primary route is disrupted.




UNIT-5 5. 4

11. On-demand multipath routing is an extension of the DSR protocol. It exploits

multipath techniques in reducing the frequency of query floods used to discover new

routes.

12. Interoperability is the ability of software and hardware on different machines from

different vendors to share data.

13. A router is a device in computer networking that forwards data packets to their

destinations, based on their addresses. The work a router does it called routing, which is

somewhat like switching, but a router is different from a switch. The latter is simply a

device to connect machines to form a LAN.

14. Routing: In internetworking, the process of moving a packet of data from source to

destination. Routing is usually performed by a dedicated device called a router.




UNIT-5 5. 5

5. MOBILE MIDDLEWARE

5.1 Mobile Middleware Mobile middleware is, as the name implies, middleware used in the context of mobile-

computing devices. Mobile middleware offers various transparencies that hide the complexities

of mobile environments. For instance, location transparency allows applications to exchange data

with other applications without any regard for their location. Similar abstractions are likewise

provided by transparencies on the transport protocol, operating system, programming and others.

Mobile middleware typically involves services like messaging and Remote Procedure Call

(RPC), resource discovery, transactions, directory, security, and storage services and data

synchronization.

5.2 Middleware for application development There are two types of middleware, adaptation middleware and mobile agent systems.

Adaptation middleware assists applications in providing the best quality of service possible to

users, given the widely fluctuating resource levels that may exist in mobile environments.

Mobile agents provide an alternative to static client/server systems for designing interesting

mobile applications that access remote data and computational services.

5.3 Adaptation Mobile computers must execute user- and system-level applications subject to a variety

of resource constraints that generally can be ignored in modern desktop environments. The most

important of these constraints are power, volatile and nonvolatile memory, and network

bandwidth, although other physical limitations such as screen resolution are also important.




UNIT-5 5. 6

In order to provide users with a reasonable computing environment, which approaches

the best that currently available resources will allow, applications and/or system software must

adapt to limited or fluctuating resource levels.

For example, given a sudden severe constraint on available bandwidth, a mobile audio

application might stop delivering a high-bit-rate audio stream and substitute a lower-quality

stream. The user is likely to object less to the lower quality delivery than to the significant

dropouts and stuttering if the application attempted to continue delivering the high-quality

stream.

Similarly, a video application might adjust dynamically to fluctuations in bandwidth,

switching from high-quality, high-frame-rate color video to black-and-white video to color still

images to black-and-white still images as appropriate. A third example is a mobile videogame

application adjusting to decreased battery levels by modifying resolution or disabling three-

dimensional (3D) features to conserve power.

5.4 Mobile Agent (MA) Mobile Agent, namely, is a type of software agent, with the feature of autonomy, social

ability, learning, and most importantly, mobility. A mobile agent is a process that can transport

its state from one environment to another, with its data intact, and be capable of performing

appropriately in the new environment.

Mobile agents decide when and where to move. Movement is often evolved

from RPC methods. Just as a user directs an Internet browser to "visit" a website (the browser

merely downloads a copy of the site or one version of it in the case of dynamic web sites),

similarly, a mobile agent accomplishes a move through data duplication. When a mobile agent

decides to move, it saves its own state, transports this saved state to the new host, and resumes

execution from the saved state.

A mobile agent is a specific form of mobile code, within the field of code mobility.

However, in contrast to the remote evaluation and code on demand programming paradigms,

mobile agents are active in that they can choose to migrate between computers at any time during




UNIT-5 5. 7

their execution. This makes them a powerful tool for implementing distributed applications in

a computer network.

An open multi-agent system (MAS) is a system in which agents that are owned by a

variety of stakeholders continuously enter and leave the system.

5.4.1 Reputation and Trust

The following are general concerns about Trust and Reputation in MA research:

1. Source of trust information is direct experience, witness information, role-based rules.

2. How trust value is calculated

3. Overall trust value

5.4.2 Differences between trust and reputation systems

Trust systems produce a score that reflect the relying party’s subjective view of an

entity’s trustworthiness, whereas reputation systems produce an entity’s (public) reputation score

as seen by the whole community.

Some advantages which mobile agents have over conventional agents:

Computation bundles - converts computational client/server round trips to

relocatable data bundles, reducing network load.

Parallel processing -asynchronous execution on multiple heterogeneous network

hosts

Dynamic adaptation - actions are dependent on the state of the host environment

Tolerant to network faults - able to operate without an active connection between

client and server

Flexible maintenance - to change an agent's actions, only the source (rather than

the computation hosts) must be updated

One particular advantage for remote deployment of software includes increased

portability thereby making system requirements less influential.

5.5 Service Discovery Middleware




UNIT-5 5. 8

The Service discovery middleware is an adaptable middleware in a device (or a mobile

computing system) that dynamically discovers services. Bluetooth Service discovery protocol,

JINI, SLP (service location protocol), UPnP (Universal Plug and Play) are the service discovery

functions

Steps for Service discovery

1. Lets nearby service network (or device or system) recognize that device

2. Lets the nearby network know of device service(s)

3. Searches and discovers a new service(s) at the network

4. Interacting with nearby network using discovered service(s)

5.6 Services The Services that offer by middleware are

Client/Server Connectivity -Middleware provides the mechanism by which network

applications communicate across the network. This includes in the case of database networking

for example the service of putting packages of query results data into network transport packets.

Microsoft SQL Server, for example, uses Sybase's Tabular Data Stream (TDS) protocol to

handle formatting of data for transport across the network. This session layer interaction may

also have its own timers and even error control to handle automatic retransmission of lost

packets. One feature common is the ability for the client to interrupt the current operation on the

server to cancel a large query response download.

Platform Transparency -Client and server don't have to have intimate knowledge of

each other in order for work to get done. Differences between platform specific encodings like

big-endian and little-endian or EBCDIC and ASCII are typically hidden by middleware.

Middleware often runs on a variety of platforms, letting the organization utilize all its existing

desktop and server hardware as applications require. Still, some middleware products find it hard

to look beyond Windows clients and UNIX or Windows NT servers. Make sure the middleware

you're buying handles all the platforms you really have deployed. Microsoft SQL Server DB-

Library middleware provides access only to Windows NT servers (since that's the only supported




UNIT-5 5. 9

SQL Server host platform), but does so from DOS, Windows (3.1, 95, NT), Mac and UNIX

clients.

Network Transparency and Isolation -Middleware often makes networking choices

transparent to application programmers. Actually, though, every middleware product we've ever

heard of runs on TCP/IP, with all the other protocols coming in a distant second. If you want to

be more prepared to run tomorrow's middleware, get on the TCP/IP bandwagon. Then again,

don't let application programmers become too divorced from networking decisions.

SQL Server supports multiple protocols between clients and servers, though some are specific to

a given platform. From Macs, the choices are TCP/IP and AppleTalk. From PCs, there are more

choices: TCP/IP, NetWare IPX/SPX, and NetBIOS/NetBEUI (Named Pipes). In some cases, the

client and server don't even have to run the same network protocol between them. An

intermediate device which might best be called a database relay can get the two end nodes

talking to each other.

Application and Tool Support (APIs) -Before middleware can be used, it must present

its own API to client applications that might use it. For shrink-wrapped tools like a database

query tool, the API support can be critical. While ODBC has provided some level of

transparency across multiple proprietary database APIs, many RDBMS vendors still encourage

using their own proprietary APIs. Be sure you know what APIs your middleware offers as well

as what APIs your tools can use. Hopefully there's a match! SQL Server offers both ODBC

standard and DB-Library proprietary APIs on the client. For more generic middleware, the API

on the server must be available as well; for RDBMS middleware, the server side is typically

hard-coded to support an RDBMS.

Language Support -Middleware often provides transparency across different SQL

database dialects. Even when coding in embedded SQL in a 3GL, the middleware might allow

the use of a single SQL dialect across a variety of RDBMS back ends. Outside of the database

specific middleware products, generic middleware products often allow different programming

languages to be used to create the distinct pieces of an application (pieces that reside on different

machines). Since SQL Server's DB-Library only supports SQL Server RDBMSs, the SQL dialect

supported is Transact SQL, a superset of ANSI 89 SQL created by Sybase and Microsoft.




UNIT-5 5. 10

RDBMS Support -When we focus on database networking middleware (also called data

access middleware), middleware may also provide a level of transparency across different data

storage formats. It will make different RDBMSs look like the same RDBMS. ODBC is one way

of hiding RDBMS differences, but middleware products often provide multiple RDBMS support

from both proprietary and standard APIs. SQL Server's DB-Library middleware does support

ODBC interfaces, but still natively gets users to SQL Server RDBMS only.

Much database networking middleware is closely tied to the RDBMS of that same

vendor. To get to even more data sources, database gateway products are needed. Third party

products like TechGnosis SequeLink or IBI EDA/SQL offer more variety in RDBMSs. Even

Microsoft has recently allied with IBI to have their multi-RDBMS connectivity solution

connected to the DB-Library network so that DB-Library clients can get to RDBMSs other than

SQL Server.

For non-data access products, RDBMS functionality can still be provided using

extensions to make accessing that kind of data directly easy over the middleware solution

deployed. NetWeave is one messaging vendor that also has database access software options.

5.7 Garbage collection:

Garbage collection is the systematic recovery of pooled computer storage that is being

used by a program when that program no longer needs the storage. This frees the storage for use

by other programs (or processes within a program). It also ensures that a program using

increasing amounts of pooled storage does not reach its quota (in which case it may no longer be

able to function).

Garbage collection is an automatic memory management feature in many modern

programming languages, such as Java and languages in the .NET framework. Languages that use

garbage collection are often interpreted or run within a virtual machine like the JVM. In each

case, the environment that runs the code is also responsible for garbage collection.




UNIT-5 5. 11

In older programming languages, such as C and C++, allocating and freeing memory is

done manually by the programmer. Memory for any data that can't be stored within a primitive

data type, including objects, buffers and strings, is usually reserved on the heap. When the

program no longer needs the data, the programmer frees that chunk of data with an API call.

Because this process is manually controlled, human error can introduce bugs in the code.

Memory leaks occurs when the programmer forgets to free up memory after the program no

longer needs it. Other times, a programmer may try to access a chunk of memory that has already

been freed, leading to dangling pointers that can cause serious bugs or even crashes.

Programs with an automatic garbage collector (GC) try to eliminate these bugs by

automatically detecting when a piece of data is no longer needed. A GC has two goals: any

unused memory should be freed, and no memory should be freed unless the program will not use

it anymore. Although some languages allow memory to be manually freed as well, many do not.

5.8 Eventing In event notification, a UPnP device notifies control points that registered a service in

control phase of changes to the services they registered to, following a publish-subscribe –style

messaging paradigm.

Universal Plug and Play, UPnP, provides a programming language and platform

independent discovery mechanism by relying on HTTP and XML. UPnP relies on listening and

responding to HTTP-based requests on a particular multicast channel. UPnP architecture consists

of control points (i.e. UPnP client devices) and UPnP devices. UPnP can be seen to contain five

phases: discovery, description, control, event notification and presentation.

5.9 Security

Just as any other platform that executes general-purpose applications; mobile platforms

need security mechanisms to protect the resources on the devices. Two important techniques can

be distinguished: memory management and software protection. Native platforms need to ensure




UNIT-5 5. 12

that applications cannot access memory that belongs to other applications or to the platform

itself. This separation is guaranteed by memory management. Some of the older mobile device

platforms such as Palm OS have no form of memory protection at all, which makes these

platforms inherently in secure.

Most modern native platforms (Windows Mobile, Symbian) do provide basic memory

protection. One of the important strengths of managed platforms (.NET Compact Framework,

Java ME) is that they have a strong memory protection model because applications have no

direct access to the memory and because these platforms guarantee type safety. Other resources

on the device such as personal data, wireless networking, or SMS messages are accessed via

APIs and are protected by the security architecture of the platform.

Security Issues

Important security mechanisms found on full-scaled platforms are omitted

The developer has very little options in customizing security mechanisms

APIs can be protected but often in an all-or-nothing way

It is hard to securely store sensitive data

A mobile device is subject to different kinds of threats

5.10 Interoperability

Interoperability is the ability of software and hardware on different machine from

different vendors to share data.

The need for interoperability between information systems is readily apparent in

peacekeeping and disaster-response operations. In these situations, a coalition of civilian and

military organizations, each with its own intelligence or other information assets, is formed on

short notice and required to operate in areas where the fixed communication infrastructure has

been severely damaged or completely destroyed. The field units are forced to rely on limited-

power devices that use an unreliable low-bandwidth data link to communicate between them and

to access information held within constituent organizations’ headquarters.




UNIT-5 5. 13

5.11 Adhoc and Sensor Networks 5.11.1 Mobile Sensor Networks Overview

As sensors become widely deployed, some sensors may be enhanced with mobility. Such

mobile sensors may be more powerful and can re-charge themselves automatically. An important

application is in the robot area.

Need of mobile sensors:

Resilient to failures

Reactive to events

To support disparate missions

5.11.2Mobile Ad-Hoc Networks – MANET Overview

Mobile Ad hoc NETworks (MANETs) are wireless networks which are characterized by

dynamic topologies and no fixed infrastructure. Each node in a MANET is a computer that may

be required to act as both a host and a router and, as much, may be required to forward packets

between nodes which cannot directly communicate with one another. Each MANET node has

much smaller frequency spectrum requirements that that for a node in a fixed infrastructure

network.

A MANET is an autonomous collection of mobile users that communicate over relatively

bandwidth constrained wireless links. Since the nodes are mobile, the network topology may

change rapidly and unpredictably over time. The network is decentralized, where all network

activity including discovering the topology and delivering messages must be executed by the

nodes themselves, i.e., routing functionality will be incorporated into mobile nodes.




UNIT-5 5. 14

Figure 5.1 MANET

MANETs

● Are rapidly deployable, self configuring.

●No need for existing infrastructure.

●Wireless links.

●Nodes are mobile, topology can be very dynamic.

●Nodes must be able to relay traffic since communicating nodes might be out of range.

●A MANET can be a standalone network or it can be connected to external networks

(Internet).




UNIT-5 5. 15

Figure 5.2 Example of a MANET

MANET usage areas

●Military scenarios

●Sensor networks

●Rescue operations

●Students on campus

●Free Internet connection sharing

●Conferences

Mechanisms required in a MANET

●Multi-hop operation requires a routing mechanism designed for mobile nodes.

●Internet access mechanisms.

●Self configuring networks requires an address allocation mechanism.

●Mechanism to detect and act on, merging of existing networks.

●Security mechanisms.

5.12 Properties of MANETs




UNIT-5 5. 16

MANET enables fast establishment of networks. When a new network is to be

established, the only requirement is to provide a new set of nodes with limited wireless

communication range. A node has limited capability, that is, it can connect only to the

nodes which are nearby. Hence it consumes limited power.

A MANET node has the ability to discover a neighboring node and service. Using a

service discovery protocol, a node discovers the service of a nearby node and

communicates to a remote node in the MANET.

MANET nodes have peer-to-peer connectivity among themselves.

MANET nodes have independent computational, switching (or routing), and

communication capabilities.

The wireless connectivity range in MANETs includes only nearest node connectivity.

The failure of an intermediate node results in greater latency in communicating with the

remote server.

Limited bandwidth available between two intermediate nodes becomes a constraint for

the MANET. The node may have limited power and thus computations need to be

energy-efficient.

There is no access-point requirement in MANET. Only selected access points are

provided for connection to other networks or other MANETs.

MANET nodes can be the iPods, Palm handheld computers, Smart phones, PCs, smart

labels, smart sensors, and automobile-embedded systems

MANET nodes can use different protocols, for example, IrDA, Bluetooth, ZigBee,

802.11, GSM, and TCP/IP.MANET node performs data caching, saving, and

aggregation.

MANET mobile device nodes interact seamlessly when they move with the nearby

wireless nodes, sensor nodes, and embedded devices in automobiles so that the seamless

connectivity is maintained between the devices.

5.13 Unique features of sensor networks




UNIT-5 5. 17

Dynamic network topology

Bandwidth constraints and variable link capacity

Energy constrained nodes

Multi-hop communications

Limited security

Autonomous terminal

Distributed operation

Light-weight terminals

5.14 Applications The set of applications for MANETs is diverse, ranging from small, static

networks that are constrained by power sources, to large-scale, mobile, highly dynamic

networks. The design of network protocols for these networks is a complex issue. Regardless of

the application, MANETs need efficient distributed algorithms to determine network

organization, link scheduling, and routing. Some of the main application areas of MANET’s are:

Military battlefield– soldiers, tanks, planes. Ad- hoc networking would allow the

military to take advantage of commonplace network technology to maintain an

information network between the soldiers, vehicles, and military information

headquarters.




UNIT-5 5. 18

Figure 5.3 MANET Applications

Sensor networks – to monitor environmental conditions over a large area

Local level – Ad hoc networks can autonomously link an instant and temporary

multimedia network using notebook computers or palmtop computers to spread

and share information among participants at e.g. conference or classroom.

Another appropriate local level application might be in home networks where

devices can communicate directly to exchange information.

Personal Area Network (PAN) – pervasive computing i.e. to provide flexible

connectivity between personal electronic devices or home appliances. Short-range

MANET can simplify the intercommunication between various mobile devices

(such as a PDA, a laptop, and a cellular phone). Tedious wired cables are replaced

with wireless connections. Such an ad hoc network can also extend the access to

the Internet or other networks by mechanisms e.g. Wireless LAN (WLAN),

GPRS, and UMTS.

Vehicular Ad hoc Networks – intelligent transportation i.e. to enable real time

vehicle monitoring and adaptive traffic control




UNIT-5 5. 19

Civilian environments – taxi cab network, meeting rooms, sports stadiums, boats,

small aircraft

Emergency operations – search and rescue, policing and fire fighting and to

provide connectivity between distant devices where the network infrastructure is

unavailable. Ad hoc can be used in emergency/rescue operations for disaster relief

efforts, e.g. in fire, flood, or earthquake. Emergency rescue operations must take

place where non-existing or damaged communications infrastructure and rapid

deployment of a communication network is needed. Information is relayed from

one rescue team member to another over a small hand held.

5.15 Challenges To design a good wireless ad hoc network, various challenges have to be taken

into account:

Dynamic Topology: Nodes are free to move in an arbitrary fashion resulting in

the topology changing arbitrarily. This characteristic demands dynamic

configuration of the network.

Limited security: Wireless networks are vulnerable to attack. Mobile ad hoc

networks are more vulnerable as by design any node should be able to join or

leave the network at any time. This requires flexibility and higher openness.

Limited Bandwidth: Wireless networks in general are bandwidth limited. In an ad

hoc network, it is all the more so because there is no backbone to handle or

multiplex higher bandwidth

Routing: Routing in a mobile ad hoc network is complex. This depends on many

factors, including finding the routing path, selection of routers, topology, protocol

etc.




UNIT-5 5. 20

5.16 Constrained Resources ●Self starting and self organizing

●Multi-hop, loop-free paths

●Dynamic topology maintenance

●Rapid convergence

●Minimal network traffic overhead

●Scalable to large networks

5.17 Security in MANET’s Securing wireless ad-hoc networks is a highly challenging issue. Understanding possible

form of attacks is always the first step towards developing good security solutions. Security of

communication in MANET is important for secure transmission of information. Absence of any

central co-ordination mechanism and shared wireless medium makes MANET more vulnerable

to digital/cyber attacks than wired network there are a number of attacks that affect MANET.

These attacks can be classified into two types:

External Attack: External attacks are carried out by nodes that do not belong to the

network. It causes congestion sends false routing information or causes unavailability of

services.

Internal Attack: Internal attacks are from compromised nodes that are part of the

network. In an internal attack the malicious node from the network gains unauthorized

access and impersonates as a genuine node. It can analyze traffic between other nodes

and may participate in other network activities.

Denial of Service attack: This attack aims to attack the availability of a node or the

entire network. If the attack is successful the services will not be available. The attacker

generally uses radio signal jamming and the battery exhaustion method.




UNIT-5 5. 21

Impersonation: If the authentication mechanism is not properly implemented a

malicious node can act as a genuine node and monitor the network traffic. It can also

send fake routing packets, and gain access to some confidential information.

Eavesdropping: This is a passive attack. The node simply observes the confidential

information. This information can be later used by the malicious node. The secret

information like location, public key, private key, password etc. can be fetched by

eavesdropper.

Routing Attacks: The malicious node makes routing services a target because it’s an

important service in MANETs. There are two flavors to this routing attack. One is attack

on routing protocol and another is attack on packet forwarding or delivery mechanism.

The first is aimed at blocking the propagation of routing information to a node. The latter

is aimed at disturbing the packet delivery against a predefined path.

Black hole Attack: In this attack, an attacker advertises a zero metric for all destinations

causing all nodes around it to route packets towards it. A malicious node sends fake

routing information, claiming that it has an optimum route and causes other good nodes

to route data packets through the malicious one. A malicious node drops all packets that it

receives instead of normally forwarding those packets. An attacker listen the requests in a

flooding based protocol.

Wormhole Attack: In a wormhole attack, an attacker receives packets at one point in the

network, tunnels them to another point in the network, and then replays them into the

network from that point. Routing can be disrupted when routing control message are

tunneled. This tunnel between two colluding attacks is known as a wormhole.

Replay Attack: An attacker that performs a replay attack is retransmitted the valid data

repeatedly to inject the network routing traffic that has been captured previously. This

attack usually targets the freshness of routes, but can also be used to undermine poorly

designed security solutions.

Jamming: In jamming, attacker initially keep monitoring wireless medium in order to

determine frequency at which destination node is receiving signal from sender. It then

transmit signal on that frequency so that error free receptor is hindered.




UNIT-5 5. 22

Man- in- the- middle attack: An attacker sites between the sender and receiver and

sniffs any information being sent between two nodes. In some cases, attacker may

impersonate the sender to communicate with receiver or impersonate the receiver to reply

to the sender.

Gray-hole attack: This attack is also known as routing misbehavior attack which leads

to dropping of messages. Gray-hole attack has two phases. In the first phase the node

advertise itself as having a valid route to destination while in second phase, nodes drops

intercepted packets with a certain probability.

5.18 Mobility First of all, mobility management has to be taken into consideration while designing the

infrastructure itself for wireless mobile networks. Effective and efficient handoff is the key

factor enabling the mobile user to move seamlessly from one cell to another cell, from one

service area to another, and so on.

Mobility management features two tasks—location management and handoff

management—that enable mobile networks to locate roaming MSs for call delivery and

maintain connections as the MSs are moving around.

Location management enables the wireless network to discover the current point of

attachment of the MS and deliver calls. The first stage of location management is the location

registration (or location update). In this stage, the MS periodically notifies the network of its

new AP, allowing the network to authenticate the user and revise the user’s location profile.

The second stage is the call delivery, in which the wireless mobile network is queried for the

MS location profile and the current position of the MS is found.

Handoff primarily represents a process of changing some of the parameters of a channel

(frequency, time slot, spreading code, or a combination of them) associated with the current

connection in progress. The handoff process usually consists of two phases: the handoff

initialization phase and the handoff-enabling phase. In the handoff initialization phase, the

quality of the current communication channel is monitored in order to decide when to trigger




UNIT-5 5. 23

the handoff process. In the handoff execution phase, the allocation of new resources by a new

BS is initiated and processed. Poorly designed handoff schemes tend to generate very heavy

signaling traffic and thereby result in a dramatic decrease in quality of integrated service in

the wireless network.

Mobility management requests are often initiated either by a MS’s movement when it

crosses a cell boundary, or by a deteriorated quality of signal received on a currently

employed channel. With the anticipated increased penetration of wireless services, the next

generation of wireless mobile networks will provide an architectural basis to support a drastic

increase in traffic bandwidth. According to the IMT-2000 outline of ITU, a simultaneous

operation of high capacity pico cells, urban terrestrial microcells and macro cells, and large

satellite cells will be exploited in IMT-2000. Much more frequent handoffs will occur when

the size of the cell becomes smaller or there is a drastic change in the propagation condition

of the signal.

Mobility management should be given more careful consideration in next-generation

wireless mobile networks. Various handoff initiating criteria have been proposed recently. In

order to decide when to trigger the handoff, the quality of the current communication channel

is monitored. Handoff is a very rigorous process; therefore, unnecessary handoffs should be

avoided. If the handoff criteria are not chosen carefully, the call might be handed back and

forth several times between two neighboring BSs, especially when the MS is moving around

the overlapping region between the coverage area boundaries of the two BSs.

If the criteria are too conservative, then the call may be lost before the handoff can take

place. Based on the link status, the measurement process determines the need for handoff and

the new target cell for transfer. Since the propagation condition between the BS and the MS

is made up of the direct radio propagation paths (direct, reflection, refraction), the following

types of handoff-initiating criteria have been proposed:

Word error indicator: A metric that indicates whether the current burst was

demodulated properly in the MS.

Received signal strength indication: A measure of the received signal strength that

indicates useful dynamic range, typically between 80 and 100 dB.




UNIT-5 5. 24

Quality indicator: An estimate of the “eye opening” for a radio signal, which is related

to the signal to interference and noise ratio, including the effects of dispersion. The

quality indicator has a narrow range (relating to the range of SIR from 5 dB to 25 dB).

In the design of a good handoff scheme, it is desirable that the blocking

probability for calls originated in a cell be minimized as much as possible. However,

from the user’s point of view, how to handle a handoff request is more important. If new

resources cannot be allocated in a timely fashion, the ongoing call has to face forced

termination, which is much more disastrous than the blocking of a new call.

In addition, attempts should be made to decrease the transmission delay of non–

real-time service calls as well as increase channel utilization in a fair manner. Therefore,

the handoff strategy for integrated service in next-generation wireless networks needs to

take different features of these services into account (i.e., the ideal handoff processes

have to be service dependent).

For example, transmission of real-time service is very sensitive to interruptions.

On the other hand, transmission delay of non–real time service does not have any

significant impact on the performance of service (i.e., non–real-time service is delay

insensitive). Therefore, a successful handoff without interruption is very important for

real-time services, but not so critical for non–real time services. In order to provide better

service for a MS with limited frequency spectrum, a wireless system must manage radio

resources efficiently.

5.19 Protocols Hybrid Protocols are

Zone Routing

The zone routing protocol (ZRP) is a hybrid of proactive and reactive protocols. It tries to

limit the scope of proactive search to the node’s local neighborhood. At the same time, global

search throughout the network can also be performed efficiently by querying selected nodes (and

not all the nodes in the network). A node’s local neighborhood is called a routing zone.

Specifically, a node’s routing zone is defined as the set of nodes whose minimum distance in




UNIT-5 5. 25

hops from the node is no greater than the zone radius. A node maintains routes to all the

destinations in the routing zone proactively. It also maintains its zone radius, and the overlap

from the neighboring routing zones.

To construct a routing zone, the node must identify all its neighbors first which are one

hop away and can be reached directly. The process of neighbor discovery is governed by the

neighbor discovery protocol (NDP), a MAC-level scheme. ZRP maintains the routing zones via a

proactive component called the intra-zone routing protocol (IARP) and is implemented as a

modified distance vector scheme. Thus, IARP is responsible for maintaining routes within the

routing zone. Another protocol called the inter-zone routing protocol (IERP) is responsible for

discovering and maintaining the routes to nodes beyond the routing zone. This process uses a

query-response mechanism on-demand basis. IERP is more efficient than standard flooding

schemes.

When a source node has data to be sent to a destination which is not in the routing zone,

the source initiates a route query packet. The latter is uniquely identified by the tuple -<source

node ID, request number>. This request is then broadcast to all the nodes in the source node’s

periphery. When a node receives this query, it adds its own ID to the query. Thus, the sequence

of recorded nodes presents a route from the source to the current routing zone. Otherwise, if the

destination is in the current node’s routing zone, a route reply is sent back to the source along the

reverse path from the accumulated record. A big advantage of this scheme is that a single route-

request can result in multiple route replies. The source can determine the quality of these

multiple routes based on such parameter(s) as hop count or traffic and choose the best route to be

used.

Fisheye State Routing

The fisheye state routing (FSR) protocol uses multilevel fisheye scopes to reduce the

routing update overhead in large networks. The key idea is to exchange link-state entries with the

neighbors with a frequency that depends on the distance to the destination. More effort is made

in collecting topological data that is more likely to be required soon. With the basic assumption

that nearby changes in network topology matter the most, FSR focuses its efforts on viewing the




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nearby changes with the highest resolution and very frequently. The changes at distant nodes are

seen with a lower resolution and less frequently.

Landmark Routing (LANMAR) for MANET with Group

Landmark ad hoc routing (LANMAR) combines the features of FSR and landmark

routing. The major addition here is to use landmarks for each set of nodes that move together as

a group (e.g., a company of soldiers in a battlefield). This reduces the overall routing update

overhead. The nodes exchange the link-state information only with their neighbors, as in FSR.

Routes within a fisheye scope are accurate, and the routes to remote groups of nodes called

subnets are “handled” by the corresponding landmarks in the neighborhood. As the packet comes

closer to the destination, it eventually switches to the accurate route provided by the fisheye. A

modified version of FSR is used for routing.

The major difference between the two routing schemes is that in FSR the routing table

contains all the nodes in the network. On the other hand, in LANMAR, the routing table contains

only the nodes within the scope and the landmark nodes. This reduces the routing table size and

overhead of the update traffic and hence increases the scalability of the scheme. While relaying a

packet, the logical subnet for the destination is looked up and the packet is routed toward the

landmark node for that subnet. However, the packet need not pass through the landmark. For the

updates in the routing table, LANMAR uses a scheme similar to that in FSR. Nodes periodically

exchange the topological information with their immediate neighbors. In each update, a node

sends entries within its fisheye scope. A distance vector with information about all the landmark

nodes is also piggybacked onto this update.

Multipath Routing Protocols

Based on the route-discovery mechanism, routing protocols are classified as either

reactive, proactive, or hybrid protocols as discussed in previous sections. Similarly, based on the

number of routes discovered between source and destination, protocols can be either unipath or

multipath protocols. Multipath protocols aim at providing redundant paths to the destination. The

availability of redundant paths to the same destination increases the reliability and robustness of

the network. Providing multiple paths is beneficial, particularly in wireless ad hoc networks

where routes are disconnected frequently due to mobility of the nodes and poor wireless link




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quality. However, multipath routing can lead to increased out-of-order delivery and resequencing

of packets at the destination along with increased collision.

Multipath routing protocols can also aid in secure routing against denial-of service

attacks by providing multiple routes between the nodes. Nodes can switch over to an alternate

route when the primary route has intermediate malicious nodes and appears to have been

compromised. Various unipath protocols discussed in earlier sections can discover multiple paths

between nodes. Diversity coding takes advantage of multiple paths for fault-tolerant

communication between nodes, where out of n paths available, m paths are used for transmitting

data and the remaining n − m paths are used for transmitting redundant information.

Multipath Routing protocol:

On-Demand Multipath Routing for Mobile Ad Hoc Networks

On-demand multipath routing is an extension of the DSR protocol. It exploits multipath

techniques in reducing the frequency of query floods used to discover new routes. It also

improves performance by providing all intermediate nodes in the primary (shortest) route with

alternate paths rather than providing only the source with alternate paths. Two multipath

extensions for DSR (MDSR) have been proposed; in both, DSR starts route discovery by

flooding the network using query messages. Each query message carries the sequence of hops it

passed through in the message header. After receiving a query packet, the destination node

replies with a reply packet that simply copies the route from the query packet and sends it back.

Each node maintains a route cache, where complete routes to desired destinations are

stored as learned from the reply packets. The destination node can receive many copies of the

flooded query messages. In the first MDSR, the destination replies to a set of query packets that

carry a source route that is link-wise disjoint from the primary source route. The primary source

route is the route taken by first query reaching the destination node. The source caches all routes

received in reply packets in its local route cache. When the primary route breaks, the remaining

shortest route is used.

The process continues still all the alternate routes are exhausted, and then a fresh route

discovery is initiated. Alternate routes are therefore provided only to the source since reply




UNIT-5 5. 28

packets sent by the destination node are addressed only to the source node. An intermediate link

failure on the primary route results in a rote error packet being sent to the source, which will then

use an alternate route. This leads to retransmissions of data packets already in transit from the

broken link.

To avoid this retransmission’s, in the second MDSR all intermediate nodes are provided a

disjoint alternate route so that in-transit data packets no longer face route loss. The destination

node now replies to each intermediate node in the primary route with an alternate disjoint route

to the destination. It is possible that not all intermediate nodes will get a different disjoint route

(especially in sparse networks), and there still may be temporary route loss due to link failures,

until an upstream node switches to an alternate route.

Thus, any intermediate node with an alternate path to the destination douses the error

packet. This continues till the source gets an error packet and has no alternate route resulting in

initiation of a new route discovery.

Ad Hoc On-Demand Distance Vector-Backup Routing

The adhoc on-demand distance vector–backing routing (AODV–BR) is a multipath

routing protocol which constructs routes on demand and uses alternate paths only when the

primary route is disrupted. This method utilizes a mesh arrangement to provide multiple alternate

paths to existing on-demand routing protocols without extra control message overhead.

Similar to its parent protocol AODV, this protocol also consists of two phases:

Route construction: Source initiates route discovery by flooding a route request

(RREQ) packet having a unique identifier so that intermediate nodes can detect and drop

duplicate packets. Upon receiving a non-duplicate RREQ, the intermediate node stores the

previous hop and the source node information in its route table. This process is also known as

backward learning. It then broadcasts the RREQ packet or sends a route reply (RREP) packet, if

it has a route to the destination. The destination node sends a RREP via the selected route when

it receives the first RREQ packet or subsequent RREQs that have a better route than the

previously replied route.

The mesh construction and the alternate paths are established during the route reply

phase. A node overhearing a RREP packet transmitted by a neighbor (on the primary route) but




UNIT-5 5. 29

not directed to it records that neighbor as the next hop to the destination in its alternate route

table. A node may receive numerous RREPs for the same route if the node is within the radio

range of more than one intermediate node of the primary route. The node then chooses the best

route among them and inserts it into the alternate route table. When the RREP packet reaches the

source, the primary route between the source and the destination is established and ready for use.

Nodes that have an entry to the destination in their alternate route table become part of the mesh

structure.

Split Multipath Routing

Split multipath routing (SMR) is an on-demand routing protocol that constructs

maximally disjoint paths between a given source destination. Multiple routes are established, and

data traffic is split into them to avoid congestion and facilitate efficient use of network resources.

These routes may not be of equal lengths. SMR like other on-demand routing protocols builds

multiple routes using request/reply cycles.

Caching and Multipath Routing Protocol

The caching and multipath routing protocol (CHAMP) makes use of temporal locality in

dropped packets and targets at reducing packet loss due to a route breakdown. Every node

maintains a small buffer for caching data packets that pass through it. When a downstream node

discovers a error in forwarding, an upstream node with the relevant data in its buffer and an

alternate route can retransmit the data. This approach can be useful only if nodes maintain

alternate routes to a destination. The main features of this protocol are therefore shortest

multipath route discovery and cooperative packet caching. Every node maintains a route cache

and a route request cache. A route cache is a list containing forwarding information to every

active destination. Each entry contains the destination identifier, distance to the destination, next

hop nodes to the destination, the last time, and the number of times each successor node was

used for forwarding. A route entry that has not been used for route lifetime is deleted. The route

request cache at a node is a list containing an entry for recent route request received and

processed.




UNIT-5 5. 30

Neighbor-Table-Based Multipath Routing in Ad Hoc Networks

Neighbor-table-based multipath routing (NTBMR) is a mixed multipath routing protocol

that deals with regular topology changes in mobile ad hoc networks. In this scheme, multiple

routes need not be disjoint as in SMR. Theoretical analysis has revealed that for error-prone

wireless links, non-disjoint multipath routing has higher route dependability. In NTBMR every

node maintains a neighbor, which records its k-hop neighbor nodes. This scheme also consists of

route discovery and route maintenance. The principal mechanism here is construction of a

neighbor table and a route cache at every node. The routes in the neighbor table are used in the

construction of route cache and are also used to establish the lifetime of wireless links to assist in

route discovery.

5.20 Auto Configuration The nodes of a network need some mechanism to interchange messages with each other.

The TCP/IP protocol allows the different nodes from the network to communicate by associating

a distinct IP address to each node of the same network. In wired or wireless networks with an

infrastructure, there is a server or node which correctly assigns these IP addresses.

Mobile ad hoc networks, on the other hand, do not have such a centralized entity able to

carry out this function. Therefore, some protocol that performs the network configuration in a

dynamic and automatic way is necessary, which will utilize all the nodes of the network (or only

part of them) as if they were servers which manage IP addresses.

Due to the dynamic topology of mobile ad hoc networks (constant movement of the

nodes that can join and leave the network frequently and even simultaneously), auto-

configuration protocols are faced with various problems in guaranteeing the uniqueness of IP

addresses and in allowing network partitioning and merging.

To guarantee the correct functioning of the network, the protocols strive to achieve

the following objectives:

Assign unique IP addresses: Ensure that two or more nodes do not obtain the

same IP address.




UNIT-5 5. 31

Function correctly: An IP address is only associated with a node for the time that

it is kept in the network. When a node leaves the network, its IP address should

then became available for association to another node.

Fix the problems derived from the loss of messages: In case of any node failure

or if message loss occurs, the protocol should operate quick enough to prevent

two or more nodes from having the same IP address.

Allow multi-hop routing: A node will not be configured with an IP address if

there aren’t any available in the whole network. Thus, if any node of the network

has a free IP address, it has to associate itself with the node which is requesting an

IP address, even though it is at two-hop of distance or more.

Minimize the additional packet traffic in the network: The protocol must

minimize the number of packets exchanged among the nodes in the auto-

configuration process. In other words, control packets traffic must cause as little

harm as possible to the data packet traffic, given that in the extreme case, the

network performance would decrease.

Verify the existence of competing petitions for an IP address: When two nodes

request an IP address at the same time, the protocol must carry out the pertinent

treatment so that the same IP address is not given to two nodes.

Be flexible to partitioning and merging of the mobile ad hoc network: The

protocol must be able to achieve the union of two different mobile ad hoc

networks as well as the possible partitioning into two networks.

Conduct synchronization: The protocol must adapt itself to the rapid changes of

the wireless network topology due to the frequent mobility of the nodes. The

synchronization is carried out periodically to ensure the configuration of the

network is as up to date as possible.




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Classification of Auto-Configuration Protocols

The auto-configuration protocols may be classified according to address management:

Stateful: The nodes know the network state, i.e., they keep tables with the IP addresses

of the nodes.

Stateless: The IP address of a node is managed by itself. Generally they create a random

address and perform a process of duplicated address detection steps to verify their

uniqueness.

Hybrid Protocols: They mix mechanisms from the previous ones to improve the

scalability and reliability of the auto-configuration. Their algorithms have a high level of

complexity.

5.21 Energy Efficient Communication Energy efficient communication in MANETs begins at the node. “In an ad hoc network,

nodes are dependent on each other and must cooperate to provide routing and other essential

services.” The energy spent running these services may be significant enough as to cause

disruption of service in the entire network if a death of even a few nodes occurs. “Because the

nodes are usually small, battery powered devices, energy management is a criticalissue for

practical deployment of ad hoc networks. The solution to prolonging the battery lifetime of

nodes and hence the useful life the network is making successful use of power save routing

protocols.

In conventional routing algorithms, which are unaware of an energy budget, connections

between two nodes are established through the shortest path possible. These algorithms may

however result in a quick depletion of the battery energy of the nodes along the most heavily

used routes in the network.” On the other hand, nodes using power saving routing protocols are

able to decide how much power a node needs at a certain time. Power-saving protocols work by

selecting intervals during which a node can put its interface into a low power sleep mode, with

minimal impact on overall network performance. An ad hoc node may function in several

different modes, or states of operation.




UNIT-5 5. 33

The four primary modes are sending, receive, idle, and sleep. To be able to transmit or

receive, a node must transition to the idle state, which requires both time and energy. In its sleep

state, a node saves power by energizing only its most critical electrical components while

waiting for a connection request to be made. However, sending and receiving are not the

dominant source of energy consumption: being awake and ready to send or receive traffic.

Therefore, “to reduce the energy consumption of the network, it is necessary to find a way for

nodes to spend more time in the sleep state and less time awake in the idle state”.

5.22 Mobility Requirements

Mobile users encounter various mobile application scenarios that require special

planning. For example, a user might start using a mobile application while away from work by

connecting through the 3G network, then switch to the corporate Wi-Fi network when arriving at

work, and then switch back to 3G when leaving the building. You need to plan your environment

to support such network transitions and guarantee a consistent user experience. This section

describes the infrastructure requirements you need to meet to support mobile applications and

automatic discovery of mobility resources.

When you use automatic discovery, mobile devices use Domain Name System (DNS) to

locate resources. During the DNS lookup, first a connection is attempted to the fully qualified

domain name (FQDN) that is associated with the internal DNS record. If a connection cannot be

made by using the internal DNS record, a connection is attempted by using the external DNS

record. A mobile device that is internal to the network connects to the internal auto discover

Service URL, and a mobile device that is external to the network connects to the external auto

discover Service URL. External requests go through the reverse proxy.




UNIT-5 5. 34

5.23 Question Bank PART – A

1. What is meant by congestion? How to reduce it?

2. What are the mobility requirements?

3. List out the features of Adhoc Network?

4. Explain Mobility in Adhoc Network?

5. Explain Security limit in Adhoc Network?

6. Explain mobile Agent and interoperability in middleware?

7. Explain Security and Eventing in middleware?

8. What are the mobility requirements?

9. What is meant by middleware?

10. List out application of middleware’s?

11. Define Garbage Collection.

12. Define Eventing.




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PART – B (16 Marks)

1. Compare the reactive and proactive routing protocols.

2. Explain the properties of MANETs.

3. How does dynamic source routing handle routing? What is the motivation behind

dynamic source routing compared to other routing algorithms fixed networks?

4. Describe security problems in MANETs.

5. Explain destination sequence distance vector routing algorithm in MANETs.

6. What are the security threats to a MANET? Why a MANET faces grater security threats

than a fixed infrastructure networks?

7. Why is routing in multi-hop ad-hoc networks complicated? What are the special

challenges?

8. Explain in detail AODV routing algorithm for MANETS.

9. What is MANET? How is it different from cellular system? What are the essential

features of MANET? What are the applications of MANET?

10. What is mobile ad-hoc network? Explain in detail about MANETS.

11. What are the disadvantages of MANETS and explain in detail?

12. Explain mobile agent and interoperability in middleware?

13. Explain Security and Eventing in middleware?

14. Explain Garbage Collection?

15. Explain in detail about the service discovery middleware.



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