1

Wireless LANs and PANs Lecture 2

Ioannis Neokosmidis

2

Introduction Fundamentals of WLANs

• Technical issues Difference between wired and wireless networks

• Use and design goals

• Types, components and functionalities

IEEE 802.11 Standard• Physical layer and MAC layer

• Optional functionalities: Security and QoS

HIPERLAN Standard• European standard

Bluetooth• Enables Communication of personal devices in the absence of infrastructure

HomeRF• Home networking

• Technical differences with other technologies (for PANs)

3

Fundamentals of WLANsTechnical Issues

Node – Station – Terminal Portable terminals vs Mobile terminals Differences between wireless and wired transmission

• Address is not equivalent to physical location• Address refers to a particular station (not always stationary)• Address may not always refer to a particular geographical location

• Dynamic topology and restricted connectivity• Network connectivity is partial at times: Mobile nodes may often go out of reach

• Medium boundaries are not well-defined• Difficult to determine the exact reach of wireless signals

– Signal strength and noise levels

• Error-prone medium• Simultaneous transmissions by nodes located within the direct transmission range• BER = 10-4 (10-9) in a wireless (fiber optic) channel• Unreliable channel – Problem? – Solution?

4

Fundamentals of WLANsTechnical Issues

Use of WLANs Flexible – Topologies depends on the application

• Users can access the Internet on the move.

• WLANs are handy in areas affected by earthquakes or other disasters.• No suitable infrastructure available• Setup networks on the fly

• WLANs are good solutions in places where wiring may not be permitted (historic buildings)

5

Design goals for wireless LANs Operational simplicity: Quick setup Power-efficient operations: Power saving features – Technologies and

Protocols License-free operation: no special permissions or licenses needed to use

the LAN Tolerance to interference: Different wireless networking technologies

(civilian & military apps) – Other uses (MW ovens) Global usability: Acceptability of the technology - spectrum (globally) Security: broadcast security (no one should be able to read my data),

privacy (no one should be able to collect user profiles), Safety requirement: (i) Interference to medical and other devices and

(ii) increased power levels lead to health hazards Design must follow the power emission restrictions ~ spectrum

Quality of service requirements: Multimedia traffic Compatibility with other technologies and applications

• Other LANs and WANs (interoperability with TCP / IP protocol)

6

Comparison: Infrastructure vs. Ad-hoc networks

WLANs can be classified into two types:• Infrastructure networks contains access points (APs) and mobile station

(STAs).

• Ad hoc LANs do not need any fixed infrastructure.

Infrastructure networks• Provide access to other networks

• Include forwarding functions

• Medium access control

Ad-hoc networks is a group of computers each with wireless adapters, connected as an independent wireless LAN.• Each node can communicate with other nodes

7

Comparison: infrastructure vs. ad-hoc networks

Infrastructure Network

Ad-hoc network

APAP

AP

Wired network

AP: Access Point

8

802.11 - Architecture of an infrastructure network

Distribution System

Portal

802.x LAN

Access Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access Point

STA1

STA2 STA3

ESS

Station (STA)• terminal with access mechanisms to

the wireless medium and radio contact to the access point

Basic Service Set (BSS)• group of stations using the same

radio frequency

Access Point (AP)• station integrated into the wireless

LAN and the distribution system

Portal• bridge to other (wired) networks

Distribution System• interconnection network to form

one logical network (EES: Extended Service Set) based on several BSS Basic Service Area: Coverage Area of an

AP

9

802.11 - Architecture of an ad-hoc network

Direct communication within a limited range• Station (STA):

terminal with access mechanisms to the wireless medium

• Independent Basic Service Set (IBSS):group of stations using the same radio frequency

802.11 LAN

IBSS2

802.11 LAN

IBSS1

STA1

STA4

STA5

STA2

STA3

10

802.11 Services Distribution Services (for APs)

• Association – Mobile stations connect themselves to base stations• MS send their identity and address to BS

• Reassociation – a station may change its preferred base station• The established association is transferred from one AP to another

• Disassociation – the station or base station breaks the association • Distribution – determines how to route frames sent to the base station• Integration – handles the translation from the 802.11 format to the format

of the destination network (Addresses – Frames)

Intracell Services (for STAs and APs)• Authentication – a station must authenticate itself before permitted to

send data. • Deauthentication – a authenticated station wanting to leave the network is

deauthenticated.• Privacy – manages the encryption and decryption (eavesdroppers) • Data Delivery – not reliable Job of higher level.

11

IEEE 802.11 Standard

802.11 was the first effort for defining a standard for wireless wideband local access

In contrast to other LAN standards, wireless standards• need to have provisions to support mobility of nodes

• Had to examine connection, link reliability and power management

IEEE 802.11b is known as Wi-Fi (wireless Fidelity). Mobile Stations (MTs) can operate two modes:

• Infrastructure mode, in which MTs can communicate with one or more APs which are connected to a WLAN.

• Ad hoc mode, in which MTs can communicate directly with each other without using an AP.

12

The 802.11 Protocol Stack

Part of the 802.11 protocol stack.

13

IEEE standard 802.11

mobile terminal

access point

fixedterminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructurenetwork

LLC LLC

14

802.11 - Layers and functions PMD (Physical Medium Dependent) : modulation, encoding/decoding (coding) PLCP (Physical Layer Convergence Protocol):

• provide a uniform abstract view for the MAC sublayer

• service access point (SAP) abstract the channel that offers up to 1 or 2 Mbps

• clear channel assessment (CCA) signal (carrier sense) used for CSMA/CA

PHY Management: channel selection, Management Information Base (MIB) Station Management: coordination of all management functions MAC: access mechanisms, fragmentation, encryption MAC Management: synchronization, roaming, authentication, MIB, power

management

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

PH

YD

LC

Sta

tion

Man

agem

ent

15

802.11 Physical Layers Infrared – 1 Mbps and 2 Mbps

• 850-950 nm, infra-red light, typical 10 m range, encoded using PPM FHSS (Frequency Hopping Spread Spectrum) uses 79 channels,

each 1 MHz wide, starting in the 2.4 GHz band.• A psudorandom number generator is used to produce the sequence of

frequencies hopped to. • The amount of time spent at each frequency, dwell time, is adjustable

<400ms• spreading, despreading, signal strength, typical 1 Mbit/s• min. 2.5 frequency hops/s (USA), 2-level GFSK modulation, 4-level GFSK

for 2Mbit/s DSSS (Direct Sequence Spread Spectrum) delivers 1 or 2 Mbps in

the 2.4 GHz band.• DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying),

DQPSK for 2 Mbit/s (Differential Quadrature PSK)• preamble and header of a frame is always transmitted with 1 Mbit/s, rest of

transmission 1 or 2 Mbit/s• chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)• max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

16

802.11 - Physical layer 802.11a uses OFDM (Orthogonal Frequency Division

Multiplexing) to deliver up to 54 Mbps in the 5 GHz band.• Orthogonal Frequency Division Multiplexing, an FDM modulation

technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver

802.11b uses HR-DSSS (High Rate Direct Sequence Spread Spectrum) to achieve 11 Mbps in the 2.4 GHz band.

802.11g uses OFDM to achieve 54 Mbps in the 2.4 GHz band. The physical layer sensing is through the clear channel

assessment (CCA) signal provided by the PLCP. The CCA is generated based on sensing of the air interface by:• Sensing the detected bits in the air: more slowly but more reliable• Checking the received signal strength (RSS): faster but no so precise

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Orthogonal Frequency Division Multiplexing (OFDM)

OFDM, also called multicarrier modulation (MCM), uses multiple carrier signals at different (lower) frequencies, sending some of the bits on each channel.

The OFDM scheme uses advanced digital signal processing techniques to distribute the data over multiple carriers at precise frequencies.• Suppose the lowest-frequency subcarrier uses the base frequency fb. The

other subcarriers are integer multiples of the base frequency, 2fb, 3fb, etc.

• The precise relationship among the subcarriers is referred to as orthogonality.• The result is the maximum of one subcarrier frequency appears exactly at a

frequency where all other subcarriers equal zero

k3

f

t

c

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Orthogonal Frequency Division Multiplexing (OFDM)

Superposition of frequencies in the same frequency rangeAmplitude

f

subcarrier: SI function=

sin(x)x

Properties• Lower data rate on each subcarrier less intersymbol interference (ISI)• interference on one frequency results in interference of one subcarrier only• no guard space necessary• orthogonality allows for signal separation via inverse FFT on receiver side• precise synchronization necessary (sender/receiver)

Advantages• no equalizer necessary• no expensive filters with sharp edges necessary• better spectral efficiency (compared to CDM)

Application: 802.11a, 802.11g, HiperLAN2, DAB (Digital Audio Broadcast), DVB (Digital Video Broadcast), ADSL

19

Comparison: infrared vs. radio transmission Infrared

• uses IR (Infra-Red) diodes, diffuse light, multiple reflections (walls, furniture etc.)

• Advantages• simple, cheap, available in

many mobile devices• no licenses needed• simple shielding possible

• Disadvantages• interference by sunlight,

heat sources etc.• many things shield or

absorb IR light • low bandwidth

• Example• IrDA (Infrared Data

Association) interface available everywhere

Radio• typically using the license free ISM

(Industrial, Scientific, Medical) band at 2.4 GHz

• Advantages

• experience from wireless WAN and mobile phones can be used

• coverage of larger areas possible (radio can penetrate walls, furniture etc.)

• Disadvantages

• limited license free frequency bands

• shielding more difficult, interference with other electrical devices

• Example

• WaveLAN (Lucent), HIPERLAN, Bluetooth

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Wireless LAN Standard

Standard Modulation Spectrum Max physical Rate

Working distance

802.11 WDM, FHSS

DSSS

2.4 GHz 2 Mbps ≈100 m

802.11a OFDM 5 GHz 54 Mbps ≈ 50 m

802.11b HR-DSSS 2.4 GHz 11 Mbps ≈ 200 m

802.11g OFDM 2.4 GHz 54 Mbps ≈ 200 m

21

Wireless LANS Devices

wireless router wireless network card

22

Medium Access Control in Wireless LANs• Because there is higher error rate and signal strength is not

uniform throughout the space in which wireless LANs operate, carrier detection may fail in the following ways: • Hidden nodes:

• Hidden stations: Carrier sensing may fail to detect another station. For example, A and D.

• Fading: The strength of radio signals diminished rapidly with the distance from the transmitter. For example, A and C.

• Exposed nodes:

• Exposed stations: B is sending to A. C can detect it. C might want to send to E but conclude it cannot transmit because C hears B.

• Collision masking: The local signal might drown out the remote transmission.

An early protocol designed for wireless LANs is MACA (Multiple Access with Collision Avoidance).

23

Wireless LAN configuration

LAN

Server

WirelessLAN

Laptops

Base station/access point

Palmtop

radio obstruction

A B C

DE

24

The 802.11 MAC Sublayer Protocol

(a) The hidden station problem.(b) The exposed station problem.

25

The 802.11 MAC Sublayer Protocol

- The hidden station problem.- The exposed station problem.

26

802.11 MAC Sublayer MAC layer tasks:

• Control medium access• Roaming, authentication, power conservation

Traffic services• DCF (Distributed Coordination Function) (mandatory): Asynchronous

Data Service based on CSMA – CA• Only service available in ad-hoc network mode• does not use any kind of central control• exchange of data packets based on “best-effort”• support of broadcast and multicast

• PCF (Point Coordination Function) (optional): Real – Time Services• AP controls medium access and avoids simultaneous transmissions by

the nodes

27

Distributed Coordination Function CSMA with Collision Avoidance

When a station wants to transmit, it senses the medium

• If the medium is idle, it starts transmission• During transmission, it does not sense the medium (transmission of a

whole frame)

• If the medium is busy, transmitter waits for the channel to become idle and then transmits

• In the case of collision, the collided stations back off for a random period of time (exponential back-off algorithm as in Ethernet)

28

Distributed Coordination Function MACA and MACAW

MACAW (MACA for Wireless) is a revision of MACA.• The sender senses the carrier to see and transmits a RTS (Request To

Send) frame if no nearby station transmits a RTS.

• The receiver replies with a CTS (Clear To Send) frame.

• Neighbors

• see CTS, then keep quiet.

• see RTS but not CTS Not at the area of the receiver

• The receiver sends an ACK when receiving an frame.

• Neighbors keep silent until see ACK.

• Collisions

• There is no collision detection.

• The senders know collision when they don’t receive CTS.

• They each wait for the exponential backoff time.

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MACA Protocol

The MACA protocol. (a) A sending an RTS to B.(b) B responding with a CTS to A.

NAV: Network Allocation Vector

30

802.11 MAC Sublayer PCF (Point Coordination Function) (optional)

• access point polls terminals according to a list• ask them if they have any frames to send

• Completely controlled by the base station. No collisions occur.

• A beacon frame which contains system parameters is periodically (10 to 100 times per second) broadcasted to invite new stations to sign up for polling service.• Hopping sequences and dwell times (for FHSS), clock

synchronization, etc.

31

802.11 MAC Sublayer PCF and DCF can coexist within one cell by carefully defining

the interframe time interval. The four intervals are depicted:• SIFS (Short InterFrame Spacing) denotes highest priority to access the

medium. It is defined for short control messages (acks)• Transmission if the channel is idle for t >= SIFS

• PIFS (PCF InterFrame Spacing) is used for real time services

• DIFS (DCF InterFrame Spacing) is used by stations that are operating under the DCF mode to transmit packets

• EIFS (Extended InterFrame Spacing) is the longest least priority to access the medium. It is used only by a station that has just received a bad or unknown frame to report the bad frame.

The result MAC scheme used in 802.11 is carrier sensing multiple access with collision avoidance (CSMA/CA) that is based on MACAW.• Use NAV (Network Allocation Vector) to indicate the channel is busy.

32

The 802.11 MAC Sublayer Protocol

Interframe spacing in 802.11.

33

t

medium busy

DIFSDIFS

next frame

contention window(randomized back-offmechanism)

802.11 - CSMA/CA access method

Station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment)

If the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (IFS depends on service type)

If the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time)

If another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness)

slot timedirect access if medium is free DIFS

34

802.11 – DFWMAC Sending unicast packets

• station can send RTS with reservation parameter (transmission duration) after waiting for DIFS (reservation determines amount of time the data packet needs the medium)

• acknowledgement via CTS after SIFS by receiver (if ready to receive)

• sender can now send data at once, acknowledgement via ACK

• other stations set its net allocation vector (NAV) in accordance with the duration field.

t

SIFS

DIFS

data

ACK

defer access

otherstations

receiver

senderdata

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

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DCF – Fragmentation

t

SIFS

DIFS

data

ACK1

otherstations

receiver

senderfrag1

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

NAV (frag1)NAV (ACK1)

SIFSACK2

frag2

SIFS

The deal with the problem of noisy channels, 802.11 allows frames to be fragmented.

Fragments are independently numbered and ackowledged Stop and wait The length of fragments is adjusted by the cell (not the standard)

36

802.11 MAC Frame format Types

• control frames, management frames, data frames

Sequence numbers• important against duplicated frames due to lost ACKs

Addresses• receiver, transmitter (physical), BSS identifier, sender (logical)

Miscellaneous• sending time, checksum, frame control, data

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4

Data CRC

2 2 6 6 6 62 40-2312bytes

Protocolversion

Type SubtypeToDS

MoreFrag

RetryPowerMgmt

MoreData

WEP

2 2 4 1

FromDS

1

Order

bits 1 1 1 1 1 1

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ETSI - HIPERLAN ETSI standard

• European standard, cf. GSM, DECT, ...

• Enhancement of local Networks and interworking with fixed networks

• integration of time-sensitive services from the early beginning

HIPERLAN family• one standard cannot satisfy all requirements

• range, bandwidth, QoS support

• commercial constraints

• HIPERLAN 1 standardized since 1996 – no products!

physical layer

channel accesscontrol layer

medium access control layer

physical layer

data link layer

HIPERLAN layers OSI layers

network layer

higher layers

physical layer

medium accesscontrol layer

logical link control layer

IEEE 802.x layers

38

Overview: original HIPERLAN protocol family

HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4

Application wireless LAN access to ATMfixed networks

wireless localloop

point-to-pointwireless ATMconnections

Frequency 5.1-5.3GHz 17.2-17.3GHz

Topology decentralized ad-hoc/infrastructure

cellular,centralized

point-to-multipoint

point-to-point

Antenna omni-directional directionalRange 50 m 50-100 m 5000 m 150 mQoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)Mobility <10m/s stationaryInterface conventional LAN ATM networks

Data rate 23.5 Mbit/s >20 Mbit/s 155 Mbit/sPowerconservation

yes not necessary

HIPERLAN 1 never reached product status, the other standards have been renamed/modfied !

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HIPERLAN - Characteristics Data transmission

• point-to-point, point-to-multipoint, connectionless

• 23.5 Mbit/s, 1 W power, 2383 byte max. packet size

Services • asynchronous and time-bounded services with hierarchical priorities

• compatible with ISO MAC

Topology• infrastructure or ad-hoc networks

• transmission range can be larger then coverage of a single node („forwarding“ integrated in mobile terminals)

Further mechanisms• power saving, encryption, checksums

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Bluetooth Idea

• The need to interconnect computer and peripherals, handheld devices, PDAs, cell phones – replacement of IrDA led to the emergence of personal area networks (PANs)

• Radio frequency (RF) technology for communication• It makes use of frequency modulation to generate radio waves in the ISM band• Short range (10 m), low power consumption, license-free 2.45 GHz ISM• Voice and data transmission, approx. 1 Mbit/s gross data rate

Bluetooth Special Interest Group (SIG)• Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba• Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola• > 2500 members• Common specification and certification of products

IEEE founded IEEE 802.15 for Wireless Personal Area Networks (WPAN) and approved a Bluetooth-based standard.

One of the first modules (Ericsson).

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Forming a Bluetooth Network: Piconet Collection of devices connected in an ad

hoc fashion One unit acts as master and the others as

slaves for the lifetime of the piconet Master determines hopping pattern,

slaves have to synchronize Each piconet has a unique hopping

pattern Participation in a piconet =

synchronization to hopping sequence Each piconet has one master and up to 7

simultaneous slaves (up to 255 could be parked)

For identification purposes, each active slave is assigned a locally unique active member address (AM_ADDR)

M=MasterS=Slave

P=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB

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Oprational States of a Bluetooth Devisestandby

inquiry page

ConnectedTransmit

Park Hold Sniff

unconnected

Connecting States

Active states

low power states

Standby: do nothingInquire: search for other devicesPaging: packet exchange process between the master and a prospective slave to inform the slave of the master’s clockConnected: participate in a piconet

Park: release AMA, get PMA Sniff: listen periodically, not each slotHold: stop ACL, SCO still possible, possibly

participate in another piconet

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Forming a Piconet All devices in a piconet hop together

• Master gives slaves its clock and device ID

• Hopping pattern: determined by device ID (48 bit, unique worldwide)

• Phase in hopping pattern determined by clock

Addressing• Active Member Address (AMA, 3 bit)

• Parked Member Address (PMA, 8 bit)

SB

SB

SB

SB

SB

SB

SB

SB

SB

M

S

P

SB

S

S

P

P

SB

44

Scatternet Linking of multiple co-located piconets through the sharing of

common master or slave devices• Devices can be slave in one piconet and master of another

• As soon as a master leaves a piconnet, all traffic within this piconet is suspended until the master returns.

Communication between piconets• Devices jumping back and forth between the piconets

M=MasterS=SlaveP=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB

M

S

S

P

SB

Piconets(each with a capacity of < 1 Mbit/s)

45

Bluetooth Specifications

The Bluetooth specification consists of two parts:• The core provides a common data link and physical layer to application

protocols and maximizes reusability of existing higher layer protocols

• The profiles specifications classify Bluetooth applications into thirteen types

The protocol stack of Bluetooth performs the functions of locating devices, connecting other devices and exchanging data

It is logically partitioned into three layers: • the transport protocol group,

• the middleware group, and

• the application group.

46

Profiles

Additional ProfilesAdvanced Audio DistributionPANAudio Video Remote ControlBasic PrintingBasic ImagingExtended Service DiscoveryGeneric Audio Video DistributionHands FreeHardcopy Cable Replacement

Profiles

Pro

toco

ls

Applications

47

Bluetooth protocol stack

Radio

Baseband

HostControllerInterface

Logical Link Control and Adaptation Protocol (L2CAP)Audio

LLC SDPRFCOMM (serial line interface)

Applications / profiles

The core protocols comprise the following elements:• Radio: specification of the air interface – frequencies, modulation, power

• Baseband: connection establishment, packet formats, timing (like MAC)

• Link management protocol: link set-up and management between devices including security functions, QoS and parameter negotiation

• Logical link control and adaptation protocol (L2CAP): adaptation of higher layers to the baseband

middleware

Link Manager

Control

48

Transport Protocol Group It is composed of the protocols designed to allow Bluetooth

devices to locate each other and to create, configure and manage the wireless links

The design of Bluetooth protocols and techniques has been done with the target of low power consumption and ease of operation

Radio: specification of the air interface – frequencies, modulation, power

Baseband: connection establishment, packet formats, timing, QoS Link management protocol: link set-up and management between

devices including security functions and parameter negotiation Logical link control and adaptation protocol (L2CAP): adaptation

of higher layers to the baseband Service discovery protocol: Device discovery plus querying of

service characteristics

49

Bluetooth Specification The middleware protocol group comprises of:

• Radio Frequency Communications (RFCOMM) emulates a serial line interface such as EIA-232 or RS-232

• Service discovery protocol (SDP): Device discovery plus querying of service characteristics

• Infrared Data Association (IrDA)• The telephony control protocol specification – binary (TCS BIN) describes a

bit-oriented protocol that defines voice and data calls between Bluetooth devices.

• The host controller interface (HCI) provides a command interface to the baseband controller and link manager, and access to the hardware status and control registers.

• TCP/IP can run on PPP or Bluetooth network encapsulation protocol (BNEP). The application group consists of applications:

• Modem dialer• Web-browsing client• Calendar and business card objects (vCalendar/vCard) can be exchanged

using the object exchange protocol (OBEX).

50

Radio (Physical Layer) It deals with the characteristics of the transceivers and design specifications such

as frequency accuracy, channel interference and modulation characteristics Two type of links:

• Voice link – SCO (Synchronous Connection Oriented)

• FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched

• Data link – ACL (Asynchronous Connectionless)

• Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched

2.4 GHz ISM band, 79 RF channels, 1 MHz carrier spacing• Channel 0: 2402 MHz … channel 78: 2480 MHz

• GFSK modulation, 1-100 mW transmit power

FHSS and TDD• Frequency hopping with 1600 hops/s

• Hopping sequence in a pseudo random fashion, determined by a master

• Time division duplex for send/receive separation

51

Baseband Layer Key functions

• Framing

• Frequency hop selection

• Connection creation

• Medium access control

Master determines a sequence of time slots each of 625μs There are two fundamental elements governing the formation of a

piconet• 48-bit address: Similar to the address of IEEE 802.xx LAN devices

• The lower address part (LAP) is used in several baseband operations: piconet identification, error checking, and security checks

• The remaining two parts of the address are related to the manufacturing organization

• 28-bit clock (native clock): It ticks 3200 times/sec or ones every 312.5μs• Twice the normal hopping rate of 1600 hops/sec

52

S

Frequency selection during data transmission

f2k

625 µs

f2k+1 f2k+2 f2k+3 f2k+4

f2k+3 f2k+4f2k

f2k

f2k+5

f2k+5

f2k+1 f2k+6

f2k+6

f2k+6

MM M M

M

M M

M M

t

t

t

S S

S S

S

53

Types of Bluetooth LinksEach frame is transmitted over a logical channel, called a link, between the master and a slave. ACL (Asynchronous Connection-Less) link, which is used for packet-switched data available at irregular intervals.

• These data come from the L2CAP layer on the sending side and are delivered to the L2CAP layer on the receiving side.

• ACL traffic is delivered on a best-efforts basis. No guarantees are given. Frames can be lost and may have to be retransmitted.

• A slave may have only one ACL link to its master.SCO (Synchronous Connection Oriented) link, for real-time data, such as telephone connections.

• This type of channel is allocated a fixed slot in each direction. • Due to the time-critical nature of SCO links, frames sent over them are

never retransmitted. • Instead, forward error correction can be used to provide high reliability. A

slave may have up to three SCO links with its master. • Each SCO link can transmit one 64,000 bps PCM audio channel.

54

Link manager protocol The link manager protocol (LMP) has the following functions:

• Authentication, pairing, and encryption

• Synchronization

• Capability negotiation: negotiate

• Quality of service negotiation

• Power control

• Link supervision

• State and transmission mode change

Major baseband states are: Standby, inquiry, page, active, low power

To save battery power, a Bluetooth device can go into one of three low power states:• Active: A Bluetooth device actively participates in the piconet.

• Sniff: listen periodically, not each slot

• Hold: stop ACL, SCO still possible, possibly participate in another piconet

• Park: release AMA, get PMA

55

L2CAP - Logical Link Control and Adaptation Protocol

Protocol multiplexing• RFCOMM (Radio Frequency Communication), SDP (Service Discovery

Protocol), telephony control Segmentation & reassembly

• Up to 64 kbyte user data, 16 bit CRC used from baseband QoS flow specification per channel

• Specifies delay, jitter, bursts, bandwidth• Flow control – Devices with big packets vs devices with small packets• All devices cannot handle packets of 64kB

56

Bluetooth Packet Format Low-level packet definition

• Access code

• Identifies master (Channel, device access)• Packet header

• 1/3-FEC, active member address (broadcast + 7 slaves), link type, alternating bit ARQ/SEQ, checksum

access code packet header payload

68(72) 54 0-2745 bits

AM address type flow ARQN SEQN HEC

3 4 1 1 1 8 bits

preamble sync. (trailer)

4 64 (4)

57

WPAN: IEEE 802.15.1 – Bluetooth Data rate

• Synchronous, connection-oriented: 64 kbit/s

• Asynchronous, connectionless

• 433.9 kbit/s symmetric• 723.2 / 57.6 kbit/s asymmetric

Transmission range• POS (Personal Operating Space) up to 10

m

• with special transceivers up to 100 m

Frequency• Free 2.4 GHz ISM-band

Security• Challenge/response (SAFER+), hopping

sequence

Cost• $30 adapter, drop to $5 if integrated

Availability• Integrated into some products, several

vendors

Connection set-up time• Depends on power-mode

• Max. 2.56s, avg. 0.64s

Quality of Service• Guarantees, ARQ/FEC

Manageability• Public/private keys needed, key

management not specified, simple system integration

Special Advantages/Disadvantages• Advantage: already integrated into several

products, available worldwide, free ISM-band, several vendors, simple system, simple ad-hoc networking, peer to peer, scatternets

• Disadvantage: interference on ISM-band, limited range, max. 8 devices/network&master, high set-up latency

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History of HomeRF HomeRF is the technique that aimed at offering voice, data and

video image at home or small scale office with a low cost by radio frequency instead of wiring.

The HomeRF standard was developed by HomeRF Working Group that is composed of major companies such as Compaq, Intel, Motorola, National Semiconductor, Proxim and Siemens.

The HomeRF standard diverged from the original 802.11 FHSS standard and incorporated the Digital Enhanced Cordless Telephone (DECT) technology used for cordless telephones in Europe.

HomeRF follows shared wireless access protocol (SWAP). SWAP is used to set up a network that provides access to a public

network telephone, the Internet (data), entertainment networks (cable television, digital audio, and video), transfer and sharing of data resources (disks, printer), home control, and automation.

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History of HomeRF and Infrared

The SWAP can support up to 127 devices, each identified by a 48-bit network identifier.• Asynchronous data node is used to communicate with other nodes.• Voice node that uses TDMA for communication• Voice and Data node than can use both CSMA/CA and TDMA for channel

access

SWAP implements strong algorithms for security

HomeRF initially supports 1.6Mbps (10Mbps version 2)

The demise of HomeRF• In 2001, Intel has started the process of abandoning the HomeRF standard

for in-home networking and is switching to IEEE 802.11b. • Eventually, HomeRF lost its supporters and market and HomeRF Working

Group disbanded in 2003.

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History of HomeRF and Infrared

The infrared technology (IrDA) has the following characteristics:

• The infrared rays can be blocked by obstacles.

• The effective range of infrared communications is about one meter.

• The power consumed by infrared devices is extremely low.

• Data rates of 4 Mbps are easily achievable.

• The cost of infrared devices is low.

Despite the restriction of line of sight (LoS), infrared devices are very popular because they cost less and consume less power.

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HomeRF Standard

Data rate• 0.8, 1.6, 5, 10 Mbit/s

Transmission range• 300m outdoor, 30m indoor

Frequency• 2.4 GHz ISM

Security• Strong encryption, no open

access Cost

• Adapter ?, base station ? Availability

• Several products from different vendors

Connection set-up time• 10 ms bounded latency

Quality of Service• Up to 8 streams A/V, up to 8 voice

streams, priorities, best-effort

Manageability• Like DECT & 802-LANs

Special Advantages/Disadvantages• Advantage: extended QoS support,

host/client and peer/peer, power saving, security

• Disadvantage: future uncertain due to DECT-only devices plus 802.11a/b for data