1_1 Introduction-JAN 2011

7/28/2019 1_1 Introduction-JAN 2011

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Sudacad Telecomm Diploma

Telecomm Principles


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Basic Communication Model

TxChannel

Rx Source the person or group or organization sending out the

message/information.

generates data to be transmitted

Transmitter

Converts data into transmittable signals

Transmission System

Carries data

Receiver the person, group or organization that is receiving the

information.

Converts received signal into data

Destination

Takes incoming data


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Simplified Communications Model


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Communications: Tasks Transmission System Utilization: refers to the need to make efficient use of

transmission

Interfacing

Signal Generation

Synchronization

Exchange Management

Error detection and correction

Addressing and routing

Recovery

Message formatting: each message contains the following three basicelements (header ,data &Footer )

Security

Network Management


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Communications: TasksTransmission system utilization refers to the need to make efficient use of

Transmission facility that are typically shared among a number of communication

devices various of techniques ( referred to as multiplexing) are used to allocate

the total capacity of transmission medium among a number of users .congestion

control techniques may be required to assure that the system is not overloaded.

Interface to communicate a device must interface with transmission system .all forms

of communication depend on use of electromagnetic signals propagated overtransmission medium ,thus once an interface is established signal generation is

required for communication the properties of signal such as formed intensity ,

must be propagated through transmission system but must be some form of

synchronization between transmitter and receiver . Exchange management if

data are to be exchange in both direction over period of time two parities must

corporate. Error detection and correction flow control is required to assure thatthe source does not over whelm the destination by sending a lots faster than can

be processed and absoved.


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Address and routing when transmission facility is shared by more than two devices ,a

source system must indicate the identity the destination .the transmission systemmust assure that the destination and only that system ,receive the data.

Recovery is concept distinct that of error correction. Recovery techniques are needed

in situation in which an information exchange ,such as dta base transaction or file

transfer, is interrupted due to the fault somewhere in the system.

Message formatting has to do with an agreement between tow parties as to the formof data to be exchanged or transmitted ,such as the binary code for characters.

It is important to provide some measure ofsecurity in data communication system

The sender of data may wish to be assured that only the intendedreciver acutly

receives the data

Network management capabilities are need to configure the system .monitor its

status, react to failure and overload.


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Primary Network Layers

Teletraffic

Switching Systems

Transmission Systems

Radio SystemsCables

FrequenciesDucts

Geography

Logical Network

Physical Network


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Wide Area Network (WAN)

Large geographical area

Crossing public rights of way

Rely in part on common carrier circuits

Alternative technologies Circuit switching

Packet switching

Frame relay

Asynchronous Transfer Mode (ATM)


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Asynchronous Transfer Mode (ATM)

Asynchronous transfer mode (ATM) is a high-performance switching technology

that organizes digital data into 53-byte units called cells. Cells are processed

independently of each other, and related cells do not necessarily travel down

the network together. For this reason, the technology is asynchronous. ATM

was designed to use identically sized packets so that switching and routing

hardware could be optimized for speed. All the cells are the same size,

meaning each switching operation is the same as the next. ATM operates ateither 155.520 Mbps or 622.080 Mbps using standard rates and frequencies.

Speeds on ATM networks can reach as high as 10 Gbps.

ATM can carry many different types of traffic such as high-speed LAN traffic,

connections between LANs, voice, video, and other multimedia applications.

Traffic is sorted for priority (which cell travels first) by setting certain bits thatindicate whether a cell is eligible to be dropped.


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Switching Circuit Switching

Dedicated communications path established for the duration of the

conversation, e.g. telephone network

Packet Switching

Data sent out of sequence

Small chunks (packets) of data at a time

Packets passed from node to node between source and destination

Used for terminal to computer and computer to computer

communications


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Local Area Network (LAN)

Smaller scope

Building or small campus

Usually owned by same organization as attached devices

Data rates much higher Usually broadcast systems

Now some switched systems and ATM are being introduced


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WAN vs LAN


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Network ownership and service type

Private Owned by individual or corporation Restricted to owners use

Typically used by large corporations +ve

Complete control

-ve Installation and operation costs

Public Owned by a common carrier Individuals or corporations can subscribe Public refers to availability not data +ve

No need for staff to install/operate network -ve

Dependency on carrier Subscription fee


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Views on a Network

Network

Economic View

Technological ViewOperational View

Planner View

long-term

short-term

User View

Management View

services!

company

quality

profit

innovation...

...


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Life Cycle of a Network

Implementation Phase

Study Phase

Idea

Decision

Launch

Break-up

Operative Phase


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Operative Phase

Dynamic of a Network

Motivation for a

Network Reconstruction

or Extension by: Growing Demand

High Network Cost

Technological Innovation

Low Quality of Service

New Services

New

Study Phase

ImplementationPhase of the

Network Recon-

struction or

Extension

>>> Decision


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Basic Topologies

Ring Tree Partly-meshed

Tree with Center Stars with Centers Rings with Centers


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Protocols

Used for communications between entities in a system

is the special set of rules that end points in

a telecommunication connection use when they communicate

Must speak the same language

Entities

User applications

e-mail facilities

Systems

Computers

Remote sensors


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Standards

Required to allow for interoperability between equipment Advantages

Ensures a large market for equipment and software

Allows products from different vendors to communicate

Disadvantages Freeze technology

May be multiple standards for the same thing


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Standards Organizations

Internet Society

ISO

ITU-T (formally CCITT)

ATM forum ETSI

ANSI

IEEE IETF

3GPP


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standards bodies ITU - International Telecommunication Union

http://www.itu.org

IETF - Internet Engineering Task Force.

http://www.ietf.org

ETSI - European Telecommunications Standards Institute

http://www.etsi.org/tiphon

ANSI - American National Standards Institute

http://www.ansi.org

TIA - Telecommunications Industry Association http://www.tiaonline.org

IEEE - Institute for Electrical and Electronics Engineers

http://www.ieee.org


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IEEE (Institute of Electrical & Electronic Engineers

It provides standards for the network hardware so that the hardware equipment by

various network hardware manufacturers can be connected with each other. The IEEE

LAN standard is the leading LAN standard nowadays. It mainly defines the 802 protocol

stack, in which 802.3 is the Ethernet standard protocol stack, 802.5 is the token ring

network, and 802.11 is the wireless network standard.

ANSI (America National Standard Institute):

ANSI is a voluntary organization composed of people from companies, government and

other organizations, which mainly defines standard for the fiber distributed data

interface (FDDI).

EIA/TIA (Electronic Industries Association/Telecom Industries Association):

It defines standards for the network connection cable such as RS232, CAT5, HSSI and

V.24. In addition, it also defines laying standards for the cable such as EIA/TIA568B.

ITU (International Telecom Union):

It defines standards for the telecom network oriented to wide area connection such

X.25 and Frame Relay.INTERNET Action Board (IAB):

It is affiliated with the Internet engineering task force, Internet task force and the

Internet committee for number allocation for definition of various INTERNET standards,

which is the most influential international standardization organization.


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Terms Service Provider (SP)

Telecom Operator/Carrier

Internet Service Provider (ISP)

Grade of Service (GoS)

Quality of Service (QoS)

Class of Service (CoS)

Quality of Experience (QoE)

Network classification: access, regional, backbone, metro, core,.. Service Level Agreement (SLA)

Leased Line

Jitter

Dark Fiber: dedicated fiber link assigned for you (not shared), connectingend points without running through a transmission network

Bit Error Rate (BER)

Operation & Maintenance Center (OMC)

Network Operations Center (NOC)

Operations Support System (OSS)

Business Support System (BSS)


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Transmission Schemes

Baseband transmission

Uses only low frequencies

Encodes data directly

Broadband transmission

Uses multiple carriers

Can use higher frequencies

Achieves higher throughput

Hardware more complex and expensive


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Baseband& broadband

The terms baseband and broadband are used to

distinguish the number of channels that a wire cancarry. The term baseband describes

acommunications system in which the media carries

one signal only. That signal may have many

components, but from the perspective of the wire

or fiber, there is only one signal. A broadband

communications system, on the other hand, lets

more than one signal use the wire at one time. Forexample, a plain old telephone system (POTS)

circuit is a baseband system. Adding a DSL signal to

the line, however, makes it a broadband system.


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Local loop

Telephone terminology

Refers to connection between residence/business and central

office

Originally for analog POTS

Plain Old Telephone Service

Crosses public right-of-way

A right of way which permits the public to travel over it, such as a

street, road, sidewalk, or footpath


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Strategic Planning

to give the network operator the answerabout

Which Telecommunication Equipment

in which Quantity

at which Location

at which Time

has to be installed in order to reach a given

strategic objective ...


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Network Management

Configuration Management

to manage network resources (hardware, software, systems)

Fault Management

to detect and overcome failures

Performance Management to measure the traffic

to maintain quality of service

Accounting Management

to get the service usage data

Security Management

to protect against fraud application


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Load and Capacity

Load

Capacity

Dem

and

Loads are a measure for the

demand that is actually realised by

a network element.

Capacities are a measure for the

maximum demand that can be

realised by this element.

Spare Load= capacity - Load


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Utilization

0,2

20%

0,6

60%

1,0

100%

Load Maximum Load !!


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Busy Hour (Peak Hour)

Time section of the day of four subsequent quarter hours in which the traffic valueof a trunk group averaged over several working days reaches its maximum.

Hourly Traffic Profile

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 2 4 6 8 10 12 14 16 18 20 22

Hour

Tra

ffic

Value

(Erl)


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Measurement Unit: the Erlang

An important measurement unit of the traffic value is Erlang (Erl)

1 Erlang = 1 holding hour pertime hour

One service element can carry a maximum traffic value of

1 Erl, two service elements max. 2 Erl, etc.

1h0,5h

0,5h=

1 Erlang: 0,1h

0,4h

= 0,3h

0,2h

1h1h

1h


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Network Availability (1)

4 x 2Mbit/s

Load Sharing Protection

50%

50%

2 x 2Mbit/s

2 x 2Mbit/s

100%

100%

4 x 2Mbit/s

4 x 2Mbit/s

99.999: network should be unavailable only for 5 min/year


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Protection

Redundant resources are fixed andpre-assigned quite simple mechanisms to switch over from a failed 'working' element to an intact

'protection' element

Restoration

Redundant resources which are not pre-assignedand have to be 'discovered' by

some network intelligence

usually controlled by the (centralized) network management

requires more complicated implementation than protection, but more efficient

resource management

Network Availability (2)


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Protection

very short detection time of failures(< 10ms in physical media)

very short recovery time

(< 50ms in SDH and WDM)

short detection time of failures

(< 10ms in physical media)

but increased recovery time

possible

extension

Splitter Switch

Working Path

Protection Path

1+1

Dedicated Protection

Switch Switch

Working Path

Protection Path

(possible with

additional load)1:1 N:1

Shared Protection


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Transmission

Sending an information (signals: analog or digital, electrical or optical)from one end to another; i.e., communication

In telecommunications, transmission is the forwarding of signal traffic over

long distances

In general information theory transmission is taken to mean the complete

process of communication of information via a channel The channel

Tx Line, Tx channel, Tx Link, Tx Medium

Guided: Copper ( STP, UTP, simple pair,.) ,Coax, Optical Fiber, Wave

Guide.

Unguided: water, air, space


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Data transmission: Energy Forms

Electric current

Audible sounds

Omni-directional electromagnetic waves

Radio Frequency

InfraRed

Directional electromagnetic waves

Point-to-point satellite channel

Limited broadcast (spot beam)

Microwave

Laser beam


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Fundamental measures Delay

The amount of time required for a bit of data totravel from one end to the other

Throughput

The number of bits per second that can betransmitted

Related to underlying hardware bandwidth

Bandwidth

Maximum times per second the signal can change


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BandwidthWhen discussing signals on networks, the speed at which the signals travel and the

type of transmission are important to keep in mind. The speed of the signals is

called bandwidth while the type of transmission can be either baseband orbroadband. This section discusses both issues. Bandwidth is the width of a band ofelectromagnetic frequencies. It is used to describe the speed at which data flowson a given transmission path and the range of frequencies that a signal occupies ona given medium. Simply put, bandwidth is proportional to the amount of data thatcan be transmitted or received in a certain amount of time. For example, it takesmore bandwidth to download a photograph in one second than it takes to

download a page of text in one second. Large sound files, computer programs, andanimated videos require still more bandwidth for acceptable system performance.Virtual reality (VR) and full-length three-dimensional audio/visual presentationsrequire the most bandwidth of all.

A digital or analog signal has a bandwidth. Today this is expanded to include fiber-opticbased light impulses. Typically the amount of bandwidth is measured by the

amount of data that can be transferred in a fixed amount of time. For digitaldevices, the bandwidth is usually expressed in bits per second (bps) . For analogdevices, the bandwidth is expressed in cycles per second, or hertz (Hz).

The term bandwidth is also used when discussing the various types of telephony-based networking.


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Delay

Propagation delay Time required for signal to travel across media

Constant for one link, depends on distance and propagation speed

Propagation speed depends on cable material

, e.g., electromagnetic radiation travels through space at the speed of

light (c=3x108 m/s)

Glass Fiber: ~200 000 km/s

Metallic Conductor: ~ 180 000 240 000 km/s

Switching delay

Fixed or nearly constant

Queuing delay

Variable , depends on throughput


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Throughput-Bandwidth Relationship

Nyquists theorem D = 2Blog2K

D: maximum data rate

B: hardware bandwidth

K: number of values used to encode data

Shannons Theorem Gives capacity in presence of noise

C = Blog2(1 + S/N)

C: the effective channel capacity

B: hardware bandwidth

S: the average signal power

N: noise power

S/N: signal-to-noise ratio


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Channel Capacity

Data rate

In bits per second

Rate at which data can be communicated

Bandwidth

In cycles per second of Hertz

Constrained by transmitter and medium

Any transmission system has a limited band of frequencies,

and this limits the data rate that can be carried


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Delay-Throughput Relationship

When network idle

Queuing delay is zero

As load on network increases

Queuing delay rises

Load defined as ratio of throughput to capacity

Called utilization


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Delay-Utilization relationship

Define

D0: propagation and switching delay

U: utilization (0 U 1)

D: total delay

Then

D = D0 / (1-U)

High utilization known as congestion

1_1 Introduction-JAN 2011

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