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CHAPTER 8CHAPTER 8

TELECOMMUNICATIONSTELECOMMUNICATIONS

AND AND

NETWORKSNETWORKS

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TELECOMMUNICATIONS

Telecommunications:Telecommunications: Communication Communication of all types of information, including of all types of information, including digital data, voice, fax, sound, and video digital data, voice, fax, sound, and video from one location to another over some from one location to another over some type of networktype of network

Network:Network: A group of computers and A group of computers and associated peripheral devices connected associated peripheral devices connected by a communication channel of sharing by a communication channel of sharing information and other resources among information and other resources among usersusers

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TextVoiceImageVideo

Types of Data

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SENDER RECEIVERMEDIUM

Basic Communications Model

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COMPONENTS OF

A TELECOMMUNICATIONS SYSTEM

Computers to process informationComputers to process information

Terminals or any input/output devices Terminals or any input/output devices that send or receive datathat send or receive data

Communications processorsCommunications processors

Communications softwareCommunications software

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Figure 8-1

COMPONENTS OF

A TELECOMMUNICATIONS SYSTEM

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PC

Data communications processors

PC

Basic components of a data communications system

Data communicationsMedium

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Transmit informationTransmit information

Establish interface between sender and Establish interface between sender and the receiverthe receiver

Route messages along most efficient Route messages along most efficient pathspaths

FUNCTIONS OF

A TELECOMMUNICATIONS SYSTEM

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Perform elementary processing of Perform elementary processing of information information

Perform editorial tasks on data Perform editorial tasks on data

Convert message speed or formatConvert message speed or format

Control flow of informationControl flow of information

FUNCTIONS OF

A TELECOMMUNICATIONS SYSTEM

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Analogue signal: a continuous wave

Digital: a discrete set of on (1) and off (0) electronic bursts rather than a continuous wave.

+1

0

0

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0

Analog and digital signals

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Communication Media/Channels

Guided Media:Twisted PairCoaxial CableOptical Fiber

Unguided Media:MicrowaveSatelliteBroadcast Radio

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Twisted Pair

Coaxial Cable

Optical Fiber

Guided Media

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Microwave- “Line of sight” media:

antennas need to see each other

Unguided Media: Microwave

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Unguided Media: Satellite

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Transmission SpeedTransmission SpeedTotal amount of info that can be transmitted through any Total amount of info that can be transmitted through any channel is measured in bits per secondchannel is measured in bits per second

Baud:Baud: change in signal from + to – or vice versa that is change in signal from + to – or vice versa that is used as a measure of transmission speedused as a measure of transmission speed

Frequency:Frequency: the number of cycles per second that can be the number of cycles per second that can be sent through that medium (in hertz)sent through that medium (in hertz)

Bandwidth:Bandwidth: the range of frequencies that can be the range of frequencies that can be accommodated on a particular communication channel accommodated on a particular communication channel

COMMUNICATIONS CHANNELS

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Front-end processor:Front-end processor: Manages communications for Manages communications for the host computerthe host computer

Concentrator:Concentrator: Collects and temporarily stores Collects and temporarily stores messagesmessages

Controller:Controller: Supervises communication traffic between Supervises communication traffic between CPU and peripheral devicesCPU and peripheral devices

Multiplexer:Multiplexer: Enables single communication channel to Enables single communication channel to carry data transmissions from multiple sources carry data transmissions from multiple sources simultaneouslysimultaneously

COMMUNICATIONS PROCESSORS AND SOFTWARE

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By geographic span Local Area Network (LAN) Wide Area Network (WAN)

By topology (physical) Star Bus Ring Mesh

By architecture (logical) Peer to peer versus client-server Centralized versus distributed versus hybrid

Computer Networks

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Network Topology: STAR

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Network Topology: Bus

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Network Topology: Ring

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Each node is connected to

each other node in the

network

Global Storage Medium

Shared Printer

Network Topology: Mesh

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Network Architecture: e.g., Client-Server

Server• provides global information and software,

• manages the use of shared printers, • provides communication within and external

to the network.

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The host computer handles all information processing, manages communication,

and stores all software and information.

Network Architecture: e.g., Centralized Network

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Private Branch ExchangesPrivate Branch Exchanges

Central switching system Central switching system

Handle firm’s voice and digital Handle firm’s voice and digital communicationscommunications

COMMUNICATIONS NETWORKS

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Local Area NetworksLocal Area Networks

Encompass a limited distanceEncompass a limited distance

Require its own communication channels Require its own communication channels

Support high volumes of data and functions Support high volumes of data and functions requiring high transmission speedrequiring high transmission speed

Gateway, router, Network Operating System (NOS)Gateway, router, Network Operating System (NOS)

COMMUNICATIONS NETWORKS

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A Local Area Network (LAN)

Figure 8-8

COMMUNICATIONS NETWORKS

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Wide Area Networks (WANs)Wide Area Networks (WANs)

Span large geographical distanceSpan large geographical distance

Consist of variety of switched and Consist of variety of switched and dedicated lines, satellite, and microwave dedicated lines, satellite, and microwave technologiestechnologies

COMMUNICATIONS NETWORKS

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Network ServicesNetwork Services

Value Added Networks: private, multipath, Value Added Networks: private, multipath, data only, third party managed networks data only, third party managed networks

Packet switching technologyPacket switching technology

Frame RelayFrame Relay

Asynchronous transfer mode (ATM)Asynchronous transfer mode (ATM)

COMMUNICATIONS NETWORKS

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Models of Connectivity for NetworksModels of Connectivity for Networks

Transmission Control Protocol/Internet Transmission Control Protocol/Internet Protocol (TCP/IP)Protocol (TCP/IP)

Open Systems Interconnect (OSI)Open Systems Interconnect (OSI)

Standards and Connectivity for Digital Integration

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(TCP/IP) Reference Model

Figure 9-2

Standards and Connectivity for Digital Integration

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Application

TCP

IP

Data Link

Physical layer

Application protocol

Transport protocol

IP protocol

Data Linkprotocol

Physical medium: e.g., Ethernet cable

PC-1 PC-2

PC to PC Communication using TCP/IP

RequestHTTP

TCP RequestHTTP

IP TCP RequestHTTP

Ethernet IP TCP RequestHTTP

RequestHTTP

TCP RequestHTTP

IP TCP RequestHTTP

Ethernet IP TCP RequestHTTP

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Packed-Switched Networks and Packet Communications

Figure 8-9

COMMUNICATIONS NETWORKS

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Packet SwitchingPacket switching breaks transmissions into packets

When a packet arrives at a switch, the switch must decide where to send the packet next

Switch

Switch

A

BC

D E

Trunk Line

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Circuit SwitchingEnd-to-end connection between phonesMay pass through multiple switches and trunk linesReserved (guaranteed) capacity during call

Reserved circuit capacity is expensive

Good for voice/bad for data

Capacity is wasted between bursts, but still must pay for capacity

Switch

Trunk LineSwitch

AB C

D E

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EDI

Direct computer to computer exchange Direct computer to computer exchange between two organizations of standard between two organizations of standard business transaction documentsbusiness transaction documents

Lower transaction costLower transaction cost

Provide strategic benefits by increasing Provide strategic benefits by increasing switching costswitching cost

ELECTRONIC DATA INTERCHANGE