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In this chapter, we will study:The basic components of a telecomm

systemThe technologies used in telecomm

systemsVarious ways to configure networksVarious ways that businesses use

networks today

Telecommunications

The transmission of different forms of data (such as text, audio, video, images, graphics) from one set of electronic devices over media to another set of geographically separated electronic devices.

The Telecommunications System

The hardware and software that transmits information from one location to another

Components include:

HardwareMediaNetworksSoftware

Data comm providers

ProtocolsApplications

Telecommunication Signals

Analog signalsContinuous wavesInformation conveyed by changing

wave characteristics (amplitude and frequency)

Digital signalsDiscrete pulsesInformation conveyed in binary form

(on or off pulses)Easily understood by computer

Communication Processors

Hardware devices utilized in data transmission and receptionModem - device that converts analog

signals to digital (and vice versa); enables signal transmission over telephone system

Multiplexor - device that transmits multiple signals over single medium

Front-end processor – specialized computer dedicated to managing communication tasks

The Five Characteristics of Channels

Characteristics Description

Transmission rate Rate at which channel carries data from one computer to another.

Volume or capacity of data that a channel can carry.

Ways by which data are transmitted. Two ways include asynchronous (one byte at a time) and synchronous (blocks of bytes).

Three directions for transmitting data include simplex, half duplex, and full duplex.

Information travels as analog or digital signals.

Bandwidth

Transmission mode

Transmission direction

Transmission signals

Wire-based Communication Channels

Twisted-pair wire (telephone wire)Cheap and easy to work withSlow; subject to interference; low

securityCoaxial cable

Carries more data; shielded from interference

More expensive; harder to work with; low security

Wire-based Communication Channels (continued)

Fiber-optic cableTransmit information as light waves

through glass fiberFast; high-capacity; secure; not

subject to interferenceHard to work with

Wireless Communication Channels

MicrowaveHigh capacity; inexpensive relative to

wireRequires line of sight transmission

towers; subject to environmental interference

SatelliteVery high capacity; large coverage areaExpensive; propagation delay; requires

encryption for security

Wireless Communication Channels (continued)

RadioSuitable for short distance

communication; inexpensive; easy to install; high speed

Interference problems; insecureCellular radio technologyInfrared

Understanding Communication Media

Transmission speedBandwidth – the range of frequencies

available in a channelMore bandwidth, more channel capacity

Transmission modeCharacter by character (asynchronous)Streams of characters (synchronous)

Transmission accuracyAccuracy controls added to messagesError detection and correction required

Telecomm Carriers and Services

Telecomm carriers – provide telecomm technology and services for data communicationCommon carriers – long-distance

phone companiesValue-added carriers – provide private

telecomm systems and services for a fee

Telecomm Carriers and Services (continued)

Telecomm servicesSwitched lines – transmission is routed along

path to destinationDedicated lines – continuous connection is

establishedWide-area Telecomm Service (WATS) – lower

cost long distance telephone service Integrated Services Digital Network (ISDN) –

high speed data transmission over existing phone lines

Digital Subscriber Lines (DSL) - high speed digital transmission over existing phone lines

Network Basics

Network – the communication devices, media, and software needed to connect two or more computer systems.

Local area networks (LANs) – a network that spans a relatively small geographic distance

Wide area networks (WANs) – network that spans a large geographic distance

Network Topology

There are three popular network topologies:

Bus topology

Ring topology

Star topology

Alternative LAN Topologies

Bus Topology

A network configuration in which all computers on the network are connected through a single circuit, such as twisted-pair cable. Messages are transmitted to all computers on the network, although only the targeted device responds to the message.

Ring Topology

A network configuration in which computers are arranged in the form of a ring using twisted-wire, coaxial cable, or fiber optics. Messages are transmitted in one direction to all devices between the sending node and the receiving node.

Star Topology

A topology in which a central host computer receives all messages and then forwards the message to the appropriate computer on the network.

Local Area Networks

Connect computers and other devices enabling resource sharing

Variety of topologies can be used, each with performance strengths and weaknesses

Several LANs can be connected via bridges

LANs can be connected to external networks via gateways