Chapter 1

Introduction

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11--1 1 DATA COMMUNICATIONSDATA COMMUNICATIONS

TheThe termterm telecommunicationtelecommunication meansmeans communicationcommunication atat aadistancedistance TheThe wordword datadata refersrefers toto informationinformation presentedpresenteddistancedistance.. TheThe wordword datadata refersrefers toto informationinformation presentedpresentedinin whateverwhatever formform isis agreedagreed uponupon byby thethe partiesparties creatingcreatingandand usingusing thethe datadata DataData communicationscommunications areare thetheandand usingusing thethe datadata.. DataData communicationscommunications areare thetheexchangeexchange ofof datadata betweenbetween twotwo devicesdevices viavia somesome formform ofoftransmissiontransmission mediummedium suchsuch asas aa wirewire cablecabletransmissiontransmission mediummedium suchsuch asas aa wirewire cablecable..

Topics discussed in this section:Topics discussed in this section:ComponentsData RepresentationData Flow

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Data Flow

Figure 1.1 Five components of data communication

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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

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11--2 2 NETWORKSNETWORKS

AA networknetwork isis aa setset ofof devicesdevices (often(often referredreferred toto asas nodesnodes))connectedconnected byby communicationcommunication linkslinks.. AA nodenode cancan bebe aacomputer,computer, printer,printer, oror anyany otherother devicedevice capablecapable ofof sendingsendingand/orand/or receivingreceiving datadata generatedgenerated byby otherother nodesnodes onon thethenetworknetwork..

Distributed ProcessingTopics discussed in this section:Topics discussed in this section:Distributed ProcessingNetwork CriteriaPhysical StructuresyNetwork ModelsCategories of Networks

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Interconnection of Networks: Internetwork

Figure 1.3 Types of connections: point-to-point and multipointg

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Figure 1.4 Categories of topology

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Figure 1.5 A fully connected mesh topology (five devices)

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Figure 1.6 A star topology connecting four stations

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Figure 1.7 A bus topology connecting three stationsg

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Figure 1.8 A ring topology connecting six stationsg

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Figure 1.9 A hybrid topology: a star backbone with three bus networks

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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

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Figure 1.11 WANs: a switched WAN and a point-to-point WAN

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Figure 1.12 A heterogeneous network made of four WANs and two LANs

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11--3 3 THE INTERNETTHE INTERNET

TheThe InternetInternet hashas revolutionizedrevolutionized manymany aspectsaspects ofof ourour dailydailyliveslives.. ItIt hashas affectedaffected thethe wayway wewe dodo businessbusiness asas wellwell asas thethewayway wewe spendspend ourour leisureleisure timetime.. TheThe InternetInternet isis aacommunicationcommunication systemsystem thatthat hashas broughtbrought aa wealthwealth ofofinformationinformation toto ourour fingertipsfingertips andand organizedorganized itit forfor ourour useuse..

Topics discussed in this section:Topics discussed in this section:A Brief HistoryThe Internet Today (ISPs)

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Figure 1.13 Hierarchical organization of the Internet

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11--4 4 PROTOCOLS AND STANDARDSPROTOCOLS AND STANDARDS

InIn thisthis section,section, wewe definedefine twotwo widelywidely usedused termsterms:: protocolsprotocols,, ff yy ppandand standardsstandards.. First,First, wewe definedefine protocol,protocol, whichwhich isissynonymoussynonymous withwith rulerule.. ThenThen wewe discussdiscuss standards,standards, whichwhichy yy y ,,areare agreedagreed--uponupon rulesrules..

Topics discussed in this section:Topics discussed in this section:ProtocolsStandards

Topics discussed in this section:Topics discussed in this section:

StandardsStandards OrganizationsInternet Standards

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