This document provides an introduction to data communications and computer networks. It discusses key topics such as data communication components like data representation and data flow. It also defines networks and describes different network topologies including point-to-point, star, bus, ring and hybrid configurations. The document then provides an overview of the Internet including its history and organization. It concludes with definitions of protocols and standards, which are sets of agreed upon rules, and discusses standards organizations.

1. 1.1
Chapter 1
Introduction
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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS
The termThe term telecommunicationtelecommunication means communication at ameans communication at a
distance. The worddistance. The word datadata refers to information presentedrefers to information presented
in whatever form is agreed upon by the parties creatingin whatever form is agreed upon by the parties creating
and using the data.and using the data. Data communicationsData communications are theare the
exchange of data between two devices via some form ofexchange of data between two devices via some form of
transmission medium such as a wire cable.transmission medium such as a wire cable.
Components
Data Representation
Data Flow
Topics discussed in this section:Topics discussed in this section:

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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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1-2 NETWORKS1-2 NETWORKS
AA networknetwork is a set of devices (often referred to asis a set of devices (often referred to as nodesnodes))
connected by communicationconnected by communication linkslinks. A node can be a. A node can be a
computer, printer, or any other device capable of sendingcomputer, printer, or any other device capable of sending
and/or receiving data generated by other nodes on theand/or receiving data generated by other nodes on the
network.network.
Distributed Processing
Network Criteria
Physical Structures
Network Models
Categories of Networks
Interconnection of Networks: Internetwork
Topics discussed in this section:Topics discussed in this section:

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

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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 stations

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Figure 1.8 A ring topology connecting six stations

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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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1-3 THE INTERNET1-3 THE INTERNET
TheThe InternetInternet has revolutionized many aspects of our dailyhas revolutionized many aspects of our daily
lives. It has affected the way we do business as well as thelives. It has affected the way we do business as well as the
way we spend our leisure time. The Internet is away we spend our leisure time. The Internet is a
communication system that has brought a wealth ofcommunication system that has brought a wealth of
information to our fingertips and organized it for our use.information to our fingertips and organized it for our use.
A Brief History
The Internet Today (ISPs)
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Figure 1.13 Hierarchical organization of the Internet

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1-4 PROTOCOLS AND STANDARDS1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms:In this section, we define two widely used terms: protocolsprotocols
andand standardsstandards. First, we define protocol, which is. First, we define protocol, which is
synonymous with rule. Then we discuss standards, whichsynonymous with rule. Then we discuss standards, which
are agreed-upon rules.are agreed-upon rules.
Protocols
Standards
Standards Organizations
Internet Standards
Topics discussed in this section:Topics discussed in this section: