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Chapter 1

Introduction

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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS

The term The term telecommunicationtelecommunication means communication means communication at a distance. at a distance.

The word The word datadata refers to information presented in refers to information presented in whatever form is agreed upon by the parties creating and whatever form is agreed upon by the parties creating and using the data.using the data.

Data communicationsData communications are the exchange of data are the exchange of data between two devices via some form of transmission between two devices via some form of transmission medium such as a wire cable. medium such as a wire cable.

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Figure 1.1 Five components of data communication

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Data Representation

1- Textrepresented as a bit pattern ( code)

2- Numbers3- Images its composed of a matrix4- Audio

it is a continuous signal5- Video

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

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1-2 NETWORKS1-2 NETWORKS

A A networknetwork is a set of devices (often referred to as is a set of devices (often referred to as nodesnodes) ) connected by communication connected by communication links(network medium)links(network medium). A . A node can be a computer, printer, or any other device node can be a computer, printer, or any other device capable of sending and/or receiving data generated by capable of sending and/or receiving data generated by other nodes on the network. Nodes use a common other nodes on the network. Nodes use a common network protocol to share resources with each other.network protocol to share resources with each other.

Distributed ProcessingNetwork CriteriaPhysical StructuresNetwork ModelsCategories of NetworksInterconnection of Networks: Internetwork

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1-2 NETWORKS1-2 NETWORKS

Network criteriaNetwork criteria : :Performance measured in Performance measured in transit time, response time Transit time : Transit time : amount of time required for a message to travel from device to device.amount of time required for a message to travel from device to device.Response time Response time : elapsed time between an inquiry and a response.: elapsed time between an inquiry and a response.

performance is evaluated by 2 networking metrics performance is evaluated by 2 networking metrics :Throughput and Delay:Throughput and Delay

Reliability : Reliability : Accuracy of delivery, frequency of failure, the time it takes a link to Accuracy of delivery, frequency of failure, the time it takes a link to recover from failure.recover from failure.

Security : Security : protecting data from unauthorized access, protecting data from damage protecting data from unauthorized access, protecting data from damage and developmentand development

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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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Categories of Networks

The category into which a network falls is determined by its size

Local Area Network: -LAN size is limited to a few kilometers-LAN can be as simple as 2 computers and a printer-IN addition to size, LAN is distinguished from other types of networks by transmission media and topology.- early LAN data flow rates from 4 to 6 Mbps, Now it is from 100 to 1000 Mbps

Wide Area Network:

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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

The The InternetInternet has revolutionized many aspects of our daily has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a way we spend our leisure time. The Internet is a communication system that has brought a wealth of communication 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 HistoryThe 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 and and standardsstandards. First, we define protocol, which is . First, we define protocol, which is synonymous with rule. Then we discuss standards, which synonymous with rule. Then we discuss standards, which are agreed-upon rules.are agreed-upon rules.

ProtocolsStandardsStandards OrganizationsInternet Standards

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