1.1

Introduction

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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS

The term The term telecommunicationtelecommunication means communication at a means communication at a distance. The word distance. The word datadata refers to information presented refers to information presented in whatever form is agreed upon by the parties creating in whatever form is agreed upon by the parties creating and using the data. and using the data. Data communicationsData communications are the are the exchange of data between two devices via some form of exchange of data between two devices via some form of transmission medium such as a wire cable. transmission medium such as a wire cable.

ComponentsData RepresentationData Flow

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The effectiveness of a data communication depends on three fundamental characteristics

Delivery: The system must deliver data to the correct destination.

• Accuracy: The system must deliver data accurately.

Timeliness: The system must deliver data in a timely manner. Data deliver late are useless.

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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

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 linkslinks. A node can be a . A node can be a computer, printer, or any other device capable of sending computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the and/or receiving data generated by other nodes on the network.network.

Distributed ProcessingNetwork CriteriaPhysical StructuresNetwork ModelsCategories of NetworksInterconnection of Networks: Internetwork

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Distributed Processing

Networks use Distributed Processing, in which a task is divided among multiple computers

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Advantages of distributed processing Security/encapsulation: Distributed database: Faster Problem solving: Security through redundancy: Collaborative Processing:

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Network Criteria

A Network must meet a number of Criteria

Performance Reliability security

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1.11

Performance

Number of Users: Having a large number of concurrent users can slow response time in a network

Type of transmission medium: The medium defines the speed at which data can travel through a connection (data rate).

Hardware: The types of hardware included in a network affect both the speed and capacity of transmission.

Software: The software used to process data at the sender, receiver, and intermediate nodes also affects network performance.

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Reliability

Frequency of failure: All networks fail occasionally. A network that fails often, however, is of little value to a user.

Recover time of a network after a failure: How long does it take to restore service?

Catastrophe: Networks must be protected from catastrophic events such as ,fire, earthquake.

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Security

Unauthorized access: Passwords, encryption techniques.

Viruses

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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

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

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1.27

Protocols and Standards

Protocols: is a set of rules that govern data communication.

A protocol defines what is communicated, how is communicated, and when it is communicated.

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Protocols key elements

Syntax: Structure or format of the data.

Semantics: meaning of each section of bits.

Timing: when data should be sent and how fast they can be sent

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Standards

A standard provides a model for development that makes it possible for a product to work regardless of the individual manufacturer.

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Standards

De facto(by fact)

De jure(by law)

e.g. TCP/ IP e.g. OSI

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Standards Organizations

Internet Society http://www.isoc.org/

ISO http://www.iso.org/

ITU-T (formally CCITT) http://www.itu.int/ITU-T/

ATM forum http://www.atmforum.com/

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Standard Organizations

Standards are developed by cooperation among standards creation committees forums.