Data communications and networking are changing the way we do business and the way
we live. Business decisions have to be made ever more quickly, and the decision makers
require immediate access to accurate information. Why wait a week for that report
from Germany to arrive by mail when it could appear almost instantaneously through
computer networks? Businesses today rely on computer networks and inter networks.
But before we ask how quickly we can get hooked up, we need to know how networks
operate, what types of technologies are available, and which design best fills which set
The development of the personal computer brought about tremendous changes for
business, industry, science, and education. A similar revolution is occurring in data
communications and networking. Technological advances are making it possible for
communications links to carry more and faster signals. As a result, services are evolving
to allow use of this expanded capacity. For example, established telephone services
such as conference calling, call waiting, voice mail, and caller ID have been extended.
Research in data communications and networking has resulted in new technolo-
gies. One goal is to be able to exchange data such as text, audio, and video from all
points in the world. We want to access the Internet to download and upload information
quickly and accurately and at any time.
This chapter addresses four issues: data communications, networks, the Internet,
and protocols and standards. First we give a broad definition of data communications.
Then we define networks as a highway on which data can travel. The Internet is dis-
cussed as a good example of an internetwork (i.e., a network of networks). Finally, we
discuss different types of protocols, the difference between protocols and standards,
and the organizations that set those standards.
Features of the Book Data Communication And Networking By Behruzon A. Forouzan 4TH Edition
Several features of this text are designed to make it particularly easy for students to
understand data communications and networking.
We have used the five-layer Internet model as the framework for the text not only because
a thorough understanding ofthe model is essential to understanding most current network-
ing theory but also because it is based on a structure of interdependencies: Each layer
builds upon the layer beneath it and supports the layer above it. In the same way, each con-
cept introduced in our text builds upon the concepts examined in the previous sections. The
Internet model was chosen because it is a protocol that is fully implemented.
This text is designed for students with little or no background in telecommunica-
tions or data communications. For this reason, we use a bottom-up approach. With this
approach, students learn first about data communications (lower layers) before learning
about networking (upper layers).
The book presents highly technical subject matter without complex formulas by using a
balance of text and figures. More than 700 figures accompanying the text provide a
visual and intuitive opportunity for understanding the material. Figures are particularly
important in explaining networking concepts, which are based on connections and
transmission. Both of these ideas are easy to grasp visually.
We emphasize important concepts in highlighted boxes for quick reference and imme-
Examples and Applications
When appropriate, we have selected examples to reflect true-to-life situations. For exam-
ple, in Chapter 6 we have shown several cases of telecommunications in current telephone
Each chapter includes a list of books and sites that can be used for further reading.
Each chapter includes a list of key terms for the student.
Each chapter ends with a summary of the material covered in that chapter. The sum-
mary provides a brief overview of all the important points in the chapter.
Each chapter includes a practice set designed to reinforce and apply salient concepts. It
consists of three parts: review questions, exercises, and research activities (only for
appropriate chapters). Review questions are intended to test the student’s first-level under-
standing of the material presented in the chapter. Exercises require deeper understanding
of the material Research activities are designed to create motivation for further study.
The appendixes are intended to provide quick reference material or a review of materi-
als needed to understand the concepts discussed in the book.
Glossary and Acronyms
The book contains an extensive glossary and a list of acronyms.
Table of Content
PART 1 Overview 1
Chapter 1 Introduction 3
Chapter 2 Network Models 27
PART 2 Physical Layer and Media 55
Chapter 3 Data and Signals 57
Chapter 4 Digital Transmission 101
Chapter 5 Analog Transmission 141
Chapter 6 Bandwidth Utilization: Multiplexing
Chapter 7 Transmission Media 191
Chapter 8 Switching
Chapter 9 Using Telephone and Cable Networks for Data
PART 3 Data Link Layer 265
Chapter 10 Error Detection and Correction 267
Chapter 11 Data Link Control 307
Chapter 12 Multiple Access 363
Chapter 13 Wired LAN’s: Ethernet 395
Chapter 14 Wireless LAN’s 421
Chapter 15 Connecting LAN’s, Backbone Networks,
and Virtual LAN’s 445
Chapter 16 Wireless WANs: Cellular Telephone and
Satellite Networks 467
Chapter 17 SONETISDH 491
Chapter 18 Virtual-Circuit Networks: Frame Relay and ATM 517
PART 4 Network Layer 547
Chapter 19 Network Layer: Logical Addressing 549
Chapter 20 Network Layer: Internet Protocol 579
Chapter 21 Network Layer: Address Mapping, Error Reporting,
and Multi casting 611
Chapter 22 Network Layer: Delivery, Forwarding,
PART 5 Transport Layer 701
Chapter 23 Process-fa-Process Delivery: UDp, TCp,
and SeTP 703
Chapter 24 Congestion Control and Quality of service 761
PART 6 Application Layer 795
Chapter 24 Domain Name System 797
Chapter 26 Remote Logging, Electronic Mail, and File Transfer 817
Chapter 27 WWW and HTTP 851
Chapter 28 Network Management: SNMP 873
Chapter 29 Multimedia 901
PART 7 Security 929
Chapter 30 Cryptography 931
Chapter 31 Network Security 961
Chapter 32 Security in the Internet: IPSec, SSUFLS, PGP, VPN,
and Firewalls 995