This book is now in its fourth edition. Each edition has corresponded to a different phase in the way computer networks were used. When the first edition appeared in 1980, networks were an academic curiosity. When the second edition appeared in 1988, networks were used by universities and large businesses. When the third edition appeared in 1996, computer networks, especially the Internet, had become a daily reality for millions of people. The new item in the fourth edition is the rapid growth of wireless networking in many forms.

The networking picture has changed radically since the third edition. In the mid-1990s, numerous kinds of LANs and WANs existed, along with multiple protocol stacks. By 2003, the only wired LAN in widespread use was Ethernet, and virtually all WANs were on the Internet. Accordingly, a large amount of material about these older networks has been removed.

However, new developments are also plentiful. The most important is the huge increase in wireless networks, including 802.11, wireless local loops, 2G and 3G cellular networks, Bluetooth, WAP, i-mode, and others. Accordingly, a large amount of material has been added on wireless networks. Another newly-important topic is security, so a whole chapter on it has been added.

Although Chap. 1 has the same introductory function as it did in the third edition, the contents have been revised and brought up to date. For example, introductions to the Internet, Ethernet, and wireless LANs are given there, along with some history and background. Home networking is also discussed briefly.

Chapter 2 has been reorganized somewhat. After a brief introduction to the principles of data communication, there arethree major sections on transmission (guided media, wireless, and satellite), followed by three more on important examples (the public switched telephone system, the mobile telephone system, and cable television). Among the new topics covered in this chapter are ADSL, broadband wireless, wireless MANs, and Internet access over cable and DOCSIS.

Chapter 3 has always dealt with the fundamental principles of point-to-point protocols. These ideas are essentially timeless and have not changed for decades. Accordingly, the series of detailed example protocols presented in this chapter is largely unchanged from the third edition.

In contrast, the MAC sublayer has been an area of great activity in recent years, so many changes are present in Chap. 4. The section on Ethernet has been expanded to include gigabit Ethernet. Completely new are major sections on wireless LANs, broadband wireless, Bluetooth, and data link layer switching, including MPLS.

Chapter 5 has also been updated, with the removal of all the ATM material and the addition of additional material on the Internet. Quality of service is now also a major topic, including discussions of integrated services and differentiated services. Wireless networks are also present here, with a discussion of routing in ad hoc networks. Other new topics include NAT and peer-to-peer networks.

Chap. 6 is still about the transport layer, but here, too, some changes have occurred. Among these is an example of socket programming. A one-page client and a one-page server are given in C and discussed. These programs, available on the book's Web site, can be compiled and run. Together they provide a primitive remote file or Web server available for experimentation. Other new topics include remote procedure call, RTP, and transaction/TCP.

Chap. 7, on the application layer, has been more sharply focused. After a short introduction to DNS, the rest of the chapter deals with just three topics: e-mail, the Web, and multimedia. But each topic is treated in great detail. The discussion of how the Web works is now over 60 pages, covering a vast array of topics, including static and dynamic Web pages, HTTP, CGI scripts, content delivery networks, cookies, and Web caching. Material is also present on how modern Web pages are written, including brief introductions to XML, XSL, XHTML, PHP, and more, all with examples that can be tested. The wireless Web is also discussed, focusing on i-mode and WAP. The multimedia material now includes MP3, streaming audio, Internet radio, and voice over IP.

Security has become so important that it has now been expanded to a complete chapter of over 100 pages.

It covers both the principles of security (symmetric- and public-key algorithms, digital signatures, and X.509 certificates) and the applications of these principles (authentication, e-mail security, and Web security). The chapter is both broad (ranging from quantum cryptography to government censorship) and deep (e.g., how SHA-1 works in detail).

Chapter 9 contains an all-new list of suggested readings and a comprehensive bibliography of over 350 citations to the current literature. Over 200 of these are to papers and books written in 2000 or later.

Computer books are full of acronyms. This one is no exception. By the time you are finished reading this one, the following should ring a bell: ADSL, AES, AMPS, AODV, ARP, ATM, BGP, CDMA, CDN, CGI, CIDR, DCF, DES, DHCP, DMCA, FDM, FHSS, GPRS, GSM, HDLC, HFC, HTML, HTTP, ICMP, IMAP, ISP, ITU, LAN, LMDS, MAC, MACA, MIME, MPEG, MPLS, MTU, NAP, NAT, NSA, NTSC, OFDM, OSPF, PCF, PCM, PGP, PHP, PKI, POTS, PPP, PSTN, QAM, QPSK, RED, RFC, RPC, RSA, RSVP, RTP, SSL, TCP, TDM, UDP, URL, UTP, VLAN, VPN, VSAT, WAN, WAP, WDMA, WEP, WWW, and XML. But don't worry. Each will be carefully defined before it is used.

To help instructors using this book as a text for a course, the author has prepared various teaching aids, including

• A problem solutions manual.
• Files containing the figures in multiple formats.
• PowerPoint sheets for a course using the book.
• A simulator (written in C) for the example protocols of Chap. 3.
• A Web page with links to many tutorials, organizations, FAQs, etc.

The solutions manual is available directly from Prentice Hall (but only to instructors, not to students).