Book Review

Interconnections: Bridges, Routers, Switches, and Internetworking Protocols, 2nd ed.

Radia Perlman
Addison-Wesley, 2000 (537pp) ISBN 0-201-63448-1

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This book is one of the Addison-Wesley Professional Computing Series, which includes books by W. Richard Stevens and other renowned authorities on computers. Radia Perlman is also an authority on network routing, having invented the spanning tree algorithm which is used in most modern routers. She describes in impressively clear and often witty language the various internetworking protocols, such as ATM, IP, CLNP, DECnet, and IPX, at all levels of detail from overall network down to each byte of their respective datagrams, and explains the problems and various solutions that have been proposed over the years, and how these protocols might have been improved. The author's enthusiasm for the topics is evident throughout the book.

The main focus of the book is routing. To function without excessive user intervention, Internet routers need to spontaneously create a self-organizing network with no circular paths so that a finite, if not necessarily optimal, path can be found between any two nodes. Unlike neurons in a brain, however, routers also need to maintain some information about the network, and need some metric such as Dijkstra's algorithm for computing a good path between nodes. The book describes addressing, link state routing, load splitting, ATM, VPNs, source routing, packet forwarding, and many other essential concepts in computer networking. A few topics, such as frame relay, are mysteriously omitted (X.25 is covered, however).

Although not essential for understanding the material in this book, it would be helpful to have been exposed to networking concepts before reading the book. Otherwise the reader may feel inundated by acronyms, which make the book seem like a Russian novel, in which the reader constantly looks up the names of the characters in the glossary. For example, in the chapter "Specific Routing Protocols", the author contrasts PNNI, RTMP, IPX-RIP, and DECnet with IS-IS, OSPF, and NLSP. Each of these routing protocols uses several different types of packets, such as 'hello' packets and LSA ('link state acknowledgment') packets, which are described in precise detail.

The last chapter, "Protocol Design Folklore", provides some of the author's thoughts and opinions about various networking topics.

There is no discussion of the physical layer or lower data link layers of the network, such as cabling, bandwidth, Gigabit ethernet, or error correction protocols, and no discussion of any of the specialized operating systems or computer architecture used by routers, bridges, or switches. Each of these topics could fill a book in itself. What Interconnections does cover, is the design principles and protocol implementations used to make routers communicate with each other and with nodes on the network. It covers these topics with exceptional clarity and expertise.

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