BKTLSWSY.RVW 20010126 "Telephone Switching Systems", Richard A. Thompson, 2000, 1-58053-088-5, U$125.00 %A Richard A. Thompson rat@tele.pitt.edu %C 685 Canton St., Norwood, MA 02062 %D 2000 %G 1-58053-088-5 %I Artech House/Horizon %O U$125.00 617-769-9750 fax: 617-769-6334 artech@artech-house.com %P 859 p. %T "Telephone Switching Systems" It is a little disturbing to have the author of a book state that it should be accessible to any dedicated reader with some background in either electrical engineering or computer science, and then have him go on to assert that he assumes everyone knows about asynchronous and synchronous digital hierarchies (ADH and SDH). (This sounds worse than it is: readers with only a moderate familiarity with telephony will recognize the "T," "DS," and "OC" multiplexing numbers.) Nevertheless, as early as the preface the text demonstrates a humanity and readability that is very promising, attractive, and, unfortunately, unusual in technical writing. Chapter one starts by defining terms and concepts, beginning with the basics of communication, touching on networks, and finishing up with fundamental telephony operations. The material is clear and comprehensive. The background provided in chapter two starts with a business oriented history and moves to a discussion of switching architectures. While there are forward references to details of the switches mentioned, readers without telephony experience may fail to grasp some points. The line side of the system, from the telco switch to the handset, is covered in chapter three, with additional practical and personal content. The concepts involved in engineering trunks, the potentially long distance connections between switches, is dealt with in chapter four. Chapter five reviews the basics of traffic theory. Chapter six looks at the Step architecture and the Strowger switch. However, the lack of a basic explanation of the switch operation is a serious limitation. The many detailed examples of special cases and exceptions are of restricted value when the primary operation is missing. Switch fabric is examined in chapter seven. Packet switching is included in the analysis, which is interesting since packet switching itself hasn't been discussed yet. Then back to a specific switch, Crossbar, in chapter eight, with a better, though still not complete, review of the physical operation. This chapter also compares Step against Crossbar in terms of maintenance. Chapter nine deals with toll points, billing, number plans, and other related issues. Enterprise switching, in chapter ten, looks at the functions, history, and business aspects of PBXs (Private Branch eXchanges) but doesn't provide much information on the "how" of what happens. Chapter eleven goes back to specific switches, in this case the computer controlled #1 ESS. Thompson states that the intention is to review the software, but the material actually concentrates on calculations of timing and load, and, when it does move into architecture, very rough outlines of subroutines calling each other. Private networks, in chapter twelve, covers some history of the rise of competition in long distance service, along with a tiny bit of technology related to fractional service from digital lines. Chapter thirteen extends these concepts with basic information about ISDN (Integrated Services Digital Network). Digital switching systems then looks at two such switches, the 5ESS and the System 75, in chapter fourteen. Chapter fifteen presents a lot of data, and more than a little opinion, on the topic of user interfaces, concentrating on human cognitive factors. The politics and legislation of the Bell System breakup are covered in chapter sixteen. The review of switching paradigms, in chapter seventeen, is presented within an extremely limited framework. For example, Thompson states that big networks can't be flat--they must be hierarchical. This is contradicted by the existence of the Internet, which is very flat and could be flatter, as well as new models for wireless networks that could replace most other existing network types. Chapter eighteen, entitled "Intelligent Networks," discusses enhanced services and the business roadblocks that might prevent their being realized. A variety of topics related to transmission infrastructure are touched on in chapter nineteen. The physics of optical and photonic components are described in chapter twenty, with additional material on division and multiplexing in twenty one. The final chapter looks to the future, but only in a very short range and with limited imagination. Each chapter has a set of questions and references. The exercises are substantial and challenging (with a few silly exceptions) but do require a very solid background in telephone engineering. The bibliography contains decent titles although it is sometimes hard to see how helpful the materials would be. The author has done a great deal of work on this text, and has put much of himself into it. In some cases this makes the work much more personal and attractive, but in others it becomes difficult to separate fact from opinion. There are other problems. Networking concepts appear to be seen primarily from telephony and wired perspectives, without a broad and encompassing background. The last third of the book is roughly divided by topic, but not very organized in terms of intent. In fact, a more rigorous structuring of the whole book would benefit the work. I'm sure this book is an excellent text for Thompson's course, and probably for others as well: it contains a great deal of material and, in skilled hands, could be presented to best effect. However, the readability of the content and the sheer size of the volume still cannot guarantee conceptual density. I'm not sure how useful the work would be for telecom professionals, even be they telephone engineers. I do know that computer and information science students and practitioners would likely be bemused. To outsiders, telephony is still an arcane art, kept deliberately secret by its practitioners. It is unfortunate that this text does relatively little to dispel that impression. copyright Robert M. Slade, 2001 BKTLSWSY.RVW 20010126