"Telephone Switching Systems", Richard A. Thompson, 2000,
%A Richard A. Thompson rat@...
%C 685 Canton St., Norwood, MA 02062
%I Artech House/Horizon
%O U$125.00 617-769-9750 fax: 617-769-6334 artech@...
%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
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
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
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
copyright Robert M. Slade, 2001 BKTLSWSY.RVW 20010126
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