BKDSLTCH.RVW   980409

"ADSL and DSL Technologies", Walter Goralski, 1998, 0-07-024679-3,
U$45.95
%A   Walter Goralski
%C   300 Water Street, Whitby, Ontario   L1N 9B6
%D   1998
%G   0-07-024679-3
%I   McGraw-Hill Ryerson/Osborne
%O   U$45.95 800-565-5758 fax: 905-430-5020 louisea@McGrawHill.ca
%P   379 p.
%T   "ADSL and DSL Technologies"

I first saw the effect on calls to my ISP (Internet Service Provider). 
Instead of getting a busy signal, I would get a voice interrupt
telling me that all circuits were busy.  (This, incidentally, played
havoc with my automated redialing attempts.)  Since my ISP happens to
also be a long distance provider, one could assume that the problem
lay with a certain lack of cooperation between the two corporate
telecom entities.  However, these voice interrupts are becoming more
frequent in local voice calls from all parts of the city.  It seems
clear that BC Tel is seeing a milder form of the "brown down" Goralski
describes in his introduction, and for which ADSL (Asymmetric Digital
Subscriber Line) is a possible solution.  Most people see ADSL simply
in terms of faster Internet (and usually Web page) access, whereas the
Goralski points out that there are advantages for the telco as well.

Chapter one gives a historical background to the Internet and the
World Wide Web, pointing to the nature of the connection to, and
traffic with, the end user.  The argument being developed is extended
somewhat in chapter two with an overview of the public switched
telephone network (PSTN).  Chapter three starts to get close to ADSL
technologies by dealing with the increasing digitization of the PSTN,
and also the physics and engineering involved in the local loop.  The
final factor in the mix is the difference between circuit switching
(necessary for voice traffic) and packet switching (the most efficient
use of bandwidth in data networks), covered in chapter four.

Chapter five looks at the various technologies that compete in the
market to provide higher speed access to the home or small business,
including high speed modems, cable modems, ISDN (Integrated Services
Digital Network), satellite, and so forth.  Each has significant
limitations not shared by ADSL.  ADSL is only one of a family of DSL
(sometimes referred to as xDSL) services, and these are introduced in
chapter six.

Chapter seven explains High-bit-rate DSL (HDSL), a symmetric
technology often used to terminate T-1 lines.  The ADSL signalling is
covered in chapter eight.  The interface and frames are explained in
chapters nine and ten.  Chapter eleven looks at applications and use. 
(I was amused, recently, to have to explain to a company that the
asymmetry involved in ADSL was a necessary function of the fact that
the telco would be able to "push" data at you faster than they could
"suck" it from your system.  They had envisaged being able to get
faster than T-1 speeds, bi-directionally, by getting two ADSL lines.) 
The telco side of ADSL is the Digital Subscriber Line Access
Multiplexer (DSLAM) discussed in chapter twelve.  One of the
advantages of ADSL is the ability to use much of the existing
infrastructure without extensive refitting.  Chapter thirteen looks at
migration issues from analogue service to ADSL, and from ADSL to
possible followons.  One such followon is Very High-speed Digital
Subscriber Line (VDSL), described in chapter fourteen.

While ADSL is starting to become available, a number of questions are
raised in chapter fifteen that remain to be addressed.  An additional
collection of international issues are presented in chapter sixteen. 
Appendix B lists a very useful set of contact information for members
of the ADSL Forum.

Goralski`s exposition here is every bit as good as good as that in his
explanation of SONET (Synchronous Optical NETwork) (cf. BKSONET.RVW),
albeit more people know, or think they know, what ADSL is.  The mass
appeal of ADSL will probably mean that most users will be looking for
something a bit shorter, although the explanations contained in this
book are clear enough for anyone.  Every ISP, though, should have a
copy on hand in order to determine what *they* (the ISPs) need to do
(see chapter twelve), and to field the inevitable questions as ADSL
starts to roll out beyond the trial areas.

copyright Robert M. Slade, 1998   BKDSLTCH.RVW   980409