The Virtual Bookcase Reviews of 'IP Telephony: Packet-Based Multimedia Communications Systems':
Reviewer amazon.com wrote:
Voice communications over the Internet--particularly the direct, sender-initiated kind--haven't yet taken off, but lots of smart people say Internet telephony is going to be huge before long. In IP Telephony, three experts on getting voice signals from here to there, intact, via Internet Protocol (IP) networks hold forth on the state of the art. Like Voice over IP (VoIP) itself, their discussion is largely academic. Rather than show how to implement VoIP with any of the tools available for that purpose, the authors put most of their effort into elaborating on the specifications that govern (or at least aspire to govern) Internet telephony. It's an approach that IP telephony software developers will appreciate. The denseness of the prose in this book is offset by high-quality conceptual diagrams. In particular, the timelines do a great job of explaining signal sequences, and flow charts communicate logical processes effectively. In the sections on the mechanics of converting sounds into bits (which are loaded with equations and other descriptions of algorithms), the discussion of the phenomena that cause signals to degrade is especially clear. As a whole, IP Telephony is a good description of a developing technology. --David Wall Topics covered: The appeal of Internet telephony, and the progress to date on standards for implementing it. The emerging H.323 protocol suite gets lots of attention, as does the Session Initiation Protocol (SIP) and the Media Gateway Controller Protocol (MGCP). Coverage also includes algorithms for converting audio information into digital data band back again, as well as quality-of-service (QoS) and conferencing with multicasting.
Reviewer Rob Slade wrote:
The preface does a rather heavy-handed sell on IP telephony, without
really backing up any claims. It doesn't really define a specific
audience, although the set of people who are listed as possibly being
interested is a fairly limited one.
The preface also expects a strong familiarity with ISDN (Integrated
Services Digital Network) and TCP/IP networking. I'm not sure that I
understand the requirement for ISDN, but a strong technical background
is a must, if you are going to tackle this book. The authors don't
appear to have made much attempt to ensure that it is readable, or
even lucid. The text resembles nothing so much as a mass of technical
trivia, only nominally organized. Ironically, despite the heavy
technical content, there does not seem to be enough detail in the work
to ensure that even dedicated readers will be able to produce some
kind of implementation.
Section one supposedly talks about application layer IP telephony
protocols, although much of the material appears to be more
appropriate to the session layer. Chapter one is huge, touching on
the H.323 standard, RTP (Real-time Transfer Protocol), security,
codecs, and an extensive H.323 session walk-through. The alphabet
soup is thick, and not always defined. RAS (Registration,
Application, Status, in this case) is not expanded at any point prior
to page six, where it is used for the first time and noted as being
defined "above," although it is based on H.225.0 which gets mentioned
"above." H.323 is a complex standard which is somewhat non-standard,
but the lack of any logical progression in the writing is not going to
help the reader follow the material. The Session Initiation Protocol
(SIP), in chapter two, appears to be something of an Internet-based
contender to the ITU's (International Telecommunications Union) H.323.
The Media Gateway Control Protocol (MGCP) seems to be a broader
technology in some competition and cooperation with both, in chapter
Section two looks at voice technology. Chapter four touches on a
number of topics related to voice quality, but mostly concentrates on
delay. Lots of math, tables, and flowcharts fail to explain much
about voice coding in chapter five, which primarily seems to be a
historical progression of standards.
Section three discusses the network. Chapter six talks about quality
of service (again emphasizing delay). Network dimensioning, in
chapter seven, provides lots of math for figuring out the minimum
bandwidth you need. IP multicast routing is the topic of chapter
Ultimately, this book might be most useful as a pointer to other
sources of information, such as the standards themselves.
copyright Robert M. Slade, 2000
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