The intent of this book is not to provide a how-to guide for IMS implementation,
but rather to offer an explanation to why the various functions within the IMS do
what they do, and what distinguishes this architecture from other implementations of
IP transport.
It is hopeful that through this book readers will gain a better understanding as to
why IMS was developed to begin with, and what value an IMS architecture brings.
Since the IMS standards themselves continue to evolve, it is likely there will be updates
to this book over the next decade.
The SIP protocol is not covered in this book but will be the subject of my next book,
Session Initiation Protocol (SIP): Controlling Convergent Networks (McGraw-Hill,
forthcoming). For a complete view from PSTN to the IMS, don??™t forget my earlier book
Signaling System #7 (McGraw-Hill, 2002), now in its fifth edition. Collectively, these
three books provide an end-to-end view of the signaling and call control within both
traditional and next-generation networks for both wireline and wireless.
xvi Introduction
Chapter 1
Architecture of the IMS
There are many different viewpoints and definitions for the IP Multimedia Subsystem
(IMS). As with any new technology introduction, as vendors work diligently to develop
products for the new technologies, there is also the period of time when there is a lot of
marketing effort to try to promote the implementation of the technology.
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