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.