SIP is essentially a simple protocol, but understanding why it's needed, what architectures it supports, and how it interacts with other protocols is key to deploying it. This book contextualizes SIP against its forebears and competitors. Because SIP is data network-based, the author provides important background in IP for engineers from the voice carriers. Other books provide the protocol anatomy and extensions; Camarillo's provides planning and implementation advice for commercial vendors. The book explains data networking programmes to telco engineers who are not necessarily IP-literate and provides a perspective on why and where SIP supplants H.323. It also outlines SIP implementations on the market in the form of single-line gateways, proxy servers, media gateways, Java toolkits, encoders/decoders and session authenticators.