Now in its third edition, the ground-breaking Artech House bestseller "SIP: Understanding the Session Initiation Protocol" offers the most comprehensive and current understanding of this revolutionary protocol for call signaling and IP Telephony. Essential reading for anyone involved in the development and operation of voice or data networks, the third edition has been significantly expanded with brand new chapters on SIP security, services in SIP, presence and instant messaging, and Peer-to-Peer SIP. The book explains how SIP is a highly-scalable and cost-effective way to offer new and exciting telecommunication feature sets. From an examination of SIP as a key component in the Internet multimedia conferencing architecture...to a look at the future direction of SIP, practitioners get the knowledge they need to design "next generation" networks and develop new applications and software stacks. This title is suitable for telecommunications/wireless engineers and professionals, professors and students whose work involves voice or data networks and the Internet multimedia architecture.