Internet Telephony is now one of the most important and fastest growing technologies on the Internet, providing a viable technical and economical alternative to current telecommunication networks. Network providers and major companies are thus investigating how this emerging technology can be implemented, and at what cost and savings, in their organizations. This book provides a comprehensive practical overview of the technology behind Internet Telephony, giving essential information to IT professionals who need to understand the background and explore the issues involved in migrating the existing telephony infrastructure to an IP-based real-time communication service. Assuming a working knowledge of IP and ISDN networking, it addresses the technical aspects of real-time applications over IP, with an in-depth coverage of voice and video applications and protocols. Drawing on their extensive research and practical development experience in VolP from its earliest stages, the authors give you access to all the relevant standards and cutting-edge techniques in a single resource. IP Telephony is organized into three clearly structured sections, focusing on protocols, voice technology and networks with a step-by-step approach. The protocols section sets IP telephony in context and then covers H.323, SIP and MGCP in detail, examining in turn their pros and cons, and using examples of particular cases and scenarios. The voice technology section describes voice quality, including the ETSI TIPHON approach, and voice coding, with summary comments on the applicability to VolP telephone gateways. The final section on networks adresses Quality of Service (QoS) issues, explores dimensioning a VolP network, and introduces Multicast routing, including a perspective on security and MBONE applications. Features: detailed, up-to-date coverage of voice and video application and emerging protocol standards: H.323, SIP, MGCP; practical strategies on how to plan and dimension a VolP network; key points to look for in choosing a VolP product and how to avoid common pitfalls in implementation; examples and illustrations of standards and techniques including feedback information on issues discussed at standards meetings; details of QoS issues, Intserv (RSVP), DiffServ, RTP, SDF, companion standards, multimedia coding standards and coding algorithms.