This book presents end-to-end system basics for IP telephony—the technology that enables private data networks to provide extended communication services and multimedia transmission over standard phone lines. Written by the chief architects of H.323, the governing protocol for IP telephony, this book delivers the most authoritative coverage of what is considered the hottest topic in networking today. Network and telecommunications professionals will find clear discussions of the principles and implementations of next generation architectures and services, as well as comprehensive coverage of the related protocols, addressing and routing issues, interworking IP with legacy systems, deploying gateways, and more. Mobility, security, and QoS aspects of H.323 systems are also explained in detail.