This learning project provides a comprehensive overview of IP telephony architectures and protocols, with emphasis on SIP, the Session Initiation Protocol. Topics include a review of classical circuit-switched telephony, especially signaling; a review of IP networking, especially routing and addressing; peer and master-slave protocols for IP telephony (SIP, H.323, MGCP); speech coding; the transport of real-time traffic over IP (RTP and RTCP); bandwidth control; and issues in network quality of service, such as traffic modeling, dimensioning, and QoS mechanisms. Emphasis on SIP includes call flows, network components, security, routing, and advanced services.[1]