Research and Implementation of the SIP protocol

SIP (Session Initiation Protocol Session Initiation Protocol) IP telephony signaling protocol proposed by the IETF (Internet Engineering Task Force ) , the traditional voice and value-added services based on the SIP protocol standards , integration , and provide the latest instant messaging services and IP video services on the network , you can provide a standard for more value-added application service providers a highly scalable platform . The system platform completely distributed architecture of the Internet , with a high degree of flexibility and scalability . It is because of the SIP this series advantages makes its wide range of applications and next-generation networks . This paper first introduces the definition of IP telephony , business type , structure , and voice communication protocols H.323 series of ITU-T and IETF Session Initiation Protocol (SIP). This paper focuses on the SIP, the origin of the SIP protocol , client / server - based network structure , grammar , and SIP proxy server, redirect server , registration server entity . Then also studied Vovida Networks SIP-based VoIP system, VOCAL , introduced the the VOCAL system configuration requirements and architecture . Finally, detailed analysis and modification of of VOCAL structure and code using VOCAL to realize the ideas and methods of the SIP system .