Analysis Of User Agent Based On The Open Source SIP Protocal

With the high development of communication, the IP-based communication mode is more and more popular. Session Initiation Protocol(SIP) is an application-layer control (signaling)protocol distributed by IETF for creating, modifying, and terminating sessions with one or more participants. It has highly research value.As one of the two standards for constructing VoIP (Voice over IP) system, SIP is becoming focal point because of being a simple, agile, and high effective tool. SIP provides a new application space to VoIP with the nicer expansibility and compatibility.This paper studies the functions and characters of SIP- with comparision to the VoIP based on SIP and H.323. According RFC2543 it analyzes deeply into the basic concept, characteristic of technology. Recongnized current reseach on SIP are based on theory, this paper emphasizes the mature open source project named Vovida OpenCommunucAtion library (VOCAL) about SIP. That is derived how the SIP stack and User Agent are implement from the partice on code analysis in depth.The purpose of this thesis is to explore the SIP and User Agent implement. So it emphasizes base classes about building the whole system. Based on it, this paper deeply analyzes bottom layer implement of VOCAL system. Eventually combination on front analysis, It analyzes a concrete application of User Agent on the SIP stack. The analysis procedure includes User Agent initialization , beginning of call and ending of call.Eventually, it gives state picture of call process.