Design And Implementation Of SIP User Agent In SoftSwitch

Since the development of the SoftSwitch technology, the IP network and the traditional PSTN network is inosculating and evolving into NGN based on packets switching. When IP and multimedia services become the irreversible trend, as a control signaling over the application layer, SIP will be a significant protocol in the construction of NGN step by step.Beginning with the definition and characteristic of the NGN, this thesis introduces the components, functions and protocols of SoftSwitch and discusses the amalgamation between SoftSwitch and legacy network. Based on this, the paper detailedly describes the functions, hiberarchy and session's operation models of SIP. SIP user agent locates at the protocal control layer in the call server of Softswitch. The thesis summarizes its advantages in Softswitch: first, it can establish sessions between any type of access network; second, it separates the basic sessions from services' implementations; third, it provides amalgamation of various protocols in services.With actual practices, the author analyses the state machines and functions of SIP user agent, and works out the designment of the module: the sending and receiving of SIP messages, the detecting of external input, and the operating of events were managed by three independent and subsequent threads. This design is advantageous in following aspects: SIP user agent could complete asynchronous communication patterns with multithreading and multiuser; also the separation of events handling is expansible, for the processing of new services could be efficiently loaded and the system could be conveniently upgraded.Finally, the paper briefly introduces the implementation of the SoftSwitch service with Parlay API, and it studies the applications of SIP UA in SoftSwitch with iNumber service and route management.