| With the rapid development of optical communication and digital transmission technology, some bottleneck problems such as bandwidth and QoS in digital communication network have been resoloved and various IP technology oriented applications are widely in use. As a typical IP application, VoIP gains much attention and development with the trend of broadband and real-time application. As a critical part of VoIP system, VoIP gateway are widely used to supply cheap VoIP application and value-added service based on VoIP for various network subscribers. For the advantages of simpleness and extensibility, SIP protocol is widely used in more and more VoIP gateway to supply signal function. A universal resolvent of SIP stack in VoIP gateway will be meaningful in practice usage because of the difference in physical access media.In this thesis, the author focuses on the network architecture of SIP protocol based on analysis of popular VoIP signal protocols and VoIP service's background, and then brings forward its extensibility mechanism and services architecture. Finally, based on requirement of VoIP communication system, the author addresses the software architecture of SIP stack in VoIP gateway well designed in portability and extensibility through importing signal conversion module and multi-dialog mechanism. Some function and design of each module are depicted in detail; also important flow chart and design method are analyzed. Among that, the key techniques and problem resolvent are emphasized. Further, the author designed test scheme to validate stack's capability, the result on different test topology present this resolvent of SIP stack matches the requirement of VoIP gateway quite well.The method of building SIP stack has been adopted in residential gateway and VoIP integrated control system. The result and practice prove it a portable solution and applicable in various situations.
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