Research And Implementation Of Softphone Based On SIP

The merging trend of two big networks which are voice network and data network forced the rapid development of VoIP. During the research of VoIP, the research towards H.323 and SIP has become major features. H.323 takes the strategies of centralization and hierarchical control to manage the network, uses the packet switching technology of traditional phone and voice. The advantage of H.323 can reflected in charging and management, but its integration with Internet is not that good. SIP is an application layer protocol which used to create, modifying and terminating one or more participants'session.SIP constructs an IP phone network base on currently existing Internet, and absorbs the experience of Web operation, so, it owns the advantages of briefness, flexibility, extensibility and so on. These advantages are in favor the research of VoIP, and it follows the develop trend of Internet.This thesis derived from Nanjing's scientific support project"Multimedia Trunk Command Scheduling System Based on Soft Switch". In this thesis, the project and related background of VoIP was briefly introduced, and then analyze the research status of VoIP and the probability and necessity of this issue research. On the basis of standard RFC3261, it primary studied SIP, including grammar, sessions, functions and so on. At the same time, the basic features of SDP and RTP was briefly introduced. Combining the theories of layering and modularization, this thesis analyzes the requirements of soft terminal in project, designs the framework of terminal software which can meet the expected functions. After deeply research of oSIP protocol stack, the soft terminal is developed base on oSIP protocol stack by using language C++. This soft terminal can support speech coding including G. 711A/Ulaw, G.723, GSM, G.729 and so on. In the thesis, the specific realization methods and primary structures of each soft terminal module have been elaborated in details. These modules including SIP module used for signal switch, graphic interface control module used for directly switch with user, network module used for network transmission and voice media module used for voice switch. At last, after basic feature test, the main functions of soft terminal design are verified, and the expected design targets are reached.