Research Of The SIP Client In The Soft Switch System Bases On CMMI

The development of SoftSwitch accelerates the combination of the traditional voice network and IP network; it will transit to NGN which bases on packet transfer gradually. VoIP is a popular technique of the emerging SoftSwitch recently and it's advantage is that it can offer more sorts of services than the traditional service with better quality. Compared with the traditional H.323 protocol, the application layer signal control protocol– SIP which is presented by IETF to manage the multimedia communicating session over IP network has much more advantages. More and more VoIP clients adopt SIP as the protocol stack.With the flourish development of the modern software industry, the software is becoming more and more large and complicated. The traditional developing mode cannot satisfy the people's demand of the software development quality. CMMI is a good solution to make out various problems met in inquiring, designing, coding and testing. A embedded OS– VxWorks wins the favor of SIP clients with its high real-time, high reliability, reducibility and support of TCP/IP protocol stack of industry standard.First, the call control protocol in IP phones mainly takes charge of the call establishment and release and the transmission of the address information, user's status and DTMF signal. The media control protocol mainly controls the establishment and release of the voice channel. This paper has researched the network structure, messages and session flow of SIP and presented its unsubstitutable advantages as the communicating protocol of VoIP clients. It also has proved that SIP can be easily established on the adopted embedded OS– VxWorks.Second, the software developing process is a process to abstract user's demand, to design, construct and test these demand. This dissertation imports the CMMI 3 software developing flow used in the development of a SIP client and summarizes, then gives out a general software developing process.Last, with long views, the competency lies in the diversity and flexibility of VAS, especially these new services should combine with Web application. This paper researches one typical service among numerous VAS and presents general mode and message flow of SIP VAS.The SIP client which is researched and developed in this paper has been produced and widely used in the Japan market. It contributes a lot to the SIP client application foreground.