| NGN (Next Generation Network) is a milestone of the telecommunication history, it mean the new era of the telecommunication network. In the perspective of development, NGN is the natural evolution of the traditional cuicuit switched PSTN to the data packet switched network. NGN bears all the services of the traditional PSTN, and offload the traffic to the cheaper IP network. NGN can add many new services because the flexibility of the IP network. SIP (Session Initiation Protocol) is a protocol to locate the end user and connect a multimedia session, and can modify that session later. This essay discussed NGN, soft switch, and compared the two most common VoIP signaling at the time. Discussed the application of SIP in VoIP. Introduced the SIP protocol, and the message flow of the SIP protocol as defined in RFC3261. Through an example of the actual message flow in SIP protocol, explained all the terms defined by RFC. Through the explanation of the text encoded SIP message in that example, showed the interaction of the SIP message in real systems. For example when a user picks up the phone, all the behavior of the SIP message, etc. then the essay gives the implementation of the SIP protocol, on the linux platform using C++. The essay discussed the internal structure of the SIP protocol, and the class, module, and thread used in the protocol, the protocol used some important data structure and using thread and the intercommunication of the process to implement the transport of the data. The stack protocol used smart pointer to ensure when a pointer not used, the memory it point to can be released automatically. VoIP is just one application of SIP, SIP protocol evolved rapidly, and many big companies put resourced to research and develop VoIP systems based on SIP. The extension of SIP is very important so we discussed it on this essay. Finally this essay give the conclusion and the outlook of the technology. |
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