Sip-based Server Design And Realization

IP telephone is evolving into a mode of formal commercial span the internet. SIP(Session Initiation Protocol), an application-layer control (signaling) protocol, is one important part of the protocols of NGN(the next generation network) that' ensure the realization of this process.After a brief introduction of the principle and the key technology of IP telephone, the paper introduce the principle and the implement mechanism of SIP in particular, and realize a SIP stack and a SIP server system based on the SEP stack. Both of them are written in C++ programming language under linux environment.In addition to sending , receiving, encoding and decoding SIP messages ,the SIP stack can support IPv6 and SNMP protocol. The SIP stack can be used in the standard SIP elements such as Proxy Server, Redirect Server, Registar Server. A.lazy-decode method is employed to decode SIP message for efficiency.The combination of proxy mode and redirected mode is adopted in the commercial SIP server system based on the SIP stack. In addition to the basic function of user locating and call routing ,the server system implement some valuable features in commercial environment that is not mentioned in the standard SIP protocol,such as user management, flexible user authentication , conformability with Radius accouting protocol,the ability to configure and manage system server.Redundancy policy is used for more efficiency, reliability and scalability, which means more than one server needed to achieve a task. A new protocol named SPP is introduced for the goal of synchronization of the two provisioning servers and the data accessing between the provisioning and it's client. Some special messages are used to synchronize register information of the terminals among those of redirect servers. Redirect server is responsible for providing the route information of the call path , which can bring more flexibility when user want to subscribe or unsubscribe some feature. The ENUM function is endued to the redirect server, which makes the E.164 telephone number can be used on the terminals that lack ENUM function.