Research And Development Of Systems Based On Sip Conference Call

With the wide development of computer network, VOIP technology, which transmits multimedia information through IP network, has been developed a lot. As an advanced communication technology, teleconference system developed by VOIP, provides an approach for convoking remote conference. Teleconference system can be applied in varieties of vocations and work efficiency could be improved a lot by using it, which has been agreed to by people.Nowadays, most of teleconference system base on H.323 protocol. SIP (Session Initiation Protocol) is an IP telephone signaling protocol, it was established by IETF in 1999. Compared with H.323, SIP has a more rational construction, a conveniently application, the unique multicast characteristic and higher efficiency. There is a lack of conference control module in the definition of SIP. So, there is great meaning and value in studying teleconference system based on SIP.Depending on analyzing SEP, there put forward a series of rational and available teleconference system design project. In the conference model, some improvement has been added into the Centralized Conference, which effectively reduces the load of conference server. In the topology structure design, distributed client/server framework is used. In the function design, point to point communication, multi-point voice conference, recording and searching are supplied; In the module division, the system is logically divided as several big modules, each module contains a detail design, it accords with the standard of high cohesion and low coupling among modules. It is special importance that the functions of cutting in, hanging up and listening in an active call are design in point to point communication. In the multi-point voice conference's process, this system offers two kinds of models that are full audio-mix conference and multicast conference. Meanwhile, the author has made a deeply theory study and application design in speech encoding, audio mix arithmetic, RTP/RTCP protocol, multicast technology, NAT passing through technology, network security and so on, which are referred to in the system.At last, teleconference system was successfully achieved based on the design project above. The author constructed an experimentation environment and made a comprehensive test on the system. In the test process, we has compared this system with teleconference system based on H.323, gives the result report.