The Research Of QoS In IP Phone System Based On H.323 Protocol

H.323 protocol, proposed by the ITU-T group, was accepted by most of the tele-communication companies worldwide. However, because IP network provides data transmitting service only in a "best-effort" manner., it does not guarantee the quality of services. We can introduce IntServ/RSVP and DiffServ mechanism into H.323 protocol to guarantee the QoS of IP telephony.IntServ/RSVP reserves the end-to-end bandwidth and buffers with RSVP signaling protocol to guarantee QoS. As the most promising technology at present. DiffServ aggregates the data streams of the same type to supply all kinds of services for clients.Theoritically, IntServ/RSVP can guarantee real-time services of low latency, small jitter and high quality supplied by IP network. Because of its intrinsic defect of awful expansibility, IntServ/RSVP cannot apply to the network of large scale. However, DiffServ classifies and divides the data streams in the networks, the quantities of status information are proportional to the types of service and independent of the quantities of stream. It is scalable and easy to implement, thus overcomes the defects of IntServ/RSVP.But DiffServ simplifies data streams with priority, this can limits its agility and capability. We can improve this method by combining IntServ/RSVP with DiffServ. It is possible to setup integrated streams defined perfectly and can be led to pipe with constant bandwidth, if DiffServ authenticates and classifies data streams of constant bit rate using the RSVP parameters or according to the types of special application.Hence we can share resources more effectively and provide guaranteed services.From April 2001 to now, as a member of a development team of IP telephony system, I have accomplished the following works:1. Read carefully the H.323 protocol stack and RFC documents about QoS of IP telephony system.2. Implemented IP gateway. It was passed the test and validation of expert group under the Ministry of Information Industry of China.3. Analysis and compare IntServ/RSVP and DiffServ, then combine them into IP telephony system based on H.323 protocol.4. Research the technologies of jitter buffer to make the irregular data packets of voice played evenly.