Research And Implementation Of QoS Of IP Phone

With the opening of global market and increasingly fierce competition, the traditional telecommunication is innovating greatly, and the competition of communication market is more and more fierce. In the recent years, with the development of IP phone technology, IP phone has had great influence upon traditional communication. IP phone network devices include gateway and other devices, and PSTN as the user's access devices. IP network is used to replace expensive conventional transmission network, thereby communication costs is reduced significantly and call costs is saved greatly. However, the QoS of IP phone can not be guaranteed because Internet is the best-effort model. If IP phone wants to compete with traditional telephone, it must improve its voice quality. Therefore, it is necessary to enhance the QoS of IP phone.The paper mainly discusses factors of impacting QoS of IP phone, as well as some measures and methods to improve the QoS. Improvement measures include two aspects. One is improving the network transmission to enhance the QoS, and the other is post-processing technology at the receiving end. At the receiving end, jitter buffer receives packets before play-out to smoothen out the delay jitter. However, buffer will enlarge the end-to-end delay. Reducing delay and smoothen delay jitter are a pair of contradictions. Therefore the paper introduces the adaptive approach to adjust the size of the jitter buffer. Increasing the length of jitter buffer when delay jitter has increased, on the contrary, the silence packets are properly disposed to reduce the end-to-end delay. Combining the Packet Loss Concealment (PLC), voice is played smoothly, and the end-to-end delay is as small as possible. The QoS of IP phone has improved greatly. The program is practice-oriented, which has been realized on the platform of PalmMicro.