Research And Implementation Of Adaptive Codec Scheme For VoIP

With the rapid development of telecommunication techniques and a growing number of intelligent mobile terminals, the technique of Vo IP(Voice over Internet Protocol) has been extensively applied. Designing adaptive Qo S(Quality of Service) support systems is one of a hotspot of today’s Vo IP research.The main works are summarized as follows:First of all, this paper describes the Vo IP platform based on Elastix that we built in our laboratory, analyses and solves the authentication and NAT(Network Address Translation) traversal problems. The traversal problem consists of signal traversal and media traversal. We propose a STUN traversal solution by analysing the SIP protocol. Compared with other NAT traversal solutions, like Application-layer Gateway, our solution is more efficient and does not require complex access control.Secondly, applying the theory of self-adaptive software to the design of Qo S supporting system, we propose a new Qo S support system based on MAPE model. Furthermore, the placement of MAPE agents, the estimation procedure as well as the feedback delivery are studied.Finally, after researched the speech quality of a set of standard Vo IP codecs given different network conditions, this paper proposes an adaptive end-to-end based codec switching scheme that fully conforms to the SIP standard. This codec switching scheme can choosing best performance codec under different network situations. So it can effectively prompt the listening voice quality. As this adaptive switching module is only required in caller and does not require any support of callee, the deployment can be done incrementally. From the result of tests, it is shown that this adaptive switching scheme can greatly improve the listening voice quality compared with static codec schemes.