Voip Voice Quality Based On Differentiated Services

Defined as the provision of telephone-like services over the Internet, IP Telephony is considered as one of the goals of the next generation network (NGN). Despite the advantages of IP Telephony, however, there are a number of barriers to keep it from more widespread use. The most prominent among them is the poor quality of voice connections on the Internet. Designed to handle non-real time data traffic, Internet can only provide "best effort" service which cannot satisfy the Quality of Service requirement for carrying voice and video. How to improve its real-time capability so that QoS of communication can be guaranteed is a critical technique issue and one of the technique difficulties of IP Telephony system. The thesis focuses on the H.323 system, want to find out a way to provide good quality VoIP service to the users.The thesis first overviews the technique background and future directions of IP Telephony. Then the critical factors of the QoS of IP Telephony, including loss, delay and jitter, are analyzed. After that discusses the method to improve the QoS of VoIP and technologies in the application layer and network layer . In the application layer, by collects the network information from RTP/RTCP, the end systems can estimate the situation of the network, know that the network is blocking or not, so that they can do something to improve the QoS. Analyses several QoS technologies use in the network layer, emphasis on the Diffserv architecture. Provides a method that just use the Diffserv technology in the bottle neck of the network, just make little change to the network can provides some QoS to the real time traffic like VoIP. In the end , check this method by simulating in the network simulator NS2 and analyses the result.