Research And Implementation Of The QoS Mechanism For VoIP System Based On SIP

VoIP is a technology that can provide voice communication and other services using Internet Protocol. Nowadays it becomes especially attractive for given low-cost voice transmission in public network and providing voice, fax and video transmission at the same time. Possibly, VoIP technology will change traditional communication method drastically.Theoretically, Voice over IP has been proven feasible for a long time. However, the technical difficulties of transporting voice and commercial implementation are challenges many companies are facing today. That's just the reason that a lot of research institutions and companies focus on VoIP technology.Lacking quality of service is a very serious technology obstacle. Real-time applications, such as VoIP, have different demands on network's quality from traditional services for it's sensitive to network delay and jitter. A reliable VoIP application requires network provide low delay, low jitter and high priority transmission. However, IP network only can provide"best effort"service currently, a feasible commercial QoS architecture doesn't exist.This paper proposes a method to improve QoS of VoIP system, which uses TC, the common traffic control tool in Linux platform, to realize Diff-Serv. When data is entering into VoIP gateway, this method classifies entering data to several classes according to the port number, modifies the DS field of real-time data such as voice stream using TC's DSMARK queuing discipline, make these real-time data's transmitting priority being highest.This paper has explained the technological background and development prospect at first, has introduced SIP, a popular singal protocol, has analysed the key factors which influence the QoS of VoIP system deeply, has discussed some methods which can improve the QoS of VoIP system. Especially, this paper has introduced the architecture and principle of DIFF-SERV technology, has explained the measure to realize DIFF-SERV in Linux platform using TC script. Finally, the test solution in the LAN is provided.The result proves: this QoS module can improve the QoS of VoIP system, especially when the network is busy.