Research And Design Of Voice-Over-IP System Using Chord

With the rapid development of computer network and multimedia technology, VOIP get more and more attention as a kind of IP communications technology. SIP protocol (Session Initiation Protocol) is a widely used VOIP protocol, and is proposed by the IETF organization. SIP is a protocol basing on text, and has many advantages such as simple structure and easy to be expanded. However, the SIP Protocol, with the client/server architecture has the shortcomings of "single point of failure" and "bottleneck". In recent years, P2P network is another hot research field of the Internet. P2P network have advantages of distributed, decentralized, scalable and robust. When the number of users increases, the ability of providing services will also increase simultaneously. There are no shortcomings of the client/server model.Therefore, people are paying attention to the combination of P2P and SIP. The two popular method of combining the P2P networks and SIP protocol are SIP-using-P2P and P2P-over-SIP. But so far, most of the works are focus on theory with less practical applications. As a Result, the combination of P2P networks and SIP protocol is still the focus in the research field of computer network and multimedia technology.In this paper, the combination of P2P networks and SIP protocol will be researched and discussed. A novel VOIP system basing on P2P networks is designed to solve the problem of "single point of failure" and the "bottleneck" of the traditional VOIP system. The design of each model is explained in the paper.P2P network and SIP protocol are combined by the way of SIP-Using-P2P. P2P networks are introduced to replace the SIP server.P2P networks provide the functions of node registration and search. The advantages of decentralized and scalable of P2P network are fully used. The fully distributed P2P networks are introduced as the underlying network architecture. The fully distributed topology (DHT) P2P networks have high efficiency of node research and good maintainability, and are suitable for the application of VOIP system. Chord is introduced to deal with node search and node location.PJSIP is the SIP protocol used in this system. PJSIP is an open source lightweight protocol with the advantages of high performance, portability, small footprint and so on. It could provide a good performance for the system and make it possible to remove the system.The PJSIP protocol and P2P networks are combined by the way of SIP-Using-P2P, the P2P model and SIP model communicate through the API of application layer. Without the model of NAT traversal, the system is a pure P2P VOIP system. All of the nodes in the system are equal and completely overcome the shortcomings of "single point of failure" and the "bottleneck" of the traditional SIP system.Finally, the system is realized in Windows environment. Various tests has been made for the designed system, and comparisons with other popular VOIP system are also be made. The test result shows that the system performs well with small call delay and good voice quality, and has overcome the disadvantages of traditional SIP system.The system achieves the desired design goals.