The Design And Implementation Of A Voip System Based On TCP

The main transmission objective of the next generation network will be real-time multimedia streaming, which has a great influence on people’s work and lifestyle. Usually, because of the characteristic of small overhead and real-time, the voice data in the VoIP system is always transmitted by UDP. However, firewalls and other network entities are widely exist in the present network environment, the firewalls always shut down the ports of UDP for security reasons, such that the voice data transmitted by UDP can’t pass through the firewalls, causing the VoIP system based on UDP can’t work. So we have to use TCP to transmit the voice data.This paper focuses on designing and implementation a scheme of using TCP to transmit the voice data. The key point of this scheme is to reduce the delay of TCP receiver when packet-loss happens. It optimizes the TCP transport strategy, offers an unordered TCP transport strategy, such that the application layer can read the unordered voice data whenever the voice data arrived, needn’t ensure the voice data in order. Furthermore, this paper comes up with a method of message boundary identification, using consistent overhead byte stuffing algorithm to encode the data and add boundary flag to both begin and end of the data, even though in network with packet loss. In order to realize this plan, this paper starts by the research of the background of the VoIP system and SIP protocol. Then analyses the requirements of the system, summarizes the functional requirements and non-functional requirements of the VoIP system. Based on the work above, this paper also completes to design the overall architecture of the system, and accomplishes the detailed design of the function modules, focus on the research of unordered TCP transport strategy and message boundary identification. Then implements the system using programing language. At last, it tests the system in the experimental network environment. The results of the tests show that this system can effectively reduce the delay of the voice data transmitted by TCP. The system can pass through the firewalls by TCP, and keep a good effect on calling even through the packet-loss happened, which is consistent with our expectations.