Tcp-friendly Congestion Control In Wireless Network Technology Research

Over the past several years, the wireless network has a tremendous growth in the use of real time multimedia streaming applications(video/audio). These applications use UDP as its transport layer protocol. However, UDP itself provides no congestion control scheme so that the great emergence of these applications will cause unfair allocation of bandwidth even congestion collapse. Presently, several TCP-Friendly congestion control mechanisms appropriate for real time streaming applications were proposed. But they are designed originally for wired network, in wireless network they don't do well. In wired network, packet loss is seen as congestion signal, it will trigger the congestion control mechanism to solve the congestion problem in order to avoid congestion collapse. But in wireless network, most of the packet loss is caused by error-prone links or wireless switch. This kind of loss unnecessarily triggers the congestion control mechanism, and it will cause the degradation of throughput and performance. Therefore, the research on how to improve the performance of the TCP-Friendly congestion control mechanism in wireless network is a hotspot of research in the present computer network area.Many proposed TCP-Friendly congestion control mechanisms are normally short of consideration about the minimal rate requirement for real time multimedia traffic. They can't guarantee the service quality of the multimedia streaming applications. To solve this problem, this paper pays much attention on the minimal rate requirement in order to achieve a good tradeoff between TCP-Friendliness and minimal rate.By comparing the current typical TCP-Friendly congestion control mechanisms, we find that TFRC(TCP-Friendly Rate Control) mechanism is very suitable for multimedia streaming applications. TFRC senders adjust its send rate so smoothly that it meets the requirement of smoothness of the multimedia traffic. Aimed at the error-prone wireless links and the minimal rate requirement, this paper presents a certified quality TCP-Friendly congestion control mechanism(CQTFCC). This mechanism includes the end-to-end congestion control and the router queue management. The routers adopt RED active queue management algorithm. The RED parameters are rationally set to achieve zero packet loss at RED gateways. With the help of ECN(Explicit Congestion Notification) marking capability, early congestion state is notified to the sender. The sender calculates the send rate by the ECN-marked packet probability instead of packet loss probability and adjusts the send rate ensuring the minimal rate requirement.