Research On Some Problems Of TCP Friendly Rate Control Protocol For Streaming Media

Streaming media is a combination of communication and multimedia technology. In recent years, with the rapid development of the Internet, workstation performance, communication technologies and multimedia compression technologies, it is possible to provide streaming media applications over the Internet. However, due to the best-effort property of the Internet and features of streaming applications, large-scale deployment of streaming media applications is still facing many challenges. In particular, how to effectively deliver the data produced by such streaming media is the key problem for streaming media applications.There has been a significant amount of previous work on the transmission rate control mechanism for streaming media and several rate control protocols have been developed. Among them, the TFRC (TCP Friendly Rate Control) protocol is the most promising solution. It has gained much popularity as a reference scheme for streaming media transport on the Internet. In fact, TFRC has become a standard RFC in 2004.However, On the basis of the systemic analysis and performance evaluation of TFRC protocol, we found that for safety and large scale deployment of TFRC on the Internet there are still some problems to be resolved. First, the TCP throughput equation used by TFRC was based on TCP Reno, which can not accurately predict the throughput of TCP NewReno, the main implementation of TCP protocol on today’s Internet. Second, TFRC’s TCP-like slow start algorithm may result in a large number of packet losses within one round trip time, which degrade the performance of TFRC and impact the quality perceived by the receiver. Third, TFRC gives poor performance over network scenarios with packet reordering because it emulates TCP and treats a packet reordered beyond 3 as lost packet.The research presented in this dissertation is concentrated on improving the performance of TFRC protocol. Different schemes of improving the performance of TFRC protocol is proposed respectively at TCP throughput equation, slow start algorithm and packet loss detection algorithm. The main contributions of this dissertation are as follows:First of all, this dissertation develops a simple and accurate analytic model for the steady state throughput of the slow but steady variant of TCP NewReno by capturing the effect of fast recovery algorithm and taking into consideration slow start phase after timeout expiration. The model describes the relation between TCP NewReno throughput and round trip time, loss event rate and retransmission timeout value. Validation by NS2 simulator shows that using TFRC’s throughput model to estimate TCP NewReno throughput may introduce significant error and the proposed model is able to accurately predict the steady-state throughput for TCP NewReno over a wide range of network conditions.Secondly, a bandwidth measurement based slow start algorithm was proposed in this dissertation. The algorithm employs effective online bandwidth measurement technology to get the available bandwidth and update the sending rate with appropriate value dynamically. It increases the sending rate with half of the sum of the current sending rate and the measured bandwidth, iterates and gradually closes up available bandwidth, of which the increment is large at start phase and small at end phase of a connection. Simulation experiments indicate that the algorithm significantly decreases the dropped packets and improves the smoothness of connections.Thirdly, this dissertation presents a delay based packet loss detection algorithm to make TFRC more robust to packet reordering and yet, when packet reordering does not occur, it is friendly to the standard implementation of TCP. In TFRC, the loss of a packet is detected by the arrival of three packets with higher sequence number. This packet loss decision is delayed in the new algorithm by a short period to allow the receiver to receive the packets that travel in different path or the link level mechanism to recover the lost packet. If at the end of the delay timer the packet is still not received, then it is treated as a packet loss due to congestion. The simulation results show that the algorithm performs consistently better than the standard TFRC under persistent packet reordering. When the case that packets are not reordered it maintains the same throughput as the typical implementation of TCP (TCP-NewReno) and shares network resource fairly.Finally, the refined TFRC protocol was implemented in NS2 simulation environment and Linux operation system. And we extensively evaluated the refined TFRC protocol through simulation and real network measurement. The results show that it is a suitable rate control mechanism for streaming media in the aspects of smoothness, TCP friendliness and the responsiveness of congestion.