Research On TCP’s Retransmission Timer Optimization In Mobile Networks

With the progress of communications technology and the proliferation of mobile devices in recent years, mobile networks have become one of the fastest growing, greatest market potential and most seductive view business. As TCP holds a strong majority in mobile networks, it is very important to ensure its performance to provide high quality communication services. Therefore, to ensure and optimize TCP’s performance in mobile networks has become particularly important. However, TCP spurious timeout retransmission often occurs in mobile networks. This is because the Radio Resource Control(RRC) transits among different states in mobile networks. Even there is no congestion, these transitions cause TCP packets’ high sudden delays, resulting in a large number of packets’ retransmissions which degrade the TCP’s performance.This paper focus on the issues of TCP timeout retransmission in mobile networks. Then we are looking forward to optimize the strategies. TCP uses RTO to ensure the transmission in wire networks. However, it may not suitable in mobile networks because of the special feature in mobile networks. The main content in this dissertation include: Firstly, this paper introduce the background knowledge of TCP timeout retransmission and RRC in mobile networks. The point that spurious timeout retransmission is related to RRC states transiton is simply stated.Secondly, This paper analyzes and proves he serious consequences of this spurious retransmission timeout:Firstly, it degrades the effective throughput and introduces the delay of TCP transmission. On this basis, serval tests were set to verify that spurious retransmission packets deduce the effective throughput and that lower cwnd, ssthresh, deviated RTO would add to the delay.Thirdly, Optimization strategies are proposed for improvements. The retransmission timer can be adjusted at the right time to avoid some of the spurious retransmissions caused by RRC state transitions. To verify the strategies, they were implemented in the kernel. From traffic, completion time, deviation of RTO and retransmission rate aspects, four tests were conducted to compare with original RFC6298 in the real environment. A 3G mobile system that deploys our strategies for TCP can enhance its transmission. Unnecessary retransmission packets can be avoided. cwnd can be maintained to shorten the completion time. The calculation of RTO can be more proper. Overall, our strategies reduce the retransmission rate.Finally, the paper points out the shortcomings and deficiencies, and gives suggestions for further improvements.