The Umts The Tcp Performance Analysis And Optimization

Universal Mobile Telecommunication System (UMTS) is one of a third-generation cellular network that enables high-speed wireless Internet access. TCP is the most commonly used transport protocol on the Internet. When it is used as transport protocol in an UMTS environment, the UMTS services will be more compatible with today's most used Internet services. So it is important to study its performance especially over UMTS. TCP does not perform well in the high error condition, such as wireless links. Since TCP assumes that packet losses induced by wireless channel are occurred by the network congestion, it unnecessarily invokes congestion control that results in poor performance. Consequently,optimizing TCP performance over UMTS mobile system is essential for providing good user experience and for optimizing system capacity.This thesis analyzes the possible reasons of TCP's poor performance in UMTS and proposes enhancements to improve TCP performance .Throughput and end to end delay are used as main performance metric in the discussion. In the thesis, we firstly describe the characteristics of TCP, including basic theory and congestion control mechanism; introduce the research results of TCP performance over wireless network,UMTS and ARQ. Secondly, we analyze the characteristics of UMTS Link and deduce their effects on TCP poor performance.In order to overcome it, we proposes enhancements on both TCP itself and the ARQ protocol in RLC. For tcp, the enhancements are: appropriate window size, increased initial window, larger ip MTU, selective acknowledgments, explicit congestion notification and TCP timestamps option. For ARQ, we conclude that properly setting the values of polltimeout and stprobtimeout has an influence on TCP performance. Analysis and computer simulation over DCH and HDSCH in NS2 have provn the correctness and the effectiveness of the enhancements. Finally, we analyze the fast scheduling algorithm of HARQ.We put forward a new scheduling algorithm to make all users to utilize the resource fairly. We have implemented the function in c++ and otcl without changing the structure of EURANE. Based on analysis and computer simulation of TCP performance,we compare the algorithm with other...