Performance Improvement of TCP Congestion Control

• Main Authors: Rung-Shiang Cheng, 程榮祥
• Other Authors: Yuan-Cheng Lai
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/40878689892475000485

碩士 === 國立成功大學 === 資訊工程研究所 === 89 === In this thesis, we first describe the framework of various TCP congestion controls, then address some specific problems of each algorithm and propose their improvements. In order to resolve the periodic congestion in TCP Reno, we propose a smooth congestion control algorithm, intended to provide a more graceful ramp of window size when the system approaches congestion status to improve network bandwidth. We also deploy this mechanism with a larger initial window and smooth-start mechanism, and investigate their interactions and relationships. TCP New-Reno, modified from TCP, can recover multiple packet losses. However, it may transmit the burst packets upon exiting fast recovery to cause further congestion. Thus, to conquer this problem, we introduce a parameter, which limits the number of packets to be sent for each ACK received. We investigate TCP Vegas in wireless environment and use the queue length to judge the cause of packet loss, to reduce the unnecessary window degradation. Finally, the unfairness problem when TCP Vegas and TCP Reno coexist is also investigated. A dynamic threshold is set to solve this problem. In this thesis, besides the algorithms resolving each problem are described, the efficiency of our proposed mechanisms is validated. The simulation results show that our mechanisms can effectively resolve the corresponding problems and indeed obtain the higher performance. Abstract in English…………………………………………………………………....v Acknowledgement……..……………………………………………………………vii Table of Contents…………………………………………………………………..viii List of Figures…………………………………………………………………………x Chapter 1 Introduction 1.1 Motivations…………………………………………………………………...1 1.2 Organization……………………………………………………………….…3 Chapter 2 Some improvements for TCP Reno 5 2.1 Introduction…………………………………………………………………..5 2.2 TCP Congestion Control……………………………………………………..6 2.3 TCP Extensions…..…………………………………………………………..7 2.3.1 Larger Initial Window………………………………………………...8 2.3.2 Smooth-Start…………………………………………………………..8 2.3.3 Smooth Congestion Avoidance………………………..……………...9 2.4 Simulation Setup……………………………………………………………11 2.5 Simulation Study of Individual Scheme….…………………………………12 2.5.1 Larger Initial Window……………………………………………….12 2.5.2 Smooth Start…………………………………………………………14 2.5.3 Smooth Congestion Avoidance………………………………...……15 2.6 Cooperation…………………………………………………………………16 2.7 Summary……………………………………………………………………20 Chapter 3 Limited Transmit for New-Reno TCP 21 3.1 Introduction…………………………………………………………………21 3.2 TCP New-Reno……………………………………………………………..22 3.3 Burst Transmission in New-Reno…………………………………………..23 3.4 Limited Transmit Policy…………………………………………………….24 3.5 Summary……………………………………………………………………29 Chapter 4 TCP Vegas in Wireless Environment 30 4.1 Introduction…………………………………………………………………30 4.2 TCP Vegas…………………………………………………………………..32 4.3 Non-Congestion Judgment……………………………………….…………33 4.4 Network Model……………………………………………………………..36 4.5 Simulation Results and Discussions………………………………...………36 4.6 Summary……………………………………………………………………42 Chapter 5 Robust TCP Vegas 44 5.1 Introduction…………………………………………………………………44 5.2 TCP Congestion Control……………………………………………………45 5.2.1 TCP Reno……………………………………………………………46 5.2.2 TCP Vegas…………………………………………………………...46 5.3 Related Works………………………………………………………………47 5.3.1 Active Queue Management………………………………….………47 5.3.2 Modification to TCP Vegas………………………………….………48 5.4 Robust TCP Vegas…………………………………………………..………49 5.5 Simulation Result and Discussions…………………………………………52 5.5.1 Network Model……………………………………………………...…52 5.5.2 Fairness Improvement…………………………………………….……53 5.5.3 Number of Connections……………………………………………..…59 5.6 Summary……………………………………………………………………62 Chapter 6 Conclusions 63 Bibliography………………………………………………………………………...65