Hybrid TCP-Friendly Congestion Avoidance Control

隨著寬頻網路的迅速成長，即時多媒體應用也隨著蓬勃發展，而目前的多媒體網路一般皆採用用戶資料通協定 (User Datagram Protocol，UDP)，利用此一非可靠性傳輸機制，並藉此得以獲得較佳傳輸效率，增加即時多媒體在播放時的品質。但由於用戶資料通協定並無相關速率控制機制，因此在網路上的傳輸，容易引發頻寬分享不公的情形。 本論文即針對即時多媒體應用在網路上傳輸所衍生的擁塞問題，提出一個新的混和式傳輸控制協定友善擁塞避免控制 (Hybrid TCP-Friendly Congestion Avoidance Control ，HTCAC)。相較於其他傳輸控制協定友善的擁塞控制機制，HTCAC為一主動式擁塞避免控制，利用網路封包來回時間 (Round Trip Time，RTT) 資訊動態的調整傳輸速率，以達到避免擁塞的目的。Due to the fast growth of high bandwidth network, real-time multimedia applications become increasingly popular. Real-time multimedia applications do not use Transmission Control Protocol (TCP) but adopt User Datagram Protocol (UDP) as transport mechanism, which may lead unfair bandwidth allocation or even shut down TCP traffic. In this thesis, a new TCP-friendly congestion control algorithm is proposed to ensure coexistence with TCP traffic, and better qualify in real-time multimedia application performance. The new algorithm is called the Hybrid TCP-Friendly Congestion Avoidance Control (HTCAC). Different from traditional TCP-friendly control algorithms, HTCAC is an active control system which does not passively wait for the happening of congestion but use Round Trip Time (RTT) information to adjust network transmission rate and to avoid network congestion!摘要 i Abstract ii Contents iii List of Figures vi List of Tables viii Chapter 1 Introduction 1 1-1. Motivation 1 1-2. Network Congestion 2 1-3. TCP-Friendly Congestion Control and HTCAC 4 1-4. Thesis Organization 6 Chapter 2 Congestion Control Mechanism 9 2-1. Transmission Control Protocol 9 2-1.1 TCP Transmission Unit 11 2-1.2 Congestion Window 13 2-2. TCP Congestion Control 14 2-2.1 TCP Reno 17 2-2.2 TCP Vegas 23 2-3. Best-Effort Service for Real-Time Multimedia Applications 27 2-3.1 Drawbacks of TCP 28 2-3.2 Best-Effort Service Protocol 30 2-4. Summary 32 Chapter 3 Survey on TCP-Friendly Congestion Control Algorithms 33 3-1. TCP-Friendly Congestion Control Algorithm Classification 34 3-1.1 Window-Based versus Rate-Based 34 3-1.2 Router-Based vs. End-to-End Approach 35 3-1.3 Sender-Based vs. Receiver-Based 36 3-2. Window-Based TCP-Friendly Congestion Control 37 3-2.1 General Additive Increase and Multiple Decrease 38 3-2.2 Binomial Congestion Control and SAIMD 42 3-3. Rate-Based TCP-Friendly Congestion Control 43 3-3.1 TCP-Friendly Rate Control 44 3-3.2 TCP Emulation at Receiver 45 3-4. Summary 49 Chapter 4 Hybrid TCP-Friendly Congestion Avoidance Control Algorithm 51 4-1. Hybrid Control and Congestion Avoidance 51 4-2. Rate Emulator 53 4-2.1 Bandwidth Estimation Model 54 4-2.2 Rate Transformation 56 4-3. Rate Predictor 57 4-3.1 Round Trip Time Smoothing 58 4-3.2 HTCAC Sending Rate Adjustment 61 4-4. Simulation Result 61 4-4.1 Leaky Bucket 62 4-4.2 Matlab Simulink Model 64 4-4.3 Expected Result 68 4-5. Procedures of the HTCAC Algorithm 69 4-6. Summary 70 Chapter 5 Conclusion 73 References 7