臺灣博碩士論文加值系統

本碩士論文首先針對有線電視網路 (CATV)，又稱為混成光纖同軸網路 (HFC)，其上應用TCP為傳輸層協定所得到的效能進行詳細的分析研究。主要影響TCP傳輸效能的因素在於有線電視網路的MAC層的控制與排程 (control and scheduling) 協定設計方式。為了加強TCP的傳輸效能，本論文提出一套有彈性的有線電視網路MAC層的控制與排程機制，可以大幅增進下載的頻寬使用率及縮短上傳的延遲時間，另外，還可以讓下行與上行的流量達到良好的平衡狀態。這套機制中有兩個最主要的方法：第一個方法是「快速上傳頻寬請求訊息」(Fast Request Transmission)，其設計可以縮短請求上行頻寬的時間，藉以提升下行頻寬使用率。第二個方法是「大封包暫緩傳送」 (Long Packet Deferring)，主要針對平衡雙向TCP封包流而設計，可以有效地讓上下行頻寬都有效利用，不會有互相壓抑的狀況。為了精確地分析我們提出的控制與排程機制對TCP傳輸效能的貢獻，我們採用數學分析方法與電腦程式模擬來交互驗證各種網路特性及各方面效能提升的程度。

Hybrid-Fiber Coaxial networks have emerged as one of the premier technologies to deliver broadband access to the homes, and the lots of applications on it using TCP as transport layer protocol. In this thesis, we investigate the effects of HFC MAC control protocol on TCP performance and propose a new adaptive FCFS MAC scheduling and allocation algorithm which comprising "Fast Request Transmission" and "Long Packet Deferring" mechanisms, which can help improve the TCP performance substantially in terms of downstream throughput, upstream channel access delay and give good balance on downstream and upstream traffic. In addition, we also introduced an analytical model for TCP Reno on DOCSIS HFC networks, which can analyze and quantify the TCP performance characteristics on DOCSIS, and we developed a DOCSIS v1.1 MAC layer module for ns2, which can be further used to conduct simulation using different traffic sources on DOCSIS HFC networks. The mechanism "Fast Request Transmission" mainly designed to degrade the asymmetric characteristics in HFC networks for improving the downstream throughput and shorten the upstream access delay, while "Long Packet Deferring" mechanism is mainly designed to balance the downstream TCP traffic and upstream TCP traffic for achieving good and fair TCP performance in both direction.

Chapter 1 Introduction ...1
1.1 Hybrid-Fiber Coaxial Networks ...2
1.1.1 MCNS DOCSIS 1.1 ...3
1.2 The Effects of Bandwidth Asymmetry on TCP Performance ...5
1.3 Related Work ...6
1.3.1 HFC MAC Scheduling Algorithms ...6
1.3.2 Performance Evaluation on HFC Networks ...7
1.3.3 The Effects of Asymmetry on TCP Performance ...7
1.3.4 TCP on HFC Networks ...8
1.4 Performance Problems of TCP on HFC Networks ...8
1.4.1 One-way TCP Transfer ...8
1.4.2 Two-way TCP Transfer ...9
1.5 Chapter Organization ...11
Chapter 2 Analysis of TCP Performance Problems due to DOCSIS MAC Control Mechanism ...12
2.1 System Model ...12
2.2 Notation and Assumptions ...15
2.3 One-way TCP transfer ...16
2.3.1 The Effects of DOCSIS MAC Layer on Bandwidth Asymmetry ...17
2.3.2 The Effects of Bandwidth Asymmetry on Round Trip Delay ...22
2.4 Two-way TCP Transfer ...24
2.4.1 The Effects of DOCSIS MAC Layer on Bandwidth Asymmetry ...25
2.4.2 The Effects of Bandwidth Asymmetry on TCP Round Trip Delay ...28
2.5 Numerical Examples and Discussion ...29
2.5.1 One-way TCP Transfer ...29
2.5.2 Two-way TCP Transfer ...31
Chapter 3 Adaptive FCFS MAC Control Algorithm ...33
3.1 Fast Request Transmission ...33
3.1.1 Operation ...34
3.1.2 Analysis on Fast Request Transmission ...36
3.1.3 Numerical Examples and Discussion ...36
3.2 Long Packet Deferring ...38
3.2.1 Description ...39
3.2.2 Analysis of Long Packet Deferring ...40
3.2.3 The Number of Deferring Steps ...42
3.2.4 Numerical Examples and Discussion ...47
3.3 Adaptive FCFS MAC Control Algorithm ...49
Chapter 4 Simulation Results ...53
4.1 Simulation Environment ...53
4.1.1 Buffering Requirements ...54
4.1.2 Parameter Setting ...54
4.1.3 Assumptions ...55
4.1.3 Traffic Sources ...56
4.1.4 Performance Metrics ...57
4.2 Simulation Results ...57
4.2.1 One-way Simultaneous TCP Transfers ...57
4.2.2 Two-way Simultaneous TCP Transfers6 ...63
4.2.3 Web-like Traffic ...69
4.2.4 Mixed Traffic ...71
Chapter 5 Concluding Remarks ...75
References ...77

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