孫雅麗Sun, Yeali臺灣大學:資訊管理學研究所黃慈霖Huang, Tzu-LinTzu-LinHuang2010-05-052018-06-292010-05-052018-06-292008U0001-3107200816025700http://ntur.lib.ntu.edu.tw//handle/246246/179926TCP在有線網路中有三項良好的傳輸特性：一、TCP藉由調整congestion window來調節傳輸速度，使TCP可以有效利用網路的可用頻寬(available bandwidth)。二、對於congestion引發的packet loss，TCP可以很快速地重傳並恢復傳輸。三、流經相同bottleneck link的TCP flows，可以達到非常公平的throughput分配。但在CSMA/CA-based的無線網狀網路上，packet loss引發TCP congestion control機制使TCP降低傳輸速度而讓TCP無法有很好的throughput。Channel access contention、hidden terminal問題以及wireless link error都會造成packet loss。本文中，我們使用spatial TDMA scheduling scheme解決channel access contention以及hidden terminal問題，並加上link-layer retransmission scheme在local link處理wireless link error。我們進行模擬實驗，討論並分析使用這些scheme下無線網狀網路TCP效能。希望藉由這些scheme建造一個無線網路環境，使TCP不經更改也能保留TCP的良好特性，一如TCP在有線網路上一般順暢地運作。實驗結果顯示，考量traffic load的spatial TDMA schedule (schedule B)可以讓TCP在無線網狀網路上保持很好的throughput和fairness並且盡可能地使用所有的可用頻寬。而對於wireless link error造成的packet loss會破壞TCP throughput和fairness，實驗結果也證明使用link-layer retransmission scheme可以保存TCP快速復原packet loss的特性，使TCP在error-prone的無線網狀網路上也能有好的效能表現。In wired networks, there are several good properties for TCP transmission: exploiting available bandwidth as much as possible, providing fairness between different flows that share the same bottleneck link, and fast recovery from packet loss due to congestion. But in CSMA/CA-based wireless mesh networks, packet loss due to channel access contention, hidden terminal, and wireless link error will trigger the TCP congestion control scheme to slow down the data sending rate, thus results in low throughput performance.n this thesis, we take spatial TDMA scheme to tackle channel access contention and hidden terminal problem in wireless mesh networks. And we also take link-layer retransmission scheme to sustain fast recovery properties. Under the proposed schemes, we analyze TCP performance in wireless mesh network in terms of the good TCP transmission properties. We want to construct a wireless environment so that one can preserve good TCP transmission properties to achieve good overall throughput performance in wireless mesh networks. Simulation results show that in a chain topology, spatial TDMA schedule (schedule B), which considering traffic demand, sustains good TCP fairness and exploits available bandwidth as much as possible. And link-layer retransmission scheme preserve properties of fast recovery of lost packets on error-prone wireless mesh networks.目錄 一目錄 三目錄 五詞 七文摘要 八bstract 九 序論 1.1. 背景介紹 1.1.1. TCP 1.1.2. 無線網狀網路 3.1.3. TCP Bandwidth Requirement 5.2. 研究動機 6.3. 研究目的 7.4. 論文架構 7. 文獻探討 8.1. MAC Layer Approach 8.1.1. Distributed Link Random Early Drop 8.2. Transport Layer Approach 9.2.1. Dynamic Adaptive Acknowledgement Strategy 9.2.2. Adaptive Pacing 10.3. Other Approach 11.4. Improving TCP performance on error-prone wireless link 12.4.1. TCP snoop 12.4.2. Local link-layer retransmission scheme 13.4.3. Split-connection 13.5. 討論 14. TDMA 排程及TCP效能分析 15.1. k=1 Model 15.2. TDMA Scheduling演算法 18.2.1. Schedule A – Equal Share on each wireless link 18.2.2. Schedule B–Demand-Based 21.2.3. 討論 26.3. 實驗結果 26.3.1. Throughput Performance 27.3.2. TCP Congestion Window 變化情形 30.3.3. TCP smoothed round-trip time 33.3.4. Link utilization 34.4. 討論 35. Wireless link errors引發的packet loss對TCP效能的影響 39.1. Packet loss at the bottleneck link 40.1.1. Throughput performance 40.1.2. TCP congestion window變化情形 44.1.3. TCP smoothed round-trip time 45.2. 討論 46. Link-layer重傳機制及TCP效能分析 47.1. Link-layer retransmission scheme 47.2. 實驗結果 48.2.1. 分析與量測 link-layer retransmission scheme的overhead 49.2.2. TCP throughput performance 52.2.3. TCP congestion window變化情形 56.2.4. TCP smoothed round-trip time 58.3. 討論 60. 總結與未來展望 62考文獻 63application/pdf1728507 bytesapplication/pdfen-USspatial TDMA schedulingTCP無線網狀網路local Retransmissionwireless mesh networkslocal retransmissionhttp://ntur.lib.ntu.edu.tw/bitstream/246246/179926/1/ntu-97-R95725036-1.pdf