無線網狀網路TCP應用之排程設計及效能評估

Preserving Good TCP Transmission Properties in Wireless Networks

黃慈霖(Tzu-Lin Huang)

指導教授 ： 孫雅麗

國立臺灣大學/管理學院/資訊管理學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.03294

摘要

TCP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。
在本文中，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。

關鍵字

spatial TDMA scheduling ； TCP ； 無線網狀網路 ； local Retransmission

並列摘要

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.
In 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.

並列關鍵字

spatial TDMA scheduling ； TCP ； wireless mesh networks ； local retransmission

參考文獻

[1] I. F. Akyildiz, X. Wang, W. Wang, “Wireless Mesh Networks: A Survey,” Computer Networks, vol. 47, no. 4, pp. 445-487, March 2005.

[5] Zhenghua Fu, Pertros Zerfos, Haiyun Luo, Songwu Lu, Lixia Zhang, Mario Gerla, “The Impact of Multihop Wireless Channel on TCP Throughput and Loss,” IEEE INFOCOM 2003.

[6] Ruy de Oliveira, Torsten Braun, “A Dynamic Adaptive Acknowledgement Strategy for TCP over Multihop Wireless Networks,” IEEE INFOCOM 2005.

[7] Ruy de Oliveira, Torsten Braun, “A Smart TCP Acknowledgment Approach for Multihop Wireless Networks,” IEEE Transaction on Mobile Computing, Febuary 2007.

[8] Sherif M. ElRakabawy, Alexander Klemm, Christoph Lindermann, “TCP with Adaptive Pacing for Multihop Wireless Networks,” ACM MobiHoc 2005.