[论文解读] Impact of Random Loss on TCP Performance in Mobile Ad hoc Networks (IEEE 802.11), A Simulation-Based Analysis

Shamimul Qamar, Kumar Manoj|arXiv (Cornell University)|Feb 11, 2010

Network Traffic and Congestion Control参考文献 2被引用 6

一句话总结

本项基于仿真的研究评估了在无线链路噪声导致的随机丢包条件下，TCP Tahoe与Reno在移动自组织网络（MANETs）中的性能表现，采用ns-2进行仿真。结果表明，尽管在低且孤立的丢包情况（1%）下Reno优于Tahoe，但当高误码率导致多个分段丢失时（30%），Tahoe显著优于Reno——恢复时间减少64.28%，表明Tahoe在高度不可靠的无线环境中更具优势。

ABSTRACT

Initially TCP was designed with the notion in mind that wired networks are generally reliable and any segment loss in a transmission is due to congestion in the network rather than an unreliable medium (The assumptions is that the packet loss caused by damage is much less than 1 percent) . This notion doesnt hold in wireless parts of the network. Wireless links are highly unreliable and they lose segments all the time due to a number of factors. Very few papers are available which uses TCP for MANET. In this paper, an attempt have been made to justify the use of TCP variants (Tahoe and Reno) for loss of packet due to random noise introduces in the MANET. For the present analysis the simulation has been carried out for TCP variants (Tahoe and Reno) by introduces 0, 10, 20 and 30 percent noise. The comparison of TCP variants is made by running simulation for 0, 10, 20 and 30 percent of data packet loss due to noise in the transmission link and the effect of throughput and congestion window has been examined. During the simulation we have observed that throughput has been decreased when a drop of multiple segments happens, further we have observed in the case of TCP variant (Reno) throughput is better at 1 percent (Figure 5) which implies a network with short burst of error and low BER, causing only one segment to be lost. When multiple segments are lost due to error prone nature of link, Tahoe perform better than Reno (Figure 13), that gives a significant saving of time (64.28 percent) in comparison with Reno (Table 4). Several simulations have been run with ns 2 simulator in order to acquire a better understanding of these TCP variants and the way they perform their function. We conclude with a discussion of whether these TCP versions can be used in Mobile Ad hoc Network.

研究动机与目标

• 评估TCP Tahoe与Reno在移动自组织网络（MANETs）中不同随机丢包水平下的性能表现。
• 分析IEEE 802.11无线链路中的随机噪声对TCP吞吐量及拥塞窗口行为的影响。
• 确定在不同丢包条件下，TCP Tahoe与Reno中哪一版本更适合用于MANETs。
• 提供关于突发性丢包对移动无线网络中TCP性能影响的实证证据。

提出的方法

• 使用ns-2网络仿真器进行仿真，以模拟具有IEEE 802.11无线链路的MANET环境。
• 在0%、10%、20%和30%的丢包率下引入随机丢包，以模拟无线链路不可靠性的不同程度。
• 测量并比较TCP Tahoe与TCP Reno变体的吞吐量及拥塞窗口动态特性。
• 分析聚焦于单分段与多分段丢失场景下的性能表现。
• 关键性能指标包括端到端吞吐量及丢包事件后的恢复时间。
• 通过多次重复仿真以确保结果的统计可靠性。

实验结果

研究问题

• RQ1 无线链路噪声导致的随机丢包如何影响MANET中TCP的吞吐量？
• RQ2 TCP Tahoe与Reno在应对单一分段与多分段丢失时有何差异？
• RQ3 在高误码率下，TCP Tahoe与Reno中哪一版本能实现更高的吞吐量和更快的恢复速度？
• RQ4 突发性丢包模式对MANET中拥塞窗口行为有何影响？
• RQ5 传统TCP变体能否在具有不可靠无线链路的移动自组织网络中有效使用？

主要发现

• 当无线链路的高误码率导致多个分段丢失时，吞吐量显著下降。
• 在低丢包条件（1%丢包）下，TCP Reno优于TCP Tahoe，实现了更高的吞吐量和更快的恢复速度。
• 在高丢包条件（30%丢包）下，TCP Tahoe相比TCP Reno将恢复时间减少了64.28%，表明其在突发性丢包环境中表现更优。
• 由于采用更具攻击性的重传策略，当多个分段丢失时，TCP Tahoe的拥塞窗口恢复效率高于TCP Reno。
• 结果表明，TCP Tahoe在频繁出现突发性错误的高不可靠无线网络中比TCP Reno更具鲁棒性。
• 本研究证实，传统TCP假设丢包源于拥塞的设定在MANET中并不成立，因为此处丢包通常源于物理层错误。