TCP-Unaware Approaches to Improve Performance of TCP Over Wireless Links

近年来，无线通信技术已得到广泛接受。 因此，与无线链路上的传输协议（如TCP）的性能相关的问题是令人感兴趣的。该提案的重点是TCP的unware技术，以提高TCP性能的路径，包括wirelesslink。 从TCP发送方到TCP接收方的路径通常包括几个中间节点，如果发生拥塞，这些节点可能会丢弃TCP数据包。 TCP隐含地假设所有的数据包丢失都是由于拥塞造成的。 由于无线链路容易出现传输错误，因此该假设对于无线链路上的TCP是不准确的。 然而，TCP减少了它的拥塞窗口时，由于transmissionerrors发生数据包丢失。 现有的提高无线链路上TCP性能的方法需要中间节点采取TCP特定的动作（这些方法被称为TCP感知的）。 例如，一个这样的协议要求中间节点解释TCP数据包，并在适当的时候丢弃一些重复的TCP数据包。 这种协议在实践中往往没有用处。 例如，当加密用于安全时，中间节点可能无法解密TCP数据包的内容。 因此，不能使用TCP感知协议。 这个项目的目标是研究TCP不知道的机制，不需要任何中间节点采取TCP指定的行动。以下问题将被调查：-TCP不知道的链路层，有助于提高TCP性能的设计。研究人员还将考虑与链路层设计相关的其他问题，包括链路层与随机早期检测（RED）的交互，为TCP数据和传输提供不同的可靠性级别，以及链路级重传的调度策略。 用于区分拥塞丢失和无线丢失的基于发送方的启发式算法：使用这种启发式算法，发送方可以确定数据包丢失是由于拥塞还是由于无线传输错误。 知道了数据包丢失的原因，发送方可以对每种类型的数据包丢失采取适当的措施。将评估此类策略对TCP性能的影响。 用于区分拥塞丢失和无线丢失的基于接收器的算法：当接收器更接近无线链路时，它可能处于更好的位置来诊断数据包是否由于无线传输错误而丢失。 评估尝试模仿TCP感知链路层机制的TCP感知方法。 所提出的技术将评估使用模拟，以及与AT T WaveLan技术建立wirelestestbed实验。 教育影响：本文提出的研究结果将发表在技术会议和期刊上。 研究结果还将纳入关于网络和移动的计算的研究生课程。 为该项目开发的软件将用于设计这些课程的实验，并分发给其他大学的教员使用。 从事该项目的学生将获得一个重要技术领域的专业知识。

Wireless communication technology has gained widespread acceptance in recent years. Therefore, issuesrelated to performance of transport protocols (such as TCP) over wireless links are of interest. The focusof this proposal is on TCP-unware techniques to improve TCP performance over paths that include wirelesslinks. The path from a TCP sender to a TCP receiver usually includes several intermediate nodes which maydrop TCP packets if congestion occurs. TCP makes the implicit assumption that all packet losses are dueto congestion. Since wireless links are prone to transmission errors, this assumption is not accurate for TCPover wireless links. Nevertheless, TCP reduces its congestion window when packet losses due to transmissionerrors occur. This phenomenon is known to result in poor throughput for TCP over wireless links.Existing approaches for improving TCP performance over wireless links require intermediate nodes totake TCP-speciffic actions { these approaches are said to be TCP-aware. For instance, one such protocolrequires that an intermediate node interpret TCP packets and drop some duplicate TCP acknowledgementswhen appropriate. Such protocols are often not useful in practice. For instance, when encryption is used forsecurity, intermediate nodes may not be able to decipher contents of TCP packets. Therefore, TCP-awareprotocols cannot be used. The objective of this project is to investigate TCP-unaware mechanisms that do not require any inter-mediate node to take TCP-speciffic actions. The following issues will be investigated:- Design of TCP-unaware link layers that help improve TCP performance. The researchers will also consider other issues related to link layer design, including interaction of link layer with Random Early Detection (RED), providing diffierent reliability levels for TCP data and acknowledgements, and scheduling policies for link level retransmissions.- Sender-based heuristics for distinguishing between congestion losses and wireless losses: Using such aheuristic, the sender can determine whether a packet was lost due to congestion or due to wirelesstransmission errors. Knowing the cause of a packet loss, the sender can take appropriate action for eachtype of packet loss. The impact of such heuristics on TCP performance will be evaluated.- Receiver-based heuristics for distinguishing between congestion losses and wireless losses: When thereceiver is closer to a wireless link, it may be in a better position to diagnose whether a packet is lostdue to wireless transmission errors or not.- Evaluation of a TCP-unaware approach that attempts to imitate a TCP-aware link layer mechanism. The proposed techniques will be evaluated using simulations as well as experimentation on a wirelesstestbed built with AT&T WaveLan technology. Educational Impact: Results from the research proposed here will be published in technical conferencesand journals. The results will also be incorporated into graduate courses on networking and mobile computing. The software developed for the project will be used to design experiments for these courses, and disseminated for use by instructors in other universities. Students working on this project will gain expertise in an important technology area.