Validating TCP tuning parameters over Wireless links


Niveditha V. Thondoti

Oral Defence Date: 

Tuesday, August 29, 2006 - 17:00


TH 935


Prof. Murphy, Prof. Hsu


The Transmission Control Protocol or TCP is a reliable transport protocol for sending data packets over the Internet. It is tuned to perform well in traditional networks where packet losses occur mostly due to congestion. Wireless networks, on the other hand, suffer from random losses. In this project we study how TCP reacts to wireless networks. TCP responds to all kinds of losses by invoking congestion control and avoidance algorithms, which results in degraded performance in wireless and lossy systems. In this project, the performance of TCP over wired networks and wireless networks is compared. The benchmarking tool httperf is used to measure the performance of client-server interactions over a TCP connection. By tuning TCP protocol parameters of the Linux Kernel, the performance of TCP is enhanced. The experimental results show that Response time and Connection time are directly proportional to increases in the workload. As the workload increases, the server becomes saturated and more errors in client requests occur. The number of errors is greater for a large file transfer when compared to a small file transfer. Response time is the highest for a large file and wired client and the lowest for a small file and wireless laptop. Connection time, on the other hand is the highest for a wireless laptop and the lowest for a wired client. When the kernel parameters are reset, (the tcp_mem default buffer value is reduced to 10,000 from 65,536 and the acknowledgements tcp_sack, tcp_dsack and tcp_fack are disabled), the response time and connection time increase for a wired client and decrease for a wireless client. For a wireless client, the reduction in response and connection times is more apparent when the acknowledgements are tuned rather than when the tcp_mem is tuned. Based on these initial observations, it is suggested that these kernel parameters be disabled for a wireless client but not for a wired client, however further study is needed before making this a general recommendation.


TCP, Wireless, Httperf, Linux


Niveditha V. Thondoti