Diagnosing Wireless TCP Performance Problems: A Case Study

Researchers have long realized that TCP performance degrades over wireless links. Many solutions, including link-layer error recovery, have been proposed to overcome this problem. This paper studies how these solutions perform in a wireless LAN network environment. The experiments are conducted using off-the-shelf products, in a controlled way. In particular, we focus on Linux 2.4 TCP performance using a USB-based Compaq 802.11b multiport wireless card, as a case study. A multi-layer view is adopted to analyze the complex interactions between layers of the network protocol stack. Our results show that the USB bus, the TCP implementation, and the wireless link-layer protocols can all affect the overall TCP performance. While the TCP and USB implementation problems can be corrected through bug-fixing and proper setting of the USB mode, the wireless-related problems, such as the data/ACK collision problem and the network thrashing problem, may require fundamental changes to link-layer protocols in wireless LANs.