Quantitative assessment of IP service quality in 802.11b networks

This paper experimentally studies the performance of 802.11b links in terms of round trip time (RTT) under load and TCP throughput in the presence of competing traffic. Our test scenarios are of specific interest to the emerging .hot spot. market, and the use of 802.11b in enterprise networks. We use commercial, standards-compliant 802.11b clients and access points, and demonstrate that CSMA/CA as currently used by 802.11b allows competing lowrate traffic (such as 128Kbps flow of 64 byte UDP or ICMP packets) to degrade concurrent TCP throughput by up to 50%. We also observe that data transfers from a remote server to a wireless client can create substantial latency spikes (over 50ms for MTU 1500 bytes) in the shared wireless segment, even when the TCP throughput is up around 4Mbps. Such spikes have a big impact on delay-sensitive applications, such as voice over IP (VoIP), online games and interactive streaming video that may be sharing the wireless medium. We also experimentally characterize the impact of the bottleneck link bandwidth, MTU sizes, and TCP window sizes in achieving maximum performance over 802.11b wireless links.