Inferring Queue State by Measuring Delay in a WiFi Network

Packet round trip time is a quantity that is easy to measure for end hosts and applications. In many wired networks, the round trip time can be used to estimate how full network buffers are because of relatively simple relationships between buffer occupancy and drain time. Thus RTT has been exploited for purposes such as congestion control and bandwidth measurement. In some networks, such as 802.11 networks, the buffer drain times show considerable variability due to the random nature of the MAC service. We examine some of the problems faced when using round trip time measurements in these networks, particularly in relation to congestion control.