Packet round trip time is a quantity that is easy to measure for end hosts and applications. In many wired networks, the round trip has been exploited for purposes such as congestion control and bandwidth measurement because of relatively simple relationships between buffer occupancy and drain time. In 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-based queue estimates in these networks, particularly in relation to congestion control. Â© Springer-Verlag Berlin Heidelberg 2009.