Measuring the Queue Sizes of IEEE 802.11 Wireless Access Points

The increasing power, lower cost and improved convenience of wireless networks is fueling the spread of IEEE 802.11 wireless access points (APs) in the residential and commercial environments. While there has been considerable study of wireless performance, little is publicly known about the queue sizes of wireless APs. This paper presents the QFind methodology for measuring wireless AP queue sizes. QFind determines the wireless saturation point, measures the baseline delay, induces the saturation rate and measures the delay with queuing, and computes the queue size. The accuracy of QFind is validated in a wireless testbed with a Host AP, where the controlled queue size is compared to the QFind measured queue size. QFind is then used to measure the queue sizes of seven wireless APs, three commercial class APs and four residential class APs targeted for residences. The results show that wireless AP queue sizes are packet-based and vary considerably across vendor and AP classes, with queue sizes ranging 50 packets to over 350 packets. This suggests additional engineering and science to determine the best mechanisms for providing AP queue sizes for a variety of traffic types.