Interarrival Histograms: A Method for Measuring Transmission Delays in 802.11 WLANs

Traditional measurement tools are not suitable for finegrain performance evaluation of 802.11 wireless networks. To improve this situation, we have developed Interarrival Histograms, a method for measuring transmission delays based on gathering statistics of interarrival intervals at a receiving station. By measuring a sufficient number of interarrival interval samples with a clock resolution of 1 μs, the precision of estimating the mean transmission delay is well under one microsecond. Unlike other proposals, it does not require expensive custommade cards, because it uses commercially available equipment. It allows flexible measurements not only of wireless cards, but also of access points, which cannot be done with other proposed methods, unless one can instrument the access point kernel. In this paper, we describe the principles of the proposed method, derive the estimation error of measurements, and experimentally demonstrate its precision by applying it to the 100 Mb/s Ethernet. To illustrate the cases in which the method can help analyzing the complex behavior of 802.11 networks, we present measurements of several commercially available access points and wireless cards to show some anomalies and differences with the standard.