Determining 802.11 link quality with passive measurements

Unlike a wired link, a wireless link changes according to the physical environment and the network traffic in the surrounding area. The link quality, capacity and reliability are dependent on the MAC layer parameters and the channel conditions. In this work, we present a new passive link quality measurement tool and study the effects of modulation rate changes, interflow and intraflow interferences on the wireless link. We observe the channel conditions (RSSI in both directions), retries, and various basic metrics to determine their usefulness in certain conditions. We found that RSSI is not a good metric for link quality since it does not correlate with the measured throughput. Other factors, such as modulation rate settings and the topology setups are also detailed in this paper.