WiFi network residual bandwidth estimation: A prototype implementation

Evaluating the available bandwidth in a wireless LAN is a challenging task because the throughput depends on several factors such as RSSI (Received Signal Strength Indication), interferers and packet size. Moreover, in a real scenario it is not sufficient to evaluate periodically the throughput of the network, but a continuous monitoring is required in order to detect as soon as possible network problems and saturation phenomena. When wireless LAN is used to transmit high priority traffic (e.g. voice and video flows), an admission control procedure based on residual bandwidth evaluation is necessary to verify that required resources are available. We propose a mechanism based on active traffic probing with low priority packets: this approach enables us to simulate a real data flow and, on the other hand, does not interfere with existing flows. Our method relies on IEEE 802.11e (WMM - Wireless MultiMedia) support and does not require any customization of network devices. Through this approach the residual bandwidth can be continuously monitored. This measurement accounts for both the characteristics of active flows (different packet sizes and rates) and external interferences, offering accurate bandwidth estimation.