Specification versus reality: Experimental evaluation of link capacity estimation in IEEE 802.11

Many wireless network protocols and algorithms rely on estimations of the link capacity in order to make informed decisions on routing data packets, selection of the optimal transmission rate, flow and admission control. In this paper we present an investigation into our Effective Link Capacity (ELC) metric which combines the use of MAC layer monitoring with knowledge of the network timing specifications to provide an accurate model of link conditions. We subject the resulting metric to an experimental investigation across a range of conditions using a conducted testbed. We demonstrate that commodity wireless devices do not conform to the IEEE 802.11 specification, thus making modeling difficult. Given that ELC and the IEEE 802.11s Airtime link metric are directly related, we compare their accuracy in estimating the link capacity. We demonstrate that ELC significantly outperforms two widely-used implementations of Airtime.