Improving on 802.11: Streaming Audio and Quality of Service

Ad hoc wireless networks present several interesting problems, one of which is Medium Access Control (MAC). Medium Access Control is a fundamental problem deciding who get to transmit next. MAC protocols for ad hoc wireless networks must also be distributed, because the network is multi-hop. The 802.11 Wi-Fi protocol is often used in ad hoc networking. An alternative protocol, REACT, uses the metaphor of an auction to compute airtime allocations for each node, then realizes those allocations by tuning the contention window parameter using a tuning protocol called SALT. 802.11 is inherently unfair due to how it returns the contention window to its minimum size after successfully transmitting, while REACT’s distributed auction nature allows nodes to negotiate an allocation where all nodes get a fair portion of the airtime. A common application in the network is audio streaming. Audio streams are dependent on having good Quality of Service (QoS) metrics, such as delay or jitter, due to their real-time nature.

Experiments were conducted to determine the performance of REACT/SALT compared to 802.11 in a streaming audio application on a physical wireless testbed, w-iLab.t. Four experiments were designed, using four different wireless node topologies, and QoS metrics were collected using Qosium. REACT performs better in these these topologies, when the mean value is calculated across each run. For the butterfly and star topology, the variance was higher for REACT even though the mean was lower. In the hidden terminal and exposed node topology, the performance of REACT was much better than 802.11 and converged more tightly, but had drops in quality occasionally.