Analysis of Retry Limit for Supporting VoIP in IEEE 802.11e EDCA WLANs

We present in this paper an analysis of retry limit for supporting VoIP in IEEE 802.11e EDCA WLANs. The proposed research considers packet delay as an important factor of QoS performance measure for providing time-bounded service, such as VoIP and video in WLANs which usually implement default parameters. We also present an analytical method based on a Markov chain model that allows us to derive theoretical bounds for retry limit analysis. Based on the Markov chain model that considers retry limit, we can analyze the performance of VoIP over EDCA mechanism. In addition, in order to resolve the bottleneck transmission in VoIP in the downlink of AP, we maintain that the best service can be achieved when the throughputs of uplink and downlink are the same. Such a cross performance point is studied with respect to different retry limit parameters. Finally, extensive simulations have been carried out to validate the analytical model as well as to find out the corresponding cross point. We demonstrate that an enhanced VoIP capacity can be achieved by selecting appropriate retry limit and contention window size parameters.