Cross-layer Solutions to Performance Problems in VoIP over WLANs

The design of WLANs was meant to extend Ethernet LANs in the most transparent way, but no particular mechanism was deployed in order to support real-time applications natively. At present VoIP calls are becoming customary, and IEEE802.11 WLANs must face the provision of guaranteed quality of service. In practice, QoS should be provided somehow a posteriori on top of the existing standard. In this paper, we address some concerns on the efficiency of WLANs for VoIP provision already remarked in literature and analyze possible solutions to increase the voice capacity of DCF IEEE802.11 WLANs. We consider two candidate solutions, the VA [1] and the M-M [2] cross-layer schemes. The efficiency of such mechanisms is evaluated in order to assess the performance gain compared to existing solutions. We provide extensive simulation results, proving that the advantage is significant, while requiring minor changes compared to the current IEEE802.11 standard.