Controle de admissão de chamadas VoIP em redes mesh sem fio

Abstract

This thesis presents a prototype of admission control for VoIP calls in wireless mesh networks, called CAC-RM, using the IEEE 802.11g protocol. This admission control goal is to avoid that incoming VoIP data flows consume excessive resources and cause degradation in the established ones. The admission control proposed in our approach only accepts new VoIP calls if the inprogress calls quality do not become degraded. The main features of our approach are: (i) an estimated ocupation time at the channel with VoIP traffic and with traffic without quality requirements, so called BE (Best effort); (ii) the resources reservation for VoIP traffic; (iii) an integration of our prototype to the OLSR proactive routing protocol (sending control messages with information about the occupancy node time with BE and VoIP traffic); (iv) an intra-flow interference estimate with admission control integrated; (v) regulation for BE traffic; and (vi) prioritization to sending and receiving VoIP traffic. The prototype was initially evaluated by simulations of a wireless mesh network in a scenario where all nodes are neighbours, considering two variations: the first one has only VoIP data flows and the second has VoIP and BE data flows. We measured the packet loss and the delays of VoIP calls and evaluated the MOS (Mean Opinion Score) measure indicating the user s satisfaction. In the first scenario, without CAC-RM, when the number of VOIP calls increases, their quality are decreased (indicated by the MOS value measured). Using the proposed calls admission control some calls were rejected and the gains is about 70% in the MOS value measured. Besides there was a reduction up to 82% and 96%, respectively, in packets losses and delays. In the second variation the proposed CAC to avoid reduction to about 29% of VoIP with quality over 3.5, and reduces too the damagethe packet VoIP losses uppon 86 %. In other scenario using multiple hops, we used VoIP traffic and hop count, ETX and ML metrics. When the network is saturated, there are no calls with enough VoIP quality. But it s possible to get satisfatory VoIP calls rejecting some calls as done by the proposed CAC. This gives a gain of MOS and reduces to 75 % the packet loss. In both scenarios, the proposed VoIP call admission control has provem efficient avoiding admission of new VoIP calls would degrade the quality of already established connections and ensuring that BE traffic does not damage VoIP packets on the wireless mesh network.