Path aggregation for voice over IP in multihop wireless mesh networks

Transferring voice traffic over multihop wireless mesh network (WMN) based on IEEE 802.11 is a challenging job. One main reason is that many small VoIP packets introduce significant overhead, and therefore greatly limits the capacity of VoIP support in WMN. To alleviate this inefficiency, in this paper, we argue for aggregation at routing layer, termed as path aggregation. With path aggregation, flows with similar directions choose routes that share as many as common links. This way, small VoIP packets from different flows can be effectively multiplexed into large packets over these common links and thus increases the utilization of wireless channel. We introduce an important performance metric, Channel Time Cost (CTC), to reflex the channel time used to deliver a voice flow. We formulate the path aggregation as an optimization problem that minimizes the sum of CTC of all flows over the network. We further propose a greedy distributed heuristic algorithm to yield approximate solution. We conduct extensive packet-level simulations and the results confirm that our path aggregation algorithm can effectively improve the VoIP capacity and increase the total throughput of WMN where mixed VoIP traffic and other Best Effort traffic co-exist.