VoIP Communications in Wireless Ad-hoc Network with Gateways

In this paper, we investigate some of the issues that arise when mobile nodes engage voice connections with remote peers by using a wireless ad hoc network (MANET-cell) to access the distribution core network. We focus on a specific network scenario where all communications are directed to a special node, called gateway, which in turn bridges traffic to and from the core network. We first derive a mathematical expression to estimate the maximum number of sustainable voice sessions in a single-hop cell, with multi-rate terminals. Then, we assess the accuracy of the formula through ns2 simulations, which allow us to determine the voice capacity of the system also in presence of hidden terminals. Hence, we analyze the impact of multi-hop paths on the voice capacity of the system. From this analysis, we propose a new cost metric that we apply to a modified version of the OLSR routing algorithm, named HOLSR. This algorithm has proved to be able to preserve stability in some scenarios that were unstable under other routing algorithms.