Mobile ad hoc network architecture allows cheap and easy deployment of network services almost anywhere and at anytime. Besides Internet access which is a best-effort service, multimedia applications are the most requested. They usually impose stringent quality of service constraints in terms of metrics including bandwidth, end-to-end delay, jitter and loss rate. In this paper, we evaluate the performance of a QoS extension of the OLSR protocol on voice communication using the OPNET simulator. The network model can represent various locations like railway stations, Campus University or traffic jam. We describe the performance end users involved in voice communication session can expect, even in presence of other traffics, like file transfer between other users in the same network.