Ad hoc networks have been proposed for a variety of applications wheresupport for real time, multimedia services may be necessary. Thisrequires that the network is able to offer service differentiation andquality of service (QoS) appropriate for the latency and jitter boundsneeded to meet the real time constraint. This paper describes adesign for realistic QoS support using a system approach that involvesco-ordinated changes at the MAC and IP layers. At the MAC layer, wepropose a priority-based scheduling mechanism to provide servicedifferentiation based on current channel status. We develop apriority-based delay model for the adaptive backoff scheme. The delaymodel allows each node to make local admission decisions. At the IPlayer, the network resource availability distribution and flowadmission in multi-hop ad hoc networks is achieved through a proposedcall admission protocol, so that each node has the correct view of theshared channel usage, and the correct flow admission decision is madebased on the estimated flow quality (accumulated delay of thepath). Analytical and simulation results show that our approach canprovide bounded latency and low jitter for real-time traffic, such asVoIP. The results also demonstrate that the aggregated networkthroughput is significantly improved given the quality requirements.