A Strict Priority Based QoS-Aware MAC Protocol for Mobile Ad Hoc Networks

To provide Quality of Service (QoS) at MAC layer in mobile ad hoc networks (MANETs), it requires that a real-time (or high priority) data frame gets a higher channel access priority to that of a best-effort (or low priority) data frame. In this paper, we propose a scheme for resolving MAC layer contention in the form of a strict priority based variant of the IEEE 802.11 DCF. The channel access priorities for different classes of traffic are realized by proper backoff timer selection method which assigns non-overlapping contention windows to traffic of different priorities irrespective of their backoff stage values. To avoid overlapping of backoff timers during countdown period, freezing of backoff timer in low priority is replaced with a resetting of backoff timer mechanism. Besides introducing channel access priorities at MAC layer, a priority-based queuing discipline is implemented in the interface queue to improve the intra-node QoS support. The performance enhancement of the proposed scheme is demonstrated for single hop scenarios using a Markov Chain model, and the accuracy of the model is validated through a detailed simulation study. Further, simulation results in a multihop scenario show suitability of our approach to provide a strict service differentiation, especially in terms of end-to-end delay and throughput provided to real-time traffic as compared to DCF.