Abstract: IEEE802. 15. 4 is one of the standards for a low rate, low power consumption wireless sensor networks. By assigning the same sets of contention access parameters for all data frames and nodes, the contention access period (CAP) of the slotted IEEE 802. 15. 4 medium access control(MAC) currently provides a priority-independent channel access functionality and no service differentiation. To solve this problem, this paper proposed a differentiated service mechanism to support high IEEE802. 15. 4 QoS rectuirements. The main idea of the mechanism is allowing different sets of access parameters and data frame lengths for different priority classes, we developed a Markov-chain-based analytical model of the CAP of the IEEE 802. 15. 4 MAC with service differentiation, under unsaturated traffic conditions. In parocular, given two priority classes, our analytical model was used to evaluate the performance of a simple and effective service differentiation strategy, in terms of throughput, average frame service time, energy consumption, as well as access probability for each class. Our analysis results show that this model for differentiated services performs well.

Key words: IEEE 802. 15. 4,CAP,Markov chain model,Service differentiation