An Analytical Model for the Contention Access Period of the Slotted IEEE 802.15.4 with Service Differentiation

The IEEE 802.15.4 standard is poised to become the global standard for low data rate, low energy consumption wireless sensor networks (WSN). 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 priorityindependent channel access functionality and no service diiTerentiation. Several recent WSN applications such as wireless body sensor networks, however, may require service dilTerentiation and traf6e prioritization support to accommodate potential highpriority traffic (e.g., alarms or emergency alerts). By allowing dilTerent sets of access parameters and data frame lengths for differentpriority classes, this paper develops a Markov-chain-based analytical model of the CAP of the IEEE 802.15.4 MAC with service dilTerentiatlon, under unsaturated traffic conditions. In particular, given two priority classes, our analytical model is used to evaluate the performance of a simple, yet eiTective, contentionwindow-based service dilTerentiation strategy, in terms of the resulting throughput, average frame service time and access priority for each priority class. The accuracy of the analytical model is validated by extensive ns-2 simulation.