In this paper, we propose QoS aware MAC protocol for Wire- less Sensor Networks and its cross layer extension to network layer for providing QoS in delay sensitive WSN scenarios. In WSNs, there can be two types of traffic one is event driven traffic which requires immedi- ate attention and another is periodic reporting. Event driven traffic is classified as Class I(delay sensitive) traffic and periodic reporting is clas- sified as Class II(Best Effort) Traffic. MAC layer adaptation can take place in terms of (i) Dynamic contention window adjustment per class, (ii) Reducing the delay suffered by difference in Sleep schedules(DSS) of communicating nodes by dynamically adjusting Duty Cycle based on Utilization and DSS delay of class I traffic, (iii) Different DIFS (DCF Inter Frame Spacing) per class, (iv) Adjusting all the three schemes pro- posed above simultaneously. Cross layer extension is also proposed, in which MAC layer uses network layer’s next hop information for better adaptation of duty cycle based on DSS delay. Routing protocols can uti- lize MAC layer parameter DSS delay to select the routes which offer least DSS delay latency, there by minimizing the overall end-to-end delay.
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