Contention-window-based priority MAC protocols for wireless sensor networks (WSNs) conventionally size each priority class's backoff window under an equal-traffic-share assumption — one that multi-event IoT sensor networks routinely violate, since emergency, alarm, and routine-monitoring classes generate packets at markedly different rates. We propose the Non-uniform Backoff Priority-based MAC (NBP-MAC) protocol, which partitions an overlapping contention window among priority classes P1–P4 in direct proportion to their actual packet-generation ratios (40%, 30%, 20%, 10%), giving the dominant class the most room to contend while preserving a proportionally narrower, collision-balanced segment for each lower-volume class. Implemented in Castalia with CC2420 radios and benchmarked against two representative baselines — BOP-MAC and PMME-MAC — across network sizes of 10–90 nodes, NBP-MAC achieves the lowest and most evenly distributed end-to-end delay of the three protocols, matches BOP-MAC's near-zero packet loss, and consumes markedly less energy than PMME-MAC, at only a marginal energy overhead over BOP-MAC in mid-sized networks. These results establish traffic-ratio-proportional window allocation as an effective, low-complexity strategy for improving fairness and latency in heterogeneous, resource-constrained IoT sensor networks.

internet of things,wireless sensor networks,medium access control,contention window allocation,non-uniform traffic priority,quality of service