Wireless sensor networks (WSN) are a kind of networks made up of thousands of tiny nodes. The node in WSN has limited computing, caching and communicating ability. Because of these differences from normal lineal networks, there are many research hotpots for quality of service (QoS) in WSN. The target of most WSN is to detect events and it pays more attention to the QoS of colony data packets. So, we present a class-based QoS mechanism. The sink node calculate the difference between required event delay (RED) and actually event delay (AED), according the difference value to dynamically adjusts the QoS levels for each event and feedback to the nodes in WSN. Because of the limited computational capabilities of WSN, the proposed mechanism import mapping table. The node finds the weight from mapping table according to the levels of events, and adjusts the transmit probability of each event, finally to adjusts the bandwidth and event delay reasonably for each event. The simulation proves that the improved mechanism algorithm is simple and effective; it has higher rate of convergence and can meet the application requirement of wireless sensor networks.
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