Abstract: Considering that IEEE 802.15.4 networks can not provide any priority scheme，this paper proposes a differentiated services-based Markov chain model for IEEE 802.15.4 wireless sensor networks supporting real-time multimedia application.The main idea of this mechanism is to assign different priorities for different data flows according to QoS requirement（delay-sensitive or not）.Data with different priorities are assigned with the different growth-factor to reduce conflicts significantly.In addition，in order to compensate for low-priority data stream，high-priority data stream，if the channel is idle at the second CCA（Clear Channel Assessment） state，competes the channel with a certain probability，instead of accessing the channel immediately.Mathematical analyses show that the reasonable protocol parameter settings for different data flows have a significant effect on the performance of data flows with high-priority，but less effect on the performance of data flows with low-priority.

Key words: IEEE 802.15.4, Markov chain model, differentiated services, growth-factor, access probability

摘要： 针对IEEE 802.15.4协议的无线传感网络不能提供数据流优先级区分的问题，提出一种基于区分服务的马尔可夫链模型以支持实时多媒体应用。该机制的主要思想是根据服务质量要求（时延敏感与否）为不同的数据流分配不同的优先级。不同优先级的数据采用不同的增长因子来更好地减少冲突。此外，为了弥补低优先级数据流，高优先级的数据流在第二次空闲信道评估发现信道空闲时并不立即接入信道而是以一定的概率竞争信道。数学分析表明，对不同数据流设置合理的增长因子和竞争概率能够显著提高高优先级数据流的性能并对低优先级数据影响较少。

关键词: IEEE 802.15.4, 马尔可夫链模型, 区分服务, 增长因子, 接入概率