Abstract: A novel subscription merging method is proposed to deal with the Denial Of Service（DOS） attacks in publish/subscribe systems.Different from the current methods，the proposed method only merges the similar subscriptions.Thus it can reduce the bandwidth cost during event forwarding after merging compared to current methods.The judgment of the similarity of subscriptions depends on the size and the location of the constraint range of each attribute of the subscription，and grouping mechanism with two steps to group similar subscriptions is proposed.Theoretically analysis shows that the proposed method has low time complexity and can control the merging granularity dynamically according to the load of nodes，thus can efficiently deal with DOS attacks.The results from the experiments show that the proposed method only increases a little bandwidth cost during event forwarding.

Key words: publish/subscribe systems, Denial Of Service（DOS） attack, subscription merging, time complexity, bandwidth cost

摘要： 针对发布订阅系统中的拒绝服务攻击，提出一种有效的订阅合并方法。不同于现有订阅合并方法，该方法要求合并的订阅具有一定的相似性，因而可以减少合并后事件转发带宽开销。订阅相似性判断根据它在每个属性上约束范围的大小和位置，采用两阶段的归组算法把相似订阅归组，把处于同一组的订阅合并。理论分析表明，该方法时间复杂度低，可以根据节点负载情况动态控制合并粒度，因而可以有效解决拒绝服务攻击的问题。实验结果表明，该方法只增加少量的事件转发带宽开销。

关键词: 发布订阅系统, 拒绝服务攻击, 订阅合并, 时间复杂度, 带宽开销