Scalable Routing for Topic-Based Publish/Subscribe Systems Under Fluctuations

The loose coupling and the inherent scalability make publish/subscribe systems an ideal candidate for event-driven services for wireless networks using low power protocols such as IEEE 802.15.4. This work introduces a distributed algorithm to build and maintain a routing structure for such networks. The algorithm dynamically maintains a multicast tree for each node. While previous work focused on minimizing these trees we aim to keep the effort to maintain them in case of fluctuations of subscribers low. The multicast trees are implicitly defined by a novel structure called augmented virtual ring. The main contribution is a distributed algorithm to build and maintain this augmented virtual ring. Maintenance operations after sub-and unsubscriptions require message exchange in a limited region only. We compare the average lengths of the constructedforwarding paths with an almost ideal approach. As a resultof independent interest we present a distributed algorithm using messages of size O(logn) for constructing virtual rings of graphs that are on average shorter than rings based on depth first search.