Algorithms for Eecient Filtering in Content-based Multicast

Content-Based Multicast is a type of multicast where the source sends a set of diierent classes of information and not all the subscribers in the multicast group need all the information. Use of ltering publish-subscribe agents on the intermediate nodes was suggested 5] to lter out the unnecessary information on the multicast tree. However, lters have their own drawbacks like processing delays and infrastructure cost. Hence, it is desired to place these lters most eeciently. An O(n 2) dynamic programming algorithm was proposed to calculate the best locations for lters that would minimize overall delays in the network 6]. We propose an improvement of this algorithm which exploits the geometry of piecewise linear functions and fast merging of sorted lists, represented by height balanced search trees, to achieve O(n log n) time complexity. Also, we show an improvement of this algorithm which runs in O(n log h) time, where h is the height of the multicast tree. This problem is closely related to p-median and uncapacitated facility location over trees. Theoretically, this is an uncapacitated analogue of the p-inmedian problem on trees as deened in 9].