Practical beacon placement for link monitoring using network tomography

Recent interest in using tomography for network monitoring has motivated the issue of whether it is possible to use only a small number of probing nodes (beacons) for. monitoring all edges of a network in the presence of dynamic routing. Past work has shown that minimizing the number of beacons is NP-hard, and has provided approximate solutions that may be fairly suboptimal. In this paper, We use a two-pronged approach to compute an efficient beacon set: 1) we formulate the need for, and design algorithms for, computing the set of edges that can be monitored by a beacon under all possible routing states and 2) we minimize the number of beacons used to monitor all network edges. We show that the latter problem is NP-complete and use various approximate placement algorithm that yields beacon sets of sizes within 1 + ln(\E\) of the optimal solution, where E is the set of edges to be monitored. Beacon set computations for several Rocketfuel Internet service provider topologies indicate that our algorithms may reduce the number of beacons yielded by past solutions by more than 50% and are, in most cases, close to optimal.