Near-Optimal Routing Lookups with Bounded Worst Case Performance

P. Gupta, B. Prabhakar, and S. Boyd

Proceedings IEEE INFOCOM, Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies, Tel Aviv, 3:1184-1192, March 2000.
Journal paper, with title Near Optimal Depth-Constrained Codes, appeared in IEEE Transactions on Information Theory, 50(12):3294-3298, December 2004.

The problem of route address lookup has received much attention recently and several algorithms and data structures for performing address lookups at high speeds have been proposed. In this paper we consider one such data structure – a binary search tree built on the intervals created by the routing table prefixes. We wish to exploit the difference in the probabilities with which the various leaves of the tree (where the intervals are stored) are accessed by incoming packets in order to speedup the lookup process. More precisely, we seek an answer to the question “How can the search tree be drawn so as to minimize the average packet lookup time while keeping the worst-case lookup time within a fixed bound?” We use ideas from information theory to derive efficient algorithms for computing near-optimal routing lookup trees. Finally, we consider the practicality of our algorithms through analysis and simulation.