Range Trees with variable length comparisons

Abstract

In this paper we introduce a new data structure for address lookup, a new tree structure which improves on the existing Range Trees allowing shorter comparisons than the address width. The proposed scheme shares among multiple concurrent comparisons common address prefixes and suffixes and also omits address parts not required for computing a next node branch. In so doing, for a given memory bandwidth, we achieve a larger number of concurrent comparisons than the original Range Tree. This results in less memory accesses and lower latency per lookup. Performance scales better as the address width and the number of address ranges increase. We describe the rules employed to construct the proposed structure and offer two heuristics which generate the “configuration” of the decision tree given a set of address ranges. The proposed Range Tree with variable-length comparisons (RT-VLC) has up to 50% less tree-levels than the original Range Tree and its memory requirements are 50% to 2× that of a linear search approach.