Know thy neighbor's neighbor: the power of lookahead in randomized P2P networks

  • Authors:
  • Gurmeet Singh Manku;Moni Naor;Udi Wieder

  • Affiliations:
  • Stanford University, CA;Weizmann Institute of Science, Rehovot, Israel;Weizmann Institute of Science, Rehovot, Israel

  • Venue:
  • STOC '04 Proceedings of the thirty-sixth annual ACM symposium on Theory of computing
  • Year:
  • 2004

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Abstract

Several peer-to-peer networks are based upon randomized graph topologies that permit efficient greedy routing, e. g., randomized hypercubes, randomized Chord, skip-graphs and constructions based upon small-world percolation networks. In each of these networks, a node has out-degree Θ(log n), where n denotes the total number of nodes, and greedy routing is known to take O(log n) hops on average. We establish lower-bounds for greedy routing for these networks, and analyze Neighbor-of-Neighbor (NoN)-greedy routing. The idea behind NoN, as the name suggests, is to take a neighbor's neighbors into account for making better routing decisions.The following picture emerges: Deterministic routing networks like hypercubes and Chord have diameter Θ(log n) and greedy routing is optimal. Randomized routing networks like randomized hypercubes, randomized Chord, and constructions based on small-world percolation networks, have diameter Θ(log n / log log n) with high probability. The expected diameter of Skip graphs is also Θ(log n / log log n). In all of these networks, greedy routing fails to find short routes, requiring Ω(log n) hops with high probability. Surprisingly, the NoN-greedy routing algorithm is able to diminish route-lengths to Θ(log n / log log n) hops, which is asymptotically optimal.