Several peer-to-peer networks are based upon randomized graph topologies that permit efficient greedy routing, e.g., random- ized hypercubes, randomized Chord, skip-graphs and construc- tions 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(logn) 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 sug- gests, 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 random- ized hypercubes, randomized Chord, and constructions based on small-world percolation networks, have diameter Θ(log n/ log logn) with high probability. The expected diameter of Skip graphs is also Θ(logn/ log logn). In all of these networks, greedy rout- ing 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 logn) hops, which is asymptotically optimal.
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