, Volume 63, Issue 4, pp 861-882
Date: 23 Jun 2011

f-Sensitivity Distance Oracles and Routing Schemes

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An f-sensitivity distance oracle for a weighted undirected graph G(V,E) is a data structure capable of answering restricted distance queries between vertex pairs, i.e., calculating distances on a subgraph avoiding some forbidden edges. This paper presents an efficiently constructible f-sensitivity distance oracle that given a triplet (s,t,F), where s and t are vertices and F is a set of forbidden edges such that |F|≤f, returns an estimate of the distance between s and t in G(V,EF). For an integer parameter k≥1, the size of the data structure is O(fkn 1+1/k log (nW)), where W is the heaviest edge in G, the stretch (approximation ratio) of the returned distance is (8k−2)(f+1), and the query time is O(|F|⋅log 2 n⋅log log n⋅log log d), where d is the distance between s and t in G(V,EF).

Our result differs from previous ones in two major respects: (1) it is the first to consider approximate oracles for general graphs (and thus obtain a succinct data structure); (2) our result holds for an arbitrary number of forbidden edges. In contrast, previous papers concern f-sensitive exact distance oracles, which consequently have size Ω(n 2). Moreover, those oracles support forbidden sets F of size |F|≤2.

The paper also considers f-sensitive compact routing schemes, namely, routing schemes that avoid a given set of forbidden (or failed) edges. It presents a scheme capable of withstanding up to two edge failures. Given a message M destined to t at a source vertex s, in the presence of a forbidden edge set F of size |F|≤2 (unknown to s), our scheme routes M from s to t in a distributed manner, over a path of length at most O(k) times the length of the optimal path (avoiding F). The total amount of information stored in vertices of G is O(kn 1+1/k log (nW)log n). To the best of our knowledge, this is the first result obtaining an f-sensitive compact routing scheme for general graphs.

The work of the second author was supported in part by The Open University of Israel’s Research Fund (grant no. 46109) and Cisco Collaborative Research Initiative (CCRI).