Algorithms for fault-tolerant routing in circuit switched networks

Abstract

In this paper we consider the k edge-disjoint paths problem (k-EDP), a generalization of the well-known edge-disjoint paths problem. Given a graph G=(V,E) and a set of terminal pairs (or requests) T, the problem is to find a maximum subset of the pairs in T for which it is possible to select paths such that each pair is connected by k edge-disjoint paths and the paths for different pairs are mutually disjoint. To the best of our knowledge, no nontrivial result is known for this problem for k>1. To measure the performance of our algorithms we will use the recently introduced flow number F of a graph. This parameter is known to satisfy F=O(\Delta \alpha^-1 \log n), where \Delta is the maximum degree and \alpha is the edge expansion of G. We show that a simple, greedy online algorithm achieves a competitive ratio of O(k^3 \cdot F) which naturally extends the best known bound of O(F) for k=1 to higher $k$. To get this bound, we introduce a new method of converting a system of k disjoint paths into a system of k length-bounded disjoint paths. Also, an almost matching deterministic online lower bound \Omega(k \cdot F) is given.In addition, we study the k disjoint flows problem (k-DFP), which is a generalization of the well-known unsplittable flow problem (UFP). The k-DFP is similar to the k-EDP with the difference that we now consider a graph with edge capacities and the requests can have arbitrary demands d_i. The aim is to find a subset of requests of maximum total demand for which it is possible to select flow paths such that all the capacity constraints are maintained and each selected request with demand d_i is connected by k disjoint paths, each of flow value d_i/k.The k-EDP and k-DFP problems have important applications in fault-tolerant (virtual) circuit switching which plays a key role in optical networks.