Single node failures represent more than 85 of all node failures in the today's large communication networks such as the Internet. Also, these node failures are usually transient. Consequently, having the routing paths globally recomputed does not pay off since the failed nodes recover fairly quickly, and the recomputed routing paths need to be discarded. Instead, we develop algorithms and protocols for dealing with such transient single node failures by suppressing the failure (instead of advertising it across the network), and routing messages to the destination via alternate paths that do not use the failed node. We compare our solution to that of Ref. [11] wherein the authors have presented a "Failure Insensitive Routing" protocol as a proactive recovery scheme for handling transient node failures. We show that our algorithms are faster by an order of magnitude while our paths are equally good. We show via simulation results that our paths are usually within 15 of the optimal for randomly generated graph with 100-1000 nodes.
Slosiar and Latin @cite_4 studied the single link failure recovery problem and presented an @math time for computing the link-avoiding alternate paths. A faster algorithm, with a running time of @math for this problem was presented in @cite_8 . Our central protocol presented in this paper can be generalized to handle single link failures as well. Unlike the protocol of @cite_5 , this single link failure recovery protocol would use optimal recovery paths.
@cite_5 @cite_4 @cite_8
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We investigate the single link failure recovery problem and its application to the alternate path routing problem for ATM networks, and the k-replacement edges for each edge of a minimum cost spanning tree. Specifically, given a 2-connected graph G, a specified node s, and a shortest paths tree Ts = e1, e2, . . . , eni1 of s, where ei = (xi, yi) and xi = parentTs(yi), find a shortest path from yi to s in the graph G for 1 · i · n i 1. We present an O(m + n log n) time algorithm for this problem and a linear time algorithm for the case when all weights are equal. When the edge weights are integers, we present an algorithm that takes O(m + Tsort(n)) time, where Tsort(n) is the time required to sort n integers. We establish a lower bound of ­(min(m p n, n 2 )) for the directed version of our problem under the path comparison model, where Ts is the shortest paths destination tree of s. We show that any solution to the single link recovery problem can be adapted to solve the alternate path routing problem in ATM networks. Our technique for the single link failure recovery problem is adapted to find the k-replacement edges for the tree edges of a minimum cost spanning tree in O(m + n log n) time. Single node failures represent more than 85 of all node failures in the today's large communication networks such as the Internet. Also, these node failures are usually transient. Consequently, having the routing paths globally recomputed does not pay off since the failed nodes recover fairly quickly, and the recomputed routing paths need to be discarded. Instead, we develop algorithms and protocols for dealing with such transient single node failures by suppressing the failure (instead of advertising it across the network), and routing messages to the destination via alternate paths that do not use the failed node. We compare our solution to that of Ref. [11] wherein the authors have presented a "Failure Insensitive Routing" protocol as a proactive recovery scheme for handling transient node failures. We show that our algorithms are faster by an order of magnitude while our paths are equally good. We show via simulation results that our paths are usually within 15 of the optimal for randomly generated graph with 100-1000 nodes. In this paper, we adapt the heuristic of Fortz and Thorup for optimizing the weights of Shortest Path First protocols suchas Open Shortest Path First (OSPF) or Intermediate System-Intermediate System (IS-IS), in order to take into account failurescenarios.More precisely, we want to find a set of weights that is robust to all single link failures. A direct application of the originalheuristic, evaluating all the link failures, is too time consuming for realistic networks, so we developed a method based on acritical set of scenarios aimed to be representative of the whole set of scenarios. This allows us to make the problem manageableand achieve very robust solutions. The increasing proportion of data traffic being carried in public networks is necessitating tractable and scalable algorithms in the design of ATM networks. In particular, the design of routing tables for ATM networks operated under the interim inter-switch signalling protocol (IISP) requires a significant amount of manual work in order to design and implement the underlying static routing tables that enable end-to-end connectivity as the network grows. This paper presents a scalable algorithm that generates IISP routing table entries such that no loops are created and so that connectivity is maintained between all origin destination nodes under single-link failures. The algorithm generates shortest (i.e., lowest-cost) primary and alternate paths for any single-link failure scenario, while also demonstrating that at least one such solution can be found for any network graph devoid of bridges. Note that re-routing for single-link failures is considered adequate when sufficient protection is provided at the lower network layers. The algorithm has been fully implemented in a practical software tool, with execution time being a polynomial function of the network complexity.