IGP Link Weight Assignment for Transient Link Failures

Intra-domain routing in IP backbone networks relies on link-state protocols such as IS-IS or OSPF. These protocols associate a weight (or cost) with each network link, and compute traffic routes based on these weights. However, proposed methods for selecting link weights largely ignore the issue of failures which arise as part of everyday network operations (maintenance, accidental, etc.). Changing link weights during a short-lived failure is impractical. However such failures are frequent enough to impact network performance. We propose a Tabu-search heuristic for choosing link weights which allow a network to function almost optimally during short link failures. The heuristic takes into account possible link failure scenarios when choosing weights, thereby mitigating the effect of such failures. We find that the weights chosen by the heuristic can reduce link overload during transient link failures by as much as at the cost of a small performance degradation in the absence of failures ( ). SPRINT ATL TECHNICAL REPORT TR02-ATL-071000 2 10 −2 10 −1 10 0 10 1 10 2 10 3 10 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Failure duration (minutes) C u m u la ti v e d is tr ib u ti o n Fig. 1. Failure duration distribution in Sprint’s network JanApril 2002 0 1 5 10 15 20 25 0 10 20 30 40 50 60 70 80 Simultaneously failed links P er ce nt ag e Transient failures (<10min) Long failures (>10min) Fig. 2. Distribution of simultaneous failures in Sprint’s network Jan-April 2002. The distribution is shown separately for transient failures ( minutes) and longer failures ( minutes)