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Abstract : |
Abstract?We describe a novel restoration strategy called virtual protection cycles (-cycles, patents pending) for extremely fast restoration in IP networks. Originally conceived for use in WDM and Sonet transport networks, we outline the adaption of the-cycle concept to an IP environment. In an IP router-based network,-cycles are implemented with virtual circuits techniques (such as an MPLS label switched path, or other means) to form closed logical loops that protect a number of IP links, or a node. In the event of failure, packets which would normally have been lost are encapsulated with a-cycle IP address and reenter the routing table, which diverts them onto a protection cycle. They travel by normal forwarding or label switching along the-cycle until they reach a node where the continuing route cost to the original destination is lower than that at the-cycle entry node. Diverted packets are deencapsulated (dropped from the-cycle) at that node and follow a normal (existing) route from there to their destination. Conventional routing protocols such as OSPF remain in place and operate as they do today, to develop a longer term global update to routing tables. Diversionary flows on the-cycle inherently cease when the global routing update takes effect in response to the failed link or node. The-cycle thus provides an immediate real-time detour, preventing packet loss, until conventional global routing reconvergence occurs. The aim of the paper is to explain the basic-cycle concept and its adaptation to both link and node restoration in the IP transport layer, and to outline certain initial results on the problem of optimized design of-cycle based IP networks. Index Terms?Internet, network design, network fault tolerance, network reliability, optimization methods, routing., |
