IP layer restoration and network planning based on virtual protection cycles

We describe a novel restoration strategy called virtual protection cycles ( p-cycles, patents pending) for extremely fast restoration in IP networks. O riginally conceived for use in WDM and Sonet transport networks, we outline the adaption of the p-cycle concept to an IP environment. In an LP router- based network, p-cycles are implemented with virtual circuits techniques (s uch 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 p-cyc le IP address and reenter the routing table, which diverts them onto a prot ection cycle. They travel by normal forwarding or label switching along the p-cycle until they reach a node where the continuing route cost to the ori ginal destination is lower than that at the p-cycle entry node, Diverted pa ckets are deencapsulated (dropped from the p-cycle) at that node and follow a normal (existing) route from there to their destination. Conventional ro uting protocols such as OSPF remain in place and operate as they do today, to develop a longer term global update to routing tables. Diversionary flow s on the p-cycle inherently cease when the global routing update takes effe ct in response to the failed link or node, The p-cycle thus provides an imm ediate real-time detour, preventing packet loss, until conventional global routing reconvergence occurs, The aim of the paper is to explain the basic p-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 p-cycle based IP networks.