Efficient construction of virtual p-cycles protecting all cycle-protectible working links

It has been shown that p-cycles, proposed by W.D. Grover and D. Stamatelakis (see Proc. ICC'98, p.537-43, 1998), have great potential in link restoration in IP networks in the event of single link failure. However, previously published schemes for computing p-cycles are time consuming and do not guarantee protection against every cycle-protectible working link. We say a working link connecting nodes u and v is cycle-protectible if there exists a simple cycle of spare links that contains both u and v. We present an efficient algorithm for constructing cycles made of spare links such that every cycle-protectible working link is protected by one of the cycles. For a network with n nodes and m spans, our algorithm runs in O(n/spl middot/(n+m)) time to construct O(m) cycles and to associate each working link to one of the cycles. We then extend our scheme to provide protection for every protectible working link, where a working link connecting nodes u and v is protectible if there exists a u-v path of spare links that does not use the span between u and v. To the best of our knowledge, our scheme is the first that guarantees protection of every cycle-protectible working link. The previous best algorithm requires O(nm/sup 3/) time for computing a single p-cycle, which is a factor of O(m/sup 2/) higher than the time complexity of our algorithm for computing all O(m) p-cycles.