Survivability schemes for optical backbone and access networks
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Network survivability, reflecting the ability of a network to maintain an acceptable level of service during and after failures, is an important requirement for WDM optical networks due to the ultra-high capacity. The most common network failure is the link failure which could cause enormous data loss and lots of service disruption to Internet users. Although single-link failures are the most common failure scenarios, double-link failures can occur in some cases and cause more severe problem. Compared to unicast sessions, multicast sessions suffer more seriously from link failures because a link may carry traffic to multiple destinations rather than to a single destination. Hence, multicast sessions demand more effective and efficient protection against link failures. With the increasing demand for access bandwidth, the access networks draw more attention. The hybrid wireless-optical broadband-access network (WOBAN) is a promising architecture for future access networks because it combines the high capacity of optical communication and the flexibility and cost-effectiveness of a wireless network.
First, we consider the problem of protecting unicast connections against double link failures. The basic idea is to use two p-Cycles, with link-disjoint protection segments, to protect each working link. To utilize spare capacity more efficiently, we also propose a new hybrid protection/restoration scheme to handle two-link failures. Our scheme uses protection to ensure that most of the affected demands can be restored using the pre-planned backup paths upon a two-link failure. For the demands not restorable with protection, we use dynamic restoration to find new backup paths for them.
Second, we propose protection schemes for multicast sessions under one link failure. An intelligent p-Cycle (IpC) scheme is presented to provide p-Cycle protection for dynamic multicast sessions. When a multicast request arrives, a multicast tree is computed for it and then the IpC scheme is used to compute a set of high efficient p-Cycles on-demand to protect each link on the multicast tree. Then we propose a p-cycle-based path protection scheme and a PXT-based path protection scheme to provide protection for dynamic multicast sessions. Basically, to protect a multicast tree, we compute one p-Cycle and one PXT for each destination node v such that the p-Cycle and the PXT can be used to restore the traffic to v when a link failure occurs on the path from the source node to v.
Finally, we propose a new protection scheme for the hybrid wireless-optical broadband-access network(WOBAN). The scheme is cost-effective in that it does not require the PONs to have self-protecting capability. Based on the proposed protection scheme, we define the maximum protection with minimum cost(MPMC) problem and present one ILP solution approach to the MPMC problem. Then we prove the MPMC problem is NP-Hard and provide one heuristic algorithm for the MPMC problem.