Abstract
Due to the huge volume of the carried data in all optical networks, the ability of these networks to cope with failures becomes crucial. One of the proposed mechanism is the protection of the routes (lightpaths and light trees) with the help of precomputed ans reserved backup routes permitting to rapidly change the routes in the case of failures. The protection with p-cycles is an efficient method, which was originally proposed to protect on-cycle and straddling links. Recently the cyclic protection was extended to protect nodes in lightpaths and in light trees. As light trees can contain some branching nodes where the incoming light is spitted to several outgoing sub trees, the protection of these kind of trees is more delicate. In opaque networks where the switches may be virtual sources, efficient cycle-based protection schemes can be computed since each node can be the source of newly inserted light branches on an arbitrary precomputed cycle. Contrarily, with the apparition of optical switches and all optical solutions in core networks, the protection scheme should correspond to stringent optical constraints. Namely, the branching nodes of a protection scheme must correspond to available splitters. That is, the protection of multicast trees is limited in all optical domains. Our paper aims with the formulation of the potential protection possibilities and give the conditions to apply NEPC based protection.