An efficient fault restoration framework is proposed for accomplishing loopback recovery in optical networks. The proposed  p -cycle-based framework achieves both a minimal spare capacity requirement and a rapid restoration time. In the proposed approach, an algorithm designated as Star-Block is used to simplify the original topology to a 2-connected graph and to partition the graph into multiple blocks, where each block contains a center node and the minimum number of neighboring nodes that collectively form a complete cycle. The simplified graph is then restored to the original topology using conventional graph rules. The Block Selection algorithm is then used to assign the edges belonging to multiple blocks to an appropriate block for fault recovery purposes. Within each block, the working flows are restored in real-time via local  p -cycles on the on-cycle and spoke fibers. The performance of the proposed protection framework is evaluated numerically in terms of the spare capacity to working capacity ratio and the length of the restoration path. The framework has a better spare capacity efficiency than existing loopback recovery schemes or the conventional  p -cycles approach. In addition, the Star-Block decomposition algorithm shortens the average length of the restoration path and therefore reduces the restoration time. Finally, the protection scheme not only provides a differentiated recovery service for traffic with different QoS requirements in the event of single-link failures within a single block, but also supports multiple-fault restoration for the case in which multiple single-link failures occur simultaneously.
['Jung-Shian Li', 'Ching-Fang Yang', 'Jian-Hong Chen']
Star-block design in two-level survivable optical networks