Capacity versus robustness: A tradeoff for link restoration in mesh networks

Link recovery in high-speed four-fiber networks can be achieved using dynam ic searches, covers of rings, or generalized loopback, We present a method to provide link recovery for all links in a network without using all links for backup traffic transmission. The method extends generalized loopback t o operate on a subgraph of the full backup graph. The backup capacity on su ch links can then be used to carry unprotected traffic, i.e,, traffic that is not recovered in case of a failure, while primary fibers on the links re tain failure protection. Although all primary fibers remain fully robust to single-link failures, reserving links for unprotected traffic reduces a ne twork's ability to recover from multiple failures. We explore the tradeoff between capacity and robustness to two-link failures for several typical hi gh-speed optical fiber networks, comparing the properties of three fink-res toration algorithms based on generalized loopback with the properties of co vers of rings. Our results demonstrate robustness comparable or superior to that available with revers of rings while providing an additional unprotec ted traffic capacity of roughly 20% of the network's primary capacity.