Modified Generalized Loopback techniques

We consider different approaches to achieve survivability in optical Wavelength Division Multiplexing (WDM) metropolitan area networks (MANs), where network topology needs to alter according to frequently changing demands, only protection switching methods are suitable that can easily adapt to changes in the network. Additionally, the survivability method should be efficient in terms of the use of network resources, and must be fast in recovery speed. Considering networks with wavelength converters, we propose two new techniques for such failure recovery in the networks: Modified Generalized Loopback method A, and method B. In method A, primary and backup paths share the same pair of fibers. Method A is suitable for networks with low link utilization. The excess capacity on the same fiber pair is used for protection. We show that our method (A), by eliminating the need for a separate pair of protection fibers, has considerable better resource utilization compared with the old generalized loopback method. Method B should be considered for networks with high link utilization. In this method, like the old generalized loopback method, an extra pair of fibers is used for protection (conjugate digraph). However, in our method B, we allow protection links use the main digraph as well, if backup links cannot be routed on the conjugated (backup) digraph due to too many simultaneous failures. We consider the recovery from multiple failures under modified generalized technique method B and will compare it with the old generalized loopback method.