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The problem of fault localization in all-optical networks is considered here. The concept of monitoring cycles (MCs) and monitoring paths (MPs) are introduced for the purpose of unique identification of single-link failures. MCs and MPs pass through one or more monitoring locations. These monitoring locations are constructed such that any single-link failure results in the failure of a unique combination of MCs and MPs that pass through the monitoring location. three-edge connectivity is a necessary and sufficient condition for constructing MCs in the case of network with only one monitoring location. heuristic approaches for constructing MCs in the presence of one or more monitoring locations is developed and the problem of constructing MCs as an integer linear program (ILP) is formulated. a fault localization technique that uses both MPs and MCs and that employs multiple monitoring locations is described for an arbitrary network. a linear-time algorithm to compute the minimum number of required monitoring locations is also provided and the effectiveness of these techniques can be studied by simulation.

Achieving fast and precise failure localization has been a highly desired feature in all-optical mesh networks.M-trail (monitoring trail) has been proposed as the most general monitoring structure for achieving unambiguous failure localization of any single page link failure.

INTRODUCTION
Due to the lack of optoelectronic regenerators, the impact of a failure propagates without electronic boundary, and a single failure can trigger a large number of redundant alarms. One of the most commonly adopted approaches is to deploy optical monitors
responsible for generating alarms when a failure is detected.Conventional link-based monitoring scheme requires one monitor at each link. Monitoring-Trail (m-trail) along with an Integer Linear Program (ILP) for m-trail design, which was proved to yield better performance.

Briefs on Monitoring Trails (M-Trails)
an m-trail can traverse a node multiple times but a page link at most once.By allocating a sufficient number of m-trails, a routing entity in the network can localize a single failure by collecting the alarm signals of the monitors of m-trails.

Deployment of M-Trails
the target of m-trail design is to minimize the linear combination of monitoring cost and bandwidth cost. Total Cost = monitoring cost + bandwidth cost

Network Topology Diversity
m-trail solutions are affected by network topologies.

ALGORITHM FOR M-TRAIL SOLUTION
The proposed algorithm takes advantage of random code assignment (RCA) and random code swapping (RCS), aiming to overcome the topology diversity in general topologies.unique alarm codes are randomly assigned to each page link one after the other. Then m-trail formation is done by examining the connectivity of the links in each page link set. To improve the solution quality, RCS is performed to update the ACT for each page link set round by round.
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