**4. Conclusion**

142 Optical Communications Systems

path. Protection can be dedicated, where each backup path has its own dedicated resources, or shared, where resource sharing among backup paths of link-disjoint working paths is allowed. After finding a backup path for the affected connections, transmission will resume. Finding the exact location of the attack and disabling the attacker before re-establishing transmission of affected connections is crucial for this step. If these conditions are not met, protection resources may be wasted and switching the transmission to backup paths may even enhance attack propagation and worsen its

A standardized approach for attack management has not yet been established. The main reason for this is the fact that optical monitoring technology hasn't yet reached its maturity and cannot provide reliable attack detection (Rejeb et al., 2006b), as well as the fact that the fault and localization methods design highly depends on the specific physical layer details (Rejeb et al., 2006a). Several frameworks for managing physical-layer attacks have been proposed in the literature. Reliable attack detection in some of them is based on the currently unrealistic assumption that all nodes are able to provide per channel monitoring, while others propose efficient monitoring placement policies, matching more realistic

Initial works on attack source identification date from the late 90's. In (Bergman et al., 1998), the authors propose a distributed algorithm for localizing jamming attacks based on the relation between the signal power metrics at the output and input of each node. Neighboring nodes exchange messages and determine the presence of an attack. The nodes are aware of their positions along every connection (i.e., whether they are upstream or downstream from the neighboring node they exchange messages with) so the algorithm is able to find the most upstream node which detects an attack along a connection, and thus

In the next decade, (Wu & Somani, 2005) provide a model of jamming attacks exploiting intrachannel crosstalk in optical switches with propagation capabilities, which enable affected lightpaths to acquire attacking capabilities and spread the attack to lightpaths which do not share any common physical components with the original attacker. They identify the assumption of all nodes being able to monitor all channels as unrealistic due to the high costs of this solution and propose a monitoring node model, their sparse placement, an additional test connection setup policy and a lightpath routing policy which

In (Mas et al., 2005), the problem of finding the exact location of the failure is extended to the presence of single and multiple failures in cases where alarms can be false and/or lost. This problem is NP-complete even when no false or lost alarms exist. The algorithm is based on building a binary tree whose branches correspond to sets of network elements which will raise an alarm when a particular network component fails. Alarms differ according to the type of the failure and equipment used. When alarms are raised during network operation, the location of the failure is determined by traversing the binary tree and finding the components whose corresponding failures justify the received alarms. The authors also propose an optimal monitoring placement scheme for minimizing the number of network elements which are candidates to have a failure and, thus, minimizing the result given by

is able to localize the source of a single crosstalk attack in the network.

effects.

network scenarios.

can identify the source of the attack.

the failure location algorithm.

This chapter presents an overview of the vulnerabilities of Transparent Optical Networks (TONs) to various physical-layer attacks. Furthermore, methods for attack detection and localization, as well as various countermeasures against attacks are described. As a result of the vulnerabilities associated with TONs stemming from optical components, transparency and high speed, new approaches to network security are increasingly needed as networks migrate to all-optical transmission. Such security frameworks require new, tailored attack detection, localization and network restoration mechanisms. In addition to upgrading existing ways of dealing with network failures and attacks, significant attention should be paid to prevention mechanisms, attack-aware planning and improved optical monitoring methods.
