# Disaster-Resilient Optical Network Survivability: A Comprehensive Survey
## 3 Disaster-Based Correlated Cascading Failures
This algorithm propelled a directing strategy that provably coordinates with the upper bound for a network. Most of the studies addressed the catastrophic consequences and critical conditions of correlated cascading disruptions. It is essential to have the knowledge of propagation of failures in time and space and the velocity at which failures propagate. Typically, cascading failures propagate with constant velocity from the center of the initial failure. In Reference [65], [PERSON] et al. studied the propagation behavior of cascading failures on spatially embedded networks, and proposed a theoretical framework to predict propagation velocity. The cross-layer reliability of optical networks has also become an issue of great interest. For example, IP-over-WDM networks comprise the upper IP-logical layer and the lower WDM-physical layer. Link establishment at logical layer correspondingly maps on the path connecting the source-destination pair in the physical layer, such that the logical connection remains established even when physical link fails. [PERSON] et al. [66] formulated an MILP to assist survivable routing constrained by at least one of the four cross-layer metrics: (1) Newly added logical links to be minimized, (2) maximization of capacity, or (3) connectivity of logical topology after physical link failure, or (4) minimum cross-layer cut to be maximized. Similarly, an ILP formulation is presented in Reference [67] for the joint multi-layer survivability problem. [PERSON] et al. proposed a proactive restoration scheme for IP-over-EON (Elastic Optical Network) to solve the problem of single optical link failure and/or IP node failure. [PERSON] et al. [68] proposed a three-fold solution to prevent and recover the connections from disaster failures considering a probabilistic risk model. A metric penalty based on SLA introduced to analyze the disaster-risk-aware provisioning through an ILP formulation. Through reactive traffic engineering solution, disrupted connections and connections under risk of correlated cascading failures are re-provisioned. Disaster impacts and their cascading failures are estimated for specific events of earthquakes, hurricanes, etc. that are occurring in geo-collocated regions. Attacking the physical layer can cause serious service degradation, loss of data, and revenue. Several physical layer attack methods and optical layer security breaches have been documented in Reference [69; 70; 71; 72; 73; 74]. Commonly, link-disjoint primary and backup paths have been proposed in the conventional survivability techniques for construction level failures (misconfiguration, hardware failure, ill maintenance, power failures etc.) that do not consider such scenarios. [PERSON] et al. [75] introduced a dedicated path protection scheme considering the concept of attack group that helps to established attack-aware disjoint primary and backup paths. Routing and wavelength assignment were handled by a 2-step ILP formulation. Weapon of Mass Destruction (WMD) attacks can also lead to multiple correlated cascading failures. [PERSON], in his technical report [76], analyzed the existing approaches and developed several novel techniques for the protection of telecom networks and other critical infrastructures against WMD attacks. The primary focus of this report was to prepare the network by considering the risks of WMD attacks in different parts of the infrastructure and recover from them. The techniques applied to mitigate the impacts of the manifold and cascading disruptions were persuaded by large-scale attacks. [PERSON] explored the conceivable target zones in the network, risk-aware routing to decline network failure in case of a WMD assault, multi-path provisioning to give partial protection when there is not sufficient capacity after a WMD-assault, the nature of cascading failures initiated by a WMD attack, and techniques to provide protection in the upper network layers. Additionally, proposed the protection schemes for WMD survivability in cloud networks.