Abstract-Recent natural disasters have revealed that emergency networks presently cannot disseminate the necessary disaster information, making it difficult to deploy and coordinate relief operations. These disasters have reinforced the knowledge that telecommunication networks constitute a critical infrastructure of our society, and the urgency in establishing protection mechanisms against disaster-based disruptions.Hence, it is important to have emergency networks able to maintain sustainable communication in disaster areas. Moreover, the network architecture should be designed so that network connectivity is maintained among nodes outside of the impacted area, while ensuring that services for costumers not in the affected area suffer minimal impact.As a first step towards achieving disaster resilience, the RE-CODIS project was formed, and its Working Group 1 members conducted a comprehensive literature survey on "strategies for communication networks to protect against large-scale natural disasters," which is summarized in this article.Index Terms-vulnerability, end-to-end resilience, natural disasters, disaster-based disruptions.

Telecommunications networks need to guarantee that all node pairs involved in critical service communications are highly available. Here we adopt a novel approach to the problem of how to provide high levels of availability in an efficient manner. The basic idea is to embed at the physical layer a high availability set of links and nodes (termed the spine) in the network topology to support protection and routing in providing end-to-end availability. We first explore the spine concept through simple topologies illustrating the potential benefits of the approach in improving the overall network availability and the capability to support quality of resilience classes. Then, we study how the structural properties of a network topology can be used to determine heuristics to select a suitable spine and compare this with the case where all network components have the same availability. This is followed by a numerical based study comparing the heuristics with all possible spanning tree based spines for sample topologies. Our results demonstrate how to best design a physical network to support protection methods in achieving high levels of availability efficiently.

The problem of how to provide, in a cost efficient manner, high levels of availability and service differentiation in communication networks was investigated in [1-3]. The strategy adopted was to embed in the physical layer topology a high availability set of links and nodes (termed the spine). The spine enables through protection, routing and cross layer mapping, the provisioning of differentiated classes of resilience with varying levels of endto-end availability. Here we present an optimization model formulation of the spine design problem, considering link availability and the cost of upgrading link availability. The design problem seeks to minimize the cost while attaining a desired target flow availability. Extensive numerical results illustrate the benefits of modifying the availability of a subset of links of the network to implement quality of resilience classes.

Disaster-based failures can seriously disrupt any communication network, making its services unavailable. Such disruptions may be caused by natural disasters, technology-related failures, or malicious attacks, and they are observably increasing in number, intensity and scale. When network services that are a part of critical infrastructure become unavailable, commercial and/or societal problems are inevitable. The issue of limiting the impact of disaster-based failures needs to be urgently addressed due to the lack of suitable mechanisms deployed in the current networks.The COST CA15127 (RECODIS) Action will fill this gap by developing appropriate solutions to provide cost-efficient resilient communications in the presence of disaster-based disruptions considering both existing and emerging communication network architectures. It will be driven by researchers from academia and industry in strong cooperation with governmental bodies.In this paper, we highlight the objectives of RECODIS, its structure, as well as planned outcomes.

Wide area backbone communication networks are subject to a variety of hazards that can result in network component failures. Hazards such as power failures and storms can lead to geographical correlated failures. Recently there has been increasing interest in determining the ability of networks to survive geographic correlated failures and a number of measures to quantify the effects of failures have appeared in the literature. This paper proposes a the use of weighted spectrum to evaluate network survivability regarding geographic correlated failures. Further we conduct a comparative analysis by finding the most vulnerable geographic cuts or nodes in the network though solving an optimization problem to determine the cut with the largest impact for a number of measures in the literature as well as weighted spectrum. Numerical results on several sample network topologies show that the worst-case geographic cuts depend on the measure used in an unweighted or weighted graph. The proposed weighted spectrum measure is shown to be more versatile than other measures in both unweighted and weighted graphs.

The problem of disaster resilience is of paramount importance in today's telecommunication networks. Here, this problem is tackled by considering 1+1 optical lightpath protection with maximally SRLG-disjoint paths and geodiversity in a transparent backbone network. Geodiversity was added to make the network more resilient to geographically correlated disasters. The aim is to estimate the increase of the path lengths (fibre lengths) and the increase in cost of the required transponders, with respect to simple link disjointness (no-SRLG nor geodiversity constraints) in a fully transparent optical network. The results obtained in a realistic test network show that SRLG-disjointness already ensures an acceptable geodiversity for the considered network.

In Software Defined Networking (SDN), the controller locations are mainly constrained by delays between switches and controllers, and between the controllers themselves. In addition to the delay requirements, the availability of the connections between switches and controllers is also a key issue for control plane performance.Here, we explore the idea of having a spanning tree substructure called the spine, * This work was partially supported by Fundação para a Ciência e a Tecnologia (FCT) under project grant UIDB/00308/2020 and was financially supported by FEDER Funds and National Funds through FCT under project CENTRO-01-0145-FEDER-029312.

The problem of calculating the shortest path that visits a given set of nodes is at least as difficult as the traveling salesman problem, and it has not received much attention. Nevertheless an efficient integer linear programming (ILP) formulation has been recently proposed for this problem. That ILP formulation is firstly adapted to include the constraint that the obtained path can be protected by a node-disjoint path, and secondly to obtain a pair of node disjoint paths, of minimal total additive cost, each having to visit a given set of specified nodes. Computational experiments show that these approaches, namely in large networks, may fail to obtain solutions in a reasonable amount of time. Therefore heuristics are proposed for solving those problems, that may arise due to network management constraints. Extensive computational results show that they are capable of finding a solution in most cases, and that the calculated solutions present an acceptable relative error regarding the cost of the obtained path or pair of paths. Further the CPU time required by the heuristics is significantly smaller than the required by the used ILP solver.