A survey of strategies for communication networks to protect against large-scale natural disasters
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paper_title: Disaster survivability in optical communication networks

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With the frequent occurrences of natural disasters damaging large portions of communication networks and the rising risk of intentional attacks, network vulnerability to multiple cascading, correlated, and collocated failures has become a major concern. Optical backbone networks provide highly-scalable connectivity across large distances. These networks exploit optical technology to carry huge aggregated data and can support ''higher-layer'' networks, such as SONET, Ethernet, IP, MPLS, ATM, etc. Given the high complexity and scale of backbone networks, multiple correlated failures can have a devastating impact on topological connectivity, which in turn can cause widespread ''end-to-end'' connection-level disruptions. These outages may affect many applications/services supported by the optical layer, irrespective of the importance of the service and/or sensitivity of the carried data. Hence, it is crucial to understand the vulnerability of optical backbone networks to disasters and design appropriate countermeasures. In this paper, we present a general classification of the existing research works on disaster survivability in optical networks and a survey on relevant works based on that classification. We also classify disasters based on their characteristics and impact on communication networks and discuss different ways to combat them. We conclude the paper with open issues and challenges.
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paper_title: Analysing GeoPath diversity and improving routing performance in optical networks

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With the increasing frequency of natural disasters and intentional attacks that challenge telecommunication networks, vulnerability to cascading and regional-correlated challenges is escalating. Given the high complexity and large traffic load of optical networks, these correlated challenges cause substantial damage to reliable network communication. In this paper, we propose a network vulnerability identification mechanism and study different vulnerability scales using real-world optical network data. We further propose geographical diversity and incorporate it into a new graph resilience metric cTGGD (compensated Total Geographical Graph Diversity), which is capable of characterising and differentiating resiliency levels among different optical fibre networks. It is shown to be an effective resilience level indicator under regional network challenges or attacks. We further propose two heuristics for solving the path geodiverse problem (PGD) in which the calculation of a number of geographically separated paths is required. Geodiverse paths can be used to circumvent physical challenges such as large-scale disasters in telecommunication networks. We present the GeoDivRP routing protocol with two new routing heuristics implemented, which provides the end nodes with multiple geographically diverse paths. Our protocol demonstrates better performance compared to OSPF when the network is subject to area-based challenges. We have analysed the mechanism by which the attackers could use to maximise the attack impact with a limited budget and demonstrate the effectiveness of restoration plans.
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paper_title: An Overview of Algorithms for Network Survivability

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Network survivability--the ability to maintain operation when one or a few network components fail--is indispensable for present-day networks. In this paper, we characterize three main components in establishing network survivability for an existing network, namely, (1) determining network connectivity, (2) augmenting the network, and (3) finding disjoint paths. We present a concise overview of network survivability algorithms, where we focus on presenting a few polynomial-time algorithms that could be implemented by practitioners and give references to more involved algorithms.
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paper_title: Resilience and survivability in communication networks : Strategies , principles , and survey of disciplines

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The Internet has become essential to all aspects of modern life, and thus the consequences of network disruption have become increasingly severe. It is widely recognised that the Internet is not sufficiently resilient, survivable, and dependable, and that significant research, development, and engineering is necessary to improve the situation. This paper provides an architectural framework for resilience and survivability in communication networks and provides a survey of the disciplines that resilience encompasses, along with significant past failures of the network infrastructure. A resilience strategy is presented to defend against, detect, and remediate challenges, a set of principles for designing resilient networks is presented, and techniques are described to analyse network resilience.
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paper_title: Resilient Routing in Communication Networks

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Introduction Principles of Communication Networks Resilience Resilience of Future Internet Communications Resilience of Wireless Mesh Networks Disruption-tolerant Routing in Vehicular Ad-hoc Networks
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paper_title: A survey on rapidly deployable solutions for post-disaster networks

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In post-disaster scenarios, for example, after earthquakes or floods, the traditional communication infrastructure may be unavailable or seriously disrupted and overloaded. Therefore, rapidly deployable network solutions are needed to restore connectivity and provide assistance to users and first responders in the incident area. This work surveys the solutions proposed to address the deployment of a network without any a priori knowledge about the communication environment for critical communications. The design of such a network should also allow for quick, flexible, scalable, and resilient deployment with minimal human intervention.
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paper_title: Analyzing the Internet Stability in Presence of Disasters

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The Internet is now a critical infrastructure for the modern, information-based, e-Society. Stability and survivability of the Internet are thus important, especially in presence of catastrophic events which carry heavy societal and financial impacts. In this work, we analyze the stability of the inter-domain routing system during several large-scale catastrophic events that affected the connectivity of massive parts of the address space, with the objective of acquiring information about degradation of service and recovery capabilities.
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paper_title: Evaluation of network resilience, survivability, and disruption tolerance: analysis, topology generation, simulation, and experimentation

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As the Internet becomes increasingly important to all aspects of society, the consequences of disruption become increasingly severe. Thus it is critical to increase the resilience and survivability of future networks. We define resilience as the ability of the network to provide desired service even when challenged by attacks, large-scale disasters, and other failures. This paper describes a comprehensive methodology to evaluate network resilience using a combination of topology generation, analytical, simulation, and experimental emulation techniques with the goal of improving the resilience and survivability of the Future Internet.
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paper_title: Critical nodes for distance-based connectivity and related problems in graphs

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This study considers a class of critical node detection problems that involves minimization of a distance-based connectivity measure of a given unweighted graph via the removal of a subset of nodes referred to as critical nodes subject to a budgetary constraint. The distance-based connectivity measure of a graph is assumed to be a function of the actual pairwise distances between nodes in the remaining graph e.g., graph efficiency, Harary index, characteristic path length, residual closeness rather than simply whether nodes are connected or not, a typical assumption in the literature. We derive linear integer programming IP formulations, along with additional enhancements, aimed at improving the performance of standard solvers. For handling larger instances, we develop an effective exact algorithm that iteratively solves a series of simpler IPs to obtain an optimal solution for the original problem. The edge-weighted generalization is also considered, which results in some interesting implications for distance-based clique relaxations, namely, s-clubs. Finally, we conduct extensive computational experiments with real-world and randomly generated network instances under various settings that reveal interesting insights and demonstrate the advantages and limitations of the proposed approach. In particular, one important conclusion of our work is that vulnerability of real-world networks to targeted attacks can be significantly more pronounced than what can be estimated by centrality-based heuristic methods commonly used in the literature. © 2015 Wiley Periodicals, Inc. NETWORKS, Vol. 663, 170-195 2015
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paper_title: Resilience and survivability in communication networks : Strategies , principles , and survey of disciplines

paper_content:

The Internet has become essential to all aspects of modern life, and thus the consequences of network disruption have become increasingly severe. It is widely recognised that the Internet is not sufficiently resilient, survivable, and dependable, and that significant research, development, and engineering is necessary to improve the situation. This paper provides an architectural framework for resilience and survivability in communication networks and provides a survey of the disciplines that resilience encompasses, along with significant past failures of the network infrastructure. A resilience strategy is presented to defend against, detect, and remediate challenges, a set of principles for designing resilient networks is presented, and techniques are described to analyse network resilience.
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paper_title: Network under joint node and link attacks: vulnerability assessment methods and analysis

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Critical infrastructures such as communication networks, electrical grids, and transportation systems are highly vulnerable to natural disasters and malicious attacks. Even failures of few nodes or links may have a profound impact on large parts of the system. Traditionally, network vulnerability assessment methods separate the studies of node vulnerability and link vulnerability, and thus ignore joint node and link attack schemes that may cause grave damage to the network. To this end, we introduce a new assessment method, called $\beta$ -disruptor, that unifies both link and node vulnerability assessment. The new assessment method is formulated as an optimization problem in which we aim to identify a minimum-cost set of mixed links and nodes whose removal would severely disrupt the network connectivity. We prove the NP-completeness of the problem and propose an $O(\sqrt{\log n})$ bicriteria approximation algorithm for the $\beta$ -disruptor problem. This new theoretical guarantee improves the best approximation results for both link and node vulnerability assessment in literature. We further enhance the proposed algorithm by embedding it into a special combination of simulated annealing and variable neighborhood search method. The results of our extensive simulation-based experiments on synthetic and real networks show the feasibility and efficiency of our proposed vulnerability assessment methods.
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paper_title: On New Approaches of Assessing Network Vulnerability: Hardness and Approximation

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Society relies heavily on its networked physical infrastructure and information systems. Accurately assessing the vulnerability of these systems against disruptive events is vital for planning and risk management. Existing approaches to vulnerability assessments of large-scale systems mainly focus on investigating inhomogeneous properties of the underlying graph elements. These measures and the associated heuristic solutions are limited in evaluating the vulnerability of large-scale network topologies. Furthermore, these approaches often fail to provide performance guarantees of the proposed solutions. In this paper, we propose a vulnerability measure, pairwise connectivity, and use it to formulate network vulnerability assessment as a graph-theoretical optimization problem, referred to as β-disruptor. The objective is to identify the minimum set of critical network elements, namely nodes and edges, whose removal results in a specific degradation of the network global pairwise connectivity. We prove the NP-completeness and inapproximability of this problem and propose an O(log n log log n) pseudo-approximation algorithm to computing the set of critical nodes and an O(log1.5n) pseudo-approximation algorithm for computing the set of critical edges. The results of an extensive simulation-based experiment show the feasibility of our proposed vulnerability assessment framework and the efficiency of the proposed approximation algorithms in comparison to other approaches.
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paper_title: Exact identification of critical nodes in sparse networks via new compact formulations

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Critical node detection problems aim to optimally delete a subset of nodes in order to optimize or restrict a certain metric of network fragmentation. In this paper, we consider two network disruption metrics which have recently received substantial attention in the literature: the size of the remaining connected components and the total number of node pairs connected by a path. Exact solution methods known to date are based on linear 0–1 formulations with at least \(\varTheta (n^3)\) entities and allow one to solve these problems to optimality only in small sparse networks with up to 150 nodes. In this work, we develop more compact linear 0–1 formulations for the considered types of problems with \(\varTheta (n^2)\) entities. We also provide reformulations and valid inequalities that improve the performance of the developed models. Computational experiments show that the proposed formulations allow finding exact solutions to the considered problems for real-world sparse networks up to 10 times larger and with CPU time up to 1,000 times faster compared to previous studies.
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paper_title: Finding critical regions and region-disjoint paths in a network

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Due to their importance to society, communication networks should be built and operated to withstand failures. However, cost considerations make network providers less inclined to take robustness measures against failures that are unlikely to manifest, like several failures coinciding simultaneously in different geographic regions of their network. Considering networks embedded in a two-dimensional plane, we study the problem of finding a critical region—a part of the network that can be enclosed by a given elementary figure of predetermined size—whose destruction would lead to the highest network disruption. We determine that only a polynomial, in the input, number of nontrivial positions for such a figure needs to be considered and propose a corresponding polynomial-time algorithm. In addition, we consider region-aware network augmentation to decrease the impact of a regional failure. We subsequently address the region-disjoint paths problem, which asks for two paths with minimum total weight between a source $(s)$ and a destination $(d)$ that cannot both be cut by a single regional failure of diameter $D$ (unless that failure includes $s$ or $d$ ). We prove that deciding whether region-disjoint paths exist is NP-hard and propose a heuristic region-disjoint paths algorithm.
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paper_title: Measuring the survivability of networks to geographic correlated failures

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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 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 a weighted graph. The proposed weighted spectrum measure is shown to be more versatile than other measures in both unweighted and weighted graphs.
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paper_title: The resilience of WDM networks to probabilistic geographical failures

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Telecommunications networks, and in particular optical WDM networks, are vulnerable to large-scale failures of their physical infrastructure, resulting from physical attacks (such as an Electromagnetic Pulse attack) or natural disasters (such as solar flares, earthquakes, and floods). Such events happen at specific geographical locations and disrupt specific parts of the network but their effects are not deterministic. Therefore, we provide a unified framework to model the network vulnerability when the event has a probabilistic nature, defined by an arbitrary probability density function. Our framework captures scenarios with a number of simultaneous attacks, in which network components consist of several dependent subcomponents, and in which either a 1+1 or a 1∶1 protection plan is in place. We use computational geometric tools to provide efficient algorithms to identify vulnerable points within the network under various metrics. Then, we obtain numerical results for specific backbone networks, thereby demonstrating the applicability of our algorithms to real-world scenarios. Our novel approach allows for identifying locations which require additional protection efforts (e.g., equipment shielding). Overall, the paper demonstrates that using computational geometric techniques can significantly contribute to our understanding of network resilience.
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paper_title: Detection of spatially-close fiber segments in optical networks

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Spatially-close network fibers have a significant chance of failing simultaneously in the event of man-made or natural disasters within their geographic area. Network operators are interested in the proper detection and grouping of any existing spatially-close fiber segments, to avoid service disruptions due to simultaneous fiber failures. Moreover, spatially-close fibers can further be differentiated by computing the intervals over which they are spatially close. In this paper, we propose (1) polynomial-time algorithms for detecting all the spatially-close fiber segments of different fibers, (2) a polynomial-time algorithm for finding the spatially-close intervals of a fiber to a set of other fibers, and (3) a fast exact algorithm for grouping spatially-close fibers using the minimum number of distinct risk groups. All of our algorithms have a fast running time when simulated on three real-world network topologies.
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paper_title: Finding geographic vulnerabilities in multilayer networks using reduced network state enumeration

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Despite advancements in the analysis of networks with respect to geographic vulnerabilities, very few approaches exist that can be applied to large networks with varied applications and network measures. Natural and man-made disasters as well as major political events (like riots) have kept the challenges of geographic failures in networks in the forefront. With the increasing interest in multilayer and virtual networks, methods to analyze these networks for geographic vulnerabilities are important. In this paper, we present a state space analysis method that analyzes multilayer networks for geographic vulnerabilities. It uses either the inability to provision an upper layer service and/or increased costs to provision as the criteria for network failure. Mapping techniques for multilayer network states are presented. Simplifying geographic state mapping techniques to reduce enumeration costs are also presented and tested. Finally, these techniques are tested on small and extremely large networks.
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paper_title: Assessing the impact of geographically correlated network failures

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Communication networks are vulnerable to natural disasters, such as earthquakes or floods, as well as to human attacks, such as an electromagnetic pulse (EMP) attack. Such real-world events have geographical locations, and therefore, the geographical structure of the network graph affects the impact of these events. In this paper we focus on assessing the vulnerability of (geographical) networks to such disasters. In particular, we aim to identify the location of a disaster that would have the maximum effect on network capacity. We consider a geometric graph model in which nodes and links are geographically located on a plane. Specifically, we model the physical network as a bipartite graph (in the topological and geographical sense) and consider the set of all vertical line segment cuts. For that model, we develop a polynomial time algorithm for finding a worst possible cut. Our approach has the potential to be extended to general graphs and provides a promising new direction for network design to avert geographical disasters or attacks.
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paper_title: Determining Geographic Vulnerabilities Using a Novel Impact Based Resilience Metric

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Various natural and man-made disasters as well as major political events (like riots) have increased the importance of understanding geographic failures and how correlated failures impact networks. Since mission critical networks are overlaid as virtual networks over a physical network infrastructure forming multilayer networks, there is an increasing need for methods to analyze multilayer networks for geographic vulnerabilities. In this paper, we present a novel impact-based resilience metric. Our new metric uses ideas borrowed from performability to combine network impact with state probability to calculate a new metric called Network Impact Resilience. The idea is that the highest impact to the mission of a network should drive its resilience metric. Furthermore, we present a state space analysis method that analyzes multilayer networks for geographic vulnerabilities. To demonstrate the methods, the inability to provision a given number of upper layer services is used as the criteria for network failure. Mapping techniques for multilayer network states are presented. Simplifying geographic state mapping techniques to reduce enumeration costs are also presented and tested. Finally, these techniques are tested on networks of varying sizes.
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paper_title: Assessing the Vulnerability of the Fiber Infrastructure to Disasters

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Communication networks are vulnerable to natural disasters, such as earthquakes or floods, as well as to physical attacks, such as an Electromagnetic Pulse (EMP) attack. Such real- world events happen in specific geographical locations and disrupt specific parts of the network. Therefore, the geographical layout of the network determines the impact of such events on the network's connectivity. In this paper, we focus on assessing the vulnerability of (geographical) networks to such disasters. In particular, we aim to identify the most vulnerable parts of the network. That is, the locations of disasters that would have the maximum disruptive effect on the network in terms of capacity and connectivity. We consider graph models in which nodes and links are geographically located on a plane, and model the disaster event as a line segment or a circular cut. We develop algorithms that find a worst- case line segment cut and a worst-case circular cut. Then, we obtain numerical results for a specific backbone network, thereby demonstrating the applicability of our algorithms to real-world networks. Our novel approach provides a promising new direction for network design to avert geographical disasters or attacks.
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paper_title: Spatiotemporal risk-averse routing

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A cyber-physical system is often designed as a network in which critical information is transmitted. However, network links may fail, possibly as the result of a disaster. Disasters tend to display spatiotemporal characteristics, and consequently link availabilities may vary in time. Yet, the requested connection availability of traffic must be satisfied at all times, even under disasters. In this paper, we argue that often the spatiotemporal impact of disasters can be predicted, such that suitable actions can be taken, before the disaster manifests, to ensure the availability of connections. Our main contributions are three-fold: (1) we propose a generic grid-based model to represent the risk profile of a network area and relate the risk profile to the availability of links and connections, (2) we propose a polynomial-time algorithm to identify connections that are vulnerable to an emerging disaster risk, and (3) we consider the predicted spatiotemporal disaster impact, and propose a polynomial-time algorithm based on an auxiliary graph to find the most risk-averse path under a time constraint.
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paper_title: Gust buffeting and aeroelastic behaviour of poles and monotubular towers

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Abstract The evolution in the constructional field and the realization of ever more slender and light structures have emphasized the increasing difficulty of properly evaluating the actions and effects of wind on poles and monotubular towers. Faced with this situation the Italian constructors, united in a consortium coordinated by ACS ACAI Servizi, entrusted the Department of Structural and Geotechnical Engineering of Genova University with the task of formulating an ad hoc calculation procedure for this type of structure. This gave rise to a wide-ranging research project in which theoretical models, experimental evaluations and engineering methods were developed in parallel through an effective and quite a unique co-operation between researchers, designers and builders. This paper illustrates the physical aspects, the general principles and the basic formulation of the method proposed, with special emphasis on gust buffeting and aeroelastic phenomena. Preliminary results of full-scale measurements of the structural damping are also presented. The conclusions highlight the scientific and technical perspectives of this research.
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paper_title: Telecommunications Power Plant Damage Assessment for Hurricane Katrina– Site Survey and Follow-Up Results

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This paper extends knowledge of disaster impact on the telecommunications power infrastructure by discussing the effects of Hurricane Katrina based on an on-site survey conducted in October 2005 and on public sources. It includes observations about power infrastructure damage in wire-line and wireless networks. In general, the impact on centralized network elements was more severe than on the distributed portion of the grids. The main cause of outage was lack of power due to fuel supply disruptions, flooding and security issues. This work also describes the means used to restore telecommunications services and proposes ways to improve logistics, such as coordinating portable generator set deployment among different network operators and reducing genset fuel consumption by installing permanent photovoltaic systems at sites where long electric outages are likely. One long term solution is to use of distributed generation. It also discusses the consequences on telecom power technology and practices since the storm.
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paper_title: Masts and Towers

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The analysis and design of masts and towers requires special knowledge and experience, especially when it concerns guyed masts. The special problems related to these structures are underlined by the many collapses during the years. The basis of design for such antenna supporting structures are sometimes many and often mutual contradictory, and the overall structural layout may have a dramatically effect on the loading on the structure. The loads are mainly meteorological from wind and ice and combination of these, and the dynamic nature of the wind has to be taken into account as masts and towers are more or less sensitive to dynamic loads. This paper gives a brief introduction to the problems related to the design, as well as several practical examples are mentioned. The aesthetic elements are becoming more and more important for antenna supporting structures and are also mentioned. The IASS Working Group No. 4 Masts and Towers is the only international forum for the exchange of knowledge and experience within the field of masts and towers, and this Working group is briefly mentioned in the paper.
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paper_title: Dynamic monitoring and numerical modelling of communication towers with FBG based accelerometers

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Abstract This study presents the dynamic monitoring of two telecommunication tall slender steel towers with an optical FBG accelerometer. Numerical simulation for both towers was used recurring to finite elements modelling in order to demonstrate the feasibility of using optical technology in this type of structural monitoring. The results show a good agreement between experimental and simulated data, demonstrating that the optical accelerometer can be a very useful tool in the monitoring of tall slender structures.
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paper_title: The past 20 years of telecommunication structures in Portugal

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Abstract This paper reviews the analysis and design of telecommunication structures and presents the main problems observed for various types of structures. The nation of Portugal is selected for a case study, and more specifically, the evolution of Portuguese structural design standards for telecommunications systems is summarised using comparative analyses that cover a subset of the most relevant topics for design, including wind profiles, drag coefficients, dynamic effects and reliability classes. These analyses focus on characterisation of the effects of wind action, which plays a fundamental role in the behaviour and design of these structures. Following the comparative analyses of standards, the more common problems observed over the past 20 years in guyed masts and towers located in Portugal are presented and discussed.
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paper_title: Telecom power planning for natural and man-made disasters

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This paper discusses a planning framework to reduce telecommunication network power supply vulnerability during natural and man-made disasters. The analysis proposes a three-part structure for a plan. The first part is an assessment of risk. Risk assessment involves identifying potential disasters at each site as well as evaluating the probability of occurrence and its impact. Impact evaluation focuses on electric grid, roads, and natural gas distribution infrastructure. The second part is an evaluation of resources and logistics. Use of alternative technologies to diversify energy supply, such as distributed generation power units, is discussed. The last part of the plan is its execution. The importance of record keeping and control of the plan outcome during this phase is emphasized, as well as conducting periodic drills to test and improve the plan.
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paper_title: STEM-NET: How to Deploy a Self-Organizing Network of Mobile End-User Devices for Emergency CommunicationComputer Communications

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Spontaneous wireless networks constructed out of mobile end-user devices (e.g. smartphones or tablets) are currently receiving considerable interest as they enable a wide range of novel, highly pervasive and user-centric network services and applications. In this paper, we focus on emergency-related scenarios, and we investigate the potential of spontaneous networks for providing Internet connectivity over the emergency area through the sharing of resources owned by the end-user devices. Novel and extremely flexible network deployment strategies are required in order to cope with the user mobility, the limited communication capabilities of wireless devices, and the intrinsic dynamics of traffic loads and QoS requirements. To this purpose, we propose here a novel approach toward the deployment of spontaneous networks composed by a new generation of wireless devices - called Stem Nodes (SNs) - to emphasize their ability to cover multiple network roles (e.g. gateway, router). The self-organization of the spontaneous network is then achieved through the local reconfiguration of each SN. Two complementary research contributions are provided. First, we describe the software architecture of a SN (which can be implemented on top of existing end-user devices), and we detail how a SN can manage its role set, eventually extending it through cooperation with other SNs. Second, we propose distributed algorithms, based on swarm intelligence principles, through which each SN can autonomously select its role, and self-elect to gateway or router, so that end-to-end performance are maximized while the lifetime of the spontaneous emergency network is prolonged. The ability of the proposed algorithm to guarantee adaptive and self-organizing network behaviors is demonstrated through extensive Omnet++ simulations, and through a prototype implementation of the SN architecture on a real testbed.
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paper_title: Network adaptability from disaster disruptions and cascading failures

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Disasters can cause severe service disruptions due to large-scale correlated cascading failures in telecom networks. Major network disruptions due to disasters — both natural (e.g., Hurricane Sandy, 2011 Japan Tsunami) and human-made (e.g., 9/11 terrorist attack) — deprive the affected population of essential network services for weeks and severely hamper rescue operations. Many techniques exist to provide fast network protection, but they are optimized for limited faults without addressing the extent of disaster failures. Thus, there is a pressing need for novel robust survivability methods to mitigate the effects of disasters on telecom networks. While researchers in climatology, geology, and environmental science have been studying how to predict disasters and assess disaster risks for certain regions, networking research can exploit this information to develop novel methods to prepare networks to handle disasters with the knowledge of risky regions and to better prepare them for a predicted disaster. The events during the aftermath of a disaster should also be considered. For instance, methods to re-arrange network resources and services on a partially damaged network, which is the property of a self-organizing network, should be developed, and new algorithms to manage the post-disaster traffic deluge and to relieve the rescue operations after a disaster, with the knowledge of the post-disaster failures, should be investigated. Since cloud services today are an integral part of our society and massive amounts of content/services have been created and shared over the cloud, loss/disruption of critical content/ services caused by disasters can significantly affect the security and economic well being of our society. As the network is becoming increasingly an end-to-content (vs. end-toend) connection provider, we have to ensure reachability of content from any point of a network, which we call content connectivity (in contrast to network connectivity) after disaster failures. This article presents the nature of possible disruptions in telecom networks caused by disaster events, and sheds light on how to prepare the network and cloud services against disasters, and adapt them for disaster disruptions and cascading failures.
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paper_title: LTE-advanced based handover mechanism for natural disaster situations

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Telecommunication networks often face power outage problems in the natural disaster affected areas. Also, owing to a sudden substantial increase in network traffic loads the battery backup power of the base stations run out quickly and therefore hampering telecommunication services. To overcome this system performance issues, we propose a Long Term Evolution (LTE)-Advanced (LTE-A)-based user equipment (UE)-controlled and base station (Evolved Node B or eNB)-assisted handover scheme. The idea is to limit the arrival of new traffic to an already overloaded eNB by diverting their handover to lightly loaded nearby eNBs. The novelty of this work is the ability of an UE to self-detect the occurrence of a natural disaster and to self-select the most suitable target eNB (TeNB) to handover with in the disaster affected areas. The handover is performed by obtaining the weighted average score (WAS) of the direction of motion (DoM) and the leftover battery backup power of the different neighboring eNBs (NeNB). The UE also predicts its DoM and dynamically adjust the weights of the two parameters if it's a disaster situation. Preliminary simulation results show that the scheme can offer up to 65% handover success rate in disaster situations.
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paper_title: Proposal of disaster avoidance control

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This paper proposes the concept of disaster avoidance control for forecasted disasters. This control is used to relocate objects to avoid or minimize the damage from forecasted disasters. This paper also illustrates a system for implementing the control and discusses the metrics used in the control. An experimental system for executing this control is also described.
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paper_title: Improving the Resilience of Transport Networks to Large-scale Failures

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Telecommunication networks have to deal with fiber cuts, hardware malfunctioning and other failures on a daily basis, events which are usually treated as isolated and unrelated. Efficient methods have been developed for coping with such common failures and hence users rarely notice them. Although less frequently, there also arise cases of multiple failures with catastrophic consequences. Multiple failures can occur for many reasons, for example, natural disasters, epidemic outbreaks affecting software components, or intentional attacks. This article investigates new methods for lessening the impact of such failures in terms of the number of connections affected. Two heuristic-based link prioritization strategies for improving network resilience are proposed. One strategy is built upon the concept of betweenness centrality, while the second is based on what we call the observed link criticality. Both strategies are evaluated through simulation on a large synthetic topology that represents a GMPLS-based transport network. The provisioning of connections in a dynamic traffic scenario as well as the occurrence of large-scale failures are simulated for the evaluation.
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paper_title: Enhancing Network Robustness via Shielding

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We consider shielding critical links to enhance the robustness of a network, in which shielded links are resilient to failures. We first study the problem of increasing network connectivity by shielding links that belong to small cuts of a network, which improves the network reliability under random link failures. We then focus on the problem of shielding links to guarantee network connectivity under geographical and general failure models. We develop a mixed integer linear program (MILP) to obtain the minimum cost shielding to guarantee the connectivity of a single source–destination pair under a general failure model, and exploit geometric properties to decompose the shielding problem under a geographical failure model. We extend our MILP formulation to guarantee the connectivity of the entire network, and use Benders decomposition to significantly reduce the running time. We also apply simulated annealing to obtain near-optimal solutions in much shorter time. Finally, we extend the algorithms to guarantee partial network connectivity, and observe significant reduction in the shielding cost, especially when the geographical failure region is small.
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paper_title: Survivable virtual network mapping to provide content connectivity against double-link failures

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In recent years, large scale natural disasters (such as earthquakes, or tsunami) have caused multiple Internet outages in different parts of the world, resulting in high infrastructures damages and capacity losses. Content providers are currently investigating novel disaster-resiliency mechanisms to maintain the service continuity in their Content Delivery Networks (CDNs). In case of such widespread failures, the content providers might not be able to guarantee Network Connectivity (i.e., the reachability of all nodes from any node in the network) and researchers have started investigating the concept of Content Connectivity (i.e., the reachability of the content from any point of the network), that can be achieved even when the network is disconnected, as long as a replica of the content can be retrieved in all the disconnected components of the network. In this paper we focus on double-link failures and consider different combinations of content connectivity and network connectivity. As guaranteeing network connectivity against double-link failures may result in very high network-resource consumption, in this work we present an Integer Linear Programming (ILP) formulation for survivable virtual network mapping to guarantee the network connectivity after single-link failures and maintain the content connectivity after double-link failures. We show that maintaining content connectivity against double-link failures costs almost the same, in terms of network resources, as providing network connectivity against single-link failures. We also investigate the trade-off between datacenter placement and the amount of resources needed to provide content connectivity in case of double-link failures.
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paper_title: Fault-tolerant virtual network mapping to provide Content Connectivity in optical networks

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We define Content Connectivity as the reachability of every content from any point of an optical network. We propose a scheme for virtual network mapping and content placement to ensure content connectivity after failures.
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paper_title: New Options and Insights for Survivable Transport Networks

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This article is devoted to a selection of recent topics in survivable networking. New ideas in capacity design and ring-to-mesh evolution are given, as well as a systematic comparison of the capacity requirements of several mesh-based schemes showing how they perform over a range of network graph connectivity. The work provides new options and insights to address the following questions. How does one evolve from an existing ring-based network to a future mesh network? If the facilities graph is very sparse, how can mesh efficiency be much better than rings? How do the options for mesh protection or restoration rank in capacity requirements? How much is efficiency increased if we enrich our network connectivity? We also outline p-cycles, showing this new concept can realize ring-like speed with meshlike efficiency. The scope is limited to conveying basic ideas with an understanding that they could be further adapted for use in IP or DWDM layers with GMPLS-type protocols or a centralized control plane.
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paper_title: Analysis of and proposal for a disaster information network from experience of the Great East Japan Earthquake

paper_content:

Recently serious natural disasters such as earthquakes, tsunamis, typhoons, and hurricanes have occurred at many places around the world. The East Japan Great Earthquake on March 11, 2011 had more than 19,000 victims and destroyed a huge number of houses, buildings, loads, and seaports over the wide area of Northern Japan. Information networks and systems and electric power lines were also severely damaged by the great tsunami. Functions such as the highly developed information society, and residents' safety and trust were completely lost. Thus, through the lessons from this great earthquake, a more robust and resilient information network has become one of the significant subjects. In this article, our information network recovery activity in the aftermath of the East Japan Great Earthquake is described. Then the problems of current information network systems are analyzed to improve our disaster information network and system through our network recovery activity. Finally we suggest the systems and functions required for future large-scale disasters.
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paper_title: A survey on rapidly deployable solutions for post-disaster networks

paper_content:

In post-disaster scenarios, for example, after earthquakes or floods, the traditional communication infrastructure may be unavailable or seriously disrupted and overloaded. Therefore, rapidly deployable network solutions are needed to restore connectivity and provide assistance to users and first responders in the incident area. This work surveys the solutions proposed to address the deployment of a network without any a priori knowledge about the communication environment for critical communications. The design of such a network should also allow for quick, flexible, scalable, and resilient deployment with minimal human intervention.
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paper_title: Bringing movable and deployable networks to disaster areas: development and field test of MDRU

paper_content:

Communication demand is paramount for disaster-affected people to confirm safety, seek help, and gather evacuation information. However, the communication infrastructure is likely to be crippled due to a natural disaster, which makes disaster response excruciatingly difficult. Although traditional approaches can partially fulfill the most important requirements from the user perspective, including prompt deployment, high capacity, large coverage, useful disaster-time application, and carrier-free usability, a complete solution that provides all those features is still required. Our collaborative research and development group has developed the Movable and Deployable Resource Unit, which is referred to as the MDRU and has been proven to have all those required features. Via extensive field tests using a compact version of an MDRU (i.e., the van-type MDRU), we verify the effectiveness of the MDRU-based disaster recovery network. Moreover, we demonstrate the further improvement of the MDRU’s performance when it is complemented by other technologies such as relay-by-smartphone or satellites.
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paper_title: Experimental emergency communication systems using USRP and GNU radio platform

paper_content:

One lesson learned from recent large-scale disasters is that the destroyed communication infrastructure severely burdens the relief operation and the recovery mission. How to establish a temporary emergency communication system (ECS) providing reliable communication channels upon deployment becomes a must. An Universal Software Radio Peripheral platform with GNU Radio is employed for experimential purpose with basic voice communications and short message services. With the aid of pre-installed APP in victims' smartphone, valuable information about the victim, such as the identity, location, or physical condition, can be automatically delivered to the developed BS, which significantly facilitates the rescue work. Furthermore, BS acting as a relay could provide direct voice connectivity between victims and relief workers, thereby avoiding considerable fatalities.
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paper_title: Emergenet: robust, rapidly deployable cellular networks

paper_content:

Cellular phone networks are often paralyzed after a disaster, as damage to fixed infrastructure, loss of power, and increased demand degrade coverage and quality of service. To ensure disaster victims and first responders have access to reliable local and global communication, we propose EmergeNet, a portable, rapidly deployable, small-scale cellular network. In this article, we describe EmergeNet, which addresses the challenges of emergency and disaster areas. EmergeNet provides free voice calling and text messaging within a disaster area, and enables users of unmodified GSM handsets to communicate with the outside world using the Skype VoIP network. We evaluate EmergeNet's ability to provide robust service despite high load, limited bandwidth, and software or hardware failures. EmergeNet is uniquely well suited to providing reliable, fairly allocated voice and text communication in emergency and disaster scenarios.
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paper_title: On-the-fly establishment of multihop wireless access networks for disaster recovery

paper_content:

This article proposes a novel approach to onthe- fly establishment of multihop wireless access networks (OEMAN) for disaster response. OEMAN extends Internet connectivity from surviving access points to disaster victims using their own mobile devices. OEMAN is set up on demand using wireless virtualization to create virtual access points on mobile devices. Virtual access points greedily form a tree-based topology, configured automatically for naming and addressing, which is then used to provide multihop wireless Internet access to users. Ordinary users can easily connect to the Internet through OEMAN as if they are connected through conventional access points. After connecting, users naturally contribute to the network extension, realizing the self-supporting capability of a disaster's local communities. The proposed scheme establishes a wireless access network quickly, which is essential in emergency relief situations. Furthermore, OEMAN is transparent to users and cost effective as it does not require additional hardware. Experimental evaluations on top of our preliminary prototype over Windows-based laptops confirm OEMAN's feasibility and its effectiveness for multihop paths of up to seven hops, and standard Internet services such as audio and video streaming.
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paper_title: Extending Network Coverage by Using Static and Mobile Relays during Natural Disasters

paper_content:

During natural disasters, such as earthquakes, apart of the Internet access infrastructure can be damaged, leaving many users disconnected. At the same time, many peopleneed to communicate to find their relatives and receive officialnotifications about the current situation. This paper presents anevaluation of different techniques for extending network coveragein such scenarios. We use real-world data to model the poweroutage probability of cellular base stations in Tokyo area andcombine it with information about batteries/power generatorsto create accurate maps of network coverage for different timeperiods after an earthquake. In our simulation, we use a realmap of evacuation sites, provided by Japanese government. Wefirst considered mobile nodes, moving between evacuation sites, and investigated their impact on network coverage. Then, wedeveloped an algorithm to determine the optimal locations forstatic relays ensuring different levels of network coverage. Ourresults show that even a small number of fixed relays, carefullyplaced between the evacuation sites, can outperform a muchhigher number of mobile nodes in terms of network coverage.
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paper_title: STEM-NET: How to Deploy a Self-Organizing Network of Mobile End-User Devices for Emergency CommunicationComputer Communications

paper_content:

Spontaneous wireless networks constructed out of mobile end-user devices (e.g. smartphones or tablets) are currently receiving considerable interest as they enable a wide range of novel, highly pervasive and user-centric network services and applications. In this paper, we focus on emergency-related scenarios, and we investigate the potential of spontaneous networks for providing Internet connectivity over the emergency area through the sharing of resources owned by the end-user devices. Novel and extremely flexible network deployment strategies are required in order to cope with the user mobility, the limited communication capabilities of wireless devices, and the intrinsic dynamics of traffic loads and QoS requirements. To this purpose, we propose here a novel approach toward the deployment of spontaneous networks composed by a new generation of wireless devices - called Stem Nodes (SNs) - to emphasize their ability to cover multiple network roles (e.g. gateway, router). The self-organization of the spontaneous network is then achieved through the local reconfiguration of each SN. Two complementary research contributions are provided. First, we describe the software architecture of a SN (which can be implemented on top of existing end-user devices), and we detail how a SN can manage its role set, eventually extending it through cooperation with other SNs. Second, we propose distributed algorithms, based on swarm intelligence principles, through which each SN can autonomously select its role, and self-elect to gateway or router, so that end-to-end performance are maximized while the lifetime of the spontaneous emergency network is prolonged. The ability of the proposed algorithm to guarantee adaptive and self-organizing network behaviors is demonstrated through extensive Omnet++ simulations, and through a prototype implementation of the SN architecture on a real testbed.
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paper_title: A smartphone-based post-disaster management mechanism using WiFi tethering

paper_content:

Natural disasters often cause the breakdown of the power grid in the affected areas hampering telecommunication services. In the absence of electrical power undamaged cellular base stations switch to battel") backup to sustain communication. However, owing to the sudden substantial increase in voice and data traffic, base stations become over-congested fast and batter) backups quickly get exhausted. We propose a smartphone-based post-disaster management mechanism for managing traffic in the affected areas using the concept of WiFi tethering. Smart phones in the affected areas may turn themselves into temporary WiFi hotspots to provide internet connectivity and important communication abilities to nearby WiFi-enabled user devices. The hotspots can self-assess the number of new connections they can serve based on their leftover battery energy. Client devices. approaching the affected areas, can also self-select the most suitable hotspot to connect to depending on their proximity and nature of motion with respect to individual hotspots. Long Term Fvolution Advanced (LTF-A) underlying networks are considered for this work.
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paper_title: Survivability as a generalization of recovery

paper_content:

Social infrastructure systems such as communication, transportation, power and water supply systems are now facing various types of threats including component failures, security attacks and natural disasters, etc. Whenever such undesirable events occur, it is crucial to recover the system as quickly as possible because the downtime of social infrastructure causes catastrophic consequences in the society. In the business continuity context, Recovery Time Objective (RTO) has been used as a criterion to specify the allowable maximum time to recover from system failure events. While RTO gives the requirement for system recovery time, performance degradation of infrastructure service during the recovery period is another dimension that should be taken into consideration. In this paper, we introduce survivability as a generalization of recovery behavior which can address the performance impacts during the recovery and show a survivability quantification example in a escalating and deferred repair system.
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paper_title: Robust Fault Tolerant uncapacitated facility location

paper_content:

In the {\em uncapacitated facility location} problem, given a graph, ::: a set of demands and opening costs, it is required to find a set of facilities $R$, so as to minimize the sum of the cost of opening the facilities in $R$ and the cost of assigning all node demands to open facilities. ::: ::: This paper concerns the {\em robust fault-tolerant} version of the uncapacitated facility location problem (RFTFL). In this problem, one or more facilities might fail, and each demand should be supplied by the closest open facility that did not fail. It is required to find a set of facilities $R$, so as to minimize the sum of the cost of opening the facilities in $R$ and the cost of assigning all node demands to open facilities that did not fail, after the failure of up to $\alpha$ facilities. ::: ::: We present a polynomial time algorithm that yields a 6.5-approximation ::: for this problem with at most one failure and a $1.5 + 7.5\alpha$-approximation for the problem with at most $\alpha > 1$ failures. We also show that the $RFTFL$ problem is NP-hard even on trees, and even in the case of a single failure.
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paper_title: Traveling repairman problem for optical network recovery to restore virtual networks after a disaster [invited]

paper_content:

Virtual networks mapped over a physical network can suffer disconnection and/or outage due to disasters. After a disaster occurs, the network operator should determine a repair schedule and then send repairmen to repair failures following the schedule. The schedule can change the overall effect of a disaster by changing the restoration order of failed components. In this study, we introduce the traveling repairman problem to help the network operator make the schedule after a disaster. We measure the overall effect of a disaster from the damage it caused, and we define the damage as the numbers of disconnected virtual networks, failed virtual links, and failed physical links. Our objective is to find an optimal schedule for a repairman to restore the optical network with minimum damage. We first state the problem; then a mixed integer linear program (MILP) and three heuristic algorithms, namely dynamic programming (DP), the greedy algorithm (GR), and simulated annealing (SA), are proposed. Finally, simulation results show that the repair schedules using MILP and DP results get the least damage but the highest complexity; GR gets the highest damage with the lowest complexity, while SA has a good balance between damage and complexity.
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paper_title: On-site configuration of disaster recovery access networks made easy

paper_content:

Catastrophic disasters can destroy large regions and, in the process, leave many victims isolated from the rest of the world. Recovering the communication infrastructure is typically slow and expensive, which is not suitable for emergency response. Multihop wireless access networks have the potential to quickly provide Internet connectivity to victims, but so far no simple and practical solution has been proposed to help people configure these networks easily. We are pursuing the approach of utilizing wireless virtualization techniques to establish wireless access networks on-the-fly using on-site mobile devices. While our previous work has demonstrated proof-of-concept solutions, it lacked fundamental communication abstractions, a rigorous design, and a thorough analysis on the effectiveness of these solutions. The main new contributions of this article are: (1) the wireless multihop communication abstraction (WMCA) as a fundamental communication concept for a practical tree-based disaster recovery access network (TDRAN), (2) the complete design and implementation details of TDRAN, and (3) a comprehensive analysis of the effectiveness of the proposed approach based on field experiments, both in indoor and outdoor settings, at different sites in Japan. The results demonstrate the effectiveness of the proposed solution for on-site configuration of wireless access networks, as it can easily extend to 20 hops by 15 m-distance and 16 hops by 30 m-distance networks, which result in 300 m and 480 m (respectively) in radius or about 1 km in diameter. This work also confirms that our approach is ready for realization as a real disaster recovery solution.
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paper_title: The Role of the Internet of Things in Network Resilience

paper_content:

Disasters lead to devastating structural damage not only to buildings and transport infrastructure, but also to other critical infrastructure, such as the power grid and communication backbones. Following such an event, the availability of minimal communication services is however crucial to allow efficient and coordinated disaster response, to enable timely public information, or to provide individuals in need with a default mechanism to post emergency messages. The Internet of Things consists in the massive deployment of heterogeneous devices, most of which battery-powered, and interconnected via wireless network interfaces. Typical IoT communication architectures enables such IoT devices to not only connect to the communication backbone (i.e. the Internet) using an infrastructure-based wireless network paradigm, but also to communicate with one another autonomously, without the help of any infrastructure, using a spontaneous wireless network paradigm. In this paper, we argue that the vast deployment of IoT-enabled devices could bring benefits in terms of data network resilience in face of disaster. Leveraging their spontaneous wireless networking capabilities, IoT devices could enable minimal communication services (e.g. emergency micro-message delivery) while the conventional communication infrastructure is out of service. We identify the main challenges that must be addressed in order to realize this potential in practice. These challenges concern various technical aspects, including physical connectivity requirements, network protocol stack enhancements, data traffic prioritization schemes, as well as social and political aspects.
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paper_title: Comparing Strategies to Construct Local Disaster Recovery Networks

paper_content:

Large-scale disasters, such as earthquakes and tsunamis, damage communication infrastructure. The damaged infrastructure is then not able to provide the means for communication, which is important after a disaster. In this paper we simulate how survivors of a disaster can place smart phones or notebooks (hereafter called devices) as stationary relay chains to connect to other evacuation centers and Internet gateways to access the Internet. To determine the time necessary to set up the network and the number of evacuation centers connected to the Internet, we create a Poisson-based simulation of evacuation centers and Internet gateways. We then compare strategies how to interconnect evacuation centers and gateways. Our results show that among the strategies to place relay chains we tested, the most promising are: (1) Link every evacuation center to the closest gateway with a relay chain and (2) link each evacuation center to the 3 closest evacuation centers or gateways with relay chains. Both these strategies seem promising and should be tested in field tests in the next step. Together with step-by-step guides for disaster survivors this work will hopefully result in a smart phone and notebook application that lets untrained disaster survivors quickly set up their own recovery network in the disaster area.
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paper_title: An Overview of Algorithms for Network Survivability

paper_content:

Network survivability--the ability to maintain operation when one or a few network components fail--is indispensable for present-day networks. In this paper, we characterize three main components in establishing network survivability for an existing network, namely, (1) determining network connectivity, (2) augmenting the network, and (3) finding disjoint paths. We present a concise overview of network survivability algorithms, where we focus on presenting a few polynomial-time algorithms that could be implemented by practitioners and give references to more involved algorithms.
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paper_title: Tunable QoS-aware network survivability

paper_content:

Coping with network failures has been recognized as an issue of major importance in terms of social security, stability and prosperity. It has become clear that current networking standards fall short of coping with the complex challenge of surviving failures. The need to address this challenge has become a focal point of networking research. In particular, the concept of tunable survivability offers major performance improvements over traditional approaches. Indeed, while the traditional approach is to provide full (100%) protection against network failures through disjoint paths, it was realized that this requirement is too restrictive in practice. Tunable survivability provides a quantitative measure for specifying the desired level (0%-100%) of survivability and offers flexibility in the choice of the routing paths. Previous work focused on the simpler class of “bottleneck” criteria, such as bandwidth. In this study, we focus on the important and much more complex class of additive criteria, such as delay and cost. First, we establish some (in part, counter-intuitive) properties of the optimal solution. Then, we establish efficient algorithmic schemes for optimizing the level of survivability under additive end-to-end QoS bounds. Subsequently, through extensive simulations, we show that, at the price of negligible reduction in the level of survivability, a major improvement (up to a factor of 2) is obtained in terms of end-to-end QoS performance. Finally, we exploit the above findings in the context of a network design problem, in which we need to best invest a given “budget” for improving the performance of the network links.
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paper_title: Tunable survivable spanning trees

paper_content:

Coping with network failures has become a major networking challenge. The concept of tunable survivability provides a quantitative measure for specifying any desired level (0%-100%) of survivability, thus offering flexibility in the routing choice. Previous works focused on implementing this concept on unicast transmissions. However, vital network information is often broadcasted via spanning trees. Accordingly, in this study, we investigate the application of tunable survivability for efficient maintenance of spanning trees under the presence of failures. We establish efficient algorithmic schemes for optimizing the level of survivability under various QoS requirements. In addition, we derive theoretical bounds on the number of required trees for maximum survivability. Finally, through extensive simulations, we demonstrate the effectiveness of the tunable survivability concept in the construction of spanning trees. Most notably, we show that, typically, negligible reduction in the level of survivability results in major improvement in the QoS performance of the resulting spanning trees.
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paper_title: Path diversification for future internet end-to-end resilience and survivability

paper_content:

Path Diversification is a new mechanism that can be used to select multiple paths between a given ingress and egress node pair using a quantified diversity measure to achieve maximum flow reliability. The path diversification mechanism is targeted at the end-to-end layer, but can be applied at any level for which a path discovery service is available. Path diversification also takes into account service requirements for low-latency or maximal reliability in selecting appropriate paths. Using this mechanism will allow future internetworking architectures to exploit naturally rich physical topologies to a far greater extent than is possible with shortest-path routing or equal-cost load balancing. We describe the path diversity metric and its application at various aggregation levels, and apply the path diversification process to 13 real-world network graphs as well as 4 synthetic topologies to asses the gain in flow reliability. Based on the analysis of flow reliability across a range of networks, we then extend our path diversity metric to create a composite compensated total graph diversity metric that is representative of a particular topology's survivability with respect to distributed simultaneous link and node failures. We tune the accuracy of this metric having simulated the performance of each topology under a range of failure severities, and present the results. The topologies used are from national-scale backbone networks with a variety of characteristics, which we characterize using standard graph-theoretic metrics. The end result is a compensated total graph diversity metric that accurately predicts the survivability of a given network topology.
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paper_title: Protection coordination for dual failure on two-layer networks

paper_content:

Network layers such as IP/MPLS and OTN/ASON each has its own failure protection scheme. We propose a coordinated protection plan, so called protection synergy, to protect all possible dual failures by utilizing existing single failure protection schemes. There are two aspects essential for effective dual failure protection: One is to guarantee the connectivity under any dual fiber failures, the other is to allocate minimum but enough spare capacity on both layers. Our model achieves both goals using a novel topology mapping technique and computing working and backup paths with an accurate path disjoint criterion. The experimental results on four networks demonstrate complete dual failure restorability and spare capacity savings of the protection synergy approach.
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paper_title: Spare capacity allocation using shared backup path protection for dual link failures

paper_content:

This paper extends the spare capacity allocation (SCA) problem from single failures to dual link failures on mesh-like IP or WDM networks. The SCA problem pre-plans traffic flows with mutually disjoint one working and two backup paths using the shared backup path protection (SBPP) scheme. The spare provision matrix (SPM) method aggregates per-flow based information and computes the shared spare capacity for dual link failures. When compared to previous two-flow based methods, it has better scalability and flexibility. The SCA problem is formulated as a non-linear integer programming model and partitioned into two sequential linear sub-models: one finds all primary backup paths, and the other finds all secondary backup paths. We extend the terminologies in the 1+1 and 1:1 link protection for the backup path protection: using '':'' to indicate backup paths with shared spare capacity; and using ''+'' to indicate backup paths with dedicated capacity. Numerical results from five networks show that the network redundancy of the 1+1+1 dedicated path protection is in the range of 313-400%. It drops to 96-180% in the 1:1:1 shared backup path protection without loss of dual-link resiliency, but with the trade-off of the highest complexity on spare capacity shared by all backup paths. The 1+1:1 hybrid path protection provides intermediate redundancy at 187-310% with the moderate complexity. It has dedicated primary backup paths and shared secondary backup paths. We also compare passive sharing with active sharing. They perform spare capacity sharing either after or during the backup path routing, i.e., the active sharing approach performs share spare capacity within the backup path routing, while the passive sharing does so only after all backup paths are found. The active sharing approaches always achieve lower redundancy values than the passive sharing. The reduction percentages are about 12% for 1+1:1 and 25% for 1:1:1 respectively. The extension of the Successive Survivable Routing (SSR) heuristic algorithm to the dual failure case is given and the numerical results show that SSR maintains a 4-11% gap from optimal on small or medium networks, and scales up well on large networks.
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paper_title: Minimizing the Risk From Disaster Failures in Optical Backbone Networks

paper_content:

Failures caused by disasters (e.g., weapons of mass destruction (WMD) attacks, earthquakes, hurricanes, etc.) can create huge amount of loss and disruptions in optical backbone networks. Due to major network disruptions in recent disasters, network operators need solutions to prevent connections from disasters, and recover them after disasters. 1) Prevention requires proactive approaches where the damage from a possible disaster should be estimated. Specifically, we propose disaster-risk-aware provisioning, which minimizes loss to a network operator in case of a disaster. 2) Recovery methods should consider that, after the initial failure, more connections might be disconnected by correlated cascading failures. Thus, we investigate a reprovisioning scheme to recover disrupted connections. Numerical examples conducted for different disaster types (WMD attack, earthquake, and tornado) show that our schemes significantly reduce the risk and loss in case of a disaster.
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paper_title: Finding critical regions and region-disjoint paths in a network

paper_content:

Due to their importance to society, communication networks should be built and operated to withstand failures. However, cost considerations make network providers less inclined to take robustness measures against failures that are unlikely to manifest, like several failures coinciding simultaneously in different geographic regions of their network. Considering networks embedded in a two-dimensional plane, we study the problem of finding a critical region—a part of the network that can be enclosed by a given elementary figure of predetermined size—whose destruction would lead to the highest network disruption. We determine that only a polynomial, in the input, number of nontrivial positions for such a figure needs to be considered and propose a corresponding polynomial-time algorithm. In addition, we consider region-aware network augmentation to decrease the impact of a regional failure. We subsequently address the region-disjoint paths problem, which asks for two paths with minimum total weight between a source $(s)$ and a destination $(d)$ that cannot both be cut by a single regional failure of diameter $D$ (unless that failure includes $s$ or $d$ ). We prove that deciding whether region-disjoint paths exist is NP-hard and propose a heuristic region-disjoint paths algorithm.
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paper_title: Enhancing network service survivability in large-scale failure scenarios

paper_content:

Large-scale failures resulting from natural disasters or intentional attacks are now causing serious concerns for communication network infrastructure, as the impact of large-scale network connection disruptions may cause significant costs for service providers and subscribers. In this paper, we propose a new framework for the analysis and prevention of network service disruptions in large-scale failure scenarios. We build dynamic deterministic and probabilistic models to capture the impact of regional failures as they evolve with time. A probabilistic failure model is proposed based on wave energy behaviour. Then, we develop a novel approach for preventive protection of the network in such probabilistic large-scale failure scenarios. We show that our method significantly improves uninterrupted delivery of data in the network and reduces service disruption times in large-scale regional failure scenarios.
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paper_title: Spatiotemporal risk-averse routing

paper_content:

A cyber-physical system is often designed as a network in which critical information is transmitted. However, network links may fail, possibly as the result of a disaster. Disasters tend to display spatiotemporal characteristics, and consequently link availabilities may vary in time. Yet, the requested connection availability of traffic must be satisfied at all times, even under disasters. In this paper, we argue that often the spatiotemporal impact of disasters can be predicted, such that suitable actions can be taken, before the disaster manifests, to ensure the availability of connections. Our main contributions are three-fold: (1) we propose a generic grid-based model to represent the risk profile of a network area and relate the risk profile to the availability of links and connections, (2) we propose a polynomial-time algorithm to identify connections that are vulnerable to an emerging disaster risk, and (3) we consider the predicted spatiotemporal disaster impact, and propose a polynomial-time algorithm based on an auxiliary graph to find the most risk-averse path under a time constraint.
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paper_title: An approach for short message resilience in disaster-stricken areas

paper_content:

Large scale disasters may destroy essential network infrastructures and cause network-based service failure over a large area. Communication between two nodes in a resilient network should continue without any support of network infrastructure. Delay and Disruption Tolerant Network (DTN) is the choice for network resilience because it is not dependent on any infrastructure and supports flexibility in link delay and availability. Network resilience must consider the power limitations of the nodes and unusually very high traffic demand after a disaster hits. Existing DTN routing protocols' performances are not satisfactory in terms of the two most important metrics of communication in a disaster-stricken area-message delivery ratio and residual energy of the communicating devices. We propose a new message routing mechanism, called Location-aware Message Delivery (LMD), for communicating among wireless devices that uses greedy forwarding towards the intended destinations. Simulation results show the effectiveness of our proposed approach in the delivery ratio and energy saving of the devices. Overall efficiency of our scheme is superior to those of compared DTN routing protocols.
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paper_title: A Spectrum- and Energy-Efficient Scheme for Improving the Utilization of MDRU-Based Disaster Resilient Networks

paper_content:

The movable and deployable resource unit (MDRU)-based network provides communication services in disaster-struck areas where the lack of spectrum and energy resources is intensified due to the high demand from users and the power outages after a disaster. The MDRU-based network attempts to apply spectrum- and energy-efficient methods to provide communications services to users. However, existing works in this field only consider spectrum efficiency or energy efficiency separately, in spite of the tradeoff relationship between them. Thus, we propose a scheme to improve the utilization of both spectrum and energy resources for better system performance. The considered MDRU-based network is composed of gateways deployed in the disaster area, which can replenish their energy by using solar panels. Our proposed scheme constructs a topology based on the top $k$ spectrum-efficient paths from each sender and applies a max flow algorithm with vertex capacities, which are the number of transmissions that each gateway can send, which is referred to as transmission capability. The transmission capability of each gateway is determined by its energy resource and distances to its neighbors. Furthermore, we show that the proposal can be used for multisender–multireceiver topologies. A new metric named spectrum–energy efficiency to measure both spectrum efficiency and energy efficiency of the network is defined. Through analyses, we prove that a value of $k$ exists such that the spectrum–energy efficiency of a given topology is maximized. Furthermore, our simulation results show that, by dynamically selecting appropriate value of $k$ , the proposed scheme can provide better spectrum–energy efficiency than existing approaches. Moreover, our experimental results verify the findings of our analysis.
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Title: A survey of strategies for communication networks to protect against large-scale natural disasters

Section 1: INTRODUCTION
Description 1: Introduce the significance of communication networks in disaster scenarios and outline the goals and structure of the survey.

Section 2: VULNERABILITY OF COMMUNICATION NETWORKS TO DISASTER-BASED DISRUPTIONS
Description 2: Discuss the assessment of communication networks' vulnerability and review existing literature on identifying and addressing vulnerabilities.

Section 3: ENHANCING THE DISASTER-RESISTANCE OF EXISTING NETWORKS AND THE DEPLOYMENT OF EMERGENCY NETWORKS
Description 3: Explore methodologies for improving the robustness of existing communication networks and strategies for deploying emergency networks post-disaster.

Section 4: DISASTER-RESILIENT ROUTING ALGORITHMS
Description 4: Review various techniques and algorithms proposed for disaster-resilient routing to ensure continued network functionality in disaster scenarios.

Section 5: CONCLUSION
Description 5: Summarize the survey's findings and emphasize the importance of resilient communication strategies in mitigating the impact of natural disasters.