eFRADIR: An Enhanced FRAmework for DIsaster Resilience

A. Pasic, R. Girao-Silva, F. Mogyorosi, B. Vass, T. Gomes, P. Babarczi, P. Revisnyei, J. Tapolcai, J. Rak IEEE Access – 2021
This paper focuses on how to increase the availability of a backbone network with minimal cost. In particular, the new framework focuses on resilience against natural disasters and is an evolution of the FRADIR/FRADIR-II framework. It targets three different directions, namely: network planning, failure modeling, and survivable routing. The steady state network planning is tackled by upgrading a sub-network (a set of links termed the spine) to achieve the targeted availability threshold. A new two-stage approach is proposed: a heuristic algorithm combined with a mixed-integer linear problem to optimize the availability upgrade cost. To tackle the disaster-resilient network planning problem, a new integer linear program is presented for the optimal link intensity tolerance upgrades together with an efficient heuristic scheme to reduce the running time. Failure modeling is improved by considering more realistic disasters. In particular, we focus on earthquakes using the historical data of the epicenters and the moment magnitudes. The joint failure probabilities of the multi-link failures are estimated, and the set of shared risk link groups is defined. The survivable routing aims to improve the network’s connectivity during these shared risk link group failures. Here, a generalized dedicated protection algorithm is used to protect against all the listed failures. Finally, the experimental results demonstrate the benefits of the refined eFRADIR framework in the event of disasters by guaranteeing low disconnection probabilities even during large-scale natural disasters.

High-Power Jamming Attack Mitigation Techniques in Spectrally-Spatially Flexible Optical Networks

G. Savva, K. Manousakis, J. Rak , I. Tomkos, G. Ellinas – IEEE Access – 2021
This work presents efficient connection provisioning techniques mitigating high-power jamming attacks in spectrally-spatially flexible optical networks (SS-FONs) utilizing multicore fibers. High-power jamming attacks are modeled based on their impact on the lightpaths’ quality of transmission (QoT) through inter-core crosstalk. Based on a desired threshold on a lightpath’s QoT, the modulation format used, the length of the path, as well as a set of physical layer characteristics, each lightpath can potentially tolerate a high-power jamming attack. In this paper, an integer linear program is thus formulated, as well as heuristic algorithms to solve the problem of attack-aware routing, spectrum, modulation format, and core allocation in SS-FONs, aiming to both efficiently provision the network in terms of network resources, as well as minimize the impact of high-power jamming attacks on the established lightpaths. Extensive simulation results are obtained for several algorithm variants with different objectives, demonstrating the validity and efficiency of the proposed techniques that can effectively mitigate high-power jamming attacks, by minimizing the number of inter-core interactions, while at the same time establishing connections with high spectral efficiency.

Design of Resilient Vehicle-to-Infrastructure Systems

J. Rak , M. Jonsson, A. Vinel, K. Jurczenia – 2020
Vehicular ad hoc networks (VANETs) have recently gained noticeable attention due to advantages in improving road traffic safety, shaping the road traffic and providing infotainment opportunities to travellers. However, transmission characteristics following from the IEEE 802.11p standard and the high mobility of VANET nodes remarkably reduce the lifetime, reach and capacity of wireless links, and often lead to simultaneous disruptions of communications at multiple links. In this chapter, we present a set of solutions to enhance the performance of VANETs (which can be applied independently of particular applications) concerning (a) design of the VANET infrastructure (location of road-side units—RSUs and gateways), (b) communications along vehicle-to-infrastructure (V2I) links and (c) resilience of VANET services to malicious human activities.

Disaster-Resilient Routing Schemes for Regional Failures

T. Gomes, D. Santos, R. Girão-Silva, L. Martins, B. Nedic, M. Gunkel, B. Vass, J. Tapolcai, J. Rak – 2020
Large-scale natural disasters can have a profound effect on the telecommunication services in the affected geographical area. Hence, it is important to develop routing approaches that may help in circumventing damaged regional areas of a network. This prompted the development of geographically diverse routing schemes and also of disaster-risk aware routing schemes. A minimum-cost geodiverse routing, where a minimum geographical distance value D is imposed between any intermediate element of one path and any element of the other path, is presented. Next, the problem of the calculation of a D-geodiverse routing solution which ensures a certain level of availability is tackled. An algorithm is described that either obtains a solution to that problem or the most available path pair satisfying the desired geographical distance value D—this can be useful for the specification of availability levels in Service Level Agreements. Finally, a case study is presented, in an optical network, to determine the cost increase in terminal equipment (transponders) of approaches to ensure a much larger separation of the paths (of the selected path pair), with respect to minimal length link-disjoint routing.

Enhancing Availability for Critical Services

T. Gomes, L. Martins, R. Girão-Silva, D. Tipper, A. Pašić, B. Vass, L. Garrote, U. Nunes, M. Zachariasen, J. Rak – 2020
Traditional approaches to provide classes of resilient service take the physical network availability as an input and then deploy redundancy and restoration techniques at various layers, often without full knowledge of mappings between layers. This makes it hard (and often inefficient) to ensure the high availability required by critical services which are typically a small fraction of the total traffic. Here, the innovative technique of embedding a higher availability substructure, designated the spine, into the network at the physical layer, is explored. In the spine-based approach, it is considered that high availability must begin at the physical level and then must be reinforced in upper layers. A recent disaster-resilience framework, named Framework for Disaster Resilience, which incorporates reliable network design (i.e. using the spine), disaster failure modelling and protection routing to improve the availability of critical services is discussed. Next, a proposal to select network links for availability upgrade to ensure high availability is presented. This is followed by a study assuming that if disaster-prone areas are known, they can be represented as obstacles which should be avoided when deploying the physical backbone of a communications network. Hence, a heuristic for a minimum-cost Euclidean Steiner tree taking into account the presence of soft obstacles is presented.

Fundamental Schemes to Determine Disjoint Paths for Multiple Failure Scenarios

T. Gomes, L. Jorge, R. Girão-Silva, J. Yallouz, P. Babarczi, J. Rak – 2020
Disjoint path routing approaches can be used to cope with multiple failure scenarios. This can be achieved using a set of k (k> 2) link- (or node-) disjoint path pairs (in single-cost and multi-cost networks). Alternatively, if Shared Risk Link Groups (SRLGs) information is available, the calculation of an SRLG-disjoint path pair (or of a set of such paths) can protect a connection against the joint failure of the set of links in any single SRLG. Paths traversing disaster-prone regions should be disjoint, but in safe regions it may be acceptable for the paths to share links or even nodes for a quicker recovery. Auxiliary algorithms for obtaining the shortest path from a source to a destination are also presented in detail, followed by the illustrated description of Bhandari’s and Suurballe’s algorithms for obtaining a pair of paths of minimal total additive cost. These algorithms are instrumental for some of the presented schemes to determine disjoint paths for multiple failure scenarios.

Fundamentals of Communication Networks Resilience to Disasters and Massive Disruptions

J. Rak , D. Hutchison, J. Tapolcai, R. Bruzgiene, M. Tornatore, C. Mas-Machuca, M. Furdek, P. Smith – 2020
Communication networks are exposed to a variety of massive failure events following from activities of nature, weather-induced disruptions, technology-implied problems, and malicious human activities. In this chapter, we first highlight the characteristics of these scenarios and discuss example failure events reported during the last three decades. Next, we explain the concept of network resilience and present an overview of major problems and related schemes further addressed in this monograph, concerning (a) measures and models for the analysis and evaluation of disaster-resilient networks, (b) techniques for design and update of disaster-resilient systems, (c) algorithms and schemes for resilient systems, and (d) advanced topics focusing, e.g. on emerging communication technologies.

Improving the Survivability of Carrier Networks to Large-Scale Disasters

A. de Sousa, J. Rak , F. Barbosa, D. Santos, D. Mehta – 2020
This chapter is dedicated to the description of methods aiming to improve the survivability of carrier networks to large-scale disasters. First, a disaster classification and associated risk analysis is described, and the disaster-aware submarine fibre-optic cable deployment is addressed aiming to minimize the expected costs in case of natural disasters. Then, the chapter addresses the improvement of the network connectivity resilience to multiple node failures caused by malicious human activities. Two improvement methods are described aiming to minimize the connectivity impact of any set of node failures. One method is based on the appropriate selection of a set of network nodes to be made robust to node attacks. The other is a topology design method aiming to select the most appropriate set of links, within a given fibre budget, that provide the best resilience to multiple node failures. The latter method can also be applied to the upgrade task of a current network topology.

Minimising the Churn Out of the Service by Using a Fairness Mechanism

The paper proposes an algorithm of bandwidth distribution, ensuring fairness to end-users in computer networks. The proposed algorithm divides users into satisfied and unsatisfied users. It provides fairness in terms of quality of experience (QoE) for satisfied users and quality of service (QoS) for unsatisfied users. In this paper, we present detailed comparisons relevant to service providers to show the advantages of the proposed algorithm over the popular max-min algorithm. Our algorithm is designed to provide service providers with a mechanism to minimize the number of end-user terminations of service, which is one of the most desired factors for service providers.

Optimization of Wireless Networks for Resilience to Adverse Weather Conditions

M. Pióro, E. Fitzgerald, I. Kalesnikau, D. Nace, J. Rak – 2020
In this chapter, we consider how adverse weather conditions such as rain or fog affect the performance of wireless networks, and how to optimize these networks so as to make them robust to these conditions. We first show how to analyze the weather conditions in order to make them useful for network optimization modelling. Using an example realistic network, we show how to optimize two types of wireless networks: free-space optical (FSO) networks and wireless mesh networks (WMN). The key difference between the two network types is that in WMNs, links interfere with each other, while in FSO networks, link rates may be assumed independent. We formulate optimization problems to protect each network type against adverse weather conditions, discuss solution methods to solve them and present a numerical study illustrating the considerations of the chapter.