This Special Issue contains a set of remarkable papers covering various recent research advances towards resilient Communication Networks for an hyper-connected World. Papers are organized into five categories: (i) Resilient Architectures for Next-Generation Networks, (ii) Edge, IoT, and Cyber-Physical Systems, (iii) Vehicular, Mobile, and Aerial Networks, (iv) Optical, Hybrid, and Satellite-based Resilient Communications, and (v) Security, Trust, and Resilience in Services and Applications. The editorial begins with an overview of the field and proceeds with a summary of the twenty-two papers included in this Special Issue.

Abstract It is essential for network operators to guarantee required levels of availability in the network without incurring in excessive costs. We address the optimization problem of upgrading links at a given cost, to achieve end‐to‐end availability guarantees in the network, via pairs of working and backup paths. These guarantees are expressed as nonlinear path pair availability constraints which cannot be readily linearized. For this reason, most works have only considered the working path availability or disaggregated models where availability guarantees are considered separately for the working and backup paths. We show that the aggregated models which jointly consider the availabilities of the working and backup paths can provide better solutions than the disaggregated models. Moreover, we present a more efficient aggregated model based on a novel strategy to linearize the path pair availability constraints, and show that it further improves previous results. It is usual to impose that the upgraded links belong to a spanning tree subgraph. We further compare the solutions with and without this imposition and show that relaxing the tree condition can provide better solutions.

This Special Section features research contributions in the area of robust and reliable networks of the future. Modern network infrastructures must support a growing demand for intensive data processing and high-speed communication, that has led, in the last decade, to a constant evolution towards convergence of networking and computing infrastructures. This convergence was made possible by the introduction of network function virtualization and by the emergence of the Software-Defined Networking (SDN) paradigm, and has enabled new forms of cloud and edge computing to cope with the strict requirements of new services and applications, as those in the realm of the Internet of Things (IoT).

This Special Section (SI) features the latest research contributions regarding recent advances in the design and management of reliable communication networks. Communication networks are constantly increasing their complexity and scale to satisfy the requirements of network services. The current trend of convergence of networking and computing infrastructures (as in today’s cloud systems and softwarized networks) calls for novel advanced strategies and solutions to support reliable services, as the development of new data-driven solutions for reliable network automation and self-diagnostic tools to ensure resilient network management.

An inherent problem in Software-Defined Networking (SDN) is the Controller Placement Problem, which addresses how many controllers to deploy in the network, and where to place them. Several variants of this problem have been addressed and researched to find the placements that adapt best to different contexts. In this article, we address a more complex variant of this problem, to satisfy QoS requirements and to offer robustness against disaster-based failures. We address the joint optimization problem of controller placement and finding a tree subgraph which can be upgraded to have enhanced availability, in order to satisfy delay and availability constraints. Additionally, we consider geodiversity constraints as a way to enhance robustness to disaster-based failures.

This special section features the latest research contributions regarding the design and management of reliable networks. Reliability of communication infrastructure is a top priority for network operators. To ensure reliable network operation, new design and management techniques for reliable communications must be constantly devised to respond to the rapid network and service evolution. As a recent and relevant example, deployments of 5G communication networks will soon enter their second phase, during which the network infrastructure will require upgrades to support new Ultra-Reliable Low-Latency Communication (URLLC) services with availabilities of up to 6 nines to be guaranteed jointly with extremely low latencies. Even in the still preliminary vision of 6G communication networks, reliability is posed as one of the most critical requirements, as 6G networks will represent the communication platform of our future hyper-connected society, supporting essential services as smart mobility, e-health, and immersive environments with application in remote education and working, just to name a few. Similarly, disaster resiliency in communication networks is now attracting the attention of media, government and industry as never before (consider, e.g., the worldwide network traffic deluge to support remote working during the current Coronavirus pandemic). Luckily, several new technical directions can be leveraged to provide new solutions for network reliability as: increased network reconfigurability enabled by Software Defined Networking (SDN); integration/convergence of multiple technologies (optical, wireless satellite, datacenter networks); enhanced forms of data/service replication, supported by, e.g., edge computing; network slicing, used to carve highly-reliable logical partitions of network, computing and storage resources. These, and many others, technological transformations can be leveraged to enable next-generation high-reliability networks.

Abstract The resilience to disasters is a very relevant problem in telecommunication networks. This work addresses the problem of 1 + 1 optical lightpath protection considering maximally shared risk link group (SRLG)‐disjoint geodiverse paths, applied in the context of an optical network. The resilience to geographically correlated disasters is accomplished by guaranteeing geodiversity of the paths. This work focuses on estimating the increase of the path lengths and the increase in cost of the required transponders, compared to simple link‐disjointness (i.e., when no constraints on SRLG‐disjointness or geodiversity are considered). Results in different networks allow to evaluate the effect of SRLG‐disjointness to ensure some geodiversity.

This work addresses the problem of dedicated protection of multicast sessions in mixed‐graph optical networks, where only a fraction of the nodes have optical splitting capabilities. A novel multicast routing algorithm for sparse splitting optical networks (the Modified Steiner Tree Heuristic [MSTH]) is initially presented and is subsequently utilized (together with two existing heuristics [MUS and MSH]) by an effective scheme for the calculation of a pair of disjoint trees. The key idea of this New Arc‐Disjoint Trees (NADT) protection technique is to gradually construct the primary tree, verifying that after the addition of each one of the destinations of the multicast session, a secondary (arc‐disjoint) tree can still be obtained. Performance results demonstrate that the proposed NADT protection technique clearly outperforms the conventional Arc‐Disjoint Trees (ADT) approach in terms of blocking ratio, while incurring only a negligible increase of the average cost of the derived pair of ADT. Furthermore, it is shown that the newly proposed algorithm, MSTH‐NADT, is the one having the best performance in terms of cost and blocking, with MSH‐NADT having similar, albeit slightly worse, performance. However, as MSH‐NADT requires much less CPU time compared to MSTH‐NADT, MSH‐NADT can be considered the best compromise technique. © 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 70(4), 360–372 2017

A new recursive heuristic is proposed to calculate a shortest simple path, from a source node to a destination node, that visits a specified set of nodes in a network. To provide survivability to failures along the path, the proposed heuristic is modified to ensure that the calculated path can be protected by a node‐disjoint backup path. Additionally, the case when both paths in the disjoint path pair are required to visit specific sets of nodes is studied and effective heuristics are proposed. An evaluation of the solutions of the heuristics is conducted by comparing with results from an integer linear programming (ILP) formulation for each of the considered problems, and also with previous heuristics. The ILP solver may require a significant amount of time to obtain a solution, especially in large networks, which justifies the need for effective, computationally efficient heuristics for solving these problems. © 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 70(4), 292–307 2017

The exact calculation of all‐terminal reliability is not feasible in large networks. Hence estimation techniques and lower and upper bounds for all‐terminal reliability have been utilized. Here, we propose using an ordered subset of the mincuts and an ordered subset of the minpaths to calculate an all‐terminal reliability upper and lower bound, respectively. The advantage of the proposed new approach results from the fact that it does not require the enumeration of all mincuts or all minpaths as required by other bounds. The proposed algorithm uses maximally disjoint minpaths, prior to their sequential generation, and also uses a binary decision diagram for the calculation of their union probability. The numerical results show that the proposed approach is computationally feasible, reasonably accurate and much faster than the previous version of the algorithm. This allows one to obtain tight bounds when it not possible to enumerate all mincuts or all minpaths as revealed by extensive tests on real‐world networks. © 2015 Wiley Periodicals, Inc. NETWORKS, Vol. 66(4), 282–295 2015