Technology-related disasters: A survey towards disaster-resilient Software Defined Networks
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paper_title: "Reconstructing normality": the use of infrastructure leftovers in crisis situations as inspiration for the design of resilient technology

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In this paper, we examine challenges people face in situations of disrupted network infrastructures and how people use surviving portions of technology to cope with these challenges. We show how an important aspect in crises is the disturbance of services caused by disruptions in underlying technological structures. In such situations, people resort to all possible means to "reconstruct normality" in the sense of restoring their ability to communicate. For doing so, people often make creative use of the remains of the technological landscape. Building on the analysis of interviews with crises witnesses and first responders, external reports and scientific literature, we propose and describe three categories of mechanisms involving the creative use of surviving technology in crisis situations. We argue that studying these mechanisms can provide a key source of inspiration to define qualities of resilient architectures, and use these mechanisms as creative input to propose architectural qualities that can potentially make communication systems more resilient in the face of crises.
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paper_title: Resilience through technology adoption: merging the old and the new in Iraq

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Citizen response to disaster has begun to receive attention in the CHI community but little attention has so far been given to how citizens use technology to adapt when their country is at war. We report on an ethnographic interview study of how technology was adopted and used by citizens to be resilient during wartime. We interviewed 45 Iraqi citizens experiencing the current Iraq war. Based on our data we identified properties of resilience: reconfiguring social networks, self-organization, redundancy, proactive practices, and repairing trust in information. Technology supported people in being resilient by enabling them to control identity, to collaborate in travel, to create an organizational memory, and to provide alternative sources of news and information. As people adopted and used technology to be resilient we found a merging of old and new cultural practices. We discuss these systemic changes and describe implications for how technology can support people in being resilient in disrupted environments.
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paper_title: Six attributes of social resilience

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The concept of resilience has attracted much attention in recent times. However, there remains a distinct knowledge gap with respect to the social aspects of resilience. This paper describes six attributes of social resilience identified through case study research. Research was undertaken by a multi-disciplinary team of researchers who worked in partnership with representatives from five key government and non-government agencies from the Wet Tropics region in North Queensland, Australia. Research findings move understanding of social resilience, which is an emerging area of interest within natural resource management, from a set of assumptions to an evidence base.
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paper_title: Catastrophic cascade of failures in interdependent networks

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Modern network-like systems are usually coupled in such a way that failures in one network can affect the entire system. In infrastructures, biology, sociology, and economy, systems are interconnected and events taking place in one system can propagate to any other coupled system. Recent studies on such coupled systems show that the coupling increases their vulnerability to random failure. Properties for interdependent networks differ significantly from those of single-network systems. In this article, these results are reviewed and the main properties discussed.
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paper_title: Topological Analysis and Mitigation Strategies for Cascading Failures in Power Grid Networks

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Energy and Power Affiliates Group, consisting of Burns and McDonnell, Westar Energy, Omaha Public Power District, and Nebraska Public Power District.
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paper_title: Techniques for Disaster Tolerant Information Technology Systems

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This paper provides a review of disaster tolerant Information Technology (IT). The state of traditional disaster recovery approaches is outlined. The risks of IT application downtime attributable to the increasing dependence on critical information technology operating in interdependent, interacting complex infrastructure systems is reviewed. General disaster tolerance techniques are summarized. While content specific approaches currently undertaken to understand and avoid cascading failures in systems are extant, opportunities exist to extend this complex systems independence analysis to the private business sector in the form of disaster tolerance. The high level of complexity of relationships between IT application availability and numerous secondary and tertiary affects of a disaster on systems that are dependent on other systems for availability has not yet been fully explored.
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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: An information centric approach for communications in disaster situations

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Disasters result in disruptions to the communication infrastructure, typically forming a multitude of fragmented networks. This makes it difficult to exchange even simple while critical messages with large portions of the affected population, including first-responders and government authorities. In this paper, we focus on a content driven data retrieval model and propose an enhanced information-centric network (ICN) approach to provide communication resilience to such disruption-prone, delay-tolerant networks. The message exchange between communities and mules takes into account the limited available resources and the fact that the interest and the data might traverse completely different paths, unlike the assumption in many of the existing ICN solutions. Moreover, we argue for the separation of the the logical faces from the actual physical interfaces taking into account the fact that the data mules behave as mobile routers and are connected to different nodes at different time periods, unlike the assumptions made in existing ICN solutions. Our preliminary evaluations show that our solution is able to outperform other approaches such as “Epidemic” and “SprayAndWait” with respect to the latency, response probability and overall performance while improving the performance (latency and response probability) for high priority messages.
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paper_title: Content Centric Networking in tactical and emergency MANETs

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Reliable and secure content distribution in a disruptive environment is a critical challenge due to high mobile and lossy channels. Traditional IP networking and wireless protocols tend to perform poorly. In this paper, we propose Content Centric Networking (CCN) for emergency wireless ad hoc environments. CCN is a novel communication architecture capable to access and retrieve content by name. This new approach achieves scalability, security, and efficient network resource management in large scale disaster recovery and battlefield networks. Existing Internet CCN schemes cannot be directly applied to wireless mobile ad hoc networks due to different environments and specific limitations. Thus, we must extend the CCN architecture by introducing features and requirements especially designed for disruptive networks. We prove feasibility and performance gain of the new design via implementation and experimentation.
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paper_title: Name-based replication priorities in disaster cases

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In the immediate aftermath of a natural disaster, network infrastructure is likely to have suffered severe damages that challenge normal communications. In addition to that, traffic substantially increases as a result of people attempting to get in touch with friends, relatives or the rescue teams. To address such requirements of a challenged network, we propose a communication framework based on messages that exploits name-based replication of content and enables ad-hoc communications with spatial and temporal scoping and prioritisation of named messages. We evaluate our design against less sophisticated replication strategies and show that important messages (e.g., from first responders) get disseminated to more nodes than less important messages.
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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 modeling framework for the resilience analysis of networked systems-of-systems based on functional dependencies

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Critical infrastructures provide services that are essential for the support of everyday activities in modern societies. Being the result of a continuous process of integration of diverse technologies and organizations, they require a multi-disciplinary, systemic approach in order to be understood. In this respect, one of the most challenging issues is the analysis of infrastructures under disturbance or malfunctioning, and their ability to resist, react and recover, in a word the resilience. This paper presents a methodology of resilience analysis of systems of systems, with infrastructures as a special instance. A conceptual representation of the infrastructure, based on the functional relationships among its components, is given and then analyzed with respect to its structural and dynamic properties. Most critical and vulnerable components are identified. The response of the system to failure propagation is simulated in order to check if it is able to cope with them and recover in a resilient fashion. The analysis outcomes are used for a resilience-informed review of the infrastructure.
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paper_title: Characterisation of router and link failure processes in UNINETT’s IP backbone network

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Backbone networks must be highly reliable. The offered availability can be predicted prior to operation if the stochastic behaviour of network components is known. The aim of this paper is provide information about failures and repairs processes in an operational network. Operational logs from UNINETT's core network were analysed to obtain distributions of the time between failures and downtimes of routers and links. The network components were classified according to their role in the network. The measured processes were fit with well-known distributions. The inter-failure times of routers and short distance links may be characterised by a Weibull distribution, but for the long distance links the gamma distribution yielded a better characterisation. The difference is discussed based on the hazard function. The parameters of each network component are made available and provide a detailed insight that may be used for dependability predictions and research.
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paper_title: Characterization of failures in an IP backbone

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We analyze IS-IS routing updates from sprint's IP network to characterize failures that affect IP connectivity. Failures are first classified based on probable causes such as maintenance activities, router-related and optical layer problems. Key temporal and spatial characteristics of each class are analyzed and, when appropriate, parameterized using well-known distributions. Our results indicate that 20% of all failures is due to planned maintenance activities. Of the unplanned failures, almost 30% are shared by multiple links and can be attributed to router-related and optical equipment-related problems, while 70% affect a single link at a time. Our classification of failures according to different causes reveals the nature and extent of failures in today's IP backbones. Furthermore, our characterization of the different classes can be used to develop a probabilistic failure model, which is important for various traffic engineering problems.
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paper_title: Catastrophic cascade of failures in interdependent networks

paper_content:

Modern network-like systems are usually coupled in such a way that failures in one network can affect the entire system. In infrastructures, biology, sociology, and economy, systems are interconnected and events taking place in one system can propagate to any other coupled system. Recent studies on such coupled systems show that the coupling increases their vulnerability to random failure. Properties for interdependent networks differ significantly from those of single-network systems. In this article, these results are reviewed and the main properties discussed.
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paper_title: Power outage communications: Survey of needs, infrastructures and concepts

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Crisis communication during power outages poses several challenges. Frist, the causes of power outages are often events such as severe weather, which also lead to complications. Second, power outages themselves lead to limitations in everyday life. Third, communication infrastructures, that are necessary for crisis communication, are often affected. This work focuses on the communication of the organizations responsible for recovery work (emergency services, public administration, energy network operators) to the public affected by the power outage. Therefore this paper investigates the perception and the information demands of citizens and communication infrastructures in different scenarios. Taking the users’ needs into consideration, an Information and Communication Technology (ICT) based concept for crisis communication, which combines general information with location-specific and setting-specific information was implemented as a prototype smartphone application and evaluated with 12 potential end users. ICT-based concepts can gain acceptance, however they should be understood as supplemental for some target groups and in some scenarios.
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paper_title: Globally networked risks and how to respond

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Today's strongly connected, global networks have produced highly interdependent systems that we do not understand and cannot control well. These systems are vulnerable to failure at all scales, posing serious threats to society, even when external shocks are absent. As the complexity and interaction strengths in our networked world increase, man-made systems can become unstable, creating uncontrollable situations even when decision-makers are well-skilled, have all data and technology at their disposal, and do their best. To make these systems manageable, a fundamental redesign is needed. A 'Global Systems Science' might create the required knowledge and paradigm shift in thinking.
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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: Information-driven network resilience: Research challenges and perspectives

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Abstract Internet designed over 40 years ago was originally focused on host-to-host message delivery in a best-effort manner. However, introduction of new applications over the years have brought about new requirements related with throughput, scalability, mobility, security, connectivity, and availability among others. Additionally, convergence of telecommunications, media, and information technology was responsible for transformation of the Internet into an integrated system enabling accessing, distributing, processing, storing, and managing the payload of these messages. Users are now visibly more interested in receiving / accessing information independently of the network location of its host. This consideration in turn revived the interest in named data-driven networking (a.k.a. Information-Centric Networking - ICN). Instead of assuming that networks are limited to the manipulation of network locator space, the basic assumption underneath is that information can be named, addressed, and matched independently of its network location leaving in turn the possibility to match message delivery delay requirements. In this paper, we summarize our research conducted in order to bring a completely different view / perspective of network resilience, originally defined as the ability of a network to assure an acceptable level of service in the face of various faults and challenges to normal operation. That is, instead of maintaining network reachability independently of its actual utility to the “end-points”, our research aimed at exchanging and confronting the key principles that would enable an information-driven resilience (networked) scheme. More precisely, knowing that the user utility function is mainly driven nowadays by information-related criteria such as accessibility (reachability), how to design network resilience schemes that would be directed toward that goal. The main challenge is thus: can one design resilience schemes that combine maximization of end-point utility function and minimization of the network-related cost?
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paper_title: Future research directions in design of reliable communication systems

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In this position paper on reliable networks, we discuss new trends in the design of reliable communication systems. We focus on a wide range of research directions including protection against software failures as well as failures of communication systems equipment. In particular, we outline future research trends in software failure mitigation, reliability of wireless communications, robust optimization and network design, multilevel and multirealm network resilience, multiple criteria routing approaches in multilayer networks, resilience options of the fixed IP backbone network in the interplay with the optical layer survivability, reliability of cloud computing networks, and resiliency of software-defined networks. Described research directions are frequently enhanced with examples.
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paper_title: OpenFlow: Meeting carrier-grade recovery requirements

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OpenFlow, initially launched as a technology-enabling network and application experimentation in a campus network, has a disruptive potential in designing a flexible network, fostering innovation, reducing complexity and delivering the right economics. This paper focuses on fault tolerance of OpenFlow to deploy it in carrier-grade networks. The carrier-grade network has a strict requirement that the network should recover from the failure within a 50ms interval. We apply two well-known recovery mechanisms to OpenFlow networks: restoration and protection, and run extensive emulation experiments. In OpenFlow, the controlling software is moved to one or more hardware modules (controllers) which can control many switches. For fast failure recovery, the controller must notify all the affected switches about the recovery action within ms interval. This leads to a significant load on the controller. We show that OpenFlow may not be able to achieve failure recovery within a 50ms interval in this situation. We add the recovery action in the switches themselves so that the switches can do recovery without contacting the controller. We show that this approach can achieve recovery within 50ms in a large-scale network serving many flows.
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paper_title: IGP-as-a-backup for robust SDN networks

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One of the main concerns on SDN is relative to its ability to quickly react to network failures, while limiting both the control-plane overhead and the additional forwarding state kept by data-plane devices. Despite its practical importance, this concern is often overlooked in OpenFlow-based proposals. In this paper, we propose a new architecture, called IBSDN, in which a distributed routing protocol flanks OpenFlow to improve network robustness, reaction to failures, and controller scalability. In deeply exploring this idea, we complement our architecture with data-plane triggered mechanisms that improve its efficiency. We prove that the resulting solution ensures robustness for any combination of topological failures, and quickly reduces the path stretch. Finally, experimenting with a prototype implementation, we show that our approach is practical and overcomes the main limitations of previous work.
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paper_title: Fast Recovery in Software-Defined Networks

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Although Software-Defined Networking and its implementation OpenFlow facilitate managing networks and enable dynamic network configuration, recovering from network failures in a timely manner remains non-trivial. The process of (a) detecting the failure, (b) communicating it to the controller and (c) recomputing the new shortest paths may result in an unacceptably long recovery time. In this paper, we demonstrate that current solutions, employing both reactive restoration or proactive protection, indeed suffer long delays. We introduce a failover scheme with per-link Bidirectional Forwarding Detection sessions and preconfigured primary and secondary paths computed by an OpenFlow controller. Our implementation reduces the recovery time by an order of magnitude compared to related work, which is confirmed by experimental evaluation in a variety of topologies. Furthermore, the recovery time is shown to be constant irrespective of path length and network size.
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paper_title: Detour Planning for Fast and Reliable Failure Recovery in SDN with OpenState

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A reliable and scalable mechanism to provide protection against a link or node failure has additional requirements in the context of SDN and OpenFlow. Not only it has to minimize the load on the controller, but it must be able to react even when the controller is unreachable. In this paper we present a protection scheme based on precomputed backup paths and inspired by MPLS “crankback” routing, that guarantees instantaneous recovery times and aims at zero packet-loss after failure detection, regardless of controller reachability, even when OpenFlow's “fast-failover” feature cannot be used. The proposed mechanism is based on OpenState, an OpenFlow extension that allows a programmer to specify how forwarding rules should autonomously adapt in a stateful fashion, reducing the need to rely on remote controllers. We present the scheme as well as two different formulations for the computation of backup paths.
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paper_title: Loop-Free Alternates with Loop Detection for Fast Reroute in Software-Defined Carrier and Data Center Networks

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Loop-Free Alternates (LFAs) are a local fast-reroute mechanism defined for IP networks. They are simple but suffer from two drawbacks. Firstly, some flows cannot be protected due to missing LFAs, i.e., this concept does not provide full protection coverage, which depends on network topology. Secondly, some LFAs cause loops in case of node or multiple failures. Avoiding those LFAs decreases the protection coverage even further. In this work, we propose to apply LFAs to OpenFlow-based networks. We suggest a method for loop detection so that loops can be avoided without decreasing protection coverage. We propose an implementation with OpenFlow that requires only a single additional flow rule per switch. We further investigate the percentage of flows that can be protected, not protected, or even create loops in different types of failure scenarios. We consider realistic ring and mesh networks as well as typical topologies for data center networks. None of them can be fully protected with LFAs. Therefore, we suggest an augmented fat-tree topology which allows LFAs to protect against all single link and node failures and against most double failures.
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paper_title: OpenState: programming platform-independent stateful openflow applications inside the switch

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Software Defined Networking envisions smart centralized controllers governing the forwarding behavior of dumb low-cost switches. But are "dumb" switches an actual strategic choice, or (at least to some extent) are they a consequence of the lack of viable alternatives to OpenFlow as programmatic data plane forwarding interface? Indeed, some level of (programmable) control logic in the switches might be beneficial to offload logically centralized controllers (de facto complex distributed systems) from decisions just based on local states (versus network-wide knowledge), which could be handled at wire speed inside the device itself. Also, it would reduce the amount of flow processing tasks currently delegated to specialized middleboxes. The underlying challenge is: can we devise a stateful data plane programming abstraction (versus the stateless OpenFlow match/action table) which still entails high performance and remains consistent with the vendors' preference for closed platforms? We posit that a promising answer revolves around the usage of extended finite state machines, as an extension (super-set) of the OpenFlow match/action abstraction. We concretely turn our proposed abstraction into an actual table-based API, and, perhaps surprisingly, we show how it can be supported by (mostly) reusing core primitives already implemented in OpenFlow devices.
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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: SPIDER: Fault resilient SDN pipeline with recovery delay guarantees

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When dealing with node or link failures in Software Defined Networking (SDN), the network capability to establish an alternative path depends on controller reachability and on the round trip times (RTTs) between controller and involved switches. Moreover, current SDN data plane abstractions for failure detection (e.g. OpenFlow “Fast-failover”) do not allow programmers to tweak switches' detection mechanism, thus leaving SDN operators still relying on proprietary management interfaces (when available) to achieve guaranteed detection and recovery delays. We propose SPIDER, an OpenFlow-like pipeline design that provides i) a detection mechanism based on switches' periodic link probing and ii) fast reroute of traffic flows even in case of distant failures, regardless of controller availability. SPIDER can be implemented using stateful data plane abstractions such as OpenState or Open vSwitch, and it offers guaranteed short (i.e. ms) failure detection and recovery delays, with a configurable trade off between overhead and failover responsiveness. We present here the SPIDER pipeline design, behavioral model, and analysis on flow tables' memory impact. We also implemented and experimentally validated SPIDER using OpenState (an OpenFlow 1.3 extension for stateful packet processing), showing numerical results on its performance in terms of recovery latency and packet losses.
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paper_title: Survivor: An enhanced controller placement strategy for improving SDN survivability

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In SDN, forwarding devices can only operate correctly while connected to a logically centralized controller. To avoid single-point-of-failure, controller architectures are usually implemented as distributed systems. In this context, recent literature identified fundamental issues, such as device isolation and controller overload, and proposed controller placement strategies to tackle them. However, current proposals have crucial limitations: (i) device-controller connectivity is modeled using single paths, yet in practice multiple concurrent connections may occur; (ii) peaks in the arrival of new flows are only handled on-demand, assuming that the network itself can sustain high request rates; and (iii) failover mechanisms require predefined information, which, in turn, has been overlooked. This paper proposes Survivor, a controller placement strategy that addresses these challenges. The strategy explicitly considers path diversity, capacity, and failover mechanisms at network design. Comparisons to the state-of-the-art on survivable controller placement show that Survivor is superior because (a) path diversity increases the survivability significantly; and (b) capacity-awareness is essential to handle overload during both normal and failover states.
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paper_title: Pareto-optimal resilient controller placement in SDN-based core networks

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Recently, Software Defined Networking (SDN) has gained a lot of attention, even for the use in core communication networks. When deploying SDN in large core networks, the number and location of controllers must be carefully planned. A first study on this topic by Heller et al. [3] was followed by more detailed publications that included resilience or dynamic controller provisioning. In our previous work [2], we provide an overview over related work and include different resilience issues in the controller placement process. We argued that it is not sufficient to look only at node-to-controller latencies but a controller placement should also fulfill certain resilience constraints especially for the control plane. The addressed resilience issues are briefly repeated in the following. Further details can be found in our original paper [2].
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paper_title: Controller placement strategies for a resilient SDN control plane

paper_content:

Software Defined Networking (SDN) provides efficient network control and management by introducing a logically centralized control plane. However, outsourcing of the control plane intelligence to an SDN controller requires reliable switch-to-controller connection. This paper presents two strategies to address the Reliable Controller Placement (RCP) problem, which protect the control plane against single link and node failures and provide seamless failover by exploiting the principles of resilient routing. The first approach considers that switches have to be connected to a controller over two Disjoint Control Paths (RCP-DCP). The second approach considers that switches have to be connected to two Different Controller Replicas (RCP-DCR) over two disjoint paths. Both approaches are finding working and protection control paths of minimum length to enable fast and efficient failover. The two models have been compared with respect to the unprotected scenario, in terms of control path length, expected control path loss in different failure scenarios and average control path availability. The results show that both models RCP-DCP and RCP-DCR improve significantly the resilience of the control plane, while adding very limited penalty to the average control path length. If link failures are the dominating failures, both RCP-DCP and RCP-DCR offer similar performance and the best strategy depends on the topological characteristics and the number of the controllers in the network. RCP-DCR provides additional protection against controller failures and it shows better performance when node failures are dominating or are comparable to link failures.
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paper_title: Reliability-aware controller placement for Software-Defined Networks

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The Software-Defined Network (SDN) approach decouples control and forwarding planes. Such separation introduces reliability design issues of the SDN control network, since disconnection between the control and forwarding planes may lead to severe packet loss and performance degradation. This paper addresses the problem of placing controllers in SDNs, so as to maximize the reliability of control networks. After presenting a metric to characterize the reliability of SDN control networks, several placement algorithms are developed. We evaluate these algorithms and further quantify the impact of controller number on the reliability of control networks using real topologies. Our approach can significantly improve the reliability of SDN control networks without introducing unacceptable latencies.
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paper_title: Joint optimization of anycast and unicast flows in survivable optical networks

paper_content:

Most of previous research on survivable networks has been related to unicast communications. In this paper we propose a new approach to network survivability of anycast communications. To the best of our knowledge, anycast defined as one-to-one-of-many technique has not received much attention recently. To provide network survivability, we use the single backup path approach, i.e. each demand has two node-disjoint paths to provide protection against a single node failure. We formulate new ILP models to find the optimal paths for anycast and unicast connections. To test the proposed approach, we run extensive numerical experiments using CPLEX solver on four example network topologies with different scenarios of number of replica servers, and the proportion between unicast and anycast traffic. Obtained results show the efficiency of our solution in terms of various parameters including cost, path length, resource utilization, and time of computation.
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paper_title: Controller Placement for Improving Resilience of Software-Defined Networks

paper_content:

Software-defined Network (SDN) is a new architectural framework for networking that decouples control plane from data plane and provides a programmatic interface to network control. SDN enables innovations of networking technologies for Internet and data centers today in order to ease the management of the highly dynamic and complex infrastructure, to support the fine-grained traffic engineering, and to better address the mobility of virtual machines, services, and end-points. However, SDN itself opens many unanswered questions regarding reliability, performance, and security. Controller placement is a critical problem in SDN that may affect many aspects of SDN. This work introduces the use of interdependence network analysis to study the controller placement for network resilience, designs a new resilience metric, and proposes a solution to improve resilience.
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paper_title: A replication component for resilient OpenFlow-based networking

paper_content:

Software-Defined Networking (SDN) provides a new paradigm for developing innovative management applications for networks and a new way to look for the resolution to the many problems which exist throughout the Internet today. The most popular approach to this paradigm is centralized network management. This approach aims to simplify the complex and difficult task of managing the services of a network. One of the problems raised by the centralized management approach is that the issue of a single point of failure can negatively compromise resilience of the whole network. The aim of this paper is to describe a novel mechanism that provides an increase of resilience in SDN using a component organization. In the SDN architecture, components run independently on top of the network OS, receiving updates from the network or updates generated from other components. Through the handling of these multiple types of updates, we have successfully developed a new component: the CPRecovery component. The CPRecovery component is based on the primary-backup mechanism which offers resilience against several types of failures in a centralized controlled network. Our results show that the building of such service for networks using SDN is straightforward, much less complex, and less prone to errors. Furthermore, it is possible to build management applications resilient to diverse types of failures using component organization approach.
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paper_title: On reliability-optimized controller placement for Software-Defined Networks

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By decoupling control plane and data plane, Software-Defined Networking (SDN) approach s i m p l i f i e s network management and speeds up network innovations. These benefits have led not only to prototypes, but also real SDN deployments. For wide-area SDN deployments, multiple controllers are often required, and the placement of these controllers becomes a particularly important task in the SDN context. This paper studies the problem of placing controllers in SDNs, so as to maximize the reliability of SDN control networks. We present a novel metric, called expected percentage of control path loss, to characterize the reliability of SDN control networks. We formulate the reliability-aware control placement problem, prove its NP-hardness, and examine several placement algorithms that can solve this problem. Through extensive simulations using real topologies, we show how the number of controllers and their placement influence the reliability of SDN control networks. Besides, we also found that, through strategic controller placement, the reliability of SDN control networks can be significantly improved without introducing unacceptable switch-to-controller latencies.
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paper_title: Five nines of southbound reliability in software-defined networks

paper_content:

In order to deploy fault-tolerant Software-Defined Networks (SDN), the logically centralized controller must be physically distributed among different devices. In this paper, we present our initial work on determining how many controllers need to be instantiated, where they must be deployed, and what network nodes are under control of each of them, in order to achieve at least five nines reliability in the southbound interface between controllers and nodes. For this, we introduce the Fault Tolerant Controller Placement problem and develop a heuristic algorithm that computes placements with (at least) the required reliability. We run such algorithm on a set of 124 publicly available network topologies. We find that each node is required to connect to just 2 or 3 controllers, which typically provide more than five nines reliability. While the total number of controllers varies greatly and is more related to the network topology than to the network size, 10 controllers or less cover 75% of the most interesting cases. Therefore, fault tolerant SDNs are achievable by carefully determining the placement of controllers.
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paper_title: Cross-layer framework with geodiverse routing in software-defined networking

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We propose a cross-layer routing framework in the SDN (software-defined networking) domain to cope with regionally-correlated challenges. By taking advantage of the failure detection model, GeoDivRP calculates multiple geodiverse paths for resilient network communications. Coupled with the optimization model, it realizes the minimized delay-skew product when decoupling traffic onto multiple paths. We evaluate our framework using MPTCP (Multipath TCP) in the face of regionally-correlated failures and it presents better performance compared to the single path routing. We further demonstrate our web framework to automate the OpenFlow experiment by programmatically importing network topologies and execute challenge emulations using the user-provided challenge regions.
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paper_title: SDX: a software defined internet exchange

paper_content:

BGP severely constrains how networks can deliver traffic over the Internet. Today's networks can only forward traffic based on the destination IP prefix, by selecting among routes offered by their immediate neighbors. We believe Software Defined Networking (SDN) could revolutionize wide-area traffic delivery, by offering direct control over packet-processing rules that match on multiple header fields and perform a variety of actions. Internet exchange points (IXPs) are a compelling place to start, given their central role in interconnecting many networks and their growing importance in bringing popular content closer to end users. To realize a Software Defined IXP (an "SDX"), we need new programming abstractions that allow participating networks to create and run these applications and a runtime that both behaves correctly when interacting with BGP and ensures that applications do not interfere with each other. We must also ensure that the system scales, both in rule-table size and computational overhead. In this demo, we show how we tackle these challenges demonstrating the flexibility and scalability of our SDX platform. The paper also appears in the main program.
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paper_title: Management patterns: SDN-enabled network resilience management

paper_content:

Software-defined networking provides abstractions and a flexible architecture for the easy configuration of network devices, based on the decoupling of the data and control planes. This separation has the potential to considerably simplify the implementation of resilience functionality (e.g., traffic classification, anomaly detection, traffic shaping) in future networks. Although software-defined networking in general, and OpenFlow as its primary realisation, provide such abstractions, support is still needed for orchestrating a collection of OpenFlow-enabled services that must cooperate to implement network-wide resilience. In this paper, we describe a resilience management framework that can be readily applied to this problem. An important part of the framework are policy-controlled management patterns that describe how to orchestrate individual resilience services, implemented as OpenFlow applications.
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paper_title: Disaster-resilient control plane design and mapping in software-defined networks

paper_content:

Communication networks, such as core optical networks, heavily depend on their physical infrastructure, and hence they are vulnerable to man-made disasters, such as Electromagnetic Pulse (EMP) or Weapons of Mass Destruction (WMD) attacks, as well as to natural disasters. Large-scale disasters may cause huge data loss and connectivity disruption in these networks. As our dependence on network services increases, the need for novel survivability methods to mitigate the effects of disasters on communication networks becomes a major concern. Software-Defined Networking (SDN), by centralizing control logic and separating it from physical equipment, facilitates network programmability and opens up new ways to design disaster-resilient networks. On the other hand, to fully exploit the potential of SDN, along with data-plane survivability, we also need to design the control plane to be resilient enough to survive network failures caused by disasters. Several distributed SDN controller architectures have been proposed to mitigate the risks of overload and failure, but they are optimized for limited faults without addressing the extent of large-scale disaster failures. For disaster resiliency of the control plane, we propose to design it as a virtual network, which can be solved using Virtual Network Mapping techniques. We select appropriate mapping of the controllers over the physical network such that the connectivity among the controllers (controller-to-controller) and between the switches to the controllers (switch-to-controllers) is not compromised by physical infrastructure failures caused by disasters. We formally model this disaster-aware control-plane design and mapping problem, and demonstrate a significant reduction in the disruption of controller-to-controller and switch-to-controller communication channels using our approach.
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Title: Technology-related disasters: A survey towards disaster-resilient Software Defined Networks

Section 1: Introduction
Description 1: This section introduces the topic of technology-related disasters and their impact on communication networks, particularly focusing on the importance of achieving disaster resilience in Software Defined Networks (SDN).

Section 2: Measures and Methodology
Description 2: This section provides a survey of experimental works that characterize network failures and methodologies to achieve high-level network design best practices for operators.

Section 3: Reliable Software Defined Networks
Description 3: This section reviews the state of the art in data and control plane reliability for SDNs, addressing issues like failure detection, failover mechanisms, and resilient routing.

Section 4: Disaster-Resilient Software Defined Networks
Description 4: This section focuses on the emerging solutions towards making SDNs resilient to disasters, discussing approaches for multi-path routing, geo-diverse paths, and optimizing virtual topologies.

Section 5: Conclusion
Description 5: This section summarizes the paper’s contributions, highlights the importance of SDN in mitigating technology-related disaster impacts, and identifies open issues and future research directions.