A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> A mobile ad-hoc network (MANET) is a self-configuring, self-organized, and infrastructureless network of mobile stations, connected by radio links. The challenge to ensure network's operation means to continuously maintain updated information about the network's topology, the characteristics of the radio links and security at all levels. Due to the decentralized nature of the network, this is quite difficult. Distributed coordination and control of MANET has always been a challenge for network designers. This paper presents a proposal for a distributed flow controller, a new approach regarding the network architecture for MANET. From the perspective of the current approaches, the entire network has to be treated as a whole, from the point of view of the management, control and data plane. Our proposed approach, based on the paradigm of SDN (Software Design Network), implies a clear separation between the data plane and the control plane. This separation leads to greater flexibility on the control network, to the possibility of dynamic reconfiguration, and to the improvement of its security. <s> BIB001 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Mission-critical networks now interconnect data enters, enterprise, customer sites and mobile entities. They thus must be resilient, adaptable and easily extensible. The emergence of Software-Defined Networking (SDN) protocols, which enables to decouple the control plane from the data plane, opens up new ways to architect such networks. In this paper, we propose DISCO, an extensible Distributed SDN Control plane able to cope with the distributed and heterogeneous nature of modern mission-critical networks. DISCO controllers manage their own network domain and communicate with each others to provide end-to-end network services. This inter-controller communication is based on a lightweight and highly manageable pub-sub mechanism used by agents to self-adaptively share aggregated local and network-wide information. We implemented DISCO on top of Floodlight, an Open Flow controller, and the AMQP protocol. We demonstrated how DISCO's control plane dynamically adapts to heterogeneous network topologies while being resilient enough to survive to disruptions and attacks and providing classic functionalities such as end-point migration. The experimentation results we present are organized around two use cases: inter-domain connectivity disruption and migration of a virtual machine. <s> BIB002 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> To address future coalition operations in congested, cluttered, contested, connected and constrained battlespace, the US Army Research Laboratory and the UK Defence Science and Technology Laboratory are developing a new research program on Distributed Analytics and Information Science International Technology Alliance. In this paper, we present an overview the two interrelated Technical Areas which when jointly studied will advance the theoretical foundations of distributed analytics and information science in the context of coalition operations. These areas are (1) Dynamic, Secure Coalition Information Infrastructures and (2) Coalition Distributed Analytics and Situational Understanding. <s> BIB003 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Future military operations require versatile and integrated mechanisms for enforcement of the security policies in all three domains of information protection: confidentiality, integrity and availability. We discuss challenges and use cases related to enforcement of integrity and availability policies in federated mission environments and we demonstrate how the concept of Content-based Protection and Release (CPR) can be extended to support such policies. Furthermore, we present an approach to cross-layer enforcement of the CPR policies and introduce a proof-of-concept implementation of the CPR enforcement mechanisms in a software-defined networking environment. <s> BIB004 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> NATO has developed a Content-based Protection and Release model to support the specification of access control policies. Enforcing such policies in different scenarios is a complex task that requires consideration of several aspects, including performance and administrative burden. We sketch a solution to this problem for the Cloud and Software Defined Networks. <s> BIB005 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> The property of a military network is much complex than general network for the former has a dynamic network infrastructure, a variety of resource distribution and increasing real-time requirements. To address the network resources management issue in military network, a flattening military network resource management framework is proposed based on SDN technologies in the paper. With it, the relationships among military operations are modeled and a pre-combination service component-based resource optimization method is also proposed. The simulation results in different situations indicate that method improves the average response time for service requests. <s> BIB006 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> We propose Software Defined Networking (SDN) framework to a fleet of naval ships that relies on multiple satellite communication systems for onboard communication. Our solution addresses practical issues in current shipboard naval networks such as sharing and load balancing of multiple satellite communication links as well as overcoming limited bandwidth constraints. To ameliorate link intermittence and outage, we propose Multi-Path Transmission Control Protocol (MPTCP), which improves end-to-end data delivery by creating several subflows under one TCP session. In our SDN framework, each ship is an SDN switch with multiple SATCOM connections. The management and classification of MPTCP subflows are handled by a remote SDN controller. The cooperation between MPTCP and SDN controller leads to an agile, bandwidth efficient, robust naval network. System analysis and numerical evaluation validate the feasibility and efficacy of our SDN-based solution for such a network. <s> BIB007 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> The dynamic nature of aerial networks often results in poor network performance from an end-user perspective due to frequent and extended link outages. With growing expectations of network availability and performance, there is an unmet need to utilize all the available information in the network environment for optimizing network decisions. We present the preliminary design of a Software Defined Networking (SDN)-based prototype system that uses the knowledge about aerial node orbits to predict future network events, especially link outages. By proactively mitigating the effects of network events through SDN-based optimizations, our prototype system is expected to increase the availability and performance of aerial networks. We expect that our generalized approach of using SDNs for leveraging operationally available information for network optimization, is applicable in many different contexts in addition to aerial networking. <s> BIB008 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Successful execution of future network-centric military operations relies on effective enforcement of both need-to-know and responsibility- to-share principles. In modern military missions and coalitions, which have an increasingly agile character, a promising solution is to enforce security policies based on the properties of individual information objects - we call this approach content-based security. This article discusses the enforcement of content-based security policies at the different layers of the TCP/ IP model, and introduces a proof-of-concept implementation of a content-based protection and release mechanism in a software-defined networking environment. Our aim is to provide consistent enforcement of security policies across multiple system layers and multiple security dimensions (confidentiality, integrity, and availability). The results of an analysis of a concrete example of a software-defined network emulated in Mininet are encouraging and confirm the effectiveness of our approach with respect to improving protection of data in transit. The work presented in this article offers a basis for further research in this area. <s> BIB009 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> There has been significant recent progress in the area of software defined networking in a quest to increase automation, improve network agility and security, simplify network configuration and reduce resources to establish and maintain the network. There are a number of studies exploring the development and utilisation of policies to achieve these goals. Applying the outcomes of these studies to military networks requires a clear understanding of the nature of military applications and available mechanisms to implement the appropriate policies in a software defined networking environment. In this paper, we identify several military networks where automated policy defined networking is crucial. We further present a prototype policy defined networking solution that automatically translates high-level policies into device level implementations. <s> BIB010 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Naval surface fleets of the United States and its allies rely on multiple satellite communication systems (SATCOM) for onboard communication with other entities such as ships, shore nodes and hosts from external networks. Current practice is for an onboard ship router to select a particular SATCOM link for each outgoing traffic flow based on a mission-specific routing policy. In this paper we propose an alternative solution by viewing the multi-SATCOM link utilization task as a traffic engineering and load balancing problem — in particular, as a Multi-Commodity Flow (MCF) optimization problem. We propose using the Flow Deviation Method (FDM) as a network-wide optimal load-balancing solution that maximizes total throughput and minimizes traffic flow delay and jitter. Our approach is equally valid for both UDP and TCP flows. Network-wide global optimization is carried out via a central controller in a Software Defined Networking (SDN) framework. For TCP flows we propose a novel solution that combines the best attributes of Multi-Path TCP, SDN and FDM. Compared to single-path TCP or MPTCP-SDN without FDM-based traffic optimizer, our proposed combined scheme is more efficient in bandwidth utilization, delay/jitter minimization and also robust against jamming and intermittent link failure. Network performance results are validated via Mininet emulation tests. <s> BIB011 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> It is essential for a naval ship system (NSS) to transmit important information with very low delay for successful network-centric warfare under given time constraints. From this perspective, quality of service (QoS) control and low delay transmission are the most important components to improve efficient network utilization in NSSs. In general networks, conventional network algorithms have been optimized to manage network devices such as gateway, switch, bridge, hub, and router in a distributed manner for ease of plug-in and play operation, but which may not be optimal for the NSS. This is because, unlike the general network environment, the NSS is equipped with various nodes, which need to be operated through a centralized hierarchical network structure in accordance with their priorities. Thereby, it is difficult to apply new network algorithms to the NSS due to the closed network environment. To overcome this limitation, we propose a novel NSS employing software defined network (SDN) technology. A novel algorithm called real-time transmission via flow rate control (RTF) is proposed for the SDN-based NSS to optimize the specific environment of NSS. In the proposed algorithm, the optimal flow rates of nodes and network devices are obtained via dual decomposition in conjunction with requirements of delay and QoS. The proposed algorithm obtains the optimal solution iteratively while measuring the performance with traffic models based on real data measured in NSS. Through simulation using Floodlight, we demonstrate that RTF significantly contributes to improving throughput in real-time transmission compared with conventional algorithms. The proposed algorithm improves the average throughput by up to 11.8% while guaranteeing real-time transmission. <s> BIB012 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Software Defined Networking (SDN) is a rapidly emerging technology that brings new flexibility to networking through the separation of the control and data plane. This paper presents one SDN based framework, among several potential valid approaches, for addressing the mobility of operational nodes within a coalition environment. The operational nodes require mobility to enable roaming, multi-homing, and handover over heterogeneous sub-networks. The paper characterizes these sub-networks as protected core networks. <s> BIB013 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> Software Defined Networking (SDN) and analogous approaches to different domains like storage, compute and security have emerged as promising paradigms for controlling and managing many different types of distributed systems. In this paper, we examine the application of software defined concepts to coalition operations. Specifically, we propose the concept of Software Defined Coalitions (SDC), a mechanism by which IT infrastructure required by dynamic Communities of Interest (CoI) among coalitions can be enabled rapidly. We examine many different coalition interoperability architectures as SDC candidates, and evaluate their key performance metrics. <s> BIB014 </s> A Systematic Literature Review on Military Software Defined Networks <s> Control Systems <s> With the battlefield becoming more challenging, the aviation swarm is considered a promising organization of air combat forces to execute both combat and non-combat air missions. As a critical component of the aviation swarm, the airborne tactical network (ATN) provides the communications capability, enabling information sharing between both manned and unmanned military aircrafts as well as surface and ground platforms. The deficiencies of legacy ATNs, particularly their inability to meet the communications demands of the aviation swarm, motivated us to employ the software-defined networking (SDN) paradigm to the ATN and to design an SDN-enabled ATN (SD-ATN) for the aviation swarm. For the SDN paradigm, the communications efficiency between the control plane and the data plane directly impacts the normal operations of the network, raising a fundamental problem of designing the SD-ATN, which is that how to ensure the QoS requirements of the non-elastic information transmitted between the control plane and the data plane (non-elastic C/D information) is met. To address this issue, a transmission framework is first proposed to make it practical to provide dedicated QoS guarantee for the non-elastic C/D information. Then, a communication protocol is designed based on the proposed framework, aiming at transmitting the non-elastic C/D information in a reliable and real-time manner. The simulation results show that, in the aviation environment, our scheme does improve the transmission efficiency of the non-elastic C/D information, which performs better than legacy solutions. <s> BIB015
As in the previous subsection, the majority of articles with research contribution related to control systems have a scope that is targeted towards monitoring and control. Nazari et al. BIB007 proposed an SDN framework for a fleet of ships that relies on multiple satellite communication systems for on-board communications. The SDN framework addresses practical issues in current naval networks, such as sharing and load balancing of multiple communication links, as well as overcoming constraints related to bandwidth limitations. To overcome link intermittence and outage, the authors propose the use of Multi Path Transmission Control Protocol (MPTCP), which improves end-to-end data delivery by creating several sub-flows under a TCP session. The cooperation between MPTCP and the SDN controller leads to an agile, bandwidth efficient, and robust naval network. The authors conducted SDN-SAT performance evaluation tests, using the Mininet emulator on a commodity laptop, where the SDN-SAT controller protocol and the MPTCP Linux kernel run on the same machine. Open vSwitch is used in order to emulate the switches, while the initial results are promising in terms of functionality support and performance, although the performance of SDN and MPTCP is not addressed when the underlying network consists of a large number of ship nodes. Additionally, Du et al. BIB011 designed and implemented SDN-SAT traffic optimization algorithms and associated SDN protocols on the SDN network emulator Mininet, with focus on naval surface fleets utilizing satelite communication systems. The SDN emulation testbed uses Mininet 2.1.0, Floodlight 1.2 (for the controller), OpenFlow 1.3 Software (for the switch) and MPTCP Linux Kernel Implementation v0.90. The Flow Deviation Method (FDM) is used as a network-wide optimal load-balancing solution that maximizes total throughput and minimizes traffic flow delay and jitter, while this optimization is carried out via a central controller in a Software Defined Networking (SDN) framework. It must be noted that the FDM algorithm convergence time and control overhead (in terms of SATCOM bandwidth) exchanged between SDN switches and their controller are not addressed in this work. Also focusing on naval networks, Lee et al. BIB012 proposed an SDN based Naval Ship System (NSS) and an algorithm called "Real-time Transmission via Flow-rate-control" (RTF) for environment specific optimization. With the proposed algorithm, SDN is employed as a new network architecture for the NSS, in order to control the QoS of real-time data over a tactical scenario. An optimization problem in terms of delay and prioritization is formulated, in order to achieve real-time transmission over SDN based NSSs. Consequently, a dual-decomposition method is applied in order to solve the non-convex optimization, while the authors measure the performance of the proposed solution by employing a tailored Floodlight SDN controller. The proposed SDN-based NSS is virtually established using Mininet, in order to verify the efficiency of the algorithm. The network topology used for the executed experiments is composed of 500 nodes and eight gateways, while Floodlight V1.1 and OpenVswitch are utilized for the implementation. Finally, the traffic of each node is generated individually, by utilizing the Hierarchical Multi-level On/Off Source (HMLOS) traffic model. In respect to coalition operations, McLaughlin et al. BIB013 proposed an SDN based framework for the mobility management of operational nodes within coalition military environments. The examined problem is analyzed in depth by the authors, providing significant insights in terms of operational, functional, and security constraints and requirements. The proposed framework seeks to implement Protected Core Networking (PCN) utilizing SDN, where PCN separates the transport and information domains, towards multinational networks that provide flexible and secure transport services. The authors describe in detail three logical topologies for the SDN controller, namely: (i) centralized, (ii) partially-meshed, and (iii) extension to static hosts. Within the same application domain, Pham et al. BIB003 summarized a set of research challenges related to Content Based Networking (CBN) in military coalition networks. As presented by the authors, in a joint military operation, the key focus is to bring together different partners into a single mission, maintaining the ability to securely share data across the distinct teams. Furthermore, it is required that the network operators are capable of performing analytics and maintain service related situational awareness in a resource constrained network. SDN is promoted by the authors as an enabler for CBN in respect of easing the complexity, and allowing the dynamic discovery of distributed information. However, centralized network control, such as OpenFlow, does not fit with disruptive networks. The paper suggests placing future research focus on: (i) hybrid SDN in order to allow network independence from the controllers, (ii) east-west control plane communication between network controllers, (iii) security implications related to dynamic distributed services, (iv) content aware networking by mapping the service request to the network control, and (v) distributed analysis in order to derive human situational understanding. Also focusing on coalition networks, Mishra et al.  examined how the principles of SDN can be utilized in order to improve cyber situational awareness in coalition environments within military networks. The authors discuss the adaptation of the Observe, Orient, Decide, Act (OODA) loop within SDN in order to improve security awareness. The OODA loop describes a decision-making process and is reflected in an SDN controller application. The authors also suggest that an east-west communication protocol is required for controllers to share what they have learned. The article explains comprehensively the concepts related to the OODA loop but does not provide an extensive discussion over the corresponding requirements and constraint for its adaptation on SDN. Consequently, Mishra et al. BIB014 examined the application of SDN across military coalition operations, proposing a mechanism for enabling dynamic Communities of Interest (CoI) within these environments, and evaluating such interoperability architectures in accordance with key performance metrics. Furthermore, this article provides a comprehensive overview of tactical communities of interest and the underlying constraints towards their deployment and management. The authors proceed by merging the two, and discussing the topic of Software Defined Coalitions (SDC), as the mechanism that is capable of facilitating the operation of dynamic tactical CoIs. Accordingly, they identify three interoperability levels, namely: (i) network, (ii) network and storage, and (iii) network, storage, and compute. They clarify that (ii) combines mechanisms from SDN and Software Defined Storage, while (iii) builds upon the concept of Software Defined Environments. Consequently, the article proposed three types of architectures, namely: (i) simplification, (ii) brokered, and (iii) federated, comparing the three in terms of complexity, trust, and standardization. The presentation and discussion of the proposed mechanisms is sound and comprehensive, although further scenario based validation/verification can be desirable. With focus on aerial networks, Iqbal et al. BIB008 proposed an SDN and SDR architecture that can predict network outage in aerial networks. Under the assumption that aerial flights have fixed orbits, the authors suggest that the radio can inform the centralized controller about its future position, allowing for the flow routes and radio links to be switched in advance and prior to network outege. Hence, the availability is expected to be increased by the use of predictive SDN. The presented architecture is based on the assumption that the radio link outage can be predicted. Accordingly a corresponding architecture is proposed and tested in a virtual environment with OpenDaylight, Quagga, and OVS. The availability is tested by comparing network convergence for Open Shortest Path First (OSPF), reactive SDN (LLDP) and proactive SDN, where the proactive SDN showed maximum availability. Nevertheless, it must be noted that the proposed solution is not compared with overlay networks such as Multiprotocol Label Switching (MPLS) with segment routing. Within the application domain of military networks, the majority of articles is focused towards policy based management. Skappel  presented a master thesis with the objective of testing how an SDN controller can be used as a tool for controlling traffic in a dynamic environment. This thesis shows that SDN can allow network monitoring, and utilize this input in combination with predefined policies in order to prioritize, police, ensure QoS, and dynamically adjust the flows for different controllers. Wrona et al. presented two consecutive articles withing the same application domain and scope BIB009 BIB004 . Within these articles, the authors discuss content-based security policies at different levels in the OSI stack, and present a proof of concept implementation in an SDN environment. They base their security concept on content based protection and release policies developed by NATO. The principle is that an information object is not labeled by a sensitivity tag, but it is labeled by a content tag that describes the object. Access control is based on the authentication of both the user and the terminal, while if both policies are accepted then the system release the object to the user. In the SDN context, a network packet header information can also have a content label that defines a security label. Their first article shows a proof of concept implementation of the proposed solution by retrieving information from different network layers, while the second article shows how an SDN controller that calculates the whole path in the network can also make the path itself a security label. The proof of concept implementation showed that the packet forwarding path can be protected in this manner. Hence, different paths can have different security protection levels, and the forwarding path can be decided based on content and access levels. Nguyen et al. BIB010 presented a short review of military policy based management methods and suggest a model for verifying, prioritizing and deploying a group of policies based on SDN. The core of the article is a graph model that detects conflicting network polices within the sum of applied network policies. The output of the model is a set of resources that a node can access. In order to detect conflicting policies, the authors suggested a step by step procedure to conform the policy and deploy it in SDN. The authors used a standard SDN controller with virtual switches to deploy policies across SDN. The core of this article relates to network policies and deconflictation, while the validation focuses primarily on policy deployment as OpenFlow rules. Moreover, Armando et al. BIB005 proposed a method for facilitating the specification of access control policies in accordance with the NATO-Content Based Protection and Release model (CBPR). The CBPR model is built upon the Attribute Based Access Control (ABAC) model, and supports the specification of access control policies in complex organizations and coalitions, with extended variety of deployed resources. Accordingly, the authors propose the replacement of monitor based policy enforcement with cryptographic enforcement, in order to reduce the administrative burden, and enhance performance specifically within cloud and SDNs. The suggested solution relies on Cipher text-Policy Attribute-Based Encryption (CP-ABE), for which as the authors describe "The key idea is that a user should be able to decrypt a ciphertext only if he/she holds a key associated to certain attributes, under the assumption that user keys are issued by some trusted party". Furthermore, the authors propose the adoption of this method to SDNs, for the enforcement of protection policies (during message forwarding decisions) in accordance with specific node and link attributes. The aforementioned statement is promoted as a suggestion by the authors, while deployment and validation is required. Mulec et al. BIB001 proposed a distributed flow controller for mobile ad hoc networks, seeking to provide dynamic reconfiguration and to improve security. The functions of the controller are (i) provisioning of AAA (authentication, authorization and accounting) services, (ii) flow management across the network nodes, (iii) centralized network traffic control, and (iv) enforcement of security policy. Unicast, multicast and broadcast communication is supported, while suitable mechanisms are provided for the management of topology changes. A core component of the proposed system is the selection mechanism, which establish the number of required controllers and their prioritization. This mechanism is mathematically analyzed, and tested within a test-bed consisting of seven wireless nodes providing positive initial results. The article provides a small scale validation, while further testing is recommended, primarily related to the size of the network and the tested mobility patterns. Furthermore, Poularakis et al.  proposed a set of novel architecture designs for SDN-enabled mobile ad hoc networks in the tactical edge, discussed the challenges raised by the ad hoc and coalition network environment, and presented corresponding solutions. The proposed approaches build on experimental evaluations, utilizing theoretical results from SDN deployments in large backbone networks. The study provides useful insights on the examined environment, yet security related aspects could benefit from further evaluation. Qing et al. BIB006 described an optimization algorithm that can be used for prioritizing service requests in military operations. According to the article, when a network does not have enough resources to serve all requests, these can be prioritized based on a predefined policy. To enable service prioritization, a set of resources that are required by the service must be prioritized. In the context of SDN, this primarily concerns prioritization of traffic on network devices. The authors suggest precombining these resources into groups, and proposed an algorithm to optimize this precombination. The authors suggested two models of optimization, where the provided results show that precombination of resource dispatching improves the network performance. Furthermore, Bouet et al. BIB002 proposed a DIstributed SDN Control (DISCO) plane which allows handling the distributed and heterogeneous nature of modern mission-critical networks. The proposed approach relies on a per domain organization, where each DISCO controller is in charge of an SDN domain, using a lightweight and manageable publish-subscribe mechanism for sharing aggregated local and network-wide information with neighbor SDN controllers. Furthermore, the authors demonstrate how DISCO dynamically adapts to heterogeneous network topologies, while providing classic functionalities such as end-point migration and being resilient enough to survive disruptions and attacks. The authors implement DISCO on top of Floodlight, an OpenFlow controller, and the Advanced Message Queuing Protocol (AMQP). The network is emulated using Mininet to create topologies and instantiate Open vSwitch switches and virtual hosts. Mininet is hosted on a dedicated VM (Virtual Machine) and the controllers are hosted on separate VMs. To measure performance, the authors show an evaluation of its functionalities on an emulated SDN according to two use cases: (i) inter-domain connectivity disruption and (ii) migration of a virtual machine. The results show how DISCO dynamically adapts to heterogeneous network topologies, while being resilient enough to survive disruptions and attacks, and further being able to provide classic functionalities such as end-point migration. Additionally, Chen et al. BIB015 proposed a transmission framework for Software Defined-Airborn Tactical Networks with the aim of providing a fundamental infrastructure for improving the communications capability between the control and data planes. Furthermore, the authors proposed a dedicated communication protocol, aiming at transmitting the non-elastic C/D information in both a reliable and timely manner. The authors conducted a simulation for the purpose of illustrating the performance of their scheme. They built a simplified avionics network in EXata 5.1 for every aircraft, and regarded an avionics network as a node of the SD-ATN. The simplified avionics network, which is considered as the common node, includes two devices that implement the functions of the platform controller and SD-ATN transmission system, respectively. The avionics network that represents the active control node includes one more device that implements the functions of the SD-ATN controller, while the devices within an aircraft are connected through wired links. Finally, Fagervoll  explored how SDN can be incorporated, both physically and logically, within heterogeneous tactical networks. Being a Master's thesis, this work provides a comprehensive introduction into the related concepts and underlying requirements, while the main contribution is focused towards the collection of network information for the establishment of topology mapping. The author evaluated three conceptual models and proposed an approach for topology mapping through local legacy routers. The traditional SDN architecture requires a node to contact the centralized SDN controller whenever it encounters a new request in which it needs to make a decision for a data plane operation, and for which it does not have the required control plane information. However, this centralized architecture is not suitable for military tactical networks with high levels of dynamism and frequent network failures that can result in slow network updates as well as significant controller overhead. The areas for further exploration include, but are not limited to: • Investigating SDN controller fail-over mechanisms to automatically take the control of the switches when a neighbour controller fails. • Describing a distributed SDN controller network architecture that can meet reliability requirements through the use of multiple remote SDN controllers with integrated redundancy features. • Exploring Software Defined Coalitions (SDCs) which share assets at increasing granularity, allowing a better sharing of the network, storage and application level services available in each of the partners. • Identifying the required and appropriate abstractions which should be exposed to the partners, in respect to the policies of the coalition members. • Creating the right interfaces for OODA (Observe, Orient, Decide and Act) based control of individual elements. • Developing appropriate routing, security, information and asset sharing mechanisms for coalition operations.