# A Systematic Literature Review on Military Software Defined Networks
## 4 Identified Significant Research Contributions
### Control Systems  
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. [PERSON] et al. [PERSON] et al. (2018) 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, [PERSON] et al. [PERSON] et al. (2018) 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, [PERSON] et al. [PERSON] et al. (2018) 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 usingMininet, 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, [PERSON] et al. [42] 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.