# A Systematic Literature Review on Military Software Defined Networks
## 7 Discussion and Recommendations for Future Work
### Architecture  
Most of the proposed SDN architectures in tactical military networks follow the key ideas of the SDN paradigm. For instance, the SDBN architecture considers four planes: forwarding, control, application, and management [15]. However, the current realizations of SDN technologies are still far from fully addressing the realistic requirements and constraints of dynamic tactical networks, and in extending military networks. Many challenges in SDN architectures require further research effort, with the main focus areas for future research being:  
* Development of prototype for East-West communication between network controllers and nations. In the case of a multi-controller-based architecture, the East-West interface protocol manages interactions between the various controllers.
* Resilience of network controllers as they currently present a single point of failure.  
\begin{table}
\begin{tabular}{c l c} \hline \hline
**Rank** & **Article** & **Citations** \\ \hline
1 & Software Defined Radio Challenges and Opportunities [118] & 241 \\
3 & Survey of Important Issues in UAV Communication Networks [23] & 215 \\
2 & Securing the Software Defined Network Control Layer [76] & 116 \\
4 & The New Frontier in RAN Heterogeneity Multi-Tier Drone-Cells [144] & 98 \\
5 & Designing and implementing future aerial communication networks [137] & 90 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Top five citations for additional contributions.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Significant Contributions** & **Additional Contributions** \\ \hline SDN & 38 & 28 \\ NFV & 0 & 8 \\ SAT & 2 & 5 \\ UAN & 0 & 3 \\ UAV & 2 & 2 \\ WSN & 0 & 17 \\ SDR & 1 & 28 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Type of articles.  
* Standardization of Northbound and Southbound interfaces to the SDN controller. The Northbound and Southbound interfaces are currently poorly defined, presenting a barrier to integration with management systems and peer-level networks.
* Data offloading techniques at the physical layer in order to reduce delay and congestion of the network.
* Mechanisms to migrate the SDN controller between nodes connected by restricted bandwidth wireless links.
* Control of network polices and how to share network policies across nations and network controllers.
* Exposure of the control plane traffic over wireless media introduce security vulnerabilities.
* Development of a suite of protocols and applications specifically designed for SDN architectures in tactical, and in extend military networks.
* Targeted study on the functions of SDN that can guarantee the routing QoS for specific operational groups, according to the urgency level of the task, and the scalability of the controller, extending to switches that can be applied to large scale networks.
* Development and testing an architecture dedicated to heterogeneous networks.
* Development of sophisticated schemes for ingress/egress filtering at each real-time SDN-enabled switch. This can help to better identify the properties of each flow (priority, class, delay, etc.) and then develop scheduling algorithms to meet their requirements.
* Enhancement of the SDN paradigm on battlefield networking (SDBN) architecture and the operational scenarios in which the architecture could be deployed. For example, the utilization of high-level policies to operate the SDBN as a whole, could be addressed by intent-based management (i.e., Autonomic Management) or service abstractions for policies (i.e., Simplified Use of Policy Abstractions--SUPA).