# A Systematic Literature Review on Military Software Defined Networks
## 5 Additional Contributions
### Network Function Virtualization  
Network Function Virtualization (NFV) refers to the concept of moving network services into a cloud environment. A characteristic networking feature in NFV is Service Function Chaining (SFC) that enforces end-user data traffic to traverse data-center services also known as middleboxes. SDN is a technology that can be used to enable such routing, where the SDN controller is responsible for steering the traffic through a chain of such NFV services. Eight articles have been found to discuss NFV in a military context [86; 87; 88; 89; 90; 91; 92; 93].  
An NFV and SDN survey by [PERSON] et al. [86] presents both civil and military application domains by coupling NFV with SDN. Content-centric networking, on-demand virtual networks, and cloud services are examples of how NFV can contribute to make a more reliable, faster and secure network. NFV contributes to solve the multi-domain SDN controller problem by abstracting the inter-domain communication to a standardized NFV orchestration level. However, orchestration, interoperability,portability, integration, management, automation and resiliency are new research challenges that must be solved.  
[PERSON] et al. [87] presents an architecture of how drones can transmit video in rural areas with the support of an NFV/SDN enabled backbone. This is an example of a military application in a distributed NFV topology, where distributed Virtual Network Functions (VNFs) are used as distributed video storage and network overlay routing. By re-encoding video, the distributed NFV services can then adapt the video quality based on bandwidth constraints, while Service Function Chains (SFC) can be used in order to select the most appropriate network path. A similar overlay network application is suggested by [PERSON] et al. [88], where distributed NFV services are used in order to route the network traffic based on an overlay network with SFCs instead of plain destination IP routing. Distributed QoS algorithms can then ensure QoS in the overlay network, based on bandwidth requirements and policies. Their results are also reflected through a paper of satellite SDN networks [90], a survey [89] of NFV in military networks and an NFV-based satellite architecture of distributed NFV.  
All authors state that distributed NFV is a new way to distribute routing, enable security policies by overlay networks, and increase network performance. [PERSON] et al. [91] also presents challenges with the management and orchestration of such typologies in the context of space-ground networks and cross-domain applications. However, all the papers suggest future work to be focused around the orchestration of the NFV services, and how to translate the security policies across the domain boundaries. It is noted that none of the reviewed papers discuss or give an example of control plane to control plane protocols of the overlay NFV networks in a military context. This corresponds to the NFV approach of using the orchestration layer for inter-domain communication. However, [PERSON] et al. [93] suggests an SDN approach for an inter-domain control plane protocol, in order to increase the performance in heterogeneous military networks. They indicate that the use of API based control plane to control plane communication is enhancing the network performance compared with traditional BGP communication.