# A Systematic Literature Review on Military Software Defined Networks
## 5 Additional Contributions
### General Software Defined Network Applications  
Twenty-six papers [59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84] have been found to discuss SDN applications in a context slightly related to military networks. SDN applications can be used to control network traffic, monitor, test, or orchestrate a network. In military networks running SDN, these applications can simplify both operational and administrative tasks in the network. This includes simplifying the management operations such as applying monitoring to network elements [59], but it can also be used in other contexts such as routing network traffic in power grids on a military base [61], or tracking moving base-stations in vehicles [63]. However, the articles that are reviewed in this sections do not apply directly to the military domain, but include general SDN applications that have been identified by the corresponding authors as adoptable to the military domain. The nature of the SDN technology is appealing to military networks, since SDN offers lower complexity and lower cost that allows for fast failovers and network redundancy in low cost networks, without using expensive technologies such as MultiProtocol Packet Label Switching (MPLS). SDN opens up for a more flexible routing mechanism, where the network routing on switches and routers can be based on more attributes than only the destination IP and MAC address. This flexible forwarding mechanism applies per flow, and therefore it is possible to use SDN to achieve multipath routing [79]. In military networks, load balancing/ multipathing of constrained bandwidth links is a cheaper alternative than overlay networks or BGP. From a security perspective, multipathing also makes it more difficult to do wiretapping, when parts of the network traffic are diverted around the  
Figure 1: Associated SDN technologies. wirelap. An alternative to physical multipathing is to use multiple radio channels or optical channels to split the traffic into multiple virtual frequency channels [73]. The concept of making advanced routing decisions based on alternative headers other than the IP addresses is also reflected through security and content routing. An approach for confusing an attacker is suggested by [PERSON] [62], by randomizing IP addresses and routing according to other attributes such as the IP option field. However, such SDN routing applications are only possible in small and closed networks. A similar approach also applies to content-based networking (CBN) [70], by extending the network devices to also be able to read the data content of a packet and base the routing decisions on content. Currently, no SDN technology is available for CBN, and no standard exists on how the network packet headers and the data content is used for making routing decisions. Advanced SDN routing can also be enabled by mixing packet header attributes. In order to enable network isolation, it is most common to use one domain identifier in the packet header, such as a VLAN ID for layer 2. [PERSON] [82] presents an abstraction layer for network programming that opens up for utilizing a combination of both layer 2 and layer 3 when making SDN forwarding rules. This enables network isolation within one VLAN when IP addresses do not overlap. Monitoring applications combined with flow control in SDN can also increase the performance of an SDN network. Due to the dynamics of SDN, network flows can be specified and changed in a per flow, per network device basis. Hence, the controller is capable of calculating the utilization of the network links and performing load balancing and prioritization of flows per link. By calculating the full paths and their bandwidth utilization, spectral graph theory can be used to increase the robustness and the performance of low bandwidth military networks [71]. A similar network performance enhancing application is also suggested in an architecture named WASP [69] that is customized for wireless networks.