# Multi-Topology Routing Algorithms in SDN-Based Space Information Networks
## 3 SDN-Based SIN Management Architecture  
This paper first establishes a SDN-based SIN management architecture. Based on SDN, this paper divides the architecture of the SIN into three parts: space-based network, air-based network and ground-based network. Three kinds of network controllers, space-based network controllers, air-based network controllers and ground-based network controllers, are established on the ground to control space-based network, air-based network, and ground-based network respectively. At the same time, according to the geographical area, the ground-based network, air-based network, and space-based network can be further divided into several domains, each domain is controlled by a single domain controller. Space-based network is mainly composed of a variety of satellites with different orbits. The satellites from far to near are geostationary orbit satellites (GEO), medium orbit satellites (MEO), and low orbit satellites (LEO). The air based network is mainly composed of stratospheric airships, balloons, manned or pilotless aircraft. The ground-based network part is mainly composed of gateway control center, large gateway station and ground public communication network [20]. A SIN resource management and dispatching center is established on the ground, which is responsible for the link calculation of the whole SIN and the control and allocation of the whole network resources. The architecture of the SIN management based on SDN is shown in Figure 2[21]. SDN-based SIN management architecture is divided into three layers: application layer, control layer, and infrastructure layer. The top layer is the application layer, which refers to a series of tasks such as emergency communication and deep space exploration completed by the SIN. At the bottom is the infrastructure layer, which includes satellites in different orbits, stratospheric vehicles, gateway base stations and other facilities serving the SIN. In the middle is the control layer, which is composed of network controller and the SIN resource management and scheduling center. In the control layer, the single-domain controller collects topology information of each node in the domain. When the intra-domain traffic arrives, the single-domain controller calculates the intra-domain links, controls the nodes by sending down the flow table, and realizes path building and traffic processing. The SIN resource management and scheduling center is responsible for the control and allocation of the whole network resources. It obtains the topological resources of each domain from the single domain controller and establishes the whole network topology. When cross domain resources come, SIN resource management and scheduling center is responsible for cross domain routing computation and cross domain transmission. In addition, due to the heterogeneity of different inter-domain networks, SIN resource management and scheduling center is also responsible for the unification of heterogeneous device interfaces to achieve cross-domain interconnection of heterogeneous devices. In the SIN management architecture based on SDN, north-oriented and south-Oriented protocols play an important role. North-oriented protocol is a series of interfaces between application layer and control layer. There is no unified standard for its interface protocol. Therefore, the control layer provides many extensible API interfaces for different users in the application layer, each API interface  
Figure 2: Space information networks (SIN) management framework based on SDN. corresponds to a corresponding application, so the control architecture can implement a variety of application services. A typical southbound protocol is OpenFlow [22], which is responsible for the interaction between the control layer and the underlying implementation switches to complete the forwarding of infrastructure layer data.