# Dynamic Routings in Satellite Networks: An Overview
## 4 Existing Works on Dynamic Satellite Routings
### Dynamic Routings in the Single-Layer Satellite Networks
#### 4.1.1 Topology Planarization  
Topology planarization involves treating the entire LEO satellite network as a two-dimensional plane in which satellites do not even change logical positions. Two-dimensional coordinates can represent the satellites to achieve the purpose of shielding the topological dynamics of the network. Table 4 summarizes the works related to the topological planarized routing algorithm. The work in [27] firstly used the topology planarization method to shield the highly dynamic nature of the satellite network topology. Based on this, an LEO satellite routing algorithm was proposed. The solution has been experimentally proven to provide low latency, high-frequency rates, and high-quality video delivery to mobile users. However, for such routing protocols, when the satellite network topology changes dynamically based on time, the initially assigned routing paths will no longer be applicable. Thus, in such an LEO satellite network, all satellite links must reacquire new routes, i.e., re-route. However, re-routing mechanisms can cause huge computational overhead in a resource-constrained LEO satellite network, affecting communication quality. Hence, connectionless routing schemes that do not require re-acquisition when the topology changes are more suitable for fast time-varying network topologies. In addition, the route needs further theoretical study in terms of mobility and traffic congestion awareness. As the satellite network technology is improving gradually and the functions of satellite network nodes are enhancing, many satellite nodes can sense geographic location information. The geolocation-based satellite routing algorithm has an inherent advantage over the other satellite routing algorithms. Hence, the research on this type of satellite routing algorithm has fundamental practical significance. The work in [28] developed a new geographic information-based routing  
Figure 5: Single-layer satellite networks. algorithm using a delta-type satellite constellation. The algorithm eliminates the need for correspondence between static logical and dynamic networks, significantly reducing the signaling overhead of processing time-varying topologies. To minimize the time latency caused by inter-satellite link switching, satellite nodes in this network are not always required to access the nearest satellite but to remain in contact with one satellite as long as possible. Simulation outcomes show that the scheme can obtain high-efficiency packet routes despite requiring less on-star computing and storage resources. In addition, it does not require the storage of large amounts of network topology data and is therefore scalable. However, the routing algorithm for LEO satellite networks with a particular orbital inclination has certain limitations. In future research, we can consider extending the algorithm to a global coverage network of 3-4 GEO satellites to provide relay datagram services to users in the polar regions. In recent years, DTN has adopted a store-carry and forward transmission strategy to provide route forwarding and storage functions for satellite networks with frequent interruptions without assuming continuous connectivity of network links. However, current dynamic routing algorithms (DRSA), including contact graph routing (GCR), cannot locate end-to-end routes over a series of time-broken links. Therefore, a new extended range routing algorithm (ERRA) was propounded in [29]. The algorithm is a GCR-enhanced routing strategy that can cope with intermittent connections in relay satellite networks. The algorithm involves calculating the satellite orbit information in the ground station and selecting the route. Nevertheless, the algorithm calculates the optimal path on a time-varying topological snapshot and could not guarantee a successful delivery rate and minimal delivery time. In particular, the scheme considers two new metrics of routing tables for link reliability when selecting routing paths, allowing it to make more efficient use of constrained satellite network resources.