# 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
To address the issue of LEO satellite networks, the work in [30] devised a geographic IP sub-network partitioning model applicable to the addressing scheme of LEO networks. The segmentation model employs a spherical coordinate system to characterize the location information of LEO satellite orbits and geographic subnetwork regions. On this basis, the author constructed a mathematical model for anomalous addressed users. In the mathematical model, the size and partition of the geographic area will determine the expected proportion of the number of anomalous users. The approach dramatically decreases the number of abnormal users by dividing the ground area into smaller area modules, simultaneously reducing the overhead of partial routing. Nevertheless, while the percentage of anomalous users has diminished during the IP area segmentation, LEO satellite network mobility management and routing table update costs have risen. Thus, the scheme can cut communication expenses by allocating appropriate ground subunits in the routing table updates and mobility management. Satellites can interact with terrestrial users within this LEO network through IP addresses. IP addresses only change when the user or satellite moves to another sub-network, shielding the satellite network from the dynamic nature to a certain extent. However, the specific relationship between partial routing expenditure and abnormally addressed users in the case of increasing abnormally addressed users remains to be studied in depth. However, the model fails to account for network traffic and anomalous user routing optimization. Geographic subnets can reduce the number and generation time of routing tables in LEO networks and maintain routing table stability. An enhanced geographic addressing strategy was propounded in [31]. Motivated by the above, the author developed a framework for the distribution of network user traffic under various geographic sub-networks and optimized the anomaly addressing model. A routing broadcast strategy was presented to address the anomaly addressing optimization issue. The routing solution reduces the system packet loss rate coming from user anomaly bands in the same geographical subnet area. Simulation results indicate that the improved geographic addressing strategy can achieve higher system throughput at a lower routing cost. Simultaneously, the throughput loss caused by anomalous addressing traffic diminishes with the reduction in the geographic sub-network partition area. Nevertheless, the routing broadcast strategy in the present scheme leads to link occupancy. Therefore, we can tackle the problem by designing load-balanced routing algorithms in the subsequent research. In particular, the anomaly addressing strategy introduced by the scheme fails to consider end-to-end delay, route reassembly rate, and other routing cost impact factors, making the performance of the strategy somewhat limited. Packets are routed to a non-specified satellite node in the geographic routing mechanism. Due to the fact that the majority of satellites are not geographically distributed with the earth, it is impossible to accurately divide the surface into the corresponding grid. To address the issue, the work in [32] introduced a new routing path selection algorithm based on MAC addresses. The scheme embeds the location of the terminal in the MAC and separates the topology data of the network from the IP address of the terminal. Based on this, the movement of the terminal may not require a full network-wide update, effectively addressing the routing issue caused by the movement of the satellite. Comparing the above approach to source routing shows that it can guarantee fast and reliable data delivery in diverse traffic scenarios. The algorithm significantly minimizes the end-to-end delay and re-route rate of the network. Meantime, geographic identifiers in MAC addresses support fast routing table lookup and switching. In addition, the routing program also investigates the satellite overload problem and employs a re-routing mechanism.