# Dynamic Routings in Satellite Networks: An Overview
## 4 Existing Works on Dynamic Satellite Routings
### Dynamic Routings in the Multi-Layer Satellite Networks  
Multi-layer satellite networks were created to overcome the single-performance layer's limitations. As shown in Figure 6, a multi-layer satellite network includes satellites with different orbital altitudes and has a more complex network structure, such as LEO/MEO, \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Proposed Algorithm/Scheme** & **Reference** & **Features/Advantages** & **Contributions** \\ \hline A discrete-time routing scheme & [44] & Divided into discrete-time virtual topology setup and discrete-time path sequence selection & Discrete the topology of the satellite network into a series of static topologies. \\ \hline A new routing algorithm based connection-oriented & [45] & Considered the topology of each moment as “state”, maximized the resources of the network & Found the optimal path for each node in each case \\ \hline A explicit multi-path routing & [46] & Mainly included route discovery, route maintenance, and traffic distribution & Effectively reduced latency in the LEO satellite network, improving system throughput and load balancing \\ \hline An improved ant colony algorithm & [47] & Updated only the pheromone concentration on the optimal route to avoid the algorithm from falling into a local optimum & Shortened algorithm convergence time and reduced snapshot generation \\ \hline Soft handover algorithm for MSVN-based satellite networks, virtual node handover & [48] & Faster and smoother & The topology allowed multiple satellites to cover a single area at the same time \\ \hline A dynamic detection routing scheme & [49] & Smaller transmission latency and higher throughput rates & Adapted well to sudden changes in the network, avoided communication delays caused by queuing and large packet loss due to link failure \\ \hline A traffic balanced routing scheme & [50] & Sustained high routing capacity under low load conditions, relieved network congestion at the cost of ISL & No additional communication overhead is added, achieved traffic balancing \\ \hline A routing algorithm combining deep-first-search Dijkstra algorithm & [51] & Utilized the strengths of both DFS and Dijkstra algorithms & Reduced computing overhead, improved routing performance \\ \hline A new distributed routing algorithm & [52] & Utilized the advantages of both DFS algorithm and Dijkstra algorithm & Outperformed other routing algorithms in different metrics such as average delay, packet loss rate, and queuing delay \\ \hline A distributed congestion control routing algorithm based on flow classification & [53] & Effectively reduced computational overhead of centralized routing, alignment of different services based on distributed routing schemes & Adapted to QoS requirements and reduced queuing time in the network \\ \hline S-IoT adaptive routing scheme & [55] & Improved hybrid Q value, reward value, and discount factor using the network congestion level and node state, respectively \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The summary of the works related to the virtual topology routing algorithms.