# Dynamic Routings in Satellite Networks: An Overview
## 2 Related Works  
There have been many existing works on satellite routings published in recent years. The majority of the existing works on routing problems in satellite systems analyze routing models and routing strategies. The current achievements of satellite routings have been analyzed from various angles. The work in [8] investigated the space-air-ground integrated network, with a special focus on two kinds of IP routing algorithms: traffic-based algorithms and QoS-based algorithms. Given that SAGIN's services have distinct QoS requirements, assigning their service flows to the proper terrestrial, satellite, or air-to-ground links based on QoS requirements and link quality is worthwhile. Therefore, the authors analyzed the traffic-based routing algorithm. The algorithm considers three classes of traffic: (i) delay-sensitive, (ii) throughput-sensitive, and (iii) best-effort. In order to achieve better performance in avoiding congestion, reducing queueing delay, lowering packet drops, and increasing total throughput, a traffic-light-based intelligent routing (TLR) scheme for satellite internet  
Figure 1: Article layout. protocol (IP) networks was developed. Traffic lights are used to indicate the congestion status at both the current node and the next node. With the growth of mobile data traffic in future terrestrial 6G wireless networks, satellite capacity is being used to reduce traffic and lighten the stress on terrestrial links. The UAV-assisted air-ground communication distance can be significantly reduced, and the capacity of the network can be increased by appropriate routing algorithms. Hence, a connectivity-based traffic-density-aware routing algorithm for vehicular and ad hoc networks (VANETs) employing uncrewed aerial vehicles (UAVs) has been proposed. By using UAVs as the relay nodes and combining the real-time traffic density based on the periodic exchange of messages, the algorithm could find the shortest stable connected path to forward packets to their destinations at each moment. In addition, the authors analyzed a multi-path QoS routing algorithm based on a polar-orbiting satellite network. They provided insight into the impact of some key factors on the observed QoS parameters. The QoS metrics mainly include end-to-end delay, delay jitter, and bandwidth in this algorithm. However, due to the high mobility of LEO satellites, some ISLs in the network are not always available. Therefore, there should be additional QoS elements to measure the network performance. The authors changed the genetic algorithm's fitness function, variation probability based on satellite congestion, and simulated annealing to handle population variety. Finally, an inter HAPs-satellite routing method is investigated to maximize satellite link capacity and achieve network load balancing. Simulations demonstrate that the algorithm can achieve the same throughput while saving 30% of the satellite's link capacity. The work in [9] reviewed the routing algorithms in satellite networks. Based on virtual nodes, the authors focus on three routing algorithms. First, the localized zone distributed routing (LZDR) scheme was analyzed. The routing process of the algorithm was divided into two parts: inter-zone and intra-zone routing. Finally, the low-complexity probability routing algorithm (LCPR) was used to solve the next-hop selection when the satellite received data packets. However, the LZDR algorithm only described the method of computing inter-domain routing based on the path with minimum hops. In addition, the LZDR algorithm is only suitable for the polar orbit of LEO satellite networks, not for the tilted orbit satellite constellations. The driven routing algorithm (DRA) derives the constellation topology from the bound ground base station. When satellite nodes or links fail, the performance of the DRA algorithm is significantly degraded. The LCPR is used to solve next-hop selection when a satellite receives a packet.