# Dynamic Routings in Satellite Networks: An Overview
## 2 Related Works
By utilizing the position message of the source node and destination node, the distributed computing method is used to obtain the optimal path. Each node can dynamically select the next-hop by informing its neighbors of the congestion state in the algorithm. Thus, the average queue time delay and packet loss rate are decreased. For multi-layer satellite networks, the authors focused on four routing algorithms. First, the authors analyzed the satellite grouping and routing protocol (SGRP). The main idea of SGRP is to transmit packets through the shortest delay path. SGRP includes three phases: delay reporting from LEO satellites to the MEO layer, delay exchange at the MEO layer, and routing table construction. In addition, the SGRP routing algorithm provides a mechanism to resolve congestion and satellite failures to avoid packet loss. Then, the authors analyzed the hierarchical satellite routing protocol (HSRP). HSRP applies to satellite-to-satellite (SOS) networks for long-distance correlation transmission. SOS is a combined network with multi-layer constellations. In SOS networks, the orbital altitude and number of layers can vary depending on the performance and type of services provided. HSRP identifies paths that meet delay constraints and improves resource efficiency. To make the satellite network autonomous, the authors analyzed the SARA algorithm. SARA partitions the network topology and calculates the routing table using ISL's connection criteria. When a node fails, the GEO satellite can recalculate the routing table for the failed area. Finally, the authors analyzed the expanding range route selection (ERRS) routing algorithm. ERRS can find the EDT optimal route by searching each snapshot of the time-varying topology. Simulations demonstrate that the algorithm can cut the end-toend transmission time and boost the network throughput. Additionally, the author also summarized routing methods in multi-layer satellite networks [10]. Firstly, the satellite group and group management (SGGM) routing were used to implement a three-layer network structure suitable for MEO/LEO two-layer satellite networks. Then, the disruption-ant network (DTN) was analyzed. Afterward, the data-driven routing algorithm (DDRA) was analyzed for the GEO/LEO two-layer satellite networks. Finally, based on region partition, an improved short hopping path was used to balance the network traffic and reduce the queue delay. Although these algorithms could provide optimal selection and dynamic adaptability, they would increase the overhead of routing protocols between satellite layer groups. The LEO satellite network, as an essential part of satellite communication network, is one of the hot spots of current research. The dynamic virtual topology routing (DVTR) algorithm introduced a two-phase routing algorithm to compute the virtual path table. The footprint handover rerouting protocol (FHRP) was analyzed to reduce the overhead of updating the routing table. FHRP was a connection-oriented routing algorithm designed to reduce network overhead caused by frequent routing table updates. Although the above approaches can balance network traffic, this type of routing algorithm cannot respond to both link load changes and link-state changes [11]. Nevertheless, the routing performance was significantly degraded when the network topology lost its regularity. Uneven terrestrial service distribution may lead to inter-satellite link congestion (LRES), making load balancing a key issue for the LEO satellite network. Therefore, by extending the range of available paths, combined with congestion avoidance mechanisms, a load balancing routing algorithm based on extended link states was analyzed in [12]. The scheme maintains path optimality and decreases network congestion. In the algorithm, the network consists of inter-satellite links (ISLs) with LEO satellites. In order to enable better data transmission in this network, the designed routing algorithm can dynamically adjust the path according to the link state in the network.