## 3 Key Technologies of UAV-Assisted SAGINs
### Routing Protocols
#### 3.1.2 Proactive Routing Protocols  
In the construction of SAGINs, proactive routing protocols maintain routing tables at each network node to achieve the real-time tracking of network topology and optimize packet transmission paths. A proactive routing protocol is a routing protocol based on global network information. In this protocol, each node periodically broadcasts routing information and maintains a routing table containing routing information for all other network nodes. These routing tables enable each node to have the global topology information of the network and thus know the optimal transmission path before data transmission. In proactive routing protocols, common routing protocols include OSPF [45], DSDV [46], WRP [47], IS-IS [48], etc. In proactive routing protocols, each node updates its routing table by periodically broadcasting routing information. This information includes the presence of neighboring nodes, link status, and the optimal path to reach each network node. Recent research has integrated machine learning techniques to enhance these protocols, particularly in the context of SAGIN IoT Networks. In [PERSON] et al. [55], an extended Extreme Learning Machine (ELM) model was proposed to predict communication blockage and improve satellite routing efficiency. When the network topology changes, such as by adding or \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Ref.** & **Routing Protocol** & **Protocol Type** & **Working Principle** & **Advantages** & **Limitations** \\ \hline
[45] & OSPF & Proactive Routing Protocol & Link state algorithm & Fast convergence, suitable for large networks & Not suitable for frequently changing network environments \\ \hline
[46] & DSDV & Proactive Routing Protocol & Distance vector algorithm & Quickly responds to topology changes & Not suitable for frequently changing network environments \\ \hline
[47] & WRP & Proactive Routing Protocol & Routing algorithm based on distance vector & Supports reliable transmission over wireless networks & The update cost is high when the topology changes \\ \hline
[48] & IS-IS & Proactive Routing Protocol & Link state routing protocol & Quickly converges and adapts to complex network topologies & Configuration and management are relatively complex \\ \hline
[49] & AODV & Reactive Routing Protocol & On-demand distance vector algorithm & Saves bandwidth, suitable for dynamic networks & Route discovery delay \\ \hline
[50] & DSR & Reactive Routing Protocol & Source routing algorithm & No need to maintain a global routing table & The cost of path discovery is high, and the response speed to link errors is slow \\ \hline
[51] & ABR & Reactive Routing Protocol & Adaptive bit rate algorithm & Improves the adaptability and user experience of video streaming & The algorithm is complex and requires accurate network state estimation \\ \hline
[52] & ZRP & Hybrid Routing Protocol & Combining active and reactive algorithms & Balances the advantages of active and reactive methods & Realizing complexity \\ \hline
[53] & TORA & Hybrid Routing Protocol & Switable for highly dynamic mobile environments, controlling message propagation range to be small and reducing network overhead & Balances the advantages of active and reactive methods & The possible use of suboptimal routing to reduce the overhead of discovering routes \\ \hline
[54] & EIGRP & Hybrid Routing Protocol & Distance vector routing selection technology based on DUAL algorithm & Fast convergence, reduced bandwidth usage, and support for multiple network layer protocols & There is a regional concept, which is suitable for networks with relatively small protocols \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analysis of routing protocols. removing links, the affected nodes generate new routing update information and broadcast it to other nodes so that all nodes can update their routing tables to reflect the new network topology.