Research On OSPF Routing Protocol Enhancement Technology For LEO Networks

Low Earth Orbit(LEO)satellite constellations offer global coverage and ultra-low latency,making them an ideal supplement to ground network infrastructure.One technical challenge of a LEO satellite network is efficient and resilient routing.Directly applying the distributed routing protocol Open Shortest Path First(OSPF)to a LEO satellite network results in frequent establishment and disconnection of inter-satellite links due to periodic topological changes.This causes the route convergence process to repeatedly occur,consuming expensive satellite link bandwidth,and compromising data transmission reliability.This article introduces the development of routing in LEO satellite networks and lists the main difficulties in routing design.It then focuses on solving the routing convergence and reliability issues caused by predictable topology changes and unpredictable link interruptions.By analyzing various centralized and distributed routing strategies and combining them with the goal of creating an integrated space and ground network,this article introduces the necessary modifications to the IP network applied in LEO satellite networks and shifts the problem to improving the traditional distributed routing protocol OSPF on the ground.Next,the article analyzes the core mechanism of the OSPF routing process and provides a detailed explanation of the details and mechanisms to be used in subsequent improvements.It then analyzes the OSPF+protocol for predictable topology changes,focusing on how it utilizes predictability and the newly added neighbor state machine.The article theoretically demonstrates the excellent convergence performance of OSPF+in the face of predictable topology changes.The article then performs a theoretical optimization analysis on some of the optimization options for the OSPF+protocol.Based on the current network topology scenario,it proposes a method of using local routing instead of flooding the entire network to update routes and fully utilizing satellite position information to generate a low-cost shortest path tree.The article theoretically analyzes the effective reduction of protocol message overhead.To solve unpredictable topology changes,the article proposes the NBOSPF(Neighbor Block OSPF)solution.The core idea of this solution is to assume an unpredictable link failure before the route failure and use local routing policies to update the routing table.It introduces a new neighbor state to distinguish between short-term recoverable and unrecoverable failures,utilizing the age feature of OSPF’s link state information to reduce subsequent routing table update notifications and mitigate the problem of low route reliability in the face of unpredictable routing issues.Finally,in conjunction with the Exata protocol simulation platform and the Chinese Academy of Sciences’ large-scale LEO satellite simulation system with the SGP4 orbit propagation model,the article compares the performance of the improved OSPF+and the original OSPF+in terms of packet overhead.It also compares the performance of NB-OSPF and OSPF in terms of packet loss rate and throughput in response to unpredictable link interruptions.The article validates that NB-OSPF reduces packet loss rate by about 3-5%compared to OSPF,and the improved OSPF+also reduces packet overhead significantly.