With the rapid development of 6G space–air–ground integrated communication networks, low Earth orbit (LEO) satellite constellations, leveraging their advantages of wide-area coverage and freedom from geographic constraints, have become key infrastructure for achieving global seamless connectivity. However, due to the relative motion among satellites in different orbits, inter-satellite links (ISLs) exhibit periodic dynamic on–off characteristics, among which a portion of the interruptions are predictable topological changes. Conventional Open Shortest Path First (OSPF) protocols compute shortest paths solely based on link distance, without considering link effective duration or bandwidth constraints, rendering them inadequate for adapting to the dynamic topological characteristics of satellite networks. Although fast reroute strategies can address sudden link failures, they consume substantial bandwidth resources and cannot provide protection for all nodes across the entire network. Therefore, how to proactively switch service paths before predictable link interruptions occur, so as to minimize service disruption and resource overhead, has become a core issue in ensuring service continuity in LEO satellite networks.
In a recent study published in Space: Science & Technology , the research team led by Huang Shanguo from the School of Electronic Engineering, Beijing University of Posts and Telecommunications, proposed a pre-rerouting strategy based on an extended OSPF protocol. The study first extends the routing information advertisement by adding two new fields—namely, "termination time of validity" and "available bandwidth"—and achieves synchronization of the link state database across the entire network through the Link Management Protocol. Furthermore, the routing metric is redefined as a weighted combination of the conventional metric and the link effective duration, enabling the Constrained Shortest Path First (CSPF) algorithm to simultaneously account for both path length and effective duration. On this basis, a pre-rerouting mechanism is established: the source node continuously monitors the remaining effective time of the label switched path (LSP); when the remaining effective time falls below the remaining service transmission duration and is less than a preset threshold, the node automatically computes the optimal backup path based on the current network state, establishes a new LSP, performs service switching, and finally releases the resources of the old path. Functional verification based on the VxWorks embedded system and FPGA hardware platform demonstrates that the pre-rerouting mechanism achieves seamless service switching before the old link interruption, with zero packet loss during the switching process. Performance verification on the EXata hardware-in-the-loop simulation platform shows that the pre-rerouting strategy attains a packet loss rate of 1%, representing a reduction of approximately 6 percentage points compared to the 7% rate of conventional rerouting schemes. This research provides an efficient, low-loss service continuity assurance solution for LEO satellite networks in dealing with predictable link interruptions, offering significant engineering application value for the stable and reliable operation of space–air–ground integrated networks.
First, this study focuses on the service interruption problem caused by dynamic changes in inter-satellite links (ISLs) within LEO satellite networks, and proposes a pre-rerouting strategy based on an extended Open Shortest Path First (OSPF) protocol. Owing to the relative motion among satellites in different orbits, ISLs exhibit periodic on–off characteristics, a portion of which can be predicted in advance based on orbital motion laws. Conventional OSPF protocols compute the shortest path solely on the basis of link distance, without accounting for constraints such as link effective duration or bandwidth availability; meanwhile, fast reroute strategies, although capable of handling sudden failures, consume substantial bandwidth resources. To address this, the study extends the routing information advertisement by adding two new fields—namely, "termination time of validity" and "available bandwidth"—to the original link state information, as shown in Fig. 1, enabling routers to acquire information on the remaining available duration and bandwidth of each link. On this basis, the routing metric computation is redefined by incorporating link effective duration as a significant weighting factor in path selection, allowing users to adjust the weighting factor according to service requirements to strike a balance between the shortest path and the longest effective duration. As illustrated in the example in Fig. 2, a path with fewer hops but an interruption after 200 seconds cannot satisfy a service duration requirement of 800 seconds; in contrast, the Constrained Shortest Path First (CSPF) algorithm can select a path with slightly more hops but an effective duration of up to 1,000 seconds, thereby validating the effectiveness of the proposed scheme in ensuring service continuity under dynamic topologies.
Second, the study elaborates on the detailed design of the trigger and execution process of the pre-rerouting strategy, and verifies its functionality through hardware experiments. As shown in Fig. 3, the source node continuously monitors the remaining effective time of the established Label Switched Path (LSP). When this remaining time falls below the remaining service transmission duration and is less than a preset time threshold, the pre-rerouting mechanism is automatically triggered: the source node recomputes the optimal path satisfying both bandwidth and duration constraints based on the current network state, reserves resources and establishes a new LSP through the constraint-based routed label distribution protocol, and releases the resources of the old path after service switching is completed. To verify this functionality, the research team built an experimental environment based on the VxWorks embedded system and an FPGA hardware platform, with the topology shown in Fig. 4, where dynamic link on–off is simulated by plugging and unplugging ports between control nodes. The functional verification results demonstrate that when the old LSP is established using a port with a shorter effective time, upon triggering of the pre-rerouting, the source node automatically constructs a new path using a port with a longer effective time, during which ping packets are transmitted normally; after the old path is released, service transmission continues without packet loss. This proves that the pre-rerouting strategy can autonomously complete path switching before link interruption and ensure service continuity.
Finally, the study quantitatively validates the performance of the pre-rerouting strategy on the EXata hardware-in-the-loop simulation platform. In the simulation topology, two alternative paths are available between the source node and the destination node, with the primary path configured with an effective duration of 100 seconds and a service duration of 500 seconds. Fig. 5 shows that the source node transmits a total of 1,000 UDP packets. In the conventional OSPF rerouting scenario, as depicted in Fig. 6, the link fails at 100 seconds, and service transmission resumes only after an interruption of approximately 20 seconds; ultimately, the destination node receives 930 packets, corresponding to a packet loss rate of 7%. In contrast, in the scenario employing the pre-rerouting strategy, as shown in Fig. 13, the service is switched to the backup path before the interruption occurs, resulting in uninterrupted transmission throughout the entire duration; the destination node receives 990 packets, with a packet loss rate of merely 1%, representing a reduction of approximately 6 percentage points compared to the conventional scheme. The experimental results demonstrate that the pre-rerouting strategy can effectively avoid service loss caused by predictable link interruptions. The study also notes that the new path established by pre-rerouting may be inferior to the original path in terms of hop count and transmission delay, and future work could further optimize transmission performance by recomputing the globally optimal path after the interruption. This strategy provides an efficient, low-loss service continuity assurance solution for LEO satellite networks in coping with dynamic topological changes.
Space: Science & Technology
Pre-rerouting Strategy to Ensure Business Continuity for Low-Earth-Orbit Satellite Network
1-Jul-2026