## 4 Proposed Routing Scheme
### Distributed Detour Routing Scheme
When a link failure occurs at the MHR edge where the source node is located (i.e., the source edge), an optimal detour path can be generated without selective flooding. For example, let us assume that the source node is located at a lower latitude and the destination node is located at a higher latitude. In this case, the source node is forwarded through the intra-ISL for the shortest path to utilize the higher-latitude inter-ISL. To find the shortest pre-detour path, the detour should occur from the point with the shortest inter-ISL and not from the source. Therefore, selective flooding is not required if the link failure is

Figure 5: Finding detour points in different MHR shapes. located at the source edge and is upward in the Northern Hemisphere or downward in the Southern Hemisphere. Similarly, let us assume that the source node is located at a higher latitude than the destination node and that a link failure has occurred at the source edge. In this case, if selective flooding is used for the pre-detour, the packet is forwarded through an inter-ISL at a lower latitude than that of the source node. If the source node is located at a higher latitude than the destination node and link failure occurs at the source edge, selective flooding is not performed. In both scenarios, the optimal detour path is obtained using the path determined through rapid detour routing. This represents the detour path established only by the rapid detour, without incurring any communication overhead from flooding. When a flooded packet encounters a link failure during selective flooding, the flooding packet detours using the same method as the rapid detour. The selective flooding packet also contains information on the source and destination, such as the data packet. The destination location is calculated using Algorithm 2. In Figure 5a, the red dotted line represents the path of selective flooding. Assuming that the link failure has occurred in the upward direction from the rapid detour point, the packet is rerouted in either the left or right direction to reach the detour point. By implementing selective flooding and rapid detour routing, we created a pre-detour path for all transmitted packets within the MHR. This allows for detour link failure with minimal communication overhead and without consuming additional computing resources. Selective flooding generates flooding messages by the size of MHR. We assume a length of MHR edge \(MHR_{l}\) in which link failure occurs. With the rapid detour, selective flooding only floods a message to the detour point from the rapid detour point. Therefore, the scenario that generates the most flooding messages corresponds to \(MHR_{l}-1\). In certain cases, a pre-detour path can be established through rapid detour routing alone. This approach is highly effective in minimizing the communication overhead in the event of link failure. By utilizing rapid detour routing with selective flooding, a pre-detour path can be established with minimal communication overhead, thereby saving satellite onboard resources and power. ### Link Recovery Process

An optimal routing path can be determined by continuously monitoring link connectivity. This monitoring includes link failures and recovery. Link-state monitoring is initiated immediately after a link failure. The link recovery process is repeated until the link is restored during the distributed detour routing. Link recovery is identified differently from link failure. Although link failures are detected after sending a packet while awaiting a response message, link recovery is confirmed through periodic hello messages. The process of confirming link recovery follows the flow of link-state monitoring, as shown in Figure 3. If a response is received from the failed link, a link recovery process is initiated. The link recovery process aims to restore the original path by undoing the pre-detour path caused by link failure. Rapid detour routing and selective flooding generate and update the detour table using detour and flooding packets.