Multicast Routing Switching Method for Low-Earth-Orbit Satellite Networks Based on Virtual Topology

Abstract

The present invention discloses a multicast routing switching method for a low-earth orbit satellite network based on virtual topology. In each time slot of the system cycle, the multicast routing switching is performed according to the following process: obtaining a discrete topology snapshot of the current time slot and representing it using an undirected graph; calculating a multicast tree based on the undirected graph for forwarding among nodes; in response to switching requirements in different switching scenarios, selecting a switching strategy from a variety of preset switching strategies according to the relationship between the target switching node and the current multicast tree to update the current multicast tree, and making the new multicast tree for forwarding among nodes; the variety of switching strategies include: path truncation strategy, path extension strategy, traditional rerouting strategy, and improved rerouting strategy. The present invention effectively reduces the computational amount caused by frequent switching, improves the current situation of frequent link switching and topology change brought about by the high-speed dynamics of low-earth orbit satellites, and improves the utilization rate of resources for the low-earth orbit satellite network.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-earth orbit satellite networks, and particularly relates to a multicast routing switching method for low-earth orbit satellite networks based on virtual topology. Background Art

[0002] With the rapid development of communication technology, low-earth orbit satellite networks have gradually become a research hotspot and received extensive research due to their characteristics of global coverage, low latency, and support for the vision of future anytime, anywhere, and high-bandwidth communication.

[0003] Due to the high-speed and periodic motion characteristics of low-earth orbit satellites and the unique inter-satellite link connection relationship of low-earth orbit satellite networks, low-earth orbit satellite networks do not fully adapt to traditional terrestrial routing technologies. To solve the routing problems in low-earth orbit satellite networks, existing research is mainly divided into the following three categories according to the topology processing method, namely virtual node routing, virtual topology snapshot routing, and dynamic topology analysis routing.

[0004] Among them, for virtual topology snapshot routing, it fully considers the predictable, periodic, regular and other characteristics of satellite networks. By dividing the system period T of the satellite network into several time slots (T1, T2,... Tn) of virtual topology routing, it shields the dynamicity of low-earth orbit satellites to a certain extent. But in fact, it is only transformed into re-routing within time slots and re-routing between time slots. Although it simplifies the calculation of low-earth orbit satellite routing to a certain extent, there is still the technical problem of frequent routing re-calculation caused by frequent link changes. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a multicast routing switching method for low-earth orbit satellite networks based on virtual topology.

[0006] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0007] A multicast routing switching method for low-earth orbit satellite networks based on virtual topology, within each time slot of the system period of the low-earth orbit satellite network, the multicast routing switching is executed according to the following process:

[0008] Obtain the discrete topology snapshot of the low-earth orbit satellite network in the current time slot, and represent the discrete topology snapshot using an undirected graph;

[0009] Based on the undirected graph, calculate the multicast tree of the low-earth orbit satellite network using the shortest path algorithm for forwarding between nodes;

[0010] In response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a variety of preset handover strategies to update the current multicast tree, and enable the new multicast tree to be forwarded and used among nodes;

[0011] Among them, the variety of handover strategies include: path truncation strategy, path extension strategy, traditional rerouting strategy, and improved rerouting strategy;

[0012] The traditional rerouting strategy is a routing strategy that calculates the shortest path for the start node and the end node based on the discrete topology snapshot;

[0013] The improved rerouting strategy is a routing strategy that calculates the shortest path for the start node and the end node based on the modified discrete topology snapshot; among them, the modified discrete topology snapshot is obtained by masking the non-path endpoints belonging to the current multicast tree in the discrete topology snapshot; the path endpoints include the start node and the end node when calculating the shortest path.

[0014] Optionally, the handover scenario includes: a multicast reception handover scenario where the target handover node is the destination node;

[0015] The step of in response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a variety of preset handover strategies to update the current multicast tree, and enable the new multicast tree to be forwarded and used among nodes, includes:

[0016] In response to the handover requirements in the multicast reception handover scenario, count the number of new destination nodes for all user terminals that need to hand over to the destination node, and determine whether the statistical value exceeds half of the original destination node numbers of these user terminals;

[0017] If it exceeds, select the traditional rerouting strategy to recalculate the shortest path between the source node and the new destination node of each user terminal, and update the current multicast tree according to the calculation results;

[0018] If it does not exceed, for each user terminal that needs to hand over to the destination node, select a handover strategy from the variety of handover strategies to update the current multicast tree according to the topological relationship between its new destination node and the current multicast tree;

[0019] After the multicast tree update operation is completed for all user terminals that need to hand over to the destination node, enable the new multicast tree to be forwarded and used among nodes.

[0020] Optionally, the step of for each user terminal that needs to hand over to the destination node, select a handover strategy from the variety of handover strategies to update the current multicast tree according to the topological relationship between its new destination node and the current multicast tree, includes:

[0021] For each user terminal whose destination node is to be switched,

[0022] if its new destination node belongs to the current multicast tree, select the path truncation strategy to update the current multicast tree;

[0023] if its new destination node does not belong to the current multicast tree, select a switching strategy from the remaining strategies to update the current multicast tree.

[0024] Optionally, the step of if its new destination node does not belong to the current multicast tree, select a switching strategy from the remaining strategies to update the current multicast tree includes:

[0025] if its new destination node does not belong to the current multicast tree, further determine whether the user terminal has a path from its original destination node to its new destination node and the path meets the preset same-orbit hop count constraint and loop avoidance constraint;

[0026] when the judgment result is yes, select the path extension strategy to update the current multicast tree;

[0027] when the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original destination node and the new destination node of the user terminal, and update the current multicast tree according to the calculation result.

[0028] Optionally, the switching scenario includes: a multicast source switching scenario where the target switching node is the source node;

[0029] In response to the switching requirements in different switching scenarios, according to the relationship between the target switching node and the current multicast tree, select a switching strategy from a preset variety of switching strategies to update the current multicast tree, and make the new multicast tree be used for forwarding among nodes, including:

[0030] In response to the switching requirements in the multicast source switching scenario, for each user terminal whose source node is to be switched, select a switching strategy from a preset variety of switching strategies to update the current multicast tree according to the topological relationship between its new source node and the current multicast tree;

[0031] After the update operation of the multicast tree is completed for all user terminals whose source nodes are to be switched, make the new multicast tree be used for forwarding among nodes.

[0032] Optionally, the step of for each user terminal whose source node is to be switched, select a switching strategy from a preset variety of switching strategies to update the current multicast tree according to the topological relationship between its new source node and the current multicast tree includes:

[0033] For each user terminal whose source node is to be switched,

[0034] If its new source node belongs to the current multicast tree, further determine whether its new source node is the backbone node of the current multicast tree; if it is the backbone node, directly switch; if it is not the backbone node, select the traditional rerouting strategy to recalculate the shortest path between the new source node and the destination node of the user terminal, and update the current multicast tree according to the calculation result;

[0035] If its new source node does not belong to the current multicast tree, further determine whether the user terminal has an original source node leading to its new source node and the path leading to it satisfies the preset same-orbit hop count constraint and loop avoidance constraint;

[0036] When the judgment result is yes, select the path extension strategy to update the current multicast tree;

[0037] When the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original source node and the new source node of the user terminal, and update the current multicast tree according to the calculation result.

[0038] Optionally, the shortest path method includes: single-source shortest path method, multi-source shortest path method or ant colony algorithm.

[0039] Optionally, the judgment method of the same-orbit hop count constraint includes:

[0040] For the two nodes at both ends of the path to be judged, calculate [S A / s] and [S B / s]; where S A , S B are the numbers of the two nodes respectively, s = n / p, n is the total number of nodes in the low-earth orbit satellite network, and p is the number of orbital planes;

[0041] If [S A / s] is equal to [S B / s], further judge whether |s - |S A - S B || ≤ k holds; k is the preset hop count, and [·] represents the rounding operation;

[0042] If |s - |S A - S B || ≤ k holds, it is determined that the path to be judged satisfies the same-orbit hop count constraint, otherwise it is determined that the path to be judged does not satisfy the same-orbit hop count constraint.

[0043] Optionally, the judgment method of the loop avoidance constraint includes:

[0044] For the path to be judged, judge whether all the remaining nodes except its starting node do not belong to the current multicast tree;

[0045] When the judgment result is yes, it is determined that the path to be judged satisfies the loop avoidance constraint;

[0046] When the judgment result is no, it is determined that the path to be judged does not satisfy the loop avoidance constraint.

[0047] Optionally, the low-earth orbit satellite network includes: the Iridium network.

[0048] In the multicast routing switching method for a low-earth orbit satellite network based on virtual topology provided by the present invention, the characteristics of large satellite bandwidth and wide coverage are utilized, the multicast routing technology is applied to the low-earth orbit satellite network, and the handover and routing are considered in combination, and a multicast routing switching method for low-earth orbit satellites based on virtual topology is developed. Among them, the present invention uses an undirected graph to represent the discrete topology snapshot of a single time slot, and calculates the multicast tree of the low-earth orbit satellite network using the shortest path algorithm based on the undirected graph, effectively combining the periodic motion characteristics of low-earth orbit satellites. Moreover, in response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, a handover strategy is selected from a variety of preset handover strategies to update the current multicast tree, comprehensively considering the relationship between the multicast tree before the handover occurs and the target handover node to be switched, and effectively combining the characteristics of the low-earth orbit satellite network based on virtual topology. Among them, the available handover strategies in the present invention include a path truncation strategy, a path extension strategy, a traditional rerouting strategy, and an improved rerouting strategy. Among them, both the path truncation strategy and the path extension strategy do not require recalculating the route; and in the improved rerouting strategy, the non-path endpoints belonging to the current multicast tree in the discrete topology snapshot are masked to calculate the shortest path between the start node and the end node. In this way, not only the number of nodes participating in the calculation is reduced, but also the recalculated path will not conflict with the original path of the current multicast tree, so there is no need to make major changes to the current multicast tree. Therefore, compared with the prior art of recalculating the routing whenever the link changes, the present invention effectively reduces the computational complexity caused by frequent handovers, reduces the routing maintenance overhead and maintenance difficulty, thereby improving the current situation of frequent link handovers and topology changes caused by the high-speed dynamics of low-earth orbit satellites, and improving the utilization rate of resources for low-earth orbit satellite networks.

[0049] The following will further elaborate on the present invention in conjunction with the accompanying drawings. Description of the Drawings

[0050] Figure 1 is a flowchart of a multicast routing switching method for a low-earth orbit satellite network based on virtual topology provided by an embodiment of the present invention;

[0051] Figure 2 is a flowchart of updating the multicast tree in the multicast reception handover scenario in an embodiment of the present invention;

[0052] Figure 3 It is a flowchart for updating the multicast tree in the multicast source handover scenario of the embodiments of the present invention;

[0053] Figure 4 shows the paths and comparison results of multicast handover using the method provided by the embodiments of the present invention and completely using the traditional rerouting strategy in the multicast receiver handover scenario;

[0054] Figure 5 shows the comparison results of the number of node changes of handover using the method provided by the embodiments of the present invention and completely using the traditional rerouting strategy in the multicast receiver handover scenario;

[0055] Figure 6 shows the paths and comparison results of handover using the method provided by the embodiments of the present invention and completely using the traditional rerouting strategy in the multicast source handover scenario;

[0056] Figure 7 shows the comparison results of the number of node changes of handover using the method provided by the embodiments of the present invention and completely using the traditional rerouting strategy in the multicast source handover scenario;

[0057] Figure 8 shows the comparison results of the curves of the path change amount with the number of new destination change nodes when using the method provided by the embodiments of the present invention and completely using the traditional rerouting strategy for handover in the multicast receiver handover scenario. Detailed implementation manners

[0058] The present invention will be further described in detail below with reference to specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0059] In the low-earth orbit satellite routing handover technology based on virtual topology, many studies are about handover between beams. For the frequent handover of topology and links, the mainstream solution is to adopt the rerouting strategy of recalculation. However, rerouting consumes a huge amount of resources and fails to effectively utilize the characteristics of the low-earth orbit satellite network.

[0060] In order to effectively reduce the calculation amount caused by frequent handover, thereby improving the current situation of frequent link handover and topology change brought by the high-speed dynamics of low-earth orbit satellites, and improving the utilization rate of resources for low-earth orbit satellite networks, the embodiments of the present invention provide a multicast routing handover method for low-earth orbit satellite networks based on virtual topology. See Figure 1 As shown, in each time slot of the system period of the low-earth orbit satellite network, the multicast routing handover is performed according to the following process:

[0061] S10: Obtain the discrete topology snapshot of the low-earth orbit satellite network in the current time slot, and represent the discrete topology snapshot using an undirected graph.

[0062] It can be understood that when dividing the system cycle into several time slots, it can be an equally spaced time slot division or an unequally spaced division considering topological changes, from which discrete topological snapshots Topo = {G1, G2, …, G t} can be obtained; among them, the network topology within each time slot is fixed and unchanged, and the satellite network topology of a single time slot can be represented by an undirected graph G = {V, E}, where V represents the set of all satellite nodes within this time slot, and E represents the set of all satellite links within this time slot. The satellite links mentioned here are the connection relationships between nodes in the undirected graph, and in practice, an adjacency matrix is used to store it.

[0063] S20: Calculate the multicast tree of the low-earth orbit satellite network based on the undirected graph using the shortest path algorithm, so that the multicast tree is used for forwarding among nodes.

[0064] Specifically, from a global perspective, the shortest path algorithm is used in a centralized manner for unified calculation and processing. The calculated and processed multicast routing information that meets the conditions forms a multicast tree, which is then used for forwarding by each satellite node. The shortest path methods mentioned here include: single-source shortest path method, multi-source shortest path method, or ant colony algorithm, and of course, it is not limited to this.

[0065] S30: In response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a variety of preset handover strategies to update the current multicast tree, and make the new multicast tree used for forwarding among nodes.

[0066] Among them, the variety of handover strategies include: path truncation strategy, path extension strategy, traditional rerouting strategy, and improved rerouting strategy.

[0067] It can be understood that the path truncation strategy is a strategy for truncating some paths in the multicast tree; the path extension strategy is a strategy for extending new paths based on the original multicast tree; the traditional rerouting strategy is a routing strategy for calculating the shortest path for the start node and the end node based on the discrete topological snapshot.

[0068] Compared with the traditional rerouting strategy, the improved rerouting strategy in the embodiments of the present invention is a routing strategy for calculating the shortest path for the start node and the end node based on the modified discrete topological snapshot; here, the modified discrete topological snapshot is obtained by masking the non-path endpoints in the discrete topological snapshot that belong to the current multicast tree; the path endpoints include the start node and the end node when calculating the shortest path, so the corresponding non-path endpoints are the nodes in the shortest path that are not path endpoints.

[0069] The core idea of step S30 is to make full use of the routing composition information (i.e., multicast tree) before the handover occurs and the relationship (including position relationship, etc.) between the new node to be switched to (i.e., the target handover node) and the multicast tree, and select a suitable handover strategy according to the specific conditions in the specific handover scenario.

[0070] Specifically, considering the virtual topology and multicast, when a handover occurs, it is always the user terminal in the LEO satellite network that searches for a satellite node to connect. Relative to the movement of the user terminal, the rapid movement between satellites affects the occurrence of the handover. Therefore, the handover mainly involves a change in the accessed satellite node, and the scenario remains the on-board topology. The actual handover scenarios can basically be divided into three categories, including: the multicast receiver handover scenario where the target handover node is the destination node, the multicast source handover scenario where the target handover node is the source node, and the handover scenario between snapshot time slots.

[0071] Among them, for the handover scenario between snapshot time slots, due to the handover of the snapshot, the on-board nodes corresponding to the user terminal will also change, and the topological connections within the corresponding snapshot will also change, and the changes are relatively large. Therefore, the method of re-routing is applicable, that is, when each new time slot arrives, the multicast tree of the LEO satellite network is recalculated based on the undirected graph corresponding to the time slot using the shortest path algorithm.

[0072] For the multicast receiver handover scenario, the default situation where the multicast destination node may change is the handover between the destination nodes connected to the user terminal, that is, the handover of the destination node connected to the user terminal due to the relative movement between the user terminal and the satellite, including two cases: 1. The destination node connected when the user terminal is fixed changes; 2. The user terminal changes, and the connected destination node changes. In this scenario, as long as the path after the handover is basically the same as the original path, the packet loss rate can be guaranteed to be small.

[0073] Specifically, as shown in Figure 2 When the handover scenario is the multicast receiver handover scenario, in response to the handover requirement in the multicast receiver handover scenario, according to the relationship between the target handover node and the current multicast tree, a handover strategy is selected from a variety of preset handover strategies to update the current multicast tree, and the new multicast tree is used for forwarding between nodes, including:

[0074] (1) In response to the handover requirement in the multicast receiver handover scenario, count the number of new destination nodes for all user terminals to be switched to the destination node (that is, count the number of destination nodes that all user terminals to be switched to the destination node are to be switched to), and determine whether the statistical value exceeds half of the original destination node number of these user terminals.

[0075] Specifically, in response to the handover requirements in the multicast reception handover scenario, for all user terminals to the target nodes to be handed over, the set of new target nodes of these user terminals is statistically calculated, and this set is expressed as:

[0076] D change ={D new1 ,D new2 ,…,D newm}, 1 ≤ m ≤ n;

[0077] where m represents the number of nodes in D change , and n represents the total number of satellite nodes in the low-earth orbit satellite network.

[0078] Then, it is judged whether m exceeds half of the number w of the original target nodes of these user terminals, that is, it is judged whether m > w / 2 holds.

[0079] (2) If it exceeds, that is, if m > w / 2, select the traditional re-routing strategy to recalculate the shortest path between the source node and the new target node of each user terminal, and update the current multicast tree according to the calculation result.

[0080] Specifically, set the source node of the user terminal as the starting node of the shortest path to be calculated, and set the new target node as the termination node of the shortest path. Based on the nodes and the connection relationships between the nodes included in the discrete topology snapshot, use the shortest path algorithm to uniformly calculate the shortest path between the original target node and the new target node of each user terminal, calculate and process to obtain the multicast routing information that meets the conditions, and use this multicast routing information to form a multicast tree to replace the current multicast tree, that is, the update of the current multicast tree is completed.

[0081] (3) If it does not exceed, that is, if m ≤ w / 2, for each user terminal to the target node to be handed over, select a handover strategy from the above-mentioned multiple handover strategies to update the current multicast tree according to the topological relationship between its new target node and the current multicast tree.

[0082] (4) After the update operation of the multicast tree is completed for all user terminals to the target nodes to be handed over, the new multicast tree is used for forwarding between nodes.

[0083] Specifically, in the above step (3), if m ≤ w / 2, as shown in Figure 2 , then for each user terminal to the target node to be handed over, if its new target node belongs to the current multicast tree, select the path truncation strategy to update the current multicast tree; if its new target node does not belong to the current multicast tree, select a handover strategy from the remaining strategies to update the current multicast tree. It can be understood that the remaining strategies mentioned here include the path extension strategy, the traditional re-routing strategy, and the improved re-routing strategy.

[0084] Among them, for the case where the new destination node of the user terminal belongs to the current multicast tree, assume that the source node of the user terminal is S, and the new destination nodes include D1, D2…D w ; the set of edges involved in the paths from S to D1, D2…D w is E tree = {edges1, edges2,…, edges w}, and the intermediate nodes passed through include M1, M2,…, M t ; then the set of multicast routing nodes related to this user terminal in the current multicast tree is V tree = {S, M1, M2,…, M t , D1, D2,…, D w}. Among them, if Node change ∈ [D1, D2,…, D w is located on the current multicast tree, that is, Node change ∈ V = {Node1, Node2, Node3,…, Node n}, then the path truncation strategy is adopted to update the current multicast tree.

[0085] More specifically, assume that edges i (1 ≤ i ≤ w) represents the set of edges from S to the original destination node of the user terminal. Then when Node change ∈ V = {Node1, Node2, Node3,…, Node n}, if Node change is exactly on the path composed of edges i (1 ≤ i ≤ w), then at this time, only the edges from S to Node i in edges change need to be retained, and the paths on the original destination node's path that are not related to the path to Node change can be truncated. If Node change is not on the path composed of edges i , then only the path from S to Node change in the current multicast tree needs to be retained, and the paths on the original destination node's path that are not related to the path to Node change are also truncated.

[0086] For the case where the new destination node of the user terminal does not belong to the current multicast tree, see Figure 2As shown, it can be further determined whether the user terminal has a path from the original destination node to its new destination node, and the path meets the preset same-orbit hop count constraint and loop avoidance constraint; among them, according to the discrete topology snapshot of the current time slot, it can be determined whether the original destination node of the user terminal can reach its new destination node.

[0087] When the judgment result is yes, that is, when the user terminal has a path from the original destination node to its new destination node and at the same time meets the same-orbit hop count constraint and loop avoidance constraint, select the path extension strategy to update the current multicast tree; specifically, add the new destination node to the original multicast tree, and add the path between the original destination node and the new destination node.

[0088] When the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original destination node and the new destination node of the user terminal, and update the current multicast tree according to the calculation result.

[0089] Specifically, when the judgment result is no, set the original destination node of the user terminal as the starting node, and set the new destination node as the ending node, and mask all the nodes in the discrete topology snapshot that belong to the current multicast tree except the original destination node to obtain a modified discrete topology snapshot; then, based on the nodes and the connection relationships between the nodes included in the modified discrete topology snapshot, use the shortest path algorithm to uniformly calculate the shortest paths between the original destination nodes and the new destination nodes of each user terminal, and add these newly calculated paths to the current multicast tree to complete the update of the current multicast tree.

[0090] It should be noted that although the rerouting strategy is used here, for the updated multicast tree compared with the original multicast tree, only some new destination nodes and the paths between these new destination nodes and the original destination nodes are added. Therefore, most of the structure of the updated multicast tree is the same as that of the original multicast tree, so the resulting switching frequency is not high.

[0091] The purpose of the above judgment of whether the same-orbit hop count constraint and loop avoidance constraint are met is to avoid loops. Specifically, when a path from the original destination node of the user terminal to its new destination node is added to the current multicast tree, the new destination node becomes a leaf node in the new multicast tree. At this time, if the new destination node and the original destination node do not meet the same-orbit hop count constraint and loop avoidance constraint, that is, the distance between the two exceeds the preset hop count constraint value, or the calculated path overlaps with the path on the current multicast tree, then the level difference between the two in the current multicast tree is very large, and the possibility of a loop existing is relatively high.

[0092] To make the layout of the specification clear, the specific judgment methods of the same-orbit hop count constraint and loop avoidance constraint will be described in detail later.

[0093] For the multicast source switching scenario, there are also mainly two cases: 1. The source node connected when the user terminal is fixed changes; 2. The user terminals connected to the source node change, resulting in the change of the connected source node.

[0094] Specifically, when the switching scenario is a multicast source switching scenario, step S30 specifically includes:

[0095] (1) In response to the switching requirement in the multicast source switching scenario, for each user terminal whose source node needs to be switched, according to the topological relationship between its new source node and the current multicast tree, select a switching strategy from a variety of preset switching strategies to update the current multicast tree;

[0096] (2) When the update operation of the multicast tree is completed for all user terminals whose source nodes need to be switched, enable the new multicast tree to be forwarded and used among all nodes.

[0097] Specifically, as shown in Figure 3 For each user terminal whose source node needs to be switched in the above step (1), if the new source node it needs to switch to belongs to the current multicast tree, further determine whether the new source node is the backbone node of the current multicast tree; if it is the backbone node, directly switch, that is, directly replace the original source node with the new source node; if it is not the backbone node, select the traditional re-routing strategy to recalculate the shortest path between the new source node and the destination node of the user terminal, and update the current multicast tree according to the calculation result.

[0098] More specifically, when the new source node is not the backbone node on the multicast tree, set the destination node of the user terminal as the starting node, and set its new source node as the ending node. Based on the nodes and the connection relationships between the nodes included in the discrete topological snapshot, use the shortest path algorithm to uniformly calculate the shortest path between the new source node and the destination node of the user terminal, calculate and process to obtain the multicast routing information that meets the conditions, and use this multicast routing information to form a multicast tree to replace the current multicast tree, that is, the update of the current multicast tree is completed.

[0099] It can be understood that since the traditional re-routing strategy is used for recalculation at this time, the calculated multicast routing information has changed greatly compared with the original multicast tree. Therefore, directly using the multicast tree formed by the calculated multicast routing information to replace the current multicast tree is sufficient.

[0100] If the new source node that the user terminal needs to switch to does not belong to the current multicast tree, as shown in Figure 3 further determine whether the user terminal has a path from the original source node to its new source node and the path to it meets the preset same-orbit hop count constraint and loop avoidance constraint;

[0101] When the judgment result is yes, that is, when the user terminal has a path from the original source node to its new source node and at the same time satisfies the same-orbit hop count constraint and the loop avoidance constraint, select the path extension strategy to update the current multicast tree; specifically, add the new source node to the original multicast tree and add the path between the original source node and the new source node.

[0102] When the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original source node and the new source node of the user terminal, and update the current multicast tree according to the calculation result.

[0103] Specifically, when the judgment result is no, set the original source node of the user terminal as the starting node, set the new source node as the ending node, and mask all the nodes in the discrete topology snapshot that belong to the current multicast tree except the original source node to obtain a modified discrete topology snapshot; then, based on the nodes and the connection relationships between the nodes included in the modified discrete topology snapshot, use the shortest path algorithm to uniformly calculate the shortest path between the original source node and the new source node of each user terminal, and add these newly calculated paths to the current multicast tree to complete the update of the current multicast tree.

[0104] It should be noted that although the rerouting strategy is used here, for the updated multicast tree compared with the original multicast tree, only some new source nodes and the paths between these new source nodes and the original source node are added. Therefore, most of the structure of the updated multicast tree is the same as that of the original multicast tree, so the resulting switching frequency is not high.

[0105] Next, the judgment methods for the same-orbit hop count constraint and the loop avoidance constraint are described.

[0106] First, the judgment method for the same-orbit hop count constraint is described, which specifically includes the following steps:

[0107] (a) For the two nodes at both ends of the path to be judged, calculate [S A / s] and [S B / s]; where S A , S B are the numbers of these two nodes respectively, s = n / p, n is the total number of nodes in the low-earth orbit satellite network, and p is the number of orbital planes;

[0108] (b) If [S A / s] is equal to [S B / s], further judge whether |s - |S A - S B || ≤ k holds; k is the preset hop count, and k can be flexibly adjusted according to factors such as the actual low-earth orbit satellite network and weather conditions, and [·] represents the rounding operation.

[0109] (c) If |s - |S A -S B || ≤ k holds, it is determined that the path to be judged satisfies the same - orbit hop - count constraint; otherwise, it is determined that the path to be judged does not satisfy the same - orbit hop - count constraint.

[0110] It can be understood that for the multicast - reception handover scenario, the path to be judged is the path from the original destination node of the user terminal to the new destination node. Therefore, only the numbers of these two nodes need to be obtained, and the same - orbit hop - count constraint can be judged according to the procedures of steps (a) to (c) above. For the multicast - source handover scenario, the path to be judged is the path from the original source node of the user terminal to the new source node it is to switch to. Similarly, only the numbers of these two nodes need to be obtained, and the same - orbit hop - count constraint can be judged according to the procedures of steps (a) to (c) above.

[0111] Then, the judgment method for the loop - avoidance constraint is described, which specifically includes the following steps:

[0112] (a) For the path to be judged, determine whether all nodes except its starting node do not belong to the current multicast tree;

[0113] (b) When the judgment result is yes, it is determined that the path to be judged satisfies the loop - avoidance constraint;

[0114] (c) When the judgment result is no, it is determined that the path to be judged does not satisfy the loop - avoidance constraint.

[0115] It can be understood that as long as all nodes except the starting node of the path to be judged do not belong to the current multicast tree, no loop will be formed in the updated multicast tree after updating the path to be judged into the multicast tree. Among them, for the multicast - reception handover scenario, the path to be judged is the path from the original destination node of the user terminal to the new destination node, and the original destination node is the starting node of this path to be judged. For the multicast - source handover scenario, the path to be judged is the path from the original source node of the user terminal to the new source node it is to switch to, and the original source node is the starting node of this path to be judged.

[0116] In the multicast routing handover method for low-Earth orbit satellite networks based on virtual topology provided by the embodiments of the present invention, the characteristics of large satellite bandwidth and wide coverage are utilized. The multicast routing technology is applied to low-Earth orbit satellite networks, and handover and routing are considered together, and a multicast routing handover method for low-Earth orbit satellites based on virtual topology is developed. Among them, the embodiments of the present invention use an undirected graph to represent the discrete topology snapshot of a single time slot, and calculate the multicast tree of the low-Earth orbit satellite network using the shortest path algorithm based on the undirected graph, effectively combining the periodic motion characteristics of low-Earth orbit satellites. Moreover, in response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, a handover strategy is selected from a variety of preset handover strategies to update the current multicast tree, comprehensively considering the relationship between the multicast tree before the handover occurs and the target handover node to be switched, effectively combining the characteristics of the low-Earth orbit satellite network based on virtual topology. Among them, the available handover strategies in the embodiments of the present invention include a path truncation strategy, a path extension strategy, a traditional re-routing strategy, and an improved re-routing strategy. Both the path truncation strategy and the path extension strategy do not require recalculating the route. And in the improved re-routing strategy, the non-path endpoints belonging to the current multicast tree in the discrete topology snapshot are masked to calculate the shortest path between the start node and the end node. In this way, not only the number of nodes participating in the calculation is reduced, but also the recalculated path will not conflict with the original path of the current multicast tree, so there is no need to make major changes to the current multicast tree. Therefore, compared with the prior art that recalculates the route whenever the link changes, the present invention effectively reduces the computational amount caused by frequent handovers, reduces the routing maintenance overhead and maintenance difficulty, thus improving the current situation of frequent link handovers and topology changes brought about by the high-speed dynamics of low-Earth orbit satellites, and improving the utilization rate of resources for low-Earth orbit satellite networks.

[0117] The embodiments of the present invention mix and use a variety of handover strategies, propose an idea of hybrid handover, and reconstruct the multicast tree using processing methods such as truncation, extension, re-routing, and loop avoidance, solving the problem of frequent route recalculation in the multicast routing handover of low-Earth orbit satellite networks based on virtual topology; among them, the embodiments of the present invention mainly utilize the characteristic of regular topological changes between time slots of low-Earth orbit satellite networks based on virtual topology, refine the handover scenarios in low-Earth orbit satellite networks based on virtual topology, combine the similarities between various different handover scenarios, and update and process the routing information on the basis of the original path, reducing the number of handovers compared with the way of frequent re-routing, and being able to effectively reduce the computational overhead caused by frequent re-routing during handover.

[0118] The low-earth orbit satellite network in the embodiments of the present invention may include, but is not limited to, the Iridium network. The Iridium network consists of 66 satellites in total, evenly distributed on six orbital planes. Each satellite has four links in the front, back, left, and right directions. Among them, the in-orbit links are always connected, and the inter-orbit links may be disconnected sometimes due to the influence of "reverse seams" and "polar regions".

[0119] The method provided by the embodiments of the present invention can be applied to an electronic device. In practical applications, the electronic device can be a desktop computer, a portable computer, or a ground station of a low-earth orbit satellite network. This is not limited here.

[0120] Figure 4 shows the paths and comparison results of multicast reception handover scenarios when using the method provided by the embodiments of the present invention for multicast handover and completely using the traditional rerouting strategy for handover. Among them, the "hybrid handover strategy" corresponds to the handover method of the embodiments of the present invention, and the "rerouting strategy" corresponds to the handover method that completely uses the traditional rerouting strategy. Figures 5 to 8 Similarly corresponding; according to Figure 4 From the data comparison in, it can be seen that the path sums of these two methods are basically equal, which shows that the path sum obtained by the embodiments of the present invention is consistent with the optimal path sum obtained by traditional rerouting.

[0121] Figure 5 shows the comparison results of the number of node changes when using the method provided by the embodiments of the present invention for handover and using the traditional rerouting strategy for handover in a multicast reception handover scenario; it can be seen from the comparison that the embodiments of the present invention effectively reduce the number of node changes, and correspondingly reduce the number of handovers.

[0122] Figure 6 shows the path sum comparison results of multicast source handover scenarios when using the method provided by the embodiments of the present invention for handover and completely using the traditional rerouting strategy for handover; it can be seen from the comparison that the path sum of the embodiments of the present invention is larger, which shows that compared with the optimal path sum obtained by the traditional rerouting strategy, the path sum of the embodiments of the present invention increases slightly.

[0123] Figure 7 shows the comparison results of the number of node changes when using the method provided by the embodiments of the present invention for handover and using the traditional rerouting strategy for handover in a multicast source handover scenario; it can be seen from the comparison that the number of node changes in the embodiments of the present invention is less, and the corresponding number of handovers is less.

[0124] Figure 8The figure shows the comparison results of the curve of the path change amount with the number of new destination change nodes when switching in the multicast reception switching scenario by using the method provided in the embodiment of the present invention and when completely using the traditional rerouting strategy for switching. It can be seen from the comparison that the number of changed nodes in the embodiment of the present invention is always lower than that of the prior art, which proves the effectiveness of the method provided in the embodiment of the present invention.

[0125] The above completes the description of the solution of the multicast routing switching method for the low-earth orbit satellite network based on virtual topology provided by the embodiment of the present invention.

[0126] It should be noted that the terms "first", "second", etc. are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present disclosure described here can be implemented in an order other than those illustrated or described here. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present disclosure.

[0127] In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0128] Although the present invention has been described in conjunction with various embodiments herein, however, in the process of implementing the claimed present invention, those skilled in the art can understand and implement other variations of the disclosed embodiments by viewing the drawings and the disclosure. In the description of the present invention, the term "including" does not exclude other components or steps, the term "one" or "a" does not exclude a plurality of cases, and the meaning of "a plurality" is two or more unless otherwise specifically defined. In addition, certain measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0129] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, an apparatus (device), or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects, which are collectively referred to herein as "modules" or "systems" for simplicity. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) that contain computer-usable program code. The computer program is stored / distributed in a suitable medium, provided together with other hardware or as part of the hardware, or can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0130] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (devices), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0131] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing devices to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that realizes the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0132] These computer program instructions can also be loaded onto a computer or other programmable data processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable devices provide steps for realizing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0133] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A multicast routing switching method for a low-earth orbit satellite network based on virtual topology, characterized in that In each time slot of the system cycle of the low-earth orbit satellite network, the multicast routing handover is performed according to the following process: Obtain the discrete topology snapshot of the low-earth orbit satellite network in the current time slot, and represent the discrete topology snapshot using an undirected graph; Based on the undirected graph, calculate the multicast tree of the low-earth orbit satellite network using the shortest path algorithm, so that the multicast tree is used for forwarding among nodes; In response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a preset variety of handover strategies to update the current multicast tree, and make the new multicast tree used for forwarding among nodes; Among them, the variety of handover strategies include: path truncation strategy, path extension strategy, traditional rerouting strategy, and improved rerouting strategy; The traditional rerouting strategy is a routing strategy that calculates the shortest path for the start node and the end node based on the discrete topology snapshot; The improved rerouting strategy is a routing strategy that calculates the shortest path for the start node and the end node based on the modified discrete topology snapshot; among them, the modified discrete topology snapshot is obtained by masking the non-path endpoints belonging to the current multicast tree in the discrete topology snapshot; path endpoints include the start node and the end node when calculating the shortest path; The handover scenarios include: the multicast reception handover scenario where the target handover node is the destination node; The step of in response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a preset variety of handover strategies to update the current multicast tree, and make the new multicast tree used for forwarding among nodes includes: In response to the handover requirements in the multicast reception handover scenario, count the number of new destination nodes for all user terminals to be switched to the destination node, and determine whether the statistical value exceeds half of the number of the original destination nodes of these user terminals; If it exceeds, select the traditional rerouting strategy to recalculate the shortest path between the source node and the new destination node of each user terminal, and update the current multicast tree according to the calculation result; If it does not exceed, for each user terminal to be switched to the destination node, select a handover strategy from the variety of handover strategies to update the current multicast tree according to the topological relationship between its new destination node and the current multicast tree; After the update operation of the multicast tree is completed for all user terminals to be switched to the destination node, make the new multicast tree used for forwarding among nodes; The step of for each user terminal to be switched to the destination node, select a handover strategy from the variety of handover strategies to update the current multicast tree according to the topological relationship between its new destination node and the current multicast tree includes: For each user terminal to be switched to the destination node, If its new destination node belongs to the current multicast tree, select the path truncation strategy to update the current multicast tree; If its new destination node does not belong to the current multicast tree, select a handover strategy from the remaining strategies to update the current multicast tree; The step of if its new destination node does not belong to the current multicast tree, select a handover strategy from the remaining strategies to update the current multicast tree includes: If its new destination node does not belong to the current multicast tree, further determine whether there is a path from the original destination node of the user terminal to its new destination node and the path meets the preset same-orbit hop count constraint and loop avoidance constraint; When the judgment result is yes, select the path extension strategy to update the current multicast tree; When the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original destination node and the new destination node of the user terminal, and update the current multicast tree according to the calculation result.

2. The multicast routing switching method for the low-earth orbit satellite network based on virtual topology according to claim 1, wherein The handover scenario further includes: a multicast source handover scenario where the target handover node is the source node; In response to the handover requirements in different handover scenarios, according to the relationship between the target handover node and the current multicast tree, select a handover strategy from a preset variety of handover strategies to update the current multicast tree, and make the new multicast tree be used for forwarding among nodes, including: In response to the handover requirements in the multicast source handover scenario, for each user terminal whose source node needs to be switched, according to the topological relationship between its new source node and the current multicast tree, select a handover strategy from a preset variety of handover strategies to update the current multicast tree; After the update operation of the multicast tree is completed for all user terminals whose source nodes need to be switched, make the new multicast tree be used for forwarding among nodes.

3. The multicast routing switching method for the low-earth orbit satellite network based on virtual topology according to claim 1, characterized in that, For each user terminal whose source node needs to be switched, according to the topological relationship between its new source node and the current multicast tree, select a handover strategy from a preset variety of handover strategies to update the current multicast tree, including: For each user terminal whose source node needs to be switched, If its new source node belongs to the current multicast tree, further determine whether its new source node is the backbone node of the current multicast tree; if it is the backbone node, directly switch; if it is not the backbone node, select the traditional rerouting strategy to recalculate the shortest path between the new source node and the destination node of the user terminal, and update the current multicast tree according to the calculation result; If its new source node does not belong to the current multicast tree, further determine whether there is a path from the original source node of the user terminal to its new source node and the path meets the preset same-orbit hop count constraint and loop avoidance constraint; When the judgment result is yes, select the path extension strategy to update the current multicast tree; When the judgment result is no, select the improved rerouting strategy to recalculate the shortest path between the original source node and the new source node of the user terminal, and update the current multicast tree according to the calculation result.

4. The multicast routing switching method for a low-Earth orbit satellite network based on virtual topology according to claim 1, characterized in that The shortest path method includes: single-source shortest path method, multi-source shortest path method or ant colony algorithm.

5. The multicast routing switching method for a low-Earth orbit satellite network based on virtual topology according to claim 1 or 3, characterized in that The judgment method of the same-orbit hop count constraint includes: For two nodes at both ends of the path to be judged, calculate and ; where are the numbers of the two nodes respectively, , is the total number of nodes in the low-earth orbit satellite network, is the number of orbital planes; If is equal to , further determine whether holds; k is the preset number of hops, represents the rounding operation; If holds, it is determined that the path to be judged satisfies the same-orbit hop count constraint; otherwise, it is determined that the path to be judged does not satisfy the same-orbit hop count constraint.

6. The multicast routing switching method for the low-earth orbit satellite network based on virtual topology according to claim 1 or 3, characterized in that The judgment method of the loop avoidance constraint includes: For the path to be judged, judge whether all nodes except its starting node do not belong to the current multicast tree; When the judgment result is yes, determine that the path to be judged meets the loop avoidance constraint; When the judgment result is no, determine that the path to be judged does not meet the loop avoidance constraint.

7. The multicast routing switching method for a low-Earth orbit satellite network based on virtual topology according to claim 1, characterized in that The low-earth orbit satellite network includes: Iridium network.

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