Route search device

Abstract

To efficiently search routes for multicast. [Solution] A route search device 100 for a source node to multicast to multiple terminal nodes in a communication network having multiple nodes and links connecting two of the nodes includes a generation unit 110 that generates a route search graph based on the topology of the communication network, in which the degree of the relay nodes that relay between the source node and the terminal nodes is less than a predetermined number, a search unit 120 that searches for a route based on the route search graph, and a mapping unit 130 that associates the searched route with the topology of the communication network.

Description

[Technical Field]

[0001] The present invention relates to an efficient route search device for realizing multicast communication with high confidentiality and reliability. [Background technology]

[0002] With the spread of real-time multi-party communication services such as video conferencing and live streaming, the importance of efficient and secure multicast communication has increased dramatically. The most basic structure of multicast communication is a distribution tree structure (single-tree multicast) that runs from the source node (sender) to the terminal node (receiver). However, with single-tree multicast, if a link or part of a node fails, communication to downstream nodes is interrupted. Furthermore, eavesdroppers can obtain information from the failed node.

[0003] Multipath routing, which distributes data across multiple routes, is known as a method for maintaining the reliability and quality of communication even when some links or nodes on the network fail. This method is also effective as a method for maintaining confidentiality against node compromise in quantum cryptography networks. Multipath routing requires simultaneously searching multiple routes and selecting the optimal one. This type of route search is generally complex, and extending it from point-to-point communication to multicast communication is not at all trivial.

[0004] One method for realizing multicast communication that is resistant to node failures is multi-tree multicast, which divides the distribution data into multiple pieces of data using Multiple Description Coding and distributes them using multiple trees in parallel. Representative methods that have been proposed include SplitStream and THAG (Topology-aware Hierarchical Arrangement Graph).

[0005] SplitStream splits data into multiple streams and distributes each stream through a different tree. It is used for large-scale data distribution and real-time video streaming. Specifically, it uses a distributed hash table (DHT) to distribute data evenly across the entire network and efficiently manages which split data each node holds. This achieves efficient routing with an average hop count of about log(N) for N nodes (this system is called Pastry). Furthermore, an application-level multicast system called Scribe has been built on Pastry, which manages which multicast group each node belongs to and supports efficient multicast (Non-Patent Document 1).

[0006] THAG realizes efficient multi-tree multicast by recognizing the physical and logical topology of the network, configuring the network hierarchically, and arranging nodes with different roles at each layer. In particular, by adopting a so-called node-disjoint tree structure in which each tree is independent and a node that is a parent node in one tree becomes a leaf node in another tree, the impact of a node failure can be contained within a single tree (Non-Patent Document 2).

[0007] In addition, technologies that further develop the concepts of SplitStream and THAG have been proposed, such as a technology that eliminates bottlenecks in video distribution routes by constructing a node-disjoint multi-tree while maintaining uniformity in link capacity (Patent Document 1), and a technology that configures routes to avoid congestion based on bandwidth estimation (Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 8,279,766 [Patent Document 2] U.S. Patent No. 9,185,024 [Non-patent literature]

[0009] [Non-Patent Document 1] M. Castro, P. Druschel, AM Kermarrec, A. Nandi, A. Rowstron, and A. Singh, “SplitStream: High-bandwidth content distribution in cooperative environments,” in Proc. Int. Workshop on Peer-to-Peer Syst. (IPTPS), pp.298-313, Oct. 2003. [Non-patent document 2] R. Tian, ​​Q. Zhang, Z. Xiang, Y. Xiong, X. Li, and W. Zhu, “Robust and efficient path diversity in application-layer multicast for video streaming,” IEEE Trans.Circuits Syst. Video Technol., vol.15, no.8, pp.961-972, Aug. 2005. Summary of the Invention [Problem to be solved by the invention]

[0010] Conventional technologies are designed to enable data recovery at any node involved in multicast communication. Therefore, if a node is compromised, there is a possibility that an eavesdropper can easily obtain and tamper with data from that node. In other words, the technology has low resistance to node compromise. The present invention has been made in light of this situation, and aims to efficiently search for a route for multicast that has high resistance to node compromise. [Means for solving the problem]

[0011] To achieve the above object, one embodiment provides a route search device for multicasting from a source node to a plurality of terminal nodes in a communication network having a plurality of nodes and links connecting two of the nodes, the route search device including: a generation unit that generates a route search graph based on the topology of the communication network, in which the input degree of a relay node that relays between the source node and the terminal node is equal to or less than a predetermined number; a search unit that searches for a route based on the route search graph; and a mapping unit that associates the searched route with the topology of the communication network. [Effects of the Invention]

[0012] According to the present invention, it is possible to efficiently search for a route for multicast that is highly resistant to node compromise. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 10 is an explanatory diagram showing an example of an actual node set. [Figure 1B] FIG. 1 is an explanatory diagram of a route search graph (X-hop grid). [Figure 1C] FIG. 10 is an explanatory diagram showing a route searched for in a route search graph. [Figure 1D] FIG. 10 is an explanatory diagram showing a search path mapped to an actual node set. [Figure 2A] 10 is a flowchart of a route search process. [Figure 2B] This is a flowchart of RAPUS. [Figure 3A] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 3B] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 3C] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 3D] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 3E] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 3F] FIG. 1 is an explanatory diagram showing a specific example of RAPUS. [Figure 4] FIG. 2 is a block diagram illustrating an example of a functional configuration of a route search device. [Figure 5] FIG. 2 is a block diagram illustrating an example of a hardware configuration of the route search device. DETAILED DESCRIPTION OF THE INVENTION

[0014] In this specification, when multiple routes are link-joint, it means that the multiple routes share one or more links, whereas when multiple routes are link-disjoint, it means that the multiple routes do not share any links.

[0015] Multiple paths are node-joint if they share one or more nodes, whereas multiple paths are node-disjoint if they do not share any nodes.

[0016] The degree of a node refers to the number of links connected to that node. The indegree of a node is the number of links connected to that node through which that node receives. The outdegree of a node is the number of links connected to that node through which that node transmits.

[0017] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0018] First, the inventors of the present invention have conducted extensive research into the prior art as described below.

[0019] The conventional technologies described in Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 can achieve high tolerance to node failures and load balancing on the network, but on the other hand, because they are designed to be able to restore data at any node, they pose the risk that eavesdroppers can easily obtain or tamper with data from a failed node.The use of encrypted virtual private networks (VPNs) and Transport Layer Security (TLS) can strengthen information security, but they cannot guarantee information-theoretic security, in which security is not threatened even with advances in computing technology, and therefore cannot be applied to data communications that require ultra-long-term confidentiality.

[0020] Quantum cryptography networks and physical layer security networks (hereafter referred to as QKD / PLSN) are attracting attention as technologies that guarantee information-theoretic security, but multicasting is not trivial. Simply overlaying the above multi-tree multicast onto a quantum cryptography network does not solve the problem of confidential information leaks due to node compromise.

[0021] In response to this, there is a technique called secure network coding, which improves multicast transmission efficiency and ensures information-theoretic security (see Non-Patent Document 3 (D. Silva and F.R. Kschischang, "Universal secure network coding via rank-metric codes," IEEE Trans. Inf. Theory, vol. 57, no. 2, pp. 1124-1135 (2011)), and Non-Patent Document 4 (H. Yao, D. Silva, S. Jaggi, and M. Langberg, "Network Codes Resilient to Jamming and Eavesdropping," IEEE / ACM Trans. Networking, vol. 22, no. 6, pp. 1978-1987 (2014))). Secure network coding also encodes distribution data into multiple packets and transmits them in a distributed manner over multiple routes. At relay nodes, input packets are further superimposed and coded before being transmitted to multiple output links. This makes it possible to achieve multicast capacity. On the other hand, secure network coding requires the assumption that the total number of eavesdropped links is below a certain threshold. However, as the number of hops increases or the number of nodes with many links increases, the probability that this threshold assumption is not met also increases, which inevitably narrows the scope of application. In other words, there is a problem with low tolerance to node compromise.

[0022] Combining QKD / PLSN (Non-Patent Document 5 (M. Peev, et al., New J. Phys. 11, 075001, 2009), Non-Patent Document 6 (M. Sasaki, et al., Opt. Express 19, pp. 10387-10409, 2011), Non-Patent Document 7 (Y.L. Tang, et al., Phys. Rev. X 6(1) 011024, 2016)) with secure network coding and encrypting information flowing through each link significantly strengthens link confidentiality, thereby effectively mitigating the degradation of the threshold assumption. However, since the entire encryption key is still leaked when a node is compromised, there is still a limit to how much the threshold assumption can be mitigated as the network scale and number of users increase. In other words, the node compromise tolerance is still insufficient.

[0023] To solve this problem, it is necessary to introduce a more appropriate path finding method. In order to cope with node failures and compromises during route discovery, it is necessary to introduce multipath routing. However, even in the case of one-to-one communication, if there are two or more metrics to be optimized, it becomes an NP-hard problem (see Non-Patent Document 8 (M. H. Dahshan, "Maximum-bandwidth node-disjoint paths," Int. J. Adv. Comput. Sci. Appl., 3(3), 2012.), Non-Patent Document 9 (J. O. Abe, H. A. Mantar and A. G. Yayimli, "k -Maximally Disjoint Path Routing Algorithms for SDN," 2015 Int. Conf. Cyber-Enabled Dist. Comput. Knowl. Disc., Xi'an, China, pp. 499-508, 2015.), Non-Patent Document 10 (T. Wang, C. Q. Wu, Y. Wang, A. Hou and H. Cao, "Multi-Path Routing for Maximum Bandwidth with K Edge-Disjoint Paths," 2018 14th Int. Wirel. Commun. Mob. Comput. Conf. , Limassol, Cyprus, pp. 1178-1183, 2018. 87-97, 2023.)).

[0024] On the other hand, the minimum Steiner tree problem in the most basic single-tree multicast is itself an NP-hard problem, so route optimization for multi-tree multicast based on multipath routing is a problem that cannot be solved by conventional methods. Thus, the route search problem for multicast is difficult to solve.

[0025] Therefore, in the embodiment of the present invention, first, a terminal node is clearly distinguished from a simple relay node, and a multicast route is designed after imposing a limit on the number of input links (input degree) to a relay node.

[0026] The requirements for multicast routes, including the input degree, are determined by the specifications of secure network coding. Specifically, when the code length of the maximum rank distance code (MRD code) used at the source node for confidentiality and error correction is n0 and the message length is k, the number of shares from the source node must be n0 or greater, and the input degree must be less than k. Relay nodes with an input degree of 2 or greater perform network coding on input packets. That is, the input packets are superimposed, coded so that the same number of code words as the output degree are generated, and then transmitted to the output link. At each terminal node, the necessary condition for decoding is that n0 linearly independent packets are available, so a multicast route is configured so that packets can be obtained from n0 links. Therefore, from source node A to each terminal node B, t In this case, the route from the source node to the different terminal nodes (A, B) is constructed. t1 ), (A, B t2 ) it is okay to share some links (i.e., link joints).

[0027] Searching for a multicast route that satisfies the above requirements while also minimizing link costs is extremely difficult. Therefore, in an embodiment of the present invention, the priority is placed on minimizing the total number of links in the entire network, and cost functions such as the capacity and delay of each link are not optimized. Even so, the number of candidate routes remains enormous. To more efficiently find routes that meet the above requirements, a type of filtering function is introduced. Specifically, a virtual grid that satisfies the input degree constraint is introduced, the configuration of the real network is mapped onto it, and route search is performed on the virtual grid. The code length of the maximum rank distance code, which is the basis for the number of shares, is assumed to be, for example, n0 = 5 to 6, and the message length is k = 3. This specification example makes it possible to achieve a good balance between error correction capability and confidentiality. Therefore, an overview of the procedure is explained below using this example.

[0028] Step 1. Establish a set of foundation nodes First, we consider a base node set V that includes a source node (Alice), multiple terminal nodes (Bob 1, Bob 2, . . . , Bob N, collectively referred to as Bobs), and a relay node (Charlies). B This node set consists of Alice, Bobs, and multiple Charlies (collectively referred to as Charlies) that can be used as relay nodes between Alice and Bobs. It includes the geographical location information of each node, and Bobs are numbered Bob 1^, ..., Bob N^ in order of proximity to Alice.

[0029] As an example, Figure 1A shows the basic node set V that is the premise of route search when n0=5 and N=6. B This set of infrastructure nodes is located in North America, with source node Alice located in South Bend and terminal nodes Bob1^ through Bob6^ located in Fort Wayne, Indianapolis, Toledo, Dayton, Cincinnati, and Columbus, respectively. The white circles in the figure represent relay nodes Charlies.

[0030] Step 2. Generation of the X-hop grid (cross-hop grid) Based on the base node set, a virtual network grid, i.e., the "X-hop grid", is generated to provide a resource-efficient and secure path from Alice to Bobs. Since path search is performed using the X-hop grid as described later, the X-hop grid is also called a graph for path search.

[0031] In the X-hop grid, from the perspective of maintaining confidentiality against the endangerment of relay nodes, the structure is such that each relay node has a maximum of four links so that the input degree constraint, i.e., "input degree < k (= 3)", is easily satisfied. The grid interval is set to be approximately the same as the average distance directly transmissible in quantum cryptography or physical layer security communication (also called physical layer encryption). As a feature of this grid, regions where no nodes exist are automatically excluded based on the geographical node distribution. In particular, when there are no candidate nodes for Bobs or Charlies, the virtual nodes and links are deleted, and a more realistic network structure is maintained. By generating this virtual grid, the search space for the communication path from Alice to Bobs is narrowed, and the complexity of path search can be significantly reduced.

[0032] Fig. 1B shows the X-hop grid XG created from the base node set shown in Fig. 1A. The dotted lines in the figure indicate the links connecting two nodes. The maximum degree of the nodes is 4. That is, each node is connected to other nodes by a maximum of four links. Since the four links extending from a single node appear in an X shape, the name "X-hop grid" is used. Based on the node positions in the actual network (Fig. 1A), virtual Alices, Charlies, and Bobs are mapped onto the nodes of the X-hop grid.

[0033] Step 3. Multicast path search On the X-hop grid, n0 link-disjoint routes are searched from Alice to each Bob. If the total number of terminal nodes is N, then a total of n0N routes are searched. After maximum rank distance coding, Alice further performs network coding on the codeword of length n0, converting it into n1 (≧n0) packets, and then transmits them over n1 links (the actual value of n1 is actually determined once the routes to all Bobs have been determined). First, we search for n0 link-disjoint paths from each Bob to Alice using a method called rank-preserving upstream path search (RAPUS), which will be described later. Among the N Bobs, the Bob who can reach Alice with the minimum number of links is named Bob 1. We then create a graph G with n0 distributed paths from Alice to Bob 1. ~(1) is confirmed. Next, by repeatedly applying RAPUS to the remaining N-1 Bobs, we obtain a graph G with n0 distributed paths from Alice to Bob 1 and Bob 2. ~(2) By repeating the same operation, the multicast route graph G from Alice to N Bobs is determined. ~(N) is confirmed.

[0034] Figure 1C shows the multicast graph G on the X-hop grid XG obtained by multicast route discovery. ~(6) Each arrow in the figure indicates the data transmission direction of the links that make up the graph.

[0035] Step 4. Remapping to the real network A virtual multicast routing graph G derived on an X-hop grid ~(N) Then, the closest real node to the virtual node is selected, and a route on the real network is set according to the topology of the virtual multicast route. In this way, the virtual multicast route graph G ~(N) From the routing graph G on the real network (N) is obtained.

[0036] Figure 1D shows the resulting graph G in the X-hop grid. ~(6) The graph G obtained by mapping (6) Shows.

[0037] Graph G (N) The routes in the figure often include sections where one or more nodes with one input and one output are connected in a continuous manner without any branching or merging. In particular, when the length of each link on the section is shorter than the typical direct transmission distance and there are unnecessary bends, it may be possible to change the configuration (route smoothing) to connect the two end points of the section with a more direct route with fewer hops. In such cases, the total number of links can be further reduced by smoothing the route as appropriate. This is particularly effective in simplifying routes and eliminating delays in wireless networks.

[0038] A route search is performed on the X-hop grid according to the above steps 1 to 4. Details of the route search will be explained below with reference to Fig. 2A (main flow) and Fig. 2B (RAPUS).

[0039] The multicast route discovery flow on an X-hop grid is explained with reference to Figure 2A. For simplicity, we assume that there is no sparse area around Alice. That is, we assume that there are four closest nodes to Alice, and four next closest nodes.

[0040] First, in step S1, as described above, the infrastructure node set V B An X-hop grid is generated based on the topology of the real network with . Alice's output degree n0 is 4.

[0041] In step S2, four links are added between Alice and the node closest to Alice to the X-hop grid, so that Alice's output degree in the X-hop grid becomes 8.

[0042] The final output degree n1 of Alice is automatically determined so as to satisfy n0≦n1≦8 when the multicast route search described below is completed for all terminal nodes. Note that Figures 1A to 1D correspond to the case where n0=n1=5. After the route search is completed, Alice calculates F based on the following formula: q -RLNC(Galois field F with q elements q Packet w by Random Linear Network Coding above j is sent over n1 links.

number

[0043] Simply define each symbol x0, x1, . . . , x that composes the codeword. n0-1 Compared to splitting the data into n0 links, F q The above scheme with -RLNC greatly simplifies the path search algorithm because all links potentially contain all symbols x0, x1,..., x n0-1 Therefore, we do not need to pay attention to packet attributes on each link, and we only need to find n0 link-disjoint routes for each Bob.

[0044] In step S3, the initial graph G ~(0) is defined as follows:

number

[0045] In step S4, a loop is started for t=1,...,N. In step S5, a loop is started for t^=1,...,N. t^ is Bob's temporary index, and t is Bob's final index.

[0046] In step S6, Bob t^ is added to the graph G ~(t-1) If it is included, step S8 is carried out next, and if not, step S7 is carried out.

[0047] In step S7, graph G ~(t-1) RAPUS is run using the following. Details will be described later with reference to Figure 2B. Running RAPUS yields the following graph:

number

[0048] In step S8, the loop for t^ ends.

[0049] For a given t, step S6 is executed N times, and step S7 is executed N-t+1 times. Once step S7 is executed, the graph G ~(t,t^) Therefore, for a given t, there are a total of N-t+1 graphs G ~(t,t^) We obtain N-t+1 graphs G ~(t,t^) In order of obtaining,

number

[0050] In step S9, N-t+1 graphs G ~(t,t^) , i.e.

number

[0051] In step S10, the loop for t ends.

[0052] When step S9 is executed once, graph G ~(1) This graph G ~(1) is obtained by running RAPUS for each of Bob 1^~N^ and determining Bob 1. Graph G ~(1) is the n0 link-disjoint path P from Alice to Bob 1. ~ 1 (1) ,···,P ~ n0 (1) It has. When step S9 is executed twice, graph G ~(2) This graph G ~(2) is obtained by running RAPUS on each of the remaining N-1 Bobs and determining Bob 2. ~(2) is the n0 link-disjoint path P from Alice to Bob 1. ~ 1 (1) ,···,P ~ n0 (1) and n0 link-disjoint paths P from Alice to Bob 2. ~ 1 (2) ,···,P ~ n0 (2) It has the following.

[0053] In this way, step S9 is executed N times, and the multicast graph G ~(N)This graph has a total of n0N paths from Alice to Bobs.

[0054] This multicast route search algorithm can efficiently obtain a multicast graph with a reduced number of links.

[0055] <rapus> The details of RAPUS in step S7 are shown in Figure 2B. RAPUS extracts the graph G ~(t-1) There are n0 link-disjoint paths (P ~ 1,···,P ~ n0 ) is performed to find n0 link-disjoint paths in the graph G ~(t-1) The search is performed so that fewer new links are found that are not included in the route.

[0056] In step S51, graph G ~(t-1) and a terminal node Bob t^ that is not included in the graph are input.

[0057] In step S52, the terminal node Bob t^ and a new link connecting the terminal node and candidate nodes (maximum of four) located in the vicinity of the terminal node is added to the X-hop grid.

[0058] In step S53, the graph G0=G ~(t-1) is set, and the initial value T0 of the tabu list (or used list) is set as an empty set.

[0059] In step S54, a loop for i=1, . . . , n0 starts.

[0060] In step S55, graph G ~(t-1) A support node v is identified in the graph G0. A support node is a node that is included in the graph G0 and can reach Bob t^ within a predetermined number of hops. Examples of support nodes will be described later.

[0061] In step S56, a route P from Alice to Bob t^ via the support node v is ~ i Then, find the taboo list T i-1 The links listed in are the paths P ~ i and graph G ~(t-1) Not included in the route of route P ~ i The number of new links added to the route P is minimized. ~ i If there are multiple candidates, the most direct route on the X-hop grid is selected.

[0062] In step S57, the taboo list is updated and T i =T i-1 ∪E i However, E i HA P ~ i is the set of edges (or links) used in

[0063] In step S58, the route P ~ i Add G to the graph. i =G i-1 ∪P ~ i Let's say.

[0064] In step S59, the loop for i ends.

[0065] In step S60, the following is determined.

number

[0066] In step S61, the multicast graph G ~(t,t^) Output.

[0067] This concludes the explanation of Figures 2A and 2B. Next, RAPUS will be visually explained with reference to Figures 3A to 3F.

[0068] FIG. 3A shows Alice, Bob 1 to Bob 3, Bob 2, and a relay node. That is, the figure shows that step S9 is executed three times and a multicast graph G for Bob 1 to Bob t (t=3) is generated. ~(3) The multicast route from Alice to Bob 2^ has not yet been found.

[0069] multicast graph G ~(3) has a total of five multicast routes to Bob 1, a total of five multicast routes to Bob 2, and a total of five multicast routes to Bob 3. Some of the links included in the multicast route from Alice to Bob 2 are common to the links included in the multicast route from Alice to Bob 1. Also, some of the links included in the multicast route from Alice to Bob 3 are common to the links included in the multicast route from Alice to Bob 1 or Bob 2.

[0070] The nodes surrounding a terminal node are divided into three groups of surrounding nodes along concentric rectangles centered on the terminal node. The first group of surrounding nodes is a group of nodes that are one hop away from the terminal node and has a maximum of eight nodes. The second group of surrounding nodes is a group of nodes that are two hops away from the terminal node and has a maximum of 16 nodes. The third group of surrounding nodes is a group of nodes that are three hops away from the terminal node and has a maximum of 24 nodes. If there is a sparse area around the terminal node, the number of nodes in the group of surrounding nodes that overlap with that area will be small.

[0071] Based on the above assumptions, the search for a multicast route from Alice to Bob 2^ will be explained below. First, a first set of neighboring nodes of Bob 2̂ is identified, which has seven nodes as shown by the solid rectangle in Figure 3A. Then, a second set of neighboring nodes of Bob 2^ is identified, which has 15 nodes as indicated by the solid circles in Figure 3A. Additionally, a third set of neighboring nodes for Bob 2^ is identified, which has 19 nodes as shown by the open square in Figure 3A.

[0072] None of the nodes in the first group of surrounding nodes belong to the already discovered multicast route. However, two of the nodes in the second group of surrounding nodes belong to the already discovered multicast route. These two nodes are identified as support nodes v1 and v2 as shown in FIG. 3B (corresponding to step S55 above). The identification of the support nodes is performed by dividing the graph G ~(t-1) This can be done by sequentially finding the node in the surrounding nodes that first reaches

[0073] We try to establish a multicast route from Alice to Bob2^ via support node v1 or v2. As mentioned above, support nodes v1 and v2 are included in the second set of surrounding nodes, so they are two hops away from Bob2^. The multicast graph G ~(3) A path from Alice to Bob 2^ via support node v1 is found using as few unused links (shown by dashed lines) as possible in v1. Similarly, a path from Alice to Bob 2^ via support node v2 is found. In Figure 3B, the paths from each of support nodes v1 and v2 to Bob 2^ are shown by dashed lines.

[0074] Among the routes found in this way, the route with the smallest number of newly added links is the first route P ~ It is specified as 1. If there are multiple routes with the same number of newly added links, the route that is more direct in the X-hop grid is chosen. If there are still multiple routes, one of them is chosen randomly.

[0075] As shown in FIG. 3B, the number of newly added links in both the route via support node v1 and the route via support node v2 is 2. Therefore, the more direct route, i.e., the route via support node v2, is selected as the first route P ~ 1 (corresponding to step S56 above). ~ The links used in 1 are registered in the taboo list (used list) T1 (corresponding to step S57 above).

[0076] Second Route P ~ The same method is used to search for route 2. However, links in tabu list T1 are excluded from the search. The support nodes to be passed through are different from the support nodes in the routes searched so far. ~ Once 2 is determined, the tabu list is ~ By adding the link used in v1, T1 is updated to T2. In this way, the tabu list is a mechanism for finding multiple link-disjoint paths. Figure 3D shows the second path P1 via support node v1. ~ Shows 2.

[0077] Similarly, as shown in Figure 3E, the third pathway P ~ 3 was explored, and the fourth pathway P was identified as shown in Figure 3F. ~ Routes 4 and 5P ~ 5 is searched. As shown in FIG. 3B, since there are two support nodes, the third route to the fifth route are routes that do not pass through any support node.

[0078] The set of routes obtained in this manner is expressed as follows:

number

[0079] Then, the multicast graph G for Bob t^ ~(t,t ^ ) is the set of paths and the graph G ~(t-1) (corresponding to step S60 above). That is, it is as follows.

number

[0080] Thus, RAPUS plays an important role in route discovery on an X-hop grid. RAPUS, a multipath routing method, discovers n0 link-disjoint routes between Alice and a certain Bob. As mentioned above, RAPUS searches for the multicast route graph G between already established nodes Alice and Bob1, …, Bob t. (t) A link-disjoint route with n0 links is searched for to add the t+1th Bob to the graph G. On the X-hop grid, four links extend from Alice and each Bob, but prior to the search, four more links are added between the nearest nodes, making a total of eight links. Then, the graph G (t) For each Bob not already in G, (t) The system searches one by one for routes that reach the upper node in as direct a manner as possible with as few links as possible, and selects n0 link-disjoint routes. When a route is found, a tabu list (used list) is created and updated while searching for a route so that duplicate links are not selected in the next route search. This ensures link disjointness.

[0081] 4 shows a route search device 100. This route search device 100 is configured to be able to communicate with each node in a real network, and includes a generation unit 110, a search unit 120, and a mapping unit 130. A communication network having source nodes, candidate nodes, and terminal nodes, and the route search device 100 can be collectively called a communication network system.

[0082] The generation unit 110 generates a route search graph (X-hop grid) from the topology of the real network. That is, the generation unit 110 executes step S1. The search unit 120 performs a route search in the route search graph. That is, the search unit 120 performs steps S2 to S11 to search for a multicast route. The mapping unit 130 associates the discovered multicast route with the topology of the real network.

[0083] 5 shows an example of the computer hardware configuration of the route search device 100. The route search device 100 includes a CPU 351, an interface device 352, a display device 353, an input device 354, a drive device 355, an auxiliary storage device 356, and a memory device 357, which are interconnected by a bus 358.

[0084] A program that realizes the functions of the route search device 100 is provided by a recording medium 359 such as a CD-ROM. When the recording medium 359 on which the program is recorded is set in the drive device 355, the program is installed from the recording medium 359 into the auxiliary storage device 356 via the drive device 355. Alternatively, the program does not necessarily have to be installed using the recording medium 359, but can also be installed via a network. The auxiliary storage device 356 stores the installed program as well as necessary files, data, and the like.

[0085] The memory device 357 reads and stores the program from the auxiliary storage device 356 when an instruction to start the program is received. The CPU 351 realizes the functions of the route search device 100 in accordance with the program stored in the memory device 357. The interface device 352 is used as an interface for connecting to other computers via a network. The display device 353 displays a GUI (Graphical User Interface) or the like according to the program. The input device 354 is a keyboard, a mouse, or the like.

[0086] Each node in the communication network also has a computer hardware configuration similar to that of the route search device 100.

[0087] In the above embodiment, in order to solve the multicast route discovery problem based on multipath routing, which is considered to be NP-hard, a virtual grid (X-hop grid) and a rank-preserving upstream route discovery algorithm (RAPUS) can be used to significantly reduce the computational complexity. The routes derived in this way are n0 link-disjoint routes distributed at appropriate intervals for each Bob, satisfying the necessary conditions for decoding the maximum rank distance code at Bob. Furthermore, some links are shared between different Bobs, so that the total number of links in the entire multicast graph can be reduced. This can also be interpreted as the structure of N lattices, when the n0 link-disjoint routes to each Bob are considered as a single lattice, being close to the minimum Steiner tree connecting Alice and all Bobs. In this way, under the input degree constraint, we can derive routes that can more efficiently realize multicast based on multipath routing suitable for secure network coding. The computational complexity during derivation can also be dramatically reduced by introducing the X-hop grid. Although the exact minimum number of links in the derived multicast route cannot be guaranteed, the route is practically comparable to other routes. An effective implementation is to incorporate a rank-maintaining upstream route search algorithm into a centrally managed controller (route search device 100). In addition, when scaling up, it is also effective to configure a hierarchical control and search method.

[0088] According to the above embodiment, a route search graph in which the input degree of relay nodes is limited is generated from the topology of the real network. Therefore, route search can be performed more efficiently than when route search is performed directly from the topology of the real network. Furthermore, since the input degree of relay nodes is limited, the amount of information that an eavesdropper can obtain is reduced even if a relay node is compromised. In other words, resistance to node compromise is improved.

[0089] Furthermore, since a multicast route is searched for that minimizes the total number of links, it is possible to reduce the network resources required for multicasting.

[0090] By identifying the support node, it is possible to efficiently search for a multicast route that minimizes the total number of links.

[0091] Furthermore, since a tabu list (used list) is used to search for multiple link-disjoint paths for each terminal node, rank deficiency, which is a problem when performing linear network coding, can be suppressed. Rank deficiency refers to the fact that the rank of a matrix, i.e., the rank number, is not full rank in the matrix calculation included in the linear network decoding performed by the terminal node. If rank deficiency occurs, it will cause problems in the matrix calculation, but according to this embodiment, rank deficiency can be suppressed as described above. Note that linear network coding is not essential in a communication network and can be performed as needed.

[0092] Although an example in which the graph with the smallest number of links is selected from among the N-t+1 graphs in step S9 has been shown, this is not limiting. As long as the full rank property of the matrix is ​​maintained, multiple graphs including the graph with the smallest number of links may be selected.

[0093] It should be noted that the embodiments of the present invention are applicable to a communication network having a plurality of nodes and a link connecting two of the nodes, examples of which include a quantum cryptography network and a physical layer security network.

[0094] The present invention provides an extremely effective means for wide-area and multicast QKD / PLSN. It can be applied to wired, wireless, and hybrid networks, and is currently considered the most feasible method for globalization via, for example, a global satellite constellation. This makes it promising for application in wide-area communication environments where efficient resource use is required, and in fields where security is a key concern.

[0095] The embodiments described above have aspects not only as an apparatus but also as a method and a computer program.

[0096] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made based on the technical concept of the present invention. [Explanation of symbols]

[0097] V B Real node set XG Cross Hop Grid v Relay node v1,v2 support node 100 Route search device 110 Generation part 120 Search Department 130 Mapping Section< / rapus>

Claims

1. A route search device for multicasting from a source node to a plurality of terminal nodes in a communication network having a plurality of nodes and a link connecting two of the nodes, comprising: a generation unit that generates a path search graph in which the input degree of a relay node that relays between the source node and the terminal node is equal to or less than a predetermined number, based on the topology of the communication network; a search unit that searches for a route based on the route search graph; a mapping unit that associates the searched route with the topology of the communication network; A route search device comprising:

2. The search unit: an individual search step of searching for a plurality of routes for each of the plurality of terminal nodes for which a route has not been determined; a determination step of determining routes searched for one or more of the terminal nodes including the terminal node with the smallest total number of links included in the plurality of routes searched for in the individual search step; Repeatedly perform The route search device according to claim 1 .

3. 3. The route search device according to claim 2, wherein in the individual search step, the search unit identifies as a support node a relay node that is included in a route related to the terminal node for which a route has been determined and that is within a predetermined number of hops to the terminal node for which a route has not been determined, and preferentially searches for a route that passes through the support node.

4. The route search device according to any one of claims 1 to 3, wherein the search unit searches for multiple routes one by one for a terminal node for which a route has not been determined, adds a set of links included in the searched routes to a used list, and searches for a certain route so as not to go through any links included in the used list.

5. A route search device according to any one of claims 1 to 3; the plurality of nodes; said link connecting two of said nodes; A communication network system having:

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