WO2024116950A1

WO2024116950A1 - Communication system, node, and program

Info

Publication number: WO2024116950A1
Application number: PCT/JP2023/041729
Authority: WO
Inventors: 將藤澤; 聡子石原; 良浩 ▲高▼橋; 裕之山下; 亥勝鄭
Original assignee: 京セラ株式会社
Priority date: 2022-11-28
Filing date: 2023-11-21
Publication date: 2024-06-06

Abstract

In a communication system that performs peer-to-peer communication between a plurality of nodes belonging to the same group, each node performs a predetermined control in response to communication with another node in the group. The predetermined control includes an acquisition process for acquiring the performance value of the other node from the other node, and a change process for changing the point value of the own node on the basis of the result of comparing the performance value of the other node with the performance value of the own node. Each node determines its own node as the representative node of the group, when the point value reaches a predetermined value.

Description

Communication system, node, and program

This disclosure relates to a communication system, a node, and a program.

In recent years, blockchain technology has been attracting attention. With blockchain technology, an autonomous decentralized network, specifically a peer-to-peer (P2P) network, is formed by multiple nodes, which has the advantage of preventing system downtime.

Blockchain technology has a mechanism whereby each node manages the history of transactions within a P2P network as a ledger. This mechanism is also known as distributed ledger technology. When a transaction occurs at one node, a calculation (verification) process is performed by all participating nodes. This provides a mechanism whereby correct transaction history that is extremely difficult to tamper with remains, even if a participating node is acting dishonestly and/or does not function properly.

Patent Document 1 describes a system that divides a P2P network into multiple hierarchical networks and manages transaction data independently for each network, in order to solve the problem of node capacity pressure caused by the expansion of transaction history (ledger) held by each node. In this system, if a trading partner is present in the own network, transaction data is shared and stored only within the own network.

JP 2018-67108 A

The communication system according to the first aspect is a communication system that performs peer-to-peer communication between multiple nodes that belong to the same group, and each of the multiple nodes is equipped with a control unit that performs a predetermined control in response to communication with another node in the group. The predetermined control includes an acquisition process that acquires a performance value of the other node from the other node, and a change process that changes a point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node. When the point value reaches a predetermined value, the control unit determines the own node as the representative node of the group.

The node according to the second aspect is a node used in a communication system that performs peer-to-peer communication between multiple nodes belonging to the same group, and includes a control unit that performs predetermined control in response to communication with other nodes in the group. The predetermined control includes an acquisition process that acquires a performance value of the other node from the other node, and a change process that changes the point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node. When the point value reaches a predetermined value, the control unit determines the own node as the representative node of the group.

The program according to the third aspect causes a node used in a communication system for peer-to-peer communication between multiple nodes belonging to the same group to execute a predetermined control in response to communication with another node in the group, the predetermined control including an acquisition process for acquiring a performance value of the other node from the other node, and a change process for changing a point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node, and a step of determining the own node as a representative node of the group when the point value reaches a predetermined value.

FIG. 1 is a diagram illustrating an example of a network configuration in a typical blockchain system. FIG. 2 is a diagram illustrating an example of the configuration of a ledger managed by each node according to the embodiment. FIG. 13 is a diagram illustrating an example of an operation when adding a new block to a ledger according to an embodiment (i.e., when updating the ledger). FIG. 13 is a diagram illustrating an example of an operation when adding a new block to a ledger according to an embodiment. FIG. 2 is a diagram illustrating an example of the configuration of each node according to the embodiment. FIG. 1 is a diagram illustrating an example of a network configuration according to an embodiment. FIG. 13 is a diagram showing a ledger management method according to an embodiment. FIG. 13 is a diagram showing a ledger management method according to an embodiment. 11 is a diagram for explaining the effect of reducing the amount of calculation when a hierarchical structure network according to an embodiment is compared with a general network configuration; FIG. 11 is a diagram for explaining a link between a higher-level ledger and a lower-level ledger according to an embodiment. FIG. FIG. 11 is a diagram showing an example of an operation in a case where, after a group (A) according to an embodiment is formed, a new group (B) is formed below the group (A). A figure showing an example of operation in a case where, after a group (A) in an embodiment is formed, a new group (B) is formed below group (A), and then a new group (C) is formed below group (A). A figure showing an example of operation in a case where, after a group (A) in an embodiment is formed, a new group (B) is formed below group (A), and then a new group (C) is formed below group (A). FIG. 11 is a diagram illustrating grouping of lower hierarchical groups according to an embodiment. FIG. 11 is a diagram illustrating grouping of lower hierarchical groups according to an embodiment. FIG. 11 is a diagram illustrating a priority order within a group according to an embodiment. FIG. 11 is a diagram illustrating a priority order within a group according to an embodiment. FIG. 11 is a diagram for explaining an example of node parameters stored in a ledger according to an embodiment. FIG. 11 is a diagram for explaining a node selection method according to an embodiment. FIG. 11 is a diagram showing an example of a point value (LP) of each node managed by itself according to an embodiment. FIG. 11 is a diagram showing another example of the own point value (LP) managed by each node according to an embodiment. FIG. 11 is a diagram illustrating an example of a flow of a node selection method according to an embodiment. FIG. 11 is a diagram for explaining, as a comparative example, a node selection method in a case where node parameters of each node in a group are stored in a ledger managed within the group. FIG. 11 is a diagram for explaining a node selection method using a point value (LP) according to an embodiment.

By grouping the nodes and managing a separate ledger for each group that conducts P2P communication, it is believed that the frequency of updates to the ledger and its expansion can be reduced. Assuming that such grouping is performed, each group is expected to have a node (also called a "representative node") that mediates interactions with other groups. However, technology for autonomously selecting a representative node within a group that conducts P2P communication has not yet been established, and with conventional technology, there is a problem in that it is difficult to autonomously select an appropriate representative node.

The purpose of this disclosure is to make it possible to autonomously select an appropriate representative node within a group conducting P2P communication.

The embodiments will be described with reference to the drawings. In the description of the drawings, the same or similar parts are given the same or similar reference numerals.

(1) Overview of Blockchain Technology First, a general block chain technology will be described with reference to Fig. 1 to Fig. 4. Fig. 1 is a diagram showing an example of a network configuration in a general block chain system. In Fig. 1, lines connecting nodes represent communication connections between the nodes.

In blockchain technology, an autonomous distributed network, specifically a P2P network, is formed by multiple nodes 100. Each node 100 is connected to each other so that they can communicate with each other. Communication between the nodes 100 may be performed via a public communication network and/or a local communication network. Note that although a total of five nodes, nodes 100a to 100e, are illustrated in FIG. 1, the number of nodes 100 is not limited to five. Each node 100 is a device having at least a communication function and a calculation processing function, such as a PC (Personal Computer). In general blockchain technology, it is assumed that each node 100 has sufficient performance (specifications).

Each node 100 manages the history of transactions within the network as a ledger. When a transaction occurs at one node 100 (for example, node 100a), all participating nodes (nodes 100a to 100e) perform a calculation (verification) process. This provides a mechanism that leaves a correct transaction history that is extremely difficult to tamper with, even if a participating node 100 commits fraud and/or does not operate normally.

Note that a transaction may be, for example, a remittance or settlement of money or points, or the occurrence of communication. In that case, the transaction data stored in a block of the ledger may be remittance or settlement data, or communication data. A transaction may be the joining or removal of a node in the network, etc. In that case, the transaction data stored in a block of the ledger may be data (parameters) of node 100. A transaction may be an update of the ledger. The transaction data stored in a block of the ledger may be data (parameters) of node 100.

In one embodiment, an example is mainly assumed in which transaction data stored in blocks of a ledger includes data (parameters) of a node 100. By managing such data (parameters) of a node 100 in a ledger, it becomes easy to guarantee that the node 100 in the network is a genuine device.

Figure 2 shows an example of the configuration of the ledger managed by each node 100.

Each node 100 stores records of transactions that occur within the network in blocks. A block has a block header, which is a header portion, and a transaction data portion that stores data of at least one transaction. The block header stores a hash value calculated from the block generated immediately before. For example, the block header of block n+1 stores a hash value calculated from block n. In this way, the ledger has a data structure in which each generated block is linked in a chain in chronological order. The block header may further include a height that indicates the number of the corresponding block, and a nonce, which is a value used to calculate the hash value.

Figures 3 and 4 show an example of the operation when adding a new block to the ledger (i.e., when updating the ledger).

As shown in Figure 3, after a transaction occurs within a group that makes up the P2P network, a node 100 called a "proposer" generates a new block corresponding to that transaction and proposes the new block by notifying the other nodes 100 of it. For example, multiple nodes 100 calculate a hash value by combining the transaction data, etc. while changing the value of the nonce, and the node 100 (proposer) that finds a hash value that satisfies certain conditions notifies the other nodes 100 of the generated block. The other nodes 100 that receive the proposed new block verify the hash value of the new block. Here, we will proceed with the explanation assuming that the verification is successful.

Next, as shown in Figure 4, other nodes 100 that receive the proposal for a new block vote for node 100 (proposer) to accept the verified block as a new block. The other nodes 100 that vote are called "voters." If node 100 (proposer) receives a certain number of votes from other nodes 100 (voters), it confirms the proposed new block and adds the new block to the ledger.

FIG. 5 shows an example of the configuration of each node 100.

As shown in FIG. 5, the node 100 has a communication unit 110, a control unit 120, and a storage unit 130. The node 100 may also have a battery 140.

The communication unit 110 includes a communication interface for communicating with other nodes. The communication interface may be a wireless communication interface. The communication interface may be a wired communication interface.

The control unit 120 performs various controls and processes in the node 100. Such processes include the processes described above and those described below. The control unit 120 includes at least one processor 121. The processor 121 executes programs stored in the storage unit 130 to perform various processes.

The storage unit 130 stores programs executed by the processor 121 and information used in processing by the processor 121. The storage unit 130 includes non-volatile memory and volatile memory.

The battery 140 stores power to be supplied to each part of the node 100 (device).

(2) Hierarchical Structure Network Next, a block chain system (also simply referred to as a "communication system") according to an embodiment will be described with reference to Fig. 6. The block chain system according to an embodiment includes a network 10 having a hierarchical structure (also referred to as a "hierarchical structure network").

As mentioned above, in blockchain technology, it is assumed that each node 100 has sufficient performance, and if a transaction occurs at any one node 100, calculations (verification) are performed at all nodes 100. For this reason, it is difficult to apply blockchain technology to devices with poor performance, such as those with small battery capacity, low computing power, or small memory capacity, such as IoT devices such as sensor devices.

In one embodiment, a hierarchical network 10 is formed, and each node 100 is placed in a hierarchical level according to the performance of the node 100. The hierarchical structure allows higher levels to have a higher calculation frequency (i.e., the frequency of updating the ledger), while lower levels have a lower calculation frequency. By placing high-performance devices in higher levels and low-performance devices in lower levels, it becomes possible to participate in the blockchain hierarchical network 10 regardless of performance.

FIG. 6 is a diagram showing an example of a network configuration according to one embodiment. In the example of FIG. 6, the hierarchical structure network 10 has a hierarchical structure consisting of three hierarchies, hierarchical levels 1 to 3. In the following, an example using three hierarchies will be mainly described, but the number of hierarchies may be two or four or more. In the example shown in FIG. 6, hierarchical level 1 is the highest hierarchical level, and hierarchical level 3 is the lowest hierarchical level.

In such a hierarchical network 10, each node 100 manages a ledger. Based on the performance of the node 100, each node 100 is placed in one of the three hierarchies according to the performance. Here, the performance of the node 100 refers to at least one of the computational power (e.g., processor power), storage capacity (e.g., memory size), and battery capacity. The performance of the node 100 may also include a sleep time, which will be described later. For example, when a new node is added, the new node or another node determines the hierarchical level in which the new node is placed based on the performance of the new node.

The nodes 100 arranged in hierarchical level 1 and the nodes 100 arranged in hierarchical level 2 form an upper hierarchical level group. In FIG. 6, an example is shown in which the only node 100 belonging to hierarchical level 1 is node 100A, but multiple nodes 100 may be arranged in hierarchical level 1.

The three nodes 100 arranged in hierarchical level 2 are node 100B1, node 100C1, and node 100D1. Each node 100 belonging to group (A) 200A, which is a higher hierarchical group, manages ledger (A), which is a higher hierarchical ledger.

The nodes 100 placed in hierarchical 2 and the nodes 100 placed in hierarchical 3 form a lower hierarchical group that manages the lower hierarchical ledger. For example, high performance equipment is placed in hierarchical 1 (or hierarchical 2), and equipment with lower performance compared to the high performance equipment is placed in hierarchical 3. In other words, the nodes 100 belonging to the lower hierarchical group have lower performance compared to the nodes 100 belonging to the higher hierarchical group.

In FIG. 6, an example is shown in which a total of three lower hierarchical groups, group (B) to group (D), are formed. However, the number of lower hierarchical groups is not limited to three, and the number of lower hierarchical groups may be one or two, or may be four or more.

Group (B) includes one node 100B1 located in hierarchical level 2 and multiple nodes 100B2 located in hierarchical level 3. Each node 100B belonging to group (B) manages ledger (B), which is a lower hierarchical ledger. Node 100B1 belongs to both group (A) and group (B) and manages both ledgers (A) and (B). In the following description of the embodiment, node 100B1 is also referred to as the parent node of group (B). Node 100B2 belongs only to group (B) and therefore manages only ledger (B).

Similarly, group (C) includes one node 100C1 located in hierarchical level 2 and multiple nodes 100C2 located in hierarchical level 3. Each node 100C belonging to group (C) manages ledger (C), which is a lower hierarchical ledger. Node 100C1 belongs to both group (A) and group (C) and manages both ledgers (A) and (C). In the following description of the embodiment, node 100C1 is also referred to as the parent node of group (C). Node 100C2 belongs only to group (C) and therefore manages only ledger (C).

Similarly, group (D) includes one node 100D1 located in hierarchical level 2 and multiple nodes 100D2 located in hierarchical level 3. Each node 100D belonging to group (D) manages ledger (D), which is a lower hierarchical ledger. Node 100D1 belongs to both group (A) and group (D) and manages both ledgers (A) and (D). In the following description of the embodiment, node 100D1 is also referred to as the parent node of group (D). Node 100D2 belongs only to group (D) and therefore manages only ledger (D).

In each group (A) to (D), the nodes 100 are connected to each other so that they can communicate with each other, and a common ledger is held and managed within the group, and processing is performed within the group in the same way as in conventional blockchains. By grouping in this way, the number of nodes in each group can be reduced, thereby preventing the ledger from becoming bloated.

In general, a low-performance node 100 (e.g., an IoT device such as a sensor device) generates transactions less frequently than a high-performance node 100. For example, a low-performance node 100 communicates intermittently to reduce power consumption, goes into a sleep state when not communicating, and no transactions occur during the sleep time.

In group (A), which is an upper hierarchical group formed by high performance nodes 100, the ledger (A) may be updated more frequently and the amount of data in the ledger (A) is more likely to become large than in lower hierarchical groups. On the other hand, in group (B) formed by low performance nodes 100, the frequency of updates to the ledger (B) can be suppressed and the increase in the amount of data in the ledger (B) can be suppressed. Similarly, in group (C) formed by low performance nodes 100, the frequency of updates to the ledger (C) can be suppressed and the increase in the amount of data in the ledger (C) can be suppressed. Similarly, in group (D) formed by low performance nodes 100, the frequency of updates to the ledger (D) can be suppressed and the increase in the amount of data in the ledger (D) can be suppressed.

However, while managing a ledger for each group individually can reduce the frequency of ledger updates and the size of the ledger, if the contents of each group's ledger are not linked to the ledgers of other groups, the reliability of blockchain technology may decrease. Therefore, in one embodiment, by linking the contents of ledgers between groups, it is possible to reduce the frequency of ledger updates and the size of the ledger while also preventing a decrease in reliability.

Specifically, in a hierarchical network 10 made up of multiple groups including a first group formed by one or more nodes 100 managing a first ledger, and a second group formed by one or more nodes 100 managing a second ledger different from the first ledger, a node 100 belonging to the second group notifies the first group of ledger information related to the second ledger. Each node 100 belonging to the first group manages the notified ledger information as part of the first ledger. This makes it possible to link the contents of ledgers between groups.

Here, the first group is one of the upper hierarchical group and the lower hierarchical group, and the second group is the other of the upper hierarchical group and the lower hierarchical group. In other words, ledgers are linked between groups that have a direct communication connection. On the other hand, ledgers are not linked between lower hierarchical groups, i.e., between groups that do not have a direct communication connection. This makes it possible to manage ledgers independently between lower hierarchical groups, without updates to the ledger in one lower hierarchical group affecting the ledgers in other lower hierarchical groups.

(3) Ledger Management Method Next, a ledger management method according to one embodiment will be described with reference to Fig. 7 to Fig. 9. As shown in Fig. 7, a node 100 belonging to an upper hierarchical group that manages an upper hierarchical ledger updates the upper hierarchical ledger in accordance with transactions within the upper hierarchical group and transactions within a lower hierarchical group.

For example, the nodes 100 (nodes 100A, 100B1, 100C1, and 100D1) belonging to group (A) 200A, which is a higher hierarchical group, not only update ledger (A), which is a higher hierarchical ledger, in response to transactions within group (A) 200A, but also update ledger (A) in response to transactions within any of the lower hierarchical groups (group (B) 200B, group (C) 200C, group (D) 200D). Figure 7 shows an example in which the nodes 100 (nodes 100A, 100B1, 100C1, and 100D1) belonging to group (A) 200A update ledger (A) in response to an update to ledger (B) in group (B) 200B.

The frequency with which the upper hierarchical ledger in the upper hierarchical group is updated is the same as the frequency with which the ledger is updated in a general hierarchical network 10 (see FIG. 1) that does not have a hierarchical structure. By reflecting transactions in the lower hierarchical groups (group (B) 200B, group (C) 200C, group (D) 200D) in ledger (A), which is the upper hierarchical ledger, reliability in blockchain technology can be maintained.

On the other hand, as shown in FIG. 8, a node 100 belonging to a lower hierarchy group that manages a lower hierarchy ledger does not update the lower hierarchy ledger in response to transactions in a higher hierarchy group, but updates the lower hierarchy ledger in response to transactions in the lower hierarchy group. In other words, even if the higher hierarchy ledger is updated, the lower hierarchy ledger is not updated. This makes it possible to reduce the frequency of updates to the lower hierarchy ledger in the lower hierarchy group.

For example, nodes 100B (nodes 100B1, 100B2) belonging to group (B) 200B, which is a lower hierarchical group, update ledger (B), which is a lower hierarchical ledger, in response to transactions within group (B) 200B, but do not update ledger (B) in response to transactions within group (A) 200A. Similarly, nodes 100C (nodes 100C1, 100C2) belonging to group (C) 200C, which is a lower hierarchical group, update ledger (C), which is a lower hierarchical ledger, in response to transactions within group (C) 200C, but do not update ledger (C) in response to transactions within group (A) 200A. Similarly, nodes 100D (nodes 100D1, 100D2) belonging to group (D) 200D, which is a lower hierarchical group, update ledger (D), which is a lower hierarchical ledger, in response to transactions within group (D) 200D, but do not update ledger (D) in response to transactions within group (A) 200A.

Also, as shown in FIG. 7, a node 100 belonging to a lower hierarchical group that manages a lower hierarchical ledger does not update the lower hierarchical ledger in response to transactions in other lower hierarchical groups. For example, even if ledger (B) is updated in group (B) 200B, which is a lower hierarchical group, other lower hierarchical groups, group (C) 200C and group (D) 200D, do not update ledgers (C) and (D). This reduces the frequency of updates to the lower hierarchical ledger in the lower hierarchical groups.

In this way, when a transaction occurs in a lower hierarchical group, the higher hierarchical ledger is updated in the higher hierarchical group, but no ledger update is required in other lower hierarchical groups. Also, even if a transaction occurs in a higher hierarchical group, the lower hierarchical ledger does not need to be updated in the lower hierarchical groups. This reduces the overall amount of calculations. Therefore, blockchain technology can be applied to devices with low computing power and/or memory capacity.

FIG. 9 is a diagram for explaining the effect of reducing the amount of calculations when a hierarchical structure network 10 according to one embodiment is compared with a general network configuration (see FIG. 1). Here, an example is shown in which a hierarchical structure using a binary tree is adopted. Also, it is assumed that there are n nodes 100 (n≧4), and that the transaction occurrence frequency in each node 100 is the same.

As shown in Figure 9, the node 100 in the top layer (Layer 1) needs to calculate transactions for all nodes, so the calculation frequency is the same as that of general blockchain technology. On the other hand, the node 100 in the bottom layer only needs to calculate transactions for the group in which it participates. In the case of a binary tree, the number of nodes in each group is 3, so the calculation frequency can be reduced to 3/n.

For example, if all layers except the top one have a two-layer structure (n=7), it is possible to reduce calculations by approximately 38%. If all layers except the top one have a three-layer structure (n=15), it is possible to reduce calculations by approximately 61%. If n is sufficiently large (limit→∞), it is possible to reduce calculations by approximately 67%. In other words, the lower the layer, the more the calculation frequency can be reduced. Therefore, compared to general blockchain technology, it is possible to reduce communication volume and the number of calculations. Therefore, blockchain technology can be used even on devices with performance that is not capable of participating in general blockchain technology.

In the network configuration shown in FIG. 9, an upper hierarchical group and a lower hierarchical group are formed between two groups that have a direct communication connection. For example, when group 200B is used as a reference, group 200A is the upper hierarchical group, and

groups

200D and 200E are each lower hierarchical groups. When

groups

200D and 200E are used as references, group 200B is the upper hierarchical group. Similarly, when group 200C is used as a reference, group 200A is the upper hierarchical group, and

groups

200F and 200G are each lower hierarchical groups. When

groups

200F and 200G are used as references, group 200C is the upper hierarchical group.

(4) Link Between Upper Hierarchy Ledgers and Lower Hierarchy Ledgers Next, a link between an upper hierarchy ledger and a lower hierarchy ledger according to one embodiment will be described with reference to Fig. 10 to Fig. 13. As shown in Fig. 10, a hierarchical structure network 10 is configured by a group (A) 200A formed by nodes 100 (nodes 100A, 100B1) that manage a ledger (A) and a group (B) 200B formed by nodes 100 (nodes 100B1, 100B2) that manage a ledger (B).

Node 100 belonging to group (A) 200A notifies group (B) 200B of ledger information related to ledger (A). For example, node 100B1 belonging to group (A) 200A notifies other node 100B2 in group (B) 200B of ledger information related to ledger (A). Then, each node 100 (nodes 100B1, 100B2) belonging to group (B) 200B manages the ledger information as part of ledger (B). In this way, each node 100 belonging to a lower hierarchical group that manages a lower hierarchical ledger manages ledger information related to a higher hierarchical ledger as part of the lower hierarchical ledger. This makes it possible to link the lower hierarchical ledger with the higher hierarchical ledger.

For example, ledger information managed as part of ledger (B), which is a lower-level ledger, may include a chain ID indicating ledger (A), which is a higher-level ledger. Ledger information managed as part of ledger (B) may include a hash value calculated from a block of ledger (A). Ledger information managed as part of ledger (B) may include a block height indicating a block number of ledger (A). Here, each node 100 (nodes 100B1, 100B2) belonging to group (B) may store the ledger information in the header portion (block header) of a block of ledger (B). This makes it easy to identify ledger (A) and search for which block of ledger (A) it is linked to when checking calculations in group (B) 200B, and also makes it easy to transmit information such as the check results from group (B) 200B to group (A) 200A.

Meanwhile, node 100 belonging to group (B) 200B notifies group (A) 200A of ledger information related to ledger (B). For example, node 100B1 belonging to group (B) 200B notifies other node 100A in group (A) 200A of ledger information related to ledger (B). Then, each node 100 (nodes 100B1, 100A) belonging to group (A) 200A manages the ledger information as part of ledger (A). In this way, each node 100 belonging to the upper hierarchical group that manages the upper hierarchical ledger manages ledger information related to the lower hierarchical ledger as part of the upper hierarchical ledger. This makes it possible to link the upper hierarchical ledger with the lower hierarchical ledger.

For example, the ledger information managed as part of the ledger (A), which is a higher-level ledger, may include a chain ID indicating the ledger (B), which is a lower-level ledger. The ledger information managed as part of the ledger (A) may include a hash value calculated from a block of the ledger (B). The ledger information managed as part of the ledger (A) may include a block height indicating a block number of the ledger (B). Here, each node 100 (nodes 100B1 and 100A) belonging to the group (A) may store the ledger information in the transaction data portion of a block of the ledger (A). As a result, even if the ledger (B) is updated infrequently and its length is not sufficiently long, it is possible to suppress a decrease in security strength by intersecting with the ledger (A), which is sufficiently long. For example, it becomes easier to check the fork protection of the ledger (B) when verifying calculations in the group (A) 200A. In other words, an incorrect (fake) blockchain does not branch out, and it becomes easier to check the correct ledger (B).

FIG. 11 is a diagram showing an example of the operation when a group (B) 200B is newly formed below group (A) 200A after group (A) 200A is formed. Here, a node belonging to group (A) 200A is called node (A), and a node belonging to group (B) 200B is called node (B). However, since a parent node belongs to both group (A) 200A and group (B) 200B, the operation of FIG. 11 may be executed within the same node (parent node).

As shown in FIG. 11, first, node (A) managing ledger (A) updates ledger (A) by adding the m-1th block to ledger (A). The m-1th block has a block header including a hash value calculated from the previous block of ledger (A) and transaction data for at least one transaction in group (A) 200A. The block header may further include at least one of a chain ID (parent chain ID) indicating ledger (A) and a block height indicating m-1, which is the block number of the block.

Secondly, group (B) 200B is formed. Node (B) that manages ledger (B) updates (generates) ledger (B) by adding the first block in ledger (B), i.e., the 0th block, to ledger (B). The 0th block includes, in its block header portion, the block of ledger (A) that is the latest at the time of adding the 0th block, i.e., the block header of the m-1th block of ledger (A), as ledger information related to ledger (A). Furthermore, the 0th block includes, in its transaction data portion, transaction data related to at least one transaction in group (B) 200B. Here, the transaction may be, for example, a node addition (node join) in group (B) 200B. The transaction data may include node parameters of the added node.

Thirdly, node (A) managing ledger (A) updates ledger (A) by adding the mth block to ledger (A). The mth block includes in its block header a hash value calculated from the (m-1)th block, which is the previous block of ledger (A). The mth block also includes in its transaction data portion transaction data relating to at least one transaction in group (A) 200A and ledger information relating to ledger (B). The ledger information includes a hash value calculated from the latest block of ledger (B) at the time of adding the mth block, i.e., the 0th block of ledger (B), and a chain ID indicating ledger (B). The ledger information may further include a block height indicating 0, which is the block number of the 0th block.

Fourthly, node (B) managing ledger (B) updates ledger (B) by adding the first block in ledger (B) to ledger (B). The first block includes, in its block header portion, the block header of the latest block in ledger (A) at the time of adding the first block, as ledger information related to ledger (A). The first block also includes, in its block header portion, a hash value calculated from the 0th block of ledger (B). The first block also includes, in its transaction data portion, transaction data related to at least one transaction in group (B) 200B. Here, the transaction may be, for example, a node addition (node join) in group (B) 200B. The transaction data may include node parameters of the added node.

Fifth, node (A) managing ledger (A) updates ledger (A) by adding the nth block to ledger (A). The nth block includes, in its block header portion, a hash value calculated from the n-1th block, which is the previous block of ledger (A). The nth block also includes, in its transaction data portion, transaction data related to at least one transaction in group (A) 200A and ledger information related to ledger (B). The ledger information includes a hash value calculated from the latest block of ledger (B) at the time of adding the nth block, i.e., the first block of ledger (B), and a chain ID indicating ledger (B). The ledger information may further include a block height indicating 1, which is the block number of the first block.

FIGS. 12 and 13 are diagrams showing an example of operation in the case where, after group (A) 200A is formed, a new group (B) 200B is formed below group (A) 200A, and then a new group (C) 200C is formed below group (A) 200A. Here, a node belonging to group (A) 200A is referred to as node (A), a node belonging to group (B) 200B is referred to as node (B), and a node belonging to group (C) 200C is referred to as node (C). Here, differences from the operation in FIG. 11 will be mainly explained.

As shown in FIG. 13, first, node (A) managing ledger (A) updates ledger (A) by adding the m-1th block to ledger (A). Second, group (B) 200B is formed. Node (B) managing ledger (B) updates (generates) ledger (B) by adding the first block in ledger (B), i.e., the 0th block, to ledger (B). Third, node (A) managing ledger (A) updates ledger (A) by adding the mth block to ledger (A). This operation is similar to that in FIG. 11.

Fourth, node (A) managing ledger (A) updates ledger (A) by adding the n-1th block to ledger (A). The n-1th block has a block header including a hash value calculated from the previous block of ledger (A) and transaction data for at least one transaction in group (A) 200A. The block header may further include at least one of a chain ID (parent chain ID) indicating ledger (A) and a block height indicating n-1, which is the block number of the block.

Fifth, group (C) 200C is formed. Node (C) that manages ledger (C) updates (generates) ledger (C) by adding the first block in ledger (C), i.e., the 0th block, to ledger (C). The 0th block includes, in its block header portion, the block of ledger (A) that is the latest at the time of adding the 0th block, i.e., the block header of the n-1th block of ledger (A), as ledger information related to ledger (A). Furthermore, the 0th block includes, in its transaction data portion, transaction data related to at least one transaction in group (C) 200C. Here, the transaction may be, for example, a node addition (node join) in group (C) 200C. The transaction data may include node parameters of the added node.

Sixth, node (A) managing ledger (A) updates ledger (A) by adding the nth block to ledger (A). The nth block includes, in its block header portion, a hash value calculated from the n-1th block, which is the previous block of ledger (A). The nth block also includes, in its transaction data portion, transaction data related to at least one transaction in group (A) 200A and ledger information related to ledger (C). The ledger information includes a hash value calculated from the latest block of ledger (C) at the time of adding the nth block, i.e., the 0th block of ledger (C), and a chain ID indicating ledger (C). The ledger information may further include a block height indicating 0, which is the block number of the 0th block.

Seventh, node (C) managing ledger (C) updates ledger (C) by adding the first block in ledger (C) to ledger (C). The first block includes, in its block header portion, the block header of the latest block of ledger (A) at the time of adding the first block, i.e., the nth block of ledger (A), as ledger information related to ledger (A). The first block also includes, in its transaction data portion, transaction data related to at least one transaction in group (C) 200C. Here, the transaction may be, for example, a node addition (node join) in group (C) 200C. The transaction data may include node parameters of the added node.

Eighth, node (B) managing ledger (B) updates ledger (B) by adding the first block in ledger (B) to ledger (B). The first block includes, in its block header portion, the block header of the latest block of ledger (A) at the time of adding the first block, i.e., the nth block of ledger (A), as ledger information related to ledger (A). The first block also includes, in its transaction data portion, transaction data related to at least one transaction in group (B) 200B. Here, the transaction may be, for example, a node addition (node join) in group (B) 200B. The transaction data may include node parameters of the added node.

Ninth, node (A) managing ledger (A) updates ledger (A) by adding the n+1th block to ledger (A). The n+1th block includes, in its block header portion, a hash value calculated from the nth block, which is the previous block of ledger (A). The n+1th block also includes, in its transaction data portion, transaction data related to at least one transaction in group (A) 200A, ledger information related to ledger (B), and ledger information related to ledger (C). The ledger information related to ledger (B) includes a hash value calculated from the latest block of ledger (B) at the time of adding the n+1th block, i.e., the first block of ledger (B), and a chain ID indicating ledger (B). The ledger information may further include a block height indicating 0, which is the block number of the first block of ledger (B). The ledger information for the ledger (C) includes a hash value calculated from the latest block of the ledger (C) at the time of adding the n+1th block, i.e., the first block of the ledger (C), and a chain ID indicating the ledger (C). The ledger information may further include a block height indicating 0, which is the block number of the first block of the ledger (C).

(5) Grouping of Lower Hierarchical Groups Next, with reference to FIG. 14 and FIG. 15, grouping of lower hierarchical groups according to one embodiment will be described. As shown in FIG. 14, the hierarchical structure network 10 has a plurality of lower hierarchical groups, group (B) 200B to group (D) 200D. The nodes 100 belonging to the plurality of lower hierarchical groups are arranged in one of the plurality of lower hierarchical groups according to the length of the sleep time of the node 100. As described above, low-performance nodes such as IoT devices perform communication intermittently to reduce power consumption, and are in a sleep state (standby state) while not communicating, and no transactions occur during the sleep time (standby time). In the second lower hierarchy and below, grouping can be performed according to the range of sleep time, so that the nodes can be grouped into groups with long sleep times and groups with short sleep times.

Specifically, devices are divided into groups based on similar sleep times. Devices with long sleep times have a low frequency of transactions and therefore a low calculation frequency, making it possible to reduce the frequency of calculations. Here, devices with long sleep times tend to have low performance, so this grouping is effective. In this way, by grouping nodes based on the frequency of transactions, it is possible to reduce the amount of calculations and the expansion of the ledger.

The sleep time of each node 100 belonging to one of the multiple lower hierarchical groups may be within a first predetermined time range. The sleep time of each node 100 belonging to another lower hierarchical group different from the one lower hierarchical group may be within a second predetermined time range different from the first predetermined time. In the example of FIG. 14, each node 100 belonging to group (B) 200B has a sleep time longer than one day. Each node 100 belonging to group (C) 200C has a sleep time of one day or less and one hour or more. Each node 100 belonging to group (D) 200D has a sleep time of less than one hour. Note that such grouping is merely an example and is not limited to the example of FIG. 14.

The maximum number of nodes 100 belonging to each group may be determined according to the performance of the nodes 100 belonging to that group. For example, the limit on the number of nodes in a group may be determined depending on the node with the lowest performance among the nodes participating in that group. The more nodes in a group there are, the more likely it is that the ledger will be updated frequently and its size will increase. For this reason, the maximum number of groups to which the node with the lowest performance belongs is determined according to the performance of that node.

As shown in FIG. 15, if the number of nodes 100 belonging to a lower hierarchical group exceeds the maximum number of nodes 100 belonging to that lower hierarchical group, a new lower hierarchical group may be formed. FIG. 15 shows an example in which the number of nodes 100 with sleep times longer than one day exceeds the maximum number (limit number) of group (B) 200B, and a new group (E) 200E consisting of nodes 100 with sleep times longer than one day is formed. In this way, when there are more nodes than the limit number, a new group with the same sleep time range is added. Alternatively, if the number of nodes 100 belonging to a lower hierarchical group exceeds the maximum number of nodes 100 belonging to that lower hierarchical group, a layer lower may be added and an even lower group may be formed.

(6) Priority within a group Next, priority within a group according to one embodiment will be described with reference to Fig. 16 and Fig. 17. As shown in Fig. 16, the nodes in each group are prioritized using performance parameters. The priority is calculated based on at least one of the performance parameters: battery capacity, computing power, memory capacity, and sleep time.

In one group, the node with the first priority is set as the parent node, the node with the second priority is set as the sub-parent node, and the rest are set as child nodes. In FIG. 16, the priority of each node 100 in group (B) 200B, which is a lower hierarchical group, is indicated by a number. For example, when a new node 100 is added to a lower hierarchical group, the new node 100 or another node 100 determines whether to set the new node 100 as a parent node, sub-parent node, or child node based on the performance of the new node 100.

The multiple nodes 100 that form one group include a parent node that belongs to both the upper and lower hierarchy groups and manages the lower hierarchy ledger and the upper hierarchy ledger, a sub-parent node that belongs to the lower hierarchy group and is changed to a new parent node when the parent node ceases to function as the parent node, and a child node 100 that belongs to the lower hierarchy group and does not correspond to either the parent node 100 or the sub-parent node 100.

Here, the sub-parent node 100 has higher performance than the child node 100, and the parent node 100 has higher performance than the sub-parent node 100. Also, the sub-parent node 100 plays more roles than the child node 100, and the parent node 100 plays more roles than the sub-parent node 100. For this reason, the roles played by the node 100 are matched with their performance.

For example, when a transaction occurs in a lower hierarchical group and the lower hierarchical ledger is updated, the parent node notifies the upper hierarchical group of the update. This causes a transaction to occur in the upper hierarchical group (the upper hierarchical ledger is updated). Specifically, the parent node notifies the node 100 belonging to the upper hierarchical group of the update to the lower hierarchical ledger in response to a transaction within the lower hierarchical group, and the node 100 belonging to the upper hierarchical group updates the upper hierarchical ledger in response to the notification from the parent node.

In addition, when the upper-level ledger of the upper-level group is updated, the parent node passes the upper-level ledger to the sub-parent node. In other words, when the upper-level ledger is updated, the parent node shares the updated upper-level ledger with the sub-parent node.

In the example of FIG. 16, when a transaction occurs in group (B) 200B and the ledger (B) is updated, the parent node of group (B) 200B notifies group (A) 200A that the ledger (B) has been updated. As a result, a transaction occurs in group (A) 200A (the ledger (A) is updated). In addition, when the ledger (A) of group (A) 200A is updated, the parent node of group (B) 200B passes the ledger (A) to the sub-parent node of group (B) 200B.

As shown in FIG. 17, if a parent node is deleted from a group for some reason (for example, the parent node leaves the group on its own or is forcibly deleted due to fraudulent activity), the sub-parent node with second priority automatically becomes the first priority, i.e., the new parent node. The priority of all other nodes is also raised by one. Furthermore, if a sub-parent node is changed to a new parent node, or if a sub-parent node ceases to function as such, the child node with the highest priority among multiple child nodes is changed to the new sub-parent node. Note that because priority needs to be linked to each group, each node 100 has a priority parameter value linked to its chain ID.

There is no problem with the node 100 initially set as the parent node, as it is selected based on performance parameters, but the new parent node set when a parent node is deleted may have insufficient performance parameters. For this reason, a threshold may be set for the performance parameters of each layer, and for parent nodes that fall below the threshold, the parent node may be changed (rotated) every certain number of transactions. In other words, if a sub-parent node is set as the new parent node in response to the deletion of a parent node, and the performance of the new parent node does not meet a certain standard, the node 100 set as the parent node may be changed every certain number of transactions. By lowering its own priority when changing, the sub-parent node becomes the next parent node. The number of transactions for rotating the parent node is held as a node parameter and can be changed.

(7) Example of Node Parameters Stored in Ledger Next, with reference to FIG. 18, an example of node parameters stored in a ledger according to one embodiment will be described.

As described above, in one embodiment, node parameters may be stored in a ledger. For example, when a new node 100 is added to the higher hierarchical group, each node 100 belonging to a higher hierarchical group may update the higher hierarchical ledger to add the parameters of the new node 100 added to the higher hierarchical group to the higher hierarchical ledger. When a new node 100 is added to the lower hierarchical group, each node 100 belonging to a lower hierarchical group may update the lower hierarchical ledger to add the parameters of the new node 100 added to the lower hierarchical group to the lower hierarchical ledger.

As shown in FIG. 18, nodes 100 other than node 100A in the top hierarchy and node 100B2 in the bottom hierarchy, i.e., node 100B1, belong to two groups. Therefore, node 100B1 needs to hold a common ledger for each group, and has two ledgers (ledger (A) and ledger (B)). Here, the two groups (group (A) and group (B)) have parameters that allow them to be distinguished in a manner linked to their respective chain IDs. As mentioned above, ledger (A), which is the higher hierarchy ledger, contains the hash value, etc., of ledger (B), which is the lower hierarchy ledger, and therefore when ledger (B) is updated, ledger (A) also needs to be updated.

The node parameters stored in the ledger are, for example, at least one of the following parameters:

　- Chain ID: A maximum of two are required. The chain ID makes it possible to determine which of two groups is the higher-level group.

- Ledger hash value: A value linked to the chain ID, up to two are required.

- Node priority: A value linked to the chain ID; a maximum of two is required.

- Parent Chain ID: This is the ID of the higher-level chain in which the group's parent node participates. By clarifying the parent-child relationships of groups, it is possible to smoothly automate the hierarchical structure.

- Validator node ID: The ID of the node that verified that the ledger is correct.

- Parent node rotation value: The number of transactions that cause parent node rotation. When the number of parent node transactions reaches this value, parent node rotation occurs.

- Parent node transaction count: The number of transactions that have occurred since becoming a parent node.

- Node performance parameters. For example, at least one of battery capacity, computing power, memory capacity (memory margin information), and sleep time.

(8) Method for Selecting Parent Node Next, a method for selecting a parent node according to an embodiment will be described with reference to Figs. 19 to 24. As described above, by storing the performance parameters (also called "performance values") of each node 100 in a ledger managed by each node 100 in one group, each node 100 can grasp the performance of each of the other nodes 100 in the group. Therefore, each node 100 can autonomously determine the node 100 with the highest performance in the group as the parent node of the group. A parent node is a special node that mediates data exchange between layers, and is also called a "representative node" or "leader". For example, a parent node has a role of reflecting ledger data of a lower layer in a ledger of a higher layer.

In this way, by storing the performance parameters of all the nodes 100 belonging to the group in the ledger, it is possible to autonomously determine the node with the highest performance value among the nodes 100 belonging to the group as the parent node. However, this method has the following problems.

As a first problem, when performance parameters of all the nodes 100 belonging to a group are stored in a ledger, the amount of data in the ledger may become large. Therefore, there is a concern that each node 100 may hold a ledger with a large amount of data, which may put a strain on the storage capacity of each node 100. For example, when the number of nodes 100 belonging to one group is "N", N performance values are managed per node, and ^N2 performance values are managed for the entire group, resulting in a large memory usage.

The second issue is that when the performance value of any of the nodes 100 belonging to a group is updated, or when a new node 100 joins the group or a node 100 that has already joined leaves the group, it is necessary to update the ledger managed by each node 100 belonging to the group. Since updating the ledger involves communication between the nodes 100, there is a concern that frequent ledger updates will increase the frequency of communication between the nodes 100, leading to increased power consumption by each node 100.

These issues become more pronounced in groups that include low-performance nodes such as IoT devices, specifically, nodes 100 that have relatively low computational and/or communication performance.

(8.1) Overview of Node Selection Method Below, we will explain a node selection method that can autonomously select an appropriate parent node (representative node) within a group while solving the problems described above. This node selection method is applicable to any communication system that performs P2P communication between multiple nodes 100 belonging to the same group.

FIG. 19 is a diagram for explaining a node selection method according to one embodiment. A group 200 is made up of multiple nodes 100 (nodes 100a to 100d) that manage the same ledger in a distributed manner.

Each node 100 stores its own performance value. Each node also stores a point value used to select a representative node within the group 200.

Each node 100 belonging to the same group 200 has a control unit 120 that performs a predetermined control in response to communication with other nodes in the group 200 (see FIG. 5). The predetermined control includes an acquisition process for acquiring the performance value of the other node from the other node, and a change process for changing the point value of the node 100 based on the result of comparing the performance value of the other node with the performance value of the node 100. When the point value reaches a predetermined value (also called the "representative node threshold"), the control unit 120 determines the node 100 as the parent node (representative node) of the group 200. In one embodiment, the parent node is the node 100 with the highest performance in the group 200, and is the node 100 that mediates exchanges between the group 200 and other groups. The group is a group that belongs to a layer other than the top layer (Layer 1), that is, any layer from the second layer onward.

In this node selection method, each node 100 in the group 200 manages its own point value. Then, when communication (P2P communication) occurs between two nodes 200 in the group 200, the point value is changed by comparing the performance of the two nodes 200. By repeating this control (predetermined control) for each P2P communication, the point value of each node 100 is changed (updated), and finally, the node 100 whose point value has reached a predetermined value is selected as the parent node.

Therefore, each node 100 does not need to store, hold, and manage the performance parameters of all nodes 100 belonging to the group 200 in a ledger, but instead can hold and manage point values. Compared to storing, holding, and managing performance parameters in a ledger, holding and managing point values, which are a small amount of data, can reduce memory usage in each node 100.

Furthermore, according to this node selection method, even if the performance value of any of the nodes 100 belonging to the group 200 is updated, or if a new node 100 joins the group 200 or a node 100 that has already joined leaves, each node 100 does not need to update the performance parameters of the node whose performance value has been updated, which are included in the ledger. Therefore, it is possible to avoid a situation in which the frequency of communication between the nodes 100 increases due to frequent ledger updates, and it is possible to suppress an increase in the power consumption of each node 100.

Therefore, even in a group 200 that includes low-performance nodes such as IoT devices, it is possible to autonomously select an appropriate parent node while suppressing increases in memory usage and/or power consumption.

In the following description of the embodiment, the point value managed by each node 100 is also referred to as LP (Leader Point). As shown in FIG. 19, each node 100 belonging to the group 200 holds its own point value (LP) and its own performance value. In the illustrated example, the point value is a value in the range of 0 to 100. As described above, the performance value (performance parameter) of the node 100 may be at least one of the battery capacity, computing power, storage capacity, and sleep time. The performance value of the node 100 may be an index value derived from one or more parameters of the battery capacity, computing power, storage capacity, and sleep time. For example, the performance value may be a statistical value (total value or average value, etc.) for the battery capacity, computing power, and storage capacity. In addition, the performance value may be set so that the shorter the sleep time, the higher the performance value. In the illustrated example, the performance value is a normalized value in the range of 0 to 100. The node 100a has a performance value of "10", which is the lowest performance in the group. Node 100c has a performance value of "75", making it the highest performing node in the group.

The point value (LP) may be a value that increases or decreases over time so as to approach a predetermined value (representative node threshold). In other words, each node 100 increases or decreases the point value of its own node 100 so that the point value of the own node 100 approaches a predetermined value (representative node threshold) over time.

FIG. 20 is a diagram showing an example of the own point value (LP) managed by each node 100. In the example shown, the initial value of the point value is "0" and is a value that is counted up as time passes. The specified value (representative node threshold) is set to "100". FIG. 21 is a diagram showing another example of the own point value (LP) managed by each node 100. In the example shown, the initial value of the point value is "100" and is a value that is counted down as time passes. The specified value (representative node threshold) is set to "0". The amount of change in the point value per unit time (also referred to as the "rate of change of the point value") is preset to be the same rate of change for each node 100.

When communicating with another node in the group 200, if the performance value of the other node is higher than the performance value of the node 100, the node 100 may change the point value of the node 100 so as to widen the gap between the point value of the node 100 and the predetermined value (representative node threshold). Specifically, under the assumption that the point value (LP) as shown in FIG. 20 is used, the gap between the point value of the node 100 and the predetermined value (representative node threshold) is widened by lowering the point value of the node 100. On the other hand, under the assumption that the point value (LP) as shown in FIG. 21 is used, the gap between the point value of the node 100 and the predetermined value (representative node threshold) is widened by increasing the point value of the node 100. In this way, when the node 100 detects another node in the group 200 with higher performance than the node 100, the node 100 can change the point value of the node 100 so as to make it less likely for the node 100 to become the representative node.

For example, each node 100 may reset the point value of its own node 100 to an initial value if the performance value of the other node is higher than the performance value of its own node 100. Specifically, under the assumption that the point value (LP) as shown in FIG. 20 is used, the point value of its own node 100 is reset to "0". On the other hand, under the assumption that the point value (LP) as shown in FIG. 21 is used, the point value of its own node 100 is reset to "100".

Alternatively, when the performance value of the other node is higher than the performance value of the node 100, each node 100 may change the point value of its own node 100 by an amount corresponding to the difference between the performance value of the other node and the performance value of its own node 100. Specifically, under the assumption that point values (LP) such as those in FIG. 20 are used, the greater the difference between the performance value of the other node and the performance value of its own node 100, the greater the point value of its own node 100 is reduced. On the other hand, under the assumption that point values (LP) such as those in FIG. 21 are used, the greater the difference between the performance value of the other node and the performance value of its own node 100, the greater the point value of its own node 100 is increased.

On the other hand, when communicating with another node in the group 200, if the performance value of the other node is lower than the performance value of the node 100, the node 100 may maintain the point value of the node 100 without resetting it. In this way, when the node 100 detects another node in the group 200 whose performance is lower than that of the node 100, the node 100 can more easily become the representative node by maintaining the point value of the node 100 without resetting it.

Alternatively, when communicating with another node in the group 200, if the performance value of the other node is lower than the performance value of the node 100, the node 100 may change the point value of the node 100 so as to narrow the gap between the point value of the node 100 and a predetermined value (representative node threshold). Specifically, under the assumption that a point value (LP) such as that in FIG. 20 is used, the gap between the point value of the node 100 and a predetermined value (representative node threshold) is narrowed by increasing the point value of the node 100. On the other hand, under the assumption that a point value (LP) such as that in FIG. 21 is used, the gap between the point value of the node 100 and a predetermined value (representative node threshold) is narrowed by decreasing the point value of the node 100. In this way, when the node 100 detects another node in the group 200 with lower performance than the node 100, the node 100 can change the point value of the node 100 so as to make it easier for the node 100 to become the representative node. Here, when the performance value of the other node is lower than the performance value of the node 100, each node 100 may change the point value of the node 100 by an amount corresponding to the difference between the performance value of the other node and the performance value of the node 100. Specifically, under the assumption that the point value (LP) as shown in FIG. 20 is used, the larger the difference between the performance value of the other node and the performance value of the node 100, the larger the point value of the node 100 is increased. On the other hand, under the assumption that the point value (LP) as shown in FIG. 21 is used, the larger the difference between the performance value of the other node and the performance value of the node 100, the larger the point value of the node 100 is decreased.

(8.2) Example of a flow of a node selection method Fig. 22 is a diagram showing an example of a flow of a node selection method according to one embodiment. Each node 100 in the group 200 executes this flow. Note that each node 100 is assumed to perform a process separate from this flow to increase or decrease the point value (LP) of the own node 100 so that the point value (LP) of the own node 100 approaches a predetermined value (representative node threshold) over time.

In step S1, node 100 (hereinafter referred to as "node 100x") performs P2P communication with another node (hereinafter referred to as "node 100y") in group 200. Here, node 100x acquires the performance value of other node 100y from other node 100y. In addition, node 100x notifies other node 100y of its own performance value. The following processing is also executed on the side of other node 100y. Furthermore, node 100x acquires the current point value (LP) of its own node 100x.

In step S2, node 100x compares its own performance value with the performance value of another node 100y.

If the performance value of the other node 100y exceeds the performance value of the node 100x (step S2: YES), in step S3, the node 100x changes the point value (LP) of the node 100x so as to widen the gap between the point value (LP) of the node 100x and a predetermined value (representative node threshold). For example, the node 100x resets the point value (LP) of the node 100x to its initial value.

On the other hand, if the performance value of the other node 100y is lower than the performance value of the node 100x (step S2: NO), in step S4, the node 100x maintains the point value (LP) of the node 100x, or changes the point value (LP) of the node 100x so as to narrow the gap between the point value (LP) of the node 100x and a predetermined value (representative node threshold).

In step S5, node 100x checks whether its own node 100x's point value (LP) has reached a predetermined value (representative node threshold).

If the point value (LP) of node 100x reaches a predetermined value (representative node threshold) (step S5: YES), in step S6, node 100x determines itself as the parent node (representative node) of group 200. However, node 100x continues this flow even after node 100x becomes the parent node. If node 100x detects another node with better performance than node 100x, it resets the point value (LP) of node 100x to the initial value (step S3), for example, and stops considering node 100x as the parent node.

On the other hand, if the point value (LP) of the node 100x has not reached the predetermined value (representative node threshold) (step S5: NO), in step S7, the node 100x may transition to a sleep state for power saving after communicating with the other node 100y. After returning from the sleep state, the process returns to step S1.

If the performance values of the node 100x and the other node 100y are equal in step S2, the node 100x selects one of steps S3 and S4 according to a predetermined rule. For example, the node 100x and the node 100y may transmit the unique identification number of the node 100 (e.g., a serial number) to the other node 100 via communication, and the node 100 with the smaller unique identification number may execute the process of step S3, and the node 100 with the larger unique identification number may execute the process of step S4. Alternatively, the nodes 100 may transmit the performance values as statistics (total or average value, etc.) for the battery capacity, computing power, and storage capacity, and separately transmit the sleep time between them, and the node 100 with the longer sleep time may execute the process of step S3, and the node 100 with the shorter sleep time may execute the process of step S4.

According to the node selection method shown in FIG. 22, node 100 that has reached a predetermined value (representative node threshold) becomes the parent node of group 200 and is responsible for mediating data with the upper hierarchy. If communication between nodes in group 200 is sufficiently active, a parent node is autonomously selected after the passage of time according to the rate of change in point value and the predetermined value (representative node threshold).

Note that when communication is sparse, there is a possibility that selection will not progress sufficiently and multiple parent nodes will be born within one group 200. In that case, since the multiple parent nodes can be detected in the upper hierarchical group, it is possible to narrow it down to one parent node in response to an instruction from node 100 in the upper hierarchical group. In addition, since it is considered that a group 200 in which multiple parent nodes are born should be further divided into multiple groups, for example, in response to an instruction from node 100 in the upper hierarchical group, the group may be further divided so that there is only one parent node within the group. However, by appropriately adjusting and setting the rate of change of the point value and a predetermined value (representative node threshold), it is possible to prevent multiple parent nodes from being born within one group 200.

In addition, if the node 100 that became the parent node is deleted or leaves the group 200, the node 100 with the second highest performance value will no longer initialize its own point value, and will be autonomously selected as the next parent node. Here, the time until the next parent node is born is determined depending on the rules for point calculation processing during communication, the rate of change in point value, and a predetermined value (representative node threshold value).

(8.3) Advantages of the Node Selection Method Advantages of the node selection method using point values (LP) as described above will be described with reference to Fig. 23 and Fig. 24. Fig. 23 is a diagram for explaining a node selection method in a comparative example in which performance parameters of all nodes 100 belonging to a group 200 are stored in a ledger managed within the group 200. Fig. 24 is a diagram for explaining a node selection method using point values (LP).

In the method shown in Fig. 24, compared to the method shown in Fig. 23, the data held by each node 100 (specifically, its own point value and performance value) is fixed and does not depend on the number of nodes in the group 200. For example, in a group 200 to which N nodes 100 belong, each node holds N pieces of data in the method of Fig. 23 and 1 piece of data in the method of Fig. 24. Considering the group 200 as a whole, the method of Fig. 23 requires ^N2 pieces of data, but the method of Fig. 24 requires only N pieces of data.

Furthermore, in the method shown in FIG. 24, compared to the method shown in FIG. 23, it is not necessary to transmit information about one's own node to all other nodes, and this makes it possible to reduce the amount of communication in the entire group 200. For example, in a group 200 to which N nodes 100 belong, the method shown in FIG. 23 requires N*(N-1)/2 communications, whereas the method in FIG. 24 requires only N-1 communications.

Therefore, according to the node selection method using the point value (LP), the amount of data and/or communication can be reduced compared to the method shown in FIG. 23. Therefore, even a low-performance node 100 can participate in the group 200 and utilize the blockchain.

(9) Other Embodiments In the node selection method according to the above embodiment, an example has been described in which the group 200 is made up of a plurality of nodes 100 that manage the same ledger in a distributed manner. However, the group 200 does not have to manage the same ledger in a distributed manner. The group 200 may be any group that performs P2P communication between the nodes 100.

In the node selection method according to the above embodiment, an example has been described in which the representative node (parent node) is the node 100 with the highest performance in the group 200. However, the representative node may also be the node 100 with the lowest performance in the group 200. In other words, it is also possible to apply the node selection method according to the above embodiment and select the node 100 with the lowest performance in the group 200 as the representative node.

In the above-described embodiment, it is primarily assumed that the node 100 is a battery-powered device. However, the hierarchical network 10 may also include devices that are powered by an external power source. For example, a device connected to an external power source may be placed in the highest hierarchical layer in the hierarchical network 10.

Each of the above-mentioned operation flows can be implemented not only separately but also by combining two or more operation flows. For example, some steps of one operation flow can be added to another operation flow, or some steps of one operation flow can be replaced with some steps of another operation flow. Also, the order of the steps in each of the above-mentioned operation flows is an example, and the order of the steps can be changed as appropriate.

A program may be provided that causes a computer to execute each process performed by node 100. The program may be recorded on a computer-readable medium. Using the computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. In addition, the circuits that execute each process performed by node 100 may be integrated, and at least a part of node 100 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless otherwise specified. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "based only on" and "depending at least in part on." Additionally, the terms "include," "comprise," and variations thereof do not mean to include only the items listed, but may include only the items listed, or may include additional items in addition to the items listed. Additionally, the term "or" as used in this disclosure is not intended to be an exclusive or. Additionally, any reference to elements using designations such as "first," "second," and the like used in this disclosure is not intended to generally limit the quantity or order of those elements. These designations may be used herein as a convenient way of distinguishing between two or more elements. Thus, a reference to a first and second element does not mean that only two elements may be employed therein, or that the first element must precede the second element in some way. In this disclosure, where articles have been added through translation, such as a, an, and the in English, these articles are intended to include the plural unless the context clearly indicates otherwise.

The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes can be made without departing from the spirit of the invention.

This application claims priority to Japanese Patent Application No. 2022-189523 (filed November 28, 2022), the entire contents of which are incorporated herein by reference.

(10) Additional Notes Additional notes will be given regarding the features of the above-described embodiment.

(Appendix 1)
A communication system for performing peer-to-peer communication among a plurality of nodes belonging to the same group,
Each of the plurality of nodes
a control unit that performs a predetermined control in response to communication with other nodes in the group;
The predetermined control is
an acquisition process of acquiring a performance value of the other node from the other node;
A change process of changing the point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node,
When the point value reaches a predetermined value, the control unit determines the node itself as a representative node of the group.

(Appendix 2)
The communication system according to claim 1, wherein the representative node is a node having the highest performance within the group.

(Appendix 3)
the point value is a value that increases or decreases over time so as to approach the predetermined value,
The communication system according to claim 2, wherein the change process includes a process of changing the point value so as to widen an interval between the point value and the predetermined value when the performance value of the other node is higher than the performance value of the own node.

(Appendix 4)
The communication system according to claim 3, wherein the change process includes a process of resetting the point value to an initial value when the performance value of the other node is higher than the performance value of the own node.

(Appendix 5)
The communication system described in Appendix 3, wherein the change process includes a process of changing the point value by an amount corresponding to a difference between the performance value of the other node and the performance value of the own node when the performance value of the other node is higher than the performance value of the own node.

(Appendix 6)
The communication system according to any one of Supplementary Notes 3 to 5, wherein the change process includes a process of maintaining the point value without resetting it when the performance value of the other node is lower than the performance value of the own node.

(Appendix 7)
The communication system according to any one of appendixes 3 to 5, wherein the change process includes a process of changing the point value so as to narrow the gap between the point value and the predetermined value when the performance value of the other node is lower than the performance value of the own node.

(Appendix 8)
The group is made up of multiple nodes that manage the same ledger in a distributed manner,
The communication system according to any one of Supplementary Notes 2 to 7, wherein the representative node is a node that mediates interactions between the group and other groups.

(Appendix 9)
A node used in a communication system for performing peer-to-peer communication among a plurality of nodes belonging to the same group,
a control unit that performs a predetermined control in response to communication with other nodes in the group;
The predetermined control is
an acquisition process of acquiring a performance value of the other node from the other node;
A change process of changing the point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node,
When the point value reaches a predetermined value, the control unit determines the node itself as a representative node of the group.

(Appendix 10)
A node used in a communication system for performing peer-to-peer communication between multiple nodes belonging to the same group,
a step of executing a predetermined control in response to communication with another node in the group, the predetermined control including an acquisition process of acquiring a performance value of the other node from the other node, and a change process of changing a point value of the own node based on a result of comparing the performance value of the other node with a performance value of the own node;
and when the point value reaches a predetermined value, determining the node itself as a representative node of the group.

10: Hierarchical network 100: Node 110: Communication unit 120: Control unit 121: Processor 130: Storage unit 140: Battery 200: Group

Claims

A communication system for performing peer-to-peer communication among a plurality of nodes belonging to the same group,
Each of the plurality of nodes
a control unit that performs a predetermined control in response to communication with other nodes in the group;
The predetermined control is
an acquisition process of acquiring a performance value of the other node from the other node;
A change process of changing the point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node,
When the point value reaches a predetermined value, the control unit determines the node itself as a representative node of the group.
The communication system according to claim 1 , wherein the representative node is a node having the highest performance within the group.
the point value is a value that increases or decreases over time so as to approach the predetermined value,
The communication system according to claim 2 , wherein the change process includes a process of changing the point value so as to widen an interval between the point value and the predetermined value when the performance value of the other node is higher than the performance value of the own node.
The communication system according to claim 3 , wherein the change process includes a process of resetting the point value to an initial value when the performance value of the other node is higher than the performance value of the own node.
The communication system according to claim 3 , wherein the change process includes a process of changing the point value by an amount corresponding to a difference between the performance value of the other node and the performance value of the own node when the performance value of the other node is higher than the performance value of the own node.
The communication system according to claim 3 , wherein the change process includes a process of maintaining the point value without resetting it when the performance value of the other node is lower than the performance value of the own node.
The communication system according to claim 3 , wherein the change process includes a process of changing the point value so as to narrow an interval between the point value and the predetermined value when the performance value of the other node is lower than the performance value of the own node.
The group is made up of multiple nodes that manage the same ledger in a distributed manner,
The communication system according to claim 2 , wherein the representative node is a node that mediates communication between the group and other groups.
A node used in a communication system for performing peer-to-peer communication among a plurality of nodes belonging to the same group,
a control unit that performs a predetermined control in response to communication with other nodes in the group;
The predetermined control is
an acquisition process of acquiring a performance value of the other node from the other node;
A change process of changing the point value of the own node based on a result of comparing the performance value of the other node with the performance value of the own node,
When the point value reaches a predetermined value, the control unit determines the node itself as a representative node of the group.
A node used in a communication system for performing peer-to-peer communication between multiple nodes belonging to the same group,
Executing a predetermined control in response to communication with other nodes in the group, the predetermined control including an acquisition process for acquiring a performance value of the other node from the other node, and a change process for changing a point value of the own node based on a result of comparing the performance value of the other node with a performance value of the own node;
When the point value reaches a predetermined value, the node itself is determined to be a representative node of the group.