Network system, root node, edge node, and program

Abstract

To provide a network system, a root node, an edge node, and a program in which the root node and the edge node communicate via a wide area communication network, and the edge node and a lower layer node communicate via a narrow area communication network.SOLUTION: A network system of an embodiment has a root node, an edge node, and a lower layer node. The root node is connected to a higher-level device. The edge node is connected to the root node with one hop via a wide area communication network. The lower layer node is connected to the root node through a hop count of two or more via the edge node. The edge node communicates with the root node using first communication means, and communicates with the lower layer node using second communication means different from the first communication means.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a network system, a root node, an edge node, and a program.

Background Art

[0002] A multi-hop network is composed of nodes that perform multi-hop communication and a root node that terminates the multi-hop network and has a communication function with the outside. A multi-hop network using wireless can communicate by relaying nodes that are within a communicable distance from each other where direct wireless does not reach. A multi-hop network may be used in IoT devices where it is difficult to lay communication cables.

[0003] In a system for collecting data from smart meters using a wireless multi-hop network, generally, nodes and a root node are installed in the area where data is collected, and the root node is connected to a wide area network and communicates with a higher-level device via the wide area network.

[0004] Since the root node needs to manage information about subordinate nodes, it is necessary to mount memory. As the number of nodes increases, the memory and processing power may increase. Therefore, when the root node manages a large number of nodes, it may not fit within the allowable mounting size of the node, such as the need to mount memory or have high CPU processing power.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a network system, a root node, an edge node, and a program capable of managing a large number of nodes.

Means for Solving the Problem

[0007] The network system of the embodiment has a root node, an edge node, and a lower layer node. The root node is connected to a higher-level device. The edge node is connected to the root node in one hop via a wide area communication network. The lower layer node is connected to the root node via the edge node with a hop count of two hops or more. The edge node communicates with the root node by a first communication means and communicates with the lower layer node by a second communication means different from the first communication means.

Brief Description of the Drawings

[0008]

Figure 1

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Modes for Carrying Out the Invention

[0009] Hereinafter, a network system, a root node, an edge node, and a program according to an embodiment will be described with reference to the drawings.

[0010] (First Embodiment) FIG. 1 is a diagram showing the configuration of a network system 1 according to the first embodiment. In the network system 1, communication is performed between the provided nodes. The network system 1 includes a root node 20, a wide area communication network 30, and a local network 40. The local network 40 includes an edge node 41 and a lower layer node 42. In the communication between the nodes in the network system 1, the root node 20 is a node higher than the local network 40. Also, in the local network 40, the edge node 41 is a node higher than the lower layer node 42.

[0011] A control protocol for forming a multi-hop network is implemented between the root node 20 and the edge node 41 and the lower layer node 42 included in the local network 40. The control protocol is, for example, RPL (Routing Protocol for Low-Power and Lossy Networks). In the following description, it is assumed that the network system 1 uses RPL as the control protocol.

[0012] The root node 20 is connected to the upper device 10. The root node 20 is connected to the wide area communication network 30. The root node 20 may be implemented as a device having an interface device for the wide area communication network 30. The root node 20 may be implemented as a software function operating on one or more servers. In the network system 1, the routers included in the wide area communication network 30 are not included in the number of hops. The root node 20 and the edge node 41 are logically connected by one hop by tunnel technology. The edge node 41 is connected to the root node 20 by one hop via the wide area communication network 30, and the lower layer node 42 is connected to the root node 20 with two or more hops. The root node 20 is provided between the upper device 10 and the wide area communication network 30, and transmits and receives data to and from the upper device 10 and the wide area communication network 30.

[0013] A physical IP address is assigned to the device on which the root node 20 operates, and a logical IP address is assigned to the root node function.

[0014] Figure 2 is a diagram showing the configuration of the root node 20. The root node 20 includes an upper device communication unit 201, a network system control unit 202, a lower device communication unit 203, and a node management information storage unit 204.

[0015] The upper device communication unit 201 transmits and receives data to and from the upper device 10.

[0016] The network system control unit 202 controls the lower device communication unit 203 to transmit data. The network system control unit 202 is realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may be realized by hardware (including circuitry) such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), or may be realized by the cooperation of software and hardware. The program may be stored in advance in a storage device (a storage device equipped with a non-transitory storage medium) such as an HDD (Hard Disk Drive) or a flash memory, or may be stored in a removable storage medium (a non-transitory storage medium) such as a DVD or a CD-ROM, and may be installed by mounting the storage medium on a drive device.

[0017] The lower device communication unit 203 transmits and receives data with the edge node 41 via the wide area communication network 30. For example, the lower device communication unit 203 transmits data to the edge node 41. The data transmitted by the lower device communication unit 203 to the edge node 41 is, for example, data or protocol information transmitted from the upper device 10 to the root node. The protocol information includes information necessary for a new node to join the network system 1 and RPL messages such as DAO-ACK.

[0018] The information necessary for a new node to join the network system 1 is the information necessary for joining at the MAC level, for example, information regarding short address allocation. In the MAC protocol defined by IEEE802.15.4, a 64-bit long address and a 16-bit short address are defined. The long address is the address unique to the terminal, but for traffic reduction, in normal communication, the lower layer node 42 can perform an operation of allocating a short address for communication in the network. The lower device communication unit 203 completes the entry of the lower layer node 42 by notifying the newly joined lower layer node 42 of the short address.

[0019] DAO-ACK is a notification for confirming that a DAO message has been received from the newly joined lower layer node 42.

[0020] The node management information storage unit 204 stores data related to node management. The node management information storage unit 204 stores, for example, short address allocation information, entry status information, or downlink communication path information.

[0021] The short address allocation information is information regarding the short address assigned to the lower layer node 42. Based on the short address allocation information, the network system control unit 202 can cause the lower device communication unit 203 to transmit information regarding short address allocation so that the newly allocated short address does not overlap with the used short address.

[0022] The entry status information is information regarding the number of lower layer nodes 42 connected to the edge node 41. The network system control unit 202 may control the lower device communication unit 203 based on the entry status information. For example, when the number of lower layer nodes 42 connected to the edge node 41 is equal to or more than a predetermined number and an entry request is received from a new lower layer node 42, the network system control unit 202 may control the lower device communication unit 203 to notify that connection to the new lower layer node 42 is not permitted.

[0023] The downlink communication path information is the path information for communicating with each lower-layer node 42. At the root node 20, when the upper device communication unit 201 acquires a packet for each lower-layer node 42, the network system control unit 202 selects an edge node 41 connected to the corresponding lower-layer node 42 based on the path information, and the lower device communication unit 203 transfers the packet to the edge node 41.

[0024] FIG. 3 is a diagram showing the configuration of the edge node 41. The edge node 41 includes a first communication unit 411, a conversion unit 412, a second communication unit 413, and a network system control unit 414.

[0025] The first communication unit 411 communicates with the lower device communication unit 203 via the wide-area communication network 30. The communication between the first communication unit 411 and the lower device communication unit 203 is performed by first communication means. The first communication means is wide-area communication means including one or both of wired communication and wireless communication.

[0026] The conversion unit 412 converts data so as to be compatible with the second communication means by the first communication means and the second communication unit 413.

[0027] The second communication unit 413 communicates with the lower-layer node 42 connected to the edge node 41. The communication between the second communication unit 413 and the lower-layer node 42 is performed by second communication means different from the first communication means. The second communication means is narrow-area communication means such as specific low-power radio at 920 MHz. The lower-layer nodes 42 also communicate with each other by the second communication means.

[0028] The network system control unit 414 controls the first communication unit 411 and the second communication unit 413 to transmit and receive data.

[0029] The network system 1 may include a plurality of edge nodes 41. Also, the network system 1 may include a plurality of root nodes 20. When the network system 1 has a plurality of root nodes 20, different network addresses are assigned to the local networks 40 connected to each root node 20. Also, in each local network 40, different node numbers are assigned to each lower-layer node 42. The network system 1 includes a management device that manages the root nodes connected to the lower-layer nodes 42, and the management device transfers the data transmitted from the upper device 10 to the root node 20 connected to the lower-layer node 42 that is the destination based on the network address. The edge node 41 and the lower-layer node 42 transfer the data to the lower-layer node 42 that is the destination of the data based on the node number.

[0030] The management device may manage the transmission destination of the data based on the serial number assigned to each lower-layer node 42. For example, the management device manages the transmission destination of the data based on the correspondence relationship between the combination of the serial number, the network address, and the node number.

[0031] FIG. 4 is a diagram showing an example of the network system 1 including a plurality of root nodes 20 and a plurality of edge nodes 41. For example, the first root node 20-1 is connected to the first edge node 41-1 and the second edge node 41-2 via the wide area communication network 30, and the second root node 20-2 is connected to the third edge node 41-3 via the wide area communication network 30.

[0032] Hereinafter, the start of connection between the root node 20 and the edge node 41 will be described. Hereinafter, the network system 1 will be described as an IP network.

[0033] FIG. 5 is a flowchart showing the start of connection between the root node 20 and the edge node 41. After the edge node 41 is connected to the wide area communication network 30, a communication path is set up between the physical IP address of the root node 20 set in the edge node 41 (step S1). Thereafter, a logical communication path is set up between the logical IP address of the root node 20 set in the edge node 41 through the established communication path (step S2).

[0034] After the logical communication path is established, the edge node 41 acquires information necessary for the network configuration from the root node 20 (step S3). The information necessary for the network configuration is, for example, a DIO (DODAG Information Object) message. The edge node 41 receives the DIO message from the root node 20 and performs a prescribed process (step S4). Thereafter, the DIO message is transmitted as the first-hop node to the connected lower layer node 42 (step S5). Each lower layer node 42 performs communication processing in accordance with the RPL regulations (step S6). Thereby, a network system in which the root node 20, the edge node 41, and the lower layer node 42 are connected is formed. As described above, the root node 20 and the edge node 41 are connected.

[0035] Hereinafter, the processing when a new lower layer node 42 joins will be described. Hereinafter, the newly joined lower layer node is referred to as the second lower layer node 42-2, and the lower layer node 42 that is connected to the edge node 41 and becomes the parent node of the second lower layer node 42-2 is referred to as the first lower layer node 42-1.

[0036] FIG. 6 is a flowchart showing the processing when the second lower layer node 42-2, which is a new lower layer node 42, joins. The second lower-layer node 42-2 receives the MAC-level beacon notified by the first lower-layer node 42-1 (step S10). After receiving the MAC-level beacon, the second lower-layer node 42-2 sends an access request to the first lower-layer node 42-1 (step S12). The first lower-layer node 42-1 forwards the access request to a higher-level node (step S14), and the access request is finally forwarded to the root node 20. The root node 20 sends the information necessary for MAC-level access to the first lower-layer node 42-1 (step S16). The root node 20, for example, assigns a short address to the second lower-layer node 42-2 and sends data regarding the assigned short address to the first lower-layer node 42-1.

[0037] The first lower-layer node 42-1 forwards the information necessary for MAC-level access to the second lower-layer node 42-2 (step S18). The second lower-layer node 42-2 accesses the MAC level based on the received information (step S20).

[0038] After the second lower-layer node 42-2 accesses the MAC level, it starts the protocol processing of RPL. The second lower-layer node 42-2 receives a DIO message from the first lower-layer node 42-1 (step S22). It performs parent selection processing and selects the first lower-layer node 42-1 as the parent node (step S24). Then, it sends a DAO (Destination Advertisement Object) message to the first lower-layer node 42-1, which is the parent node, with the root node 20 as the destination (step S26).

[0039] When the root node 20 receives the DAO message, as the downlink communication path management, it records that it can communicate with the second lower-layer node 42-2 via the edge node 41 (step S28). The root node 20 sends a DAO-ACK message to the second lower-layer node 42-2 as the delivery confirmation of the DAO message (step S30). Thus, a new lower-layer node 42 joins. After the second lower-layer node 42-2 joins, it starts notifying its surrounding DIO messages.

[0040] According to the first embodiment, it is not necessary to install root nodes everywhere, and it is possible to implement root nodes with server devices having required capabilities and memory amounts. Thereby, a large number of nodes can be managed.

[0041] Also, the root node can notify that connection is not permitted to a new lower-layer node that requests access, based on the access state information. Thereby, without managing lower-layer nodes at the edge node, the number of nodes connected to the edge node can be restricted.

[0042] The network system 1 can include a plurality of edge nodes. Thereby, even if each edge node is installed at a remote location, the network system can be configured.

[0043] The network system 1 can include a plurality of root nodes. Thereby, the processing capabilities and memory amounts required for each root node can be reduced, and the influence range in case of failure can be minimized.

[0044] The network system 1 includes a management device and can manage data transmitted to different root nodes. Thereby, it is easy to determine the root node through which the data passes. Also, by using a serial number unique to the lower-layer node, communication independent of the network configuration can be realized.

[0045] (Second Embodiment) FIG. 7 is a diagram showing the configuration of the edge node 41 according to the second embodiment. The edge node 41 according to the second embodiment includes a root node monitoring unit 415 in addition to the edge node 41 according to the first embodiment.

[0046] The root node monitoring unit 415 monitors the communication state with the root node 20. For example, the edge node 41 monitors the communication state with the root node 20 by sending a communication confirmation request to the root node 20. The root node monitoring unit 415 detects a communication abnormality with the root node 20. For example, the root node monitoring unit 415 detects a communication abnormality when it does not receive a communication confirmation response to the communication confirmation request from the root node 20 within a certain time. For example, the root node monitoring unit 415 detects normal communication when it receives a communication confirmation response to the communication confirmation request from the root node 20 within a certain time.

[0047] The lower layer node 42 performs parent selection with reference to a plurality of conditions. The conditions are, for example, the number of hops when passing through a certain parent candidate node, the signal strength (RSSI) of the signal received from the parent candidate, the transmission quality (for example, the packet arrival rate to the parent candidate node or the packet arrival rate to the root node), etc., and include the presence or absence of communication with the root node. The lower layer node 42 performs parent selection without including the presence or absence of communication with the root node as a condition to be referred to for a certain time after the communication abnormality is notified or until the communication normality is notified after the communication abnormality is notified. If the communication normality is not notified even after a certain time has passed, or if the communication normality is notified before a certain time has passed, the lower layer node 42 performs parent selection including the presence or absence of communication with the root node as a condition to be referred to.

[0048] FIG. 8 is a flowchart showing an example of the operation of the network system 1 according to the second embodiment. The edge node 41 sends a communication confirmation request to the root node 20 (step S40). When the root node 20 receives the communication confirmation request, it sends a communication confirmation response to the edge node 41 (step S42). The edge node 41 receives the communication confirmation response and detects normal communication (step S44).

[0049] Again, the edge node 41 sends a connection confirmation request to the root node 20 (step S50). Since the edge node 41 does not receive a connection confirmation response within a certain period of time, it detects a connection abnormality (step S52). The edge node 41 notifies the lower-layer node 42 of the connection abnormality (step S54). When notified of the connection abnormality, the lower-layer node 42 changes the condition for selecting a parent node (step S56).

[0050] After that, the edge node 41 sends a connection confirmation request to the root node 20 (step S58). When receiving the connection confirmation request, the root node 20 sends a connection confirmation response to the edge node 41 (step S60). The edge node 41 receives the connection confirmation response and detects normal connection (step S62). The edge node 41 notifies the lower-layer node 42 of the normal connection (step S64). When notified of the normal connection, the lower-layer node 42 changes the condition for selecting a parent node and returns to the original setting (step S66). Even if the lower-layer node 42 is not notified of normal connection after a certain period of time has elapsed, it may change the condition for selecting a parent node and return to the original setting.

[0051] When the root node 20 stops due to a failure or maintenance and communication with the edge node 41 becomes impossible, in the parent selection method that includes communication with the root node as a condition for determining parent selection, the lower layer node 42 switches its connection to another parent node. Normally, since neighboring lower layer nodes 42 are connected to the same edge node, the participation process is started in all lower layer nodes 42, and the configuration of the network system 1 cannot be maintained. In the network system 1 according to the second embodiment, when the lower layer node 42 is notified of a communication abnormality, it switches the parent node selection setting and does not select a parent node based on the communication state. Therefore, the parent selection process based on the communication state with the root node is not started in the lower layer node 42, and the multi-hop network connection state up to the edge node can be maintained. If communication with the root node is restored within the specified time, communication with the root node is also restored as it is. If communication with the root node is not restored within the specified time, parent selection based on the communication state with the root node is performed. If there is a network including an edge node that can communicate with the root node in the vicinity, redundancy against a single failure of the edge node can be provided in order to connect to that network.

[0052] According to at least one of the embodiments described above, the edge node 41 communicates with the root node 20 by the first communication means and communicates with the lower layer node 42 by a second communication means different from the first communication means. Thereby, a network system can be configured in which the root node 20 and the edge node 41 communicate via a wide area communication network, and the edge node 41 and the lower layer node 42 communicate via a local area communication network. Therefore, according to the network system of the embodiment, a large number of nodes can be managed by the root node 20.

[0053] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0054] 1... Network system, 10... Upper device, 20.. Route node, 30... Wide area communication network, 40... Local network, 41... Edge node, 42... Lower layer node, 201... Upper device communication unit, 202... Network system control unit, 203... Lower device communication unit, 204... Node management information storage unit, 411... First communication unit, 412... Conversion unit, 413... Second communication unit, 414... Network system control unit, 415... Route node monitoring unit

Claims

1. A root node connected to an upper device, An edge node connected to the root node via a wide area communication network in one hop, A lower layer node connected to the root node via the edge node with a hop count of two hops or more, comprising, The edge node communicates with the root node by a first communication means and communicates with the lower layer node by a second communication means different from the first communication means, The number of the lower layer nodes connected to the edge node is equal to or greater than a predetermined number, and when a new lower layer node is connected to the edge node, the root node notifies that connection to the new lower layer node is not permitted, A network system.

2. The first communication means is a wide area communication means including one or both of wired communication and wireless communication, The second communication means is a narrow area communication means, The network system according to claim 1.

3. Protocol information for controlling the network system is transmitted and received by communication using the first communication means and the second communication means, The network system according to claim 1 or claim 2.

4. The root node includes route information for communicating with each lower layer node, When a packet for each lower layer node is acquired, an edge node connected to the corresponding lower layer node is selected, and the packet is transferred to the edge node, The network system according to any one of claims 1 to 3.

5. Comprising a plurality of the edge nodes, The network system according to any one of claims 1 to 4.

6. comprising a plurality of said root nodes; different network addresses are assigned to each root node, edge node, and lower-level node connected to said root node; The network system according to any one of claims 1 to 5.

7. A plurality of root nodes connected to a higher-level device, edge nodes connected to said root node via a wide area communication network in one hop, lower-level nodes connected to said root node via said edge node with a hop count of two hops or more, comprising said edge node communicates with said root node by a first communication means and communicates with said lower-level node by a second communication means different from said first communication means, different network addresses are assigned to each root node, edge node, and lower-level node connected to said root node, a serial number is assigned to each lower-level node, data transmitted to the lower-level node is managed based on the correspondence relationship of the combination of said serial number, said network address, and the node number of the lower-level nodes connected to each edge node, A network system.

8. said edge node monitors the communication state with said root node, when detecting a communication abnormality, notifies the lower-level node of the communication abnormality, The network system according to any one of claims 1 to 7.

9. A root node connected to a higher-level device, edge nodes connected to said root node via a wide area communication network in one hop, lower-level nodes connected to said root node via said edge node with a hop count of two hops or more, comprising The edge node communicates with the root node by means of a first communication means, and communicates with the lower layer node by means of a second communication means different from the first communication means. The edge node monitors the communication state with the root node. When detecting a communication abnormality, it notifies the lower layer node of the communication abnormality. The lower layer node uses the presence or absence of communication with the root node as one of the selection conditions for the parent node, and excludes the presence or absence of communication with the root node from the selection conditions for the parent node for a predetermined time after the communication abnormality is notified, or until communication normality is notified after the communication abnormality is notified. Network system.

10. A root node connected to a host device, Communicates with an edge node connected to a lower layer including lower layer nodes connected to the root node with a hop count of 1 hop and 2 hops or more from the root node, Communicates with the edge node by a first communication means different from the second communication means between the edge node and the lower layer node. When the number of the lower layer nodes connected to the edge node is equal to or more than a predetermined number, and when a new lower layer node is connected to the edge node, it notifies the new lower layer node that the connection is not permitted. Root node.

11. A root node connected to a host device, Communicates with an edge node connected to a lower layer including lower layer nodes connected to the root node with a hop count of 1 hop and 2 hops or more from the root node, Communicates with the edge node by a first communication means different from the second communication means between the edge node and the lower layer node. Different network addresses are assigned to each of the root node, the edge nodes connected to the root node, and the lower layer nodes. A serial number is assigned to each lower layer node. Data transmitted to the lower-layer nodes is managed based on the correspondence relationship between the serial number, the network address, and the node numbers of the lower-layer nodes connected to each edge node. Root node.

12. A root node connected to a higher-level device, communicating with an edge node connected to a lower layer including lower-layer nodes connected to the root node in one hop and lower-layer nodes connected to the root node in two or more hops, communicating with the edge node by a first communication means different from the second communication means between the edge node and the lower-layer nodes, the edge node monitors the communication state with the root node, when detecting a communication abnormality, notifies the lower-layer nodes of the communication abnormality, the lower-layer nodes use the presence or absence of communication with the root node as one of the selection conditions for the parent node, and exclude the presence or absence of communication with the root node from the selection conditions for the parent node for a predetermined time after the communication abnormality is notified, or until communication normality is notified after the communication abnormality is notified. Root node.

13. A program for causing a processor of a root node connected to a higher-level device to communicate with an edge node connected to a lower layer including lower-layer nodes connected to the root node in one hop and lower-layer nodes connected to the root node in two or more hops, communicate with the edge node by a first communication means different from the second communication means between the edge node and the lower-layer nodes, when the number of the lower-layer nodes connected to the edge node is equal to or more than a predetermined number and a new lower-layer node is connected to the edge node, notify the new lower-layer node that the connection is not permitted. Program.

14. A processor of a root node connected to a higher-level device, Causing communication with an edge node connected to a lower layer including a lower layer node connected to the root node with a hop count of 2 hops or more and connected to the root node with 1 hop, and causing communication with the edge node by a first communication means different from a second communication means between the edge node and the lower layer node, the program being: Different network addresses are assigned to each root node, edge node connected to the root node, and lower layer node, A serial number is assigned to each lower layer node, Data transmitted to the lower layer node is managed based on the correspondence relationship of the combination of the serial number, the network address, and the node number of the lower layer node connected to each edge node. Program.

15. In a processor of a root node connected to a host device, Causing communication with an edge node connected to a lower layer including a lower layer node connected to the root node with a hop count of 2 hops or more and connected to the root node with 1 hop, and causing communication with the edge node by a first communication means different from a second communication means between the edge node and the lower layer node, the program being: The edge node monitors the communication state with the root node, When a communication abnormality is detected, notifies the lower layer node of the communication abnormality, The lower layer node uses the presence or absence of communication with the root node as one of the selection conditions for the parent node, and excludes the presence or absence of communication with the root node from the selection conditions for the parent node for a predetermined time after the communication abnormality is notified, or until communication normality is notified after the communication abnormality is notified. Program.

16. An edge node connected to a root node connected to a host device with 1 hop and connected to one or more lower layer nodes connected to the root node with a hop count of 2 hops or more via itself, Communicate with the root node through the first communication means, and communicate with the lower lower-layer nodes that are connected to the one or more lower-layer nodes within one hop through a second communication means different from the first communication means. The number of the connected lower-layer nodes is equal to or greater than a predetermined number. When a new lower-layer node is connected, the root node notifies that connection to the new lower-layer node is not permitted. Edge node.

17. An edge node connected to a root node connected to a higher-level device and one or more lower-layer nodes connected to the root node through itself with a hop count of two hops or more. Communicate with the root node through the first communication means, and communicate with the lower lower-layer nodes that are connected to the one or more lower-layer nodes within one hop through a second communication means different from the first communication means. Different network addresses are assigned to each root node, edge node connected to the root node, and lower-layer node. A serial number is assigned to each lower-layer node. Data transmitted to the lower-layer nodes is managed based on the correspondence relationship of the combination of the serial number, the network address, and the node numbers of the lower-layer nodes connected to each edge node. Edge node.

18. An edge node connected to a root node connected to a higher-level device and one or more lower-layer nodes connected to the root node through itself with a hop count of two hops or more. Communicate with the root node through the first communication means, and communicate with the lower lower-layer nodes that are connected to the one or more lower-layer nodes within one hop through a second communication means different from the first communication means. The edge node monitors the communication state with the root node. When a communication abnormality is detected, the lower-layer nodes are notified of the communication abnormality. The lower-level node uses the presence or absence of communication with the root node as one of the selection conditions for the parent node, and excludes the presence or absence of communication with the root node from the selection conditions for the parent node for a predetermined time after the communication abnormality is notified, or until the communication normality is notified after the communication abnormality is notified. Edge node.

19. A root node comprising a processor, wherein the processor executes the program according to any one of claims 13 to 15, the root node, An edge node according to any one of claims 16 to 19, A network system comprising.

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