JP2013243485A - Communication terminal and multi-hop communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication terminal and a multi-hop communication system capable of minimizing a communication impossible state among nodes in a multi-hop communication network even when any change occurs in a communication route of a node.SOLUTION: A communication terminal A includes: an event detection section K3 that detects occurrence of an event which changes a state of a communication link with a node through which the communication terminal A directly performs communication in a communication route established by the communication terminal A; and a communication section K2 that, when the event detection section K3 detects an occurrence of a change event, transmits a piece of route change information to the node.

Description

  The present invention relates to a communication terminal that performs multi-hop communication and a multi-hop communication system.

  Conventionally, when communicating between nodes existing on a communication network, if communication cannot be performed directly between nodes to which information is to be transmitted, communication can be performed by using another node as a relay for communication. Multi-hop communication systems are known. For example, each of a plurality of child nodes constructs a communication route with one parent node and performs multi-hop communication (see, for example, Patent Document 1).

  Such multi-hop communication is used for transmission of meter reading data by a child node provided in each consumer, for example, in a remote meter reading system such as commercial power, water supply, and gas. When a child node that transmits meter reading data cannot directly communicate with a parent node that collects meter reading data, a communication route that uses other child nodes for relaying communication is communicated with the parent node. To construct.

Japanese Patent No. 3985828

  In multi-hop communication, when a link configured between nodes is interrupted due to a change in system configuration, system environment, or the like, each node needs to reconstruct a communication route. For example, when a node leaves a multi-hop communication network, when a node switches communication channels, or when the communication quality of a communication route constructed by a node has deteriorated significantly, other neighboring nodes communicate. It may be necessary to rebuild the route.

  However, the disconnection of the link formed between the nodes can be detected only when one node cannot receive the routing packet from the other node for a certain period. Furthermore, a node that moves between cells cannot recognize that it has moved between cells until it receives a routing packet from a node belonging to the destination cell. This is the same even when only one communication channel is used without switching the communication channel used for communication.

  FIG. 8 shows a configuration of a conventional multi-hop communication system. The parent node 101 constructs a communication cell C101 with a plurality of subordinate child nodes 201, and the child node 201 constructs a communication route with the parent node 101. The parent node 102 constructs a communication cell C102 with a plurality of subordinate child nodes 202, and the child node 202 constructs a communication route with the parent node 102. Note that the communication cell C101 and the communication cell C102 use different communication channels for multi-hop communication and prevent interference between communication cells.

  In the communication cell C102, the child node 202b establishes a communication route that reaches the parent node 102 via the child node 202a. However, when the child node 202a switches to a new communication route that reaches the parent node 101 via the child node 201a of the communication cell C101, the child node 202b loses the communication route that reaches the parent node 102, and the parent node 102 Communication with is impossible.

  Furthermore, since the child node 202a newly entering the communication cell C101 uses the communication channel of the communication cell C101, communication with the child node 202b belonging to the communication cell C102 becomes impossible. Therefore, the child node 202b cannot receive the routing packet from the child node 202a. The routing packet stores information such as a communication route and communication quality, and each node constructs, maintains, and changes the communication route based on the received routing packet.

  Then, when the child node 202b does not receive the routing packet from the child node 202a for a predetermined period, the child node 202b starts reconstructing the communication route based on the routing packet transmitted by a node other than the child node 202a.

  However, it takes too much time for the child node 202b to start reconstructing the communication route after losing the communication route to the parent node 102, and the period during which communication with the parent node is disabled becomes long. There was a problem. Therefore, the child node 202b fails in communication even if there is a packet to be transmitted to the parent node during a period when communication with the parent node is impossible. Further, the child node 202b cannot receive this packet even if there is a packet to be received from the parent node during a period when communication with the parent node is not possible.

  As described above, when a communication route of a node changes due to a change in the system configuration, the system environment, or the like, it is required to shorten the communication impossible state between the nodes in the multi-hop communication network as much as possible. .

  The present invention has been made in view of the above-described reasons, and its purpose is to make the communication impossible state between nodes in a multi-hop communication network as short as possible when a communication route of a certain node changes. It is an object of the present invention to provide a communication terminal and a multi-hop communication system.

  The communication terminal of the present invention includes a plurality of nodes set as a parent node or a child node, and each of the plurality of child nodes establishes a communication route with one parent node and performs multi-hop communication. A communication terminal used for the node of a multi-hop communication network, wherein a change event is generated that changes a state of a communication link with the node with which the terminal directly communicates on a communication route established by the terminal. An event detection unit to detect, and a communication unit that transmits route change information to the node when the event detection unit detects the occurrence of the change event.

  In this invention, it is preferable that the transmission destination of the route change information includes at least the node that establishes the communication route including the own terminal and can directly communicate with the own terminal.

  In this invention, it is preferable that the destination of the route change information is only the node that can directly communicate with the own terminal.

  In this invention, it is preferable that the transmission destination of the route change information is all the nodes belonging to the same multi-hop communication network as the terminal itself.

  In this invention, it is preferable that the change event is that the own terminal leaves the multi-hop communication network.

  In this invention, it is preferable that the change event is that the node that directly communicates with the terminal on the communication route established by the terminal leaves the multi-hop communication network.

  In this invention, it is preferable that the change event is that the communication quality of the communication link falls below a predetermined threshold.

  In this invention, it is preferable that the change event is that the communication link is disabled.

  In the present invention, when the communication unit receives the route change information, the communication unit preferably transfers the route change information.

  In this invention, it is preferable that the communication unit transmits the route change information only when the event detection unit detects the occurrence of the change event and matches a specific condition.

  In this invention, it is preferable that the communication unit transmits the route change information only when there is the child node constructing the communication route including its own terminal.

  In the present invention, the communication unit includes the route change information in a hello packet that is intermittently transmitted to notify the existence of the terminal itself, and transmits the transmission timing of the hello packet including the route change information as the route change. It is preferable that the transmission timing of the hello packet not including information is earlier than the transmission timing.

  In the present invention, the communication unit includes a time length from when the event detection unit detects the occurrence of the change event to when the hello packet including the route change information is transmitted. It is preferable that the shorter the number of child nodes constructing the route, the shorter.

  In this invention, it is preferable to provide a route creation unit for reconstructing the communication route when the route change information is received.

  In this invention, when the route change information is received, a route creation for reconstructing the communication route if the communication quality of the communication route constructed by the terminal falls below a predetermined threshold due to the occurrence of the change event. It is preferable to provide a part.

  In this invention, the communication unit intermittently transmits a hello packet for notifying the existence of its own terminal, and when the route creation unit reconstructs the communication route, the communication unit includes information on the reconstructed communication route. It is preferable that the transmission timing of the hello packet including the information of the reconstructed communication route is transmitted earlier than the transmission timing of the hello packet not including the information of the reconstructed communication route.

  In this invention, it is provided with a storage unit for storing information of the communication route constructed by the terminal, and when the multi-hop communication network is re-entered after leaving the multi-hop communication network, the storage unit before the departure It is preferable to re-enter the multi-hop communication network using the communication route information stored in the network.

  In this invention, after leaving the multi-hop communication network, only when re-entering the multi-hop communication network within a certain time, using the information of the communication route stored in the storage unit before leaving, It is preferable to re-enter the multi-hop communication network.

  In this invention, when this terminal is used as the child node, the communication unit preferably transmits predetermined measurement data to the parent node using multi-hop communication.

  In the present invention, the nodes perform multi-hop communication with each other using a first communication channel, and the communication unit transmits the measurement data to a maintenance terminal existing outside the multi-hop communication network. It is preferable to communicate with the maintenance terminal using a second communication channel different from the communication channel.

  The multi-hop communication system of the present invention includes a plurality of nodes set as a parent node or a child node, and each of the plurality of child nodes establishes a communication route with the one parent node to perform multi-hop communication. The node detects the occurrence of a change event that changes the state of the communication link with the node with which the node directly communicates on the communication route established by the node. An event detection unit and a communication unit that transmits route change information to the node when the event detection unit detects the occurrence of the change event.

  As described above, according to the present invention, a communication terminal that detects the occurrence of a change event that changes the state of a communication link transmits a route change information to change the communication route. Can be known efficiently and quickly. Therefore, when a change occurs in the communication route of a certain node, there is an effect that the communication impossible state between the nodes in the multi-hop communication network can be shortened as much as possible.

(A) (b) It is a block diagram which shows the outline of the multihop communication system of Embodiment 1, and a communication terminal. It is a block diagram which shows the structure of a communication terminal same as the above. It is a flowchart figure which shows operation | movement same as the above. FIG. 9 is a flowchart showing the operation of the second embodiment. FIG. 10 is a flowchart showing the operation of the third embodiment. It is a flowchart figure which shows another operation | movement same as the above. FIG. 10 is a time chart illustrating the operation of the fourth embodiment. It is a block diagram which shows the conventional multihop communication system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
1A and 1B show schematic configurations of a multi-hop communication system and a communication terminal A according to the present embodiment. One parent node 1 and a plurality of child nodes 2 construct a communication cell C1 that is a local network, and the child node 2 constructs a communication route with the parent node 1. The child node 2 has a function of wirelessly transmitting or wire-transmitting commercial power meter reading data (measurement data) at each consumer to one parent node 1. The parent node 1 has a function of acquiring meter reading data from a subordinate child node 2 wirelessly or by wire and transmitting the acquired meter reading data to an upper management server (not shown) using an optical fiber line or the like.

  Parent node 1 and child node 2 transmit and receive packets to and from each other by multi-hop communication. That is, in this multi-hop communication network, communication is performed directly or indirectly between the parent node 1 and the child node 2, and the child node 2 that cannot directly communicate with the parent node 1 is connected to another child at a communicable distance. Node 2 relays packets sequentially to perform indirect communication with parent node 1.

  The child node 2 stores information (communication route information) related to the communication route established with the parent node 1 with which the node communicates, and the meter reading data to which the communication route information is added is the next hop node. To unicast. The communication route information is represented by the terminal IDs of the child nodes 2 that are routed in the communication route from the child node 2 to the parent node 1 being sequentially arranged. The child node 2 of the next hop that has received the meter reading data refers to the communication route information added to the received meter reading data, and further unicasts the received meter reading data to the next hop node, thereby transmitting the meter reading data. Relay. In this way, the meter reading data is sequentially relayed by the child node 2 constituting the communication route, and reaches the parent node 1 which is the final transmission destination. In addition, the child meter 2 that can directly communicate with the parent node 1 does not relay the other child node 2, and the transmitted meter reading data directly reaches the parent node 1.

  FIG. 2 is a block diagram of the communication terminal A used for the parent node 1 and the child node 2. In the present embodiment, the same communication terminal A is used for the parent node 1 and the child node 2. For example, the communication terminal A is set to “parent” using setting means such as a jumper switch or a changeover switch. It functions as a parent node 1 and functions as a child node 2 by being set to “child”. Further, hereinafter, when the parent node 1 and the child node 2 are not distinguished, they are referred to as communication terminals A.

  The communication terminal A includes a storage unit K1, a communication unit K2, an event detection unit K3, and a route creation unit K4.

  The storage unit K1 includes a nonvolatile memory such as a ROM, a rewritable nonvolatile memory such as an EEPROM, and a volatile memory such as a RAM. Then, the storage unit K1 stores communication route information, link information related to communicable adjacent terminals (parent node 1 or child node 2 capable of direct communication), and the like in a nonvolatile memory. Further, the storage unit K1 stores programs such as a control program for operating the communication terminal A, information necessary for executing each program, and the like.

  The communication unit K2 has a function of transmitting / receiving a packet to / from another communication terminal A.

  The event detection unit K3 has a function of detecting the occurrence of a change event. A change event is a change in the state of a communication link with another communication terminal A (communication terminal A that is one hop higher than the own terminal) with which the own terminal communicates directly on the communication route established by the own terminal. It is an event.

  Next, the operation of this multi-hop communication system will be described. In order to identify the child nodes 2 individually, the child nodes 2a, 2b, 2c,. . . Is used.

  In FIG. 1, the child node 2 a constructs a communication route from the child node 2 a to the parent node 1. The child node 2b constructs a communication route of the child node 2b → the child node 2a → the parent node 1. The child node 2c constructs a communication route of the child node 2c → the child node 2b → the child node 2a → the parent node 1. The child node 2d constructs a communication route of child node 2d → child node 2c → child node 2b → child node 2a → parent node 1.

  Here, it is assumed that the child node 2b has left this multi-hop communication network for communication with the maintenance terminal 3. The maintenance terminal 3 is carried by a meter reader. When the meter reader who visits each customer operates the maintenance terminal 3 in the vicinity of the child node 2b, the maintenance terminal 3 directly receives the meter reading data from the child node 2b. get. At this time, a communication channel (second communication channel) used for communication between the maintenance terminal 3 and the child node 2b is a communication channel (first communication channel) used by the parent node 1 and the child node 2 for multihop communication in the communication cell C1. It is desirable to be different from the communication channel. This is because when the maintenance terminal 3 uses a communication channel used for inter-node communication in the communication cell C1, there is a possibility of affecting inter-node communication in the communication cell C1.

  Then, when the communication channel is switched during communication with the maintenance terminal 3, the child node 2b temporarily leaves the multi-hop communication network of the communication cell C1. When the child node 2b leaves the multi-hop communication network, the child nodes 2c and 2d lose the communication route established with the parent node 1, and communication with the parent node 1 becomes impossible. It is necessary to construct a new communication route that does not use the node 2b.

  Therefore, when a change event occurs in which the child node 2b leaves the multi-hop communication network, the child node 2b transmits this change to the child node 2 (child node 2 including the own node in the communication route) lower than the own node. Notify that a change event has occurred.

  Specifically, as shown in the flowchart of FIG. 3, the event detection unit K3 of the child node 2b determines that a change event has occurred in which the own node leaves the multi-hop communication network for communication with the maintenance terminal 3. Detect (S1). This change event occurs when the child node 2b receives a communication request from the maintenance terminal 3 using the communication channel of the communication cell C1.

  The communication unit K2 of the child node 2b uses the communication channel of the communication cell C1 to switch the route change information before switching to the communication channel with the maintenance terminal 3 when the event detection unit K3 detects the occurrence of the change event. Is transmitted (S2). The route change information stores terminal identification information (for example, IP address, MAC address, etc.) of the child node 2b that is the transmission source, and data indicating that the multi-hop communication network is to be disconnected.

  The communication unit K2 of the child node 2b transmits this route change information to all the nodes within one hop by broadcast. In this case, the child node 2b transmits the route change information only to all the parent nodes 1 and child nodes 2 that can directly communicate with the own node. That is, only the adjacent node of the child node 2b can receive the route change information. The child node 2 that has received the route change information determines whether or not the transmission source of the route change information is included in the communication route of the own node based on the terminal identification information included in the route change information. Then, if the child node 2b that is the transmission source of the route change information is included in the communication route of the own node, the child node 2 starts processing for reconstructing the communication route. If the child node 2b that is the transmission source of the route change information is not included in the communication route of the own node, the child node 2 discards the route change information and maintains the current communication route.

  Therefore, when a change event occurs that the child node 2b leaves the multi-hop communication network, the child node 2c can immediately recognize the occurrence of the change event.

  Further, when the communication unit K2 of the child node 2c receives the route change information from the child node 2b, the communication unit K2 obtains the terminal identification information of the child node 2c that is the transfer source before the route creation unit K4 starts to reconstruct the communication route. The added route change information is transferred by broadcast. In this case, the child node 2c transmits the path change information only to all the parent nodes 1 and child nodes 2 that can directly communicate with the own node. The child node 2 that has received the route change information determines whether or not the transfer source of the route change information is included in the communication route of the own node based on the terminal identification information included in the route change information. Then, if the child node 2c that is the transfer source of the path change information is included in the communication route of the own node, the child node 2 starts processing for reconstructing the communication route. If the child node 2c, which is the transfer source of the route change information, is not included in the communication route of the own node, the child node 2 discards the route change information and maintains the current communication route.

  Here, the child node 2d is a node that establishes a communication route including the child node 2c and can directly communicate with the child node 2c. The child node 2d that has received the route change information can recognize that the child node 2c that is one hop higher than the own node may change the communication route.

  Therefore, when the change event that the child node 2b leaves the multi-hop communication network occurs, the route creation unit K4 of the child nodes 2c and 2d can immediately start the process of reconfiguring the communication route. In this case, an increase in communication traffic due to transmission of route change information can be suppressed and route change information can be notified efficiently compared to the case where flooding described later is used.

  In FIG. 1, the route creation unit K4 of the child node 2c reconstructs the communication route that passes through the child node 2e, and the route creation unit K4 of the child node 2d rebuilds the communication route that passes through the child node 2f. Communication with the parent node 1 is possible.

  As described above, the communication terminal A that has detected the occurrence of the change event that changes the state of the communication link transmits the route change information, so that the change in the communication route can be efficiently performed in the multi-hop communication network. Can be quickly known. Therefore, the multihop communication system using the communication terminal A can shorten the communication impossible state between the nodes in the multihop communication network as much as possible when the communication route of a certain node changes. Further, when the child node 2 rebuilds the communication route, the child node 2 may rebuild the communication route with the parent node 1 of a communication cell (not shown) different from the communication cell C1.

  Further, when the communication unit K2 of the child node 2c receives the route change information from the child node 2b, it adds the terminal identification information of the child node 2c that is the transfer source after the route creation unit K4 completes the reconstruction of the communication route. The route change information may be transferred by broadcast. In this case, the child node 2c can notify the child node 2d that communication via the child node 2e is possible using the reconstructed communication route. Therefore, the child node 2d can select not only the communication route via the child node 2f but also the communication route via the child node 2c.

  Further, the communication unit K2 of the child node 2b may transmit this route change information by flooding. In this case, the child node 2b transmits the route change information by broadcast, and all the parent nodes 1 and child nodes 2 that have received this route change information also sequentially transmit the received route change information by broadcast. Therefore, all the parent nodes 1 and child nodes 2 in the multi-hop communication network of the communication cell C1 can receive the route change information. Whether the child node 2 that has received the route change information includes the source of the route change information (in this case, the child node 2b) based on the terminal identification information included in the route change information. Judge whether or not. Then, if the child node 2b that is the transmission source of the route change information is included in the communication route of the own node, the child node 2 starts processing for reconstructing the communication route. If the child node 2b that is the transmission source of the route change information is not included in the communication route of the own node, the child node 2 discards the route change information and maintains the current communication route.

  Therefore, when a change event that the child node 2b leaves the multi-hop communication network occurs, the child nodes 2c and 2d can immediately recognize the occurrence of the change event. Then, the route creation unit K4 of the child nodes 2c and 2d can immediately start the process of reconstructing the communication route. In this case, since the path change information can be notified to all the child nodes 2 in the multi-hop communication network of the communication cell C1, it is assumed that a failure or the like has occurred in the node that cannot directly communicate with the child node 2b. In addition, it becomes possible to make known the route change information.

  Further, the communication unit K2 of the child node 2b may transmit this route change information by unicast. In this case, the communication unit K2 of the child node 2b constructs a communication route including the child node 2b as a transmission destination of the path change information, and can directly communicate with the child node 2b (child node 2c (child Set to the child node 2c) one hop below the node 2b. The child node 2c that has received the route change information can recognize that the child node 2b that is one hop higher than its own node leaves the multi-hop communication network. That is, the child node 2c can immediately recognize the occurrence of the change event when the change event that the child node 2b leaves the multi-hop communication network occurs. Then, the route creation unit K4 of the child node 2c can immediately start the process of reconstructing the communication route.

  Further, when the communication unit K2 of the child node 2c receives the route change information from the child node 2b, before the route creation unit K4 starts to reconstruct the communication route, the communication unit K2 Then, the route change information is transferred by unicast. The child node 2d that has received the route change information can recognize that the child node 2c that is one hop higher than the own node may change the communication route. Therefore, the route creation unit K4 of the child node 2d can immediately start the process of reconstructing the communication route.

  Further, the communication unit K2 of the child node 2 transmits (transfers) the route change information only when there is a child node 2 (child node 2 lower than the own node) constructing a communication route including the own node. Including). Accordingly, since there is no child node 2 lower than the child node 2d, the communication unit K2 of the child node 2d does not transmit path change information. In FIG. 1, child nodes 2d, 2f, 2g, 2h, 2i, 2j, and 2k are nodes that do not execute transmission of route change information. Therefore, since unnecessary transmission of route change information can be suppressed, an increase in communication traffic can be suppressed and route change information can be notified efficiently.

  Moreover, there is a possibility that communication traffic in the network increases due to the process of reconstructing the communication route. Therefore, the route creation unit K4 determines the communication route only when the communication quality of the communication route constructed by the own node is lower than a predetermined threshold at the time when a certain time has elapsed after receiving the route change information. You may start the process to rebuild. Thus, even if the route change information is received, if the communication quality of the communication route does not deteriorate significantly due to the occurrence of the change event, the route creation unit K4 does not reconstruct the communication route, thereby causing unnecessary communication traffic. Can be suppressed.

  Further, when the communication terminal A that has left the multi-hop communication network re-enters this network, it re-enters the network using the communication route information stored in the storage unit K1 before leaving. The communication terminal A, which is fixedly arranged, has a high probability that the communication route information used before leaving can be used even at the time of re-entry because the communication route hardly changes in a short period of time. Therefore, the communication terminal A can use the communication route information used before leaving at the time of re-entry, thereby eliminating the need to re-create the communication route information and reducing the time required for re-entry.

  Alternatively, the communication route information used before leaving may be used at the time of re-entry only when the length of time from leaving the multi-hop communication network to re-entry is within a certain time. The longer the time from leaving the network to re-entering, the higher the probability that the communication route information will change and the communication route information used before leaving the network cannot be used. Therefore, when the time length from when the network leaves the network to when it reenters exceeds a certain time, the communication terminal A starts to construct a new communication route without using the communication route information used before leaving the network. . Therefore, at the time of re-entry, processing using communication route information before leaving is not executed, and processing required for re-entry can be executed efficiently.

  Moreover, you may apply this multihop communication system to remote meter-reading systems, such as water supply and gas, besides commercial power.

(Embodiment 2)
The multi-hop communication system of the present embodiment has the same configuration as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted. The operation of the communication terminal A of this embodiment is shown in the flowchart of FIG.

  The event detection unit K3 of the communication terminal A of the present embodiment is configured such that another communication terminal A (communication terminal A one hop higher than the own terminal) that directly communicates with the own terminal on the communication route constructed by the own terminal is multi-hopped. Detecting leaving the communication network as a change event.

  In FIG. 1, it is assumed that the child node 2b leaves this multi-hop communication network for communication with the maintenance terminal 3. The child node 2b transmits a network leaving notification when the own node leaves the multi-hop communication network.

  First, in order to shift the child node 2b to the communication mode with the maintenance terminal 3, the meter reader transmits a communication request from the maintenance terminal 3 to the child node 2b using the communication channel of the communication cell C1. The communication unit K2 of the child node 2b that has received the communication request from the maintenance terminal 3 transmits a network disconnection notification using the communication channel of the communication cell C1 before switching to the communication channel with the maintenance terminal 3.

  The communication unit K2 of the child node 2b transmits this network leave notification by unicast. The communication unit K2 of the child node 2b constructs a communication route including the child node 2b as a transmission destination of the network leaving notification and can directly communicate with the child node 2b (from the child node 2b). Set to child node 2c) one hop lower. The event detection unit K3 of the child node 2c that has received the network disconnection notification detects that a change event has occurred in which the child node 2b leaves the multi-hop communication network (S11). That is, the child node 2c can immediately recognize that the child node 2b leaves the multi-hop communication network. Then, the route creation unit K4 of the child node 2c can immediately start the process of reconstructing the communication route.

  Further, the communication unit K2 of the child node 2c, when the event detection unit K3 detects the occurrence of the change event described above, before the route creation unit K4 starts to reconstruct the communication route, The route change information is transmitted by unicast to 2d (S12). The child node 2d that has received the route change information can recognize that the child node 2c that is one hop higher than the own node may change the communication route. Therefore, the route creation unit K4 of the child node 2d can immediately start the process of reconstructing the communication route.

  In FIG. 1, the route creation unit K4 of the child node 2c reconstructs the communication route that passes through the child node 2e, and the route creation unit K4 of the child node 2d rebuilds the communication route that passes through the child node 2f. Communication with the parent node 1 is possible.

  As described above, the communication terminal A that has detected the occurrence of the change event that changes the state of the communication link transmits the route change information, so that the change in the communication route can be efficiently performed in the multi-hop communication network. Can be quickly known. Therefore, the multihop communication system using the communication terminal A can shorten the communication impossible state between the nodes in the multihop communication network as much as possible when the communication route of a certain node changes.

  The child node 2c may transmit the route change information by flooding or broadcasting as in the first embodiment.

(Embodiment 3)
The multi-hop communication system of the present embodiment has the same configuration as that of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted. The operation of the communication terminal A of this embodiment is shown in the flowchart of FIG.

  The event detection unit K3 of the communication terminal A of the present embodiment changes that the communication quality of the communication link with the node with which the own terminal directly communicates on the communication route established by the own terminal is below a predetermined threshold. Detect as an event.

  In FIG. 1, it is assumed that the communication quality of the communication link between the child node 2b and the child node 2a falls below a threshold value. The communication quality of this communication link is a Hello packet (hereinafter referred to as “H packet”) in which each communication terminal A intermittently notifies the other communication terminals A of the existence of its own terminal. Is derived on the basis of the received signal strength and the like. The derivation of the communication quality is a known technique and will not be described in detail.

  Then, the child node 2b notifies the occurrence of the above-described change event by transmitting path change information to the child node 2 (child node 2 including the own node in the communication route) lower than the own node. The transmission of the route change information is performed in the child node 2b before the route creation unit K4 starts processing for reconstructing the communication route due to the deterioration of the communication quality of the communication link.

  Specifically, the event detection unit K3 of the child node 2b detects that a change event has occurred that the communication quality of the link between the child node 2b and the child node 2a has fallen below a threshold (S21). Further, it may be detected that a change event has occurred only when this change event has continued for a certain period of time. This change event occurs due to a change in the communication environment such as the presence or absence of an obstacle or communication interference.

  When the event detection unit K3 detects the occurrence of the above-described change event, the communication unit K2 of the child node 2b transmits route change information before the route creation unit K4 starts processing for reconstructing the communication route ( S22). In this path change information, data such as terminal identification information (eg, IP address, MAC address, etc.) of the child node 2b, deterioration of communication quality of the communication link, and the like are stored.

  The communication unit K2 of the child node 2b transmits this route change information by unicast. The communication unit K2 of the child node 2b constructs a communication route including the child node 2b as a transmission destination of the route change information and can directly communicate with the child node 2b (from the child node 2b). Set to child node 2c) one hop lower. The child node 2c that has received the route change information can recognize that the communication quality of the communication link has deteriorated in the child node 2b that is one hop higher than its own node. That is, the child node 2c can immediately recognize the occurrence of this change event when the communication quality of the communication link is deteriorated in the child node 2b. Then, the route creation unit K4 of the child node 2c can immediately start the process of reconstructing the communication route.

  Furthermore, when the communication unit K2 of the child node 2c receives the route change information from the child node 2b, before the route creation unit K4 starts to reconstruct the communication route, the child node 2c Route change information is transferred by unicast. The child node 2d that has received the route change information can recognize that the child node 2c that is one hop higher than the own node may change the communication route. Therefore, the route creation unit K4 of the child node 2d can immediately start the process of reconstructing the communication route.

  In FIG. 1, the route creation unit K4 of the child node 2c reconstructs the communication route that passes through the child node 2e, and the route creation unit K4 of the child node 2d rebuilds the communication route that passes through the child node 2f. Communication with the parent node 1 is possible.

  As described above, the communication terminal A that has detected the occurrence of the change event that changes the state of the communication link transmits the route change information, so that the change in the communication route can be efficiently performed in the multi-hop communication network. Can be quickly known. Therefore, the multihop communication system using the communication terminal A can shorten the communication impossible state between the nodes in the multihop communication network as much as possible when the communication route of a certain node changes.

  The child node 2c may transmit the route change information by flooding or broadcasting as in the first embodiment.

  Further, the event detection unit K3 of the communication terminal A may detect as a change event that the communication link with the node with which the self terminal directly communicates is disabled on the communication route established by the self terminal. Good. For example, as shown in the flowchart of FIG. 6, it is assumed that the event detection unit K3 of the child node 2b detects that a change event has occurred that the communication link between the child node 2b and the child node 2a has become unavailable. (S31). When the event detection unit K3 detects the occurrence of the change event, the communication unit K2 of the child node 2b transmits the route change information before the route creation unit K4 starts to reconstruct the communication route (S32). . In this case, the same effect as described above can be obtained.

(Embodiment 4)
The multi-hop communication system according to the present embodiment has the same configuration as that of any one of the first to third embodiments.

  The communication unit K2 of the communication terminal A intermittently transmits H packets in order to notify the existence of its own terminal. This H packet has a function as a routing packet used when establishing a communication route between nodes. When the change event occurs, the communication unit K2 of the present embodiment transmits the H packet including the route change information. At this time, the communication unit K2 advances the transmission timing of the H packet P2 including the path change information earlier than the transmission timing of the normal H packet P1 that does not include the path change information.

  For example, as illustrated in FIG. 7, the communication unit K2 of the communication terminal A transmits a normal H packet P1 that does not include route change information at a period T1 when no change event has occurred. When the event detection unit K3 detects the occurrence of a change event (t0), the communication unit K2 uses the transmission timing t2 of the H packet P2 including the path change information as the transmission timing of the H packet P1 that does not include the path change information. It is earlier than t1.

  Also, when the communication terminal A transfers the received H packet P2 to a node lower than its own node, the communication terminal A generates the H packet P2 including the received route change information, and sets the transmission timing of the H packet P2 as H It is earlier than the transmission timing of the packet P1.

  Therefore, the communication terminal A does not need to provide a new packet to transmit the path change information by using the H packet that is transmitted intermittently as the notification packet of the path change information. Thus, a route change information notification sequence can be easily constructed, and further, route change information can be efficiently notified by suppressing an increase in communication traffic due to transmission of the route change information.

  Further, the time length D from the change event detection timing t0 to the transmission timing t2 of the H packet P2 may be shortened as the number of child nodes 2 whose own node is set as a higher-level terminal increases. That is, the time length D is shortened as the number N of child nodes 2 lower than the own node increases. Based on the communication route information stored in the storage unit K1, the communication unit K2 of the communication terminal A can grasp the number N of child nodes 2 lower than the own node. Therefore, the communication unit K2 derives the time length D = Ta / N when the constant Ta is used. For example, the child node 2b in FIG. 1 has N = 2 child nodes 2 lower than its own node, and when the child node 2b transmits the H packet P2, the time length D = Ta / 2.

  Therefore, when a plurality of child nodes 2 transmit route change information based on the same occurrence event, if each of the plurality of child nodes 2 transmits the route change information at the same time, communication traffic temporarily The probability of occurrence of packet collision increases. However, as described above, by setting the time length D = Ta / N when transmitting the H packet P2, the transmission timing of the H packet P2 can be individually set for each child node 2, and communication traffic is distributed. can do. Furthermore, the upper child node 2 (the child node 2 having a larger number N of child nodes 2 lower than the own node) has a shorter time length D and can transmit the route change information earlier. In other words, the key child node 2 can make the path change information known in a shorter time.

  Further, the child node 2 that has received the path change information and reconstructed the communication route creates an H packet P3 including the reconstructed communication route information, and the transmission timing of the H packet P3 is also a normal H packet. It is earlier than the transmission timing of P1. Accordingly, the reconstructed communication route information can be made known more quickly in the multi-hop communication network.

A communication terminal 1 parent node 2 (2a, 2b, ...) child node K2 communication unit K3 event detection unit

Claims (21)

The node of a multi-hop communication network comprising a plurality of nodes set as a parent node or a child node, and each of the plurality of child nodes constructs a communication route with one parent node and performs multi-hop communication A communication terminal used for
An event detector that detects the occurrence of a change event that changes the state of the communication link with the node with which the terminal directly communicates on the communication route constructed by the terminal;
A communication terminal, comprising: a communication unit that transmits route change information to the node when the event detection unit detects the occurrence of the change event.   The communication terminal according to claim 1, wherein the destination of the route change information includes at least the node that establishes the communication route including the terminal and can directly communicate with the terminal. .   3. The communication terminal according to claim 2, wherein the destination of the route change information is only the node capable of direct communication with the own terminal.   The communication terminal according to claim 2, wherein the destination of the route change information is all the nodes belonging to the same multi-hop communication network as the own terminal.   The communication terminal according to any one of claims 1 to 4, wherein the change event is that the own terminal leaves the multi-hop communication network.   5. The change event according to claim 1, wherein the change event is that the node that directly communicates with the terminal on the communication route constructed by the terminal leaves the multi-hop communication network. Communication terminal.   The communication terminal according to claim 1, wherein the change event is that the communication quality of the communication link falls below a predetermined threshold.   The communication terminal according to claim 1, wherein the change event is that the communication link is disabled.   The communication terminal according to claim 1, wherein the communication unit transfers the route change information when the route change information is received.   The communication unit transmits the path change information only when the event detection unit detects the occurrence of the change event and matches a specific condition. Communication terminal.   The communication terminal according to claim 10, wherein the communication unit transmits the route change information only when the child node constructing the communication route including the terminal is present.   The communication unit includes the route change information in a hello packet that is intermittently transmitted to notify the existence of the terminal itself, and does not include the transmission timing of the hello packet that includes the route change information. The communication terminal according to claim 1, wherein the communication terminal is earlier than a transmission timing of the hello packet.   The communication unit sets its own terminal as an upper terminal for a time length from when the event detection unit detects the occurrence of the change event to when the hello packet including the path change information is transmitted. 13. The communication terminal according to claim 12, wherein the communication terminal is shortened as the number of child nodes increases.   The communication terminal according to claim 1, further comprising: a route creation unit that reconstructs the communication route when the route change information is received.   A route creation unit configured to reconstruct the communication route when the route change information is received and communication quality of the communication route constructed by the terminal falls below a predetermined threshold due to the occurrence of the change event; The communication terminal according to any one of claims 1 to 13. The communication unit is
Intermittently send hello packets to report the existence of the terminal,
When the route creation unit reconstructs the communication route, it transmits the hello packet including information on the reconstructed communication route,
The transmission timing of the hello packet including the information on the reconstructed communication route is advanced from the transmission timing of the hello packet not including the information on the reconstructed communication route. Communication terminal. A storage unit for storing information on the communication route constructed by the terminal;
When re-entering the multi-hop communication network after leaving the multi-hop communication network, re-entering the multi-hop communication network using the information on the communication route stored in the storage unit before leaving. The communication terminal according to any one of claims 1 to 16.   After leaving the multi-hop communication network, only when re-entering the multi-hop communication network within a certain time, using the information on the communication route stored in the storage unit before leaving, the multi-hop communication network The communication terminal according to claim 17, wherein the communication terminal re-enters the network.   19. The communication terminal according to claim 1, wherein when the terminal is used as the child node, the communication unit transmits predetermined measurement data to the parent node using multi-hop communication. . The nodes perform multi-hop communication with each other using a first communication channel,
The communication unit communicates with the maintenance terminal using a second communication channel different from the first communication channel when transmitting the measurement data to the maintenance terminal existing outside the multi-hop communication network. The communication terminal according to claim 19, wherein: A multi-hop communication system comprising a plurality of nodes set as a parent node or a child node, and each of the plurality of child nodes constructs a communication route with one parent node and performs multi-hop communication. ,
The node is
An event detector that detects the occurrence of a change event that changes the state of the communication link with the node that the node directly communicates with on the communication route constructed by the node;
A communication unit that transmits path change information to the node when the event detection unit detects the occurrence of the change event.

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