JP2008306314A - Adjacent node conforming method in multi-hop communications network, and node of the multi-hop communications network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To immediately detect that a root for communication data transmission between nodes has become unavailable, and to make the detected root not to be selected at next route selection. <P>SOLUTION: In a multi-hop communications network constituted of a plurality of nodes N, a communication quality acquisition means 12 transmits a "hello message" in a suitable timing, and determines a link cost for direct communication with an adjacent node N, to register the cost in an adjacent node table Tb1. A root for communication data transmission is selected for each node N, by using the link cost registered in the adjacent node table Tb1. If an acknowledgement from a destination node N is not received, after a source node N on the root transmits communication data, to the adjacent node when the communication data is transmitted using the selected root, an evaluation value modification means 15 increases the link cost with the destination node N, in an adjacent node table Tb1 of the source node N. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a method for selecting an appropriate route between nodes transmitting information in a multi-hop communication network that enables relaying of communication by other nodes when communicating between nodes existing on the communication network. The present invention relates to an adjacent node confirmation method in a multihop communication network and a node of a multihop communication network corresponding to the adjacent node confirmation method.

  Conventionally, when communicating between nodes (that is, communication terminals) existing on a communication network, when communication cannot be performed directly between nodes to which information is to be transmitted, another node is used as a relay for communication. A technique for enabling communication by using this technique is known, and it has been proposed to use this technique particularly in a wireless network that is one of communication networks. This type of wireless network is called a multi-hop wireless network.

  In wireless networks, the communication quality of the communication route changes over time due to the movement of the node and the influence of noise, and the route to the node that was able to communicate is interrupted. In order to maintain communication between nodes, it is necessary to exchange route information between nodes, search for usable routes, and have good communication quality among the available routes. It is necessary to select a route.

  By the way, the above-mentioned problem in the wireless network also occurs in a PLC network which is a communication network constructed using a technique of power line carrier communication (hereinafter abbreviated as “PLC” (Power Line Communication)) using a power line as a transmission path. . As an application of the PLC network, for example, a system that centrally monitors and controls the equipment of each dwelling unit by installing a node in each dwelling unit and a management room in an apartment house has been proposed.

  In this type of system, the power line is used as a route to transmit information using a high-frequency carrier signal, so weak power is used for the carrier signal, and the total extension of the power line is similar to that of an apartment house. If it becomes longer, there may be a case where communication cannot be performed directly from the node installed in each dwelling unit to the node in the management room. In addition, because the PLC network connects nodes to power lines, noise generated by load equipment connected to the power lines affects communication quality. Will change the network topology.

  Accordingly, in the PLC network as well as the multi-hop wireless network, a technique for a multi-hop communication network that uses other nodes for relaying communication and searches for and selects a route is required. A case where a technology of a multi-hop communication network is applied to a PLC network is known (for example, see Patent Document 1).

  By the way, in a multi-hop communication network, it is necessary to search and select which node a route is used before starting communication. The route search is a process of finding a possible route existing between the starting point node and the arriving point node to be communicated, and the route selection is a route having a higher communication quality among the possible routes. This is the process of selecting.

  To search for a route, it is first necessary to detect a pair of nodes (in other words, a link between nodes) that can communicate without relaying other nodes. If such a link is known, it is possible to trace a route connecting nodes between the start point and the arrival point of communication data by following the link. On the other hand, in order to select a route, it is necessary to evaluate the communication quality for each link. In other words, it is desirable to adopt a route with good communication quality among the routes obtained by searching. Therefore, evaluate the communication quality of each link with an appropriate evaluation value, and use this evaluation value from the starting point. The communication quality up to the arrival point is estimated, and a route with good communication quality is selected.

As a technique for detecting a pair of nodes that can communicate without relaying other nodes, in Patent Document 1, each node transmits and receives a signal called a hello message in a timely manner, and the node receives the hello message. A technique is disclosed in which a communication quality in the transmission direction is acquired by the transmission-side node by acquiring communication quality in the reception direction and transmitting a hello message including the communication quality in the reception direction from the reception-side node.
JP 2006-67557 A

  By the way, in a multi-hop communication network, the network topology changes with the passage of time, and this change is detected by each node sending a hello message at regular intervals and other nodes receiving the hello message. ing.

  The hello message includes the first hello message in which each node transmits only its own address, the communication quality in the receiving direction obtained by receiving the hello message from another node, and the address of the node that has transmitted the hello message. There is a second hello message including the following information.

  For example, when a node newly enters the communication network, in response to the first hello message of the existing node, the newly entered node sends a second hello message and requests the communication quality from the existing node. Then, the existing node that has received this request responds with the second hello message, thereby confirming the quality of the link between the new node and the existing node. In addition, there is a case where one of the existing nodes disappears or the hello message is one-way with another node.

  In order to cope with such a change in the network topology, the communication quality acquired by the hello message and the address of the adjacent node are registered in the adjacent node table for the adjacent node that can communicate without relaying by other nodes. The second hello message including the address of the adjacent node registered in the table and the communication quality information is transmitted in a timely manner to request acquisition of the communication quality, and the second hello message transmitted in response to the request The communication quality is constantly checked.

  Accordingly, the second hello message including the address of the adjacent node and the communication quality information is frequently transmitted to the communication network, leading to an increase in traffic. In addition, it is possible to store the first hello message and the second hello message in the same packet and transmit them, but since the packet becomes longer, the traffic also increases. Therefore, there is a problem that the bandwidth that can be used for the original data communication is narrowed by the process used for detecting the network topology.

  The present invention has been made in view of the above reasons, and its purpose is to reduce the number of times the second hello message is transmitted compared to the prior art, thereby reducing the traffic due to the hello message and using it for original data communication. An object of the present invention is to provide an adjacent node confirmation method in a multi-hop communication network and a node of the multi-hop communication network that can expand a bandwidth that can be used.

  The invention according to claim 1 is an adjacent node which is a node capable of communicating without relaying by other nodes in a multi-hop communication network having a plurality of nodes and enabling relaying of communications by other nodes when communicating between the nodes. Each node is transmitting a hello message including its own address for each specified time interval, and has an adjacent node table that registers and associates addresses and communication quality for adjacent nodes, A normal mode in which the first hello message not including the address of the adjacent node and the communication quality is transmitted, the address of the adjacent node selected from the adjacent node table, and the communication quality information in the reception direction from the adjacent node. 2 for confirming the communication quality between adjacent nodes. When an event that requires the above occurs, the mode is changed from the normal mode to the confirmation mode. In the confirmation mode, the second hello message is transmitted within the limited number of transmissions, and then the normal mode is restored. .

  According to a second aspect of the present invention, in the first aspect of the present invention, the event that shifts to the confirmation mode is registration of only the communication quality in the receiving direction of the adjacent node in the adjacent node table.

  In the invention of claim 3, in the invention of claim 1, the event that shifts to the confirmation mode is reception of a second hello message including the address of the own node from a node not registered in the adjacent node table. Features.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the event that shifts to the confirmation mode is reception of a second hello message from a node in which only communication quality in the reception direction is registered in the adjacent node table. It is characterized by that.

  In the invention of claim 5, in the invention of claim 1, the event of shifting to the confirmation mode is a state in which a hello message is not received from a node whose communication quality in the reception direction and transmission direction is registered in the adjacent node table. Is that the period of time corresponding to the limited number of transmissions is continued.

  In the invention of claim 6, in the invention of any one of claims 1 to 5, the event of shifting to the confirmation mode is registered in the communication quality in the receiving direction detected when the hello message is received and in the adjacent node table. The difference between the received communication quality and the received communication quality is outside the specified allowable range.

  In the invention of claim 7, in the invention of any one of claims 1 to 6, the event that shifts to the confirmation mode is a time lapse of a fixed time longer than a time obtained by multiplying the time interval by the number of transmissions. It is characterized by being.

  The invention of claim 8 is a node used in a multi-hop communication network having a plurality of nodes and capable of relaying communication by other nodes at the time of communication between the nodes, and specifying a hello message including its own address. Communication means for transmitting at each time interval, adjacent node table for registering addresses and communication quality in association with adjacent nodes, and communication quality for registering communication quality in the receiving direction in the adjacent node table when a hello message is received Normal mode for transmitting the first hello message not including information on the acquisition node, the address of the adjacent node and the communication quality, the address of the adjacent node registered in the adjacent node table, and the communication quality in the receiving direction from the adjacent node An operation mode with a confirmation mode for transmitting a second hello message including the information of Link confirmation means; and communication quality registration means for registering the communication quality in the transmission direction included in the second hello message in the adjacent node table when the second hello message received from the adjacent node includes its own address. The link confirmation means shifts from the normal mode to the confirmation mode when an event that requires confirmation of the communication quality with the adjacent node occurs, and in the confirmation mode, the second is performed within the limited number of transmissions. It is characterized by returning to the normal mode after transmitting the hello message.

  Note that the number of transmissions may be limited to a case where the number of transmissions is limited to a predetermined maximum number, or a case where the number of transmissions is limited by a time limit.

  According to the configuration of the first and eighth aspects of the invention, when an event that requires the presence of an adjacent node occurs, the second hello message is transmitted a limited number of times. Thus, compared to the case where the second hello message is always transmitted, the average data length per transmission can be shortened, and as a result, the second hello message is transmitted without limitation. The traffic can be reduced compared to the case.

  According to the configuration of the invention of claim 2, since the node in which only the communication quality in the reception direction of the adjacent node is registered in the adjacent node table transmits the second hello message, the first hello message is received. Thus, when only the communication quality on the receiving side is registered in the adjacent node table, the acquisition of the communication quality on the transmitting side can be requested immediately.

  According to the configuration of the invention of claim 3, since the node that has received the second hello message including the address of its own node from a node that is not registered in the adjacent node table transmits the second hello message, It is possible to notify the link quality to nodes that have not been recognized as, and to obtain bidirectional communication quality.

  According to the configuration of the invention of claim 4, the communication quality in the transmission direction can be acquired by receiving the second hello message for the node in which only the communication quality in the reception direction is registered. Furthermore, since the second hello message is transmitted within the limited number of transmissions even after acquiring the bidirectional communication quality between the reception direction and the transmission direction, it is possible to cope with a change in communication quality.

  According to the configuration of the fifth aspect of the present invention, even if the communication quality in the receiving direction and the transmitting direction is registered, the second hello message is transmitted when the hello message is not received for a long time. Thus, it can be confirmed whether or not the node exists as an adjacent node. Further, when it is determined that communication with the node is no longer possible, the ridge is made the node by the second hello message, so that the node can also recognize the link disconnection and avoid the link state recognition mismatch.

  According to the configuration of the invention of claim 6, when the communication quality in the receiving direction detected by receiving the hello message changes beyond the allowable range with respect to the communication quality registered in the adjacent node table, the communication quality is Since it needs to be corrected, it can be updated to the latest communication quality by transmitting the second hello message.

  According to the configuration of the seventh aspect of the invention, since each node transmits the second hello message at regular time intervals, it is possible to detect the presence or absence of fluctuations in communication quality with adjacent nodes at regular time intervals. The content of the adjacent node table can be updated to the latest communication quality in response to a change in communication quality with the adjacent node.

(Basic configuration)
In a multi-hop communication network, in order to determine the route between nodes that are the starting point and the arriving point of communication data, a pair of nodes that can communicate directly without relaying other nodes is detected, and It is necessary to evaluate the communication quality in the link between nodes. Further, it is necessary to search for a communication path (route) that can be taken between the starting point and the arriving point of the communication data, and to select a route with high communication quality among communicable routes.

  In the embodiment described below, for the evaluation of the communication quality of the route, the reception strength of the signal transmitted by the adjacent node and the number of links connecting the adjacent nodes with respect to the nodes included in the route transmitting the information (hereinafter, (Referred to as “hop count”) means that two nodes are able to communicate between two nodes without being relayed by another node, and the number of hops between adjacent nodes is one ). Therefore, the number of hops is a value obtained by subtracting 1 from the number of nodes constituting the route (including nodes at both ends of the route). The route communication quality is evaluated to be better as the signal strength is larger and the number of hops is smaller, and a route with the best communication quality is selected from the searched routes.

For example, a value obtained by dividing the signal strength between nodes capable of direct communication into a plurality of stages (for example, 10 stages) and coding (hereinafter, this code is referred to as SQ (Signal Quality)) is used in the communication network. Communication quality between two nodes transmitting communication data is evaluated by a route cost obtained by the following equation. That is, the route cost becomes an evaluation value of communication quality.
(Route cost) = Ka × (sum of SQ values for each link in the route) + Kb × (hop count)
However, Ka and Kb are weighting factors. Hereinafter, a case where Kb = 0 is described.

  If there is a route with two nodes to be relayed between the node that is the starting point and the arriving point of communication data, and the SQ of each link is 3, 4, and 5, respectively, the route cost is Ka × ( 3 + 4 + 5) + Kb.times.3 = 12.Ka + 3.Kb.

  By the way, the value obtained by multiplying the SQ value for each link in the route cost by the weighting factor Ka is an evaluation value of the communication quality regarding the link between two nodes that are adjacent nodes capable of direct communication. Then, this evaluation value is called a link cost. The link cost may change depending on which node is the transmitting side between two communicating nodes. Therefore, the link cost obtained from the reception strength of the signal from the other node (the communication quality of the receiving side) (Evaluation value) is called a reception link cost, and a link cost (evaluation value of communication quality on the transmission side) obtained from the reception strength when the other node receives a signal from the own node is called a transmission link cost.

  Each node includes an adjacent node table that registers the received link cost and the transmitted link cost in association with the address of the counterpart node with respect to the adjacent node. As the link cost of each link in the communication network, the larger one of the reception link cost and the transmission link cost is used. That is, the link cost of each link is evaluated based on the worse communication quality.

  As shown in FIG. 6, the adjacent node table registers items such as an address assigned to each adjacent node (adjacent node address), a reception link cost for each adjacent node, and a transmission link cost for each adjacent node. Field. The route cost is a route cost obtained by the above-described calculation. However, since the link cost of each link included in the route has already been multiplied by the weighting factor Ka, Ka × (the sum of SQ values for each link in the route) is determined by the sum of the link costs of each link included in the route. Desired. The higher cost will be described later. Note that the adjacent node table actually holds information on the address of the node on the route and the link cost of each link of the route as data on the higher cost, but here, for the sake of simplicity of explanation. In addition, the higher cost is treated as the sum of the link costs on the route, and the address of the node is not considered.

  First, an operation for acquiring a link cost by focusing on two adjacent nodes will be described. Even when a plurality of nodes are adjacent to one node, the basic procedure for acquiring a link cost is the same. In order to obtain the link cost, a hello message transmitted at an appropriate time interval is used separately from the communication data. Each node transmits the hello message including its own address by broadcast transmission.

  Now, as shown in FIG. 5, paying attention to the two nodes A and B for which the link cost is obtained, a case where the node A first transmits a hello message is assumed. When transmitting the hello message H1 from the node A, if the node B can directly receive the hello message H1 transmitted by the node A, the node B acquires the received link cost. The received link cost acquired by the node B is registered in association with the adjacent node address of the node A in the adjacent node table of the node B as shown in FIG. 6A (here, the received link cost is “8”). "). Although the hello message H1 is transmitted in a timely manner, it is usually periodically transmitted at regular time intervals.

  Next, the node B transmits the hello message H2 including the address of the node A that is the transmission source of the hello message H1 and the received link cost. Since the node A that has received the hello message H2 can determine the received link cost when the signal from the node B is received by the hello message H2, the received link cost is set to the node as shown in FIG. It is registered in the adjacent node table in association with the address B (here, the received link cost is “5”). Further, since the hello message H2 includes the own address and the reception link cost when the partner node B receives the hello message H1, this reception link cost is set as the transmission link cost from the node A to the node B. It is registered in the adjacent node table in association with the address of Node B (that is, the transmission link cost for Node B is “8”).

  After that, the node A transmits the hello message H3 again. The hello message H3 includes the received link cost and the address of the node B when the hello message H2 is received from the node B in the information. Therefore, the node B can acquire the transmission link cost when the hello message H2 is transmitted to the node A as the information included in the hello message H3 (that is, the transmission link cost for the node A is “5”). In the node B, as shown in FIG. 6C, the reception link cost received from the node A is set as the transmission link cost from the node B to the node A and registered in the adjacent node table in association with the address of the node A.

  As described above, the bidirectional link cost can be registered in the adjacent node table by transmitting and receiving the hello messages H1 to H3 three times between the nodes A and B which are adjacent nodes. Further, as is apparent from the above-described procedure, after the transmission / reception of the three hello messages H1 to H3, the contents of the adjacent node table of the adjacent nodes become complementary contents. Here, being complementary means that even if one content is lost, the other content can be restored.

  Incidentally, the actual communication network includes a large number (seven in the illustrated example) of nodes N0 to N6 as shown in FIG. Although the nodes N0 to N6 can be handled equally, here, description will be made using a master-slave type communication network in which one node N0 is a parent node. In the master-slave type communication network, the other nodes N1 to N6 other than the parent node N0 are child nodes, one end of the route for transmitting communication data is the parent node N0, and the other end is one of the child nodes N1 to N6. Become. In the master-slave type communication network, the child nodes N1 to N6 excluding the child nodes N1 to N6 that become one end of the route for transmitting communication data relay communication as necessary. Each child node N1 to N6 can be said to be lower as the number of child nodes N1 to N6 intervening with the parent node N0 increases (that is, as the number of hops increases). Which child node N1 to N6 is included in the route with the parent node N0 and relays is determined by the procedure described below. Further, although a master-slave type communication network is used for convenience of explanation, the nodes N0 to N6 may have an equal relationship.

  As described above, the reception link cost and the transmission link cost can be acquired by transmitting and receiving the hello messages H1 to H3 three times between the adjacent nodes N0 to N6.

  Here, the communication network shown in FIG. 7 (the network topology is assumed not to change during acquisition of the link cost) is considered. In a multi-hop communication network, until data is registered in the adjacent node table, nodes N0 to N6 that can be directly communicated without relay are unknown, so the hello messages H1 to H1 that are transmitted to search for adjacent nodes are unknown. H3 is transmitted by broadcast.

  That is, each of the nodes N0 to N6 transmits a hello message (corresponding to the hello message H1) by broadcasting. However, since it is a master-slave type communication network, transmission of a hello message is started from the parent node N0. When the child nodes N1 and N2 adjacent to the parent node N0 receive the hello message, the child nodes N1 and N2 receive the link cost and the transmission link with the parent node N0 according to the procedure described with reference to FIGS. Find the cost.

  When the child nodes N1 and N2 acquire the transmission link cost, each of the child nodes N1 and N2 transmits a hello message by broadcasting. The parent node N0 has already acquired the reception link cost and the transmission link cost, but responds to the hello message (corresponding to the hello message H1) transmitted by the child nodes N1 and N2. By repeating such an operation sequentially, each of the child nodes N1 to N6 acquires the reception link cost and the transmission link cost with the adjacent node, and the reception link cost and the transmission with the adjacent node in the adjacent node table. Register the link cost.

  Taking the child node N6 as an example, the procedure from acquisition of the reception link cost to acquisition of the transmission link cost will be described in more detail. Since the child node N6 receives the hello message from the adjacent child nodes N1, N3, N4, and N5, as shown in FIG. 8, the received link cost for each child node N1, N3, N4, and N5 is set to the adjacent node address. And registered in the adjacent node table.

  Here, since each of the nodes higher than the child nodes N1, N3, N4, and N5 has a reception link cost and a transmission link cost, the larger of the reception link cost and the transmission link cost The link costs of the child nodes N1, N3, N4, and N5 are used, and the child nodes N1, N3, N4, and N5 are routed to reach the parent node N0 through any one of the upper child nodes N1, N3, N4, and N5. Each time, the minimum value of the sum of link costs is obtained. The minimum value obtained in this way is called “higher cost” for each of the child nodes N1, N3, N4, and N5. At this time, the child node N6 has not acquired the transmission link cost between the adjacent child nodes N1, N3, N4, and N5. However, the child node N1, N3, N4, and N5 have already acquired the transmission link cost. It is obtained and the upper cost is determined. The higher cost is also registered in the adjacent node table. As described above, the information on the higher-order cost is actually as individual information on the address of each node on the route from each child node N1, N3, N4, N5 to the parent node N0 and the link cost of each link. In order to obtain the higher-order cost that has been registered, the sum of the link costs is obtained for the links on the route.

  Now, the transmission link cost is determined between the nodes N0 to N6 in FIG. 7 except between the child nodes N1, N3, N4 and N5 and the child node N6, and the value is determined by the adjacent nodes N0 to N5. It is assumed that the value is described in association with a straight line (link) connecting. Also, it is assumed that only the received link cost is known by detecting the hello message between the child nodes N1, N3, N4, N5 and the child node N6 (values marked with * in FIG. 7 are received). Link cost).

  According to FIG. 7, the received link costs acquired when the child node N6 receives the hello message sent from the child nodes N1, N3, N4, and N5 are 15, 28, 6, and 7, respectively. As shown in FIG. 4, the addresses of the child nodes N1, N3, N4, and N5 are registered as the adjacent node addresses in the adjacent node table of the child node N6, and the received link costs are registered.

  In the example of FIG. 8, the link cost is the smallest among the routes to the parent node N0 for each of the child nodes N1, N3, N4, and N5. The parent node N0, the child node N1 → the parent node N0, The route of the node N2 → the parent node N0 (or the child node N1 → the parent node N0), the child node N3 → the child node N1 → the parent node N0, and the sum of the transmission link costs of each route (that is, the higher cost) is 11, 20 (= 11 + 9), 30 (= 20 + 10 or = 11 + 9 + 10), 16 (= 11 + 5), respectively.

  Therefore, the added value of the reception link cost between each adjacent child node N1, N3, N4, N5 and the child node N6 of interest and the upper cost of each adjacent child node N1, N3, N4, N5 Is a provisional route cost reflecting the transmission link cost from the child node N6 of interest to the parent node N0. The temporary route cost obtained in this way is registered in the item of “route cost” in association with each adjacent child node N1, N3, N4, N5 in the adjacent node table of the child node N6 of interest. In FIG. 8, the addition of * to the route cost indicates a provisional route cost obtained from the higher cost and the received link cost.

  By the way, in order to obtain the transmission link cost in the adjacent node table of the child node N6, it is necessary to transmit a hello message from the child node N6 to each of the adjacent child nodes N1, N3, N4, and N5. However, when there are a plurality of routes from the child node N6 to the parent node N0, it is desirable to select a route with the smallest possible link cost.

  In the example described above, there are four child nodes N1, N3, N4, and N5 adjacent to the child node N6 of interest, and each child node N1, N3, N4, and N5 passes through each child node N1, N3, N4, and N5. Since the minimum value of the sum of the link costs is obtained as the higher cost for each of the nodes N1, N3, N4, and N5, attention is given if the communication quality (link cost) is compared for the four types of routes for which the higher cost is obtained. It is considered that the child node N6 can select a route suitable for transmitting information to the parent node N0.

  Therefore, the route from the child node N6 of interest to the parent node N0 is evaluated based on the temporary route cost. Here, the target child node N6 may transmit a hello message to each of the four child nodes N1, N3, N4, and N5 adjacent to the child node N6, but one type of route is actually used. Therefore, an appropriate number of routes (about two routes) are selected from the highest communication quality including the spare route, and a hello message is transmitted. In the example of FIG. 8, the child nodes N1, N3, N4, and N5 adjacent to the child node N6 of interest have temporary route costs up to the second highest, that is, the child node N1 and the child node N5. Therefore, the hello message (corresponding to the hello message H2 in FIG. 5) is transmitted from the child node N6 only to the two child nodes N1 and N5.

  Receiving this hello message, the child nodes N1 and N5 use the hello message (corresponding to the hello message H3 in FIG. 5) to return the received link cost registered in the child nodes N1 and N5 to the child node N6. That is, as shown in FIG. 9, the child node N6 can acquire the transmission link cost for the child nodes N1 and N5. As for the route that reaches the parent node N0 through the child nodes N1 and N5 that have acquired the transmission link cost in this way, by adding the transmission link cost and the higher-order cost, the formal route cost is obtained instead of the temporary route cost. Since it can be obtained, the value of the route cost is updated. That is, as shown in FIG. 9, a formal route cost is obtained for the nodes N1 and N5 that have acquired the transmission link cost, and a temporary route cost is used for the other nodes N3 and N4.

  By the above-described procedure, in the child node N6 that communicates with the parent node N0, the formal route cost is obtained for the two routes that the child nodes N1 and N5 relay the communication. The fact that the official route cost is obtained means that a bidirectional link cost between the reception link cost and the transmission link cost is required for the adjacent node. Hereinafter, this state is referred to as “2WAY”. The case where only the reception link cost is obtained for the adjacent node is referred to as “1WAY”. The state where the link cost is not obtained or the adjacent node has disappeared is called “LOST”.

  When the child node N6 communicates with the parent node N0, the route having the minimum route cost (the sum of the link costs toward the parent node N0) is selected as the best route. For such route search and selection, for example, a minimum link cost route selection algorithm such as Dijkstra method may be used. The selected route is notified to the parent node N0 using the topology notification message, and the parent node N0 can obtain route information to the child node N6. The topology notification message may be transmitted in a timely manner, but is normally transmitted periodically at regular time intervals.

  That is, in the example of FIG. 9, since the route cost is obtained for the route passing through the child node N5, the topology notification message is transmitted using the route of the child node N6 → the child node N5 → the child node N1 → the parent node N0. The At this time, the child node N6 includes not only the child node N5 but also the route cost for the two child nodes N1 and N5 for which the official route cost has been obtained as information in the topology notification message, and unicasts to the child node N5. Send. Since the child node N1 passing from the child node N5 to the parent node N0 is known in the child node N5, the child node N5 transmits the contents of the topology notification message received from the child node N6 to the child node N1 by unicast. . Similarly, the child node N1 transmits a topology notification message toward the parent node N0. The parent node N0 grasps the network topology with the child node N6 using the content of the received topology notification message.

  As shown in FIG. 10, the hello message used to register the reception link cost and the transmission link cost in the adjacent node table of each child node N1 to N6 includes the own address SID of the node that is the transmission source, and the message type. TY indicating node type, node type NC indicating the type of the source node, and sub-messages SB1, SB2, SB3, and SB4 in which at least one type is selected from four types according to the content of the hello message. Yes.

  In the hello message, the type TY indicates a hello message, and the node type NC is the source of the hello message, so there are cases of a parent node and a child node. The Hello messages H1, H2, and H3 shown in FIG. 5 have the same type TY but have different sub-messages SB1, SB2, SB3, and SB4.

  The sub message SB1 includes the number of hops of the route that each child node N1 to N6 forms when communicating with the parent node N0 (that is, the number of nodes up to the parent node N0), the address of each node on the route, and each node. The link cost information is transmitted to the lower child nodes N1 to N6 as the contents of the hello message H1 in FIG. The lower child nodes N1 to N6 that have received the content of the sub message SB1 can know the upper cost.

  The sub-message SB2 indicates that the child nodes N1 to N6 of “1WAY” for which only the reception link cost is obtained for the adjacent nodes are the addresses and link costs (partner nodes) for an appropriate number of adjacent nodes having higher reception link costs. The transmission link cost) is transmitted to the upper node that is the transmission source of the hello message H1 as the content of the hello message H2 in FIG.

  The sub message SB3 is used when the node “2WAY” from which the reception link cost and the transmission link cost are obtained returns the reception link cost detected by the hello message H2 to the child nodes N1 to N6 on the other side. That is, it has information on the address and link cost of the lower adjacent node (transmission link cost of the partner node), and is transmitted to the lower child nodes N1 to N6 as the contents of the hello message H3 in FIG.

  The sub message SB4 notifies the parent node N0 of the address of the adjacent node that is lost when the loss of the adjacent node is detected by the hello message (when the lower node does not respond to the hello message of the upper node). The information includes the address and link cost of the adjacent node that has been used and disappeared.

  Therefore, each sub message SB1, SB2, SB3, SB4 distinguishes four types of submessages SB1, SB2, SB3, SB4 by sub message type STY as shown in FIG. It has a variable-length format having information on the number of nodes included in SB4 (the number of hops to the parent node N0 in the sub message SB1), the address NID of each node, and the link cost LC.

  As described above, since the hello message H1 includes the addresses and link costs of the nodes on the route from the child nodes N1 to N6 of the transmission source to the parent node N0, the lower child node N1 that has received the hello message H1. In the adjacent node table of N6, as shown in FIG. 12, the link cost (LC) and the address (NID) are individually held in order from the first hop for each node up to the parent node N0. The link cost and address for each node correspond to the contents of the higher cost in FIG. In the adjacent node table shown in FIG. 12, the link status (1WAY, 2WAY, LOST) is included in the item. The information corresponding to the link state can be known by the presence / absence of information on the reception link cost and the transmission link cost.

  As shown in FIG. 13, the topology notification message includes fields of a type TY indicating the type of message, a node type NC indicating the type of the transmission source node, and three types of sub messages Sb1, Sb2, and Sb3. That is, the format of the topology notification message is almost the same as that of the hello message. However, the contents of the sub messages Sb1, Sb2, and Sb3 are different.

  In the topology notification message, the type TY indicates a topology notification message, and the node type NC is a child node because it is a node that is the transmission source of the topology notification message.

  The sub message Sb1 indicates a route to the parent node N0 and includes child nodes (child node N6 in the above example) including the child node (child node N6 in the above example) included in the route to the parent node N0. In this example, the addresses of the child nodes N6, N5, N1) are arranged in order. That is, the content is almost the same as that of the sub message Sb1 in the hello message, except that the address of the own node is included.

  The sub message Sb2 includes the addresses of the child nodes (child nodes N1 and N5 in the above example) for which the root cost is obtained among the higher-level nodes adjacent to the child node of the transmission source (child node N6 in the above example). It is done.

  The sub message Sb3 is an address of a node that is no longer an adjacent node among nodes that are adjacent nodes. That is, the child node that has not formed a route from the child node (child node N6 in the above example) to the parent node N0 is notified to the parent node N0.

  Each sub message Sb1, Sb2, Sb3 has a variable length. The sub message Sb1 is essential for the topology notification message and cannot be omitted, but the sub messages Sb2 and Sb3 can be omitted.

(Embodiment)
In the present embodiment, the following functions are added to the basic configuration described above. In the following description, similarly to the basic configuration, a master-slave type communication network including a parent node N0 and child nodes N1 to N6 is assumed. However, the technology described below is applicable to communication networks other than the master-slave type. Applicable.

  The node N is a communication terminal having a communication function and a microcomputer that performs processing to be described later, and includes a communication unit 11 as shown in FIG. The communication unit 11 transmits and receives communication data, and also transmits and receives hello messages and topology notification messages.

  The node N is provided with the adjacent node table Tb1 as described above. As described above, the contents of the adjacent node table Tb1 are the adjacent node address, the reception link cost, the transmission link cost, etc., and the communication quality acquisition means 12 sends a hello message to other nodes via the communication means 11. By transmitting and receiving, the contents of the adjacent node table Tb1 are registered. The hello message includes its own address.

  In the present embodiment, for example, when a new node N enters the communication network, a link cost with the existing node N changes, or an existing node N disappears, the adjacent node table corresponds to the case. The link cost of Tb1 is updated. Therefore, the hello message Ha which does not have the sub messages SB2, SB3 and SB4 (however, SB1 may be present) and any of the sub messages SB2, SB3 and SB4 described above. Hello messages Hb, Hc, and Hd having Hereinafter, a hello message having no sub message is referred to as a first hello message Ha, and a hello message having a sub message SB2 is referred to as a second hello message Hb.

  In the node N, when the communication unit 11 receives the first hello message Ha from the adjacent node, the communication quality acquisition unit 12 obtains the received link cost from the first hello message Ha and registers it in the adjacent node table Tb1. Is provided. Further, the node N is provided with a link confirmation unit 13 for confirming a link cost with an adjacent node. The link confirmation means 13 has two types of operation modes, a normal mode for transmitting the first hello message Ha and a confirmation mode for transmitting the second hello message Hb. When the link confirmation unit 13 transmits the second hello message Hb through the communication unit 11, the transmission link cost from the adjacent node to the own node can be given to the adjacent node together with the own address of the node N.

  When the second hello message Hb received by the communication unit 11 includes the address of the own node, the node N registers the transmission link cost associated with the own node in the adjacent node table Tb1. Also equipped. The link confirmation unit 13 has a function of transmitting hello messages Hc and Hd including the sub messages SB3 and SB4 when the communication quality registration unit 14 detects the second hello message Hb including the address of the own node. The communication quality registration unit 14 has a function of performing processing to be described later on the adjacent node table Tb1 when the hello messages Hc and Hd are received.

  Hereinafter, the operation of the node N will be described. When the link confirmation means 13 is operating in the normal mode, the first hello message Ha is transmitted at regular intervals. The first hello message Ha does not have a sub message (but may have only SB1) and has a short data length, so the traffic on the communication network is not significantly increased.

  On the other hand, when an event described below occurs, the link confirmation unit 13 shifts to the confirmation mode. In the confirmation mode confirmation mode, the second hello message Hb including the address of the adjacent node satisfying the prescribed condition and the reception link cost among the adjacent nodes registered in the adjacent node table Tb1 is transmitted within the limited number of transmissions. . To transmit within the limited number of transmissions, the maximum number of transmissions of the second hello message Hb is limited, and the node N includes its own address from the adjacent node after the transmission of the second hello message Hb. When the hello message Hc is received, it means that the transmission of the second hello message Hb is ended even if the number of transmissions does not reach the maximum value. Therefore, when the adjacent node responds to one transmission of the second hello message Hb and receives the hello message Hc including its own address in the sub message SB3, the transmission of the second hello message Hb is terminated. If Hc is not obtained, the second hello message Hb is repeatedly transmitted within the limited number of transmissions. The number of transmissions may be limited by the number of times itself or when the expiration date is set and the number of transmissions is limited by time. Hereinafter, a case where the number of transmissions is limited by the number of times itself will be described.

  The event of causing the link confirmation means 13 to shift to the confirmation mode and transmitting the second hello message Hb is when the own node newly enters the communication network or when communication with a new adjacent node becomes possible. When only the received link cost is registered in the adjacent node table Tb1 (that is, “1WAY”), even if the node N is in the “2WAY” state, the node N has the first hello message Ha or the second When the difference between the received link cost detected at the time of receiving the hello message Hb and the received link cost registered in the adjacent node table Tb1 is out of the specified allowable range, the time per fixed time specified in the node N In some cases, it has passed.

  In the initial state of the communication network, each node N transmits the first hello message Ha, so “1WAY” is set. However, since the second hello message Hb is not transmitted as it is, the node N does not become “2WAY”. Accordingly, among the adjacent nodes of “1WAY”, an appropriate number of nodes having a higher receiving link cost (preferably comparing the receiving link cost with an appropriate threshold) are selected, and the addresses of these nodes and the receiving link cost are selected. The second hello message Hb including the information in the sub message SB2 is transmitted. When shifting from the normal mode to the confirmation mode at regular intervals, the time interval for transmitting the first hello message Ha or the second hello message Hb is multiplied by the upper limit value of the number of transmissions of the second hello message Hb. The mode is shifted to the confirmation mode every time longer than the set value.

  By such an operation, when the communication state of the link with the adjacent node changes and the link cost changes greatly, the second hello message Hb can be transmitted to reconfirm the link cost. Even if there is no significant change in link cost, the second hello message Hb is periodically sent to reconfirm the link cost with the adjacent node, and if there is a change, update to the latest link cost. can do. Here, since the number of transmissions of the second hello message Hb is limited, an increase in traffic on the communication network can be suppressed.

  In order to limit the number of transmissions of the second hello message Hb, the adjacent node table Tb1 of each node N in this embodiment is provided with an item of an expiration date or the number of transmissions as shown in FIG. Then, both are listed, but only one is required). The mode switching between the normal mode and the confirmation mode may be performed for each adjacent node, or while the expiration date remains or there are one or more adjacent nodes whose transmission count is 1 or more. May be managed collectively so as to be in the confirmation mode. By the way, when the response of the hello message Hc cannot be obtained from the adjacent node within the limit of the number of transmissions, or when the hello message Ha from the adjacent node is not received at all within a certain time, the adjacent node becomes incapable of communication. It is thought. The adjacent node may be unable to communicate when the adjacent node is removed or fails or the communication quality is extremely lowered.

  Therefore, the second hello message Hb is transmitted a plurality of times within the limit of the number of transmissions, and when no response to the hello message Hc is obtained, or the hello message Ha from the adjacent node is received at all within a certain time. If not, it is determined that the network topology has changed, the adjacent node has disappeared and the state of the adjacent node has changed to “LOST”, and the communication quality registration unit 14 determines the address of the adjacent node in the adjacent node table Tb1. Delete the link cost information leaving only. Even if no hello message is received from the adjacent node, if the transmission path state is incapable of communication in only one direction, the adjacent node on the side determined to be LOST will send a hello message to the node determined to be LOST. May have been received. In other words, it is determined that LOST is in one node, and it is erroneously determined that the link exists normally in the other node, and a link state mismatch occurs. For this reason, the adjacent node and the neighboring nodes N are notified that the adjacent node has become “LOST”.

  In order to notify the neighboring node N that the adjacent node has become “LOST”, the hello message Hd including the “LOST” sub-message SB4 described in the basic configuration is transmitted. The hello message Hd having the “LOST” sub message SB4 is transmitted a plurality of times which is the maximum value of the number of transmissions in the confirmation mode. That is, the network topology change is reliably transmitted to each node N. If the hello message having the sub message SB4 never reaches the adjacent node determined to be LOST, the adjacent node does not receive the hello message for a certain period. The link with the node that has transmitted the hello message is determined to be LOST. In this case as well, both recognize as LOST as a result, and it is possible to avoid a state mismatch.

  By providing the confirmation mode as described above and transmitting the second hello message Hb, the state of the node N changes as shown in FIGS. 3 and 4 show the same contents.

  The horizontal row in FIG. 3 shows the current state of each node N in the adjacent node table Tb1, and “LOST” (state in which no information exists as an adjacent node in the adjacent node table Tb1) and “1WAY” (adjacent to the adjacent node table Tb1). In a state where only the reception link cost of the node is registered), “2WAY” (when the reception link cost and transmission link cost of the adjacent node are registered in the adjacent node table Tb1) is shown.

  Also, the column in FIG. 3 is information on adjacent nodes acquired by the hello message from the adjacent node. When receiving the first hello message Ha from the top, when receiving the second hello message Hb, 2 is a response to the hello message Hb, and the hello message Hc including the own address is received. If the hello message Hd includes the sub message SB4 “LOST” and the own address is included, the hello message is fixed. This represents a case where the time is not received (this time may be the same as the time when the mode is shifted to the confirmation mode every certain time).

  The state of the node N changes according to the reception state of the hello message, and changes the number of transmissions of the second hello message Hb and the state of the adjacent node in the adjacent node table Tb1 as necessary. In FIG. 3, changes in the number of transmissions and the state of adjacent nodes are shown in the cells where the row and the column intersect. In FIG. 4, the current state of the node N is represented by a triangular vertex, and each side is associated with the reception state of the hello message and the change in the number of transmissions, and the direction of state change is indicated by the → direction of each side. . Here, the number of transmissions varies depending on whether it is set to 0 or set. If the number of transmissions is set, the second hello message Hb can be transmitted a plurality of times up to the set number. When the number of transmissions is set to 0, the second hello message Hb is not transmitted and the normal mode is set.

  First, a node that is not registered as an adjacent node in the adjacent node table Tb1 (a “LOST” node) will be described. That is, since it is not registered in the adjacent node table Tb1, the first hello message Ha is received in many cases. In this case, the number of transmissions is set to 0 and the adjacent node is recorded as “1WAY”. That is, only the received link cost is registered.

  On the other hand, the second hello message Hb or hello message Hc may be received from the “LOST” node. This is because when the own node transmits the hello message Ha first and the adjacent node that receives it transmits the hello message Hb or has been registered as an adjacent node once, This is a case where it is deleted from the adjacent node table Tb1 due to a change or the like. In this case, since bidirectional link cost information is obtained, the adjacent node is set to “2WAY”, and the link quality needs to be notified to the adjacent node, so the number of transmissions is set.

  Since the node is “1WAY” in the initial state of the communication network, the second hello message Hb including the address of the node having the higher reception link cost and the reception link cost in the sub message SB2 is included in the number of transmissions limited. Send with. The adjacent node that has received the second hello message Hb and the node that has received the hello message Hc in response to the second hello message Hb can change the adjacent node table Tb1 to “2WAY”.

  By the way, when the second hello message Hb is received from the adjacent node of “1WAY”, the number of transmissions is set, the second hello message Hb is transmitted within the number of transmissions, and the number of transmissions is decremented. Further, when the hello message Hc is received from the adjacent node of “1WAY”, the transmission of the second hello message Hb after that becomes unnecessary, so the number of transmissions is set to zero.

  The node where both the reception link cost and the transmission link cost are registered (the node of “2WAY”) is the same as the case of shifting from “1WAY” to “2WAY”, and the second hello message Hb is received. In this case, the number of transmissions is set, and when the hello message Hc is received from an adjacent node, the number of transmissions is set to zero. However, since it is already “2WAY”, the state is maintained.

  By the way, regardless of whether it is “1WAY” or “2WAY”, the hello message is not received within the expiration date (whether the second hello message Hb is transmitted a plurality of times or there is no response), or “LOST”. When the hello message Hd including the sub message SB4 is received, the adjacent node is set to “LOST”. With the above processing, the state of each adjacent node can be properly managed.

  The above-described configuration example is assumed to be used for the PLC network described in the conventional configuration, but uses a wireless transmission path such as a communication network using another wired transmission path, or a wireless LAN using low-power radio. The above-described technique may be applied to various multi-hop communication networks such as a wireless network.

  Furthermore, the PLC network is known to have a low-speed PLC that uses a low frequency band of 10 to 450 kHz and a high-speed PLC that uses a high-frequency band of 2 to 30 MHz. Since the transmission speed is slow, it is particularly effective to be able to grasp the network topology even with low traffic as in the above configuration, and it is only necessary to have an adjacent node table even if each node does not have a link of the entire communication network. The capacity of the memory to be mounted on can be reduced. In addition, compared with the case where other wired transmission lines are used, the network topology and communication quality are easily changed in the PLC depending on the on / off and operating state of the electrical equipment serving as each node, so the technique of the present invention is effective. .

It is a block diagram which shows the node used for embodiment. It is a figure which shows the example of the adjacent node table used for the same as the above. It is a figure which shows the state change of the node used for the same as the above. It is operation | movement explanatory drawing which shows the state transition of the node used for the same as the above. It is operation | movement explanatory drawing which shows a hello message. It is operation | movement explanatory drawing which shows the change of the adjacent node table by a hello message. It is a figure which shows the structural example of a communication network. It is a figure which shows an example of an adjacent node table. It is a figure which shows an example of an adjacent node table. It is a figure which shows the format of a hello message. It is a figure which shows the structural example of the submessage in a hello message. It is a figure which shows an example of an adjacent node table. It is a figure which shows the format of a topology notification message.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Communication means 12 Communication quality acquisition means 13 Link confirmation means 14 Communication quality registration means H1-H3 Hello message Ha-Hd Hello message N node N0-N6 node Tb1 Adjacent node table

Claims (8)

  A method of confirming an adjacent node that is a node capable of communicating without relaying by another node in a multi-hop communication network having a plurality of nodes and capable of relaying communication by other nodes during communication between nodes. Each node transmits a hello message including its own address at a specified time interval, and has an adjacent node table that registers and registers addresses and communication qualities for adjacent nodes. A normal mode in which the first hello message that does not include the information is transmitted, and a second hello message that includes the address of the adjacent node selected from the adjacent node table and the communication quality information in the reception direction from the adjacent node is transmitted. It is necessary to confirm the communication quality between adjacent nodes. In the multi-hop communication network, wherein a transition is made from the normal mode to the confirmation mode when the error occurs, and in the confirmation mode, the second hello message is transmitted within the limited number of transmissions and then the normal mode is restored. Node confirmation method.   2. The adjacent node confirmation method in a multi-hop communication network according to claim 1, wherein the event of shifting to the confirmation mode is registration of only the communication quality in the reception direction of the adjacent node in the adjacent node table.   2. The neighbor in the multi-hop communication network according to claim 1, wherein the event to shift to the confirmation mode is reception of a second hello message including an address of the own node from a node not registered in the neighbor node table. Node confirmation method.   2. The multi-hop communication network according to claim 1, wherein the event of shifting to the confirmation mode is reception of a second hello message from a node in which only communication quality in the reception direction is registered in the adjacent node table. Method for confirming adjacent nodes.   The event of shifting to the confirmation mode continues for a time corresponding to the number of transmissions in which the state of not receiving a hello message from a node whose communication quality in the reception direction and the transmission direction is registered in the adjacent node table is limited. The adjacent node confirmation method in the multi-hop communication network according to claim 1, wherein:   The event of transition to the confirmation mode is that the difference between the communication quality in the reception direction detected when the hello message is received and the communication quality in the reception direction registered in the adjacent node table is outside the allowable range defined. 6. The adjacent node confirmation method in a multi-hop communication network according to claim 1, wherein the adjacent node confirmation method is provided.   7. The event according to claim 1, wherein the event that shifts to the confirmation mode is a lapse of time for each fixed time that is longer than a time obtained by multiplying the time interval by the number of transmissions. For confirming neighboring nodes in multi-hop communication networks.   A node used in a multi-hop communication network that has a plurality of nodes and enables relaying of communication by other nodes during communication between nodes, and transmits a hello message including its own address at specified time intervals. An adjacent node table for registering the address and communication quality in association with each other for the adjacent node; a communication quality obtaining unit for registering the communication quality in the receiving direction in the adjacent node table when a hello message is received; A normal mode in which the first hello message not including the address and the communication quality information is transmitted, and the second node including the address of the adjacent node registered in the adjacent node table and the communication quality information in the receiving direction from the adjacent node. A link confirmation means having an operation mode with a confirmation mode for transmitting a hello message; Communication quality registration means for registering the communication quality in the transmission direction included in the second hello message in the adjacent node table when the second hello message received from the adjacent node includes its own address, and a link confirmation means Shifts from the normal mode to the confirmation mode when an event that requires confirmation of the communication quality between adjacent nodes occurs, and transmits the second hello message within the limited number of transmissions in the confirmation mode. A node of the multi-hop communication network, wherein the node returns to the normal mode after the operation.

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