JP4871154B2 - Wireless communication network system, network construction method, center station, relay station, terminal station, and program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a time required for switching a communication path in order to avoid a fault when the fault has occurred in the communication path. <P>SOLUTION: A center station 10 stores information associating an address of a first master station connected to a relay station 20 by a main communication path and an address of a second master station connected to the relay station 20 by a backup communication path with the relay station 20 for each relay station 20, in a storing portion 130 as network definition information 131. The network definition information 131 is transmitted to the relay station 20 upon network construction, and stored in a storing device 230 as network definition information 231. The relay station 20 transmits an associate request to the relay station 20 with the address of the second master station stored in the network definition information 231 when a fault has occurred in a communication path between the relay device itself and the first master station, and switches the master station to which the relay device itself is connected to a relay station 20 having transmitted an acceptance response when the acceptance response of the associate request is received from the relay station 20. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

The present invention relates to a wireless LAN (Local Area Network) or wireless PAN (Personal Area Network) radio communication network system for use in such, network construction method, cell pointer station, relay station, a terminal station and its program.

  In a factory or the like, various sensors are installed in various places for various purposes. For example, there are sensors that detect abnormal heat generation, abnormal beeping sound, electrical leakage, etc. near production machines, sensors that measure the concentration of pollutants in exhaust gas outlets and drains, and offices and work Sensors that detect temperature, humidity, brightness, and the like are installed at the site. Data acquired by such a sensor is collected by a center computer or the like via a wireless LAN or the like and used for environmental management of a factory or a workplace.

  Such sensors and communication devices are often installed outdoors or outdoors. When installed outdoors or outdoors, the sensors and communication devices are often battery driven. In that case, since it is necessary to reduce the man-hours for maintenance such as battery replacement, the sensor and the communication device are required to have low power consumption.

  For example, Patent Document 1 discloses an example of a multi-hop wireless communication network that is used for such a wireless PAN and enables route selection that is effective in suppressing battery consumption of a relay station.

  As a standard specification of a wireless communication network suitable for the same wireless PAN or the like, there is an IEEE 802.15.4 standard. The IEEE 802.15.4 standard defines wireless communication specifications for the physical layer and MAC (Media Access Control) layer in wireless communication networks, but the communication speed is kept as low as 250 kbit / sec. It is said that it is easy to reduce the power consumption, size and cost of the device.

Furthermore, there is ZigBee compiled by the industry group ZigBee Alliance as a specification that complies with the IEEE 802.15.4 standard and defines the wireless communication network specification of the upper layer. ZigBee supports star, tree, mesh, etc. as the network topology, and between the terminal station (End Device) and the center station (Coordinator), it can be connected via multiple relay stations (Router). Hop communication is supported. Moreover, ZigBee provides various application interfaces for building and using networks. Therefore, if ZigBee is used, a wireless PAN can be easily constructed.
JP 2006-246202 A ZigBee Standards Organization, “ZigBee Specification”, ZigBee Alliance, June 27, 2005

  A PAN for the purpose of collecting sensor data or the like is usually configured by a network having a tree structure with a center station as a vertex, and sensor data is transmitted from a terminal station to a center station via a relay station. In that case, the communication path from the terminal station to the center station is uniquely determined due to the nature of the tree-structured network. That is, there is only one communication path. In such a case, when a failure occurs in the intermediate relay station or path, communication between the terminal station and the center station becomes impossible.

  Therefore, in ZigBee, when data is transmitted from the terminal station to the center station, if a relay station or route that cannot be communicated is discovered, communication until the center station is reached so as to avoid the relay station or route that cannot be communicated. Switch the route. In other words, the terminal station or relay station that has discovered a relay station or route that cannot communicate, searches for the presence of another relay station or center station that can communicate with itself, The route is changed so as to be connected to the relay station or the center station.

  However, such a route change in ZigBee has a disadvantage that it takes time to change the route. That is, when a terminal station or relay station finds a relay station or route that cannot communicate, it performs an active scan for the first time and searches for other relay stations or center stations that can communicate with itself. To do. Therefore, for example, it takes longer to switch the route than when searching for another relay station or center station that can communicate in advance.

  In view of the above-described problems of the prior art, an object of the present invention is to shorten the time required for switching a route when a failure occurs in the relay station or the route in a tree-structured wireless communication network system.

In order to achieve the above object, in the wireless communication network system according to the present invention,
The center station has a relay station and a terminal station included in the tree-structured network as child stations, and for each of the child stations, a center station or relay station connected as a parent station to the child station in a tree structure. A first master station, a relay station or a center station different from the first master station is a second master station, and the identification information of the first master station and the second Storage means for storing information registered in association with the identification information of the master station in advance as network definition information, and when receiving a connection request transmission from the relay station, refer to the network definition information When the local station is registered as the first master station or the second master station for the relay station, the mobile station transmits an acceptance response to the connection request to the relay station, and sends the relay station to the network. Together it is pressurized, and a networking means for transmitting the network definition information stored in the storage unit to the relay station,
The relay station receives a connection request from the slave station, with the storage means for storing the network definition information transmitted from the center station, and any of the other relay stations and terminal stations other than the own station as a slave station. If the local station is registered as the first master station or the second master station of the slave station with reference to the network definition information, an acceptance response to the connection request of the slave station is transmitted. Network construction means for transmitting the network definition information stored in the storage means to the slave station when the slave station is the relay station.
The terminal station performs a neighbor search, transmits a connection request to the relay station that has responded to the neighbor search, and when receiving an acceptance response to the connection request from the relay station, the relay station that has transmitted the acceptance response Network construction means for joining the network with the station as the parent station of the station is provided.

  In a tree-structured wireless communication network system, when a failure occurs in the relay station or the route, the time required for the route switching can be shortened.

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

<Configuration of wireless communication network system>
FIG. 1 is a diagram illustrating an example of a configuration of a wireless communication network system according to an embodiment of the present invention. As shown in FIG. 1, the wireless communication network system 1 is configured by connecting a plurality of relay stations 20 and a plurality of terminal stations 30 in a tree shape with a center station 10 as a vertex.

  In FIG. 1, a solid line connecting the center station 10 and the relay station 20, a solid line connecting the relay stations 20, and a solid line connecting the relay station 20 and the terminal station 30 connect the center station 10 and the terminal station 30. It indicates that it is the main communication channel. Further, the broken line connecting the relay stations 20 and the broken line connecting the relay station 20 and the terminal station 30 indicate that they are backup communication paths that are switched and used when a failure occurs in the main communication path. Yes.

  In the wireless communication network system 1, communication between the center station 10 and the terminal station 30 is performed via the relay station 20 in principle. In wireless communication, interposing one or more relay stations 20 means that the communicable area of the center station 10 is expanded, and the terminal station 30 can be arranged at a location farther from the center station 10. It becomes like this. Note that communication performed through one or more relay stations 20 is referred to as multi-hop communication.

  In the present specification, the center station 10, the relay station 20, and the terminal station 30 are collectively referred to as communication stations hereinafter. In FIG. 1, of two communication stations that are directly connected by a solid line or a broken line wireless communication path, a communication station that includes the center station 10 and is closer to the center station 10 is called a parent station. A communication station far from the remote station is called a slave station.

  The characteristics of the network in the wireless communication network system 1 are as follows. First, the main communication path from the center station 10 to the terminal station 30 is in a tree shape, and secondly, one slave station is in principle a plurality of master stations. Is connected.

  Here, the plurality of master stations indicate a master station connected to the master station by itself and a master station connected by a backup communication path. Further, in the case of the relay station 20 of the first hop from the center station 10, the parent station of the relay station 20 is only the center station 10, and therefore, between the center station 10 and the relay station 20 of the first hop, There is no directly connected backup communication path. However, as the backup communication path, a communication path with another relay station connected to the center station 10 may be used.

  In the wireless communication network system 1 of FIG. 1, the terminal station 30 is connected to a data generation source such as a sensor (not shown). Then, the terminal station 30 transmits the data generated by the data generation source to the center station 10 through the relay station 20 along the main communication path at normal times. When a failure occurs in the main communication path connecting the certain slave station (terminal station 30 or relay station 20) and the master station (relay station 20) or in the master station itself, the slave station transmits the data to the backup communication path. Send to the master station connected with. By doing so, data transmitted from the terminal station 30 is delivered to the center station 10 even when a failure occurs in the main communication path or the relay station 20 on the way.

  In the wireless communication network system 1 according to the present embodiment described above, the specifications of physical layer and MAC layer communication performed between any two communication stations conform to the IEEE 802.15.4 standard. .

  In the example of the wireless communication network system 1 shown in FIG. 1, the main communication path from the center station 10 to the terminal station 30 is a communication path having a three-hop configuration in which two relay stations 20 are interposed. However, they need not all have the same number of hops, and need not be limited to 3 hops. Further, there may be a terminal station 30 connected to the center station 10. There may be a plurality of master stations connected to one slave station via a backup communication path.

<Block configuration of center station, relay station and terminal station>
FIG. 2 is a diagram showing an example of a block configuration of the center station 10, the relay station 20, and the terminal station 30 according to the embodiment of the present invention. As shown in FIG. 2, the center station 10, the relay station 20, and the terminal station 30 are configured to include communication units 110, 210, 310, processing units 120, 220, 320, and storage units 130, 230, 330, respectively. The

  Here, the communication units 110, 210, and 310 are a transmission / reception unit (not shown) that transmits and receives a carrier wave, a channel selection unit (not shown) that selects a signal of a predetermined channel, and a conversion between a carrier signal and a digital signal. A modulation / demodulation unit (not shown) for performing communication signal processing in the physical layer mainly defined by the IEEE 802.15.4 standard is executed.

  The processing units 120, 220, and 320 include a CPU (Central Processing Unit) (not shown) and a memory (not shown) including a semiconductor RAM (Random Access Memory) and a flash memory. A predetermined program created in advance is stored in the memory. The CPU realizes the functions that the processing units 120, 220, and 320 should have by executing the program.

  The storage units 130, 230, and 330 are configured to include a semiconductor RAM, a flash memory (not shown), and the like, and store information processed by the processing units 120, 220, and 320 in the form of a table or the like. The storage units 130, 230, and 330 and the memories of the processing units 120, 220, and 320 may be configured as a physically integrated storage device. The storage units 130, 230, and 330 may include a hard disk device as necessary.

  Further, as shown in FIG. 2, in the center station 10, the processing unit 120 includes processing function blocks such as a data communication processing unit 121, a network construction processing unit 122, and a frequency change processing unit 123. The storage unit 130 also stores information such as network definition information 131, routing information 132, and adjacent station information 133.

  In the relay station 20, the processing unit 220 includes processing functions such as a data communication processing unit 221, a network construction processing unit 222, a route switching processing unit 223, a route return processing unit 224, a roaming processing unit 225, and a frequency change processing unit 226. Consists of blocks. The storage unit 230 stores information such as network definition information 231, routing information 232, parent station information 233, and adjacent station information 234.

  In the terminal station 30, the processing unit 320 includes processing functions such as a data communication processing unit 321, a network construction processing unit 322, a route switching processing unit 323, a route return processing unit 324, a roaming processing unit 325, and a frequency change processing unit 326. Consists of blocks. In addition, the storage unit 330 stores information such as relay station definition information 331, parent station information 332, and adjacent station information 333.

<Functional overview of processing function block>
In the center station 10, the relay station 20, and the terminal station 30 described above, the data communication processing units 121, 221 and 321 control data communication performed between the communication stations. Here, the data communication control is not limited to data transmission / reception control but also includes protocol control in the MAC layer and the network layer. However, the protocol control in the network layer excludes those related to the function of the processing function block described below. Note that the details of the processing in the data communication processing units 121, 221 and 321 can be realized according to a general known technique, and thus description thereof is omitted in this specification.

  Further, the processing of the network construction processing units 122, 222, and 322 is processing for causing the relay station 20 or the terminal station 30 to participate in the network managed by the center station 10 and acquiring the routing information and the like. It is executed in each of the relay station 20 and the terminal station 30. The processing contents of the network construction processing units 122, 222, and 322 will be separately described in detail with reference to FIGS.

  The processing of the path switching processing units 223 and 323 determines that the slave station (the terminal station 30 or the relay station 20) has a failure in the master station (the relay station 20) or its communication path in communication with the master station. Is a process of switching the communication path to a backup communication path, and is executed in each of the relay station 20 and the terminal station 30. The processing contents of the route switching processing units 223 and 323 will be described separately in detail with reference to FIGS.

  The processing of the route restoration processing units 224 and 324 is performed when the slave station (the terminal station 30 or the relay station 20) has been rerouted so as to communicate with the master station connected via the backup communication path. Is performed at each of the relay station 20 and the terminal station 30. The processing contents of the route return processing units 224 and 324 will be described separately in detail with reference to FIGS. 17 and 18.

  The processing of the roaming processing units 225 and 325 is processing for connecting the terminal station 30 to the center station 10 through a communication channel other than the main communication channel or backup communication channel registered at the time of network construction. Each of 30 is executed. The processing contents of the roaming processing units 225 and 325 will be described separately in detail with reference to FIG.

  The processing of the frequency change processing units 123, 226, and 326 is processing for changing the frequency of a communication channel that is being used in communication between the center station 10 and the terminal station 30. It is executed in each terminal station 30. The processing contents of the frequency change processing units 123, 226, and 326 will be described separately in detail with reference to FIGS.

<Configuration of network information and relay station definition information>
FIG. 3 is a diagram showing an example of the configuration of the network definition information 131 and 231 and the relay station definition information 331. In the following, first, FIG. 3A shows an example of a network configuration in the wireless communication network system 1, and FIG. 3B shows a network definition in accordance with the network configuration example of FIG. An example of the configuration of the information 131 and 231 is shown, and FIG. 3C shows an example of the configuration of the relay station definition information 331.

  In FIG. 3A, the circled x represents the center station 10, and ZC represents its address. A double circle (◎) represents the relay station 20, and ZRi (i = 1, 2,...) Represents its address. A circle (O) represents the terminal station 30, and ZDj (j = 1, 2,...) Represents its address.

  Here, each communication station (center station 10, relay station 20, and terminal station 30) is assigned a static address that does not overlap each other, and each communication station assigns the assigned address to a non-volatile memory such as a flash memory. It is assumed to be stored in a memory (may be a part of the area of the storage units 130, 230, and 330). Then, after the communication station once joins the network, the address is not changed even if the communication station is disconnected from the network or rejoins when switching the route. Therefore, in the wireless communication network system 1, a communication station can be uniquely identified by the address.

  Therefore, hereinafter, the center station 10 whose address is ZC is described as “center station ZC” or simply “ZC”, and the relay station 20 whose address is ZRi is referred to as “relay station ZRi” or The terminal station 30 whose address is ZDj is simply described as “terminal station ZDj” or simply “ZDj”.

  Next, as shown in FIG. 3 (b), the network definition information 131, 231 includes, for each relay station 20 included in the network managed by the center station 10, the master station when the relay station 20 is a slave station. Is associated information. In the present embodiment, a plurality of master stations are associated with a single slave station, except for the case where the center station 10 becomes a master station. Degree information is retained.

  Here, the priority is information for identifying whether the parent station is a parent station connected through the main communication path or a parent station connected through the backup communication path, and is the highest priority. The master station with a high is the master station connected through the main communication path. Therefore, in the present embodiment, a plurality of relay stations 20 can be set as the master station connected through the backup communication path. In the example of FIG. 3B, the priority “1” is the highest priority, and the priority “2” is the next highest priority. The same priority may be set.

  Note that the number of hops from the center station 10 of the parent station connected via the main communication path may be different from the number of hops from the center station 10 of the parent station connected via the backup communication path. However, the relay station 20 included in the network connected to the lower side of the master station connected via the main communication path cannot be the master station connected via the backup communication path.

  FIG. 3B is an example of the network definition information 131 and 231 corresponding to the example of FIG. According to FIG. 3B, the relay stations ZR1 and ZR3 are each connected to one parent station (center station ZC), and the relay stations ZR2 and ZR4 are respectively connected to two parent stations (relay stations ZR1 and ZR3). )It is connected to the. Further, the master station connected through the main communication path of the relay station ZR2 is ZR1, and the master station connected through the main communication path of the relay station ZR4 is ZR3.

  In FIG. 3B, the “No.” column simply contains a number indicating the order, and the “No.” column does not have a significant function. Is not necessary. 3 (c), FIG. 4, FIG. 5 and the like which will be described later have a “No.” column, similarly, the “No.” column has no particularly significant function.

  As described above, the network definition information 131 and 231 is information defining the main communication path and the backup communication path between the center station 10 and the relay station 20.

  Note that the information that is the basis of the network definition information 131, 231 predicts the communication quality and traffic between the communication stations when the center station 10 and the relay station 20 are installed in a premises such as a factory, for example. It is set by a system administrator after being measured or actually measured. The set information is first stored in the storage unit 130 of the center station 10 as the network definition information 131, and then the center station 10 and the relay station 20 execute the processing of the network construction processing units 122 and 222. In the process, it is distributed to each relay station 20 and stored in the storage unit 230 of each relay station 20 as network definition information 231.

  Note that the relay station 20 may store the network definition information 231 in a non-volatile memory area of the storage unit 230 from the beginning instead of setting the network definition information 231 by distribution from the center station 10. In this case, part of the processing can be omitted in the network construction processing (see FIG. 6 and the like) described later.

  In the storage unit 330 of the terminal station 30, relay station definition information 331 is stored as information replacing the network definition information 131 and 231. The relay station definition information 331 is information on a plurality of master stations held by each terminal station 30, and the master station information includes a master station address and a priority. At this time, the master station with the highest priority address is the master station connected through the main communication channel, and the master stations with other addresses are master stations connected through the backup communication channel.

  FIG. 3C is an example of the relay station definition information 331 held by the terminal station ZD1 in the example of FIG. According to FIG. 3C, the terminal station ZD1 is connected to two master stations (relay stations ZR2 and ZR4), of which the master station connected via the main communication path is ZR2 and is connected via the backup communication path. The parent station is ZR4.

  The relay station definition information 331 is set by a system administrator or the like in consideration of the arrangement position of the relay station 20 and the arrangement position of the terminal station 30, and is stored in a non-volatile storage area such as a flash memory of the storage unit 330. Remembered.

<Configuration of routing information>
FIG. 4 is a diagram showing an example of the configuration of the routing information 132 and 232. As shown in FIG. 4, the routing information 132, 232 is information in which the adjacent destination address is associated with the destination address. Here, the transmission destination address is the address of the communication station that is the transmission destination when information is transmitted from the local station to a communication station located in the lower direction of the tree structure, and the adjacent transmission destination address is the transmission destination. This is the address of a communication station that is included in the transmission path for transmitting information and is directly adjacent to the local station. In other words, the transmission address is a network layer transmission address, and the adjacent transmission destination address is a MAC layer transmission address.

  That is, when the center station 10 or the relay station 20 transmits information to a communication station located in the lower direction of the tree structure, the routing information 132 and 232 should be a transmission destination among neighboring communication stations with which the local station can communicate. This is information indicating a communication station, and the communication station may be not only a communication station connected via a main communication path but also a communication station connected via a backup communication path.

  That is, the routing information 132 and 232 are created when the network is constructed by the network construction processing units 122 and 222 and stored in the storage units 130 and 230. Further, the routing information 132 and 232 are changed as appropriate when the route is changed by the route switching processing unit 223, the route return processing unit 224, and the roaming processing unit 225.

  FIG. 4 is an example of the routing information 132 held in the center station ZC in the network of FIG. 3A. Here, all lower communication stations are connected by the main communication path. .

  Further, the relay station 20 and the terminal station 30 hold parent station information 233 and 332 (see FIG. 2), respectively. The parent station information 233, 332 indicates the address of the parent station that should be the transmission destination at that time among the adjacent communication stations with which the own station can communicate when transmitting information from the own station to the upper communication station. Yes. In other words, the master station information 233 and 332 indicates the address of the master station that is actually the communication destination of the slave station at that time regardless of the main communication path or backup communication path.

  The master station information 233 and 332 are created when the network construction processing is executed by the network construction processing units 222 and 322, as with the routing information 132 and 232. When the route is changed by the units 224 and 324 and the roaming processing units 225 and 325, the route is changed as appropriate. Note that the adjacent station information 234 and 333 to be described next substantially include the contents of the master station information 233 and 332, and therefore can be substituted.

<Configuration of adjacent station information>
FIG. 5 is a diagram showing an example of the configuration of the adjacent station information 133, 234, 333. Neighboring station information 133, 234, 333 is created in each communication station, and for a communication station located in the vicinity of the communication station (hereinafter referred to as an adjacent station), the address of the adjacent station, the type of the adjacent station, and the adjacent station Is stored information such as connection status, LQI (Link Quality Indicator), hop count, channel number, transmission failure count, and the like.

  Here, the type of the adjacent station is information indicating whether the adjacent station is the center station 10, the relay station 20, or the terminal station 30. The connection state is information indicating the parent-child relationship registered in the routing information 132, 232 and the master station information 233, 332 at that time. When the adjacent station is the master station, the master station connection is established. If the slave station is a slave station, the slave station is connected, and the other cases are not connected. The LQI is information indicating the quality of communication with the adjacent station, and may be, for example, RSSI (Received Signal Strength Indicator) obtained from the communication units 110, 210, and 310. The number of hops is the number of hops in the communication path that connects the center station 10 and its adjacent stations. The channel number is a number for selecting the frequency of the carrier wave when communicating with the adjacent station. Also, the number of transmission failures stores the number of failures when information is transmitted to the adjacent station.

  FIG. 5 shows adjacent station information 234 held in the relay station ZR1 in the network of FIG. 3A. In this case, ZC, ZR2, ZR3, ZR4, and ZD1 are registered as adjacent stations of ZR1. ing.

<Network construction processing>
Hereinafter, the network construction process executed by the network construction processing units 122, 222, and 322 will be described in detail with reference to FIGS. Here, the network construction process includes a network participation process in which a communication station (relay station 20 or terminal station 30) participates in the network managed by the center station 10 one by one, and the network is constructed. 1 includes routing information registration processing for registering the routing information 132 and 232.

(Network participation processing)
FIG. 6 is a diagram illustrating an example of a processing flow of network participation processing executed between the master station and the slave station. FIG. 7 is a diagram schematically illustrating a procedure for the relay station 20 and the terminal station 30 to participate in the network by executing the network participation process of FIG. 6, and FIG. 8 is a diagram illustrating the relay station 20 and the terminal station 30. It is the figure which showed typically the procedure in which a predetermined | prescribed network is constructed | assembled by repeating participation in a network. Here, for convenience of explanation, the explanation of FIG. 7 and FIG. 8 is performed prior to the explanation of FIG.

  First, in FIG. 7 (1), the system administrator determines the arrangement of the center station ZC, the relay stations ZR1 to ZR4, and the terminal stations ZD1 and ZD2, and stores the network definition information 131 corresponding to the arrangement in the center station ZC. Set the initial state of the network. Then, the center station ZC is turned on to start its operation, and then the relay stations ZR1 to ZR4 and the terminal stations ZD1 and ZD2 are joined to the network to construct a predetermined network.

  Hereinafter, in the example described with reference to FIG. 7 and the like, the network of the example of FIG. In the initial state, it is assumed that the center station ZC holds the network definition information 131 in the example of FIG. 3B, and the relay stations ZR1 to ZR4 do not hold the network definition information 231. The following figure is described.

  Next, in FIG. 7 (2), the relay station ZR1 close to the center station ZC first performs an active scan. Here, the active scan means a peripheral search for searching for a communication station that can communicate with the periphery, and the communication station outputs a carrier wave of a predetermined signal and obtains a response from the peripheral communication station that has received it. Refers to processing.

  Next, in FIG. 7 (3), the center station ZC and the relay stations ZR2 to ZR4 existing in the vicinity of the relay station ZR1 respond to the active scan from the relay station ZR1. However, the relay stations ZR2 to ZR4 do not respond when the power is not turned on or when the relay stations are not the master station (including the case where the network definition information 231 is not held).

  Next, in FIG. 7 (4), the relay station ZR1 sequentially transmits an association request to the center station ZC and the relay stations ZR2 to ZR4 that responded to the active scan. Here, the associate request means a connection request, and in the present embodiment, for the partner communication station, forming a parent-child communication path with the partner communication station as the master station and itself as the slave station. Say what you want.

  Next, in FIG. 7 (5), each of the center station ZC and the relay stations ZR2 to ZR4 that has received the association request determines whether or not a communication path can be formed with the relay station ZR1 as its own slave station. If the communication path can be formed, a response for accepting the associate request is transmitted, and if not, a response for rejecting the associate request is transmitted.

  Here, the center station ZC and the relay stations ZR2 to ZR4 that have received the association request refer to the network definition information 131 and 231 to determine whether or not they are registered in the master station information of the relay station ZR1. If registered as parent station information, a communication path of parent-child relationship can be formed, and an association request acceptance response is transmitted. At this time, the priority in the master station information is not necessarily the highest.

  In the example of the network definition information 131 in FIG. 3B, since the parent station is ZC only when the slave station is ZR1, only the center station ZC transmits an association request acceptance response, and the relay station ZR2 to ZR4 transmit an association request rejection response. Further, the relay stations ZR2 to ZR4 also transmit an association request rejection response even when the network definition information 231 is not held yet. The relay stations ZR2 to ZR4 may ignore (no response) the received association request without transmitting the association request rejection response.

  Next, in FIG. 7 (6), the relay station ZR1 is connected as a slave station of the center station ZC, and the center station ZC transmits the network definition information 131 to the relay station ZR1, and the relay station ZR1 , And is stored in the storage unit 230 as network definition information 231.

  Through the procedure described above, the relay station ZR1 has joined the network managed by the center station ZC.

  Next, in FIG. 8A, in addition to the relay station ZR1, the relay station ZR3 joins the network according to the same procedure as in FIG.

  Further, in FIG. 8 (2), the relay stations ZR2 and ZR4 join the network according to the same procedure. However, at this time, it is assumed that the relay station ZR2 is connected to the parent station ZR3 which is not the highest priority because there is some failure in the communication path with the relay station ZR1. In that case, a route return process described later is executed at that time.

  The route restoration process reserved for execution is executed at predetermined time intervals, for example, to check whether or not the failure of the communication path between the relay station ZR2 and the relay station ZR1 has been recovered, and the failure is recovered. In this case, as shown in FIG. 8 (3), the master station of the relay station ZR2 is returned (switched) to the relay station ZR1 which is the master station having the highest priority.

  Finally, the terminal stations ZD1 and ZD2 join the network according to the same procedure as in FIG. However, the network construction here is network construction in the physical layer or MAC layer, and in order to complete the network construction in the network layer, it is necessary to perform a routing information registration process described later.

  In the network construction procedure described above, the active scan does not necessarily have to be performed from the relay station ZR1, but in general, the number of hops until connection to the center station ZC is small. It is more efficient to start from a relay station that is physically located near the relay station or the master station. Further, the return to the relay station ZR1 which is the highest priority master station of the master station in FIG. 8 (3) may be performed after the terminal stations ZD1 and ZD2 in FIG. 8 (4) join the network. .

  Next, network participation processing executed by the center station 10, the relay station 20, and the terminal station 30 in order to realize the above network construction procedure will be described with reference to FIG. In FIG. 6, the processing of the relay station 20 or the terminal station 30 that intends to participate in the network is shown as the processing of the slave station, and the processing of the center station 10 or another relay station 20 that functions as the parent station is the parent station. Shown as station processing.

  As shown in FIG. 6, the network participation process is started when a slave station that wants to participate in the network performs an active scan (step S01: see FIG. 7 (2)). On the other hand, the center station 10 or the other relay station 20 that has received the active scan (hereinafter, these parent station candidate communication stations are also simply referred to as a parent station for convenience) responds to the active scan (step S02: FIG. 7 (3)).

  Next, when there is a master station that responds to the active scan (Yes in step S03), the slave station selects one of the responding master stations (step S04), and for the selected master station The associate request is transmitted (step S05: refer to FIG. 7 (4)). When there are a plurality of master stations responding to the active scan, when selecting the master stations one by one, the neighboring station information 234 and 233 are preferably selected in order of increasing LQI.

  On the other hand, the master station that has received the association request refers to the network definition information 131 and 231 to determine whether or not it is registered in the master station information when the communication station that has transmitted the association request is a slave station. Based on the result, an acceptance or rejection response to the associate request is transmitted (see step S06: FIG. 7 (5)). At this time, when self is registered in the master station information, an acceptance response is transmitted. When self is not registered in the master station information, or when the network definition information 231 is not held, a rejection response is transmitted. Send.

  However, when the communication station that transmitted the association request is the terminal station 30, the network definition information 131, 231 held by the parent station does not include the parent station information about the terminal station 30. Therefore, when the slave station that has transmitted the association request is the terminal station 30, the master station may in principle transmit an acceptance response. Alternatively, the master station may transmit an acceptance response when the LQI for the slave station is equal to or greater than a predetermined value with reference to the adjacent station information 133 and 234.

  Next, when the slave station receives an acceptance response to the associate request (Yes in step S07), the slave station sets the address of the master station that transmitted the acceptance response in the master station information 233 and 332 (step S08). When the slave station receives a rejection response to the associate request (No in step S07), the slave station determines whether or not all the master stations responding to the active scan are selected in step S04 (step S16). Are not selected (No in step S16), the process returns to step S04, and the processes after step S04 are repeated.

  On the other hand, when the master station transmits an acceptance response to the associate request (Yes in step S09) and the slave station is the relay station 20 (Yes in step S10), the master station further holds it. The network definition information 131, 231 is transmitted to the slave station (step S11: see FIG. 7 (6)). The master station does not transmit an acceptance response to the associate request (No in step S09), or when the slave station is not the relay station 20 (that is, when it is the terminal station 30). (No in step S10), the master station does not transmit the network definition information 131, 231 to the slave station.

  In response to the processing of the master station, when the slave station is a relay station (Yes in step S12), the slave station receives the network definition information 131, 231 transmitted from the master station (step S13), and Store in the storage unit 230. Further, when the slave station is not a relay station (that is, when it is the terminal station 30) (No in step S12), the network definition information 131, 231 is not transmitted from the master station. Therefore, the process of step S13 is skipped.

  Next, the slave station refers to its own network definition information 231 or relay station definition information 331 subsequent to step S12 or step S13, and the priority of the master station registered in the master station information 233, 332 is the highest. (Step S14), and when the priority of the master station is highest (Yes in Step S14), the slave station successfully joins the network, and the process ends. If the priority of the master station is not the highest (No in step S14), the route return process is executed (step S15), and then the slave station successfully joins the network and the process ends. The route return processing will be described in detail separately with reference to FIGS. 17 and 18.

  On the other hand, if there is no master station that responds to the execution of the active scan (step S01) (No in step S03), or the acceptance response is not received for the association request, and the active scan is not performed. If all the responding master stations have been selected (Yes in step S16), an error process (step S17) of network participation failure is performed and the process is terminated.

  Here, the error processing is processing for notifying an application or the like that the network participation has failed. Further, when the slave station succeeds in joining the network, the network construction of the procedure shown in FIG. 8 can be realized by sequentially executing the above network joining processing in all the communication stations. .

  In the above description, the relay station 20 does not hold the network definition information 231 in the initial state. However, as described above, the relay station 20 stores in advance in the nonvolatile memory area of the storage unit 230. It may be held. In that case, in FIG. 6, the slave station and the master station can omit the execution of the active scan (step S01) and the response to the active scan (step S02), respectively. The master station and the slave station can omit transmission / reception of network definition information (steps S11 and S13).

(Routing information registration process)
FIG. 9 shows an example of a processing flow of routing information registration processing executed between the master station and the slave station. FIG. 10 registers the routing information 132 and 232 in the center station 10 and the relay station 20. FIG. 11 is a diagram schematically illustrating the procedure, and FIG. 11 is a diagram illustrating an example of the routing information 132 and 232 registered in the center station 10 and the relay station 20, respectively. Here, for convenience of explanation, the explanation of FIGS. 10 and 11 will be made prior to the explanation of FIG.

  In order to register the routing information 132 and 232 in the center station 10 and the relay station 20, a route request command is transmitted from the lower communication station in the tree structure to the center station 10. The route request command is a command for registering routing information up to the own station in the upper communication station.

  In general, a message such as a route request command transmitted in a network is attached with a source address and a destination address of the network layer. In this case, the source address is the address of the communication station that originally transmitted the message, and the destination address is the address of the communication station that finally receives the message. When the message is physically transmitted and received between the two communication stations, the addresses of the two communication stations are further added to the message as the source address and destination address of the MAC layer.

  Accordingly, the communication station that has received the route request command uses the communication station that has transmitted the route request command as the transmission destination based on the network layer source address and the MAC layer source address attached to the route request command. It is possible to know the destination address of the MAC layer. Therefore, the communication station that has received the route request command uses the network layer transmission source address attached to the route request command as the transmission destination address, and uses the MAC layer transmission source address as the adjacent transmission destination address. , 232 (see FIG. 11).

  Therefore, as shown in FIG. 10 (1), the terminal station ZD1 transmits a route request command to the center station ZC. The route request command is first received by the relay station ZR2, and in the relay station ZR2, information that sets the terminal station ZD1 as the transmission destination and the adjacent transmission destination as ZD1 is registered in the routing information 2322 (see FIG. 11) of the ZR2.

  In FIG. 10 (2), the route request command is transmitted to and received by the center station ZC via the relay station ZR1. In the relay station ZR1 that has received the route request command, information in which the terminal station ZD1 is the transmission destination and the adjacent transmission destination is ZR2 is registered in the routing information 2321 of ZR1 (see FIG. 11). Further, in the center station ZC, information in which the terminal station ZD1 is the transmission destination and the adjacent transmission destination is ZR1 is registered in the routing information 1321 of the ZC (see FIG. 11).

  In FIG. 10 (3), the center station ZC transmits ACK (Acknowledge) confirming that the route request command has been received to the terminal station ZD1. At this time, the ACK is transmitted to the terminal station ZD1 according to the routing information 1321, 232, and 1322 previously registered in the center station ZC, the relay station ZR1, and the relay station ZR2, respectively. Therefore, when the ACK arrives at the terminal station ZD1, it is confirmed for the first time that the registered routing information 1321, 232, and 2322 are correct.

  Therefore, in FIG. 10 (4), the routing information 2322, 2321, 1321 when the transmission destination is ZD1 is registered in the relay stations ZR2, ZR1 and the center station ZC on the route from the terminal station ZD1 to the center station ZC. It will be done.

  Next, in FIG. 10 (5), the relay station ZR2 transmits a route request command to the center station ZC, whereby routing information 2321 and 1321 when the transmission destination is ZR2 are registered. Further, when the relay station ZR1 transmits a route request command to the center station ZC, the routing information 1321 when the transmission destination is ZR1 is registered.

  Next, in FIG. 10 (6), the terminal station ZD2 and the relay stations ZR4 and ZR3 similarly transmit the route request command to the center station ZC, so that the transmission destinations are ZD2, ZR2, and ZR4, respectively. The routing information 2324, 2323, and 1321 when registering are registered. This completes the registration of all routing information.

  In the above routing information registration process, in order to acquire the routing information as the transmission destination of the relay station 20, it is necessary to transmit a route request command from the relay station 20 to the center station. The station 20 may not necessarily need to transmit a route request command to the center station.

  In order to realize this, when the route request command transmitted from the terminal station 30 passes through the relay station 20, the relay station 20 adds the address to an area other than the source address area of the MAC layer of the route request command. In other words, the address is added to the route request command every time it passes through the relay station 20. Therefore, the higher-order relay station 20 or center station 10 that has received the route request command can acquire route information from the terminal station 30 to the relay station 20 or the center station 10, and the route information. Thus, routing information whose destination is the terminal station 30 or the relay station 20 on the route can be registered.

  Such a method for registering routing information is effective in shortening the routing information registration process because it is only necessary to transmit a route request command from the terminal station 30.

  As shown in FIG. 11, through the above procedure, the routing information 1321 is registered in the center station ZC, and the routing information 2321 to 2324 is registered in the relay stations ZR1 to ZR4, respectively.

  Next, a routing information registration process executed by the center station 10, the relay station 20, and the terminal station 30 in order to realize the above routing information registration procedure will be described with reference to FIG. In FIG. 9, the process of the relay station 20 or the center station 10 that registers routing information is shown as the process of the master station, and the process of the terminal station 30 that transmits the route request command or the relay station 20 on the lower side is Shown as station processing.

  As shown in FIG. 9, the routing information registration process is started when the slave station transmits a route request command (step S20). When receiving the route request command (step S21), the master station uses the network layer source address and the source MAC layer address attached to the route request command as the destination and the adjacent destination, and the routing information 132. , 232 (step S22).

  Next, when the master station itself is the relay station 20 (Yes in step S23), the received route request command is further transmitted to a higher-order master station (relay station 20 or center station 10) ( Step S24) waits for the reception of an ACK returned from the upper master station (step S25). Further, when the parent station is not the relay station 20 (No in step S23), that is, when it is the center station 10, it is not necessary to execute steps S24 and S25. When the master station receives the ACK returned from the higher-order master station (Yes in step S25), the master station transmits ACK to the slave station (step S26), and ends the routing information registration process as the master station. Further, when the master station does not receive the ACK from the higher-order master station (No in step S25), the master station executes error processing (step S27) and ends the process.

  In the error processing in step S27, for example, a NAK (Negative Acknowledge) indicating that an ACK has not been received from the upper master station is transmitted to the slave station. In this case, information such as failure in registration of routing information in the upper master station can be transmitted to the slave station more quickly. Alternatively, the error processing in step S27 may be processing (no processing) that does nothing. Even if the error processing is not processed, the slave station monitors the ACK reception by timeout, and can detect the registration failure of the routing information in the upper master station by detecting the timeout.

  On the other hand, after transmitting the route request command (step S20), the slave station waits for the ACK to be returned from the parent station, and when the returned ACK is received (Yes in step S28), the routing information registration is successful. As a result, the process is terminated. If no ACK is received from the master station (No in step S28), an error process is executed (step S29), and the process ends. The error process is a process for notifying an application or the like that the participation in the routing information registration has failed.

<Route switching process>
Hereinafter, the route switching process executed in the relay station 20 or the terminal station 30 will be described in detail with reference to FIGS. Here, FIG. 12 is a diagram illustrating an example of a processing flow of the route switching processing.

  The path switching process is a process of changing the initially set path so as to avoid a failure when a failure occurs in a communication path connecting communication stations or in the communication station itself in a once constructed network. Therefore, the path switching process is performed when, for example, a certain relay station 20 or terminal station 30 transmits information to its parent station a predetermined number of times, but no ACK is returned. It is executed in the relay station 20 or the terminal station 30 that has not received the ACK reply.

  In the following description of FIG. 12, for convenience of explanation, the relay station 20 or the terminal station 30 that is executing the path switching process is referred to as a switching communication station. In addition, a part of the routing information 132 and 232 and the parent station information 233 and 332 of the related communication station is changed by the route switching process.

  As shown in FIG. 12, when starting the path switching process, the switching communication station first discards its parent station information 233 and 332 (step S41), and when it is the relay station 20 (in step S42). (Yes), the communication with the slave station is cut off by itself, or the reception of information from the slave station is stopped by transmitting an ACK indicating that the upper communication path is disconnected to the slave station (step S43). When the switching communication station itself is not the relay station 20, that is, when it is the terminal station 30 (No in step S42), the switching communication station skips the process of step S43.

  Next, the switching communication station refers to the network definition information 231 (when it is the relay station 20) or the relay station definition information 331 (when it is the terminal station 30), in descending order of priority of the master station. An associate request is transmitted to the master station (step S44). When the acceptance response to the associate request is received from the master station that transmitted the associate request (Yes in step S45), the switching communication station sets the address of the master station in its own master station information 233, 332 (step S54). As described above, the master station connected to the switching communication station is switched.

  Therefore, the switching communication station transmits a route request command from the local station to the center station 10 and executes a routing information registration process (step S55). Further, the communication station connected to the lower side of the own station also transmits a route request command to the center station 10 and executes a routing information registration process. As a result, in the communication station on the route from the switching communication station to the center station 10, the routing information 132 and 232 whose destinations are the switching communication station and the lower communication station of the switching communication station are changed.

  Also in this case, in the routing information registration process (step S55), the routing information registration method added at the end of the description of FIG. 10 can be used. In that case, it is possible to omit the transmission of the route request command starting from the switching communication station and the relay station 20 connected to the lower level of the switching communication station. The route request command is a terminal station connected to the lower level of the switching communication station. It is only necessary to transmit a route request command from 30 to the center station 10.

  When the above routing information registration process is completed, the switching communication station resumes reception from the slave station (step S56), and ends the process as a successful path switching.

  On the other hand, the switching communication station does not receive an acceptance response even if it transmits an association request to the parent station (No in step S45), and has not transmitted an association request to all the parent stations (step S46). No), the process returns to step S44. Further, the switching communication station does not receive an acceptance response even if it transmits an association request to the parent station (No in step S45), and when it has transmitted an association request to all the parent stations (Yes in step S46). ), An active scan is performed (step S47), and a communicable communication station existing in the vicinity of the local station is searched.

  When there is a master station that responds to the active scan (a communication station that is a neighboring communication station and is not a communication station that is located below it) (Yes in step S48), one of the responding master stations Is selected (step S49), and an association request is transmitted to the selected master station (step S50). When the switching communication station receives an acceptance response to the association request from the master station (Yes in step S51), the switching communication station moves the process to step S54.

  On the other hand, when the acceptance response to the association request is not received from the master station (No in step S51), the switching communication station determines whether or not all the master stations responding to the active scan are selected in step S49 (step S49). S52) If not all of the master stations have been selected (No in step S52), the process returns to step S49, and the processes in and after step S49 are repeated.

  Further, when all the master stations are selected in the determination in step S52 (Yes in step S52), or when there is no master station that responds to the active scan in the determination in step S48 (No in step S48), switching is performed. Since there is no connectable master station, the communication station performs error processing (step S53), and ends the processing as a path switching failure. Error processing is processing for notifying an application or the like that route switching has failed.

  FIG. 13 is a diagram schematically illustrating an example of a path switching procedure in the case of a terminal station path disconnection.

  As shown in FIG. 13 (1), first, it is assumed that the terminal station ZD1 detects a path disconnection between the terminal station ZD1 and the relay station ZR2. In this case, the terminal station ZD1 executes the path switching process shown in FIG. Then, the terminal station ZD1 refers to the relay station definition information 331, transmits an association request to the parent station with the next highest priority, that is, the parent station connected through the backup communication path, and receives an acceptance response from the parent station. Is received, as shown in FIG. 13 (2), the priority is connected to the next master station. That is, the route of terminal station ZD1-relay station ZR2 is switched to the route of terminal station ZD1-relay station ZR4, which is a backup communication path.

  Next, in FIG. 13 (3), the terminal station ZD1 transmits a route request transmission command toward the center station ZC along the switched path. Then, the relay stations ZR4, ZR3 and the center station ZC existing on the route change the adjacent transmission destination for the routing information 2324, 2323, 1321 when the transmission destination is the terminal station ZD1. In FIG. 13 (4), it is confirmed that the ACK is transmitted from the center station ZC to the terminal station ZD1, and the path is switched.

  FIG. 14 schematically shows an example of a route switching procedure (first half part) in the case of inter-relay station route disconnection, and FIG. 15 shows an example of a route switching procedure (second half part) in the case of inter-relay station route disconnection. FIG.

  As shown in FIG. 14 (1), it is assumed that the relay station ZR2 first detects a path disconnection between the relay stations ZR2 and ZR1. In this case, the relay station ZR2 executes the path switching process shown in FIG. Then, the relay station ZR2 refers to the network definition information 231 and transmits an association request to the parent station having the next highest priority, that is, the parent station connected through the backup communication path, and receives an acceptance response from the parent station. Then, as shown in FIG. 14 (2), the priority is connected to the next master station. That is, the route of relay stations ZR2-ZR1 is switched to the route of relay stations ZR2-ZR3, which is a backup communication path. At this time, since the relay station ZR2 blocks reception from the slave station, the path between the terminal station ZD1 and the relay station ZR2 on the slave station side is also disconnected.

  Next, in FIG. 14 (3), the relay station ZR2 transmits a route request transmission command toward the center station ZC along the switched path. Then, in FIG. 14 (4), it is confirmed that the ACK is transmitted from the center station ZC to the relay station ZR2 and the path is switched.

  Next, in FIG. 15 (5), since the terminal station ZD1 is in a disconnected state, the terminal station ZD1 executes the network participation process shown in FIG. In this case, the terminal station ZD1 is connected to the relay station ZR2 which is the parent station having the highest priority. Next, in FIG. 15 (6), the terminal station ZD1 transmits a route request transmission command to the center station ZC, and changes the routing information 232 and 132 related to the related communication stations. In FIG. 15 (7), it is confirmed that the ACK is transmitted from the center station ZC to the terminal station ZD1, and the path is switched.

  Note that variations may occur in the procedures shown in FIGS. 14 (1) to 15 (7). For example, when the relay station ZR2 fails to connect to the relay station ZR3, or when the connection is delayed, the terminal station ZD1 is connected to the terminal station ZD1-relay as shown in FIG. The path disconnection between the stations ZR2 is detected first. In this case, as shown in FIG. 15 (6 '), the terminal station ZD1 is connected to the relay station ZR4, which is the next highest priority station. After that, as shown in FIG. 15 (7 '), the relay station ZR2 connects to the relay station ZR3, which is the next highest priority station.

  FIG. 16 is a diagram schematically illustrating an example of a path switching procedure in the case of center station path disconnection.

  As shown in FIG. 16 (1), it is assumed that the relay station ZR1 detects a path disconnection between the relay station ZR1 and the center station ZC. In this case, the relay station ZR1 is not set with the parent station with the next highest priority, so as shown in FIG. 16 (2), the relay station ZR1 is connected to the relay station ZR2 which is the child station. The communication path is disconnected or ACK indicating that the upper communication path is disconnected is transmitted to the slave station ZR2. Then, as shown in FIG. 16 (3), the relay station ZR2 that is a child station of the relay station ZR1 executes the path switching process shown in FIG. 12, and the relay station ZR2 is the parent station with the next highest priority. Connect to a certain relay station ZR3.

  In this case as well, the procedure may vary as in the case of FIG. For example, if the relay station ZR2 fails to connect to the relay station ZR3, or if the connection is delayed, the terminal station ZD1 is connected to the terminal station ZD1-relay as shown in FIG. The path disconnection between the stations ZR2 is detected first. In this case, as shown in FIG. 16 (4 '), the terminal station ZD1 is connected to the relay station ZR4, which is the next highest priority station. Thereafter, the relay station ZR2 connects to the relay station ZR3, which is the next highest priority station.

<Route return processing>
Hereinafter, with reference to FIG. 17 and FIG. 18, the route restoration process executed in the relay station 20 or the terminal station 30 will be described in detail. Here, FIG. 17 is a diagram showing an example of the processing flow of the route restoration process, and FIG. 18 is a diagram schematically showing an example of the route restoration procedure.

  The route return process is a process for returning the connected master station to the highest priority master station when the relay station 20 or the terminal station 30 is connected to a master station that is not the highest priority master station. Note that the routing information 132 and 232 and part of the parent station information 233 and 332 of the related communication stations are changed by the route return processing.

  When the relay station 20 or the terminal station 30 refers to the network definition information 231 or the relay station definition information 331 and determines that the relay station 20 or the terminal station 30 is not connected to the parent station having the highest priority, the relay station 20 or the terminal station 30 returns the route every predetermined time. Execute the process. Hereinafter, in the description of FIG. 17, for convenience of description, the relay station 20 or the terminal station 30 that is executing the route return process is referred to as a return communication station.

  When the returning communication station starts the route returning process, it first performs an active scan (step S61). When the parent station (neighboring communication station) responding to the active scan has a highest priority parent station ( In step S62, the association request is transmitted to the highest priority master station (step S63).

  Next, when the returning communication station receives an acceptance response to the association request from the parent station (Yes in step S64), the returning communication station releases the connection with the parent station that is not the highest priority connected at that time, and FIG. The path switching process shown in FIG. 6 is executed (step S65). Then, the return communication station is connected to the highest priority parent station by the path switching process. Note that the timing at which the returning communication station releases the connection with the parent station may be before the association request is transmitted in step S63.

  When the master station (neighboring communication station) responding to the active scan does not have a master station with the highest priority (No in step S62), or when no acceptance response is received for the associate request (step In S64, the return communication station performs error processing (step S66). The error process is a process for notifying an application or the like that the route has not been returned.

  In the above route restoration processing, the relay station 20 or the terminal station 30 stores the address of the master station having the highest priority in the network definition information 231 or the relay station definition information 331. Therefore, the active scan (step S61, S62) can be omitted. At that time, the time required for the route return can be shortened.

  Subsequently, the description is made with reference to FIG. In FIG. 18 (1), the relay station ZR2 is connected to the relay station ZR3, which is a parent station that is not the highest priority parent station, and therefore performs a route return process. First, the relay station ZR2 performs an active scan. Here, the relay station ZR1, which is the highest priority parent station, responds to the active scan.

  Next, in FIG. 18B, when the relay station ZR2 transmits an association request to the relay station ZR1, the relay station ZR2 receives a permission response from the relay station ZR1. Then, the relay station ZR2 releases the connection with the relay station ZR3 and performs a path switching process. In FIG. 18 (3), the relay station ZR1 is connected to the relay station ZR1, which is the highest priority parent station, by the path switching process.

<Roaming process>
Hereinafter, the roaming procedure will be described in detail with reference to FIG. Here, FIG. 19 is a diagram schematically illustrating an example of a roaming procedure. Note that roaming is a function for causing the terminal station 30 to temporarily join the network, and when the terminal station 30 is moved to a location different from a predetermined location or when the terminal station 30 is not scheduled to be incorporated into the network. Used when connecting to the network.

  The roaming is basically realized by a procedure in which the terminal station 30 joins the network. That is, the terminal station 30 may first execute the process on the slave station side of the network participation process of FIG. In this case, the terminal station 30 may process the network participation process as if the relay station definition information 331 is present or not. The only difference is whether or not the path switching process and the path return process are executed or not executed when the terminal station 30 is disconnected or connected.

  FIG. 19 shows an example of a roaming procedure in which the terminal station ZD1 connected to the relay station ZR2 is moved to another location and used. In FIG. 19 (1), the terminal station ZD1 is disconnected from the relay station ZR2 and moved closer to the relay station ZR1. In this case, when the terminal station ZD1 holds the relay station definition information 331 (for example, refer to FIG. 3C), the terminal station ZD1 has a route to the relay station ZR4 that is the next highest priority station. Perform the switching process. However, since the distance between the terminal station ZD1 and the relay station ZR4 is large, the connection switching fails.

  Next, in FIG. 19 (2), the terminal station ZD1 performs an active scan and searches for a connectable master station. Here, the relay station ZR1 and the center station ZC respond. Next, in FIG. 19 (3), the terminal station ZD1 requests the relay station ZR1 and the center station ZC that responded to the active scan to associate. However, at this time, since the LQI of the relay station ZR1 is larger than the LQI of the center station ZC, the relay station ZR1 is requested to associate first, and the request acceptance is received from the relay station ZR1. As a result, the terminal station ZD1 is connected to the relay station ZR1.

  Next, in FIG. 19 (4), the terminal station ZD1 transmits a route request command to the center station ZC, and changes the routing information 132 and 232 in the center station ZC and the relay station ZR1. In FIG. 19 (5), an ACK is transmitted from the center station ZC to the terminal station ZD1, and the roaming path for the terminal station ZD1 is confirmed.

<Frequency change processing>
Hereinafter, the frequency changing process executed in the center station 10, the relay station 20, and the terminal station 30 will be described in detail with reference to FIGS. The frequency changing process is a process for changing the frequency channel used for communication when the radio wave condition of the frequency channel being used for communication deteriorates due to external radio waves or the like.

  In order to perform this frequency change processing, the center station 10 and the relay station 20 have a function called ED scan (Energy Detect Scan), perform ED scan at predetermined time intervals, and measure LQI and the like in mutual communication. . Then, the center station 10 collects the LQI measured by the relay station 20 and determines whether the radio wave condition is good or bad. As a result, when it is determined that the radio wave condition has deteriorated, frequency change processing is executed, and the frequency channel used for communication is changed.

  FIG. 20 is a diagram illustrating an example of a processing flow of frequency change processing executed in the center station 10, the relay station 20, and the terminal station 30. The frequency change process starts at the center station 10 and is sequentially executed at lower slave stations along the tree-structured network. In FIG. 20, the frequency change process is shown by the relationship between the master station and the slave station. Note that there are two methods of transmitting a frequency change notification from the master station to the slave station, which are broadcast and unicast, and in the present embodiment, one of them can be selected as appropriate.

  As shown in FIG. 20, when the master station itself is the center station 10 (Yes in step S71), the master station first determines whether or not to transmit a frequency change notification by broadcast (step S73). Based on the determination result, the master station broadcasts a frequency change notification to the slave station (step S74) when transmitting by broadcast (Yes in step S73). On the other hand, when not transmitting by broadcast (No in step S73). The frequency change notification is unicast to the slave station (step S75). After that, the master station changes its communication frequency (step S76).

  On the other hand, if the master station itself is not the center station 10 (No in step S71), that is, if it is the relay station 20, the frequency transmitted from the center station 10 or the higher-order relay station 20 A change notification is received (step S72). Thereafter, the processes after step S73 are executed.

  Note that the center station 10 and the relay station 20 store in the storage units 130 and 230 flag information for identifying whether the frequency change notification is broadcast or unicast, and channel information of the communication frequency. . The flag information and channel information are set as appropriate in the center station 10, and the set flag information and channel information are sequentially notified to the slave stations by frequency change notification.

  In FIG. 20, the slave station receives a frequency change notification broadcast or unicast from the master station (step S81). If the slave station itself is the relay station 20 (Yes in step S82), It is determined whether or not a frequency change notification is transmitted by broadcast (step S83). Based on the result of the determination, the slave station broadcasts the frequency change notification to the lower slave station (step S84) when transmitting by broadcast (step S83), while when not transmitting by broadcast (step S83). No), the frequency change notification is unicast to a lower slave station (step S85). Thereafter, the slave station changes the frequency of its own communication (step S86).

  On the other hand, if the slave station itself is not the relay station 20 (No in step S82), that is, if it is the terminal station 30, it is not necessary to execute steps S82 to S85, but step S81. Immediately following the above, it is sufficient to change the frequency of its own communication (step S86).

  FIG. 21 is a diagram schematically illustrating an example of a frequency changing procedure. In this example, the frequency channel of each communication station is changed from ch1 to ch2 by broadcasting.

  In FIG. 21 (1), the center station ZC broadcasts a frequency change notification, and then changes its own frequency channel to ch2. In FIG. 21 (2), the relay stations ZR1 and ZR3 that have received the frequency change notification broadcast by the center station ZC broadcast the frequency change notification to the lower communication stations, and then set their frequency channel to ch2. change.

  Next, in FIG. 21 (3), the relay stations ZR2 and ZR4 that have received the frequency change notification broadcast by the relay stations ZR1 and ZR3 broadcast the frequency change notification to the lower communication stations, and then their own frequency channels. Is changed to ch2. Next, as shown in FIG. 21 (4), when the terminal stations ZD1 and ZD2 receive the frequency change notification broadcasted by the relay stations ZR2 and ZR4, their own frequency channel is changed to ch2, and the broadcast is completed. FIG. 21 (5) shows a state where the frequency change is completed in all the communication stations.

  Note that in broadcasting, communication between communication stations exceeding the hierarchy of the tree structure is possible. Therefore, in the case of FIG. 21, the relay stations ZR2 and ZR4 may receive the frequency change notification broadcast by the center station ZC, or the terminal stations ZD1 and ZD2 may receive them.

  Further, the frequency change procedure in the case of unicast is similar to the frequency change procedure in the case of broadcast, and thus its illustration is omitted. However, in the case of broadcast, it is not possible for the transmission source to determine whether the broadcast frequency change notification is actually received by the receiving station. However, in the case of unicast, the transmission source does not respond to the transmitted frequency change notification. Since the ACK reply can be received from the transmission destination, the frequency change notification can be reliably transmitted to the transmission destination.

  Note that the relay station 20 or the terminal station 30 that has not correctly changed the frequency by the frequency changing process described above changes the frequency correctly by starting over from the network joining process or by performing the path switching process. Can do.

  As described above, according to the present embodiment, the relay station 20 holds the network definition information 231 including the information of the master station connected through the main communication path and the information of the master station connected through the backup communication path. Therefore, even when a failure occurs in the connected master station or the communication path to the master station, the route can be quickly switched to a route that avoids the failure.

  In the present embodiment, a fixed address is assigned to the communication station, and the address is not changed even when the route is switched. Therefore, management of the communication station in the network becomes easy. Therefore, a roaming function can be easily added, and even if the terminal station 30 moves, the location (that is, information on which relay station is connected) can be easily determined by the roaming function. be able to.

The figure which showed the example of the structure of the radio | wireless communication network system which concerns on embodiment of this invention. The figure which showed the example of the block configuration of the center station, relay station, and terminal station which concern on embodiment of this invention. The figure which showed the example of a structure of network definition information and relay station definition information. The figure which showed the example of the structure of routing information. The figure which showed the example of the structure of adjacent station information. The figure which showed the example of the processing flow of the network participation process performed between a main | base station and a sub_station | mobile_unit. The figure which showed typically the procedure which a relay station and a terminal station participate in a network by performing the network participation process of FIG. The figure which showed typically the procedure in which a predetermined | prescribed network is constructed | assembled when a relay station and a terminal station repeat participation in a network. The figure which showed the example of the processing flow of the routing information registration process performed between a master station and a slave station. The figure which showed typically the procedure which registers routing information in a center station and a relay station. The figure which showed the example of the routing information registered into each of a center station and a relay station. The figure which showed the example of the processing flow of a path | route switching process. The figure which showed typically the example of the path | route switching procedure in the case of a terminal office path | route cutting | disconnection. The figure which showed typically the example of the path | route switching procedure (first half part) in the case of the path | route disconnection between relay stations. The figure which showed typically the example of the path | route switching procedure (second half part) in the case of the path | route disconnection between relay stations. The figure which showed typically the example of the path | route switching procedure in the case of center station path | route cutting | disconnection. The figure which showed the example of the processing flow of a route return process. The figure which showed the example of the route return procedure typically. The figure which showed the example of the roaming procedure typically. The figure which showed the example of the processing flow of the frequency change process performed in a center station, a relay station, and a terminal station. The figure which showed the example of the frequency change procedure typically.

Explanation of symbols

1 wireless communication network system 10, ZC center station 20, ZR1, ZR2, ZR3, ZR4 relay station 30, ZD1, ZD2 terminal station 110, 210, 310 communication unit 120, 220, 320 processing unit 121, 221, 321 data communication processing Unit 122, 222, 322 Network construction processing unit 123, 226, 326 Frequency change processing unit 130, 230, 330 Storage unit 131, 231 Network definition information 132, 232 Routing information 133, 234, 333 Adjacent station information 223, 323 Route switching Processing unit 224, 324 Route return processing unit 225, 325 Roaming processing unit 233, 332 Base station information 331 Relay station definition information

Claims (26)

A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure Because
The center station,
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first advance correspondence information registered by the second identification information of the master station, a storage means for storing a network definition information,
When a connection request is transmitted from the relay station, referring to the network definition information, when the local station is registered as the first master station or the second master station for the relay station, Network construction means for transmitting an acceptance response to the connection request to the relay station, causing the relay station to participate in the network, and transmitting network definition information stored in the storage means to the relay station ;
With
The relay station is
Storage means for storing the network definition information sent from the center station,
As a child station or other relay station and the terminal station other than the own station, when receiving the transmission of the connection request from the slave station, by referring to the network definition information, the own station is the slave station When registered as one master station or second master station, an acceptance response to the connection request of the slave station is transmitted, the slave station is joined to the network, and the slave station is the relay station Is a network construction means for transmitting the network definition information stored in the storage means to the slave station ;
With
The terminal station is
Performed around search, to said relay station in response to the peripheral search, transmits a connection request, when receiving an acceptance response to the connection request from the relay station, the relay station itself which has transmitted the acceptance response a wireless communication network system comprising: a network construction unit participating in the network as a master station of the station. Each of the relay station and the center station is
When a route request command transmitted from the terminal station to the center station is received, the identification information of the source station or relay station of the network layer attached to the route request command is used as the transmission destination, and the route information for the identification information of the transmission source terminal station or a relay station attached to the request command MAC layer and the adjacent destination, a storage unit that stores as the routing information, further to claim 1, characterized in that it comprises The wireless communication network system described. Before Symbol relay station,
When a failure is detected in communication with the first master station specified by the network definition information, a connection request is transmitted to the second master station specified by the network definition information ; Path switching means for switching the parent station with which the local station actually communicates from the first parent station to the second parent station when receiving an acceptance response from the second parent station in response to the connection request;
And further ,
The terminal station is
Storage means for storing identification information designating the first master station and the second master station to which the local station is communicably connected as relay station definition information ;
When a failure is detected in communication with the first master station specified by the relay station definition information, a connection request is transmitted to the second master station specified by the relay station definition information And a path switching means for switching the master station with which the local station actually communicates from the first master station to the second master station when receiving an acceptance response from the second master station in response to the connection request. ,
The wireless communication network system according to claim 1 or 2 , further comprising: Each of the relay station and the terminal station is
When the master station with which the local station actually communicates is the second master station, a connection request is transmitted to the first master station every predetermined time, and the connection is sent from the first master station. The wireless communication network according to claim 3 , further comprising route return means for returning the master station with which the local station actually communicates to the first master station when an acceptance response to the request is received. system. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure The network construction method in
The center station,
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first The information registered in advance in association with the identification information of the master station 2 is stored in the storage device as network definition information,
When a connection request is transmitted from the relay station, referring to the network definition information, when the local station is registered as the first master station or the second master station for the relay station, Sending an acceptance response to the connection request to the relay station, causing the relay station to participate in the network, and transmitting network definition information stored in the storage means to the relay station ,
The relay station is
Storing the network definition information sent from the center station to the storage device,
As a child station or other relay station and the terminal station other than the own station, when receiving the transmission of the connection request from the slave station, by referring to the network definition information, the own station is the slave station When registered as one master station or second master station, an acceptance response to the connection request of the slave station is transmitted, the slave station is joined to the network, and the slave station is the relay station Transmits the network definition information stored in the storage means to the slave station ,
The terminal station is
Performed around search, to said relay station in response to the peripheral search, transmits a connection request, when receiving an acceptance response to the connection request from the relay station, the relay station itself which has transmitted the acceptance response network construction method characterized by participating in the network as a master station of the station. Each of the relay station and the center station further includes:
When a route request command transmitted from the terminal station to the center station is received, the identification information of the source station or relay station of the network layer attached to the route request command is used as the transmission destination, and the route 6. The network construction according to claim 5 , wherein information having the identification information of the source station or relay station of the MAC layer attached to the request command as an adjacent transmission destination is stored in a storage device as routing information. Method. Before Symbol relay station, further,
When a failure is detected in communication with the first master station specified by the network definition information, a connection request is transmitted to the second master station specified by the network definition information ; When an acceptance response is received from the second master station in response to the connection request, the master station with which the local station actually communicates is switched from the first master station to the second master station,
The terminal station further includes:
The identification information designating the first master station and the second master station to which the local station is communicably connected is stored in the storage device as relay station definition information ,
When a failure is detected in communication with the first master station specified by the relay station definition information, a connection request is transmitted to the second master station specified by the relay station definition information And, when receiving an acceptance response from the second master station in response to the connection request, the master station to which the own station actually communicates is switched from the first master station to the second master station. The network construction method according to claim 5 or 6 . Each of the relay station and the terminal station further includes:
When the master station with which the local station actually communicates is the second master station, a connection request is transmitted to the first master station every predetermined time, and the connection is sent from the first master station. The network construction method according to claim 7, wherein when receiving an acceptance response to the request, the master station with which the local station actually communicates is returned to the first master station. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure A center station used for
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first advance correspondence information registered by the second identification information of the master station, a storage means for storing a network definition information,
When a connection request is transmitted from the relay station, referring to the network definition information, when the local station is registered as the first master station or the second master station for the relay station, Network construction means for transmitting an acceptance response to the connection request to the relay station, causing the relay station to participate in the network, and transmitting network definition information stored in the storage means to the relay station ;
A center station characterized by comprising: When the route request command is received, the identification information of the network layer transmission source station or relay station attached to the route request command is used as the transmission destination, and the MAC layer transmission source terminal attached to the route request command The center station according to claim 9 , further comprising storage means for storing, as routing information, information having the identification information of the station or relay station as an adjacent transmission destination. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure A relay station used for
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first Storage means for storing, as network definition information, information registered in advance in association with identification information of two master stations;
As a child station or other relay station and the terminal station other than the own station, when receiving the transmission of the connection request from the slave station, by referring to the network definition information, the own station is the slave station When registered as one master station or second master station, an acceptance response to the connection request of the slave station is transmitted, the slave station is joined to the network, and the slave station is the relay station Is a network construction means for transmitting the network definition information stored in the storage means to the slave station ;
Relay stations comprising: a. When a route request command transmitted from the terminal station to the center station is received, the identification information of the source station or relay station of the network layer attached to the route request command is used as the transmission destination, and the route 12. The storage device according to claim 11 , further comprising storage means for storing, as routing information, information having the identification information of the source station or relay station of the MAC layer attached to the request command as an adjacent transmission destination. The described relay station. When a failure is detected in communication with the first master station specified by the network definition information, a connection request is transmitted to the second master station specified by the network definition information; Route switching means for switching the master station with which the local station actually communicates from the first master station to the second master station when receiving an acceptance response from the second master station in response to the connection request
Providing further
The relay station according to claim 11 or 12, characterized in that: When the master station with which the local station actually communicates is the second master station, a connection request is transmitted to the first master station every predetermined time, and the connection is sent from the first master station. 14. The relay station according to claim 13 , further comprising: path return means for returning a master station with which the local station actually communicates to the first master station when an acceptance response to the request is received. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure A terminal station used for
The relay station is configured such that each of the relay station and the terminal station included in the network is a child station, and each of the child stations is connected to the child station in the tree structure as a parent station, or The relay station is a first master station, the relay station or the center station that is different from the first master station is the second master station, and the identification of the first master station with respect to the identification information of the slave station Storage means for storing, as network definition information, information registered in association with information and identification information of the second master station in advance,
The terminal station is
A relay station that performs a peripheral search, transmits a connection request to the relay station that responded to the peripheral search, and the relay station that has received the connection request has received, from the network definition information, a first master station for the terminal station or When receiving an acceptance response to be transmitted when registered as the second master station, network construction means is provided for joining the network with the relay station that has transmitted the acceptance response as the master station of the own station. Terminal to do. The terminal station is
Storage means for storing identification information designating the first master station and the second master station to which the local station is communicably connected as relay station definition information ;
When a failure is detected in communication with the first master station specified by the relay station definition information, a connection request is transmitted to the second master station specified by the relay station definition information And a path switching means for switching the master station with which the local station actually communicates from the first master station to the second master station when receiving an acceptance response from the second master station in response to the connection request. ,
The terminal station according to claim 15 , further comprising: The terminal station is
When the master station with which the local station actually communicates is the second master station, a connection request is transmitted to the first master station every predetermined time, and the connection is sent from the first master station. when receiving an acceptance response to the request, the path returning means for returning the master station station itself actually communicated to the first master station and further, according to claim 15 or claim 16, characterized in that it comprises End station. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure The center station program used for
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first Storing the information registered in advance in association with the identification information of the two master stations in the storage device as network definition information;
When a connection request is transmitted from the relay station, referring to the network definition information, when the local station is registered as the first master station or the second master station for the relay station, sends an acceptance response to the connection request to the relay station, along with join the relay station to the network, the network construction process of transmitting network definition information stored in the storage unit to the relay station,
A program that causes a computer to execute. When the route request command is received, the identification information of the network layer transmission source station or relay station attached to the route request command is used as the transmission destination, and the MAC layer transmission source terminal attached to the route request command The program according to claim 19 , further causing a computer to execute a routing information registration process for storing information having the identification information of a station or relay station as an adjacent transmission destination in a storage device as routing information. A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure A relay station program used for
Each of the relay station and the terminal station included in the network is defined as a slave station, and the center station or the relay station connected to the slave station as a master station in the tree structure is defined as a slave station . a first master station, the first master station and said different relay station or the center station as the second master station, to identification information of the slave station, the said first identification information of the master station first Processing for storing network definition information in a storage device, information registered in advance in association with identification information of two master stations,
As a child station or other relay station and the terminal station other than the own station, when receiving the transmission of the connection request from the slave station, by referring to the network definition information, the own station is the slave station When registered as one master station or second master station, an acceptance response to the connection request of the slave station is transmitted, the slave station is joined to the network, and the slave station is the relay station is a network construction process of transmitting network definition information stored in the storage unit to the slave station,
Program for causing a computer to execute the. When a route request command transmitted from the terminal station to the center station is received, the identification information of the source station or relay station of the network layer attached to the route request command is used as the transmission destination, and the route A process of storing, as routing information, information stored in the storage device as identification information of the terminal station or relay station of the MAC layer attached to the request command as an adjacent transmission destination;
21. The program according to claim 20 , wherein the program is further executed by a computer. When a failure is detected in communication with the first master station specified by the network definition information, a connection request is transmitted to the second master station specified by the network definition information; A path switching process for switching the master station with which the local station actually communicates from the first master station to the second master station when receiving an acceptance response from the second master station in response to the connection request
The program according to claim 20 or 21 for causing a computer to execute the above. If the master station that actually communicates with the relay station is the second master station, the relay station transmits a connection request to the first master station every predetermined time, and when receiving an acceptance response to the connection request from the master station, the path restoration process for restoring the master station to the first master station by the own station actually communicate further to claims 20 to be executed by a computer The program according to any one of claims 22 . A wireless communication network system including a center station, a plurality of relay stations, and a plurality of terminal stations that communicate with each other by radio signals, and a network that connects the center station, the relay station, and the terminal stations to each other forms a tree structure A terminal program used for
The relay station is configured such that each of the relay station and the terminal station included in the network is a child station, and each of the child stations is connected to the child station in the tree structure as a parent station, or The relay station is a first master station, the relay station or the center station that is different from the first master station is the second master station, and the identification of the first master station with respect to the identification information of the slave station Storage means for storing, as network definition information, information registered in association with information and identification information of the second master station in advance,
The terminal station performs a peripheral search, transmits a connection request to the relay station that responds to the peripheral search, and the relay station that has received the connection request uses the network definition information to determine the When receiving an acceptance response to be transmitted when registered as one master station or a second master station, a network construction process for joining the network with the relay station that sent the acceptance response as the master station of the own station is performed. A program that causes a computer to execute. A process of storing identification information designating the first and second parent stations to which the own station is communicably connected as relay station definition information in a storage device;
When a failure is detected in communication with the first master station specified by the relay station definition information, a connection request is transmitted to the second master station specified by the relay station definition information A path switching process for switching the master station with which the local station actually communicates from the first master station to the second master station when receiving an acceptance response from the second master station in response to the connection request; ,
25. The program according to claim 24 , further causing a computer to execute. When the master station that is actually communicating with the terminal station is the second master station, the terminal station transmits a connection request to the first master station every predetermined time, and the first station when receiving an acceptance response to the connection request from the master station, the path restoration process for restoring the master station station itself actually communicated to the first master station and further to claim 25 for causing a computer to execute The program described.

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