JP4157002B2 - Wireless communication device - Google Patents

Description

  The present invention relates to a wireless communication apparatus that relays wireless transmission of communication data between a terminal in a network segment formed in a predetermined mobile body and an external network formed along the movement path.

In recent years, in order to connect to an external network such as the Internet from a terminal (such as a mobile device owned by a passenger) in a moving body such as a train to perform broadband communication, relay wireless communication with the external network. The spread of wireless communication devices is required.
In such a wireless communication device, a wireless device (hereinafter referred to as a moving-side wireless device) that is mounted on a train (moving body) and moves along the train moving path (that is, along the track). ) It is effective to transmit radio signals to / from a plurality of radio devices (hereinafter referred to as fixed-side radio devices).
Here, when only one moving side radio is mounted on a train, the fixed side radios must communicate with each other in order to perform signal transmission continuously while the train is running (moving). It is necessary to arrange the possible area so as to overlap with the adjacent fixed-side radio.

On the other hand, in the case of a moving body having a certain length in the moving direction such as a train, if the moving-side radio is composed of a plurality of radios provided at intervals in the moving direction, the fixed-side The arrangement interval of the wireless devices can be widened.
For example, by arranging a plurality of radios as the mobile radios at a predetermined interval within the maximum communicable distance of the fixed radios from the top to the tail of the train, After the first radio enters the communicable area with respect to the fixed radio, at least one radio is used until the train moves and the last radio exits the communicable area. Is always present in the communication area of one of the fixed-side radios. Accordingly, the interval between the adjacent fixed-side radios can be extended to a distance obtained by adding the train length to the communicable distance of each of the fixed-side radios.
In such a configuration, if a router is provided for each radio on the train side and the router is connected to a terminal in the train, wireless communication between the terminal in the train and the external network can be relayed.

As described above, when a plurality of routers are provided on the mobile unit side, it is necessary to switch which router is used to communicate with the external network (fixed side radio side). However, it is not realistic to change the setting for each terminal on the mobile unit each time it communicates with an external network.
Conventionally, Non-Patent Document 1 and Non-Patent Document 2 show Cisco Hot Standby Router Protocol (HSRP) as a technique for dynamically switching a communication path with an external network.
This HSRP is dynamically connected to a spare router without any changes to the terminal settings in the network segment when a failure occurs in a gateway router that connects a network segment (LAN) and an external network. Is a technology to switch
In HSRP, a plurality of gateway routers operating in a network segment share one virtual address, and the terminal is set to transmit data packets (communication data) destined for an external network using the virtual address as a destination. In practice, however, only one active router processes the packet.
Each gateway router is assigned a priority value, and the router with the highest priority value among the routers currently participating in the network becomes the active router, and the next router becomes the standby router.
If any failure occurs in the active router, the standby router immediately takes over the routing function and becomes the active router. Since the standby router takes over the virtual address at the same time, the terminals in the network segment can send data packets to the same virtual address to the external network through the new active router without knowing the change of the active router. Can be connected with.
Internet Engineering Task Force (IETF) Request For Comments (RFC): 2281 United States Patent Number 5,473,599

However, HSRP is a technology that originally aims to take over the routing function to an alternative router without changing the terminal settings in the event of a failure, so the router that accesses the outside from the inside of the mobile unit is switched instantaneously and dynamically. There are several disadvantages as means for achieving this.
HSRP does not allow unconditional replacement of active routers even when routers with higher priority values than active routers participate in the network segment. A new router with a high priority value first transmits a coup message to the current active router, and after a handshake that the current active router acknowledges it and returns a resign message, the replacement is executed for the first time.
However, in a mobile wireless communication device, router switching is performed periodically, and when HSRP is applied to this, there is a problem in that router switching is delayed due to handshaking, resulting in frequent communication failure.
In HSRP, routers other than the active router are set so as not to perform routing by address filters. However, in applications where routers that can communicate with external networks are changing one after another, routing operations are not performed. If the number of routers to be used is limited to only one, there is a problem that there is a high possibility that packets transmitted from the terminal will be lost at the timing of switching.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is that a terminal in a mobile network segment switches a router used for communication with an external network among a plurality of routers. It is an object of the present invention to provide a wireless communication apparatus that can perform communication without being aware of the problem and can perform router switching while preventing occurrence of communication failure.

In order to achieve the above object, the present invention provides an external network provided in a network segment formed in a predetermined mobile body and formed along one or a plurality of terminals in the network segment and a moving path of the mobile body. A plurality of wireless transmission means for transmitting wireless signals to and from the external network, and the external network provided for each of the wireless transmission means A plurality of routers that perform routing of the communication data to and from a network segment, a transmission source that relays transmission of the communication data between the routers and between the router and the terminal, and is set in the communication data The transmission route of the communication data is learned based on the address, and the communication data is determined according to the learning result. Comprising one or a plurality of learning bridge to change the transmission path of the data, a plurality of said wireless transmission means, either of which the movable body along a moving path arranged plurality of said external network side of the Arranged at intervals in the moving direction of the mobile body so that the wireless communication means exists within any communicable range of the wireless communication means, each of the routers has a predetermined internal virtual address for the network segment as a destination The wireless communication apparatus is configured to perform routing to the external network for the communication data set as an address.
With such a configuration, the terminals in the mobile network segment can communicate with the external network without being aware that the router used for communication with the external network is switched between a plurality of routers. Data (communication packets) can always be communicated with the external network simply by setting and transmitting the internal virtual address as a destination address.
Further, since the communication data in which the internal virtual address is set as the transmission destination by the learning bridge transmission path learning function is transmitted only to any one of the routers, one communication data is transmitted from a plurality of the routers. Routing to the external network can be prevented.

Here, only the priority router, which is one of the plurality of routers, routes the communication data received from the external network into the network segment, and transmits the communication data for performing the routing. It is possible to set the internal virtual address as the original address.
Thereby, since the transmission path of the learning bridge is learned from the communication data routed by the priority router, the communication data transmitted from the terminal with the internal virtual address as the destination address is transmitted to the priority router. It will be transmitted reliably.
In this case, priority determination means for determining the priority for data transmission to the external network for each of the routers, and priority router selection for selecting one of the routers based on the priority and setting the priority router It is conceivable to have a means.
As a result, the router having a high priority is dynamically set as the priority router.
For example, the priority router selection means sends priority notification means for notifying the priority of the router to each of the other routers from each of the routers, and assigns the priority corresponding to the router in each of the routers to the other routers. Priority router setting means for setting itself as the priority router when a predetermined requirement is satisfied in comparison with the priority notified from the priority, and the priority from the router set as the priority router by the priority router setting means Priority router setting notification means for notifying other routers that the router has been set, and when the router already set as the priority router receives notification from the other routers by the priority router setting notification means It is conceivable to have priority router canceling means for canceling the setting of the priority router of its own.
As a result, the router having the best wireless link state with the external network is selected as the priority router.

In addition, when the router is set as the priority router, the router may transmit predetermined route learning data having the internal virtual address as a transmission source address in the network segment.
As a result, all communication data destined for the external network (that is, communication data in which the internal virtual address is set as a transmission destination) will be transmitted to the priority router within the network segment. The learning bridge signal transmission path is quickly learned.
Further, when the communication data in which the internal virtual address is set as a transmission destination address is received in the network segment when communication with the external network is not possible, the communication data is transmitted from the other routers. It may be returned after receiving route learning data.
As a result, it is possible to prevent loss of communication data (communication packet) that has arrived at the router in a communication disabled state.

In addition, if the router receives a predetermined response request in which the internal virtual address is set as a destination address in the network segment and responds only when the router is set as the priority router, It is possible to prevent the learning result of the learning bridge from being disturbed by a response from a router other than the priority router.
In addition, as the priority determination means, for example, the priority is determined based on the received electric field strength in wireless communication with the external network or the average value and / or the dispersion value thereof, or the position of the wireless communication device The priority may be determined based on information, etc. Further, each of the routers sets a predetermined external virtual address for the external network as a source address of the communication data for routing to the external network. The priority router may be a router that routes the communication data in which the external virtual address is set as a destination address from the external network to the network segment.
As a result, when the router other than the priority router routes communication data to the external network, or when the response data is returned after the communication data is routed to the external network, the priority router is switched. Even in this case, the response data can be routed to the network segment by the priority router having a good wireless communication state at that time.

According to the present invention, each of a plurality of routers in a mobile network segment performs routing to the external network for the communication data in which a predetermined internal virtual address for the network segment is set as a destination address. The terminal in the network segment is not aware that the router used for communication with the external network is switched between a plurality of routers, and the communication data (communication packet) desired to be routed to the external network is as follows: Communication with the external network becomes possible only by always setting and transmitting the internal virtual address as a destination address.
Furthermore, since a learning bridge is provided between the routers and between the router and the terminal, the communication data in which the internal virtual address is set as a transmission destination by the transmission route learning function of the learning bridge is: It is transmitted only to any one of the routers, and one communication data can be prevented from being routed from a plurality of the routers to the external network.
In addition, only the priority router that is one of the plurality of routers performs routing of the communication data received from the external network into the network segment, and the transmission source of the communication data that performs the routing By setting the internal virtual address in the address, the learning bridge transmission path is learned from the communication data routed by the priority router. Henceforth, the terminal transmits the internal virtual address as the destination address. The communication data is surely transmitted to the priority router.
Further, priority determination means for determining the priority for data transmission to the external network for each router, and priority router selection means for selecting one of the routers based on the priority and setting the priority router And a router having a good communication state with the external network at each time point can be dynamically set as the priority router by a router having a high priority. It is possible to switch the router while preventing it.
In addition, when the router is set as the priority router, the router transmits a predetermined route learning data having the internal virtual address as a transmission source address in the network segment. All the learning bridge signal transmission paths so that the communication data destined for (ie, the communication data in which the internal virtual address is set as the transmission destination) is reliably transmitted to the priority router in the network segment. Are learned quickly. Accordingly, communication data can be prevented from being transmitted to routers other than the priority router whose communication state with the external network is not good, resulting in communication failure.
Further, when the communication data in which the internal virtual address is set as a transmission destination address is received in the network segment when communication with the external network is not possible, the communication data is transmitted from the other routers. By returning the data after receiving the route learning data, it is possible to prevent the communication data (communication packet) reaching the router in the communication disabled state from being lost (communication failure).
In addition, if the router receives a predetermined response request in which the internal virtual address is set as a destination address in the network segment and responds only when the router is set as the priority router, It is possible to prevent the learning result of the learning bridge from being disturbed by a response from a router other than the priority router.
Each of the routers sets a predetermined external virtual address for the external network as a source address of the communication data for routing to the external network, and the priority router sets the external virtual address as a destination address. If the set communication data is routed from the external network to the network segment, a router other than the priority router routes the communication data to the external network, or the communication data is routed to the external network. Even if the priority router is switched from when the response data is sent back to the network segment, the response data is routed to the network segment by the priority router having a good wireless communication state at that time. Can Can, it is possible to prevent the occurrence of a communication failure.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
Here, FIG. 1 is a schematic configuration diagram of a train radio communication system Z in which a radio communication device X according to an embodiment of the present invention is mounted on a train, and FIG. 2 shows the radio client (radio transmission means) in the radio communication system Z and FIG. 3 is a flowchart showing the arrangement relationship of the wireless access points, FIG. 3 is a flowchart showing a processing procedure at the time of “initial status” of the on-vehicle router in the wireless communication device X, and FIG. FIG. 5 is a flowchart showing the processing procedure for the “connection status” of the onboard router in the wireless communication device X, and FIG. 6 is the “priority status” for the onboard router in the wireless communication device X. 7 is a flowchart showing the processing procedure of FIG. 7, and FIG. Diagram illustrating an example of Tsu bets, FIG. 8 is a diagram showing an example of a field configuration of a state database onboard router in the wireless communication apparatus X has.

First, the configuration of a train radio communication system Z in which a radio communication device X according to an embodiment of the present invention is mounted on a train will be described with reference to FIG.
The train radio communication system Z is roughly composed of a network segment 60 (hereinafter referred to as a train LAN 60) formed in a train 2 moving on the track 1, and an external network 70 formed along the moving direction of the train 2. It is divided into.
The external network 70 includes a wireless access point (AP) 30 that is a plurality of ground side wireless communication means arranged along the moving direction 1 a of the train 2 moving on the track 1, and the wireless access points 30. A communication packet (communication data) flowing through the relay link 49 is connected via the relay link 49 and transmitted to the wireless access point 30, and the communication packet transmitted from the wireless access point 30 is relayed to the relay link 49. A plurality of switching hubs 40 (SW-HUB) that transmit to the link 49, and a ground router 50 that routes communication packets between the switching hub 40 and the Internet 51 that is an upper network are provided. Note that the switching hub 40 can be applied to the present invention even if it is a normal HUB having no learning function.
As the relay link 49, for example, it is conceivable to use an optical fiber connection or a VDSL connection for long-distance transmission of 100BaseFX standard, or a connection using a coaxial cable of IEEE802.3 standard when the distance is short.

On the other hand, the train LAN 60 is provided with a plurality of wireless clients 20 that are wireless transmission means (radio devices) that transmit wireless signals to and from the wireless access point 30 of the external network 70, and for each wireless client 20. One or a plurality of terminals such as a plurality of on-vehicle routers 21 for routing communication packets between the network 70 and the train LAN 60 and a personal computer used by a user who receives a connection service from the train 2 to the external network 70 10 and relaying communication packets between the on-vehicle routers 21 and between the on-vehicle router 21 (an example of the plurality of routers) and the terminal 10 and communicating based on the source address set in the communication packet The packet transmission path is learned, and the communication packet transmission path is changed according to the learning result. And a car on the learning bridge 22.
It is conceivable that each device in the train LAN 2 is wired by IEEE802.3 standard twisted pair cable, coaxial cable, etc., but the signal transmission path can be changed by installing a radio (wireless access point, etc.) on the transmission path. You may comprise so that wireless transmission may be performed about part or all.
A portion of the train LAN 60 excluding the terminal 10 is the wireless communication device X according to the embodiment of the present invention.

Next, the arrangement relationship between the wireless client 20 and the wireless access point 30 will be described with reference to FIGS.
As shown in FIG. 2 (a), each of the wireless access points 30 is adjacent to the adjacent wireless access point 20 (represented by NG1 and Ng2 in the figure) and does not overlap. Arranged so that the interval wx in the train movement direction 1a between the communicable ranges w of the wireless access points NG1 and NG2 that match each other is equal to or less than the interval wac between the wireless clients Na and Nc on the most upstream side and the most downstream side in the train movement direction 1a Is done.
Further, as shown in FIG. 2B, each of the wireless clients 20 (represented by Na, Nb, and Nc in the figure) has a length of a communicable range w in the train moving direction 1a of each of the wireless access points 20. It is arranged at an interval w0 of less than or equal to
Due to the arrangement configuration of the wireless access point 30 and the wireless client 20, any one of the wireless clients Na, Nb, and Nc is always within the communicable range w with any of the wireless access points 30. Will do. Thereby, even if the train 2 moves, if the wireless client 20 is switched, that is, if the corresponding on-vehicle router 30 is switched appropriately, the terminal 24 can be continuously connected to the Internet. Can be maintained.
Further, since the interval wx in the train moving direction 1a between the communicable ranges w of the adjacent wireless access points 30 can be increased to almost the entire length of the train 2, the number of the wireless access points 30 arranged can be increased. Can be reduced.
Here, FIG. 2 shows an example in which three wireless clients Na, Nb, and Nc are provided. However, the present invention is not limited to this, and two or four or more may be considered.

The wireless communication device X enables the terminal 10 in the moving train LAN 60 to communicate without being aware that the router used for communication with the external network 70 is switched between the plurality of on-vehicle routers 21. The on-vehicle router 21 is switched while preventing the occurrence of communication failure between the terminal 10 and the external network 70.
In the train radio communication system Z, when the terminal 10 is connected to the external network 70 in order to enable the terminal 10 to communicate without being aware of the switching of the on-vehicle router 21, the terminal 10 A predetermined internal virtual address (the virtual address corresponding to the MAC address) for the train LAN 60 is set as the address. This internal virtual address is shared by each on-vehicle router 21.
When each of the on-vehicle routers 21 receives a communication packet in which the internal virtual address is set as a transmission destination address (hereinafter referred to as an uplink communication packet), it routes the packet to the external network 70.
Here, it is preferable that the uplink communication packet is transmitted through a plurality of the on-vehicle routers 21 having the best communication state (wireless link state) with the external network 70.
As will be described later, in the wireless communication device X, a wireless link with the best wireless link state (hereinafter referred to as a priority router) is determined from among the plurality of on-vehicle routers 21, and only the priority router is the external router. The communication packet received from the network 70 is routed into the network segment 60, and the internal virtual address is set as the source address of the communication packet to be routed.
Further, when the priority router is determined, a predetermined communication packet (route learning data) having the internal virtual address as a transmission source address is broadcast from the priority router into the train LAN 60. Thereby, in all the learning bridges 22, the signal transmission path is quickly learned so that the uplink communication packet is transmitted to the priority router.
For this reason, the terminal 10 transmits the uplink communication packet to the internal virtual address as a destination without being aware of the change of the priority router (without switching the transmission destination each time), and the communication packet is , Transmitted to the priority router by the learning bridge 22, and transmitted from the priority router to the external network 70 (Internet).
On the other hand, since the number of on-vehicle routers 21 for routing the uplink communication packet is not limited to one, learning of the learning bridge 22 is slightly delayed when the priority router is switched. Even when the upstream communication packet is transmitted to the on-vehicle router 21 other than the priority router, the routing is performed without omission as long as the on-route router 21 can communicate with the external network 70. Therefore, packet loss at the time of switching the priority router can be minimized.

Next, the process of selecting the priority router from the onboard router 21 will be described.
The on-board router 21 is in one of four states of “initial status”, “disconnection status”, “connection status”, and “priority status”, and executes different processing for each state (status). Here, the on-vehicle router 21 in the “priority status” is the priority router.
Hereinafter, the procedure of the priority router selection process by each on-vehicle router 21 will be described with reference to the flowcharts of FIGS. The on-board router 21 includes an attached CPU and its peripheral devices such as ROM, RAM, nonvolatile memory, and the like, and a predetermined program stored in advance in the ROM is executed by the CPU. The process shown in is executed.

("Initial status")
First, the processing procedure in the “initial status” which is the first transition state after a predetermined initialization process is performed after the on-board router 21 is activated (power is turned on) will be described with reference to the flowchart of FIG. Hereinafter, S11, S12,... Represent processing procedure (step) numbers.
In the “initial status”, first, the on-board router 21 waits for a status message from each of the other on-board routers 21 until the initial timer set with a predetermined time times out (S11, S12). When the status message is received (Y side of S11), the status database is updated from the status message (S13).
FIG. 7 shows an example of the data format of the status message.
The status message includes a unique address d1 (in this case, a MAC address) of the on-board router 21 (source router) that is the source of the status message, and a status d2 at that time of the source router 21 (“disconnect” described later) ”,“ Connected ”, or“ priority ”state) and the current priority value d3 of the source router 21 are included.
The priority value d3 is determined for each of the on-board routers 21 and is information regarding the priority for data transmission with the external network 70, and the wireless link state (communication state) with the external network 70 is good. The value is higher when it is considered to be a state or a good state.
For example, a means (an example of the priority determining means) for detecting the received electric field strength in the wireless communication of the wireless client 20 with the external network 70 is provided, and the detected value is set (determined) as the priority value d3. Can be considered.

FIG. 8 shows an example of the field configuration of the state database held by each on-vehicle router 21 stored in a non-volatile memory.
In the status database, in addition to the unique address d1, the status d2, and the priority value d3 of the source router 21 included in the status message, an aging value d4 indicating the elapsed time since the status message was received is stored. Is done. Each on-board router 21 deletes the record data as invalid data when the aging value d4 is a value indicating that a predetermined time or more has elapsed.
Each on-vehicle router 21 collects the status message from each of the other on-vehicle routers 21 in the “initial status” until the timeout time of the initial timer elapses, and updates the status database. Never send a message.
On the other hand, each on-vehicle router 21 has a time interval shorter than the time-out time of the initial timer in the “connection status” and “priority status” states in which the wireless link of the external network 70 has been established as will be described later. Since the status message is transmitted, in this “initial status” stage, the unique address d1, the status d2, and the priority for all the other on-vehicle routers 21 that have established wireless links with the external network 70. The value d3 is collected.

Next, when the initial timer times out, the state of the wireless link between the wireless client 20 connected to the on-vehicle router 21 and the wireless access point 30 (ie, the external network 70) is evaluated, and the priority value d3 is set. The better the link state is, the higher priority value is set (determined).
As the priority value d3, in addition to setting the reception field strength of the radio link itself, an average value of the reception field strength is used to smooth the priority value d3 to prevent frequent changes, In order to use this as an evaluation index, the dispersion value may be reflected as a negative factor (subtracted) from the average value of the received electric field strength. Alternatively, the relative distance to the wireless access point 30 may be obtained from the position information of the train 2, and the priority value d3 may be increased as the relative distance is shorter. The position information of the train 2 may be detected by the GPS mounted on the train 2 or the travel distance from the nearest station of the train, or by a predetermined sensor provided along the track.
Further, as a result of the evaluation of the priority value d3, it is determined whether or not a wireless link with the external network 70 can be established (S15), and when the wireless link can be established (communication enabled state) When the state transitions to “connection status” and the state cannot be established (communication impossible state), the state transitions to “disconnection status”.

("Disconnect status")
Next, a processing procedure of the on-board router 21 when the state is changed to the “disconnection status” will be described with reference to the flowchart of FIG.
In the “disconnection status”, the on-vehicle router 21 performs a reception check of the status message from the other on-vehicle router 21 (S21) and a status evaluation (S22) of the radio link with the external network 70, This is repeated until a wireless link with the external network 70 is established (N side of S23). At this time, if the status message is received, the status database is updated based on the content (S24). Thereby, the states of the other on-vehicle routers 21 are collected.
When a wireless link with the external network 70 is established (Y side in S23), the state transitions to the “connection status”.

("Connection status")
Next, the processing procedure of the on-board router 21 when transitioning to the “connection status” will be described using the flowchart of FIG.
In the “connection status”, the on-board router 21 determines whether or not the status message has been received from another on-board router 21 until a message timer in which a predetermined time shorter than the set time of the initial timer has timed out. Check (S31), evaluation of the state of the radio link with the external network 70 (S32), and check of the connection state of the radio link with the external network 70 (S33) are repeated. At this time, when the status message in which the priority value d3 is set is received from another on-vehicle router 21 (Y side of S31), the status database is updated based on the status message (S35). .
If the wireless link with the external network 70 is disconnected (the link cannot be established) before the message timer times out (Y side in S33), the status d2 is set to “disconnection status”. The status message in which the priority value d3 (low priority value) at that time is set is transmitted to all the other on-vehicle routers 21 (S36), and then the state transitions to the “disconnection status”. .

On the other hand, when the message timer times out, the priority value d3 of the on-vehicle router 21 is compared with the priority value d3 of another on-vehicle router 21 with reference to the state database (S37).
Here, when it is determined that the priority value d3 of the on-vehicle router 21 is not the highest value (self is the highest), the status d2 is set to the “connection status”, and the priority value d3 of the current point in time is set to the own priority value d3. After transmitting the set status message to all the other on-vehicle routers 21 (S38, an example of the function of the priority notification means), the process returns to S31 and the above-described processing is repeated.
On the other hand, when it is determined that the priority value d3 of the on-vehicle router 21 is the highest value (i.e., the highest), the on-route router 21 is declared to be in “priority status”. The status d2 is set to "priority status", and the status message notifying the priority value d3 at that time is transmitted (transmitted) to all the other on-vehicle routers (S39, function of the priority notification means) (An example of the function of the priority router setting notification means), and further, predetermined route learning data having an internal virtual address which is a virtual address (here, a MAC address) in the train LAN 60 as a transmission source address. After broadcast transmission in the train LAN 60 (S39), the state transitions to “priority status” (ie, the front of itself) To set the priority router). As the route learning data, for example, it is conceivable to use an arp response (called a gratuitous arp message) without an arp request.
Thereby, route learning based on the route learning data is performed in all the on-vehicle learning bridges 22, and thereafter, when a communication packet having the internal virtual address as a transmission destination address is transmitted from the terminal 10, The on-board learning bridge 22 transmits the communication packet only to the on-board router 21 (the on-board router 21 that lastly transmitted the route learning data).
Further, since the communication packet having the internal virtual address as the transmission source transmits only the priority router (the transmission source of the status message is a unique address (MAC address) of each on-vehicle router 21), the on-vehicle learning is performed. The route learning of the bridge 22 is not disturbed.

("Priority Status")
Next, the processing procedure of the on-board router 21 in the case of transition to the “priority status” will be described using the flowchart of FIG.
In the “priority status”, each on-vehicle router 21 checks whether or not the status message is received from another on-vehicle router 21 until the message timer times out (S41), and wirelessly communicates with the external network 70. The link state evaluation (S42) and the wireless link connection state check with the external network 70 (S43) are repeated.
Meanwhile, when the status message is received (Y side of S41), the status database is updated based on the status message (S45), and the status d2 of the status message is “priority status”. And whether the priority value d4 is larger (higher) than the own priority value d4 (of the on-vehicle router 21) is checked (S46, S47). Is satisfied, the status d2 is set to "connection status", and the status message in which the priority value d3 at that time is set is transmitted to all the other on-route routers 21 (S48), The state transitions to “connection status” (Y side of S47).
As a result, the state where the on-vehicle router 21 is the “priority status” (i.e., the priority router) is released, and the replacement of the priority router is completed.
One said priority router is determined by the process of S37-S39 in FIG. 5 mentioned above and the process of S46-S48 in FIG. 6 (an example of the process of the said priority router selection means).
If both conditions are not satisfied, the process proceeds to S42 and the process is repeated as it is.

On the other hand, if the radio link with the external network 70 is disconnected before the message timer times out (Y side in S43), the status d2 is set to "disconnection status" and the priority at that time is further set. After transmitting the status message in which the value d3 (low priority value) is set to all the other on-vehicle routers 21 (S36), the status transitions to the “disconnection status”.
As a result, the on-vehicle router 21 is released from the “priority status” state (priority router), and at any of the other on-vehicle routers 21, the processing of S37 and S39 described above (FIG. 5) is performed. Is executed, the priority router is switched.
In S46 and S47, after receiving the status message indicating that the “priority status” has been received from the other on-vehicle router 21, the own “priority status” is canceled (transition to “connection status”). Therefore, the priority router is smoothly switched without going through the state where the priority router does not exist.
On the other hand, when the message timer times out, the status d2 is set to "priority status", and the status message in which the priority value d3 at that time is set is transmitted to all the other on-vehicle routers 21 (S50), and then S41 The process described above is repeated after returning to step S2.

As described above, by the processing shown in FIGS. 3 to 6, among the plurality of on-vehicle routers 21 in the train LAN 60, one on-vehicle router 21 whose wireless link is considered to be most stable is promptly “ Priority status "(priority router).
In addition, according to the route learning data broadcast from the on-vehicle router 21 that has become “priority status”, a packet with the internal virtual address as the destination (transmission destination) is transmitted to each of the on-board learning bridges 22 by “ Since the terminal 10 is quickly learned so as to be transmitted to the on-vehicle router 21 (priority router) having the “priority status”, the terminal 10 does not recognize the change of the “priority status” priority router, but only for the internal segment. By sending a packet to the virtual address, it is possible to send the packet to the Internet.
Here, depending on the rare timing, when the on-vehicle router 21 is in a state where communication with the external network 70 is impossible, that is, when the priority value d3 is less than a predetermined lower limit value, the in-house LAN 60 (network There may be a case where a communication packet in which the internal virtual address is set as a transmission destination address is received within a segment. In this case, the onboard router 21 returns the received communication packet after receiving the route learning data from the other onboard router 21.
As a result, the returned communication packet is reliably transmitted to the new priority router (that is, the onboard router 21 that can communicate with the external network 70) by the learning bridge 22 after learning. Loss of communication packets at the time of switching can be prevented.

In general, the terminal 10 performs various communications with a router (the on-vehicle router 21) in a network segment (the in-house LAN 60) in order to construct or maintain a network. In response to a request packet from one side, the other side returns a response packet. For example, ARP for obtaining a physical address for the IP address of the transmission partner, ICMP ping for checking whether IP communication with the communication partner is possible, or the like.
In the wireless communication device X, when the on-board router 21 receives the request packet (an example of the predetermined response request) in which the internal virtual address is set as a transmission destination address in the in-house LAN 60, A response packet is returned only when is set in the priority router (in the “priority status” state).
Thereby, the route learning of the learning bridge 22 is not disturbed.

On the other hand, each on-vehicle router 21 sets a predetermined external virtual address for the external network 70 as a source address of a communication packet that is routed to the external network 70, and the priority router (“priority status”). In this state, the on-board router 21) routes the communication packet in which the external virtual address is set as the transmission destination address from the external network 70 to the train LAN 60.
As a result, when the on-board router 21 other than the priority router routes the communication packet to the external network 70, the communication packet is routed to the external network 70 and the response packet is returned. Even when the priority router is switched, the response packet can be routed to the train LAN 60 by the priority router, which is the on-board router 21 in which the wireless communication state at that time is good.

  In the above embodiment, the onboard router 21 exchanges the priority value d3 with each other via the train LAN 60. However, the onboard router 21 is provided with signal transmission means other than the train LAN 60. The priority value d3 may be exchanged between each other, or predetermined calculation means connected to each of the on-vehicle routers 21 may be separately provided, and the priority value d3 may be compared by the calculation means. A priority router may be determined and notified to the corresponding on-vehicle router 21 to that effect.

    The present invention can be used for a wireless communication apparatus that relays wireless communication between a terminal in a moving body and an external network on the movement path.

The schematic block diagram of the train radio | wireless communications system Z which mounts the radio | wireless communication apparatus X which concerns on embodiment of this invention on the train. FIG. 3 is a diagram illustrating an arrangement relationship between the wireless client (wireless transmission unit) and the wireless access point in a wireless communication system Z. The flowchart showing the process sequence at the time of "initial status" of the on-vehicle router in the wireless communication device X. The flowchart showing the process sequence at the time of "disconnection status" of the on-vehicle router in the wireless communication apparatus X. The flowchart showing the process sequence at the time of "connection status" of the on-vehicle router in the radio | wireless communication apparatus X. The flowchart showing the process sequence at the time of "priority status" of the on-vehicle router in the wireless communication apparatus X. The figure showing an example of the data format of the status message which the onboard router in the radio | wireless communication apparatus X transmits / receives. The figure showing an example of the field structure of the state database which the on-vehicle router in the radio | wireless communication apparatus X hold | maintains.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Track 2 ... Train 10 ... Terminal 20 ... Wireless client (wireless transmission means)
21 ... On-vehicle router (router)
22: On-vehicle learning bridge (learning bridge)
30 ... Wireless access point 60 ... Train LAN (network segment)
70 ... External network S1, S2, ... Processing procedure (step)

Claims (12)

Provided in a network segment formed in a predetermined mobile body, and relays wireless transmission of communication data between one or more terminals in the network segment and an external network formed along the movement path of the mobile body Wireless communication device
A plurality of wireless transmission means for transmitting wireless signals to and from the external network;
A plurality of routers provided for each of the wireless transmission means for routing the communication data between the external network and the network segment;
The transmission of the communication data is relayed between the routers and between the router and the terminal and the transmission path of the communication data is learned based on the source address set in the communication data, and the learning result One or a plurality of learning bridges that change the transmission path of the communication data according to
The plurality of wireless transmission means are present in a communicable range of any one of the plurality of wireless communication means on the external network side arranged along the movement path of the mobile body. Arranged in the moving direction of the moving object at intervals,
Each of the routers performs routing to the external network for the communication data in which a predetermined internal virtual address for the network segment is set as a transmission destination address.   Only the priority router that is one of the plurality of routers performs routing of the communication data received from the external network into the network segment, and sets the source address of the communication data to be routed. The wireless communication apparatus according to claim 1, wherein the internal virtual address is set. Priority determination means for determining the priority of data transmission with the external network for each of the routers;
The wireless communication apparatus according to claim 2, further comprising priority router selection means for selecting one of the routers based on the priority and setting the selected router as the priority router. The priority router selection means is
Priority notification means for notifying each of the routers of the priority of the router to the other routers;
In each of the routers, priority router setting means for setting itself as the priority router when the priority corresponding to the router is compared with the priority notified from the other routers and satisfies a predetermined requirement;
Priority router setting notification means for notifying other routers that the priority router has been set as the priority router from the router that has set itself as the priority router by the priority router setting means;
Priority router cancellation means for canceling the setting of the priority router when the router already set as the priority router receives notification from the priority router setting notification means from another router;
The wireless communication device according to claim 3, comprising:   5. The router according to claim 3 or 4, wherein when the router is set as the priority router, the router broadcasts predetermined route learning data having the internal virtual address as a transmission source address in the network segment. Wireless communication device.   When the router receives communication data in which the internal virtual address is set as a destination address in the network segment when the router is in a state where communication with the external network is not possible, the communication data is transferred from another router. The wireless communication apparatus according to claim 5, which is returned after receiving the route learning data. 3. The router, when receiving a predetermined response request in which the internal virtual address is set as a destination address in the network segment, responds only when the router is set as the priority router. The radio | wireless communication apparatus in any one of -6.   The wireless communication apparatus according to claim 3, wherein the priority determination unit determines the priority based on a received electric field strength in wireless communication with the external network.   9. The wireless communication apparatus according to claim 8, wherein the priority determination unit determines the priority based on an average value and / or a dispersion value of received electric field strength in wireless communication with the external network.   The wireless communication apparatus according to claim 3, wherein the priority determination unit determines the priority based on position information of the wireless communication apparatus.   Each of the routers sets a predetermined external virtual address for the external network as a source address of the communication data for routing to the external network, and the priority router has the external virtual address set as a destination address. The wireless communication apparatus according to claim 2, wherein the communication data is routed from the external network to the network segment.   12. The router according to claim 11, wherein when the router is set as the priority router, the router broadcasts predetermined external route learning data having the external virtual address as a source address to the external network. Wireless communication device.

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