JP7740797B2 - Relay device, relay method, and computer program - Google Patents

Description

This disclosure relates to a relay device, a relay method, and a computer program.

Patent Document 1 describes a traffic control system including a central device installed in a traffic control center, one or more line aggregation devices (relay devices), and one or more terminal devices.
In the traffic control system of Patent Document 1, the line aggregation device communicates with a central device using an upper-side transmission method that includes a mobile line in the communication path, and communicates with multiple terminal devices (traffic signal controllers, optical beacons, vehicle detectors, traffic information boards, etc.) using a lower-side transmission method that uses a wired medium as the communication path.

Japanese Patent Application Laid-Open No. 2020-87144

In a traffic control system that remotely controls traffic signal controllers, downlink information provided by a central device to the traffic signal controllers includes signal control commands, etc., and uplink information provided by the traffic signal controllers to the central device includes signal control execution information and signal operation status information, etc.
On the other hand, mobile lines can be unstable depending on the radio wave conditions, so if a mobile line is included in the communication path from the line aggregation device to the central device, there is a concern that the above information may not be transmitted during periods of communication interruption on the mobile line.

If uplink information such as signal control execution information and signal operation status information, which are collected by the central device as management information for traffic signal controllers, is missing from the above information, it may not be possible to respond to inquiries about the situation when a traffic accident occurs near an intersection.
The present disclosure aims to provide a relay device that can prevent the loss of uplink information collected by a central device.

A device according to one aspect of the present disclosure is a relay device that communicates with a central device via an upper-side transmission method that includes a mobile line as a communication path, and communicates with a traffic signal controller via a lower-side transmission method that uses a wired medium as a communication path. The device comprises an upper-side transceiver that performs signal processing based on the upper-side transmission method, a lower-side transceiver that performs signal processing based on the lower-side transmission method, a communication control unit that relays downlink frames from the upper-side transceiver to the lower-side transceiver and uplink frames from the lower-side transceiver to the upper-side transceiver, and a memory unit that has a storage area for uplink information included in the uplink frames. When the communication control unit detects a communication interruption on the mobile line, it stores the uplink information in the memory unit, and when it detects communication recovery on the mobile line, it outputs the uplink frames including the uplink information stored in the memory unit to the upper-side transceiver.

A method according to one aspect of the present disclosure is a relay method executed by a relay device that communicates with a central device via an upper-side transmission method that includes a mobile line as a communication path, and communicates with a traffic signal controller via a lower-side transmission method that uses a wired medium as a communication path, and includes the steps of relaying downstream frames from an upper-side transceiver that performs signal processing based on the upper-side transmission method to a lower-side transceiver that performs signal processing based on the lower-side transmission method, relaying upstream frames from the lower-side transceiver to the upper-side transceiver, and, when a communication interruption on the mobile line is detected, storing the uplink information in a memory unit of the relay device, and, when a communication recovery on the mobile line is detected, outputting an upstream frame including the uplink information stored in the memory unit to the upper-side transceiver.

A computer program according to one aspect of the present disclosure causes a computer to function as a relay device that communicates with a central device via an upper-side transmission method that includes a mobile line as a communication path, and communicates with a traffic signal controller via a lower-side transmission method that uses a wired medium as a communication path. The computer program causes the computer to function as an upper-side transceiver that performs signal processing based on the upper-side transmission method, a lower-side transceiver that performs signal processing based on the lower-side transmission method, a communication control unit that relays downlink frames from the upper-side transceiver to the lower-side transceiver and relays uplink frames from the lower-side transceiver to the upper-side transceiver, and a memory unit having a storage area for uplink information included in the uplink frames. When a communication interruption on the mobile line is detected, the communication control unit stores the uplink information in the memory unit, and when a communication recovery on the mobile line is detected, the communication control unit outputs an uplink frame including the uplink information stored in the memory unit to the upper-side transceiver.

The present disclosure can be realized not only as a system and device having the characteristic configuration described above, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the system and device.

This disclosure provides a relay device or the like that can prevent loss of uplink information collected by a central device.

FIG. 1 is a block diagram showing an example of the overall configuration of a traffic control system. FIG. 2 is a definition diagram showing an example of a format of a signal control command. FIG. 3 is a definition diagram showing an example of the format of the signal control execution information. FIG. 4 is a definition diagram showing an example of the format of the signal operation status information. FIG. 5 is a block diagram showing an example of the internal configuration of a line aggregation device. FIG. 6 is a state transition diagram showing an example of changes in the uplink operation of the communication control unit. FIG. 7 is an explanatory diagram showing an example of a transmission path of uplink information.

Overview of the embodiments of the present disclosure
The following provides an outline of embodiments of the present disclosure.
(1) A relay device of this embodiment is a relay device that communicates with a central device by an upper-side transmission method that includes a mobile line in the communication path, and communicates with a traffic signal controller by a lower-side transmission method that uses a wired medium as the communication path, and is equipped with an upper-side transceiver unit that performs signal processing based on the upper-side transmission method, a lower-side transceiver unit that performs signal processing based on the lower-side transmission method, a communication control unit that relays downlink frames from the upper-side transceiver unit to the lower-side transceiver unit and relays uplink frames from the lower-side transceiver unit to the upper-side transceiver unit, and a memory unit that has a storage area for uplink information included in the uplink frames, and when the communication control unit detects a communication interruption of the mobile line, it stores the uplink information in the memory unit, and when it detects communication recovery of the mobile line, it outputs an uplink frame including the uplink information stored in the memory unit to the upper-side transceiver unit.

According to the relay device of this embodiment, when the communication control unit detects a communication interruption on the mobile line, it stores uplink information in the memory unit, and when it detects communication recovery on the mobile line, it outputs an upstream frame including the uplink information stored in the memory unit to the upper transceiver unit.
Therefore, the uplink information transmitted by the traffic signal controller during the period of communication interruption of the mobile line can be provided to the central unit after communication is restored on the mobile line, thereby preventing the central unit from losing the uplink information it collects.

(2) In the relay device of this embodiment, when the uplink information includes first uplink information that includes time information but does not include date information, it is preferable that the communication control unit adds date information corresponding to the reception time of the upstream frame including the first uplink information to the first uplink information, and stores the first uplink information with the date information in the memory unit.
In this case, the central device can determine the chronological order of the plurality of pieces of first uplink information by using a combination of date information and time information included in the first uplink information.

(3) In the relay device of this embodiment, the first uplink information preferably includes signal control execution information indicating the control content executed by the traffic signal controller in the previous cycle.
The reason is that the signal control execution information defined in the current standard (e.g., "U-type traffic signal controller U-type communication application standard") includes time information but does not include date information, and is therefore suitable as the first uplink information.

(4) In the relay device of this embodiment, when the uplink information includes second uplink information that does not include both time information and date information, it is preferable that the communication control unit adds time information and date information corresponding to the reception time of the upstream frame including the second uplink information to the second uplink information, and stores the second uplink information with the time information and date information in the memory unit.
In this case, the central device can determine the time of occurrence of the second uplink information and the chronological order of the multiple pieces of second uplink information by combining the time information and date information contained in the second uplink information.

(5) In the relay device of this embodiment, the second uplink information preferably includes signal operation status information indicating the operation status of the traffic signal controller in the current cycle.
The reason is that the signal operation status information defined in the current standard (e.g., "U-type traffic signal controller U-type communication application standard") does not include both date information and time information, and is therefore suitable as second uplink information.

(6) In the relay device of this embodiment, it is preferable that the storage unit includes a non-volatile memory having a storage area for the uplink information, and that the communication control unit, upon detecting a communication interruption on the mobile line, writes the uplink information from a predetermined time before the time of detection into the non-volatile memory.

In this case, since the uplink information is stored in a nonvolatile memory, the stored uplink information is not erased even if a power outage occurs in the relay device.
In addition, since uplink information from a predetermined time before the time of detection is written to non-volatile memory, the possibility that the written uplink information will be data that is outdated from the time the central device determines that there is a defect is reduced, thereby increasing the usefulness of the information.

(7) In the relay device of this embodiment, it is preferable that the communication control unit has a volatile memory in which a ring buffer that constantly buffers the uplink information is set, and when a communication interruption of the mobile line is detected, the communication control unit writes data from a read point to a write point of the ring buffer to the non-volatile memory.
In this case, a nonvolatile memory capable of reading uplink information from a predetermined time before the detection time can be easily implemented by simply setting a ring buffer.

(8) The relay method of this embodiment is a method executed by the relay devices described above in (1) to (7). Therefore, the relay method of this embodiment has the same effects as the relay devices described above in (1) to (7).
(9) The computer program of this embodiment is a program that causes a computer to function as the relay device described above in (1) to (7). Therefore, the computer program of this embodiment has the same effects as the relay devices described above in (1) to (7).

<Details of the embodiment of the present disclosure>
Hereinafter, details of embodiments of the present disclosure will be described with reference to the drawings. Note that at least some of the embodiments described below may be combined in any manner.

[Overall system configuration]
FIG. 1 is a block diagram showing an example of the overall configuration of a traffic control system 10.
As shown in FIG. 1, a traffic control system 10 of this embodiment includes a central device 1, one or more line consolidation devices 2, and one or more terminal devices 3.
The central device 1 is installed in a traffic control center or the like. The line concentrating device 2 is a type of relay device installed at an intersection or road relatively far from the central device 1. The terminal device 3 is installed at an intersection or road relatively close to the line concentrating device 2.

In this embodiment, information included in a downstream transmission signal from the central device 1 to the terminal device 3 is referred to as "downlink information DL." Information included in an upstream transmission signal from the terminal device 3 to the central device 1 is referred to as "uplink information UL."
The communication between the central device 1 and the line consolidation device 2 is called "upper side communication," and the transmission method used for the upper side communication is called "upper side transmission method." The communication between the line consolidation device 2 and the terminal device 3 is called "lower side communication," and the transmission method used for the lower side communication is called "lower side transmission method."

The upper-side transmission method is, for example, the "UD type transmission method." The UD type transmission method conforms to the "UD type interface standard" established by the Universal Transport Management System Association (UMTS Association), and is a transmission method capable of IP (Internet Protocol) communication.
The lower-level transmission method is, for example, the "U-type transmission method." The U-type transmission method conforms to the "U-type interface standard" established by the UMTS Association, and is a serial communication method in which IP communication is not possible.

The lower-side transmission method is not limited to the U-type transmission method, but may be any other transmission method defined by the UMTS Association (for example, the M-type transmission method or the S9-type transmission method).The lower-side transmission method may also be the same method as the upper-side transmission method (for example, the UD-type transmission method).
When two or more terminal devices 3 are connected to one line aggregation device 2, the lower-level transmission method may be a mixture of at least two types of transmission methods.

The central device 1 is, for example, a personal computer (PC) server, and includes a communication device (not shown) capable of communication based on a predetermined upper-level transmission method. The terminal device 3 is, for example, a traffic signal controller that controls the lighting status of traffic lights included in traffic signals at intersections.
The terminal devices 3 connected to the line aggregation device 2 may include traffic control devices such as optical beacons, vehicle detectors, and traffic information boards in addition to the traffic signal controller. Furthermore, one or more other terminal devices may be connected downstream of the traffic signal controller 3.

The line aggregation device 2 is a type of relay device (gateway) capable of both upper-side communication with the central device 1 based on an upper-side transmission method and lower-side communication with one or more terminal devices 3 based on a lower-side transmission method.
The communication path for the upper side communication includes a wireless medium (mobile line) 5 conforming to standards such as LTE (Long Term Evolution) or the fifth generation mobile communication system (5G). The communication path for the lower side communication includes a wired medium (communication cable) 6 such as a dedicated line or a private line.

The central device 1 transmits a transmission signal based on the upper transmission method, including downlink information DL intended for the subordinate traffic signal controller 3, to the wireless base station 4. The wireless base station 4 transfers the received transmission signal to the line aggregation device 2.
The line consolidation device 2 extracts the downlink information DL from the received transmission signal, and generates a transmission signal based on the lower-side transmission method, including the extracted downlink information DL. The line consolidation device 2 transmits the generated transmission signal to the traffic signal controller 3 of the predetermined destination.

The traffic signal controller 3 transmits a transmission signal based on the lower-side transmission method, including uplink information UL for the central device 1, to the line aggregation device 2.
The line consolidation device 2 extracts the uplink information UL from the received transmission signal, and generates a transmission signal based on the upper-side transmission method, including the extracted uplink information UL. The line consolidation device 2 transmits the generated transmission signal to the wireless base station 4. The wireless base station 4 transfers the received transmission signal to the central device 1.

[Examples of downlink and uplink information]
The control methods for remotely controlling the traffic signal controller 3 executed by the central device 1 are roughly classified into a "step control type" and a "table control type."
The step control type is a system in which the central device 1 transmits a control signal (called a "step command") that commands the turning on or off of a signal lamp to the traffic signal controller 3. In this case, the central device 1 determines a signal control plan that specifies the duration of each step of the signal lamp, and transmits a step command at the time when the step changes in the determined signal control plan.

The table control type is a system in which the central device 1 transmits "signal control commands" (see Figure 2), which are the source data for the signal control plan, to the traffic signal controller 3. In this case, the traffic signal controller 3 determines the signal control plan based on the received signal control commands.
The traffic signal controller 3 turns on or off the signal lamps included in the traffic signal to which it supplies power in accordance with a signal control plan determined by the controller 3. The signal control plan is determined for each cycle for a predetermined period of time equal to or longer than the cycle.

The traffic control system 10 employs a table control method. Therefore, the downlink information DL generated by the central device 1 includes a "signal control command" (see FIG. 2).
In the table control system, the central device 1 does not determine the signal control plan, so it is necessary for the central device 1 to manage the control results of the traffic signal controller 3. Therefore, the uplink information UL generated by the traffic signal controller 3 includes "signal control execution information" (see FIG. 3) and "signal operation status information" (see FIG. 4).

The signal control execution information is information that indicates the control content that the traffic signal controller 3 executed in the previous cycle. The signal operation status information is information that indicates the operation status of the traffic signal controller 3 in the current cycle.
In the following, the signal control command, signal control execution information, and signal operation status information may be abbreviated as "control command,""executioninformation," and "status information," respectively.

Fig. 2 is a diagram showing an example of a format of a signal control command, Fig. 3 is a diagram showing an example of a format of signal control execution information, and Fig. 4 is a diagram showing an example of a format of signal operation status information.
The formats shown in Figures 2 to 4 are defined in the "U-Type Traffic Signal Controller U-Type Communication Application Standard" established by the UMTS Foundation. Therefore, details of the information included in each format are described in the standard.

When the central device 1 performs traffic-responsive control based on detector signals measured by vehicle detectors, it generates a signal control command and transmits the generated signal control command to the subordinate traffic signal controller 3 that is the object of control.
As shown in FIG. 2, the information stored in the signal control command includes the cycle length (seconds) to be executed by the traffic signal controller 3 in the next cycle, split n (n=1 to 6), and offset reference time.

The offset reference time of a signal control command is the time information for the first step at which the offset begins. The offset reference time (hours, minutes, and seconds) is expressed as binary values in bits D0 to D7, and the time range is 00:00:00 to 23:59:59.

The traffic signal controller 3 generates signal control execution information for the previous cycle and transmits the generated execution information to the central device 1 at the start of the current cycle.
As shown in Figure 3, the information stored in the signal control execution information includes the cycle start time of the previous cycle (start time of the first step), the number of seconds for each executed step, the sensory execution type indicating the type of terminal sensory control executed, and detector information measured by the vehicle detector (traffic volume and occupancy time).

The cycle start time of the signal control execution information is the time information of the first step when the cycle started. The cycle start time (hour, minute, second) is expressed as a binary value in bits D0 to D7, and the time range is 00:00:00 to 23:59:59.
As described above, the signal control execution information includes the cycle start time of the previous cycle, but does not include date information.

The traffic signal controller 3 generates signal operation status information at a predetermined cycle (for example, every second) that is shorter than the execution information, and transmits the generated status information to the central device 1 at the predetermined cycle.
As shown in Figure 4, the signal operation status information includes current stage information including the current indication status and stage number, and operation status for notifying of abnormal operation of the own device (such as timer abnormality or CPU abnormality). The current stage information is always transmitted to the central device 1 at the timing when the stage progresses. Note that the signal operation status information does not include date information or time information.

[Internal configuration of line aggregation device]
FIG. 5 is a block diagram showing an example of the internal configuration of the line consolidation device 2. As shown in FIG.
As shown in FIG. 5, the line consolidation device 2 includes a housing 20 that houses a plurality of electronic devices, and a wireless communication device 21 connected to the housing 20 .
The wireless communication device 21 is a communication device capable of wireless communication conforming to a mobile communication standard such as LTE or 5G, and wired communication conforming to an upper-side transmission method.

The electronic devices housed in the housing 20 of the line aggregation device 2 include an upper-side transmitting/receiving unit 22, a plurality of lower-side transmitting/receiving units 23, a communication control unit 24, a storage unit 25, a synchronization processing unit 26, and the like.
The housing 20 has one upper port P that conforms to an upper transmission method (e.g., a UD-type transmission method) and multiple lower ports Qi (i = 1, 2...n) that conform to a lower transmission method (e.g., a U-type transmission method).

The upper port P is electrically connected to an upper transmitting/receiving unit 22 , which is electrically connected to a communication control unit 24 .
One end of a wired medium (communication cable) 7 conforming to the upstream transmission method is connected to the upstream port P. The other end of the wired medium 7 is connected to a wireless communication device 21.

The lower side ports Qi are electrically connected to the lower side transceivers 23 in one-to-one correspondence, and the plurality of lower side transceivers 23 are electrically connected to the communication control unit 24, respectively.
One end of a wired medium 6 (see FIG. 1) conforming to the downstream transmission method is connected to at least one of the multiple downstream ports Qi. The other end of the wired medium 6 is connected to a traffic signal controller 3. Traffic control devices other than the traffic signal controller 3 (such as optical beacons, vehicle detectors, and traffic information boards) can also be connected to the downstream port Qi.

The upper-side transceiver 22 is a communication interface that performs predetermined signal processing (modulation/demodulation, AD/DA conversion, etc.) based on the upper-side transmission method. The upper-side transceiver 22 demodulates the transmission signal (carrier signal) input from the upper-side port P to reproduce the downstream frame.
The upper side transmitting/receiving unit 22 outputs the regenerated downstream frame to the communication control unit 24. The upper side transmitting/receiving unit 22 modulates the upstream frame input from the communication control unit 24 into a transmission signal of a predetermined frequency. The upper side transmitting/receiving unit 22 outputs the modulated transmission signal to the upper side port P.

The wireless communication device 21 recovers downstream frames from the transmission signal (radio wave) received from the antenna, modulates the recovered downstream frames into a transmission signal of a predetermined frequency, and outputs the modulated transmission signal to the wired medium 7.
The wireless communication device 21 recovers an upstream frame from a transmission signal (carrier signal) received from the wired medium 7. The wireless communication device 21 modulates the recovered upstream frame into a transmission signal (radio wave) of a predetermined frequency, and transmits the modulated transmission signal from an antenna.

The downstream side transmitting/receiving unit 23 is a communication interface that performs predetermined signal processing (modulation/demodulation, AD/DA conversion, etc.) based on the downstream side transmission method. The downstream side transmitting/receiving unit 23 demodulates the transmission signal (carrier signal) input from the downstream side port Qi to regenerate the upstream frame.
The lower-side transmitter/receiver 23 outputs the reproduced upstream frame to the communication control unit 24. The lower-side transmitter/receiver 23 modulates the downstream frame input from the communication control unit 24 into a transmission signal of a predetermined frequency. The lower-side transmitter/receiver 23 outputs the modulated transmission signal to the lower-side port Qi.

The communication control unit 24 is composed of a processing unit including a central processing unit (CPU) and random access memory (RAM). The storage unit 25 is composed of an auxiliary storage device including at least one nonvolatile memory selected from the group consisting of a hard disk drive (HDD) and a solid state drive (SDD). The storage unit 25 may also include a flash read-only memory (ROM), a universal serial bus (USB) memory, an SD card, or the like.
The communication control unit 24 reads out the computer program stored in the storage unit 25 into the main memory (RAM) and performs various information processing in accordance with the program.

The communication control unit 24 may include an integrated circuit including a field-programmable gate array (FPGA) and an application-specific integrated circuit (ASIC) instead of or in addition to the CPU.
The communication control unit 24 is capable of performing relay processing involving format conversion on communication frames in both the uplink and downlink directions input from the respective transmitting/receiving units 22 and 23 .

Specifically, the communication control unit 24 converts downstream frames of an upper-side transmission method (e.g., UD-type transmission method) input from the upper-side transceiver unit 22 into a format of a lower-side transmission method (e.g., U-type transmission method).
The communication control unit 24 outputs the converted downstream frame of the lower-side transmission method (for example, the U-type transmission method) to the lower-side transceiver unit 23 corresponding to the traffic signal controller 3 of the predetermined destination. Note that the communication control unit 24 has preset information for determining to which lower-side transceiver unit 23 the converted downstream frame should be output.

Conversely to the above, the communication control unit 24 converts the upstream frame of the lower-side transmission method (e.g., U-type transmission method) input from the lower-side transceiver unit 23 into a format of the upper-side transmission method (e.g., UD-type transmission method).
The communication control unit 24 outputs the converted upstream frame of the upper side transmission method (for example, the UD type transmission method) to the upper side transmitting/receiving unit 22.

Note that if the upper-side transmission method and the lower-side transmission method are the same (for example, if both are UD-type transmission methods), the communication control unit 24 does not perform the above format conversion, and routing is performed based on MAC addresses, IP addresses, etc. The path information required for routing is set in advance in the communication control unit 24.

The storage unit 25 has a storage area for uplink information UL. The uplink information UL stored in the storage area includes the signal control execution information and signal operation status information described above.
The communication control unit 24 can store the uplink information UL contained in the upstream frame in the memory unit 25 and transmit the stored uplink information UL to the central device 1 depending on the communication status of the mobile line used for upper-level communication.

Specifically, when the communication control unit 24 detects a communication interruption on the mobile line, it extracts uplink information UL from the upstream frame input from the upper transceiver unit 22 and stores the extracted information in the memory unit 25 (data accumulation processing).
When the communication control unit 24 detects that communication has been restored when communication on the mobile line is interrupted, it generates an upstream frame of the upper transmission method including the uplink information UL read from the memory unit 25, and outputs the generated upstream frame to the upper transceiver unit (transmission process of stored data).

The synchronization processing unit 26 is a processing unit for achieving time synchronization with other communication nodes such as the central device 1 using a predetermined synchronization method. The communication control unit 24 determines the reception time and transmission timing of a communication frame according to the local time generated by the synchronization processing unit 26.
The synchronization method of the synchronization processing unit 26 may be, for example, a synchronization method based on the output of a GNSS (Global Navigation Satellite System) receiver, or a synchronization method using communication frames such as NTP (Network Time Protocol) and PTP (Precision Time Protocol).

[Uplink operation of communication control unit]
FIG. 6 is a state transition diagram showing an example of changes in the uplink operation of the communication control unit 24.
As shown in FIG. 6, in the normal state (state S1) after startup by turning on the power, the communication control unit 24 executes "normal uplink processing."
Normal uplink processing involves converting the format of an upstream frame input from the lower-side transceiver 23 and then outputting the frame to the upper-side transceiver 22. Note that if the transmission method is the same on the upper and lower sides, format conversion is not required.

When a communication interruption (condition C1) of the mobile line is detected in the normal state (state S1) and the state changes to a communication interruption state (state S2), the communication control unit 24 executes a "data accumulation process" of the uplink information UL.
When communication recovery (condition C2) of the mobile line is detected in a communication interruption state (state S2), and the state is restored (state S3), the communication control unit 24 executes "normal uplink processing" and "accumulated data transmission processing."

When the recovery state (state S3) is restored and the state returns to normal (state S1) by detecting completion of data transmission (condition C3) of the accumulated uplink information UL, the communication control unit 24 executes only "normal uplink processing."

The communication control unit 24 may determine the communication state of the mobile line using, for example, the following first to fifth methods: The first method is a method that uses the data loss rate of downlink information DL (e.g., signal control command).
In this case, the communication control unit 24 determines that communication on the mobile line has been interrupted if the data loss rate remains above a predetermined threshold for a predetermined period of time or more, and then determines that communication on the mobile line has been restored if the data loss rate returns to below the predetermined threshold for a predetermined period of time or more.

In the first method, to prevent chattering in determining whether communication has been interrupted or restored, it is preferable to set the first threshold for determining whether communication has been interrupted and the second threshold for determining whether communication has been restored to different values, and to provide hysteresis, for example, so that the first threshold is greater than the second threshold.

The second method is to use a dedicated message defined for monitoring mobile lines, which is sent from the central device 1 to the line aggregation device 2 periodically (for example, every second).
In this case, the communication control unit 24 determines that communication on the mobile line has been interrupted if reception of the dedicated message has ceased for a predetermined period of time (e.g., 10 seconds) or more, and determines that communication on the mobile line has been restored if periodic reception of the dedicated message resumes thereafter. Note that a periodic reception of the dedicated message resumes when, for example, a dedicated message transmitted every second is received three or more times in a row at one-second intervals.

The third method is a method that uses communication (for example, Ping) sent and received between the central device 1 and the terminal device 3 to check communication.
In this case, the communication control unit 24 determines that communication on the mobile line has been interrupted if the packet loss rate stated in the response message of the terminal device 3 remains above a predetermined threshold for a predetermined period of time or more, and then determines that communication on the mobile line has been restored if the packet loss rate has returned to below the predetermined threshold for a predetermined period of time or more.

In the third method, too, to prevent chattering in determining whether communication has been interrupted or restored, it is preferable to set the first threshold for determining whether communication has been interrupted and the second threshold for determining whether communication has been restored to different values, and to provide hysteresis, for example, so that the first threshold is greater than the second threshold.

The fourth method is a method that uses a status signal such as a CD (Carrier Detect) signal output by the wireless communication device 21 .
In this case, the communication control unit 24 determines that communication on the mobile line has been interrupted when the status signal notified from the wireless communication device 21 turns off (disconnected), and then determines that communication on the mobile line has been restored when the status signal returns to on (communicating).

The fifth method is a method in which, when the central device 1 and the line consolidation device 2 communicate using a DATEX-ASN message sequence, the line consolidation device 2 issues an acknowledgement (accept) immediately before the response timeout time.
In this case, the communication control unit 24 determines that communication on the mobile line has been interrupted if the retransmission time has elapsed after sending a message requiring a response from its own device 2, or if past communication history indicates that the response may have been interrupted, and determines that communication on the mobile line has been restored if a delayed response is received or if a separate sequence message is received prompting reconnection of the DATAX message.

In the DATEX-ASN message sequence, several types of timers are defined, including the following timers Tc1 to Tc3, but any of the timers may be used.
Tc1: Response waiting timer for session establishment requests and session termination requests from the client side. Tc2: Response waiting timer for information requests and file reception completion requests from the client side. Tc3: Session maintenance request issuance period timer from the client side.

[Uplink information transmission path]
FIG. 7 is an explanatory diagram showing an example of a transmission path of the uplink information UL.
As described above, in the normal state S1, the communication control unit 24 executes normal uplink processing (see FIG. 6).
Therefore, the uplink information UL (for example, execution information and status information) transmitted by the traffic signal controller 3 is not stored in the memory unit 25 of the line concentrator 2 but is transferred to the central device 1 by the line concentrator 2 .

As described above, in the communication cutoff state S2, the communication control unit 24 executes the data accumulation process (see FIG. 6).
Therefore, the uplink information UL (e.g., execution information and status information) sent by the traffic signal controller 3 is not transferred to the central device 1, but is stored in the memory unit 25 of the line aggregation device 2. In the communication cutoff state S2, the traffic signal controller 3 cannot obtain the downlink information DL (e.g., signal control command), so it controls the signal lamp for a set number of seconds or calculates the split using an automatic generation function, for example.

As described above, in the recovery state S3, the communication control unit 24 executes both the normal uplink process and the process of transmitting stored data (see FIG. 6).
Therefore, when the uplink information UL (e.g., execution information and status information) transmitted by the traffic signal controller 3 is transferred to the central unit 1 by the line aggregation device 2, the uplink information UL stored in the memory unit 25 is transmitted to the central unit 1 by the line aggregation device 2.

[Add date information]
As shown in FIG. 3, the signal control execution information includes the cycle start time (start time of the first stage) but does not include date information.
Therefore, for example, if the following three types of execution information A to C are stored in the memory unit 25 and then the line aggregation device 2 simultaneously transmits these pieces of execution information A to C to the central device 1, the central device 1 cannot identify the chronological order of the acquired execution information A to C.

Execution information A: Cycle start time = 23:58:20 (actual date is November 10th)
Execution information B: Cycle start time = 00:00:20 (actual date is November 11th)
Execution information C: Cycle start time = 00:02:20 (actual date is November 11th)

In other words, if execution information A, whose cycle start time is before midnight, and execution information B and C, whose cycle start time is after midnight, are sent to the central unit 1 simultaneously, the receiving central unit 1 cannot determine whether the chronological order of the execution information is A → B → C or B → C → A.
Therefore, in this embodiment, in the data accumulation process of the execution information, the communication control unit 24 of the line aggregation device 2 adds date information to the execution information and stores it in the storage unit 25. The date to be added to the execution information may be determined, for example, from the reception time of the upstream frame including the execution information.

When the recovery state is reached, the communication control unit 24 reads out a plurality of pieces of execution information to which date information has been added from the storage unit 25 and transmits an upstream frame including the read execution information to the central device 1 .
Therefore, the central device 1 can determine the chronological order of a plurality of pieces of execution information based on the combination of time information and date information contained in the execution information.

[Addition of time and date information]
As shown in FIG. 4, the signal operating status information does not include time information and date information.
Therefore, for example, if multiple pieces of status information received at different times are stored in the memory unit 25 and then the line aggregation device 2 simultaneously transmits these pieces of status information to the central device 1, the central device 1 cannot identify the time of occurrence of the execution stage information contained in the status information or the chronological order of the multiple pieces of status information.

In this embodiment, the communication control unit 24 of the line aggregation device 2 adds time information and date information to the status information during the data accumulation process of the status information and stores it in the memory unit 25. The time and date to be added to the status information may be determined, for example, from the reception time of the upstream frame containing the status information.

When the signal is restored, the communication control unit 24 reads the signal operation status information with the time information and date information added from the storage unit 25 and transmits an upstream frame including the read status information to the central device 1.
Therefore, the central device 1 can determine the occurrence time of the execution stage information contained in the status information and the chronological order of multiple status information by combining the time information and date information contained in the status information.

[Improving efficiency in terms of accumulation frequency and type of information]
One possible method for determining which data (e.g., execution information and status information: hereinafter referred to as "accumulated data") accumulated during a period of communication interruption on the mobile line to send to the central device 1 is to make the determination in response to a request from the central device 1.
Specifically, this method involves the central device 1 determining whether or not there is any missing execution information and status information at predetermined intervals (e.g., every few days), and sending a request to the line aggregation device 2 to resend information for the missing time period.

In this case, the line consolidation device 2 extracts from the storage unit 25 the accumulated data for the time period specified by the information retransmission request, and transmits an upstream frame including the extracted accumulated data to the central device 1 .
In the case of a line aggregation device 2 aggregating multiple wired media 6 (for example, four lines), if the memory capacity is 1 MB and one cycle takes an average of 60 seconds, the signal control execution information is 246 bytes, so it can only store a maximum of about 0.7 days' worth of data. Therefore, if the central device 1 issues a retransmission request once every few days, there is a possibility that data will be lost from the stored data.

To solve this problem, the memory capacity can be increased, but this increases the manufacturing cost of the line consolidation device 2, so it is preferable to reduce the data capacity of the stored data.
Possible methods for reducing the amount of stored data include streamlining the storage frequency (hereinafter referred to as "Method 1") and streamlining the type of information to be stored (hereinafter referred to as "Method 2"). In this embodiment, data storage processing is performed only during periods when communication is interrupted on the mobile line (state S2 in FIG. 6), so it can be said that Method 1 is the appropriate storage frequency.

One example of the efficiency improvement of information type (method 2) is to store only the first 39 bytes of the "control execution information" portion of the signal control execution information (see FIG. 3). The information after the control execution information is measurement information such as sensor information, and loss of data in the central device 1 does not pose much of a problem.
If only the first 39 bytes are to be stored, for example, if the memory capacity is 1 MB and one cycle takes an average of 60 seconds, the amount of storage can be increased to a maximum of four days' worth.

[Simultaneous use of volatile and non-volatile memory]
If the accumulated data is stored in a volatile memory, the accumulated data will be erased when the power is turned off. Therefore, it is preferable to store the accumulated data in a non-volatile memory of the storage unit 25.
However, the nonvolatile memory (flash ROM) commonly used in the line aggregation device 2 has an upper limit (for example, 10 million times) on the number of times it can be written to. Therefore, if execution information and status information are unconditionally written to the storage unit 25, there is a possibility that the number of times it can be written to will reach the upper limit in a short period of time.

In this regard, in this embodiment, the data accumulation process is performed only during the period when communication on the mobile line is interrupted (state S2 in FIG. 6), which has the advantage of reducing the number of times accumulated data is written to the storage unit 25, which is made of non-volatile memory.
On the other hand, in the method of storing data in response to the detection of a communication interruption, the data may be stored with a slight delay from the time when the central device 1 determines that there is a loss.

Therefore, in the data accumulation process triggered by the detection of a communication interruption, it is preferable to add and accumulate data for a predetermined period of time (for example, several seconds) before the communication interruption is detected.
Specifically, a ring buffer having a predetermined data capacity is set in the volatile memory 24 of the communication control unit, and the signal control execution information and operation status information are always buffered in the ring buffer.

In this case, the communication control unit 24 can copy the data from the read point to the write point in the ring buffer to the nonvolatile memory when it detects a communication interruption on the mobile line. In this way, the accumulated data from a predetermined time before the communication interruption is detected can be copied to the nonvolatile memory.
Copying from the ring buffer in the volatile memory to the nonvolatile memory may be performed not only when a communication interruption is detected, but also periodically, at night, or when the CPU load is light.

[Effects of line aggregation devices]
As described above, according to the line aggregation device (relay device) 2 of this embodiment, when the communication control unit 24 detects a communication interruption on the mobile line, it stores the uplink information UL in the memory unit 25 (state S2 in FIG. 6: data accumulation processing), and when it detects a communication recovery on the mobile line, it outputs an upstream frame including the uplink information UL stored in the memory unit 25 to the upper-side transceiver unit 22 (state S3 in FIG. 6: accumulated data transmission processing).

As a result, uplink information UL (e.g., signal control execution information and signal operation status information) transmitted by the traffic signal controller 3 during a mobile line communication outage can be provided to the central device 1 after mobile line communication is restored. This prevents a loss of uplink information UL collected by the central device 1.

[Other Modifications]
The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of equivalents to the configurations described in the claims.

For example, in the above-described embodiment, the wireless communication device 21 may be housed in the housing 20. Furthermore, the upper transceiver 22 may not be housed in the housing 20, but may be integrated into the wireless communication device 21 connected to the housing 20. Furthermore, the wireless communication device 21 and the upper transceiver 22 may be integrated into an interface such as a single communication board.
In the above-described embodiment, the storage unit 25 may be an external auxiliary storage device provided outside the housing 20 .

1 Central device 2 Line aggregation device (relay device)
3. Terminal device (traffic signal controller)
4. Wireless base station 5. Wireless medium (mobile line)
6. Wired media (communication cables)
7. Wired media (communication cables)
10 Traffic control system 20 Housing 21 Wireless communication device 22 Upper side transceiver unit 23 Lower side transceiver unit 24 Communication control unit 25 Storage unit 26 Synchronization processing unit P Upper side port Qi Lower side port UL Uplink information (signal control execution information, signal operation status information)
DL Downlink information (signal control command)

Claims (12)

A relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit;
a storage unit having a storage area for uplink information included in the upstream frame,
The communication control unit
when detecting a communication interruption of the mobile line, storing the uplink information in the storage unit, and when detecting a communication recovery of the mobile line, outputting an upstream frame including the uplink information stored in the storage unit to the upper transceiver unit;
The uplink information includes:
First uplink information including time information but not date information is included;
The communication control unit
A relay device that adds date information corresponding to the reception time of the upstream frame including the first uplink information to the first uplink information and stores the first uplink information with the date information in the memory unit. The first uplink information includes:
The relay device according to claim 1, further comprising signal control execution information indicating the control content executed by the traffic signal controller in the previous cycle. A relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit;
a storage unit having a storage area for uplink information included in the upstream frame,
The communication control unit
when detecting a communication interruption of the mobile line, storing the uplink information in the storage unit, and when detecting a communication recovery of the mobile line, outputting an upstream frame including the uplink information stored in the storage unit to the upper transceiver unit;
The uplink information includes:
second uplink information that does not include both time information and date information;
The communication control unit
A relay device that adds time information and date information corresponding to the reception time of the upstream frame including the second uplink information to the second uplink information, and stores the second uplink information with the time information and date information in the memory unit. The second uplink information includes:
4. The relay device according to claim 3, further comprising signal operation status information indicating the operation status of the traffic signal controller in the current cycle. A relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit;
a storage unit having a storage area for uplink information included in the upstream frame,
The communication control unit
when detecting a communication interruption of the mobile line, storing the uplink information in the storage unit, and when detecting a communication recovery of the mobile line, outputting an upstream frame including the uplink information stored in the storage unit to the upper transceiver unit;
The storage unit
a non-volatile memory having a storage area for the uplink information;
The communication control unit
When a communication interruption of the mobile line is detected, the relay device writes the uplink information from a predetermined time before the time of the detection into the nonvolatile memory. The communication control unit
The relay device according to claim 5, further comprising a volatile memory configured with a ring buffer that constantly buffers the uplink information, and when a communication interruption of the mobile line is detected, the relay device writes data from the read point to the write point of the ring buffer to the non-volatile memory. A relay method executed by a relay device, which communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
relaying a downstream frame from an upper-side transceiver that performs signal processing based on the upper-side transmission method to a lower-side transceiver that performs signal processing based on the lower-side transmission method;
relaying an upstream frame from the lower-side transceiver unit to the upper-side transceiver unit;
a step of storing uplink information included in the uplink frame in a storage unit of the device when a communication interruption of the mobile line is detected, and outputting an uplink frame including the uplink information stored in the storage unit to the upper transceiver unit when a communication recovery of the mobile line is detected;
When the uplink information includes first uplink information that includes time information but not date information, adding date information corresponding to the reception time of the upstream frame that includes the first uplink information to the first uplink information, and storing the first uplink information with the date information in the memory unit. A relay method executed by a relay device, which communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
relaying a downstream frame from an upper-side transceiver that performs signal processing based on the upper-side transmission method to a lower-side transceiver that performs signal processing based on the lower-side transmission method;
relaying an upstream frame from the lower-side transceiver unit to the upper-side transceiver unit;
a step of storing uplink information included in the uplink frame in a storage unit of the device when a communication interruption of the mobile line is detected, and outputting an uplink frame including the uplink information stored in the storage unit to the upper transceiver unit when a communication recovery of the mobile line is detected;
When the uplink information includes second uplink information that does not include both time information and date information, adding time information and date information corresponding to the reception time of the upstream frame including the second uplink information to the second uplink information, and storing the second uplink information with the time information and date information in the memory unit. A relay method executed by a relay device, which communicates with a central device by an upper-side transmission method including a mobile line as a communication path, and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
relaying a downstream frame from an upper-side transceiver that performs signal processing based on the upper-side transmission method to a lower-side transceiver that performs signal processing based on the lower-side transmission method;
relaying an upstream frame from the lower-side transceiver unit to the upper-side transceiver unit;
when a communication interruption of the mobile line is detected, storing uplink information included in the uplink frame in a storage unit of the device itself, and when a communication recovery of the mobile line is detected, outputting an uplink frame including the uplink information stored in the storage unit to the upper transceiver unit,
A relay method in which the processing performed when a communication interruption of the mobile line is detected is to write the uplink information from a predetermined time before the time of detection into a non-volatile memory included in the memory unit and having a storage area for the uplink information. A computer program for causing a computer to function as a relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
The computer
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit; and
a storage unit having a storage area for uplink information included in the upstream frame;
The communication control unit
when detecting a communication interruption of the mobile line, storing the uplink information in the storage unit, and when detecting a communication recovery of the mobile line, outputting an upstream frame including the uplink information stored in the storage unit to the upper transceiver unit;
The uplink information includes:
First uplink information including time information but not date information is included;
The communication control unit
A computer program that adds date information corresponding to the reception time of the upstream frame including the first uplink information to the first uplink information, and stores the first uplink information with the date information in the memory unit. A computer program for causing a computer to function as a relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
The computer
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit; and
a storage unit having a storage area for uplink information included in the upstream frame;
The communication control unit
When a communication interruption of the mobile line is detected, the uplink information is stored in the storage unit, and when a communication recovery of the mobile line is detected, an upstream frame including the uplink information stored in the storage unit is output to the upper transceiver unit;
The uplink information includes:
second uplink information that does not include both time information and date information;
The communication control unit
A computer program that adds time information and date information corresponding to the reception time of the upstream frame including the second uplink information to the second uplink information, and stores the second uplink information with the time information and date information in the memory unit. A computer program for causing a computer to function as a relay device that communicates with a central device by an upper-side transmission method including a mobile line as a communication path and communicates with a traffic signal controller by a lower-side transmission method using a wired medium as a communication path,
The computer
an upper-side transceiver that performs signal processing based on the upper-side transmission method;
a lower-side transceiver that performs signal processing based on the lower-side transmission method;
a communication control unit that relays downstream frames from the upper-side transceiver unit to the lower-side transceiver unit and upstream frames from the lower-side transceiver unit to the upper-side transceiver unit; and
a storage unit having a storage area for uplink information included in the upstream frame;
The communication control unit
When a communication interruption of the mobile line is detected, the uplink information is stored in the storage unit, and when a communication recovery of the mobile line is detected, an upstream frame including the uplink information stored in the storage unit is output to the upper transceiver unit;
The storage unit
a non-volatile memory having a storage area for the uplink information;
The communication control unit
A computer program that, when a communication interruption of the mobile line is detected, writes the uplink information from a predetermined time before the time of the detection into the nonvolatile memory.