JP2010226671A - On-vehicle communication device, data distribution method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase transmission efficiency by selecting and receiving suitable data when acquiring version-managed data through respective access points with respect to data communication between a plurality of wireless LAN ground communication devices scattered along a railroad line and an on-vehicle communication device on a train. <P>SOLUTION: A reception necessity decision unit 401 determines that reception is unnecessary when the whole data to which a holding version ID which is the same as or newer than a transmission version ID that a cache server can transfer is added is already stored. When it is determined that reception is necessary and partial data of a transmission version ID is already stored, a data reception unit 403 receives the remaining data from the cache server through a wireless access point. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to data communication between a plurality of wireless LAN terrestrial communication devices scattered along a railway line and an on-vehicle communication device of a train.

  Patent Document 1 “Data Distribution Support Method for Mobiles” (Japanese Patent Application Laid-Open No. 2006-165828) discloses a wireless LAN that has been connected before if the wireless LAN access point to be connected changes when distributing content to a mobile. The cache server connected to the access point receives information on the delivered part, undelivered content, etc. from the cache server connected to the access point, and resumes delivery without interruption.

  This prior art aims to ensure continuity when exchanging one content with a mobile unit, and when the content is no longer received during wireless switching or the content version for each access point It is not possible to deal with cases such as different.

  Patent Document 2 “Communication System and Method, Communication Terminal Device, Communication Center Device, and Computer Program” (Japanese Patent Application Laid-Open No. 2004-020220) describes as much as possible in order to reduce useless inquiries for updating car navigation map data. It is a technology that processes only data inquiries that have passed a certain period of time from the storage date.

  In this prior art, there is only one data server, and it is not possible to cope with a case where multiple versions of the same data are scattered.

  In the prior art, even if there are a plurality of terrestrial wireless connection locations and cache servers, there is only one data server in the center, and the latest version of the data (content) is stored there. In this state, communication traffic was reduced and download time was shortened.

Japanese Patent Laid-Open No. 2006-165828 JP 2004-020220 A

  When the on-board communication device installed on the moving body of the transportation system acquires version-controlled data via each access point, it selects the appropriate data and receives it to increase transmission efficiency. Is an issue.

On-vehicle communication device according to the present invention,
It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. (1) Received data storage unit for storing received data by version (2) Retained version ID for each version of data stored in the received data storage unit (3) A transmission version ID indicating a version of data held by the cache server is received from the cache server via the wireless access point, and a transmission version ID is stored. Holding newer than the same holding version ID or sending version ID as the ID Or determined, Version ID is stored in the received data storage unit the entire data attached,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination unit that determines that reception is necessary when the entire equivalent or new data is not stored. (4) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data receiving unit that stores the transmission version ID in the retained version management table as a new retained version ID.

Also,
The on-board communication device further deletes, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire data of the transmission version ID is received. It has the part.

Also,
The retained version management table further associates with the retained version ID for each version, the received data of the retained version data stored in the received data storage unit, and the full data size of the entire retained version data. Remember the size,
The reception necessity determination unit determines that the entire data is stored when the received data size is equal to the full data size corresponding to the retained version ID,
The data receiving unit further receives the full data size of the data of the transmission version ID from the cache server via the wireless access point, associates the full version size with the transmission version ID as the holding version ID, The data size and the received data size of the data stored in the received data storage unit are stored in the retained version management table.

Also,
The unnecessary data deletion unit determines that the entire data of the transmission version ID has been received when the full data size and the received data size are equal in any of the retained version IDs.

Also,
The reception necessity determination unit receives an effective section on the route from the cache server via the wireless access point,
The data receiving unit requests data transfer only when the current position is within the valid section.

Also,
Using the data expiration date as the retained version ID,
The data receiving unit requests data transfer only when the current time is within the expiration date.

Also,
The route is a railway, and the moving body is a train.

The data distribution method according to the present invention includes:
It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. On-vehicle communication having a received data storage unit for storing received data by version and a retained version management table for storing a retained version ID for each version of data stored in the received data storage unit A data distribution method by an apparatus, comprising the following elements: (1) A version connected to a wireless access point and a version of data held by the cache server from the cache server via the wireless access point Receiving transmission version ID and holding version same as transmission version ID It is determined whether D or new retention version ID than the transmission version ID is stored in the received data storage unit the entire data attached,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination step for determining that reception is necessary when the entire equivalent or new data is not stored. (2) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data receiving step of storing the transmission version ID in the retained version management table as a new retained version ID.

Also,
The data distribution method further includes an unnecessary data deletion step of deleting, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire data of the transmission version ID is received It is characterized by having.

The program according to the present invention is:
It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. On-vehicle communication having a received data storage unit for storing received data by version and a retained version management table for storing a retained version ID for each version of data stored in the received data storage unit (1) Connect to a wireless access point and transmit from the cache server via the wireless access point indicating the version of data held by the cache server. Receiving version ID and holding version ID same as transmission version ID Check whether stores a whole was given the new retention version ID than the transmission version ID data in received data storage unit,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination procedure for determining that reception is necessary when the entire equivalent or new data is not stored (2) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data reception procedure for storing the transmission version ID in the retained version management table as a new retained version ID.

Also,
The program further executes an unnecessary data deletion procedure for deleting, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire transmission version ID data is received. It is characterized by making it.

  By receiving only appropriate data, it is possible to reduce the processing load and to effectively use the communication band.

It is a figure which shows the outline | summary of the assumption case (the 1). It is a figure which shows the outline | summary of an assumption case (the 2). It is a figure which shows the hardware constitutions of a vehicle-mounted communication apparatus. It is a figure which shows the software structure of a vehicle-mounted communication apparatus. It is a figure which shows the example (the 1) of a holding | maintenance version management table. It is a figure which shows the example (the 2) of a holding | maintenance version management table. It is a figure which shows the whole processing flow of a communication apparatus on a vehicle. It is a figure which shows a reception necessity determination processing flow. It is a figure which shows a data reception process flow. It is a figure which shows the existing version update process flow. It is a figure which shows a new version addition process flow. It is a figure which shows an unnecessary data deletion process flow. It is a figure which shows the old version deletion process flow. FIG. 10 is a diagram illustrating an example of a retained version management table according to the second embodiment. FIG. 10 is a diagram illustrating a new version addition processing flow according to the second embodiment. It is a figure which shows the existing version update process flow which concerns on Example 2. FIG. It is a figure which shows the existing version update process flow which concerns on Example 3. FIG. It is a figure which shows the outline | summary of the assumption case which concerns on Example 4. FIG. It is a figure which shows the example of the holding | maintenance version management table concerning Example 4. FIG. FIG. 10 is a diagram illustrating a new version addition process flow according to the fourth embodiment. It is a figure which shows the existing version update process flow which concerns on Example 4. FIG. It is a figure which shows the existing version update process flow which concerns on Example 5. FIG.

  In a data distribution system in which a plurality of wireless access points that can be connected to the center server are installed along the railroad line, when it is not always connected, it may be isolated due to a line failure with the center, or the line speed is Even when the synchronization with the center server is delayed, the “latest” data is distributed as efficiently as possible on the vehicle (see FIG. 1).

FIG. 1 is a diagram showing an outline of an assumed case (part 1). A copy of the data stored in the center server is arranged in the cache server along the line. The following situation is assumed for each cache server.
(1) The cache server A is connected to the center server through a high-speed always-on line and stores the latest data. For example, the Internet or an intranet is used.
(2) The cache server B holds only the old version data due to a line failure.
(3) The cache server C has not yet been updated to the latest version because it takes time for line connection waiting or transmission. For example, a case where a connection is intermittently made through a dial-up line or a line having a low transmission rate is assumed.

In addition, the following measures are realized.
(1) When the on-board communication device installed in the train completes reception of the latest data (Ver4) from the cache server A, the old data (Ver2 and Ver3) of the cache server B and the cache server C are Do not receive.
(2) When the on-board communication device leaves the communication area of the wireless access point A while receiving the latest data (Ver4) from the cache server A halfway, incomplete partial data (Ver4) When it is stored and enters the communication area of the next wireless access point B, the old data (Ver2) is received because it is better than no. Further, when entering the communication area of the next wireless access point C, data (Ver3) newer than the data (Ver2) that has been received first is received. When the data reception of Ver3 is completed, unnecessary data (Ver2) is deleted.

Furthermore, in the case assumed in FIG.
(3) The on-board communication device leaves the communication area of the wireless access point A while receiving the latest data (Ver4) from the cache server A halfway, stores incomplete partial data (Ver4), and wirelessly When entering the communication area of the access point B, the old data (Ver2) is received, and when entering the communication area of the wireless access point C, it is received from the continuation of the incomplete latest data (Ver4). In other words, a part of the interrupted data is saved and old data is acquired. Then, the remaining data of some data is acquired again from another access point.

  As shown in FIGS. 1 and 2, the wireless access point installed along the railway is connected to the cache server, and the cache server holds data distributed from the center server. When the on-board communication device installed in the train approaches the wireless access point, it connects to the wireless access point by wireless communication and operates to receive data held in the cache server.

  FIG. 3 is a diagram illustrating a hardware configuration of the on-vehicle communication device. The on-vehicle communication device includes a CPU 301, a memory 302, an HDD 303, a wireless LAN device 304, and a position information receiving unit 305. The CPU 301 is an example of an arithmetic device, and the memory 302 and the HDD 303 are examples of a storage device. The program is normally stored in the HDD 303 and is loaded into the memory 302 and sequentially read into the CPU 301 for processing. The wireless LAN device 304 is used for wireless LAN communication. Thereby, communication with the wireless access point is controlled. The position information receiving unit 305 is configured to acquire the current position.

  FIG. 4 is a diagram illustrating a software configuration of the on-vehicle communication device. The on-vehicle communication device includes a reception necessity determination unit 401, a retained version management table 402, a data reception unit 403, a reception data storage unit 404, and an unnecessary data deletion unit 405. The reception necessity determination unit 401 determines whether it is necessary to receive data, the retained version management table 402 manages the version of the retained data, and the data reception unit 403 receives the necessary data. The received data storage unit 404 stores the received data, and the unnecessary data deletion unit 405 is configured to delete data that is no longer needed.

  The retained version management table 402 will be described. FIG. 5 is a diagram illustrating an example (part 1) of the retained version management table. A record is provided for each version, and the storage version ID, full data size, received data size, and file name items are associated and stored. The version ID is data version identification information stored in the received data storage unit 404. The full data size is the total size when the version of the data is complete. The received data size is the size of the data currently stored in the received data storage unit 404. The file name is the name of the file used when the received data storage unit 404 stores the file name.

  FIG. 5 shows a state in which data is being received in the communication area of the wireless access point C in the assumed case (part 1) shown in FIG. 1, and FIG. 6 shows a state in the assumed case (part 2) shown in FIG. Show.

  Subsequently, the processing operation will be described. FIG. 7 is a diagram showing an overall processing flow of the on-board communication device. This process is activated when the train approaches the access point and can be connected. When it is determined that reception is not necessary in the reception necessity determination process (S701) by the reception necessity determination unit 401, the process ends. On the other hand, when it is determined that reception is necessary, a data reception process (S702) by the data reception unit 403 and an unnecessary data deletion process (S703) by the unnecessary data deletion unit 405 are performed. Each process will be described in detail below.

  FIG. 8 is a diagram showing a flow of reception necessity determination processing (S701). A transmission version ID request is transmitted to the cache server via the wireless access point, and the transmission version ID is received (S801). The transmission version ID is identification information of a version of data that the cache server holds and can transmit. Then, the following processing is repeated for each retained version of the retained version management table 402 (S802).

  When the received data size of the retained version is equal to the full data size (S803) and the transmission version ID is less than or equal to the ID of the retained version (S804), that is, the transmitted version is the same as the retained version or from the retained version If it is old, it is determined that reception is not necessary, and the process ends (S805).

  On the other hand, when the received data size of the retained version is different from the full data size (S803), the processing of the other retained version is repeated (S806). Alternatively, when the transmission version ID is larger than the holding version ID (S804), that is, when the transmission version is newer than the holding version, the processing of another holding version is repeated (S806). Then, if it is not determined that any of the retained versions does not require reception, it is determined that reception is necessary (S807).

  FIG. 9 is a diagram showing a flow of data reception processing (S702). The following processing is repeated for each retained version of the retained version management table 402 (S901). If the transmission version ID is equal to the ID of the retained version (S902), the existing version update process (S904) received from the continuation of the existing data is performed. On the other hand, if the versions do not match (S902), the process is repeated for other held versions (S903), and if they do not match in any held version, new version addition processing (from the beginning of the data) ( S905) is performed.

  FIG. 10 is a diagram showing a flow of the existing version update process (S904). A transfer start address is obtained by adding 1 to the received data size of the retained version, the transfer start address is designated, and a data transfer request is transmitted to the cache server (S1001). In this example, 1 is used as the transfer start address, but if the specification is such that subsequent data is received by specifying the transferred data size, the received data size is used as the transfer start address.

  Then, the data received from the cache server is added to the existing file in the received data storage unit 404 identified by the file name of the retained version (S1002). Finally, the received data size is added to the received data size of the retained version (S1003).

  FIG. 11 is a diagram showing a new version addition processing flow. A data transfer request is transmitted to the cache server by designating the start of data as a transfer start address (S1101). Then, the full data size is received, and further transfer data is received (S1102). The received data is stored as a new file in the received data storage unit 404 (S1103). Finally, the new version, full data size, received data size, and new file name are written in the new record of the retained version management table (S1103).

  FIG. 12 is a diagram showing a flow of unnecessary data deletion processing (S703). The following processing is sequentially performed for the retained version of the retained version management table 402 (S1201). If the received data size of the retained version is equal to the full data size of the retained version (S1202), the old version deletion process is performed with the retained version as the received completion version (S1203). If the received data size is different from the full data size, the processing for the other retained version is repeated (S1204).

  FIG. 13 is a diagram showing a flow of old version deletion processing (S1203). The following processing is repeated for each retained version of the retained version management table 402 (S1301). If the retained version ID is smaller than the reception completion version ID (S1302), the retained version file is deleted (S1303), and the retained version record is deleted (S1304). When this processing is all performed for the retained version, the process is terminated (S1305).

  In this embodiment, the data expiration date is used as the version, and control is performed so that data whose expiration date has expired is not received.

  FIG. 14 is a diagram illustrating an example of a retained version management table according to the second embodiment. As shown in the figure, an expiration date is used as the retained version ID. Alternatively, the expiration date is included in the retained version ID.

  FIG. 15 is a flowchart illustrating a new version addition process (S905) according to the second embodiment. Instead of the process of FIG. 11, the process of FIG. 15 is performed. It is determined whether it is within the expiration date specified by the transmission version ID (S1501), and data is received only when it is within the expiration date. If it is outside the expiration date, the process ends without receiving data.

  FIG. 16 is a diagram illustrating a process flow of the existing version update process (S904) according to the second embodiment. Instead of the process of FIG. 10, the process of FIG. 16 is performed. It is determined whether it is within the expiration date specified by the transmission version ID (S1601), and data is received only when it is within the expiration date. If it is outside the expiration date, the process ends without receiving data.

  In this embodiment, incomplete data files are deleted when the expiration date has expired.

  FIG. 17 is a flowchart illustrating an existing version update process (S904) according to the third embodiment. Instead of the process of FIG. 10, the process of FIG. 17 is performed. It is determined whether it is within the expiration date specified by the transmission version ID (S1701), and data is received only when it is within the expiration date. If it is outside the expiration date, the existing version of the file stored in the received data storage unit 404 is deleted without receiving the data (S1705). Further, the existing version record in the retained version management table 402 is deleted (S1706).

  In this embodiment, the concept of an effective section is provided for each version. The valid section is a range on the route where the version of the data is valid.

  In operation regulation information that depends on weather conditions, the effective section may change over time. For example, if the vicinity of the regulation range that regulates the speed according to the rainfall is set as the effective section, it is necessary to receive a continuation of the driving regulation information that is incomplete data when the rainfall area fluctuates and the train is out of the regulation range Disappears.

  FIG. 18 is a diagram illustrating an outline of an assumed case according to the fourth embodiment. In the state where the data of Ver4 whose effective range is position i to position c has been received partway, the train leaves the communication area of the wireless access point A, and then the data of Ver5 whose effective range is narrowed to position a to position b is Assume a delivered state. In this state, if the train enters the communication area of the wireless access point B, it is outside the valid section, so control is performed so that Ver5 is not received.

  FIG. 19 is a diagram illustrating an example of a retained version management table according to the fourth embodiment. Each version is configured to store a valid section in association with each other. It is specified by an upstream end point and a downstream end point that are positions on the route. The position on the route is specified by the distance from the reference point on the route, for example.

  The valid section is received together with the transmission version ID in S801 of the reception necessity determination process (FIG. 8).

  FIG. 20 is a diagram illustrating a flow of new version addition processing (S905) according to the fourth embodiment. Instead of the process shown in FIG. 11, the process shown in FIG. 20 is performed. The current position information is acquired from the position information receiving unit 305 (S2001), the valid section received together with the transmission version ID is acquired by the reception necessity determining unit 401 (S2002), and it is determined whether the current position is within the valid section (S2003). ). Data is received only when it is within the valid interval. In S2007, the valid section is also associated and stored. If it is outside the valid interval, the process ends without receiving data.

  FIG. 21 is a flowchart illustrating an existing version update process (S904) according to the fourth embodiment. Instead of the process of FIG. 10, the process of FIG. 21 is performed. The current position information is acquired from the position information receiving unit 305 (S2101), the valid section of the version is read from the retained version management table 402 (S2102), and it is determined whether the current position is within the valid section (S2103). Data is received only when it is within the valid interval. If it is outside the valid interval, the process ends without receiving data. Note that the valid section received together with the transmission version ID by the reception necessity determination unit 401 can also be used.

  In the fourth embodiment, an existing version file is deleted.

  FIG. 22 is a diagram illustrating an existing version update process flow according to the fifth embodiment. If it is outside the valid section, the existing version file is deleted (S2207), and the existing version record is deleted (S2208).

  In the above-described second to fifth embodiments, it is also effective to delete data that has passed the valid period or data that is outside the valid section asynchronously with data reception. Thereby, unnecessary data can always be deleted.

  The on-board communication device is a computer, and each element can execute processing by a program. Further, the program can be stored in a storage medium so that the computer can read the program from the storage medium.

  In the above-described example, the case where the present invention is applied to a railway has been described. However, the present invention can also be applied to a traffic system related to another moving body such as a route bus or a monorail.

301 CPU
302 Memory 303 HDD
304 Wireless LAN Device 305 Location Information Receiving Unit 401 Receiving Necessity Determining Unit 402 Retained Version Management Table 403 Data Receiving Unit 404 Received Data Storage Unit 405 Unnecessary Data Deleting Unit

Claims (11)

It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. On-board communication device characterized by having the following elements: (1) Received data storage unit for storing received data by version (2) For each version of data stored in the received data storage unit , Retained version management table for storing retained version ID (3) Connect to a wireless access point, and receive a transmission version ID indicating the version of data retained by the cache server from the cache server via the wireless access point From the same holding version ID or transmission version ID as the transmission version ID Or determined new retention version ID is stored in the received data storage unit the entire data attached,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination unit that determines that reception is necessary when the entire equivalent or new data is not stored. (4) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data receiving unit that stores the transmission version ID in the retained version management table as a new retained version ID.   The on-board communication device further deletes, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire data of the transmission version ID is received. The on-vehicle communication device according to claim 1, further comprising a unit. The retained version management table further associates with the retained version ID for each version, the received data of the retained version data stored in the received data storage unit, and the full data size of the entire retained version data. Remember the size,
The reception necessity determination unit determines that the entire data is stored when the received data size is equal to the full data size corresponding to the retained version ID,
The data receiving unit further receives the full data size of the data of the transmission version ID from the cache server via the wireless access point, associates the full version size with the transmission version ID as the holding version ID, 3. The on-board communication device according to claim 2, wherein the data size and the received data size of the data stored in the received data storage unit are stored in the retained version management table.   4. The vehicle according to claim 3, wherein the unnecessary data deleting unit determines that the entire data of the transmission version ID is received when the full data size and the received data size are equal in any of the retained version IDs. Upper communication device. The reception necessity determination unit receives an effective section on the route from the cache server via the wireless access point,
The on-vehicle communication device according to claim 4, wherein the data receiving unit requests data transfer only when the current position is within the valid section. Using the data expiration date as the retained version ID,
5. The on-vehicle communication device according to claim 4, wherein the data receiving unit requests data transfer only when the current time is within the validity period.   The on-board communication device according to claim 1, wherein the route is a railroad, and the moving body is a train. It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. On-vehicle communication having a received data storage unit for storing received data by version and a retained version management table for storing a retained version ID for each version of data stored in the received data storage unit A data distribution method by an apparatus, characterized in that it has the following elements: (1) Data stored in the cache server from a cache server connected to the wireless access point via the wireless access point Receives the transmission version ID indicating the version of the same as the transmission version ID Lifting version or determined ID or new retention version ID than the transmission version ID is stored in the received data storage unit the entire attached data,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination step for determining that reception is necessary when the entire equivalent or new data is not stored. (2) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data receiving step of storing the transmission version ID in the retained version management table as a new retained version ID.   The data distribution method further includes an unnecessary data deletion step of deleting, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire data of the transmission version ID is received 9. The data distribution method according to claim 8, further comprising: It is an on-board communication device mounted on a mobile unit that can connect to a wireless access point installed along the route of transportation and receive versioned data from a cache server connected to the wireless access point. On-vehicle communication having a received data storage unit for storing received data by version and a retained version management table for storing a retained version ID for each version of data stored in the received data storage unit A program for causing a computer as an apparatus to execute the following procedure: (1) A transmission version ID indicating a version of data held by the cache server from the cache server via the wireless access point connected to the wireless access point Received and the same version ID as the sent version ID Check whether stores a whole was given the new retention version ID than the transmission version ID data in received data storage unit,
When the entire equivalent or new data is stored, it is determined that reception is unnecessary,
A reception necessity determination procedure for determining that reception is necessary when the entire equivalent or new data is not stored (2) When it is determined that reception is necessary, a part of the data of the transmission version ID in the reception data storage unit Is stored, and
When the partial data of the transmission version ID is stored, the cache server is requested to transfer the remaining data to the stored partial data via the wireless access point, and the received data is collected. In addition to the part data, it is stored in the received data storage part,
When a part of the data of the transmission version ID is not stored, the transfer of the entire data is requested to the cache server via the wireless access point, and the received data is newly stored in the received data storage unit. A data reception procedure for storing the transmission version ID in the retained version management table as a new retained version ID.   The program further executes an unnecessary data deletion procedure for deleting, from the received data storage unit, data with a retention version ID older than the transmission version ID that has been received when the entire transmission version ID data is received. The program according to claim 10, wherein:

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