System, method, and program for collecting data

Abstract

The purpose of this disclosure is to provide a system which does not require large amounts of network resources even when data is collected from a large number of data sources.　This disclosure relates to a system for collecting data from a plurality of data sources in a server, and a method. In the system, the plurality of data sources each acquire a rule for determining a transmission policy from outside, on the basis of the rule, determine a transmission policy corresponding to a data transfer requirement therefor, and on the basis of the transmission policy, autonomously transmit the data.

Description

Technical Field

[0001] The present disclosure relates to communication control for data collection.

Background Art

[0002] User terminals, sensors, and in-vehicle systems have been developing, and the number of sensors and the amount of data generated from each sensor have increased significantly. In the conventional communication method for collecting such data, the communication processing on the receiving side may become a bottleneck.

[0003] As a high-speed data transfer method, RDMA (Remote Direct Memory Access) has been considered. In RDMA, DMA transfer of data (direct data transfer between peripheral devices and main memory (RAM) etc. without going through the CPU) is performed from the memory of a local computer to the memory of a different remote computer. Therefore, since RDMA does not require CPU processing for data transfer, the bottleneck on the receiving side can be avoided.

[0004] A remote transfer technology using this RDMA has been proposed (see, for example, Non-Patent Document 1). However, in Non-Patent Document 1, in order to transfer data by RDMA in a wide-area communication network, it is necessary to set a communication path for each flow in advance. Therefore, when collecting data from a large number of data sources, a large amount of network resources are required.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure aims to provide a system that does not require a large amount of network resources even when collecting data from a large number of data sources.

Means for Solving the Problems

[0007] The system and method of the present disclosure are a system for collecting data from a plurality of data sources to a server and a method executed by the system, wherein the plurality of data sources acquire rules for determining a transmission policy from the outside, determine a transmission policy according to the data transfer requirements of its own device based on the rules, and autonomously transmit data based on the transmission policy.

[0008] The present disclosure is a data source device that transmits data to a server and a method executed by the data source device, wherein the data source device acquires rules for determining a transmission policy from the outside, determines a transmission policy according to the data transfer requirements of its own device based on the rules, and autonomously transmits data based on the transmission policy.

[0009] Devices such as the controller and data source of the present disclosure can also be realized by a computer and a program, and it is also possible to record the program on a recording medium or provide it through a communication network. The program of the present disclosure is a program for realizing a computer as each functional unit provided in the device according to the present disclosure, and is a program for causing a computer to execute each step included in the method executed by the device according to the present disclosure.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a system that does not require a large amount of network resources even when collecting data from a large number of data sources.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These examples are merely illustrative, and the present disclosure can be implemented in various modified forms based on the knowledge of those skilled in the art. In this specification and the drawings, components having the same reference numerals indicate the same components as each other.

[0013] FIG. 1 shows an example of the system configuration of the present disclosure. The system of the present disclosure includes a plurality of data sources 10, a transmission control controller 20, a path management controller 30, and a server 40. The plurality of data sources 10, the transmission control controller 20, the path management controller 30, and the server 40 are connected by a communication network 80. The data source 10 is a terminal having user-side sensing data. The server 40 is a terminal that collects data from the data source.

[0014] In this embodiment, an example is shown in which the transmission control controller 20 and the path management controller 30 are separately arranged. However, these controllers may be provided in a common device, or may be composed of a plurality of devices arranged dispersedly. The device of the present invention can also be realized by a computer and a program, and it is also possible to record the program on a recording medium or provide it through a communication network.

[0015] FIG. 2 shows an example of the configuration of the communication network 80. The communication network 80 is composed of a plurality of network devices 81. In this embodiment, the network devices 81 used between the data source 10 and the server 40 are predetermined. For example, the data source 10A and the server 40 are connected by the network devices 81A and 81B, the data source 10B and the server 40 are connected by the network devices 81A and 81C, and the data source 10C and the server 40 are connected by the network devices 81D and 81E.

[0016] When each of the network devices 81A to 81E receives data from the data sources 10A to 10C destined for the server 40, it knows which network device to transfer the data to. Therefore, even if the data sources 10A to 10C do not know which network device 81 to use, if they specify the server 40 and send the data, the data will be sent to the server 40. From this, the present disclosure can transfer data losslessly and in a wide band when a communication path is generated.

[0017] In the present disclosure, in order to realize data transfer by RDMA, a method of allocating a lossless and wide-band communication path to the necessary data source 10 at the necessary timing is proposed. In the system of the present disclosure, when data to be transmitted to the server 40 is generated in each of the plurality of data sources 10, a communication path is generated using the network device 81 defined for the own device at the transmission timing determined by the transmission policy of the own device. Thereby, each data source 10 can autonomously transmit sensing data to the server 40 based on the transmission policy of the own device.

[0018] Examples of the transmission policy can be, for example, the following. First transmission policy: Generate a communication path immediately after data generation, perform data transfer, and release the communication path immediately after data transfer completion. Second transmission policy: Generate a communication path after a certain amount of data has accumulated, perform data transfer, and release the communication path immediately after data transfer completion. Third transmission policy: Generate a communication path immediately after data generation, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer completion. Fourth transmission policy: Generate a communication path after a certain amount of data has accumulated, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer completion.

[0019] Here, when the transmission control controller 20 distributes the transmission policy of each data source 10, when the transmission policy determination flow for determining the rules for determining the transmission policy is changed, each data source 10 will receive the transmission policy from the transmission control controller 20 all at once. At this time, the access from the data source 10 to the transmission control controller 20 will be concentrated, the load on the transmission control controller 20 will increase, and it may become impossible to distribute the transmission policy, or it may take time to distribute it.

[0020] Therefore, in the system of the present disclosure, the transmission control controller 20 distributes the transmission policy determination flow. Each data source 10 determines a transmission policy that suits the data transfer requirements of its own device according to the transmission policy determination flow. Thereby, each data source 10 can obtain a transmission policy that suits the data transfer requirements of its own device.

[0021] Each data source 10 notifies the path management controller 30 of a connection request or a release request for the communication path according to the transmission policy, and controls the timing of generating or releasing the communication path. Thereby, this embodiment controls the trade-off between the immediacy of data transmission and the shortening of the communication path usage time. This will be described in detail below.

[0022] (First Embodiment) FIG. 3 shows a configuration example of the server 40. The server 40 includes a data reception function 41, a memory 42, and an application 43. The data reception function 41 receives sensing data from each data source 10. The memory 42 stores the sensing data from the sensor 50. The application 43 collects the sensing data from the sensor 50. The application 43 is an arbitrary application that collects arbitrary sensing data detected or generated by a user terminal, a sensor, an in-vehicle system, or the like.

[0023] Fig. 4 shows a configuration example of the data source 10. The data source 10 includes a transmission policy determination function 12, a data transmission timing control function 13, a communication path setting function 14, a data transmission function 15, a communication path release function 16, a generated data storage function 17, a requirement table 18, and a transmission policy table 19.

[0024] The generated data storage function 17 stores the sensing data from the sensor 50. The transmission policy determination function 12 receives a transmission policy determination flow from the transmission control controller 20, reads out data transfer requirements from the requirement table 18, determines a transmission policy according to the read data transfer requirements, and stores it in the transmission policy table 19. The data transmission timing control function 13 controls the communication path setting function 14, the data transmission function 15, and the communication path release function 16 according to the transmission policy table 19. The communication path setting function 14 transmits a connection request for the communication path to the path management controller 30. The data transmission function 15 transmits the sensing data stored in the generated data storage function 17 to the server 40. The communication path release function 16 transmits a release request for the communication path to the path management controller 30. The requirement table 18 stores data transfer requirements for each data source 10. The transmission policy table 19 stores a policy for transmitting sensing data from the data source 10 to the server 40.

[0025] Fig. 5 shows an example of the information stored in the requirement table 18 of each data source. In the requirement table, as data transfer requirements, the allowable delay time, data generation frequency, and data generation amount of each data source 10 are stored in association with the application. The allowable delay time is the allowable delay time from when the data is generated until it reaches the server. The data generation amount is the amount of data generated at the sensor 50 at one time.

[0026] Fig. 6 shows a configuration example of the transmission control controller 20. The transmission control controller 20 includes a transmission policy determination flow generation function 26 and a transmission policy determination flow distribution function 23.

[0027] Fig. 7 shows an example of a flow for determining a transmission policy. The transmission policy determination flow generation function 26 generates a transmission policy determination flow (S101). The transmission policy determination flow distribution function 23 distributes it to each data source 10 (S102). Each data source 10 receives the transmission policy determination flow transmitted from the transmission control controller 20. The data source 10 refers to the requirement table 18 provided in its own device and determines the transmission policy of its own device according to the received transmission policy determination flow (S103).

[0028] Fig. 8 shows an example of the operation of the transmission policy determination function 12 provided in each data source 10. When the transmission policy determination function 12 acquires data transfer requirements (S11), it determines the requirement for the allowable delay time (S12). If the requirement for the allowable delay time is 100 ms or less (Yes in S12), it is determined to generate and transmit a communication path immediately after data generation (S13). On the other hand, if the requirement for the allowable delay time exceeds 100 ms (No in S12), it is determined to store a certain amount of sensing data and then transmit it (S14). Next, the transmission policy determination function 12 determines the data generation frequency (S15). If the data generation frequency is 4 times / s or less (Yes in S15), it is determined to release the communication path immediately after data transmission (S16). On the other hand, if the data generation frequency exceeds 4 times / s (No in S15), it is determined to wait for a certain time after data transmission is completed and then release the communication path (S17).

[0029] For example, in the case of the data transfer requirements shown in Fig. 5, the transmission policy determination function 22 determines as follows. · Data source A: Since the set time of the allowable delay time is 1000 ms and the set value of the data generation frequency is 4 times, the transmission control controller 20 determines the transmission policy to be the second transmission policy. · Data source B: Since the set time of the allowable delay time is 200 ms and the set value of the data generation frequency is 10 times, the transmission control controller 20 determines the transmission policy to be the fourth transmission policy. · Data source C: Since the set time of the allowable delay time is 100 ms and the set value of the data generation frequency is 5 times, the transmission control controller 20 determines the transmission policy to be the third transmission policy. Thereby, a transmission policy as shown in FIG. 9 is given to data sources A to C.

[0030] Here, the data transfer requirement may include application information. In this case, the transmission policy determination function 12 sets a threshold value in steps S12 and S15 in consideration of the requirements included in the application information.

[0031] When the data source 10 determines a transmission policy, it stores it in the transmission policy table 19. Thereby, as shown in FIG. 9, a transmission policy suitable for each data source 10 is stored in the transmission policy table 19 of each data source 10.

[0032] FIG. 10 shows a configuration example of the path management controller 30. The path management controller 30 includes a path setting request receiving function 31, a path setting function 32, and a path setting location table 33.

[0033] The path setting request receiving function 31 receives a connection request or a release request for a communication path from each data source 10. The path setting function 32 generates or releases a communication path according to a connection request or a release request for a communication path from each data source 10. The path setting location table 33 manages the setting information (generation / release) of the communication path from each data source 10 to the server 40.

[0034] FIG. 11 shows an example of the path setting location table 33. The path setting location table 33 stores information on network devices 81 that transfer sensing data from each data source 10. For example, in the case of the data source 10A, the information on the network device 81 includes the identification information of network devices 81A and 81B that connect the data source 10A and the server 40, and the setting information (generation / release) of the communication paths in the network devices 81A and 81B.

[0035] FIG. 12 shows an example of transmission of sensing data from the data source 10B to the server 40. The data source 10B transmits the sensing data according to the fourth transmission policy. The data source 10B accumulates the sensing data generated by the sensor 50, and when the data reaches 20 MB, it transmits a connection request for the communication path to the path management controller 30 (S201). When the path management controller 30 receives a connection request for the communication path, it sets the communication paths of the network devices 81A and 81C and generates a communication path (S202). When the generation of the communication path is completed, the path management controller 30 transmits a communication path generation completion notification to the data source 10B (S203). When the data source 10B receives the communication path generation completion notification, it transmits the sensing data to the server 40 (S204-1 and S204-2). Then, it waits for 50 ms to transmit a release request for the communication path. If sensing data is generated during that time, the sensing data is transmitted each time (S204-3). When 50 ms has elapsed since the last data transmission (step S204-3), the data source 10B transmits a release request for the communication path to the path management controller 30 (S205). When the path management controller 30 receives the release request for the communication path, it releases the communication paths of the network devices 81A and 81C, and transmits a communication path release completion notification indicating that the release of the communication path is completed to the data source 10B (S206).

[0036] Fig. 13 shows an example of transmitting sensing data from the data source 10A to the server 40. The data source 10A transmits the sensing data according to the second transmission policy. The data source 10A accumulates the sensing data generated by the sensor 50, and when the data reaches 15 MB, it transmits a connection request for the communication path to the path management controller 30 (S301). When the path management controller 30 receives the connection request for the communication path, it generates a communication path from the network device 81E to the server 40 (S302). When the generation of the communication path is completed, the path management controller 30 transmits a communication path generation completion notification to the data source 10A (S303). Then, when the data source 10A receives the communication path generation completion notification (S303), it transmits the accumulated sensing data to the server 40 all at once (S304-1, S304-2, S304-3). After that, the data source 10A immediately transmits a release request for the communication path to the path management controller 30 (S305).

[0037] Fig. 14 shows an example of transmitting sensing data from the data source 10C to the server 40. The data source 10C transmits the sensing data according to the third transmission policy. When data is generated by the sensor 50 in the data source 10C, it transmits a connection request for the communication path to the path management controller 30 (S401). When the data source 10C receives the communication path generation completion notification (S403), it transmits the sensing data to the server 40 (S404-1), and then waits for 20 ms to transmit a release request for the communication path. If sensing data is generated during that time, it transmits the sensing data each time (S404-2, S404-3). When 20 ms has elapsed since the last data transmission (step S404-3), the data source 10C transmits a release request for the communication path to the path management controller 30 (S405).

[0038] As shown in FIGS. 12 to 14, in this embodiment, by time-divisionally allocating communication paths at necessary timings, depletion of network resources is prevented and RDMA communication with a large number of data sources is realized. Since the communication path is allocated only for the period necessary for the data source 10 that wants to transmit sensing data, the utilization rate of the communication path can be improved and network resources can be reduced.

[0039] As described above, in the present disclosure, the transmission control controller 20 distributes the transmission policy determination flow, and each data source 10 determines a transmission policy that matches the data transfer requirements of its own device according to the transmission policy determination flow. Thereby, each data source 10 can obtain a transmission policy that matches the data transfer requirements of its own device according to the transmission policy determination flow.

[0040] In the present disclosure, since the transmission policy determination flow is distributed to the data source 10, even if there is a change in the transmission policy determination flow, access to the transmission control controller 20 does not concentrate. Therefore, the present disclosure can reduce the load due to concentrated access to the transmission control controller 20.

[0041] Since each data source 10 determines a transmission policy and generates a communication path for each data source 10 according to the transmission policy, the communication path can be time-divisionally allocated at necessary timings. Therefore, the present disclosure shortens the communication path utilization time from each data source 10 to the server 40, facilitates the reuse of the communication path, and reduces the required number of communication paths for the entire communication network 80, with respect to the trade-off between the immediacy of data transmission and the shortening of the communication path utilization time.

[0042] (Second Embodiment) The system of this embodiment does not include the path management controller 30 shown in FIG. 1. In this embodiment, the data source 10 directly sends a connection request for a communication path to the network devices 81A to 81E. By reflecting the settings received by the network devices 81A to 81E, the labor required to generate a communication path can be omitted. As a result, in this embodiment, the communication path can be set in a shorter time.

[0043] In this embodiment, the communication path setting function 14 sends a connection request for generating a communication path with the server 40 to the network device 81. Also, the communication path release function 16 sends a release request for releasing the communication path with the server 40 to the network device 81.

[0044] When sensing data is generated, the data source 10 sends a connection request for a communication path to the network device 81. The receiving device 81 reflects the settings. For example, when the data source 10A sends sensing data, the data source 10A sends a connection request for a communication path to the network device 81B. Then, the network device 81B generates a communication path with the data source 10A.

[0045] For each network device 81 set in the transmission route of the sensing data, the connection destination of the communication path of the sensing data is set in advance. Thus, in the present disclosure, the predetermined network devices 81B and 81A that connect between the data source 10A and the server 40 generate a communication path between the data source 10A and the server 40. The communication path can use any means capable of transmitting sensing data, and may be virtual such as a VLAN or physical such as an optical path.

[0046] For the connection request of the communication path, data in any format readable by the network device 81 can be used. For example, the Attribute ID field provided in the header of an RDMA (Remote Direct Memory Access) packet can be used.

[0047] FIG. 15 shows an example of the Attribute ID area. When using RoCE (RDMA over Converged Ethernet) v2 used in the UDP (User Datagram Protocol), the network device 81 can identify the negotiation based on the description in the Attribute ID field in the MAD Header. The MAD Header is stored in the DATH Header in the Base Transport Header.

[0048] The negotiation includes, for example, ConnectRequest for making an RDMA connection request, ConnectReply indicating an RDMA connection response, ReadyToUse indicating a usable state, DisconnectRequest for making an RDMA release request, and DisconnectReply indicating an RDMA release response. The value of the Attribute ID is determined for each negotiation. For example, if the Attribute ID is 0x0010, it can be used as a trigger for path generation in the network device 81B.

[0049] FIG. 16 shows an example of the sequence when generating and releasing a communication path. When using RDMA, the data source 10A triggers a ConnectRequest to generate a communication path to the server 40. At this time, the network device 81B transfers the ConnectRequest to the next network device 81A. After the completion of the generation of the communication path, the network device 81A also transfers the ConnectRequest to the server 40. The server 40 uses the generated communication path to send a ConnectReply to the data source 10A. When the data source 10A receives the ConnectReply from the server 40, it sends a ReadyToUse to the server 40. This enables RDMA communication from the data source 10A to the server 40.

[0050] When releasing a communication path, the process is the same as when generating a communication path. Specifically, data source 10A triggers a Disconnect Request to release the communication path up to server 40. At this time, when the release of the communication path is completed, network device 81B transfers the Disconnect Request to network device 81A. The same applies to network device 81A. When server 40 receives the Disconnect Request, it sends a DisconnectReply to data source 10A.

[0051] In network devices 81B and 81A, the timing for transferring the ConnectRequest is, for example, after the completion of generating the communication path. However, the present disclosure is not limited to this. For example, network devices 81B and 81A may transfer the ConnectRequest without waiting for the completion of generating the communication path.

[0052] FIG. 17 shows an example of the sequence when generating and releasing a communication path. In this example, network devices 81B and 81A transfer the ConnectRequest without waiting for the completion of generating the communication path. In this case, network devices 81B and 81A are equipped with a function of sending a path setting completion notification to data source 10A, which is the source of the ConnectRequest. In the present disclosure, since the transmission route of the sensing data is predetermined, data source 10A can confirm that the communication path has been set in all network devices 81B and 81A of the transmission route by counting the number of path setting completion notifications sent from network devices 81B and 81A. Once this confirmation is made, data source 10A sends ReadyToUse to server 40. Thereby, RDMA communication from data source 10A to server 40 becomes possible.

[0053] When releasing the communication path, data source 10A sends a Disconnect Request to server 40. Server 40 releases the communication path and sends a Disconnect Reply to data source 10A. Since the communication path is released at server 40, the communication paths are also released in network devices 81A and 81B.

[0054] This embodiment realizes a lossless and broadband communication network 80 with a communication path, does not require a large amount of network resources, and enables RDMA communication with a large number of data sources. Furthermore, since the present disclosure can prevent data loss in communication network 80, reliable data transfer using RDMA can be realized.

[0055] (Effect of the present disclosure) Therefore, the present disclosure can realize a lossless and broadband communication network 80 with a communication path, does not require a large amount of network resources, and enables RDMA communication with a large number of data sources. Furthermore, since the present disclosure can prevent data loss in communication network 80, reliable data transfer using RDMA can be realized.

[0056] In this embodiment, an example in which the data collected by server 40 is sensing data is shown. However, the present disclosure is applicable to any data that is required to be collected, such as user terminals, sensors, in-vehicle systems, etc.

[0057] Also, in the above-described embodiment, an example of setting a lossless and broadband communication path between data source 10 and server 40 is shown. However, a data transfer path with unguaranteed quality may be set as the communication path.

Industrial applicability

[0058] The present disclosure can be applied to the information and communication industry.

Explanation of reference numerals

[0059] 10, 10A, 10B, 10C: Data Source 20: Transmission Control Controller 30: Path Management Controller 40: Server 50: Sensor 12: Transmission Policy Determination Function 13: Data Transmission Timing Control Function 14: Communication Path Setting Function 15: Data Transmission Function 16: Communication Path Release Function 17: Generated Data Storage Function 18: Requirement Table 19: Transmission Policy Table 21: Requirement Reception Function 22: Transmission Policy Determination Function 23: Transmission Policy Determination Flow Distribution Function 24: Transmission Policy Determination Flow 31: Path Setting Request Reception Function 32: Path Setting Function 33: Path Setting Location Table 41: Data Reception Function 42: Memory 43: Application 80: Communication Network 81A, 81B, 81C, 81D, 81E: Network Equipment

Claims

1. In a system for collecting data from a plurality of data sources to a server, the plurality of data sources acquire from the outside a rule for determining a transmission policy, determine a transmission policy according to the data transfer requirements of its own device based on the rule, and autonomously transmit data based on the transmission policy, a system, wherein the transmission policy is one that generates a communication path immediately after data generation to perform data transfer and releases the communication path immediately after data transfer completion, one that generates a communication path after a certain amount of data has been accumulated to perform data transfer and releases the communication path immediately after data transfer completion, and one that generates a communication path immediately after data generation to perform data transfer and continues to hold the communication path for a certain period of time even after data transfer completion, one that generates a communication path after a certain amount of data has been accumulated to perform data transfer and continues to hold the communication path for a certain period of time even after data transfer completion, a system including the above.

2. The data transfer requirements include an allowable delay time and a data generation frequency, and the transmission policy is determined based on the allowable delay time and the data generation frequency, The system according to claim 1.

3. Further comprising a controller that determines the rule and distributes it to the plurality of data sources, The system according to claim 1 or 2.

4. A method executed by a system for collecting data from a plurality of data sources to a server, wherein the data source acquires from the outside a rule for determining a transmission policy, determines a transmission policy according to the data transfer requirements of its own device based on the rule, and autonomously transmits data based on the transmission policy, a method, wherein the transmission policy is one that generates a communication path immediately after data generation to perform data transfer and releases the communication path immediately after data transfer completion, one that generates a communication path after a certain amount of data has been accumulated to perform data transfer and releases the communication path immediately after data transfer completion, and one that generates a communication path immediately after data generation to perform data transfer and continues to hold the communication path for a certain period of time even after data transfer completion, one that generates a communication path after a certain amount of data has been accumulated to perform data transfer and continues to hold the communication path for a certain period of time even after data transfer completion, a method including the above.

5. Acquire from the outside a rule for determining a transmission policy, Determine a transmission policy according to the data transfer requirements of its own device based on the rule, Autonomously transmit data based on the transmission policy A data source device, The transmission policy is Generate a communication path immediately after data generation, perform data transfer, and release the communication path immediately after data transfer is completed; Generate a communication path after a certain amount of data has been accumulated, perform data transfer, and release the communication path immediately after data transfer is completed; and Generate a communication path immediately after data generation, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer is completed; Generate a communication path after a certain amount of data has been accumulated, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer is completed; A data source device including the above.

6. A method executed by a data source device that transmits data to a server, wherein the data source device acquires from the outside a rule for determining a transmission policy, determines a transmission policy according to the data transfer requirements of its own device based on the rule, and autonomously transmits data based on the transmission policy. A method, wherein the transmission policy is Generate a communication path immediately after data generation, perform data transfer, and release the communication path immediately after data transfer is completed; Generate a communication path after a certain amount of data has been accumulated, perform data transfer, and release the communication path immediately after data transfer is completed; and Generate a communication path immediately after data generation, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer is completed; Generate a communication path after a certain amount of data has been accumulated, perform data transfer, and continue to hold the communication path for a certain period of time even after data transfer is completed; A method including the above.

7. A program for realizing a computer as the data source provided in the system according to any one of Claims 1 to 3.

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