JP3600444B2 - Data communication method, data communication device, and data communication system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data communication method for performing data communication via a line, a data communication apparatus, and a technique for preventing data from being repeatedly registered in a data communication system.
[0002]
[Prior art]
For example, many public telephones connected to a telephone line network are often centrally managed by a center device connected to the telephone line.
[0003]
The center device downloads, for example, data for a charge table to the managed public telephone, and each public telephone uses the usage data (the telephone number of the call destination, the card number used, the call charge, the call time, etc.). For example, when the number of storages reaches a predetermined number, the usage data is transmitted to the center device and registered in the memory of the center device, and then the contents of the usage data memory are deleted.
[0004]
In the data communication between the public telephone and the center device, confirmation messages indicating that the data have been received are transmitted to each other. As described above, when transmitting the usage data from the public telephone to the center device, When the confirmation message from the center device is received by the public telephone, it is known that the transmitted usage data has been reliably received by the center device, and if the confirmation message is not returned from the center device, Assuming that the transmitted usage data was not correctly transmitted to the center device, the usage data was retransmitted to the center device.
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional system, even if the confirmation message is transmitted to the line from the center device side, even if the public telephone is not received due to a temporary failure of the line or the like, the public telephone remains the same. The use data is retransmitted to the center, so that the center device duplicately registers this use data as new use data in the memory, and the management of the public telephone cannot be performed correctly.
[0006]
An object of the present invention is to provide a data communication method, a data communication device, and a data communication system that solve such a problem of the communication system.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a data communication method according to claim 1 of the present invention comprises:
A data communication method for transmitting data stored in a first memory of one communication device to another communication device connected via a line and registering the data in a second memory of the other communication device,
Transmitting the data stored in the first memory from one communication device to the other communication device together with identification information for identifying whether the data is for new transmission or for retransmission;
Registering the data received by the other communication device together with the identification information for new transmission in the second memory;
Comparing the data received by the other communication device with the identification information for retransmission and the data last registered in the second memory;
Discarding the received data when the data received by the other communication device matches the data last registered in the second memory, and registering the received data in the second memory when they do not match,
A step of discarding the received data or returning the other communication device registered in the second memory to the one communication device with a confirmation message;
Determining whether a confirmation message from the other communication device has been received by the one communication device;
When the confirmation message is received by one of the communication devices, the data transmitted by the one communication device immediately before is deleted from the first memory, and when the confirmation message is not received by the one communication device, the data is transmitted immediately before the confirmation message. Leaving the data transmitted by one of the communication devices as data for retransmission in the first memory, and setting the data to be transmitted together with the identification information for retransmission when the data is retransmitted. And
[0008]
Further, the data communication method of claim 2 of the present invention,
A data communication method for transmitting data stored in a first memory of one communication device to another communication device connected via a line and registering the data in a second memory of the other communication device,
The data stored in the first memory is transmitted from one communication device to the other communication device together with identification information for identifying whether the data is for new transmission or retransmission, and a transmission number assigned to the data. Stage to
Determining whether the transmission number received by the other communication device matches the reception number indicating the total number of data received from the one communication device,
Discarding the data received with the transmission number when the transmission number received by the other communication device and the reception number do not match,
When the transmission number received by the other communication device and the reception number match and the identification information indicates a new transmission, registering the data received together with the identification information in the second memory;
When the transmission number received by the other communication device matches the reception number and the identification information indicates retransmission, the data received together with the identification information and the data last registered in the second memory. Comparing with
Discarding the received data when the data received by the other communication device matches the data last registered in the second memory, and registering the received data in the second memory when the data does not match,
A step of discarding the received data or returning the other communication device registered in the second memory to the one communication device with a confirmation message;
When the confirmation message is received by one of the communication devices, the data transmitted immediately before by one of the communication devices is erased from the first memory, and when the confirmation message is not received, the one of the communication devices immediately erases the data. Leaving the transmitted data in the first memory as data for retransmission, and setting the data to be transmitted together with the identification information for retransmission when the data is retransmitted.
[0009]
Also, the data communication device according to claim 3 of the present invention,
A data communication device that performs data communication with another device configured to return a confirmation message to a transmission source every time data is received via a line,
Memory and
Transmission data writing means for writing data for transmission to another device and identification information for identifying whether the data is for new transmission or for retransmission to the memory,
Data transmission means for transmitting the data stored in the memory and identification information corresponding to the data to another device at a predetermined timing,
Message reception determination means for determining whether a confirmation message returned from another device for the data transmitted by the data transmission means has been received,
When it is determined that the confirmation message has been successfully received by the message reception determining means, data erasing means for erasing data transmitted immediately before from the memory,
Identification information setting means for setting identification information of the memory corresponding to data transmitted immediately before when the message reception determination means has failed to receive a confirmation message, for retransmission.
[0010]
Further, the data communication device according to claim 4 of the present invention,
In a data communication device that receives data sent via a line and identification information for identifying whether the data is for new transmission or retransmission, and returns a confirmation message to the transmission source,
Memory and
Identification information determining means for determining whether the received identification information is for new transmission or retransmission,
When the received identification information is determined to be for new transmission by the identification information determination means, first data registration means for registering data received with the identification information in the memory;
A data comparing means for determining whether or not the data received together with the identification information and the data last registered in the memory are coincident when the received identification information is determined to be for retransmission by the identification information determining means; When,
Data discarding means for discarding the received data, when the received data and the data last registered in the memory are determined to match by the data comparing means,
A second data registration unit that registers the received data in the memory when the data comparison unit determines that the received data and the data last registered in the memory do not match. And
[0011]
Further, the data communication system according to claim 5 of the present invention provides:
Data is exchanged between a public telephone having at least one of the data communication devices according to the third and fourth aspects and a center device having at least the other data communication device.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a communication system including a public telephone equipped with a communication device according to an embodiment of the present invention and a center device.
[0013]
1, a public telephone ₂₀ 1 to 20 _n of a plurality N, are connected to each line ₂ 1 to 2 _n of the telephone network 1, a center for managing these public telephone ₂₀ 1 to 20 _n device 35 is connected to the line 2 ₀ in the telephone network 1 through a modem 3. The center device 35 may be connected to a plurality of lines via a plurality of modems 3, respectively.
[0014]
Each public telephone 20 ₁ to 20 _n, the card processing device for collecting a call charge 21, a coin processing apparatus 22, a dial 23 for inputting a telephone number of the call destination at the time of call activity, the call by voice It has a communication circuit 24 including a handset for performing communication, a line interface 25, and a communication control unit 26 for controlling these.
[0015]
When a card having a residual number is inserted into the card processing device 21 or a coin is inserted into the coin processing device 23, the call control unit 26 connects the dial device 23 to the line, and the call input by key operation. The destination telephone number is output from the dialing device 23 to the line, the telephone line network 1 makes a call to the destination, and when there is a response from the destination, the communication circuit 24 is connected to the line to enable a call. At the same time, a call charge is collected from the remaining number of the inserted card or the inserted coin, and when the call is completed, the card or the remaining coin is returned.
[0016]
Based on the control information of the call control unit 26, the usage data writing unit 27, every time the call is completed, a telephone number of the call destination, or a card number, a call time, a call charge, and the like in the case of a call using a card. Are written into the usage data memory 28 in the order of addresses.
[0017]
The usage data memory 28 has a capacity capable of storing, for example, 100 usage data. The usage data memory 28 (which may be another memory) stores the number of usage data that needs to be retransmitted as identification information J for identifying whether the data is for new transmission or retransmission. A storage area is provided.
[0018]
The usage data communication processing unit 30 stores the usage data stored in the usage data memory 28 into a predetermined number m (eg, 80) when the usage data memory 28 stores a predetermined number (for example, 80) or more of usage data. 5) and transmits the data to the center device 35 via the modem 31. When the confirmation message is received from the center device 35, the transmitted predetermined number of usage data is deleted from the usage data memory, and the next predetermined number of data is deleted. The operation of transmitting the usage data is repeated. In transmitting the usage data, the identification information J is also transmitted.
[0019]
On the other hand, the center device 35 is constituted by, for example, a personal computer, communicates with each public telephone connected to the telephone line network 1, manages information of each public telephone, displays the management information or As shown in FIG. 1, in order to collect usage data of each public telephone, which is one of the management information, the usage data communication processing unit 36 and the usage data It has a center memory 37 for storing usage data of each public telephone obtained by communication of the communication processing unit 36.
[0020]
Next, the usage data registration processing of the usage data transmission process and the center apparatus 35 of the public telephone 20 ₁ to 20 _n 2, will be described with reference to the flowchart of FIG.
[0021]
FIG. 2 is a flowchart showing a procedure of a process of transmitting usage data on the public telephone. In FIG. 2, the public telephone checks the number of usage data in the usage data memory 28 when no call processing is performed, as shown in processes S1 to S3, for example, as shown in FIG. If the usage data memory 28 stores usage data D (1) to D (M) of a predetermined number M (M is, for example, 80) or more, a call is made to the center device 35.
[0022]
If a response from the center device 35 is not obtained for this call, a timer for a predetermined time (for example, 3 minutes) is started, and after the timer expires, a call is re-issued to the center device 35, and the timer is reset. If there is a call process before the time is up, the process returns to step S1 to prioritize the use of the call (S4 to S7).
[0023]
When the center device 35 responds to this call, the sequence number (transmission number) ST and the number of retries RT of the transmission data are initialized to 0, and the variable A is set to 0, as shown in steps S8 and S9. After initializing the address of the use data to be transmitted first (fixed to 0 in this case), m (for example, m = 5) use data D (A + 1) to D from the (A + 1) th to A + mth of the use data memory 28 are used. The transmission data including (A + m) as a set is transmitted to the center device 35 together with the identification information J and the sequence number ST stored in the usage data memory 28 (data transmission means).
[0024]
The set of m pieces of usage data D (A + 1) to D (A + m) includes information for identifying the calling public telephone, the type of information to be transmitted, and the like, for example, as shown in FIG. It is inserted into the data area B following the header section H and output to the line.
[0025]
In the data area B, Br is an area for the identification information J and the sequence number ST. When all the usage data stored in the usage data memory 28 is for new transmission, (a) in FIG. ), The value of the identification information J is 0, and when, for example, up to three pieces of usage data D (1) to D (3) from the top are for retransmission, the value of the identification information J is 3.
[0026]
In this case, the usage data is transmitted in units of m, and if a confirmation message for the transmitted data is not received as described later, the line is disconnected, and transmission of this data is started at the next call. Therefore, among the usage data stored in the usage data memory 28, the number of usage data for retransmission, that is, the value of the identification information J is always m or less.
[0027]
Then, as in processes S10 and S11, a timer for a predetermined time is started after transmitting this data, and it is determined whether or not a confirmation message ACK is received from the center device 35 before the timer expires ( Message reception determination means).
[0028]
When the reception of the confirmation message ACK is confirmed, the values of the identification information J in the usage data memory 28 are reset to 0, the sequence number S is incremented and updated by 1 and the retry count RT is set to 0 as in steps S12 to S13. Then, the m use data D (A + 1) to D (A + m) transmitted to the center device 35 are erased from the use data memory 28 as shown in FIG. 4B (data erasing means).
[0029]
Thereafter, the variable A is incremented by m and updated until the number p of the usage data remaining in the usage data memory 28 becomes smaller than m, and the processing from S9 to S14 is repeated (S14, S15).
[0030]
When the number p of use data remaining in the use data memory 28 is smaller than m and p is not 0, the p pieces of use data are identified as identification data J (M is used as a set of transmission data). If it is greater than m, the value of the identification information J at this time is 0) and transmitted to the center device 35 together with the sequence number ST, and upon receipt of the confirmation message ACK from the center device 35, p transmitted to the center device 35 The usage data is deleted from the usage data memory 28 and the line is disconnected (S16 to S21). Note that the line is disconnected even when the number p of remaining use data is 0 in the processing S16.
[0031]
Further, as shown in steps S22 to S27, when the usage data is transmitted in units of m, a negative acknowledgment message NAK indicating that data reception has failed before the timer times out is received. Or, when the message from the center device cannot be received, retransmission of data is performed up to twice while updating the retry number RT. When the confirmation message ACK from the center device 35 still cannot be received, The value of the identification information J in the usage data memory 28 is set to m (identification information setting means), and the entire data remaining in the usage data memory 28 is stored so as to be shifted to the head address which has been erased and becomes free. And disconnect the line.
[0032]
For example, when m is 5, when the usage data D (1) to D (5) are transmitted, a confirmation message from the center device can be received, and the next usage data D (6) to D (10) are transmitted. At times, when the confirmation message from the center device is not received, the identification information J of the usage data memory 28 is set to m, and the usage data D (1) is set as shown in FIG. ) To D (5) are erased and the use data D (6) to D (M) subsequent to D (6) are stored again at the start address side which is empty and the new use data is used as the use data D It is stored after (M).
[0033]
Similarly, as shown in steps S28 to S33, when the last p pieces of usage data have been transmitted, a negative acknowledgment message NAK indicating that data reception has failed by the time-out of the timer is received. Or, when the message from the center device cannot be received, retransmission of data is performed up to twice while updating the retry number RT. When the confirmation message ACK from the center device 35 still cannot be received, The value of the identification information J in the usage data memory 28 is set to p (identification information setting means), and the entire data remaining in the usage data memory 28 is stored so as to be shifted to the vacant and free top address side. Then, disconnect the line.
[0034]
By this processing, at the time of the next call, the use data stored in the head address of the use data memory 28 and from which the confirmation message could not be received at the previous transmission can be transmitted in order.
[0035]
On the other hand, the center device 35 performs the use data reception registration process according to the flowchart of FIG.
[0036]
That is, as shown in process S41 to S44, for example, automatically responds to this when there is an incoming call to the center device 35 by the call from the public telephone 20 _k, and initialize the sequence number SR for receiving the 0, public telephone 20 Receives data from the _k- side.
[0037]
Then, as in steps S45 and S46, the sequence number ST and the sequence number SR included in the received data are compared, and when they match, whether the value of the identification information J included in the received data is 0 or not. No, that is, whether or not the received usage data includes all new data or retransmission data (identification information determination means).
[0038]
Then, as processing S47～S49, if the value of the received identification information J is 0, as shown in FIG. 6 (a), previously registered in the registration area of the public telephone 20 _k of the center memory 37 After the _a use data D _{1 to} D _a , the m (or p) use data D (A + 1) to D (A + m) received this time are stored in the center memory 37 from the (a + 1) th to the (a + m) th use data. After registering as Da _{+ 1 to} Da _{+ m} (first data registering means), the receiving side updates the sequence number SR on the receiving side by one and returns a confirmation message ACK. It should be noted that which public telephone the received usage data belongs to is identified by the information in the header portion.
[0039]
If the value of the received identification information J is not 0, as in steps S50 and S51, the J usage data from the beginning of the received usage data and the usage data already registered in the center memory 37 are read. The last registered J use data (use data Da _{+ m + 1-j to} Da _{+ m} when use data _{Da + m} are registered as shown in FIG. 6A) are compared. It is determined whether the two match (data comparison means).
[0040]
If they do not match, all of the usage data received this time is registered in the center memory 37 (second data registration means), and if they match, as received in steps S52 and S53, From the top of the usage data, J data are discarded as already registered (data discarding means), and when there is remaining usage data (when J is smaller than m or P), the remaining usage data is stored in the center memory. After registering at 37, a confirmation message ACK is returned.
[0041]
If the sequence numbers do not match in step S45, all the received usage data is discarded as in step S54, and the process shifts to step S48 to return a confirmation message ACK.
[0042]
The processing from S44 to S54 is performed until the line is disconnected by the disconnection request on the public telephone side in processing S55.
[0043]
By the above processing, all the usage data D (1) to D (M) stored in the usage data memory 28 of the public telephone are stored in the center memory 37 of the center device 35 as a + 1 as shown in FIG. It is registered without overlapping as usage data _{D a +} 1 _~D a + _M to a + M-th from th.
[0044]
In addition, even if the confirmation message is not transmitted to the public telephone due to a line failure or the like and the line is disconnected while the usage data D (1) to D (M) is being transmitted, the center device receives and registers at that time. Since the data and the first data transmitted next time match, there is no duplicate registration in the center device.
[0045]
For this reason, the center device 35 can accurately manage each public telephone based on the use data registered in the center memory 37.
[0046]
As described above, in the communication system of this embodiment, the data is transmitted from the public telephone to the center device together with the identification information for identifying whether the data is for new transmission or retransmission, and the center device receiving the data transmits the data to the public device. A confirmation message is returned to the telephone, and if the identification information is for new transmission, the received data is registered.If the identification information is for retransmission, the received data is compared with the last registered data. If they do not match, the received data is registered, and if they do match, the received data is discarded. Then, the public telephone retransmits the transmission data that has not received the confirmation message from the center device together with the retransmission identification information.
[0047]
For this reason, even when the confirmation message output from the center device to the line cannot be received by the public telephone due to a line failure, there is no possibility that the data is repeatedly registered in the memory of the center device when data is retransmitted.
[0048]
The transmission number is transmitted together with the data from the public telephone, and the center device determines whether the received data is registrable data by comparing the received transmission number with the reception number.
[0049]
For this reason, regardless of whether the data transmitted from the public telephone is for new transmission or retransmission, the data can be registered in the center device in the correct order without duplication or omission.
[0050]
In this embodiment, m pieces of use data are used as one set of transmission data, but the value of m is arbitrary. However, for example, when the total number of use data to be transmitted is 100, if the value of m is smaller than the total number, such as 1 or 2, the number of times of data transmission and reception between the public telephone and the center device becomes extremely large. Therefore, if the value of m is too large, such as 50, the efficiency at the time of retransmission is reduced. Therefore, the value is set according to the total number of used data to be transmitted.
[0051]
Further, in the above embodiment, when the usage data stored in the usage data memory of the public telephone reaches a predetermined number, the public telephone calls the center device to transmit the data. For example, the public telephone may call the center device and transmit data at regular time intervals or at a preset time, or the public telephone may be called from the center device. A call may be made to request data transmission, and the public telephone receiving the request may transmit the data in the usage data memory to the center device.
[0052]
Further, in the above embodiment, each time a confirmation message is returned from the center device for the transmitted data, the transmitted usage data is sequentially deleted from the usage data memory. However, this is a limitation of the present invention. Until the last usage data in the usage data memory is transmitted, or until the line is disconnected, only confirm the return of the confirmation message and do not delete the usage data. All the usage data may be deleted when the confirmation message is returned, or the usage data for which the reception of the confirmation message has been confirmed immediately before the line is disconnected may be collectively deleted.
[0053]
Further, in the above-described embodiment, the number of pieces of data to be used for retransmission included in the data to be transmitted is used as the identification information. However, this is not intended to limit the present invention. If the number of pieces of use data to be transmitted is always fixed, it is only necessary to identify whether or not the data is for retransmission regardless of the number of pieces of use data to be retransmitted.
[0054]
If the number of pieces of usage data transmitted at one time is always fixed, and the number of pieces of usage data transmitted at one time is L, the number of usage data stored in the usage data memory is an integer multiple of L. If the transmission to the center device is started when the time becomes, all the usage data can be transmitted to the center device without generating a fraction. Further, if transmission to the center device is started when the number of usage data stored in the usage data memory is not an integral multiple of L, the number of usage data less than L remains. The data may be transmitted together with other usage data at the next transmission.
[0055]
In the above-described embodiment, the case where the usage data of the public telephone is transmitted to the center device has been described. However, the data to be transmitted is not limited to the usage data, and may be arbitrary, and may be program data or table data. The present invention can also be applied to the case where data is transmitted from the device to the public telephone.
[0056]
In the above-described embodiment, the data communication system including the public telephone and the center device has been described. However, the present invention is not limited to these devices, and is similarly applied to data communication between other devices. be able to.
[0057]
【The invention's effect】
As described above, in the present invention, data is transmitted from one communication device to another communication device together with identification information for identifying whether the data is for new transmission or retransmission, and the other The communication device returns a confirmation message to one of the communication devices, and registers the received data when the identification information is for new transmission, and has already registered the received data when the identification information is for retransmission. The data is compared with the last data, and if they do not match, the received data is registered, and if they match, the received data is discarded. Then, one communication device retransmits the transmission data that has not received the confirmation message from the other communication device together with the retransmission identification information.
[0058]
For this reason, even if a confirmation message output to the line from the other communication device cannot be received by one communication device due to a line failure, data is repeatedly registered in the memory of the other communication device when data is retransmitted. There is no fear of being caught.
[0059]
Also, the transmission number is transmitted together with the data from one communication device, and the transmission number received by the other communication device is compared with the reception number to determine whether the received data is registerable data.
[0060]
Therefore, regardless of whether the data transmitted from one communication device is for new transmission or for retransmission, the data can be registered in the other communication device in the correct order without duplication or loss.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment of the present invention; FIG. 2 is a flowchart showing a processing procedure of a main part of a public telephone according to an embodiment; FIG. FIG. 4 is a memory diagram of a public telephone according to an embodiment; FIG. 5 is a diagram illustrating an example of a data format according to an embodiment; FIG. 6 is a memory diagram of a center device according to an embodiment; Explanation of reference numerals]
20 _{1 to} 20 _n Public telephone 27 Usage data writing unit 28 Usage data memory 30 Usage data communication processing unit 31 Modem 35 Center device 36 Usage data communication processing unit 37 Center memory

Claims (5)

A data communication method for transmitting data stored in a first memory of one communication device to another communication device connected via a line and registering the data in a second memory of the other communication device,
Transmitting the data stored in the first memory from one communication device to the other communication device together with identification information for identifying whether the data is for new transmission or for retransmission;
Registering the data received by the other communication device together with the identification information for new transmission in the second memory;
Comparing the data received by the other communication device with the identification information for retransmission and the data last registered in the second memory;
Discarding the received data when the data received by the other communication device matches the data last registered in the second memory, and registering the received data in the second memory when they do not match,
A step of discarding the received data or returning the other communication device registered in the second memory to the one communication device with a confirmation message;
Determining whether a confirmation message from the other communication device has been received by the one communication device;
When the confirmation message is received by one of the communication devices, the data transmitted by the one communication device immediately before is deleted from the first memory, and when the confirmation message is not received by the one communication device, the data is transmitted immediately before the confirmation message. Leaving the data transmitted by one of the communication devices as data for retransmission in the first memory, and setting the data to be transmitted together with the identification information for retransmission when the data is retransmitted. Data communication method. A data communication method for transmitting data stored in a first memory of one communication device to another communication device connected via a line and registering the data in a second memory of the other communication device,
The data stored in the first memory is transmitted from one communication device to the other communication device together with identification information for identifying whether the data is for new transmission or retransmission, and a transmission number assigned to the data. Stage to
Determining whether the transmission number received by the other communication device matches the reception number indicating the total number of data received from the one communication device,
Discarding the data received with the transmission number when the transmission number received by the other communication device and the reception number do not match,
When the transmission number received by the other communication device and the reception number match and the identification information indicates a new transmission, registering the data received together with the identification information in the second memory;
When the transmission number received by the other communication device matches the reception number and the identification information indicates retransmission, the data received together with the identification information and the data last registered in the second memory. Comparing with
Discarding the received data when the data received by the other communication device matches the data last registered in the second memory, and registering the received data in the second memory when the data does not match,
A step of discarding the received data or returning the other communication device registered in the second memory to the one communication device with a confirmation message;
When the confirmation message is received by one of the communication devices, the data transmitted immediately before by one of the communication devices is erased from the first memory, and when the confirmation message is not received, the one of the communication devices immediately erases the data. Leaving the transmitted data in the first memory as data for retransmission, and setting the data to be transmitted together with the identification information for retransmission when the data is retransmitted. . A data communication device that performs data communication with another device configured to return a confirmation message to a transmission source every time data is received via a line,
Memory and
Transmission data writing means for writing data for transmission to another device and identification information for identifying whether the data is for new transmission or for retransmission to the memory,
Data transmission means for transmitting the data stored in the memory and identification information corresponding to the data to another device at a predetermined timing,
Message reception determination means for determining whether a confirmation message returned from another device for the data transmitted by the data transmission means has been received,
When it is determined that the confirmation message has been successfully received by the message reception determining means, data erasing means for erasing data transmitted immediately before from the memory,
Identification information setting means for setting, for retransmission, the identification information of the memory corresponding to the data transmitted immediately before it is determined that the confirmation message has not been received by the message reception determination means. Data communication device. In a data communication device that receives data sent via a line and identification information for identifying whether the data is for new transmission or retransmission, and returns a confirmation message to the transmission source,
Memory and
Identification information determining means for determining whether the received identification information is for new transmission or retransmission,
When the received identification information is determined to be for new transmission by the identification information determination means, first data registration means for registering data received with the identification information in the memory;
A data comparing means for determining whether or not the data received together with the identification information and the data last registered in the memory are coincident when the received identification information is determined to be for retransmission by the identification information determining means; When,
Data discarding means for discarding the received data, when the received data and the data last registered in the memory are determined to match by the data comparing means,
A second data registration unit that registers the received data in the memory when the data comparison unit determines that the received data and the data last registered in the memory do not match. Data communication device. Data communication between a public telephone provided with at least one data communication device according to claim 3 and a center device provided with at least another data communication device. system.

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