JP2003188858A - Device and method for packet data transmission, and program for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for packet data transmission and a program for the same by which a necessary band can be suppressed by reducing a data quantity in the case of retransmission in a data communication system having a procedure of retransmission in the case of detecting an error. <P>SOLUTION: The device is provided with an error check means for performing the error check of packet data received from a transmission destination, a storage means for storing the packet data when the packet data includes an error, a retransmission control means for requesting the retransmission of a part of the packet data to the transmission destination, and a packet composing means for connecting and composing a part of the packet data retransmitted from the transmission destination in response to a request for retransmission from the retransmission control means and a part except for a part of the transmitted packet data among the packet data stored in the storage means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet data transmission device, a packet data transmission method, and a program for receiving packet data from a destination when the received packet data has an error.

[0002]

2. Description of the Related Art In recent years, the traffic of data communication via a network has been significantly increasing. In data communication, unlike voice communication, it is necessary for the receiving side to completely restore the transmitted data. Therefore, in order to cover bit errors and the like that occur during transmission, the TC
Means that use a retransmission protocol such as P has become mainstream.

On the other hand, the transmission quality has been gradually improved, and the frequency of bit errors occurring in the transmission line has become considerably low.

[0004]

Under such a background,
In the retransmission protocols up to now, when a packet including a bit error is detected, all the packets are retransmitted, so that there is a problem that the communication band becomes large due to the retransmission.

The present invention has been made in view of the above problems, and divides data into a plurality of blocks for transmission and reception, and the reception side has an error detection function, and when an error is detected, a retransmission request is sent to the transmission side. In the data communication method having a procedure of performing a retransmission request when the transmitting side receives the retransmission request, a packet data transmission device and a packet data transmission device capable of reducing the data amount at the time of retransmission and suppressing the required bandwidth in the data communication method. A transmission method and a program therefor are provided.

[0006]

In order to achieve such an object, the invention according to claim 1 is an error check means for checking an error of packet data received from a destination, and a result of the error check by the error check means. ,
When there is an error in the packet data, storage means for storing the packet data, and when the error check means has an error in the packet data, retransmission control means for requesting the destination to retransmit a part of the packet data And a part of the packet data retransmitted from the transmission destination in response to the request for retransmission by the retransmission control means and a part of the packet data stored in the storage means excluding a part of the transmitted packet data. And packet assembling means for connecting and assembling.

According to a second aspect of the present invention, in the first aspect of the present invention, the error check means performs an error check on a part of the retransmitted packet data, and the retransmission control means performs an error check by the error check means. As a result, when a part of the packet data has an error, the destination is requested to further retransmit a part of the packet data,
The packet assembling means is characterized in that it concatenates only when there is no error in a part of the retransmitted packet data as a result of the error check by the error checking means.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the invention described above, the error check means performs an error check on the packet data connected by the packet assembling means, and when there is an error in the packet data,
The retransmission control means is characterized by requesting the destination to retransmit a part of the packet data other than a part of the retransmitted packet data.

According to a fourth aspect of the present invention, an error check means for checking an error of packet data received from a destination and an error check means for checking the packet data when the packet data has an error as a result of the error check by the error check means. When there is an error in the packet data by the storage means for storing and the error check means, the transmission destination is requested to retransmit the first half of the packet data, and in response to the retransmission request by the retransmission control means, It is characterized by having a packet assembling means for connecting and assembling the first half of the packet data retransmitted from the destination and the latter half of the packet data stored in the storage means.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, an error check is performed on the first half of the retransmitted packet data, and the retransmission control means causes an error check on the first half of the packet data by the error check means. When there is an error, the destination further requests the first half of the packet data to be retransmitted, and the packet assembling means determines that the first half of the retransmitted packet data has no error as a result of the error check by the error checking means. It is characterized by connecting only.

The invention according to claim 6 is the invention according to claim 4 or 5.
In the invention described above, the error check means performs an error check on the packet data connected by the packet assembling means, and when there is an error in the packet data,
The retransmission control means is characterized by requesting the destination to retransmit the latter half of the packet data.

According to a seventh aspect of the present invention, there is an error in the packet data as a result of the first error check step for checking the error of the packet data received from the destination and the error check by the first error check step. Sometimes, a storing step of storing packet data and a first error request step requests the destination to retransmit a part of the packet data when there is an error in the packet data as a result of the error check by the first error checking step. Of the packet data stored in the storing step and a part of the packet data retransmitted from the transmission destination in response to the retransmission request step of 1) and the retransmission request in the first retransmission request step. A first packet assembling step of connecting and assembling a portion excluding a part of data It is characterized in Rukoto.

According to an eighth aspect of the invention, in the invention of the seventh aspect, an error check of a part of the packet data retransmitted from the transmission destination is made in response to the retransmission request by the first retransmission request step, When there is an error in part of the packet data as a result of the error check performed by the second error check step and the second error check step performed before the concatenation by the first packet assembly step , A second retransmission request step of further requesting retransmission of a part of the packet data.

The invention according to claim 9 is the invention according to claim 7 or 8.
In the invention described above, as a result of the third error check step of performing an error check on the packet data connected by the first packet assembling step and the error check by the third error check step, an error occurs in the connected packet data. When there is, a third retransmission request step of requesting the destination to retransmit another part of the packet data other than a part of the retransmitted packet data is further provided.

According to the tenth aspect of the present invention, there is an error in the packet data as a result of the first error check step of performing an error check on the packet data received from the destination and the error check by the first error check step. When there is an error in the packet data as a result of the storage step of storing the packet data and the error check by the first error check step,
A first retransmission request step for requesting the destination to retransmit the first half of the packet data, and a first half of the packet data retransmitted from the destination in response to a retransmission request by the first retransmission request step, First assembling by connecting the latter half of the packet data stored by the storing step
And a packet assembling step.

According to an eleventh aspect of the invention, in the tenth aspect of the invention, the first half of the packet data retransmitted from the transmission destination in response to the retransmission request in the first retransmission request step There is an error in the first half of the packet data as a result of the second error check step of performing an error check of the first half of the packet data before the concatenation by the packet assembling step and the error check by the second error check step. Sometimes, to the destination,
A second retransmission request step for further requesting retransmission of the first half of the packet data.

According to a twelfth aspect of the present invention, in the tenth or eleventh aspect of the invention, there is provided a third error check step of performing an error check on the packet data connected by the first packet assembling step, and a third error check step. As a result of the error check by the check step, if there is an error in the concatenated packet data,
A third retransmission request step for requesting retransmission of the latter half of the packet data, and a second half of the packet data retransmitted from the destination in response to the retransmission request by the third retransmission request step, and the first packet It further comprises a second packet assembling step of connecting and assembling the first half of the packet data connected by the assembling step.

According to a thirteenth aspect of the present invention, in the invention according to the twelfth aspect, an error check of the latter half of the packet data retransmitted from the transmission destination is performed in response to the retransmission request in the third retransmission request step. When there is an error in the second half of the packet data as a result of the error check by the fourth error check step and the fourth error check step performed before the concatenation by the second packet assembling step, the destination is sent to the destination. , And a fourth retransmission request step for further requesting retransmission of the latter half of the packet data.

According to a fourteenth aspect of the present invention, there is an error in the packet data as a result of the first error check process for checking the error of the packet data received from the destination and the error check by the first error check process. At the time, as a result of the storage process of storing the packet data and the error check by the first error check process, when there is an error in the packet data, the first requesting the destination to retransmit a part of the packet data is made. Of the packet data stored in the storage process and a part of the packet data retransmitted from the destination in response to the retransmission request process of 1) and the retransmission request in the first retransmission request process. It is characterized by causing a computer to execute a first packet assembling process for connecting and assembling a part except a part of data. It is set to.

According to a fifteenth aspect of the present invention, in the fourteenth aspect of the invention, an error check is performed on a part of the packet data retransmitted from the destination in response to the retransmission request by the first retransmission request process. A second error check process performed before the connection by the first packet assembly process;
As a result of the error check by the second error check process, when there is an error in a part of the packet data, a second retransmission request process for further requesting the destination to retransmit a part of the packet data is further provided. It is characterized by making a computer execute.

According to a sixteenth aspect of the invention, in the invention of the fourteenth aspect or the fifteenth aspect, there is provided a third error check process for performing an error check on the packet data connected by the first packet assembly process, and a third error check process. As a result of the error check by the check process, when there is an error in the concatenated packet data, the transmission destination is requested to retransmit a part of the packet data other than a part of the retransmitted packet data. It is characterized in that the computer further executes the resend request process.

According to the seventeenth aspect of the present invention, there is an error in the packet data as a result of the first error check process for checking the error of the packet data received from the destination and the error check by the first error check process. Sometimes, when there is an error in the packet data as a result of the storage process for storing the packet data and the error check by the first error check process, the first requesting the destination to retransmit the first half of the packet data. Of the packet data retransmitted from the transmission destination in response to the retransmission request processing of the first retransmission request processing and the first half of the packet data stored by the storage processing are connected. The first packet assembling process of assembling is performed by the computer.

According to an eighteenth aspect of the invention, in the invention of the seventeenth aspect, an error check of the first half of the packet data retransmitted from the transmission destination is performed in response to the retransmission request by the first retransmission request processing, When there is an error in the first half of the packet data as a result of the error check performed by the second error check process and the second error check process performed before the concatenation by the first packet assembling process, the destination is notified to the destination. , A second retransmission request process for further requesting retransmission of the first half of the packet data, and a computer.

According to a nineteenth aspect of the invention, in the seventeenth or eighteenth aspect of the invention, there is provided a third error check process for performing an error check on the packet data connected by the first packet assembly process, and a third error check process. As a result of the error check by the check processing, when there is an error in the concatenated packet data, the third retransmission request processing for requesting the destination to retransmit the latter half of the packet data and the third retransmission request processing A second packet assembling process for assembling and assembling the latter half of the packet data retransmitted from the transmission destination and the first half of the packet data concatenated by the first packet assembling process in response to the request for retransmission. , Are further executed by a computer.

According to a twentieth aspect of the invention, in the invention according to the nineteenth aspect, an error check of the latter half of the packet data retransmitted from the transmission destination is made in response to the retransmission request by the third retransmission request process, When there is an error in the second half of the packet data as a result of the error check by the fourth error check process and the fourth error check process performed before the concatenation by the second packet assembling process, the destination is sent to the destination. , And a fourth retransmission request process for further requesting retransmission of the latter half of the packet data.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION First, the present invention will be outlined. In FIG. 1, the error check unit 2 has a function of dividing the data including the received error into two data of the first half and the second half and writing the data into the memory unit 6. Upon receiving the retransmission request, the transmitting side first retransmits only the first half of the corresponding packet. The packet assembling unit 7 connects the retransmitted first half packet and the second half of the original packet including the error. Error check unit 2
Performs error check again. In this way, by making the size of the retransmitted packet half the size of the original packet, it is possible to reduce the bandwidth used for retransmission.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a packet data transmission device which constitutes a packet data transmission system according to an embodiment of the present invention. The packet data transmission device includes a data receiving unit 1, an error checking unit 2,
It includes a selection unit 3, a data transmission unit 4, a retransmission control unit 5, a memory unit 6, and a packet assembly unit 7.

The data receiving section 1 receives data from the line. The data transmitter 4 outputs the data to the line.

The error check unit 2 has a function of checking an error in received data. A CRC (Cyclic Redundancy Check) operation, a checksum, etc. are available as means for error checking. Also, the error check unit 2
Based on the header of the received packet, the retransmitted packet is sent to the packet assembling unit 7, the first received packet that has an error is divided into two, and the memory unit 6 is used. Distribute.

The selection unit 3 selects the packet received without error and the packet restored by the retransmission and outputs it to the next stage. The retransmission control unit 5 transmits a retransmission request message for a packet in which an error has occurred. To identify the packet,
SN (sequence number) or the like is used. The packet assembling unit 7 reads the first half packet of the retransmission received from the error checking unit 2 from the second half of the packet read from the memory unit 6, or the second half from the error checking unit 2 into the first half from the memory unit 6. It has a function to connect.

Next, the operation (packet data transmission method) of the packet data transmission device in the embodiment of the present invention will be described. FIG. 2 is a flowchart for explaining the operation of the packet transmission device according to the embodiment of the present invention.

In FIG. 2, first, the error check unit 2
Checks an error in the input packet received by the data receiving unit 1. If there is an error (Step A
1), the error check unit 2 divides the error packet into the first half and the second half and stores them in the memory unit 2 (step A2).

Next, the retransmission control unit 5 makes a retransmission request for the first half of the packet of the corresponding SN to the transmission side via the data transmission unit 4 (step A3). Next, when the first half packet for retransmission is received (step A4), an error check is performed on the first half packet for retransmission (step S4).
A5).

If the first half packet for retransmission is again in error (step A5 / Y), the packet is retransmitted until it can be received without error (steps A3 and A4). When the packet is normally received (step A5 / N), the error check unit 2 passes the first half packet to the packet assembling unit 7.

The packet assembling unit 7 reads the second half packet having the same SN as the received first half packet from the memory unit 2 and connects them (step A6). After connecting, the error check unit 2 performs error check again (step A7).

If there is no error (step A7 / N),
The assembled packet is delivered to the selection unit 3 and the processing ends. If the assembled packet has an error (step A7 / Y), the packet assembling unit 7 overwrites only the first half packet in the memory unit 2 and requests the retransmission control unit 5 to retransmit the latter half packet unit (step A8). ).

For the second half packet for retransmission, the same processing as the first half packet for retransmission is repeated until it is received without error (steps A8 to A10). When the packet is normally received (step A10 / Y), the packet assembling unit 7 reads the first half packet having the same SN as the second half packet received from the error checking unit 2 from the memory unit 2 and connects them (step A11). , To the selection unit 3. At this time, since the normality of each of the first and second halves has already been guaranteed by the previous retransmission, it is not necessary to perform error check again after assembling.

Next, a concrete data assembly will be described. FIG. 3 is a diagram showing a format of packet data according to the embodiment of the present invention. In FIG. 3, the header part and FCS (frame check sequence) are included in the original packet and the retransmitted packet, respectively.
Parts and are given. SN field 2 in the header
There are 0, 24 and 28, which identify the packet to be retransmitted or concatenated. Further, the Flag parts 21, 25, 29
Is the packet type (original / first half of retransmission / second half of retransmission)
Identify.

Next, a second embodiment of the present invention will be described. In the above embodiment, the unit of retransmission is divided into the first half and the second half, but this is divided into three.
It may be divided. In that case, there is also a method in which the number of divisions is decided beforehand between the transmitting side and the receiving side at the start of communication.

The packet data transmission method of the present invention can be realized by causing a computer to execute a program. The program includes an optical recording medium, a magnetic recording medium, a magneto-optical recording medium, and a semiconductor IC (integrated ci
rcuit) Recorded on a recording medium and provided. Alternatively, it is provided by being downloaded from a program server by FTP (File Transfer Protocol).

The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications may be made without departing from the scope of the invention. Is possible.

[0043]

As is apparent from the above description, the effect of the present invention is that the data size at the time of retransmission is half the original data size.
By doing so, the bandwidth for retransmission can be suppressed.

Normally, there is at most one error portion contained in one packet. Therefore, the error occurrence part is mostly included in either the first half or the second half. When m-byte data per packet makes an error n times, assuming that no error occurs when retransmitting,
Although it is necessary to retransmit m × n bytes, in the method of the present invention, since the original packet can be restored with a probability of ½ by retransmitting only the first half, (½ × m ×
n) + (1/2 × 1/2 × m × n) = 3/4 × m × n bytes, that is, the bandwidth for retransmission can be suppressed to 3/4.

By arbitrarily setting the unit of division for retransmission, it is possible to perform flexible processing in consideration of traffic volume and error occurrence frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a packet data transmission device that constitutes a packet data transmission system according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the packet data transmission device according to the embodiment of the present invention.

FIG. 3 is a diagram showing a format of packet data according to the embodiment of the present invention.

[Explanation of symbols]

1 Data receiver 2 Error check section 3 selection section 4 Data transmitter 5 Retransmission control unit 6 memory section 7 Packet assembly department

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5K014 AA01 DA02 FA05                 5K030 GA01 GA11 HA08 LA01 LE14                 5K033 AA01 AA06 CB03 CC01 DB13                 5K034 AA01 AA04 DD01 EE11 FF02                       HH01 HH02 HH10 HH11 HH12                       HH17 HH26 MM01 MM03 MM25

Claims (20)

[Claims] 1. An error check means for checking an error of packet data received from a destination, and a result of the error check by the error check means,
A storage unit that stores the packet data when the packet data has an error, and a part of the packet data is retransmitted to the destination when the packet data has an error by the error check unit. A part of the packet data retransmitted from the transmission destination in response to the retransmission request by the retransmission control part, and the packet data stored in the storage part, which is transmitted. A packet data transmission device comprising: a packet assembling unit that connects and assembles a part of the received packet data except a part thereof. 2. The error check means performs an error check on a part of the retransmitted packet data, and the resend control means sets an error check result by the error check means,
When there is an error in part of the packet data, the destination further requests retransmission of part of the packet data, the packet assembling means, as a result of the error check by the error check means,
The packet data transmission device according to claim 1, wherein the packet data transmission device is connected only when there is no error in a part of the retransmitted packet data. 3. The error check means performs an error check on the packet data connected by the packet assembling means, and when there is an error in the packet data, the retransmission control means sets the destination to the destination. The packet data transmission device according to claim 1 or 2, wherein a request is made to retransmit a part of the retransmitted packet data other than the retransmitted packet data. 4. An error check means for checking an error of packet data received from a destination, and a result of the error check by the error check means,
Storage means for storing the packet data when the packet data has an error; and retransmission of the first half of the packet data to the destination when the packet data has an error by the error check means. And a first half of the packet data retransmitted from the destination in response to a retransmission request by the retransmission control means, and a second half of the packet data stored in the storage means. A packet data transmission device comprising: a packet assembling unit that is connected and assembled. 5. The error check means performs an error check on the first half of the retransmitted packet data, and the retransmission control means causes the error check means to detect an error in the first half of the packet data. In the above, the destination is further requested to retransmit the first half of the packet data, and the packet assembling means, as a result of the error check by the error check means,
5. The packet data transmission device according to claim 4, wherein connection is made only when there is no error in the first half of the retransmitted packet data. 6. The error check means performs an error check on the packet data connected by the packet assembling means, and when there is an error in the packet data, the retransmission control means sets the destination to the destination. 6. The packet data transmission device according to claim 4, wherein retransmission of the latter half of the packet data is requested. 7. A first error check step of performing an error check on packet data received from a destination, and when the packet data has an error as a result of the error check by the first error check step, A storage step of storing packet data; and a step of requesting the destination to retransmit a part of the packet data when there is an error in the packet data as a result of the error check by the first error check step. 1, a part of the packet data retransmitted from the destination in response to the retransmission request by the first retransmission request step, and the packet data stored by the storage step, The first packet that links and assembles the part of the transmitted packet data And a packet assembling step. 8. An error check of a part of the packet data retransmitted from the transmission destination in response to the retransmission request in the first retransmission request step, before the concatenation in the first packet assembling step. And a second error check step to be performed, and as a result of the error check by the second error check step, when there is an error in a part of the packet data, the destination receives a part of the packet data. The packet data transmission method according to claim 7, further comprising: a second retransmission request step for further requesting retransmission. 9. A third method for performing an error check on the packet data connected by the first packet assembling step.
And the error check step of the third error check step, when there is an error in the concatenated packet data, a part of the retransmitted packet data is removed to the destination. The packet data transmission method according to claim 7, further comprising a third retransmission request step of requesting retransmission of another part of the packet data. 10. A first error check step of performing an error check on packet data received from a destination, and when the packet data has an error as a result of the error check by the first error check step, A storage step of storing packet data; and a step of requesting the destination to retransmit the first half of the packet data when there is an error in the packet data as a result of the error check by the first error check step. 1 retransmission request step, and the first half of the packet data retransmitted from the destination in response to the retransmission request by the first retransmission request step, and the latter half of the packet data stored by the storage step. A first packet assembly step of connecting and assembling Packet data transmission method that. 11. The first half of the packet data retransmitted from the destination in response to the request for retransmission by the first retransmission request step, before the concatenation by the first packet assembling step. A second error check step of performing an error check of the first half of the packet data, and as a result of the error check by the second error check step, when there is an error in the first half of the packet data, to the destination, The packet data transmission method according to claim 10, further comprising a second retransmission request step of further requesting retransmission of the first half of the packet data. 12. A third error check step of performing an error check on the packet data connected by the first packet assembling step, and a result of the error check by the third error check step, wherein the connected packet data is obtained. When there is an error in the transmission destination, the transmission destination is transmitted in response to a third retransmission request step for requesting the transmission destination to retransmit the latter half of the packet data, and a retransmission request by the third retransmission request step. A second packet assembling step of connecting and assembling the latter half of the packet data retransmitted from the first half and the first half of the packet data connected by the first packet assembling step. Claim 10 or 11
The described packet data transmission method. 13. An error check of the latter half of the packet data retransmitted from the destination in response to the retransmission request by the third retransmission request step, before the concatenation by the second packet assembly step. And a fourth error check step to be performed, and when there is an error in the second half of the packet data as a result of the error check by the fourth error check step, The packet data transmission method according to claim 12, further comprising: a fourth retransmission request step for further requesting retransmission. 14. A first error check process for checking an error of packet data received from a transmission destination, and when the packet data has an error as a result of an error check by the first error check process, A storage process for storing packet data; and a request to retransmit a part of the packet data to the destination when the packet data has an error as a result of the error check by the first error check process. 1, a part of packet data retransmitted from the transmission destination in response to a retransmission request by the first retransmission request process,
Of the packet data stored by the storage processing, a portion excluding a part of the transmitted packet data,
A computer-readable program for causing a computer to execute a first packet assembling process of assembling by assembling. 15. An error check of a part of the packet data retransmitted from the transmission destination in response to a retransmission request by the first retransmission request process, before the concatenation by the first packet assembling process. When a part of the packet data has an error as a result of the second error check process performed by the second error check process and the second error check process, a part of the packet data is sent to the destination. 15. The computer-readable program according to claim 14, further comprising: a second retransmission request process for further requesting retransmission, and: 16. A third error check process for performing an error check of the packet data connected by the first packet assembling process, and a result of the error check by the third error check process, the connected packet data. When there is an error in, the third re-transmission request process for requesting the destination to re-send another part of the re-transmitted packet data to the computer The computer-readable program according to claim 14 or 15, characterized in that: 17. A first error check process for performing an error check on packet data received from a transmission destination, and when there is an error in the packet data as a result of the error check by the first error check process, A storage process for storing packet data; and, as a result of an error check by the first error check process, when there is an error in the packet data, a request is made to the destination to retransmit the first half of the packet data. No. 1 retransmission request process, and the first half of the packet data retransmitted from the destination in response to the retransmission request by the first retransmission request process, and the latter half of the packet data stored by the storage process. And a first packet assembling process for connecting and assembling the computer and the computer. Readable program. 18. The error check of the first half of the packet data retransmitted from the destination in response to the request for retransmission by the first retransmission request process is performed before the concatenation by the first packet assembling process. And a second error check process to be performed, and as a result of the error check by the second error check process, when there is an error in the first half of the packet data, The computer-readable program according to claim 17, further comprising: a second re-transmission request process for further requesting re-transmission, and: 19. A third error check process for performing an error check on the packet data connected by the first packet assembling process, and a result of the error check by the third error check process, the connected packet data. When there is an error in the transmission destination, the transmission destination is transmitted in response to a third retransmission request process for requesting the transmission destination to retransmit the latter half of the packet data, and a retransmission request by the third retransmission request process. A second packet assembling process for connecting and assembling the latter half of the packet data retransmitted from the first half and the first half of the packet data combined by the first packet assembling process. The computer-readable program according to claim 17 or 18. 20. An error check of the latter half of the packet data retransmitted from the transmission destination in response to a retransmission request by the third retransmission request processing is performed before the concatenation by the second packet assembly processing. And a fourth error check process to be performed, and when there is an error in the second half of the packet data as a result of the error check by the fourth error check process, the destination of the second half of the packet data is 20. The computer-readable program according to claim 19, further comprising: a fourth retransmission request process for further requesting retransmission, and: