JP4583318B2 - Data communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a data communication method ensuring high reliability communication by enhancing reduction in communication processing capacity and total throughput. <P>SOLUTION: Transmission of data packet is requested from a reception server 20 to a transmission server 10. In response to that request, the transmission server 10 transmits a plurality of previously divided data packets continuously. Upon receiving the data packet, the reception server 20 judges a data packet which could not be received and requests retransmission of that data packet. In response to the retransmission request, the transmission server 10 transmits that data packet continuously and UDP is used as the transport protocol of each communication. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a data communication method for transmitting a large amount of data at high speed from a transmission side to a reception side using a communication line (wireless line and wired line).

  For example, UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) are conventionally used as protocols that fulfill the functions of the transport layer in TCP / IP communication in order to transmit and receive image data and the like over the Internet. .

  UDP is a connectionless protocol that performs communication without confirming the data reception status of the other party. For this reason, UDP communication has a small load at the time of transmission and reception and can perform processing at a high speed, but there is a problem that data reliability is low.

TCP, unlike UDP, is a connection-type protocol. A session is established between the transmission side and the reception side, and when the reception side receives data, a reception response (ACK) is returned. The transmission side uses the logic of the window control logic. The next packet is transmitted after waiting for a reception response (see Non-Patent Document 1).
It also has a flow control function for controlling the transmission speed according to the reception status. For this reason, TCP can transmit user data in an orderly and reliable manner and has high reliability. However, since the retransmission interval is adjusted within the protocol, there is a problem in communication with speed restrictions.

Therefore, when performing highly reliable communication, TCP is used, and when pursuing high speed, UDP is often used.
In the case of a network such as a control system that requires both reliability and high speed at the same time, it is common to use UDP to confirm the completion of transmission using response data one packet at a time. This type of communication is often used for communication with mobile units.
Furthermore, when response data of a plurality of continuous UDP packets are collectively monitored by one timer, data communication is performed within a limited communication time, and transmission is not completed even after a certain time from the start of transmission processing, There has also been proposed a data communication system that can cancel the transmission process and cope with the next communication (Patent Document 1).

JP 2001-339434 A (pages 3 to 4, FIG. 1) RFC675,761,793: Transmission Control Protocol

  In recent data transmission, the data size has increased compared to the conventional case, and the method of returning response data one packet at a time and confirming the completion of transmission has a drawback in that the transmission efficiency decreases. If TCP is used, communication with high transmission efficiency can be performed. However, since the retransmission interval is adjusted within the protocol, the retransmission timer value fluctuates, which is not suitable for sending data within a limited time. This is because the retransmission timer value becomes long and communication cannot be completed within a limited time.

In addition, the method proposed in Patent Literature 1 can perform reliable data communication within a limited communication time, and if the transmission is not completed even after a certain time from the start of the transmission process, the transmission process is performed. Is a data communication method that can cope with the next communication, and specifically takes the following method. (A) using UDP as a transport protocol, (b) transmitting communication data by dividing it into an optimal packet length, (c) monitoring response data of a plurality of consecutive packets together with one timer, (D) After the set time of the timer elapses, an unaccepted packet that has not been replied is retransmitted. (E) On the other hand, the response data of the received correct packet is returned on the receiving side.
In the method of Patent Document 1, the receiving side returns response data of the received correct packet to the transmitting side, and the transmitting side uses a timer, and a packet that has not been received triggered by the set time of the timer elapses. Since a complicated transmission / reception process needs to be performed at the same time, there is a problem that a relatively high communication processing capability is required for transmission and reception apparatuses.
In addition, since retransmission control is performed only after the timer times out, there is a problem that a time delay occurs until retransmission control is started, and this time delay causes a reduction in total throughput.

  The present invention has been made to solve the above-described problems, and provides a data communication method capable of performing highly reliable communication while reducing communication processing capacity and improving total throughput. Is aimed at.

In the data communication method according to the present invention, in the data communication method for transmitting data from a transmission side having a plurality of communication areas to a reception side which is a mobile body using UDP as a transport protocol, the data communication method is within the communication area. A first procedure for continuously transmitting transmission request packets for requesting transmission of data packets from the receiving side to the transmitting side. On the transmitting side, a plurality of pieces of data each having a sequence number formed by dividing data in advance. A second procedure for continuously transmitting packets in response to reception of a transmission request packet, a data packet continuously transmitted from the transmission side by this second procedure is received at the reception side, and the last data packet is When received, it determines the data packet that could not be received from the received sequence number, and the data that could not be received In response to the reception of the retry request packet and the third procedure for continuously transmitting the retry request packet to the transmission side using the sequence number of the packet, the transmission side receives the data packet requested for retransmission. The transmission side and the reception side receive packets from the other party because the reception side has left the communication area during the execution of any one of the second procedure to the fourth procedure. Is not received for a certain period of time, the transmission side stops sending packets, the reception side continuously transmits transmission request packets to the transmission side, and the reception side is one of a plurality of communication areas. when entering the inner, de transmission side has received the transmission request packet is continuously transmitted to the receiving side the resumption notification packet is a resume notification, the receiving side that has received the requesting retransmission By sending the retry request packet including the sequence number of the packet should sender in which data communication between the sender and receiver is resumed.

As described above, the present invention is in a communication area in a data communication method for transmitting data from a transmission side having a plurality of communication areas to a reception side which is a mobile body using UDP as a transport protocol. A first procedure for continuously transmitting transmission request packets for requesting transmission of data packets from the receiving side to the transmitting side. On the transmitting side, a plurality of pieces of data each having a sequence number formed by dividing data in advance. A second procedure for continuously transmitting packets in response to reception of a transmission request packet, a data packet continuously transmitted from the transmission side by this second procedure is received at the reception side, and the last data packet is When received, it determines the data packet that could not be received from the received sequence number, and the data packet that could not be received In response to receiving the retry request packet in the third procedure for continuously transmitting the retry request packet to the transmission side using the sequence number, the transmission side continuously transmits the data packet requested for retransmission to the reception side. The transmission side and the reception side keep the packet from the other party constant because the reception side leaves the communication area during the execution of any one of the second procedure to the fourth procedure. When the time is not received, the transmission side stops transmitting the packet, and the reception side continuously transmits the transmission request packet to the transmission side, and the reception side is in any one of the communication areas. when this happens, the transmission side which has received the transmission request packet is continuously transmitted to the receiving side the resumption notification packet is a resume notification, the receiving side that has received the data packet for requesting the retransmission By sending the retry request packet including a sequence number to the transmitting side, the data communication between the sender and receiver is resumed, it can compare the processing to the case of using a TCP fast and complex It is not necessary to perform transmission / reception processing at the same time, and it is possible to reduce the communication processing capability required for the transmission side and the reception side which is a mobile body.

Embodiment 1 FIG.
The first embodiment will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a data communication method according to Embodiment 1 of the present invention.
In FIG. 1, a packet is transmitted from a transmission server 10 constituting a transmission side to a reception server 20 constituting a reception side in communication areas 30, 40 and 50. The receiving server 20 is movable, and can receive a packet from the transmitting server 10 when moving into the communication areas 30, 40, 50.
FIG. 2 is a flowchart showing the flow of packets transmitted and received between the transmission side and the reception side in the data communication method according to Embodiment 1 of the present invention.

Next, the operation will be described with reference to FIG.
The transmission server 10 divides data to be transmitted in advance into an optimal packet length, clearly indicates that the data is included in each UDP datagram, and further generates a “data packet” with a series of sequence numbers. Keep it.

The receiving server 20 enters the communication area 30 while continuing to transmit the UDP “transmission request packet” (step S1) (first procedure).
When the wireless communication link between the transmission server 10 and the reception server 20 is established, a “transmission request packet” transmitted from the reception server 20 arrives at the transmission server 10, and the transmission server 10 that has received the “transmission request packet” Packets "are continuously transmitted to the receiving server 20 (step S2) (second procedure).
Receiving server 20 receives “data packets” continuously transmitted from transmitting server 10 and receives the last packet, and receives “data packet” that could not be received from the sequence number in the received plurality of packets. Judgment is made, the request for retransmission is clearly indicated in the UDP datagram, and a “retry request packet” in which the sequence number of the packet to be retransmitted to the transmission server 10 is embedded is generated and continuously transmitted to the transmission server 10 (Step S3) (third procedure).

  The transmission server 10 receives the “retry request packet” continuously transmitted from the reception server 20 and, when receiving the last packet, continuously transmits the “data packet” requested to be retransmitted to the reception server 20. (Step S4) (fourth procedure).

Receiving server 20 receives “data packets” continuously transmitted from transmitting server 10 and receives the last packet, and receives “data packet” that could not be received from the sequence number in the received plurality of packets. Then, a “retry request packet” in which the sequence number of the packet to be retransmitted is filled is generated again to the transmission server 10, and continuously transmitted to the transmission server 10 (step S3).
The transmission server 10 receives the “retry request packet” continuously transmitted from the reception server 20 and, when receiving the last packet, continuously transmits the “data packet” requested to be retransmitted to the reception server 20. (Step S4).

  When the reception server 20 receives all “data packets” by repeating this step S3 and step S4, data in the UDP datagram for reporting to the transmission server 10 that all “data packets” have been received. A "data reception completion packet" provided with a reception completion flag is transmitted to the transmission server 10, and a series of data communication is terminated (step S5).

The above-described series of sequences is an example in the case where all data communication is completed only in the communication area 30. However, when the moving speed of the reception server 20 is fast or the communication area 30 is narrow, the transmission server 10 When the communication time with the receiving server 20 is short, the receiving server 20 leaves the communication area 30 before transmission of all data packets is completed.
Next, a data communication resuming method in this case will be described.

Each of the transmission server 10 and the reception server 20 has a timer. When the communication is started and the reception of a packet from the other party is awaited, the timer is started and the packet from the other party is received for a certain period of time. If not received, it is determined that the other party is not in the communicable area, and the transmission server 10 and the reception server 20 return to the initial state in the timeout process (step S6).
That is, the reception server 20 continuously transmits “transmission request packets”, and the transmission server 10 enters a state of waiting for reception of “transmission request packets” from the reception server 20.

When the receiving server 20 enters the next communication area 40, the "transmission request packet" (step S7) that the receiving server 20 continues to transmit reaches the transmitting server 10, and the transmitting server 10 terminates the data communication in the middle In order to notify the receiving server 20 and report what the “data packet” the receiving server 20 wants, a “resume notification packet” clearly indicating that it is a restart notification in the UDP datagram. The transmission continues to the receiving server 20 (step S8).
When receiving the “resume notification packet”, the receiving server 20 transmits a “retry request packet” in which the sequence number of the “data packet” to be retransmitted is filled to the transmitting server 10, thereby resuming data communication. (Step S9).
The transmission server 10 continuously transmits “data packets” to the reception server 20 in response to the reception of the “retry request packet” (step S10).
By repeating step S9 and step S10, if all the “data packets” are received by the receiving server 20, a “data reception completion packet” is transmitted to the transmitting server 10 to end a series of data communication ( Step S5).

  This data communication method is a method of accepting a retransmission request from the receiving server 20 after the transmission server 10 has finished throwing all “data packets”. When data communication is performed, the retransmission request sequence is performed many times, and the total throughput is extremely deteriorated. On the contrary, in a communication area where the radio channel quality is very excellent, the occurrence of a retransmission request sequence is suppressed to a minimum, and an extremely high total throughput can be obtained.

  Although the first embodiment has been described on the assumption that the transmission server 10 and the reception server 20 are linked by a wireless line, data communication can be performed in the same manner when the link is fixedly made by a wired line. it can.

In the above, it is described that the packet is continuously transmitted. However, when the communication line is particularly a wireless line, it is often the case that the packet does not reach the other party in one packet transmission. This is because it is necessary to keep sending.
In addition, since the transmission of the “transmission request packet” from the receiving server 20 in steps S1 and S7 continues to generate unnecessary radio waves, the communication area is measured by some method such as an external device measuring the electric field strength. It is also possible to take a method of detecting the intrusion into the network and starting transmission of a “transmission request packet” triggered by the detection.

In the method of the first embodiment, the end of the “data packet” in steps S2, S4, and S10 and the end of the “retry request packet” in steps S3 and S9, that is, all the “data packets” have been thrown once. And it is necessary to report to the receiving server 20 and the transmitting server 10 that the “retry request packet” has been thrown all once. This is because the reception server 20 and the transmission server 10 need to obtain timing for starting transmission.
As the method, a flag that clearly indicates the last packet is provided in the “data packet” and “retry request packet”, and the last packet is set with the flag, ”And“ retry request packet ”, and then a“ data packet transmission end packet ”and a“ retry request packet transmission end packet ”are transmitted.

Further, when the communication line is a wireless line in particular, it is often the case that the packet does not reach the other party in one transmission, and therefore it is necessary to continue to transmit the last packet.
Alternatively, instead of continuing to transmit the last packet, a method of continuing to transmit all the packets may be used. In this case, it is assumed that the "data packet" and "retry request packet" have all been thrown once. In the “data packet” and “retry request packet”, a flag that clearly indicates that it has been transmitted once is provided, and in the second and subsequent transmissions, the flag is set to indicate “data packet” and “retry request packet”. Send "Retry Request Packet" repeatedly.

In addition, as a method for reporting to the transmission server 10 that the receiving server 20 has received all “data packets”, a method of transmitting a “retry request packet” in which the sequence number is not filled, or “retry request packet transmission end” A method of transmitting only “packets” or “data reception completion packet” provided with a data reception completion flag in the UDP datagram for reporting to the transmission server 10 that all “data packets” have been received. There is a method of transmitting to the transmission server 10.
If the receiving server 20 receives all “data packets”, it is not necessary to transmit / receive packets thereafter. If the packet transmission is stopped, the other party automatically terminates data communication due to a timeout. There is also a method in which the receiving server 20 does not dare to report to the transmitting server 10 that all “data packets” have been received.

According to the first embodiment, since UDP is used as a transport protocol and communication data is divided into an optimal packet length and transmitted, the processing can be performed at a higher speed and complicated than when TCP is used. This eliminates the need for simultaneous transmission / reception processing, reduces the communication processing capability required of the transmission / reception device, and responds immediately to a packet retransmission request sent from the receiving side, so total throughput within a limited communication time Can be increased.
In addition, “transmission request packet”, “data packet”, “retry request packet” and “data reception completion packet” continue to be transmitted, and the transmission server and reception server did not receive any packets from the other party for a certain period of time. For example, by taking a method of interrupting data communication and returning to the initial state using the trigger as a trigger, for example, data communication starts from the moment when the receiving server enters the wireless communicable section from the transmitting server, and from the wireless communicable section The data communication is interrupted when it is disconnected, and the data communication is performed when entering the next wireless communicable section, thereby enabling high-speed and highly efficient data communication.

Embodiment 2. FIG.
FIG. 3 is a schematic diagram showing a data communication method according to Embodiment 2 of the present invention.
In FIG. 3, a plurality of transmission servers 11, 12, and 13 constituting the transmission side are connected to the management server 60 via the terrestrial network 70. Each of the transmission servers 11, 12, and 13 has a communication area as shown in FIG. 1, and transmits a packet to the reception server 20 that has moved to this communication area.

Next, the operation will be described.
When there are a large number of communication areas, it is practically impossible to cover them with a single transmission server 10, so a large number of transmission servers and their communication area configurations as shown in FIG. 1 are arranged and managed. A management server 60 is provided at the upper level, and a method of connecting the management server 60 and the transmission servers 11, 12, and 13 via the ground network 70 is employed.

  The management server 60 divides a plurality of files to be transmitted to the receiving server 20 into small files that can be sufficiently transferred within a plurality of communication areas managed by one transmission server, and the small file group is divided into each file. The data is transmitted to the transmission servers 11, 12, and 13.

When the reception server 20 enters the communication area managed by the transmission server 11, the small file group is transmitted from the transmission server 11 to the reception server 20 according to the procedure described in the first embodiment. When the receiving server 20 exits the communication area managed by the transmission server 11, the transmission server 11 reports to the management server 60 information on small files that could not be transmitted among all small file groups to be sent.
The management server 60 transmits the received content to the other transmission servers 12 and 13 to prepare for the next communication area entry of the reception server 20.

Next, when the receiving server 20 enters the communication area managed by the transmitting server 12, the transmitting server 12 transmits a small file group that has not been received by the receiving server 20 to the receiving server 20.
Thereafter, the same procedure is followed to transmit all small file groups to be transmitted to the receiving server 20.
The reception server 20 combines the received small file groups and restores the original file at an appropriate timing.

  If the receiving server 20 travels in a certain direction, such as a railway vehicle, in one direction, the communication area of the transmitting server that the receiving server 20 enters next is determined. The transmission server to which the small file information 60 is not received may be only the transmission server next to the transmission server that has received the report.

  According to the second embodiment, since the communication area is increased by the plurality of transmission servers, the range in which the reception server can move is widened.

It is a schematic diagram which shows the data communication method by Embodiment 1 of this invention. It is a flowchart which shows the flow of the packet transmitted / received by the transmission side and receiving side of the data communication method by Embodiment 1 of this invention. It is a schematic diagram which shows the data communication method by Embodiment 2 of this invention.

Explanation of symbols

10 transmission server 11 transmission server 1
12 Transmission server 2
13 Sending server N
20 Receiving server 30 Communication area 1
40 Communication area 2
50 Communication area N
60 Management server 70 Terrestrial network

Claims (15)

In a data communication method for transmitting data from a transmission side having a plurality of communication areas to a reception side which is a mobile body using UDP as a transport protocol,
A first procedure for continuously transmitting a transmission request packet for requesting transmission of a data packet from the reception side in the communication area to the transmission side;
On the transmission side, a second procedure that is formed by dividing the data in advance and that sequentially transmits a plurality of data packets each having a sequence number in response to reception of the transmission request packet;
The data packet transmitted continuously from the transmission side by the second procedure is received by the reception side, and when the last data packet is received, the data packet that could not be received is determined from the received sequence number. A third procedure for continuously transmitting a retry request packet for requesting retransmission using the sequence number of the data packet that could not be received to the transmitting side;
And in response to receiving the retry request packet, the transmitting side includes a fourth procedure of continuously transmitting the retransmission requested data packet to the receiving side,
When the transmitting side and the receiving side do not receive a packet from the other party for a certain period of time because the receiving side has left the communication area during the execution of any one of the second to fourth procedures, The transmission side stops transmitting packets, and the reception side continuously transmits the transmission request packet to the transmission side, and the reception side enters one of the communication areas of the plurality of communication areas. When the transmission side receives the transmission request packet, the transmission side continuously transmits a restart notification packet, which is a restart notification, to the reception side. A data communication method characterized in that data communication between the transmission side and the reception side is resumed by transmitting a retry request packet including a message to the transmission side .   2. The data communication method according to claim 1, wherein a flag indicating that the data packet is the last data packet is set in the last data packet transmitted in the second procedure.   A data packet transmission end packet is transmitted next to the last data packet so that the receiving side can determine that the data packet is the last data packet transmitted in the second procedure. The data communication method according to claim 1.   3. The data communication method according to claim 2, wherein the last data packet is continuously transmitted in the second procedure.   4. The data communication method according to claim 3, wherein the data packet transmission end packet is continuously transmitted in the second procedure.   2. The data according to claim 1, wherein in the second procedure, the data packet is repeatedly transmitted, and a flag indicating that the data packet has been transmitted once is provided in the second and subsequent data packet transmissions. Communication method.   The data communication method according to claim 1, wherein a flag indicating that it is the last retry request packet is set in a last retry request packet of the retry request packet transmitted by the third procedure.   A retry request packet transmission end packet is transmitted next to the last retry request packet so that the transmission side can determine the last retry request packet of the retry request packet transmitted by the third procedure. The data communication method according to claim 1.   8. The data communication method according to claim 7, wherein the last retry request packet is continuously transmitted in the third procedure.   9. The data communication method according to claim 8, wherein the retry request packet transmission end packet is continuously transmitted in the third procedure.   In the third procedure, a retry request packet is repeatedly transmitted, and a flag indicating that the retry request packet has been transmitted once is provided in the second and subsequent retry request packet transmissions. The data communication method described.   When the receiving side has received all the data packets by the second procedure and the fourth procedure, the receiving side transmits a retry request packet having no sequence number to the transmitting side. The data communication method according to claim 1.   When the receiving side receives all data packets by the second procedure and the fourth procedure, the receiving side transmits only the retry request packet transmission end packet to the transmitting side. The data communication method according to claim 8.   When the receiving side has received all data packets according to the second and fourth procedures, the receiving side transmits a data reception completion packet having a flag indicating completion of data reception to the transmitting side. The data communication method according to claim 1. A transmission server that performs data communication with the receiving side according to the movement of the receiving side even when the receiving side moves due to management of a management server connected to a plurality of transmitting servers constituting the transmitting side via a network The data communication method according to any one of claims 1 to 14 , wherein the data is switched.

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