JP2010063070A - Flow control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow control method for highly precisely preventing overflow in communication equipment and reducing cost of communication equipment itself. <P>SOLUTION: It is decided whether interruption transmission of a flow control data signal instructing stop of data transmission can be performed or not in a confronted device being a communication opposite party based on a non-transmission data amount of a protocol data unit (PDU), which is in the middle of transmission to the confronted device from communication equipment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a data communication flow control method for transmitting and receiving data for each protocol data unit (PDU) such as a packet or a frame.

  A communication device used in Ethernet defined by the Institute of Electrical and Electronics Engineers (IEEE) 802.3x standard has a buffer memory (reception buffer) for temporarily storing received frames. Such a communication apparatus performs processing of received frames in accordance with the frame reception order. However, since the capacity of the buffer memory is finite and the amount of data that can be stored is determined, if the amount of received data is larger than the amount of processed data, the amount of unprocessed received data will reduce the capacity of the buffer memory. Received frames that exceed and cannot be accumulated are discarded without processing (ie, overflow). In such a state, a frame received exceeding the processing capability of the communication device is lost, so that data communication by the communication device is not accurately performed.

  As a method for avoiding congestion discard as described above, in the case of full-duplex communication, it is conventionally known to perform flow control defined by the IEEE 802.3x MAC control protocol. Specifically, when a data amount equal to or greater than the threshold value of the reception buffer is accumulated in the reception buffer of the communication device, a communication device that transmits a pause frame (Pause frame) to the communication device on the other side of communication and receives the pause frame Frame transmission from is stopped for a predetermined time. Patent Document 1 discloses a flow control method as described above and a communication device used therefor.

  However, the following problems have occurred in the flow control method described above. Problems in the conventional flow control method will be described with reference to FIG.

  As illustrated in FIG. 1, when the communication device A receives the nth frame from the communication device (opposite device) B, the nth frame is accumulated in the reception buffer of the communication device A. When the nth frame is accumulated in the reception buffer, if the frame is accumulated up to the reception buffer capacity threshold (pause frame transmission threshold), the communication apparatus A transmits a pause frame to the opposite apparatus B. However, since the communication apparatus A is transmitting the (m + 1) th frame to the opposite apparatus B, the communication apparatus A transmits a pause frame after the transmission of the (m + 1) th frame is completed. Due to the pause frame transmission delay, the communication apparatus A receives the (n + 1) th frame while waiting for the pause frame transmission, and accumulates frames exceeding the capacity threshold of the reception buffer.

  When the n + 2 frame is being transmitted from the opposite device B at the time when the pause frame is transmitted from the communication device A, the transmission of the frame of the opposite device B is stopped after the transmission of the n + 2 frame is completed. The That is, the opposite apparatus B stops transmission of the (n + 3) th and subsequent frames. Accordingly, the communication apparatus A accumulates the n + 2th frame in the reception buffer following the above-described n + 1th frame.

  Due to the transmission delay of the pause frame in the communication apparatus A described above, it is necessary to store two frames in the reception buffer exceeding the capacity threshold of the reception buffer. Therefore, it is twice the maximum frame size that can be transferred from the capacity of the reception buffer. The value obtained by subtracting the amount of data needed to be set as the threshold value. That is, the communication apparatus needs to start the transmission activation of the pause frame in a state where there is a sufficient space in the buffer free space. As a result, the communication device needs to have a large-capacity reception buffer, which raises the problem of an increase in the cost of the communication device itself.

The reason why the data amount to be reduced is twice the maximum transferable frame size is to prevent overflow even when the (n + 1) th and (n + 2) th frames have the maximum transferable frame size.
JP 2004-7180 A

  The present invention has been made in view of the above circumstances, and provides a flow control method capable of preventing overflow in a communication device with high accuracy and reducing the cost of the communication device itself.

  In order to solve the above-described problem, the flow control method of the present invention is configured so that the amount of data stored in a reception buffer of a communication device is predetermined in data communication in which data is transmitted and received for each protocol data unit (PDU). When the threshold value is exceeded, a flow control data signal for instructing the opposite device, which is a communication partner of the communication device, to stop data transmission is generated and transmitted to the opposite device, and predetermined based on the flow control data signal. Is a flow control method for stopping data transmission from the opposite device to the communication device for a period of time, wherein the flow control data signal is sent to the opposite device based on the amount of untransmitted PDU being transmitted from the communication device to the opposite device. It is characterized by determining whether or not to transmit an interrupt.

  According to the flow control method of the present invention, whether or not the interrupt transmission of the flow control data signal instructing the stop of data transmission to the opposite device that is the communication partner can be performed is being transmitted from the communication device to the opposite device. By determining based on the untransmitted data amount of the PDU, overflow in the communication device can be prevented with high accuracy, and the cost of the communication device itself can be reduced.

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

  First, the configuration of a communication apparatus to which a flow control method according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of a communication apparatus to which the flow control method according to the embodiment of the present invention is applied.

  As shown in FIG. 2, the communication device 10 and the communication device (opposing device) 20 are connected via a transmission path 30. The communication device 10 and the communication device 20 are communication devices used in the Ethernet specified by the Institute of Electrical and Electronics Engineers (IEEE) 802.3x standard, and perform communication for each frame in accordance with the IEEE 802.3x standard. Do.

  The communication device 10 includes a transmission buffer unit 11, a transmission frame management unit 12, a reception buffer unit 13, and a reception frame management unit 14. The communication device 20 has the same configuration as that of the communication device 10 and includes a transmission buffer unit 21, a transmission frame management unit 22, a reception buffer unit 23, and a reception frame management unit 24.

  The transmission buffer unit 11 temporarily accumulates transmission frames. In addition, the transmission buffer unit 11 performs frame transmission and transmission stop to the transmission frame management unit 12 in response to a transmission instruction and transmission stop instruction from the transmission frame management unit 12.

  The transmission frame management unit 12 instructs the transmission buffer unit 11 to transmit and stop transmission of frames. Further, the transmission frame management unit 12 responds to a signal notified when the amount of data stored in the reception buffer unit 13 exceeds a threshold value, and a pause frame (a flow control data signal for instructing stop of frame transmission). Pause frame) is generated. Furthermore, the transmission frame management unit 12 can specify the transmission stop time using data in the generated pause frame. The transmission frame management unit 21 selects one of the frame supplied from the transmission buffer unit 11 and the generated pause frame, and transmits the selected frame to the communication device 20 via the transmission path 30. Further, the transmission frame management unit 21 stops frame transmission in response to a transmission stop instruction from the reception frame management unit 14. The transmission frame management unit 12 can also instruct transmission resumption by designating the transmission stop time to “0”. For example, after transmitting a pause frame to the communication device 20, the communication device 10 generates a transmission resumption instruction data signal for requesting frame transmission resumption, and transmits the transmission resumption instruction data signal to the communication device 20. Can be sent to. As a result, transmission of frames from the communication device 20 to the communication device 10 is resumed.

  Further, the transmission frame management unit 12 determines the total data amount of the frame being transmitted (that is, the frame size) and the transmitted data according to the signal notified when the accumulated data amount of the reception buffer unit 13 exceeds the threshold value. The amount of untransmitted data is calculated from the amount. Here, the transmission frame management unit 12 can confirm the total data amount of the frame from the header information of the frame being transmitted. Further, since the transmission frame management unit 12 constantly monitors the transmission status of each frame, the transmission frame management unit 12 acquires the transmitted data amount of the frame being transmitted at the time when the notification that the accumulated data amount exceeds the threshold is received. be able to. The transmission frame management unit 12 compares the calculated untransmitted data amount with a preset threshold data amount (an abort data remaining amount threshold) of the untransmitted data amount. The transmission frame management unit 12 causes the transmission buffer unit 11 to cancel frame transmission when the amount of untransmitted data is larger than the abort data remaining amount threshold, and sets the frame for which transmission has been stopped as a frame including only transmitted data. Frame transmission is completed (ie, abort processing is executed). Thereafter, the transmission frame management unit 12 transmits the generated pause frame to the communication device 20. As described above, the transmission of the frame being transmitted is aborted, and the transmission of the pause frame interrupts, whereby the transmission of the frame from the communication device 20 is stopped early.

  On the other hand, when the amount of untransmitted data is smaller than the abort data remaining amount threshold, the transmission frame management unit 12 waits for the completion of transmission of the frame being transmitted and transmits the generated pause frame to the communication device 20. As described above, when the amount of untransmitted data is smaller than the abort data remaining amount threshold value, the abort process is not performed, and the pause frame is transmitted after the frame transmission is completed, so that the number of abnormal frame transmission and frame retransmission can be reduced. It is suppressed. As a result, a decrease in the data transfer rate associated with the frame retransmission process is suppressed, and frame retention in the transmission buffer 11 is prevented. That is, not performing the abort process in the above-described case has an effect of avoiding overflow and frame discard in the transmission buffer 11.

  The abort data remaining amount threshold described above is a set value that can be changed by, for example, an input signal of an input unit (not shown) of the communication device 10 or a signal from a central control unit (not shown). . In addition, the above-described abort data remaining amount threshold is set such that, for example, when a pause frame is transmitted from the communication apparatus 10 to the communication apparatus 20 after waiting for transmission of a frame being transmitted, the communication apparatus 10 communicates after transmitting the pause frame. It is determined based on the maximum amount of data received from the device 20.

  The reception frame management unit 14 identifies a frame supplied from the communication device 20. For example, when a normal frame is supplied from the communication device 20, the reception frame management unit 14 temporarily stores the supplied frame in the reception buffer unit 13. When a pause frame is supplied from the communication device 20, the reception frame management unit 14 instructs the transmission frame management unit 12 to stop transmission of a frame based on information (stop time, etc.) in the supplied pause frame. And indicate stop time.

  The reception buffer unit 13 temporarily accumulates frames supplied from the reception frame management unit 14. The reception buffer unit 13 notifies the transmission frame management unit 12 that the accumulated data amount exceeds the buffer threshold when the accumulated data amount exceeds a preset buffer capacity threshold (buffer threshold). At the same time, it requests transmission of a pause frame. The buffer threshold described above can be changed according to the processing capability of the communication device 10. For example, the buffer threshold is changed by an input signal of an input unit (not shown) of the communication device 10 or a signal from a control CPU (not shown).

  The communication device 20 has the same configuration as that of the communication device 10, and thus description of each component of the communication device 20 is omitted.

  Next, a flow control method according to an embodiment of the present invention will be described with reference to FIG.

  The reception buffer unit 13 constantly monitors the amount of data stored in the buffer (step S1). Furthermore, the reception buffer unit 13 determines whether the amount of data stored in the buffer exceeds the buffer threshold (step S2). If the accumulated data amount in the buffer does not exceed the buffer threshold (step S2: No), the reception buffer unit 13 continues to monitor the accumulated data amount in the buffer. When the accumulated data amount in the buffer exceeds the buffer threshold (step S2: Yes), the reception buffer unit 13 notifies the transmission frame management unit 12 that the accumulated data amount in the buffer has exceeded the buffer threshold. At the same time, a pause frame transmission is requested (step S3).

  The transmission frame management unit 12 that has received the notification from the reception buffer unit 13 checks whether or not a frame is currently being transmitted (step S4). When the frame is being transmitted from the transmission buffer unit 11 (step S4: Yes), the transmission frame management unit 12 acquires the total data amount (that is, the frame size) of the frame from the header information of the frame being transmitted. To do. In addition, the transmission frame management unit 12 monitors the frame being transmitted and acquires the transmitted data amount of the frame being transmitted. Further, the transmission frame management unit 12 calculates the untransmitted data amount of the frame being transmitted by subtracting the already transmitted data amount from the total data amount of the frame being transmitted (step S5).

  Next, the transmission frame management unit 12 compares the untransmitted data amount calculated in step S5 with the abort data remaining amount threshold that is a preset data amount, and determines whether the untransmitted data amount is larger than the set value. It is determined whether or not (step S6). If the untransmitted data amount is larger than the abort data remaining amount threshold (step S6: Yes), the transmission frame management unit 12 instructs the transmission buffer unit 11 to stop transmission of the frame being transmitted (step S7). In response to the transmission stop instruction from the transmission frame management unit 12, the transmission buffer unit 11 stops transmission of the frame being transmitted (step S8).

  Subsequently, the transmission frame management unit 12 includes only the data amount (that is, the transmitted data amount) obtained by subtracting the untransmitted data amount from the frame in which transmission in step S8 is stopped (that is, the frame including untransmitted data). Complete transmission as a frame. Thereby, the transmission of the frame being transmitted is aborted (step S9). Note that such an incomplete frame is recognized as an abnormal frame in the Ethernet standard frame check sequence by the reception frame management unit 24 of the communication apparatus 20 which is the communication counterpart, and is then discarded. Furthermore, the transmission frame management unit 11 generates a pause frame that includes a predetermined transmission stop time in the data, and transmits the pause frame to the communication device 20 via the transmission path 30 (step S10). Upon receiving the pause frame, the reception frame management unit 24 of the communication device 20 that is the communication partner side instructs the transmission frame management unit 22 to stop transmission of the frame based on the information (stop time, etc.) in the received pause frame. And indicate stop time. After the transmission of the pause frame, the transmission frame management unit 12 instructs the transmission buffer unit 11 to retransmit from the top data of the aborted frame (step S11). Based on the retransmission instruction, the transmission buffer unit 11 supplies again to the transmission frame management unit 12 the frame that was being transmitted when transmission was stopped (step S12). Thereafter, the transmission buffer unit 11 continues to transmit the temporarily accumulated frames.

  In this way, the abort process of the frame being transmitted is executed, and the transmission of the pause frame interrupts, whereby the transmission of the frame from the communication device 20 is stopped early.

  On the other hand, when the untransmitted data amount is smaller than the set value (step S6: No), the transmission frame management unit 12 waits for the completion of transmission of the frame being transmitted (step S13). Subsequently, the transmission frame management unit 12 instructs the transmission buffer unit 11 to stop transmission of a frame (next frame) to be transmitted next (step S14). The transmission frame management unit 12 may instruct the stop of transmission of the next frame during frame transmission. The transmission buffer unit 11 stops transmission of the next frame in response to the transmission stop instruction from the transmission frame management unit 12 (step S15). Subsequently, the transmission frame management unit 11 generates a pause frame that includes a predetermined transmission stop time in the data, and transmits the pause frame to the communication device 20 via the transmission path 30 (step S16). Upon receiving the pause frame, the reception frame management unit 24 of the communication device 20 that is the communication partner side instructs the transmission frame management unit 22 to stop transmission of the frame based on the information (stop time, etc.) in the received pause frame. And indicate stop time. After transmission of the pause frame, the transmission frame management unit 12 instructs the transmission buffer 11 to resume frame transmission (step S17). The transmission buffer unit 11 resumes frame transmission from the next frame (step S18).

  In this way, when the amount of untransmitted data is smaller than the abort data remaining amount threshold, the abort process is not performed, and the pause frame is transmitted after the frame transmission is completed, thereby suppressing the number of abnormal frame transmissions and frame retransmissions. Is done. As a result, a decrease in the data transfer rate associated with the frame retransmission process is suppressed, and frame retention in the transmission buffer 11 is prevented. That is, not performing the abort process in the above-described case has an effect of avoiding overflow and frame discard in the transmission buffer 11.

  If the frame is not being transmitted from the transmission buffer unit 11 (step S4: No), the transmission frame management unit 12 instructs the transmission buffer unit 11 to stop transmission of the next frame to be transmitted next (step S14). ). Thereafter, the transmission buffer unit 11 stops transmission of the next frame (step S15), the transmission frame management unit 12 transmits a pause frame (step S16), the transmission frame management unit 12 instructs to start transmission of the next frame (step S17), and transmission. Transmission of the next frame (step 18) by the buffer unit 11 is sequentially performed. Steps S14 to S18 are the same as those described above, and a description thereof will be omitted.

  As described above, according to the flow control method of the present invention, it is determined from the communication device whether or not the interrupt transmission of the data signal for flow control instructing the opposite device as the communication partner to stop the data transmission can be performed. By determining based on the untransmitted data amount of the PDU being transmitted to the opposite device, overflow in the communication device can be prevented with high accuracy, and the cost of the communication device itself can be reduced.

  In the above-described embodiments, the unit of data transfer used for communication between communication devices has been described as the case of a frame. However, data transfer used for communication between communication devices is not protocol data other than frames. A unit (PDU: Protocol Data Unit), for example, a packet or segment transfer unit may be used. Further, in the above-described embodiment, the case of communication by Ethernet defined by the IEEE 802.3x standard has been described. However, the flow control method of the present invention transmits dedicated data for flow control such as a PUASE frame. The present invention can be applied to all communication methods that execute flow control so as to stop data transmission from a communication partner device and devices that perform the communication.

It is a time chart figure in the conventional flow control method. It is a block diagram which shows the structure of the communication apparatus with which the flow control method which is an Example of this invention is applied. It is a sequence diagram of the communication apparatus to which the flow control method which is an Example of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Communication apparatus 11 Transmission buffer part 12 Transmission frame management part 13 Reception buffer part 14 Reception frame management part 20 Communication apparatus (opposite apparatus)
21 Transmission buffer unit 22 Transmission frame management unit 23 Reception buffer unit 24 Reception frame management unit 30 Transmission path

Claims (6)

In data communication in which data is transmitted / received for each protocol data unit (PDU), when the amount of data stored in the reception buffer of the communication device exceeds a predetermined threshold, the opposite device that is a communication partner of the communication device A flow control data signal for instructing to stop data transmission is generated and transmitted to the opposite device, and data transmission from the opposite device to the communication device is performed for a predetermined time based on the flow control data signal. A flow control method for stopping,
A flow control method comprising: determining whether to interrupt-transmit the flow control data signal to the opposite device based on an untransmitted data amount of a PDU being transmitted from the communication device to the opposite device. .   It is determined whether to interrupt-transmit the flow control data signal to the opposite device based on a comparison result between an untransmitted data amount of the PDU being transmitted and a preset threshold data amount. The flow control method according to claim 1.   When the flow control data signal is transmitted from the communication device to the opposite device after waiting for transmission of the PDU being transmitted, the threshold data amount is determined after the flow control data signal is transmitted. A flow control method, wherein the apparatus is determined based on a maximum amount of data received from the opposite apparatus.   4. The flow control method according to claim 1, wherein when an interrupt transmission of the data signal for flow control is performed, the transmission of the PDU being transmitted is aborted. 5.   5. The flow control method according to claim 4, wherein the PDU in the aborted transmission is retransmitted after the flow control data signal is transmitted.   The communication device generates a transmission resumption instruction data signal for resuming data transmission from the opposite device after transmitting the flow control data signal, and transmits the data signal to the opposite device. 6. The flow control method according to any one of 1 to 5.

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