JPH09233082A - Flow control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method by which transfer performance of flow control is not deteriorated even when a transfer delay time of control information of the flow control is increased. SOLUTION: A round transmission delay time from a time when an initializing processing section 71 of a transmitter side equipment sends a frame describing an initializing frame identifier at initialization of communication to a receiver side equipment till a time when the receiver side equipment returns a reply frame describing number of frames capable of being stored in a reception buffer and the transmitter side equipment receives the reply frame, is measured based on a clock 72. When a half of the round transmission delay time is larger than the time required for transmission of data corresponding to the number of frames capable of being stored in the reception buffer extracted from the reply frame at a credit extract section 64, the number of frames more than the number of frames capable of being stored in the reception buffer is allowed for transmission.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control method for preventing a receiving buffer of a receiving device from overflowing.

[0002]

2. Description of the Related Art ANSI (American National Standard)
for Information Systems), HIPPI (High P
The specifications of a high-speed parallel interface called erformance Parallel Interface) are defined. HI
Since the maximum transmission distance of PPI is 25 m, it cannot be used for long-distance communication.

On the other hand, ATM is becoming the standard as a high-speed interface for wide area networks. By converting HIPPI into ATM, high-speed communication becomes possible between computers having a remote HIPPI interface.

On the HIPPI interface, flow control is performed using a signal line different from the main signal line called ready. When converting HIPPI to ATM,
In the ATM communication section, flow control that is different in form from HIPPI flow control is performed.

Hereinafter, HIPP specified by ANSI
A flow control method in I-ATM conversion will be described.

FIG. 1 shows a configuration of a conventional transmitting side device, for example, 10, in which 11 is an upper layer transmission processing section,
Reference numeral 12 is a control processing unit, 13 is a credit processing unit, 1
Reference numeral 4 is a transmission buffer, 15 is a transmission buffer control unit, 16 is a credit extraction unit, 17 is a transmission transmission processing unit, 18 is a reception transmission processing unit, 19 is an initialization frame generation unit, 20 is a selector, and 21 is a credit counter. . Also, A, B
Is a transmission path.

FIG. 2 shows a configuration of a conventional receiving side device, for example, 30, in which 31 is a reception transmission processing unit, 32 is a transmission transmission processing unit, 33 is a reception buffer, 34 is a credit cell generation unit, 35 is a buffer read control unit, 36 is a clock, 37 is a ready counter, 38 is an upper layer reception processing unit, 39 is a received frame signal, and 40 is a flow control signal.

FIG. 3 shows the structure of a conventional frame, for example, 50. In the figure, 51 is a frame type, 52 is a destination address, 53 is a source address, 54 is a credit number, and these are frame headers 55. And also
Reference numeral 56 is user information, which constitutes a payload 57.

The operation will be described below.

The flow control processing unit 12 transmits to the upper layer transmission processing unit 11 pulses of the number of frames that can be stored in the transmission buffer 14 at the time of initialization of communication. Each time the transmission buffer control unit 15 reads a frame from the transmission buffer 14, the flow control processing unit 12 transmits one pulse. The upper layer transmission processing unit 11 is capable of transmitting frames of the received pulse number. The initialization frame generation unit 19 transmits the frame (hereinafter, referred to as initialization frame) 50 in which the identifier indicating the initialization frame is described in the frame type 51 before starting the communication, to the transmission transmission processing unit. After performing transmission processing such as cell formation at 17, the data is transmitted to the transmission path A.

When the initialization frame 50 arrives at the receiving side device 30, the reception transmission processing unit 31 performs transmission processing such as frame assembly processing and reproduces the initialization frame. When the frame type 51 of the received frame 50 describes an initialization frame identifier, the credit cell generation unit 34 regards the frame 50 as an initialization frame, and sets the frame type 51 to a response frame identifier for the initialization frame. The number of frames that can be stored in the reception buffer 33 of the reception side device 30 is described in the credit number 54, the response frame 50 is converted into cells by the transmission and transmission processing unit 32, and then transmitted to the transmission path B.

When the transmission side device 10 receives the cellized response frame from the transmission path B, the reception transmission processing section 18 assembles the frame into a frame. The credit extraction unit 16
When recognizing that the identifier of the response frame is described in the frame type 51 of the received frame 50, the credit processing unit 13 is notified of the credit number 54 of the frame 50.

The credit processing unit 13 sets the notified credit number 54 in the credit counter 21.
The credit processing unit 13 notifies the transmission buffer control unit 15 that transmission is possible when the value of the credit counter 21 is "1" or more, and the transmission buffer control when the value of the credit counter 21 is "0". The unit 15 is notified that transmission is not possible.

When the transmission permission is notified, the transmission buffer control unit 15 performs transmission processing such as cell formation processing on the frame stored in the transmission buffer 14 by the transmission transmission processing unit 17, and then transmits the transmission path A. To credit processing unit 1
3 counts down the credit counter 21 every time a frame is transmitted from the transmission buffer 14, and the flow control processing unit 12 outputs 1 pulse to the upper layer transmission processing unit 11.
Send to The transmission buffer control unit 15 stops the transmission when the value of the credit counter 21 is “0”.

The upper layer reception processing unit 38 transmits as many pulses to the flow control signal 40 as the number of frames which can be stored in the upper layer reception processing unit 38 at the time of initialization of communication, receives the frame 50, and receives the frame 50. When the processing is completed and a new frame can be received, one pulse is transmitted to the flow control signal 40. The buffer read control unit 35 counts the number of received pulses by the ready counter 37, and counts down the ready counter 37 every time one frame is read from the reception buffer 33.

When the receiving device 30 receives the cellized frame, the reception transmission processing unit 31 assembles the frame into a frame and stores the frame in the reception buffer 33.
When the ready counter 37 is “1” or more, the buffer read control unit 35 transfers the frame stored in the reception buffer 33 to the upper layer reception processing unit 38.

By the operation of the transmitting side device 10 and the receiving side device 30 as described above, the transmitting buffer 14 and the receiving buffer 3
3 and the overflow of the reception buffer of the upper layer reception processing unit 38 can be avoided.

In recent years, research has been conducted in various places with the aim of realizing high-speed communication between end systems of 1 Gbit / s or higher. In the United States, a high-speed test network called a gigabit test bed is used to connect universities and research institutes, and research on high-speed communication protocols and applications using high-speed communication is being conducted on it.

[0019]

Generally, in data communication, flow control is performed in order to avoid overflow of the receiving buffer of the receiving side device. Communication distance becomes longer,
When the transmission speed becomes high, the relative transfer delay with respect to the transmission speed between the transmission side device and the reception side device increases, and the relative delay of the arrival time of the control information of the flow control increases.

The above-described conventional flow control method has a problem that when the transmission delay increases, the transmission side device excessively suppresses transmission even though the reception side device can receive, and the transfer performance deteriorates. .

It is an object of the present invention to provide a flow control method in which the transfer performance of flow control does not deteriorate even if the transfer delay time of control information for flow control increases.

[0022]

According to the present invention, in order to solve the above-mentioned problems, the receiving side device notifies the transmitting side device of the number of frames read from the receiving buffer, and the transmitting side device transmits the data based on the notification. In a flow control method for controlling a transmission amount, a transmission side device transmits an initialization frame to a reception side device at the time of initialization of communication, and when the reception side device receives the initialization frame, the reception side device The device's receive buffer sends back a response frame that describes the number of frames that can be stored, and the sending device measures the time from when the initialization frame is sent until the response frame is received, and the round trip transfer delay time is measured. ½ of the round trip transfer delay time is longer than the time required to transmit data for the number of frames that can be stored in the reception buffer of the reception side device described in the response frame. If the number of frames allowed for transmission is greater than the number of frames that can be stored in the receiving buffer of the receiving side device, the receiving side device periodically measures the number of frames read from the receiving buffer, and The frame that describes the time difference from the measurement time of this time to the current measurement time is periodically transmitted to the transmission side device, and when the transmission side device receives the frame, it receives the measurement result and the time difference described in the frame. The flow control is characterized in that the frame reading speed from the receiving buffer of the side device is obtained, and the increase amount of the number of frames permitted for transmission is obtained based on the reading speed and the round-trip transfer delay time. Suggest a method.

Conventionally, the receiving side device notifies the transmitting side device of the number of frames that can be stored in the receiving buffer, and the transmitting side device transmits up to the notified number of frames. On the other hand, in the present invention, based on the transfer delay of the frame between the transmission side device and the reception side device, the reading speed of the frame from the reception buffer of the reception side device, and the empty capacity of the reception buffer of the reception side device. The difference is that the number of frames permitted to be transmitted to the transmission side device is determined.

According to the present invention, the number of frames permitted to be transmitted to the transmission side device is determined based on the transfer delay between the transmission side device and the reception side device and the reading speed of the frame from the reception buffer of the reception side device. By deciding, the transmission distance between the transmitting side device and the receiving side device becomes long, and the transfer performance does not deteriorate even when the frame transfer delay becomes large.
Further, when the free capacity of the reception buffer of the reception side device decreases, the risk of overflow of the reception buffer of the reception side device can be reduced by reducing the number of frames permitted to be transmitted to the transmission side device.

[0025]

4 to 6 show an example of an embodiment of a flow control method of the present invention.

FIG. 4 shows the configuration of a transmitting side device, for example, 60. In the figure, 61 is an upper layer transmission processing unit, 62 is a flow control processing unit, 63 is a transmission buffer, 64 is a credit extraction unit, and 65 is a unit. A transmission buffer control unit, 66 is a transmission transmission processing unit, 67 is a reception transmission processing unit, 68 is a credit counter, 69 is a credit calculation processing unit, 70 is a selector, 71 is an initialization processing unit, and 72 is a clock. A is a transmission transmission line and B is a reception transmission line.

FIG. 5 shows a configuration of a receiving side device, for example, 80. In the figure, 81 is a reception transmission processing unit, 82 is a transmission transmission processing unit, 83 is a reception frame counter, 84 is a credit frame generation unit, and 85. Is a reception buffer, 86 is a transmission clock, 87 is a buffer read control unit, 88 is an upper layer reception processing unit, 89 is a reception burst, and 90 is a flow control signal.

FIG. 6 shows the structure of a frame, for example, 100, in which 101 is a frame type, 102 is a destination address, 103 is a source address, 104 is a transmission interval, 105 is the number of accumulated frames, and 106 is a credit. A number, which make up the frame header 107, and
Reference numeral 108 is user information, which constitutes a payload 109.

The operation will be described below.

The flow control processing unit 62 transmits to the upper layer transmission processing unit 61 as many pulses as the number of frames that can be accumulated in the transmission buffer 63 at the time of initialization of communication. The frame 100 is transmitted from the transmission buffer 63, and the transmission buffer 63
Each time the empty capacity for one frame increases, the flow control processing unit 62 transmits one pulse to the upper layer transmission processing unit 61. The upper layer transmission processing unit 61 includes the flow control processing unit 6
It is possible to transmit frame 100 up to the number of pulses that 2 transmits.

The initialization processing unit 71 causes the transmission / transmission processing unit 66 to perform the initialization processing for the initialization frame 100 in which the identifier indicating that the frame is an initialization frame is described in the frame type 101 when the communication is initialized. After performing the transmission process, it is transmitted to the transmission path A.

When the cellized initialization frame 100 arrives at the reception side device 80, the reception transmission processing section 81 assembles the reception cells into an initialization frame. The credit frame generation unit 84 uses the frame type 10 of the initialization frame.
When recognizing that the initialization frame identifier is described in 1, the response frame identifier for the initialization frame is described in the frame type 101, and the number of credits is 10
A response frame in which an initial credit (Cinit), which is the number of frames that can be stored in the reception buffer 85, is written in the area 6 is made into cells by the transmission / transmission processing unit 82, and then transmitted to the transmission path B.

When the cellized response frame arrives at the transmission side device 60, it is assembled into a frame by the reception transmission processing unit 67, and the initialization processing unit 71 responds to the initialization frame with the frame type 101 of the reception frame. When the frame identifier is described, the time from the transmission of the initialization frame to the reception of the response frame is measured by the clock 72, and the measurement result is used as the round-trip transfer delay time, which is the credit calculation processing unit. Notify 69.

On the other hand, the credit extraction unit 64 notifies the credit calculation processing unit 69 of the initial credit described in the credit number 106 of the response frame 100. The credit calculation processing unit 106 sets the initial credit in the credit counter 68. When the value of the credit counter 68 is “1” or more and the transmission frame is stored in the transmission buffer 63, the transmission buffer control unit 65
Transmits the frame to the transmission line A through the transmission / transmission processing unit 66.

The credit counter 68 counts down each time a frame is transmitted from the transmission buffer 63. When the value of the credit counter 68 is “0” or the frame is not stored in the transmission buffer 63, the transmission buffer control unit 65 does not transmit the frame from the transmission buffer 65.

The credit frame generator 84 is the number of frames (credits) read from the reception buffer 85.
Is measured at regular intervals, an identifier indicating that the frame is a frame in which credits are described in the frame type 101, the measurement cycle in the transmission interval 104, the credits in the credit number 106, and the frame accumulation number. 105
Then, the frame in which the number of frames stored in the reception buffer 85 at that time is described is transmitted to the transmission path B through the transmission transmission processing unit 82.

When the transmission side device 60 receives the frame from the transmission line B, the credit extraction unit 64 causes the transmission interval 104, the frame accumulation number 105,
The credit amount 106 is notified to the credit calculation processing unit 69. The credit calculation processing unit 69 performs flow control based on the notified initial credit, transmission interval, frame accumulation number, and credit.

The flow control algorithm based on these notification information will be described below.

First, variables defined in the following description will be defined.

Cinit is an initial credit, Rate is a transmission line speed, Tprop is a round trip transfer delay time of the transmission line, Cnew is a credit, Tc is a credit transmission period, Credit_count is a value of a credit counter 68, Fsize is a frame size, C
Let offset be the increment value of the credit value, and Rbuf be the number of frames read from the reception buffer of the reception side device per unit time. At the time of initialization of communication, these variables are initialized to 0.

The credit calculation processing unit 69, when the time required to transmit the notified number of frames of the initial credit (Cinit) is larger than 1/2 of the round trip transfer delay time (Tprop), that is, Cinit × Fsize. / Rate ≧ Tprop / 2 (1) When the condition (1) is satisfied, the following processing is performed.

First, the credit counter 68 (Credit_count) such as Credit_count = Cinit (2)
Set the initial credit (Cinit) to.

When the receiving side device 80 subsequently receives a frame in which credits are described periodically, it performs the process of Credit_count = Cnew + Credit_count (3).

When the time required to transmit a frame that can be stored in the reception buffer 85 is shorter than 1/2 of the round trip transfer delay time, that is, when Cinit × Fsize / Rate <Tprop / 2 (4) is satisfied, The following processing is performed.

When the transmission side device 60 receives the response frame of the initialization frame, the credit number of the frame is 10
The initial credit described in 6 is set in the credit counter 68, that is, Credit_count = Cinit (5).

When the transmission side device 60 receives the frame 100 in which the credit is written, which is periodically transmitted from the reception side device 80, the frame per unit time from the reception buffer 85 of the reception side device 80 is received. The read number (Rbuf) is calculated as Rbuf = Cnew / Tc (6) from the credit (Cnew) and the credit transmission interval (Tc).

Based on the value described in the frame credit number 106, Coffset = (Tprop / 2-Cinit * Fsize / Rate) * Rbuf * Fsize / Rate-Coffset Credit_count = Credit_count + Cnew + Coffset (7) , A value is set in the credit counter 68.

The transmitting side device 60 performs the above processing each time it receives a frame in which a credit is described.

Further, by replacing the equation (7) with Coffset = (Tprop / 2−Cinit × Fsize / Rate) × Rbuf × Fsize / Rate-Coffset Credit_count = Credit_count + Cnew + α × Coffset (8), the receiving buffer 85 It is possible to reduce the risk of overflow (but
α is a value less than 1. ).

When the difference between the value of the accumulated frame number 105 described in the frame 100 that is periodically received and the initial credit becomes less than a specific value, the transmitting side device 60 credit_count = Credit_count + Cnew. The value is set in the credit counter 68 by (9).

[0051]

As described above, according to the present invention, the transfer delay time between the transmission side device and the reception side device is measured at the time of initialization of communication, and the measurement result is stored in the reception buffer of the reception side device. If it is longer than the time required to send the data for the number of possible frames, set the number of frames that the sending device is allowed to send to the transfer delay time and the amount of data that can be stored in the receiving buffer of the receiving device. It is possible to perform flow control in which the transfer performance does not deteriorate even if the transfer delay time increases by increasing the transfer delay time in proportion to the difference in time. In addition, the number of frames read from the reception buffer that is periodically transmitted from the reception side device to the transmission side device and the transmission cycle thereof allow the transmission side device to obtain the reading speed from the reception buffer of the reception side device. By setting the number of frames permitted to be transmitted to the transmission side device by the read speed, highly efficient flow control can be performed while avoiding overflow of the reception buffer according to the processing speed of the upper layer of the reception side device. it can.

Further, by multiplying the increase amount of the number of frames permitted to be transmitted to the transmission side device by a coefficient of less than 1, it is possible to perform flow control with a further reduced risk of overflow.

Furthermore, the receiving side device transfers the accumulated number of frames in the receiving buffer from the receiving side device to the transmitting side device and obtains the difference between the accumulated number of frames and the number of frames that can be stored in the receiving buffer. Of the receiving buffer of the receiving side device, and when the free space becomes less than a certain value, the receiving device overflow of the receiving side device can be prevented by reducing the increase amount of the number of frames permitted to be transmitted to the transmitting side device. It is possible to prevent it.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a transmission side device showing an example of a conventional flow control method.

FIG. 2 is a block diagram of a receiving side device showing an example of a conventional flow control method.

FIG. 3 is a frame configuration diagram showing an example of a conventional flow control method.

FIG. 4 is a configuration diagram of a transmission side apparatus showing an embodiment of a flow control method of the present invention.

FIG. 5 is a configuration diagram of a receiving side apparatus showing an embodiment of a flow control method of the present invention.

FIG. 6 is a frame configuration diagram showing an embodiment of a flow control method of the present invention.

[Explanation of symbols]

60 ... Transmission side device, 61 ... Upper layer transmission processing unit, 62
... Flow control processing unit, 63 ... Transmission buffer, 64 ... Credit extraction unit, 65 ... Transmission buffer control unit, 66 ... Transmission transmission processing unit, 67 ... Reception transmission processing unit, 68 ... Credit counter, 69 ... Credit calculation processing unit, 70 ... Selector, 71 ... Initialization processing section, 72 ... Clock, 80 ... Reception side device, 81 ... Reception transmission processing section, 82 ... Transmission transmission processing section, 83 ... Reception frame counter, 84 ... Credit frame generation section, 85 ... Reception buffer, 86 ... Transmission clock, 87 ... Buffer reading control unit, 88 ... Upper layer reception processing unit, 89 ... Reception burst, 90 ... Flow control signal, 100 ... Frame, 101 ... Frame type, 102
... destination address, 103 ... source address, 104 ... transmission interval, 105 ... frame accumulation number, 106 ... credit number, 107 ... frame header, 108 ... user information, 1
09 ... Payload, A, B ... Transmission line.

Claims (4)

[Claims] 1. A flow control method in which a receiving device notifies a transmitting device of the number of frames read from a receiving buffer, and the transmitting device controls a data transmission amount based on the notification, in which the transmitting device communicates. At the time of initialization, the initialization frame is transmitted to the reception side device, and when the reception side device receives the initialization frame, the response frame describing the number of frames that can be stored in the reception buffer of the reception side device. The transmission side device measures the time from the transmission of the initialization frame to the reception of the response frame to measure the round trip transfer delay time, which is half the round trip transfer delay time. If the time is longer than the time required to transmit the data of the number of frames that can be stored in the reception buffer of the receiving side device described in the response frame, the number of frames permitted for transmission is set to the receiving side device. The number of frames that can be stored in the reception buffer is increased, and the receiving device periodically measures the number of frames read from the reception buffer, and describes the measurement result and the time difference from the previous measurement time to the current measurement time. The frame is periodically transmitted to the transmission side device, and when the transmission side device receives the frame, the reading speed of the frame from the reception buffer of the reception side device is obtained from the measurement result and the time difference described in the frame, A flow control method, wherein an increase amount of the number of frames permitted to be transmitted is obtained based on the read speed and the round-trip transfer delay time. 2. The increase amount of the number of frames permitted to be transmitted is 1
The flow control method according to claim 1, wherein a value obtained by multiplying the coefficient by less than is set as the increase amount. 3. The number of frames accumulated in the reception buffer of the receiving side device at that time is described in the frame transmitted from the receiving side device to the transmitting side device. Knowing the free space in the receiving buffer of the receiving device by finding the difference with the number of frames that can be stored in the receiving buffer, and when the free space in the receiving buffer is below a certain value, the number of frames to allow transmission The flow control method according to claim 1, wherein the increase amount is reduced. 4. The number of frames permitted to be transmitted to the transmission side device is increased when the free capacity of the reception buffer of the reception side device changes from below a specific value to above a specific value. The described flow control method.