JPS60254948A - Communication control system - Google Patents

Abstract

PURPOSE:To shorten a time required for an error recovery and to prevent a reception stop due to outstanding, etc., by providing a data communication device as a data transmitting device with a resending means which detects an X frame and resends a frame that a receiver does not receive, and performing an error recovery. CONSTITUTION:When data is inputted from a channel 2, namely, when the communication deivce serves as the transmitting device, frames inputted through a circuit 10 and a circuit reception control part 8 are supplied to an I frame resending control part 9. The I frame resending control part 9 detects a frame SR(n) showing a request to send and further frames X.Y, and outputs a request to resend a corresponding frame I(n,0) to a scheduling control part. Further, a request to send a frame RR(0)P is outputted to the scheduling control part after a unit or plural frames are transmitted for a specific time. If the receiver is busy when the frame X.F is received, transmission, for example, is stopped for a specific time.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a data communication device, and particularly to a communication control method for performing error recovery.

(2) Background of the technology In the past, a centralized processing method in which all processing was performed by a single computer was often used, but now computer equipment itself has become cheaper, and with the development of microcomputers, a two-distributed processing method has become popular. It is often used.

Distributed processing performs processing on multiple computers, so its processing speed is much faster than conventional centralized processing.

The plurality of computers used in the above-mentioned distributed processing method require a function to transfer data to each computer, and serial data transfer and parallel data transfer are generally used. These data transfers naturally have the problem that transfer errors occur. In particular, when data is transferred via a line or the like, there is a lot of noise, and the number of errors increases proportionally.

(3) Prior art and problems Currently, in order to ensure reliable data transfer as described above, data such as parity and checksum are added, and it is difficult to determine whether the data sent using that data is correct or not. Error recovery is performed by detecting frame by frame. For example, there is a method that adds numbers to frames. FIG. 1 is an explanatory diagram of a conventional error recovery system. This is a method in which a number is added to the frame and the frames are sent in the order of two numbers. I (n, O) indicates a transmission frame.

n is the number of that frame. First, the transmitting device transmits frame I (0,0), and then sequentially sends frame I (1,0).
, ..., T (6,0) is transmitted.

Assume that an error occurs in frame I (0, O) during this transmission. Although each frame is sent out sequentially.

The receiving device transmits a frame 5REJ(0) (hereinafter referred to as SR(0)) informing the frame number of the error.The transmitting device then inserts the erroneous frame into consecutive frames and transmits it again. In order to check whether the sending device has received each frame normally,
Send frame RR(0)P to the receiving device. Frame R
R(0)P is a frame that requests the receiving device to send the reception status of consecutively received I frames to the transmitting device. When the receiving device receives this frame, it transmits a frame RR(m+1)F notifying the last number m of consecutively received frames or a frame 3R(m+1)F notifying the error frame number. In Figure 1, an error occurs in the first frame 41 (0,0) and the subsequent frame 1 (L O) is received, so the receiving device transmits frame SR (0) F. . Upon receiving this frame SR(0)'F, the transmitting device retransmits frame I (0,0). Note that the aforementioned frame SR(m+1)F is a response frame to frame RR(0)P. When the receiving device normally receives frame I (0, O), it sends frame RR (6) as the second frame.
Send. This frame RR' (7) simply indicates that up to frame I (5,0) has been received without error.

In FIG. 1, an error occurs at frame I (6,0). Even though the sending device has sent frame I (6°0), it receives frame RR (6) notifying that up to frame I (5, O) has been received, so it sends the file RR (0) again. ) P to the receiving device.

The receiving device sends frame RR(6)F in response to frame RR(0)P. The sending device is RR(6)F
, frame I (6,0) is sent to the receiving device, assuming that frame I (6,0) has not been received. In the above example, the frame to be transmitted is I
(0,O)~T (6,0), so frame I (
After sending frames RR(0,0) to I(6,O)
)P etc. and the corresponding frame SR(0)F,
Although RR(6)F and frame RR(6) are being received,
If there are more consecutive frames to be transmitted, it is inserted into the consecutive frames.

In the conventional system described above, the receiving device sends frame SR(m+1) to the transmitting device in response to an error frame that has occurred. Also, for example, frame RR(m+1) is sent to the originating device for a certain period of time or after receiving a specific frame. Furthermore, as a response to frame RR(0)P, frame RR(m+1)F and frame SR(m+1
) is sending F. In the conventional system, since such frames are inserted into frames that are sent out in a concatenated manner to deal with errors that occur sequentially, there is a problem in that it takes a lot of time for error recovery. Furthermore, when there is a lot of noise and many errors occur, it takes a lot of time to process the error frames, so the buffer that stores the concatenated frames to be sent in the transmitting device may become full. In other words, a busy state was occurring. For this reason, there was a problem in that the reception stopped.

(4) Purpose of the Invention The present invention solves the above-mentioned problems, and its purpose is to provide communication control that shortens the time required for error recovery, prevents reception stoppage due to outstanding etc., and improves transfer efficiency. The goal is to provide a method.

(5) Structure of the Invention The feature of the present invention is that in a communication system (HD LC) in which data is transferred by transmitting a select reject (SREJ) frame, a receiving device receives
- Transmit a frame with the newest transmission sequence number among the frame transmission sequence numbers and at least one frame sequence number that requests retransmission.X
A frame transmitting means and a transmitting device detect the X frame.

The receiver apparatus is characterized in that it has a retransmission means for retransmitting frames that have not been received by the receiving apparatus, and performs error detection.

(6) Examples of the invention The present invention will be described in detail below using two drawings.

FIG. 2 is a principle diagram illustrating the principle of an embodiment of the present invention. Similar to the transfer in Figure 1, the frame to be transferred is I
(0,O)~I (6,0).

Assume that an error occurs in frames I (0,0) and I (6', O), and that an error also occurs in retransmitted frame I (0,0) corresponding to frame 5R(0).

In the embodiment of the present invention, as in the conventional method shown in FIG. 1, this is to check whether each frame has been received normally.

Send frame RR(0)P to the receiving device. When the receiving device receives the frame RR(0)P.

Transmit frame X-F. Frame X-F is a frame for notifying the state of the own station, that is, the receiving side device, to the other station, that is, the transmitting side device. FIG. 3 is a configuration diagram showing the flags, etc. of the above-mentioned frame X-F. The frame has an F bit consisting of 1 byte at the beginning and end. This bit is a response bit to frame RR(0)P sent from the transmitting device. After the first flag F, addresses, control field C, sequence it numbers sl to S1 . Frame check sequence FC8
continues. Here, the control field C (including the P/F bit) and the frame check sequence FC3 consist of 2 bytes, and the others are 1 byte. Control field C has data indicating the frame type and sequence number So. Note that the sequence number So indicates the newest value among the transmission sequence numbers of each received frame I (n', 0). Sequence numbers S1 to S are transmission sequence numbers of each frame I (n, O) for which retransmission is requested. The sequence number S1 is the smallest number among the frames requested for retransmission.

In other words, this sequence number S1 indicates that up to the number (S+1) immediately before this sequence number has been received. Note that a 1-bit busy flag B is added to the end of the sequence number S+. When B=1, it means that the own station is in a busy state, and when B=0, it means that the own station is in a non-busy state.

The transmitting device that has received this frame X-F can receive it without error and know the frame from the sequence number S1. Further, frames in which an error occurs and are not received are detected from sequence numbers 81 to Sfl. Furthermore, since the transmitting side device stores the transmitted transmission sequence number, it detects up to which frame it has received from the sequence number So. For example, when the frame with the last transmitted sequence number is not received due to the occurrence of an error, the error can be detected by the sequence number So.

The transmitting device retransmits the frame with the sequence number S+-3 which was not received due to an error due to the above-mentioned frame X-F, and furthermore, the frame with the last sequence number in which the error occurred. Note that the error frame detected by the sequence number So is not necessarily the last sequence number, but if errors occur consecutively, the error frame detected by the sequence number So is the sequence number C.
The last sequence number of the frame sent from 3°+1) becomes the error frame number, and at this time all the frames are retransmitted. The above-mentioned frame has a flag indicating whether the receiving station, that is, the receiving device is busy or not.

When the receiving device is busy, the transmitting device stops transmitting frames for a specific period of time.

FIG. 4 is a circuit diagram of an embodiment of the present invention.

The embodiment of the present invention shown in FIG. 4 has the functions of both a transmitter and a receiver.

When it is a transmitting side device, an l frame creation control unit 4. The I frame retransmission control section 9 operates, and when the device is on the receiving side, the reception frame order control section 12. The sequence error P bit reception detection section 11, 5REJ, and X frame transmission control section 13 operate. Note that the inter-channel transmission/reception control unit 3, line transmission control unit 61, line reception control unit 8. The scheduling control unit 5 operates during both transmission and reception. The inter-channel transmission/reception control section 3 connected to the channel 2 of the computer system I is a device that transfers data to and from the channel 2. When data is transmitted from the computer system 1, the inter-channel transmission/reception control unit 3 is a device that transfers data to and from the channel 2. When data is transmitted from the computer system 1, the inter-channel transmission/reception control section 3 transmits the data input via the channel 2.
It is output to the frame creation control section 4. The l-frame creation control section 4 creates a (i) frame (the above-mentioned I (n, 0), etc.) in order to send out the input data frame by frame, and outputs it to the scheduling control section 5 in frame units. The scheduling control unit 5 allocates transmission of I frames sequentially added from the frame creation unit and stores them in a transmission buffer until the transmission is completed. As will be described later, when there is a request for transmission of a specific frame, etc. from the I frame retransmission control section 9, transmission allocation of the requested frame is performed. Then, the scheduling control section 5 sequentially outputs the frames stored in the buffer in accordance with the transmission assignment, that is, the scheduling, and sends them out to the line 7 via the line transmission control section 6. The line transmission control section 6 forms a pair with the line reception control section 8, and this control section 6.7 constitutes a commonly used modem.

When data is input from channel 2, that is, when the device is on the transmitting side, the frame input via the 1-line 102 line reception control section 8 enters the I frame retransmission control section 9. ■The frame retransmission control unit 9 detects the frame SR(n) indicating the retransmission request shown in FIG. 2, and also the frame X-F mentioned above,
A request to retransmit the corresponding frame I (n, 0) is output to the scheduling control unit. Furthermore, after transmitting a specific time unit or multiple frames, frame RR(0)P
It also outputs a request to send to the scheduling control unit. Note that when the receiving side device is busy when receiving the above-mentioned frame X-F, the transmission is stopped for a specific time, for example.

On the other hand, when one device is a receiving device, that is, when data is transferred to a computer system, frames input via the line 10 and the line reception control unit 8 are received by the sequence error P bit reception detection unit 11. Frame order control unit 1
Join 2. The received I frame order control section 12 detects the frame numbers of input frames and outputs them to the channel 2 of the computer system 1 via the inter-channel transmission/reception control section 3 in the order of 9 numbers. The sequence error P-bi-node reception detection unit 11 detects the frame number and sends a request to transmit a frame SR(n) corresponding to a frame that is not received due to an error caused by a line, etc., in other words, a frame that is not consecutive. 5REJ, output to the X frame transmission control unit.

Further, the sequence error P bit reception detection section 11 detects the frame RR(0)P and also outputs a request to transmit the response frame X-F for that frame to the 5REJ and the X frame transmission control section.

The '5REJ,

In the conventional circuit, frame SR(0)F was sent back in response to frame RR(0)P.

In an embodiment of the invention, the frame RR(0)P
The frame sequence error 'P-bi-node receiving section 11 detects the frame sequence error, and the 5REJ and X-frame transmission control section creates an X-F frame, which is sent to the transmitting side.

is being sent back to the device. This frame X-F enables the transmitting side device to detect the receiving state of the receiving side device at the time of receiving this frame X-F, and the necessary retransmission frame. can be resent.

The embodiment of the present invention shown in FIG. 4 has the transmitting side and receiving side devices as described above, and the configuration shown in FIG. 4 is used oppositely, so that retransmitted frames etc. can be easily detected and retransmitted. becomes possible.

Note that this is a case of bidirectional data transfer.

When one device is only for reception and the other device is only for transmission, data transfer is unidirectional. 1 frame retransmission control section 9, and the transmission-only device receives frame order control section 12. The sequence error P bit reception detection section 11, 5REJ, and the X frame transmission control section 13 are not required.

(7) Effects of the Invention As described above, the present invention uses the newest value among the transmission sequence numbers of each received I frame.

Transmission sequence number of the I frame for which retransmission is requested.

By transmitting the status of the station, such as whether the station is busy or not, in one frame, error recovery is made easier and more efficient, and transmission can be temporarily stopped when the receiving side device is busy. Yes 2 According to the present invention, a communication control system with high transfer efficiency is possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram explaining the conventional communication control method for error recovery, FIG. 2 is an explanatory diagram of the communication control method of the present invention,
FIG. 3 is a frame configuration diagram of an embodiment of the present invention, and FIG. 4 is a configuration diagram of an embodiment of the present invention. 3----------Inter-channel transmission/reception control section, 4
--------=-1 frame creation control section, 5------
------ Scheduling control section, 6.----1.- line transmission control section, 8.-- 1 line reception control section. 9----------■Frame retransmission control section, 11-
-1111 Sequence error P bit reception detection unit. 12------1 Reception ■Frame order control unit. 1st 2F Figure 3 1 bar 4t IJ loud i byte I bar 4t 5o=5 sl=. 1 No. 1) 21 (4) I B4

Claims (2)

[Claims] (1) In a communication method (HDLC) in which data is transferred by transmitting a selection project (SREJ) frame, the receiving device sends the latest transmission sequence number among the transmission sequence numbers of the received frame and at least one retransmission. The transmitting device includes an X frame transmitting means for transmitting a frame having the requested frame sequence number, and the transmitting device has a retransmitting means for detecting the X frame and retransmitting the frame not received by the receiving device. A communication control method characterized by error recovery. (2) The communication control method according to claim 1, wherein the X frame also includes a busy flag having information indicating whether the receiving device is in a busy state.