JPS61208939A - Data communication repeater - Google Patents

Abstract

PURPOSE:To obtain a high line operating efficiency by returning a frame of an input data whose error is detected to a sending side, adding newly an order number to the data without error and sending the result to the next line. CONSTITUTION:An input data added with a specific order number and a redundancy bit is subject to frame recognition by a frame recognizing circuit 2 and an error is detected by an error detection circuit 3, then the frame is sent to a sending side via a return circuit 4 and the sending side applies re-transmission procedure of the data. The frame not detected for the error is stored in the buffer circuit 5, the data from the circuit 5 is added with a new order number by a number adding circuit 6 and inputted to a frame generation circuit 7. The circuit 7 sends the frame generated with a redundancy bit added to the next line via a transmission circuit 10 and stores it in a buffer circuit 8. Then the state confirming frame from the line is inputted to a confirming signal receiving circuit 9 from a terminal 12 and when error detection is informed, the data of the circuit 8 is retransmitted via the circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a relay device for cascading and connecting a plurality of data communication lines that perform communication by dividing data into frames.

(Prior art and its problems) In data communication, there is a method of constructing and transmitting a data frame consisting of one section of information data and a bit sequence for identifying the data. A redundant bit called a frame check sequence (Fe2) is usually added to this data frame, so that it is possible to detect a bit error 9 on the frame that occurs on the line. In data communication,
A method of controlling the recovery of Ia accumulation using erroneous detection by Fe2 is often used. In other words, if an incorrect tb is detected on the receiving side, FC8lat! The state based on the information is sent back using the opposite line, and if there is an error tb on the receiving side, the same data frame is sent back on the sending side again. In this mb detection retransmission means, 1
Waiting for a reception status acknowledgment response every data frame before sending the next frame, or retransmitting the same frame, would result in poor use efficiency of one line due to propagation delay. For this reason, a method has been considered in which each data frame is numbered and the frame is retransmitted without waiting for a reception status confirmation response. There are various methods like this, but the one called the selective repeat method retransmits only frames that have been confirmed to be erroneous, and prepares a buffer on the receiving side so that erroneous frames are retransmitted. The information receiver transmits the information to the receiver after holding the subsequent frame and restoring the frame order, and is characterized by high line usage efficiency. In order to further improve efficiency, there is also a method of sending retransmission frames multiple times to avoid repeating retransmissions.

However, when such data communication lines are connected in series, the following problems occur.

In other words, if one error occurs in the data frame output from one data communication line in the relay device,
If something is interrupted for a while and no data is sent to a new line, and the error is corrected by retransmission, a large number of data frames will be sent at once, making it difficult to use one line effectively. The disadvantage is that it becomes hard.

(Object of the Invention) An object of the present invention is to provide a relay device that can provide high line utilization efficiency in data communication lines connected in cascade.

(Structure of the Invention) According to the present invention, there is provided a data frame to which a unique sequence number and redundant bits for detecting errors are added to data, and a method for notifying the error state detected by the redundant bits. In a data communication system in which multiple data communication lines are cascaded and communicated using a status confirmation frame, an error t) occurs due to redundant bits added to the data frame received from the first data communication line. a frame receiving means that detects the presence or absence of a status check frame, returns the status confirmation frame to the transmitting station using a transmission path in the opposite direction of the communication line, and outputs only the necessary data; By reading the sequence number added to the data frame received from the storage means for temporary storage and the first data communication line and comparing it with the sequence number read previously, the number of output ports for data having the sequence number is determined. a number comparison means for determining, and a new data frame is created by taking the data stored in the storage means as input and adding a new sequence number and a new redundant bit; a frame creating means for outputting a number of times, and a second data frame for either a newly created data frame or a data frame held for retransmission
The present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 8, a data frame coming from a first data communication line via terminal 1 is input to a frame recognition circuit. The frame recognition circuit 2 recognizes one frame by finding the start and end delimiters of each frame.

The frame output from the frame recognition circuit is input to the error detection circuit 3. The error detection circuit 3 performs error detection using redundant bits added to the frame.

The sequence number of the frame for which the erroneous tυ detection result is determined to be correct is sent to the number comparison circuit 14. The number comparison circuit 14 compares the sequence number to see if it is the same as the number input immediately before, and outputs the result to the error detection circuit 3. ! l#l) If the detection circuit 3 determines that the 1 number comparison circuit 14 has assigned the same number, that frame is discarded.

The error "&υ detection result is sent to the return circuit 4, and in the return circuit, a status confirmation frame is sent to the transmission path in the opposite direction of the first data communication line via the terminal 13, and is sent to the data frame sending station. The sending station uses this status confirmation frame to perform data retransmission procedures.

On the other hand, among the frames for which the error detection circuit has made an error detection judgment, those determined to be errors are discarded, and the remaining frames are stored in the buffer circuit 5. A data frame is output from the buffer circuit 5 in a first-in, first-out manner as necessary, and the data frame is outputted from the number addition circuit 6.
is input.

In the number addition circuit 6, a new number is added in the order of newly received frames for the second data communication line.

This number is different from the number added to the first data communication line.
A number for the data communication line is assigned at this stage.

Also, since numbering cannot be done infinitely, numbering is usually done with a cycle that is sufficiently long compared to the round-trip propagation delay. The frames numbered by the number addition circuit 6 are output to the frame creation circuit 7. On the other hand, a portion of the data output from the buffer circuit 7 indicating the sequence number is input to the number comparison circuit 15. The number comparison circuit 15 compares the input sequence number with the value in the maximum number storage circuit 16, and if the former is smaller than the latter by a predetermined value or more, the frame creation circuit stores multiple frames. instructs to send out. If the incoming sequence number is larger than the maximum number, the sequence number is output to the maximum number storage circuit 16, and the contents of the maximum number are updated. In the frame creation circuit 7, the WA on the second data communication line
A circuit for adding redundant bits to detect errors and a bit string indicating the start/end delimiter of a frame are added.

In addition, the frame creation circuit temporarily stores the data frame and outputs it multiple times according to instructions from the number comparison circuit.

i.e. compared to previously arrived frame numbers.

Frames with small numbers are retransmission frames, and by sending them multiple times, the probability that a frame retransmitted on the first data communication port will be retransmitted again on the second data communication line is reduced. , which eliminates wasted transmissions caused by buffer overflows on the receiving side. The output of the frame creation circuit is branched into two, one being the sending circuit lO
The other signal is input to the buffer circuit 8 in preparation for retransmission due to an error. On the other hand, a status confirmation frame is input from the terminal 12 through the second data communication line. The frame input from the terminal 12 is input to the confirmation signal receiving circuit 9, which outputs an output indicating whether or not the previously transmitted data frame has been received without error. If reception of the data frame is confirmed, the data frame stored in the buffer circuit 8 is deleted. Furthermore, if a false detection is notified, the data frame is retransmitted to the second data communication line via the transmission circuit 10. In this case, the retransmission frame is sent multiple times to avoid retransmission due to an error.

In the sending circuit 10, a frame to be newly sent stored in the buffer circuit 5 and a frame to be retransmitted stored in the buffer circuit are selected based on the output of the confirmation signal receiving circuit 9, and the frames to be retransmitted are selected via the terminal 11. The data is sent to the second data communication line. In this embodiment, frame recognition circuit 2. Mistake detection circuit 3. and return circuit 4 constitute frame receiving means, number comparison circuit 15 and maximum number storage circuit 16 constitute number comparison means, number addition circuit 6 and frame creation circuit 7 constitute frame creation means, and buffer circuit 8 ．． The confirmation signal receiving circuit 9 and the sending outlet path 10 constitute frame sending means. As described above, a relay device that can effectively use the second data communication line output from the terminal 11 can be provided.

FIG. 2 is a diagram showing a configuration example of a receiving side device that receives a data frame sent through a second communication line in the present invention. In the figure, a data frame input from a second data communication line via a terminal 101 is input to a frame recognition circuit 102. Frame recognition circuit 10
2, we wllIll one frame by finding the start and end delimiters of each frame. The frame output from the frame recognition circuit is input to the error detection circuit 103. The error tb detection circuit 103 performs error detection using redundant bits given to the 7 frames. The sequence number of the frame for which the error detection result is determined to be correct is sent to the number comparison circuit 114. The number comparison circuit 114 compares the sequence number to see if it is the same as the number input immediately before, and outputs the result to the error detection circuit 103. Erroneous “&” detection circuit 3
If the number comparing circuit 114 determines that the frames have been assigned the same number, that frame is discarded. This cancels the transmission of multiple frames during retransmission on the second data communication line. The error detection result is sent to the return circuit 104, and in the return circuit, the status confirmation frame is sent to the transmission path in the opposite direction of the first data communication line via the terminal 110, and is sent to the data frame sending side. . The sending station uses this status confirmation frame to perform data retransmission procedures. On the other hand, among the frames for which the erroneous error detection judgment has been made in the erroneous error detection circuit, those determined to be erroneous tb are discarded, and the remaining frames are sent to the number detection circuit 105. In the number detection circuit 105, the number of the data frame added for the second data communication line is read.

The data frame output from the number addition circuit 105 is input to the buffer circuit 106. Buffer circuit 106 stores the data frame at an appropriate location according to instructions from number detection circuit 105. That is, if an error occurs in the second data communication line, the storage location of the frame to be discarded is cleared and stored, and when the frame is received by retransmission, it is stored at the location where it should be stored. .

Frames are output from the buffer circuit 106 in the order in which they are arranged in the buffer, and if a frame vacancy occurs, frame output is interrupted until the frame vacancy is cleared by retransmission. In this way, it is possible to recover from a difference in frame arrival order caused by an error in the second data communication line. The frame output from the buffer circuit 106 is input to the number detection circuit 107 0 number detection circuit 10
At 7, the number of the data frame attached for the first data communication line is read. The read number is compared with the number of the previous frame, if it is the same number.

The frame is discarded. As a result, redundant transmission on the second data communication line can be canceled by retransmission occurring on the first data communication line. The data frame output from the number detection circuit 107 is input to the buffer circuit 108. Buffer circuit 108 stores the data frame at the appropriate location as instructed by numbering circuit 107 . In other words, the storage location of the frame whose arrival order was delayed due to being discarded due to an error that occurred in the first data communication line is cleared and stored, and when the frame is received by retransmission, the storage location of the frame is It is stored where it should be. Output of frames from the buffer circuit 108 is suspended until it is canceled by random retransmission. In this way, differences in the order of arrival of frames caused by errors in the first data communication line can be recovered, and the frames are output at terminal 109 in the same order as originally sent by the transmitting station.

In this way, it becomes possible to receive frame transmissions in order in data communication using the relay device.

In each of the embodiments, data frames are transmitted in one direction, such as being sent from one transmitting station, passing through a relay device, and being received by one receiving station, but normally transmission in the opposite direction is also performed at the same time. In the return circuits 4 and 104, it is also possible to send out not only the status confirmation frame but also the data frame at the same time, or to superimpose the status confirmation frame on the data frame.

(Effects of the Invention) As described above, according to the present invention, in a system in which a plurality of data communication lines are cascaded, bit errors occurring on the transmission path can be detected and retransmitted. Even with various transmission methods, transmission that can effectively use lines is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a configuration of a receiving device for receiving data frames supplied to a second data communication line connected to the relay device of the present invention. It is a figure which shows an example.

Claims (1)

[Claims] 1. A data frame to which a unique sequence number and redundant bits for detecting errors are added to the original data, and a status confirmation frame for notifying the error status detected by the redundant bits. A data communication relay device that cascades and connects multiple data communication lines that communicate using Frame receiving means detects the presence or absence of occurrence, returns a status confirmation frame to the transmitting station using a transmission path in the opposite direction of the communication line, and outputs data excluding the redundant bits. (b) Storage means for temporarily storing data output from the frame receiving means. (c) Number comparison means that reads the sequence number added to the data frame received from the first data communication line and compares it with the sequence number read previously to determine the number of times data with the sequence number is transmitted. (d) A frame that takes the data stored in the storage means as input, adds a new sequence number and new redundant bits to create a new data frame, and outputs the number of times specified by the number comparison means. (e) switching either the newly created data frame or the data frame held for retransmission according to instructions from the status confirmation frame received from the second data communication line; 1. A data communication relay device comprising frame sending means for outputting a frame to a second data communication line.