JPH0621952A - Data transmission system for loop-shaped transmission line - Google Patents

Abstract

PURPOSE:To secure reliability, to reduce hardware scale and to shorten transmission delay time by connecting first and second loop-shaped transmission lines through monitor nodes and sending required frames from nodes. CONSTITUTION:A first loop-shaped LAN 10 composed of plural nodes 14-16 and a monitor node 12 and a second loop-shaped LAN 11 similar to the first LAN are connected through the node 12 and a monitor node 13 of the LAN 11. Then, frame data formed with a communication data area and a control data area to write the data of the transmission source and the transmission destination are sent from the node 14 or the like and these data run around the LAN 10 and 11. Therefore, no useless traffic is generated, transmission delay can be reduced, the communication of the remaining loop can be guaranteed even when one loop generates any fault, reliability can be secured, the scale of the hardware can be reduced, and transmission delay time can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transmits / receives data between nodes in a loop type transmission line such as a LAN (local area network) in which nodes are connected in a loop, by a fixed length frame circulating on the transmission line. The data transmission method to be performed.

[0002]

2. Description of the Related Art FIG. 12 is a block diagram showing a general structure of a loop LAN. As shown in this figure, the loop-type LAN usually includes a node 41, a node 42, and a node 4.
3 and a monitoring node 40 for monitoring the states of the plurality of nodes 41, 42, 43 are connected by a transmission line 44.

FIG. 13 shows an example of a conventional configuration for connecting a plurality of loop LANs. As shown in this figure, in a conventional LAN-to-LAN connection, a loop type LA is used.
Two LANs 50 and 5 of N50 and loop type LAN 51
In order to connect 1 between nodes, another loop type LAN 52 is used as a backbone LAN, and LAN 50
And the LAN 51.

[0004]

However, in such a conventional LAN-to-LAN connection, the LAN-to-LAN connection is also performed when the loop type LAN 52 used as a backbone is incapable of transmitting and receiving data. There was a problem that it would be impossible. In addition, loop type LAN50
Since another LAN 52 is interposed between the loop type LAN 51 and the loop type LAN 51, there are problems that the reliability of data is lowered, the hardware scale is increased, and the transmission time is delayed.

The present invention has been made in view of such circumstances, and by connecting two loop type transmission lines between monitoring nodes, the reliability of the two loop type transmission lines to be connected can be ensured. It is intended to provide a data transmission system in a loop type transmission line which enables reduction of hardware scale and transmission delay time.

[0006]

According to the present invention, a first and a second loop type transmission line composed of a plurality of nodes and a monitoring node for monitoring the states of these nodes are connected to each other by a monitoring node, and a communication data area is provided. And a control data area in which the data of the transmission source and the destination of the communication data are written are transmitted from the node, and the frame is circulated in the first and second loop type transmission lines, thereby And a data transmission / reception between the nodes of the second loop type transmission line.

In the above transmission method, the loop type transmission line to be transmitted is determined by setting the transmission loop number in the control data area of the frame, and the monitoring node detects the set transmission loop number. When selecting a loop type transmission line to transmit and performing broadcast communication, the frame that has circulated around the first loop type transmission line to which the node that sent the frame belongs is discarded at the node that sent the frame, It is preferable that the frame that has circulated around the second loop type transmission line is discarded at the monitoring node of the second loop type transmission line.

[0008]

According to the present invention, since the monitoring nodes are connected to the first and second loop type transmission lines, useless traffic does not occur, and the transmission delay can be reduced. Even if a failure occurs in the loop, the communication of the remaining loop can be guaranteed.

Further, in the above transmission method, by setting a transmission loop number in the control data area of the frame, the frame is transferred from the first loop type transmission line to the second loop type transmission line or the second loop type transmission line. From the type transmission line to the first loop type transmission line, it becomes possible to freely transmit,
When performing simultaneous broadcast communication, the first node to which the own node belongs
The frame that has circulated around the loop type transmission line is discarded at its own node, and the frame that has circulated around the second loop type transmission line is discarded at the monitoring node of the second loop type transmission line. Broadcast communication can be performed simultaneously on the two loop type transmission lines.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

FIG. 1 is a block diagram showing the configuration of a loop type LAN as an example of a loop type transmission line used in the data transmission system of the present invention. In the figure, 10 and 11 are loop-type LANs, 14, 15, 16, 17, 18, and 19 are nodes that realize interfaces with various terminals, and 12, 13
Is a monitoring node that monitors the state of the node.

As shown in this figure, the loop type LAN to which the present invention is applied is a loop type LAN 10 including a monitoring node 12, a node 14, a node 15 and a node 16.
And a loop type LAN 11 including a monitoring node 13, a node 17, a node 18, and a node 19, and these two LANs are connected by the monitoring node 12 and the monitoring node 13.

According to the data transmission method of the present invention, by connecting monitoring nodes of two loop type LANs to each other, data can be freely transmitted and received between the nodes in the two loop type LANs. .

That is, a frame is used for data transmission / reception, and the loop number of the transmission destination is set in the header part of the frame to transmit the data to an appropriate loop. Also, during broadcast communication (broadcast communication), by adding a bit indicating the loop number (SR) of the transmission source to the header part of the frame, the broadcast data is transmitted to the own loop (loop to which the own node belongs). If so, the node discards the frame, and if broadcast data is transmitted to another loop (a loop to which the node does not belong), the monitoring node in the other loop discards the frame.

When a failure occurs in one loop, the other loop stops transmission / reception of data with the one loop and guarantees communication in the other loop. Further, when two loop type transmission lines are connected, there are two monitoring nodes. Therefore, by setting the operation monitoring node frame, the two monitoring nodes are divided into an operation monitoring node and a backup monitoring node. It is like this.

FIG. 2 is a block diagram showing the configuration of the monitoring nodes 12 and 13. As shown in this figure, data arranged in a predetermined frame format is sent from the previous node (previous node). The frame sent from the previous node is received by the REP (repeater) 20 through the transmission path.

4 and 5 are explanatory views showing the arrangement of the frames. As shown in FIG. 4A, the arrangement of frames is made up of an 8-byte frame header, a 64-byte data area, and a 2-byte CRC check area. Of these, the first byte (indicated by # 0 in the figure) of the frame header is an 8-bit destination address DA7 to DA0 as shown in FIG. 4B, and indicates the address of the destination node of the data. ing. The second byte (indicated by # 1 in the figure) of the frame header is an 8-bit source address SA7 to SA0, as shown in (c) of FIG.
It shows the address of the source node of the data. As shown in (d) of FIG. 4, the third byte (indicated by # 2 in the figure) of the frame header includes the usage status bit USD, the destination loop number DR1 and DR0, and the source loop as the lower 5 bits. The numbers SR1 and SR0 are set, and the remaining upper 3 bits are unused.

When the use status bit USD is "0", the frame is not used, and when it is "1", the frame is being used. If the destination loop number DR1 or DR0 is '00', setting is prohibited, if it is '01', it is sent only to Loop 0, if it is '10', it is sent only to Loop 1, '11'. If it is', it indicates the case of transmitting to both loops 0 and 1. Source loop number SR
1, SR0 is prohibited if set to '00' and '11',
If it is '01', it is '10' when transmitting from loop 0
If so, the case of transmitting from loop 1 is shown.

The 2 bytes of the CRC check area indicate the value of the remainder of the result obtained by calculating all the bits of the frame header and the data area with the generator polynomial (see FIG. 5).

The repeater 20 shown in FIG. 2 supplies a signal indicating the start position of the received frame to the timing generation section 21, and makes the received frame parallel in units of 8 bits to generate a U signal.
SD detector 22, destination node number detector (DR detector) 23, source node number detector (SR detector) 2
4 and the selector 1 section 26.

FIG. 6 is a circuit block diagram showing the details of FIG. 2, and includes a timing generation section 21, a USD detection section 22, and a DR.
Detector 23, SR detector 24, and selector controller 25
The circuit of FIG.

In FIG. 6, the timing signal generator 80 is shown in FIG.
It is the timing generation unit 21 shown by. The timing signal generator 80 uses the received frame timing signal to
For latching the third byte data (see FIG. 4D) of the frame header shown in FIG. 4, which is a timing signal, and the CRC byte data (see FIG. 5). CR which is a timing signal
The CTIM signal is generated, the USTIM signal is supplied to the US latch unit 81, the DR latch unit 82, and the SR latch unit 83, and the CRCTIM signal is supplied to the CRC latch unit 86.

The US latch unit 81 corresponds to the USD detection unit 22 of FIG. 2 and latches the usage status bit USD set in the third byte of the frame header by the latch timing signal USTIM. The DR latch unit 82 is
It corresponds to the DR detection unit 23 in FIG. 2, and the destination loop numbers DR1 and DR0 are set by the latch timing signal USTIM.
Latch. The SR latch unit 83 corresponds to the SR detection unit 24 in FIG. 2 and latches the transmission source loop numbers SR1 and SR0 by the latch timing signal USTIM.
The CRC latch unit 86 receives the latch timing signal CRCT.
The IM latches the 2-byte CRC check bit set in the CRC check area of the received frame.

Comparators 84 and 85 and A at the subsequent stage
The ND-OR circuit 88 corresponds to the selector control unit 25 in FIG. The comparator 84 compares the destination loop number from the DR latch unit 82 with its own node loop number,
If they match, "1" is output to the match signal, and if they do not match, "1" is output to the mismatch signal. Comparator 85
Compares the source loop number from the SR latch unit 83 with its own node loop number, and outputs "1" to the match signal when they match and "1" to the mismatch signal when they do not match.
Is output. The CRC check circuit 87 outputs "1" to the alarm detection signal when an alarm is detected and "0" to the alarm detection signal when no alarm is detected as a result of the check by the generator polynomial.

In accordance with the above latch output, comparator output, and CRC output, the next AND-OR circuit 88 generates signals for frame other loop transmission instruction, frame repeat instruction, frame discard instruction, and CRC alarm detection.

As for the frame other loop transmission instruction signal, a mismatch signal is output from the comparator 84, and the comparator 85
The match signal is output at, and the US latch unit 81 outputs USD =
It is generated when '1' is output. So this is
This is a signal generated when a frame is transmitted from a node of the own loop to a node of another loop.

The frame repeat instruction signal is generated when the comparator 84 outputs the coincidence signal, the comparator 85 outputs the coincidence signal, and the US latch section 81 outputs USD = '1'. That is, this is a signal generated when a frame is transmitted to another node in the own loop.

The frame discard instruction signal is sent to the comparator 8
4, the match signal is output, the comparator 85 outputs the non-match signal, and the US latch unit 81 outputs USD = '1'. That is, this is a signal generated when a broadcast frame from another loop to the own loop goes around the own loop and is then discarded. When this signal is output, the USD detector 2a in FIG.
Then, "0" is written in the USD bit of the corresponding frame.

The CRC alarm detection signal is generated when USD = '1' is output from the US latch section 81 and the alarm detection signal = '1' is output from the CRC check circuit 87.

Based on the above analysis result, the selector 1 section 26 and the selector 2 section 27 are switched by an instruction from the selector control section 25 in FIG.

On the other hand, on the transmission side in FIG. 2, the DR detection unit 28 detects the destination loop number set in the third byte of the frame header of the frame received from the one-side LAN, and the selector control unit It sends that information to 2b. Further, the SR detection unit 29 detects the transmission source loop number set in the third byte of the frame header and sends the information to the selector control unit 2b. Then, the USD detection unit 2a detects the usage status bit set in the third byte of the frame header and sends the information to the selector control unit 2b. Upon receiving these latch outputs, the selector control unit 2b generates a signal for receiving its own node and a signal for not receiving its own node, and switches the selector 3 unit 2c.

FIG. 3 is a block diagram showing the configuration of the loop type LAN nodes 14, 15, 16, 17, 18, 19 shown in FIG. As shown in this figure, data arranged in a predetermined frame format is sent from the previous node. The frame sent from the previous node is received by the REP (repeater) 30 through the transmission path.

The repeater 30 shown in FIG. 3 supplies a signal indicating the start position of the received frame to the timing generation unit 31, and makes the received frame parallel in units of 8 bits to generate a U signal.
SD detection unit 32, destination address detection unit (DA detection unit) 3
3, source address detector (SA detector) 34, destination loop number detector (DR detector) 35, source loop number detector (SR detector) 36, and selector 1 unit 3
Supply to 8.

FIG. 7 is a circuit block diagram showing the details of FIG. 3, and includes a timing generation section 31, a USD detection section 32, and a DA.
The circuits of the detection unit 33, the SA detection unit 34, the DR detection unit 35, the SR detection unit 36, and the selector control unit 37 are shown.

In FIG. 7, the timing signal generator 90 is shown in FIG.
It is the timing generation unit 31 shown by. The timing signal generator 90 uses the received frame timing signal to
The DATIM signal, which is a timing signal for latching the first byte data (see FIG. 4B) of the frame header shown in FIG. 4, and the second byte data (see FIG. 4).
The signal of SATIM which is a timing signal for latching (see (c)) and the data of the third byte (FIG. 4 (d)).
UST, which is a timing signal for latching
An IM signal and a CRCTIM signal which is a timing signal for latching CRC byte data (see FIG. 5) are generated. Then, the DATIM signal is supplied to the DA latch unit 91, the SATIM signal is supplied to the SA latch unit 93, the USTIM signal is supplied to the US latch unit 95, the DR latch unit 96, and the SR latch unit 97, and the CRCTIM is supplied.
The signal is supplied to the CRC latch unit 9a.

The DA latch unit 91 is the DA detection unit 3 of FIG.
3 and the latch timing signal DATIM
Latch the destination address set in the first byte of the frame header. The SA latch unit 93 corresponds to the SA detection unit 34 in FIG. 3, and latches the transmission source address set in the second byte of the frame header by the latch timing signal SATIM. The US latch section 95 is shown in FIG.
Corresponding to the USD detection unit 32 of the latch timing signal U
The STIM latches the usage status bit set in the third byte of the frame header. DR latch unit 9
6 corresponds to the DR detection unit 35 in FIG. 3, and latches the destination loop number by the latch timing signal USTIM. The SR latch unit 97 corresponds to the SR detection unit 36 in FIG. 3, and latches the transmission source loop number by the latch timing signal USTIM. The CRC latch unit 9a latches the CRC check bit set in the CRC check area of the received frame by the latch timing signal CRCTIM.

The comparators 92, 94, 98, 99 and the AND-OR circuit 9c at the subsequent stage correspond to the selector control section 37 in FIG. The comparator 92 compares the destination address from the DA latch unit 91 with its own node address, and outputs “1” to the match signal when they match and outputs “1” to the mismatch signal when they do not match. The comparator 94 compares the source address from the SA latch unit 93 with its own node address, and outputs “1” to the match signal when they match and outputs “1” to the mismatch signal when they do not match. The comparator 98 compares the destination loop number from the DR latch unit 96 with its own node loop number, and outputs "1" to the match signal when they match and outputs "1" to the mismatch signal when they do not match. To do. The comparator 99 compares the transmission source loop number from the SR latch unit 97 with its own node loop number, and outputs “1” to the match signal when they match, and outputs “1” to the mismatch signal when they do not match. To do. The CRC check circuit 9b outputs "1" to the alarm detection signal when an alarm is detected and "0" to the alarm detection signal when an alarm is not detected as a result of the check by the generator polynomial.

According to the above latch output, comparator output, and CRC output, the next AND-OR circuit 9c generates signals for frame reception instruction, frame repeat instruction, frame discard instruction, and CRC alarm detection.

The frame reception instruction signal is sent to the comparator 9
A match signal is output at 2, a mismatch signal is output at the comparator 94, a match signal is output at the comparator 98, and USD = '1' is output at the US latch unit 95. That is, this is a signal generated when a frame addressed to the own node is received.

Regarding the frame repeat instruction signal, the comparator 92 outputs a mismatch signal, the comparator 94 outputs a mismatch signal, and the US latch unit 95 outputs USD =
It is generated when '1' is output. So this is
This is a signal generated when a frame addressed to another node is received.

The frame discard instruction signal is sent to the comparator 9
When the mismatch signal is output at 2, the match signal is output at the comparator 94, the match signal is output at the comparator 98, the match signal is output at the comparator 99, and the USD = '1' is output at the US latch unit 95. Is generated. In other words, this is a signal that is generated when the frame sent by the local node is circulating on the transmission path, and when the broadcast frame for the local loop sent by the local node is discarded after cycling around the local loop. Is a signal generated by. If this signal is output,
'0' is written in the USD bit of the corresponding frame by the inside USD operation unit 3e.

The CRC alarm detection signal is generated when the US latch unit 95 outputs USD = '1' and the CRC check circuit 9b outputs the alarm detection signal = '1'.

Based on the above analysis result, the selector 1 section 38 and the selector 2 section 39 are switched by an instruction from the selector control section 37 in FIG.

On the other hand, on the transmitting side in FIG. 3, the DA operating unit 3a writes the destination node address into the destination address of the first byte of the frame header of the frame to be transmitted. The SA operation unit 3b writes the own node address in the source address of the second byte of the frame header of the frame to be transmitted. The DR operation unit 3c writes the loop number of the partner node into the destination loop number of the third byte of the frame header of the frame to be transmitted. S
The R operation unit 3d writes the loop number of its own node in the source loop number of the third byte of the frame header of the frame to be transmitted. The USD operation unit 3e writes "1" in the usage status bit of the third byte of the frame header of the frame to be transmitted when transmitting a valid frame and "0" when discarding the frame.

As described above, the monitoring nodes 12 and 13
And the nodes 14, 15, 16, 17, 18, and 19 control the frame.

Next, the operation of each bit of the frame header in each case of P-P (point-to-point) communication and broadcast communication will be described. 8 and 9
[Fig. 6] is an operation explanatory diagram when data is transmitted by PP communication. In this example, monitoring node 102, node 10
4, a loop type LAN 100 (node number is 0), and a monitoring node 103, a node 107, a node 108, and a node 1.
Loop type LAN 101 consisting of 09 (the loop number is 1
2) and a loop node LAN
2 and the monitoring node 103 are connected. In this case, the operation of transmitting a frame from the node 105 to the node 108 in another loop will be described.

As shown in FIG. 8, first, in the node 105, at the time of frame transmission, the destination address '108' is written in DA7 to DA0 of the first byte of the frame header and transmitted to SA7 to SA0 of the second byte. Write the original address '105' and write '1' in the 3rd byte USD.
Is written, and “10” corresponding to the destination loop number 1 is written to the third bytes DR1 and DR0, and “01” corresponding to the source loop number 0 is written to the third bytes SR1 and SR0. After that, the data is written in the data area, the CRC check bit is added, and the frame is transmitted.

This transmitted frame is sent to the node 10
4, monitoring node 102, monitoring node 103, node 10
After passing 9, the packet is received by the node 108. Node 108
Then, as shown in FIG. 9, after receiving this frame,
The frame is discarded by writing "0" in the third byte USD of the frame header when sending out again to the transmission path. By the above operation, P-P communication between different loops is realized.

FIG. 10 and FIG. 11 are diagrams for explaining the operation when transmitting a broadcast frame. In this case, the operation when the frame is transmitted from the node 105 to all the nodes of the own loop and all the nodes of the other loop will be described.

As shown in FIG. 10, first, the node 105
Then, when transmitting a frame, write “FF” indicating all destination addresses in the first byte DA7 to DA0 of the frame header, write the source address “105” in the second byte SA7 to SA0, and write the third byte Write "1" to the USD of the eye and write "11" to the destination loop numbers 0 and 1 of both loops in the third bytes DR1 and DR0.
And write '01' corresponding to the source loop number 0 in SR1 and SR0 of the third byte. afterwards,
The data is written in the data area, the CRC check bit is added, and the frame is transmitted.

This transmitted frame is sent to the node 104.
Then, the copy / reception is performed and the data is sent to the monitoring node 102. In the monitoring node 102, the relevant frame is copied and transmitted to the monitoring node 103.
Send the frame to. The frame received by the monitoring node 103 is copied / received by the nodes 109, 108 and 107. The frame transmitted from the monitoring node 102 to the node 106 is copied and received by the node 106.

After that, in the node 107, as shown in FIG. 11, after copying / receiving this frame, the frame is transmitted again to the monitoring node 103. Upon receiving this frame, the monitoring node 103 recognizes this as a broadcast frame, and when sending this frame to the transmission path again, writes "0" in the third byte USD of the frame header to discard the frame. To do.
Further, the frame copied and received by the node 106 is transmitted again to the transmission source node 105, and the node 10
In 5, the packet is recognized as a broadcast frame, and when this frame is transmitted to the transmission path again, by writing "0" in the third byte USD of the frame header,
Discard the frame. The above-described operation realizes broadcast communication between different loops.

During the transmission of such a frame, when a communication error occurs in a transmission line or node of one loop, the node that has detected the communication error is in an abnormal state with respect to the monitoring node in the loop to which the node belongs. Notification of. At this time, the monitoring node shuts off the interface with the other loop. As a result, even if a failure occurs in one loop, the other loop is not affected and normal communication can be guaranteed.

In the case of the above configuration, since there are two monitoring nodes on the transmission line, one of the monitoring nodes is the operation monitoring node and the other is the standby monitoring node, and the monitoring on the transmission line is performed. Limit the number of nodes to one. That is, '010' is placed in the unused byte position of the upper 3 bits shown in the third byte # 2 of the frame header of FIG.
By writing, the special frame called the operation monitoring node frame that exists only on the transmission line is set,
The monitoring node holding this frame is the operation monitoring node. In this case, when a failure occurs in the operation monitoring node, the operation monitoring node frame is released and the spare monitoring node becomes the operation monitoring node.

[0055]

As described above, according to the present invention,
Since the two loop type transmission lines are connected between the monitoring nodes, the loop type transmission line for connection is unnecessary.
Therefore, the data transmission / reception time can be shortened,
Since the scale of hardware is small, it is possible to construct a loop type transmission line at low cost. In addition, since the connection of two loop type transmission lines, which is conventionally performed by the node, is made by the monitoring node, the node can be effectively utilized. Further, even if a failure occurs in the first loop type transmission line, it does not affect the second loop type transmission line, and it greatly contributes to the improvement of system reliability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a loop LAN used in a data transmission system of the present invention.

FIG. 2 is a block diagram showing a configuration of a monitoring node.

FIG. 3 is a block diagram showing a configuration of a node.

FIG. 4 is an explanatory diagram showing the arrangement of frames.

FIG. 5 is an explanatory diagram showing the arrangement of frames.

FIG. 6 is a circuit block diagram showing details of FIG.

FIG. 7 is a circuit block diagram showing details of FIG.

FIG. 8 is an explanatory diagram of an operation when transmitting data by PP communication.

FIG. 9 is an explanatory diagram of an operation when transmitting data by PP communication.

FIG. 10 is an explanatory diagram of the operation when transmitting a broadcast frame.

FIG. 11 is an explanatory diagram of an operation when transmitting a broadcast frame.

FIG. 12 is a block diagram showing a general configuration of a loop LAN.

FIG. 13 is an explanatory diagram showing a conventional configuration when connecting a plurality of loop LANs.

[Explanation of symbols]

 10,11 Loop type LAN 12,13 Monitoring node 14,15,16,17,18,19 Node 2a, 22,32 USD (usage status bit) detector 2b, 25,37 Selector controller 2c Selector 3 part 3a DA (Destination address) operation unit 3b SA (Source address) operation unit 3c DR (Destination loop number) operation unit 3d SR (Source loop number) operation unit 3e USD (Usage status bit) operation unit 20, 30 Repeater 21, 31 timing generation unit 23, 28, 35 DR (transmission destination loop number) detection unit 24, 29, 36 SR (transmission source loop number) detection unit 26, 38 selector 1 unit 27, 39 selector 2 unit 33 DA (destination address) Detection unit 34 SA (source address) detection unit

Claims (2)

[Claims] 1. A first and a second loop type transmission line composed of a plurality of nodes and a monitoring node for monitoring the states of these nodes are connected between the monitoring nodes, and a communication data area and a transmission source of the communication data are transmitted. A frame composed of the control data area in which the previous data is written is transmitted from the node, and the frame is circulated around the first and second loop type transmission lines, whereby the first and second loop type transmission lines are formed. A data transmission method in a loop type transmission line that consists of transmitting and receiving data between nodes. 2. A loop type transmission line for determining a loop type transmission line to be transmitted by setting a transmission loop number in a control data area of a frame, and transmitting by detecting the set transmission loop number by a monitoring node. When selecting, and performing broadcast communication, the frame that has circulated around the first loop type transmission line to which the node that sent the frame belongs is discarded by the node that sent the frame, and the second loop type transmission is performed. The frame that orbits the road is the second
The data transmission method in a loop type transmission line according to claim 1, wherein the data is discarded at the monitoring node of the loop type transmission line.