JPH11205366A - Data transfer system for ring network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a state mismatching of each station on the occurrence of a fault in a transmission frame in the case of data exchange between a master station collecting/distributing data by circulating a transmission frame twice around the ring network and a slave station conducting data transmission/ reception to/from the master station. SOLUTION: In this system, a ring network is established by interconnecting a master station and plural slave stations via a transmission line. Each station is provided with a detection means that detects an error of a transmission frame. When a fault is detected by the fault detection means, a relay operation of the transmission frame is interrupted, and an abort frame consisting of a frame start code and a frame end code is generated by an abort frame generating means 14, and sent to downstream stations so as to allow all the stations on the ring network to recognize the occurrence of the fault. Thus, all the stations are forced to shift to a unified state to prevent mismatching of the state shift of each station.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring network constructed by a master station and a plurality of slave stations. A transmission frame is caused to make two rounds in the ring network. In a data transfer system in a ring network having a protocol for completing a data exchange process by performing a process in a different form, a state transition of each station is appropriately performed when an abnormality occurs in any of the stations. .

[0002]

2. Description of the Related Art As a data transfer system in a ring network of this kind, for example, as shown in FIG. 5, a master station M for collecting / distributing data and transmitting / receiving own station data to / from this master station M are shown. A plurality of, for example, four slave stations A to D are connected in a ring via a transmission line T to form a ring network, and one transmission frame is made to make two rounds in this ring network, and each station is made to make a first round and a second round. There has been proposed a data transfer system having a protocol for completing a data exchange process by performing a different state and operation in a week.

[0003] In one example, the relay station transmits data while adding its own data to the first data collection frame transmitted by the master station M, and further removes the data added by itself from the second data collection frame. Thus, data exchange is performed while improving transmission efficiency.

That is, as shown in FIG.
Transmits, to the slave stations A to D, a transmission frame F including a control code for collecting data, status, and the like of each of the slave stations A to D in order to collect / exchange data.

[0005] First, the master station M transmits to the slave stations A to D a data collection frame CF to which a frame identification code indicating a data collection frame is added in the first cycle. Each of the slave stations A to D is in a reception waiting mode. When receiving the data collection frame CF, the slave stations A to D analyze the frame identification code part and recognize that the received frame is a data collection frame, and then enter the additional transmission mode. Transition is made, the own station data is added to the end of the data section arranged next to the header in the data collection frame CF and transmitted to the succeeding station. When the transmission is completed, the own station data is removed / relayed. The state transits to the transmission mode and waits for reception of the second frame.

With all slave stations A to D sequentially adding their own data, the data collection frame CF returns to the master station M which first transmitted the frame by making a round of the ring network.

The master station M that has generated and transmitted the frame
Similarly to the slave station, the data and status of the own station are added to the frame, and the frame is relayed to the slave stations A to D as a second frame SF.

Each of the slave stations A to D receiving the second frame SF sequentially removes the data added by the own station, and finally adds the own station to the master station which first transmitted the frame. Only data comes back.

[0009] In such a system in which the transmission frame is looped twice, the stations connected to the ring network can exchange data with each other regardless of the connection order and position, and alternately add and delete. As a result, transmission efficiency can be increased as compared with the token pass method.

In a ring network, it is general to change the state before all the received frames are received and start a relay transmission operation in consideration of transmission efficiency and transmission data buffer resources of each station. is there. Therefore, a frame is defined together with a destination station address and the like, and a frame identification code, which is important information used as control information such as reception availability and state transition, is usually arranged at the head of the frame.

At the time of receiving a frame, each station temporarily stores a header portion including a frame control code in a buffer, analyzes it, performs operations such as a next relay / transmission state and a frame removal from a reception state, and performs relay transmission. To start. The shorter the time from reception to the start of relay transmission, the less the delay time consumed at each station, and the higher the transmission efficiency.

In such a data transfer system in a ring network, a case is considered in which the master station transmits a data collection frame and each slave station performs additional transmission of its own station data. The slave stations A and B, which have successfully added data to the first frame, subsequently transition from the second data collection frame to a state in which the data added by the own station is removed.

However, as shown in FIG. 7, when an abnormality occurs in the data collection frame CF between the slave station B and the slave station C, the slave station C temporarily changes the identification code in the header part of the frame. After recognizing and transiting to the own station data addition transmission mode, an abnormality can be detected and the mode can return to the normal mode. However, the received abnormal frame is relayed and transmitted to the downstream station as it is. Similarly, the slave stations D and E similarly detect an abnormality and return to the normal mode. At this point, the slave stations A and B on the system are in their own station data deletion mode, and the slave stations C and D are in the normal mode. Would.

Similarly, the master station M also receives the first frame and relays it as the second frame. However, if this abnormal frame is relayed as the second frame, the slave stations A and B cannot transmit their own data. Is the second frame to be deleted, but the slave stations C and D are the first frames to which the own station data should be added. Therefore, there is a problem in the protocol that completes one sequence by making two rounds of the frame. Will happen.

In order to prevent this, conventionally, as shown in FIG. 8, the master station M receives all the frames of the first cycle so that the data collection frame of the first cycle containing the abnormality is not relayed as the frame of the second cycle. It responded by sending the second lap after it was over. Also, it monitors whether or not the data collection frame sent by the master station M returns normally. If not, it considers that some abnormality has occurred.
In order to perform recovery processing such as resetting of the state transition of each slave station, a measure has been taken by transmitting a reset command frame RF as shown in FIG.

[0016]

However, the data transfer system in the above-mentioned conventional ring network has a protocol for completing the data exchange process by making one transmission frame go around twice. Due to the nature of the protocol, it is inevitable that inconsistencies occur in the operation sequences of the slave stations as shown in FIG. Therefore, it is necessary to perform recovery (recovery) such as a sequence abnormality or a failure in data exchange due to the sequence error.

In the conventional example, when an abnormality occurs, processing for notifying the abnormality and maintaining and managing the network system including transition to the normal state is entrusted to the master station M. Needed resources and waiting time. However, when the number of connected stations and the number of data are large, the maximum frame length becomes long. The master station M must prepare a buffer of a size larger than the maximum frame length,
There are problems in terms of cost, system expandability, and the like.

Further, since it is necessary to wait for the transmission of the second round until the completion of the reception of the first round, the transmission band is wasted, and the reduction in transmission efficiency due to the dead time increases in proportion to the frame length. Therefore, one protocol 2 for efficiently exchanging data by making one transmission frame go around twice.
The advantage of the frame-structured data transfer method cannot be enjoyed.

As described above, in the conventional example, if the master station of the frame transmission source attempts to recover the ununiform state of the state transition generated in the slave station, the processing of the master station becomes complicated. In addition, there is an unsolved problem that a long time elapses from the occurrence of the abnormality to the recovery, the transmission efficiency is greatly reduced, and the real-time control is impaired.

The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and performs active recovery processing when each station connected to the ring network detects an abnormality. By doing so, a data transfer system in a ring network capable of improving the transmission efficiency by simplifying the structure, processing and buffer resources of the master station and eliminating wasteful transmission bandwidth due to waiting time and the like can be provided. It is intended to provide.

[0021]

In order to achieve the above object, a data transfer system in a ring network according to the present invention comprises: a master station for collecting / distributing data; A plurality of slave stations that exchange data are connected to a ring network, and one transmission frame is made to make two rounds in the ring network, and each station performs different types of processing in the first round and the second round so that data is transmitted. In a data transfer system of a ring network configured to complete an exchange process, the station includes an abnormality detecting unit for detecting an abnormality in a processing system of the transmission frame and an abnormality in a reception frame for each station, and detects an abnormality in a transmission frame in a first round. If any abnormality is detected during processing, the relay transmission operation is suspended, and an abort frame is spontaneously generated and transmitted. It is characterized in that.

Further, in the data transfer system in the ring network according to the second aspect, in the invention according to the first aspect, when each of the stations receives the abort frame while waiting for the second round of the transmission frame, In addition to the transition from the cycle waiting state to the normal state, the transmission control state of another downstream station is also changed from the second cycle waiting state to the normal state by reproducing and transmitting an abort frame.

Furthermore, in the data transfer system in the ring network according to the third aspect, in the invention according to the first or second aspect, the respective stations autonomously maintain uniformity of transmission control state transition of the entire ring network. It is characterized by being constituted so that.

According to a fourth aspect of the present invention, there is provided the data transfer system in the ring network according to any one of the first to third aspects, wherein the abort frame is modulated and demodulated without requiring frame analysis, buffer storage, and the like. It is characterized in that only a part is composed of a frame start and end code that can be recognized and generated.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. Also in the present embodiment, similarly to FIG. 5 described above, the master station M and the four slave stations A to D
Are connected in a ring via a transmission line T, and a ring network LN is constructed.

Each station is configured as shown in FIG. That is, the frame transmitted from the upstream station is demodulated by the demodulation circuit 11, and the frame is analyzed. First, the start delimiter unit SD arranged at the head of the received frame is detected, and the frame start detection signal is transmitted. 12 and outputs all the frame data to the header storage delay buffer 13, detects the end delimiter section ED arranged at the end of the received frame, and outputs a frame end detection signal to the transmission / reception control circuit 12. , Further detects an abnormality in the received frame, and transmits an abnormality detection signal to the transmission / reception control circuit 12, the abort frame generation circuit 1
4 and a transmission data selection circuit 15 described later.

The header storage delay buffer 13 sends the header section HD and the data section DT to the transmission / reception control circuit 12 via the serial / parallel conversion circuit 16. The transmission / reception control circuit 12 monitors whether the received frame is the first round or the second round. When the received frame is the first round, the header is added so that the additional data of the own station is added to the end of the data part DT of the received frame. The output of the storage delay buffer 13 is controlled, and the frame data synthesizing circuit 17 to be described later is controlled. In the second round, the header storage delay is added so that the own station additional data added to the data part DT is deleted. In addition to controlling the buffer 13, it controls the transmission frame data synthesizing circuit 17 and further reads the self-addressed data in the data section DT to read the data in the upper data link layer /
Notify the application layer 18.

In the data link layer / application layer, a predetermined arithmetic process performed by the own station is executed. The predetermined process is performed based on the received data, and transmission data such as a processing result is generated. The data is stored in the own-station additional data buffer 19 as the own-station additional data, and the own-station additional data stored in the own-station additional data buffer 19 is converted into serial data by the parallel / serial conversion circuit 20 and then transmitted. Output to the synthesis circuit 17.

In this transmission frame data synthesizing circuit 17, in the own station data addition mode, after selecting from the beginning of the frame data output from the header storage delay buffer 13 to the end of the data part DT, the parallel / serial conversion circuit By selecting the own-station additional data output from 20, the own-station additional data is added to the end of the data section DT, and the end delimiter section ED output from the header storage delay buffer 13 is added last. Thus, a transmission frame F is formed and sent to the frame data selection circuit 15.

In the frame data selection circuit 15, when the abnormality detection signal is not supplied from the demodulation circuit 11, the transmission frame F input from the data frame synthesizing circuit 17 is selected and output to the modulation circuit 21 to be transmitted to the subsequent station. When the abnormality detection signal is supplied, the abort frame AF generated by the abort frame generation circuit 14 is selected, output to the modulation circuit 21, and transmitted to the subsequent station.

Here, in the abort frame generation circuit 14, when the abnormality detection signal is input from the demodulation circuit 11, only the start delimiter SD which is the frame start code and the end delimiter ED which is the end code shown in FIG. The generated abort frame AF is generated and output to the frame data selection circuit 15.

Next, the operation of the above embodiment will be described with reference to a time chart shown in FIG. That is, first, when the master station M is powered on and started up,
In addition to grasping the configuration and number of each of the slave stations A to D connected to the network, grasping the connection position of these stations, that is, the order in which the slave stations are connected from the master station M to the downstream side. And each of the slave stations A to D
And the connection information such as the allocation of the write information and the read information of each station, and determines the format of the fixed-length transmission frame based on the collected information, and sends the data to each of the slave stations A to D according to the determined format. On the other hand, when the transmission frame F is received, the data access position for the received frame is notified as data access information.

Thereafter, as shown in FIG. 2A, the master station M creates a data collection frame CF which includes only the start delimiter section SD, header section HD and end delimiter section ED and does not include the data section DT. Is transmitted to the slave station A, which is the succeeding station.

When the slave station A receives the data collection frame CF from the master station M, it demodulates it in the demodulation circuit 11 and stores it in the header storage delay buffer 13, and also analyzes the start delimiter S by frame analysis.
When D is detected, a frame start signal is output to the transmission / reception control circuit 12.

For this reason, the transmission / reception control circuit 12 determines that the data transmission frame of the first cycle has been received, maintains the own station data addition mode which is the normal mode, The HD data is read through the serial / parallel conversion circuit 16 to determine whether there is data addressed to itself. However, since there is no data addressed to itself, the frame data synthesizing circuit 17 is connected to the header storage delay buffer 13 side. At the same time, the start delimiter SD and the header HD are sequentially output from the delay buffer 13, and a predetermined byte position, that is, the header H
When the end of D has been read, the frame data synthesizing circuit 17 is switched to the parallel / serial conversion circuit 20 and the parallel / serial conversion circuit 20 outputs preset fixed-length own-station additional data dA from the parallel / serial conversion circuit 20. Let
When the end of the own station additional data dA is output, the frame data synthesizing circuit 17 is switched again to the header storage delay buffer 13 to output the end delimiter section ED, and the data collection frame CF to which the own station additional data is added is output. The data is sequentially output to the modulation circuit 21 via the frame data selection circuit 15 to form a start delimiter SD and a header HD for the received data collection frame CF as shown in FIG. A data collection frame CF is transmitted to the subsequent slave station B after a station delay time of one minute.

In the slave station B, the slave station A
2C, the data dA added by the slave station A in the data section DT as shown in FIG.
Next, the own station additional data dB is added to form a data collection frame CF, which is transmitted to the subsequent slave station C,
Hereinafter, in the slave stations C and D, FIG.
As shown in the figure, the data portion DT of the data collection frame CF
, Add own station additional data dC and dD, and return the data collection frame CF to the master station M.

When the master station M receives the data collection frame CF that has completed one cycle, the master station M reads the own station additional data dA to dD from the slave stations A to D stored in the data part DT, and reads the data. A data collection frame CF is formed by adding the own-station additional data dM representing the processing result and the like, and the station delay is substantially equal to that of the other slave stations A to D without waiting until all the data collection frames CF are received. The time is transmitted to the slave station A.

When the slave station A receives the data collection frame CF, it determines that it is the second round, and enters the additional data erasing mode, where the transmission / reception control circuit 12 stores the data stored in the header storage delay buffer 13. A data collection frame CF in which the additional data dA added by the own station is deleted is formed from the collection frame CF, and the data collection frame CF is sent to the modulation circuit 21 via the frame data synthesis circuit 17 and the frame data selection circuit 15 as it is. The additional data d transmitted to the slave station B and added by the master station M
M is read, and this is notified to the data link layer / application layer 18.

Similarly, the slave stations B to D sequentially delete the own station additional data dB to dD, and the master station M
2B. Therefore, as shown in FIG. 2E, the data collection frame CF in which only the additional data dM of the master station M is stored in the data section DT from the slave station D. Return to M.

Thus, in the normal state, the data collection frame CF is transmitted between the master station M and the slave stations A to D.
, The data exchange can be performed. However, as shown in FIG.
When an abnormality occurs in the data collection frame CF between the data collection frame CF and the slave station C, the slave station C that has received the abnormal data collection frame CF performs frame analysis in the demodulation circuit 11 to detect the abnormality in the data collection frame CF. Is detected.

At this time, as shown in FIG. 3D, if the abnormality of the data collection frame CF is the additional data dB added by the slave station B, an abnormality detection signal is transmitted and received when this abnormality is detected. The data is output to the control circuit 12, the abort frame generation circuit 14, and the frame data selection circuit 15.

Therefore, the transmission / reception control circuit 12 is in its own station data addition mode in the normal mode until the abnormality detection signal from the demodulation circuit 11 is input.
The frame data stored in the header storage delay buffer 13 is sequentially relayed and transmitted to the subsequent slave station D.

Then, the demodulation circuit 1 is transmitted to the transmission / reception control circuit 12.
When the abnormality detection signal is input from the header storage delay buffer 13 at the position where the fixed length corresponding to the additional data dB in which the abnormality has occurred ends, that is, at the position where the own station starts writing the additional data dD. While interrupting the relay operation,
Maintain the mode in the normal mode.

On the other hand, in the frame data selection circuit 15,
When the abnormality detection signal is input from the demodulation circuit 11, the state is switched to a state in which the abort frame generation circuit 14 is selected at a predetermined timing.
In FIG. 3D, an abnormal detection signal is input from the demodulation circuit 11 so that the abort frame AF including only the start delimiter unit SD and the end delimiter unit ED at a predetermined timing as shown in FIG. The signal is transmitted to the modulation circuit 21 via the selection circuit 15 and transmitted to the slave station D.

Therefore, in the slave station D, as shown in FIG.
As shown in the figure, by receiving the abort frame AF after the data collection frame until the interruption, the data transmission frame and the abort frame AF are relayed as they are without adding the own station additional data dD, and the master station M is received. Return to

In the master station M, as shown in FIG. 3A, since the abort frame AF is added after the received frame, the slave station A relays the data without adding the additional data dM of the own station. , And transits to the normal mode.

In this slave station A, since it is the second round of the data collection frame CF, as shown in FIG.
The data collection frame and the abort frame AF from which the own station additional data dA has been erased are transmitted to the slave station B, and the slave station B also erases the abnormal own own station additional data dB as shown in FIG. Transmits a data collection frame and an abort frame AF including a start delimiter section SD and a header section HD to the slave station C,
Transition to normal mode.

Since the slave station C does not add its own additional data to the previous data collection frame of the first round, the start delimiter section SD does not need to be erased as shown in FIG. The data collection frame and the abort frame AF including the header section HD are transmitted to the slave station D, and the slave station D performs the same processing as shown in FIG.

The master station M returns to the normal state by generating a new data collection frame CF and transmitting it to the slave station A. As described above, in the first embodiment, each station monitors the data collection frame CF to detect an abnormality. When an abnormality is detected, the abort frame AF is generated and transmitted to each station. In addition, it is possible to notify each station of the ring network of the transition from the waiting state to the normal state caused by the abnormality.

Therefore, the waiting time involved in the recovery processing of the master station and the processing for managing the state of the slave station are not required, and each station can autonomously maintain the uniformity of the transmission control state transition of the entire ring. Become.

In the first embodiment, the case where the abort frame AF is composed of only the start delimiter section SD and the end delimiter section ED has been described. However, the present invention is not limited to this. An identification code indicating an abort frame may be added to the end delimiter unit ED.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, as shown in FIG. 4, a function of detecting an abort frame AF is added to the demodulation circuit 11, and when the abnormality of the received frame is detected and the abort frame AF is detected by the frame analysis described above. 1 in the above-described first embodiment except that the abnormality detection signal is output to the transmission / reception control circuit 12, the abort frame generation circuit 14, and the frame data selection circuit 15 when this is done. 1 are given the same reference numerals, and detailed description thereof is omitted.

According to the second embodiment, as described above, the abort frame AF is controlled by the start delimiter unit SD.
And only the end delimiter ED,
The abort frame AF can be detected by performing frame analysis in the demodulation circuit 11.

Therefore, when the demodulation circuit 11 detects the abort frame AF, the abnormality detection signal is transmitted to the transmission / reception control circuit 1
2, the transmission / reception control circuit 12 changes the processing mode to the normal mode as in the case of the above-described abnormality occurrence, the abort frame AF is propagated to each station, and the master station M transmits the abort frame in the second cycle. The AF may be removed to prevent the abort frame AF from going around indefinitely.

As described above, according to the second embodiment, since the demodulation circuit 11 detects the abort frame AF, there is no need to perform a relay operation via the transmission / reception control circuit 12, so the logic and configuration of the transmission / reception circuit In addition, since the abort frame AF is a physically essential element including the frame start and end codes including other frames, a circuit necessary for generating the abort frame is separately prepared. There is no need to do so, and implementation is easy even in a slave station having a low function as a station, and there is no effect on cost or circuit size.

In the first and second embodiments, the case where the master station M adds own station additional data to the data collection frame CF has been described. However, the present invention is not limited to this. The own station additional data may be added to the first round of the frame CF, and data may be read in the first round of the data collection frame CF at each slave station.

In the first and second embodiments, all of the slave stations A to D have their own additional data dA to dA.
The case where dD is added to the data collection frame CF has been described. However, the present invention is not limited to this. A part of the slave stations A to D is an input device only for transmission, and the other is an output device only for reception. In this case, the additional data of the own station may be added to the data collection frame CF only by the input device in the first round of the data collection frame CF, and the additional data may be removed by the input device in the second round. In the apparatus, the data may be read after the additional data is added by the master station.

[0058]

As described above, according to the first aspect of the present invention, when any abnormality is detected in the received transmission frame of the first round, the station that has detected the abnormality relays the transmission frame. The master station not only interrupts and changes its own state and returns to the normal mode, but also instructs the downstream station to change its control state by an abort frame. When the first frame is received, it is not necessary to have a frame buffer to prevent the first transmission frame including the abnormality from being relayed as the second frame, and the first frame is used as the second frame similarly to the slave station. Relay transmission can be performed. As a result, the structure, processing and buffer resources of the master station can be simplified, and useless transmission due to waiting time and the like can be achieved. There is no consumption of range, the effect is obtained that it is possible to improve transmission efficiency.

According to the second aspect of the present invention, each station is provided with a function of relaying an abort frame in the waiting state in the second round, so that a state transition caused by an abnormality detected at any given station is prevented. An effect is obtained that the matching state can be transmitted at high speed to all the downstream stations including the master station starting from the station where the abnormality is detected.

Further, according to the third aspect of the present invention, it is possible to solve the problem caused by the inconsistent states of the stations connected to the ring network, and to recover from the inconsistency of the states. It is not necessary to manage the state transition of each station at the time of occurrence of an error, which was processed by the master station.
The effect is obtained that the processing time, that is, the recovery time from the abnormal state can be reduced.

According to the fourth aspect of the present invention, since the abort frame is composed only of the frame start code and the end code, the route from detection of the abort frame to reproduction and relay transmission bypasses the transmission / reception control circuit. Can be used to simplify the logic and configuration of the circuit, and since the frame start code and end code are physically essential elements including other frames, they are necessary to generate an abort frame. There is no need to separately prepare a simple circuit, and it is easy to implement even a slave station having a low function as a station, and the effect that the cost and the circuit size are not affected is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a specific configuration of each station according to a first embodiment of the present invention.

FIG. 2 is a time chart for explaining a normal operation of the first embodiment;

FIG. 3 is a time chart for explaining the operation of the first embodiment when an abnormality occurs.

FIG. 4 is a block diagram showing a specific configuration of each station according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a ring network.

FIG. 6 is a time chart for explaining the normal operation of the conventional example.

FIG. 7 is an explanatory diagram showing an abnormal state of the related art.

FIG. 8 is a time chart for explaining the operation of the conventional example at the time of abnormality.

[Explanation of symbols]

 M Master station A to D Slave station 11 Demodulation circuit 12 Transmission / reception control circuit 13 Header storage delay buffer 14 Abort frame generation circuit 15 Frame data selection circuit 16 Serial / parallel conversion circuit 17 Frame data synthesis circuit 18 Data link layer / application layer 19 Own Station additional data buffer 20 Parallel / serial conversion circuit 21 Modulation circuit

Claims (4)

[Claims] 1. A master station for collecting / distributing data and a plurality of slave stations for transmitting / receiving data to / from the master station are connected to a ring network, and one transmission frame is connected to the ring network. In a ring-shaped network data transfer system in which each station performs a different form of processing in the first and second rounds to complete the data exchange processing. An error detection unit that detects an error in the system and an error in the received frame is provided. When any error is detected during the processing of the first transmission frame, the relay transmission operation is interrupted and an abort frame is spontaneously generated. A data transfer system in a ring-shaped network, wherein the data is transmitted. 2. When each of the stations receives the abort frame in a waiting state for a second round of a transmission frame,
2. The system according to claim 1, wherein a transition is made from the second round waiting state to the normal state, and the transmission control state of another downstream station is also changed from the second round waiting state to the normal state by reproducing and transmitting an abort frame. Data transfer system in a ring network. 3. The ring network according to claim 1, wherein each station is configured to autonomously maintain uniformity of transmission control state transition of the entire ring network. Data transfer system. 4. An abort frame comprising a frame start and end code that can be recognized and generated only by a modem unit that does not require frame analysis, buffer storage, and the like. A data transfer system in a ring network according to any one of claims 1 to 3.