JP2526602B2 - Data transmission method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a data transmission method when data is transferred using an HDLC loop mode.

(Prior Art) FIG. 9 is a diagram showing a basic configuration of a standard data transmission system using a conventional HDLC loop system. In the figure,
Reference numeral 54 is a data line, and the data transmission direction is indicated by an arrow.

Each of the primary station 51 and the secondary stations 52, 53 is connected to the transmission terminal and the reception terminal of a station different from each other to form a so-called tandem connection. Data is transmitted according to the HDLC protocol.

FIG. 10 is a diagram showing the structure of a data frame transmitted by the primary station 51.

The start flag 61 is composed of 8 bit data of 01111110.

The transmitted data portion 62 is usually a receive address indicating the number of the receiving station, a control field for controlling the data transfer procedure, and other actual transmitted data.
-Divided into fields.

The CRC code section 63 is for identifying an error in the transmission data section 62.

When "1" is 5 bits in succession in the transmission data part 62 and CRC code part 63 at the time of transmission, "0" is inserted, and when receiving "1" 5 bits in succession, the next " It is configured to insert and remove 0 bits except "0".

The GO-AHEAD flag 64 is composed of 0111111111 8-bit data.

The secondary stations 52 and 53 transmit the data one bit behind while monitoring the received data.

If the bit "1" is consecutive 6 bits, the beginning and end of the data frame can be detected.

Furthermore, if 7 bits are consecutive in 1 bit, GO-AHE
It is regarded as an AD flag, and the last one bit is changed to "0", that is, the data frame start flag or the end flag is exchanged for transmission, and the local station data frame is transmitted.

When the secondary stations 52 and 53 finish transmitting their own data, they transmit a GO-AHEAD flag in which at the end of the data frame, a bit "0" is followed by a bit "1" of 7 bits or more.

As a result, when the data is returned to the receiving terminal of the primary station 51 in one round, the data frames of the respective devices are arranged in the order of 51, 52, 53 separated by flags.

In the above-mentioned data transmission system, only one primary station can be provided in the data transmission system, and the data transmission system cannot be secured when a failure occurs in the primary station.

Therefore, a method of providing a plurality of primary stations in the data transmission system depending on the line state of the data transmission system has been considered.

This system is a means to monitor the line status to each data transmission device, a means to send a GO-AHEAD flag to start transmission in loop mode, a primary station mode to send a GO-AHEAD flag and loop transmission. Means for switching the secondary station mode and means for transmitting a line disconnection identification flag in the transmission data frame, and switching the primary station mode and the secondary station mode based on the transmission identification flag. The data transmission system is secured even when the condition is deteriorated or the line is disconnected.

(Problems to be Solved by the Invention) In the former one of the above-mentioned conventional methods, since only one primary station exists in one loop system, timing of data transmission or data frame The primary station is performing an operation of monitoring the flow of.

Therefore, GO-A from the primary station due to line deterioration or line disconnection
When the HEAD flag and the data frame cannot normally make a round in the loop, there is a drawback that the secondary station cannot start the transmission and the data exchange between the secondary stations becomes impossible.

Further, when the latter data transmission method is used, the data arriving at the data transmission device in the primary station mode in the disconnection portion of the loop-shaped line is re-routed by the primary station data transmission device. If you do not send in the reverse direction, data transfer to the destination data transmission device may not be completed,
Due to this procedure, there is a dead time in the data transfer, and the processing of the primary station regarding the data transfer is complicated.

An object of the present invention is to provide a data transmission system which can solve the above-mentioned drawbacks of the former and the latter.

(Means for Solving Problems) In order to achieve the above object, the present invention provides a data transmission device having a data communication function in an HDLC loop mode with two LOOP-like lines that transmit data in opposite directions. In the data transmission method in which data is transmitted and received between data transmission devices connected to each other, a monitoring means for monitoring the line status and a GO-AHEAD flag for starting transmission in loop mode are transmitted to each data transmission device. GO-AHEAD flag transmitting means, switching means for switching between the primary station mode for transmitting the GO-AHEAD flag and the secondary station mode for loop transmission, and the identification flag transmission for transmitting the line disconnection identification flag in the transmission data frame. Means, storage means for storing the identification flag received from each data transmission device on the line, and control means for controlling data transfer, respectively. When transferring data from the other data transmission device is configured to switch the direction in which to search the identification flag received from the data transmission apparatus on the line, and transmits to the two loop lines.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In the case of the conventional example shown in FIG. 9, only the primary station 1 always activates the data transmission.

Also, when transferring data from a secondary station to another station, it is necessary for the primary station to control the delivery of data via the primary station.

If the GO-AHEAD flag is not passed because the primary station 51 fails or the line 54 is deteriorated or disconnected, the data transmission is possible even if the secondary station is functioning normally. I can't do it.

FIG. 11 shows an example of using a data transmission system for switching between the primary station mode and the secondary station mode in order to supplement this secondary point.

The example of FIG. 11 comprises data transmission devices 21, 22, 23, 24, an outer data line 25 and an inner data line 26.

Here, the names of the data lines that go outside and inside are given for convenience in order to distinguish the data transfer direction.

In this data transmission method, as described above, the primary station and the secondary station are loop-connected by two data lines, an outer ring and an inner ring, which have different data transfer directions.

Each primary station and secondary station has a function of monitoring the data line and switching between the primary station mode and the secondary station mode when the line is deteriorated or a line disconnection state is detected.

Here, for convenience of explanation, the data transmission device 21 is set to the primary station mode, the GO-AHEAD flag is transmitted to the outer and inner loops, and the secondary stations 22, 23 and 24 receive and transmit the data in the loop mode. I shall.

Conventionally, in such a data transmission system, for example, when a command is transferred from the data transmission device 24 which is in the secondary station mode to the data transmission device 22, when the data is transmitted to the outer loop line 25, the primary station mode is set. Data transmission equipment
It was necessary to confirm the transfer destination of the data received by 21 and perform control to pass the data to the transfer destination data transmission device.

FIG. 1 is a block diagram showing an embodiment of a data transmission device used in the method of the present invention.

The data transmission device 1 of this figure is an HDLC loop data communication means.
4,5, idle frame storage means 6, line monitoring means 7, and data transfer control means 8, switching between the primary station mode and the secondary station mode depending on the line status, and activation of transfer of the line status identification flag. , The line identification flag received from each data transmission device of the data transmission system is searched to switch the data transfer direction. 2 is an outer data line, and 3 is an inner data line.

Next, the operation of the data transmission method according to the present invention will be described.

In FIG. 1, each data transmission device sends a LOOP BREAK flag (LBF), which indicates the receiving state of the line for the device number of each device and the inward and outward bidirectional signals, to all stations on a loop. To send.

Data transmission to all stations is possible by making the receive address a global address.

This data frame is called an idle frame. The structure of this data frame is shown in FIG.

On such a data line, for example, from the secondary station 22 to the secondary station
When sending a command to 24, the secondary station 22 sends a data frame for the command following the sending of its own idle frame or before sending the idle frame, and then sends the GO-AHEAD flag. To do.

The secondary station 23 does not receive the data frame when the receive address is not its own address or the global address, and the received data is transmitted as it is, so the secondary station 22
The command frame transmitted by the device passes through the secondary station 23 and reaches the secondary station 24.

FIG. 3 shows the structure of the data frame transmitted by the secondary station 22.

Next, the operation of each device when the data line is disconnected will be described with reference to FIG.

Here, in addition to the data transmission system of FIG. 1, it is assumed that a line disconnection has occurred at position 27. At this time, the secondary station 22
Then, the line break is detected in the inner data line and in the secondary station 23 in the outer data line.

The secondary station detecting the line disconnection switches to the primary station mode in the same direction. That is, the secondary station 22 becomes the primary station for the inner route and the secondary station 23 for the outer route, and starts transmitting the idle frame of its own device and the GO-AHEAD flag.

Further, the idle station is set with a primary station flag LBF indicating that a line break has occurred in each direction.

The primary station 21 receives each idle frame and receives each LBF.
Switch to the secondary station mode in the same direction as.

Therefore, the GO-AHEAD flag is exchanged between the secondary stations 22 and 23, and this flag can be used as a trigger for starting transmission to transfer data between the devices on the data line.

FIG. 5 shows the data transmission system when a failure occurs in the primary station.

In this case, the secondary station 22 and the secondary station 24 detect a fault in the data transmission system as an outer loop line and an inner loop line, respectively, and the primary station mode is set.

In this case, the secondary station 22 sends an idle frame and the secondary station 24 sends an idle frame and a GO-AHEAD flag inward, thereby enabling data exchange between the secondary stations between the two-way devices.

However, in the data transmission method described above, for example, when data is transferred from the data transmission device 23 to the data transmission device 22, if the data is placed on the outer loop line, the data is lost in the data transmission device 21 and is transferred to the data transmission device 22. Does not arrive, and what is considered there is a method of retransmitting the data received by the data transmission device 24, which is the primary station, inward in the opposite direction.

However, in this method, since data is once collected in the data transmission device 24 and data is retransmitted at the timing when the data transmission device 24 starts data transfer to the loop line 26, a time delay occurs, and There is a drawback that the processing of the primary station 24 is also complicated.

In the data transmission system according to the present invention, it is determined which direction of the loop line should be transmitted to each secondary station based on the idle frame received from both directions of the loop line and the primary station flag LBF. A data link on the line is established by having a function of switching the direction of data transfer.

FIG. 6 shows a data string which the data transmission device 24 receives from both directions of the loop line in the normal data transmission system of FIG.

In this case, it is assumed that the loop-shaped line is in the primary station mode in which 22 is the inner ring and 23 is the outer ring because the data transmission devices 22 and 23 are connected last and the loop is closed.

FIG. 6 (a) is a data string received from the outer data line, and FIG. 6 (b) is a data string received from the inner data line.
In the primary station mode, each data transmission device adds a flag LBF indicating the primary station mode to the data line and sends it to all data transmission devices on the line.

Here, for example, from the data transmission device 24 to the data transmission device
Consider forwarding a command frame to 22.

First, the I data string of the outer data string (a) is searched for whether it can be transmitted to the inner data line. Since the data transmission device 22 does not appear in the data stream I, it can be considered that the command frame cannot be transmitted through the inner data line.

Next, the O data string of the inner data string (b) is searched for whether it can be transmitted to the outer data line. Since it can be confirmed that the data transmission device 22 exists in the data string O, the data transmission device 24 can transfer the command frame to the outer data line.

FIG. 7 shows a data string received by the data transmission device 24 from both directions of the loop line in the data transmission system in the fault state shown in FIG.

In the figure, (a) is the data string received from the external circuit, (b)
Is a data string received from the inner loop line.

In this case, 22 is the inner station and 23 is the outer station, which is the primary station mode.

FIG. 7A shows a data string received from the outer data line, and FIG. 7B shows a data string received from the inner data line.

Here, for example, from the data transmission device 24 to the data transmission device
Consider forwarding a command frame to 22.

First, the I data string of the outer data string (a) is searched for whether it can be transmitted to the inner data line. Since the data transmission device 22 does not appear in the data stream I, it can be considered that the command frame cannot be transmitted through the inner data line.

Next, the O data string of the inner data string (b) is searched for whether it can be transmitted to the outer data line. Since it can be confirmed that the data transmission device 22 exists in the data string O, the data transmission device 24 can transfer the command frame to the outer data line.

FIG. 8 shows a data string which the data transmission device 24 receives from both directions of the loop line in the data transmission system in the fault occurrence state of FIG.

In the figure, (a) is the data string received from the external circuit, (b)
Is a data string received from the inner loop line.

In this case, 22 is the inner station and 23 is the outer station, which is the primary station mode.

FIG. 8A shows a data string received from the outer data line, and FIG. 8B shows a data string received from the inner data line.

Here, for example, from the data transmission device 24 to the data transmission device
Consider forwarding a command frame to 22.

First, the I data string of the outer data string (a) is searched for whether it can be transmitted to the inner data line. Since the data transmission device 22 is included in the data string I, the command frame can be transferred through the inner data line.

(Effects of the Invention) As described above, according to the present invention, when a failure occurs in a line, the data transmission device that has detected the failure becomes the primary station and activates the data transmission timing and is in the primary station mode. To each data transmission device on the line, and when transmitting the command frame, each data transmission device searches for the data string received from each of the outer and inner routes and confirms in which direction it should be transmitted. Therefore, it is possible to establish a data link between the secondary station data transmission devices without fixing a specific primary station.

[Brief description of drawings]

FIG. 1 is a block diagram of a data transmission system showing an embodiment of a data transmission system according to the present invention. 2 is a diagram showing the structure of an idle frame, FIG. 3 is a diagram showing a data transmission system in which a data transmission line has a failure, and FIG. 4 is a diagram showing a data transmission system in which a data transmission device has a failure. FIG. 5 is a diagram showing the structure of a data sequence of an idle frame received by the data transmission device 4 in FIG.
FIG. 6 is a diagram showing the structure of a data sequence of an idle frame received by the data transmission device 4 in FIG. 3, and FIG. 7 is a structure of a data sequence of an idle frame received by the data transmission device 4 in FIG. FIG. FIG. 8 is a diagram showing a configuration of a data string received by the data transmission device from both directions of the loop line in the data transmission system in the fault occurrence state of FIG. FIG. 9 is a diagram showing the configuration of a conventional loop type data transmission system. FIG. 10 is a diagram showing the structure of a telegram sent by each data transmission device to the loop line. FIG. 11 is a diagram showing an example of the configuration of a data transmission device for switching between the primary station mode and the secondary station mode. 1 ... Data transmission device 2 ... Outer data line 3 ... Inner data line 4,5 ... HDLC loop data communication means 6 ... Idle frame storage means 7 ... Line monitoring means 8 ... Data transfer control means 11 , 61 …… Start flag 12,62 …… Sending data section 13,63 …… CRC code 14,64 …… GO-AHEAD flag 15 …… Receive address (global address) 21,22,23,24… … Data transmission equipment 25 …… Outer data line 26 …… Inner data line 27 …… Line break point 31,35,39 …… Start / end flag 32,40 …… Receive address (global address) 33,41 …… Idle frame data 34,38,42 …… CRC code 36 …… Command transfer destination address 37 …… Command data 51 …… Primary station 52,53 …… Secondary station 54 …… Data line

Claims (1)

(57) [Claims] 1. A data transmission system in which a data transmission device having a data communication function in an HDLC loop mode is connected by two loop lines that transmit data in opposite directions, and data is transmitted and received between the data transmission devices. In, in each of the data transmission device, the line monitoring means for monitoring the line status, the GO-AHEAD flag transmitting means for transmitting the GO-AHEAD flag for starting the transmission in the loop mode, and the GO-AHEAD flag are transmitted. Switching means for switching between the primary station mode and the secondary station mode for loop transmission, and an identification flag transmitting means for transmitting a line disconnection identification flag in a transmission data frame,
When transferring the data from each data transmission device to another data transmission device, a storage means for storing the identification flag received from each data transmission device on the line and a data transfer control means for controlling the data transfer are provided. A data transmission system characterized in that the identification flag received from each data transmission device on the line is searched and the transmission direction is switched to two loop lines.