JPH08307324A - Method for detecting failure position in communication system and method for reestablishing transmission line - Google Patents

Abstract

PURPOSE: To attain a counter plan for a fault without preparing a stand-by transmission line. CONSTITUTION: Signal transmission is executed among a master station 1 and slave stations 2-1 to 2-n by using a single direction wired circulation transmission line tar executing time-division transmission. When a fault such as disconnection is generated on a certain portion in the transmission line and asynchronization is detected by a CPU 1d in the master station 1, a return command for switching a selector 2e to a B side is applied from the CPU 1d to any one off the slave stations through the transmission line. When the portion related to the fault generation is on the upstream side of the slave station, asynchronization is continuously generated. In this case, the CPU 1d applies a return command to the upstream side slave stations. When the operation 15 successively repeated, synchronization can be established on any position and then normal communication can be recovered among partial slave stations and the master station 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure location detecting method and a transmission path reestablishing method in a communication system using a wired cyclic transmission path.

[0002]

2. Description of the Related Art In a small area such as a factory, a time division multiplex communication system by one-way communication control is used as shown in FIG. In this system, the signal transmitted from the transmission circuit 1a of the master station 1 first circulates among the slave stations in the order of the slave stations 2-1, 2-2, 2-3, ... 2-n. The signals reaching the last slave station 2-n are in the reverse order, that is, the slave stations 2-n, ... 2-3, 2-2, 2
It goes around each slave station in the order of -1, and returns to the receiving circuit 1b of the master station 1. In the course of this transmission, each slave station 2-1, 2-2, 2-
The receiving circuits 2a of 3, ... 2-n take out the signal addressed to the own station from the signals transmitted from the master station 1, and the transmission circuit 2b transmits the signal addressed to the master station 1 through the OR gate 2c. Send to the road.

In the system having such a configuration, when a failure occurs in any of the slave stations 2-1, 2-2, 2-3, ... 2-n and a wired cyclic transmission line connecting them,
On the transmission path, the signal is no longer transmitted from the fault occurrence part. Therefore, when using such a system,
As a measure against communication failure, the master station 1 and the slave stations 2-1 and 2-
A plurality of transmission lines connecting 2, 2-3, ... 2-n are provided in parallel. Normally, one of a plurality of transmission lines is used, and when a failure occurs in the working transmission line, the backup transmission line (one of them) is used. It is possible to appropriately deal with the occurrence of a failure.

[0004]

However, if a failure is to be dealt with by such a method, an additional transmission line is required in addition to the current transmission line, which results in an increase in the number of cables and an increase in equipment costs. I will end up. In addition, if not only the working transmission path but also the protection transmission path is affected by the failure, or if any of the slave stations is abnormal, for example, the communication failure state cannot be avoided even by the above method. .

The present invention has been made to solve the above problems, and relates to a communication system for executing communication between a master station and a plurality of slave stations using a wired cyclic transmission line. By providing a means for switching the transmission path configuration, it is possible to continue the communication for at least some of the slave stations and to identify the location where the abnormality has occurred.

[0006]

In order to achieve such an object, according to the present invention, a signal transmitted from a master station is a first slave station, a second slave station, ... An nth slave station ( n: natural number, n ≧
2) and then the nth slave station, the n-1th slave station, ...
In a communication system in which a wired cyclic transmission path is provided so as to return to the master station in the order of the first slave station, the signal transmitted is transmitted through the wired cyclic transmission path despite the elapse of a predetermined time after transmission. When a failure condition in which the master station does not loop back is detected, the master station determines that the master station is the i-th slave station (i: natural number, 1 ≦ i ≦ n−
1) the first step for instructing loopback transmission via the wired cyclic transmission path, and the i-th slave station receiving the loopback transmission command from the master station via the wired cyclic transmission path From the i + 1th slave station, the second step of changing the connection relationship between the wired cyclic transmission line, the ith slave station, and the i + 1th and i + 1th slave stations. .

Further, the present invention gradually changes the value of i to a smaller value when the fault condition continues even though the i-th slave station is instructed to perform the return transmission via the wired cyclic transmission path. While having the third step of repeating the first and second steps described above until the fault condition is resolved.

[0008]

In the present invention, when a failure condition is detected, the master station sends a loopback transmission command to the i-th slave station via the wired cyclic transmission path. When the above-mentioned failure is caused on the downstream side of the i-th slave station (i + 1th, i + 2, ... Nth slave station or the transmission path around these slave stations), this command is issued. i child station. The i-th slave station that has received the loopback transmission command is the first + 1 + 1 until then.
The wired cyclic transmission line that was also connected to the slave station side of
Switching from the first slave station to the i-th slave station through the i-th slave station. That is, the slave stations farther than the (i + 1) th slave station are disconnected from the connection to the master station-side wired cyclic transmission path. As a result, a normal communication state, that is, a state in which the signal transmitted from the master station loops back to the master station via the wired cyclic transmission path is formed again.

On the contrary, when the above-mentioned fault condition is caused by the i-th slave station or the upstream thereof, the i-th slave station:
I cannot receive the return transmission command sent from the master station. Therefore, in this case, since the connection of the wired cyclic transmission line is not changed, the normal communication state is not always formed.

As described above, according to the present invention, since the master station transmits the loopback transmission command to the i-th slave station via the wired cyclic transmission path when the failure state is detected,
Depending on whether or not the normal communication state is formed again, the master station can detect whether the failure is upstream or downstream of the i-th slave station, and the failure is downstream by the i-th slave station. If there is, communication can be restarted partially.

Further, according to the present invention, if the failure state continues even though the loopback transmission command is transmitted from the master station to the i-th slave station via the wired cyclic transmission path, i
The above-described operation is repeated while the value of is changed to a smaller value by one. By gradually changing the value of i in this way, the destination slave station of the loopback transmission command changes to a further upstream slave station, that is, a slave station closer to the master station on the wired cyclic transmission path. Therefore, when the slave station, which is the destination of the loopback transmission command, reaches the upstream side of the part that is the cause of the fault condition, the fault condition described above is resolved and normal communication is possible. Therefore, in the present invention, the fault condition that has occurred in the system is temporarily eliminated,
It is possible to reestablish a state in which normal communication is possible at least between the slave station and the master station on the upstream side of the portion that has caused the failure state. At that time, it is not necessary to provide a spare transmission line in addition to the working transmission line, and the facility cost does not increase.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. The same or corresponding components as those of the conventional example shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows the configuration of a communication system according to an embodiment of the present invention. In this example,
The master station 1 is provided with a CPU 1d and a counter 1e, and each slave station 2-1, 2-2, 2-3, ... 2-n has a C.
The PU 2d and the selector 2e are provided. CPU1
In the d, each 8-bit signal is time-divisionally supplied to the transmission circuit 1a and sent out on the transmission path. Further, the CPU 1d inputs each 8-bit signal received by the receiving circuit 1b. The counter 1e is used for detecting synchronization establishment which will be described later.

Further, each slave station 2-1, 2-2, 2-3, ...
The 2-n CPU 2d inputs each 8-bit signal received by the receiving circuit 2a via the transmission path, and outputs each 8-bit signal to be transmitted to the transmitting circuit 2b and the OR gate 2c.
Via the transmission line. The CPU 2d is the receiving circuit 2
The corresponding selector 2e is controlled according to the content of the control channel among the signals transmitted via a. The selector 2e is normally controlled to supply the A input to the Y output, and is controlled to output the B input to the Y output when receiving a loopback command described later. In principle, the A input of each selector 2e is a signal input from the station on the right side in the figure, and the B input is a signal input from the station on the left side in the figure. Regarding the slave station 2-n at the right end in the figure, since the signal from the station on the left is supplied to both the A input and the B input, even if the A input is selected by the selector 2e,
You can choose the input, but in this example,
Always set to the B input side.

FIG. 2 and FIG. 3 show the fault detection and the transmission line in the operation of the master station 1 and the slave stations 2-1, 2-2, 2-3, ... 2-n in this embodiment. A flow of operations relating to re-establishment is shown.

First, as shown in FIG. 3, each slave station 2-
1, 2-2, 2-3, ... 2-n, selector 2
e is initially controlled to the A input side (200). As a result, the connection state of the transmission line in the communication system shown in FIG. 1 becomes the same as that of the conventional example shown in FIG.

In this state, the CPU 1d of the master station 1 has 8
The bit signal is time-divisionally supplied to the transmission circuit 1a and sent out on the transmission path (100). The signal transmitted on the transmission line has a frame format as shown in FIG. 4, for example. In this frame format, the first 8 bits of a frame of 125 μs in total are used as a synchronization channel and the subsequent 8 bits are used as a control channel, and the remaining part of the frame is used for each slave station 2-1, 2-2 ,.
Used as 8 bits for each of the call channels related to the call between 2-3, ... 2-n and the master station 1.

Each slave station 2-1, 2-2, 2-3, ... 2-n
The CPU 2d extracts the control channel and the communication channel addressed to itself from the receiving circuit 2a while securing the synchronization with the master station 1 by the synchronization channel among the signals transmitted on the transmission path by the master station 1 (202). Unless the extracted control channel content is a loopback transmission command (20
6), the CPU 2d executes a normal transmission operation as needed while maintaining the selector 2e on the A input side (20).
4). That is, signals of the control channel and the speech channel of 8 bits are supplied to the corresponding transmission circuit 2b, and the control channel and the speech channel are inserted into the frame on the transmission path.

If the receiving circuit 1b receives a frame having a synchronization channel having the same content as the synchronization channel of the transmitted frame within a predetermined time after transmitting the frame from the transmission circuit 1a, the master station 1 can communicate. It is assumed that the operation is performed normally, that is, the synchronization is maintained. vice versa,
When the frame having the synchronization channel having the same content as the synchronization channel of the transmitted frame cannot be received within the predetermined time from the transmission, the CPU 1d considers that the synchronization is lost (102). That is, it is considered that a failure has occurred in any part of the system shown in FIG. 1 and a slave station downstream from the part cannot receive the signal from the master station 1.

When the loss of synchronization is detected in this way, the CPU 1d of the master station 1 sets the destination i to n-1 (104), and then starts counting by the internal counter 1e (106). The CPU 1d of the master station 1 sets a loopback command for the i-th slave station 2-i in the control channel of the frame to be transmitted, and transmits this frame to the transmission circuit 1a.
To send it out on the transmission path. At this point, the destination i
Since n-1 is set to, the n-1th slave station 2- (n-1) is qualified to receive the loopback command.
Only.

If the fault is located downstream of the slave station 2- (n-1), the slave station 2- (n-1) can receive a loopback command by its receiving circuit 2a via a transmission path. . In that case (206), the CPU 2d switches the corresponding selector 2e to the B input side (208). As a result, the part causing the failure, that is, the nth
The second slave station 2-n and the transmission path around it are in a state of being separated from the transmission path from the master station 1 to the slave station 2- (n-1). That is, the transmission path is connected to the (n-1) th slave station by-(n
Since it is returned at -1), the loss of synchronization due to an abnormality of the n-th slave station 2-n or a cable breakage related to this slave station is canceled. On the contrary, if there is a fault at the slave station 2- (n-1) or its upstream, this slave station 2- (n-1)
Cannot receive a loopback command, it remains out of sync as usual.

The CPU 1d of the master station 1 has an internal counter 1e.
After starting the counting by (1), the transmission of the frame in which the loopback command is set in the control channel is transmitted (108), and the counting of the predetermined time by the internal counter 1e is completed (
10) or repeat until a synchronization establishment is detected (112). In the case of this embodiment, the CPU 1d detects, for example, a frame having a synchronization channel having the same content as the synchronization channel of the transmitted frame by the receiving circuit 1b (10
8) and if this detection is successful for at least 11 consecutive transmissions (112), it is determined that synchronization has been established. When the synchronization is established, the slave stations from the first slave station 2-1 to the i-th slave station 2-i and the master station 1
Normal communication is executed between and.

If synchronization is not yet established at the time when the counting by the internal counter 1e is completed, the CPU
1d subtracts 1 from the destination i (114), and repeats the operations from step 106 onward. As a result, the slave station which is the destination of the loopback command sequentially changes to the slave station on the left side in FIG. If the synchronization is still not established even when i becomes 0 (116), it is considered that the communication state cannot be restored, and the operation of the system is ended (118).

As described above, according to the present embodiment, since the failure countermeasure can be realized without providing the backup transmission line, the equipment load for the failure countermeasure can be reduced as compared with the conventional case. Further, even if a failure occurs in any part of the system, the transmission path is normally reestablished upstream from this part, that is, between the slave station and the master station 1 on the left side in FIG. Communication can be resumed.

The internal counter 1 for detecting synchronization establishment
The count value of e may be set to a time sufficiently longer than the time required to establish synchronization. For example, in FIG. 4, when the communication speed in the transmission path is 2.048 Mbps, the synchronization channel length is 8 bits = 3.9 μs, and the number of times of synchronization detection for determining that “synchronization is established” is 11, The minimum time required to detect establishment is 1 frame length × (number of synchronization detections−1) + synchronization channel length + transmission delay = 1253.
9 μs + transmission delay, so if the synchronization channel could not be detected several times or transmission delay = delay in device × number of devices +
Even if the number of cables is taken into consideration, it is sufficient that the counter value of the internal counter 1e is about 3 ms.

Although specific numerical values have been shown in the above description, the present invention is not limited to these numerical values.

[0027]

As described above, according to the present invention,
When the failure state is detected, the master station commands the i-th slave station to perform loopback transmission via the wired cyclic transmission path, and receives the loopback transmission command from the master station via the wired cyclic transmission path to the i-th slave station. Since the slave station switches the wired cyclic transmission path accordingly, whether the signal transmitted from the master station returns to the slave station through the wired cyclic transmission path after switching the wired cyclic transmission path. With this, it is possible to detect a failure point in the communication system using the wired cyclic transmission path, that is, a point that causes the failure state, and restart communication partially.

Further, according to the present invention, i is gradually changed to a small value when the fault condition continues even though the i-th slave station is instructed to perform the return transmission via the wired cyclic transmission line. Moreover, since the above-described operation is repeated until the failure state is resolved, it is possible to deal with the failure without providing a backup transmission path and thus without increasing the facility cost. Further, at this time, a normal communication state can be continuously maintained between a large number of slave stations and a master station, although it is a part.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a communication system according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of operation of a master station in this embodiment.

FIG. 3 is a flowchart showing a flow of operation of each slave station in this embodiment.

FIG. 4 is a diagram showing an example of a frame format in this embodiment.

FIG. 5 is a block diagram showing a configuration of a communication system according to a conventional example.

[Explanation of symbols]

1 master station, 1a transmitting circuit, 1b receiving circuit, 1d C
PU, 1e counter, 2-1, 2-2, 2-3, ... 2
-N slave station, 2a receiving circuit, 2b transmitting circuit, 2c
OR gate, 2d CPU, 2e selector.

Claims (2)

[Claims] 1. The signal transmitted from the master station is the first slave station,
2nd slave station ... Circular order of nth slave station (n: natural number, n ≧ 2), then nth slave station, n-1th slave station, ... 1st slave station In a communication system in which a wired cyclic transmission path is installed so that the transmitted signal returns to the master station, a failure condition is detected in which the transmitted signal does not return via the wired cyclic transmission path even if a predetermined time has elapsed after transmission. In this case, the parent station determines that the i-th child station (i: natural number, 1
≦ i ≦ n−1), the first step of instructing loopback transmission via the wired cyclic transmission line, and the i-th slave station receiving the loopback transmission command from the parent station via the wired cyclic transmission line And a second step of changing the connection relationship between the wired cyclic transmission line and the i-th slave station and the (i + 1) th slave station so that the i + 1th slave station and beyond can be separated from the wired cyclic transmission line. Characteristic failure location detection method. 2. When the failure state continues even though the loopback transmission is instructed to the i-th slave station through the wired cyclic transmission line, the failure state is changed while gradually changing the value of i to a small value. The method for reestablishing a transmission path, comprising a third step of repeating the first and second steps according to claim 1, until