JP2918009B2 - Clock switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock switching system, and more particularly to a clock switching system in which a plurality of transmission devices are connected in a ring, and all of these transmission devices operate in synchronization with one clock. The present invention relates to a clock switching method for switching a clock when a transmission line fails in a system having a synchronous ring configuration to be performed.

[0002]

2. Description of the Related Art Conventionally, in this type of synchronous ring configuration system, a master device (hereinafter referred to as a master transmission device) and a transmission device (hereinafter referred to as a slave transmission device) which operates in accordance with a clock from the master transmission device. Each transmission device can transmit data in both directions according to the clock. Specifically, the slave transmission device extracts a clock transmitted in one direction from the master transmission device, uses it as the clock of the slave transmission device, and transmits the clock in one direction to the next transmission device. I was Hereinafter, by the same operation, the clock is sequentially transmitted in one direction and finally returned to the master transmission device.

In this configuration, if a failure occurs in the transmission line for transmitting the clock and the clock cannot be received, the transmission device located downstream from the failure occurrence position cannot extract the clock of the transmission line. .

In this case, a failure is detected in a slave transmission device located immediately after the failure occurrence position, and a clock generated in the slave transmission device is transmitted to a transmission line instead of a clock from the master transmission device. ing. As described above, in a system that transmits the clock of the slave transmission device instead of the clock of the master transmission device, network synchronization cannot be achieved.

[0005] On the other hand, when a failure occurs, the slave transmission devices may be sequentially switched so that each slave transmission device extracts a clock transmitted from the master transmission device on a transmission line in a direction opposite to the conventional transmission line. Is being done. In this case, each slave transmission device needs to switch the transmission path from which the clock is extracted. The switching of the transmission line in each transmission device, that is, the switching of the clock, is usually performed manually sequentially from the master side to the transmission device detecting the transmission line failure. Further, even when the failure of the transmission line is recovered, the transmission line, that is, the clock is switched back manually in each transmission device.

[0006]

However, in such a conventional clock switching system, clock switching must be manually controlled when a transmission line fails. For this reason, there is a problem that the switching requires manual labor and the system does not function as a synchronous network synchronized with the clock of the master transmission device until the switching is completed.

[0007] In view of the above drawbacks, the technical problem of the present invention is to provide a synchronous network system having a ring configuration.
An object of the present invention is to provide a method of automatically switching a clock signal when switching a clock extraction direction when a transmission line failure occurs.

[0008]

According to the present invention, a master transmission device and a plurality of slave transmission devices are connected in a ring, and the plurality of slave transmission devices are synchronized with a clock from the master transmission device. In a clock switching method used for a ring-shaped synchronous network capable of transmitting clockwise and counterclockwise directions, one of the slave transmission devices transmits a clock transmitted from a master transmission device in a predetermined direction. When the stop is detected, the one slave transmission device transmits the stop of the clock to the master transmission device in the predetermined direction,
In the master transmission device, a clock switching method is characterized in that a switching request signal instructing to switch a transmission direction in a direction opposite to a predetermined direction is transmitted in a reverse direction to a slave transmission device that has detected a clock stop. can get.

[0009]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1A, FIG. 1B, FIG. 1C, FIG.
Referring to (E) and (F), the clock switching method according to the embodiment of the present invention is based on the master transmission device 10 and the first to fifth slave transmission devices 11, 12, 13, 14, and 15. Is applied to a synchronous network connected in a ring by an outer transmission line 16 and an inner transmission line 17. Here, it is assumed that data is transmitted in the counterclockwise direction on the outer transmission line 16, while data is transmitted in the clockwise direction on the inner transmission line 17.

The master transmission device 10 is provided with a master clock generator 20 for generating a master clock, and the master clock is transmitted from the master transmission device 10 to transmission lines 16 and 17 which are inward and outward. ing. In each of the slave transmission devices 11 to 15, in the normal state, it is assumed that the master clock is extracted from the outer transmission line 16 and an internal clock pulse is generated. As described above, in the normal state, each of the slave transmission devices 11 to 15 operates in accordance with the internal clock pulse synchronized with the master clock, and transmits data clockwise or counterclockwise through the inward or outward transmission lines 16 and 17. It is assumed that data is transmitted clockwise according to the master clock. Therefore, in the normal state, all the transmission devices 10 to 15 operate in synchronization with one counterclockwise master clock as shown in FIG. Although not shown in FIG. 1A, each of the slave transmission devices 11 to 15 includes an internal clock generator that generates an internal clock.

Here, as shown in FIG. 1B, it is assumed that a transmission path failure has occurred at the point X between the fifth slave transmission device 15 and the fourth slave transmission device 14.
In this case, the fourth slave transmission device 14 cannot extract the master clock, and detects the occurrence of the transmission line failure by monitoring the interruption of the master clock. Here, the fourth slave transmission device 14 is referred to as a failure detection source device.

When the occurrence of a failure is detected, the fourth slave transmission device 14 switches to an internal clock generator and sends out a data signal using this internal clock. The data signal includes an overhead, and the fourth slave transmission device 14 transmits a failure occurrence signal FD indicating the occurrence of a transmission line failure to the overhead via the outer transmission line 16 in the third direction in the counterclockwise direction. To the slave transmission device 13. The third to first slave transmission devices 13 to 11 sequentially transmit the fault occurrence signal FD, and the fault occurrence signal FD is finally given to the master transmission device 10.

As shown in FIG. 1C, the master transmission device 10 generates a failure occurrence signal FD indicating the occurrence of a transmission line failure.
Is received, the clock switching request signal SW is transmitted to the first slave transmission device 11 in the clockwise direction using the overhead. The first slave transmission device 11 receives the switching request signal SW and switches the clock extraction source. As a result, the first slave transmission device 11 extracts the clock from the inner transmission line 17.

In the first slave transmission device 11 that has switched the clock extraction source, as shown in FIG.
Switching request signal S toward second slave transmission device 12
W is transferred using overhead, and device 12
The switching request signal SW is received, the clock extraction source is switched, and the switching request signal SW is transmitted to the third slave transmission device 13. As a result, the second slave transmission device 12
Is switched so as to extract the clock from the inner transmission line.

In the third slave transmission device 13, FIG.
As shown in (E), after receiving the switching request signal SW, the clock extraction source is switched, and the switching request signal SW is transmitted to the fourth slave transmission device 14, that is, the failure detection source device.

As shown in FIG. 1F, when the failure detection source device 14 receives the switching request, the clock is switched from the internal clock to the clock extracted from the clockwise transmission line data, and the switching completion indicating the completion of the switching is performed. The signal SC is transmitted counterclockwise to the master transmission device 10 via the third to first slave transmission devices 13 to 11 using the overhead.

FIGS. 2A, 2B, 2C and 2D
The procedure for switching back the clock when the failure at the point X is recovered will be described with reference to FIG. If the failure recovers,
As shown in FIG. 2A, the fourth slave transmission device 14
Returns the clock extraction source to the counterclockwise transmission line data, and sends a return request signal RR to the third slave transmission device 13 using overhead.

Next, as shown in FIG. 2B, after the third slave transmission device 13 also receives the switchback request, the clock extraction direction is switched from the inner transmission line 17 to the outer transmission line 16, A switchback request signal RR is sent to the second slave transmission device 12. Hereinafter, similarly, the second and first slave transmission devices 12 and 11 sequentially switch the clock extraction direction back to the outer transmission line 16 (FIGS. 2C and 2D).

Request RR to switch back to master transmission device 10
Is transmitted, network synchronization is established in a state before the failure occurs in the entire ring-structured synchronous network.

Referring to FIG. 3, the configuration of the slave transmission device performing the above operation will be described. Since the first to fourth slave transmission devices 11 to 14 have the same configuration, in FIG. 3, the slave transmission device is indicated by 1n.
The illustrated slave transmission device 1n (n is a positive integer) is connected to outer and inner transmission lines 16 and 17, and sends data signals in the counterclockwise and clockwise directions via these transmission lines 16 and 17, respectively. can do.

The illustrated slave transmission device 1n has a first
Input disconnection detection circuit 31, first overhead termination section 3
2 and a first overhead insertion unit 33, all of which are connected to the external transmission line 16. The first input disconnection detection circuit 31 detects the interruption of the clock transmitted from the upstream transmission device, and generates an interruption detection signal indicating the interruption detection. On the other hand, the first overhead termination unit 3
2 extracts overhead from the external transmission path 16 and generates an overhead signal. The first overhead insertion unit 33 inserts an overhead into the data signal on the external transmission line 16 and sends the data signal to a downstream transmission device in a counterclockwise direction.

Further, the slave transmission device 1n includes a second input disconnection detection circuit 36 connected to the
, An overhead termination unit 37, a second overhead insertion unit 38, which are respectively a first input disconnection detection circuit 31, a first overhead termination unit 32, and a first overhead termination unit 32.
The same operation as the overhead insertion unit 33 is performed.

The interruption detection signal and the overhead signal are supplied to the first and second input disconnection detection circuits 31, 36, the first and second input disconnection detection circuits.
Are sent to the overhead analysis control unit 40 from the overhead termination units 32 and 37. The overhead analysis control unit 40 analyzes the interruption detection signal and the overhead signal, and generates a control signal as indicated by a broken line.

In FIG. 3, the slave transmission device 1n includes:
An internal clock generator 41, a clock extraction circuit 42, a first selector 46 connected to both the internal clock generator 41 and the clock extraction circuit 42, and a second selector 47 connected to the outer and inner transmission lines 16, 17. And Of these, the first and second selectors 46 and 4
7 is the first and second overhead insertion units 33 and 38
At the same time, it is controlled by the overhead analysis control unit 40.

Referring to FIG. 4, master transmission device 10 receives data signals from outer transmission line 16 and inner transmission line 17 and receives data signals from inner transmission line 17 and outer transmission line 1.
6 to send a data signal. The illustrated master transmission device 10 is connected to a first master overhead terminator 51 connected to the outer transmission line 16, a first master overhead insertion unit 52 connected to the inner transmission line 17, and connected to the inner transmission line 17. A second master overhead terminating unit 53 and a second master overhead inserting unit 54 connected to the external transmission line 16 are provided. The master overhead analysis control unit 55 analyzes the overhead signals detected by the first and second master overhead terminating units 51 and 52, and transmits the master signals to the first and second master overhead inserting units 52 and 54 according to the analysis result. Send a control signal.

The original clock CL from the master clock generator 28 is supplied to a master input disconnection detecting circuit 57 and also to a clock receiving unit 58. The master input disconnection detection circuit 57 monitors the original clock, and generates an input disconnection detection signal when the disconnection of the original clock is detected. On the other hand, the clock receiving unit 58 converts the original clock CL into the intermediate clock C
Generate Lm. The intermediate clock CLm from the clock receiving unit 58 is provided to the selector 62 together with the internal clock CLi from the master clock generating circuit 61. The selector 62 sends the selected clock as a master clock to the outer transmission line 16 and the inner transmission line 17, and sends the selected clock to the inside of the master transmission device 10 as an internal clock.

In this configuration, in a normal state, the intermediate clock CLm from the clock receiving unit 58 is selected by the selector 62 and sent to the outer and inner transmission lines 16 and 17 as a master clock, while the original clock CLm is output.
Is detected, the internal clock CLi is switched to the selector 6
2 and output as a master clock. The illustrated master overhead analysis control unit 55 has a function of controlling the first master overhead insertion unit 51, inserting the switching request signal SW into the overhead, and transmitting the switching request signal SW to the inward transmission path 17. ing.

The operation of the slave and master transmission devices 1n and 10 will be described with reference to FIGS. Slave transmission device 1n shown in FIG.
5A and 5B operate as an intermediate transmission device for transferring the failure detection signal FD and the like. In this relation, in FIG. 5A and FIG. The operations of the detection source device, the intermediate transmission device, and the master transmission device will be described.

In a normal operation state, the failure detection source device monitors the master clock on the external transmission line 16 by the first input disconnection detection circuit 31. In this state, the second
Selector 47 selects the data signal O on the external transmission path 16, and the first selector 46 selects the output N of the clock extraction circuit 42. As a result, the failure detection source device operates by extracting the master clock on the external transmission line 16. When the failure detection source device detects the disconnection of the master clock on the external transmission line 16, the overhead analysis control unit 40 sends a control signal to the first selector 46 and selects the output E of the internal clock generation circuit 41. The first selector 46 is switched so as to perform the operation. For this reason, the output E of the internal clock generation circuit 41 is transmitted as a clock to the downstream side of the external transmission line 16. At this time, the overhead analysis control unit 40 sends a control signal to the first overhead insertion unit 33, and inserts the fault detection signal FD into the overhead.

The failure detection signal FD is transmitted to the external transmission path 16
To the intermediate transmission device, and the intermediate transmission device transfers the failure detection signal FD to the master transmission device 10.

In the master transmission device 10, when the first master overhead termination unit 51 and the master overhead analysis control unit 55 receive and detect the failure detection signal FD sent via the external transmission line 16, the first By controlling the master overhead insertion unit 52, the switching request signal SW is inserted into the overhead. This switching request signal S
W is transmitted to the intermediate transmission device via the inward transmission line 17.

The intermediate transmission device transmits the switching request signal SW to the second
Of the second selector 4 when it is detected by the overhead termination unit 27 and the overhead analysis control unit 40 (FIG. 3).
7 is switched to the inward transmission line 17 side.
To select the signal I. As a result,
The clock extraction circuit 42 extracts a clock from the inward transmission line 17 and sends the extracted clock to the inside as a device clock via the first selector 46.
It is also sent out on the inward transmission path 17. At this time, the second overhead insertion unit 38 controls the overhead analysis control unit 4
Under the control of 0, the switching request signal SW is inserted into the overhead and transferred to the failure detection source device.

In the failure detection source device, when the second overhead terminating unit 37 and the overhead analysis control unit 40 detect a switching request signal SW from the inward transmission line 17, the second selector 47 is switched to the inward transmission line 17. , And the first selector 46 is switched to the output N side of the clock extraction circuit 42. Subsequently, the first overhead insertion unit 31 transmits the switching completion signal SC to the external transmission line 16 under the control of the overhead analysis control unit 40. The switching completion signal SC is sent to the intermediate transmission device via the external transmission line 16, and is transferred from the intermediate transmission device to the master transmission device.

Referring to FIG. 5B, in the failure detection source device, the first input disconnection detection circuit 31 and the overhead analysis control unit 40 detect the reception of the master clock from the master transmission device, thereby detecting the failure. Recovery is detected. Upon detection of the failure recovery, the second selector 47 is switched so as to select the signal O on the external transmission line 16 side. Next, from the first overhead insertion unit 33,
The return request signal RR is sent out on the external transmission line 16 and sent to the intermediate transmission device.

In the intermediate transmission device, the return request signal RR
Is received, the second selector 47 switches the external transmission line 16
After switching to select the signal O on the side, the switchback request signal RR is transferred to the master transmission device 10.

The operations of the above-mentioned fault detecting device and the intermediate transmission device can be represented by the flowchart shown in FIG. 6, while the operations of the master transmission device can be represented by the flowchart shown in FIG. it can. The operation shown in the flowchart is the same as the above-described operation, and the description is omitted here.

[0038]

According to the switching method of the present invention, the switching of the clock in the event of a transmission line failure requires no manual operation, and the synchronization clock can be recovered automatically and at a high speed. There is an effect that it is possible to switch back.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a procedure of clock switching control proposed by the present invention.

FIG. 2 is a diagram for explaining a procedure of switching back when a failure is recovered in the present invention.

FIG. 3 is a block diagram for explaining a slave transmission device used in the switching system of the present invention.

FIG. 4 is a block diagram for explaining a master transmission device used in the switching system of the present invention.

FIG. 5 is a time chart for explaining an operation in the transmission device of FIGS. 3 and 4;

FIG. 6 is a flowchart illustrating an operation procedure of the slave transmission device in FIG. 3;

FIG. 7 is a flowchart illustrating an operation procedure of the master transmission device in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Master transmission apparatus, 11, 12, 13, 14, 15 Slave transmission apparatus 16 Outer transmission path 17 Inner transmission path 20 Master clock generator 21 Internal clock oscillator at the time of transmission path failure

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-252180 (JP, A) JP-A-5-235974 (JP, A) JP-A-5-63721 (JP, A) 14383 (JP, A) JP-A-4-292203 (JP, A) JP-A-3-117245 (JP, A) JP-A-61-26346 (JP, A) JP-A-58-68335 (JP, A) (58) Fields surveyed (Int.Cl. ⁶ , DB name) H04L 12/437 H04L 7/00 JICST file (JOIS)

Claims (3)

(57) [Claims] A master transmission device and a plurality of slave transmission devices are connected in a ring shape by two transmission paths , and the plurality of slave transmission devices are synchronized with a clock from the master transmission device so as to be clockwise and In a clock switching method used in a ring-shaped synchronous network capable of transmitting data in a counterclockwise direction, in one of the slave transmission devices, a stop of a clock transmitted from a master transmission device in a predetermined direction is detected. When, the one slave transmission device switches the internal clock to the master transmission device, in the predetermined direction, said internal clock
Thus, while transmitting the data signal indicating the stop of the clock, the master transmission device detects the stop of the clock in the reverse direction with a switching request signal instructing to switch the transmission direction to the predetermined direction. Said one
And transmitted to the slave transmission apparatus, whereby said Ma
From the star transmission device side to the one slave transmission device
Wherein the transmission path is sequentially switched . 2. The clock switching method according to claim 2, wherein the one transmission device that has detected the stop of the clock receives the switching request signal and converts the internal clock to a clock extracted from transmission line data. A clock switching method, wherein a switching completion signal indicating switching and switching completion is transmitted to a master transmission device. 3. The clock switching method according to claim 1, wherein when the stop of the clock is restored, the switching back of the transmission path is sequentially performed from the slave transmission device whose clock is stopped to the master transmission device. Characteristic clock switching method.