JP2655460B2 - 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 in a communication system. Particularly, in a ring network in which a plurality of nodes are connected by transmission lines in opposite directions, and in a ring synchronization network in which all nodes operate in synchronization with a master node clock, the distribution of the clock and the clock at the time of transmission line failure Switching method.

[0002]

2. Description of the Related Art In a conventional ring configuration system, a clock is extracted from transmission line data in a certain direction transmitted from a master device and used as a clock of the device, and data is transmitted to the next device. I do. Therefore, at the time of transmission line failure, it is not possible to extract the clock of the transmission line, and network synchronization cannot be obtained because the data of the transmission line is transmitted by the clock generated in the device that has detected the failure. Therefore, in the related art, it has been manually switched to use the clock extracted by the transmission path for the transmission path failure in the opposite direction to the normal transmission path.

[0003]

In this conventional clock switching method, clock switching must be manually controlled in the event of a transmission line failure. Therefore, there is a problem in that a manual operation is required for switching and a clock synchronized with a clock of the master device cannot be obtained until the switching is completed.

The present invention solves the above-mentioned drawbacks,
It is an object of the present invention to provide a clock switching method capable of automatically recovering a synchronous clock.

[0005]

SUMMARY OF THE INVENTION The present invention forms a ring network in which one master device and a plurality of transmission devices are connected by two transmission lines for transmitting signals in opposite directions .
Each transmission from the master device to one of the transmission paths
The clock is extracted from the transmission data transmitted on the
In the clock switching method of ring synchronous network having means for performing period, the transmission apparatus detects a transmission line fault
When switching to the clock of the own device's clock oscillator
And count the number of clock status signals with the overhead signal.
Means for transmitting a value to an adjacent transmission device;
The clock state of the overhead signal from the transmission device
When a signal is received, the value of the clock status signal is
Sequentially add the overhead signal to the master device.
And means for transmitting, the master device in the opposite direction
Depending on the transmission path, the clock status of the overhead signal
From the data transmitted in the opposite direction, including the same value as the signal
Means for transmitting a clock switching signal requesting switching to the extracted clock, wherein the transmission device transmits the clock switching signal transmitted from the master device .
Numerical value and numerical value of clock status signal of above overhead signal
When the value matches, the clock is switched and the clock status is changed.
It is characterized by including means for stopping the addition of the numerical value of the signal .

[0006] The transmission apparatus can include means for adding 1 to the clock state signal received from the adjacent transmission apparatus and transmitting the clock state signal to the next adjacent transmission apparatus.

[0007]

According to the clock switching method of the present invention, an overhead signal of a transmission line is used as clock switching information at the time of a transmission line failure. Is sent. In the following equipment, the number will be +
One. A numerical value "N" is transmitted from the transmission device that has detected the failure to the master device via the N transmission devices.
The master device transmits the value “N” transmitted as the switching signal as data in the opposite direction. The Nth device receives the value of “N” from the master device, and switches to the clock extracted from the opposite transmission line because the values match,
Stop adding +1 to the overhead signal. That is,
The Nth device sends the value of "N-1" sent from the (N-1) th device to the master device, and the master device also sends "N-1" as a switching signal, and 1) Request clock switching for the device. This is repeated up to the device that has detected the failure, and after the device that finally detected the failure, that is, the downstream device sends “0”, and when all the devices are switched, the overhead signal reaching the master device is “0”. , Indicating that all switching has been completed.

Conversely, when the fault is recovered, the device which detected the fault receives the value which is a normal signal, switches back to the original normal clock, sends the normal signal to the next device, and repeats this until the Nth device. Finally, the clocks of all the devices return to the normal state.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a clock switching procedure when a failure occurs in a transmission line in a ring synchronous network according to an embodiment of the present invention.

First, the configuration of the ring synchronous network in the present embodiment will be described. This ring synchronous network has a configuration in which a master device 1 and slave transmission devices 2 to 6 are connected on a ring by two transmission lines in opposite directions, and the master device 1 becomes a master of the ring synchronous network. The configuration includes a clock oscillator 7.

In the present embodiment, in such a ring synchronous network, among the transmission devices 2 to 6, the device 3 which has detected a transmission line failure switches its clock to its own internal clock oscillator 8, Means for transmitting the clock status signal as a numerical value to the overhead signal to the next transmission device 4, and the transmission devices 4 to 6 belonging to the downstream of the transmission device that has detected the failure detect the clock status signal with a numerical value “1”. Means for sequentially transmitting “1” to the master device 1 and transmitting the overhead signal to the master device 1. The master device 1 uses the transmission path in the opposite direction based on the numerical value of the clock signal of the overhead signal. Means for transmitting a switching signal requesting a switch to a clock extracted from transmission data in the direction,
6 includes means for switching to the clock extracted from the transmission data in the opposite direction by the switching signal transmitted from the master device 1 and stopping the addition of the numerical value of the clock state signal.

Next, the procedure of clock switching according to this embodiment will be described.

The state shown in FIG. 1A is a normal state,
All devices operate in synchronization with one master clockwise counterclockwise, and send FF (hexadecimal) as an overhead signal as a clock status signal. FIG.
When a transmission path failure occurs at the point Y as shown in FIG. 3B, the device 3 switches to the internal clock oscillator 8 and sends out "01" as a clock status signal. Add one to the value of the signal. The master device 1 receives “04” as the clock state signal,
A clock switching request is made to the device sending “04”, that is, the device 6 (FIG. 1B). The device 6 receives the switching request from the master device 1 and switches the clock to the master clock transmitted from the master device 1 via the clockwise transmission path, and stops incrementing the value by one at the same time. Then, since master device 1 receives “03” as the clock status signal, master device 1 receives clock status signal “0”.
A clock switching request is issued to the device 5 issuing 3 "(FIG. 1 (c)). Finally, the devices 3 to 6
"00" is transmitted as a clock state signal, and the state is synchronized with the master clock in this ring synchronous network (FIG. 1 (f)).

Next, a description will be given of the procedure for switching back the clock when the fault is recovered.

FIG. 2 shows a procedure for switching back the clock when the fault is recovered. First, as shown in FIG. 2A, when the fault is recovered, the device 3 receives the FF, which is a normal signal, from the device 2, switches back the clock, and sends the FF to the next device. Switching back to the device 4, the device 5, and the device 6 one after another. Eventually,
All devices send FFs as the clock signal of the overhead signal and return to the normal state (FIG. 2 (d)).

[0017]

As described above, the present invention can be automatically performed in a ring synchronous network without requiring any manual operation for clock switching at the time of transmission line failure.

[Brief description of the drawings]

FIGS. 1A to 1F are diagrams for explaining a clock switching procedure according to an embodiment of the present invention;

FIGS. 2A to 2D are diagrams for explaining a clock switching procedure when a failure is recovered.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Master device 2-6 Transmission device 7 Clock oscillator used as master 8 Internal clock oscillator at the time of transmission line failure occurrence

Claims (2)

(57) [Claims] A ring network in which one master device and a plurality of transmission devices are connected by two transmission lines for transmitting signals in opposite directions.
, And the transmission devices transmit the transmissions from the master device, respectively.
From transmission data transmitted on one of the
In the clock switching method of ring synchronous network having means for performing synchronization by extracting click, the transmission device, when detecting a transmission line failure, the self-device
Switch to the clock of the clock oscillator of
The clock status signal as a numerical value
Means for transmitting to a transmitting device, and
The above clock status signal of the overhead signal is received.
Time, add the value of the clock status signal
Means for transmitting the overhead signal to the master device, wherein the master device transmits the overhead signal through a transmission path in the opposite direction.
The same value as the clock status signal value of the bar head signal
Switching to clock extracted from transmitted data in the opposite direction
Means for transmitting a clock switching signal requesting switching, wherein the transmission device transmits the clock switching signal transmitted from the master device .
The lock switching signal value and the overhead signal
The clock is switched when the value of the lock status signal matches
Means to stop adding the value of the clock status signal
Clock switching method, which comprises a. 2. The clock switching system according to claim 1, wherein said transmission device includes means for adding 1 to a clock status signal received from an adjacent transmission device and transmitting the signal to the next adjacent transmission device.