JPH0661986A - Clock switching system - Google Patents

Abstract

PURPOSE:To attain a clock switching so that a system can operate synchronously with the clock of a master station even at the time of the occurrence of a fault of a transmission path, in a four fiber ring system which operates synchronously with the clock of the master station. CONSTITUTION:In the four fiber ring system constituted of a master station 20 which operates by receiving the clock from a clock feeder 19, and the slave stations 21-23 which operate by the clock extracted from signals received from the transmission path, the slave stations 21-23 operate by selecting one from among the clocks extracted from the four signals which input the clock in a device.

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 for a 4-fiber ring system in an optical communication system,
In particular, it relates to a clock switching method for a 4-fiber ring system that synchronizes all devices with the clock of one station which is a master station.

2. Description of the Related Art A four-fiber ring system in an optical communication system receives a clock from a network synchronous clock supply device and receives it from an optical fiber transmission line (hereinafter abbreviated as transmission line) and a master station which operates as a clock in the device. It is composed of a slave station that operates with a clock generated by extracting timing from a signal as an internal clock. The slave station is configured to synchronize with a signal input from a transmission line in a fixed direction, and the direction in which the clock from the master station is transmitted is fixed to one direction for the entire ring. The clock supplied to a normal device has a dual structure. Since there are two input signals of the working system and the standby system in one direction in a 4-fiber ring, the clock extracted from both of them is used as a duplication. Operates as a clock extracted from the signal input from the active transmission line, and when a failure occurs in the active transmission line, switches the signal to the standby system and also switches the clock to the standby system clock extracted from the standby transmission line. As a result, it is possible to operate in synchronization with the clock of the master station.

FIG. 3 is a block diagram showing an example of a conventional clock switching system. In FIG. 3, the active transmission line 5,
Reference numeral 15 is an optical fiber transmission line of the working system, and standby system transmission lines 6 and 16 are optical fiber transmission lines of the standby system. Each of the receiving circuits 1, 3, 12 and 14 reproduces an input optical signal from the transmission line into an electric signal and then transfers to an internal clock.
The switch circuits 7 and 9 switch the signal paths so that the signals can be sent to the standby transmission paths 6 and 16 when the transmission path fails.

The switch circuits 7 and 9 are active transmission lines 5 and 1, respectively.
When a failure occurs in 5, the output signal is
When a failure occurs in both the working transmission line and the protection transmission line, the loopback is performed and a signal is transmitted to the protection line in the opposite direction. Signal 8
Indicates a D / I circuit that performs drop and insert, and performs drop and insert on a channel determined from an input signal. The transmission circuits 2, 4, 12 and 14 convert the electric signal into an optical signal and send it to the transmission path. Selector 1
When selecting a dual internal clock, 1 inputs the clock extracted by the receiving circuits 1 and 3 from the received signals from the active transmission line 5 and the standby transmission line 6, and selects one of them.

[0004]

In this conventional clock switching system, in the four-fiber ring system, when the working transmission line is switched to the protection transmission line at the time of failure, the clock is also changed to the clock extracted from the protection transmission line. Since it was possible to save the signal and operate in synchronization with the clock of the clock supply device of the master station, the clock from the master station could be used if both the active and standby transmission lines in the same direction failed. Since the clock supply synchronized with the power supply is cut off, all the devices downstream from the fault point will either lose all signals or have an internal oscillator to prevent the loss, and the fault detection station will switch the internal clock to the output of the oscillator. Even if it operates, the oscillator has a problem in signal quality because it is not synchronized with the clock of the master station.

When the clocks of the active system and the standby system are extracted from the transmission lines in the opposite directions,
There is also a drawback that when a failure occurs in a certain section, clock switching must be performed by all devices downstream from the failure section.

[0006]

According to the clock switching system of the present invention, a master station device which operates by receiving a clock from a synchronous network clock supply device and a clock extracted from a signal input from a transmission line are synchronized in the device. In the slave station device of the 4-fiber ring system, which is configured to have a plurality of slave station devices that operate as clocks, and is normally supplied with a clock in a fixed direction by the master station, the active systems connected in opposite directions to each other Means for selecting one clock from the four clocks extracted from the signals input to the transmission line and the backup transmission line to be used as a clock in the device, and the active transmission line that supplied the clock during normal operation Means for switching to the clock extracted from the protection system transmission line when a failure occurs, the working system transmission line and the protection system And means for switching the clock extracted from the opposite side of the service line when sending passage of both disorders,
If a failure also occurs on the opposite side active transmission line,
And a means for switching to the clock extracted from the transmission line on the opposite side.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention.

In FIG. 1, working transmission lines 5 and 15 are working optical fiber transmission lines, and backup transmission lines 6 and 16 are used.
Is a backup optical fiber transmission line. Receiver circuit 1, 3, 1
Reference numerals 2 and 14 respectively reproduce an input optical signal from the transmission line into an electric signal and then transfer to the internal clock. The switch circuits 7 and 9 switch the signal paths so that the signals can be sent to the backup system transmission path when the transmission path has a failure. Switch circuit 7,
Reference numeral 9 indicates that an output signal is sent to the protection transmission line when a failure occurs in the working transmission line, and loopback is performed when a failure occurs in both the working transmission line and the protection transmission line, and the backup system in the reverse direction is performed. It is configured to send a signal to the transmission line.

Signal 8 is D / for drop and insert.
The drop and insert are performed on the channel determined from the input signal of the I circuit. The drop and insert are performed on the channel determined from the input signal of the D / I circuit. The transmission circuits 2, 4, 12 and 14 convert the electric signal into an optical signal and send it to the transmission path. The selector 17 normally selects one of the clocks extracted by the receiving circuits 1 and 3 from the signal synchronized with the clock of the master station from the upstream. The selector 18 uses one of the clocks input from the backward active system transmission line 15 and the reverse system transmission line 16 for use as an internal clock when both the active system transmission line 5 and the standby system transmission line 6 have a failure. select. The selector 11 selects one of the clocks selected by the selector 17 and the selector 18.

Normally, the clock extracted by the receiving circuit 1 is selected by the selector 17, and the selector 11 selects the clock selected by the selector 17. When a failure occurs in the active transmission line 5, the selector 17 selects the clock extracted by the receiving circuit 3. The selector 11 selects the clock selected by the selector 18 when a failure occurs in both the active transmission path 5 and the standby transmission path 6. Selector 1
At 8, the clock extracted by the normal receiving circuit 12 is selected. Further, when a failure also occurs in the active transmission line 15, the selector 18 selects the clock extracted by the receiving circuit 14 and operates this clock as the in-device clock.

When both the active system transmission line 5 and the standby system transmission line 6 are disconnected, the signal input in synchronization with the clock of the master song is disconnected, but the fault detection station is caused by communication using the overhead of the transmission frame. It is possible to synchronize with the master station by controlling to switch to the clock extracted from the active transmission line 15 in the reverse direction in all the downstream devices.

FIG. 2 is a block diagram showing the clock supply path of the 4-fiber ring system of this embodiment. 1 in the figure
9 is a clock supply device, 20 is a master station, 21
23 to 23 indicate slave stations. 24,2 between each station
6, 28, 30 are the active transmission lines, 25, 27, 29,
Reference numeral 31 indicates a backup transmission line. FIG. 2A shows a clock supply path at a normal time, and FIG. 2B shows a master station 2
0 shows a clock supply path when a failure occurs in the active transmission line 24 between the slave station 21 and the slave station 21. The slave station 21 operates with the clock extracted from the standby transmission line 25, and the other stations operate. No need to switch clocks.
FIG. 2C shows a clock supply path when a failure occurs in both the active system transmission path 24 and the standby system transmission path 25. In this case, the slave stations 21 to 23 have the active system in the opposite direction to the normal system. It operates with the clock extracted from the transmission line. In this state, the working transmission line 26 between the slave stations 21 and 22 is further added.
If a failure occurs in the slave station 21, the slave station 21 operates by switching to the clock extracted from the standby system transmission line 27.

[0013]

As described above, according to the present invention, the clock to be used in the device is selected from the four clocks extracted from the signals input from the bidirectional working and protection transmission lines according to the fault condition. As a result, even if both the active transmission line and the protection transmission line in the same direction have a failure, all the devices in the ring can operate in synchronization with the clock from the master station.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing a clock supply path of the present embodiment.

FIG. 3 is a block diagram of an example of a conventional clock switching system.

[Explanation of symbols]

 1, 3, 12, 14 Receiver circuit 2, 4, 10, 13 Transmitter circuit 5, 15, 24, 26, 28, 30 Working transmission line 6, 16, 25, 27, 29, 31 Backup transmission line 7, 9 switch circuit 8 D / I circuit 11, 17, 18 selector 19 clock supply device 20 master station 21-23 slave station

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H04B 10/02 H04J 3/14 Z 4101-5K H04L 7/027 H04Q 11/04 304 B 9076-5K

Claims (1)

[Claims] 1. A master station device that operates by receiving a clock from a synchronous network clock supply device, and a plurality of slave station devices that operate using a clock extracted from a signal input from a transmission line as a synchronous clock in the device. In the slave station device of the 4-fiber ring system in which a clock is supplied in a fixed direction by the master station during normal operation, the signals input to the active system transmission line and the standby system transmission line connected in opposite directions A means for selecting one clock from the extracted four clocks to be used as a clock in the device, and a standby transmission line when a failure occurs in the active transmission line that has been supplying the clock during normal operation. If the means for switching to the clock extracted from the above and the working system transmission line and the protection system transmission line both have a failure, the working system transmission line on the opposite side is used. A clock switching method characterized by having a means for switching to the clock extracted from the other side and a means for switching to the clock extracted from the protection path on the opposite side when a failure occurs on the transmission path on the opposite side. .