JP2609834B2 - Clock switching method in ring network - 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 method in a ring network, and more particularly, to a clock switching processing method when a failure occurs in a ring network requiring a network synchronization configuration.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram of a ring network using such a clock switching method. That is, FIG.
Describes a clock switching state in a normal state. The master node 10 and each of the slave nodes 30 to 40
The nodes are connected by a DH (synchronous digital hierarchy) optical transmission line, each node has a clock priority table and a quality division table, and the surplus bits of the overhead in the SDH transmission path signal indicate the active quality division table. Sending / Transferring synchronous message. Normally, the operation is performed by the clockwise clock of the master node 10, but the switching operation will be described below.

[0003] The master node 10 is a node that controls the ring network, and the slave nodes 20 to 40 are configured to operate in synchronization with the clock of the master node 10. Each node has a priority order table indicating the priority order of clocks used in its own station, and the master node 10
The external clock 101 has priority 1 (hereinafter referred to as P = 1), the external clock 102 has priority 2 (hereinafter referred to as P = 2), and the quality classification table of the external clocks 1 and 2 is held as Q = 2. . Slave nodes 20, 30, 4
0 indicates that the clock from the clockwise optical transmission line 50 is P = 1,
The clock from the left-hand optical transmission line 60 is P = 2, the clock generated by the own node is P = 3, and the quality classification table of the clock generated by the own node is Q = 5.

The master node 10 always uses the external clock 101 of P = 1, and transfers the synchronization message Q = 2 of the quality division table to the surplus bits of the overhead in both directions of the slave node 20 and the node 40. Next, in the slave node 20, since the clock from the optical transmission line 50 is P = 1 and has the highest priority, the clock is extracted and the internal synchronization is established. Since the slave node 20 operates in synchronization with the clock from the master node 10 in this state, the slave node 20 transfers the synchronization message Q = 7 to the master node 10 which is not directly related to the quality but prevents the loop lock timing. I do.

Further, in order to notify the slave node 30 that the slave node 30 is operating with the clock from the master node 10, a synchronous message Q = 2 is transferred with an extra bit of overhead. The slave nodes 30 and 40 are in the same state as the slave node 20. As described above, the ring network normally maintains clock synchronization in the ring clockwise with respect to the master node 10.

Next, the operation at the time of failure will be described with reference to FIG. FIG. 3 is a block diagram showing an example of a case where a transmission line failure occurs between the master node 10 and the slave node 20. The illustrated state shows a final state in which the switching operation at the time of failure has been completed, and the clock synchronization configuration from right to left in the ring around the master node 10.

Next, the operation transition to this state will be described.
First, the slave node 20 detects a failure of the optical transmission line 50 by a separately provided monitoring unit, and changes the synchronization message received from the master node 10 from Q = 2 to Q = 7 by this failure signal. I do. The second priority is the optical transmission line 60. However, since the synchronization message Q = 7 is transferred to the clock from the node 30, the quality classification table has a quality level Q = 5 better than Q = 7. Switching to the internal clock of a certain priority 3 is performed. That is, a high-quality clock is selected by giving priority to the value of the synchronization message rather than setting the priority.

The slave node 20 has a slave node 3
For 0, the transfer of the synchronization message is changed from Q = 2 to Q = 5 and transmitted. The slave node 30 similarly transfers the synchronization message Q = 5 as it is. Next, the slave node 40 compares the synchronization message Q = 5 sent from the slave node 20 and the slave node 30 with the synchronization message Q = 2 sent from the master node 10, and determines that the higher quality Q = 2 as the synchronization message. Switch to By this switching, the slave node 40 changes the synchronization message to the slave node 30 to Q = 2 and transfers it. Each of the slave nodes 20 and 30 selects the clock from the slave node 40 since the synchronization message has higher clock quality when Q = 2 than when Q = 5. As described above, clock synchronization in the ring is maintained in the left-hand direction shown in FIG.

Further, when the failure is recovered in this state, the slave node 20 receives the clock from the master node 10 and the synchronization message Q = 2, and switches to this clock having a high quality classification and a high priority to synchronize. At the same time, this clock is transferred to the slave node 30. The slave nodes 30 and 40 also perform clock switching in the same manner, and eventually return to the original state shown in FIG.

[0010]

As described above, in the conventional clock switching method, clocks in the ring are usually synchronized by clockwise clocks. However, when a failure occurs, each slave node performs clock switching. Synchronization is achieved by clockwise rotation. Further, when the failure is restored, each node switches clocks and returns to a state where synchronization is achieved with the first clockwise clock. However, it takes a long time to enter the state of clockwise rotation when a failure occurs, because there is a process of synchronizing with the clock of the slave. In addition, in the state of the clockwise counterclockwise synchronization at the time of the failure, since the quality classification of the clock is Q = 2, the switching is performed even though there is no problem in the operation of the system. Therefore, there is a problem that the number of times of clock switching increases as a whole and the time becomes longer.

[0011]

According to a clock switching method in a ring network according to the present invention, in a bidirectional ring network in which a master node and a plurality of slave nodes are connected in a ring, the master node has its own station. The slave node sends out the clock generated in step (1) to the clockwise circuit and the counterclockwise circuit of the ring network, and each of the slave nodes sets the clock from the clockwise circuit to priority 1 and the clock from the clockwise circuit to priority 2 The clock generated by the station is given priority 3, the quality division indicating the quality of the clock is generated by the master node, the clock generated by the master node is classified into quality division 1, the clock generated by the slave node is classified into quality division 2, and the downstream slave is classified. The clock that is looped back and received by the node is defined as quality category 3, and is used for synchronization used by its own station. Locking is performed by first selecting the one with the higher quality division and, if the two clocks have the same quality division, switching so as to select the higher priority one. In the clock switching method of selecting the clock of the clock line and selecting and using the clock of the counterclockwise line when a line failure occurs, the master node or the slave node serving as the failure end in the case of the line failure is transmitted to the failure line side. By changing the quality class of the clock from 1 to 1.5, the degree of quality being intermediate between 1 and 2, each of the slave nodes does not switch back when the line failure is recovered, and the state remains unchanged. It is supposed to be maintained.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a clock switching operation in a normal state, and FIG. 2 is a block diagram illustrating a clock switching operation at the time of failure according to the present embodiment.

The master node 10 and each slave node 30
40 to 40 are connected by an SDH (Synchronous Digital Hierarchy) optical transmission line, each node has a clock priority table and a quality classification table, and operates on surplus bits of overhead in SDH transmission line signals. The synchronization message of the quality classification table is carried and transmitted / transferred. Normally, the operation is performed by the clock of the master node 10 clockwise. The switching operation will be described below.

The master node 10 is a node that controls the ring network, and the slave nodes 20 to 40 are configured to operate in synchronization with the clock of the master node 10. Each node has a priority order table indicating the priority order of clocks used in its own station. The master node 10 assigns the external clock 101 to priority order 1 (hereinafter referred to as P = 1),
The external clock 102 is given priority 2 (hereinafter referred to as P = 2)
And the quality classification table of the external clocks 1 and 2 is Q
= 2. The slave nodes 20, 30, and 40
The clock from the right-hand optical transmission line 50 is P = 1, the clock from the left-hand optical transmission line 60 is P = 2, the clock generated by the own node is P = 3, and the quality classification of the clock generated by the own node. Hold the table as Q = 5.

The master node 10 always uses the external clock 101 of P = 1, and transfers the synchronization message Q = 2 of the quality division table to the extra bits of the overhead in both directions of the slave node 20 and the node 40. Next, in the slave node 20, since the clock from the optical transmission line 50 is P = 1 and has the highest priority, the clock is extracted and the internal synchronization is established. Since the slave node 20 operates in synchronization with the clock from the master node 10 in this state, the slave node 20 transfers the synchronization message Q = 7 to the master node 10 which is not directly related to the quality but prevents the loop lock timing. I do.

Further, in order to notify the slave node 30 that the slave node 30 is operating with the clock from the master node 10, a synchronous message Q = 2 is transferred with an extra bit of overhead. The slave nodes 30 and 40 are in the same state as the slave node 20. As described above, the ring network normally maintains clock synchronization in the ring clockwise with respect to the master node 10.

Next, the operation at the time of failure will be described with reference to FIG. FIG. 2 is a block diagram showing an example of a case where a transmission line failure occurs between the master node 10 and the slave node 20. The illustrated state shows a final state in which the switching operation at the time of failure has been completed, and the clock synchronization configuration from right to left in the ring around the master node 10.

Next, the operation transition to this state will be described.
First, the slave node 20 detects the failure of the optical transmission line 50 by a monitoring unit provided separately, and, based on the failure signal, synchronizes the synchronization message from the master node 10 which has been received so far from Q = 2 to Q = 2. Change to 7. The second priority is the optical transmission line 60. However, since the synchronization message Q = 7 is transferred to the clock from the node 30, the quality classification table has a quality level Q = 5 better than Q = 7. Switching to the internal clock of a certain priority 3 is performed. That is, a high-quality clock is selected by giving priority to the value of the synchronization message rather than setting the priority.

The slave node 20 has the slave node 3
For 0, the transfer of the synchronization message is changed from Q = 2 to Q = 5 and transmitted. The slave node 30 similarly transfers the synchronization message Q = 5 as it is. Next, the slave node 40 is the slave node 20, the slave node 30
Synchronization message Q = 5 sent from master node 10
, And switches to the higher quality Q = 2 as the synchronization message. By this switching, the slave node 40 changes the synchronization message to the slave node 30 to Q = 2 and transfers it. Each of the slave nodes 20 and 30 selects the clock from the slave node 40 since the synchronization message has higher clock quality when Q = 2 than when Q = 5.
As described above, clock synchronization in the ring is maintained around the left as shown in FIG.

On the other hand, the master-slave 10 detects the occurrence of a fault at the same time as the slave node 20 by means of a monitoring device provided separately, thereby adding 1 to the synchronization message Q = 2 transferred to the master-slave 10. 3 is performed. This synchronization message Q = 3 is continuously transferred to the failed slave node 20 side.

In this state, when the failure is recovered, the master node 20 receives Q = 3 for the clock and the synchronization message from the master node 10, but since the quality is lower than Q = 2 for the counterclockwise clock, the master node 20 switches the clock. Is not performed and the left-handed state is maintained.

The above description is an example in which a failure has occurred in the optical transmission line between the master node 10 and the slave node 20. However, when a failure has occurred in another optical transmission line section, the clock of the clockwise clock is generated. There is no switching operation at the node upstream from the node where the failure is detected, and the clock is switched to the counterclockwise clock at the node downstream. At the time of recovery, clock switching is not performed as described above.

[0023]

As described above, the clock switching method of the present invention is a simple process of adding 1 to the value of the synchronization message transferred to the failed section when a failure occurs,
Unnecessary switchback operation at the time of failure recovery can be suppressed, and this inoperative can reduce the frequency of the time-consuming switching operation from clockwise clock synchronization to clockwise counterclockwise synchronization in the normal state. This has the effect of reducing the switching time.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a clock switching state in a normal state.

FIG. 2 is a block diagram illustrating an embodiment in FIG.

FIG. 3 is a block diagram illustrating a conventional example in FIG. 1;

[Explanation of symbols]

 10 Master node 20, 30, 40 Slave node 50, 60 Optical transmission line

Claims (1)

(57) [Claims] 1. A bidirectional ring network in which a master node and a plurality of slave nodes are connected in a ring, wherein the master node clocks a clock generated by its own station on a clockwise circuit and a counterclockwise circuit of the ring network. Each slave node sends the clock from the right-handed line to priority 1, the clock from the left-handed line to priority 2, the clock generated by the own station to priority 3, and the quality of the clock. A clock generated by the master node to generate a quality class indicating the level of
The clock generated at the slave node is set to quality class 2 and the clock folded back and received by the downstream slave node is set to quality class 3, and the synchronization clock used by the own station is first selected from the high quality class. If the two clocks are of the same quality division, by switching to select the higher priority, each of the slave nodes always selects the clock of the clockwise circuit,
Also, in the clock switching method for selecting and using the clock of the left-handed line when a line failure occurs, the master node or the slave node serving as the failure end in the case of the line failure receives the clock transmitted to the failed line side. A ring network in which each of the slave nodes does not switch back when the line failure is restored by changing the quality classification from 1 to 1.5, the degree of quality being between 1 and 2. Clock switching method.