JPH10322379A - Clock path changeover method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop a switch-back on the occurrence of a fault restoration and to attain automatic switch-back. SOLUTION: The system according to the clock path changeover method is made up of a master node 10 that receives a synchronizing clock from other network and transmits data to a ring of a synchronous digital hierarchy SDH and up of slaves nodes 20, 30, 40 that extract the clock signal from optical transmission lines 50, 60 of the SDH ring in the system, operate the inside of themselves synchronously with the clock signal and transmit data to other nodes. Then each node is provided with a priority table and a quality management table used to select any of external clock signals CLK 1, 2 and an internal CLK (INT), and a system configuration that transfers the selected quality management table in excess bits of an overhead OH of the SDH to each of the nodes 10, 20, 30, 40 as a synchronizing message to select automatically the optimum CLK mode as the system based on the tables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock path switching method, and more particularly, to a clock path switching method when a failure occurs in a ring network requiring a network synchronization configuration.

[0002]

2. Description of the Related Art A conventional clock path switching method will be described with reference to the drawings.

FIG. 4 is a state diagram showing a state of a clock path in a system at the time of a transmission line failure in the first conventional clock path switching method.

In FIG. 4, this first conventional example shows the contents disclosed in Japanese Patent Application Laid-Open No. 8-288959. First, the slave node 120 detects the failure of the optical transmission line 150 by a monitoring unit provided separately. The synchronization message from the master node 110 that has been received until now is changed from Q = 2 to Q = 7 by this failure signal. The second priority is the optical transmission line 160. However, since the synchronization message Q = 7 is transferred to the clock from the node 130, 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.

[0005] The slave node 120 transfers the synchronization message to the slave node 130 from Q = 2 to Q = 2.
Change to 5 and send. Similarly, the slave node 130 transfers the synchronization message Q = 5 as it is. Next, the slave node 140 compares the synchronization message Q = 5 sent from the slave nodes 120 and 130 with the synchronization message Q = 2 sent from the master node 110, and compares the synchronization message Q = 2 with the higher quality Q = 2 as the synchronization message. Switch to By this switching, the slave node 140 changes the synchronization message to the slave node 130 to Q = 2 and transfers it. Since each of the slave nodes 120 and 130 has higher clock quality for the synchronization message when Q = 2 than for Q = 5, the slave node 140
Select the clock from. As described above, clock synchronization in the ring is maintained counterclockwise.

On the other hand, the master node 110 uses a monitoring device provided separately to notify the slave node 120 of the occurrence of a fault.
At the same time, the detection is performed, but a process of adding 1 to the synchronization message Q = 2 transferred to the master node 110 to obtain 3 is performed. The synchronization message Q = 3 is continuously transferred to the failed slave node 120.

In this state, when the fault is recovered, the slave node 120 receives Q = 3 for the clock and the synchronization message from the master node 110, but since the quality is lower than Q = 2 for the counterclockwise clock, the slave node 120 switches the clock. Is not performed and the counterclockwise state is maintained.

FIG. 5 is a state diagram showing a state of a clock path in the system at the time of a transmission line failure in the second conventional example.

In FIG. 5, this second conventional example shows the contents disclosed in Japanese Patent Laid-Open Publication No. Hei 6-152623.
A transmission line failure occurs at point A between 14 and 215, and at this time, the stations 214 and 215 are performing failure detection. Station 21
Reference numeral 5 switches to the internal CLK from the internal CLK generator 205 due to the disconnection of the reference CLK. At that time, only the station 215 (CLK fault detecting station) that has detected that the reference CLK cannot be extracted issues the CLK switching request d1. The station 214 detects a fault, but since the reference CLK has been extracted,
No CLK switching request d1 is issued (not a CLK failure detection station).

Here, the switching request d1 from the transmission station 215
Will be described. In the slave station 216, C
LK extraction becomes impossible, and the reference CLK coming from the transmission line 203 in the counterclockwise direction is used in order to maintain the operation as a synchronous network. For example, the slave station 21
1, when the CLK cannot be extracted from the clockwise transmission line 202, the specific master station serving as the destination of the CLK switching request d1 is the station 212, and the slave stations 213, 214, 21
The station 210 is the specific master station that is the destination of the CLK switching request d1 when the CLK extraction at 5, 216 and 217 becomes impossible. If there is a plurality of master stations and a certain master station no longer receives the synchronization reference CLK from the synchronization network reference CLK generator 204, this station becomes a slave station to extract the reference CLK and switch the CLK. C
The direction of sending the CLK switching request d1 in the slave station from which the LK extraction cannot be performed is based on the information of the CLK extracting direction and is transmitted to the transmission path in the same direction as the extraction direction.
Is transmitted, there is no need to consider the existence of a plurality of master stations. Therefore, the CLK switching request d1 sent by the station 215 is resent to the clockwise transmission line 202. The switching control processing unit 210 of the station 216 transmits the CLK switching request d transmitted by the station 215.
1 and prepares to perform CLK switching when a CLK switching signal e1 described later arrives, and retransmits the CLK switching request d1 to the station 217 to the clockwise transmission path 202.

[0011]

In the conventional clock path switching method, in the first conventional example shown in FIG. 4, a master node and each slave node are connected by an SDH optical transmission line, and Has a clock priority table and a quality management table, and transmits / transfers a synchronization message of the active quality management table to the surplus bits of the overhead (hereinafter referred to as OH) in the SDH transmission path signal. A failure occurs in the optical transmission line between the master node and the slave node, and after switching the clock path, the master node adds “1” to the synchronization message in the quality management table and transmits the synchronization message to the failure transmission line.

In the second conventional example shown in FIG.
The master node and the slave nodes constitute a ring-shaped network system, and each node has a clock path switching control processing unit. When a failure occurs in the transmission line between the master node and the slave node, the slave node detects the clock interruption, switches to INT once at the slave node, and transfers the synchronization message "5" to the master node. Since the quality control table of the master node is “2”, a clockwise clock path is formed. In addition, the master node adds “1” to the currently transmitted quality management table for the transmission line on which the failure is detected, and transmits “3”. Thereby, even if the transmission tail between the master node 10 and the slave node is restored, the counterclockwise state is maintained.

In other words, these conventional clock path switching methods have a problem that when a fault is repeatedly generated / restored, it is added as needed, and a large table area must be secured.

[0014]

SUMMARY OF THE INVENTION A clock path switching method according to the present invention receives a plurality of synchronization clocks from another network and connects the network to a synchronous digital hierarchy (SDH) double ring optical transmission line network. In a clock path switching method comprising a master node to send and a plurality of slave nodes connected to the network and operating on an internal clock synchronized with a clock received from one of the optical transmission lines, the master node and the plurality of slave nodes Each of the slave nodes indicates a priority order table in which the priorities of the use of the plurality of synchronization clocks and the internal clocks are determined, and indicates a quality order and a fault of each clock when the respective clocks are selected. And a quality control table in which the stored code is stored. The quality order of the selected clock in the quality control table is transferred as a synchronization message to the extra bits of the overhead (OH) of the DH as a synchronization message, and a quality code indicating the failure is generated when one of the double rings fails. And the operation of the system is continued on the optical transmission line of the other ring which has no failure even if the failure is recovered.

According to the clock path switching method of the present invention, a plurality of synchronization clocks are inputted from another network, one of the plurality of synchronization clocks is selected and synchronized, and a bidirectional synchronous digital hierarchy (SDH) is provided. A master node that transmits to the optical transmission line of the ring, and a clock that is extracted from the optical transmission line in one direction of the SDH ring and operates internally with an internal CLK synchronized with the extracted clock, and the clock is used for the other side. A plurality of slave nodes transmitting to the other slave node or the master node via the optical transmission line, and the master node and the slave node are given priority in using the plurality of synchronization clocks and the internal CLK. And a priority order table and a quality order and a fault when selecting the plurality of synchronization clocks and the internal CLK. Has a quality management table predetermined code is stored, the SD with respect to the master node and slave nodes to automatically select an optimum clock paths as a system based on these tables
The code number of the selected quality order in the quality management table is transferred as a synchronization message to the extra bits of the overhead (OH) of H, and the whole system operates with one clock of the master node. After the switching of the clock path after the occurrence of the failure in the optical transmission line, it is fixed at the node where the failure has occurred so as not to transition to the clock path on the optical transmission line side where the failure has occurred, and the clock on the original optical transmission path side is restored again after the recovery of the optical transmission line failure. A process that does not execute the switching back of the clock path to return to the above state, and at the time of recovery from the failure of the optical transmission line, can also be set so that the switching back of the clock path that returns the clock path to the original optical transmission line can be controlled.

[0016]

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

FIG. 1 is a diagram showing a network configuration according to an embodiment of the present invention. FIG. 2 is a state diagram showing a state of a clock path in the system when a transmission line fails in the embodiment.
FIG. 3 is a state diagram showing the state of the clock path in the system at the time of transmission line failure recovery in the present embodiment.

In FIG. 1, the present embodiment uses a synchronization clock (external clock: external CLK) 1 from another network.
2 and a master node 10 for transmitting to an optical transmission line 50, 60 of a synchronous digital hierarchy (SDH) ring in synchronization with one of the external clocks, and a ring of the master node 10 and the SDH ring. The external clocks are extracted from the optical transmission lines 50 and 60 connected by the double optical transmission lines 50 and 60, the internal operation is performed by an internal clock (INT) synchronized with the extracted external clocks, and the external clocks are extracted to other slaves. The master node 10 has three slave nodes 40 for transmitting external clocks. The master node 10 has the external clock 1 as priority 1 (P = 1) and the external clock 2 as priority 2 (P = 2). Priority table and the S
And a quality control table for storing a predetermined code number indicating a clock quality order and a failure in selecting a clock on the dual optical transmission lines 50 and 60 of the DH ring. The quality control table of FIG.
= 2, Q = lowest clock selection or failure case
7 is set in advance.

In the slave nodes 20, 30, and 40, the internal clock (INT) is set to P = 3 as the priority of the clock in the priority table, the quality code of the internal clock is set to Q = 5 in the quality control table, and the clock selection is performed. Q = 7 in common with the master node in the case of the lowest rank or failure
There is.

As described above, in the present embodiment, a ring-shaped network in which the master node 10 and the slave nodes 20 to 40 are connected by the double optical transmission lines 50 and 60 is configured. Each of the nodes 10, 20, 30, and 40 has a clock path priority table (hereinafter referred to as P) and an external clock and an internal clock (INT) quality control table (hereinafter referred to as Q). In order to select a path, a quality management table being selected is transferred as a synchronization message to a surplus bit of overhead (hereinafter, OH) of a synchronous digital hierarchy (hereinafter, SDH) for each node.

Next, the operation of this embodiment will be described with reference to FIGS.
This will be described with reference to FIGS.

FIG. 1 shows a state where the optical transmission lines 50 and 60 are normal in the ring network system. All the nodes in the ring operate in synchronization with the clock (hereinafter referred to as CLK) of the master node 10. Each node has a priority table as follows as an example, and the master node 10 has priority 1 (hereinafter, referred to as P = 1): external CLK1, priority 2 (hereinafter, P
= 2): external CLK2, and external CLK1,
2 is held as “Q = 2”. Nodes 20 to 40 have P = 1: optical transmission line 50, P = 2: optical transmission line 60, P = 3: internal CLK (hereinafter referred to as INT), and IN
The quality control table of T is held as “Q = 5”. The master node 10 supplies the external CLK1 of priority 1 and
Synchronous with the external CLK1. The master node 10 determines that it is operating with the external CLK1, and outputs the OH of SDH.
Then, the synchronization message “Q = 2” of the quality management table is transferred to the slave nodes 20 to 40 via the surplus bits. Next, in the slave node 20, the optical transmission path 50
Since the setting of the priority order is the highest, the clock component (external CLK1) is extracted from the optical transmission line 50 and operates in synchronization with the master node 10. The slave node 20
In this state, the external CLK1 from the master node 10
Therefore, the synchronization message “Q = 7” of the quality control table is transferred to the master node 10 to prevent loop timing. Also, the external C is synchronized with the master node 10 for the slave node 30.
The synchronization message “Q = 2” is transferred to the surplus bits of the OH to transfer that it is operating at LK1. The slave nodes 30 and 40 perform the same transfer method as the slave node 20.

As described above, if the priority order is set as shown in FIG. 1, the ring network normally keeps the clock in the ring clockwise with respect to the master node 10.

Next, an operation at the time of a transmission line failure in the present embodiment will be described with reference to FIG.

Master node 10 and slave node 20
An example will be described in which a transmission path failure has occurred between them. As a final system, a clock synchronization configuration from clockwise to counterclockwise is formed in the ring around the master node 10. Figure 2 as the final system
However, the clock operation transition in the node will be described using the slave node 20.

The slave node 20 is connected to the master node 1
It is determined that a failure has occurred in the optical transmission line 50 which is a connection to the slave node 20, and the synchronization message is changed from “Q = 2” to “Q” in the slave node 20.
= 9 ". The second priority is the optical transmission line 60, but in the normal state of FIG. 1, the slave node 30 sends the synchronization message" Q = 7 "through the extra bits of the OH. Is transferred, the quality management table is temporarily switched to INT having a priority level P = 3 whose quality level is “5” higher than “Q = 7”. The slave node 20 transfers the synchronization message to the slave node 30 from “Q = 2” to “Q = 5 "before transferring. Slave node 30
Transfers the synchronization message "Q = 5" from the slave 20 as in the normal state of FIG. 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 outputs “Q = 2” having high quality as the synchronization message. Switch to ". By this switching, the slave node 40 changes the synchronization message sent to the slave node 30 to “Q = 2” and transfers it.

Next, the operation at the time of recovery from a transmission line failure in this embodiment will be described with reference to FIG.

Master node 10 and slave node 20
When the failure in the optical transmission path between the nodes is restored, the master node 10
, The synchronization message “Q = 2” is transferred to the slave node 20. Inside the slave node 20, even if the synchronization message "Q = 2" is transferred from the master node 10, it is internally fixed to "Q = 9" of the previous state.
The clock path is not switched, the operation is performed with the clock from the slave node 30, and the clock is operated in a counterclockwise state without switching back. Also, from no cutback,
To return to the previous state, a switching request is output (or a command is sent) to the node fixed at “Q = 9” to release “Q = 9”, and the quality management table from the transmission path is used. Can transition. And by switching the strap,
It is possible to use not only the method without switching back but also the method with switching back to return to the previous state at the time of failure recovery.

As described above, in the clock path switching method according to the present embodiment, when a failure occurs, the synchronization message transmission side does not fix the synchronization message to a value at which the clock path does not transition, but instead causes the optical transmission path failure. The detected synchronous message receiving side performs a fixed processing of the synchronous message, and is a clock path switching method that can be switched back by strap switching or the like. Therefore, the system operation is more flexible than the conventional method.

Further, since the synchronization message is transferred using the surplus bits of the OH of the SDH, a new signal line is not required.

[0031]

As described above, according to the present invention, when a failure occurs, the surplus bits of the SDH, which
Since the process of restoring the clock path switching of the node is performed without performing the method of fixing the synchronization message through H and transferring it to the entire system, there is an effect that the clock switching time of the entire system can be reduced.

In addition, the conventional automatic switchback can be performed by switching the strap and the like, and it is possible to select whether or not the switchback is performed. Therefore, there is an effect that the clock system can be made flexible.

Further, since the synchronous message is transferred using the excess bits of the OH of the SDH, there is an effect that a new signal line is not required.

[Brief description of the drawings]

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

FIG. 2 is a state diagram showing a state of a clock path in the system at the time of a transmission line failure in the present embodiment.

FIG. 3 is a state diagram showing a state of a clock path in the system at the time of recovery from a transmission line failure in the present embodiment.

FIG. 4 is a state diagram showing a state of a clock path in the system at the time of a transmission line failure in the first conventional example.

FIG. 5 is a state diagram showing a state of a clock path in a system at the time of a transmission line failure in the second conventional example.

[Explanation of symbols]

 1 external clock (external CLK1) 2 external clock (external CLK2) 10 master node 20, 30, 40 slave node 50, 60 optical transmission line

Continuation of the front page (72) Inventor Takashi Shibamata Miyagi NEC Corporation 2nd Thunder God, Yoshioka, Yamato-cho, Kurokawa-gun, Miyagi Prefecture

Claims (3)

[Claims] 1. A master node that receives a plurality of synchronization clocks from another network and sends out the same to a network of a synchronous digital hierarchy (SDH) double-ring optical transmission line, and a master node connected to the network. In a clock path switching method including a plurality of slave nodes operating on an internal clock synchronized with a clock received from one of the optical transmission lines, the master node and the plurality of slave nodes each include the plurality of synchronization clocks and A priority table that defines the priority of use of the internal clock, and a quality management table in which a predetermined code indicating a quality priority and a failure of each clock when selecting each of the clocks is stored, The surplus bits of the overhead (OH) of the SDH of the network The quality ranking of the selected clock in the quality management table is transferred as a synchronization message, and if a failure occurs in one of the double rings, a quality code indicating the failure is transferred as a synchronization message, even if the failure is recovered. A clock path switching method characterized by continuing the operation of the system on the optical transmission line of the other ring without any failure. 2. A plurality of synchronization clocks are input from another network, one of the plurality of synchronization clocks is selected, synchronized, and transmitted to an optical transmission line of a synchronous digital hierarchy (SDH) bidirectional ring. A clock is extracted from the optical transmission line in one direction of the SDH ring and an internal CLK synchronized with the extracted clock operates internally, and the clock is transmitted through the optical transmission line in the other direction. A plurality of slave nodes that transmit to the other slave node or the master node, and a priority order in which the master node and the slave node use the plurality of synchronization clocks and the internal CLK. A table and a predetermined code indicating a quality order and a failure when selecting the plurality of synchronization clocks and the internal CLK are described. The SDH overhead (O / O) is provided to the master node and the slave node in order to automatically select an optimal clock path as a system based on the stored quality control tables.
H) The code number of the selected quality order in the quality management table is transferred as a synchronization message to the surplus bits of H). Further, the entire system operates with one clock of the master node, A clock path that is fixed at a node where a failure has occurred so as not to transition to the clock path on the side of the optical transmission path after the switching of the clock path after the occurrence of the failure, and returns to the original clock on the side of the optical transmission path again after recovery from the failure of the optical transmission path A clock path switching method, which performs a process that does not execute switchback. 3. The clock path according to claim 2, wherein when the failure of the optical transmission line is recovered, the clock path can be switched back to the original optical transmission line. Switching method.