JP3592261B2 - Clock path switching method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a clock path switching method in a ring network, and more particularly to a clock path switching method when a failure occurs in a ring network requiring a network synchronization configuration.
[0002]
[Prior art]
In this type of conventional clock path switching method, it is desired to suppress the occurrence of clock path switching as much as possible while avoiding entering an independent synchronization state using an internal clock with a low quality order. To this end, a quality order is assigned to each selectable clock, and if a failure occurs in the clock being used, the clock path of the next quality order is switched, and the quality order of the failed clock is lowered. As a result, a method is employed in which automatic switchback is not performed even if the failure of the upper clock is recovered thereafter, and operation is continued while avoiding unnecessary momentary interruption of the main signal. However, in this case, the following problems remain.
[0003]
The first problem is that even if the higher-level clock in which the fault has occurred is recovered, there is no switching back, so that the operation is performed using a clock of lower quality order, and the reliability in the network is low. It is to be a system operation.
[0004]
The second problem is that since a method is employed to avoid unnecessary switching by lowering the quality order of the clock in which a failure has occurred, a quality management table that updates the quality order when the occurrence and recovery of the failure occur repeatedly. Is complicated and a large area must be secured.
[0005]
[Problems to be solved by the invention]
The above-described conventional clock path switching method has a drawback that, even when the higher-order clock in which a failure has occurred is restored, the switching is not performed, so that the operation is performed using a clock with a lower quality order. Further, by lowering the quality order of the clock in which the fault has occurred, there is a disadvantage that when the occurrence and recovery of the fault occur repeatedly, the quality management table for updating the quality order becomes complicated and a large area must be secured.
[0006]
An object of the present invention is to eliminate such a conventional drawback by temporarily lowering the quality rank of a clock by one rank when a failure occurs in a clock having a higher rank and then recovered. Switching back can be prevented when operating with clocks of the same initial quality rank. Then, when a failure occurs in the clock after switching, the clock lowered by one rank is returned to the original quality rank. Another object of the present invention is to provide a clock path switching method capable of performing a highly reliable system operation by selecting a clock having the highest quality order from clocks that can be selected at that time.
[0007]
[Means for Solving the Problems]
According to the clock path switching method of the present invention, a master node that receives a plurality of synchronization clocks from another network and transmits the same to a synchronous digital hierarchy (SDH) double-ring optical transmission path, A sub-master node that receives a plurality of synchronization clocks from another network on behalf of the master node and transmits the same to the next node via the optical transmission path; and A plurality of slave nodes operating on an internal clock synchronized with a clock received from any of the transmission lines and transmitting to the next node via the optical transmission line, wherein the master node and the sub-master node and wherein each of the plurality of slave nodes, the priority table defining priority among the synchronous clock and the internal clock selectable And a quality management table of the predetermined quality code indicating the quality ranking and disorders of the clock is stored in the case of selecting the clock and automatically selects the optimal clock path as a system based on two tables, When the sub-master node and the slave node recover from the failure in the optical transmission line, the sub-master node and the slave node change the clock from the failed optical transmission line to a lower-ranked quality rank by a rank higher in quality, and Is selected, and when a failure occurs in the optical transmission path after switching, the original quality order is restored .
[0008]
Further, each of the master node, the sub-master node, and the plurality of slave nodes selects a clock having the highest quality rank among selectable clocks, and selects a surplus bit of the overhead (OH) of the SDH. It is characterized in that the clock quality order is transmitted to the next node as a synchronization message.
[0009]
Further, the master node receives the plurality of synchronization clocks from another network, selects a clock having a high priority based on the priority table, and transmits the clock to each of the double ring optical transmission lines. It is characterized by:
[0010]
Further, the sub-master node is characterized in that the synchronization clock received by the sub-master node from another network is set to a quality lower by one rank than the synchronization clock received by the master node from another network. And
[0011]
When detecting that a failure has occurred in one of the optical transmission lines of the double ring, the sub-master node and the slave node set a quality code indicating the failure and set a quality code indicating the failure in the quality management table. , And transfers the synchronization message changed to the quality code of the switched clock to the next node.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a ring network as an embodiment to which a clock path switching method of the present invention is applied.
[0014]
The present embodiment shown in FIG. 1 receives two external clocks for synchronization (external CLK) 1 and 2 from another network, performs internal operation in synchronization with one of the clocks, and performs double optical transmission. The master node 10 transmits data to the paths 50 and 60, and the clock transmitted from the master node 10 via the optical transmission paths 50 and 60 is extracted, and the extracted clock and the external clocks 1 and 2 input from outside are extracted. A clock having a higher quality order is selected, an internal operation is performed in synchronization with the selected clock, and a sub master node 30 that sends data to the optical transmission lines 50 and 60 and another sub master node 30 via the optical transmission lines 50 and 60 The two slave nodes 20 and 40 that extract a clock transmitted from the node and perform internal operations in synchronization with the extracted clock and transmit data to the next node. It is configured Ri.
[0015]
That is, in this embodiment, the master node 10, the sub-master node 30, and the slave nodes 20, 40 are connected in a ring-shaped optical transmission line 50, 60 of a synchronous digital hierarchy (SDH) ring. Make up the network.
[0016]
The master node 10, the sub-master node 30, and the slave nodes 20 and 40 have a priority table in which the use priorities of a plurality of external clocks for synchronization 1 and 2 and an internal clock (internal CLK) are determined. A quality control table storing predetermined code numbers indicating clock quality orders or failures when selecting those clocks on the optical transmission lines 50 and 60, and selecting an optimal clock path as a system. To this end, the quality code of the selected clock is transmitted as a synchronization message to the extra bits of the overhead (OH) of the SDH to the next node.
[0017]
Next, an operation based on the clock path switching method of the present embodiment will be described in detail with reference to FIG.
[0018]
FIG. 1 shows a case where the external clocks 1 and 2 and the optical transmission lines 50 and 60 are both normal in the SDH ring network system. Here, each node is provided with, for example, a priority table in which clock priorities (P values) are set and a quality management table in which quality codes (Q values) are set as follows. .
[0019]
In the master node 10, the external clock 1 has priority 1 (P = 1), the external clock 2 has priority 2 (P = 2), the clock from the optical transmission line 50 has priority 3 (P = 3), A priority table is set in which the clock from the transmission line 60 has priority 4 (P = 4) and the internal clock has priority 5 (P = 5), and the quality code 2 (Q = 2), a quality code 5 (Q = 5) for the internal clock, and a quality code 7 (Q = 7) indicating the lowest or failure in clock selection are set in the quality management table.
[0020]
In the submaster node 30, the clock from the optical transmission line 50 has priority 1 (P = 1), the clock from the optical transmission line 60 has priority 2 (P = 2), and the external clock 1 has priority 3 (P = 1). = 3), a priority table in which the external clock 2 has priority 4 (P = 4) and the internal clock has priority 5 (P = 5), and a quality code 3 (Q = 3), a quality code 5 (Q = 5) for the internal clock, and a quality code 7 (Q = 7) for the lowest clock selection are set in the quality management table.
[0021]
For the slave nodes 20 and 40, the clock from the optical transmission line 50 is given priority 1 (P = 1), the clock from the optical transmission line 60 is given priority 2 (P = 2), and the internal clock is given priority 3 (P = 1). = 3), and a quality code 5 (Q = 5) for the internal clock and a quality code 7 (Q = 7) for the lowest clock selection are set in the quality management table.
[0022]
First, the master node 10 selects the external clock 1 (P = 1) with the highest use priority setting and operates internally, and when synchronized with the external clock 1, the quality code 2 ( Q = 2) is transmitted as a synchronization message to the slave nodes 20 and 40 via the optical transmission lines 50 and 60, respectively.
[0023]
The slave node 20 extracts the clock from the optical transmission line 50 (Q = 2) with the highest quality order, that is, the external clock 1 selected by the master node 10, and operates internally in synchronization with the external clock 1. I do. Also, the slave node 20 transfers the quality code 2 (Q = 2) to the downstream sub-master node 30 as a synchronization message to indicate that the slave node 20 is operating with the external clock 1 from the master node 10, Since operation is performed in synchronization with the external clock 1 from the master node 10, the lowest quality code 7 (Q = 7) is transmitted as a synchronization message to the master node 10 in order to prevent occurrence of loop lock timing. I do.
[0024]
The submaster node 30 extracts the external clock 1 from the optical transmission line 50 (Q = 2) with the highest quality order setting, and operates internally in synchronization with the external clock 1. Further, the sub-master node 30 transfers the quality code 2 (Q = 2) as a synchronization message to the slave node 40 to indicate that the slave node 40 is operating with the external clock 1 from the master node 10, and the slave node 20 , The lowest quality code 7 (Q = 7) is transmitted as a synchronization message to prevent the occurrence of loop lock timing.
[0025]
The slave node 40 extracts the external clock 1 from the optical transmission line 50 with the highest quality order setting, and operates internally in synchronization with the external clock 1. Also, the slave node 40 transfers the quality code 2 (Q = 2) to the downstream master node 10 as a synchronization message to indicate that the slave node 40 is operating with the external clock 1 from the master node 10, and To the node 30, the lowest quality code 7 (Q = 7) is transmitted as a synchronization message in order to prevent occurrence of loop lock timing.
[0026]
By the above operation, the master node 10, the sub-master node 30, and the slave nodes 20 and 40 perform the clockwise operation by the transmission line 50 by the external clock 1 having the highest priority and highest quality selected by the master node 10. And all nodes in the ring are synchronized.
[0027]
Next, an operation when a failure occurs in the optical transmission line 50 between the master node 10 and the slave node 20 will be described. FIG. 2 is a block diagram illustrating an operation when a failure occurs in the optical transmission line 50.
[0028]
First, when a failure occurs in the optical transmission line 50 between the master node 10 and the slave node 20, the slave node 20 operates in synchronization with the external clock 1 from the optical transmission line 50. The synchronization message for the optical transmission line 50 is fixed from quality code 2 (Q = 2) to quality code 9 (Q = 9) indicating a failure by internal processing. At this time, since the quality code 7 (Q = 7) of the clock (P = 2) from the optical transmission line 60 with the next highest priority is transferred from the submaster node 30 as a synchronization message, the quality control is performed. An internal clock (Q = 5) having a higher quality rank than the quality code 7 (Q = 7) is selected from the table, and the quality code 2 (Q = 2) to the quality code 5 (Q = 5) is transmitted.
[0029]
The submaster node 30 receives the quality code 5 (Q = 5) received from the slave node 20, the quality code 7 (Q = 7) received from the slave node 40, and the quality code 3 (Q = 3) of the external clocks 1 and 2. And switches to the external clock 1 (Q = 3) having the highest quality order, and transmits a synchronization message in which the quality code 2 (Q = 2) is replaced with the quality code 3 (Q = 3) to the slave node 40. I do.
[0030]
The slave node 40 compares the quality code 3 (Q = 3) received from the sub-master node 30 with the quality code 2 (Q = 2) received from the master node 10, and determines the optical transmission path 60 (Q = 2) is selected. Also, the slave node 40 transfers the synchronization message in which the quality code 7 (Q = 7) is changed to the quality code 2 (Q = 2) as a synchronization message to the sub-master node 30, and sends the quality code to the master node 10. The synchronization message changed from (Q = 2) to the quality code (Q = 7) is transmitted.
[0031]
The sub-master node 30 compares the quality code 2 (Q = 2) transferred from the slave node 40 with the quality code 3 (Q = 3) of the external clock 1 and determines the clock from the optical transmission line 60 having a higher quality order. Switch to work. The sub-master node 30 transfers the synchronization message, which has been changed from the quality code 7 (Q = 7) to the quality code 2 (Q = 2), as a synchronization message to the slave node 20, and sends the quality code to the slave node 40. The synchronization message changed from (Q = 3) to the quality code (Q = 7) is transmitted.
[0032]
By the above operation, the clock path of the ring network switches counterclockwise and operates. According to this switching method, the quality code transferred as a synchronization message in the node is prioritized over the clock priority set in each node, so that the clock can be shifted to a higher quality clock.
[0033]
Next, an operation when the failure of the optical transmission line 50 generated between the master node 10 and the slave node 20 is recovered will be described. FIG. 3 is a block diagram for explaining the operation of the optical transmission line 50 after the recovery from the failure.
[0034]
In the slave node 20, when the failure of the optical transmission line 50 is recovered, the quality code 2 (Q = 2) of the synchronization message with respect to the clock from the optical transmission line 50 is set to 1 from the quality code 9 (Q = 9) indicating the failure. The quality code 3 (Q = 3) whose rank has been lowered is fixed by internal processing. Further, the slave node 20 does not perform the switching because the quality order of the clock from the optical transmission line 60 is the highest in the quality code 2 (Q = 2), and performs the clockwise operation with the clock from the optical transmission line 60. continue.
[0035]
Next, an operation when a failure occurs in the optical transmission line 60 between the master node 10 and the slave node 40 will be described. FIG. 4 is a block diagram illustrating an operation when a failure occurs in the optical transmission line 60.
[0036]
First, in the slave node 40, when a failure occurs in the optical transmission line 60 between the master node 10 and the slave node 40, the optical transmission line operates in synchronization with the clock from the optical transmission line 60. The synchronization message for the path 60 is fixed from quality code 2 (Q = 2) to quality code 9 (Q = 9) indicating a failure by internal processing.
[0037]
Subsequently, at the time when the synchronization message is transferred to the slave node 20 in the same manner as at the time of occurrence of the failure in the optical transmission line 50, the slave node 20 sets the quality code for the optical transmission line 50 fixed by the internal processing. 3 (Q = 3) is restored to the quality code before the occurrence of the failure, that is, the original quality code 2 (Q = 2) received from the master node 10 as an extra bit of overhead and a synchronization message. By restoring the quality code for the optical transmission line 50, it is possible to select a clock (Q = 2) from the optical transmission line 50 with the highest quality order, and the clock is switched clockwise to operate.
[0038]
As described above, in the clock path switching method according to the present embodiment, a fault occurs in a clock having a higher quality order, and after switching from clockwise (or counterclockwise) to counterclockwise (or clockwise), a fault occurs. Even if the higher-level clock is restored, the quality order is temporarily lowered by one level with respect to the failed clock. Continue operation after switching without occurrence.
[0039]
Next, when a failure occurs in the clock to be switched to, the already recovered clock returns its quality ranking to the quality ranking before the failure occurred, and the highest quality clock can be selected from the clocks that can be selected at that time. Switch to the next clock. Further, even if a failure occurs in a plurality of clocks, it is possible to operate with the highest quality clock including the clock recovered at that time. Therefore, operation can be performed with the highest clock while avoiding unnecessary switching, and a highly reliable clock system can be operated.
[0040]
In addition, since there is no conventional switching back / with switching back, and the setting can be made by switching the strap or the like, the clock system is flexible.
[0041]
【The invention's effect】
As described above, according to the clock path switching method of the present invention, when a failure occurs sequentially in the upper clock, if the higher clock is recovered, the switching to the higher clock is performed. The effect can be obtained.
[0042]
The first effect is that operation can be performed with a clock having the highest quality order among selectable clocks in a network where a failure has been recovered, and highly reliable system operation can be performed. .
[0043]
The second effect is that even if the clock switched by the failure is restored, unnecessary switching does not occur in the case of the same quality order, so that there is no influence on the main signal.
[0044]
The third effect is that even if the occurrence / recovery of a fault is repeated, the quality order of the failed clock is limited to the internal processing of each node, so that it is not necessary to secure a large area for the quality management table. .
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a ring network as an embodiment to which a clock path switching method of the present invention is applied.
FIG. 2 is a block diagram illustrating an operation when a failure occurs in the optical transmission line 50.
FIG. 3 is a block diagram for explaining an operation after recovery from a failure in the optical transmission line 50;
FIG. 4 is a block diagram illustrating an operation when a failure occurs in the optical transmission line 60.
[Explanation of symbols]
1, 2 External clock (external CLK)
Reference Signs List 10 master node 30 sub-master node 20, 40 slave node 50, 60 optical transmission line

Claims (5)

A master node that receives a plurality of synchronization clocks from another network and transmits the same to a synchronous digital hierarchy (SDH) double-ring optical transmission path, and another one that replaces the master node when the master node fails. A sub-master node that receives a plurality of synchronization clocks from the network and transmits the same to the next node via the optical transmission line; and a clock connected to the optical transmission line and received from any of the optical transmission lines. through the optical transmission path as well as operates at an internal clock which is synchronized more structure and a plurality of slave nodes for transmitting to the next order of the nodes in the master node, each of said sub-master node and said plurality of slave nodes , the priority table defining priority among the synchronous clock and the internal clock selectable, wherein each of the case of selecting the clock And a lock quality management table predetermined quality code indicating the quality rank and failure is stored in, the clock path switching method of automatically selecting an optimum clock path as a system based on two tables, the sub-master When the failure of the optical transmission line is restored, the node and the slave node select a clock with a higher quality order based on the result of changing the clock from the optical transmission line in which the failure has occurred to a lower quality order by one rank. A clock path switching method for returning to the original quality order when a failure occurs in the optical transmission path after switching. Each of the master node, the sub-master node, and the plurality of slave nodes selects a clock having the highest quality order from among the selectable clocks, and uses the surplus bit of the overhead (OH) of the SDH to determine which clock is being selected. 2. The clock path switching method according to claim 1, wherein the quality order is transmitted as a synchronization message to the next node. The master node receives the plurality of synchronization clocks from another network, selects a high-priority clock based on the priority table, and sends the clock to each of the double-ring optical transmission lines. 3. The clock path switching method according to claim 1, wherein: The sub-master node is characterized in that a synchronization clock received by the sub-master node from another network is set to a rank lower in quality by one rank than a synchronization clock received by the master node from another network. 4. The clock path switching method according to claim 1, 2 or 3. When the sub-master node and the slave node detect that a failure has occurred in one of the optical transmission paths of the double ring, the sub-master node and the slave node set a quality code indicating the failure and set the next quality set in the quality management table. 5. The clock path switching method according to claim 1, wherein the clock is switched to a higher-ranked clock, and the synchronization message changed to the quality code of the switched clock is transferred to a next node.

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