JP2000324148A - Subordinate synchronization changeover system and method for loop communication network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a subordinate synchronization changeover system by which a clock path is switched through integrated control from a terminal station device without causing a block state of the clock path in a loop network on the occurrence of a fault of a transmission line of an active system. SOLUTION: In this subordinate synchronization method for loop network, on the occurrence of a fault in a transmission line, when a clock signal is extracted from the active system of transmission lines in duplicate and one terminal station device is operated by a master clock in the loop network and the other terminal station devices are operated in subordination with the master clock, each of the terminal station devices following the subordinate synchronization operation is operated by a self-running clock signal in response to the fault of the transmission line and then is operated in subordinate synchronization with the master clock signal extracted from the active system transmission line in response to the restoration of the fault in the transmission line. Thus, occurrence of a clock block state between two adjacent stations is prevented from occurring due to the fault in the active system transmission line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subordinate synchronous switching system and system in a loop communication network, and more particularly to a subordinate synchronous switching system and a method thereof. A loop-like network including a plurality of network synchronizers, each of which is provided with a corresponding one of the terminal devices and generates a clock signal for network synchronization of the corresponding terminal device based on an extracted clock signal from the corresponding terminal device. The present invention relates to a dependent synchronization switching method in a communication network.

[0002]

2. Description of the Related Art In subordinate synchronous transmission in a loop network, when each device synchronizes by extracting a clock signal from an operating system of a duplicated transmission line, one device constituting the loop network becomes a master. The clock operates, and other devices operate while being dependent on the clock. FIG. 4 shows a schematic system configuration of such a configuration.

Referring to FIG. 1, there is shown an example of a ring-shaped SDH (Synchronous Digital Hierarchy) transmission network in optical communication, in which an N-system (working system) and an E-system (standby system) have a duplex transmission line. It is. A plurality of terminal devices 11 to 14 are arranged in the middle of the duplex ring transmission line, and network synchronizers 21 to 24 are provided corresponding to each of these terminal devices. Each terminal device 1
1 to 14 operate in synchronization with clock signals CLK1 to CLK4 generated and output from the corresponding network synchronization devices 21 to 24, respectively.

A network synchronizer 21 corresponding to the terminal device 11 operates as a master network synchronizer, and a clock signal CLK1 generated from the master network synchronizer 21 serves as a master clock signal. Synchronizers 21 and 2
4 operates as a slave. That is, the terminal device 11 transmits a data signal synchronized with the master clock signal CLK1 from the master network synchronizer 21 and sends the data signal to both transmission lines, and the other terminal devices 12 to 14 transmit the data signal. Each of the corresponding network synchronizers 22 to 24 extracts a clock signal from the received data obtained from the path and supplies the clock signal to the corresponding network synchronizer 22 to 24. Each of the corresponding network synchronizers 22 to 24 synchronizes with the supplied clock signal. To 14 synchronizing clock signals CLK2 to CLK4.

In this case, two clock paths Ni, Ei (i indicates 2, 3, 4) are provided between each of the terminal devices 12 to 14 and each of the network synchronizers 22 to 24. As shown, the output path of the clock signal extracted from the N-system data signal by each terminal device is Ni, and the output path of the clock signal extracted from the E-system data signal is Ei.

In such a network, for example, if an active system (in this example, N system) transmission line failure occurs at a location A indicated by "x", the terminal device 13 in which the failure has occurred has an active system failure. When the switching occurs, the clock path is also switched from N3 of N system to E3 of E system. At this time, the terminal device 13
Is dependent on the clock signal of the clock path from the terminal device 14 which is the opposite station where no failure has occurred, but since the operation system in the terminal device 14 has not changed, the terminal device 14
Depends on the clock path of the terminal device 13. As a result, a closed state of the clock path is generated between the terminal devices 13 and 14, and the subordinate synchronization with the master clock cannot be obtained.

[0007]

In the event that a failure occurs in the active transmission line, the slave station is provided on the slave side in order to avoid the occurrence of the above-described blockage of the clock path. The clock path of the device is not switched, and the device is operated in a clock free running state. In this case, the switching of the clock path of the loop network has been manually performed by the maintenance person so that the blocked state does not occur.

[0008] An object of the present invention is to switch a clock path by collective control from a certain terminal device without causing a blocked state of a clock path in a loop network when an active transmission line failure occurs. An object of the present invention is to provide a dependent synchronization switching system and a method thereof.

[0009]

According to the present invention, one of a plurality of terminal devices constituting a ring transmission line having a duplex configuration operates synchronously with a master clock signal.
Another terminal device is a slave synchronization switching system in a loop communication network configured to perform slave synchronization in accordance with an extracted master clock from the transmission line, and each of the other terminal devices has a transmission line failure. In response to the operation by the free-running clock signal, and subsequently dependently synchronized with the extracted clock signal from the transmission line of the system instructed from outside via the one terminal device. A dependent switching scheme is obtained.

According to the present invention, a ring-shaped transmission line having a duplex configuration having first and second paths for transmitting data synchronized with a master clock signal, and each of the ring-shaped transmission lines is disposed in the middle of these ring-shaped transmission lines, A plurality of terminal devices each having a function of extracting the first and second clock signals from each transmission data of the first and second transmission paths, and a corresponding terminal device provided corresponding to these terminal devices; And a plurality of network synchronization devices for generating a network synchronization clock signal for the corresponding terminal device based on one of the first and second clock signals extracted from the slave synchronization switching system in the loop communication network. Wherein each of the terminal devices has means for shutting down the output of the first and second clock signals in response to a failure in one of the first and second transmission lines, Each of the network synchronizers has a corresponding end Means for controlling the network synchronization clock signal generating means to a self-running state in response to disconnection of the first and second clock signals from the apparatus, and supplying the self-running clock signal to a corresponding terminal apparatus. And a dependent synchronous switching system characterized by the following.

Each of the terminal devices responds to the recovery from the failure of one of the first and second transmission lines, and outputs the extracted clock signal from the reception signal of the transmission line of the system specified from the outside. And a means for outputting to the corresponding network synchronization device, wherein each of the network synchronization devices synchronizes the network synchronization clock signal generation means with a clock signal supplied from the corresponding terminal device. It has a means for outputting a clock signal of the network synchronization clock signal generating means to the corresponding terminal equipment.

According to the present invention, a ring transmission line having a duplex configuration having first and second paths for transmitting data synchronized with a master clock signal, and each of the ring transmission lines is disposed in the middle of these ring transmission lines, A plurality of terminal devices each having a function of extracting the first and second clock signals from each transmission data of the first and second transmission paths, and a corresponding terminal device provided corresponding to these terminal devices; And a plurality of network synchronizers for generating a network synchronization clock signal for the corresponding terminal device based on one of the first and second clock signals extracted from the subordinate synchronization switching method in the loop communication network. Disconnecting the output of the first and second clock signals in response to one of the first and second transmission lines in each of the terminal devices; In each of the devices Controlling the network synchronization clock signal generating means to a free running state in response to the disconnection of the first and second clock signals from the corresponding terminal device, and supplying the free running clock signal to the corresponding terminal device; And a dependent synchronization switching method is provided.

In each of the terminal devices, in response to restoration of one of the first and second transmission lines,
Outputting a clock signal extracted from a reception signal of a transmission path of a system instructed from the outside to a corresponding network synchronization device, and further comprising, in each of the network synchronization devices, a supply from a corresponding terminal device. A step of synchronizing the network synchronization clock signal generation means with a clock signal and outputting the clock signal of the network synchronization clock signal generation means at this time to the corresponding terminal device.

The operation of the present invention will be described. In the slave synchronization method in the loop network, a clock signal is extracted from the operating system of the duplicated transmission line, and each terminal device is operated in synchronization with the extracted clock signal, and one terminal device operates on the master clock in the loop network. However, when the other terminal devices operate in accordance with the master clock, it is possible to avoid the occurrence of a clock blockage state between two adjacent stations due to a failure in the active transmission line, and to reduce the clock path due to the transmission line failure. Are switched by collective control.

[0015] For this purpose, each of the terminal stations performing the subordinate synchronous operation is made to operate by the free-running clock signal in response to the transmission path failure, and is externally instructed in response to the restoration of the transmission path failure. And operates in synchronism with the extracted master clock signal from the transmission line.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic system configuration of a communication network of a ring-shaped slave synchronization system having a duplex configuration to which the present invention is applied, and the same parts as those of FIG. This example is also an example of the SDH network in the optical communication as described in the related art, but is not particularly limited thereto.

In FIG. 1, a network synchronizer 21 supplies a master clock to this loop network through a terminal device 11. The terminal device 11 performs N-system selection control and E-system selection control for each of the terminal devices 12 to 14 by using an empty bit of the main signal by external control. Each network synchronization device 22-
Numeral 24 receives N-system and E-system clock paths Ni and Ei (i is 2 to 4) from corresponding terminal devices 12 to 14, and both N-system and E-system clock paths receive clock signals. When both are normal, the signal of the N-system dependent clock path is used. When the N-system clock path is abnormal and the E-system clock path is normal, the signal of the N-system dependent clock path is used. When both system clock paths are abnormal, the signal of the free-running clock path that does not depend on either
It is supplied to each of the terminal devices 12 to 14, respectively.

Each of the terminal devices 12 to 14 detects an E-system transmission line abnormality and an N-system transmission line abnormality in the loop network using the vacant bits of the main signal, and the N-system selection control from the terminal device 11 is performed. If an N-system transmission line abnormality occurs in the loop network after the above operation, the output of both the N-system and E-system clock paths to the network synchronizer is stopped. Make the output of the system clock path a normal output.

When an E-system transmission line abnormality in the loop network occurs after the E-system selection control from the terminal station device 11, the N-system and E-system clock path output to the network synchronization device is output. Is stopped, and when the E-system transmission path abnormality is recovered, the output of the E-system clock path is set to a normal output. With such a switching method, the switching of the clock path of the loop network can be performed collectively.

This will be described in more detail. In FIG. 1, after the terminal station device 11 is selectively controlled in N system by external control, a main signal synchronized with the master clock from the terminal station device 11 is transmitted to the N system by using the network synchronization device 21 as a master clock. / E system. Each terminal device 12-14 is N
An N-system clock signal is extracted from the main signal of the system and extracted to the N-system clock path ni, and an E-system clock signal is extracted from the main signal of the E system and output to the E-system clock path Ei.

Each of the network synchronizers 22 to 24 synchronizes with a clock signal supplied from a clock path to generate a clock signal CL.
K2 to K4 are generated, and the generated clock signals CLK2 to CLK4 are supplied to the terminal devices 12 to 14, respectively.
Each of the terminal devices 12 to 14 receives these clock signals CLK2 to CLK2.
4 are output to the N-system / E-system transmission paths, respectively.

Each of the network synchronization devices 22 to 24 is
It is assumed that the clock signals of the N-system clock paths 〜14 to 選 択 14 are respectively selected, and the N-dependent slave clock signals are supplied to the terminal devices 12 to 14. In this state, if the transmission line abnormality A occurs in the N-system transmission line from the terminal devices 12 to 13, the terminal device 13 cuts off the clock path output of both systems, and the corresponding network synchronization device 23 is in the self-running state. Becomes Similarly, each of the terminal devices 12 and 14 also shuts off the clock paths of both systems based on the N-system transmission line abnormality occurrence information in the loop network from the vacant bits of the main signal, and the network synchronizers 22 and 24.
Also becomes self-propelled.

As described above, when the E-system selection control is performed on the terminal device 11 in a state where all the network synchronizers in the loop network are self-running, the E-bit is transmitted using the empty bit of the main signal. The system selection control is performed, and each of the terminal devices 12 to 14 is switched from the both-system clock path output cutoff state to the state where the E-system clock path is normally output. Since the E-system clock path is normally output, each of the network synchronizers 22 to 24 supplies a clock signal of a clock path dependent on the E-system clock path to each of the terminal devices 12 to 14.

As described above, the switching of the clock path due to the transmission path failure is notified to each terminal device of the information on the occurrence of the transmission path failure at some point by using the vacant bit of the main signal. The synchronizer turns off the outputs of the clock paths of both systems, thereby making the clock signal state of the clock path in the loop network free-running, and then controlling the E-system selection control from the terminal device to which the master clock is distributed. By performing the above, it is possible to switch to the clock path of the transmission line of the protection system by the collective control.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a network synchronizer 21 supplies a master clock to this loop network. Each terminal device 12-14
Is caused by an N-system or E-system transmission line abnormality, external control from the terminal device 11, N-system selection control / E
System selection control and the like are notified. The network synchronizers 22 to 24 receive the output supply of the N-system and E-system clock paths from the terminal devices 12 to 14, and output the clock signals CLK2 to CLK4 dependent on the clock signal of one of the paths. 14 respectively.

In this loop network, the network synchronization device 21 is used as a master clock after the terminal device 11 is N-system selection controlled by external control. The terminal device 11 passes a main signal synchronized with the master clock to the N system / E system. Each of the terminal devices 12 to 14 extracts the output of the N-system / E-system clock path from the main signal and outputs it to each of the network synchronizers 22 to 24 according to the flow shown in FIG.

Each of the network synchronizers 22 to 24 supplies a clock path output to each of the terminal devices 12 to 14 in accordance with the flow of FIG. In this state, if a transmission line abnormality occurs in the N-system transmission line from the terminal devices 12 to 13, the terminal device 13 does not perform the E-system selection control as shown in the flow of FIG. Due to the occurrence of an N-system transmission path error in the network,
The output of both system clock paths is cut off (steps S1, S2,
S3). Similarly, the output of both system clock paths is cut off for the other terminal devices 12 and 14 according to the flow of FIG.

The network synchronizer 23 follows the flow of FIG.
Since the N-system clock path abnormality and the E-system clock path abnormality have occurred, they become self-running (steps S11, S12, S12).
13). Similarly, the network synchronizers 22 and 24 become self-running according to the flow of FIG. 3 because of the occurrence of the N-system clock path abnormality and the E-system clock path abnormality.

At this time, each of the network synchronizers is operated in a self-running manner, and is operated by four types of clock sources in this loop network. Since the self-propelled state is guaranteed, the main signal is operated without error. When the E-system selection control is performed on the terminal device 11 in the above state, the terminal device 14
As shown in the flow, since the N-system selection control is not performed and the E-system transmission path abnormality does not occur in the network, the E-system clock path becomes normal output after both system clock paths are cut off (step S5). S6, S8). Other terminal devices 12,
13, the N-system selection control is not performed, and the E-system transmission path abnormality does not occur in the network. Become.

The network synchronizer 24 follows the flow of FIG.
Since the N-system clock path is abnormal and the E-system clock path is normal, the E-system clock path is subordinated from self-running (steps SS11, S12, and S15). Other network synchronizer 2
Similarly, according to the flow shown in FIG. 3, the N-system clock paths 2 and 23 become self-running and become dependent on the E-system clock path because the N-system clock path is abnormal and the E-system clock path is normal.

[0031]

As described above, according to the present invention, the N-system and E-system transmission path abnormalities, the external control from the terminal equipment, and the N-system selection control / E-system selection are performed by using the vacant bits of the main signal. The following effects can be obtained by notifying each terminal device of control and the like, and controlling the clock path output to each network synchronization device by each terminal device.

That is, when a failure in the transmission line of either system occurs, the terminal equipment that detects the failure cuts off the clock path output of the N system and the E system, thereby outputting the clock path output to the terminal equipment. The network synchronization device supplying the network synchronization becomes self-running, thereby avoiding a network synchronization blockage that occurs when the network synchronization device immediately switches the clock path.

Further, by controlling the clock output to the network synchronization device on the terminal device side, the operation of the network synchronization device does not require a special flow operation particularly considering the loop network. It is possible to realize a synchronous network without introducing a device. Furthermore, since the clock path in the loop network can be switched by the collective control in the terminal station device,
A highly maintainable and reliable synchronous network can be realized.

[Brief description of the drawings]

FIG. 1 is a system schematic diagram of a ring network having a duplex configuration to which the present invention is applied.

FIG. 2 is a flowchart showing the operation of the terminal device.

FIG. 3 is a flowchart showing the operation of the network synchronization device.

FIG. 4 is a schematic system diagram for explaining a conventional technique.

[Explanation of symbols]

 11-14 Terminal equipment 21-24 Network synchronizer

Claims (7)

[Claims] 1. A terminal device among a plurality of terminal devices constituting a ring transmission line of a duplex configuration operates synchronously with a master clock signal, and another terminal device extracts a master signal from the transmission line. A slave synchronization switching system in a loop communication network configured to operate in synchronization with a clock, wherein each of the other terminal devices operates by a free-running clock signal in response to a transmission line failure, A slave switching system, wherein the slave switching system is slaved to an extracted clock signal from a transmission line of a system instructed from outside via the one terminal device thereafter. 2. A ring transmission path having a duplex configuration having first and second paths for transmitting data synchronized with a master clock signal, and each of the first and second ring transmission paths is disposed in the middle of the ring transmission path. A plurality of terminal devices each having a function of extracting the first and second clock signals from each transmission data of the second transmission line, and the terminal devices provided for these terminal devices and extracted from the corresponding terminal devices. A slave synchronization switching system in a loop communication network including a plurality of network synchronization devices that generate a network synchronization clock signal for the corresponding terminal device based on one of the first and second clock signals, Each of the terminal devices has means for shutting down the output of the first and second clock signals in response to a failure of one of the first and second transmission lines, Each is from the corresponding terminal equipment Means for controlling the network synchronization clock signal generating means in a self-running state in response to the disconnection of the first and second clock signals, and supplying the self-running clock signal to a corresponding terminal device. Dependent synchronous switching system. 3. The terminal device according to claim 2, wherein each of the terminal devices has means for outputting an extracted clock signal from a received signal on a transmission line of a system specified from the outside to a corresponding network synchronization device. Dependent synchronous switching system. 4. Each of the network synchronization devices synchronizes the network synchronization clock signal generation means with a clock signal supplied from a corresponding terminal station device, and converts the clock signal of the network synchronization clock signal generation means at this time. 4. The slave synchronization switching system according to claim 3, further comprising means for outputting to the corresponding terminal equipment. 5. A ring-shaped transmission line having a duplex configuration having first and second paths for transmitting data synchronized with a master clock signal, and each of the first and second ring-shaped transmission lines is disposed in the middle of these ring-shaped transmission lines. A plurality of terminal devices each having a function of extracting the first and second clock signals from each transmission data of the second transmission line, and the terminal devices provided for these terminal devices and extracted from the corresponding terminal devices. A slave synchronization switching method in a loop communication network including a plurality of network synchronization devices that generates a network synchronization clock signal for the corresponding terminal device based on one of the first and second clock signals, In each of the terminal devices, in response to a failure of one of the first and second transmission lines, turning off the output of the first and second clock signals; and in each of the network synchronization devices, , Compatible terminal equipment Controlling the network synchronization clock signal generating means in a self-running state in response to the disconnection of the first and second clock signals, and supplying the self-running clock signal to the corresponding terminal device. A slave synchronous switching method. 6. In each of the terminal devices, in response to restoration of a failure of one of the first and second transmission lines, an extracted clock signal from a reception signal of a transmission line of a system specified from outside is received. The method according to claim 5, further comprising the step of outputting to a corresponding network synchronization device. 7. In each of the network synchronization devices, the network synchronization clock signal generation means is synchronized with a clock signal supplied from a corresponding terminal station apparatus, and the clock signal of the network synchronization clock signal generation means at this time is used. 7. The slave synchronization switching method according to claim 6, further comprising the step of outputting to the corresponding terminal device.