JP3000466B2 - Clock synchronization method for ring network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] Transmission from a master node (M) having a reference clock to subordinate nodes (S ₁ , S ₂ ...) Arranged in a ring form clockwise and counterclockwise for subordinate synchronization relates spare system clock synchronization method for synchronizing clock of the working system when switching the road to the spare system clock CK ₂ when duplexed to the working system and the clock WK supplied as a spare system clock CK ₁ failure, the Prevents disturbance of clock synchronization in the ring network when a failure occurs in the working system clock received from the main node M at the subordinate node, and keeps the recovery time of the line failure within the high-speed hardware switching time. For this purpose, a plurality of slave nodes are slave-synchronized with a reference clock supplied from a master node arranged on a duplexed ring network in which the working system and the protection system are respectively reversed. In the clock synchronization method of the ring network, a switch for selecting a working reference clock and a protection clock supplied from a main node to each slave node; When there is no signal, a pull-in oscillator which self-oscillates a signal having almost the same frequency as that of the reference clock is provided. When the working reference clock becomes no signal, the switch is switched to the backup reference clock by the switch. Until,
The signal from the pull-in oscillator is transmitted to an adjacent node as a reference clock for the working system and the standby system.

[Industrial applications]

According to the present invention, when a digital signal transmission path is formed in a ring shape, such as a LAN (Local Area Nntwork) or a ring network conforming to the digital hierarchy recommended by CCITT, the digital signal transmission line is arranged in a ring shape from a main node M having a reference clock. Nodes S ₁ , S ₂ ... The transmission line is duplicated clockwise and counterclockwise for subordinate synchronization, and backup clock CK is supplied in the event of failure of clock CK ₁ of the current system that supplies clocks as the current system and the standby system. _{The present invention} relates to a clock synchronization method for synchronizing clocks of a standby system and a working system when switching to ₂ .

[Conventional technology]

The ring-shaped transmission path, a plurality of dependent nodes of the ring from the primary node M S _1, S ₂ ··· S clock to be supplied to the _n-1 is as generally in Figure 4, transmission path working and protection 2 in the system
, The synchronization clock to each of the subordinate nodes S ₁ , S ₂ ... Normally depends on, for example, a clockwise working clock CK ₁ (solid line) from the main node M, active-system clock CK ₁ clockwise is the case where an obstacle, has a configuration in which synchronization dependent switch counterclockwise of the standby clock CK ₂ (dotted line) is taken.

[Problems to be solved by the invention]

In the ring network, the failure of the working system clock CK ₁ Given procedure until switching to the spare system clock CK _2, in the fifth diagram of LAN-type ring network, for each dependent node S _1, S ₂ · · · the operating state, has a monitoring collectively by the network monitoring device NSP main node M, for example when an obstacle between the subordinate node S ₂ and the dependent node S _n-1 is temporarily dependent nodes S ₁ , S all ₂ · · · · S _n after disconnecting from the primary node M, connected to the subordinate node S _1, S ₂ ··· S _n sequentially one by one primary node M, sequentially in the software previously prepared The normal and abnormal judgments are made and the location of the failure is detected. For this reason, there has been a problem that it takes too much time to recover the failed part.

In the ring network conforming to the digital hierarchy recommended by the CCITT shown in FIG. 6, the main node M does not judge the failure by the network monitoring device NSP, but switches the clocks when a failure occurs between the nodes A, B and C. Signal C
Switching to the standby system is performed autonomously according to the condition of SEL (in the figure, a failure occurs between the master node M and the subordinate node A patent).
This switching does not rely on software as in the case of the above-mentioned LAN type, but switches to the standby system by hardware using the high-speed switch SW, thereby shortening the time for failure recovery.

However in case of a failure of the active system is primarily because the node clock CK ₁ of the primary system for receiving the M is the cross-sectional, dependent nodes are in the input mode of the clock CK ₁ subordinate synchronization therewith
A, B, clock nascent PLOa in C becomes immediately period out by the cross-sectional of the clock CK _1, oscillates at a preset self oscillation accuracy, thereby resulting the first disturbance in the clock generator PLOa, the dependent When the disturbance of the clock generator PLOa of the node sequentially propagates to the lower nodes, there is a problem that the recovery of the failed part is delayed.

An object of the present invention is to prevent disturbance of clock synchronization when a failure occurs in a working clock at each subordinate node S that subordinately synchronizes its own clock generator to a clock received from a main node M, and to prevent a line failure from occurring. The recovery time is kept within the switching time of the high-speed hardware switch.

[Means for solving the problem]

According to the present invention, there is provided a ring in which a plurality of subordinate nodes subordinately synchronize to a reference clock supplied from a main node arranged on a ring network in which a working system and a standby system are respectively duplicated on transmission lines of opposite directions. In the clock synchronization method of the network, a switch for selecting a working system reference clock and a protection system clock supplied from the main node to each subordinate node; subordinate synchronization when the reference clock is a signal; When there is no signal, a pull-in oscillator which self-oscillates a signal having almost the same frequency as the frequency of the reference clock is provided, and when the working system reference clock becomes no signal, the switch is switched to the standby system reference clock by the switch. During
The signal of the drop oscillator is transmitted to an adjacent node as a reference clock of a working system and a protection system, and is achieved by a clock synchronization method of a ring network.

[Action]

In the principle diagram of FIG. 1 showing a basic configuration of a subordinate node of the clock synchronization system of the ring network of the present invention, a switch (SW) is a subordinate node of a ring network in which transmission paths are arranged in a ring shape, for example, a node S _1. , For example, a clockwise working clock supplied from the main node M
Receiver working to receive the CK ₁ (OR1) 3 ₁ output clock
In case of a failure of CK _1, counterclockwise the standby clock CK ₂ receivers (OR @ 2) 3 ₂ of switching the output clock CK _2.

Pull oscillator (PLO) 2, the switch (SW) 1 but oscillates dependent synchronism with the advance input of the selected working system clock CK _1, the failure of the clock CK ₁ by a switch (SW) 1, spare receiver vessel (OR @ 2) 3 ₂ is during the switch to the backup system clock CK ₂ counterclockwise received is self-oscillating signal of the same frequency almost the frequency of the clock CK ₁ with high stability.

Then pull oscillator (PLO) 2 transmitters of self-oscillating output current (OS1) 4 ₁ and spare transmitter (OS2) to 4 ₂ to clockwise and counterclockwise adjacent node S _2, S _3, M, which until the active system taking the clock CK ₁ and a standby system clock CK ₂ is instead sent.

As mentioned above, the clock synchronization method of the ring network of the present invention, the transmitter working when the working system clock CK ₁ having received fails in the dependent node (OS1) 4 ₁ and spare transmitter ( OS2) 4 ₂ is, working system pull oscillator (PLO) 2 which had been slave synchronization with the frequency of the clock CK ₁ is self-oscillating by also dependent clock accuracy when the interruption of the clock CK ₁ until then,
By transmitting the oscillation output to the adjacent nodes S ₂ , S ₃ , M, disturbance of clock synchronization in the adjacent nodes S ₂ , S ₃ is prevented. And the problem is solved.

〔Example〕

FIG. 2 is a block diagram showing the configuration of the clock synchronization system of the ring network according to the embodiment of the present invention, and FIG. 3 is a time chart for explaining the operation thereof. ₆ is a time chart of the output of the pull-in oscillator PLO at the time of the fault of ₁ .

Each subordinate node of the ring network of the embodiment of FIG.
Each of S ₁ , S ₂ , and S ₃ is provided with a switch SW, to which the PLO of the pull-in oscillator 2 is connected. This pull oscillator when there is active-system clock CK ₁ selected beforehand oscillates subordinate synchronization with the clock CK _1, the clock C
Input of K ₁ is self-oscillating signals a high stability of the same frequency almost the frequency of the clock CK ₁ also when a cross.

And each dependent node, the third view as the time chart (1) of the OR1 clock, active-system clock CK ₁ clockwise the receiver OR1 working had received an obstacle, when a clock loss is By switching the switch SW of each node from contact point to contact point, the time chart (4)
As in the SW operation, the output changes from the state of “L” to the state of “H”, and the counterclockwise protection system clock C received by the spare receiver OR2 such as (2) the OR2 clock in the time chart.
Although switched to K _2, in between, during the free-running time T shown in (4) of the timing chart, as shown in (3) PLO output clock of the timing chart, the self oscillation output of pull oscillator PLO is the active system Transmitter OS1 and standby transmitter OS2
And sent to the adjacent node, clockwise working clock
Only T between the CK ₁ until switched to the standby system clock CK ₂ counterclockwise, since the working system clock CK ₁ maintains a state before the disconnection, pull oscillator between changeover switch PLO
Has no effect on adjacent nodes. When the switching of the switch SW is completed, the pull-in oscillator
PLO even if adapted to slave synchronization to the standby system clock CK ₂ counterclockwise received by receiver OR2 of the standby system, the protection system clock CK ₂ is clockwise working system clock received by the receiver OR ₁ active system at the same frequency as CK _1, the frequency of the output of the pull-in oscillator PLO immediately before receiving the supply of the protection system clock CK ₂ is not out of the same as the frequency of throat working system clock CK ₁ N殆, ring by switching the switch SW Eg nodes in the network
At the subordinate nodes S ₁ and S ₃ adjacent to S ₂ , there is no problem because re-drawing that causes disturbance does not occur.

〔The invention's effect〕

As described above, the working clock CK according to the present invention is used.
Oscillator is oscillated in subordinate synchronization when ₁ is input, and a self-oscillation PLO that self-oscillates with subordinate synchronous clock accuracy is provided at each subordinate node of the ring network until switching to the standby clock even when CK ₁ is cut off. Switch SW
Does not occur even after switching to the standby system clock, the disturbance to the lower node due to the interruption of the active system clock is eliminated.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a basic configuration of a subordinate node of a clock synchronization system of a ring network according to the present invention. FIG. 2 is a block diagram showing a configuration of a clock synchronization system of a ring network according to an embodiment of the present invention. FIG. 4 is a time chart for explaining the operation of the embodiment of the present invention. FIG. 4 is a clock configuration diagram of a conventional ring network. FIG. FIG. 6 is a block diagram of a transfer method of a switching signal when a clock failure occurs in a conventional CCITT ring network. Switch 1 for switching the received working system clock and a standby system clock in the figure, pull oscillator 2 to weakly bind to the active-system clock, 3 _1, 3 ₂ the receiver of the active system clock and a standby system clock of the receiver, 4 _1, 4 ₂ are transmitter and a standby system transmitter of the active system.

Claims (1)

(57) [Claims] 1. A ring network in which a plurality of subordinate nodes subordinately synchronize with a reference clock supplied from a main node disposed on a ring network in which a working system and a standby system are respectively duplicated on transmission lines of opposite directions. A switch for selecting a working reference clock and a protection clock supplied from a main node to each subordinate node, and subordinate synchronization when the reference clock is a signal, and the reference clock is In the case of a signal, a pull-in oscillator which self-oscillates a signal having almost the same frequency as the frequency of the reference clock is provided, and when the working system reference clock becomes no signal, the switch is switched to the backup system reference clock by the switch. During this time, the signal of the pull-in oscillator is transmitted to an adjacent node as a reference clock for a working system and a protection system. Clock synchronization method of work.