JP2967655B2 - Clock switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to clock switching of a transmission line, and more particularly to a system in which a plurality of transmission stations having a synchronous network ring structure operate by synchronizing all transmission stations with a reference clock. It relates to a clock switching method.

[0002]

2. Description of the Related Art In a conventional network system having a synchronous network ring configuration, a master station for supplying a synchronous network reference clock is set as an upstream station, and a slave station located downstream of the master station extracts a clock component from data received from the upstream. Then, the clock distribution is performed by transmitting data to the downstream station in synchronization with the extracted clock.

FIG. 6 shows a configuration example of a conventional synchronous network ring. In the figure, g is a synchronous network reference clock, and station 0 is a master station. Each transmission station 0, 1, 2, 3, 4, 5
A clock disconnection monitoring unit and a processing unit z for inserting / determining / transferring switching information and signals are provided, and communication of clock switching information and signals is performed between transmission stations.

[0004] Under normal conditions, all stations are clockwise one.
Operating in synchronization with two reference clocks, and master station 0
Outputs the transmission line monitoring data i: 00 (hexadecimal) to the clockwise transmission line c from the processing unit z as the transmission line monitoring data i (hereinafter, H indicates hexadecimal). In the normal state, since the clockwise reference CLK is selected, the slave stations 1 to 5 receive the monitoring data 0
0 (H) is transferred to the transmission path. By returning 00 (H) from the clockwise transmission path b to the processing unit z of the master station 0, the reference clock state (clock cut) of the synchronous network can be monitored.

FIG. 7 shows the occurrence of a point C transmission path failure at the stations 3 and 4. Station 4 that detected this transmission path failure
Switches to the internal clock and clock switching information j: 04
(H) is transmitted to the transmission path b. The station 5 receives the clock switching information 04 (H) sent from the station 4, and furthermore,
(04 is the former, 0 indicates the transmission direction, and the latter, 4 indicates the station).

[0008] FIG. 8 shows that the master station 0 uses the clock switching information 04 instead of the monitoring data i: 00 (H) issued by the own station.
(H), the processing unit z sends the clock switching signal k: F0 (H) to the counterclockwise transmission line c, and the processing unit of the station 5 that receives the clock switching signal F0 (H). z indicates that the reference clock is switched from the transmission line data in the counterclockwise direction.

[0007] In the same process, as shown in FIG.
Clock switching is performed, and the internal clock transmitted by the station 4 is switched to the counterclockwise reference clock, and the clock switching is completed.

[0008]

However, in the conventional synchronous network clock switching system, when a failure occurs in the transmission line, the transmission information is transmitted, received, analyzed, and transmitted to the master station. And the clock could not be switched quickly. Also, regardless of the position of the point of failure,
Since the clock switching information was transmitted only in one direction, it took time to transfer the clock switching information to the master station.

Accordingly, it is an object of the present invention to provide a clock switching system capable of shortening the clock switching control time in view of the above-mentioned drawbacks.

[0010]

According to the present invention, a plurality of transmission stations have a ring configuration, a master station supplying a reference clock of a synchronous network is an upstream station, and a slave station located downstream of the master station is a master station. In a synchronous network system that distributes clocks by transmitting data to downstream stations in synchronization with a clock extracted from data received from the upstream,
When detecting a transmission path failure, each transmission station specifies the master station based on station chain information, which is information on the connection state of each station set in advance, and sends switching request information in the shortest path direction to the specific master station. A clock switching system is provided, comprising a transmitting unit and a switching unit for performing clock selection switching based on switching control information supplied from the specific master station.

Further, according to the present invention, a plurality of transmission stations have a ring configuration, a master station for supplying a reference clock of a synchronous network is defined as an upstream station, and a slave station located downstream of the master station receives signals from the upstream. In a synchronous network system that distributes clocks by transmitting data to downstream stations in synchronization with a clock extracted from data, each transmission station detects a transmission path failure and sets a predetermined connection state of each station. Transmitting means for specifying the master station based on station chain information as information and transmitting switching request information in the shortest path direction to the specific master station; and clock selection switching based on switching control information supplied from the specific master station. And a switching unit for passing the switching request information and the switching control information. That.

According to the present invention, there is provided station chain information which is information on the connection status of each station having a ring configuration, and when a failure occurs in a transmission line, the failure detecting station specifies the master station based on the above information. Means for transmitting clock switching information in the direction of the shortest path to the specific master station, and an intermediate station between the fault detecting station and the clock supply station having a line for passing clock switching information and a signal, wherein each intermediate station does not retransmit. The clock switching method is characterized by having the following.

[0013]

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

FIGS. 1 and 4 are schematic block diagrams of an embodiment of the present invention. FIG. 4 shows a normal state of the embodiment of the present invention. The stations 0 and 2, which are master stations, do not transmit the monitoring data of the transmission path. As a result, when there are a plurality of master stations, the processing unit a of the master station does not need to change the monitoring data and perform the communication process. Further, the processing unit a 'of the slave station transfers the clock switching information e and the CLK switching signal f to the downstream station via the communication lines d and d', so that the processing of the processing unit a 'is not necessary.

FIG. 1 shows a case where a transmission line failure occurs at point A between transmission stations 3 and 4. At this time, the stations 3 and 4 detect a failure, and the station 4 switches to the internal clock because the reference clock is cut off. Further, both stations specify the master station 0 based on the station chain information, and the shortest route direction to the specified master, that is, the station 3
Sends the clock switching information e: 00 (H) to the counterclockwise transmission line c, and the station 4 sends the cook switching information 00 (H) to the clockwise transmission line b. Clock switching information arrives at the specific master station from the clockwise transmission line b and the counterclockwise transmission line c, but the master station starts switching processing with the clock switching information that has arrived first.

Transmitted from the station 4 to the clockwise transmission line b,
A description will be given using the clock switching information 00 (H). The processing unit a 'of the station 5 transmits the clock switching information 00 transmitted by the station 4.
(H) is received, and when the clock switching signal f is received, preparation is made so that clock switching can be performed, and termination is performed. The clock switching information 00 (H) passed through the clear line d of the station 5 is as follows.
The clock switching time can be shortened by reaching the master station 0 even while the processing unit a ′ of the station 5 is executing the processing (here, 00 is the former 0 indicating the switching information, and the latter 0 is the master station requested to switch). 2 shows that the master station 0 has received the clock switching information 00 (H) for its own station, so that the clock switching signal f: F0 is transmitted from the processing unit a to the counterclockwise transmission line c.
(H), and the processing unit a 'of the station 5 that has received the clock switching signal F0 (H) switches to output the reference clock from the counterclockwise transmission line data. Since all the intermediate stations have a transparent line d ', they reach the fault detecting station without passing through the processing unit a' (here, F0 indicates the switching signal of the former F, and 0 of the latter requests the switching. Indicate the master station. Switching of the clock switch in the station is first performed by both the switching information and the switching signal.)
As shown in FIG. 3, clock switching up to the station 4 is performed by the same processing, the internal clock transmitted from the station 4 is switched to the counterclockwise synchronous reference clock, and the clock switching is completed.

As shown in FIG. 5, when there are a plurality of clock master stations, when a failure occurs at the point B of the stations 3 and 4, the station 4 switches to the internal clock due to the cutoff of the reference clock. Then, at this time, as in the above-described embodiment, both detection stations 3,
4 specifies the master station 0 based on the station chain information, the station 3 transfers the clock switching information 00 (H) to the counterclockwise transmission line c in the shortest path direction, and the station 4 also determines the clock switching information 00 (H) The signal is transmitted to the counterclockwise transmission line c in the route direction. The clock switching control is performed when the clock switching signal F0 (H) from the specific master station 0 returns.

In the ring-structured slave station, the same clock switching control as described above can be performed by removing the communication lines d and d 'which do not pass the processing unit and replacing the processing unit a' with the processing unit a.

[0019]

As described above, according to the present invention, even when one or more clock master stations exist, the fault detecting station specifies the clock master station based on the station chain information, and the specified clock master station. Clock switching information can be transmitted in the shortest path direction to the clock, and clock switching can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram when a failure occurs in an embodiment of the present invention.

FIG. 2 is a schematic block diagram when a failure occurs in the embodiment of the present invention.

FIG. 3 is a schematic block diagram when a failure occurs in the embodiment of the present invention.

FIG. 4 is a schematic block diagram in a normal state in the embodiment of the present invention.

FIG. 5 is a schematic block diagram when a plurality of clock master stations exist in the embodiment of the present invention.

FIG. 6 is a schematic block diagram of a conventional example during normal operation.

FIG. 7 is a schematic block diagram when a failure occurs in a conventional example.

FIG. 8 is a schematic block diagram when a failure occurs in a conventional example.

FIG. 9 is a schematic block diagram when a failure occurs in the conventional example.

[Explanation of symbols]

 0, 1, 2, 3, 4, 5, 6, 7 Transmission stations A, B, C Failure points a Clock switching information / signal processing section of master station a 'Station clock switching information / signal processing section of slave station b, c Transmission line d, d 'transparent circuit e clock switching information: 00 (H) f clock switching signal: F0 (H) g synchronous network reference clock i transmission line monitoring data: 00 (H) j clock switching information: 04 (H) k Clock switching signal: F0 (H) z Conventional clock switching information and signal processing unit

Claims (3)

(57) [Claims] 1. A plurality of transmission stations have a ring configuration, a master station supplying a reference clock of a synchronous network is an upstream station, and slave stations located downstream of the master station are extracted from data received from the upstream. In a synchronous network system that performs clock distribution by transmitting data to a downstream station in synchronization with a clock, each transmission station transmits station chain information, which is information on a preset connection state of each station when a transmission path failure is detected. Transmitting means for specifying the master station based on the switching request information in the shortest path direction to the specific master station, and switching means for performing clock selection switching based on switching control information supplied from the specific master station. A clock switching method characterized by having 2. A plurality of transmission stations have a ring configuration, a master station supplying a reference clock of a synchronous network is an upstream station, and a slave station located downstream of the master station is extracted from data received from the upstream. In a synchronous network system that performs clock distribution by transmitting data to a downstream station in synchronization with a clock, each transmission station transmits station chain information, which is information on a preset connection state of each station when a transmission path failure is detected. Sending means for identifying the master station based on the switching request information in the shortest path direction to the specific master station, switching means for performing clock selection switching based on switching control information supplied from the specific master station, Means for passing the switching request information and the switching control information. 3. It has station chain information, which is information on the connection status of each station having a ring configuration, and when a fault occurs on a transmission line, the fault detecting station specifies a master station based on the above information, and sends a signal to the specified master station. A means for transmitting clock switching information in the shortest path direction, an intermediate station between the fault detection station and the clock supply station having a line for passing clock switching information and a signal, and each intermediate station having means for not retransmitting. Clock switching method.