JPH05244143A - Clock switching system - Google Patents

Abstract

PURPOSE:To provide a clock switching system which can specify a master station that requires no station chaining information with simple constitution when a transmission line has a fault. CONSTITUTION:The slave stations 2 and 4-8 have the information showing the extracting direction of an extracted reference clock (g). When a transmission line has a fault A, only the slave station 6 that is unable to extract the clock (g) around the single direction 11 transmits the clock switching information (e) in the direction 11 based on the information on the reference clock extracting direction 11 out of both stations 5 and 6 which detect the fault A. Then a master station 1 receives the information (e) and transmits a clock switching signal (f) in the direction 12 opposite to the direction 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission line clock switching system, and more particularly to a clock switching system when a transmission line failure occurs in a transmission system in which a plurality of transmission stations having a synchronous network ring are operated in synchronization with a reference clock. Regarding

[0002]

2. Description of the Related Art Conventionally, in this type of clock switching system, as shown in FIG. 5, a master station 20, 22 which supplies a synchronous network reference clock g as an upstream station is used as a master station 20,
The slave stations 21, 23-27 located downstream of 22 extract the reference clock component g from the received data from the upstream,
The reference clock g is distributed by transmitting data to the downstream station in synchronization with the extracted reference clock g.

Specifically, the master station 20 for the slave station 21 and the master station 22 for the slave stations 23 to 27.
Is provided with a processing unit 33 for inserting / determining / transferring switching information / signals, and the slave stations 21, 23-
The same processing unit 34 can also be provided at 27. However, in the slave stations 21, 23-27, the plain line 35
Since the clock switching information e (see FIG. 6) and the clock switching signal f (see FIG. 7) are transferred to the downstream station via the, the transfer processing in the processing unit 34 is not required. Further, each of the stations 20 to 27 has station chain information as connection information of ring configuration. Then, by using these processing units 33 and 34, the clock switching information e or the signal f clock switching back information or the signal is communicated between the transmission stations 20 to 27.

As a result, in the normal state, all the transmission stations 20 to 27 operate in synchronization with one reference clock g. Then, as shown in FIG. 6, when a transmission path failure B occurs between the transmission stations 24 and 25, both stations 24 and 25 detect the failure and the transmission station 24 switches to the internal clock. In parallel with this operation, both stations 24 and 25 identify the master station 20 from the plurality of master stations 20 and 22 based on the station chain information, and the transmission station 24 causes the clock switching information e:
00 (00 is a hexadecimal number, the leading 0 indicates switching information, and the trailing 0 indicates the specified master station 20) is transmitted to the counterclockwise transmission line 32, and the transmission station 25 transmits the clockwise direction. The clock switching information e is transmitted to the transmission line 31. In the identified master station 20, the switching process is performed based on the clock switching information e that arrives first among the two clock switching information e from the transmission lines 31 and 32.

A specific operation will be described using the clock switching information e sent from the transmission station 25 to the clockwise transmission line 31. Clock switching information e from the transmission station 25
Upon receiving the clock switching signal f from the master station 20, the processing unit 34 of the transmission station 26 that has received the signal prepares and terminates the clock so that the clock can be switched. The clock switching information e that has passed through the plain circuit 35 of the transmission station 26 is sent to the next transmission station 27 even while the processing unit 34 of the transmission station 26 is executing processing, and the transmission station 27 also uses the processing unit 34 to transmit the clock switching information e. The same processing as 26 is performed.

That is, the clock switching information e from the transmission station 25 reaches the master station 20 in a short time through the plain circuit 35 of the transmission stations 26 and 27. Master station 2 which has received this clock switching information e
As shown in FIG. 7, the clock switching signal f: F0 (F0 is 1 is 0 from the processing unit 33 to the counterclockwise transmission line 32).
Hexadecimal number, F indicates a switching signal, and 0 indicates the identified master station 20). In the transmission station 27 which has received the clock switching signal f from the master station 20,
The processing unit 34 switches so as to extract the reference clock g from the data transmitted from the counterclockwise transmission line 32. In parallel with this, the clock switching signal f is
Since it is sent to the next transmission station 26 through the pass-through circuit 35 of the transmission station 27, the transmission station 26 also switches in the same manner as the transmission station 27. Then, when the transmission station 25 receives the clock switching signal f, it switches from the internal clock to the extraction processing of the counterclockwise reference clock g, and the clock switching operation ends therewith.

[0007]

In the above-described conventional clock switching system, the transmission station 2 that has detected a transmission line fault.
Since 4 and 25 specify the master station 20 based on the station chain information, unless the station chain information is set in all transmission stations in advance, clock switching control at the time of failure is performed. There is a drawback that you cannot do it. When there are a plurality of master stations in the ring network, only one master station to which the clock switching signal f should be sent is specified from among the plurality of master stations, and a failure is detected in this particular master station. Since the method of transmitting the clock switching information e from the transmission station to the specific master station is adopted, there is a drawback that the clock switching control system becomes very complicated.

The present invention has been made in order to solve the above-mentioned conventional problems. When the transmission line fails, the master station can be specified without the need for the station chain information, and the master station can be identified with a simple structure. An object is to provide a clock switching method that can be specified.

[0009]

In order to achieve the above object, the present invention provides reference clocks in both directions from one or more master stations, and a plurality of slave stations ring-configured with the master station are provided with the above reference. Of the clocks, the reference clock for one direction is extracted and synchronized, and the slave station that receives the clock switching information and the clock switching signal among the plurality of slave stations when the transmission path fails is the reference clock for the other direction. In the clock switching method for switching the reception state so as to extract the above, the slave station has information indicating the extraction direction of the extracted reference clock, and when the transmission path fails, one of the slave stations that has detected the failure. Only slave stations that can no longer extract the reference clock around the direction are based on the information on the reference clock extraction direction. The clock extraction direction sends the clock switching information, the master station receiving the clock switching information is a configuration for transmitting the clock switching signal to the reference clock extraction direction opposite to the direction.

[0010]

According to such a configuration, when a transmission path fails, two slave stations connected by the failed transmission path detect the failure. Of these slave stations, only the slave station that cannot extract the reference clock in one direction sends the clock switching information in the reference clock extraction direction. The clock switching information is received by the master station and the slave station that is interposed between the slave station that sent the clock switching information and the master station. When the clock switching information is received, the master station sends a clock switching signal in the opposite direction to the clock switching information sending direction.
As a result, the clock switching signal is received by the slave station that has sent the clock switching information and the slave station that is interposed between this slave station and the master station, and the reception status of these slave stations is a reference in one direction. The state of extracting the clock is switched to the state of extracting the reference clock in the other direction.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the clock switching system of this embodiment. Reference numerals 1 to 8 denote ring-shaped transmission stations. The transmission station 1 is a master station for the transmission station 2 as a slave station, and the transmission station 3 is a master station for the transmission stations 4 to 8 as slave stations. The master stations 1 and 3 are provided with a clock switching processing unit 13 having information on the extraction direction of the reference clock g, and the slave stations 2, 4 to 8 are provided with a clock switching processing unit 14 having the same function and a plain circuit 15. And are provided. When detecting that the reference clock g cannot be extracted, each of the stations 1 to 8 determines the clock that specifies the shortest clockwise master station in the same direction as the clock extraction direction based on the information on the clock extraction direction. It also has a function of transmitting the switching information e. In the normal state, as shown in FIG. 4, the reference clock g from the master stations 1 and 3 is sent out to the clockwise transmission line 11, and each of the transmission stations 1 to 8 receives this transmission line 11
The reference clock g sent to the above is extracted from the received data for synchronization.

As shown in FIG. 1, when a transmission path failure A occurs between the transmission stations 5 and 6, the transmission stations 5 and 6 detect the occurrence of the transmission path failure A. Since the transmission station 6 cannot extract the reference clock g due to the transmission path fault A, the clock switching information e is sent from only the transmission station 6. The transmission direction of the reference clock g before the occurrence of the transmission path fault A is the clockwise direction, and since the transmission station 6 has extracted the clockwise reference clock g, the clock switching processing unit 14 of the transmission station 6 , Information on the clockwise clock extraction direction is held. Therefore, based on the information on the clock extraction direction, the transmission station 6 acts as the master station and the transmission station 1
The clock switching information e destined for is sent to the clockwise transmission line 11.

On the other hand, since the transmission station 5 can extract the reference clock g, it does not send the clock switching information. The clock switching information e from the transmission station 6 is sequentially received by the transmission stations 7 and 8, and the transmission stations 7 and 8 are prepared so that the clock switching can be performed when the clock switching signal f is received.
Terminate.

Further, since the clock switching information e that has passed through the plain circuit 15 of the transmission stations 7 and 8 reaches the master station 1 even while the clock switching processing unit 14 of the transmission stations 7 and 8 is executing the clock switching information e. Shortened. Figure 2
As shown in, the master station 1 that has received the clock switching information e addressed to itself sends a clock switching signal f from the clock switching processing unit 13 to the counterclockwise transmission line 12. When the transmission stations 7 and 8 receive the clock switching signal f from the master station 1, the clock switching processing unit 1
4 is switched so as to extract the reference clock g from the data transmitted through the counterclockwise transmission line 12. (Clock switching is executed by receiving both the switching information e and the switching signal f.)

Further, the clock switching signal f passing through the plain circuit 15 reaches the transmission station 6 which has detected the failure, and the transmission station 6 switches from the internal clock to the counterclockwise reference clock g, as shown in FIG. The switching of the reference clock g is completed. In this way, the transmission station 6 that cannot extract the reference clock g in the clockwise direction due to the failure
If the clock switching information e is transmitted in the same direction (clockwise direction) as the clock extraction direction based on the information on the clock extraction direction, the master station 1 is inevitably specified, so that the existence of another master station 3 exists. There is no need to consider.

When the slave station 2 cannot extract the clockwise reference clock g due to a failure, the specific master station that is the destination of the clock switching information e is the transmission station 3 and the slave stations 4, 5, and 5. When the clockwise reference clock g cannot be extracted at 7 and 8, the specific master station that is the destination of the clock switching information e is the transmission station 1.

When the reference clock g does not come to any of the master stations 1 and 3, it becomes a slave station,
The reference clock g is extracted from the transmission data and the clock is switched.

Further, in the slave stations 2, 4-8,
The plain line 15 that does not pass the clock switching information e and the signal f to the clock switching processing unit 14 is removed, and the clock switching processing unit 14 is replaced with the clock switching processing unit 13.
Alternatively, the reference clock switching control similar to that described above can be performed.

[0019]

As described above, according to the present invention, only the slave station that cannot extract the reference clock due to the transmission path failure sends the clock switching information in the reference clock extraction direction based on the information in the reference clock extraction direction. Therefore, it is not necessary to set the station chain information for each station, and even when there are multiple master stations, clock switching information can be sent without being aware of these multiple master stations. As a result, there is an excellent effect that the structure of clock switching control can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing a clock switching method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing reception of clock switching information and transmission of a clock switching signal in a specific master station.

FIG. 3 is a block diagram showing a reception state in each slave station with respect to a clock switching signal from a specific master station.

FIG. 4 is a block diagram showing a transmitting / receiving state of a reference clock in a normal state.

FIG. 5 is a block diagram showing a conventional clock switching system.

FIG. 6 is a block diagram showing a state in which clock switching information is transmitted from a slave station that has detected a failure.

FIG. 7 is a block diagram showing reception of clock switching information and transmission of a clock switching signal in a specific master station.

FIG. 8 is a block diagram showing a reception state in each slave station with respect to a clock switching signal from a specific master station.

[Explanation of symbols]

 1, 3 ... Master station 2, 4 to 8 ... Slave station 11 ... Clockwise direction transmission line 12 ... Counterclockwise direction transmission line 13, 14 ... Clock switching processing unit 15 ... Transparent circuit e ... Clock switching information f ... Clock switching Signal g ... Reference clock

Claims (1)

[Claims] 1. A plurality of slave stations ring-configured with the master station, which supplies reference clocks in both directions from one or more master stations,
Of the above-mentioned reference clocks, the reference clock in one direction is extracted and synchronized, and in the case of a transmission path failure, the slave station that received the clock switching information and the clock switching signal is the one in the other direction. In the clock switching method for switching the reception state so as to extract the reference clock of, the slave station has information indicating the extraction direction of the extracted reference clock, and when the transmission path fails, the slave station that detected the failure Among them, only the slave station that cannot extract the reference clock around the one direction sends the clock switching information in the reference clock extraction direction based on the information about the reference clock extraction direction and receives the clock switching information. The master station sends the clock switching signal in the opposite direction to the reference clock extraction direction. Clock switching method characterized by issuing.