JP3040316B2 - Termination circuit of redundant transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminating circuit for a redundant transmission line in a digital data transmission device, and more particularly to a system for switching a redundant system without instantaneous interruption.

[0002]

2. Description of the Related Art There is a transmission system in which two systems of transmission lines are connected between digital data transmission devices in order to quickly respond to transmission line failures and improve reliability. In such a transmission system, the transmission-side digital data transmission device sends out the same data to the transmission lines of the respective systems, the reception-side digital data transmission device simultaneously terminates the data from the transmission lines of the respective systems, Select one and import it inside.

Conventionally, as a termination circuit for a redundant transmission line in such a digital data transmission apparatus on the receiving side, a conventional circuit shown in FIG.
The configuration shown in FIG.

The transmission signal from the 0-system transmission line is transmitted by the 0-system frame synchronization detection unit 10-0 to the transmission line input data,
It is separated into a transmission line frame pulse and a transmission line clock. When the transmission path is an optical fiber, the signal is photoelectrically converted before being input to the frame synchronization detection unit 10-0. The separated transmission line input data is supplied to a selector (SEL) 11-
0, and is input to the selector 11-0 after being delayed by a predetermined time (time shorter than one frame) via the delay circuit 12-0, and is input to the selector 11-0 based on a phase comparison output described later. Is selected and input to the error stick store unit (ES unit) 15-0. Similarly, the separated transmission line frame pulse is directly input to the selector (SEL) 13-0, is delayed by the predetermined time via the delay circuit 14-0, and is input to the selector 13-0. One is selected by the selector 13-0 based on the phase comparison output, and is input to the error stick store unit 15-0. The separated transmission line clock is stored in the error stick store unit 15-0.
Is input to

[0005] The error stick store unit 15-0 includes:
A frame pulse and a clock generated in the apparatus irrespective of the transmission path are input as those for reading. Thus, the error stick store unit 15-0 replaces the transmission line timing with the in-device timing while preventing the data from being read twice or missing based on the jitter of the transmission line clock. The phase comparison output corresponding to the phase difference of the frame pulse in the device is supplied to the selectors 11-0 and 13-0 to prevent the occurrence of slip.

For a transmission signal from the transmission line of the first system,
The same processing is executed by the frame synchronization detection unit 10-1, the selector 11-1, the delay circuit 12-1, the selector 13-1, the delay circuit 14-1, and the error stick store unit 15-1.

The error stick store unit 15 of each system
0 and 15-1 are both selectors (S
EL) 16, the selector 16 selects the data of the system indicated by the system switching command signal, and outputs it to a data processing stage (not shown).

[0008]

However, the duplicated transmission lines are laid almost in the same manner. However, as the length of the transmission lines increases, it takes longer for the transmission lines to reach the receiving digital data transmission device. The transmission delay time is different, and even if there is a relay device or the like on the transmission path, the transmission delay time until reaching the receiving digital data transmission device is different.

If the difference (phase difference) in the transmission delay time between the 0-system transmission line and the 1-system transmission line is small, the error stick stores 15-0 and 15-1 change the timing to the internal timing. The difference can be absorbed, and duplication or omission of data can be prevented even when the system is switched. That is, the switching without instantaneous interruption can be executed.

However, the error stick store unit 15-
Although 0 and 15-1 are generally configured to absorb phase fluctuations within one frame, depending on their internal configuration, the difference in transmission delay time between the 0-system transmission line and the 1-system transmission line is different. If the (phase difference) becomes considerably large (one frame or more), it is not possible to guarantee instantaneous interruption at the time of system switching. That is, there is a possibility that data duplication or omission may occur at the time of system switching.

[0011]

In order to solve the above-mentioned problems, according to the present invention, the timing of input data from each transmission line of the redundant system is changed to the timing in the device, and then the system switching command is issued. The terminating circuit of the redundant transmission line that selects and outputs the data of the signal indicating system includes the following units.

That is, selection candidate data creation means provided for each system for forming transmission line input data as a plurality of selection candidates different from the transmission line input data of the own system by a predetermined time, and a plurality of created candidate data. Selecting means based on the selection command data from the transmission path input data of the selection candidates, selecting means provided for each system, detecting the phase difference between the transmission path input data of each system, and detecting this phase difference , Active system at that time
Transmission line selected by the above-mentioned selection means of the system
Select by the above selection means of the standby system based on the input data
The phase of the transmission line input data obtained is in units of the predetermined time.
The transfer selected by the above-mentioned selection means of the active system
Selection of standby system to match the route input data
Create command data and select command data for the active system.
As the standby system just before the system became the active system
Selection command data or the selection specified for the start of communication.
A non-instantaneous interruption phase control means common to each system for continuously outputting selection command data is provided.

[0013]

According to the present invention, the terminating circuit of the redundant transmission line adjusts the timing of the input data from each of the redundant transmission lines.
After switching to the timing in the apparatus, the data of the instruction system of the system switching command signal is selected and output, and through such timing switching, a small phase difference of each system transmission line is absorbed.

According to the present invention, in addition to the above-described structure for absorbing a small phase difference, a structure for absorbing a phase difference in units of a considerably long predetermined time (for example, one frame) is provided. That is, for each system, the selection candidate data creation means forms transmission path input data as a plurality of selection candidates that differ by a predetermined time, and the selection means outputs selection command data from the created plurality of selection candidate transmission path input data. Choose one based on

The selection command data for each system is created or output by the instantaneous interruption-free phase control means common to each system . Instantaneous interruption phase
The control means detects the phase difference of the transmission line input data of each system.
Then, this detection phase difference and the active system at that time
Transmission line input data selected by the selection means of the system
Based on the transmission path selected by the selection means in the standby system
When the phase of the input data is in units of the predetermined time,
The transmission line input data selected by the above-mentioned selection means of the working system
Selection command data for the standby system so that
create. In addition, the instantaneous interruptionless phase control means selects the active system.
Standby system immediately before the system becomes the active system as command data
Command data at the time of
Continuously outputs the selected command data. This
Thus, the phase of the transmission line input data selected by the selection means of each system can be matched when the unit is a predetermined time.
You.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a redundant transmission line termination circuit according to the present invention;

FIG. 1 shows the overall configuration of this embodiment, and the same or corresponding parts as those in FIG. 2 are denoted by the same reference numerals. FIG. 3 shows a detailed configuration of the instantaneous interruption-free phase control circuit in FIG.

In FIG. 1, the termination circuit of this embodiment is
In addition to the configuration of the conventional circuit, four 1-frame delay circuits 21-0 to 24-0 and 21-1 to 24-1 for each system and selectors (SEL) 25-0 and 25- for each system are provided. 1 and an instantaneous interruption-free phase control circuit 30 common to both systems are newly provided.

Four 1-frame delay circuits 21-
Numerals 0 to 24-0 and 21-1 to 24-1 are cascade-connected to respective stages of the selectors 11-0 and 11-1 for selecting transmission line input data provided for preventing slip. ing.

In other words, the selectors 11-0, 11-
The processing system up to 1 is the same as the conventional one. That is, the transmission signal from each system transmission line is transmitted to the frame synchronization detection unit 10-0,
The transmission line input data, the transmission line frame pulse, and the transmission line clock are separated by 10-1. The separated transmission line input data is directly input to the selectors 11-0 and 11-1, and the delay circuit 12- The signals are delayed by a predetermined time via 0 and 12-1 and input to the selectors 11-0 and 11-1, and one of them is selected by the selectors 11-0 and 11-1 based on a phase comparison output described later. In addition,
The separated transmission line frame pulse is supplied to the selector 13-
0, 13-1 and the delay circuit 14-
0, 14-1 and is input to the selectors 13-0 and 13-1 after being delayed by a predetermined time, and one of them is selected by the selectors 13-0 and 13-1 based on the phase comparison output, and the error stick store is performed. The points that are input to the units 15-0 and 15-1 and the separated transmission line clocks are input to the error stick store units 15-0 and 15-1 are the same as in the related art.

The transmission line input data output from the selectors 11-0 and 11-1 of each system for selecting the transmission line input data are respectively connected to the cascade-connected 1-frame delay circuit groups 21-0 to 21-0 of the own system. 24-0, 21-1 to 24-1, and thereby, five different transmission line input data, one frame by one frame, are taken out in parallel and input to newly provided selectors 25-0, 25-1. Is done.

The selectors 25-0 and 25-1 of each system respectively transmit five transmission line input data different by one frame in accordance with selection command data formed by the non-interruptible phase control circuit 30 as described later. Is given to the error stick store units 15-0 and 15-1.

Error stick store section 15 of each system
0 and 15-1 write the input data given from the selectors 25-0 and 25-1 of the own system into the internal memory based on the transmission line frame pulse and the transmission line clock,
The write data is read based on a frame pulse and a clock generated independently of the transmission path side in the device, thereby changing the timing and outputting the read data to the selector 16 common to both systems. At this time, the phase comparison output corresponding to the phase difference between the transmission line frame pulse and the in-device frame pulse is output to selectors 11-0 , 11-1 and 13-0 , 1
3-1 to prevent the occurrence of slip.

The selector 16 selects one of the data output from the error stick store units 15-0 and 15-1 of each system based on the system switching command signal and outputs it to a data processing stage (not shown). .

That is, in this embodiment, the difference (phase difference) of the transmission delay time of both transmission lines exceeding one frame is calculated as follows :
Through the selection operation of the selectors 25-0 and 25-1 of both systems, conversion is performed within one frame, and the phase difference between the two systems within one frame thus converted is stored in the error stick store unit 15-0 of both systems. 15-1 and the output data is instantaneously interrupted even at the time of system switching.

The system switching command signal may be formed on the basis of the instruction information included in the data and transmitted from the transmitting side, or may be formed in accordance with the result of detection of the transmission path failure. It may be what you did.

Next, the detailed configuration of the instantaneous interruption-free phase control circuit 30 will be described in detail with reference to FIG.

Referring to FIG.
Is a multi-frame address determination unit 31-0 for each system,
31-1; a working / standby phase difference detecting unit 32 common to both systems; and a selection command data creating unit 33-0, 3 for each system.
And a 3-1 Prefecture.

In the case of this embodiment, data input from the transmission line constitutes 16 or 32 multi-frames, and a multi-frame at the beginning of each frame clarifies which of the multi-frames. The address has been inserted.

Multi-frame address judging section 31 of each system
−0 and 31-1 are their own selectors 11-0,
The multi-frame address included in the transmission line input data output from 11-1 is converted into the selector 13-
The multi-frame address is extracted based on the transmission line frame pulses from 0 and 13-1, and the obtained multi-frame address is provided to the working / standby system phase difference detection unit 32. Note that the multi-frame address determination units 31-0 and 31-1 of each system respectively
The data indicating the validity / invalidity of the output multi-frame address, such as whether the multi-frame address has been extracted or not, is also supplied to the working / standby-system phase difference detection unit 32.

The active / standby system phase difference detecting section 32 includes:
In addition to the data from each of the multi-frame address determination units 31-0 and 31-1, an in-device frame pulse and a system switching command signal are also provided.

The active / standby system phase difference detecting section 32 first synchronizes the multi-frame address of each system with the frame pulse in the apparatus, and then subtracts the multi-frame address of system 1 from the multi-frame address of system 0. A first phase difference value indicating the lead / lag of the system 0 as viewed from the system 1
A second phase difference value indicating the lead / lag of the system 1 as viewed from the system 0 obtained by subtracting the system 0 multi-frame address from the system multi-frame address is obtained. Selects the first phase difference value when indicates the 0 system, and selects the second phase difference value when the system switching command signal indicates the 1 system, and selects the phase difference between the active system and the standby system. A signal is formed and given to the selection command data creation units 33-0 and 33-1 of each system.

The active / standby system phase difference detecting section 32
Can be switched without instantaneous interruption based on the selection state by the selection command data creation units 33-0 and 33-1 and the phase difference between the active system and the standby system when the system switching is instructed at that time. It is also determined whether or not there is no instantaneous interruption determination result output indicating the fact to the transmission side of the system switching command signal.

The selection command data creating units 33-0 and 33-1 of both systems mutually communicate with each other by the selectors 25-0 or 25-.
1 can be exchanged. Also,
The transmission command frame pulse and the system switching command signal are also supplied to the selection command data creating units 33-0 and 33-1 for both systems.

Selection command data creation unit 33-0 or 33-1 for the system designated as the active system by the system switching command signal
Maintains its own system selection state of the selector 25-0 or 25-1 to date, also party system selectors determined based on the selected state of the active system / standby phase difference signal and the working system 25 An instruction value of the selection instruction data of 1 or 25-0 is created and given to the selection instruction data creation unit 33-1 or 33-0 of the system designated as the standby system by the system switching instruction signal. Selection command data creation units 33-0 and 33-1 for each system
Supplies selection command data synchronized with the transmission line frame pulse of the own system to the selectors 25-0 and 25-1 of the own system.

When the apparatus is started, the selection command data creation unit 3 for the current system (generally, the system 0) at that time is used.
3-0 or 33-1 is the selector 25-0 or 25-1
To select the transmission line input data at the intermediate position (therefore, the transmission line input data output from the one-frame delay circuit 22-0 or 22-1).

Next, the operation of the terminating circuit of the redundant transmission line of this embodiment, in particular, the operation of absorbing the phase difference between the two systems for each frame will be described with reference to the timing chart of FIG. It should be noted that the system 0 is designated as the active system, and the system 0
The system will be described from the state where transmission line input data output from the one-frame delay circuit 22-0 is selected by the selector 25-0.

The system 0 to which the transmission line frame pulse shown in FIG. 4A is supplied from the selector 13-0 and the transmission line input data having the multi-frame address shown in FIG. 4B is supplied from the selector 11-0. The multi-frame address determination unit 31-0 extracts the multi-frame address included in the transmission path input data and supplies the multi-frame address to the working / standby system phase difference detection unit 32. Similarly, the transmission path frame pulse shown in FIG.
The multi-frame address determination unit 31-1 of the first system to which the transmission line input data having the multi-frame address shown in FIG. Is extracted and given to the active / standby system phase difference detection unit 32.

In the active / standby phase difference detecting section 32, the multi-frame addresses of these two systems are shown in FIG.
As shown in (F) and (G), the phase difference is captured in synchronization with the in-device frame pulse shown in FIG. The first phase difference value and the second phase difference value shown in I) are calculated. In this example, a value (2) that the system 0 is ahead of the system 1 by two frames is obtained as the first phase difference value, and the system 1 is delayed by two frames from the system 0 as the second phase difference value. Value (-
2) is obtained.

Further, a phase difference detecting section 3 between the active system and the standby system
2 selects the first phase difference value or the second phase difference value based on the system switching command signal shown in FIG. 4 (J), and forms the active system / standby shown in FIG. The inter-system phase difference signal is supplied to the selection command data creation units 33-0 and 33-1 for both systems. In this example, when the 0 system before the time t1 and after the time t2 is the active system, a phase difference signal between the active system and the standby system having a value (2) indicating that the active system is ahead of the standby system by two frames is output. When the one system between time t1 and time t2 is the active system, a phase difference signal between the active system and the standby system having a value (-2) indicating that the active system is delayed by two frames from the standby system is output.

Before time t1, system 0 is the active system. Therefore, the selection command data generator 33-0 for system 0 selects transmission line input data delayed by two frames as before. The selection command data shown in FIG. 4 (L) is output to the selector 25-0 in synchronization with the transmission line frame pulse of the own system (0 system). Also, the 0-system selection command data creating unit 33-0 determines that the active system (0 system) is only 2 frames (although the difference within one frame is ignored) than the standby system (1 system). Since the transmission line input data is advanced and the own system is selecting transmission line input data delayed by two frames, the transmission line input delayed by 0 frames is sent to the selection command data creation unit 33-1 of the first system. A value (0) shown in FIG. 4 (M) for instructing data selection is given, whereby the selection command data creation unit 33-1 of the first system sets its own system (1).
The selection command data shown in FIG. 4 (N) is output to the selector 25-1 in synchronization with the transmission line frame pulse of (system).

On the other hand, during the period from the time point t1 to the time point t2, since the system 1 is the active system, the selection command data creating unit 33-1 of the system 1 transmits the transmission data delayed by 0 frames as before. 4 is selected in synchronization with the transmission system frame pulse of the own system (system 1) .
The selection command data shown in (N) is output to the selector 25-1. In addition, the selection command data creation unit 33-1 of the first system
Indicates that the active system (system 1) is 2 times smaller than the standby system (system 0).
Since the transmission line is delayed by the frame (although the difference within one frame is ignored) and the own system selects transmission line input data delayed by 0 frames, the selection command data generation unit for the 0 system FIG. 4 instructing 33-0 to select transmission path input data delayed by two frames
(O) is given, whereby the 0-system selection command data generating unit 33-0 synchronizes with the transmission line frame pulse of its own system (0 system) and outputs the selection command shown in FIG. The data is output to the selector 25-0.

It should be noted that the numerical values X shown in FIGS.
Indicates that the selectors 25-0 and 25-1 select transmission line input data delayed by X frames.

After time t2, the system 0 is the active system, so the selection command data creation units 33-0, 33-
1 outputs selection command data to the selectors 25-0 and 25-1 of the own system in the same manner as before time t1 described above.

By the selection operation based on the selection command data, as shown in FIGS. 4 (P) and (Q), the phase difference is made within one frame from the selectors 25-0 and 25-1 of both systems. The transmission line input data is output and provided to the corresponding error stick store units 15-0 and 15-1.

Each error stick store unit 15-0, 1
5-1 changes the data timing to the internal timing based on the internal frame pulse and the internal clock, whereby the output data from the error stick store units 15-0 and 15-1 of both systems are: FIG.
As shown in (R) and (S), they have the same phase.

As a result, even though the system is switched by the final-stage selector 16 in response to the system switching command signal, although not shown, data having a continuous phase without instantaneous interruption is transmitted.

In practice, the difference (phase difference) in the transmission delay time from the transmission paths of both systems slightly changes due to jitter and the like.
In most cases, the phase difference is the same when viewed on a frame basis, and the selection command data output from the selection command data creation units 33-0 and 33-1 of each system rarely changes. .

The phase difference detector 32 between the active system and the standby system
Is, as described above, based on the selection state by the selection command data creation units 33-0 and 33-1 and the phase difference between the active system and the standby system, if there is a command to switch the system at that time, there is no instantaneous interruption. It is also determined whether or not the switching can be performed by using the command, and an instantaneous interruption determination result output indicating that is given to the transmission side of the system switching command signal. In the example of FIG. 4, no instantaneous interruption determination result output indicating that instantaneous interruption switching cannot be performed is not output.

FIG. 5 shows the relationship between the input phase difference between the two systems and the output of the result of the instantaneous interruption determination. FIG. 5A shows a case where the phase difference between the two systems is one frame or more when the working system is selecting transmission line input data delayed by 0 frames (when the working system is advanced by one frame or more). When the instantaneous interruption judgment result output is disabled for instantaneous interruption switching, the standby system selects transmission line input data delayed by 0 frame, and when the phase difference between both systems is 0 frame, the instantaneous interruption judgment result is output. The output can be switched instantaneously without interruption, and the standby system can select transmission line input data delayed by 0 frames. When the phase difference between both systems is -1 frame (when the active system is delayed by 1 frame) , The instantaneous interruption determination result output can be switched without interruption, and the standby system can select transmission line input data delayed by one frame. Similarly, FIG. 5 (B),..., FIG. 5 (E) show that the active system has one frame, two frames, three frames,
When the transmission line input data delayed by four frames is selected, the contents of the output of the hitless interruption determination result and the type of the transmission line input data to be selected by the standby system are shown.

Before the time point t1 and after the time point t2 in FIG. 4, the case where the working system selects the transmission line input data delayed by two frames as shown in FIG. Corresponds to two frames, where the instantaneous interruption determination result output can be switched without instantaneous interruption, and the standby system selects transmission line input data delayed by 0 frames.

The period from time t1 to time t2 in FIG. 4 is a case where the active system is selecting transmission line input data delayed by 0 frames as shown in FIG. This corresponds to the case where the phase difference is −2 frames, in which the instantaneous interruption determination result output is enabled for instantaneous interruption switching, and the standby system selects transmission line input data delayed by two frames.

As described above, according to the above embodiment, even if the input data from the transmission paths of both systems has a phase difference of one or more frames, the configuration for absorbing the phase difference in frame units is an error. Since the phase difference within one frame is absorbed by the error stick storage unit, the data can be input to the apparatus without instantaneous interruption even when the system is switched. That is, it is possible to prevent duplication or omission of data at the time of system switching.

Further, according to the above-described embodiment, since the instantaneous interruption determination result is output from the instantaneous interruption phase control circuit 30 to the transmission side of the system switching command signal, the instantaneous interruption switching cannot be performed. In this case, the transmission side of the system switching command signal can stop switching the system, and from this point, the instantaneous interruption switching is guaranteed to some extent.

In the above embodiment, the redundant transmission line is a double transmission line. However, the present invention can be applied to a termination circuit of a transmission line of a triple or more transmission line. Further, in the above embodiment, the redundant system of the 0 system / 1 system is shown, that is, the system which gives priority to the 0 system is basically shown, but the present invention is applied to a redundant system having no priority in each system. Can be applied.

Further, in the above-described embodiment, in order to absorb the phase difference on a frame-by-frame basis, the transmission line input data of five frames different by one frame is used as a selection candidate. The range may be wider.

Furthermore, in the above-described embodiment, the configuration for each system for absorbing the phase difference in units of frames 21-
0-25-0, 21-1 to 25-1 are connected to the selector 11-
0, 11-1 and the error stick store unit 15-0,
Although the one provided between 15-1 is shown, the installation place is not limited to this. For example, the error stick store unit 15
−0, 15-1 may be provided on the output side, and the selectors 11-0, 11-1 and the slip prevention delay circuit 12
−0, 12-1 may be provided on the input side.

In the above embodiment, since the error stick store units 15-0 and 15-1 that can absorb the phase difference within one frame are applied, the unit having a large phase difference absorption is one frame unit. However, the present invention is not limited to this. That is, a unit having a large phase difference absorption may be appropriately selected according to the phase difference absorption capability of the error stick store units 15-0 and 15-1. For example, when the error stick store units 15-0 and 15-1 that can absorb the phase difference within two frames are applied, six one-frame delay circuits are cascaded,
By selecting from seven inputs, a unit having a large phase difference absorption may be a two-frame unit.

[0059]

As described above, according to the redundant transmission line terminating circuit of the present invention, transmission line input data as a plurality of selection candidates that are different from each other by predetermined time from the transmission line input data of the own system are formed. Selection candidate data creation means provided for each system, and selection means provided for each system, for selecting one based on the selection command data from a plurality of selection candidate transmission line input data created, The phase difference of the transmission line input data of the system is detected, and this detected phase difference is
Transmission line input selected by the selection means of the system
Based on the data and selected by the selection means of the standby system
The phase of the transmission line input data is in units of the predetermined time.
Sometimes, the transmission path selected by the above-mentioned selection means of the active system
Selection command for standby system to match input data
Create data and use it as selection command data for the active system.
When the system was the standby system just before it became the active system,
Selection command data or selection finger specified for communication start
Command data, which continuously outputs the command data, and a non-instantaneous interruption phase control means common to each system, so that even if there is a large phase difference in the input data from each system transmission line, the phase difference can be absorbed Data duplication or omission at the time of switching can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an embodiment.

FIG. 2 is a block diagram showing the entire configuration of the related art.

FIG. 3 is a block diagram illustrating a detailed configuration of a non-interruptible phase control circuit according to the embodiment;

FIG. 4 is a timing chart of each part of the embodiment.

FIG. 5 is an explanatory diagram showing a relationship between an input phase difference of both systems and an output of a hitless interruption determination result according to the embodiment;

[Explanation of symbols]

15-0, 15-1 ... error stick store unit (ES
), 16... System selection selector, 21-0 to 24-0,
21-1 to 24-1 ... 1 frame delay circuit, 25-0,
25-1: selector for selecting input data phase, 30: phase control circuit without instantaneous interruption, 31-0, 31-1: multi-frame address judging section, 32: phase difference detecting section between active / standby system, 33-0 , 33-1 ... Selection command data creation unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-46430 (JP, A) JP-A-4-49730 (JP, A) JP-A-62-249538 (JP, A) JP-A-6-249538 177866 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 1/22 H04L 7/00 H04L 29/14

Claims (2)

(57) [Claims] 1. A redundant transmission line for selecting and outputting instruction system data of a system switching command signal after changing the timing of input data from each of the redundant system transmission lines to the timing in the device. A plurality of selection candidate data generating means provided for each system, for forming transmission line input data as a plurality of selection candidates different from each other by a predetermined time from the transmission line input data of the own system; Selecting means provided for each system to select a transmission line input data of selection candidates based on the selection command data; detecting a phase difference between transmission line input data of each system ; The above options for the system that is currently active
Based on the transmission path input data selected in the step,
Of the transmission line input data selected by the selection means
When the phase is in units of the specified time, the selection of the working system
It matches the transmission path input data selected by the selection means.
When the selection command data for the standby system is created,
In addition, as the selection command data for the active system,
Command data or communication when the standby system was
Continue to output the selection command data specified for
And a non-instantaneous power loss phase control means common to each system. 2. The system switching command when the detected phase difference is so large that the phase of the transmission line input data selected by the selecting unit of each system cannot be matched. 2. The redundant transmission line termination circuit according to claim 1, wherein information to that effect is given to the signal transmission side.