JP3166777B2 - Automatic line 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 an automatic line switching system, and more particularly to automatic switching to backup when line quality is degraded and line is disconnected, and automatic recovery when line is restored.

[0002]

2. Description of the Related Art Conventionally, for example, a dedicated line is used between modems, and an INS line is used as a backup separately from this line, and switches are connected to both ends of each modem. The configuration is common. In FIG. 2 showing an example of a conventional line, a modem 13,
In the case where the connection between the dedicated lines between the terminals 14 is lost due to a failure, the host 11 and the data terminal equipment (DTE) 1
Since data transmission cannot be performed between the host 11 and the host 6, the host 11 normally monitors the communication protocol and detects an abnormality. After the abnormality is detected, the maintenance person of the system manually switches the switches 12 and 15 to connect the data communication path to the backup line 17 to perform backup.

To automatically switch the line, the output of a carrier detection circuit built in each of the modems 13 and 14 is used. The output of the carrier detection circuit is ON when there is a carrier on the line and OFF when there is no carrier. Therefore, if the carriers in the modems 13 and 14 are always in a transmission state, the line is disconnected due to a failure. Only if
Detect carrier break. Therefore, automatic switching can be performed by switching the switches 12 and 15 using the output of the carrier detection circuit as a control signal. When the line is restored, the carrier is turned on and the output of the carrier detection circuit is turned on, whereby the switches 12 and 15 can be automatically returned. Here, the modems 13 and 14
Has been described as an example, but the same can be performed if the data transmission apparatus has an identification bit or the like indicating the presence or absence of data transmission.

[0004]

However, in the above-described circuit, when the carrier in the modem is used in the polling mode of ON or OFF (that is, when transmitting data from the host or the DTE, the carrier is set to O).
In the case of a mode in which the other party confirms data reception by transmitting N), even if an attempt is made to detect a line disconnection failure, it is determined whether the carrier is off in the normal data idle state or the carrier is off in the failure. There is a problem that can not be done. Therefore, in such a case, automatic line switching cannot be performed.

Further, in the case of the conventional automatic detection by detecting the carrier disconnection, the automatic switching operation is started after the carrier disconnection is detected, so that the time for establishing the backup line is always required for the automatic switching. There is a problem that it is included in the time required. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic line switching system that enables automatic backup even when used in a polling mode. Another object of the present invention is to provide an automatic line switching system in which the time for establishing a backup line is not included in the time required for automatic switching.

[0006]

According to the present invention, a terminal device is provided.
Signal indicating that it is ready to receive data (R
S), a signal (CS) for transmitting a carrier, and
Signal indicating that the error rate of the transmitted data is greater than the specified value
By monitoring (SQD), normal operation status and backup
Automatic line switching that automatically switches to the backup state
RS detection circuit for detecting the RS
And an SC detection circuit for detecting the CS,
The ratio of the ON time of the SQD within the interval is predetermined.
SQ for detecting ON of the SQD when the reference value is exceeded
D detection circuit and terminal device by receiving the switching instruction
Switching connection between transmission device or terminal device and backup circuit
Switch circuit and an instruction or
ISDN by receiving an instruction to disconnect the backup line
Establish or disconnect the backup data line via
Performing the ISDN interface circuit and the switch circuit
And controlling the operation of the ISDN interface circuit.
A control device, wherein in the normal operation state, the control
The apparatus detects the RS with the RS detection circuit.
Normally, when the CS is detected by the SC detection circuit,
It is determined that the vehicle is in operation and the switch circuit communicates with the terminal device.
Command to keep the transmitter connected, and
The output circuit detects the RS, but the SC detection circuit
If CS is not detected, it is judged that the line quality has deteriorated.
The backup for the ISDN interface circuit
Instructs line establishment, and the SQD detection circuit
When ON is detected, a switching finger
Display, and in the backup state, the
In the control device, the SQD detection circuit turns off the SQD signal.
When a detection is detected, the switching instruction to the switch circuit is stopped.
The switch circuit stops and the terminal receives
Make a connection between the device and the transmission device,
The release of the up state is completed, and the
Thus, an automatic line switching method is obtained.

[0007]

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an automatic line switching device according to one embodiment of the present invention. First, RS, CS, S
A process in which an automatic backup is performed by monitoring each signal of the QD and a transition is made during the backup will be described. Here, RS is a signal indicating that the terminal device is ready to receive data, CS is a signal for transmitting a carrier,
The SQD is a signal indicating that the error rate of the received data is larger than a specified value. When data transmission is normally performed using the transmission device, the RS is received from the terminal device via the connector 21 and CS is returned to the terminal via the connector 31 from the transmission device. That is, both signals are ON.

Since the automatic line switching device is installed between the terminal device and the transmission device, the RS detection circuit 23 and the CS detection circuit 2
In step 8, when the ON state of both signals is detected, the control circuit 26 determines that normal operation is being performed, and instructs the switch circuit 25 to keep the terminal device and the transmission device connected. That is, no switching instruction is issued. Switch circuit 26
Is an initial state in which the terminal device and the transmission device are connected. Only when a switching instruction is received, the terminal device and the ISDN are connected.
It is assumed that an interface circuit is connected. When the line quality between the transmission devices fluctuates and deteriorates and begins to hinder data transmission, the transmission device starts retraining to equalize the characteristics of the line. At this time, the transmission device turns off CS. The CS detection circuit 28 notifies the control circuit 26 that CS is OFF. The control circuit 26 is the RS detection circuit 23
And when RS is ON, it judges that the line quality has fluctuated or deteriorated, and issues a backup line establishment instruction to ISDN interface circuit 27. Upon receiving this, the ISDN interface circuit 27
Establish a data line for backup via.

Here, if the transmission device cannot fully equalize the line characteristics and the error rate of the received data becomes larger than a specified value, the SQD signal of the transmission device is turned on. The SQD detection circuit 29 turns on the SQD signal when the ratio of the ON time of the SQD signal per unit time exceeds a predetermined reference value.
Is notified to the control circuit 26. The control circuit 26 starts a switching instruction to the switch circuit 25. When the switch circuit 25 connects the terminal device to the ISDN interface circuit 27, it is also connected to the ISDN DSU or ISDNLINE via the connector or the connection unit 32, and the automatic backup is completed, and the process proceeds to the backup.

Next, the process of releasing the backup by monitoring the SQD signal during the backup and shifting to the normal operation will be described. During backup, the control circuit 26 constantly monitors the detection result from the SQD detection circuit 29. When the line quality is restored and the error rate of the received data becomes smaller than a specified value, the SQD signal of the transmission device is turned off. The SQD detection circuit 29 detects the SQD within a unit time.
When the ratio of the signal ON time falls below a predetermined reference value,
The control circuit 26 is notified that the SQD signal is OFF. The control circuit 26 that has sensed that the SQD signal is OFF stops the switching instruction to the switch circuit 25.
The switch circuit 25 completes the release of backup by connecting the terminal device and the transmission device in response to the stop of the switching instruction, and shifts to the normal operation.

[0012]

As described above, according to the present invention, the signal indicating that the terminal device is ready to receive data is turned off.
However, since this is due to the end of data transmission by a signal for transmitting a carrier, it is determined whether the transmission is due to fluctuation or deterioration of line quality, a data line for backup is established, and the error rate of received data is further reduced. Automatic backup is possible even when the carrier in the modem is used in the polling mode of ON or OFF by switching between the working line and the backup line according to the monitoring result of the signal indicating that it is larger than the specified value In addition, there is an effect that the time for establishing the backup line is not included in the time required for automatic switching.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an automatic line switching system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a conventional line switching device.

[Explanation of symbols]

 21 Connector to Host or Terminal Device 23 RS Detection Circuit 25 Switch Circuit 26 Control Circuit 27 ISDN Interface Circuit 28 CS Detection Circuit 29 SQD Detection Circuit

Claims (1)

(57) [Claims] A terminal device is ready to receive data.
Signal (RS) indicating that the carrier
Error rate of signal (CS) and received data is less than specified value
By monitoring the large signal (SQD)
Automatically switch between the normal operation state and the backup state.
An automatic line switching system that dynamically performs detection of the RS.
And an RS detection circuit for detecting the CS.
SC detection circuit and ON of the SQD within a unit time
When the time ratio exceeds a predetermined reference value, the SQ
An SQD detection circuit for detecting ON of D, and a switching instruction
Terminal device and transmission device or terminal device and back
A switch circuit that switches and connects the
Receive an instruction to establish a backup line or disconnect the backup line.
Backup data via ISDN.
ISDN interface for establishing or disconnecting a data line
And the switch circuit and the ISDN interface.
A control device for controlling the operation of the source circuit.
In the operation state, the control device is operated by the RS detection circuit.
And the SC detection circuit detects the RS.
Is detected, it is determined that normal operation is being performed, and the switch
Keep the terminal equipment and transmission equipment connected to the circuit.
And the RS detection circuit detects the RS
If the SC detection circuit does not detect the CS,
Judging that the quality is degraded, the ISDN interface circuit
To the backup line establishment to the SQD
When the detection circuit detects that the SQD is ON, the switch is turned off.
Switch instruction to the switch circuit, and
In the up state, the control device is connected to the SQD detection circuit.
Detects that the SQD signal has been turned OFF.
Stops the switching instruction for the road, and the switch circuit switches.
When the instruction is stopped, the connection between the terminal device and the transmission device is established.
This completes the release of the backup state,
Automatic line, wherein the automatic line shifts to the normal operation state.
Switching method.