JPH0213034A - Transmission line switching circuit - Google Patents

Abstract

PURPOSE:To avoid a problem that changeovers are successively generated when living and spare both systems are in trouble by using a signal format provided with a transmission line changeover control bit, inquiring a changeover propriety by means of the control bit of the spare system when the living system is abnormal, and executing a line changeover only in the case of reception at the time of no problem. CONSTITUTION:When a fault is generated to an N-system transmission line, a line fault detecting circuit 23 informs a line changeover control circuit 25 of a fault generation. The line changeover control circuit 25 instructs a transmission line changeover (propriety signal transmission/reception circuit 28 on the sending of a transmission line changeover propriety signal in an S bit position to opposed terminal equipment. On the other hand, at the opposite terminal equipment, the transmission line changeover propriety signal is received by the transmission line changeover propriety signal transmission/reception circuit 28. At such a time, when the output of a line fault detecting circuit 24 does not indicate an abnormal detection at the opposite terminal equipment, the line changeover control circuit 25 indicates the return of a changeover capable signal in the S bit position to a transmission changeover propriety signal transmission/reception circuit 8 with respect to transmission side terminal equipment, and thereafter, the changeover of the living and spare is executed by a line selecting circuit 26.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applied to a duplex transmission line between terminal devices,
The present invention relates to a switching circuit for switching transmission lines.

[Conventional technology]

First, FIG. 5 shows a system configuration when a pair of terminal devices are connected through a duplex transmission line.

Referring to FIG. 5, terminal devices 8 and 8' each have two lines of line termination device interface circuits 1゜2 and 1/,
2/ is equipped. Line termination device ink face circuit 1
and 2 are connected to a service office in the relay transmission line 6 by respective subscriber transmission lines 7 independent of the line termination devices 3 and 4, respectively.

Similarly, the two line termination interface circuits 1' and 2' are connected to the service office 5 by line termination devices 3' and 4', respectively, and respective independent subscriber transmission lines 7'.

Since mutually independent subscriber systems are constructed in this way, if one transmission line becomes unavailable due to a failure, communication between terminal devices can be routed to the other transmission line. It is possible to continue.

In the duplex transmission line described above, at the terminal device.

A circuit (transmission path switching circuit) is required to select which transmission path to use for transmitting and receiving data.

Conventionally, this type of transmission line switching circuit has a 2-line interface circuit 8 and a 92-line fault detection circuit lO as shown in FIG.
and 112 line line switching circuit 12° and line selection circuit 1
3, and constantly monitors the operating status of the working line.
Based on the fault detection results by the line fault detection circuits 10 and 11, the multi-line switching control circuit 12 controls the line switching circuit 13 to switch between the working line and the protection line.

In the case of the above-mentioned switching method, two communications are always carried out using one of the transmission lines, so for the backup transmission line.

No data is sent.

[Problem that the invention seeks to solve]

In the case of the conventional transmission line switching described above, one communication is always performed using one transmission line, so no data is sent to the backup system. Therefore, it is not possible to monitor transmission line failures in the protection system, and there is a problem in that switching occurs continuously when both the active and protection systems fail. Further, depending on a fault in a relay transmission path, the fault may not be transmitted to opposing terminal devices at the same time, so the fault may be detected only in two terminal devices. In this case, transmission path switching is performed only in terminal devices capable of detecting failures, so there is a problem in that the transmission paths used between the terminal devices are different and normal communication cannot be performed. moreover.

In FIG. 5, when a failure occurs between the line device interface circuit of the terminal device and the line termination device, the two-line termination device detects the loss of synchronization of the received signal frame from the terminal device, but depending on the two-line termination device, Since the frame of the signal sent to the service office is normally changed and sent, there is a problem that the opposing terminal device cannot detect the failure.

[Means for solving problems]

According to the present invention, a transmission line switching circuit is provided with a relay transmission line and is used when transmitting information communication signals between a pair of terminal apparatuses using a communication line in which the transmission line between the terminal apparatuses is duplicated. A format signal in which control information used to determine validity/invalidity of the information communication signal is multiplexed with the information communication signal is transmitted between the terminal devices, and the duplex transmission path a detection means for detecting a transmission line failure in each of the transmission line failures; and when the transmission line failure is detected, transmitting a transmission line switchability signal to the control information position of the transmission line, and receiving the transmission line switchability signal. and control information transmitting/receiving means for sending back information indicating whether or not the transmission line can be switched, and switching control means that controls switching between working and standby transmission lines based on the transmission line switchability signal. A switching circuit is obtained.

According to the second invention, a relay transmission path is provided.

This is a transmission path switching circuit used when transmitting information communication signals between a pair of terminal devices using a communication line in which the transmission path is duplicated between the pair of terminal devices.

Signals are transmitted between the terminal devices in a format in which control information used to control the terminal devices is multiplexed with the information communication signal, and detection is performed to detect transmission path failures in each of the duplex transmission paths. With means.

When the transmission path failure is detected, control information transmitting/receiving means transmits a transmission path switchability signal to the control information position of the transmission path, receives the transmission path switchability signal, and returns transmission path switchability information. and.

current use of the transmission line based on the transmission line switchability signal;
A transmission line switching circuit is obtained, characterized in that it has a switching control means for controlling switching of a backup.

〔Example〕

Next, the present invention will be explained with reference to examples.

FIG. 1 is a block diagram showing an embodiment of a terminal device to which the present invention is applied.

Referring to FIG. 1, 21 is an N-system line termination device interface circuit, 22 is an E-thread line termination device interface circuit, and 23 is an N-system line fault detection circuit.

24 is an E-system line fault detection circuit, 25 is a line switching side @ circuit, 26 is a line selection circuit, and 27 and 28 are N- and E-system transmission path switchability signal transmission/reception circuits, respectively.

Here, the active system is assumed to be N system, and the standby system is assumed to be E system. Transmission and reception signals of the terminal device are transmitted through the N-system line termination device interface circuit 21.
It is input/output via terminal A.

At this time, the two-line termination device interface circuit 21 matches the signal level within the device. Fault detection circuits 23 and 24 detect faults in their respective transmission paths, and detect transmission path faults that cause two communication failures, ie, frame synchronization loss and input signal disconnection. And failure detection circuits 23 and 24
The detection output is input to the line selection circuit 25.

Here, FIG. 2 shows the frame format of the signal used in this embodiment. Referring also to FIG. 2, information communication signals (data) between terminal devices are data transmission bits (H
The transmission line switching control signal is transmitted using the transmission line switching control bit (S bit). And H
A frame synchronization bit (F bit) for separating the S bit and the S bit is allocated. This control bit (S bit) is provided in advance by the network provider as a bit for determining validity/invalidity of data.

When the aforementioned fault occurs in the N-system transmission line, the two-line fault detection circuit 23 notifies the line switching control circuit 25 of the fault occurrence.

The line switching control circuit 25 instructs the transmission line switching permission signal transmitting/receiving circuit 28 to send a transmission line switching permission signal to the S bit position to the opposing terminal device.

On the other hand, in the opposite terminal device, the transmission path switching permission signal is received by the transmission path switching permission signal transmitting/receiving circuit '2-8.

At this time, if the output of the line fault detection circuit 24 does not indicate abnormality detection in the opposite terminal device, the two-line switching control circuit 25 sends a transmission line switching permission/reception signal transmission/reception circuit 8 at the S pit position with respect to the transmitting terminal device. After instructing the return of a switchable signal, the single line selection circuit 26 executes switching between active and standby lines.

When the transmitting terminal device receives a switchable signal from the opposite terminal device, it switches between working and standby. If the opposite terminal device receives a switch-disabled signal or there is no response, switching is not performed.

Next, other embodiments of the present invention will be described.

FIG. 3 is a block diagram showing another embodiment of a terminal device to which the present invention is applied. In this example.

Transmission path switching enable/disable signal transmitting/receiving circuits 27 and 2 shown in FIG.
N-system and E-system control information transmitting/receiving circuits 37 and 38 between opposite terminal devices are used for the 8 lines, respectively.

Here, FIG. 4 shows another example of the frame format of the signal used in this embodiment. Referring also to FIG. 4, information communication signal data between terminal devices is data transmission bit (H
Control information bits (C bits) are transmitted between opposing terminal devices, and in order to transmit information for terminal device control such as monitoring inside the terminal device and return control to the opposing terminal device, control information bits (C bits) are transmitted.
bits) are proportioned. The F bit is allocated as a frame synchronization bit for separating the H bit and C bit. That is, a part of the information transmission format is allocated to control information for controlling the terminal device.

In FIG. 3, a control information transmitting/receiving circuit 27 transmits and receives control signals through the active and backup transmission lines.

Now, if the N system is currently in use, the C bit on the N system transmission path is used to send and receive information between opposing terminal devices that the N system transmission path is currently in use, while the C bit on the E system transmission path is used to send and receive information that the N system is in use. is being sent and received.

Here, when the above-mentioned fault occurs in the N-system transmission line, the line fault detection circuit 23 notifies the line switching control circuit 25 of the occurrence of the fault. As a result, the line switching control circuit 25 issues an instruction to the control information transmitting/receiving circuit 38 to transmit an inquiry signal to the opposite terminal device, inquiring whether or not the E system can be switched to the current one. In response, if the opposite terminal device returns an ACK signal, the line switching control circuit 25 controls the line selection circuit 26 to use the current line.

Switch spares. On the other hand, if the opposite terminal device returns a NACK signal or does not respond, the backup system can also be recognized as abnormal, so switching is not performed.

〔Effect of the invention〕

As explained above, in the present invention, a signal fall equipped with a transmission line switching control bit is used, and in the event of an abnormality in the working system, the control bit of the standby system is used to determine whether switching is possible or not, and the line is switched only when a "key" is received. Therefore, the problems of the conventional technology can be solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a terminal device to which the present invention is applied, and FIG. 2 is a diagram showing a frame format used in the terminal device shown in FIG. 1. FIG. 3 is a block diagram showing an embodiment of a terminal device to which the present invention is applied. 4 is a diagram showing a frame format used in the terminal device shown in FIG. 3; FIG. 5 is a diagram for explaining a duplex transmission path; FIG. 6 is a diagram showing another embodiment of the terminal device;
The figure is a diagram for explaining a conventional transmission line switching circuit. 21...Line termination device interface circuit (N system) 2
2...Line termination device interface circuit (E system) 23
. . . Line failure detection circuit (N system), 24 . . . Line failure detection circuit (E system), 25 . . . Line switching control circuit. 26... Line selection circuit, 27... Transmission path switchability signal transmission/reception circuit (N system) 28... Transmission path switchability signal transmission/reception circuit (E system), 37... Control information transmission/reception circuit between opposing devices (N system), 38... Control information transmission/reception circuit between opposing devices (E system).

Claims (1)

[Claims] 1. A transmission line that is provided with a relay transmission line and is used when transmitting information communication signals between a pair of terminal apparatuses using a communication line in which the transmission line between the terminal apparatuses is duplicated. a switching circuit that controls whether the information communication signal is valid or not between the terminal devices;
A signal is transmitted in a first format in which control information used in determining invalidity is multiplexed with the information communication signal, and a detection means for detecting a transmission line failure in each of the duplex transmission lines; , when the transmission path failure is detected, transmitting/receiving control information that sends a transmission path switchability signal to the control information position of the transmission path, receives the transmission path switchability signal, and returns transmission path switchability information. and a switching control means for controlling switching between active and standby transmission lines based on the transmission line switching enable/disable signal. 2. In the statement of claim 1, instead of the first format, a second format is used between the terminal devices in which control information used for controlling the terminal devices is multiplexed on the information communication signal. A transmission line switching circuit characterized in that signals are transmitted in this format.