JP2003249992A - Leased line terminating device and state restoring method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leased line terminating device and a state restoring method for the same, which prevent state inconsistency between a terminating device on the control side and that on the controlled side to improve maintainability even in the case of occurrence of a line fault during a remote loop back test. <P>SOLUTION: The leased line terminating device on the control side and that on the controlled side individually detect whether a leased line is faulty or not during the remote loop back test and are individually restored to the normal state from the remote loop state at the time of occurrence of a fault of the leased line. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leased line terminating device and a state restoring method for the device, and particularly to 56 kbps.
The present invention relates to a leased line terminating device used for terminating a high-speed leased line having a line speed of (Bit Per Second) to about 6 Mbps and a method for restoring the state of the device.

[0002]

2. Description of the Related Art In recent years, with the increase in performance of computers and the increase in capacity of networks, it has become common to use computers by connecting them to the network. In particular,
In companies, it is becoming commonplace to improve the efficiency of work by connecting computer networks laid in each department to each other using high-speed dedicated lines to share information. The dedicated line includes an electric transmission line using a coaxial cable and an optical transmission line using an optical fiber. In recent years, an optical transmission line in which the line quality (communication speed) does not deteriorate so much even over a long transmission distance. Is often used as a dedicated line.

A terminal device (DSU (Digital Service Unit)) is provided at both ends of such a dedicated line. This terminating device may be provided with a loopback test function (for example, a remote loopback function compliant with ITU-T Recommendation V54) as one of the functions for diagnosing a line failure. Here, the remote loopback test is a loopback test performed between the terminating devices provided at both ends of the leased line. In the remote loopback test, one of the terminating devices (for example, the terminating device installed in the station) provided at both ends of the leased line becomes the control side, and the other (for example, the terminating device installed in the subscriber's premises). The terminating device) is the controlled side.

In the remote loopback test, the terminating device on the control side first sends a remote loop start command to the terminating device on the controlled side via a dedicated line. Upon receiving this command, the controlled-side terminating device transmits a remote loop start response command to the controlling-side terminating device via the leased line, and the remote loop state is set. Then, when the remote loop start response command transmitted is received, the terminating device on the control side is in the remote loop state. When both the terminating device on the control side and the terminating device on the controlled side are in the remote loop state, the remote loopback test is performed.

When the remote loopback test is finished, the terminating device on the control side sends a remote loop release command to the terminating device on the controlled side via a dedicated line. When this remote loop release command is sent, the terminating device on the control side is in the normal state (communication possible state).
Return to. On the other hand, the terminal device on the controlled side returns to the normal state at the time of receiving the remote loop release command transmitted from the control side via the dedicated line.

[0006]

By the way, as described above, when the remote loopback test is completed in the conventional termination device, the termination device on the control side is in the normal state at the time of transmitting the remote loop release command. However, the terminal device on the controlled side returns to the normal state when it receives the remote loop release command transmitted from the control side via the dedicated line.

Therefore, for example, if a line failure occurs during the remote loopback test, the terminating device on the control side receives the remote loop release command and returns to the normal state even though it has returned to the normal state. A situation occurs in which the terminating device on the control side cannot receive the remote loop release command transmitted by the terminating device on the control side and has not returned to the normal state. The controlled-side terminating device returns to the normal state only after receiving the remote loop release command transmitted by the controlled-side terminating device, so that when the line is restored, the controlling-side terminating device is in the normal state. The controlled-side terminating device remains in the remote loop state, the two states are different, and communication cannot be performed.Furthermore, between the controlled-side terminating device and the controlled-side terminating device. There was a problem that it could not be restored automatically and maintainability was poor.

The present invention has been made in view of the above circumstances. Even when a line failure occurs during the remote loopback test, the termination device on the control side and the termination device on the controlled side are not affected by the situation. An object of the present invention is to provide a leased line terminating device capable of improving maintainability without causing discrepancies and a method of restoring the state of the device.

[0009]

In order to solve the above-mentioned problems, a leased line terminating device of the present invention communicates the state of the device in a leased line terminating device (1a, 1b) that terminates a leased line (N). A status setting unit (1) for setting one of the status and the communication test status via the dedicated line (N).
9), a fault detection unit (22) for detecting the presence / absence of a fault in the dedicated line (N), and a case where the state of the device is set to the communication test state, the fault detection unit (2)
When a failure of the leased line (N) is detected in 2),
A state control unit (21) for controlling the state setting unit (19) to restore the state of the device from the communication test state to the communication state. According to the present invention, the presence / absence of a failure in the leased line is detected when the status of the leased line termination device is set to the communication test state, and when the leased line fails, the communication test state is changed to the communication state. Since it is designed to recover, even if a line failure occurs during the communication test via the dedicated line, there is no discrepancy between the states of the dedicated line terminators, improving maintainability. Can be made. Further, in the leased line terminating device of the present invention, the state setting unit transmits the signal from the leased line (N) when the state of the device is set to the communication state, and the state of the device is When the communication test state is set, a loopback unit (1) that loops back the signal from the dedicated line (N) and sends it to the dedicated line (N).
It is preferable to include 9). Also, in the leased line terminating device of the present invention, the state control unit (21) controls the state setting unit (19) when a communication test cancellation signal is transmitted from the leased line (N). It is preferable that the state of the device is returned from the communication test state to the communication state. In order to solve the above problems, a leased line terminating device of the present invention is a leased line terminating device for terminating a leased line (N), wherein the state of the device is a communication state and a communication test state via the leased line (N). A status setting section (19) for setting the status to one of the two states, a failure detection section (22) for detecting the presence / absence of a failure in the leased line (N), and a communication test activation signal from the leased line (N). When transmitted, the state setting unit (19) is controlled to set the state of the device to the communication test state, and the failure detection unit (22).
In the case where a failure of the leased line (N) is detected, the status control section (1) controls the status setting section (19) to restore the status of the device from the communication test status to the communication status.
6, 21) are provided. Further, in the leased line terminating device of the present invention, the state setting unit transmits the signal from the leased line (N) when the state of the device is set to the communication state, and the state of the device is If the communication test status is set, the dedicated line (N)
It is preferable to include a loopback section (19) for looping back the signal from the above and sending it to the dedicated line (N). Further, the leased line terminating device of the present invention is the state control unit (21).
However, when a communication test release signal is transmitted from the dedicated line (N), the state setting unit (19) is controlled to restore the state of the device from the communication test state to the communication state. Is preferred. In order to solve the above problems, a leased line terminating device of the present invention is a leased line terminating device for terminating a leased line (N), wherein the state of the device is a communication state and a communication test state via the leased line (N). A status setting unit (19) for setting the status to either one of the statuses, a sending unit (12) for sending a status control signal for controlling the status of the leased line terminating device on the partner side to the leased line (N), and Failure detection unit (2) that detects the presence or absence of a failure in the leased line (N)
2) and the sending unit (12) sends to the dedicated line (N) a communication test start signal for setting the state of the other party's dedicated line terminating device to the communication test state as the state control signal, and When the response signal to the communication test activation signal is received via the dedicated line (N), the state setting unit (19) is controlled to set the state of the device to the communication test state, and the failure detection unit ( 22) In the dedicated line (N)
And a status control section (16, 21) for controlling the status setting section (19) to restore the status of the device from the communication test status to the communication status when a failure is detected. I am trying. Further, in the leased line terminating device of the present invention, the state control unit (21) includes the transmission unit (1).
When 2) sends a communication test cancellation signal for canceling the communication test status of the other party's dedicated line terminating device to the dedicated line as the status control signal, the status setting unit (19)
Is preferably controlled to return the state of the device from the communication test state to the communication state. In order to solve the above-mentioned problems, the state restoration method of a leased line terminating device terminates a leased line (N), and the state is either a communication state or a communication test state through the leased line (N). In the method for recovering the state of the leased line terminating device (1a, 1b) set in step 1, a detection step of detecting the presence or absence of a fault in the leased line (N), and the state being set to the communication test state, And a return step of returning the state from the communication test state to the communication state when a failure of the leased line (N) is detected in the detecting step.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A leased line terminating device and a state restoring method for the device according to an embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an installation example of a leased line termination device according to an embodiment of the present invention. In FIG. 1, N is a high-speed leased line having a transmission speed of, for example, about 6 Mbps. The dedicated line may be either an electric transmission line using a coaxial cable or an optical transmission line using an optical fiber, but in the present embodiment, the case of an optical transmission line will be described.

At both ends of the leased line N, the leased line terminators 1a and 1b of the present embodiment are connected, respectively.
Is terminated. A router 3a is connected to the leased line terminating device 1a. This router 3a is connected to the local area network N1. The local area network N1 includes a computer 2 as illustrated.
A terminal device such as a is connected.

Further, the dedicated line termination device 1b has a router 3
b is connected, and this router 3b is connected to the local area network N2. The local area network N2 includes a computer 2b as shown in the figure.
And other terminal devices are connected. As described above, the leased line terminators 1a and 1b of the present embodiment terminate the leased line N, and the local area network N is connected via the leased line N.
1 and the local area network N2 are connected to each other.

Next, the internal configuration of the leased line terminating device of this embodiment will be described. FIG. 2 is a block diagram showing an internal configuration of the leased line termination device according to the embodiment of the present invention. Since the leased line termination device 1a and the leased line termination device 1b shown in FIG. 1 have the same configuration, the leased line termination device 1a will be described as a representative in FIG. The description of the internal configuration is omitted.

As shown in FIG. 2, the leased line terminating device 1a
Is a receiver unit 10, a speed conversion unit 11, a transmission unit 12, a framer / deframer unit 13, an electric / optical conversion unit 14, and an optical / optical conversion unit.
The electrical conversion unit 15, the reception unit 16, the buffer unit 17, the speed conversion unit 18, the folding unit 19, the driver unit 20, the logic circuit unit 21, and the detection unit 22 are included. The receiver unit 10 receives a signal (for example, a packet format signal) output from the router 3a.

The speed conversion unit 11 detects the speed of the signal output from the receiver unit 10 via the loopback unit 19 (router 3
The transmission rate on the a side) is converted into the transmission rate on the dedicated line N side. The transmission unit 12 converts the signal output from the speed conversion unit 11 into a format suitable for transmitting to the private line N side, and controls the timing of transmitting the converted signal to the private line N.

Further, the transmission section 12 is a dedicated line terminating device 1a.
When the power is turned on and when a specific operation is performed by the user, the state of the dedicated line terminating device (the dedicated line terminating device 1b in the example of FIG. 1) connected to the dedicated line N is changed. Outputs the remote loop start command to set the state in the remote loop. On the contrary, the leased line N
When the remote loop start command transmitted via the is received, the remote loop start response command is output. The transmitter 12 corresponds to the transmitter of the present invention, and the remote loop start command output by the transmitter 12 corresponds to one communication test start signal of the state control signal of the present invention.

The framer / deframer unit 13 is a transmitter unit 1.
The signal output from 2 is converted to frame format and converted to electricity /
The light / electricity converter 15 outputs the light to the light converter 14.
The electrical signal output from the device is deframed. The electric / optical conversion unit 14 converts the signal output from the framer / deframer unit 13 into an optical signal and sends the optical signal to the dedicated line N.
The optical / electrical conversion unit 15 converts the optical signal transmitted from the dedicated line N into an electric signal, and the framer / deframer unit 1
Output to 3.

Here, the framer / deframer unit 13 is
The signal output from the optical / electrical converter 15 is constantly monitored,
A detection unit 22 is provided which detects the presence or absence of a fault in the leased line N and outputs a detection signal to the logic circuit unit 21. This detection unit 22
Corresponds to the failure detection unit according to the present invention. Receiver 16
Indicates that the signal output from the framer / deframer 13 includes any one of a remote loop start command (communication test start signal), a remote loop start response command (response signal), and a remote loop cancel command (communication test cancel signal). Monitor whether or not When any of these is included in the signal output from the framer / deframer 13, the detection signal indicating that is output to the logic circuit unit 21.

The buffer unit 17 is for temporarily storing the data output from the framer / deframer 13 in order to absorb the difference between the transmission speed on the private line N side and the transmission speed on the router side 3a side. is there. Speed converter 18
Converts the speed of the signal output from the buffer unit 17 (transmission speed on the dedicated line N side) into the transmission speed on the router 3a side.

The loopback section 19 includes the leased line terminating device 1a.
Is in a normal state (communication possible state: communication state referred to in the present invention), the signal output from the speed conversion unit 18 is output to the driver unit 20, and the state in the remote loop (referred to in the present invention). , Communication test status)
The signal output from the speed conversion unit 18 is output to the speed conversion unit 11. That is, the loopback unit 19 transmits a signal from the leased line in the normal state and loops back the signal from the leased line in the remote loop state. The folding back portion 19 corresponds to the state setting portion (folding portion) according to the present invention.

The driver unit 20 outputs the signal output from the speed converting unit 18 via the folding unit 19 to the router 3a. The logic circuit unit 21 outputs a detection signal indicating that a failure has occurred in the leased line N from the detection unit 22, and a detection signal indicating that the remote loop release command has been received from the reception unit 16. In the folding part 19
In response, the control signal for controlling the signal output from the speed conversion unit 18 to be output to the speed conversion unit 11 is output.

Further, in the logic circuit section 21, the transmitting section 12 transmits the remote loop start command to the other party's dedicated line terminating device (in the example of FIG. 1, the dedicated line terminating device 1b) via the dedicated line N. When a detection signal indicating that the remote loop start response command has been received is output from the receiving unit 16 later, the signal output from the speed converting unit 18 to the loopback unit 19 is output to the driver unit 20. Outputs a control signal for controlling. The logic circuit section 21 and the receiving section 16 described above correspond to the state control section according to the present invention.

The configuration of the leased line termination device according to the embodiment of the present invention has been described above. Next, the state change when the leased line termination devices 1a and 1b perform the remote loopback test will be described. In the following description, it is assumed that the leased line termination device 1a is on the control side and the leased line termination device 1b is on the controlled side. Further, in the initial state, both the leased line termination devices 1a and 1b are in the normal state. In the remote loopback test, the control side and the controlled side of the leased line termination devices 1a and 1b are not fixed, and when one becomes the control side, the other becomes the controlled side.

FIG. 3 is a diagram showing a communication state between the leased line termination devices 1a and 1b during the remote loopback test. Further, FIG. 4 shows dedicated line termination devices 1a and 1b.
2A is a state transition diagram showing state transitions during the remote loopback test of FIG. 3A is a state transition diagram of the leased line termination device 1a, and FIG. 3B is a state transition diagram of the leased line termination device 1b. .

The power of the leased line termination device 1a is turned on,
When the user performs a specific operation, the transmitter 12 (see FIG. 2) of the leased line terminating device 1a outputs a remote loop activation command to the framer / deframer unit 13.
When the framer / deframer unit 13 frames the remote loop activation command and outputs it to the electric / optical conversion unit 14, the electric / optical conversion unit 14 converts it into an optical signal and sends the remote loop activation command to the dedicated line N ( Step Tr1). When the leased line termination device 1a sends a remote loop start command, the leased line termination device 1a
Becomes a state in which the remote loop is being activated (see FIG. 4A).

The remote loop start command sent as an optical signal to the leased line N is received by the leased line terminating device 1b, converted into an electric signal by the optical / electrical conversion unit 15, and deframed by the framer / deframer unit 13. To be done. still,
Since the leased line termination device 1a and the leased line termination device 1b have the same configuration, the internal configuration of the leased line termination device 1b will also be described with reference to FIG.

When the signal including the remote loop start command is output from the framer / deframer section 13, a detection signal indicating that the remote loop start response command has been received by the receiving section 16 is output to the logic circuit section 21. It
When this detection signal is input, the logic circuit unit 21 controls the folding unit 19 to output the signal output from the speed conversion unit 18 to the speed conversion unit 11. As described above, the leased line terminating device 1b is in the remote loop state.

Upon completion of the above processing, the transmitter 12
The remote loop start response command is output to the framer / deframer 13. When the framer / deframer unit 13 frames the remote loop activation response command and outputs it to the electrical / optical conversion unit 14, it is converted into an optical signal by the electrical / optical conversion unit 14 and the remote loop activation response command is sent to the dedicated line N. (Step Tr2).

The remote loop start response command sent as an optical signal to the leased line N is the leased line terminating device 1a.
The optical / electrical conversion unit 15 converts the electric signal into an electric signal, and the framer / deframer unit 13 deframes the electric signal. When the signal including the remote loop start response command is output from the framer / deframer unit 13, the receiving unit 1
A detection signal indicating that the remote loop start response command has been detected in 6 is output to the logic circuit unit 21.

When this detection signal is input, the logic circuit section 2
1 controls the folding unit 19 to output the signal output from the speed converting unit 18 to the speed converting unit 11. As described above, the leased line terminating device 1a is in the remote loop. By following the above procedure, both the dedicated circuit termination device 1a and the dedicated circuit termination device 1b
A remote loopback test is performed because the system is in a loop.

If no failure occurs in the leased line N during the remote loopback test, the transmitter 12 of the leased line termination device 1a outputs a remote loop release command, and the framer / deframer 13 sends a frame. After being converted, the electric / optical conversion unit 14 converts the signal into an optical signal and sends the remote loop release command to the dedicated line N (step Tr3). When the remote loop release command is sent to the leased line N, the leased line terminating device 1a returns to the normal state, and the loopback unit 19 outputs the signal output from the speed conversion unit 18 to the driver unit 20. Controlled.

The remote loop release command sent as an optical signal to the leased line N is received by the leased line terminating device 1b, converted into an electrical signal by the optical / electrical conversion unit 15, and deframed by the framer / deframer unit 13. After being generated and output, it is detected by the receiving unit 16. When the receiving unit 16 outputs the detection signal indicating that the remote loop cancel command is received to the logic circuit unit 21, the logic circuit unit 21 sends the signal output from the speed converting unit 18 to the folding unit 19 to the driver unit 20. Control to output. by this,
The leased line termination device 1b returns to the normal state.

Next, a case where a failure occurs in the leased line N during the remote loopback test will be described. During the remote loopback test, the leased line termination devices 1a, 1
Both b are in loopback. remote·
If a failure occurs in the leased line N during the loopback test, as shown in FIGS. 4 (a) and 4 (b), the detector 22 provided in the leased line termination device 1a and the leased line termination device 1b causes the leased line N to operate. The fault occurring in step 1 is detected (detection step), and a detection signal indicating that the fault has occurred is output to the logic circuit unit 21.

When this detection signal is input, the logic circuit unit 21 causes the speed converter 18 to turn back the unit 19.
The signal output from is output to the driver unit 20. This control is performed by both the leased line terminating device 1a and the leased line terminating device 1b. As a result, as shown in FIGS. 4A and 4B, both the leased line terminating device 1a and the leased line terminating device 1b return from the state in the remote loop to the normal state (return step).

As described above, according to the leased line terminating device and the state restoring method of the device according to the embodiment of the present invention, when the leased line terminating devices 1a and 1b are in the loop back state, Since both of the terminating devices 1a and 1b individually detect the failure of the leased line N and return from the loop back state to the normal state, the leased line terminating devices 1a and 1b do not cause the state to be maintained and are maintained. It is possible to improve the sex.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be freely modified within the scope of the present invention. For example, in the above-described embodiment, the case where a failure occurs in the private line N during the remote loopback test has been described as an example, but in addition to this, a private line that occurs when the operation mode of the private line N is changed. It can also be used to prevent state discrepancies between end devices.

FIG. 5 is a diagram showing a modification of the operation mode of the private line N. Now, as shown in FIG. 5, the leased line termination device 1a is connected to one end of the leased line N and the leased line termination device 1b is connected to the other end of the leased line N.
Consider the case where a and 1b are in the remote loopback test.

During the remote loopback test, for example, by exchanging the leased line terminating device 1b or changing the connection route of the leased line N, the operation mode of the leased line N is changed to the leased line connection device 1a and the leased line connection device 1c. When the operation mode is changed to the connection between and, there is a possibility that a discrepancy may occur between the state of the leased line termination device 1a and the state of the leased line termination device 1b.

In order to prevent a discrepancy in the state between the leased line terminators 1a and 1b, conventionally, the leased line terminator 1a, 1
It was necessary to shut off both power supplies of 1b to return them to the normal state. However, if the leased line terminators 1a and 1b of the present embodiment are used, replacement of the leased line terminator 1b,
Alternatively, when the connection route of the private line N is changed, the detection unit 22
Since it is detected as an abnormality in the leased line, it is possible to return to the normal state by both the leased line terminators 1a and 1b, and there is no discrepancy in the state, and maintainability can be improved.

[0040]

As described above, according to the present invention,
When the state of the leased line termination device is set to the communication test state, the presence or absence of a fault in the leased line is detected, and when the leased line fails, the communication test state is restored to the communication state. Therefore, even if a line failure occurs during the communication test via the dedicated line, there is no discrepancy in the state between the dedicated line terminators, and the maintainability can be improved. There is.

[Brief description of drawings]

FIG. 1 is a diagram showing an installation example of a leased line termination device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of a leased line termination device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a communication state between the leased line termination devices 1a and 1b during a remote loopback test.

FIG. 4 is a state transition diagram showing state transitions of the leased line termination devices 1a and 1b during a remote loopback test, where (a) is a state transition diagram of the leased line termination device 1a, and (b) is It is a state transition diagram of the leased line termination device 1b.

FIG. 5 is a diagram showing a modification example of the operation mode of the leased line N.

[Explanation of symbols]

1a, 1b Dedicated line termination device 12 Transmitter (transmitter) 16 Receiver (state controller) 19 Folding part (state setting part) 21 Logic circuit section (state control section) 22 Detection unit (fault detection unit) N leased line

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5K027 BB04 CC06 KK02 LL05                 5K035 AA07 BB01 DD01 GG08 JJ06                 5K101 LL04 MM04 VV02

Claims (9)

[Claims] 1. A dedicated line terminating device for terminating a dedicated line, a state setting unit for setting the state of the device to one of a communication state and a communication test state via the dedicated line; A fault detection unit that detects the presence or absence of a fault, and a case where the state of the device is set to the communication test state, and when the fault detection unit detects a fault in the leased line, the state setting is performed. A dedicated line termination device, comprising: a state control unit that controls a unit to return the state of the device from the communication test state to the communication state. 2. The state setting unit transmits a signal from the leased line when the state of the device is set to the communication state, and the state of the device is set to the communication test state. 2. The leased line terminating device according to claim 1, further comprising a loopback unit that loops back a signal from the leased line and sends the signal to the leased line. 3. The state control unit controls the state setting unit to change the state of the device from the communication test state to the communication state when a communication test release signal is transmitted from the dedicated line. The leased line terminating device according to claim 1 or 2, which is restored. 4. A leased line terminating device for terminating a leased line, a state setting unit for setting the state of the device to one of a communication state and a communication test state via the leased line, A failure detection unit that detects the presence or absence of a failure, and when a communication test start signal is transmitted from the dedicated line, controls the state setting unit to set the state of the device to the communication test state, A dedicated state control section that controls the state setting section to restore the state of the device from the communication test state to the communication state when a failure of the dedicated line is detected by the detection section. Line terminator. 5. The state setting unit transmits a signal from the leased line when the state of the device is set to the communication state, and when the state of the device is set to the communication test state. 5. The leased line terminating device according to claim 4, further comprising a loopback unit that loops back a signal from the leased line and sends the signal to the leased line. 6. The state control unit controls the state setting unit to change the state of the device from the communication test state to the communication state when a communication test release signal is transmitted from the dedicated line. The leased line terminating device according to claim 4 or 5, which is restored. 7. A leased line terminating device for terminating a leased line, a state setting section for setting the state of the device to either one of a communication state and a communication test state through the leased line, and a dedicated party on the other side. A sending unit for sending a status control signal for controlling the status of the line terminating device to the dedicated line, a failure detection unit for detecting the presence / absence of a failure of the dedicated line, and the sending unit for sending the status control signal to the other side. When the communication test start signal for setting the state of the leased line terminating device to the communication test state is sent to the leased line and the response signal to the communication test start signal is received via the leased line, the state setting unit To set the state of the device to a communication test state, and when the fault detection unit detects a fault in the leased line, controls the state setting unit to set the state of the device to the communication state. Private network unit characterized by comprising a state controller to return to the communication state from the test state. 8. The status control unit, when the sending unit sends a communication test cancel signal for canceling a communication test status of the other party's dedicated line terminating device to the dedicated line as the status control signal, 8. The leased line terminating device according to claim 7, wherein the state setting unit is controlled to return the state of the device from the communication test state to the communication state. 9. A state restoration method of a leased line terminating device, wherein a leased line is terminated and the state is set to either one of a communication state and a communication test state via the leased line. And a detection step of detecting the presence or absence of the presence of the communication line, and the state is set to the communication test state, and when a failure of the leased line is detected in the detection step, the state is returned from the communication test state to the communication state. A method for restoring the state of a leased line terminating device, comprising: