JPH08340382A - Line monitoring system - Google Patents

Abstract

PURPOSE: To provide a line monitoring system capable of transmitting performance information to a center side by using facility to support a superframe format. CONSTITUTION: A central terminal 1, when detecting step out in reception from a remote terminal, sends out a synchronous alarm to the remote terminal 12. Line quality information is generated by a far end PM(performance) detection circuit 27, etc., based on a signal received by the remote terminal 12. The remote terminal 12 uses all the sync bits of a frame format to be transferred to a central terminal side as ordinary synchronization information while the synchronous alarm arrives from the central terminal side. When no more synchronous alarm arrives, the line quality information is transmitted to the central terminal 11 by using a part (F12 bit) of the sync bit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line monitoring system for monitoring the line quality of a digital communication line, and more particularly to a line monitoring system for centrally managing line quality information at a central terminal.

[0002]

2. Description of the Related Art In recent years, there have been many opportunities to transmit various data other than voice signals through a line, and a line quality higher than that required for voice signal transmission is required. Further, in the operation, maintenance and management of the transmission system including the transmission line, it is required to easily and cost-effectively perform these operations. In order to efficiently meet these requirements, the management of transmission systems is shifting to a centralized management system in the station building.

In the communication between a remote terminal that collects remote subscribers and a central terminal arranged in the center, there is an increasing demand for centralized control of the line quality on the central terminal side. Communication between the remote terminal and the central terminal is carried out through a primary group digital line in which signals of a plurality of subscriber units connected to the remote terminal such as voice signals of a telephone are digitized and time-division multiplexed. The transmission rate of the signal of the primary group digital line is 1544
It is Kbps, and low speed signals from 24 channel subscriber units are time division multiplexed. The primary group speed signal transmitted by the primary group digital line is a DS1 signal,
The signal to and from the low speed subscriber unit will be referred to as the DS0 signal.

FIG. 4 shows an outline of the configuration of the primary group digital signal transmission system. A plurality of telephone devices 101 _{1 to} 101 _N in remote locations are remote terminals 10
It is housed in 2. The remote terminal 102 is connected to the central terminal 105 through the upstream primary group digital line 103 and the downstream primary group digital line 104. Repeaters 106 _{1 to} 106 ₄ for compensating for transmission loss are arranged in the transmission paths of the upstream and downstream primary group digital lines 103 and 104.
The central terminal 105 also has a subscriber exchange 1
07 is connected.

The frame format of the DS1 signal of the primary group velocity is a superframe format (Superfra format).
Two formats, the Me Format) and the Extended Superframe Format, are the American National Standard Institute (ANS).
Represented as I. ) T103.

FIG. 5 shows the signal format of the superframe format. One frame 111
Is a 1-bit frame bit 112 (hereinafter referred to as F bit) and 24 time slots 113 _{1 to} 11
It is composed of 3 ₂₄ . Further, each time slot has 8 bits. The F bit is used for frame synchronization and monitoring of transmission errors. Each frame is composed of 193 bits by combining the F bit and the time slot of 24 channels. The DS1 signal in the superframe format handles 12 frames as one unit, and a group of 12 frames is called a multiframe. Also, each multi-frame is 1.5m
s is transmitted.

FIG. 6 shows a signal format of the extended super frame format. Each frame structure of the extended super frame format is the same as that of the super frame format. However, 24 frames are handled as one unit, and one multiframe 121 is transmitted in 3 ms.

The superframe format has 12 F bits in one multiframe, and the role of each bit is defined in units of 12 bits. 2 in extended superframe format
The role of each bit is defined by the recommendation in units of 24 F bits for 4 frames.

FIG. 7 shows the function allocation of each bit in the superframe format.
The leftmost frame number 131 represents the frame number in each multiframe. F bit application 132
Indicates the use of the F bit in each frame. F _T
Represents a bit used as a synchronization bit for frame synchronization and the value to be taken by the F bit.
F _S represents the F bit used as a signal bit for transmitting various information and the value at that time.

The F bit of the twelfth frame (hereinafter referred to as F12
Expressed as a bit. ) 133 is used as an alarm for notifying the source of the presence or absence of a fault when a fault in the line quality is detected based on the signal received from the partner terminal. The bit usage 134 of each channel represents the usage of each bit in each time slot. The bits of each time slot are used as a data bit 135 for transmitting arbitrary information and a signaling bit for transmitting a predetermined signal.

FIG. 8 shows the function allocation of each bit in the extended superframe format. As in the case of the super frame format, the frame number 141, the F bit usage 142, the bit usage 143 of each channel, and the signaling bit usage 144 are defined. Where the extended
24 multiframes in superframe format
Since it is composed of bits, it has 12 more F bits than the multiframe of the superframe format. These bits are allocated to the bits indicated by "M" in the FDL (145) column of the F bit application 142 and are used for transmission of an arbitrary message.

The extended superframe format is 4 Kb due to the F bits represented by "M".
An it / sec data link is provided. That is, it is possible to transmit 4 Kbit information using F bits in 1 second. As a result, in the extended super frame format, information about the line quality detected by the remote terminal is transmitted to the central terminal. The information about the line quality transmitted from the remote terminal to the central terminal is called performance information. The performance information indicates not only the presence / absence of a line failure but also the line quality in more detail, such as how much the line quality is degraded.

[0013]

In the superframe format, only F12 bits are allocated for transmission in the line state, so that only the presence or absence of line failure can be transmitted to the central terminal. Therefore, if the existing transmission system can support only the superframe format, there is a problem that the central quality control of the line quality between the remote terminal and the remote terminal located at the center station cannot be finely performed. If all existing equipment is modified to support the extended superframe format, performance information can be transmitted using the F bit for messages, and the line quality can be properly managed on the central terminal side. it can. However, there is a problem in that a large amount of capital investment is required to change all of the remote terminal, the central terminal, and the repeater between them so that the extended superframe format can be supported.

SUMMARY OF THE INVENTION An object of the present invention is to provide a line monitoring system capable of transmitting performance information to the central terminal side by utilizing equipment supporting the superframe format.

[0015]

According to a first aspect of the present invention, there is provided a receiving means for receiving a signal transmitted from a partner station, and a line indicating the channel quality between the partner station based on the received signal. Line quality information generating means for generating quality information,
A synchronization alarm detecting means for detecting a synchronization alarm indicating that synchronization has been lost at the reception of the signal at the partner station included in the received signal, and a plurality of synchronization bits for establishing synchronization among them. A framing means for converting information to be transmitted into a predetermined frame format capable of detecting the presence or absence of out-of-sync with only the remaining synchronization bits excluding arbitrary bits, and a signal framed by this framing means is transmitted to the partner station And the synchronization alarm detecting means detects that the transmission signal of the transmitting means is received by the partner station without being out of synchronization, the line quality is set to a predetermined information transmission synchronization bit among a plurality of synchronization bits. A terminal device provided with a synchronization bit diversion means for carrying information, and a predetermined frame format sent from this terminal device. , A synchronization alarm generation means for generating a synchronization alarm when the synchronization detection means detects that synchronization is lost, and a synchronization alarm generation means for generating a synchronization alarm. A transmission means for transmitting a signal carrying a synchronization alarm to the terminal equipment, and when the synchronization detection means detects that there is no out-of-synchronization when receiving the signal from the terminal equipment A line monitoring system, comprising: a central station device having line quality information extracting means for extracting line quality information from an information transmission synchronizing bit in an existing signal.

That is, according to the first aspect of the invention, information is transmitted from the terminal station side to the central station side by a frame format capable of detecting out-of-sync even if a part of a plurality of synchronization bits is excluded. And the terminal device
When synchronization is established at the central office equipment side, part of the synchronization bit is used to transmit the line quality information, and when synchronization is not established at the central office equipment side, the synchronization information is sent by that bit. There is. As a result, the same bit can be used for two purposes of establishing synchronization and transmitting the line quality information, and the line quality information can be transferred without the dedicated bit.

According to the second aspect of the invention, the predetermined frame format is a multi-frame composed of a plurality of unit frames each having a synchronization bit, and the information transmission synchronization bit is a synchronization of a predetermined predetermined unit frame. Bits are used.

That is, according to the second aspect of the invention, the line quality information is transferred by utilizing the synchronization bit of a predetermined frame in the multi-frame. Since a synchronization bit is provided for each frame of the multi-frame, it is possible to identify whether or not synchronization is lost even if some of these are used for information transfer.

According to the third aspect of the present invention, the line quality information is larger than the number of information transmission synchronization bits, and the synchronization bit diversion means uses each bit of the line quality information for information transmission synchronization of a plurality of predetermined frame formats. It is listed in the bit order.

That is, according to the third aspect of the present invention, the line quality information is divided into a plurality of pieces and sequentially placed on the information transmission sync bits. For example, if there is only one synchronization bit that can be used for information transmission in one frame format, but the line quality information needs to be transmitted about once per second, the line quality information is divided into a plurality of frames. It can be transmitted.

According to the fourth aspect of the invention, the synchronization detecting means establishes synchronization by referring to all of the plurality of synchronization bits at the time of synchronization pull-in, and after the synchronization pull-in is completed, a certain number or more of synchronization bits are detected. It is determined that the synchronization is lost only when the synchronization is lost.

That is, in the invention described in claim 4, when the synchronization pull-in is performed, the bits allocated for information transmission are referred to for establishing the synchronization, and once the synchronization is established, a predetermined number or more of synchronizations are performed. Only when the bit goes out of sync, it is determined that the bit is out of sync. After the synchronization is established, the line quality information having an arbitrary value is transmitted by a specific synchronization bit, and thus this bit may indicate a state of being out of synchronization. However, since the synchronization loss of a certain number of synchronization bits or less is ignored, the synchronization alarm is not sent to the partner station. As a result, the partner station can continue to carry the line quality information in the synchronization bit.

In the invention described in claim 5, the predetermined frame format is a super frame format used in the primary group interface.

That is, in the invention described in claim 5, the line quality information is transmitted by using a predetermined bit among the synchronization bits of the superframe format.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows an outline of the configuration of a line monitoring system according to an embodiment of the present invention. The line monitoring system is composed of a central terminal 11 and a remote terminal 12, and an upstream primary group digital line 13 and a downstream primary group digital line 14 that connect them. The remote terminal 12 is provided with a synchronization detection circuit 21 for performing frame synchronization of the DS1 signal of the super frame format sent through the downlink primary group digital line 14. The synchronization detection circuit 21 is
Frame synchronization is established based on the F bit, and the F bit that is a synchronization signal and the DS0 signal included in each time slot of 24 channels are identified. When the synchronization is confirmed, the timing signal 22 is output.

The remote alarm detection circuit 23 has a timing signal 22 and a superframe format DS1.
A signal is being input. Remote alarm detection circuit 23
Is the DS1 sent from the Central Terminal 11
It is a circuit for extracting the remote alarm information 24 from the signal based on the timing signal. Remote alarm information 2
Reference numeral 4 indicates whether or not the central terminal side is out of synchronization when the central terminal side receives the signal transmitted from the remote terminal 12 toward the central terminal 11 side.

The DS1 signal in the superframe format from the central terminal 11 is a near end performance detection circuit (hereinafter, near end PM).
Represented as a detection circuit. ) 25. The near-end PM detection circuit 25 is a circuit that monitors an error condition in the DS1 signal. The error detection is performed by mismatching the transmission code transmission rules or comparing the patterns of the synchronization signals after confirmation of synchronization. That is, the one that multiframe has
The extent to which the two F-bit bit patterns agree with a predetermined pattern is checked to identify the degree of error. The near-end PM detection circuit 25 integrates the detected error information for a certain period of time and outputs it as performance information 26.

The performance information 26 output from the near-end PM detection circuit 25 is the remote terminal 1
It is sent to the performance management unit (not shown) on the second side and is used for error display on the remote side. Performance information 2 output from the near-end PM detection circuit 25
6 is a far end performance detection circuit (hereinafter,
It is referred to as a far-end PM detection circuit. ) 27 is input. The far-end PM detection circuit 27 is a circuit that converts performance information into a format suitable for transmission to the central terminal 11 side. For example, it converts the surplus bits such as an error check code for error processing when a header part of a higher protocol or a transmission error is mixed into the framed performance information 28 in which performance information is added.

The framed performance information 28 and the remote alarm information 24 output from the remote alarm detection circuit 23 are input to the performance information insertion circuit 29. Further, the F12 bit signal 3 is generated from the F12 generation circuit 31 that generates the F12 bit as the synchronization signal.
2 is input to the performance information insertion circuit 29. The performance information insertion circuit 29 uses the F12 generation circuit 31 as the F12 bit of the superframe format.
It is a circuit that switches whether to load the F12 bit signal 32 from the device or the framing performance information 28 based on the remote alarm information 24. The performance information insertion circuit 29 selects the F12 signal 31 when the remote alarm information indicates that the central terminal has lost synchronization, and selects the F12 signal 31 when the remote alarm information indicates that synchronization has not occurred. It is designed to be selected.

If the information amount of the framed performance information is 120 bits, the performance information insertion circuit 29 outputs F12 bit by bit from the beginning.
It is a circuit that sequentially sends out as bits. Therefore, if the framed performance information is 120 bits, it is transmitted to the central terminal side by 120 frames, that is, 10 multiframes.

The F _T generation circuit 33 is a multi-frame 1
It is a circuit for generating the F _T bit portion shown in FIG. 7 out of the two F bits. Performance information insertion circuit 29
F 12 bit signal output from the F _T generation circuit 33
The DS0 signal of PCM (Pulse Code Modulation) data obtained by converting the F _T bit signal from the above and the voice signal from each subscriber device into a digital signal is input to the multiplexing circuit 34. The multiplexing circuit 34 is a circuit that multiplexes these signals into the signals of the super frame format shown in FIG. 5 and sends them to the central terminal 11 side.

The central terminal 11 is provided with a sync detecting circuit 41 for frame synchronization of the DS1 signal of the super frame format sent through the upstream primary group digital line 13. The synchronization detection circuit 41 is F
Frame synchronization is established based on the bits, and the F bit that is a synchronization signal and the DS0 signal included in each time slot of 24 channels are identified. When the synchronization is confirmed, the timing signal 42 is output. The DS1 signal and the timing signal 42 from the downlink primary group digital line 13 are
Both are input to the performance information detection circuit 43. The performance information detection circuit 43 is a circuit for extracting performance information sent by using F bits of multiframe.

The remote alarm generation circuit 44 is a circuit that detects out-of-synchronization in reception on the central terminal side or an error in the reception circuit and generates remote alarm information to be sent to the remote terminal side based on this. The Remoto alarm generation circuit 44 detects out-of-sync based on the F bits, but synchronization is performed even if 2 to 3 out of 12 F bits in one multiframe differ from a predetermined bit pattern. It is designed not to discriminate that it has come off. This is because when the performance information is sent by the F12 bit, at least that bit changes in accordance with the performance information, so it may differ from the predetermined value. When the F12 bit is different from the value as the synchronization bit, the remote alarm generation circuit does not immediately determine that the F alarm is out of synchronization even if the F bits have a pattern mismatch of several bits or less. ing.

The F _T generation circuit 45 and the F 12 generation circuit 46 have the same functions as those of the remote terminal 12. The multiplexing circuit 47 uses the DS0 signal 4
8 and F from the F _T generation circuit 45 and the F 12 generation circuit
The bit and the remote alarm information from the remote alarm generation circuit 44 are D in the super frame format.
This is a circuit that multiplexes the S1 signal and sends it out.

FIG. 2 shows an example of the frame structure of the framed performance information sent from the remote terminal. This figure shows the LAPD (Link Access Procedure) used when transmitting performance information in the extended superframe format.
e on the D-channel). The first byte 51 represents the start flag of the frame. The second and third bytes 52 and 53 represent addresses, and the fourth byte 53 represents control bytes. These are defined in ANSI Recommendation T1.403. A from the 5th byte to the 12th byte
Performance Report on NSI T1.403
It is defined as a message 54. Each bit of the performance report message is defined in the error number of the error information of the frame signal of the remote terminal, out-of-sync information, slip information and the like. The 13th byte and the 14th byte 55, 56 are assigned to a code for a frame check sequence for detecting an error in the frame structure shown in FIG. The last 15th byte 57 is defined in the end flag indicating the end of the frame.

FIG. 3 shows the definition of each bit of the performance report message. The bit column 61 represents each bit in the performance report message 54 shown in FIG. Value field 62
Indicates the value at which the bit is valid. The definition field 63
The contents represented by each bit when they are valid are shown. For example, when the bit of "G1" is "1", it means that the number of frame errors is one. Further, when the bit of "G2" is "1", it means that the frame error is 1 or more and 5 or less. Thus, not only the presence / absence of an error, but also the extent of the error, the place where the error occurred, and the like are shown in detail.

Next, the operation of the line monitoring system will be described.

First, synchronous pull-in is performed on the side of the central terminal. At the time of synchronization, DS1 from the remote terminal side is set by all F bits including F12.
Synchronization confirmation is performed on the signal. Until the synchronization pull-in is completed, the remote alarm generation circuit 44 issues a remote alarm, which is transmitted to the remote terminal side. The performance insertion circuit 29 of the remote terminal 12 detects that the central terminal side is out of synchronization by the remote alarm information, and
The F12 bit signal 32 output from the 12 generation circuit 31 is inserted. As a result, the F12 bit is used as a synchronization signal during the synchronization pull-in. Further, since the timing signal 42 is not output from the synchronization detection circuit 41 until the synchronization pull-in is completed, the performance information detection circuit 43 ignores the F12 bit from the remote terminal and does not adopt it as performance information.

When the synchronization pull-in is completed, the remote alarm is no longer issued from the central terminal side. As a result, the remote terminal side identifies that the central terminal side is in synchronization. Then, the performance information insertion circuit 29 uses the near-end PM detection circuit 25 and the far-end PM detection circuit 27.
The performance information 28 generated by is selected as the F12 bit. As a result, performance information is transmitted from the remote terminal to the central terminal using the F12 bit. Since the central terminal side is synchronized, it outputs the timing signal 42. In response to this, the performance information detection circuit 43
Is F contained in the DS1 signal from the remote terminal
12 bits are extracted as performance information.

When the LAPD protocol shown in FIG. 2 is used, the performance information is sent between a start flag and an end flag, and an address and a frame check sequence used for error processing are added. come. The performance information detection circuit 43 analyzes this data string and monitors the line quality of the received signal at the remote terminal.

In the state where the synchronization is confirmed, the F12 bit is used for the transmission of the performance information, so that the F-bit synchronization error is detected at a rate of at least 1 in 12. However, unless a few or more errors are detected, the remote alarm is not issued, so performance information continues to be transmitted from the remote terminal.

Similar to the performance information used in the extended super frame format, the near end PM detected by the remote terminal is set to 1 per second.
It is assumed that the far-end PM calculates and sends out at a rate of times.
In this case, in the format shown in FIG. 2, 120 bits (8 bits × 15 bytes) are used for one performance information transmission.
Requires. In the superframe format of the primary group digital line, 10 frames can be transferred in 1.5 ms, that is, 10 F12 bits can be transferred in 1.5 ms, so that 666.7 bits of information can be transferred by F12 bits per second. Since 120 bits are sufficient for one transmission of the performance information, it is sufficiently possible to transmit the performance information at a rate of once per second using F12 bits of the superframe format.

In the embodiment described above, the same frame format as LAPD is used for transmitting the performance information, but if it is less than the transmission amount of the data link obtained by F12 bits, it is transferred in another format. Good. Further, although the embodiment has been described by taking the superframe format as an example, the present invention can be applied to other formats. In other words, the F12 bit is
Normally, the presence or absence of an error is transmitted, but in the superframe format, the presence / absence of error is sent 667 times per second. This is obviously redundant, and it is enough to transfer the error information about once per second. Therefore, if such a bit is provided, a lot of information can be transferred using the bit.

In particular, the present invention is intended for a frame format that includes a plurality of synchronization bits for synchronization and can detect out-of-synchronization even if some of the bits are excluded. It is possible to transmit the line quality information by utilizing it. Moreover, if the bit is used for synchronization only when the synchronization is pulled in and then used for transmitting a message after the synchronization is matched, the same bit can play two roles. That is,
If the message is out of synchronization, it cannot be received normally even if the message is transmitted. Therefore, it is used for synchronization during this period. As a result, it is possible to improve the accuracy of synchronization and shorten the pull-in time. Further, it is determined whether a bit for transferring information is used as a synchronization bit or a bit for transferring line quality information depending on whether or not synchronization is lost. This allows
It is not necessary to provide a special bit for determining the purpose of the sync bit.

[0046]

As described above, according to the first aspect of the present invention, when synchronization is established in the partner station, part of the synchronization bit is used to transmit the line quality information and the partner station When the synchronization is not established at, the synchronization information is sent by that bit. As a result, the same bit can be used for establishing synchronization and for transmitting the line quality information.
It can be used for one purpose and can transfer line quality information without having a dedicated bit.

According to the second aspect of the invention, the line quality information is transferred by utilizing the synchronization bit of a predetermined frame in the multi-frame. Since the multi-frame is provided with a synchronization bit for each frame, it is possible to identify whether or not synchronization is lost even if some of these are used for information transfer.

According to the third aspect of the present invention, the line quality information is divided into a plurality of pieces and sequentially placed on the synchronization bits. For example, even if there is only one synchronization bit that can be used for information transfer in one frame format, line quality information need only be transmitted about once per second. Therefore, divide this into multiple frames for transmission. You can

According to the fourth aspect of the invention, once synchronization is established, even if a certain number or less of synchronization bits are out of synchronization, it is not identified that synchronization is lost. Therefore, even if the line quality information is transmitted by using the synchronization bit, the central office device side does not recognize that the synchronization is lost.
As a result, since the synchronization alarm is not transmitted to the partner station, the partner station can continue to carry the line quality information in the sync bit.

Further, according to the invention of claim 5, the line quality information is transmitted by using a predetermined bit among the synchronization bits of the superframe format. Therefore, it is possible to transmit the line quality information similar to the extended superframe format by using the transmission system that can support only the superframe format.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a configuration of a line monitoring system in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a frame structure of framed performance information sent from a remote terminal.

FIG. 3 is an explanatory diagram showing a definition of each bit of a performance report message.

FIG. 4 is an explanatory diagram showing an outline of the configuration of a conventionally used primary group digital signal transmission system.

FIG. 5 is an explanatory diagram showing a signal format of a super frame format.

FIG. 6 is an explanatory diagram showing a signal format of an extended superframe format.

FIG. 7 is an explanatory diagram showing function allocation of each bit in the superframe format.

FIG. 8 is an explanatory diagram showing function allocation of each bit in the extended superframe format.

[Explanation of symbols]

11 Central Terminal 12 Remote Terminal 13, 14 Primary Group Digital Line 21, 41 Synchronization Detection Circuit 23 Remote Alarm Detection Circuit 25 Near End PM Detection Circuit 27 Far End PM Detection Circuit 29 Performance Information Insertion Circuit 31, 46F12 Generation Circuit 33, 45 F _T generation circuit 34,47 the multiplexing circuit 43 performance information detection circuit 44 remote alarm generating circuit

Claims (5)

[Claims] 1. Receiving means for receiving a signal transmitted from a partner station, and channel quality information generating means for generating channel quality information representing the channel quality with the partner station based on the received signal. Synchronous alarm detection means for detecting a synchronous alarm indicating that out-of-synchronization occurs at the reception of the signal at the other station included in the received signal,
A framing means for converting information to be transmitted into a predetermined frame format which has a plurality of synchronization bits for establishing synchronization and which can detect the presence or absence of synchronization only by the remaining synchronization bits excluding arbitrary bits among them, and When transmitting means for transmitting the signal framed by the framing means to the partner station, and when it is detected by the synchronization alarm detecting means that the partner station receives the transmission signal of the transmitter without being out of synchronization. Of the plurality of synchronization bits, a terminal station device provided with a synchronization bit diversion means for mounting the line quality information on a predetermined information transmission synchronization bit, and a predetermined frame format of the predetermined frame format sent from the terminal station device. A synchronization detecting means that receives a signal and detects the synchronization thereof, and that the synchronization detecting means detects that the synchronization is lost. Synchronization alarm generation means for generating the synchronization alarm, transmission means for transmitting a signal carrying the synchronization alarm generated by the synchronization alarm generation means to the terminal station device, and the synchronization detection means for the termination Line quality information extracting means for extracting the line quality information from the information transmission synchronization bit in the signal being received when it is detected that synchronization is not lost when the signal is received from the station device. And a central station device. 2. The predetermined frame format is a multi-frame composed of a plurality of unit frames each having a sync bit, and the information transmission sync bit is a sync bit of a predetermined predetermined unit frame. The line monitoring system according to claim 1, wherein 3. The line quality information is more than the number of the information transmission synchronization bits, and the synchronization bit diversion means converts each bit of the line quality information into a plurality of information transmission synchronization bits of the predetermined frame format. The line monitoring system according to claim 1, wherein the line monitoring systems are sequentially loaded. 4. The synchronization detecting means establishes synchronization by referring to all of the plurality of synchronization bits at the time of synchronization pull-in, and after completion of the synchronization pull-in, a certain number or more of synchronization bits are out of synchronization. The line monitoring system according to claim 1, wherein it is determined that the synchronization is lost only when the line monitoring is performed. 5. The line monitoring system according to claim 1, wherein the predetermined frame format is a super frame format used in a primary group interface.