JPS58171161A - Testing system of spare digital terminal module - Google Patents

Abstract

PURPOSE:To make it possible to always check the normality of a digital terminal module held as a spare one by testing the folding operation of said digital terminal module. CONSTITUTION:In the spare digital terminal module DMT5, a channel signal separated from a demultiplexer DMPX by a back word subhighway S-HWB0 is branched and inputted to a selector SEL5. The channel signal separated to the highway S-HWB0 is selected by a central controlling device and inputted to the transmitting circuit XMT5 of the spare module DTM5 by the highway S-HWB5 through the selector SEL5 to be sent to the line side. Since a loop is formed by a switch l5, however, the channel signal is folded and received by a receiving circuit RCV5 and inputted to a data comparator COMP by the highway S-HWF5 through the selector SELT to check the normality.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a digital terminal module preliminary test method, and more specifically, to a time-division communication channel device by terminating a PCM line and performing synchronization processing and other necessary processing on the signal. This invention relates to a test method for a digital terminal module that is on standby as a standby when a digital terminal module is used in an N+1 standby format with a multiplexing module installed in the N+1 standby format.

Prior Art and Problems A trunk/tf that terminates a PCM line and accommodates a plurality of digital terminal modules that interface with the PCM line and time-division channel equipment via a multiplex highway.
- In the previous case, when taking the N+1 reserve scheme for digital terminal modules, that is, one digital terminal module for every N digital terminal modules that are always used in digital trunk b. - When adopting a method of keeping modules on standby as a spare, according to the conventional technology, the spare digital terminal module was left unused, so this spare digital terminal module was put into active use. It is not necessary to be sure that the digital terminal module will operate normally when the switch is made.Also, it is necessary to automatically confirm that the faulty digital terminal module has been restored to the normal state, and after confirming that the faulty digital terminal module has returned to the normal state, the current The problems of the above-mentioned prior art will be further explained with reference to the drawings.

FIG. 1 is a diagram showing the connection configuration of the digital terminal and tomobi held by the company.

In the figure, DTMo = DTMs is a digital terminal module, SEL o = SEL s is a selector, M-PX is a multiplexer, DMPX is a demultiplexer, M is a maintenance control monitoring circuit, and PCMo-P
CMati Digital line such as PCM line, HwF.

I (WB titt shown in the diagram) 1 time division communication path device (digital communication path device) Forward highway and backward highway for the interface between the TDNW and this digital trunk / 鱈心揖菖-Φ .Naori o# b41 fO'' f4 is a changeover switch controlled by a central control device (not shown).

Digital terminal module DTMo~DTM
a has the same configuration and operates in the same way. XMT is the digital terminal DTM.

is a transmitting circuit which converts the nine-channel signals generated by the demultiplexer DMPX to a level suitable for the line PCM and transmits the converted signals. RCVo is a receiving circuit that matches the channel signal input from the line PCM to the timing of the exchange, converts it to a level suitable for the exchange, and forwards it to the sub-highway S-HWF.
a” to the multiplexer MPX.

DET o is a failure detection circuit, and the reception circuit RCVo
- When a failure such as clock interruption, frame synchronization loss, or slip is detected, this is notified to the maintenance control monitoring circuit M via the alarm IIALMo.

In the above, the lines are five lines PCMo to PCM4, and each line PCM, -PCM4 is provided with a digital terminal module DTM, to DTM4, respectively.・One digital terminal module DT as a spare for terminal modules DTMo to DTM4
Ms is provided.

Under normal conditions, the selector switch bo% b41 fO~
f4 is in the position shown under the control of the central controller.

The inputs of the lines PCMo""PCMa and PCMa are respectively the receiving circuits RCVo-RCV4 and the forward sub-highway S-HWF o-S-H.
WF a, selector sgt.

~5EL4 (in this case, these selectors are controlled by the central controller to select and pass the output of the above-mentioned sub-highway), input to 1 multiplexer, and the output of each of the above-mentioned sub-highway The upper channels are time-division multiplexed onto a multiplexed highway provided as a forward highway HWF, and are time-division multiplexed onto a multiplexed highway provided as a forward highway HWF.
Enter.

After the exchange, the signals of each channel output from the time division communication path device TDNW are sent to a backward highway HWB configured as a multiplexed highway and a backward multiplexer D.
MPX, where the channel is separated into each backward sub-highway 8-HWB, ~5-HWB, and transmitting circuits XMT o ~XMT a and changeover switch bo of each digital terminal DTM, -DTM.
-b4 to the transmission line of IPCM o-PCM a.

Now, for example, digital terminal module D
If some fault occurs in TM, the fault detection circuit DET. is detected, and via the alarm line ALMo,
The maintenance control monitoring circuit M is notified. Based on this notification, the maintenance control monitoring circuit M notifies the central control unit that a fault has occurred in the digital terminal module DTMO.

Based on this notification, the central control unit detects the faulty digital terminal module DTM.

Control the changeover switches bo and fo corresponding to
Forward sub-highway S-HWF 5 of module DTM5 is selected and passed;
It controls the passage of the input from the forward sub-highway S-HWF o from the faulty digital terminal module DTMo, and also controls the selector 8EL5 to prevent the passage of the input from the forward sub-highway S-HWF o from the faulty digital terminal module DTM from the demultiplexer DMPX. Only the signal on the backward sub-highway 8-HWB o towards o is output to its output, that is, the backward sub-highway 5-HWB5 leading to the transmitting circuit XMT5 of the spare digital terminal module DTM5. . In addition, this highway (HWF, HWB
) is also not connected.

Under the control of said central control unit, the faulty digital terminal module DTMo was disconnected and the input signals of the spare digital terminal module D--i.e., line PCM, were switched (closed) instead. ) selector switch f. , normal spare digital terminal module DTM 5 receiving a circuit RCV5, forward sub-highway S-H'wF5, selector SEL
, to the multiplexer MPX via , and
Demultiplexer DMPX color, backward sub to the affected digital terminal module DTM
The signal of the channel separated and sent out to the highway 5-HWB is branched to the selector 5EL5.
Passing EL5, Backward Sub-Highway S
−H'wB5, and the transmitting circuit XMT5 of the digital terminal module DTMs, which was a spare.
, and a switched transfer switch b. via line PC
M.

sent to.

Since the conventional technology is the same as that described in Figure 1,
N+1 for a digital module that terminates a digital line such as PCM and interfaces the digital line with a time-division channel device via a multiplex highway.
When taking a standby approach, according to conventional technology, if the active digital terminal module encounters a fault,
Automatically immediately replaces the currently active digital terminal module with a normal spare digital terminal module, but since the spare digital terminal module is out of operation, it immediately becomes normal when switched. There is no guarantee that it will work, and furthermore, it is not possible to automatically confirm that the faulty digital terminal module has returned to its normal state, and it is not possible to automatically return it to active use after it has been restored to its normal state. There was a drawback.

OBJECTS OF THE INVENTION The present invention provides a highus! system for terminating a digital line such as PCM and multiplexing the line and a time-division channel device. In practice, N+ for digital terminal modules.
When using the 1 backup method, the above-mentioned drawbacks of the prior art are eliminated, the digital terminal module can be used as a backup and can be operated even during standby, and it is possible to confirm that it is operating normally, and it is also possible to・The purpose is to automatically confirm that the terminal module has returned to its normal state.

Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 shows a digital trunk xy implementing the present invention.
-T(/ is a diagram showing the connection configuration. ゛In Fig. 2, the symbols are the same as in Fig. 1.
is a digital terminal module DMTo-DM
This is a round switch that creates a loop circuit on the T50 line side, and its state is controlled by a central controller (not shown). T
STC is a verification test circuit, MEM is a data memory for verification, COMP is a data verification circuit, and 8EL is a verification test circuit.
T is a return verification data selector and the selector BELT
The selection operation is controlled by a central control device (not shown).

In this embodiment, digital terminal modules DTM, .
4 are each switched to a spare digital terminal module DTM, but the corresponding circuit ffi
is normal and is operating normally.

In this case, the selector switch bo%b4. fo-f4 are controlled by the central control device and occupy the positions shown in the figure, and roof-circuit creation switches lO to It5 are also located at the positions shown in the figure.
A loop circuit is not configured for TMo''-DTM4, but a loop circuit is configured for the spare digital terminal module DTM5 on the line side by switch 15. Selector 8KLo~ 8EL4
is forward sub no 1 way 5-HWF, -5
-Select the input of HWF4 and multiplexer MPX
It is controlled by the central controller to output to selector 5E.
L5 selects as test data, for example, the data of the channel separated into backward sub-way 5-HWBQ, which is output from the demultiplexer DMPX.
This backward sub-highway S-HWB o
Turn the upper signal backwards into Sub-Highway 3-H'W
Also output on Bg.

The signals input from lines PCM and -PCM4 are switches for creating loop circuits! . ~74+Tagital・
Receiving circuits RCV O to RCV4 of terminals 7 joules DTM and DTM4 *Forward sub-no. The signal channels on each sub-highway are time-division multiplexed onto the forward highway HWF and input to the time-division channel unit TDNW.

After the exchange, the signal output from the time division communication path device TDNW is input to the backward highway HWB multiplexer DMP The signals of each channel are sent to the transmitting circuits XMT of each digital terminal DTMo~DTM4.
o-XMT 4 and changeover switch b. It is transmitted to line PCM, -PCM4 via -b4.

A spare digital terminal during this normal state.
The status of module DMT 5 will be explained. The signals of the channels separated from the demultiplexer DMPX to the backward sub-highway 5-HWB are branched and input to the selector 5EL5. In this case, under the control of the central controller, this backward sub-highway 5
-HWBO, the next channel signal is selected, and this signal passes through the selector 5ELs and is sent to the transmitter circuit XM of the spare digital terminal module DTMs by the backward sub-highway S-HWBs.
The signal is input to T5 and is then transmitted to the line side, but since a loop circuit is formed by the switch 15, the above transmission output is looped back by the loop circuit and input to and received by the receiving circuit RCV5. , Forward Subhighway 8-HWF 5, Selector 5ELT (
In this case, the central controller has selected the signal on the forward sub-highway 8-HWF B.

) and then input to the data matching circuit COMP. on the other hand,
The above-mentioned signal carrying the test data is branched off at the output of the selector 5EL5, and the data carried by this signal is stored in a verification data memory MKM, and the data carried by this signal are passed through the storage contents and the above-mentioned digital terminal module DTM s. The contents of the signal returned by the above data matching circuit CO
Check with MP. It matches if the digital terminal module DTM 5 is normal, and it does not match if it is faulty. If they match, the data matching circuit COMP outputs a signal indicating normality, and if they do not match, the data matching circuit COMP outputs a signal indicating normality.
The OMP outputs a signal indicating a fault and sends a signal to the maintenance control monitoring circuit M.
Let me know.

In addition to the signal indicating the verification result of the data verification circuit COMP, the maintenance control monitoring circuit M also receives various digital signals.
Terminal module failure detection circuit DET o=
Alarm lines ALM, -ALM, from DETs are also drawn in to constantly monitor the normality of each digital terminal module. The above failure detection circuit D-ETo~DET
5, if the clock is disconnected and the frame is normal, no failure information is input to the maintenance control monitoring circuit M.
Transmission and reception operations are performed while continuously maintaining the above state.

Here, the current digital terminal module D
Suppose that a fault occurs in one of the TM o "D TM4, for example the digital terminal module DTMo. This fault is detected by the fault detection circuit DET.

A signal indicating a fault is detected on the alarm line ALM.

It is sent to the maintenance control monitoring circuit M via. The maintenance control monitoring circuit M receives the above signal and notifies the central control unit that the digital terminal module DTMa has failed. Based on this failure information, the central control unit detects the failure digital terminal module DTMa. Corresponding to the changeover switch bo.

Switch fO and switch l for loop circuit creation. to create a loop circuit, control selector 5KLO, and connect the spare digital terminal module DMT.
Forward Sub Highway S from 5 - HWF
The signal on S is selected and passed to multiplexer MPX, and also to the affected digital terminal module D.
Forward sub-highway S-HW from TMo
F. Block the passage of the above signal.

The central controller then performs the necessary controls in connection with the spare digital terminal modules. That is, the loop circuit creation switch 15 is opened, the selector SEL is controlled, and the demultiplexer DM is
Backward sub-highway S - separated by PX
Only the signal of the channel to be output to HWB o is selected and passed to the backward sub-way S-HWB 5.

If the central control unit is performing the above control, the affected digital terminal module DTM
o is turned by switch bo @ PCM.

and is instead connected to the digital terminal module DTM5-1)E several lines PCM by switches fO,bo. That is, line PCM.

The other input signals are the switched (closed) changeover switch fo, the switched switch j5 + the receiving circuit R of the normal spare digital terminal module DTM5.
CVs, Forward Sub-Highway 5-HWF
5. Multiplexer MPX via selector 5KLo
The signal input to the backward sub-highway S-HWB from the demultiplexer DMPX to the affected digital terminal module DTMo is branched to one input of the selector 5EL5, which After passing 5EL5, backward sub-
Transmission circuit XM of digital terminal module DTM5, which outputs to Highway 5-HWB5 and was a spare
T 5 and 4 times via switched changeover switch bo
1 PCM, transmitted.

Meanwhile, the affected digital terminal module D
For TM, switch 7 is switched, so
Its transmitting circuit XMT o to its receiving circuit Rev.

A return loop circuit is constructed, and a return test is performed through this circuit.

That is, the signal outputted by the channel separated from the demultiplexer DMPX to the backward sub-highway 5-HWBo is also used as a signal carrying return test data, and is sent to the transmitting circuit of the digital terminal module DTMo. X-MT Os Switch
o (switched), receiving circuit RCVos forward sub-highway 8-HWF, to selector 5EL-r of verification test circuit T8TC! (In this case, the affected digital terminal module D
TMo's Forward Sub-Highway 19- HW
It is controlled by a central controller to select the F o branch. ) and then input to the data matching circuit COMP.

Furthermore, backwards from the demultiplexer DMPX
The same signal U as above (signal carrying test data) outputted by the channel separated to the sub-highway s-'nwBo is branched to the selector 5EL5, passes through it, and is transmitted backward as described above. Output to sub-highway 5-HWBj. This signal is the selector SEL
, and the test data carried by the signal is stored in the verification data memory MEN, and is further input to the data verification circuit COMP.

As described above, the data collation circuit COMP compares and collates the direct data from the backward sub-highway 8-HWBo with the data returned from the digital terminal module DTMo.

If they match, the data matching circuit COMP outputs information indicating normality; if they do not match, it sends fault information to the digital terminal module DTM.

The alarm line ALM of the digital terminal module DTMO is sent to the maintenance control monitoring circuit M to determine whether it is normal or not.
If fault information is sent from o or from the data matching circuit COMP of the test matching circuit TSTC, the maintenance control monitoring circuit M determines that the DTMO is faulty and notifies the central control unit to this effect, The central controller continues the control state described above.

Therefore, the digital trunk l-□ is the affected digital terminal module DTM.

A spare digital terminal module D that is normal
Switched to MT 5 and works fine.

Digital terminal module D that is currently affected
If TMO is restored to normal state, the fault detection circuit DIT
The signal from o to the alarm line ALM and the output signal of the data verification test circuit COMP change from a fault signal to a normal signal.

Upon receiving the above normal signal, the maintenance control monitoring circuit M knows that the affected digital terminal module DTM has returned to normal, and notifies the central control unit to restart the digital trunk υ fog. It is possible to restore the terminal to the state before the digital terminal module→D TM a became a problem. In other words, digital
The terminal module DTM 5 can be kept in reserve.

FIG. 3 is a connection configuration diagram of a different embodiment of the present invention.

In FIG. 3, the symbols are the same as in FIGS. 1 and 2. In addition, SWF 1+ 8WF 21 SWB
4 aSWB 2 has multiple input lines and output lines,
It is a switch configured to connect any pair of each input line and each output line, and is a changeover switch network that has a similar effect to the changeover switch fo "" fa + bo -ba in the gg diagram. , the configuration of an example thereof is shown in FIG.

In this example, five cycles llPcMo to PCM4 are used.
, six digital terminal modules DTM, -DTM, one more than that, are provided, each time 'flJ PCMo -PCM4 is connected to the switching network s.
W.F.

SWF 2.8WB + and SWB 2 are connected to any digital terminal module for transmission and reception, and one digital terminal module that is at risk of being used is kept on standby as a spare.

The changeover switch network 5WFI in FIG. 3 has, for example, the configuration shown in FIG. 4. In Figure 4, COO~Gos
, G11. G22, 05M, G441G45 etc. are included in 1
The gate circuit is provided between 1Lo to L4 and the output line Ma%M5, and can be composed of, for example, a mechanical switch that is normally open, or a transistor (PNPN), and each gate circuit Conduction and non-conduction are controlled by a central controller. In the changeover switch network BWF1, the input side (reception line) of the line PCMo-PCM4 is the input 11[L of the changeover switch network 8WF'.

~L4, its output lines M, -M, are switches JO~l.

Through each digital terminal module DTM
o = DTMs f) Receiving circuit RCVo ~ RCVs
connected to.

In FIG. 4, the changeover switch network 5WB1 has an input $L
, ~L4 is the output line, output line MO%M5 is the input line and output line, -L4 is the output line.
- k DTMo ~ DTM5 transmitter circuit xM'ro
~ Connect the transmitting side of XMT5 to input line Mo%M5.

The switch SWF 2 has six inputs 11Le to L5 and six output lines MB-Ms, and each digital terminal module DTMo to DTM5 reception circuit R-c.
Connect the output side of va-RCV5 to its input lines LO to L5, and connect the five outputs 1!
Mo NM4 t-Forward Sub Highway 5
-HWFo=5-HWF4 to be input to the multiplexer MPX, and one output line M5 is connected to be input to the data collation circuit COMP of the collation test circuit T8TC.

In addition, the changeover switch network SWB 2 is the changeover switch network B
Constructed and connected in the same way as WB 1, there are five backward sub-highways S −HWB o = S −H
WB a is connected to the input line, and the six output lines are connected to the transmitting circuit XMT o =XMT s of each digital terminal module DTMO to DTM5.

The central controller controls each switch network SWF 1+ SWF
2.

SWB 1. Control SWB 2, for example, line PC
The receiving line of Mo-PC-M4 is connected to each digital terminal module D-TMo = DTM4 receiving circuit RCV, - through the changeover switch network SWF +.
The input side of the RCV4 is further connected to the output side of the receiving circuit through the switching switch network SWF2.
These forward sub-highway S
-HWF O to S - The channels on HWF 4 are input to a multiplexer MPX, multiplexed, and reach the time division channel device TDNW via the forward highway HWF.

Backward data output from time division communication path device TDNW
...Each backward sub with multiplexed channel e-demultiplexer DMPX on iway HWB!・Separated into highway S - HWB o = S - HWB a. Each backward sub-nome Iway8-)IWB
O~5-f (-WB4 is the changeover switch network 8 in this case)
WB, then digital terminal module D
TM o~DT-M4 transmitting circuit XMT, -XMT
, connected to the input side of the transmitting circuit XMT o = XM
The output side of T4 is connected to the transmission line of the line PCMo-PCMa via the changeover switch network SWB1.

In the above case, the digital terminal 'module D
The TMs are not connected to the line (PCMo to PCMa) and stand by as a standby. And while waiting as a backup,
Its normality is tested.

Switch network 8WF1°S under the control of the central control device
WB, is controlled by the digital terminal module
- The module DTMs are disconnected from the line (PCMo NPCM4), and by switching the switch 15, a return loop circuit is constructed for the digital terminal module DTMs, and the output of the receiving circuit RCV5 is It is connected to the output line M5 through the changeover switch network 5WF2, and is further connected to the data verification circuit C of the verification test circuit T8TC.
Connected to OMP. In addition, the input side of the transmitting circuit
(doubly connected to O). That is, the data carried by the signal on the backward sub-highway 5-HWBO will be used as the return test data.

In the above condition, digital terminal module D
TMo to DTMa perform transmission and reception operations for the lines PCMo to PCMa, but the digital
A health test is performed on the terminal modules DTMs. In the above case, the demultiplexer DXP
X Yo Shibatsward Sub-Highway 8- HWB
The signal of the channel that is separated and output is sent to the transmitter circuit XMTo of the current digital terminal module DTMo through the changeover switch network 5WBz, and is also sent to the spare digital terminal module as test data.
Transmission circuit XMT of module DMTs! It is also sent to l. Before this signal is input to the transmitting circuit Remember. On the other hand, the above signal passes through the transmitter circuit XMTS of the digital terminal module DTMs, and further passes through the return loop circuit constituted by the switch 15 to the receiver circuit RC.
Vs, and further outputs the receiving port *R-CV s, passes through the changeover switch network 5WF2, and inputs it to the data verification circuit COMP via its output 11M5, and receives the data for verification.
Input from memory MEN. Compare and match data that should be the same and detect a match. If a match is detected, the normality of the digital terminal module DTMs is confirmed, and if a mismatch is detected, it is a fault. This coincidence detection information is notified to the maintenance control monitoring circuit M. In this way, the digital terminal
The normality of the module DTMs is confirmed in the maintenance control monitoring circuit M.

Currently in use digital terminal module DT
Assume that a failure occurs in one of Ma to DTM4, for example, in DTMO. A fault is detected by a fault detection circuit DET o and sends fault information to its alarm line ALMo.

This information reaches the maintenance control monitoring circuit M and is further notified to the central control unit. Based on the fault information of this digital terminal module DTMo, the central control unit transfers the switching network SWF.

Controlling 8WF 2, SWB 1.8WB 2,
The faulty digital terminal module DT
Mo is disconnected from the line PCMo, and further the digital terminal module DTMs is switched to the connection state in which it was previously placed, that is, to the connection state in which it stands by as a standby; Digital terminal modules DTMs
Connecting to the line PCMo instead of TMo, the ± quantity e continues to operate normally. The digital terminal module DTMo that has been switched to the standby state is then subjected to the same foldback test by the foldback loop circuit that the digital terminal module DTMs was subjected to while on standby as a standby state.

Furthermore, as long as the normality of the digital terminal module that has been replaced as a backup has been confirmed, no matter which one of the current digital terminal modules is affected,
Immediately switch the spare digital terminal module to the switch network 8WF1゜8WF 218WB 1. SW
It can be switched by B2. In this example, any digital terminal module (DTM
o NDTM s ) to any line (PCMo =
PCMa), and those not currently connected can be used as backups, providing great flexibility.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the technical scope thereof.

Effects of the Invention Present Inventiveness As configured as described above, a digital terminal module for terminating a digital line such as a P-0M line and interfacing the line and a time-division channel device via a multiplex highway is provided. N+1 for Joule
When using the standby method, the digital
The terminal module can be returned and its operation tested to confirm its normality, and digital terminal modules that have been damaged and switched to the standby state can also be automatically tested in the same manner as above. This has the effect of automatically confirming that the normal state has been restored.

In the embodiment shown in Fig. 2, a specific Digital Joule is switched to the backup unit and temporarily stands by as a backup, but during this time it is tested and when it is restored normally, it is confirmed and put into active use. Returning to the above-mentioned specific digital
The operation of switching the terminal module to the spare one can be performed automatically without any manual intervention. In the embodiment shown in FIG.
There is no need to fix a specific module, and there is great flexibility, and other effects are similar to those of the embodiment shown in FIG. flc2.

[Brief explanation of drawings]

Figure Wl1 is a diagram showing the digital terminal/connection configuration it possesses, and Figure 2 is a diagram showing the connection configuration of an embodiment of the present invention.
FIG. 3 is a connection configuration diagram of a different embodiment of the present invention, and FIG. 4 is a connection configuration diagram of a different embodiment of the present invention.
・・Digital terminal module, XMTO～
XMT5... Transmission circuit, RCVo - RCVs - Receiving circuit, DIT o - DET s - Failure detection circuit, 8
E.L. ~5ELs, BELT...Selector, MPX...
・Multiplexer, DMPX...Demultiplexer,
T8TC...Verification test circuit, MEM...Data memory for verification, COMP...Data verification circuit, fo%
f4 + k) o -b<"" changeover switch, jO-
15... Loop circuit configuration switch, SWF I T
8WF t + SWB 1r SWB 2... Changeover switch network, M... Maintenance control monitoring circuit. Patent applicant Fujitsu Limited

Claims (1)

[Claims] A digital trunk terminal that terminates digital circuits and accommodates a plurality of digital terminal modules that interface with time-division channel equipment via a multiplexed highway, and that takes the form of N+1 spares for the digital terminal modules. ↓At the second floor, the digital terminal module that is waiting as a backup is disconnected from the line and the multiplex highway, and when the return loop circuit on the PCM line side is enabled, the test input as the transmission input is performed. The input test data is returned and the data output as a reception output is verified in a verification test circuit provided in common to each digital terminal module to check the normality of the preliminary digital terminal module. A digital terminal module preliminary test method that is characterized by its ability to be tested.