Testing unit by which communication links can be selected and tested, and method thereof

A testing unit allows an operator to select and test communication links of a communication system between an intermediate station and remote stations. Each remote station contains another communication link for establishing a second communication system between the intermediate station and the remote stations. The testing unit contains a first communication link for receiving and transmitting signals generated from a computer. This first communication link is part of the second communication system. The testing unit also includes a control unit which is connected to the first communication link for receiving and transmitting signals therefrom, and a second communication link which is connected to the control unit for receiving and transmitting signals therefrom. The second communication link is part of the second communication system so that communication can be established between the computer and the remote stations via the intermediate station by means of the second communication system. Finally, the testing unit includes a switching system controlled by the control unit and interconnecting the corresponding communication links with a generating and measuring device, whereby the operator can select at least one of the links between the intermediate station and one of the remote stations by sending command signals via the second communication system, and monitor a test procedure on the link that has been selected via the second communication system.

BACKGROUND OF THE INVENTION 
The present invention relates to testing units by which an operator can 
select and test communication links of a communication system that links 
an intermediate station to remote stations, and to a method of testing 
these links. 
Known in the art, there is the U.S. Pat. No. 4,998,240 granted on Mar. 5, 
1991, and naming Clifton B. WILLIAMS as the inventor. This patent 
describes a system and a method for remote and unattended testing of a 
ISDN protocol at a central office. An object of this invention is to test 
customer ISDN lines without the necessity to dispatch personnel to a 
customer site or central office. 
In the system described in U.S. Pat. No. 4,998,240, the link connecting the 
equipments to be verified is also used for sending command signals 
relating to the test to be performed. Accordingly, if the link is broken 
or cannot efficiently convey the data signal, then it is not possible to 
do a test. Also, the nature of the tests that are performed is very 
specific and relates to the verification of transmission protocol and data 
integrity. These tests do not provide any information on the quality of 
the link itself. Also, the system can only operate with AT&T (trademark) 
equipment and uses functions already programmed in the system. 
Also known in the art, there is the U.S. Pat. No. 4,055,808 granted on Oct. 
25, 1977, naming Jerry L. HOLSINGER et al. as inventors. In this patent, 
there is described an intermediate location testing unit for connection to 
a communication unit located at an intermediate location in a data 
communication network. The network additionally includes first data 
transmission means for conveying signals to an upstream port of the 
communication network from a central location. The communication unit also 
includes a downstream port for conveying signals to other data 
transmission means that connect to remote locations. The signals have 
first characteristics at the upstream port and second characteristics at 
the downstream port. The data communication network further includes a 
central testing unit at the central location for transmitting a test 
control word having a command portion and an address portion. The system 
uses an address command protocol within a test control word circulating 
within the communication data network. With this system, it is not 
possible to verify circuits that are out of order to the point where they 
cannot receive or transmit the test control word. There is also no direct 
communication between the central station and the remote stations. 
Also known in the art, there are the following U.S. patents describing 
different testing apparatus and methods for testing a communication 
system: 
U.S. Pat. No. 5,027,343 (CHAN et al.) 
U.S. Pat. No. 4,945,554 (KRAUSE et al.) 
U.S. Pat. No. 4,937,851 (LYNCH et al.) 
U.S. Pat. No. 4,918,623 (LOCKITT et al.) 
U.S. Pat. No. 4,682,347 (LYNCH) 
U.S. Pat. No. 4,611,101 (WALTER et al.) 
U.S. Pat. No. 4,419,751 (CHOLAT-NAMY et al.) 
U.S. Pat. No. 4,076,961 (HOLSINGER et al.) 
One drawback with all of these testing apparatus and methods resides in the 
fact that if a communication link of the system is totally out of order or 
deficient to the point where it cannot transmit information, it is not 
possible to perform a test on this link. 
Accordingly, an object of the present invention is to provide a testing 
unit and a testing method by which an operator can select and test 
communication links of a communication system even if this communication 
link is out of order or broken down. 
The objects, advantages and other features of the present invention will 
become more apparent upon reading of the following non restrictive 
description of a preferred embodiment thereof, given for the purpose of 
exemplification only with reference to the accompanying drawings. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a testing unit by 
which an operator can select and test communication links of a first 
communication system that links an intermediate station to remote 
stations. The testing unit is located at the intermediate station. Each of 
the remote stations are connected to another communication link to 
establish a second communication system between the intermediate station 
and the remote stations. Each of the remote stations contain a control 
module which is connected to the second communication system from which 
command signals can be received. Each of the control modules are also 
connected to the corresponding communication links of the first system so 
that at least one of the links can be selected between the intermediate 
station and one of the remote stations the testing unit comprises: 
a first communication link for receiving and transmitting signals generated 
from a computer, said first communication link being part of said second 
communication system; 
a control unit connected to said first communication link for receiving and 
transmitting signals therefrom; 
a second communication link connected to said control unit for receiving 
and transmitting signals therefrom, said second communication link being 
part of said second communication system so that communication can be 
established between said computer and said remote stations via said 
intermediate station by means of said second communication system; 
a signal generating and measuring device connected to said control unit, 
having an input for receiving a signal to be measured and an output for 
generating a predetermined signal; 
a switching system controlled by said control unit and interconnecting the 
corresponding communication links of the first system with said generating 
and measuring device, by which one of the corresponding communication 
links can be selected by said control unit and connected to said input and 
output of said signal generating and measuring device; whereby said 
operator can select at least one of said links between said intermediate 
station and one of said remote stations by sending command signals via 
said second communication system, and monitor a test procedure on said 
link that has been selected by said operator via said second communication 
system. 
Also according to the present invention, there is provided a method by 
which an operator provided with a computer can select and test 
communication links of a communication system that links an intermediate 
station to remote stations. The intermediate station is provided with a 
testing unit equipped with a first communication link for communication 
with the computer, and a second communication link for communication with 
the remote stations. The method comprises the steps of: 
(a) establishing a first connection between said computer and said 
intermediate station, upon commands issued from said computer; 
(b) establishing a second connection between said intermediate station and 
one of said remote stations that has been selected by said operator, upon 
commands issued from said computer for selecting a communication link 
between said intermediate station and the remote station that has been 
selected; 
(c) sending command signals to said testing unit via said first connection 
for initiating a test procedure on said communication link that has been 
selected, upon commands issued from said computer; and 
(d) transmission of results of said test procedure from said testing unit 
to said computer via said first connection, whereby an operator can select 
a particular communication link by means of step (b), initiate said test 
procedure on said particular link by means of step (c) and be informed of 
the result of said test procedure by means of step (d).

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to FIG. 1, there is shown a testing unit 2 by which an 
operator situated at a remote location 4 can select and test communication 
links 6 of a first communication system that links an intermediate station 
8 to remote stations 10. Each communication link is made of two 
transmission wires and two reception wires. The testing unit 2 is located 
at the intermediate station 8. Each of the remote stations 10 comprises a 
modem 12 to establish a second communication system between the 
intermediate station 8 and the remote stations 10. Each of the remote 
stations 10 comprises a control module 14 for receiving command signals 
from its corresponding modem 12. The control module 14 is connected to the 
corresponding communication links 6 so that at least one of the links 6 
can be selected between the intermediate station 8 and one of the remote 
stations 10. 
Referring now to FIGS. 1 and 2, the testing unit 2 comprises a first modem 
18 for receiving and transmitting signals generated from a computer 22 
equipped with a modem 21 situated at the remote location 4. The first 
modem 18 at port 24b is part of the second communication system. The 
testing unit comprises a control unit 24 at port 24c connected to the 
first modem 18 for receiving and transmitting signals therefrom. A second 
modem 28 is provided. It is connected to the control unit 24 for receiving 
and transmitting signals therefrom. The second modem 28 is part of the 
second communication system so that communication can be established 
between the remote location 4 and the remote stations 10 via the 
intermediate station 8 by means of the modems 12 of the second 
communication system. 
A signal generating and measuring device 30 is provided. It is connected to 
the control unit 24 at point 24d and has inputs 32 and 33 for receiving a 
signal to be measured and an output 34 for generating a predetermined 
signal. 
The testing unit 2 also comprises a switching system 36 controlled by the 
control unit 24 with a connection 24a and interconnecting the 
corresponding communication links 6 with the generating and measuring 
device 30, by which one of the corresponding communication links 6 can be 
selected by the control unit 24 and connected to the inputs 32 and 33 and 
output 34 of the signal generating and measuring device 30, whereby the 
operator can select at least one of the links 6 between the intermediate 
station 8 and one of the remote stations 10 by sending command signals via 
the second communication system, and monitor a test procedure on the link 
6 that has been selected by the operator via the second communication 
system. 
Referring now more specifically to FIGS. 2 and 3, the inputs 32 and 33 of 
the signal generating and measuring device 30 comprises a tap input 32 for 
receiving a tap connection of the communication link 6 that has been 
selected and a direct input 33 for receiving the communication link 6 that 
has been selected. The signal generating and measuring device 30 comprises 
first coupling transformer 40 having an input connected to the direct 
input 33, first and second amplifiers 44 and 46 having high impedance 
inputs connected respectively to an output of the transformer 40 and the 
tap input 32, first switching device 48 having two inputs connected 
respectively to outputs of the first and second amplifiers 44 and 46, 
second switching device 50 having an input 52 connected to an output of 
the first switching device 48, and a third amplifier 53 having a high 
impedance input connected to the output of the second switching device 50. 
The signal generating and measuring device 30 also comprises a second 
coupling transformer 56 having an input connected to an output of the 
third amplifier 53, and an output connected to the output 34 of the signal 
generating and measuring device 30; a measuring unit 60 having an input 
connected to the output of the first switching device 48; a signal 
generator 62 having two outputs connected respectively to inputs of the 
second switching device 50; and a microprocessor 64 having an input 
connected to the control unit 24, and different connections (not shown in 
FIG. 3) with the switching devices 48 and 50, the measuring unit 60 and 
the signal generator 62, whereby the operator can monitor the test 
procedure by sending command signals to the microprocessor 64 via the 
second communication system. 
It should be appreciated that the second communication system is 
constituted by telephone lines and modems. In FIG. 3, the connection 
between the microprocessor 64 and the control unit 24 is made by a RS 232 
connection. The output of the first switching device 48 is also connected 
to an input of the second switching device 50 by means of an amplifier 49 
having a gain of 16 db. The signal generator 62 is a programmable 
sinusoidal generator having a first output 61 of 0 db and a second output 
63 of -8 db. The measuring unit 60 comprises a 8 bit analog-to-digital 
converter 65 and a AC/DC RMS converter 67. The coupling transformers 40 
and 56 are 1:1 transformers. The generator 62 is capable of generating a 
sinusoidal wave signal having a frequency varying from 300 to 3000 Hz at 0 
db and -8 db. The converter 67 converts an alternating signal into a DC 
signal which is the RMS value of the alternating signal. 
Referring now to FIG. 4, there is shown one of the control modules disposed 
at each of the remote stations. This control module 14 is connected to its 
corresponding modem 12. This control module 14 comprises first switching 
device 70 having an input connected in series with the corresponding 
communication link 6; a first coupling transformer 71 having an input 
connected to an output of the first switching device 70; second switching 
device 72 having an input connected to an output of the first coupling 
transformer 71; third switching device 74 having an input connected to an 
output of the second switching device 72; a second coupling transformer 76 
having an input connected to an output of the third switching device 74; 
fourth switching device 78 having an input connected to an output of the 
second coupling transformer 76, and an output connected in series with the 
corresponding communication link 6; a measuring unit 80 having an input 
connected to the output of the second switching device 72; and a signal 
generator 82 having an output connected to an input of the third switching 
device 74. The control module 14 also comprises a microprocessor 84 
connected to the corresponding modem 12, and different connections (not 
shown in this FIG. 4) with the switching devices 70, 72, 74 and 78, the 
measuring unit 80 and the signal generator 82, whereby the operator can 
monitor a test procedure at one of the remote stations 10 by sending 
command signals to the corresponding microprocessor 84 via the second 
communication system. 
The control module 14 also comprises fifth switching device 86 having an 
input connected in parallel with the corresponding communication link 6; 
sixth switching device 88 having an input connected to an output of the 
fifth switching device 86, and an output connected to the corresponding 
communication link 6; and a tap connection 90 having an input connected to 
the output of the fifth switching device 86, and an output connected to an 
input of the second switching device 72. The microprocessor 84 has also 
different connections (not shown in this FIG. 4) with the fifth and sixth 
switching devices 86 and 88, whereby the operator can monitor additional 
test procedures at the remote stations 10 by sending command signals to 
the corresponding microprocessor 84 via the second communication system. 
Referring now to FIG. 5, there is shown another embodiment of one of the 
control modules disposed at each of the remote stations. It should be 
appreciated that the portion of this circuit disposed between the 
switching device and the modem 12 can also be used to replace the signal 
generating and measuring device shown in FIG. 3. This control module 14 is 
connected to its corresponding modem 12. This control module 14 comprises 
a first switching device 100 having a four-connection input connected with 
one of the corresponding communication links 6. Each communication link 6 
comprises two reception wires and two transmission wires. The switching 
device 100 also comprises a two-wire input 102, and a first two-wire 
output 104. A first coupling transformer 108 has an output connected to 
the two-wire input 102. A second coupling transformer 110 has an input 
connected to first two-wire output 104. A variable gain amplifier 112 has 
an output connected to an input of first transformer 108 via a resistor 
114 of 600 ohms. A second switching device 116 has an output connected to 
an input of first amplifier 112. A signal generator 118 has an output 
connected to an input of second switching device 116. A third switching 
device 120 has a first input connected to the output of first transformer 
108 via a buffer 122, and a second input connected to an output of second 
transformer 110. A second variable gain amplifier 124 has an input 
connected to an output of third switching device 120. A fourth switching 
device 126 has an input connected to an output of second amplifier 124, 
and an output connected to an input of second switching device 116. 
The control module 14 also comprises a central processing unit 128 
connected to the corresponding modem 12, and different connections (not 
shown in this FIG. 5) with the switching devices 100, 116, 120 and 126, 
the amplifiers 112 and 124, and the signal generator 118, whereby the 
operator can monitor a test procedure at one of the remote stations by 
sending command signals to the corresponding central processing unit 128 
via the second communication system. 
The control module 14 further comprises a differential amplifier 130 
connected to a second output 106 of first switching device 100, and an 
output connected to a second input of fourth switching device 126; a 
sinusoidal wave detector 132 having an input connected to the output of 
fourth switching device 126, and an output connected to an input of 
central processing unit 128; and an anti-aliasing filter 134 having an 
input connected to the output of fourth switching device 126, and an 
output connected to an input of central processing unit 128. 
A resistor 140 of 600 ohms is connected at the output of transformer 110. 
Variable gain amplifiers 112 and 124 have their gain controlled by the 
central processing unit 128. By means of switching device 126, the central 
processing unit 128 can select a different type of input signal. By means 
of switching device 120, the central processing unit 128 can select a 
normal measurement of the link or a noise measurement of the link. The 
filter 134 is needed for the sampling performed by the central processing 
unit. The sinusoidal wave detector 132 is needed for converting its input 
signal into a square wave signal. The buffer 122 is needed for measuring 
the noise on the selected link. The amplifier 130 is needed for performing 
a bridge measurement of the selected link. 
With the equipments shown in these FIGS. 1 to 5, a method according to the 
present invention can be performed, by which an operator provided with a 
computer 22 equipped with a modem 21, situated at a remote location 4, can 
select and test communication links 6 of a communication system that links 
an intermediate station 8 to remote stations 10. The intermediate station 
8 is provided with the testing unit 2 equipped with the first modem 18 for 
communication with the remote location 4, and a second modem 28 for 
communication with modems 12 located at the remote stations 10. The method 
comprises steps of (a) establishing a first connection between the modem 
21 of the remote location 4 and the first modem 18 of the intermediate 
station 8, upon commands issued from the computer 22; (b) establishing a 
second connection between the second modem 28 of the intermediate station 
8 and the modem 12 of one of the remote stations 10 that has been selected 
by the operator, upon commands issued from the computer 22 for selecting a 
communication link between the intermediate station 8 and the remote 
station that has been selected; (c) sending command signals to the testing 
unit 2 via the first connection for initiating a test procedure on the 
communication link that has been selected, upon commands issued from the 
computer 22; and (d) transmission of results of the test procedure from 
the testing unit 2 to the computer 22 via the first connection, whereby an 
operator can select a particular communication link by means of step (b), 
initiate the test procedure on the particular link by means of step (c) 
and be informed of the results of the test procedure by means of step (d). 
The method can further comprise a step of sending command signals issued 
from the computer 22 to the intermediate station 8 via the first 
connection, and to the remote station that has been selected via the first 
and second connections, for temporarily disconnecting the communication 
link that has been selected from the communication system by means of 
switching devices present at the stations, so that the test procedure 
performed during step (c) can be a closed loop test procedure. 
Each of the remote stations 10 is provided with a control module 14 
connected between the corresponding modem 12 and to the corresponding 
communication links 6. The method can further comprise a step of sending 
command signals to the control module 14 of the remote station that has 
been selected via the first and second connections to initiate a test 
procedure from the remote station that has been selected over the 
communication link that has been selected, upon commands issued from the 
computer 22. 
The present system and method can be specifically adapted to verify 
four-wire communication systems generally used for transmitting human 
voice and data. With the present system, it is possible to verify the 
links of a communication system by measuring the db level of a signal on 
each link, by generating different tone signals over each link, and by 
forming a closed loop circuit with a link to perform a closed loop test 
procedure. All of these operations can be initiated from a microcomputer 
situated anywhere where a tone telephone line is available and with the 
necessary devices for connecting the microcomputer to the tone telephone 
line. 
The microcomputer can be an IBM (trademark) microcomputer or an IBM clone 
provided with a 80286 microprocessor with a monochrome or color V.G.A. 
type monitor. It has been found that a color monitor is preferable. An 
integrated or external modem capable of communicating at a 2400 baud and 
that is HAYES compatible is recommended. A 31/2 or a 51/4 disk drive 
should be provided for loading the software. The computer should also be 
provided with a graphic adapter. 
The intermediate station is provided with two modems having characteristics 
similar to the one mentioned above. These modems are connected 
respectively to different telephone lines. The testing unit of the 
intermediate station is connected to a switching system made of several 
banks of circuits, which are respectively equipped with a line adapter and 
an address decoder. The links to be verified are passing through each of 
the banks by means of appropriate connectors. The control module of each 
of the remote stations is equipped with a modem set in a response mode and 
with several line interfaces connected to the links to be verified. 
In operation, from a communication menu, the operator can select the link 
to be verified. A directory containing preprogrammed links allows this 
option. By using the telephone option, the operator enters commands into 
the microcomputer so that it makes a call via its modem to the testing 
unit of the intermediate station. This testing unit which is in stand-by 
mode answers the call and confirms reception to the microcomputer. Then, 
the microcomputer sends command signals to the testing unit so that it 
selects the links chosen by the operator and calls via its other modem 28 
and another telephone line the remote station corresponding to the link 
that has been selected. The control module of the remote station answers 
the call, selects the link to be verified and confirms everything. The 
testing unit of the intermediate station then confirms to the computer 
that everything is ready for a test procedure. The operator can then 
monitor different operations to identify a problem on the line that has 
been selected or simply take some measures on the link that has been 
selected in order to know the quality of this link. The operator can also 
monitor a frequency scanning on the selected link to obtain a curve 
indicative of the frequency response of the selected link at each interval 
of 100 Hz between 300 and 3000 Hz. When the tests are completed, the 
operator, by means of a communication menu, terminates the different 
communications established with the equipment. All the functions that have 
been activated return to their stand-by mode of operation. The system is 
now ready for verifying another link. 
As previously noted, the operator can select and test a communication link 
by means of a communication menu produced by a software program stored in 
the microcomputer. This software program has been written to perform this 
communication menu. 
An explicit listing of this actual program follows. 
##SPC1## 
Although the present invention has been explained hereinabove by way of a 
preferred embodiment thereof, it should be pointed out that any 
modifications of this preferred embodiment, within the scope of the 
appended claims is not deemed to change or alter the nature and scope of 
the invention.