GB2070893A - Improvements in or relating to circuit arrangements for checking subscriber connection networks of time division telephone exchanges - Google Patents

Abstract

A circuit arrangement is provided for testing the connection network of a PAM time division multiplex telephone exchange of the type having a main telephone line HF for interconnecting subscriber circuits CUI-CUi, telephone junctions GUI-GUi, for other exchanges, and various centralized devices at the exchange, and a telephone channel HR for sending response signals to a control unit UCL of the exchange. The circuit arrangement comprises switching devices DCI-DCi for connecting the subscriber circuits to their telephone lines or to a service telephone channel HS and for connecting the service channel to the telephone lines. A first group of test units SI, GD, MP, RS, RT, PU, GB, GM is connected to the service channel HS whereas a second group of test units MAb, MDb, MAt, MDt, GUp is connected to the main telephone line HF. <IMAGE>

Description

SPECIFICATION Improvements in or relating to circuit arrangements for checking subscriber connection networks of time division telephone exchanges The present invention relates to circuit arrangements for checking for correct operation of a network for connecting subscribers of a time-division telephone exchange using the PAM (pulse amplitude modulation) technique.

The connection networks of telephone exchanges of such type essentially comprise a telephone channel allotted periodically to each call and for short time intervals. During each allotment, one pair of subscriber circuits is connected to the telephone channel by closing two respective switches and obtaining in that way a signal sample according to the resonane transfer principle. In addition to the aforesaid subscriber circuits, some centralized devices such as tone generator and selection digit receivers are connected to the telephone channel.

According to the invention, there is provided a circuit arrangement for checking operation of a network for connecting subscribers in a time-division telephone exchange of the type comprising a plurality of subscriber circuits for connection to respective subscriber telephone lines, a plurality of telephone junctions for connection to respective telephone exchanges, a plurality of centralized devices for switching signals to the subscriber circuits and to the telephone Junctions, a main telephone line arranged to permit the switching of signals between the subscriber circuits, the telephone junctions, and the centralized devices, and a telephone channel fortrans- mission to a unit for controlling the subscriber lines of responses concerning execution of operations instituted by the control unit, the circuit arrangement comprising a plurality of switching devices arranged to connect the subscriber circuits to the respective subscriber telephone lines or to a service telephone channel and to connect the service telephone channel to the subscriber telephone lines, a first group of test units arranged to be connected to the service telephone channel, and a second group of test units arranged to be connected to a main telephone line of the exchange.

It is thus possible to provide a circuit arrangement suitable for checking periodically the correct operation of both subscriber circuits and centralized devices in orderto detect in good time, with the connecting network in operation, any devices which are out of order.

The invention will be further described, by way of example, with reference to the accompanying drawing, which is a block diagram of a telephone exchange using the PAM technique and including a circuit arrangement constituting a preferred embodiment of the invention.

As shown in the drawing a communication link HF is connected through respective switches to the following units: subscriber circuits CU ...., . . , CU1 each connected to a telephone set TLe .... . . .TALI through a correspond- ing subscriber line; telephone junctions GU1 .... . GUi through which signal samples to and from other telephone exchanges CTI, .... CTi pass; a tone generator GT; a group of digit receivers RC1; ,RCj; . . . ,RC,; and an inclusion capacitor CI suitable for the inclusion of the operator in a call taking place between any two subscribers. Each subscriber circuit can also receive rining signalss produced by a ringing signal generator GSU, and chargeable time signals t generated by a chargeable time signal generator GTS.

The connection of the above mentioned units to the communication link HF is controlled by a line control unit UCL, which in correspondence with each time phase supplies at its output an address of a device for the switching of signals, as well as control signals indicating the type of operation to be carried out by the device indicated by the address. The unit UCL is described in the Italian patent No. 932.422 as well as in the Review "TELECOMUNICAZIONI" March-June, 1975 - issues Nos. 54-55 published by SOCIETA' ITALIANA TELECOMUNICAZIONI SIEMENS S.p.A. The addresses are supplied to an address decoder DCI whose output signals di control closing of the above-described switches.The control signals are supplied to a control decoder DCC which supplies at its output corresponding signals dc for controlling the execution of a generic operation by the device indicated by the associated address.

The connection network includes a channel HR for the transmission of responses, through which the digit receivers RC, the telephone junctions GU and the subscriber circuits CU send to the line control unit UCL responses relevant to the received control signals.

In order to check for correct operation of the devices of the connection network, a circuit arrangement constituting a preferred embodiment of the invention comprises a first group of functional units connected to a service telephone channel HS through respective switches and a second group of functional units connected to the transmission line HF.

The subscriber telephone lines are connected to the subscriber circuit CUI, .... CUi via respective connecting devices DCIr .... DCi also arranged to connect the subscriber circuits CU to the service telephone channel HS and to disconnect the subscriber circuit and connect the service telephone channel HS directly to the subscriber lines.

There is also provided a further telephone channel HP, through which some test units transmit the result of the measurements that have been carried outtothe unitUCL.

The line control unit UCL has in each cycle of operations one or more phases reserved for checking correct operation of the above mentioned units.

In particular, during such a test phase, the control unit UCL addresses a a generic subscriber circuit CUI and controls the execution of a sequence of tests arranged to ascertain correct operation before addressing the subscriber circuit CU1+1. For each subscriber circuit CU, the following test procedures are carried out.

1 ) Correct operation of the units of the subscriber circuit CU for the detection of engagement is checked. The line control unit UCL, during a phase reserved for the test procedures, controls the con nection to the service teleph- le channel HS of both the subscriber circuit CU unaer rest and a unit SI which simulates an engagement condition. After a predetermined numberofcycies, if the devices of the subscriber circuit for the detection of engage ment are working correctly, there is supplied to the channel HR for transmitting the responses a code expressing the detection of engagement. The unit UCL verifies whether the received response is in accordance with the control signal sent.

2) Correct operation of the devices of the subscriber circuit for detecting the decade selection digits is checked. When the previous test is ended the unit UCL, during a test phase, keeps unchanged the address of the subscriber circuit and addresses a unit GD arranged to generate decade selection digits, which are supplied through the telephone channel HS and the switching devices DC to the subscriber circuit under test. The unit UCL controls a generic digit, and if the subscriber circuit devices for the detection of the decade selection digits are cor rectify working they send, after a predetermined number of cycles, a code expressing the recognized digit to the unit UCL which in turn compares the received digit with the digit whose transmission has been caused by the unit itself.

3) The voltage supplied by a supply bridge allocated to the subscriber circuits CU is checked. After finishing the previous test, the unit UCL supplies, during one of the test phases, the address of the subscriber circuit, and the address of a unit MP for measuring the voltage supplied by the supply bridge of the subscriber circuits. The unit MP is connected to the service telephone channel HS, which is connected in turn to the subscriber circuit under test.

The unit MP thus receives a signal whose level is compared with a reference signal, and the result of the comparison is sent to the unit UCL through the telephone channel HP.

4) The level of the ringing signal generated by the unit GSU is checked in order to ascertain whether the peak value coincides with the expected one.

After finishing the previous test, and during one of the test phases, the unit UCL addresses a unit RS for the reception of the ringing signal, which is connected to the service telephone channel HS. The unit UCL controls activation of the unit GSU whose out put signals is supplied to the unit RS through the telephone channel HS. The unit RS receives a continuous level signal proportional to the peak value of the signal received, and compares it with a reference signal. The unit UCL is informed about the result of the comparison through the telephone line HP.

5) The level of the chargeable time signal is checked in order to ascertain whether it coincides with the expected one. This measurement is not described in detail because it is similar two the previ ous one with the exception that in this case a unit RT for measuring the level of the chargeable time signal is connected to the service telephone channel HS thus involving the activation of the unit GTS.

6) The electrical characteristics of the subscriber telephone line are checked. The unit UCL, after the execution of the previous test and during one of the test phases, keeps unchanged the address of the subscriber circuit CLI while controlling the switching of the relevant device DC in order to connect the service telephone channel HS to the subscriber tele phone line, ar.d addresses a unit PU for checking the electrical characteristics of the subscriber line. The particular arrangement of the unit PU is described in Italian patent application No. 19584 A/80. After a predetermined interval of time the unit PU transmits to the unit UCL the result of the measurements through the telephone line HP.

7) The attenuation and crosstalk of the subscriber circuit under test is checked. The line control unit connects a speech band generator GB (e.g. 3 Kc/s) to the service telephone channel HS and connects the subscriber circuit CU under test to the service telephone channel HS and to the main telephone line HF, to which it also connects a unit MAb for measuring the speech band attenuation and a unit MDb designed for measuring the crosstalk of the speech band signal. During a generic test phase a the speech band signal is sent to the unit MAb whereas during the phase oitl the unit MDb measures the energy of the speech band signal present in the main telephone line HF.The unit MAb thus receives a continuous level signal proportional to the peak value of the received signal, compares it with a reference signal, and transmits the comparison result to the unit UCL through the telephone channel HP. The unit MDb receives a continuous level signal proportional to the signal which is present on the telephone line HF and after comparing it with a reference signal transmits the comparison result to the unit UCL via the telephone channel HP.

8) The telephone junctions GU are checked. To carry out this type of test, the connection network includes two test junctions ring-connected to each other and schematically indicated in fig. 1 at GUp.

The unit UCL then connects the unit GB to the service telephone channel HS, and connects both the unit GUp and units May and MDb to the main telephone line HF. This type of test requires the engagement of three consecutive phases of test. In phase a; the speech band signal is sent to the first of the test junctions allocated to the unit GUp which is ring-connected to the second test junctions so that in phase j , the speech band signal is sent to the unit MAb, while in phase ai the unit MDb measures the signal present on the main telephone line HF. The units MAb and MDb transmit to the unit UCL the result of their respective comparisons in the same way as described before.

9) The attenuation and crosstalk caused by the inclusion capacitor Cl are measured. This type of measurement req uires the connection of the unit GB to the service telephone channel HS and of both the unit Cl and the units MAb and MDb to the maintele phone line HF. This type of measurement also requires the engagement of three test time-phases since in phase or the speech band signal is sent to the inclusion capacitor Cl, in phase a;i the unit Cl send the signal sample received during phase a1to the attenuation meter MAb, whereas in phase Oi,, the unit MDb measures the level of the signal which remains in the main telephone line HF.After a predetermined number of cycles of operation, the units MAb and MDb transmit to the unit UCL through the telephone channel HP the result of the measure ments that have been carried out.

10) The attenuation and crosstalk of the tone signal generated by the unit GT are measured. The line control unit UCL connects to the main telephone line HF the tone generator GT, a unit MAt for measuring the tone signal attenuation, and a unit MDt for measuring the crosstalk of the tone signal. Both unit MAt and MDt are equivalent to units MAb and MDb and they differ only in working frequency.

The measurement requires the engagement of two test phases. During phase a; the unit GT sends the tone signal to the unit MAt, and during phase oi+i the unit MDt measures the tone signal which remains in the main telephone line HF. The detection procedure for attenuation and crosstalk is similar two that described before and is similar to the procedure according to which the units in charge transmit the results of the measurements to the unit UCL.

11) The selection digit receivers of multi-frequency type are tested. A multi-frequency selection digits generator GM is connected to the service telephone channel HS, which is also connected to a subscriber test circuit CUp. The circuit CUp and the digit receiver RC1 which is to be tested and connected to the main telephone line HF. The unit UCL causes the unit GM to select a generic digit which is supplied to the unit RC1. After a predetermined interval of time, the unit RCi communicates to the unit UCL the recognized digit through the telephone channel HR transmitting the responses. The unit UCLthen checks whether the received digit coincides with the digit which was sent by the unit UCL itself.

The units of the connection network provided for testing are not described in detail as they may be of known type and may easily be realised by a man skilled in the art.

Claims (5)

1. A circuit arrangement for checking operation of a network for connecting subscribers in a timedivision telephone exchange of the type comprising a plurality of subscriber circuits for connection to respective subscriber telephone lines, a plurality of telephone junctions for connection to respective telephone exchanges, a plurality of centralized devices for switching signals to the subscriber circuits and to the telephone junctions, a main telephone line arranged to permitthe switching of signals between the subscriber circuits, the telephone junctions and the centralized devices, and a telephone channel for transmission to a unit for controlling the subscriber lines of responses concerning execution of operations instituted by the control unit, the circuit arrangement comprising a plurality of switching devices arranged to connect the subscriber circuits to the respective subscriber telephone lines orto a service telephone channel and to connect the service telephone channel to the subscriber telephone lines, a first group of test units arranged to be connected to the service telephone channel, and a second group of test units arranged to be connected to a main telephone line ofthe exchange.

2. A circuit arrangement as claimed in Claim 1, in which the first group of test units comprises a unit arranged to simulate engagement, a unit arranged to generate digits of decade selection type, a unit arranged to measure the voltage supplied by a supply bridge of the subscriber circuits, a unit arranged to measure the ringing signal level, a unit arranged to measure the level of the chargeable time signal, a unit arranged to measure the electrical characteristics of the subscriber telephone lines, a unit arranged to generate a speech band signal, and a unit arranged to generate digits of multi-frequency selection type.

3. A circuit arrangement as claimed in claim 2, in which the second group of test units comprises, a unit arranged to measure a signal supplied by the speech band generator after it has been transmitted, during a predetermined test phase, to a subscriber circuit under test, to a pair of test telephone junctions ring-connected to each other, orto a condenser for the inclusion of the operator in a call taking place between two generic subscriber circuits; a unit arranged to measure the level of the signal supplied by the speech band signal generator remaining in the main telephone line during the phase following the said predetermined test phase, a unit arranged to measure the signal supplied, in another predetermined phase, by a tone generator to the main telephone line; a unit arranged to measure the level of the signal supplied by the tone generator remaining in the main telephone line during the phase following the said other predetermined phase; and a subscriber test circuit arranged to be connected in time-division mode to the generator of the multigrequency selection digits and to a generic receiver of multi-frequency selection digits arranged to be connected to the main telephone line.

4. A circuit arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

5. Atime division telephone exchange including a circuit arrangement as claimed in any one of the preceding claims.