IE44651B1 - Automatic test system for an automatic switching exchange - Google Patents

Abstract

In order to make it possible to set up test communications between a requesting unit and a requested unit, without withdrawing any unit or any trunk from the normal traffic, the test traffic being incorporated therein without disturbing it, the device includes, linked with the control units of the automatic switch unit (AUT), a test module (EE) formed of a control set (PC) and an information memory (MI), a transcoder (TS), a printer (IM) and test identifiers situated on the units. The control set comprises means making it possible to designate the units and the trunks which a test call is to track a test call and the memory (MI) makes it possible to record the identity of all the units and trunks engaged during this test call made from the control set. The transcoder (TS) is capable of reading the information written into the memory and of forwarding it to the printer. The device can be used for maintenance and repair of a telephone or telegraph automatic switch unit.

Description

The invention relates to an automatic test system for an automatic switching exchange having a plurality of distributed control units; e.g. a telephone or a telegraph exchange.

Automatic testing systems for modern exchanges must be capable of complete testing of an exchange, and in particular of automatically proceeding to systematically test all. units and circuits liable to be engaged in setting up signalling and speech paths.

There is a wide range of means for this purpose, such as circuit and switching path testing apparatus which simulates the operation of circuits and subscriber lines connected to the exchange; common control testing apparatus, including register testers which simulate the interaction of control units and the exchange in general, and so forth.

In exchanges in which control and supervision of the switching network is vested in a large computer, testing and maintenance are usually carried out under the control of appropriate programs. In the particular case where the status of given or of all connection points, whether electronic or electro-mechanical, is stored and read by the computer, a test program may permit systematic testing of all units, and also of all trunks (known also as links), interconnecting such connection points within the switching system. 4465 - 3 But in the case of exchanges, or parts of exchanges, in which logic functionsare distributed rather than centralised, and in which the selection of trunks and switching units, amongst the many available, is determined by distributed control units whether randomly or by applying priorities, systematic testing necessarily involves direct action on the switch ing units, which must be isolated for testing, that is, rendered inaccessible for traffic handling, and similar direct action is required on said control units and their random distributers (if any). This applies, as it is known, to electromechanical exchanges, in which control logic functions are vested in a number of distributed units, both electrochemical and electronic. In such exchanges, a test call cannot be set up on a predetermined path, without inhibiting operation of all other paths available for that call. This implies that a test call over a predetermined path effectively busies out a much greater proportion of the exchange than does any call (test or ordinary) that is not required to follow a predetermined path.

The present invention provides an automatic test system for an automatic switching exchange having a plurality of distributed control units including registers, the test system comprising central test apparatus connected to the control units of the automatic exchange via an information network, and means in the control units to co-operate with the central test apparatus, the central test apparatus including a store for storing the identity of the oontrol units and trunks involved in a test call, means for designating the control units and the trunks to be used in a test call from a designated calling unit to a designated called unit, said calling and called units being input/ output units of the exchange reserved for test purposes, and means for following the progress of a test call step by step through the exchange, and the said means in the control units for co-operating with the central test apparatus including test call identifiers arranged to ensure that no designated control unit or trunk is seized for a test call until a test call is identified at an input to the designated control unit or trunk, whereby designated control units remain available for normal traffic through the exchange except only for the time during which they are actively engaged in setting up the test call.

The testing system therefore does not withdraw any control unit from its normal use for normal traffic, and since the test call occupies no more of the switching system than an ordinary call, test calls can be integrated into normal traffic without disturbance. In other words a test call using pre-determined switches, markers, register and translator only busies those predetermined units as would an ordinary call, thus hardly degrading the grade of service offered to normal traffic at any point in the exchange.

The test system may be used to advantage in connection with maintenance facilities that identify all units and paths taken for a call that has been ineffective, because of a fault in the exchange.

Such maintenance facilities can be used to hold and render inaccessible the units engaged in setting up said ineffective call, and to print out a message indicating the existence of the fault, so that maintenance personnel may follow the path held, and find the point at which failure occurred. The test system may also be used during slack traffic periods, to reproduce all calls that during a foregoing period gave rise to fault message printing, taking precisely the same paths through the exchange.

The term input/output unit is intended to cover 4 6 51 - 5 both subscriber line circuits and exchange junctors.

The invention will be better understood with the assistance of an application, described solely as an example, and with reference to the following figures; Figure 1, which represents the section of the exchange which handles originating and outgoing calls, namely subscriber selection or preselection, plus routing and o/g selection. Figure 2, which represents the section of the exchange which handles incoming and terminating calls, namely i/c selection and subscriber selection. Figure 3, which is a block diagram of a testing system in accordance with the invention. Figure 4, which is a block diagram of the means employed for switching unit and trunk designation in the subscriber stages. Figure 5, which shows the means employed to predetermine control unit seizing in preselection. Figure 6, which is a block diagram of the means for identification contained in a local register of the exchange. Figure 7, which is a block diagram of the identification and designation equipment used in outgoing selection.

Figures 8 and 9, which are block diagrams of identification and designation equipment used in incoming selection. 4651 - 6 The application described in the following, as an example, concerns the test system of a large capacity telegraph exchange, which has two separate switching sections, one termed originating-outgoing and the other incoming-terminating, and in which local calls go through each of these sections in succession.

With reference to Figure 1: subscriber line equipments Ab are connected to subscriber selection BA comprising two stages AB1 and AB2 of cross-bar switches. Outgoing selection comprises routing selection ACD in two stages of finders-connectors AC1, AC2, plus secondary routing selection SD, and final selection TO with respective switches Si and Tl, followed by a bank of outgoing junctors JS. This section of the exchange also comprises a number of local registers END, directed by routing indicators IAD (also known as translators).

Each level of selection BA, ACD, SD and TO is controlled by a respective marker MQ1, MQ2, MQ3 and MQ4.

In the exchange as described here, connection between registers and routing indicators is by means of an electronic coupler CPLl capable of serving 30 registers and 2 routing indicators. Register selection is performed by a single stage of register findersconnectors CHE.

With reference to figure 2: in incoming selection, incoming junctors JE are directly connected to the routing selectors ACA, controlled by a marker MQ5 and similar to and grouped in the same way as the two stages of routing selectors ACD in the outgoing section, and also followed by a secondary routing stage SA controlled by a marker MQ6. The incoming junctors are also connected to incoming registers ENA by a two-stage group ϊ of junctor finders and register connectors CHA, comprising finders CJE and connectors CE and controlled by a marker MA. Abbreviations BA and Ab refer to the same 4 6 5 1 items as in figure 1.

An exchange of this structure is described in the review Commutation Electronique No 46, July 1974, pages 56 to 69.

Certain features of the exchange will now be outlined, and other indications will follow in the description of this example of application of the system according to the invention.

The switching network and electromechanical finders-connectors are trunk-interconnected crossbar switches of 10 verticals and 12 horizontals each.

Although identical in construction, these switches are variously wired and operated, to provide 20 crosspoints (i.e. connection points) per vertical in subscriber selection and routing selection (all stages), and 12 crosspoints per vertical in o/g and i/c selection. Verticals may be variously multipled in tiers and levels, much as uniselectors.

Subscriber line equipments Ab are formed into groups of 2,000, each group working independently in preselection. A number of registers and routing indicators is allocated to each group.

In the manner known in crossbar systems, subscriber line equipments are connected in multiples to crosspoints of the switches in stage AB2, the verticals of two AB2 switches being trunked to the levels multipled across one AB1 switch, one AB1 and two AB2 switches forming a selection unit, of which there are 8 per subscriber line equipment subgroup of 200 lines.

On appearance of an originating call, the operation of the tens and units digits identification relays, and of a break contact of the vertical in which the line equipment is connected in each AB2 switch in the tier, result in operation of a marking relay MMO - MM7 (Fig. 4), but only if a trunk between one of these AB2 4 6 51 verticals and an AB1 level in its selection unit is free.

In switches AB1, 5 of the 10 verticals are finders for originating calls, and 5 are connectors for terminating calls. Thus, with 8 selection units, any originating call has an available field of 5 x 8 = 40 trunks towards the routing and o/g selection stages.

The local register finders are controlled by call connector CA in selecting a path from a calling connection circuit to a free register, and setting up connection. One CA serves a group of 10 registers END and 60 connection circuits CC.

The automatic test system embodying the invention is shown as a block diagram in fig. 3 and comprises test apparatus EE associated with the exchange AUT, and composed of a control position PC, data storage MI, associated within the system with a transcoder TS and a printer IM. Storage MI stores the identity of each unit and trunk engaged in each test call initiated from the control position PC, whether directed or random, effective or ineffective. The transcoder can read data in the storage in any code, and can feed out these data to the printer as directed by a program. A unit of this type is described in French patent 2,279,156 of 16th. July, 1974 of the present applicant, and entitled Transcoder especially for a printing unit.

Control position PC controls and supervises the entire test system. In particular, it comprises facilities for the prior designation of calling and called terminal equipments, and of the switching or other units and trunks to be busied in setting up the connection between the two. In the application described, these designators are manually operated selectors offering the following choices: - originating-outgoing calls (Fig. 1): switches and - 9 trunks in the stages AB2-AB1 (designators US and VAB1 (Fig. 4)), the call connector CA, the register finder-connector trunk CHE, the local register END and routing indicator IAD, trunks in switch stages AC1AC2, trunks SI and TI; - incoming-terminating calls (Fig. 2): register finderconnector CHA trunk, incoming register ENA, routing indicator IAA, ACA stage trunks, SA stage trunks, and subscriber BA stage trunks.

We shall now describe a call set up on a totally designated path, indicating the means used in each stage to identify the call as a test call within the normal traffic flow of the exchange, and the means used for unit and trunk designation.

In an exchange of the type described here, control is distributed, comprising special-purpose units such as registers and routing indicators, markers MQ1 to MQ6, MA, and call connector CA, in the various stages of the switching network.

Groups of information transfer lines INF between the control units in the various stages of the exchange and the testing system EE are also shown in figures 1 and 2.

A principle which will be encountered in various types of stages, is the use for identification purposes of the marking facilities already provided for the units performing the connections. It is in fact well known, that availabilities are tested and trunks selected before making a connection, this resulting in marking for connection. For test purposes, each control unit has a test call identifier consisting of one or several test relays ES (Fig. 4) operated from the control position PC. The contacts of these relays ES shunt the marking wires towards the control position PC, in which 4 6 51 - 10 these wires, i.e. the INF wire-bundles, are connected to storage facilities, comparators, and command transmitters .

In setting up an originating-outgoing test call, assuming that one subscriber line equipment is reserved in each rack for test purposes, it is sufficient to designate the rack, for the test call to start with simulation of the calling condition by that subscriber line equipment (Fig. 4).

The rack is designated by designators, in this case manually operated selectors GA (subscriber group) and BG (rack in the group), which energize a test relay ESI in the rack's marker MQ1.

For example, assuming a rack of 100 subscriber line equipments, the subscriber line equipment taken for the test is designated, at the control position, by setting manually operated selectors D and U, to which all the line equipment tens and units digit identification wires of each rack in the exchange are connected. These manually operated selectors control the connection of tens and units digit identification relays ID and IU, which are operated on matching of the manual selection made and the number of the line equipment busied for the test.

An auxiliary relay ESA1 is operated to indicate that the test call is directed, and not random: it is controlled via a contact of relay ESI and a contact adi of relay ADI in the control position (i.e. one of the relays ADI to AD20 described below with reference to Figure 7.).

In directed test calls, the selection unit to be used is then designated by the extension into the testing system of one operating wire per relay MMO - MM7 by closure of contacts esal, and the extension of earth on one of these wires by means of manually operated - 11 selector US. Wires mm indicate the availability of the 40 trunks, and are distributed in the call connector CA in the same way as the call pairs over the register finders connectors. Earth marking polarity is applied to each wire mm across a MAKE contact of relays MMO to MM7 of the selection unit and a BREAK contact of the corresponding ABl vertical. In fig. 4, these contacts, which denote the availability of the verticals, are shown as v followed by two figures: the first, 0 to 4, is the number of the vertical, and the second, 0 to 7, is the number of the selection unit. Designation of an ABl vertical is obtained by extending the marking earths of all the available originating trunks to the control position across contacts of relay ESAl, and contacts 0 to 4 of manually operated selector VAB1.

Precautions are taken to ensure that the test call will be connected at random, in the event of a designation or identification error: for example, fig. 4, shows that if a relay ID or IU fails to operate, relay ND will do so, and will take over extension of the marking earth, on all wires mm.

As the register finder-connector CHE serves up to 60 connection circuits CC, call connector CA (Fig. 5) has 60 wires mm connected to it, in 12 groups of 5. A -group finder CQ in the call connector CA scans continuously, stopping on the first earthed wire mm. A coil of a multiple 5-group marking relay AQI is then energized, and by means of contact aql, marks a position on unit finder CU, thereby operating a unit marking relay AU (not shown.).

Identification of the wire mm across contacts aql and aul operates a test relay TC, in series with a relay TA in marker MQ1, which is thereby notified of call progressing initiation. A contact of TA relays - 12 this information to the control position by operating relay TP in the latter, across a contact gr of a relay GR (not shown) stating the group of 27000 subscribers .

When several subscriber stage trunks are available for the test call, a call connector is selected by notifier NOT: a call connector will not be offered to take a call, unless one of the ten registers it nerves is free; the identification wires of the ten registers are connected, on the one hand, to scanner EX, and on the other, to a common relay DX, which will be at pickup while at least one register is free.

Busying wire ap of notifier NOT is taken across a MAKE contact of relay DI. Response of NOT to continuity of wire ap causes it to energize a relay PR, thereby permitting the busying of the call connector.

The pick-up of subscriber line equipment identification relays in the control position, and that of relays TC and PR in call connector CA, sets up a chain of contacts id, iu, tp, gr, and tc, pr, to energize relay ES2 in the' call connector, whereby the latter recognizes the waiting call as a test call. Earth is then extended across a relay contact to storage MI for recording of the busied call connector's number, as indicated by the pick-up in the control position of a relay PM.

Operation in designation is as described below, firstly in respect of the connection circuit CA for the AB1 trunk already designated: two manually operated selectors, DQ and DO, are set to the desired 5-group and units digit positions. These positions are compared by comparators Cl and C2 with those of the 5-group and unit finders CQ and CU (contact banks CQ' and CU'), across MAKE contacts of relay ESA2, the latter being operated at designation of the register finder-connector rack, and hence of a call connector CA, by the setting of - 13 manually operated selector BCHE at the control position. This selector is controlled by a circuit UV, which connects power to it only if one abl vertical, and one only, has been designated.

Whatever the nature of a call, that is to say, whether it is a test call or not, an available register is found for it by scanner EX, connected to a pulse generator (not shown) delivering pulses to wire g. If a register is specifically designated to handle a test call, the generator is inhibited, and wire g is transferred to an auxiliary pulse generator Ge in the control position, by a contact of relay ESA2.

The number of the designated register is selected with manually operated selector NE, of which the position is compared with that of scanner EX by comparator C3, which cuts off the generator Ge, when they match.

Register addressing is by connector CN, controlled by manually operated selectors BCHE and NE, which supply it with the number of the 10-register group, namely that of the rack of register finder-connectors, and that of the register in the group.

Connector CN then directs earth polarity through to the register, to pick up relay ES3, of which contact es3 extends ready polarity on wire dis to the control position. The register can no longer be busied to handle a normal call. If, however, it is busy when designated, the control position will simply await appearance of the ready polarity, before proceeding with the test call.

A routing indicator IAD may be designated by notifying the register-routing indicator coupler of the position to go to on recognition of the call by the register busied for the test . The routing indicator is notified that the call is a test call on the direct connection L, shown in Fig. 1, at the instant of the 4 6 51 - 14 coupler CPL1 connects the register END to the routing indicator or 1AD.

Writing in storage of busied unit identities (direct or random test calls) can be seen in Fig. 6.

The numbers of the CC 5-group q, CC in the 5-group u, register nE, register group gE, subscriber group gA, are put into storage MI. Signals nE, gE, and gA direct extension by multiple relay RM of energizing polarity to test call relay ES4 in the register: the pick-up of this relay diverts signalling received by the register to the test system. A contact es4 also permits operation of a relay ESA3, to indicate directed test call, which is energized by the test system EE across contact adi, in multiple connection to all registers (i.e. across one of contacts adi to ad 20 as described below) In the routing and selection phases of call progress, the two same basic functions of trunk designation and identification are re-encountered. In an exchange as chosen for this example of an application of the invention, selection of a free trunk to progress a call of any nature, is performed by means of selection guides gs (Fig. 7.) which form a network identical in pattern with .the trunking of the routing and selection stages. In other words, each guide reflects the avail25 ability or otherwise of a trunk, and these guides are graded in exactly the same way as the trunks of that part of the switching system, which they represent.

At each stage, an electronic selection guide reader scans the guides: there is only one bundle of guides, and only one reading may be performed at any time. The reader therefore requires permission to read, obtained from a reading distributer DL (Fig. 7).

In the example chosen, the crossbar switches have 20 cross-points per vertical, so that there are 20 levels and hence 20 guides per selection unit. As the - 15 selection unit is designated by a guide on its inlet side, the reader has only 20 scanning positions. In routing selection, there is only one reader for the two stages, and it is used in succession for the scanning of selectors ACl and AC2.

Designating one trunk of the 20 is performed by inhibiting the availability of the guides corresponding to the 19 others, so that the reader can but stop on the one left available.

Identification of the ACI vertical serving the connection circuit taken for the call is as follows: The A and S wires between the subscriber line equipment and the switching stages are diverted, as usual in such systems, to the register by the connection circuit, for registering of selection signals. These wires are conventionally referenced Al, BI ahead of the register, and A2, B2 after the register.

In the system discussed, the wire A2 at the register is switched to the control position by a MAKE contact of relay ES4 mentioned above (via Q wire A3), and the signalling received on wire A2 is returned to the register on Q wire A4.

The test call signal is sent to pick up a relay ES5 in marker MQ2 of the routing stage, by connecting an off-ground supply AL via the wires A3, A2.

Routing selection has a circuit identifier, not shown, which by means of a multiple marking relay (RA) a) relays the register-register finder (END-CHE) signalling wires to the reader, wire A2 in particular, and b) connects selection guides gs, according to the selection unit, served by the connection circuit CC, to that reader (relays US1 to USn).

Power supply AL is cut in by contacts SP1 of a relay SP1 (not shown): negative is extended to relay ES5 in each routing stage of the exchange, while - 16 positive is connected on the wire A3 through the register finder CHE and marking bus RA to the stage concerned. The identity £ of the ACI vertical is transmitted to the control position in EE across contacts of ES5, and stored by circuit MJ. On effecting storage, MJ operates a relay VA to switch wire A3 to a signalling relay S, which has a 3000 Ohm and a 400 Ohm coil.

Wire A2 is connected by bus RA via common point p to a 1000 Ohm earth and to amplifier AP, provided to busy reader distributer DL. At pick-up of relay VA, the 3000 Ohm coil Of relay S is energized, but the potential at point £ does not drop sufficiently to allow amplifier AP to conduct.

Relay S connects power across relay RC to manually operated selector CAC, provided for designation of an ACI stage trunk. The selector CAC puts one relay ADI to AD20 in series with RC, while circuit CT checks I that one and only one of the 20 AD relays has picked up, whereupon CT will operate relay CAD to notify o/g selection of the designation and initiate busying of the reader distributer DL: relay SL is energized across a contact of CAD, closes contact SL and connects the 400 Ohm coil of relay S to wire A3. This switches amplifier AP on, and reader distributer DL permits reading by the prepared reader by operating relay CL.

The reader has a 20-point scanner CRL. At each step, scanner CRL controls a reading amplifier AL1-AL20, each controlling a relay LI-L20.

The twenty selection guides gs are offered to amplifiers AL1-AL20 by multiple relays USl-USn. An amplifier will conduct only if the selection guide offered to it is carrying current, and only when scanner CRL reaches its step in the scanning field. The scanner then stops, and the corresponding L1-L20 relay picks up to permit connection of the corresponding ACI trunk. 4 6 51 - 17 In the case of a call involving prior designation of the ACI trunk, the pick-up of relays RC and CAD energizes test relay ESA4, in stage ACI. This relay offers 20 wires connecting to earth across break contacts adl-ad20 of relays AD1-AD20, to the amplifiers AMI-AM20, of which the outputs each control a reading amplifier AL1-AL20. Thus, the AM amplifiers grounded by closed break contacts adl-ad20, the corresponding relays AD1-AD20 being de-enargi2ed, will not alicw their reading' amplifiers AL to conduct, so that designation (pick-up of one AD relay only) leaves the reader with only one choice. On completion of reading, whether the call be random or directed, the number of the trunk taken is notified to the control position by contacts of relays ES5 and L1-L20, and is stored by ML.

Similar designating and identifying facilities are employed for and in stages AC2, and SD - TO, as also in i/c-terminating selection.

To inhibit a unit in the case of faults, it is necessary to inhibit timeouts. These can be inhibited by using a manually operated control when a directed or random test call is being progressed, and exclusively in the chain of control units in connection with the control position in handling that call.

In i/c selection, the test apparatus will be used to designate the i/c junctor, a complete path of units and trunks, and the terminating subscriber line equipment. The following description is limited to primary and secondary i/c selection, because a) the principles involved are the same as in o/g selection, and b) designation of the trunk in secondary i/c selection simultaneously designates the i/c vertical of the subscriber stage, and consequently also the selection unit. Subscriber line equipments are multipled to two verticals AB2 of the same selection unit, so that one - 18 : of’these verticals would remain to be designated. However, this possibility is not used in the example chosen.

Please refer to fig. 2: the allocation of a register to a calling i/c junctor JE is performed by marker MA, controlling switches CJE and CE of the register finder-connector CHA. The junctors are connected at the levels of stage CJE, and each has access to several verticals. These CJE and CE switches are interconnected vertical to vertical, and the registers are connected at the CE levels. Thus, one CJE or CE vertical has access to 12 registers, which constitute a group.

Marker MA, shown in figs. 8 and 9, has a scanner composed of 4 counters CRl to CR4, which determine the group and number of the selected register (CRl - CR2), and the 12-group and unit number of the i/c junctor (CR3, CR4) .

A calling junctor connects positive (earth) across a contact p of a relay P (not shown) and a diode Di, to calling wire ap into the marker.

In the marker, each wire ap is connected across a de-coupling diode D2 to a BREAK-contact vj of each CE vertical CE (Fig. 2), to which that junctor has access. The other side of contact vj is connected to a point K1 of counter CRl pertaining to the group of registers accessible from Vertical VJ.

Each register extends earth, while free, into the marker on a wire dp. Wires dp from the registers of the same group are connected across decoupling diodes D3 to the same point in counter CRl.

Counter CRl is driven by a flip-flop to run in continuous cycle, while the negative at points K1 and K2, at each step, appears at its control input Va. The polarity at Kl may be changed by a wire ap, and that at K2 by a wire dp, thereby stopping the counter on a marked calling wire having access to a free vertical, but - 19 only if a register is free in the 12-group served by that vertical.

The stopping of CRl permits marking by multiple relays of the reading wires of counters CR2 to CR4, and then transmission of a busying signal to the junctor and register. The junctor's class (discrimination) must then be notified to the register: as the discrimination wire bundle is common to several units, a marker must first obtain access to it from a marker distributer DM, which it busies at the stopping of CRl. Response from DM energizes a seizing relay PN.

At positioning of counters CR2, CR3, and CR4, a signal is returned on the calling wire ap to the junctor, by connecting 48 V across contacts Dj and uj of the junctor 12-group and unit number marking relays, and a contact of seizing relay PN. This signal is sent back into the market pr on wire apl, and to the register across another contact of relay PN. In the register, it will operate a junctor discriminating relay DIS.

I The call acceptance signal, also for the register, is an earth polarity extended across relay PN contacts and register number and group marking relay contacts ne and NG, on a wire p to energize relay PND, which controls energization of relay DIS.

All junctors have a test call relay ESS. If a call is a test call, the testing system sends a signal csl to pick up this relay in the designated junctor.

Two contacts of ES6 and a contact bo, of looping relay BO (not shown) extend wire ap on wire ap2 into the marker, where, across a PN relay contact pn it is transmitted to a test discrimination relay ES? in the register, identified by a register number storage circuit PME in the testing system (fig. 9).

The test call signal CSL sent to the junctor is also extended into the marker on wire cs2 to operate a relay ESS, used far transmission to the testing system - 20 of the positions of counters CR1 to CR4.

For this, the counter outputs are connected to inputs xl to xl6 of amplifiers AX1 to AX16, which transmit identification polarities to the testing system across contacts of relay ES8. In the testing system, this information is stored by ME at the instant of pickup of ES8, but not permanently stored until confirmation by reception of the register number from ME, on wire Van (fig. 9). If Van signal does not appear, the data is erased.

As we shall see, register designation is performed by complete take-over of the marker by the testing system, that is to say, control of counter-stepping and of marker distributer DM busying. The register is reserved for a test call, as in o/g selection, by transfer of its ready wire to the testing system.

The progressing of a test call, and designation of the units in the chain, are performed as follows: - The operator designates a junctor and register, determining the stopping positions of counters CR1 CR4 by setting manually operated selectors CT1 to CT4, of which the settings will be compared with the outputs of amplifiers AX1 to AX16, by comparators CPI to CP4.

After handling a call, the marker allows the testing system the possibility of busying the marker distributer DM (wire aa, fig. 8). Busying signals between the marker MA, testing system EE (wires aa, ad), and the distributer DM, are transmitted by gating circuits PS. A test call may be initiated once the testing system has obtained permission to busy the distributer DM, and the ready signal from the register. It can then notify the marker of a directed test call by signal CSA, picking up test call relay ESA5 in the latter, - 21 This signal inhibits normal control of counters CR1 to CR4: the control input va of each counter receives negative across respective resistors Rl to R4. Normally cancelled by an opposite polarity across a BREAK contact of ESA5, this negative is connected when the relay is picked up, and prevents the stopping of the free-running counters. For each counter separately, the negative is removed again from va, when the counter reaches the same position as that of the corresponding manually operated selector, by positive on wires AVI to AV4, from the comparators.

The distributer DM is then busied by the testing system on wire ad, and its response permits pick-up of seizing relay PN (fig. 8).

When the counters stop, marking follows as In the case of a call without prior designation of units.

In the case of a directed call, storage of the information is not confirmed by the register number only, but also by comparator outputs, on the following circuit: output of PME, MAKE contact of relay ADI (indicating directed test call), AND gate PE, also receiving comparison signals on wires AVI to AV4. In the i/c selection discussed, the test call indication is sent to the routing indicator by the register through the coupler, at the same time as information for translation. As in o/g selection, designation is performed by controlling the coupler.

The testing system described thus makes it possible to set up test calls from designated calling to called terminals, both while allowing common control to select the path through the switching system, as a function of priorities or of previous choices, or at random, and by designating all the units and trunks to be taken.

The system also allows partial path designation 44651 such as by predetermining all trunks up to a given stage, from AB2 as far as AC2, for example, in o/g selection, the remaining trunks being selected by the exchange control. It is also possible not to designate certain units, such as the registers and routing indicators: in this case, as in any directed or random test call, the storage of the identities of all trunks and units engaged in the call remains possible.

The invention is not restricted to the applicable) ion described: it is applicable to an exchange of any type employing distributed control of the selection of units and circuits, but is not dependent on the technology of the exchange.

Claims (12)

CLAIMS:

1. An automatic test system for an automatic switching exchange having a plurality of distributed control units including registers, the test system comprising central test apparatus connected to the control units of the automatic exchange via an information network, and means in the control units to co-operate with the central test apparatus, the central test apparatus including a store for storing the identity of the control units and trunks involved in a test call, means for designating the control units and the trunks to be used in a test call from a designated calling unit to a designated called unit, said calling and called units being input/ output units of the exchange reserved for test purposes, and means for following the progress of a test call step by step through the exchange, and the said means in the control units for co-operating with the central test apparatus including test call identifiers arranged to ensure that no designated control unit or trunk is seized for a test call until a test call is identified at an input to the designated control unit or trunk, whereby designated control units remain available for normal traffic through the exchange except only for the time during which they are actively engaged in setting up the test call.

2. A test system according to claim 1, wherein the means for designating the control units and trunks to be used in a test call includes both designator selectors and means for confirming and verifying the designation.

3. A test system according to claim 1 or 2, wherein the test call identifier of each successive control unit involved in a test call connection is responsive to a test call identifying signal relay from the previous control unit once its test call identifier 4465 I has operated.

4. A test system according to any preceding claim, wherein the identity of a control unit involved in a test call is signalled to the central test apparatus 5. By the test call identifier by means of a signal potential which is isolated from the exchange power supply, the central apparatus returning said isolated potential signal to the said control unit.

5. A test system according to claim 3 or 4, 10 wherein the test call identifiers comprise test call relays operated, in those parts of a test call connection which follow connection to a register, by a test call identifying signal being applied to the one of the A and B wires of the test call in the register via a connection 15 between the register and the central test apparatus.

6. A test system according to any preceding claim, wherein the means for designating the control units and trunks to be used in a test call include at least some manually-operated selectors operable from a 20 control position.

7. A test system according to claim 2 applied to an exchange where the distributed control units include markers controlling finders-connectors, and wherein the means for confirming and verifying designation of control units 25 and trunks includes comparators for comparing the designation as set in the central apparatus with signals sent to the central apparatus from the test call identifiers and identifying the control unit at which a test call has been identified.

8. A test system according to claim 2, applied to control units in which the search for an available trunk towards an associated control unit is performed by - 25 scanners and/or scanning counters comprising a driving and a stopping circuit, wherein the designation of the trunk to be taken is performed by the means provided for control of said scanners and/or counters.

9. A test system according to claim 8, in which a trunk to be taken is designated by a circuit extending inhibiting signals to all points of the aforementioned scanners and/or scanning counters, except for the point selected.

10. A test system according to claim 7 or 8, in which a trunk to be taken is designated by an inhibiting circuit in the stopping circuit of the aforementioned scanning counter, inhibition of said stopping circuit preventing the counter from stopping at points corresponding to free trunks, a comparator removing the inhibition when the scanning counter reaches the point corresponding to the chosen trunk.

11. A test system according to claim 7 or 8 in which designation of a trunk to be taken is performed by a controlling circuit comprising means of inhibiting scanner stepping and a pulse generator, which takes over from the normal drive circuit of the scanner and which is cut off by a comparator when the scanner's position is the designated position.

12. A test system substantially as herein described with reference to the accompanying drawings.