Telephone routing system

June 10, 1947.

R. C. AVERY

2,421,919

TELEPHONE ROUTING SYSTEM

Filed April 29, 1944

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ATTORNEY

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June (10, 1947.

R. C. AVERY

2,421,919

TELEPHONE ROUTING SYSTEM

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Filed April 29, 1944

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INVENTOR

S S y

Patented June 10, 1947

2,421,919

UNITED STATES PATENT OFFICE

2,421,919

TELEPHONE ROUTING SYSTEM

Robert Campbell Avery, Jackson Heights, N. Y., assignor to American Telephone and Telegraph

Company, a

Application April 29,

Claims.

This invention relates generally to telephone exchange systems and, more particularly, to panel-type dial systems in which connections between subscribers’ lines terminating in different offices of the telephone exchange are established by automatic switching mechanisms over groups of interoffice trunks.

In exchange areas having a large number of local offices, it is not always economical to provide direct groups of trunks for interconnecting any two offices of the exchange area, particularly where the traffic between these offices is not heavy. In some exchange areas, therefore, it may be economical to route some or all of the traffic between certain offices through a tandem office which may serve as a common intermediate distributing point.

It has heretofore been proposed to render more efficient the trunking arrangement between any two offices by reducing the number of direct trunks between those two offices and by automatically re-routing the remaining traffic between these offices to a tandem office where this traffic may then be routed to the desired office. To accomplish the re-routing of calls through a tandem office in systems employing central office senders which control the setting of selector switches to establish connections, each sender must receive a signal in order that it may take the necessary steps when such re-routing is required to re-route succeeding connections for that trunk group over a different trunk group extending to the intermediate tandem office. Each sender must also receive another signal to reemploy the direct route between the two offices when the direct route again becomes available.

It is an object of this invention to provide a re-route signal when all trunks of the direct trunk group extending between two offices are busy. It is another object of this invention to provide a re-route signal when all but a predetermined number of the trunks of such a group are busy. Any arrangement to accomplish the latter object will prevent the loss of certain calls which would otherwise occur because of the time interval after selections by the sender are started and before the selector switch controlled by the sender is actually positioned on the terminals of the desired trunk. A sender may be given information to route a call to a trunk of a direct SO trunk group extending to a desired office and may proceed to cause the selection of a trunk in such a group when there is only one such trunk idle. If the signal to the sender to reroute succeeding calls should be delayed until 55 :on of New York

1944, Serial No. 533,314 (CI. 179—18) after the seizure of the last idle trunk such calls would not be completed if these were initiated during the interval after the sender starts its selections and before the selector switch con5 trolled by the sender completes contact with the terminals of the last idle trunk. Hence, the selector switches operated to complete such calls to the desired direct trunk group would be driven to the overflow position. To guard against any 10 such contingency, it is desired to signal the sender for the re-routing of calls when all but a predetermined number of the trunks, such as one or two of the trunks, for example, are busy.

It is a. further object of this invention to set 15 the re-route signal in response to the action of the selector switches as they reach a predetermined terminal near the top of the trunk group contacted by the selector switch.

Another object of this invention is to auto20 matically set the re-routing signal as required and to release it automatically upon the release of the previously busy trunks. This object may be accomplished by the action of a test circuit common to one or more trunk groups, the test 25 circuit being arranged to test the trunks of each of the groups in regular order and to control the re-route signal for each such trunk group. Thus, the test circuit may operate to complete calls by means of the original route, or it may 30 re-route these calls, all of which may be controlled by the information reaching the common test circuit. The use of a test circuit common to a plurality of trunks or trunk groups will materially reduce the amount of equipment hereto35 fore required for re-routing calls.

Another object of this invention is to provide a common test circuit for testing different parts of the trunk group at different times, then to record the results of such tests and thereafter 40 to set the re-route signal in accordance with the cumulative results of the tests of all of the parts of the trunk group.

Another object of this invention is to provide arrangements for transmitting calls through dif45 ferent tandem centers so that calls which would be normally routed over a trunk to any one of such tandem centers may be transmitted over trunks to other of such centers whenever traffic conditions warrant such a change in routing.

The apparatus of the invention is designed to set the re-route signal or to restore the conditions to normal when calls for a particular trunk. group are in progress in the decoders without interference with such calls. The apparatus is arranged to effect a change in the

2,421,919 routing information after a route relay in a decoder has operated and before the decoder has completed its functions.

As is disclosed in Patent No. 1,862,549, dated June 14, 1932, to R. Raymond et al., the establishment of connections from an originating office to any other office of the exchange area is made possible by district and office selectors which are set to select an idle trunk of the group of trunks extending to the office in which a desired subscriber’s fine terminates by a sender common to all subscribers’ lines of the originating office. A plurality of senders, any of which may be taken for use by a calling line, is provided, each sender having registers for registering both the office and numerical designations of a desired line dialed by a calling subscriber, and controlling apparatus for the setting of the district selector and an office selector to extend a connection to the office in which the desired line terminates and for controlling other apparatus in the selected office for completing the connection. A plurality of decoders is also provided common to all of the senders, an idle one of which becomes associated with a sender taken for use by a calling subscriber. The decoder is provided with office code registers to which the office code is transferred from the registers of the associated sender and is also provided with as many route relays as there are trunking points to which calls may be trunked from the originating office. The combined setting of the office code registers of the decoder determines which one of these route relays shall be operated for any particular call. The operated route relay is then instrumental in establishing in the associated sender a registration for directing the sender to control· the setting of the district and office selector switches or. the setting of the district selector alone to select a group of trunks extending to the office in which the desired line terminates.

In accordance with the present invention each trunk group extending directly from one office to another office to which it is desirable to apply alternate routing through a tandem office or other type of switching center, is provided with a- cut-in relay or relays for connecting the sleeve terminals of the trunks to a test circuit common to a number of such trunk groups. The cut-in relay or relays are operable by the common test circuit which is arranged to determine the busy and idle conditions with respect to the trunks of the group. Each such trunk group is also provided with a relay for setting or restoring the re-route signal in the various decoders. The latter relay may be operated for setting the signal in accordance with the action of the selector switch as it passes a predetermined terminal near the top of the trunk group. It may also be operated to set the signal and it may be released to restore the signal under control of the common test circuit which, as it is connected to the sleeve leads of the various trunks, determines the busy or idle condition with respect thereto. The setting of the re-route signal in response to the action of the selector switch as it reaches the predetermined terminal near the top of the trunk group, assures that the re-routing of traffic will occur only if all preceding terminals of the trunk group have been passed and found busy. Thus, the re-routing of traffic will occur only when all trunks below a predetermined trunk are found busy.

The common test circuit to which the sleeve terminals of the various trunks may be connected through the contacts of the cut-in relay or relays is arranged to test a number of trunks, such as 10, at any one time. The testing apparatus is also equipped with a rotary selector and an associated relay circuit so that the test circuit may successively test other similar groups of trunks. The test circuit will be shown to control the operation of the cut-in relay for the trunks to be tested. The test circuit will also include a group of auxiliary relays, one common to each of the trunks to be tested, and each such auxiliary relay will be operated if the trunk is found busy. The auxiliary relays are arranged in a chain to close one of a number of different circuits in accordance with the busy conditions of the various trunks. One of these circuits will be closed if all of the trunks are busy. Another circuit will be closed if all but one of the trunks are busy. Still another will be closed if all but one of the trunks are busy. Still another will be closed if all but two of the trunks are busy. And so on. One or more of the latter circuits may be connected to re-route relays for controlling the routing of traffic when such auxiliary relays have become operated.

This invention will be better understood from the more detailed description hereinafter following when read in connection with the accompanying drawing, in which Figure 1 illustrates some of the equipment which may be employed for routing and re-routing telephone calls in accordance with the principles of the invention, Fig. 2 illustrates an arrangement which may be connected to the Fig. 1 arrangement, Fig. 2 including, among other things, a common testing circuit for testing the various trunks of one or more groups of trunks shown in Fig. 1, and Fig. 3 shows some of the apparatus that may be included in a decoder when set up to practice the invention.

Referring now to Figs, 1 and 2 of the drawing, there is shown a calling subscriber SB connected to a line finder LF, a district selector DS, an office selector OS, a district finder DF, a sender selector SE, a sender SD and a decoder connector DC, all of which are of a well-known type. In order to simplify the drawings, these devices have been shown only schematically herein. For a more complete disclosure and description thereof, reference may be had to the R. Raymond et al. patent already recited above. The decoder connector DC may be connected to a number of decoders which will be referred to again in regard to Fig. 3.

In response to dialing, the office code and numerical designations of the called party’s telephone station (not shown) are registered in the sender SD in a well-known manner, and following the registration of the office code designation, the decoder connector DC is operated to associate one of a plurality of decoders with the sender SD. Each decoder may be provided with the usual receiving registers to which an associated sender transfers the registered office code designation, a route relay corresponding to each route over which connections may be extended from the originating office and transmitting registers which are selectively set by any operated route relay. The transmitting registers are employed to transfer routing information to the registers of the associated sender which in turn control the functioning of the sender to establish the desired connection over district and office selectors in accordance with the operated route relay of the decoders.

It may be assumed that a call has been started by the sender SD and that a selector switch SS of the office selector OS proceeds to hunt over a group of terminals such as AT which may be

2,421,919 ten in number. The sequence switch SQ will cause the relay L of the selector switch SS to become operated at certain intervals to cause the mechanism to hunt past busy sleeve terminals such as So . . . S5. Upon reaching a grounded sleeve terminal such, for example, as Ss of a busy trunk, the relay L (previously operated by the closing of the sequence switch SQ) will be held operated over a holding circuit established through its right armature and make contact and extending to ground at the sleeve terminal S5. As the relay L becomes operated and held operated, it completes a circuit through its left armature and make contact to energize the updrive magnet UP, causing the up-drive of the selector switch SS to continue past the grounded sleeve terminal in question. When a sleeve terminal is reached which does not have ground connected thereto such as Ss, for example, the relay L will release, thereby causing the up-drive mechanism of the selector switch SS to stop. When this happens the brushes of the selector will be centered upon the trunk terminals in a wellknown manner to advance the calling party’s line through the the available or idle trunk.

In the present arrangement of the invention a predetermined terminal such as AA of the group of terminals AT has been set aside for operating the re-route mechanism. Terminal AA is not connected to a trunk. When the selector switch SS in moving upward in search of an ungrounded sleeve terminal reaches the terminal AA, a circuit is completed from battery through the winding of relay L, the make contact of its right armature, the sleeve contact of terminal AA, then over the upper winding of relay AR to ground. Relay AR is the re-route relay of the trunk group AT. It is a fast operating relay and its upper winding is of low resistance. The ground connected to its upper winding acts as a busy condition to the hunting selector switch SS and it holds the relay L operated so as to continue the up-drive past the terminal AA. Although the up-drive continues past terminal AA, the relay AR and relay L, which are connected in series, are both operated. The hunting selector SS will proceed to seize the next upper trunk associated with the sleeve such as S7 to complete the connection from the calling party’s set SB to the called office, provided sleeve Sr is ungrounded. After relay AR is operated, it is locked in its operated position over a circuit which includes battery, the lower winding of relay AR, the make contact of armature Li of relay AR, the normal contacts associated with armature Ti of relay Clo and ground. Relay AR also applies ground at its armature L2 to a start lead ST which is connected to the associated common test circuit shown in Fig. 2, the purpose of which will be described later. The relay AR also transfers the code leads I i, 12 and 13 of three decoders (not shown) from the normal route relays connected to conductors 14, 15 and 16 which are in turn connected to the back contacts of the upper armatures Τι, T2 and T3, respectively, to the alternate route relays of the three decoders connected to conductors Η, ί 8 and 19, respectively, the latter relays being associated with the alternate route trunk group. This will be further described with regard to Fig. 3. Thus, when relay AR is unoperated, calls will be directed to the normally associated trunk group, but when relay AR becomes operated, these calls will be transferred to the trunk group for the alternate route.

Terminal AA of the trunk group AT preferably should be so located that there will be one terminal above it for completing the call which may have caused the operation of the re-route relay AR. If desired two or more working terminals may be positioned above terminal AA of group AT for completing calls which may have already been routed to this trunk group but have not reached it at the time when relay AR operates. The number of the additional terminals appearing above terminal AA will depend on the probability of calls being initiated during the critical interval just before relay AR operates. If desired, two terminals such as AA may be connected in parallel for causing the operation of relay AR should relay AR not be sufficiently fast to operate as the selector switch SS passes but one such terminal. When relay AR becomes operated, it will remain operated to cause the rerouting of calls in the associated decoders but relay AR will be released by the common test circuit of Fig. 2 whenever trunks become available again for such calls, as will be explained hereafter. The common test circuit of Fig. 2 is arranged to test the several trunks of group AT at one time. The common test circuit may be arranged to function only when the relay AR is operated, or it may be arranged to operate continuously whether or not relay AR is operated, or it may make busy tests at predetermined intervals. These alternatives are controlled by keys BC, IC and KST of Fig. 2 and will be explained hereinafter.

Assuming that the busy control key BC of Fig. 2 is operated, tests will be made to determine the busy conditions of the trunks of group AT, but these tests will be initiated only after relay AR operates, and the tests will be stopped as soon as the relay AR releases as will now be shown. Upon the operation of relay AR and the connection of ground at its armature L2 to the start lead ST, a path will be completed to energize the windings of relays STA and Clo, this path including the grounded start lead ST, the contacts of key BC, conductor 21, the armature T2 of relay RL on its back contact, the winding of relay STA to battery and ground. In parallel with the winding of relay STA there is the circuit including the feed brush FBi of one arc of a rotary selector, the main, brush MBi of the same arc of the rotary selector, terminal 3 of the rotary selector upon which its main brush MBi may be assumed to be resting, conductor LDo, the winding of relay Clo, battery and ground. The ground connected to conductor 21 in the manner above described is also closed through the armature T2 of relay RL, to the upper winding of relay PT and battery. Conductor 21 is also connected through the armature L2 of relay STA and its back contact to the lower winding of relay PT and battery. Relay PT is employed in this circuit together with condenser K and resistances R and Ri in order to introduce a time interval in the operation of the connected circuit arrangement. With ground connected to· both of its windings as above, the magnetic effect of the lower winding of relay PT is stronger than that of its upper winding and the relay is consequently set on its back contact. A parallel circuit will be provided also from the grounded conductor ST through key BC, conductor 21, the armature Li of relay RL and its back contact, the stepping magnet SM of the rotary selector, battery and ground. Although the stepping magnet SM is energized at this time,

2,421,919 it will not step the rotary selector to its next contact until the stepping magnet becomes released. The energization of the windings of relays STA and CIo will cause the relay CIo to become immediately operated, but due to the slowoperate property of relay STA, this relay will remain released for a brief interval sufficient to insure that relay PT will be propertly positioned on its back contact.

The operation of relay CIo will transfer the locking path of relay AR previously completed through the normal contacts associated with armature Ti of relay CIo to lead 32 Which is connected to ground through the back contact of armature Li of relay RLA and the normal contacts associated with the armature Ti of relay RL. Thus, relay AR will be held operated as long as both relays RLA and RL remain unoperated. Relay CIo also connects the sleeves So to S9 of the various trunks of trunk group AT through the corresponding make contacts and armatures of relay CIo to the windings of relays Po to Ρθ, respectively, the windings of each of the latter relays being also connected to ground through a battery. The latter circuits interconnecting the sleeves of the trunks to the windings of relays Po to Po are shown only schematically by a dotted line 31. It will be understood that sleeve S9 will be connected by one make contact of relay CIo to the winding of relay P9, that sleeve Ss will likewise be connected through another make contact of relay CIo to the winding of relay Ps, and so on for all other sleeve contacts of the trunk group AT. Thus, the operation of relay CIo will connect the various trunk sleeve terminals to the windings of the separate relays Po to P9 which are part of the common test circuit for testing the busy conditions of the trunks associated with those sleeve terminals. Inasmuch as each busy trunk has ground connected to its sleeve terminal, the corresponding relays of the group Po to P9 will become operated while relays of the group Po to P9 connected to idle trunks will be released.

The several relays Po to Pe have windings which are of high resistance so that the hunting selector OS may test the various sleeve terminals in the manner already described without any interference arising from the connection of the windings of these relays Po to P9 to these sleeve terminals. Hence, the connection of the winding of any relay, such as Pe, to the sleeve terminal S9 through the corresponding armature and make contact of relay CIo will not interfere with the action of selector switch SS and relay L in detecting the absence of ground on the terminal S9 when the associated trunk is idle. Each of the relays Po to P9 has but one armature which is employed to control a corresponding relay of the group TTo to TTe. Thus, the several relays Po to P9 control the operation of the corresponding relays TTo to TT9 which are also part of the common test circuit.

It will be observed that when a sleeve contact such as Ss is found grounded due to the busy condition of the associated trunk, the corresponding relay P5 will become operated, and relay Ps in turn will operate relay TT5. Consequently, the various relays of group TTo to TT9 will be operated or released depending upon whether or not the corresponding sleeve contacts of the trunk group AT are grounded or ungrounded. If there are ten trunks in the group and if all of the sleeve contacts So to S9 are grounded, for example, all of the relays Po to Po will be operated as well as the corresponding relays TTo to TT9. If all of the sleeve contacts, except sleeve Ss for example, are grounded, then relays Pe and TTe will be the only unoperated relays of the two groups of relays Po to P9 and TTo to TT9 controlled by the sleeves So to S9. If there should be less than ten trunks in the group, the contacts of relay CIo which are not associated with trunks are connected to ground so that the corresponding P and TT relays will be operated in the same manner as for busy trunks. In the present instance the contact of relay CIo corresponding to terminal AA of group AT will be so wired, causing relays P6 and TTe to be operated.

Although the winding of relay STA is connected in parallel with the winding of relay CIo as already shown, relay STA is slow in operating to insure that relay PT has ample time to close its back contact as hereinbefore described. After this interval of time has elapsed, relay STA operates and disconnects ground from the lower winding of relay PT by the opening of the circuit through its armature L2 and associated back contact. This allows condenser K to become charged in a circuit extending from battery, through the lower winding of relay PT to ground. As this charge is taking place, the magnetic effect of the lower winding of relay PT is gradually reduced. When the effect of the lower winding is reduced to less than that of the upper winding, the relay PT operates.

Relay PT in operating causes relay RLA to operate in a circuit from the previously mentioned ground already connected to conductor 21, through armature T2 of relay RL and its back contact, armature Li of relay STA and its front contact, the armature and front contact of relay PT, the winding of relay RLA, battery and ground. The delay introduced in the operation of relay RLA by means of the condenser timing arrangement described above is sufficient to allow relays CIo, Po to P9 and TTo to TTo to be fully operated. Relay RLA in operating provides a ground at the make contact of its armature T2 over conductor 24 and through the armature T2 and back contact of relay RL, armature Li and the corresponding front contact of relay STA and the armature and front contact of relay PT to lock the relay RLA in its operated position. This locking path to ground will also hold relays STA, PT and CIo and the stepping magnet SM operated. Furthermore, the operation of relay RLA will cause the energization of the winding of relay RL over a circuit which includes the armature Ti of relay RLA and its make contact, conductor 25, the winding of relay RL, battery and ground. Relay RL is of the slow operating type and, therefore, will not respond immediately after relay RLA becomes operated. The operation of relay RLA also opens a path at the normally made contacts associated with its armature Li which previously extended to the winding of relay AR, over lead 32 and the armature Ti and make contact of relay CIo. The opening of this path will serve to release the relay AR which controls the alternate route control circuit if the relay AR is operated, provided the results of the tests to be described indicate that the associated route has again become available. The operation of relay RLA also connects ground at the normal contacts of armature Ti of relay RL through its own armature Li and make contact, through the lower armature of relay Qi and its back contact, through the lower armature

2,421,919 of relay Q2 and its back contact, and then through the lower armature and back contact of relay Q3 to the armature U2 of relay TT9. The connection of ground to the armature U2 of. relay TT9 in response to the operation of relay RLA will serve to hold relay AR operated, if it is already operated, or to operate it if it has become released, if the associated route is not available as indicated by the tests performed by relays Po to P9 and relays TTo to TT9. This will now be explained.

The ground connected to the upper armature U2 of relay TT9 will be applied through the various contacts of relays TTo to TTg to one of the four conductors AO, BO, CO or DO in accordance with the number of relays of the group TTo to TT9 that are unoperated at any one time. If all of the relays TTo to TT9 are operated, as would be the case if all the trunks of group AT were busy, ground at the armature U2 of relay TT9 will be applied to the conductor AO over a circuit which includes the make contact of armature U2 of relay TT9, and then through the other armatures U2 of relays TTs, TTv . . . TTo and their corresponding make contacts. If all of the relays TTo to TT9 except one, such as TTs, are operated, then ground will be applied to the conductor BO over a. circuit which includes the armature U2 of relay TT9 and its make contact, the armature U2 of relay TTs and its back contact, then through the armature Ui of relay TT7 and its make contact, and through the other armature Ui of relays TTo, TTs . . . TTo and their make contacts to· conductor BO. If all of the relays TTo to TT9 are operated except two, such as TT7 and TTs, ground at the armature U2 of relay TT9 will be applied to conductor CO over a circuit which includes the armature U2 of relay TTo and its make contact, the armature U2 of relay TTs and its back contact, the armature Ui of relay TT7 and its back contact, and then through the armature Li of relays TTo, TTb . . . TTo and their make contacts to conductor CO. If three or more of the relays TTo to TT9 are unoperated, as for example, relays TT7, TTs and TTo, ground at the armature U2 of relay TT9 will be applied to the conductor DO over a circuit which includes the armature U2 of relay TTo and its back Contact, the armature Ui of relay TTs and its back contact, the armature Li of relay TT7 and its back contact and then to conductor DO. Thus, ground will be applied to any one of the conductors AO, BO, CO and DO depending upon whether no one of the trunks of group AT is idle or one trunk is idle, or that two trunks are idle, or three or more trunks are idle, respectively. The presence of ground on any one of these four conductors may be. employed in this invention to cause relay AR either to be operated or to be released, as desired, to provide either the alternate routes or the normal routes, as will be further explained.

The conductor AO is connected to the lower winding of the relay AR oyer a circuit which includes the feeder brush FB2 of the rotary selector, the main brush MB2 of the same selector, terminal 3 of the arc of the rotary selector, conductor 30 to the lower winding of relay AR. The application of ground to the conductor AO therefore will operate relay AR if it should be released, or hold it operated if it is already operated. Thus, when the common testing circuit applies ground to the conductor AO, the relay AR will be energized so as to connect the alternate route to the system. Should it be desired to employ the alter10 nate route when all of the trunks of group AT but one are busy, as well as when all are busy, then the conductor CO will be wired to the terminal 3 associated with brush MB3 of the rotary selector. In that case relay OT will be operated over a circuit which includes the feeder brush FBs and the main brush MB3 of the rotary selector and its terminal 3, conductor CC, the armature U2 of relay STA and its make contact, the upper winding of relay OT, battery and ground. When so wired, the relay AR will be energized upon the application of ground to the conductor BO whenever all of the trunks but one are busy. The circuit from grounded conductor BO¹ to the winding of relay AR will include in addition to grounded conductor BO, the upper armature of relay TB and its back contact, the upper armature of relay OT and its make contact, conductor 31, the brushes FB2 and MB2 and their associated terminal 3 of the rotary selector, conductor 30 to the lower winding of relay AR. Thus, the relay AR will be operated under these conditions, if it is not already operated. Similarly, if it is desired to provide the alternate route when all of the trunks but two are busy, the conductor EE will be wired between terminal 3 associated with brush MB3 of the rotary selector and the armature Ui of relay STA, thereby causing relay TB to become operated. The operation of relay TB will supply ground at conductor CO to the lower winding of relay AR over a circuit similar to that already described to operate that relay AR or hold it operated, whenever all but two of the trunks are busy. Relay TB also connects conductor BO to the lower winding of relay AR if only one trunk should be found idle under these conditions. This arrangement may be extended to provide the alternate route path when any desired proportion of the trunks of group AT are busy.

It is apparent from the foregoing that the operation of relay RLA in response to the operation of relay AR opens the locking path for relay AR at the back contact of the armature Li of relay RLA and at the same time closes a path at the make contact of armature Li of relay RLA to apply ground to the armature U2 of relay TT9 of the common test circuit so as to hold relay AR operated or to reoperate it if it has become released. This in turn will depend upon the number of trunks which have become idle, the idle condition being indicated by the application of ground to one of the various conductors AO, BO, CO or DO. The operation of relay RLA will also complete a path at the make contact of its armature Ti to operate relay RL, as already pointed out, but the latter relay is of the slow-operate type in order to allow sufficient time for the relay AR to become operated or released.

The operation of relay RL will apply ground at the make contact of its armature Ti to the lower winding of relay AR if relay AR is operated, over a path which includes conductor 32, the armature Ti of relay CIo and its make contact, and the armature Li of relay AR and its make contact. This ground will lock relay AR in its operated condition. The operation of relay RL also opens the circuit connected to the back contact of its armature T2 and thereby releases relays CIo, STA, PT and RLA. The opening of the circuit of the stepping magnet SM at the back contact of armature Li of relay RL will release the stepping magnet SM which then causes the main brushes ΜΒι, MB2 and MB3, which are mounted on a common shaft, to be moved to their

2,421,919 next terminal 4. The reason for operating the rotary selector will be explained hereinafter. The' release CIo also- closes the locking path for relay AR previously established, if relay AR is operated at this time, through the armature Li of relay AR and its make contact and the normal contacts associated with armature Ti of relay CIo. The release of relay CIo also disconnects the sleeve contacts So to So of the trunk group AT from the corresponding windings of relays Po to P9 and the release of the latter relays will in- turn release the corresponding relays TTo to ΤΤ». The release of relay RLA will remove the supplementary ground previously connected by its armature T2 to the start lead ST through the path of armature T2 of relay RLA, conductors 24 and 21 and key BC. The release of relay RLA also releases relay RL by opening the circuit to its- winding at the make contact of the armature Ti of relay RLA. Both relays RL and RLA are slow to release, however, so as to permit all elements of the common test circuit to be returned to normal before another test of the trunks of the group AT is initiated.

The arrangement of this invention may be employed for testing a group of trunks of any size. For example, 30 trunks (only some of which are shown) may be arranged in three groups, such as AT, BT and CT, and three relays, such as CIo, CIi and CI2, may be employed for separately connecting the sleeves of one of the three trunk groups AT, BT and CT respectively, to the windings of the relays Po to P9. Only one re-route relay such as AR-will be associated with the three cut-in relays CIo, CIi and CI2, and the lower armature Li of relay AR will be connected to normal contacts of the relay CIo in the manner already considered for a group of ten trunks. The terminals 1,2 and 3 associated with the main brush MBi may be wired through leads LD2, LDx and LDb to the windings of the relays CI2· CIi and CIo, respectively, as shown. Assuming also that the alternate route is to be made available when but two of the trunks of the three groups are idle, then conductors FF, AA and DD will be positioned on terminals 1,2 and 3 associated with the main brush MB3 of the-rotary selector. All of the main brushes MBt, MB2 and MB3 may be considered to be positioned on terminal 1 at the beginning of a test of such a series of three trunk groups. It is noted, however, that the main brush MB3 is of the bridging type, being adapted to close one of its terminal before it is completely disconnected from a pervious terminal. The other main brushes MBx and MB2 are of the non-bridgingtype.

When the selector switch SS of the office selector OS moves upward in hunting for an ungrounded sleeve terminal, it will cause the relay AR to become operated as soon as it reaches the predetermined terminal AA, as already described. Ground at the armature L2 of relay AR will be applied to the start lead ST and will complete a circuit to Operate relay CI2, this circuit including in addition to the start lead ST, key BC, conductor 21, the armature T2 and back contact of relay RL, the brushes FBx and MBi of the rotary selector and the associated terminal I, lead LD2, the winding of relay CI2, battery and ground. The relay CI2 will now connect the sleeves So to S9 of the trunk group CT to the windings of the relays Po to P9, respectively, over circuits similar to those generally designated 37 and the relays Po to P9 will then control the corresponding relays TTo to TT9 as already described. Relays STA and

PT will operate and cause the operation of relay RLA as before. Upon the operation of relay STA, relay AD will become operated over a circuit which includes battery, the winding of relay AD, conductor 36, the make contact and armature U3 of relay STA, conductor FF, terminal I and brushes MBs and FB3 of the rotary selector and ground. The relay AD will be employed to control the relays Vi, V2 and Vs and relays Qi, Qa and Q3 for counting the number of idle trunks in the trunk groups to be tested.

If one of the trunks of the group CT is found idle, the conductor BO will be grounded by the relays TTo to TT9 in the manner already described, and this grounded conductor will be connected through the contacts Of relay AD to the winding of relay Vi for operating the latter relay. The operating circuit for relay Vi will include the grounded conductor BO, the upper armature and back contact of relay TB, the upper armature and back contact of relay OT, th'e armature U2 and make contact of relay AD, the upper armature and back contact of relay Qi, the winding of relay Vi, battery and ground. With relay RL released, relay Qi will be short-circuited by the contacts of relay Vi. That is, ground will be connected to the lower terminal of relay Qi over a circuit which includes the make contact and armature of relay Vi, the back contact and armature Ux of relay Q2, the back contact and upper armature of relay Q3, the make contact and armature L2 of relay AD, and ground; and ground will likewise be connected to the upper terminal of the winding of relay Qx over a circuit which includes the upper armature and back contact of relay Qx, the make contact and armature U2 of relay AD, the back contact and upper armature Of relay OT, the back contact and upper armature of relay TB to the grounded conductor BO. However, when relay RL becomes operated in response to the operation of relay RLA, as already pointed out, the ground on conductor BO will be removed from the make-before-break contact of relay RL and hence relay Qi will be operated. The operating circuit for relay Qi may be considered to include battery, the windings of relays Vi and Qx, the make contact and armature of relay Vi, the back contact and armature Ui of relay Qa, the back contact and upper armature of relay Q3, the make contact and armature L2 of relay AD and ground. Thus, both of the counting relays Vi and Qi will be operated in response to ground applied to the conductor BO by the testing relays TTo and TTo.

Should the testing relays TTo to TTo apply ground to the conductor CO· instead of conductor BO, as would be the case, for example, if two of the trunks of the group CT are found idle, the relay Va will then be operated over a circuit which includes battery, the winding of relay V2, the armature U2 and back contact of relay Q2, the make contact and armature Ui of relay AD, the back contact and armature Li of relay OT, the back contact and armature Lx of relay TB to the grounded conductor CO. The winding of relay Qa will also be short-circuited by the contacts of relay V2, but this short circuit will be removed upon the operation of relay RL to cause the relay Qa to be operated. Thus, the relays V2 and Qa of the counting circuit will be operated in response to the application of ground to the conductor CO.

Should ground be applied to the conductor DO by the testing relays TTo to TT9 by virtue of the idleness of three or more of the trunks of

3,421,919 '/the group CT, relay. V3 will, become operated and /thereby short-circuit the winding of relay Q3. Relay Q3 will also become operated upon the operation of relay RL.

.While the main brushes ΜΒι, MB2 and MB3 are positioned on their respective first terminals /designated I, the relay AR cannot be operated if it· is released because lead 30—which extends to 'the lower winding of relay AR—is on terminal· 3 of the rotary selector, and terminal I is open. For: this reason, if ground should be applied to conductor: AO at this time due to all trunks of. group CT being found busy, this ground has no. effect. Similarly, relay AR cannot be released if‘it us-operated at this time because its locking path is controlled by the make-beforebreak contacts of relay CIo and the latter relay has not yet been operated. The relay AR can be controlled only when the rotary selector

- reaches terminal 3, as will be explained herein-,

- after.

The counting relays Vi, Vz and V3 and Qi, Qa : and Q3 are employed to store the results of the tests made on the 10 trunks of the group CT so that these results may be added to the results subsequently obtained by tests on the other trunk

- groups BT-and AT for determining whether or not the re-route relay⁷ AR is to be operated or -released after- the testing cycle has been completed.

⁷ Let it be assumed that in testing the trunks of the group CT only one trunk is found idle, there^: by causing- the operation of relays Vi and Qi. 'The operation of relay RL⁷ will break the circuit of the stepping magnet SM, thereby advancing the- main brushes⁷ MB:, MBz and MB3 of the rotary selector to their next terminal designated 2. Moreover, relays RLA, STA, PT, CI2 and RL

- will be released in the⁷ manner already described. -As the main- brush MB3 reaches its terminal 2,_;it will hold relay AD operated over a circuit which includes battery, the winding of relay AD, the • conductor AA, terminal 2 and the brushes MB3 and FB3 of -the rotary selector and ground. By holding- relay AD operated the counting relays Vi and Qr will be held operated while the next group of trunk terminals BT are tested. The relay Qi will-transfer the ground at the makebefore-break contacts of relay RL to the armature Ui of- relay TT9 over a circuit which includes the armature Li of^h relay RLA and its

- make contact; and the lower armature and make contact of relay Qi. This has the effect of increasing by one the number of trunks to be

- found idle in group BT.

With the main brushes of the rotary selector

- on-their terminals designated 2, the relay CIi will: become operated over a circuit which includes ground at the armature L2 of relay AR, the start lead ST, the key BC, conductor 2 i, the armature T2: and back contact of relay RL, brushes FBi and MBi and terminal 2 of the rotary selector, conductor LDi, the winding of relay CIi,; battery and ground. Relay CIrwill connect -the- sleeve terminals of the trunks of the group BT to the Windings of relay Po to Ps, respectively, which in turn will control the relays TTo to TT9 for testing these various sleeve ter- • minals in the manner already described. Should one of the trunks now be found idle, after let us say only-one trunk was found idle in the previous trunk group CT, the ground applied to the

- lower armature of relay: Qi by the operation of relay RLA, will be closed through make contacts of relay Qi to armature Ui Of relay TTsand then to conductor/CO. The application of ground to conductor CO will cause relay V2 to operate over - a circuit similar to that .previously traced. Relay Q2 will likewise become operated after relay 5 / RL releases. It seems hardly necessary to state that if a second sleeve.terminal-were also found grounded in the trunk group BT, the relays V3 and Q3 would become: operated due to ground being applied to the-conductor DO, but this situa10- tion will-be passed at this time. The operation of relay Q2 Will open the circuit to the windings of relays Vi and Qi, releasing them, and in a similar manner if relay Qs should be operated instead of Qs, it would open the circuit either, to relays Vi 15 - and Qt ox· V2 and Q2,-releasing either pair of these

-relays that may have been operated depending upon the number of trunks-previously found idle. Upon the operation of relay RL at the end of the test, the stepping magnet SM will-become 20 deenergized/ thereby advancing the main brushes of-the-rotary selector to their next terminal designated- 3. The ground from lead ST closed to the feeder brush FBi will then be applied through lead LDo to-the winding of relay CIo, thereby op25 erating this-relay. Accordingly, the sleeve terminals of the trunk group AT will now be connected to the windings of relays Po to Po in the manner already described for testing this group of trunks. The sequence of events Occurring 30 upon the operation of relay CIo have already been outlined and need not be repeated. If relay Q2 is operated, however, the-ground from the back contact associated with armature Ti of relay RL, through operated contacts Li of relay RLA, is 35 closed through the-lower armature and back contact of relay Qi, lower armature and make contact of relay Q2, to the armature Li. of relay TT9. This has the effect of increasing by two the number of trunks to be found idle in group AT. If 40 relay Q3 is operated,· due to three or more trunks having previously been: found idle, the . circuit described above is disconnected from relay TT9, so that relay'AR cannot be. operated, regardless of the- number of trunks found idle in group AT. 45 Upon - reaching, terminal 3, the relay TB will become operated over a circuit which includes battery, the winding of relay AD, the lower winding of relay TB, conductor DD, terminal 3, : and the' brushes MB3 and FB3 of the rotary selector 50 and ground. This circuit includes the winding of relay AD and, therefore, relay AD is held operated while the-main brushes are on their terminal 3. Consequently, the previously operated . counting relays will be held operated.

With relay TB operated the re-route relay AR will be energized if it has become deenergized, or will be held operated if it is already operated and if the alternate route is to be cut in when -.not more .than two trunks of the three groups go AT, BT and CT have been found idle. In this - connection it. is observed that the make contact of the armature Li of the relay TB is wired to the feeder brush FB2 and thence through lead 30 to the lower winding of relay AR. In a similar G5 manner, relay AR Will be operated or held if only one trunk in the three groups should be found idle, by closure from conductor BO through the upper armature and make contact at relay TB to the feeder brush FB2.

hq Were, it desired to cut the re-route path into the system upon the location of but one idle trunk, the conductor BB would replace the conductor DD at terminal 3 associated with the main brush MB3. - With conductor BB on. terminal 3, the relay OT will be operated instead of the re2,421,919 lay TB, the operating circuit for relay OT including battery, the winding of relay AD, the lower winding of relay OT, conductor BB, terminal 3 and the associated brushes MB3 and FB3 of the rotary selector and ground. Under these conditions the grounding of conductor BO, in response to the location of a single idle trunk in any of the various trunk groups AT, BT or CT, will be transferred through the upper armature and make contact of relay OT, over conductor 31 and through the brushes FB2 and MB2 to lead 30 and to the lower winding of relay AR. In either of the above cases, if all of the trunks in groups CT, BT and AT are found busy, ground will be connected to conductor AO which will cause the relay AR to be operated or held operated as hereinbefore described, without regard to relays TB or OT.

On the other hand,, if the alternate route path is to be cut into the system only when all trunks are found busy, conductor GG will be positioned on the terminal 3 associated with the main brush MB3 of the rotary selector. Ground applied through brushes FB3 and MB3 to conductor GG will hold any of the counting relays operated, but relay AD will be released. The system is, therefore, flexible and may be made to respond to any desired or predetermined condition in the trunks of a large group.

Upon the operation of relay AR or its release at the end of the test of the three groups of trunks CT, BT and AT, the re-routing path may be cut in or omitted as determined by the testing apparatus. However, when relay RL operates at the end of the test, the stepping magnet SM will again be released to advance the main brushes ΜΒι, MB2 and MB3 .to their next terminal designated 4. When this happens the relays OT or TB will be released if either of these relays has been operated under the separate conditions already referred to, and relay AD will also be released if it is operated. Likewise, all of the counting relays will be released upon the release of relay AD, or upon the removal of ground from conductor GG. If three or more trunks are found idle during the test of any group of trunks, such as CT, or on a cumulative basis during successive tests over all of the three groups CT, BT and AT, in consequence of which counting relays V3 and Q3 have become operated, the relay AR will become released and the regular route will therefore be employed for subsequent calls through the system. Should it be desired to use the alternate route for these trunk groups when three or more trunks are found idle, it will be understood that additional counting relays and appropriate wiring may be added to the system for this purpose.

The other terminals 4, 5, 6, etc., of the rotary selector switch may be wired to additional cut-in relays such as Clio, CI20, etc., and corresponding re-route relays such as AR10, AR20, etc., in accordance with the principles already outlined with respect to a group of trunks such as CT. One route relay and one cut-in relay may be associated with each trunk group. As the main brushes of the rotary switch are moved from terminal to terminal, the trunks of a trunk group such as DT associated with another of the cut-in relays, such as Clio, will be tested and the reroute path controlled by the re-route relay, such as AR10, may be added or omitted as determined by the testing apparatus. Further description along these lines would be merely repetitious and has, therefore, been omitted.

The rotary selector is arranged to pass by spare terminals which are not required for actuating alternate route control circuits. When such a terminal is reached, relays STA and PT operate as before, thereby causing relay RLA to become operated and in turn cause the relay RL to become operated. The operation of the relay RL will, of course, release the stepping magnet and advance the main bushes of the rotary selector beyond any such spare terminal.

To allow the common test circuit to make continuous tests regardless of whether or not any associated trunk group is busy, the keys BC and IC will be left unoperated and key KST will be operated. In that case the operation of relay AR upon contact with terminal AA of Fig. 1 is not required and the wiring for such operation may be omitted.

If it is desired to make tests at periodic intervals, the interrupter control key IC will be operated. An interrupter INT is shown connected through contacts 50 of the key IC and through the upper winding of relay I to battery and ground. Hence relay I will be operated at the intervals determined by the interrupter INT. Upon the operation of relay I this relay will be locked over a locking circuit provided by its lower winding, contacts 51 of the key IC and the make contact and upper armature of relay I and ground. Ground will also be applied to the contacts associated with armatures Li and T2 of relay RL over a circuit which includes the upper armature and make contact of relay I, contacts 52 of key IC, the normal contacts of key BC and conductor 21. The conductor II will be wired to any particular terminal associated with the brush MB3 of the rotary selector. With relay I operated, the tests will be made and repeated at the intervals determined by the interrupter INT for all selector terminals prior to the one to which conductor H is connected. When the terminal to which conductor H is wired is reached, the relay I will be released. This is because ground is applied to the lower winding of relay I over a circuit including the brushes FB3 and MB3, conductor Π, contacts 53 of key IC and to the armature and lower winding of relay I, thereby short-circuiting the lower winding of relay I. The release of relay I will disconnect ground from the contacts associated with armatures Li and T2 of relay RL and replace this ground with the ground connected to brush FB3. The new ground is applied over a circuit including the brushes FB3 and MB3, conductor II, contacts 53 of key IC, lower armature and back contact of relay I, contacts 52 of key IC, the normal contacts of key BC and conductor 21 to the armatures Li and T2 of relay RL. However, when the selector passes the terminals to which conductor Π is connected, this ground is disconnected and therefore no further tests will be made until the interrupter again causes the relay I to be reoperated.

Fig. 3 illustrates a modification of certain of the apparatus of each decoder circuit of the telephone system to permit the setting and restoring of the normal and alternate routes at any time without causing interference with calls already in progress. Here the two route relays designated RRi and RR2 are shown which, when operated, establish the normal routes for calls. One of these relays, such as RRi, would be associated with the re-route relay AR of Fig. 1, and the other would be associated with a similar re-route relay, such as AR10, for example. The

2,421,919 termined number of said testing relays are simultaneously operated.

3. In a telephone system, the combination of a plurality of trunks each having a sleeve terminal, said trunks being divided into separate groups, a plurality of testing relays each of which corresponds to one of the trunks of a group, an intermediate relay having a plurality of contacts each of which connects the sleeve terminal of one of said trunks to the winding of the corresponding testing relay, a re-route relay, means controlled by said testing relays for registering the number of trunks that are idle in all of said groups, and means controlled by said registering 15 means for operating said re-route relay when the number of idle trunks is below a predetermined number.

4. In a telephone system, the combination of a plurality of trunk sleeve terminals corresponding to different telephone trunks, a selector adapted to hunt successively over said sleeve terminals to locate an .ungrounded terminal, a re-route relay connected to a predetermined one of said sleeve terininals, said re-route relay being operated when said predetermined sleeve terminal is reached by said selector, means responsive to the operation of said re-roUte relay to simultaneously test all of said sleeve terminals to deterriiine whether said sleeve terminals are grounded or ungrounded, and means for operating said re-route relay when a predetermined number of said sleeve terminals are grounded and for releasing said re-route relay when less than said predetermined number of said sleeve terminals are grounded.

5. In a telephone system, the combination of a plurality of trunk sleeve terminals corresponding to different trunks, said sleeve terminals being arranged in separate groups, a selector adapted to hunt successively over said sleeve terminals, a re-route relay connected to a predetermined one of said sleeve terminals and being operated when said predetermined sleeve terminal is reached by said selector, means controlled by said reroute relay to separately test all of the sleeve terminals in the various groups in succession and to register the number of ungrounded sleeve terminals detected, and means for operating said re-route relay when the number of sleeve termi- nals found ungrounded is less than a predetermined number and for releasing said re-route relay when the number of ungrounded sleeve terminals equals or exceeds said predetermined number.

6. In a telephone system, the combination of a plurality of trunks arranged in groups, a testing circuit which may be connected to all of the trunks in any one group at one time, said testing circuit being capable of simultaneously testing all of the trunks in each group to determine the number of idle trunks in the group, means for successively connecting said testing circuit to said groups of trunks, and means for additively indicating the number of idle trunks in all of said groups of trunks.

7. In a telephone system, the combination of a plurality of trunks arranged in groups, testing apparatus which may be connected to all of the trunks in any one group at one time, said testing apparatus serving for simultaneously .

testing all of the trunks of any one group to determine the number of idle trunks in the group, said testing apparatus including means for preventing interference with service over said trunks of the group while they are being tested, and conductors i 3 arid 16 of Fig. 1 are shown connected to the code point CPi and one terminal of the winding of the relay RRi, respectively. The other code point CPz and one terminal· of the winding of relay RR2 are likewise connected to contacts of their associated re-route relay. These relays RRi and RR2 are connected in parallel with respect to the winding of a relay GSi so that relay GSi will be operated if either of the relays RRi or RR2 becomes operated. In other words, if the relay AR of Fig. 1, for example, is released, the relay RRi will be operated to establish normal routing for the calls received by the trunk group associated with relay AR, and the relay GSi will also be operated. However, when the relay AR becomes operated, relays RRi and GSi will both be released.

Fig. 3 also shows the conductor 19 associated with relay AR of Fig. 1 connected in series with the winding of an alternate route relay RP and 20 another relay GS2 which is similar to relay GSi. Relays RP and GS2 will be operated only when the corresponding re-route relay AR has been operated. It is to be noted that both relays GSi and GSi are of the slow-release type. Consequently, upon the operation of relay AR, the relay GSi will remain operated for' a predetermined time interval so that both relays GSi and GS2 will simultaneously hold their back contacts open. Hence, the connection of ground at the armature of relay GS2 to the point RLX will be interrupted for the time during which it takes relay GSi to become fully released. The terminal RLX is connected in the ground supply circuit which is part of the apparatus for advancing the sender (not shown) . Thus the operation of the sender will be delayed and this will allow sufficient time for the route relay RR: to release, and in-turn to release any relays which it may have operated for routing the call to the normal trunk group. However, upon the release of the relay GSi calls will be routed under control of the re-route relay RP.

While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit , of the invention and the scope of the appended ' claims.