US2199543A - Telephone system - Google Patents

Description

May 7,-1940. c. E. LOMAx TELEPHONE 1SYSTEM Filed Oct. 13, 1958 43 Sheets-Sheet l INVENTOR. Elm-'anne E. Lnmax ATTORNEYS.

May 7, 1940- c. E. LoMAx TELEPHONE SYSTEM Filed Oct. 13, 1938 s Smets-sheet 2 IMI @Nb INVENTOR. Elarence E. Lomax ATTORNEYS.

May 7, 1940. c. E. LoMAx TELEPHONE SYSTEM Filed oct. 15, 195s 5 Smets-Sheet 3 Sul ' lNvENToR BY a Clarence E. Lomax ATTORNEYS.

u adapted for use in an automatic telephone systhe line is` found by the finder switch of an idle 50 menta May 7, 1940 l ,2,199,543

UNITED STATT-:s PATENT oFFlcE TELEPHONE SYSTEM jClarence. E. Lomax, Oak Park, IIL, assignor to Associated Electric Laboratories, Inc., Chicago, IIL, a corporation of Delaware Application october 13, 193s, serial No. 234,751

s1 claims. (ci. 11s-11) The present invention relates to automatic stations associated with the subscriber lines in telephone systems and more particularly to inr the system. proved line circuits associated with the lines Another object of the invention is to provide thereof and to improved combined line and cutin a telephone line circuit an improved combined 5 o relays adapted for use in the line circuits line and cut-olf relay which is of simple and 5 thereof. rugged construction and arrangement, and

In an automatic telephone system, usually a which is economical to manufacture and thorline circuit is individually associated with each oughly reliable in operation. line thereof, which line circuit conventionally It is a further object of the invention to procomprises separate and distinct line, cut-off and vide in a telephone line circuit a combined line 10 lockout relays-mounted upon a supporting panel. and cut-off relay including a support, line and These three relays are ordinarily so connected cut-oil magnets carried by the support, the line and arranged that the automatic switches in the magnet being of the two-step operating type, and systeml having access to a line are controlled in an improved mechanical arrangement for con- 16 accordance with the various operations thereof trolling the operation of the line magnet. 15 to set up, by way of the line, outgoing call con- A further object of the invention is to provide nections from and incoming call connections to a an improved automatic telephone system in subscriber substation associated with the line, which there are incorporated line circuits of the and that the line is marked as busy to the autotype described, each including a combined line go matic switches having access thereto in theevent and cut-oli relay of the construction noted. 20

a fault appears upon the line. Further these re- The features of the present invention are illuslays are so connected and arranged that the trated as being incorporated inl an automatic automatic switches in the system having access telephone system including a plurality of subto the line are controlled in accordance with other scriber lines, some of the lines being of the multig5 operations thereof to set up, by way of the line, party type, each line having a line circuit of the 25 reverting call connections between two of the type described incorporating acombined line and subscribersubstations associated with the line, cut-offrelay of the construction noted individuin the event the line is of the multiparty type. ally associated therewith, and a number of find- While line circuits of the type briefly described er-connector links for setting up connections beabove are entirely satisfactory in operation, they tween the various lines. A number of subscriber 30 are more expensive to manufacture and to mainsubstations are associated with each of the lines tain in service than is desirable, primarily due of the multiparty type; and a distributor of the to the fact that three separate and distinct represelective type is provided for the purpose of lays are required in each line circuit in order to assigning the links to the use of calling ones of render the previously-mentioned services by way the lines in a predetermined order. Two differ- 35 of the associated line. ent forms of the line circuit are illustrated which Accordingly it is an object of the present inmay be associated alternatively with each of the vention to provide an improved line circuit adaptlines in the system. lIn the first form of the ed for use in an automatic telephone system line circuit the line and cut-oit relays are so con- 40 which comprises line and cut-0E relays, which nected and arranged that a, calling line is marked 40 two relays are so connected and arranged that as busy to the connector switches of the links the automatic switches in the system are conhaving access thereto when the associated line. trolled thereby to render, by way of a subscriber is found by the nder switch of an idle one of line with which the line circuit is associated, the links having access thereto. In the second calling, called and reverting call services to the form of the line circuit the line and cut-oli relays 45 subscriber substations associated with the subare so connected and arranged that a calling line scriber line. is marked as busy to the connector switches of It is another object of the invention to provide the links having access thereto immediately the an improved line circuit of the type described call is initiated on the line and prior to the time tem which is economical to manufacture and one of the links having access thereto. 'I'he which is positive in operation in order to control combined line and cut-off relay incorpo-rated in the automatic switches in the system in a each form of the line circuit comprises a supthoroughly reliable manner, whereby the desired port, line and cut-off magnets carried by the u services may be rendered to the subscriber subsupport, a movable contact actuating member operatively associated with the line magnet, a movablecontzatcty actuating member operatively associated with the cut-ofi magnet, contacts respectively associated with the members, and latching means for controlling the operation of the first-mentioned member in two steps.

In accordance with one feature of the inventionrthe line circuit is adapted for use in an automatic telephone system including a line accessible to an automatic switch, and comprises, in combination, line and cut-oil relays, the line relay having rst and second operated positions, means responsive to the creation of a calling condition on the line for causing the line relay to be operated to the iirst position, means responsive to the seizure of the line by the automatic switch for causing' the cut-off relay to be operated, means controlled by the operation of the cut-off relay for causing the line relay to be operated to the second position, and automatic switch control circuits and line marking circuits governed by the line and cut-of! relays.

In accordance with another feature of the invention the line and cut-offrelays and the automatic switch control and line marking circuits in the line circuit are so connected and arranged that the automatic switches in the system are controlled thereby to set up, by way of the line, outgoing call connections from the substations associated with the line, incoming call connections to the subscriber substations associated with the line, and reverting call connections between two of the subscriber substations associated with the line, and that the line is marked as busy to the remainder of the automatic switches not em-`J ployed in a connection including the line while the connection including the line is set up, and that the line is marked as busy to the automatic switches in the event a fault appears thereon.

In accordance with another feature of the invention the line circuit also comprises means responsive to the creation of a calling condition on the line for causing theline relay to be operated to the rst position, means responsive to the seizure of the line by one of the automatic switches for causing the cut-oil' relay to be operated, means controlled by the operation of the cut-off relay for causing the line relay to be operated to the second position, means for releasing the one automatic switch, means responsive to the release of the one automatic switch for causing the cut-off relay to be restored, and means for causing the line relay to remain operated to the second position subsequent to the restoration of the cut-off relay in the event a calling condition remains on vthe line. Furthermore, means is provided which is controlled, when the line relay is operated to the second position and the cut-off relay is restored, for marking the line as busy to the automatic switches.

In accordance with a further feature of the invention a telephone system is provided which comprises a line, a plurality of l'subscriber substations associated with the line, a number of automatic switches having access to the line, and a. line circuit of the type described associated with the line. Further the telephone system comprises means responsive to the initiation of a call at a calling one of the substations for creating a calling condition on the line, means responsive to the creation of a calling condition on the line for causing the line relay to be operated to the rst position, means controlled by the operation of the line relay to the first position i'or causing an idle one of the automatic switches to seize the line, means responsive to the seizure of the line by the one automatic switch for causing the cut-oil. relay to be operated, and means controlled by the operation of the cut-oil' relay for causing the line relay to be operated to the second position. Furthermore, the telephone system comprises impulse responsive means operative to cause ringing current to be projected by way of the one automatic switch over the line subsequent to the termination of the calling condition thereon and to cause the cut-oit relay to remain operated, means responsive to the answering of the call at a called one of the substations for causing the one automatic switch to be released and for creating a new calling condition on the line, means responsive to the release of the one automatic switch for causing the cut-oil relay to be released, means responsive to the creation of the new calling condition on the line for causing the line relay to remain operated to the second position subsequent to the restoration of the cut-ofi' relay, and means controlled, when the line relay is operated to the second position and the cut-ot! relay Vis restored, for marking the line as busy to the i automatic switches.

In accordance with a further feature of the invention a telephone system is provided which comprises a line, a number of inder and connector switches having access to the line, and a line circuit of the type described associated with the line. Also, the telephone system comprises means controlled by the operation of the line relay to the irst position for marking the line as busy to the connector switches and for causing an idle one of the connector switches to seize the line, and additional nder and connector switch control circuits and additional line marking circuits governed by the line and cut-off relays.

In accordance with a further feature of the invention a combined line and'cut-oi relay is provided which is adapted for use in a telephone line circuit, and comprises, in combination, a support, line and cut-off magnets carried by the support and each provided with an energizing winding, a movable contact actuating member operatively associated with the line magnet and having a normal position, a movable contact actuating member operatively associated with the cut-o magnet and having a. normal position, contacts respectively associated with the members,

mechanical means for limiting the movement of the first-mentioned member away from its normal position, and means controlled by the energization of the cut-01T magnet winding for controlling the release of the mechanical means. The mechanical means is so constructed and arranged that the first-mentioned member is moved a limited distance away from its normal position in response to the energization of the line magnet winding prior to the energization of the cut-of! magnet winding, and that the first-mentioned member is moved a further distance away from its normal position in response to the energization of the line magnet winding subsequent to the energization of the cut-off magnet winding.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention,

both as to its organization and method of operation, together. with further objects. and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which Figs. 1 and 2 taken together illustrate diagrammatically a telephone. system including two improved forms of line circuitsl and embodying the present invention; Fig. 3 is a front elevational view of a combined line and cut-oi relay adapted to be incorporated into each of the line circuits shown in Fig. 1 and embodying the present invention; Fig. 4 is a side elevational view, partly broken away, oi the relay shown in Fig. 3; Fig. 5 illustrates diagrammatically the arrangement of the switch springs associated with the combined line and cut-off relay when it is incorporated in the line circuit shown on the left-hand side of Fig. 1; and Fig. 6 illustrates diagrammatically the arrangement of the switch springs associated with the combined line and cut-olf relay when it is incorporated in the line circuit shown on the right-hand side of Fig. 1.

Referring now more particularly to Figs. 1 and 2 of the drawings, the telephone system there illustrated comprises an exchange having a plu-` rality of subscriber lines including the subscriber lines |50 and |60 terminating thereat, and provided with a plurality of finder-connector links including the link for setting up connections between the various subscriber lines. Also a distributor |03 is provided for assigning idle ones of the links to the use of calling ones of the subscriber lines; and a number of reverting call switches, including the reverting call switch 200, are provided for the purpose of projecting code ringing current over a subscriber line when a reverting call is initiated thereon. More specifically, the exchange has an ultimate capacity of one hundred lines, and the number of links is determined by the amount of trailic which the exchange is required to handle, usually ten links being adequate to render satisfactory service.

Each of the links may be identical to the link |00 which comprises a finder portion or switch |0| and a connector portion or switch |02, each having access to each subscriber line in the system. The nder switchand the connector switch included in each link may be one of any of a number of Well-known types. However, it is preferable that each of these switches includes a. switching mechanism of the Strowger type and the usual control apparatus therefor, the wipers of the switching mechanism included in the iinder switch 0| being illustrated at |80, |8| and |82, and the wipers of the switching mechanism included in the connector switch |02 being illustrated at |83, |84, and |85. Also the connector switch |02 comprises impulse responsive apparatus of any desired type for projecting code ringing current over an idle called subscriber line after it has been seized by the switching mechanism included therein, which is so connected and arranged that a divided ringing circuit may be employed in the system. The distributor |03 may be one of any of a number of well-known types. However, it is preferable that the distributor |03 is of the preselective type, such that an idle link is selected to be assigned to the use of a calling line prior to the initiation of a call on the line.

At least a number of the subscriber lines terminating at the exchange are of the party type, the subscriber lines |50 and |80 being party lines, each serving a number of subscriber substations, respectively, including the subscriber substations A, B and C, D. Each of the subscriber substations is provided with a telephone instrument, a. dial mechanism, and a ringer. The/subscriber substatlons associated with each party line are arranged in two groups, the ringer at each substation in the first group being connected between one line conductor of the subscriber line and. ground, and the ringer at each substation in the second group being connected between the other line conductor of the subscriber line and ground, whereby a divided ringing circuit is employed in the system.

A line circuit is individually associated with each subscriber line in the system, the line circuit |04 being individually associated with the subscriber line |50, and the line circuit |05 being individually associated with the subscriber line |60. As previously noted, two different forms of line circuits may be alternatively employedV in the system, the line circuit |04 being a line circuit of the rst form, and the line circuit |05 being a line circuit of the second form. Each of the line circuits of the rst form may be identical to the line circuit |04 which comprises a combined line and cut-off relay of the construction shown in Figs. 3 and 4 including a line magnet or relay RI20, a cut-off magnet or relay RI l0, and al switch spring assembly of the Aconstruction and arrangement shown in Fig. 5. Each of the line circuits of the second form may be identical to the line circuit |05 which comprises a combined line and cut-off relay of the construction shown in Figs. 3 and 4 including a line magnet or relay R|30, a cut-oi magnet or relay Rl40, and a switch spring assemblyof the con' struction and arrangement shown in Fig. 6.

Each of the reverting call switches may be identical to the reverting call switch 200 which comprises two minor switches 280 and 290, a line relay R230, a hold relay R240, two transfer relays R260 and R210, a ring cut-off relay R255, a switching-through relay R220, two control relays R2| 0 and R250, the control and controlled circuits therefor, and a'transformer 20|. The minor switch 280 comprises two rotary switches 28| and 282 provided with contact banks 284 and 286, respectively, and associated wipers 283 and 285, respectively, a rotary magnet M236 for simultaneously rotating the wipers of the rotary switches 28| and 282, and a release magnet M231 for releasing the wipers of the rotary switches 28| and 282 and for causing these wipers to be returnedv to their normalpositions. Also two switch springs 234 are associated with the wipers of the rotary switches 28| and 282, which are actuated into engagement when these wipers are rotated by the rotary magnet; M236 away from their normal positions. The minor switch 290 comprises two rotary switches 29| and 292 provided with contact banks 294 and 290, respectively, and associated wipers 293 and 295, respectively, a rotary magnet M238 for simultaneously rotating the wipers of the rotary switches 29| and 292, and a release magnet M239 for releasing the wipers of the rotary switches 29| and 292 and for causing these wipers to be returned to their normal positions. Also two switch springs 235 are associated with the wipers of the rotary switches 29| and 292, which are actuated into engagement when these wipers are rotated by the rotary magnet M238 away from their normal positions. Also it is'noted that the reverting call switch 200 is connected and arranged to project code ringing current over a calling subscriber line by way of the trunk line when a connection is established therebetween by way of an operatedone of the links, in such a manner that a divided ringingv circuit may be employed in the system.

\ outwardly extending flange 30| to which a line magnet core 302 and a cut-od magnet core 303 are respectively secured by two screws 304 and 335, the cores 302 and 303 being arranged in spaced parallel relationship with respect to each other and to the body portion oi the plate 300.

The body portion of the supporting plate 300 is provided with two spaced apart tabs 306 and 301 arranged adjacent the pole faces of the cores 302 and 303, respectively. A supporting bracket 308 carrying a pivot pin 309 is suitably secured to the tab 306; and a supporting bracket 3|0 carrying a pivot pin 3| I is suitably secured to the tab 301. An armature 3I2 is pivotally supported on the pivot pin 309 adjacent the pole face of the core 302; and an armature 3|3 is pivotally supported on the pivot pin 3I| adjacent the pole face of the core 303. The armature 3I2 is provided with a downwardly extending arm 3 I4 having a rearwardly projecting finger 3I5 on the outer end dthereof extending through an aperture SIG formed in the supporting plate 300; and the armature 3I3 is provided with a downwardly extending arm 3I1 havingV a rearwardly projecting finger 3|8 extending through an aperture 3I9 formed in the supporting plate 300. A switch spring assembly 320 comprising a plurality of individual switch springs suitably insulated from each other and 'from the supporting plate 300 is secured to the rear side of the supporting plate, and cooperates with an insulating button 32| carried by the ringer 3|5 in such a manner that the individual switch springs in this switch spring assembly are actuated into engagement and disengagement with each other in a predetermined manner, when the armature 3I2 is rotated about the pivot pin 309. Also a switch spring assembly, not shown, comprising a plurality of individual switch springs suitably in'- sulated from each other and from the supporting plate 300 is secured to the rear side of the supporting plate, and cooperates with an insulating button carried by the ringer 3I8 in such a manner that the individual switch springs in this switch spring assembly are actuated into engagement and disengagement with each other in a predetermined manner, when the armature 3I3 is rotated about the pivot pin 3| I.

A blocking or latching spring 322 is secured, intermediate the ends thereof, to the front side of the supporting plate 300 in a position disposed between the cores 302 and 303 by an arrangement comprising an insulating bushing 323 and a screw 324. One end 325 of the latching spring 322 is positioned in a recess 326 formed in the edge of the ange 30| in order to retain the latching spring in place, and the other end 321 of the latching spring 322 entends to a position adjacent the armatures 3I2 and 3|3. The end 321 of the latching spring 322 is bifurcated; comprising two spaced apart fingers 328 and 329 cooperating with two projecting lugs 330 and 33|, respectively, carried by the armatures 3I2 and 3|3. The ringer 328 constitutes a latching nger and is so constructed and arranged that it normally projects into the path of movement of the lug 330 carried by the armature 3I2 when this armature is rotated in a clockwise direction, as viewed in Fig. 4, about the pivot pin 309, thereby to permit only a limited rotational movement o! the amature 3I2 about the pivot pin 309. 'nie ilnger 320 constitutes a tripping ringer and is so constructed and arranged that it normally projects into the path of movement of the lug 33| carried by the armature 3|3 when this armature A is rotated in a clockwise direction, as viewed in Fig. 4, about the pivot pin 3| I. When the armature 3I3 isrotated in a clockwise direction about the pivot pin 3I| the lug-33| carried thereby engages the tripping finger 329 and bends the end 321 of the latching spring 322 away from the supporting plate 300. thereby to move the latching iinger 328 out of the path of movement of the lug 330 carried by the armature 3I2 in order to allow further rotational movement of.I

the armature 3I2 in a clockwise direction about the pivot pin 309. From the foregoing description of the construction and arrangement of the latching spring 322 it will be understood that when the armature 3I2 is rotated in a clockwise direction about the pivot pin 309 it is initially rotated only a predetermined distance, at which time the latching nger 328 arrests further ro tation thereof. Subseguently, when the armature 3I3 is rotated in a clockwise direction about the pivot pin 3I| the tripping finger 329 releases the latching nger 328, thereby to permit further rotation of the armature 3I2 in a clockwise direction about the pivot pin 309.

The line magnet core 302 is provided with a winding arrangement which is effective, when energized, to attract the armature 3I2, thereby to rotate this armature in a clockwise direction about the pivot pin 309; and the cut-oli' magnet core 303 is provided with a winding.arrangement which is effective, when energized, to attract the armature 3|3, thereby to rotate this armature in a clockwise direction about the pivot pin 3H. Thus it will be understood that, when the winding arrangement of the line magnet is energized, the armature 3I2 is rotated in a clockwise direction about the pivot pin 309 a predetermined distance, and then subsequently, when the winding arrangement of the cut-off magnet is energized to rotate the armature 3|3 in a clockwise direction about the pivot pin 3| I, the armature 3I2 `is rotated an additional distance in the clockwise direction about the pivot pin 309. Also, it will be understood that the initial rotation of the armature 3I2 is effective to cause a predetermined actuation of the switch spring assembly 320 associated therewith, and the further rotation thereof is effective to cause a further predetermined actuation of the switch spring assembly .320; and the rotation of the armature 3I3 is effective to cause a predetermined actuation of the switch spring assembly associated therewith. Thus, the line magnet 302 is of the two-step type. A

Referring now more particularly to Fig. 5 of the drawings, it will be observed that the switch spring assembly associated with the line and cutoff magnets RI20 and RIIO, respectively, corresponding to the switch spring assembly incorporated in the line circuit |04, is so constructed and arranged that, when the line magnet RI20 is energized, the armature indicated at 3I2a is rotated in a clockwise direction about the pivot pin 309a a predetermined distance, thereby to move the switch spring RAI28 intoy engagement with the associated switch spring in order to close these X contacts, and to move the switch spring RAI2I into engagement with the switch spring RCI22 in order to close these X contacts, at which time the outer end of the armature 3| 2a engages the latching ringer 328a.

Subsequently, when the cut-oli magnet Rl I0 is energized the armature indicated at 3|3a is rotated in a counterclockwise direction about the pivot pin 3| la, thereby to move the switch springs RAI I2 and RCI I3 into disengagement. to move the switch springs RAI I2 and RCI I4 into engagement, to move the switch springs RAI I5 and RAIIG into engagement, and then to move the' switch springs RAI I6 and RCI I'I into disengagemove the switch springs RA|23 and RC|24 into disengagement, to move the switch springs RA|25 and RA|2B into engagement, and then to move the switch springs RAI26 and RCIZ'I into disengagement.

Referring now more particularly to Fig. 6 of the drawings, it will be observed that .the switch spring assembly associated with the line and cutoff magnets R|30 and R|40, respectively, corresponding to the switch spring assembly incorporated in the line circuit |05, is so constructed and arranged that, when the line magnet R|30 is energized, the armature indicated at 3|2b is rotated in a clockwise direction about the pivot pin 30912 a predetermined distance, thereby to move the switch springs RAI33 and RC|33 into disengagement in order to open these X contacts, to 'move the switch springs RAI33 and RCI34 into engagement in order to close these X contacts, to move the switch springs RA|3| and RCI 32 into engagement in order to close these X contacts, and to move the switch spring RAI3'I into engagement with the associated switch v,

spring in order to close these X contacts, at which time the outer end of the armature 3| 2b engages the latching iinger 32817. Subsequently, when the cut-oli magnet'RI40 is energized the armature indicated at 3|3b is rotated in a counterclockwise direction about the pivot pin 3| Ib, thereby to move the switch springs-RAIN and RCI43 into engagement, to move the switch springs RAIM and RC|45 into engagement, to move the switch springs RANG and RAIN into engagement, and then to move the switch springs RAIIIB and RCI48 into disengagement, to move the switch spring RAME and the associated switch spring into disengagement, to move the switch spring RA|40' and the associated switch spring into disengagement, and iinally to move the switch spring RA|4| and the associated switch spring into disengagement in order to open these Y contacts. Also when the armature 3I3b is rotated in a counterclockwise direction about the pivot pin 3||b, the tripping finger 3291) is engaged by the outer end of the armature 3|3b, thereby to release the latching finger 328D. The armature 3I2b is then rotated a further distance in the clockwise direction about the pivot pin 30911, thereby to move the switch spring RA|38 and the associated switch spring into disengagement, to move the switch spring RAI39 and the associated switch spring into engagement, to move the switch spring RAI30' and the associated switch spring into disengagement, and to move the switch springs RA|36 and RC|35 into disengagement.

The connection and arrangement of the system will best be understood from a consideration of the following description, with reference to Figs. 1 and 2 of the drawings, of the operation of the apparatus incorporated therein to set up the different connections between the various subscriber lines.

A call which is to be extended from the subscriber substation A to the subscriber substation C is rst initiated at the substation A by removing the receiver of the telephone instrument thereat from its hook, thereby to complete a bridge path at the telephone instrument at the substation -A between the line conductorsCIBI and C|52 of the subscriber line |50 extending to the substation A. When this bridge path is completed between the line conductors of the subscriber line |50 a bridge circuit is completed for energizing in series the upper and lower windings of the line magnet RI20 in the line circuit |04 individually associated with the subscriber line |50, which extends from battery at the upper winding of RI20 by way of the upper winding of RI20, RAIII, CI5I, the bridge path at the substation A between CI5| and CI52, CI52, RCI I1, RAI I6, and the lower winding of RI20 to ground. When energized over the above-traced circuit the line magnet RI20 partially operates, thereby to close the X contact associated with the switch springs RA|2| and RCI22 and to close the X contact associated with the spring RAIN and the associated switch spring, further actuation of the switch springs associated with the line magnet RI20 being positively prevented, at this time, by the mechanical locking arrangement under the control of the cut-0E magnet RIIO. More particularly, the line magnet RI20 completes, at RAI28, a path for applying ground potential to the start conductor C| extending into the distributor |03, this path extending from ground, at RAI26, by way of RCIZ'I, RAI28, and CISI to the start conductor C|90. This application of ground potential to the start conductor C|90 initiates the operationof the distributor |03, and causes the distributor to operate and assign the previously selected idle link to the use of the calling subscriber line |50. Assuming that theA illustrated link |00 is assigned by the distributor |03 to the use of the calling subscriber line |50, the distributoralso marks with ground potential by way of the conductor C|03 the level in the contact bank of the Strowger mechanism included in the finder switch |0I, wherein the calling subscriber line |50 terminates. Also the linemagnet RI20 completes, at RA|2I and RCI22, a path for applyingV battery potential to the control conductor CI53, this path extending from battery at the winding of the cut-off magnet RI I0 by way of the winding of RIIO, RAI23, RCI24, RCI22, and RAI2I to the control conductor CI53. This application of battery potential to the control conductor C|53 marks the radial position of the contact set in the level in the contact bank of the Strowger mechanism included in the finder switch |0I, wherein the calling subscriber line |50 terminates.

The Strowger mechanism included in the finder switch |0| then operates to move the wipers |00, |8I, and |82 thereof in the vertical direction to the level wherein the calling subscriber line |50 terminates. This Strowger mechanism then operates to move the wipers thereof in the radial direction to the radial position of the contact set wherein the calling subscriber line |50 terminates, at which time the Wipers |00 and |82 application of ground potential to the wiper |8| completes a circuit for energizing the cut-olf magnet RIIO, this circuit extending from the grounded wiper |8I by way of the contact terminating the control conductor C|5 3,l RAIZI, RCI22, RCIZA, `RA|23, and the winding of RI| to battery. Also this application of ground potential to the wiper I8I completes a path for applying ground potential to the control conductor C|54 of the subscriber line |50 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access thereto, thereby to mark the subscriber line |50 as busy to the connector switches of these links` This path extends from the grounded control conductor C|53 by way of.

RA|2I and RC|22 to the control conductor CI54.

Whenenergized over the above-traced circuit the cut-oi magnet RI I0 operates to complete, at RAI I5 and RAI I6, an obvious holding circuit for energizing in series the upper and lower windings of the line magnet R|20, and interrupts, at'

RAIIB and RCIII, and at RAIII, points in the original bridge circuit for energizing the windings of the line magnet RI20, thereby to free the line conductors CI5| and CI52 of the subscriber line releases the locking arrangement associated with the armature of the line magnet RI 20, thereby to alllow the line magnet RI20 to operate fully. Upon fully" operating, the line magnet R|20 interrupts, at RA|23 and RCI24, a point in the original circuit for energizing the winding of the cut-off magnet RI I0, and interrupts, at RAI26 and RCI2'I, a point in the path for applying ground potential to the start conductor C|90 extending to the distributor |03. When ground potential is removed from the start conductor CIBO the distributor |03 operates to select an idle link in the group of links to be assigned to the use of the next calling subscriber line. When the nder switch |0| seizes the calling subscriber line I 50, the connector switch |02 operates to condition the Strowger mechanism therein to be responsive to dialed digits.

The subscriber at the substation A then dials the first digit of the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a rst series of impulses over the loop circuit extending by way of the subscriber line |50 between the substation A and the connector switch |02. Impulse responsive apparatus in the connector switch |02 operates in response to this rst series of impulses in order to cause the wipers |83, |84, and |85 of the Strowger mechanism included therein to be moved in the vertical direction to the level in the contact bank therein, wherein the called subin a characteristic manner.

scriber line |60 is terminated. The subscriber at the substation A then dials the second digit of the directory number of the called subscriber line at thel dial mechanism thereat, thereby to transmit a second series of impulses by way of the previously mentioned loop circuit to the connector switch |02 in order to cause the wipers noted of the Strowger mechanism included therein to be moved in the radial direction to the position of the contact set in the contact bank therein, wherein the called subscriber line |60 is terminated. The subscriber at the substation A then dials the third digit of the directory number of the called substation C at the dial mechanism thereat, thereby to transmit a third series of impulses by way of the previously mentioned loop circuit to the connector switch |02 in order to cause the connector switch to select a corresponding code ringing current to be projected a over the called subscriber line |60 in the event this: subscriber line is idle. ,4

At this time the wipers |83 and |85 engage the contacts in the contact bank terminating the line conductors CI6I and CI62, respectively, and the wiper |84 engages the contact in the contact bank terminating the control conductor CIGS of the called.' subscriber line I 60.. At this time `ground potential appears upon the control conductor C|63 in the event the called subscriber line |60 is busy. On the other hand, battery potential appears upon the control conductor CI63 in the "event the called subscriber line |60 is idle.

Assuming that the called subscriber line |60 is busy, ground potential derived in the line circuit |05 appears upon the control conductor C|63 thereof, thereby to complete a path for energizing a busy relay included in the connector switch |02, which busy relay operates to cause busy tone current to be returned over the loop circuit extending to the calling subscriber substation A, in the usual manner. The production of busy tone in the receiver of the telephone instrument, at the calling substation A indicates to the subscriber thereat that the desired connection cannot immediately be had due to the busy condition of the called subscriber line |60. The subscriber at the calling substation A then releases the operated link |00 and the line circuit |04 by replacing the receiver of the telephone instrument at the substation A upon its hook. 'I'he exact manner in which these operated pieces of apparatus are released is described in detail hereinafter. a

Assuming that the called subscriber line |60 is idle, battery potential appears upon the control conductor CI63 thereof, this battery potential being derived at the winding of the cut-oil' magnet RI and extending therefrom by way of the Winding of RMU, RA|30,RC|33,and RARI tothe control conductor CI63. This application of battery potential to the control conductor CI63 completes a path for short-circuiting the busy relay included in the connector switch |02, thereby to cause theconnector switch |02 to operate and project ringing current of the previously selected code over the called subscriber line in order to cause the ringer at the substation C to operate This characteristic operation of the ringer at the substation C indicates to the subscriber thereat that the substation C is the called substation. Also, a switch-through relay in the connector switch |02 operates to apply direct ground potential to the Wiper I 8l.

This application of direct ground potential to the u wiper |84 completes a circuit for energizing the cut-oi magnet R|40, this circuit extending from the grounded wiper |84 by way of C|63, RAISS, RC|33, RAI30', and the winding of R140 to battery. When energized over the above-traced circuit the cut-ofi magnet R|40 operates to complete, at RA|44 and RC|45, a holding circuit for energizing the winding thereof, this circuit extending from the grounded control conductor CI63 by way of RAI, RC|45, and the winding of R|40 to battery. Also, upon operating, the cut-oil' magnet R|40 completes, at RA|45 and RAI41, a holding circuit for energizing the line magnet R|30, this circuit extending from ground, at the lower winding of R|30, by way of the lower winding of R|30, RA|46, RAI41, and the upper winding of R|30 to battery. Also, upon operating, the cut-01T magnet R|40 releases the locking arrangement associated with the armature of the line magnet R|30, thereby to allow the line magnet R|30 to operate fully. When energized over the above-traced circuit the line magnet R|30 fully operates to complete, at RAI 3| and RC|32. a path for applying ground potential to the control conductor C|64 of the subscriber line |60 extending to the contact banks of the Strowger mechanisms included in the finderl switches of the links having access thereto, thereby to mark the subscriber line |60 as busy, this path extending from the grounded control conductor C|63 by way of RC|43, RA|42, RC|32, and RA|3| to the control conductor C|64. The subscriber at the substation C then answers the call by removing the receiver of the telephone instrument thereat from its hook, thereby to cause the connector switch |02 to operate in order to interrupt the projection of ringing current over the called subscriber line and to complete an established communication connection between the calling subscriber line |50 and the called subscriber line |60 by way of the operated link |00.

Assuming that the release of this established connection is under the control of the last subscriber to replace the receiver of the telephone instrument at his substation upon itsA hook, when the last subscriber at one of the substations replaces the receiver of the telephone instrument thereat upon its hook the operated link is released in the usual manner. thereby to interrupt the established connection extending between the subscriber lines |50 and |60. When the link |00 is released ground potential therein is removed from the wiper 8|, thereby to interrupt the previously traced holding circuit for energizing the winding of the cut-ofi magnet R||0. The cut-oi magnet R||0 then restores, thereby to interrupt, at RAI I2 and RCI I4, a further point in the holding circuit for energizing the winding thereof, and to interrupt, at RAI I5 and RAI I5. the previously traced circuit for energizing in series the upper and lower windings of the line magnet R|20. Also, upon restoring, the cut-off magnet R| In prepares, at RA|||, and at RA||6 and RC| I1, the previously traced bridge circuit for energizing the windings of the line magnet R|20. The line magnet R| then restores to complete, at RA|23 and RC|24. the previously traced path for applying battery potential, at the winding of the cut-off magnet Ri I0, to the control conductor C|54 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access thereto, thereby to mark the subscriber line |50 as idle. Also the line magnet R|20 prepares, at RA|26 and RCIZ'I, a point in the previously traced path for applying ground potential to the start conductor C |90, and interrupts, at RAI-28, a point in this path. Finally, the line magnet R|20 interrupts, at RA|2| and RC|22, the connection between the control! conductor C|53 and C|54, thereby to .interrupt the paths for applying ground or battery potential to the control conductor C|53 extending to the contact banks of the Strowger mechanisms included in the finder switches of the links having access thereto, in order to mark the subscriber line |50 as idle. At this time the subscriber line |50 is marked as idle to the iinder and connector switches of the links having access thereto, and the line circuit |04 is completely released.

Also, when the link |00 is released ground potential therein is removed from the wiper |84, thereby to` interrupt the previously traced holding circuit for energizing the winding of the cut-oil' magnet R|40. The cut-oil" magnet R|40 then restores, thereby to interrupt at RA|44 and RC| 45, a further point in the holding circuit for energizing the winding thereof, to interrupt, at

the line-magnet R|30, and prepares, at RAMI,

and at RA|46 and RC|48, pointsin a bridge circuit for energizing the windings of the line magnet R|30. The line magnet R| then restores to complete, at RA|30', and at RA|33 and RC|33, the previously traced path for applying battery potential. at the winding of the cut-ofi magnet R|40, to the control conductor C|63 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access thereto, thereby to mark the subscriber line as idle. Also the line magnet R|30 interrupts, at RA|3| and RC|32, the connection between the control conductors C|63 and C|64, thereby to interrupt the path for applying ground or battery potential to the control conductor C|64 extending to the contact banks of the Strowger mechanisms included in the finder switches of the links having access thereto, therebyv to mark the subscriber line |60 as idle. At this time the subscriber line |60 is marked as idle to the finder and connector switches of the links having access thereto, and the line circuit |05 is completely released.

A call which is to be extended from the subscriber substation C to the subscriber substation A is rst initiated at the substation C by removing the receiver of the telephone instrument thereat from its hook, thereby to complete a bridge path at the telephone instrument at the substation C between the line conductors C|6| and C|62 of the subscriber line |60 extending to the substation C. When this bridge path is completed between the line conductors of the subscriber line |60 a bridge circuit is completed for energizing in series the upper and lower windings of the line magnet R|30 in the line circuit |05 individually associated with the subscriber` line |60, which extends from battery at the upper winding of R|30 by way of the upper winding of R|30, RAMI, C|6 l, the bridge path at the substation C' between CIBI and C|62, Cl62, RC'I48, RAME, and the lower winding of R|30 to ground. When energized over the above-traced circuit the line magnet R|30 partially operates, thereby to close the X contact associated with the switch springs RAI3|l and RC|32, to close the X contact associated with the switch springs RA|33 and RC| 34 to close the X contact associated with the switch spring RA|3`I and the associated switch spring, and to open the X contact associated with the switch springs RA|33 and RC|33. Fur-l ther actuation` of the switch springs associated with the line magnet RI30 is positively prevented, at this time, by the mechanical locking arrangement under the control of the cut-oil' magnet RMU. More particularly, the line magnet R|30 completes, at RAI31, a path for applying ground potential to the start conductor C|90 extending into the distributor, |03, this path extending from ground, at RA|31, by way of RA|38, and C|92 to the start conductor C|90. This application of ground potential to the start conductor C|90 initiates the operation of the distributor |03, and causes the distributor to operate and assign the previously selected idle link to the use of the i calling subscriber line |60. Assuming that the illustrated link |00 is assigned by the distributor .|03 to the use of the calling subscriber line |60,

. path for applying battery potential to the control conductor C|64, this path extending from battery, at the Winding of the cut-01T magnet RMO, by way of the Winding of RMO, RAl30', RC|32, and RAISI, to the control conductor CIM. This application of battery 'potential to the control conductor CIM marks the radial position of the contact set in the level in the contact bank of the Strowger mechanism included in the finder switch |0|, wherein the calling subscriber line |60 terminates. Further the line magnet R|30 completes, at RAI33 and RCI, a path for applying ground potential to the control conductor C|63 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access thereto, there- 'by to mark the subscriber line |60 as busy immediately, and prior to the time the iinder switch |0| of the link |00 operates to seize this subscriber line, this path extending from ground, at RAI36, by way of RCI35, RCI34, and RAI33,`to the control conductor C|63. Finally, the line magnet R|30 interrupts, at RA|33 and RC |33, a point in the previously traced connection between the control conductor CI63 and the winding of the cut-off magnet RMO, thereby to prevent the application of ground potential to the control conductor C|63 from causing premature energization of the cut-oir magnet RMO prior to the time the iinder switch |0| operates to seize the calling subscriber line |60.

The Strowger mechanism included in the iinder switch IOI then operates to move the wipers |80, IBI, and I82'thereof in the vertical direction to the'level wherein the calling subscriber line |60 terminates. 'I'his Strowger mechanism then operates to move the wipers thereof in the radial direction to the radial position of the contact set wherein the calling subscriber line |60 terminates, at which time the Wipers and |82 thereof engage the contacts terminating the line conductors C|6| and Cl62, respectively, and the wiper |8| engages the contact terminating the control conductor CIBG of the calling subscriber line |60. The presence of battery potential upon the control conductor C|64 completes a circuit' for energizing a relay in the iinder switch 0| operative to arrest further operation of the Strowger mechanism included therein, which relay also operates to complete a path for applying ground potential to the wiper IBI. I'I'his application of ground potential to the wiper |8| completes a circuit for energizing the cut-off magnet RMD, this circuit extending from the grounded wiper |8| by way of the contact terminating the control conductor C|64, RAIBI, RCI32, RAI30', and-the winding of RMD to battery. g

When energized over the above-traced circuit the cut-off magnet RMU operates to complete, at RAM2 and RCM3, and at RAM4 and RCMS, a holding circuit for venergizing the winding thereof, this circuit extending from the grounded control conductor C|64 by way of RAI3I, RCI, RAM2, RCM3, RAI, RCMS, and the winding of R|40 to battery. Also the cut-ofi' magnet RMO completes, at RAMZ and RCM3, a connection between the control conductors CI|i3` and CI64, thereby to complete a path for applying ground potential appearing upon the control conductor C|64 to the control conductor C|63 extending to the contact banks of the Strowger mechanisms included in the 'connector switches ofthe links having access thereto, this path extending from the control conductor C|64 by way of RAIII, RC|32, RAM2, and RCIII3, to the control conductor C|63. This path for applying ground po-J tential tothe control conductor C|63 causes the subscriber line |60 to be marked. as busy to the connector switches of the links having access thereto after the line magnet R|30 operates completely to interrupt, at RAI36 and RC|35, the previously traced path for applying ground potential to the control conductor Cl63. Also the cut-oil. magnet R|40 completes, at RAME and RAM1, the holding circuit for energizing in series y the upper and lower windings of the line magnet R|30, this circuit'extendingfrom ground, at the lower winding of R|30, by way of the lower winding of R|30, RAMS, RAM1, and the upper winding of RI30 to battery. Finally, the cut-oil' magnet RMO interrupts, at RAM6 and ROMS, and

at RAMI, points in the original bridge circuit for energizing the windings of the line magnet R|30, thereby to free the calling subscriber line |60 of impedance elements. Also, upon operating, the cut-ofi' magnet RI40 releases the locking arrangement associated with the armature of the line magnet R|30, thereby to allow the line magnet RI30 to operate fully. Upon fully operating, the line magnet RI30 interrupts, at RAI30, a point in the original circuit for energizing the winding of the cut-oil magnet RMU, and interrupts, at RA|38, a point in the path for applying ground potential to the start conductor CI extending to the distributor |03. When ground potential is removed from the start conductor CI90 the distributor |03 operates to select an idle link in the group of links to be assigned tothe use of the next calling subscriber line. Also, upon operating, the line magnet R|30 interrupts, at RA|36 and RCI35, a point in the original path for applying ground potential, at RAISS, to the control conductor C|63 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access thereto, ground potential being applied to the control conductor C |63 at this time by way of the previously traced path from the control conductor CIM. When the iinder switch IOI seizes ,the calling subscriber line |60, the connector switch |02 operates to condition the Strowger mechanism therein to be responsive to dialed digits. f

'Ihe subscriber at the substation C then dials the rst digit of the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a ilrst series of lmpulses over the loop circuit extending by way of the subscriber line |60 between the substation C and the connector switch |02. Impulse responsive apparatus in the connector switch |02 operates in response to this iirst 'series of impulses in order to cause the wipers |83, |84, and |85 of the Strowger mechanism included therein to be moved in the vertical direction to the level in the contact bank therein, wherein the called subscriber line |50 is terminated. The subscriber at the substation C then dials the second digit o1' the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a second series of impulses by way of the previously mentioned loop circuit to the connector switch |02 in order to cause the wipers noted of the Strowger mechanism included therein to be moved in the radial direction to the position of the contact set in the contact bank therein, wherein the called subscriber line I 50 is terminated. The subscriber at the substation C then dials the third digit of the directory number of the called substation A at the dial mechanism thereat, thereby to transmit a third series of impulses by way of the previously mentioned loop circuit to the connector switch |02 in order to cause the 'connector switch to select a corre-- sponding code ringing current to be projected over the called subscriber line |50 in the event this subscriber line is idle.

At this time the wipers |83 and |85 engage the contacts in the contact bank terminating the line conductors C|5I and CI52, respectively, and the wiper |84 engages the contact in the contact bank terminating the control conductor CI54 of the called subscriber line 50. At this time ground potential appears upon the control conductor C |54 in the event the called subscriber line |50 is busy. On the other hand, battery potential appears upon the control conductor C|54 in the event the called subscriber line I 50 is idle.

Assuming that the called subscriber line |50 is busy, ground potential derived in the line circuit |04 appears upon the. control conductor CI54 thereof, thereby to complete a path for energizing the busy relay included in the connector switch |02, which busy relay operates to cause busy tone current to he returned over the loop circuit extending to the calling subscriber substation C, in the usual manner. The production of busy tone in the receiver of the telephone instrument at the calling substation C indicates to the subscriber thereat that the desired connection cannot immediately be had due. to the busy condition of the called subscriber line |50. The subscriber at the calling substation C then releases the operated link and the line circuit |05 by replacing the receiver of the telephone instrument at the substai-ion C upon its hook. The exact manner in which these operated pieces of apparatus are released is described in detail hereinafter.

Assuming that the called subscriber line |50 is f idle. battery potential appears upon the control conductor C|54 thereof. this battery potential being derived at the winding of the cut-oil' magnet RI In and extending therefrom by way ofthe winding of RI I0, RAI23, and RCI24 to the control conductor Cl54. This application ofbattery potential to the control conductor C|54 completes a path for short-circuiting the busy relay included in the connector switch |02, thereby to cause the connector switch |02 to operate and project ringing current of the previously selected code over the called subscriber line |50 in order to cause the ringer at the substation A to operate in a characteristic manner. This characteristic operation of the ringer at the substation A indicates to the subscriber thereat that the substation A is the called substation. Also, 4the switch-through relay ln the connector switch |02 operates to apply i direct ground potential to the wiper |84. 'I'his application of direct ground potential to the wiper |84 completes a circuit for energizing the cut-oi magnet RI I0, this circuit extending from the grounded wiper |84 by way of CI 54, RCI 24, RAI 23, and the winding of RI I0 to battery.

When energized over the above-traced circuit the cut-off magnet RI I0 operates to complete, at RAI I2 and RCI I4, a holding circuit for energizing the Winding thereof, this circuit extending from the grounded control conductor CI54 by way of RAI |2, RCI I4, and the winding of R| |0 to battery. Also, upon operating, the cut-off magnet R||0 completes, at RAI and RAI I6, the holding circuit for energizing the line magnet R|20, this circuit extending from ground at the lower winding oi' RI 20 by way of the lower winding of R|20, RAI I8, RAI I5, and the upper winding of R|20 to battery. Also, upon operating, the cut-oi magnet RI I0 releases the locking arrangement associated with the armature of the line magnet RI 20, thereby to allow the line magnet RI20 to operate fully. When energized over the above-traced circuit the line magnet R120 fully operates to complete, at RAI2| and RCI22, a path for applying ground potential to the control conductor C|53 of the subscriber line |50 extending to the contact banks of the Strowger mechanisms included in the finder switches of the links having access thereto, thereby to mark the subscriber line |50 as busy, this path extending from the grounded control conductor CI54 by way of RCI 22 and RA|2| to the control conductor CI53. The subscriber at the substation A then answers the call by removing the receiver of the telephone instrument thereat from its hook, thereby to cause the connector switch |02 to operate in order to interrupt the projection of ringing current over the called subscriber line and to complete an established communication connection between the calling subscriber line |60 and the called subscriber line |50 by way of the operated link |00.

'I'he release of this established connection is under the control of the last party to replace the' receiver of the telephone instrument at his station upon its hook, as previously assumed; and the exact manner in which the operated link I 00 and the operated line circuits |05 and |04, respectively, individually associated with the subscriber lines |60 and |50 are released is the same as that previously described.

A reverting call which is to be extended from the subscriber substation A to the subscriber substation B is first initiated at the substation A by removing the receiver of the telephone instrument thereat from its hook, thereby to complete the previously traced bridge circuit for energizing in series the windings of the line magnet Rl20. When thus energized the line magnet R|20-par tially operates, as previously explained, thereby to close the ,X contacts associated `with the switch springs RA|2| and RCI22, and RA|28 and the associated switch spring, in order to cause battery potential to be applied to the control conductor CI53 and ground potential to be applied to the start conductor C|90, as previously noted. This application of ground potential to the start conductor C|90 causes the distributor |03to oper- .conductor CI12.

group of links to the use oi the calling subscriber line |50.

|50, this application of ground potential to the start conductor C|30 and this application of battery potential to the control conductor C |53 marks the position of the contact set in the contact bank of the Strowger mechanism included in the nder switch IOI at which the subscriber line .|50 is terminated. The finder switch IOI then operates in the previously described manner, thereby to seize the calling subscriber line |50. When the calling subscriber line |50 is seized the cut-oir magnet RI I operates to release the latching arrangement associated with the armature of the line magnet R|20, and to complete the previously traced holding vcircuit for energizing in series the upper and lower windings of the line magnet RI20 in order to allow the line magnet RI20 to operate fully. At this time the line and cut-oil' magnets RI20 and RI I0 are completely operated, as previously noted.

The connector switch |02 is conditioned to be responsive to a series of dialed digits at this time. The subscriber at the substation A then dials at the dial mechanism thereatsuccessively two predetermined digits into the connector switch |02, thereby to cause the connector switch to operate and select the rst trunk line terminating-thereat to which an idle reverting call switch is connected. When these two predetermined digits are successively dialed the connector switch |02 operates as a trunk hunting connector switch in order to select a trunk line associated with an idle one of the reverting call switches or to return busy tone current over the loop circuit extending to the calling subscriber substation A in the event that all Vof the reverting call switches are busy. Assuming that the illustrated reverting call switch 200 is the iirst idle switch, the connector switch- |02 operates to seize the trunk line extending thereto. The reverting call switch 200 is marked as idle or busy, respectively, by thepresence of battery or ground potential upon the control conductor CI12 of the trunk line |10. At this' time, the reverting call switch-200 being idle, battery potential appears upon the control conductor CI12 of the trunk line |10` the path for connecting battery potential to the control conductor CI12 extending from battery at the resistor 206 by way of the resistor 206, RA21I, RC242. RA24I, and RA256 to the control When the connector switch |02 selects the trunk line |10 extending to the idle reverting call switch 200, further operation thereof is arrested due to the presence of battery potential upon the control conductor CI 12'thereof, in the usual manner.A

When the trunk line |10 is thus seized by the connector switch |02, this connector switch operates to complete a. loop circuit between the calling subscriber substation A and the line relay R230 in the reverting call switch 200, this loop circuit extending from ground at the lower winding of R230 by way of the lower winding of R230, RC229, and RA221 to CI13, and from battery at the upper winding of R230 by way of the upper winding of R230, RC222, and RA22| to CI1I, the line conductors C|1| and CI13 of the trunk line |10 being connected by way of the operated link |00 to the line conductors CI5I and C|52, respectively, of the calling subscriber line |50, and the telephone instrument at the substation A being included in a bridge path extending between the line conductors CI5I and CI52 of the subscriber line |50.

Assuming that the illustrated link |00 `is assigned to the use of the calling subscriber line l 2,199,643 ateand assign a previously selected idle link in the When energized'over the above-traced circuit the line relay R230 operates to complete, at RA23| and RC232, an obvious circuit fior energizing the Vhold relay R240. When thusenerglzed `the hold relay R240 operates to interrupt. at RA24| and RC242, a point in the path for' applying battery potential to the control conductorC|12 oi Vthe trunk line |10, and completes, at RA24| and RC243, a path for applying ground potential to the control conductor-CI12, this path extending from ground, at RC243, by way of .RA24|, and RA256 to the control conductor CI12. This application of ground potential to the control conductor CI12 of the trunk line |10 marks this trunk line as busy to the connector switches of the links having access thereto, and causes the switchthrough relay in the connector switch |02 to operate. When the switch-through relay in the connector switch I 02 operates, ground potential inthe operated link |00 is removed from the wipers I8I and |34 of the iinder and connector switches I 0| and |02, respectively,.thelink|00 and the line circuit |04 being retained in its operated position at this time due to the application of ground potential to the control conductor CI12 of the trunk line |10. Also, upon operating, the relay R240 prepares, at RA245, a point in an impulse circuit traced hereinafter for energizing the rotary magnets M230 and M238 of the minor switches 280 and 290, respectively, included in the reverting call switch 200. l

'I'he subscriber at the calling substation A then dials at the dial mechanism thereat a third digit corresponding to the last digit of the directory number of the calling substation A, thereby to transmit a series of impulses by way of the previously mentioned loop circuit to the line relay R230. The relay R230 follows the dialed impulses in theV usual manner, restoring each time the loop circuit is interrupted and operating each time the loop circuit is completed. Each time the relay R230 restores, it interrupts, at RA23I and RC232, the circuit for energizing the hold relay R240, and completes, at RA23| and RC233, a circuit for energizing in multiple 'the relay R250 and the rotary magnet M236 of the minor switch 280. The last-mentioned circuit extends from ground, at RA23| by way of RC233, RA245, and RA262 to RC204, one branch of this circuit extending from RC264` by wayA of the winding of R250 to battery, and the other branch extending from RC264 by way of RA213, RC216, and the winding of M236 to battery. The relays R240 and R250, being of the slow-to-release type, remain operated during impulsing. Each time the circuit for energizing the rotary magnet M230 is completed and interrupted, this magnet operates to drive the wipers 283 and 285 of the rotary switches 28| and 282, respectively, included in the minor switch 280 one step away from their normal positions. When the wipers noted of the rotary switches 28| and 282 are driven away from their normal positions, the switch springs 234 are actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the transfer relay R210, this circuit being interrupted at this time, at RA25I, by the operated relay R250. In response to this digit the wipers 283 and 285 of the rotary switches 28| and 202,*respectively, are-driven a number of steps away from their normal positions corresponding to this dialed digit and into engagement with corresponding contacts in theassociated contact banks 284 and 280, respectively.

' At the conclusion of the third digit the line relay R230 reoperates. thereby to interrupt, at RA| and RC233, the circuit for energizing in multiple the relay R250 and the rotary magnet M236 in order to cause the relay R250 to restore shortly thereafter and to arrest further operation of the rotary magnet M236. Upon restoring, the relay R250 completes, at RAI, the previously mentioned circuit for energizing the transfer relay R210, this circuit extending from ground, at the switch springs 234, by way of the switch springs 234, RA25I, and the winding of R210 to battery. When thus energized the relay R210 operates to complete, at RA212, an obvious holding circuit for energizing the winding thereof, to interrupt, at RA213 and RC2'I6, a further point in the previously traced circuit for energizing the rotary magnet M236, and to prepare. at RA213 and RC214, a point in a circuit traced hereinafter for energizing in multiple the relay 20 R250 and the rotary magnet M230 of the minor switch 290.

The subscriber at the calling substation A then dials at the dial mechanism thereat a fourth digit corresponding to the last digit of the directory number of the called substation B, thereby to transmit another series of impulses by way of the previously mentioned loop circuit to the line relay R230. The relay R230 follows the dialed impulses in the usual manner. Each time the relay R230 restores it interrupts, at RA23I 'and -RC232, the circuit for energizing the hold relay R240, and completes, at RA23| and RC233, the previously mentioned circuit for energizing in multiple the relay R250 and the rotary magnet M238 of the minor switch 290. The last-mentioned circuit extends from ground, at RA23I, by way of RC233, RA245, and RA262 to RC264. one branch of this circuit extending from RC264 by way of the winding of R250 to battery, and the other branch extending from RC264 by way of RA213, RC214, and the winding of M238 to battery. Each time the circuit for energizing the rotary magnet M238 is completed and interrupted, this magnet operates to drive the wipers 293 and 295 of the rotary switches 29| and 292.

respectively, included in the minor switch 290 one step away from their normal positions. When the wipers noted of the rotary switches 29| and 292 are driven away from their normal positions the switch springs 235 are actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the transfer relay R260, this circuit being interrupted at this time, at RA252, by the operated relay R250. In response to this digit the wipers 293 and 295 of the rotary switches 29| and 292, respectively, are driven a number of steps away from their normal positions corresponding to this dialed digit 'and into engagement with corresponding contacts in the associated contact banks 294 and 296, respectively. At the conclusion of the fourth digit the line relay R230 reoperates, thereby to interrupt, at RA23| and RC233, the circuit for energizing in multiple the relay R250 and the rotary magnet M238 in order to cause the relay R250 to restore shortly thereafter and to arrest further operation of the rotary magnet M238. Upon restoring, the relay R250 completes, at RA252, the previously mentioned circuit for energizing the transfer relay R260, this circuit extending from ground, at the switch springs 235, by way of the switch springs 235, RA252, and the winding of R260 to battery. When thus energized the relay R260 operates to complete, at RA26I, an obvious holding circuit for energizing the winding thereof, to interrupt, at RA262 and RC2, a further point in the previously traced circuit for energizing in multiple the relay R250 and the rotary magnet M230, and to prepare, at RA202 and RC263, a circuit traced hereinafter for energizing the relay R2|0.

Shortly after `the conclusion of the fourth digit dialed the subscriber at the substation A replaces the receiver of the telephone instrument thereat upon its hook, thereby to interrupt the loop circuit extending to the line relay R230 in order to cause the latter relay to restore. Upon restoring, the relay R230 completes, at RA23| and RC233, the previously mentioned circuit for energizing the relay R2l0, this circuit extending from ground,`at RA23I, by way of RC233, RA245, RA262, RC263, RA258, and the winding of R2|0 to battery. When thus energized the relay R2|0 operates to complete, at RA2| I, an obvious path for applying ground potential to the ringing machine start lead C206, to prepare, at RA2I2, a holding circuit traced hereinafter for energizing the switch-through relay R220, to complete, at RA2I3, a path extending from battery, at the winding of R220, by way of the winding of R220, RA225, RC226, and RA2|3 to the ring pick-up lead C2|5 for applying battery potential to C2|5, and to complete, at RA2I4, an obvious holding circuit for energizing the hold relay R240. The hold relay R240, being of the slow-to-release type, does not restore incident to the restoration of the line relay R230, and is retained in its operatedposition over the above-mentioned holding circuit for energizing the winding thereof. Accordingly, ground potential is not removed from the control conductor C|`|2 of the trunk line |10 incident to the restoration of theline relay R230.

Shortly thereafter and at the beginning of a code ringing cycle, ground potential is applied in the ringing machine to the ring pick-up lead C2l5, thereby to complete a circuit for energizing the switch-through relay R220, this circuit extending from the grounded ring pick-up lead C2I5 by way of RA2I3, RC226, RA225, and the winding of R220 to battery. When thus energized the relay R220 operates to complete, at RA224 and RA225, a holding circuit for energizing the winding thereof extending from ground, at RA2l2, by way of RA224, RA225, and the Winding of R220 to battery, and to interrupt, at RA225 and RC226. the original circuit for energizing the winding thereof by way of the ring pick-up lead C2|5. Also, the relay R220 interrupts. at RA22| and RC222, and at RA221 and RC229, further points in the loop circuit for energizing the line relay R230, and completes. at RA22| and RC223, and at RA221 and RC228, points in a circuit traced hereinafter for projecting ringing current from the ringing machine associated with the trunk line 206' by way of the operated reverting call switch 200, the trunk line |10, and the link |00 over the subscriber line |50, the exact circuit for projecting ringing current from the ringing machine associated with the trunk line 206 over the subscriber line depending upon the positions of the wipers of the rotary switches included in the minor switches 280 and 290, in a manner more fully described subsequently.

As previously noted, a divided ringing circuit is employed in the-system, a first group of sub scriber substations associated with each party line having ringers thereat connected between one line conductor of the party line and ground, and a second group of subscriber substations associated with each party line having ringers thereat connected between the other line conductor of the party line and ground. The operation of the reverting call switch 200 depends upon whether the calling and called subscriber substations A and B are in the same group. In the event these subscriber substations are in the same group, the reverting call switch 200 operates to cause ringing current of the code corresponding to the called subscriber substation to be projected over the line conductor of the subscriber line |50, to which the ringers at each of the subscriber substations A and B are connected. In the event these subscriber substations are in different groups, the reverting call switch 200 operates first to cause ringing current of the code corresponding to the called subscriber substation to be projected over the line conductor of the subscriber line |50, to which the ringer at the called substation B is connected, and then to cause ringing current of the code corresponding to the calling subscriber substation to be projected over the line conductor of the subscriber line |50, to which the ringer at the calling substation A is connected. Also, it is noted that the subscriber substations associated with the subscriber line |50 and having ringers connected to one line conductor thereof are assigned directory numbers comprising a third odd digit, and the subscriber substations associated with the subscriber line |50 and having ringers connected to the other line conductor thereof are assigned directory numbers comprising a third even digit.

Assuming that the third digit of the directory number of the calling subscriber substation A is the No. 1, and the third digit of the directory number of the called subscriber substation B is the No. 3, the wipers of the rotary switches of the minor switch 280 engage the first contacts in the associated contact banks, and the wipers of the rotary switches of the minor switch 290 engage the third contacts in the associated contact banks. At this time a circuit is completed for projecting ringing current of the code corresponding to the called subscriber substation B over the subscriber `line |50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor M3, the third contact in the contact bank 294 and the associated wiper 293 of the rotary switch 29|, the upper winding of the ring cut-oil' relay R255, RC223, and RA22I, to the line conductor C|1| of the trunk line |10, and therefrom by way of the operated link |00, the line conductor C|5| of the subscriber line |50, and` a condenser and .the ringer at the called substation B, to ground.

Also, a circuit is prepared for energizing the upper winding of the ring cut-off relay R255, which is completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its hook, this circuit extending, when completed, by way of the previously traced path to the line conductor C|5| of the subscriber line |50, and therefrom by way of the bridge path at the substation B between the line conductors C|5| and C|52 of the subscriber line |50, CI52, the operated link |00, the line conductor C|13 of the trunk line |10, RA221, RC228, and the windings 202 and 203 of the transionner 20| to ground.

Assuming that the third digit of the directory number of the calling subscriber substation A is the No. 2, and the third digit of the directory number of the called subscriber substation B is the No. 4, the wipers of the rotary switches of the minor switch 280 engage the second contacts in the associated contact banks, and the wipers of the rotary switches of the minor switch 290 engage the fourth contacts in the associated contact banks. At this time a circuit is completed for projecting ringing current of the code corresponding to the called subscriber substation B over the subscriber line |50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor M4, the fourth contact in the contact bank 295 and the associated wiper 295 of the rotary switch 292, and the windings 205 and 204 of the transformer 20| to ground at RA220. This ringing current traversing the windings 204 and 205 of the` transformer 20| induces a corresponding ringing current in the windings 202 and 203 thereof, which traverses a path extending from ground by way of the windings 203 and 202, RC228, RA221, to the line conductor C|13 of the trunk line |10, and therefrom by way of the operated link |00, the line conductor C|52 of the subscriber line I 50, and the condenser and the ringer at the called substation B to ground. Also, a circuit is prepared for energizing the upper winding of the cut-of! relay R255, which is completed Awhen the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its hook, this circuit extending, when completed, from battery at the resistor 201, by way of the resistor 201, the second contact in the contact bank 284 and the associated wiper 283 of the rotary switch 28|, the fourth contact in the contact bank 294 and the associated wiper 293 of the rotary switch 29|, the upper winding of' R255, RC223, RA22|, the line conductor C|1| of the trunk line |10, and the operated link to the line conductor C|5|, and therefrom by way of the bridge path at the substation B between the line conductors C|| and C|52 of the subscriber line 50, and a portion of the previously traced circuit to ground, at the winding 203 of the transformer 20|.

Assuming that the third digit of the directory number of the calling subscriber substation A is the No. 1, and the third digit of the directory number of the called subscriber substation B is the No. 2, the wipers of the rotary switches of the minor switch 280 engage the first contacts in the associated contact banks, and the wipers of the rotary switches of the minor switch 290 engage the second contacts in the associated contact banks. At this time a circuit is completed for projecting ringing current of the code corresponding to the called subscriber substation B over the subscriber line |50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor M2, the second contact in the contact bank 296 and the associated wiper 295 of the rotary switch 292, and the windings 205 and 204 of the transformer 20| to ground at RA220. This ringing current traversing the windings 204 and 205 of the transformer 20| induces a corresponding ringing current in the windings 202 and 203 thereof which is projected by way ofthe previously traced path over the line conductor C|52 of the subscriber line |50 to ground at the ringer at the called substation B. Also a circuit is completed for projecting ringing current of the code corresponding to the calling subscriber substation A over the subscriber line |50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor MI, the first contact in the contact bank 284 and the associated wiper 283 of the rotary switch 28|,

the second contact in the contact bank 294'and the associated wiper 293 of the rotary switch 29|, the upper winding of the ring cut-off relay R255, RC223, RA22|, the line conductor C|1| of the trunk line |10. the operated link |00, the line conductor C|| of the subscriber linev |50, and a condenser and the ringer at the calling substation A .to ground. 'ihe ringing machine operates to complete the circuits for applying ringing currents to the ringing conductors MI to M5, inclusive, sequentially, thereby to cause the ringer at the called substation B and the ringer at the calling substation A to be operated alternatively. Also a circuit is prepared for energizing the upper winding of the ring cut-off relay R255,'which is completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its hook, this circuit extendinghwhen completed, from the ringing conductor MI by way of the previously traced path to ground at the winding 203 of the transformer 20|.

Assuming that the third digit of the directory number of the calling subscriber substation A is the No. 2, and the third digit of the directory number of the called subscriber substation B is the No. 1, the wipers of the rotary switches of the minor switch 280 engage the second contacts in the associated contact banks, and the wipers of the rotary switches of the minor switch 290 engage the rst contacts in the associated contact banks. At this time a circuit is completed for projecting ringing current of the code corresponding to the calling subscriber substation B over the subscriber line |50, this circuit extending frorn the ungrounded terminal of the ringing machine winding by way of the ringing conductor MI, the iirst contact in the contact bank 294 and the associated wiper 293 of the rotary switch 29|, the upper winding of R255 and a portion of the previously traced circuit including the line conductor C|5| of the subscriber line |50 to ground at the ringer at the called substation B. Also a circuit is completed for projecting ringing current of the code corresponding to the calling substation A over the subscriber line |50-, this circuit extending from the ungrounded terminal of the ringing machine Winding by way of the ringing conductor M2, the second contact in the contact bank 288 and the associated wiper 285 of the rotary switch 282, the rst contact in the contact bank 296 and the associated wiper 295 of the rotary switch 292, and the windings 205 and 204 of the transformer 20| to ground, at RA220.` This ringing current traversing the windings 204 and 205 of the transformer 20| induces a corresponding ringing current in the windings 202 and 203 thereof which is projected by way of the previously traced circuit including the line conductor C|52 of the subscriber line |50 to ground at the ringer at the calling substation A. As previously noted, the ringers at the called and calling subscriber substations B and A, respectively, are operated alternatively. Also a circuit is prepared for energizing the upper winding of the ring cut-oil relay R255, which is completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its hook, this circuit extending, when completed, from the ringing conductor MI by way of the previously traced path to ground at the winding 203 of the transformer 20|.

When the subscriber at the called substation B answers the call, one of the previously traced circuits forv energizing the upper winding ofthe ring cut-o relay R255 is completed, depending upon whether the calling and called substations A and B, respectively, are in the same or different groups, as previously noted. When thus energized the ring cut-oi relay R255 operates to complete, at RA251, a holding circuit for enrgizing the lower winding thereof, this circuit extending from ground, at RA244, by way of RA251 and the lower winding of R255 to battery. Also the relay R255 interrupts, at RA256, the previously traced path for applying ground potential to the control conductor C|12 of the trunk line |10, and interrupts, at RA258; the circuit for energizing the relay R2 0, thereby to cause the latter relay to restore. Upon restoring, the relay R2|0 interrupts, at RA2| the previously traced path for applying ground potential to the ringing machine start lead C206 in order to arrest further operation of the ringing machine associated with the reverting call switch 200, to interrupt, at RA2 I2, the holding circuit for energizing the relay R220 in order to cause the latter relay to restore, and to interrupt, at `RA2|4, the previously traced holding circuit for energizing the hold relay R240. Shortly thereafter the hold relay R240 restores to interrupt, at RA244, the holding circuit for energizing the lower winding of the ring cut-off relay R255 in order to cause the latter relay to restore shortly thereafter, and to complete, at RA246, a. circuit for energizing the release magnet M239 of the minor switch 290, this circuit extending from ground, at RA246, by way of RA265, RC265, and the winding of M239 to battery. When thus energized the release magnet M239 operates to release the wipers of the rotary switches 29| and 292 of the minor switch 290, thereby to cause these wipers to be returned to their normal positions. When the wipers noted of the rotary switches of the minor switch `,290 are returned to their normal positions, the

switch springs 235 are actuated into disengagement, thereby to interrupt the holding circuit for energizing the transfer relay R260. The transfer relay R260 then vrestores to interrupt, at RA265 and RC266, the circuit for energizing the release magnet M239, and to complete, at RA265 and RC261, a circuit for energizing the release magnet M231 of the minor switch 280, this circuit extending from ground, at RA246, by way of RA265, lRC261, RA211, and the winding of R231 to battery. When thus energized the release magnet M231 operates to release the wipers of the rotary switches 28| and 282 of the minor switch 280, thereby to cause these wipers to be returned to their normal positions. When the wipers noted of the rotary switches of the minor switch 280 are returned to their normal positions, the switch springs '234 are actuated into disengagement, thereby to interrupt the holding circuit for energizing the transfer relay R210. The transfer relay R210 then restores lto interrupt, at RA211, the circuit for energizing A call switch 200 operates when the call is answered at the called subscriber substation B to interrupt, at RAZSB, the path for applying ground potential to the control conductor C| 'I2 of the trunk line |10, thereby to cause the link |00 to be released and interrupt the holding circuit for energizing the winding of the cut-oli magnet RI|0 inthe line circuit |04 individually associated withy the subscriber line |50. The cut-oit magnet R| I0 then restores to complete, .at RAI |6 and RCII'l, and at RAIN, a bridge circuit for energizing the windings of the line magnet RI20, thereby to retain this line magnetV in its fully operated position. This circuit extends from ground, at the lower winding of R|20, by way of the lower winding of RI20, RAIIS, RCIII, CI52, the bridge path including the telephone instrument at the called subscriber substation B between the line conductors C|52 and C|5I of the subscriber line |50, C|5|, RAIII, and the upper winding of RI to battery. Also, upon restoring, the cut-off magnet R||0 interrupts,'`

at RAI I5 and RAI i6, the previously traced holding circuit for energizing in series the upper and lower windings of the line magnet R|20, interrupts, at RA||2 and RCIM, a 4further point in by way of RA| and RC||3 to RAII2, one

branch of this path extending from RA||2 to CISI, and the other branch extending from RAII2, by way of RC|22 and RAI2I, to CI53. This application of ground potential to the control conductor CISI, extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access to the subscriber line |50, marks the subscriber line as busy thereto. Also, this application of ground potential to the control conductor CI53, extending to the contact banks of the Strowger mechanisms included in the nder switches of the links having access to the subscriber line |50, marks this subscriber line as busy thereto. Due to the fact that the bridge circuit for energizing the windings of the line magnet R|20 is completed prior to the interruption of the holding circuit for energizing the windings thereof, as previously noted, the line magnet R|20 remains in its fully operated position. At this time the line circuit |04 is operated to lock the subscriber line |50 out of service; and talking battery is supplied by way of the previously traced bridge circuit to the telephone instrument at the called subscriber substation B.

As previously noted, when the subscriber at the called substation B answers the call Athe reverting call switch 200 is released, thereby to interrupt the circuit for projecting ringing current over the subscriber line |50 in order to cause furtherroperation of the ringer-at the calling subscriber substation A to be arrested. When the operation or the ringer at the calling subscriber substation A is arrested, the subscriber thereat is advised that the subscriber at the called substation B has answered the call. The subscriber at the substation A. then removes the receiver of the telephone instrument thereat from its hook, thereby to complete an established connection between the calling and called subscriber substations A and B, respectively, for twoway communication therebetween, talking battery being supplied to the substation A by way ot the previously traced bridge circuit.

The release of this established connection between the'subscriber substations A and B is under the control of the last subscriber to replace the receiver of the telephone instrument at his substation upon its hook. When the last subscriber replaces the receiver of the telephone instrument at his substation upon its hook, the

bridge circuit for energizing the' windings of the line magnet RI20 is interrupted, thereby to cause this line magnet to restore completely, as previously noted. At thistime the established connection between the subscriber substations A and B is completely released, and the line circuit |04 individually associated with the subscriber line |50 is released, thereby to mark this subscriber line as idle to the finder and connector switches of the links having access thereto.

A reverting call which is to beextended from the subscriber substation C to the subscriber substation D is iirst initiated at the substation C by removing the receiver of the telephone instrument thereat from its hook, thereby to complete the previously traced bridge circuit for y energizing in series the windings of the line magthe holding circuit for energizing the winding of net Rl30. When thus energized the line magnet R| partially operates, as previously exlplained, thereby to close the X contacts associated with the switch springs RAISI, RCl32, and RAI33, RCI, and RAI31 and the associated switch spring, and to open the X contact associated with the switch springs RAI33, RCI33, in order to cause battery potential to be applied to the control conductor CIE4, ground potential to be applied to the control conductor CIGS, and ground potential to be applied to the start conductor C|00, as previously noted. This application of ground potential to the start conductor C|90 causes the distributor |03 to operate and assign a previously selected idle link in the group of links to the use of the calling subscriber line |60. Assuming that the illustrated link |00 is assigned to the use of the calling subscriber line |60, this application of ground potential to the start conductor CI90, and this application o! battery potential to the control conductor Cl, marks the position of the contact set in the contact bank of the Strowger mechanism included in the iinder switch |0| at which the subscriber line |60 is terminated. The finder switch IOI then operates in the previously described manner, thereby to seize the calling subscriber line |60. When the calling subscriber line |60 is seized, the cutoi magnet R|40 operates to release the latching arrangement assoelated with the armature of the line magnet RI30, and to complete the previously traced holding circuit for energizing in series the upper and lower windings of the line magnet RI 30 in order to allow the line magnet Rl30 to operate fully. At this time the line and -cut-off magnets R|30 and R|40 are completely operated, as previously noted.

The connector switch |02 is conditioned to be responsive to a sexies of dialed digits at this time. The subscriber at the substation C then dials at the dial mechanism thereat successively two predetermined digits into the connector switch |02, thereby to cause this connector switch to operate as'a trunk hunting connector switch and seize an idle line in the group of trunk lines extending to reverting call switches in the event there is an idle reverting call switch in this group, or to return busy tone current over the loop circuit extending to the calling subscriber substation C in the event all of the reverting call switches in this group are busy. Assuming that the reverting call switch 200 is the first idle switch in this group, the connector switch |02 operatesto seize the trunk line |10 extending thereto, this trunk line being marked as idle by the presence of battery potential upon the control conductor CH2, in the previously described manner. When the trunk line |10 is seized by the l connector switch |02, further operation of this connector switch is arrested, and the reverting call switch 200 is conditioned to be responsive to two series of successively dialed digits. Also the reverting call switch 200 operates to apply ground potential to the control conductor C|12 of the trunk line |10, thereby to cause the switchthrough relay in the connector switch |02 to operate. When the switch-through relay in the connector switch |02 operates, a loop circuit is completed between the calling subscriber substation C and the reverting call switch 200, and ground potential is removed in the operated link from the wipers |8| and |84 of the inder `and connector switches |0| and |02, respectively,

the link |00 and the line circuit |05 individually associated with the subscriber line |60 being retained in their operated positions at this time due to the presence of ground potential upon the control conductor C|12 of the trunk line |10.v Ihe subscriber at the calling substation C then dials successively two digits at the dial' mechanism thereat into the reverting call switch 200, the third digit dialed corresponding to the third digit of the directory number of the calling subscriber substation C, and the fourth digit corresponding to the third digit of the directory number of the called subscriber substation D. The subscriber at the calling substation C then replaces the receiver of the telephone instrument thereat upon its hook, and the reverting call switch 200 then operates, as previously described, thereby to project ringing current over the line conductor of the subscriber line |60 to which the ringers at the calling and called subscriber substations C and D, respectively, are connected in the event the ringers at both of these subscriber substations are included in the same group, and to project alternately ringing current over the line conductors of the subscriber line |60 in the event thatthe calling and called subscriber substations C and D, respectively, are included in different groups, as previously noted. This ringing current projected over the subscriber line 60 causes the ringer at the called subscriber substation D to operate in a characteristic manner, thereby to indicate to the subscriber thereat that the substation D is the called substation.

The subscriber at the called substation D then answers the call by removing the receiver of the telephone instrument thereat from its hook, thereby to complete a loop circuit for energizing the upper winding of the ring cut-on' relay R255 in the reverting call switch 200 and extending between the substation D and reverting call switch 200. When thus energized, the ring cut-o relay R255 operates, in the previously described manner, thereby to interrupt, at RAZ-56, the path for applying ground potential to the control conductor C|12 of the trunk line |10, and to cause the reverting call switch 200 to be released.

When the path for applying ground potential to the control conductor C|12 of the trunk line is interrupted, the operated link |00 is released for further use, and the holding circuit for energizing the cut-oi! magnet RMU in the line circuit |05 individually associated with the subscriber line |60 is interrupted, thereby to cause the latter magnet to restore. Upon restoring, the cut-oil' magnet RMO completes, at RAME and RCMB, and at RAMI, a bridge circuit for energizing the windings of the line magnet R|30, this circuit extending from ground, at the lower winding of R|30, by way of the lower winding of R|30, RAM6, RCMO, Cl62, the bridge path at the telephone instrument .at the called substation D between the line conductors C|62 and CISI of the subscriber line |60, C|6|, RAMI, and the upper winding of R|30 to battery. Also the cutoff magnet RMO interrupts, at RAM6 and RAM1, the previously traced holding circuit for ener. gizing in series the upper and lower. windings of the line magnet R|30 subsequent to the completion of the above-traced bridge circuit for energizing these-windings of the line magnet R|30. Thus the line magnet R|30 remains in its fully operated position. magnet RMO interrupts, at RAI and RCM5, a further point in the holding circuit for energizing the winding thereof, and interrupts, at RAM2 and RCM3, the connection between the control kconductor C|63 and the control conductor C|64 of the subscriber line |60. Further, the cut-off magnet RMO completes, at RAM9, a path for applying ground potential to the control conductor C |63, extending to the contact banks of the Further, the cut-off i this path extending from ground, at RA|30, by

scriber line |60 is operated to lock this subscriber Y line out of service.

As previously noted, when the subscriber at the called substation D answers the call, the re.

verting call switch 200 is released, thereby to interrupt the circuit for projecting ringing current over the subscriber line |60 in order to cause further operation of the ringer at the calling subscriber substation C to be arrested. When the operation of the ringer at the calling subscriber substation C is arrested, the subscriber thereat is advised that the subscriber at the called substation D has answered the call. The subscriber at the substation C then removes the receiver of the telephone instrument thereat from its hook, thereby to complete an established connection between the calling and called subscriber substations C and D, respectively, for two-way communication therebetween, talking battery being supplied to the substation C by way of the previously traced bridge circuit.

'I'he release of this established connection bereplaces the receiver of the telephone instrument at his substation upon its hook, the bridge circuit for energizing the windings of the line magnet RIS!! is interrupted, thereby to cause this line magnet to restore completely, as previously noted. At this time the established connection between the subscriber substations C and D is completely released, and the line circuit |05 individually asociated with the subscriber line |60 is released, thereby to mark this subscriber line as idle to theiinder and connector switches of the links having access thereto.

Also it is noted that a. timing arrangement is incorporated in the connector switch |02 which is operative in the event the switch-through relay therein does not operate within a predetermined time interval, due to the fact that the connector switch has not been fully operated to 29 seize a line accessible thereto, to cause ground potential to be removed from the Wiper IBI. For

example, the link may be seized in the previously described manner by the appearance of a fault on one of the subscriber lines, in which case the connectorswitch |02 thereof would not be operated subsequently to seize a line accessible thereto in order to cause the operation of the switch-through relay therein, whereby ground potential would be removed from the wiper I8 I, as previously noted. Under these conditions where ground potential is removed from the wiper |8|, the holding circuit for energizing the cut-off magnet in the line circuit associated with the line having the fault thereon is interrupted, thereby to cause the cut-oli magnet to restore. In the event the line having a fault thereon has a line circuit of the 'connection and arrangement of that of the line circuit |04, the cut-oi magnet therein, corresponding to the cut-oli magnet u RIIO, restores to cause the line to be locked out of service in the manner previously described in connection with the extension of a reverting call between the subscriber substations A. and B. In the event the line having a fault thereon has a line circuit of the connection and arrangement of that of the line circuit |05, the cut-ofi magnet therein, corresponding to the cut-oli magnet RMU, restores to cause the line to be locked out of service in the manner'previously described in connection with the extension of a reverting call between the subscriber substations C and D.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A line circuit adapted for use in a telephone system including a line accessible to an automatic switch, said line circuit comprising, in combination, line and cut-oi relays, said line relay having a. restored position and rst and second operated positions, means responsive to the creation of a calling condition on said line for causing said line relay to be operated from its restored ,position to its rst operated position, means responsive to the seizure of said line by said automatic switch for causing said cut-oil relay to be operated, means controlled by the operation of said cut-off relay for causing said line relay to be operated to its second operated position, and circuits for controlling said automatic switch governed in accordance with the positions of said line and cut-oil? relays.

2. A line circuit adapted for use in a telephone system including a line accessible to an autol matic switch, said line circuit comprising, in combination, line and cut-off relays, said line relay having a restored position and iirst and second operated positions, said line relay being operative from its restored position to its iirst operated position in response to the creation of a. calling condition on said line. means eective to prevent op eration vof said line relay to its second operated position, said cut-oil relay being operative in response to the seizure of said line by said automatic switch, meanscontrolled by the operation oi' said cut-off relay for rendering said lastmentioned means ineffective, whereby said line relay is operated to its second operated position, and circuits for controlling said automatic switch` governed in accordance with the positions of said line and cut-oli relays.

3. lA line circuit adapted for use in a telephone system including a line accessible to an automatic switch. said line circuit comprising, in combination, line and cut-ofi relays, said line relay having a restored position and iirst and second operated positions, said line relay being operative from its restored positionto its rst operated position in response to the creation of a calling condition on said line, mechanical means effective to prevent operation of said line relay toits second operated position, said cut-off relay being operative in response to the seizure of said line by said automatic switch, means controlled by the operation of said cut-oli relay for actuating said mechanical means, whereby said line relay is operated to its second operated position. and circuits for controlling said automatic switch in accordance with the positions of said line and cut-off relays.

, 4. A line circuit adapted for use in a telephone system including a line provided with at least one line conductor and accessible to an automatic switch, said line circuit comprising, in combination, line and cut-off relays, said line relay having a restored position and iirst and second operated positions, a rst circuit including said line conductor for said line relay, a holding circuit for said line relay, said iirst circuit being completed in response to the creation of a calling condition on said line, whereby said line relay is operated from its restored position to its iirst operated position, said cut-off relay being operative in response to the seizure of said line by said automatic switch, means controlled by the operation of said cut-oir relay for completing said holding circuit and for interrupting said rst circuit, whereby said line relay is operated from its rst operated position to its second operated position, and circuits for controlling said automatic switch governed in accordance with the positions of said line and cut-oit relays.

5. A line circuit adapted for use in a telephone system including a line provided with at least one line conductor and accessible to an automatic switch, said line circuit comprising, in combination, line and cut-oli' relays, said line relay having a restored position and rst and second op erated positions, a iirst circuit including said line conductor for said line relay, a holding circuit for said line relay, said nrst circuit being completed in response to the creation of a calling condition on said line, whereby said line relay is operated from its restored position to its first operated position, mechanical means eilective to prevent operation of said line relay to its second operated position, said cut-oi relay being operative in response to the seizure of said line by said automatic switch, means controlled by the operation of said cut-off relay for actuating said mechanical means, means controlled by the operation of said cut-oii relay for completing said holding circuit and for interrupting said rst circuit, whereby said line relay is operated from its rst operated position to its second operated position, and circuits for controlling said automatic switch governed in accordance with the positions of said line and cut-off relays.

6. A line circuit adapted for use in a telephone system including a line having a plurality of subscriber substations associated therewith and accessible to a number of automatic switches; said line circuit comprising a circuit network consisting solely of line and cut-off relays and automatic switch control and line marking circuits governed by said line and cut-oil? relays, said cir; cuit network being so connected and arranged that said automatic switches are controlled to render by way of said line calling; called and reverting call services to said substations, and that said line is marked as busy to the remainder of said automatic switches not employed in rendering a service by way of said line while a service is being rendered by way of said line.

7. A line circuit adapted for use in a telephone system including a line having a plurality of subscriber substations associated therewith and [accessible to a number of automatic switches; said line circuit comprising a circuit network consisting solely of line and cut-ofi relays and cuits governed by said line and cut-off relays; said circuit network being so connected and ai;- ranged that said automatic switches are controlled to set up by way of said line outgoing call connections from said substations, incoming call connections to said substations and reverting call connections between two of said substations, and that said line is marked as busy to the remainder of said automatic vswitches not employed in a connection including said line while a connection including said line is set up.'

8. A line circuit adapted for use in a telephone system including a line having a plurality of subscriber substations associated therewith and accessible to avnumber of automatic switches; said line circuit comprising a circuit network consisting solely of line and cut-oi relays and automatic switch control and line marking circuits governed by said line and cut-oil relays; said circuit network being so connected and arranged that said automatic switches are controlled to set up by way of said line outgoing call connections from said substations, incoming call connections to said substations and reverting call connections between two of said substations, and that said line is marked as busy to the remainder of said automatic switches not employed in a connection including said line while a connection including said line is set up, and that said line is marked as busy to said automatic switches in the event a fault appears thereon.

9. In a telephone system, a line, a number of nder switches and a number ofconnector switches having access to said line, a line circuit associated with said line and including line and cutof! relays, said line relay having a restored position and rst and second operated positions, means responsive to the creation of a calling condition on said line for causing said line relay to be operated from itsrestored position to its rst operated position, means controlled by the operation of said line relay to its rst operated position for causing an idle one of said nder switches to seize said line, means responsive to the seizure of said line by said one finder switch for causing said cut-of! relay to be operated,

means controllecY'by the operation oi said cut off relay for causing said line relay t0 be opera ed from its rst operated position to its secondaperated position, and circuitsv for controlling said connector switches governed in accordance with the positions of said line and cut-pff relays.

10. In a telephone system, 'a line. a number ofv nder switches having access t said line, a line circuit associated with said line and including line and cut-ofi relays, a distributor associated with said iinder switches and operative to cause an idle one of said nder switches to operate and seizey a line marked as a calling line, said line relay having a restored position and ilrst and sec ond operated positions, means responsive to the creation of a calling condition on said-line for causing said line relay to be operated from its restored position to its first operated position, means controlled by the operation of said line relay to its first operated position for initiating operation of said distributor and for marking said line as a calling line, means responsive to the seizure of said line by one of said nder switches for causing said cut-olf relay to be operated, means controlled by the operation of said cut-oli relay for causing said line relay to be op- /erated from its first operated position to its second operated position, and means controlled by automatic switch controland line marking cirthe operation of said line relay to its second operated position for arresting the operation of said distributor.

11. In a telephone system, a line, a number of finder switches having access to said line, a line circuit associated with said line and including line and cut-oli relays, a distributor associated with said finder switches and operative to cause an idle one of said finder switches to operate and seize a 1in` marked as a calling line, said line relay having restored position and rst and second operated positions, means responsive to the creation of a calling condition on said line for causing said line relay to be operated from its restored position to its rst operated position, mechanical means effective to prevent operation of said line relay to its second operated position, means controlled by the operation of said line relay to its rst operated position for initiating operation of said distributor and for marking said line as a calling line, means responsive to the seizure of said line by one of said iinder switches for causing said cut-oi relay to be operated, means controlled by the operation of said cut-ofi relay for actuating said mechanical means and for causing said line relay to be operated from its iirst operated position to its second operated position, and means controlled by the operation of said line relay to its second operated position for arresting the operation of said distributor.

12. In a telephone system, a line provided with at least one line conductor, a number of inder switches having access to said line, a line circuit associated With said line and including line and cut-off relays, a distributor associated with said nder switches and operative to cause an idle one of said iinder switches to operate and seize a line marked as a calling line, said line relay having a restored position and rst and

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