US2214203A - Telephone system - Google Patents

Description

Sept. 10, 1940. E. s. PETERSON TELEPHONE SYSTEM Filed Dec. 27, 1938 7 Sheets-Sheet 2 Ewggmw mmhQ o .MQZYIDXM INVENTOR Edward 5. Fe'l'ersun E E:

ATTORNEY$- E. s. PETERSON TELEPHONE SYSTEM Sept. 10, 1940.

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Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Edward S. Peterson, Elmwood Park, 111., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application December 2'7, 1938, Serial No. 247,837

30 Claims.

The present invention relates to telephone systems and more particularly to improvements in telephone systems including exchanges of the remotely controlled type wherein the automatic 1 switching apparatus of two or more tandem connected small automatic exchanges is controllable from a main or central exchange to set up connections between the lines extending to the sub- J exchanges. 10"

over trunk lines interconnecting the exchanges. 16

The automatic switching apparatus provided in each of the subex'changes conventionally comprises one 'or more finder-connector links. Usually, a single link in each exchange is sufiicient to provide reasonably good service to the small number of lines extending to the associated exchange. With such an arrangement, the switching apparatus provided in the tandem connected subexchanges can serve only one calling line at a time and, hence, it is necessary to provide, in conjunction with the automatic switching apparatus, a lookout arrangement for guarding an established connection against intrusion occasioned by other calls. It is also desirable that calls, initiated at a time when the automatic switching apparatus provided in the subexchanges is busy, be stored until the apparatus is freed and then forwarded to the control operator in the main or central exchange.

It is, therefore, an object of the present invention to provide, in a tandem exchange system of the character described, an improved line lockout and call storing arrangement which is operative to guard an established connection against intrusion and to forward a waiting call to the central exchange operators position when the automatic switching apparatus provided in the tandem connected subexchanges is released.

It is a further object of the invention to provide, in a system of the character described and including two tandem connected subexchanges, an improved arrangement for rendering the finder switch embodied in the automatic switching apparatus of one of the subexchanges inactive when a call is initiated on a line extending to the other subexchange or on the trunk line extending to the operators position in the central exchange.

It is a still further object of the invention to provide, in a system of the character described,

. an improved arrangement for storing a call initiated on one of the lines extending to one of the subexchanges at a time when the automatic switching apparatus of the tandem connected subexchanges is busy and for initiating the o-p eration of the finder switch having access to the line upon which the stored call was initiated when the automatic switching apparatus becomes idle.

In the illustrated embodiment of the invention, there are provided a main or central exchange in which the operators position equipment is located, a tandem exchange and a subexchange, together with a first trunk line extending between the main and tandem exchanges and a second line extending between the tandem and subexchanges. The subexchange terminates a plurality of subscribers lines and has provided therein automatic switching apparatus controllable over the indicated first and second trunk lines from the operators position in the main 20 exchange to set up connections between calling and called ones of the subscribers lines. More particularly, this automatic switching apparatus includes a finder switch having access to the subscribers lines and normally operative to select a calling line therefrom, and a connector switch controllable from the operators position to select a called one of the subscribers lines. The tandem exchange similarly comprises automatic switching apparatus terminating a plurality of additional lines and controllable over the above-mentioned first trunk line from the operators position in the main exchange to set up connections between calling and called ones of the additional lines. The automatic switching 35 apparatus provided in the tandem exchange is also utilized in establishing connections between the subscribers lines extending to the subexchange and comprises a second finder switch and a connector switch each having access to the lines extending to the subexchange and to the second trunk line which interconnects the tandem exchange with the subexchange.

In accordance with one feature of the present invention, there is provided in the subexchange apparatus controllable over the second trunk line, mentioned above, and operative in response to the initiation of a call on one of the additional lines extending to the tandem exchange for preventing the finder switch located in the subexchange from operating. Through this arrangement a connection resulting from a call initiatedon one of the lines extending to the tandem exchange is guarded against intrusion occasioned by a call initiated on one of the lines extending to the subexchange. This apparatus is also operative to prevent the finder switch located in the subexchange from operating when a call is initiated on the first trunk line extending between the main and tandem exchanges. More particularly, the apparatus for rendering the finder switch located in the subexchange inactive comprises a group of relays which are 0perative to open a point in the operating circuit for the operating magnet of the indicated finder switch in response to the application of a predetermined potential, namely, negative battery potential, to one of the conductors of the trunk line extending between the tandem exchange and the subexchange. In the tandem exchange there is further provided a lockout relay which operates to apply this predetermined potential to the indicated trunk line conductor when the finder switch provided in the tandem exchange operaates to seize a calling one of the subscribers lines extending to the tandem exchange. Following the operation of the apparatus described above, if a second call is initiated on one of the lines extending to the subexchange, means comprising the line relay associated with the calling line are provided for storing the call until the automatic switching apparatus provided in the tandem exchange and the subexchange is released. Appa ratus jointly controlled by the storing means just mentioned and the lockout apparatus described above is also provided for initiating the operation of the finder switch in the subexchange to seize the calling line when the busy condition of an automatic switching apparatus is terminated. By virtue of this arrangement, it is unnecessary for a calling subscriber repeatedly to initiate a call to a desired substation since, when a call is once initiated, the automatic switching apparatus provided in the tandem and subexchanges wil ultimately route the call to the control opertors position so that the control operator can resignal the calling subscriber by ringing back over the calling line.

Further features of the invention pertain to the particular arrangement of the circuit elements whereby the above and additional operating features are attained.v

The novel features believed to be characteristic Q 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 specification taken in conjunction with the accompanying drawings, in which Figure 1 schematically illustrates an automatic telephone system having the features of the present invention embodied therein, Fig. 2 illustrates the mode of assembling the remaining figures of the drawings to form a unified system, and Figs. 3 to 8, inclusive, considered together, illustrate the details of the switching apparatus embodied in the system shown in Fig. 1.

Referring now more particularly to Fig. l. of the drawings, the system there illustrated comprises a main exchange 8, a tandem exchange ill, and two satellite or subexchanges II and It interconnected by trunk lines I3, I4 and N. More particularly, the first trunk line I3 extends between an operators position I5 provided in the main exchange 9 and the automatic switching apparatus provided in thetandem exchange Iii, the second trunk line I l extends between the automatic switching apparatus provided in the tandem exchange Ill and the automatic switching apparatus provided in the subexchange II, and the third truck line I! extends between the automatic switching apparatus provided in the tandem exchange II] and the automatic switching apparatus provided in the subexchange I2.

The automatic switching apparatus provided in the tandem exchange II) comprises a finderconnector link I6 including a finder switch and a connector switch each having access to the trunk lines I4 and I1 and also to a plurality of additional lines including two subscribers lines I8 and I9 respectively extending to the substations T1 and T2. More particularly, the lines I4, I'I, I8 and I9 individually terminate in line circuits which are diagrammatically illustrated as a group at 20. The apparatus provided in the sub-exchange II similarly comprises a finderconnector link 2| including a finder switch and a connector switch each having access to a plurality of subscribers lines including the two lines indicated at 22 and 23 respectively extending to the substations T3 and T4. These lines have individually associated therewith line circuits which are diagrammatically illustrated as a group at 24. The switching apparatus provided in the subexchange I2 is identical with that provided in the subexchange I I and comprises a finder-connector link 25 including a finder switch and a connector switch each having access to a plurality of subscribers lines, two of which are indicated at 26 and 21 as extending to the substations T5 and T6, respectively. These lines individually terminate in the exchange I2 in line circuits which are diagrammatically illustrated as a group at 28. The subscribers lines extending to the exchanges I0, II and I2 are of the wellknown magneto type, each subscribers substation being equipped with a hand generator or magneto for projecting ringing current over'the associated line and with local'batteries for voice frequency current transmission. These lines may be of the single party or multiparty type as desired.

Neglecting for the present the details of the automatic switching apparatus provided in the exchanges I0, H and I2 and considering the operation of the system generally, when a call is initiated on a line extending to any one of the three exchanges II), II and I2, the call is forwarded to the operators position I5 in the main exchange 9 and the automatic switching apparatus provided in each of the three exchanges is rendered nonresponsive to calls initiated before the apparatus is thereafter released. For example, if a call intended for the substation T2 is initiated at the substation T1, the finder switch of the finder-connector link I6 functions under the control of the line circuit individual to the calling line I8 to seize the calling line and to transmit a signal to the operators position 5 indicating that a call is present on the trunk line I3 which should be answered. The control apparatus embodied in the finder-connector link It also functions, when the calling line I8 is seized, to apply a predetermined potential, namely, negative battery potential, to one conductor of each of the two trunk lines I4 and I1. Certain of the relays embodied in the control apparatus of the finder-connector link 2| respond to the application of negative battery potential to the indicated conductor of the trunk line I4 by operating to open a point in the operating circuit for the operating magnet of the finder switch included in the link 2I, thereby to render this switch nonresponsive to calls initiated on lines extending to the subexchange II. In a similar manner, the finder-connector link 25 provided in the subexchange I2 is locked out of service for the duration of the call initiated at the substation T1 on the line l8.

After answering the call and ascertaining from the calling subscriber the number of the desired substation or the name of the desired party, the operator attending the position l5 dials the directory number of the desired substation in the usual manner. The calling party is expected to hang up before the dialing and ringing operations are performed by the operator. The connector portion of the link l6 responds to the dialing operation by selecting the desired called line or, in the case assumed, the line [9. Following the dialing operation, the operator actuates the ringing key provided in her cord circuit tocause ringing current to be projected over the calling and called lines, thereby to energize the signaling devices or ringers respectively provided at the calling and called substations. Finally, the desired connection is completed when the call is answered at the calling and called substations. The release of the established connection is entirely under the control of the operator attending the operators position l5. More particularly, when the connection is no longer desired, it is expected that either the calling or the called party will operate his hand generator to transmit a disconnect signal to the control operator. Upon receiving this signal, the operator clears out the connection, permitting the operated finder-connector link l6 and the line circuits associated with the calling and called lines l8 and [9, re-

spectively, to be released. During the release of this apparatus, battery potential is removed from the above-mentioned conductors of the trunk lines l4 and I1, respectively, with the result that the relays embodied in the links 2| and 25 operate to reprepare the circuits for energizing the operating magnets of the finder switches respectively included in these links. In this manner, the automatic switching apparatus provided in the three exchanges H], H and I2 is conditioned for further use.

If the call originating at the substation T1 associated with the line [8 and routed to the operators position I5 is to be extended to a line terminating at one of the subexchanges II and I2, the operator, upon ascertaining the telephone number of the desired station, dials two digits, the first digit being utilized to cause the connector portion of the link l6 to seize the trunk line extending to the proper subexchange,

as, for example, the exchange II, and the second digit being repeated through the operated finder-connector link Hi to the connector control apparatus of the finder-connector link provided in the selected exchange. For example, if the call is to be routed to the substation T3 associated with the line 22, the operator first dials the digit corresponding to the trunk line l4, whereby the connector portion of the link It is caused to seize this trunk line. The impulses of the second digit dialed at the operators position are repeated through the control apparatus of the link I6 to the connector portion of the link 2|, causing the connector switch in this link to select the desired called line 22. After the called line is selected, the operator actuates her ringing key to cause ringing current to be projected over the established connection, whereby the signaling devices respectively provided at the calling and called substations are energized. Finally, the desired conversational circuit is fully established when the call is answered at the calling and called substations. Here again, the release of the connection is entirely under the control of the operator attending the position Hi, the manner in which the release of the apparatus is effected being substantially similar to the release of the apparatus as described above.

A call originating on a line extending to one of the subexchanges is first routed through the automatic switching apparatus of the corresponding exchange and is then extended through the finder-connector link l6 and over the trunk line It to the operators position 95. For example, if a subscriber at the substation T3 initiates a call at a time when the automatic switching apparatus provided in the three exchanges IE5, I! and I2 is idle, the finder portion of the link 2i is caused to operate to seize the calling line 22, after which a seizing pulse of current is transmitted over the trunk line H to seize the link it. The finder portion of the last-mentioned link, in turn, operates to seize the calling trunk line 14 and to transmit a splash of signaling current to the operators position l5. When the finder switch of the link 16 operates to seize the line M, the control apparatus of the link l6 functions to impress negative battery potential upon one conductor of the trunk line ll, and the control apparatus of the link 25 provided in the exchange [2 responds by rendering the finder portion of the link 25 nonresponsive to calls initiated on the lines extending to the exchange 52. The call signal device provided at the operators position l5 responds to the splash of signal current by operating to signal the operator that an incoming call on the trunk line l4 should be answered. After answering the call and conversing with the calling subscriber to ascertain the directory number of the desired substation, the operator may cause the desired connection to be set up by dialing the appropriate line selecting digits in the manner explained above. For example, if the call is to be forwarded to a substation on the line It, the operator dials the single digit designating this line to cause the connector portion of the link is to seize the called line. Alternatively, the call may be forwarded to another line terminating at the exchange I l, in which case the operator dials the two digits of the directory number designating the called line. The connector portion of the link It responds to the impulses of the first digit by seizing the trunk line I4 and establishing a pulsing circuit including the conductors of this trunk line over which the impulses of the second digit may be transmitted to the connector portion of the link 2i. The impulses of the second digit are then repeated through the control apparatus of the link it and over the established pulsing circuit including the trunk line It to the connector switch of the link 2!, and this switch responds by seizing the desired called line. If the call forwarded to the operators position i5 from the calling line 22 is to be routed to a subscribers line terminating at the subexchange 52, the operator first dials the digit designating the trunk line H, whereby the connector portion of the link I6 is caused to operate to seize the line H and the connector portion of the link 25 is conditioned to respond to the impulses of the second digit designating the desired called line. In any case, after the dialing operation is completed, the operator actuates her ringing key to cause ringing current to be projected over the calling and called lines and the desired connection is fully completed when the call is answered at the calling and called substations.

Calls routed to the operators position I5 from lines extending to the main exchange 9 may be routed, under the control of the operator attending the position, over the trunk line I3 to any one of the subscribers lines terminating in the exchanges I0, II and I2. To this end, the operator seizes the trunk line I3 and dials the directory number of the desired line, the connector switches of the links provided in one or more of the exchanges ill, II and I2 responding to the dialed impulses by establishing a connection including the trunk line I3 to the desired line in the manner previously explained. When the line I3 is initially seized, the finder switch of the link I6 is rendered nonresponsive to calls initiated on the subscribers lines extending to the exchange I0, and the control apparatus of the link I6 operates to impress negative battery potential upon one conductor of each of the trunk lines I4 and 1. in the links 2! and 25 responds to this potential by operating to render the finder switches of the two enumerated links nonresponsive to calls initiated on the lines to which they have access.

As explained above, in all instances where a call is initiated on the trunk line I3 or on a line terminating at one of the three exchanges 50, II and I2, the automatic switching equipment respectively provided in the three exchanges is rendered nonresponsive to other calls initiated on other lines before the automatic switching apparatus is released. To eliminate the necessity for a subscriber repeatedly to initiate a call in order to obtain access to the automatic switching apparatus after it becomes idle, provisions are made whereby a call, originated at a time when the automatic switching apparatus is busy, is stored until the automatic switching apparatus is released and is then automatically forwarded to the operators position I5 in the exchange 9. For example, if a call is initiated on the line 22 at a time when the automatic switching apparatus provided in the three exchanges I0, I I and I 2 is busy, the combined line, cut-01f and call storing relay associated with the line 22 operates and remains operated even though the calling subscriber abandons the call. Thereafter and when the automatic switching apparatus is released, the operated line relay associated with the line 22, in conjunction with certain of the apparatus embodied in the link 2!, functions to initiate the operation of the finder portion of the link 2I to seize the line 22. From this point on, the manner in which the call is forwarded to the operators position I 5 in the main exchange 9 is exactly the same as described above. In a similar manner, calls originating on lines extending to the exchanges I0 and I2 at times when the automatic switching apparatus is busy are stored until the switching apparatus is released, after which they are automatically forwarded to the .operators position I5. The operator attending this position, upon answering such a call and failing to receive a response from the calling subscriber, may ring back over the calling line to signal the calling substation, and hence it is unnecessary for the calling subscriber to attend the calling substation during the interval when the automatic switching apparatus is busy.

Referring now in greater detail to the switch apparatus embodied in the system and consider ing the equipment provided at the operators po- The control apparatus respectively included sition- I5, this equipment comprises, as shown in the right-hand portion of Fig. 3, a repeating transformer 310 having primary windings 373 and 314 terminating the conductors of the trunk line I3, and secondary windings 3H and 372 connected by means of conductors C385 and C386 to the contacts of a call and answer jack 369 through which the trunk line I3 is rendered accessible to the operators cord circuit. This equipment further includes a signal device in the form of a drop 315 which is energized over the trunk line I3 on calls incoming to the operators position I5 when the exchange battery provided in the tandem exchange II is connected across the line conductors C361 and C368. There is also provided at the operators position I5 a calling key 380 and a calling or impulsing device 382 which is operative in the usual manner to deliver current pulses through the springs of the calling key 380 and over the trunk line I3 to the control apparatus of the finder-connector link I6 provided in the tandem exchange I0.

As previously indicated, the subscribers line extending to the tandem exchange I0 are of the well-known magneto type and each thereof may have associated therewith a plurality of substations of the character diagrammatically illustrated at T1 and T2. At each substation there is provided a manually operable magneto or hand generator which is utilized in the initiation of calls, the generators of this character provided at the substations T1 and T2 being indicated at 653 and Gill, respectively. The line circuit associated with the line I8 comprises a relay R680 whichis arranged to perform all of the functions incident to the initiation and completion of calls involving the line I8. More particularly, this relay functions as a combined line, cut-off and call storing relay. An identical line circuit, schematically indicated at 690, is provided in association with the subscribers line I9.

The line circuits individually associated with the trunk lines I4 and. I1 extending to the tandem exchange I0 are of different arrangement than the line circuits individually associated with the subscribers lines. More particularly, the line circuit associated with the trunk line I4 comprises a line relay R630, a line switching relay R6I0, and a slow-to-operate cut-off relay R620. The line circuit associated with the trunk line I! similarly comprises line, cut-off and line switching relays R610, R660 and R650, respectively. The two line circuits just described are arranged partially to be controlled by a common lockout relay R640, which relay functions to apply negative battery potential to one line conductor of each of the two trunk lines I4 and I1 when a call is initiated on the trunk line I3 or one of the other lines extending to the exchange I0.

The finder-connector link I6 embodied in the tandem exchange I0 comprises a finder switch 500 and a connector switch 550, both of which are of the wellknown rotary step-by-step type. More particularly, the rotary finder switch 500 comprises four sets of contacts 505 to 508, inclusive, each including eleven contact points, wipers 50I to 504, inclusive, individually associated with the enumerated contact sets, and means comprising an operating magnet 530 and a ratchet and pawl mechanism, not shown, for driving the enumerated wipers over the contacts of their respective associated contact sets. For the purpose of controlling the operation of the finder switch to seize a calling one of the lines extending to the exchange I0, there are provided in the control apparatus of the link a pulsing relay R5l0 and a finder start relay R520. The rotary connector switch 550 comprises four sets of contacts 555 to 558, inclusive, four wipers 55| to 554, inclusive, individually associated with the enumerated contact sets, an operating magnet 540 for driving the wipers over the contacts of their associated contact sets, and a set of off-normal springs 542 which are operated into engagement when the enumerated wipers are moved to their respective first off-normal positions.

The control apparatus of the link l6 includes, in addition to the finder start and pulsing relays R520 and R5l0, respectively, a line relay R330, a slow-to-release hold relay R320, a slow-to-re-' lease pulse responsive control relay R455, a pair of control relays R440 and R410, and a pair of digit responsive transfer relays R460 and R465. This apparatus further comprises a line test relay R4l0, an alternating current control relay R450, a pendulum type timing relay R480, a slowto-operate link release relay R3l0 under the control of the pendulum relay R380, and two line switching and control relays R420 and R430. For the purpose of transmitting a splash of battery current over the trunk line l3 to the operators position l5 when the link [6 is seized, there are also provided in the control apparatus of this link two additional relays R350 and R355, the first of which is of the slow-to-operate type and the second of which is slow-acting. In .order to transmit a waiting tone to a calling subscriber after the link I8 is seized, there is provided a tone relay R340 which functions to impress an alternating signal voltage across the secondary line terminals of the repeater 380. For the purpose of releasing the finder-connector link IS in the event a call routed by way thereof to the operators position |5.is not answered within a predetermined time interval after the link is seized, there is also provided a link release relay 381 of the thermal type.

As previously indicated, the lines terminating at the subexchange II are also of the magneto type, each substation being provided with a hand generator adapted for use in initiating calls. The hand generators provided at the substations T4 and T5 are indicated at 115 and SM, respectively. The line circuits associated with these lines are of identical arrangement with the line circuits individually associated with the subscribers lines terminating at the tandem exchange l0. More particularly, the line circuit associated with the line 22 comprises a combined line, cut-off and call storing relay R100, while the line circuit associated with the line 23 comprises a similar relay R8l0. The automatic switching apparatus provided in the subexchange II is, in general, similar to the apparatus embodied in the tandem exchange l0. Thus, the finder-connector link 2| comprises a finder switch 800 and a connector switch 850, both of -which are of the single motion rotary step-bystep type. The switch 800 comprises four sets of bank contacts 805 to 808, inclusive, each including eleven contacts, wipers Bill to 804, inclusive, respectively associated with the enumerated contact sets and means comprising an operating magnet M6 and a ratchet and pawl mechanism, not shown, for driving the enumerated wipers over the contacts of their respective associated contact sets. The connector switch 850 is of ,similar construction but comprises only three contact sets 855, 856 and 851, three wipers 85! to 853, inclusive, individually associated with the contact sets, and a driving mechanism including anoperating magnet BIB for driving the enumerated wipers over the contacts of their respective associated contact sets. This connector switch also includes a set of off-normal springs 821 which are operated into engagement when the wipers of the switchare stepped to their respective first off-normal positions. The control apparatus of the link or, more particularly, the relay equipment embodied therein, comprises a finder start relay R825, finder switch pulsing relay R820, and a line test relay R120 which is operative to arrest the operation of the finder switch 800 when the wipers of this switch are moved to engage the contacts terminating a calling line. The control apparatus further includes a line relay R140, a slow-acting hold relay R135, a slow-to-release control relay R'H0, an alternating current relay R139, and a slow-to-release pulse responsive relay R830 arranged for parallel energize-tion with the connector switch operating magnet 8E8. In order to transmit a splash of battery current over the trunk line M to the tandem exchange l0, thereby to cause seizure of the link It when the finder switch 800 operates to a seize a calling one of the lines extending to the exchange H, there are provided two additional relays R155 and R180 which are of the slow-to-operate and slow-torelease types, respectively. For the purpose of transmitting a waiting tone to a calling subscriber following seizure of the link 2!, the control apparatus of this link further includes a tone relay R145 which corresponds to the similar relay R840 embodied in the link IS.

01121 initiated on a subscribers Zine extending to the tandem exchange Referring now in greater detail to the operation of the system and considering first a call initiated on one of the subscribers lines extending tothe tandem exchange l0, if the call is initiated at the substation T1 associated with the line NJ, for example, the combined line, cut-off and call storing relay R080 is caused to operate. More particularly, when the calling subscriber operates the hand generator 893, alternating current is projected over the line E8 to energize the upper winding of the relay R880. The path of this current may be traced as extending from one terminal of the generator 693 by way of the springs 694 which are operated into engagement when the magneto armature is turned, the line conductor C581, the upper winding of R680, RA883 and C553to the opposite terminal of the generator 883. When its upper winding is energized over this circuit, the relay R680 first operates to close the X contacts associated with RA684, thereby to complete a circuit including the resistor 685 for energizing its lower winding. Thereafter, the relay R080 completes its operation to open, at RLA083, a point in its original operating circuit as traced above and to complete,

at RA882, a path including the conductor C153 for marking the calling line l8 in the bank contacts of the finder switch 500. At RA68I, the relay R880 completes a circuit for energizing the finder start relay R520, this circuit extending from ground at RA451 by way of RA45I, C485, the wiper 554, and its associated home contact, C483, RA442, RA4I3, C484, RA68I, C484 and the winding of R520 to battery. The relay R520 now operates to prepare, at RA522, a point in the circuit, traced hereinafter, for energizing the line test relay R410 when the wipers of the finder switch 500 are operated into engagement with the set of contacts terminating the conductors of the calling line 18. At RA521, the relay R520 completes a circuit for energizing the operating magnet 530 of the finder switch 500, which circuit may be traced as extending from ground at RA411, by way of C486, RA521, RA511 and the winding of the magnet 530 to battery. When energized over this circuit, the magnet 530 actuates its associated ratchet and pawl mechanism, thereby to condition this mechanism to step the wiper of the switch 500 one step when the operating magnet is subsequently deenergized. At the armature 531, the magnet 530 completes an obvious circuit for energizing the upper winding of the pulsing relay R510, which latter relay, in turn, operates to open, at RA511, a point in the above-traced circuit for energizing the magnet 530. When the magnet 530 is thus deenergized the associated ratchet and pawl mechanism steps the wipers of the switch 500 one step and the armature 531 is restored to open the circuit for energizing the relay R510. The relay R510 now restores to recomplete the operating circuit for the magnet 530, causing this magnet to again attract the armature 531, thereby to recomplete the operating circuit for the relay R510. The interrelated operation of the pulsing relay R510 and the magnet 530 continues until the wipers of the switch 500 are driven into engagement with the contacts terminating the conductors of the calling line 18. More particularly, when the wiper 503 is operated into engagement with the contact terminating the test conductor C513, the above-mentioned circuit is completed for energizing the upper winding of the line test relay R410 in series with the lower winding of the pulsing relay R510. This circuit extends from ground at RA682 by way of C513, the wiper 503, the lower winding of R510, RA522, C492 and the upper winding of R410 to battery. When its lower winding is energized over this circuit, the pulsing relay R510 is held in its operated position independently of the magnet 530 so that the stepping operation of the finder switch 500 is arrested. Also, when this circuit is completed, the relay R410 operates and completes, at RA415, a holding circuit for itself, which holding circuit may be traced as extending from ground at RA441 by way of R A415 and the lower winding of R410 to battery. At RA411 and its associated resting contact, the relay R410 opens a point in the above-traced circuit for energizing the finder switch operating magnet 530. At RA413 and its associated resting contact, the relay R410 opens a point in the previously traced operating circuit for the finder start relay R520, which latter relay now restores to open, at RA522, a point in the previously traced circuit for energizing the lower winding of the pulsing relay R510 and the upper winding of R410 in series. The relay R510 now restores, at RA414, the relay R410 completes a. path for short-circuiting the lower winding of the line relay R680, this path extending from ground at RA452 by way of RA414, 0491, the Wiper 504, the conductor C511, the lower winding of R680 and RA684 to ground. When its lower winding is short-circuited over this path, the relay R680 restores to reconnect its upper winding across the conductors of the line 18.

At RA411 and its associated, working contact, the relay R410 completes a circuit for energizing the lookout relay R040, this circuit extending from ground at RA411 by way of C482 and the winding of R640 to battery. Upon operating, the relay R640 completes paths for impressing negative battery potential upon one of the line conductors of each of the twotrunk lines 14 and 11. Thus, at RA643 and itsassociated working contact, the relay R640 completes a path extending by way of the resistor 646, RA621, R0614 and RA613 for impressing negative battery potential upon the conductor C161 of the trunk line 14. Similarly, at RA542, the relay R540 completes a path extending by way of the resistor 645, RA661, R0654 and RA653 for impressing negative battery potential upon the conductor 0604 of the trunk line 11. At RA544, the relay R640 opens a point in the holding circuit, traced hereinafter, for the line relay R030 and prepares a point in the holding circuitQtraced hereinafter, for the cut-off relay R620. At RA641, the relay R040 similarly opens a point in the locking circuit for the line relay R510 and prepares a point in the holding circuit for the cut-off relay R660.

When negative battery potential is impressed upon the conductor C161 of the trunk line 14, the control apparatus of the link 2|, shown in Figs. 7 and 8, operates to open a point in the operating circuit for the finder switch operating magnet 816. More particularly, when the negative terminal of the battery provided in the tandem exchange 10 is connected to the trunk line conductor C161, the line relay R is energized over a circuit including this line conductor, RA164 and the winding 152. When energized over this circuit, the line relay R140 operates to complete, at RA141, an obvious circuit for energizing the slow-acting hold relay R135. The hold relay, in turn, operates to complete, at RA130, a circuit for energizing the sloW-to-operate relay R155 and, at RA131, a circuit for energizing the slow-to-release relay R110. The relay R110, upon operating, opens, at RA111 and RA 112, respectively, points in the operating circuits, traced hereinafter, for the relays R and R160, respectively. The relay R155, upon operating, opens, at RA151 and its associated resting contact, a point in the holding circuit for the relay R160 and prepares, at RA156 and RA151, a point in its own holding circuit. At RA158, the relay R155 opens a point in the circuit, traced hereinafter, for energizing the respective lower windings of the line test relay R120 and the finder pulsing relay R820 in series. At RA159, the relay R opens a point in the circuit, traced hereinafter, for energizing the operating magnet 816 of the finder switch 800, thereby to prevent this magnet from being energized in response to the operation of one of the line relays R100, R810, etc. Thus, the finder switch 800 is rendered nonresponsive to the initiation of calls on the lines extending to the exchange 11 throughout the period when the automatic switching apparatus provided in the tandem exchange 10 is busy. In a similar manner, the link circuit apparatus of the finder-connector link 25 provided in the subexchange 12 responds to the application of negative battery potential to the conductor C604 of the trunk line 11 by operating to render the finder portion of the link nonresponsive to calls initiated on lines extending to the subexchange 12.

Continuing now with the operation of the finder-connector link 10, when the line test relay R410 operates in the manner explained above, it connects, at its armatures RA416 and RA411, the link line conductors C495 and 0496 to the link line conductors C398 and C399, respectively,

thereby to connect the conductors C563 and C561 of the calling line l8 through to the lineterminals of the repeater 350. At RA4|3 and its associated working contact, the relay R4I0 completes a circuit for energizing the upper winding of the tone relay R340, this circuit extending from ground at RA451 by way of RA45I, C485, the wiper 554 and its associated home contact, C483, RA442, RAMS, C392, the upper winding of R340 and the resistor 342 to battery. An obvious branch of this circuit extends through the heating element 338 of the thermal relay 381 to battery. When its upper winding is energized over the circuit just traced, the relay R340 completes, at RA34 I, an obvious path for short-circuiting its upper winding and, as a consequence, immediately restores and then reoperates. Thus, the relay R34ll operates in the manner of a buzzer, its upper winding being alternately energized and deenergized in response to the short-circuiting action of its armature RA34I. As a consequence, an induced undulating voltage is developed in the lower winding of R340 which is impressed across the link line conductors C398 and C300 over a path including the condenser 334 and the restored armature RA322 of the hold relay R320. This voltage serves to energize the receiver of the telephone instrument provided at the calling substation, thereby to indicate to the calling subscriber that the automatic switching apparatus provided in the exchange I is idle and that the call is being forwarded to the operators position in the exchange 9.

The line test relay R4I0, upon operating, also completes, at RA4I2, a circuit for energizing the slow-acting relay R355, this circuit extending from ground at RA44| by way of RA4l2, C390, RA352, R0353 and the winding of R355 to battery. The relay R355 now operates to complete, at RA356, an obvious circuit for energizing the slow-to-operate relay R350. At its armatures RA358 and RA359 and their associated working contacts, the relay R355 connects the line conductors C361 and C368 of the trunk line [3 to opposite terminals of the exchange battery provided in the exchange l0, thereby to complete a circuit for energizing the drop 315 provided at the operators position I in the exchange 0. More particularly, this drop or signal device is energized over a circuit extending from ground by way of RA359, C368, the winding 314, the switch springs 311 and 310, the winding of the drop 315, the winding 313, C361, RA358 and the resistor 351 to battery. The drop 315 now operates to signal the operator attending the position I 5 that an incoming call on the trunk line i3 should be answered. Shortly following the operation of the relay R355, the slow-to-operate relay R350 operates to complete, at RA35I and RA352, a holding circuit for itself, which holding circuit extends from ground at RA44| by way of RA4l2, C390, RA352, RA35I and the winding of R350 to battery. At RA352 and RC353, the relay R350 opens a point in the previously traced operating circuit for R355, causing the last-mentioned relay to restore after an interval to disconnect the line conductors of the trunk line l3 from the terminals of the exchange battery and to reconnect these line conductors to the line terminals of the repeating transformer windings 36l and 362. In this manner, the desired talking connection between the calling substation T1 and the equipment provided at the operators position I5 is fully completed.

As indicated previously, if the operator attending the position l5 fails to answer a call within a predetermined time interval after the finderconnector link I5 is seized, the thermal relay 381 functions to cause the release of the operated switching apparatus. More particularly, when the heating element 388 of the relay 381 is energized in response to the operation of the line testrelay R4l0, the heat energy developed by this element causes the bimetallic strip 388 to be deflected to the right. After a predetermined time interval, the free end of this strip is moved sufliciently to bring the contacts 389' into engagement, thereby to complete an obvious circuit for energizing the line relay R330. This relay, upon operating, completes, at RA33I, an obvious circuit for energizing the slow-acting hold relay R320. The bold relay, upon operating, opens, at RA322, a point in the above-traced path for impressing waiting tone voltage across the link line conductors C398 and C300, thereby to terminate the signal being received by the calling subscriber. At RA32I, the relay R320 cornpletes an obvious circuit for energizing the control relay R410, which latter relay, in turn, operates to complete, at RA415, an obvious circuit for energizing the line switching and control re- At RA414, the relay R410, upon operating, prepares a point in the circuit, traced hereinafter, for energizing the slow-to-release relay R455 in parallel with the connector switch operating magnet 540. At RA412, the relay R410 completes a multiple holding circuit for the relay R350, this holding circuit extending from ground at RA412 by way of C39l and the winding of R350 to battery. At RA412, the relay R410 also completes a multiple holding circuit for the line test relay R4l0, this circuit extending by way of the grounded conductor C39l, RA35l, RA352, C300, RAMZQRA4I5, and the lower winding of R410 to battery. At RA41l, the relay R410 prepares a holding circuit for the lock-out relay R040, which holding circuit is completed in response to the subsequent operation of the relay R440 and extends from ground at RAM! by way of RA4H, C482 and the winding of R540 to battery. At RAM! and its associated resting con tact, the relay R440, upon operating, opens a point in the initially completed holding circuit for the relay R410 and a point in the original holding circuit for the relay R350. At RA442, the relay R440 opens a point in the above-traced circuit for energizing the upper winding of the tone relay R340 in parallel with the heating element 388 of the thermal relay 381, thereby to arrest the operation of the tone relay and to denenergize the heating element 308. At RA444, the relay R440 completes a holding circuit for itself, this holding circuit extending from ground This relay now restores to open, at RA33| and ing of R455 to battery and the other branch extending by way of RA434 and C408 and the winding of the magnet 540 to battery. When energized over this circuit, the relay R455 operates to prepare, at RA456, an operating circuit, traced hereinafter, for the relay R400, and to open, at RA458, a point in the operating circuit for the relay R430. Shortly following the completion of the above-traced circuit for energizing the magnet 540, the hold relay R320 restores to open, at RA32I, the operating circuit for the control relay R470, which latter relay, in turn, restores to open, at RA475, the operating circuitfor the control relay R440. At RA472, the relay R470 opens the above-traced alternative holding circuits for the two relays R350 and R iie, causing both of these relays to restore. At RA4'H and its associated working contact, the relay R470, upon restoring, opens a point in the above-traced holding circuit for the lock out relay R540, causing this relay to restore. At RAM! and its associated resting contact, the relay R470 completes a circuit for energizing the pendulum relay R480, this circuit extending from ground at RAM! by way of RA47I and the winding of R480 to battery. When the relay R480 is energized over this circuit, vibratory movement of the weighted armature RA48I is initiated,

thereby intermittently to complete a circuit including the conductor C395 for energizing the relay R350. Due to its slow-to-operate characteristic, the relay R3l0 does not operate when intermittently energized over this circuit. At RA474, the relay R470, upon restoring, interrupts the circuit, traced above, for energizing the magnet 540 in parallel with the relay R455, causing the last-mentioned relay to restore. When the magnet 54-0 is deenergized, it operates to step the wipers of the connector switch 550 one step from the home position and to close the ofinormal springs 542, thereby to complete a circuit for energizing the relay R430, which circuit may be traced as extending from ground by way of the springs 542, C490, RA458 and the winding of R430 to battery. Upon operating, the relay R430 completes, at RA435, an obvious holding circuit for itself and prepares, at RA433, an alternative circuit for repeatedly energizing the magnet 540 to return the wipers of the connector switch 550 to normal. After an interval, the vibration of the weighted armature RA48| ceases and this armature settles into resting engagement with its associated working contact to hold the operating circuit for the relay R3l0 completed. The relay R3I0 now operates to interrupt, at RA3l l, the above-traced holding circuit for the relay R440. UpOn restoring, the relay R440 opens, at RA444, a further point in its holding circuit and completes, at RA443 the above-mentioned alternative circuit for energizing the magnet 540. This circuit extends from ground by way of the springs 542, C400, RA443, RA433, 0488, the armature 547 and the winding of the magnet 540 to battery. Due to the circuit interrupting action of the springs associated with the armature 541, the magnet 540 operates, buzzer fashion, to drive the wipers of the switch 550 to their respective home or eleventh positions, at which time the off-normal springs 542 are opened. When these springs are opened, the holding circuit for the relay R430 is interrupted and a point is opened in the circuit, just traced, for energizing the magnet 540. Following the restoration of the relay R430, the control apparatus of the link 76 is fully restored to normal.

When the lockout relay R040 restores in the manner explained above, it functions to disconnect negative battery potential from the conductors C787 and C604 of the trunk lines I4 and 77, respectively. When negative battery potential is removed from the conductor C767, the line relay R740, embodied in the link 2|, is deenergized and restores to open, at RA74I, the operating circuit for the hold relay R735, thereby to cause the sequential restoration of the hold relay, the relay R755, and the control relay R7l0. Before the hold relay R735 falls back, a circuit is momentarily completed for energizing the relay R830 in parallel with the connector switch operating magnet 8 I 8, this circuit extending from ground by way of RA74I, RA738, C849 and through the respective windings of the magnet B78 and the relay R830 to battery. When energized over this circuit, the relay R830 operates, but without efiect at this time. Shortly there after and when the hold relay R735 restores, the circuit, just traced, is interrupted at RA738, causing the relay R830 to restore and the magnet 8l8, in conjunction with its ratchet and pawl mechanasm to step the wipers of the switch 850 to their respective first oil-normal positions. When this occurs, the off-normal springs 827 are moved into engagement to complete an alternative circuit for energizing the magnet 8E8 in parallel with the relay R830, this circuit extending from ground at RA736 by way of 0847, the springs 827, the armature BIS and through the respective windings of the magnet 8l8 and the relay R830 to battery. The resultin reoperation of the relay R830 is without effect at this time. Due to the circuit interrupting action of the springs associated with the armature M9, the magnet 8l8 operates, buzzer fashion, to drive the wipers of the switch 850 over the contacts of their respective associated contact sets and back to their respective home positions, at which time the off-normal springs 827 are opened. When these springs are disengaged, a point is opened in the alternative operative or release circuit for the magnet 8|8. Following the release operation on the part of the connector switch 850, the control apparatus of the finder-connector link 2| is fully restored to normal and this link is conditioned for further use.

If the call'as routed to the operators position 15 is answered before the thermal relay 387 operates, in the manner just explained, to initiate the release of the switching apparatus, operation of the relay 387 is arrested and the switching apparatus is maintained operated. To answer the call, the operator attending the position l5 inserts the plug terminating her cord circuit in the jack 369 and operates the calling key 380 to its off-normal position. When this key is operated to its off-normal position, the springs 376 and 3'57 are disengaged to open a further point in the above-traced circuit for energizing the drop 375, the drop 375 is restored to normal, and a simplex circuit is completed for energizing the line relay R330. One branch of this simplex circuit may be traced as extending from ground through the winding of R330 and by way of the winding 362, RA359, C368, the winding 374, the switch springs 377 and 378, and the pulsing springs 383 to battery. The other branch of the indicated simplex circuit extends by way of the winding of R330, the winding 36L RA358, C367, the winding 373, the switch springs 379 and 38l,

and the pulsing springs 383 to battery. When energized over this circuit, the line relay R330 operates to cause the sequential operation of the hold relay R323 and the two control relays R410 and RAM in the order named and in the manner explained above. When the two relays R410 and R540 operate, the previously traced holding circuit for the lockout relay R 38 is completed at the armatures RAM and RAE'H. At RAMZ, the relay Rd'lfl completes the above-traced alternative holding circuits for the relays R358 and RAPE. The relay R441 upon operating, completes its holding circuit and opens, at RAM'Z, a point in the above-traced circuit for energizing the heating element 388 of the thermal relay 387 in parallel with the upper winding of the tone relay RS ili, thereby to prevent further deflection of the bimetallic strip 389 and to arrest the operation of the tone relay R330. At RAM! and its associated resting contact, the relay R440 opens a point in the initially completed holding circuit for the relay R NG. The last-mentioned relay is, however, held operated over its alternative holding circuit as traced above. At RA443, the relay R549 prepares a circuit, traced hereinafter, for energizing the transfer relay R MS. At RAMS and RAMS, the relay HMO prepares a link connection between the calling line l8 and the called line to be selected. Following the operation of the four relays R335), R326, R410 and R448, the control apparatus of the link it is conditioned to respond to impulses transmitted thereto over the trunk line l3 from the operators position l5.

From the foregoing description it will be apparent that the calling subscriber at the substation T1 may initiate a call which is forwarded to the operators position 15 by operating the hand generator 693 and without removing the receiver of the telephone instrument provided at the calling substation from its hook. If the call is initiated in this manner, the operator, upon answering the call and challenging the established connection, receives no response from the calling subscriber. If the calling subscriber fails to answer when the operator challenges the connection, the operator may recall the calling subscriber by operating the ringing key conventionally provided in her cord circuit, thereby to cause ringing current to be projected over the line conductors C385 and C385, through the repeating transformer 3W, over the trunk line 13, through the repeating transformer 360, over the link line conductors C398, C399, C595 and CH6, and out over the calling line 8 to energize the signal device provided at the calling substation T1. A portion of this current is by-passed through the winding of the alternating current relay R450, which relay operates to open, at RA452, a point in the above-traced path for short-circuiting the lower winding of the line relay R1680. Another portion of the ringing current is conducted through the upper winding of the line relay R680, causing this relay to operate and complete, at RASBQ, the previously described circuit for energizing its lower winding. When its lower winding is energized, the relay R680 fully operates to disconnect, at BABES, its upper winding from across the conductors C563 and C561 of the calling line 18. Thus, the impedance of this winding is removed from across the conductors of the calling line 18 and the major portion of the ringing current is conducted over the line to energize the signal device at the calling substation. At the end of the ringing operation and when the operator restores her ringing key to relay R680.

disconnect the ringing current source from the line conductors C385 and C386. the alternating current relay R450 is deenergized and restores to recomplete, at RAQM, the previously traced path for short-circuiting the lower winding of the line As a result, this line relay again restores to connect its upper winding across the line conductors of the calling line l8.

When the calling subscriber at the substation T1 removes his receiver from its hook in response to the calling operation just described, the desired conversational circuit is fully completed between the calling substation T1 and the telephone set being used by the operator at the position l5. In this regard it is pointed out that transmission current is supplied to the loop extending between the calling substation T1 and the repeater 3% from the local battery conventionally provided at the substation T1. Transmission current for the loop extending from the operators telephone set to the repeater 3TH] is derived from the exchange battery provided in the main exchange d. Following the completion of the talking connection between the calling substation T1 and the operators telephone set in the manner just described, the operator may converse with the calling subscriber and ascertain the directory number of the desired substation or the name of the desired party.

If the call is to be forwarded to a substation associated with a line terminating at the main exchange 9, the operator may cause the desired connection to be set up in the manner conventionally employed in manual exchange practice.

Routing the call to a subscribers Zine terminating at the tandem exchange If the substation desired by the calling subscriber is associated with a subscribers line terminating at the tandem exchange it, the operator attending the position l5 operates the calling device 382 to dial the directory number of the called substation. For example, if the substation T2 is the desired substation, the operator dials a single digit of four impulses, thereby to cause the wipers of the connector switch 550 to be moved into engagement with the contacts terminating the conductors of the line 59. More particularly, when the calling device 382 is operated, the above-described simplex operating circuit for the line relay Rtt is interrupted a number of times at the pulsing springs 383 determined by the number of the dialed digit. Each time this circuit is opened, the line relay R336} restores to open, at RAtiil and its associated working contact, the operating circuit for the hold relay Rt''ll and to complete, at RA33i and its associated resting contact, the previously traced circuit for energizing the relay R455 in parallel with the connector switch operating magnet Mil. The relay BASE operates at the beginning of the digit and, due to its slow-to-release characteristic, remains operated until shortly after the digit is ended. Since the hold relay new is also of the slow-acting type, this relay likewise remains operated throughout each pulsing period. When the relay R655 operates, it prepares, at RA SEG, the previously traced circuit for energizing the transfer relay RAM and opens, at RA45l, a point in the path traced hereinafter for short-circuiting the holding winding of the combined line, cut-oil and call storing relay associated with the line to be selected. At RA EEB, the relay R555 opens a point in the above-traced circuit for energizing the control relay R430. Each time 7 v the operating magnet 5&0 of the connector switch 55E] is energized and deenergized, the wipers of this switch are operated one step so that, at the conclusion of the digit, these wipers are left standing in engagement With the contacts terminating the called line. In the present assumed case, wherein the directory number designating the called line l9 comprises: four impulses, the magnet 54% is energized and deenergized four times so that, at the conclusion of the digit, the wipers 55! to 55%, inclusive, engage their respective associated fourth contacts. When these wipers are moved to their respective first 01T- normal positions, the off-normal springs 5&2 are closed to prepare the previously traced circuit for energizing the relay Rest).

At the end of the digit, the above-traced simplex circuit including the two conductors of the trunk line it is recompleted and the line relay R338 remains in its operated position to hold open the above-traced circuit for energizing the magnet 5 16 and the relay R455 in parallel. Upon restoring, the relay R455 completes, at RA458, the above-traced circuit for energizing the relay R539. At RA456, the relay R455 opens the prepared operating circuit for the relay R460 and, at Purl-?, prepares the above-mentioned path for short-circuiting the holding winding of the line relay associated with the called line l9. The relay R439, upon operating, completes, at RA ZSE'), its previously traced holding circuit and prepares, at RA 'iBS, a point in the previously traced alternative circuit for energizing the magnet 566 during the release of the connector switch 558. At RA E32, the relay R430 prepares a circuit, traced hereinafter, for energizing the line switching relay R426. At RA43l, the relay R430 prepares the operating circuit for the relay R460. Finally, at "EL i435 and RA lS'l, the relay R436 completes a link connection between the calling line 58 and the called line I9.

Following the dialing operation, the operator supervising the call operates her ringing key to cause ringing current to again be projected over the trunk line it and through the repeater 360. From this point on, the ringing current divides between the calling and called lines, a portion of this current being projected through the operated armatures RA lHi and RAM! of the relay Edit and the wipers em and 502 of the finder switch 508 out over the calling line l8, and another portion of the current being projected through the armatures RAMS, RAMS, RA436, RA lSl, RA SZZ and RAME and the wipers 55! and 552 of the connector switch 550 out over the conductors of the called line l9. Another portion of the current is by-passed through the winding of the alternating current relay R 550, which relay operates to open, at RAMS! and RAdSZ, respectively, points in the above-described paths for short-circuiting the holding windings of the line relays respectively associated with the lines l9 and I S. A part of the ringing current conducted to the line it is lay-passed through the upper winding of the line relay R689 with the result that this relay operates to complete the circuit for energizing its lower winding in series and then assumes its fully operated position to disconnect its upper winding from across the conductors of the line I8. In a similar manner, the line relay associated with the line l9 operates in response to the operation of the alternating current relay R459 to disconnect its operating winding from across the conductors of the called line H9. The ringing current projected over the calling and called lines l8 and I9 serves to energize the ringers or signal devices respectively provided at the calling and called substations T1 and T2. In this connection, it is pointed out that, if the line I 9 is of the multiparty type, such that a number of substations are connected thereto, the operator actuatesher ringing key in accordance with the code designating the desired substation T2. Each time this key is restored to disconnect ringing current from the trunk line I3, the relay R lfiil restores to recomplete, at RAGE I the above-traced path for shortcircuiting the lower winding of the line relay R689 associated with the calling line 18. Also, when the relay R450 restores it completes the above-mentioned path for short-circuiting the holding winding of the line relay associated with the called line l9, this path extending from ground at RA457 by way of RA lfii, 0485, the wiper 554, G594 and the holding winding of the indicated line relay to ground. Conversely, each time the ringing key is operated to project ringing current over the trunk line E3, the relay R 350 reoperates to open the above-described shortcircuiting paths, thereby to permit the line relays respectively associated with the calling and called lines fully to reoperate. At the end of the ringing operation, the alternating current relay R450 is deenergized and remains in its restored position. With this relay in its restored position, the holding winding of the line relay R680 is short-circuited and the corresponding winding of the line relay associated with the called line as is also short-circuited. Accordingly, these relays are caused to restore.

The desired conversational circuit between the calling and called substations is completed following the ringing operation and when the calling party removes the receiver of his telephone instrument from its supporting hook and the called party answers the call. It will be noted that the talking circuit thus established includes the finder switch wipers 50! and 502, the link line conductors C495 and 0496, the operated armature springs of the three relays R m], RAM and R438, the restored armature springs of the relay R429, the link line conductors C493 and C494, and the wipers 55| and 552 of the connector switch 550. Transmission current is supplied to the talking circuit from the local batteries conventionally provided at each of the two substations T1 and T2. Obviously, the operator attending the position l5 may continuously monitor the connection if she so desires. In any event, the calling key 380 is retained in its operated off-normal position until the connection is ready to be released. The operator is expected to monitor the connection from time to time, for the purpose of ascertaining when the conversation is terminated in order that she may initiate the release of the apparatus promptlv following the end of the conversation.

Routing the call to a subscribers line terminating at a subezcchange As indicated previously, calls initiated on lines terminating at the tandem exchange II] may be routed, under the control of the operator attending the position l5, to any desired line terminating at either of the two subexchanges II and i2. In this case, the operator, upon answering the call and ascertaining the substation desired by the calling subscriber, dials the two digits of the directory number designating the desired line, the impulses of the first digit being utilized to cause the connector switch 550 to position its wipers on the contacts terminating the trunk line extending to the particular subexchange terminating the desired line, and the impulses of the second digit being routed through the control apparatus of the link it to the control apparatus of the link provided in the selected exchange tocause the connector switch of the selected exchange to select the desired line. For example, if the call initiated at the substation T1 and routed to the operators position H5 in the main exchange 9 is intended for the substation T4 associated with the line 22 terminating at the subexchange l l, the operator dials the two digits of the directory number designating the line 22. In this assumed case, the first digit dialed by the operator comprises a single impulse so that, at the conclusion thereof, the wipers of the connector switch 556 are positioned in engagement with their respective associated first contacts. Shortly following the end of this digit and when the slow-to-release relay R455 restores, in the manner explained above, it completes, at RA458, the previously traced operating circuit for the relay R 333, causing the last-mentioned relay to operate to perform the line switching and control functions described previously. On this type of call, namely, a trunk call, the relay RASQ also completes a circuit for energizing the line switching and control relay R625 in series with the line switching relay REM! embodied in the line circuit associated with the selected trunk line M. This circuit may be traced as extending from ground by way of the winding of R426, RA lSZ, R0469,

RA458, C687, the wiper 553 and its'associated first contact, (359i in the cable 568, and the winding of RBW to battery. Both of the relays R420 and RSH) operate, when energized over this circuit. The relay R420, upon operating, prepares, at its four armatures RA l2l, RA SZZ, RA424 and RA425 a simplex pulsing circuit which includes the two conductors of the trunk line It and extends through the winding of the line relay R746 provided in the link 25. This pulsing circuit is completed at the armatures- RASIZ, RAG l3, RASIE and RASIB when the relay R55!) operates. At RABIES and RCEM, the relay R650 opens the original energizing circuit for the line relay R'l lil following the completion of the simplex pulsing circuit just mentioned. At RASH and RAMS, the relay RSIG disconnects the conductors of the trunk line M from the line conductors C565 and C55! extending to the contacts of the finder switch 58k]. The above-mentioned simplex pulsing circuit, which is completed in response to the operation of the two relays R420 and R6), may be traced as extending from battery by way of the resistor 333 and RA332 to C39! where it divides, one branch extending by way of RAM! RAQZZ, C493, the wiper 552, G585, RAMZ, RAMS, C167, RAIE l, the winding 152 and the winding of the line relay R740 to ground, and the other branch extending by way of RA424, RA425, 048 3, the wiper 55!, 058i, RAME, RAMs, C166, RATES, the winding and the winding of R'MU to ground. Following the completion of this circuit, the control apparatus of the two links 16 and M is conditioned to respond to the impulses of the second digit designating the particular desired line terminating at the subexchange ll. At the beginning of the first impulse of the second digit, the operating circuit for the relay R55 is again completed, it being observed that, due to the energized condition of the relay R439, the operating circuit for the connector switch magnet 540 is now open at RA434. Upon operating, the relay R455 completes, at RA456, the previously mentioned circuit for energizing the digit transfer relay R460, this circuit extending from ground at RAfilil by way of RA456, RAMiB and the winding of R560 to battery. The relay R E-Ell, upon operating, completes a path for short-circuiting the winding of the relay R465, this path extending from ground by way of the off-normal springs 5&2, C 390, RAM3, RAMH, the winding of R465, RA466, RA456, and RAM! to ground. Due to its slow-to-release characteristic, the relay R 555 remains operated throughout the second series of impulses to maintain this short-circuiting path completed. During each impulse of the second digit, the line relay R330 alternately restores and reoperates, thereby to open and complete, at RA332, a point in the previously traced simplex pulsing circuit which extends through the winding of the line relay Rl lt. Thus, the impulses of the second digit are repeated to the line relay R'Mll of the link 24 through the operation of the control apparatus embodied in the link 95.

The line relay R148 follows the pulses and causes the connector switch 850 to position its wipers on the contacts terminating the conductors of the desired called line. More particularly, at the beginning of the first impulse, when the line relay R'Mfl restores, it completes, at RAME, the previously traced circuit for energizing the slow-to-release relay Riiliil in parallel with the connector switch operating magnet M8. The relay R839 operates, when it is first energized and, due to its slow-to-release characteristic, remains operated throughout the pulsing period. At RASM, the relay R830, upon operating, opens a point in the path, traced hereinafter, for short-circuiting the holding winding of the line relay R'lfifi associated with the called line 22. At RlA832, the relay R836 opens a point in the connection between the repeating transformer E50 and the line wiper 852 of the connector switch 8513, thereby to prevent interference with conversations ensuing on subscribers lines occupied with reverting calls. In the present case, the conductors of the called line are terminated at the respective first contacts of the connector switch contact bank and, accordingly, the second digit dialed at the operators position IE will necessarily comprise a single impulse so that, at the end of the digit, the Wipers of the switch 859 are left standing in engagement with their respective associated first contacts. When these wipers are moved to their respective first oiT-normal positions, the ofi-normal springs 821 are closed to prepare the previously traced circuit for energizing the operating magnet 818 during the release of the connector switch. Shortly following the end of the second digit and with the line relay R'i lfi in its operated position, the slow-torelease relay R836 restores to connect, at RABSZ, the line wiper 8512 to the link line conductor C863 and to prepare, at RA83i, the above-mentioned path for short-circuiting the holding winding of the line relay R700.

At the end of the second digit and with the line relay R330 of the link l6 in its operated position, the operating circuit for the slo-w-to-release relay R455 is held open at the armature RASSI. As a result, the relay R55 restores shortly following the end of the second digit to open, at Bi -A56, a point in the above-traced path short-circuiting the winding of the relay R485. The winding of the last-mentioned relay is now energized in series with thewinding of the relay R460 over a circuit which extends from ground by way of the oiT-normal springs 542, C499, RA443, RA46| and the series connected windings of the relays R465 and R466 to battery. The relay R460 remains in its operated position and the relay R4fi5 operates when the above-traced short-circuiting path is interrupted and the series circuit, just traced, is established. Upon operating, the relay R465 opens, at RAMS, a further point in the operating circuit for the relay R460 as well as a further point in the abovetraced path for short-circuiting its own winding. At RA461 and RA468, the relay R 365 completes an alternative circuit for energizing the switching relay Rlilfl, this alternative circuit extending from ground at RA413 by way of RAfilBl', RA liia, C437, the wiper 553, C59l and the winding of R6") to battery. Thereafter, the relay RG35 opens, at RA458 and RC lES, a point in the abovetraced circuit for energizing the relays R629 and REID in series. The relay R420 is now deenergized and restores to complete, at RA422 and RA425 and their respective associated contacts R0423 and R0426, an alternative simplex circuit for maintaining the line relay R'i lu of the link 2! energized. One branch of this alternative simplex circuit may be traced as extending from battery by way of the winding of the impedance element 365, the winding 363, C398, RA-tlit, RAAlEB'i, R0525, RAMS, Catt, the wiper i, C58l, RASlfi, RAElt, CW6, RA'itii, the winding 15! and the winding of the relay RHil'i to ground. The other branch of this circuit extends from battery through the winding of the impedance element 365 and by way of the winding 3%, C389, RAMS, RA436, RC423, RAtZiZ, C493, the wiper 552, C585, RABIZ, RAMS, C'l't'i, RATM, the winding 152 and the winding of R148 to battery. After the completion of this simplex circuit the original simplex circuit extending by way of the resistor 333 is interrupted at the armatures RAdZl, RA 322, RA424 and RA425 during the restoration of the relay R42il. Following the restoration of the relay R423 in the manner just described, the desired connection is fully completed between the calling and called lines it! and 22 respectively, and also between each of these two lines and the operators position H5 in the main exchange 9. To signal the calling and called subscribers, the operator supervising the call at the operators position i5 actuates her ringing key to cause ringing current to be projected over the established connection and the calling and called lines to energize the signal devices respectively provided at the calling and called substations. Here again, if the called substation is associated with a line of the multiparty type, coded ringing may be utilized to signal the desired substation. Each time the ringing current source is connected across the line conductors C385 and C386, ringing current is projected over the trunk line l3 and through the repeater 360 to the link line C398, C399. A portion of this current is transmitted back over the calling line to energize the signal device provided at the calling substation, thereby to signal the calling subscriber that the called substation is being rung. In addition, the alternating current relay R458 is caused to operate at the beginning of each ringing period and to restore at the end of each ringing period to perform the control functions previously described with reference to the call routed to the substation T2. During each ringing interval, a further portion of the ringing current is transmitted over the trunk line H, through the repeater 150, over the link line conductors C863 and (38%, and out over the called line 22 to energize the signal device provided at the substation T4. A part of this ringing current is shunted through the winding of the alternating current relay R136, causing this relay to operate and open, at RA'l3l, a point in the above-mentioned path for short-circuiting the holding winding of the line relay R100. During the initial part of each ringing period a part of the ringing current which is conducted over the line is shunted through the upper winding of the line relay R700, causing this relay to operate to complete at RA'HJZ, a circuit including the resistor 35 for energizing its lower winding. Thus, during each ringing interval, the relay R70!) is fully operated so that its upper winding is disconnected at RA'lEll from across the conductors of the line 22. Accordingly, this winding is prevented from shunting the ringing current away from the signal device provided at the called substation T4, At the end of each ringing interval, the alternating current relay R130 is deenergized and restores to complete, at RA13I the above-mentioned path for short-circuiting the lower winding of the relay R700, this shortcircuiting path extending from ground at RAl'3l by way of CfidhRABSH, the wiper 853, C844, the lower winding of R100 and RA'I02 to ground. As a result, the relay R'lflll restores to reconnect, at RA'iili, its upper winding across the conductors of the line 22. The desired conversational circult between the calling and called substations is completed following the ringing operation and when the calling party removes the receiver of his telephone instrument from its supporting hook and the call is answered at the called substation T4. In this regard, it is pointed out that transmission current is supplied to the loop extending between the called substation T4 and the repeater 513 from the local battery conventionally provided at the indicated substation. Transmission current is similarly supplied to the loop extending between the calling substation T1 and the repeater 758 from the local battery provided at the substation T1. Here again, the operator attending the ope-rators position l5 in the central exchange 9 may continuously monitor the connection if she so desires. Alternatively, she may monitor the connection at intervals to determine when the connection is ready to be released. In any case, the calling key 380 is held in its off-normal position to hold the switch train operated until the operator ascertains that the connection is no longer desired.

Reverting call on a subscribers Zine extending to the tandem exchange If the call, as forwarded to the operators position it from the substation T1, is intended for another substation associated with the calling line is, the only operation performed by the operator is that of actuating her ringing key in accordance with the coded ring designating the desired substation, thereby to energize the signaling devices individually provided at the substations associated with this line. The coded character of the ringing indicates to the called subscriber that his substation is being rung and to the calling subscriber that the ringing operation is in progress. After the ringing operation is terminated and the calling and called subscribers operate their receivers to connect the telephone instruments, respectively provided at the calling and called substations to the line 18. the desired conversational circuit is fully completed. On this type of call, only the line extending between the two substations is utilized in the connection. Accordingly, the operator attending the position I5 may release the operated link It immediately the ringing operation is completed, thereby to render the automatic switching apparatus provided in the three exchanges I9, I! and 92 available for further use. In this regard, it will be noted that no provision is made for guarding the line 18 against seizure while the conversation being held thereover is in progerss. No interference with the conversation will result, however, if the operator in the exchange 9 monitors each established connection after completing a dialing operation and before starting the ringing operation. On a call of this character, the calling and called subscribers are not expected to ring off at the end of the conversation since operation of either of the two generators respectively provided at the calling and called substations would result in seizure of the link it in the manner previously explained.

It will be apparent that a call between two substations connected to the same subscribers line may be completed without the assistance of the operator attending the operators position IS in the main exchange 9. For example, if the calling subscriber at the substation T1 desires a connection with a second substation connected to the line 18. the desired substation may be signaled directly by operating the hand-generator 693 in accordance with the coded ring designating the desired substation. In such case, however, the call is forwarded to the operators position 55 in the manner explained previously, assuming that the automatic switching apparatus provided in the three exchanges H], H and i2 is idle at the time the call is initiated. If the automatic switching apparatus is busy. the call is stored by the line relay R680 and is thereafter forwarded to the operato-rs position, in the manner subsequently explained, when the apparatus becomes idle. If a reverting call is completed in this manner, the operator, upon answering the call as forwarded to the operators position [5, may release the operated switching apparatus without performing any service whatever.

Release of the automatic switching apparatus When the conversation being held over a connection including two of the subscribers lines extending to the exchanges II], II and I2 is ended, one of the two subscribers utilizing the connection is expected to ring off in order to transmit a disconnect signal to the operator attending the position i5. For example, the calling subscriber at the substation T1 may operate the hand generator 693 for a short time interval to cause ringing current to be projected over the established connection to the operators position 15, thereby to energize the receiver of the operators telephone set so that the operator is signaled that the connection is ready to be released. When the hand generator 693 is operated for this purpose, the upper winding of the line relay R58 is energized by the ringing current, and the alternating current relay Refill bridging the connection is also energized and operates. In addition, a portion of the ringing current is conducted over the established connection and through the operating winding of the line relay associated with the called line. Thus, if the established connection extends between the lines l8 and I9, the operating winding of the line relay embodied in the line circuit 690 is energized by the ringing current and operates. When the relay R lfiii operates, it opens, at its armatures RAQS! and RAQEZ, points in the abovetraced paths for respectively short-circuiting the holding windings of the respective line relays associated with the calling and called lines. As a result, the respective holding windings of the two line relays individually associated with the calling and called lines are energized in series,

and the respective operating windings of these relays are disconnected from across the conductors of the respective associated lines.

If the established connection extends between the line it and the line 22 terminating at the subexchange H, a portion of the ringing current is projected over the established connection and divides between the alternating current relay RRQ, the upper or operating winding of the line relay RIM and the signal device provided at the called substation. As a result, the two relays Rlilil and R'i3i3 operate. The relay ares, upon operating, opens, at RA'iSl, a point in the path for short-circuiting the lower winding of the relay R198, permitting the lower winding of this relay to be energized so that the upper winding of the relay is disconnected from across the conductors of the line 2?; during the period when the generator 693 is being operated. When the operation of the generator @9 5 is arrested, the relay R'iml restores to short-circuit the holding windingof the line relay R6863 over the path traced previously, whereby this relay is caused to restore. Also, if the established connection includes the line Hi, the holding winding of the line relay embodied in the line circuit 598 is also short-circuited and restores. Alternatively, if the connection extends between the lines 58 and 22, the relay RISE! restores at the end of the ring-off period to complete, at RAHI, the previously traced path for shcrt-circuiting the lower winding of RIM), causing the last-mentioned relay to restore and reconnect its upper winding across the conductors of the line 22. The relay operations just described occur during and following the ring-oii period, irrespective of whether the calling or the called party operates his hand generator to transmit the r ng off or disconnect signal to the operator.

When the operator attending the operators position l5 receives the disconnect signal or, alternatively, challenges the established connection and finds that the connection is no longer being used, she may initiate the release of the operated switching apparatus by restoring the calling key 380 to its normal position. When this key is returned to its normal position, the switch springs 316 and 3' are closed to reconnect the winding of the drop 315 across the conductors C36! and C388 of the trunk line it. At the switch springs M1, 378, 379 and 358i, the abovetraced simplex operating circuit for the line re lay R330 is interrupted. The line relay R3353, upon restoring, opens, at RAZitl, the operating circuit for the hold relay R328, thereby to cause the sequential restoration of this relay and the relay Rd?!) in the order named. Upon restoring, the line relay R33!) completes, at RAtil l, the pre viously traced operating circuit for the slow-torelease relay R455. Shortly thereafter and when the relay Rdl'li restores, this circuit is interrupted at RA lld. The momentary reoperation of the relay R455 is without effect at this time. When the relay R410 restores, it completes, at RA HI,

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