US2249459A - Telephone system - Google Patents

Description

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INVENTOR ThomasF.' Crocker BY M ,MM A TORNEYS July 15, 1941. T. F. cRocKER TELEPHONE SYSTEM I Filed Deo. 29, 1939 6 Sheets-Sheet 4 July 15, 1941. T. F. cRocKER TELEPHONE SYSTEM Filed Deo. 29, 1959 6 Sheets-Sheet- 5 ATTORNEYS .6 She'ets-Sheet 6 l HNQ 86 INVENTOR Thom as F Crocker BY ,Ga/uw,

T. F. CROCKER TELEPHONE SYSTEM Filed Dec.

` July 15, 1941.

`Patented July 1941 TELEPHONE SYSTEM Thomas F. Crocker, Chicago, Ill., assignor to Associated Electric Laboratories, Inc., Ill., a corporation of Delaware Chicago,

Application mmm 29,1939, serial No. 311,551

'i3 Claims.

'Ihe present invention relates to telephone systems and more particularly to improved arrangements or distributing calls in telephone systems ot the semi-automatic type. v

In a conventional telephone system of the semi-automatic type the various manual telephone lines terminate in jacks at the A and B operator positions; and an automatic switch train provided with a distributing system is interposed between the A operator positions and theB operator positions. In a telephone system of this type, calls on the telephone lines are answered directly by the operators at the A operator positions and routed by the switch train under the control of the distributing system to the B operator positions to be completed.

Accordingly in telephone systems of this type, the trailic between the A operator positions and the B operator positions is governed by the distributing system. However, the traillc between the calling telephone lines and the various A operator positions is not governed but remains under the manual control of the operators at the A operator positions,.rendering the number of calls on the telephone lines answered by an operator at a given A operator position .and routed therefrom-to the B operator positions to be completed entirely within the discretion of the operator at the given A operator position.

Accordingly, it is an object of the present invention to provide in a telephone system oi the type described, improved apparatus for distributing calls on telephone lines Ito a number of A operator positions to be answered.

Another object of the invention is to provide in a telephone system including a number of A operator positions and a number of B operator positions, an improved arrangement for distributing and for storing incoming calls on telephone lines to the A operator positions to be answered and recalls on established connections from the B operator positions to the A operator positions to be answered.

Another object of the invention is to provide in a telephone system including a number of operator positions, an improved arrangement for distributing and for storing incoming calls' on telephone lines rtothe operator positions to be answered.

Another object of the invention is to provide in a telephonesystem including a number of operator positions provided with facilities for establishing connections between telephone lines, an improved arrangement for distributing and storing recalls on the established connections to the operator positions to be answered.

A further object of the invention is to provide in a telephone system including an operator position, improved switching apparatus for routing a call to the operator position to be answered and for extending the call from the operator position after it has been answered.

A further object of the invention is to provide vin a telephone system including an operator position, an improved switching link i'or establishing a connection between a calling line and a called line, which switching link is under the joint control of automatic apparatus and an operator at the operator position.

A further object of the invention is rto provide .in a telephone system including an operator position, an improved switching link selectively operative to establish a connection between a calling line and a called line including the operator position and to establish a direct connection between the calling line and the called line excluding the operator position, and apparatus under the control of an operator at the operator position for selectively controlling the operation of the switching link,

A further object of the invention is to provide in a telephone system including an operator position, improved apparatus at the operator position for supervising calling telephone lines in the system and established connections between telephone lines in the system and for performing service functions over the telephone lines in the system.

The' features of the present invention are illustrated as being incorporated in a telephone System comprising an exchange terminating a plurality of manual telephone lines and including a number of A operator positions, a number of B operator positions and a number of switching links. The switching links have access to the telephone lines, to the A operator positions and to the B operator positions; while the B operator positions have access to the telephone lines. The telephone lines comprise three classes which are rendered corresponding classes o! services consisting of flat rate service, call register service and prepay service.

In accordance with one feature of Ithe invention the telephone system comprises a plurality of subscriber lines, a plurality of A operator positions, a, B operator position and a storage unit. Also, the system comprises means ior routing a call upon any one of the subscriber lines to an idle one of the A operator positions to be answered when one of the A operator positions is idle, means for routing a call-upon the one Asubscriber line to the storage unit to be stored when all of the A operator positions are busy, means for routing a-call upon the one subscriber line stored in the storage unit to an idle one of the A operator positions to be answered when one,.of the A operator positions becomes idle, means for routing a call from the one A operator position to the B operator position, and means for establishing a connection between the one subscriber line and the B operator position independent of the one A operator position, thereby to route a call from the one subscriber line 'to the B operator position. Further, the system comprises means for routing a recall by the operator at the B operator position upon the established connection to an idle one of the A operator positions to be answered when one of the A operator positions is idle, means for routing a recall upon the established connection to the storage unit to be stored when all of the A operator positions are busy, and means for routing a recall upon the established connection stored in the storage unit to an idle one of the A operator positions to be anwsered when one of the A operator positions becomes idle.

In accordance with another feature of the invention the telephone system comprises a switching link including an answer switchhaving ac- 'cess to the telephone lines and a finder switch having access to the operator positions and to a number of storage settings provided in the storage unit, means controlled by the presence of a call on one of the telephone lines ior initiating substantially simultaneous operations oi the answer switch and the ilnder switch, means controlled when the answer switch nnds a calling one of the telephone lines for arrestingoperation of the answer switch, thereby to extend a call from the one telephone line to the link, means controlled when the finder switch nnds an idle one of the operator positions or a prepared one o! the storage settings of the storage unit for arresting operation of the nder switch, thereby to extend a call from the link to the one operator position to be answered or to store a call on the link in the one storage setting of the storage unit. Also, the system comprises means for preparing the storage settings of the storage unit in a predetermined order when all ot the operator positions are busy, and additional means controlled when one of the operator positions becomes idle for initiating reoperation of the finder switch.

In accordance with another object of the invention, in the telephone system, each switching link includes a first branch provided with an answer switch, a second branch provided with a call switch and a third branch provided with a finder switch having access to the operator positions and to the storage settings of the storage unit. Also, the system comprises a link distributor for assigning idle ones of the switching links for use in a predetermined order, a position distributor for assigning idle ones of the operator positions for use in a predetermined order; while each operator position includes telephone apparatus. The answer switches of assigned links are operative to seize calling telephone lines, thereby to extend the calls to the assigned links; while the finder switches of assigned links are operative to seize assigned ones of the operator positions, thereby to route the calls o n the assigned links to the assigned operator positions to routed to the operator positions to be answered in the event there are no assigned operator positions and routed to the storage unit to be stored in the event there are no assigned operator positions. Subsequently the calls on the assigned links stored in the storage settings of the storage unit are routed by the finder switches to assigned ones of the operator positions to be answered as the operator positions are assigned for use. Also, the system comprises calling means at each operator position operative to cause the call switches of the assigned links to seize called telephone lines, thereby to complete connections between the calling telephone lines and the called telephone lines including the rst, the second and the third branches of the assigned links and the telephone apparatus at the operator positions. and transfer means at each of the operator positions operative to cause the completion of connections between the calling telephone lines and the called telephone lines including the first and the second branches of the assigned links and excluding the third branches ofthe assigned links and the telephone apparatus at the operator positions.

In accordance with a iurther feature of the invention,l the telephone system comprises means under the joint control or any one of the calling telephone lines and an operator at any one of the operator positions to which a call on the corresponding one-of the assigned links is routed for releasing the connection prior to the operation of the calling means at the one operator position, and means 4under the joint control ot any one of the calling lines and the corresponding one oi the called lines for releasing the connection subsequent to the operation of the transfer means at the one of the operator positions to which the call on the corresponding one of the assigned links was routed.

In accordance with a further object of the invention, the telephone system comprises means controlled when a call on any one of the assigned links is routed to an idle one of the operator positions or to the storage unit for preventing the release of the one assigned link, and means under the control of an operator at any one of the operator positions to which the call on any one of the aislitgned links is routed for releasing the assigned l In accordance with a further feature of the invention the telephone system comprises a storage unit of limited storage capacity and a conservator o! unlimited conservation capacity. The switching links are operative to route calls to the operator positions to be answered when the operator positions are -idle, to route calls to the storage unit to be stored when all of the operator positions are busy, and to route calls to the conservator to be conserved when the storage capacity of the storage unit is exhausted. Also. the switching links are operative to route calls stored in the storage unit to .the operator positions to be answered when the operator positions become idle, and to route calls conserved in the conservator to the storage unit to be stored when the storage capacity of the storage unit is replenished.

In accordance with a further feature of the invention, in the telephone system, the iinder switch of each link is provided with a number of first settings individually correspondingtp the operator positions and a second number of settings individually corresponding to the storage settings of the storage unit. Also. lthe system comprises means controlled when all of the operator positions are busy'for causing the nder switches having calls thereon to be operated to different-ones of the second settings, thereby to store the calls on the finder switches in the different storage settings oi the storage unit, means controlled when there are no calls on the nder switches stored on the storage unit for causing the ilnder switches having calls thereon to be operated to diilerent ones of the first settings corresponding to idle ones of the operator positions, thereby to route the calls on the finder switches to the operator positions to be answered, and means controlled when there are calls on the finder switches stored in the storage settings of the storage unit for causing the nder switches to be reoperated from the diiIerent ones of the second settings to different ones of the ilrst settings corresponding to idle ones of the operator positions, thereby to route the calls stored in the different storage settings of the storage unit to idle ones of the operator positions to be answered. Further, the system comprises a storage distributor governed in accordance with the different ones of the second settings of the finder switches for controlling the order of reoperation oi' the finder switches, whereby the calls on the finder switches are routed to the operator positions to be answered in the same order that the calls on the finder switches are routed to the different storage settings of the storage unit to be stored.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional operating 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 Figure 1 illustrates the general arrangement of a telephone system including a local exchange and a distant exchange embodying the present invention; and Figs. 2 to 6, inclusive, taken together, illustrate the details of a system having incorporated therein the features oi.' the invention, as briefly outlined above.

DESCRIPTION OF THE APPARATUS INCOR- PORATED IN THE TELEPHONE SYSTEM Referring now more particularly to Fig. 1 of the drawings the -telephone system there illustrated comprises a local exchange 20, a distant exchange 30. and a plurality of one-way trunk lines, including the trunk line 410, extending therebetween. The local exchange 20 and the distant exchange 30 are of the manual type, each serving a number of groups of telephone sta.- tions to which different classes of service are rendered. For example, the local exchange 2l serves a group of subscriber substations,- includ.- ing the subscriber substation TI, which is rendered fiat rate service; a group of party subscriber substations, including the party sub-l scriber substations T2 and T3, which is rendered 225; the two-party line register circuit 240 is individually associated with the telephone line 210; and the prepay manual line circuit 280 is individually associated with the telephone line 285.

call register service; and a group of paystations,

Each of the subscriber substations and paystations in the local exchange 20 is provided with station equipment, including a telephone instrument and a ringer.

Also, the local exchange 20 comprises a number of A operator positions, including the first A operator position 500, a number oi B operator positions, including the rst B operator position 494, and a number of toll operator positions, including the toll operator position 499. Each A operator position has a trunk individuallyextending thereto, the trunk 520 individually extending to the first A operator position 500; each B operator position has a'group of trunks individually extending thereto, the trunk 490 being included in the groupv of trunks individually extending to the first B operator position 494; and each toll operator position has a group of trunks individually extending thereto, the trunk 495 being-included in the group of trunks individually extending to the toll operator position 499. Each trunk extending to each B operator position is provided with a trunk line circuit individual thereto, the trunk line circuit 480 being individual to the trunk 490extending to the first B operator position 494. Each trunk extending to each toll operator position is provided with a trunk line circuit individual thereto, the trunk line circuit 491 being individual to the trunk 495 extending to the toll operator position 499. Also each trunk line extending between the local exchange 20 and a B operator position 498 in the distant exchange 30 is provided with a trunk line circuit individual thereto, the trunk line circuit 412 being individual to the trunk line 410 extending between the local exchange 20 andthe -B operator position 498 in the distant exchange Further the local exchange 2U comprises a number of finder-selector links, including the finder-selector link illustrated, and a distributor 30| for assigning idle ones of the links to the use of the telephone stations. For example, the link illustrated includes a iinder switch 300 and a selector switch 400. Also a sequence switch is individually associated with each of the links, the sequence switch 380 being individually associated with the link illustrated. Finally the local exchange 20 comprises an A operator position distributor 830 for assigning idle ones of the A operator positions to receive incoming calls to the local exchange and a call storage unit 600.

Each of the iinder switches, such, for example, as the finder switch 300, constitutes an answer switch having access to each of the telephone lines in the local exchange; each of the selector switches. such, for example, as the selector switch 400, constitutes a call switch having access to each of the trunks extending to the B operator positions and to the toll operator positions and to each of the trunk lines extending to the distant exchange 30; and each of the sequence switches,

such, for example, as the sequence switch 390, constitutes a position and storage finder switch having access toeach of the trunks individually extending between the local exchange 20 and the distant exchange 30 is terminated at the B operator4 position 498 in the distant exchange 30.

Preferably, each of the iinder-selector links is identical to the link illustrated which comprises a finder switch 300 and a selector switch 400, as

previously noted. The finder switch 300, as best shown in Fig. 3, comprises a switching mechanism 310 o f the G-point Strowger type including a carriage provided with a rst wiper set, including the wipers 311, 312 and 313, a second Vwiper set, including the wipers 314, 315, 316 and 311, and a control' wiper 318. It is noted that the wipers 3| 1, 312 and 313 of the first wiper set and the wipers 314, 315, 316 and 311 of the second Wiper set are capable of both vertical and rotary movements; while the control wiper 318 is capable of vertical movement. Further the mechanism 310 comprises a circumferentially disposed main contact bank provided with two sections respectively associated with the first and second wiper sets and a vertical control contact bank associated with the control wiper 318. Accordingly, in the mechanism 310, the first and second wiper sets respectively have access to.flrst and second groups of one hundred lines each, respectively terminated by the first and second sections o the main contact bank. Also, the mechanism 310 is provided with a vertical magnet M365 for movlng the rst and second wiper sets thereof in the vertical direction, a rotary magnet M361 for moving the first and second wiper sets thereof in the rotary direction and a release magnet M369 for releasing the first and second wiper sets thereof and for causing these wiper sets to be returned to their normal positions. Finally the mechanism 310 has three sets of switch springs S310, S311 and S312 operatively associated therewith which are controlled in accordance with the movements of the first and second wiper sets thereof, in a manner more fully described subsequently.

Also, the nder switch 300 comprises a number of relays, including two switching relays R320 and R330, a start relay R340 and a cut-in relay R350 connected and arranged in a manner more fully described subsequently.

The selector switch 400, as best shown in Fig. 4, comprises a switching mechanism 410 of the i00- point Strowger type including a carriage provided with a Wiper set including the wipers 41 1, 412 and 413. It is noted that the wipers 411,1312 and 413 of the wiper set are capable of both vertical and rotary movements. Further the mechanism 410 comprises a circumferentially disposed main contact bank associated with the wiper set. Accordingly, the wiper set has access to a group of one hundred lines terminated by the main contact bank. Also the mechanism 410 is provided with a vertical magnet M414 for moving the wiper set thereof in the vertical direction, a rotary magnet M416 for moving the Wiper set thereof in the rotary direction and a release magnet M418 for releasing the wiper set thereof and for causing the wiper set to be returned to its normal position. Finally the mechanism l410 has a number of Y switch springs.S419, S420, S421 and S422 operatively associated therewith which are controlled in accordance with the movements oi the Wiper set thereof in a manner` more fully described subsequently.

Also the'selector switch 400 comprises a number of relays including a lockout relay R425, a battery supply relay R430, a control relay R440, a call back relay R445, an error relay R460, e. line relay R455, a hold relay R460, a transfer relay R465 and a switching relay R410 connected and arranged in a manner more fully described subsequently.

Preferably, eachof the sequence switches is identical to the sequence switch 380 individually access to each of the links in the local exchange 20 and is operative to assign an idle one of the links to the use of any one of the telephone stations in the local exchange. The details of the connection and arrangement of the distributorv 301 are not disclosed as they'form no part of the present invention. However, for reference purpose itis noted that the connection and arrangement of a distributor of the type of the distributor 301 is shown in the copending application of Edward S. Peterson, Serial No. 233,021. filed October 3, 1938. Also a marking network 305, shown in Fig. 3, is associated with the distributor 301 in order to initiate operation thereof when a call is initiated on one of the telephone lines extending to a telephone station in the local exchange 20.

Preferably, each of the fiat rate linecircuits is identical to the ilat rate line circuit 200 individually associated with the telephone line 225 extending to the subscriber substation T1, shown in Fig. 2, which comprises aline and cutoff relay R210 and a busy relay R220 connected and arranged in a manner more fully described subsequently. Further it is noted that a tone transformer 21B is commonly associated with each of the fiat rate line circuits.

Preferably, each of the two-party line register circuits is identical to the two-party line register circuit 240 individually associated with the telephone line 210 extending to the party subscriber substations T2 and T3, shown in Fig. 2, which comprises a line and cutoff' relay R260, a lockout relay R250, a control relay R245 and two registers respectively provided with register magnets M241 and M242, and connected and arranged in a manner more fully described subsequently. Also a signal lamp L243 is individually associated with the two-party line register circuit 240.

Preferably each of the prepay manual line circuits is identical to the prepay manual line circuit 280 individually associated with the telephone line 285 extending to the paystation T4, shown in Fig. 2. The prepay manual line circuit 280 comprises a line circuit of any known connection and arrangement; the details of the connection and arrangement of the line circuit 280 are not disclosed as they form no part of the present invention..

Preferably each of the trunk line circuits is identical to the trunk line circuit 400 individually associated with the trunk 490 extending to the ilrst B operator position 494, shown in Fig, 4, which comprises a line relay R400 and a busy relay R485 connected and arranged in a manner more fully described subsequently.

Preferably each of the B operator positions in the local exchange 20 lis identical to the rst B operator position 494, shown in Figs. 4 and 2. Theilrst B operator position 494 comprises conventional answering equipment, not shown: conventional calling equipment including a number of call jacksJ J20I, .7202 and .1203 'respectively terminating the telephone lines' 225, 210 and 205;

and a number of conventional cord circuits, not

shown.

Preferably each of the A operator positions is identical to the ilrst A operator position 500, shown in Figs. 5 and 6, which comprises a trunk circuit provided with a set of position keys including an error release key K550, a permanent lockout releasekey K555, a reverting call key K510, a split key K515, a coin collectkey K500, a coin return key K505, a first register key X595, a second register key K590, a transfer key K5" and a control key K560. Also the trunk circuit at the first A operator position 500 comprises a telephone instrument including a transmitter 500 and a receiver 501, a repeater 50|, an impedance element 1559, a key sender K520 and a number of relays including three tone relays R5|5, R520 and R525, a rear split relay R530, a front split lrelay R535, an impulse relayR540 and two signal relays R665 and R690. Also Vassociated with the rst A operator position 500 are a peg count meter provided with a register magnet M541 and three signal lamps including a fiat rate signal lamp 1.680, a message register signal lamp L08| and a prepay sign-al lamp L602. I'he key sender X520 ls oi' a well-known type; accordingly, the details oi the connection and arrangement thereof are not disclosed as they form no part of the present invention. i

The call storage unit 600, .shown in Fig. 6, comprises six marking relays iM to 0M, inclusive, a control relay R6|0 and a release relay R620, connected and arranged in a manner more fully described subsequently. Also six storage lamps L60| to 1.606, inclusive, are associated with the call storage unit 600 and commonly associated with each of the A operator positions.

The A operator position distributor 630, shown in Fig'. 6. comprises a number of hold relays R630, R640. R645, etc., respectively corresponding tothe A operator positions; a number of position relays R650, R660, R665, etc., respectively corresponding to the A operator positions; and a control relay R610 connected and arranged in a manner more` fully described subsequently.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system will be facilitated from a consideration of the detailed operation of the various pieces of apparatus incorporated therein incident to the completion and the handling of the various calls at the first A operator position 500, as will appear hereinafter.

GENERAL OPmaA'noN or' THE SYs'rEM Considering now the general operation ofthe system with reference to Fig. 1 of the drawings, it is noted that when a call is initiated at any one of the subscriber substations or at any one of the paystations in the `local exchange 20 the the distributor 30| operates at this time in orderl linecircuit individually associated withthe telephone line extending thereto is controlled, thereby to initiate operation of the distributor 30|. The distributor 30| is of the'preselective type and operates to select an idle one of the links when a previously selected link is assigned to the use of a calling telephone. station. Accordingly to assign a previously selected one of the links, such, for example, as the link illustrated, to the use of the calling telephone station; whereupon the finder switch 300 operates to seize the telephone line extending to the calling telephone station, and operation of the sequence switch 080 individually associated with the link illus-A trated is initiated. When the iinder switch 300 seizes the telephone line extending to the calling telephone station the distributor 30| is released and operates to preselect another idle link, as previously noted.

The A operator position distributor 630 preselects an idle one of the A operator positions for use, and when a preselected one of the A operator positions is taken for use the A operator position distributor 630 operates to preselect another idle one of the A operator positions for use. Upon operating the sequence switch 380 seizes the trunk extending to the previously selected A operator position, thereby to extend the call from the calling telephone station to the selected A operator position. The operator at the selected A operator position answers the call and then operates the key sender at her position, thereby to control the operation ofthe selector switch 400 in orderl to extend the call to its destination. In this connection it is noted that the selector switch 400 may be selectively controlled to extend the switch 400 is controlled in order to route the call to an idle B operator position in the local ex-f/ change 20. The operator at the idle B operator position in the local exchange 20 answers the call and then extends the call to the called telephone station in the local exchange 20, in the usual manner. In the `event the call is to be routed to a telephone station in the distant exchange 30 the selector switch 400 is controlled in order to route the callfto the B operator position 490 in the distant exchange 30. The operator at the B operator position 490 in the distant exchange 30 answers the call and then extends the call to the called telephone station in the distant exchange 30, inthe usual manner. In the event the call is tov be routed toll the selector switch 400 is controlled in order to route the call to an idle one of the toll operator positions in the local exchange 20. The operator at the idle toll operator position in the local exchange 20 answers the call and then routes the call toll in the usual manner.

After the call` has been routed from the idle A operator position in the local exchange 20 to an idle one of the B operator positions in the local exchange 20, to an idle one of the toll operator positions in the local exchange Z0 or to the B operator position 090 in the distant exchange 30 and the information concerning the extension of the call has been conveyed to the called operator,

the Operator at the idle A operator position re-dl leases the connection between her position and the nnder switch 300 and the selector switch 400, whereupon a direct connection is completed `between the finder switch 300 and the selector switch 400, excluding the A operator position.

It is noted that the called operator to which the call is routed by the selector switch 400 may recall the operator at an idle one of the A operator positions in the local exchange 20 by causing the sequence switch 380 individually associated with the link illustrated to seize the trunk extending to the idle A operator position under Ythe control of the A operator position distributor 630, in the manner previously explained.

In the event all of the A operator positions in thelocsl exchange 20 are busy when operation of the sequence switch 380 is initiated, the sequence switch 300 seizes the call storage unit 600. More particularly, the sequence switches individually associated with the links in the local exchange 2l seize the respective positions of the call storage unit 300 in a predetermined order, thereby t cause the calls and recalls to be stored in the call storage unit 600 in a predetermined order when all of the A operator positions in the local exchange 20 are busy. At this time, when a number of calls and recalls on a number oi.' the links are stored in the call storage unit 600 and one of the A operator positions in the local exchange 2l becomes idle the A operator position distributor 630 operates to assign the idle A operator position for use and causes the call storage unit 603 to initiate operation of the sequence switch corresponding to the first stored call or recall in the call storage unit 600. The sequence switch corresponding to the first stored call or recall in the call storage unit 600 then operates to find the assigned A operator position. The call storage unit 600 then operates to cause each of the remainder of the sequence switches to be advanced one position, thereby to advance by one position the calls and recalls stored in the cali storage unit- 300. Accordingly the call storage unit 630 operates to cause incoming calls and recalls to be stored in a predetermined order when all of the A operator positions in the local exchange 20 are busy; and causes the stored calls and recalls to be released to be answered at the A operator positions in the same predeterminedI order as the A operator positions in the local exchange 20 become idle. f

After a call from a ceiling telephone station has been extended from one of the A operator Flat rate subscriber substation call A call from a at rate subscriber substation, such, for example, as the subscriber substation Ti, is initiated by removing the receiver of the telephone instrument thereat from its switchhook. When the receiver of the telephone instrument at the subscriber substation Ti is removed from its switchhook, a bridge path is completed between the line conductors C226 and C221 of the telephone line 225 extending to the subscriber substation TI. When this bridge path is completed between the line conductor of the telephone line -225 a. circuit is completed for energizing in series the windings of the line and Cutci! relay R2 I 0. 'I'his circuit extends from ground by way of the lower winding ot R2 I 0, the contacts 2 i2, C221, the bridgepath between the line cnductors C221 and C226, C226, the contacts 2li and the upper and intermediate windings of R2 I 0 to battery. When energized over the abovetraced circuit the line and cutoiI relay R2|0 operatespartially, thereby to complete, at the contacts 2|4, a path for applying ground potential to the start conductor C230 and t0 complete, at

the contacts 2I3, an obvious connection between e the control conductors C223 and C220 of the telephone line 226. The path for applying ground potential to the start conductor C230 extends from ground by way oi' the contacts 22 I, 2|! and 2|4 to the start conductor C230. The application of ground potential to the start conductor C230 completes an obvious path for applying ground potential by way of the resistor 304 of the marking network 300 to the start conductor C300 extending to the distributor 30|, and completes an obvious path for applying direct ground potential to the first contacts in the vertical control contact banks of the ilnder switches. The application of ground potential to the start conductor C303 initiates operation ot the distributor 30| and the application of direct ground potential to the i'irst contacts in the vertical control contact banks," of the finder switches marks the telephone line 220 as terminating in the rst level of the main contact banks of the finder switches.

The distributor 30| is of the preselective type and operates to select another idle link as soon as the nnder switch of a previously selected link operates to iind a calling telephone line after it has been taken for use. Assuming that the distributor 30| has previously selected the link i1- lustrated to be taken for use at this time, the dis. tributor 30| operates to cause ground potential to be applied to the start conductor C302, thereby to complete an obvious circuit for energizing the winding of the start relay R340. The start relay R340 then operates to interrupt, at the contacts 343, a point in a multiple path for applying ground potential to the all-link-busy conductor C303/and to complete, at the contacts 342, an ob. vious path for applying ground potential to the control conductor C363 of the trunk 360. The previously mentioned path for applying ground potential to the all-link-busy conductor C300 in the nnder switch from ground by way of the contacts 343 and the set of switch springs S312 to the all-link-busy conductor C303. Also the start relay R340 completes, at the contacts` 343, obvious multiple circuits for energizing the lower windings of the switching relays R320 and R330, thereby to render each of these switching relays extremely fast to operate in the event the upper winding thereof is energized. Further the start relay R340 prepares, at the contacts 341. a circuit traced hereinai'ter for energizing the vertical magnet M365 and prepares, at the contacts hereinafter for energizing M361.

The distributor 30| then operates to cause ground potential to be applied to the vertical conductor C305, thereby to complete the previously mentioned circuit for energizing the vertical magnet M365, this circuit extending from the grounded vertical conductor C305 by way of the contacts 341 and M365 to battery. When energized over the above-traced circuit the vertical magnet M365 operates to drive the rst and second wiper sets of the mechanism 3I0 one step 346, a circuit traced the rotary magnet 300 extends, when completed,

` ductor C306.

`application of ground potential to the interrupter conductor C306 causes the distributor 30| to interrupt the application of ground potential to the vertical conductor C305; whereupon the vertical magnet M365 restores to interrupt, at the contacts 366, the previously mentioned path for applying ground potential to the interrupter con- Accordingly the vertical magnet M365 operates intermittently, thereby to drive the rst and second wiper sets of the mechanism 3|0 step by step in the vertical direction until the control wiper 3I8 engages a contact in the associated vertical contact bank having direct ground potential thereon; whereupon anobvious path is completed for applying ground potential to the test conductor C301 extending to the distributor 30|. In the present instance the nrst and second wiper sets of the mechanism 3I0 are driven only one step in the vertical direction;

whereupon the vertical control wiper 3 l0 engages the first contact in the associated vertical control contact bank having ground potential thereon. The application of ground potential to the test vconductor C301 causes the distributor 30| to operate, thereby to interrupt the application of ground potential to the vertical conductor C306 and to apply ground potential to the rotary conductor C304. The application oi' ground potential to the rotary conductor C304 completes the previously mentioned circuit for energizing the rotary magnet M361, this circuit extending from the grounded rotary conductor C304 by way of the contacts 346, 330 and 328 and M361 to battery. When energized over the above-traced circuit the rotary magnet M361 operates to drive the ilrst and second wiper sets of the mechanism 310 one step in the rotary direction and to complete, at the contacts 368, an obvious path for applying ground potential to the interrupter conductor C306. lThis application of ground potential to the interrupter conductor C306 causes the distributor 30i to remove the application of ground potential to the rotary conductor C304, whereupon the rotary magnet M361 restores to interrupt, at the contacts 368, the previously mentioned path for applying ground potential to the interrupter conductor C306. Accordingly the rotary magnet M361 operates intermittently, thereby to drive the ilrst and second wiper sets of the erates exceedingly fast, thereby to complete, at'

the contacts 326, a holding circuit for energizing the intermediate winding thereof, this circuit extending from the grounded control conductor C363 of the trunk 360 by way of the contacts 336 and 325 and the intermediate winding oi R320 to battery. Also, upon operating, the switching relay R320 interrupts, at the contacts 328, a point in the previously traced circuit for energizing the rotary magnet M361, thereby positively to arrest further operation of the mechanism 3,|0. Further the switching relay R320 interrupts, at the contacts 326, a point in a circuit traced hereinafter `for energizing the upper winding of the switching relay R330, thereby positively to prevent operation of the latter relay at this time. Also the switching relay R320 interrupts, at the contacts 32|, a point in a circuit traced hereinafter for energizing the release magnet M363 and completes, at the contacts 321, a connection between the rotary conductor C304 and the guard conductor C303, this connection extending from the rotary conductor C304 by way of the contacts 346, 330, 321 and 344 to the guard conductor C303. When the rotary conductor C304 is connected to the guard conductor C303 operation of the distributor 30| to control the iinder switch 300 is arrested, whereupon the distributor 30| operates automatically to select for use another idle one of the links.

Also it is noted that when the carriage of the mechanism 3I0 is driven one step in the vertical mechanism 3|0 step by step in the rotary di- Y rection until either the control Wiper 3|3 or the control wiper 3|1 of the respective rst and second wiper sets engages the control conductor of a calling telephone line having battery potential thereon. In the present example the telephone line 225 is included in the first section of the main contact bank of the mechanism 310.

Accordingly, when the control wiper 3|3 of the iirst wiperV set of the mechanism 3| 0 engages the contact of the contact set in the first section of the main contact bank of the mechanism 3 0 terminating the control conductor C228 of the telephone line 225, a circuit is completed for energizingthe upper winding of the switching relay R320. This circuit extends from ground by way of the contacts 22|, 2|5 and 2| 4, thestart conductor C230, the control wiper 3I8, the upper above-traced circuit the switching relay R320 opdirection the sets of switch springs S310, S31! and S312 are actuated. More particularly, the set of switch springs S310 is actuated into engagement, thereby to prepare a further point in the previously mentioned circuit for energizing the release magnet. M363; while the set of switch springs S312 is actuated into disengagement, thereby to interrupt a further point in the previously traced path for applying ground potential to the all-link-busy conductor C303. Finally the contactsl312 of the set of switch springs S31| are actuated into engagement, thereby to prepare a path traced hereinafter for applying ground potential to the guard conductor C303. Finally, upon operating theswitching relay R320 completes, at the contacts 322, 323 and 323, connections between the conductors of the-trunk 360 extending between the finder switch 300 and the selector switch 400 and the first wiper set of the mechanism 310. More particularly, a low resistance circuit is completed, at the contacts 320, for energizing the intermediate winding of the line and cutoff relay R210, this circuit extending Irom the grounded control conductor C363 of the trunk 360 by way of the contacts 336 and 324, the Wiper 3|3, the control conductor C223 of the telephone line 223, the contacts 2|3 and the intermediate Winding of R2|0 to battery. When the intermediate winding of the line and cutoff relay R210 is thus energized this relay operates completely, thereby to interrupt, at the contacts 2|5, the previously traced path for applying ground potential to the start conductor C230 extending to the marking network 305 in order to arrest operation of the distributor 30|. Further the line and cutoil relay R2 i0 interrupts, at the contacts 2| i and 2 l2, the previously traced circuit for energizing the windings thereof across the line conductors C226 and C221 of the tele-p phone line 225, thereby to clear the telephone line 225 of impedance elements. At this time ground potential appearing upon the control conductor C223 of the telephone line 225 is ap- S312, as previously noted. Also ground potential is applied to,the guard conductor C303 in the i finder switch 300, thereby to prevent the distributor 30| from preselecting the link illustrated at this time due to the busy condition of the finder switch 300. The path for applying ground potential in the nder switch 300 to the guard conductor C303 extends from ground by way of the contacts 312 of the set of switch springs S31| and the contacts 345 to the guard conductor C303, the start relay R340 being restored at this time. Further it is noted that the start relay R340 is of the slow-to-release type and restores shortly after the distributor 30| is released. Upon restoring the start relay R340 interrupts, at the contacts 342, the previously traced path for applying ground potential to the control conductor C363 of the trunk 360, ground potential being applied to the control conductor `C363 of the trunk 360 in the selector switch 400 at this time. Further the start relay R340 interrupts, at the contacts 343, the previously` mentioned multiple circuit for energizing the lower windings of the switching relays R320 and R330, the switching relay R320 being retained in its operated position at this time due to the completed holding circuit for energizing the intermediate winding thereof.

When the trunk 360 is connected to the telephone line 225 a loop circuit is completed for energizing in series the upper and lower windings of the error relay R450 and the upper and lower windings of the line relay R455 in the selector switch 400. This circuit extends from ground by way of the lower winding of R455, the lower winding of R450, the line conductor C362 of the trunk 360, the contacts 356, 334 and 323 and the wiper 3|2 to the line conductor C221 of the telephone line 225, and from battery by way of the upper winding of R455, the upper winding of R450, the line conductor C36| of the trunk 360, the contacts 353, 332 and 322 and the wiper 3|| to the line conductor C226 of the telephone line 225, the line conductors C226 and C221 of the telephone line 225 being connected together by way of a bridge path at the subscriber substation Tl. When the upper and lower windings of the error relay R450 are thus energized this relay remains in its restored position, this relay being of the differential type. On the other hand, when the upper and lower windings of the line relay R455 are thus energized this relay operates to complete, at the contacts 456, a circuit for energizing the winding of the hold relay R460, this circuit extending from ground by Way of the contacts 415 and 456 and the winding of R460 to battery. When thus energized the hold relay R460 operates to complete, at the contacts 462, an obvious multiple circuit for applying ground potentialto the control conductor C363 of the trunk 360, as previously noted. Also the hold relay R460 completes, at the contacts 463, an obvious circuit for energizing the lower winding of the switching relay R410, thereby to render the switching relay R410 exceedingly fast to operate when theupper winding thereof is energized. Further the hold relay R460 prepares, at the contacts 46|, a circuit traced hereinafter for energizing the upper winding of the switching relay R410 and prepares, at the contacts 464, a circuit traced hereinafter for energizing in multiple the lower winding of the transfer relay R465 and the vertical magnet M4I4.

When ground potential is applied to the control conductor C363 a circuitis completed for energizing the upper winding of the transfer relay R465, this circuit extending from the grounded control conductor C363 of the trunkv 360 by way of the contacts 421 and 454, the set of switch springs S420 and the upper winding of R465 to battery. Whenthus energized the transfer relay R465 operates to prepare, at the contacts 461, a further point in the previously mentioned multiple circuit for energizing the lower winding thereof and the vertical magnet M4|4 and to interrupt, at the contacts 469', a point in a circuit traced hereinafter for energizing the rotary magnet M4|6. Finally, upon operating the transfer relay R465 completes, at the contacts 466, an obvious path for applying ground potential to the control conductor C364 of the trunk 360. This application of ground potential to the control conductor C364 of the trunk 360 completes an obvious circuit for energizing the intermediate winding of the cutin relay R350, thereby to render the cutin relay R350 exceedingly fast to operate when the upper winding thereof is energized. Also the application of ground potential to the control conductor l C364 of the trunk 360 prepares a circuit traced hereinafter for energizing the upper winding of the cutin relay R350 and completes a circuit for energizing the rotary magnet M393 of the sequence switch 330. The circuit for energizing the rotary magnet M393 of the sequence switch 380 extends from the grounded-control conductor C364 of the trunk 360 by way of the contacts 350 and 394 and M393 to battery. When thus energized the rotary magnet M393 operates to condition the wipers noted of the sequence switch 380 to be driven one step in the clockwise direction and to interrupt, at the contacts 394, the previously traced circuit for energizing the rotary magnet M333; whereupon the rotary magnet M393 restores to drive the wipers noted of the sequence switch 380 one step in the clockwise direction and to recomplete, at the contacts 394, the previously traced circuit for energizing the rotary magnet M393. Accordingly the rotary magnet M393 operates intermittently, thereby to drive the wipers noted of the sequence switch 330 step by step in the clockwise direction until the cutin relay R350 is operated in a manner more fully described hereinafter to interrupt, at the contacts 350, the previously traced circuit for energizing the rotary magnet M393.

At this point it is noted that immediately the distributor 30| assigns the link illustrated to the use of the calling subscriber substation Ti, the operations of the finder switch 300 and the selector switch 400 previously described are initiated and that the operation of the selector switch 400 initiates operation of the sequence switch 380 individually associated with the link illustrated. Accordingly, operation of the sequence switch 300 to find an assigned one of the A operator positions or to find a storage position in the call storage unit 600 is initiated prior to the aaeafiue y 9 seizure of the telephone line 22B extending to the calling subscriber substation TI by the finder -switch 300.

Priorto continuing'with the operation of the sequence switch 300 it is noted that the A opera.-

tor position distributor 630 is operative to preselect an idle one of the A4 operator positions to be seized by the sequence switch 300. Assuming that the rst A operator position 600 has been preselected 4by the A operator position distributor 630 to be seized by the sequence switch 300 at this time, a holding circuit is completed for energizing in series the winding of the control relay R610 and the right-hand winding of the position relay R650, the position relay R650' corresponding extends from ground :by Way of the winding of R610, the contacts 662 and 653 and the righthand winding of R650 to battery. The operated position relay R650 retains interrupted, at the contacts 654, a holding circuit traced hereinafter for energizing the winding of the control relay R610 in series with the right-hand winding of the position relay R666 and completes, at the contacts 652, a path for applying ground potential to the control 4conductor C612. The path for applying ground potential to the control conductor C612 extends from ground by way of the contacts 636' and 652 to the control conductor C612. Finally the operated position relay R650 retains prepared, at the contacts 65|, a point in a circuit traced hereinafter for energizing Ithe left-hand Winding ofthe position relayy R660 corresponding to the second A operator position. Further it is noted that no potential whatever appears upon the marking conductors C530 to C535, inclusive; while battery potential appears upon the'marking conductor C536. The path for applying battery potential to the marking conductor C536 extends from battery by way of the winding of the marking relay IM and the contacts 62| to the marking conductor C536.

Continuing now with the operation of the sequence switch 380 the rotary magnet M393 continues to operate intermittently in order to drive the wipersnoted of the sequence switch 360 step' by step. in the clockwise direction until the wiper 39| engages the seventh contact in the associated contact bank 392 terminating the marking conductor C536; whereupon a circuit is completed for energizing in series the upper winding of the cutin relay R350 and the winding of the marking relay IM. This circuit extends from the grounded control conductor C364 of the trunk 360 by Way of the upper winding of R350, C326, the wiper 39| and engaged seventh contact inthe associated contact bank 392 of the sequence switch 360, the marking conductor C536, the contacts` 62| and the winding of iM to battery. When the upper winding of the cutin relay R350 is thus energized this relay operates exceedingly fast to interrupt, 'at the contacts 350, the previously traced circuit for energizing the rotary magnet M393, thereby positively to arrest further operation of the sequence switch 360. Further the cutin relay R350 completes, at the contacts 359 and 359, an obvious circuit for ener-V gizing the lower winding thereof, thereby to render the cutin relay R350 exceedingly fast to restore when the previously traced circuit for energizing the upper winding thereof is interrupted.

When the windingof the marking relay |M is `thus energized it operates to complete, at the I operate type.

5 of R620 and the winding of R6|0 to battery.

When the above-traced series circuit is completed the release relay R620 operates immediately.

However, the control relay R6|0 operates shortly l thereafter, the latter relay being of the slow-to- Upon operating the release relay R620 completes, at the contacts 62|', an obvious holding circuit for energizing in series the winding of the release relay R620 and the winding of the control relay R6|0 including the control conductor C612. fvAlso, the release relay R620 to the first A operator position 500. This circuitv completes, at the contacts 622, a path for applying battery potential to the control conductor `-C526 ofthe trunk 520 extending to the iirst A operator position 500, this path extending from 0 battery by way of the resistor 6|2, the contacts 622, C614, the contacts 634, the winding of the hold relay R630 and C521 to the control conductor C526 of the trunk 520. It is noted that the control conductor C526 of the trunk 520 extending-to the first A operator position 500 is terminated by the eighth contact in the contact bank 392 associated with the wiper 39| of the sequence switch 360. Y

Finally, upon operating the release relay R620 interrupts, at the contacts 62|, the previously traced series circuit for energizing the winding v of the marking relay iM and the upper winding I of the cutin relay R350, thereby to cause the marking relay IM to restore and to cause the cutin relay R350 to restore exceedingly fast. Up-

on restoring the cutin relay R350 recompletes, at the contacts 350, the previously traced circuit for energizing the rotary magnet M393 of the sequence switch 380, thereby to cause the rotary magnet M393 again to operate intermittently.

` In the present instance the lrotary'magnet M393 operates and restores only once; whereuponthe Wiper 39| engages the eighth contact in the associated contact bank 392 of the sequence switch 300, thereby to complete a series circuit for energizing the upper winding of the cutin relay R350 and the Winding of the hold relay R630. This circuit extends from the grounded control conductor C364 of the trunk 360 by way of the upper winding of R330, C326, the wiper 39| and engaged eighth Contactin the associated contact bank 392 of the sequence switch 380, the control conductor C526 of the trunk 520, C521, the winding of R630, the contacts 636, C614, the contacts 622 and the resistor 6|2 to battery. kWhen this series circuit is completed the cutin relay R350 again operates and the hold relay R630 operates. Upon operating the cutin relay R350 completes, at the contacts 366 and 359, the previously mentioned 6'0 circuit for energizing the lower winding thereof,

thereby to render the cutin relay R350 exceedingly fast to restore when the previously traced circuit for energizing the upper winding thereof is interrupted. Further the cutin relay R360 interrupts, at the contacts 350, the previously traced circuit for energizing the rotary magnet e M393, thereby .positively to arrest .further operation of the sequence switch 360. Accordingly, at this time the wipers noted of the sequence switch 360 engage the contacts in the associated contact banks thereof terminating the concluetors of the trunk 520 extending to the first A op- .erator position 500.

Upon operating, the hold relay R630 completes.

contacts |M2, a circuit for energizing in series at the contacts 632 and 633, an alternative holdof the hold relay R830 and the upper winding o! the cuun relay am, this circuit extending from e battery by way of the resistor 543, the contacts 588 of the transfer key X585 at the first A operator position 500, C531, the contacts 832 and 538, the winding o1' R885, C521, the control conductor C5280! the trunk 520, the wiper\38| and engaged contact in the associated contact bank 332 of the sequence switch 880, C328, the upper winding of R350 and the contacts 358 to ground. Also, upon operating the hold relay R830 interrupts, at the contacts 834, the previously traced original series circuit for energizing the upper winding of the cutin relay R380 and the Winding of the hold relay R880 including battery at the resistor 8|2. Further the hold relay R830 interrupts, `at the contacts 888, the previously traced series circuit for energizing the windingot` the control relay R8|0 and the vwinding oi the release relay R820, thereby to cause the latter relays to restore. Also the hold relay R880 completes, at the contacts 835, the previously mentioned circuit for energizing the left-hand winding ofthe position relay R880, this circuit extending from ground by way of the contacts 835 and 85| and the lefthand winding of R880 to battery. When thus energized the position relay R880 operates to complete, at the contacts 88|, a holding circuit for energizing the right-hand winding thereof in series with the winding of the control relay R810, this circuit extending irom'ground by way of the winding of R810, the contacts 881 and 88| and the right-hand winding of R880 to battery. Further the position relay R880 interrupts, at the contacts 882, the previously traced series holding circuit for energizing the winding of the control relay R810 and the right-hand winding that the call storage unit 800 and the A operator of the position relay R880, thereby to cause the position relay R850 .to restore. Also the position relay R880 prepares, at the contacts 883, a circuit for energizing the left-hand winding of the position relay R888 and completes, at the contacts 884, an obvious alternative path for applying ground potential to the control conductor C812. Upon restoring the position relay R850 prepares, at the contacts 884, a holding circuit for energizing in series the winding of the control relay R810 and the right-hand winding of the .position relay R885, interrupts, at the contacts 853, a further point in the previously traced series holding circuit for energizing the Winding of the control relay R810 in series with the righthand winding of the position relay R850, and interrupts, at the contacts 85|, the previously traced circuit for energizing the left-hand winding of the position relay R880.

Accordingly at this time the A operator position distributor 830 has operated in order to select the second A operator position to be used by the next calling telephone station, a circuit substantially identical to that previously traced being prepared for applying battery potential |by way of the resistor 8|2 and the winding of the hold relay R840 to the control conductor C840 terminated by the ninth contact in the contact bank 392 associated with the Wiper 39| of the sequence switch-380 and terminated by corresponding contacts in the corresponding contact banks of the other sequence switches. Also ground potential is applied by way of the upper winding of the cutin relay R850 and the wiper 38| to the control conductor C528 of the trunk 520 extending to the first A operator position 500. Hence the trunk 520 terminated by the other seposition distributor 830 will cause the next operating sequence switch to seize the trunk line.

extending to the second A operator position.

Continuing now with the operation oi' the apparatus at the first A operator position 530 incident to the seizure of the trunk 520 extending to the first A operator position 500, it is noted that when the hold relay R830 operates it also v completes, at the contacts 83|, an obvious path for applying ground potential to the control conductor C528. 'I'he application of ground potential to the control conductor C528 completes a circuit for energizing the winding of the tone relay R5|5, this circuit extending from the grounded control conductor C528 by way of the contacts 528 and the winding of R8|5 to batte When the winding of the tone relay R5|5 is 'thus energized this relay operates shortly thereafter, this relay being of the slow-to-operate type. Upon operating the tonerelay R5|8 completes, at the contacts 5|8, an obvious circuit for energizing the winding of the tone relay R520, thereby to cause the latter relay to operate shortly thereafter, the latter relay being of the slow-tooperate type. Upon operating the tone relay R520 completes, at the contacts 523, an obvious circuit for energizing the winding of the tone relay R525, thereby to cause the latter relay to operate shortly thereafter, the latter relay being of the slow-to-operate type. Upon operating the tone relay R525 completes, at th contacts 521, an obvious holding circuit for energizing the winding thereof and interrupts, at the contacts 528, the previously traced circuit for energizing `the winding of the tone relay R5l5, thereby to cause the latter relay to restore. Upon restoring the tone relay R5I5 interrupts, at the contacts 5|8, the previously mentioned circuit for energizing the winding of the tone relay R520, thereby to cause the latter relay to restore.

Assuming that the plugs associated with the transmitter 808. and 'the receiver 801 are inserted into the associated jacks J808 and J505 at this time, a circuit is completed for energizing in series the transmitter 508 and the control relay R5l0. 'Ihis circuit extends from ground by way of the winding 502 of the repeater 50|, the jack .T505 and associated plug, the transmitter 508, the plug and associated jack J508 and the winding of R5|0 to battery. When the winding of the control relay R5|0 is thus energized it operates to interrupt, at the contacts 5| I, an obvious path for applying ground potential to the control conductor C528 of the trunk 520. At this point it is noted that when the plugs associated with the receiver 501 and the transmitter 508 are withdrawn from the associated jacks J808 and J505, the previously traced circuit for energizing the winding of the control relay R5|0 is interrupted, thereby to cause the latter relay to restore; whereupon the previously mentioned path Afor applying ground potential to the control conductor C528 of the trunk 520 is completedf` When ground potential is applied to the control conductor C528 of the trunk 520 the trunk 520 is marked as busy to the sequence switches having access thereto. Hence it will be understood that the iirst lAoperator position 500 is selectable by4 one of the sequence switches only when the| plugs associated with the receiver 5.01 and the transmitter 500 are inserted into the associated .jacks .1505 and J 500.

Also at thisv time the receiver 501 is operatively associated with the 'winding 504 of the repeater 50| by wayof a circuit extending from one ter minal of the receiver 501 over the plug and associated jack J505, the winding 504 and the jack J505 and associated plug to the other terminal of the receiver 501.

`Also `upon operating the cutin relay R350 interrupts, at the contacts 353 and` 356, the previously traced connection between the telephone line 225 and the trunk 350 and completes, at the contacts 352 and 355, a loop circuit between the calling subscriber substation T| and the repeater 50| at the iirstoperator position 500. This loop circuit extends from the line conductor C226 ci the telephone line 225 by way of the wiper 3| the contacts 322, 332 and 35,2, the line conductor C322, the wiper 385 and engaged contact in the associated contact bank 333 of the sequence switch 330, the line conductor C522 of the trunk 520, the contacts 53| and 5|5, the windings 503 and 504 of the repeater 50|, the condenser 509, the contacts 533, the line conductor 052| of the trunk 520, the wiper 383 and engaged contact in the associated contact bank 304 of the sequence switch 380, the line conductor C324, the contacts 355, 334 and 323 and the wiper 3|2 to the line conductor C221 of the telephone line 225, the

line conductors C225 and C221 of the telephone line 225 being connected together by way of the bridge path at the calling subscriber substation TI. -Also the cutin relay R350 completes, at the contacts 35| and 354, a loopcircuit between the line relay R455 in the selector switch 400 and the repeater 50|, this loop circuit extending fromv ground by way of the lower winding of R455, the lower winding of R450, the line conductor C362 of the trunk 350, the contacts 354, the line conductor C323, the wiper 381 and engaged contactv in the associated contact bank 380 of the sequence switch 380,` the line conductor C524 of the trunk 520, the contacts 544 and 533, the condenser 505, the windings 504 and 503 of the repeater 50|, the contacts 5|6,` the contacts 535 and 502, the line conductor C523 of the trunk 520, the wiper 389 and engaged contact in the associated contact bank 330 of the sequence 4 switch 330, the line conductor 032|, the contacts 35|, the line conductor 036| of the trunk 360, the upper winding of R450 and the upper winding of R455 to battery. Also it is noted that the loop circuit extending between the repeater 50| and the calling subscriber substation T|, including the line conductors C52| and C522 of the trunk 520, and the loop circuit extending between the `repeater 50| and the line relay R455 in the selector switch 400, including the line conductors C523 and C524 of the trunk 520, are metallically interconnected, and interconnected by the retarder coil 530, thereby to prevent restoration of the line relay R455 in the selector switch 400. Accordingly ground potential is supplied by way of the lower winding of the line relay R455 and the line conductor C520 of the trunk 520 to one terminal of the condenser 509; and battery potential is supplied by way of the upper winding of the line relay R455 and the line conductor C523 of the trunk 520 and the windings 503 and 504 of the repeater 50| to the otherterminal of the condenser 500, the receiver 501 being arranged in a circuit including the winding `504 or thd repeater 50|, aspreviously noted. i,

` Accordingly, whenthe tone relay R5|5 operates it interrupts, at the contacts 5|3, the previouslytraced connection between-the windings 503 and 504 of the repeater 50| and the interconnected loop circuits respectively extending to the calling subscriber substation T| and to the line relay R455 in the selector switch 400 and completes, at the contacts '5|1, an alternative circuit for charging the condenser 503 including the tone conductor C5|2. -This circuit for charging the condenser 5 03 extends from the ungrounded terminal of a grounded source of tone current by way of the conductor CM2, the contacts 522 and 5|1 and the windings 503 and 504 of the repeater 50| to one terminal of the condenser 509, the other terminal of the condenser `50|! having ground potential connected thereto. as previously noted. Upon operating the tone relay R520 interrupts, at the contacts 522, the above-traced circuit for charging the condenser 509 and prepares, at the contacts 52|, an alternative circuit for'charging the condenser 503, Upon operating the tone relay R525 completes, at the contacts 520, thealternative circuit for charging .the condenser 509, this circuit extending from the tone conductor C5I2 by way of the contacts 526, 52|, 5|1 and the windings 503 and 504 of the Arepeater 50| to one terminal of the condenser 509, the other terminalof the condenser 509 having ground potential connected thereto, as previously noted. Finally when the tone relay R5|5 restores it interrupts, at the contacts 5| 1, the above-traced alternative circuit for charging the condenser 503 and recompletes, at the contacts 5|6, the interconnection between the repeater 50| and the loop circuits respectively extending to the calling subscriber substation T| and to the line relay R455 in the selector switch ,400. The alternate completion and interruption. of the circuits for vcharging the condenser 505, including the tone conductor C5|2,` causes the winding 504 of the repeater 50| to be alternately energized and deenergized with tone current, thereby to cause the receiver 50| at the first A operator position 500 to be alternately operated, whereupon a distinct zip-zip tone is produced thereby. The production of the zip-zip tone by the receiver 501 at the iirst A operator position 500 indicates to the operator thereat that an incoming call has been extended to her position by one of the sequence switches.

Finally, upon operating the hold relay R530 completes, at the contacts 53|, a circuit for illuminating the `iiat rate signal lamp 5.500, in the present instance the signal relays R505 and R690 being restored at this time. The circuit for illuminating the fiat rate signallamp L080 extends from ground by way of theeontacts 63| and 686 and L030 to battery. The illumination of the Y fiat rate signal lamp L530 indicates to the operator at the rst A operator position 500 that the incoming call which is extended to her position originates at a subscriber substation to which flat rate service is rendered and that it is not necesthe calling subscriber substation T| and asv certain the destination of the call. -After learning the destination o! the call the operator at the -iirst 1i operator position 500 initiates the exten.

sion1oi the call by operating the key sender X520 in order appropriately to control the selector f switch 40|.

Extension. of a call from an A operator position In order to extend a call from an A operator position, such, for example, as a. call from the subscriber substation TI to the first A. operator position 500, the operator at the first A operator position 600 operates the key sender X520, thereby to cause the impulse relay R540 to operate. Upon operating the impulse relay R540 completes, at the contacts 54| and 543;' an alternative loop circuit substantially identical to that previously traced between the line relay R455 in the selector viously traced circuit for energizing the winding of the hold relay R460 and completes, at the contacts 451, the previously mentioned multiple circuit for energizing the lower winding 'of the transfer relay R465 and the vertical magnet M4|4. This circuit extends from ground by way of the contacts 415, 451, 464 and 461 and the lower winding of R465 to battery, and from the contacts 461 and the vertical magnet M4I4 to battery. Due to the fact that thehold relay R460 and the transfer relay R465 are of the slow-to-release type, these relays remain operated during impulsing. Each time the vertical magnet M4|4 is energized it operates, thereby to drive the wiper set of the mechanism 4|0 one step in the vertical direction. Whenthe wiper set of the mechanism 4I0 is driven one step in the vertical direction the set of switch springs S420 is actuated into disengagement, thereby to interrupt the previously traced circuit for energizing the upper winding of the transfer relay R465; the set of switch springs S4|9 is actuated into engagement,ther`eby to prepare a circuit traced hereinafter for energizing the release magnet M4N;-

and the set of switch springs S42| is' actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the rotary magnet M4|6.

At the conclusion of the digit transmitted byv the key sender X520 the impulse relay R540 restores, thereby to recomplete, at the contacts 542 and 544, the previously traced loop circuit extending between the repeater. 50| and the line relay R455 in the selector switch 400 and to interrupt, at the contacts 54| and 543, the previously mentioned alternative loop circuit extending between the key sender X520 and the selector switch 400. Shortly following the conclusion of the digit transmitted from the key sender X520 to the selector switch 400 the transfer relay R465 restores to interrupt, at the contacts 461, a further point in the previously traced multiple circuit for energizing the lower winding thereof and the vertical magnet M4|4 and to complete, at the contacts 466', the previously mentioned circuit for energizing the rotary magnet M4N. This circuit extends from ground by ,way oi' the contacts 415, 456, 4|1 and 460', the set of switch springs 842| and M4|6 to battery. When thus energized the rotary magnet M4|6 operates to drive the wiper set of the mechanism 4|0 one step in the rotary direction and to interrupt, at ther contacts 4|1, the previously traced circuit tor energizing the rotary magnet M4l6, vthereby to cause the rotary magnet M4|0 to restore. Upon restoring the rotary magnet M4|6 recompletes, at the contacts 4|1, the previously traced circuit for energizing the rotary magnet M4ll. Accordingly the rotary magnet M4|6 operstes intermittently, thereby to drive the wiper set of the vmechanism 4|0 step by step in the rotary direction until the wiper 4|3 oi the wiper set engages a contact terminating the control conductor of a trunk having battery potential thereon, battery potential being present upon the control conductor of the trunk in the event the trunk is idle, whereupon a circuit is completed for energizing the upper winding of the switching relay R410. The circuit for energizing the upper winding of' the switching relay R410 extends from the grounded control conductor C363 of the trunk 360 by wayv of the contacts 421 and 454 and the upper winding of R410, the contacts 46| and the wiper 4|3 to the control conductor oi' the trunk having battery potential thereon. When this circuit is completed the switching relay R410 operates lexceedingly fast, thereby to complete, at the contacts 414, a holding circuit for energizing the intermediate winding thereof, this circuit extending from the grounded control conductor C363 oi' the trunk 360 by way of the contacts 421, 454 and 414 and the intermediate winding of R410 to battery. Also upon operating the switching relay R410 interrupts, at the contacts 415, the previously traced circuit for energizing the rotary magnet M4I6, thereby positively to arrest further operation of the wiper set of the mechanism 4|0. Further the switching relay R410 interrupts, at the contacts 415, the previouslyl traced circuit for energizing the winding of the hold relay R460, thereby to cause the latter relay to restore shortly thereafter. Finally the switching relay R410 completes, at the contacts 41|, 412 and 413, a connection between the selector switch 400 fand the trunk seized by the wiper set of the mechanism 410, thereby to complete a loop circuit for energizing in series the upper and lower windings of the battery supply relay R430. 'I'his loop circuit extends from ground by way of the lower winding of R430, the contacts 412 and the Wiper 4|2 to one of the line conductors of the seized trunk and from battery by way of the upper winding of R430, the contacts 41| and the wiper 4|| to the other line conductor of the seized trunk, the line conductors of the seized trunk being connected together at the operator position terminating the seized trunk. When thus energized the battery supply relay R430 operates to complete, at the contacts 433, an obvious circuit for energizing the winding of the control relay R440, thereby to cause the latter relay to operate shortly thereafter, the latter relay being of the slow-to-operate type. Upon operating the control relay R440 completes, at the contacts 44|, an obvious alternative path for applying ground potential to the control conductor C363 of the trunk 360. Further it is noted that the loop circuit extending between the repeater 50| and the line relay R455 in the selector switch 400 is operatively connected by the condensers 428 and i129 to the loop circuit extending between the battery supply relay R439 in the selector switch 40|) and the trunk seized by the' wiper set of the mechanism 4|0. v

In the eventl the call which is extended from the first A operator position 500 is utlimately to be completed in the local exchange 20 the operator at the first A operator position 500 controls the key sender K520, thereby to cause the selector switch 400 to seize an idle trunk inthe group of trunks extending to an idle one of the B operator positions in the localexchange 20. For example, the selector switch 400 may be `controlled to `seize an idle one of thetrunks,

such, for example, as the trunk 490 in the group of trunks extending to the idle first B operator position 494 in the local exchange 2|). The trunk 490 extending to the first B operator position 494 is marked for seizure by the presence of battery potential upon the control conductor C493 thereof, the path for applying ground potential to the control conductor C493 of the trunk 490 extending from battery by way of the winding of the line relay R480 and the contacts 486 to the control conductor C493. When theswitching relay `R410 operates it completes, at the contacts 413, an obvious path for applying ground potential by way of the wiper 4|3 to the control conductor C498 of the trunk 490, thereby to complete an obvious circuit for energizing the winding of the line relay R480. When thus energized the line relay R480 operates to interrup,`at the contacts 48|, a circuit for energizing the `busy relay R485. Accordingly, at this time a loop circuit is completed between the battery supply relay R430 in the selector switch 400 and the rst B operator position 494. When the trunk 490 is seized by the selector switch 400 a signal is transmitted to the rst B operator position 494; whereupon the operator at the first B operator position 494 answers the call and communicates with the operator at the first A operator position 500 concerning the extension of the call to a called subscribersubstation in the local exchange 20. The operator at the first B operator position 494 then proceeds to extend the call to the called subscriber substation in the local exchange 20 in the usual manner.

At this point it is noted that the operator at the first B operator position 494 may render the trunk 490 extending thereto busy by causing battery potential to be applied to the line conductor C492 of the trunk 490 prior to seizure of the trunk 490. The application of battery potential to the line conductor C492 of the trunk- 490 completes an obvious circuit for' energizing the winding of the busy relay R485, thereby to cause the latter relay to operate. Upon operating the busy relay R485 interrupts, at the contacts 486, the previously traced path for applying battery potential by way of the winding of the line relay R480 to the control conductor C493 of the trunk 490, and completes, at the contacts 481|, an obvious path for applying ground potential to the control conductor C493 of the trunk 499, the application of ground potential to the control conductor C493 of the trunk 490 being effective to mark the trunk 499 as busy to the selector switches having access thereto.

Reconsidering now the operation of the selector switch 400 it is noted that in the event the call which is extended from the rst A operator position 500 is ultimately to be completed in the distant exchange 30, the operator .at the iirst A operator position 500 controls the key sender trunk line 410 to operate in a manner similar` to the trunk line circuit 480 previously described. When the trunk line 410 is seized by the selector switch 400-a signal is transmitted to the B operator position 498 in the distant exchange 30; whereupon the operator at the B operator position 498 answers the call and is advised by the operator at the first A operator position 500 concerning the extension of the call to a subscriber substation in the distant exchange 30. The operator at the B operator position 498 then extends the call to the called subscriber substation in the distant exchange ,30 in the usual manner.

Considering further the operation of the selector switch 400 it is noted that in the event the call which is extended from Vthe first A operator position 500 is a `toll call, the operator at the first A operator position 500 controls the key sender K520, thereby tocause the selector switch 400 to seize an idle one oi the trunks in one of the groups of trunks extending to an idle one of the` toll operator positions, such, for example, as the trunk 495 in the group of trunks extending to the toll operator position 499,V thereby to cause the trunk line circuit 491 individually associated with the trunk 495 to operate in a manner similar to the trunk line circuit 480 previously described. When the trunk 495 is seized by the selector switch 400 a signal is transmitted to the toll operator position499; whereupon the operator at the toll operator position 499 answers the call and is advised by the operator at the first A operator position 500 concerning the routing of the call. The operator at the toll operator position 499 then routes the call toll in the usual manner.

Again considering the operation of the selector switch 400 to extend the call from the iirst A operator position 500 to the first B operator position 494, it is noted that when the battery supply relay R430 operates it prepares, at'the contacts 43|, a circuit for energizing the busy relay R220 in the'flat rate line circuit 200 'in dividually associated with the telephone line 225. Further it is noted that the circuit 'for energizing the winding of the busy relay R220 is completed in the event the link illustrated is the last available link, rendering all of the links busy'atl this time. In this event the circuit for energizing the winding of the busy relay R220'is completed and extends from ground by way'of' the chain conductor C449, the contacts 43l, C23|` and the winding of R220 to battery. `When thus energized the busy relay R220 operates to interrupt, at the contacts 22|, a point in the previously traced path for applying ground potential to the start conductor C230. Further it is noted that a path is normally completed for shortcircuiting the winding 2 i0 of the transformer 2|9 which extends from ground by way of the contacts 22| and the winding 2 lli of the transformerv 2|| to ground. Accordingly, upon operating the busy relay R220 interrupts, at the contacts 22|, the above-traced path for short-circuiting the winding 2|8 of the transformer 2|B. Similarly the busy relay in each of the flat rate linecircuits in the group of at rate line circuits irlcluding the line circuit 200 is operated. Accordingly. when the next call is initiated at one oi the subscriber substations in the group of subscriber substations, including the subscriber substation TI, the operation of the line and cut-oli relay in the iiat rate line circuit individually associated therewith will not cause ground potential to be applied to the start conductor C230 but will cause busy tone current to be returned to the receiver of the telephone instrument at the calling subscriber substation. By Way of example, the analogous circuit for returning busy tone current over the telephone line 225 to the receiver of the Atelephone instrument at the subscriber substation T| under these operating conditions extends from ground by way oi' the winding 2| 5 of the transformer 2|5, the contacts 2|5 and 2|4, the condenser 2|9, the contacts 2||, C225, the bridge path between the line conductors C225 and C221 of the telephone line 225 at the subscriber substation TI, C221, the contacts 2|2 and the lower winding of R2|0 to ground; the winding 2|1 of the transformer 2|5 being connected to a suitable sourcerof busy tone current and being inductively coupled to the winding 2|8.

In connection with the extension of the call from the iirst B operator position 494 to a called telephone station in the local exchange 20 after the call has been answered at the first B operator position 494, it is noted by way oi' example, that the call may be extended to either one of the subscriber substations TI or T2 by inserting the calling plug oi the cord circuit at the rst B operator position 494 into the jack J220 terminating the telephone line 210 extending to the subscriber substations T2 and T3.

When the operator at the ilrst A operator position 500 extends the call from her position to the first B operator position 494 she may wish to converse with the operator at the first B operator position 494 to the exclusion of the subscriber at the calling subscriber substation TI. In order to accomplish this result the operator at the first A operator position 500 operates the split key K515, thereby to complete, at the contacts 519 thereof, an obvious circuit for energizing the rear split relay R530 and to complete, at the contacts 515 and 511 thereof, an obvious connection between the impedance element 1559 and the control conductors C545 and.v C541. Also when the split key K515 is operated an obvious connection is completed at the contacts 515 thereof between the line conductors C52| and C522 of the trunk 520 including the condenser 545. When thus energized the rear split relay R530 operates to interrupt, at the contacts 53| and 533, the previously traced loop circuit extending between the calling subscriber substation TI and the repeater 50| and to complete, at the contacts 532 and 534, an alternative loop circuit between the calling subscriber substation Ti and the impedance element 1555. This alternative loop circuit extends from ground by way of the lower winding of the impedance element 1558, the contacts 515 of the split key X515, C541 and the contacts 534 to the line conductor C526 of the trunk 520, and from battery by way of the upper winding of the impedance element 1555, the contacts 517 of the split key K515i, C555, and the contacts 532 to the line conductor C522 of the trunk 529; the line conductors (252| and C522 of the trunk 520 being included in the previously traced loop circuit extending to the calling subscriber substation T|. With the split key K515 thus operated, the operator at the first A operator position tilt may converse with the operator at the first B operator position 494 to the exclusion of the subscriber at the calling subscriber substation Ti. After the termination of the conversation between the operators at the first A operator position 500 and the iirst B operator position 494 the operator at ,the first A operator position 500 returns the split key K515 to its normal position, thereby to interrupt, at the contacts 519, the previously mentioned circuit for energizing the.

winding of the rear split relay R530; whereupon the rear split relay R530 restores to recomplete, at the contacts 53| and 533, the previously traced loop circuit between the calling subscriber substation TI and the repeater 50|. Also, at the contacts 515 and 511 oi' the split key H515, the impedance element 1558 is disconnectedirom the control conductors C540 and C541.

In the event the operator at the nrst A operator position 500 should make an error in registering the digit to be transmitted to the selector switch 400 upon the key sender X520, the operated selector switch 400 may be restored to its normal position by operating the error release key K550 at the first A operator position 500. When the error release key K550 is thus operated an obvious circuit is completed, at the contacts 552 thereof, for energizing the winding oi' the front split relay R535, thereby to cause the latter relay to operate and complete, at the contacts 539, a path i'or applying ground potential to the line conductor C352 oi' the trunk 350, this path extending from ground by way of the contacts 55| of the error release key K550, the contacts 539 and 544, the line conductor C524 of the trunk 520, the wiper 331 and engaged contact in the associated contact bank 335 of the sequence switch 330, the line conductor C323 and the contacts 354 to the line conductor C352 of the trunk 350. This application oi' ground potential to the line conductor C332 of the trunk 350 completes an obvious path for short-circuitlng in series the lower winding of the error relay R450 and the lower winding of the line relay R455. When the lower winding or the line relay R455 is thus short-circuited this relay remains in its operated position; however, when the lower winding of the error relay R450 is thus short circuited this relay operates, as the error relay R450 is of the dilferential type. Upon operating th error relay R450 completes, at the contacts 45|, a circuit for energizing the winding of the lockout relay R425, this circuit extending from ground by way of the contacts 55| of the error release key K550, the resistor 505, the contacts 531 and 542, the line conductor C523 of the trunk 520, the wiper 389 and engaged contact in the associated contact bank 380 of the sequence switch 380, the line conductor 032|, the contacts 35|, the line conductor C35i of the trunk 390, the contacts 45| and the winding of R425 to battery. When this circuit ior energizing the winding of the lockout relay R425 is completed, the latter relay does not operate due to the series resistance of this circuit, the lockout'relay R425 being of the marginal type. Also the error relay R450 completes, at the contacts 953, an obvious alternative path for applying ground potential to the control conductor C353 of hte trunk 350, thereby to retain the finder switch 309 in its operated position and to interrupt, at the contacts 454, the previously traced holding circuit for energizing the intermediate windlng of the switching relay R410, thereby to cause the latter relay to restore. Finally the error relay R450 completes, at the con'-

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