US2265151A

US2265151A - Telephone system

Info

Publication number: US2265151A
Application number: US329071A
Authority: US
Inventors: Thomas F Crocker
Original assignee: Associated Electric Laboratories Inc
Current assignee: Associated Electric Laboratories Inc
Priority date: 1940-04-11
Filing date: 1940-04-11
Publication date: 1941-12-09
Anticipated expiration: 1958-12-09
Also published as: FR938800A

Description

9 Sheets-Sheet l INVENTOR THOMAS F. GROCKER BY 26mm/M ATTORNEYS Dec. 9, 1941. T. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet 2 mmmb @N NWN NQ u NVENTOR THOMAS F. OROCKER M Mun@ ATTORNEYS BY ,OMM/IM Filed April 1l, 1940 9 Sheets-Sheet I5 THOMAS FA CROCKER ATTORNEYS Dec. 9, 1941. 1'. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 SheeCS--Sheeil 4 .NSE n @@v/ Em YnQI ATTORNEYS T. F. CROCKER TELEPHONE SYSTEM Dec, 9, 1941.

9 Sheets-Sheet 5 Filed April 1l, 1940 THOMAS F. CROGKER TTORNEYS.

Dec. 9, 1941. T, F. cRocKER TELEPHONE SYSTEM 9 sheetssheet s Filed April 11, 1940 @mu E@ am? vmmm. m6@ n Im uw @www mg @S k .w Q

lD/5 TRIBU ToR Kwon u mvw/ m mv@ f m MIN@ w @5U oo@ QE n Et@ wmdz x Eu Q@ lNvENToR THOMAS F. CROGKER 'M M ATTORNEYS www *mmm Dec. 9, 1941. 'r. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet 7 THOMAS F. CROOKER ATTORNEYS 9, 1941- T. F. cRocKER TELEPHONE SYSTEM 9 Sheets-Sheet 8 Filed April l1, 1940 ATTORNEYS 9 1941- T. F. cRocKER TELEPHONE SYSTEM Filed April 11, 1940 9 Sheets-Sheet 9 l |9||)|.\Nm u R Mmm. 4 hmmbx m Tl T .R am@ m m. N F E S vv A Qmmm m wma@ .vmm l mmm @IMS i @a NE# e Num/J www www. .TTI mmilfmwm f Nwmh @mmm :wma Sm@ ml mm2 f m l "mm fr @Q3 i Sm l QSI s@ o C o o o o o o o o v o o o amy c Sm Qmo mo m ww o Sm@ man Sm 4 @om IV IMI. "Ce SC mwtm mmz otmn @mu/ laD Qm @mu mmm@ PatentediDea 9, 1941 UNITED TELEPHONE SYSTEM yThomas F. Crocker, Chicago, Ill.,4 assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application April 11, 1940, Serial No. 329,071I

56 Claims.

The present invention relates to telephone systems and more particularly to improvements in private automatic branch exchanges.

A private automatic branch exchange or P. `A. B. X is usually associated -with a central oice by way of a nunber of two-Way trunk lines extending therebetween and conventionally comprises an operator position, a number of telephone stations having lines extending thereto and switching apparatus. Ordinary local calls between the various telephone stations in the P. A. B.` X are completed by the switching apparatus underthev control of the subscribers at the telephone jstations without the assistance of the operator at theoperatr position; while both incoming and outgoing trunk calls are completed betweenthe central oice and the various telephone stations in the P. A. B. X either directly by or with the assistance of the operator at the operator position.

It is an object of the present invention to provide in a telephone system of the character noted an improved arrangement for selectively contherebetween; wherein the P. A. B. X comprises necting ay number of trunks to an operator position and for selectively controlling the operation of a number o`f trunk switches individually associated with the trunks to seize a number of lines accessible thereto. e v

Another object of the invention is to provide in 4a telephone system of the character noted an improved switching arrangement selectively operativefto establish local and trunk connections and to hold trunk connections.

Another object of the invention 'is to provide in a telephone system an improved arrangement for selectively marking a number of lines and for causing switching apparatus toseize marked ones of the lines.

Another object of the invention is to provide in a telephone system an improved arrangement for selectively marking any one of a number of lines for selection by switching apparatus having access thereto, which marking arrangement is'selectively controlled by both manual means and automatic means.

A further object of the invention is to provide in a telephone system an improved arrangement for releasing a rst switch train operated to establish a connection to a given line when a second switch train is operated to establish a connection to the given line.

A further object of 'the invention is to'provide in a telephone system an improved arrangement for identifying a calling line included in an established connection extending to an operator position. l

A further object of the invention is to provide in a telephone system an improved switching arrangement for establishing connections between calling lines and an operator position, which switching apparatus is selectively controlled in accordance with the classes of calls on the lines.

rA further object of the invention is to provide in a telephone system improved switching ap.. 4

an operator position, a number of telephone stations having telephone lines extending thereto and switching apparatus. The switching apparatus provided in the P. A. B. X comprises a number of trunk switches individually associated with the trunk lines, a number oi local links and a position switch associated with the operator position. f l

ln, accordance with one feature of the invention, the P. A. BrX comprises an operator position, a plurality of groups of lines each including a plurality ofsubgroups of lines, an automatic switch associated with the operators p0- sition and having access to the lines, and a key set associated with the operator position and including a number of keys. Also, the arrangement comprises means controlled by initial operation of one of the keys in the key set for ,marking a corresponding onel of the groups of lines, means controlled by further operation of one of the keys in the key set for marking a corresponding one of the subgroups of lines in the marked group of lines, means controlled by a nal operation of one of the keys in the key set for marking a corresponding one of the lines in the marked subgroup of lines inthe marked i -means including the switch for establishing a connection between' the operator position and the selected line.

In accordance with another feature of the invention, the P. A. B. X comprises la number of trunk switches individually terminating the trunks extending vbetween. the central oiiice and the P. A. B. X, the lines extending to the telephone stations in the P. A. B. X being accessible 'the operator position for causing `the one oi the trunk switches terminating the one trunk to seize any one of the lines, thereby to complete a connection between the one trunk and the one line including the operator position, and means controllable from the operator position for disassociating the one trunk from the operator position, thereby to complete a connection between the one trunk and the one line excluding the operator position.

In accordance with another feature of the invention, each of the trunks extending between the central oiiice and the P. A. B. X comprises normally connected central oice and branch exchange sections; and a trunk circuit and a line circuit are individually associated with each trunk, the trunk circuit being operative in a rst manner to disconnect the central omce and branch exchange sections of the trunk and to connect a bridge to the central oflice. section of the trunk and to connect the branch exchange section of the trunk to the line circuit andopera-.

tive in a second manner to reconnect the central yomce and branchexchange sections of the trunk and to disconnect the bridge from the central oice section of the trunk and to disconnect the f branch exchange section of the trunk from. the line circuit. Also, the arrangement comprises means for completing a connection between the central office and any one of the telephone stations including the trunk, means at the one telephone station for selectively controlling over the trunk the manner of operation vofthe trunk circuit, and means controlled when a bridge is connected to the central oice section of the trunk for retaining the connection to the central oiiice. Also, the P. A. B. X comprises a number of switching links, means controlled when the branch exchange section of the trunk is connected to the line circuit for causing the -one of the switching links to seize the line circuit and for retaining the one switching link operated, and means controllablerfrom the one telephone station over thel trunk and the line circuit for causing theswitching link to seize another of the telephone stations, thereby to complete a connection between the one telephone station and the other telephone station. Also, the trunk circuit is operative in a further manner to cause a signal to be transmitted to the operator position, thereby to indicate the presence of a recall on the established connection between the central oice and the one telephone station; and means is provided at the one telephone station for operating the trunk circuit in the further manner over the trunk.

In accordance with another feature of the invention, the P. A. B. X comprises a marking network which is so connected and arranged that it is manually controllable from the key set associated with the operator position and automatiin order respectively to cause any one of thelines'to be marked for selection or to cause the line seized by the operated switching link to be marked for selection.

In accordance with a further feature of the invention, the switching links are so connected and arranged that when a line is marked for selection by the marking vnetwork due to the seizure of the line by an operated one of the switching links, the one switching link is automatically released when the trunk switch terminating one of the trunks operates to seize the marked line.

In accordance with a further feature of the invention, the arrangement comprises a link distributor adapted to connect. the switching links to calling ones of the lines in a predetermined order, each of the switching links including control apparatus governable over a calling one of the lines connected to the switching link and a register, the control apparatus included in each of the switching links being selectively governable to cause the link to be connected to any one of the called lines and selectively to operate the register included in the switching link, the register included in each of the switching links being selectively operative to mark the link as occupied by diierent classes of calls. Also, a position switch is associated with the operator position and has access to the switching links. Control ymeans is provided at the operator position which is operative in a iirst manner to cause the position switch to seize one of the switching links marked as occupied by acall of a first class and operative in a second manner to cause the position switch to seize one of the switching links marked as occupied by a call of a second class.

In accordance with a further feature of the invention, an identity device is associated with the operator position which is so connected and arranged that it is controlled jointly by the operation of one ofthe switching links to seize a calling line and the operation of the position switch to seize the one link in order to identify the calling line in the event the calling line has a call thereon of a iirst class. Furthermore, when the trunk switch associated with one of the trunks is operated to seize the calling line previously seized by the switching link mentioned, the identity device is released.

Further features of the invention pertain to the particular arrangement of the circuit ele- Varrangement of a telephone system, including a central ofIice and a private automatic branch exchange, embodying the present invention; Figs.

.-2 to 9, inclusive, taken together, illustrate the details of a' system having incorporated therein the features of the invention, as briefly outlined above; and Fig. 10 illustrates the mode of comf bining Figs. 2 to 9, inclusive, of the drawings to form a unied system.

Description of the apparatus incorporated in `the telephone system.

Referring nowniore particularly to Fig. 1 of the drawings the telephone system there illusltrated comprises a central ofiice 50, a private automatic branchexchange or P. A. B. X 60 and aplurality of two-Way trunk lines, including the trunk line 490, extending therebetween. The central ofiice 50 and the' P. A. B. X 60 are of the automatic dial type, the P. A. B. X 60 comprising an operator position 800 and a number of telephone stations including the stations TI and T2. Further the P. A. B. X 60 comprises a number of local links, including the local link illustrated, and a distributor 680 for assigning idle ones of the local links to the use of the telephone stations. For example, the local link illustrated includes a local finder switch 600 and a local connector switch 100. Also a trunk circuit and a trunk finder switch are individually associated with each of the trunk lines, the trunk circuit 400. and the trunk finder switch 500 being individually associated with the trunk line 490.

A telephone line having al line circuit individually associated therewith extends to.each telephone station in the P. A. B. X; the telephone lines 605 and 150 respectively extending to the telephone stations TI and T2 and the line circuit 690 being individually associated with the telephone line 605. Further an auxiliary line circuit is individually associated with each trunk circuit, the auxiliary line circuit 494 being individually associated with the trunk circuit 400. Finally an operator key set and marking circuit 200, an identity lamp and trunk finder start circuit 300, and an operator finder switch 900 are associated -with the operator position 800.

Each of the local finder` switches, such, for Zexample, as the local finder switch 600, each of the local connector switches, such, for example,I as the local connector switch 100, and each of the trunk finder switches, such, for example, as the trunk finder switch 500, has access to each telephone line in the P. A. B. X. Also the operator position 800 has direct access to 'each trunk line extending between the central office and the P. A. B. X and to each trunk finder switch. Further the operator position 800 has access by way of the operator finder switch 900 to each local link.

Preferably `each of the local links in the P. A. B. X ls' identical to the local link illustrated which comprises a local finder switch 600 and a local connector switch 100, as previously noted. The'nder switchf600, as best shown in Fig. 6, YVcomprises a switching mechanism 6I0 of the 200- point Strowger type including a carriage provided with a first wiper set,v including the wipers 6I3, 6I4 and 6I5, a second wiper set, including the wipers 6I6, 6I1 and 6I8, and three control wipers 6I I, 6l2 and 6I9. It is noted that the Wipers 6I3, 6I4 and 6I5 of the first wiper setand the wipers 6I6, 6I1 and 6I 8 of the second wiper set are capable of both vertical and rotary movements; the control wipers 6I I, and 6I9 are. capable of vertical movements; and the control wiper SI2 is capable of rotaryI movement.. Further the mecha- LA,nism 6I0 comprises a circumierentially disposed main contact bank provided with two sections respectively associated with the first and second wiper sets, two vertical control contact banks anism 6I0 the rstand second wiper sets respectively have access to first and second groups of,

one hundredlines each respectively terminated by the flrst and second sections of the main contact bank. Also the mechanism 6I0 is provided with a vertical magnet M62I for moving the first and second wiper sets thereof in the vetrical vdirection, a rotary magnet M623- for moving the first and second wiper sets thereof in the rotary direction, and a release magnet M625 for releasing the first and second wiper sets thereof and for causing these wiper setsto be returned to their normal positions. Finally the mechanism 6I0 has two sets of switch springs S625 and S621 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 finder switch 600 comprises a number of relays including two switching relays R640 and lR650, a hold relay R660 and an identity relay 4 R610 connected and arranged in a manner more fullyldescribeld subsequently. y

The connector switch 100, as best shown in Fig.

r 7, comprises a switching mechanism 110 of the ZOO-point Strowger type including a carriage provided with a first wiper set, including the wipers 11|, 112 and 113. and a second wiper set, includ-- ing the wipers 114, 115 and 116. It is noted that the wipers 11|, 112 and 113 of the first wiper set and the wipers 114, 115 and 116 of the second wiper set are capable of both vertical and rotary movements. Further the mechanism 110 comprises a circumferentially disposed main contact bank provided with two sections respectively associated with the first and second wiper sets. Accordingly, in the mechanism 110, the rst and second wiper sets respectively have access to first and second groups of one hundred lines each respectively terminated by the first and second sec- Vtions of the main contact bank. Also the mechanism 110 is provided with a vertical magnet M111 for moving the first and second wiper sets thereof in the vertical direction, a rotary magnet M118 for moving the first and second wiper sets thereof in the rotary direction, \and a release magnet M119 for releasing the rst and second wiper sets thereof and for causing these wiper setsA to be returned to their normal positions. Finally, the mechanism 110 has a number of sets of switch springs S180, S182 and S185 operatively associated therewith which are controlled in accordance with the-movements of the first and associated with the control wipers 6H and.6l9,.

second wiper sets thereof, in a manner more fully Adescribed subsequently.

Also the connector switch includes a con trol switch 190 of the Minor type including three rotary wipers 19|, 193and 195 provided with individually associated rotary contact banks '192, 1.94 and 196. Also the controlswitch 190 is provided with a rotary magnet M191 for moving the wipers noted in the rotary direction and a release magnet M198 for releasing the wipers noted and for causing these wipers to be returned to their normal positions. Finally the control switch 190 includes two sets of switch springs S191 and S198 which are controlled in accordance with the movements of the wipers noted in a manner more fully described subsequently.

Also the connector switch 100 comprises a number of relays including a line relay R100, a battery supply relay R105, three transfer relays R1I0, R120 and R130, a busy relay R140, a cutoi relay R and two switching relays R160vand wiper I1.

the first and second wiper sets respectively have,

poses it is noted that the connection and ar-l rangement of a vdistributor of the type of the distributor 680 is shown, in the copending applil cation of Edward S. Peterson, Serial No. 233,021,A

filed October 3, 1938.` Also a marking network 596, shown in Fig. 6, ,is associated with the distibutor 080 in order to initiate operationthereof hen a call is initiated on one of the telephone I lines `extending to a telephone station in the P. A.B. X.

Preferably each f the trunk finder switches is identical tothe trunk finder switch 500 individually associated with the trunk line 590, shown in Fig. 5, which comprises a switching mechanism 5I0 of the 200 -point Strowger type includtimerrelay R640, afi answer relay R460 and a control relay R420, connected and arranged in a manner more fully described subsequently. Further the trunk circuit 400 comprises a line lamp L406, a busy lamp M05 and ka. hold lamp L4M.

Preferably, each of the line circuits is identical to the line circuit 690 individually associated with the telephone line 605 extending to the telephone station TI, shown in Fig. 6, which comprises a line and cutoff relay R690 connected and arranged in a manner more fully described subsequently. Preferably, each of the auxiliary line circuits is identical to the auxiliary line circuit 595 individually associated with the trunk circuit 400, shown in Fig. 4, which auxiliary line circuit is connected and arranged in any suitable manner, such, for example, as the line circuit 690 individually associated with the telephone line 005 extending to the telephone stal tion TI.

lng a carriage provided with a first wiper set,

including the wipers 5II, 5I2 and 5I3, a' second wiper set, including the wipers Elfi, 5I5 and 5I6, and two control wipers 511 and 5I8. It is noted that the wipers 5I I, 5I 2 and 5I3 of the first wiper set and the wipers 5m, 5I5 and 5I 5 of the second wiper set are capable of both vertical and rotary movements; the control wiper 5I8 is` capable of vertical movement; and. the control wiper 5H is capable of rotary movement. Further the mechanism 5I0 comprises a circumferentially disposed main contact bank provided with two sections respectively associated with the first and second Wiper sets, a vertical control contact bank associated with the control wiper 5I8 and a rotary vcontrol contact bank associated with the control Accordingly, in the mechanism '5I0 access toI rst and second groups of one hundred lines each, respectively terminatedl by the iirst and second sections of the main contact bank.

Also the mechanism 5I0 is provided with a vertical magnet M5I9 for moving the` lrst and second wiper sets thereof in the vertical direction, a

rotary magnet M52! for moving the rst 'and second wiper sets thereof in the rotary direction, and a release magnet M523 for releasing the rst and second wiper sets thereof and for causing these wiper sets to be returned to their normal positions.' Finally, the mechanism 5m has two sets of switch springs S520 and S525 operatively associated therewith, which are controlled in accordancel with the movements of the first and second wiper sets thereof in a manner more fully described subsequently.

Also the finder switch 500 comprises a, number of relays including a hold relay R505, a connect relay R500, a cutoff relay R550, a trunk-offer relay R560, a start relay R510, a busy relay R500,

two switching relays R5I0 and R520, a step relay R585 and a transfer relay R590 connected and arranged in a manner more fully described subsequently.

Preferably each of the trunk circuits is identical to the trunk circuit 400 individually assol t ring-up relay R445, a transfer relay R050, a

Each of the telephone stations in the P. A. B. X 60 is provided with station equipment including a telephoneinstrument, a ringer, a push button and calling device or dial.

The operator position 800comprises, as shown in Figs. 4 and 8, a trunk circuit provided with a set of position keys including an information key X850, an information hold key X855, a common ytrunk key X850, a common trunk 1hold key X865, a trunk offer key X840 and a release key X810. Also the trunk circuit at the operator position 800 is provided with an individual trunk key and an individual trunk hold key individual toreach trunk line extending betweenthe central'oice 50 andthe P. A. B. X 60, the individual trunk key X080 and the individual trunk hold key X590 being individual to the trunk line 490 extending between the central ofhce 50 and the P. A. B. X 50. operator position 800 comprises a telephone instrument including a transmitter I and 'a receiver 802, a calling device or dial 805, a repeater `9, is of the'rotary type and comprises six

rotary wipers

001, 903, 905, 901, 909 and SII provided rwith individually associated

rotary contact banks

902, 900, 906, 008, 9I0 and 9I2 and a rotary magnet M9I5 for driving the wipers noted. Further the operator finder switch 800 comprises a number of relays including a stop relay R940,y

a control relay R950, a trunk relay R960, an information relay R9'I0 and two pilot relays R980 and R500, connected and arranged'in a manner more fully described subsequently.

` The operator key set and marking circuit 200, shown in Fig. 2 and associated with the operator position 800, comprises ten respective digit keys XI to X0, inclusive, an error key XII and a\ number of relays including three transfer relays R220, R225 and R230, an error relay R210, three control relays R240, R250 and R260, a start relay R215, a release relay R265, a rst group of marking relays IC and 2C, a second group of marking relays ID, 2D, 3D and 0D, anda third group of marking relays-IU, 2U, .3U and 4U.

It is noted that the digit keys KI to X0, inclui sive, are operated successively to set up a hundred'digit, a ten digit and a unit digit, thereby Also the trunk circuit at the cluding the marking relays IC and 2C to register the hundred digit, to cause the second group of nlmarking relays including the marking relays ID,

2D; 3D and 4D to register the ten digit, and to cause the third group of-marking relays including the marking relays IU, 2U, 3U and 4U to register the unit digit. Furtherthe operator key set and marking circuit 200 is connected and arranged with respect to the trunk circuit at the first operator position 800 in a manner more fully described subsequently.

The identity lamp and trunk iinder start unit 300, shown in Fig. 3 and associated with the operator position 600, comprises a first group of identity lamps including the identity lamps CLI and CL2, a second group of identity lamps including the identity lamps DLI to DLIO, inclusive, and a third group of identity lamps including the identity lamps ULI to ULIO, inclu sive. It is noted that the rst group of identity lamps including the identity lamps CLI and CL2,

" the second group of identity lamps including the identity lamps DLI to DLIO, inclusive, and the third group of identity lamps including the identity lamps ULI to ULIO, inclusivefrespectively correspond` to the hundred, ten and unit digits of the directory number of a calling telephone .station in the?. A. B. X. Finally the indentity lamp and trunk iinder start unit 300 comprises a number of relays including a start relay R3I0 -and two marking' relays R320 and R330 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 b'e facilitated from a consideration of the detailed operation of the various pieces of apparatus incident to the completion of diiierent calls and the handling of v applying ground potential by way of the resistor various calls at the operator position 800, as will appear hereinafter.

'Local call from one station to another station in the P. A. B. X

A local call which is to be extended from one from its switchhook. For example, in extending a call. from the telephone station TI to the telephone stationT2 the call is first initiated at the station TI by removing the receiver of the telephone instrument thereat from its switchhook, thereby to 4complete a bridge path including the receiver of the telephone instrument between the line conductors C606 and C601 of the telephone line 605 extending to the telephone station TI. When this bridge path is'completed between the line conductors of the telephone line 605 a circuit is completed for energizing in series the windings of the line and cutoff relay R690 included in the line circuit 690 individually associated with the telephone line 605. This circuit extends from ground by way of the lower winding of R690, the contacts 692, C601, the bridge path between the line conductors C601 and C606, C606, the contacts 69|, and the upper and'intermediate windings of R690 to battery. When energized over the above-traced circuit the line and cutoi relay R690 operates partially, thereby to complete, at the contacts 695, an obvious path for applying ground potential to the start conductor C691 and to complete, at the contacts 693,

649 of the marking `network 696 to the start conductor C688 extending to the Ldistributor 680, and

an obvious path `for applying" direct ground potential by way of the conductor C698 to the iirst contacts in the vertical control contact baul-rsv of the local finder switches. The application of ground potential to the start conductor C686 initiates operation of the distributor 680 and the application of direct-ground potential to the ilrst` contacts in the vertical control contact banks of the locali-Inder switches marks the telephone line 605' as terminating in the rst level of the main contact banks of the local nder switches.

The distributor 680 is of the preselective type and operates to select another idle local link as soon as the finder switch of a previously selected local link operates to find a calling telephone line after it has been taken for use. Assuming that the distributor 680 has previously selected the local link illustrated to be taken for use at this time, the distributor 680 operates to cause ground potential to be applied to the start conductor C682, thereby to complete an obvious circuit for energizing the winding of the hold relay R660.l The hold relay R660 then operates to interrupt, at the contacts 66I, a point iny a multiple path for applying groundpotential to the all-linkbusy conductor C661, and to complete, at the contacts 662, \an obvious path for applying ground potential to the control conductor C618 of the trunk 615. The previously mentioned path for applying ground potential to the all-linkbusy conductor C68I in the local iinder switch 600 extends, when completed,y from ground by way of the contacts 66I and 626 to the all-linkbusy conductor C68Ij.l IAlso the hold relay R660 completes, at the contacts 663, obvious multiple circuits for energizing\the lower windings of the switching relays R640 and R650, thereby to render each of the switching relays extremely fast to operate in the event the upper winding there-- of is energized. Further the hold relay R660 prepares, kat the contacts 661, a circuit traced hereinafter forA energizing the vertical magnet M62I and prepares, at the contacts 666, a circuit traced hereinafter for energizing the rotarymagnet M623. The distributor 680 then operates t'o cause ground potential to be applied to the vertical conductor C686, thereby to complete the previously mentioned circuit for energizing the vertical magnet M62I, this circuit` extending from the grounded vertical conductor C686 by way of the contacts 661 and M62I to battery. When energized over the above-traced circuit the vertical magnet M62I operates to drive the rst and second wiper sets of the mechanism 6 I 0 one step in the vertical direction and to complete, at the contacts 622, an obvious path for applying ground potential to the interrupter conductor C685. The application of ground potential to the interrupter conductor C685 causes the distributor 680 'to interrupt the application of ground potential to the vertical conductor C686, whereupon the vertical magnet M62I restores to interrupt, at the contacts 622, the previously mentioned path for applying ground potential to the interrupter conductor C685. Accordingly, the vertical magnet M62I operates intermittently, thereby to drive the iirst and second wiper setsof the mechanism 6I0 step by step in the vertical direction until the control wiper 6I9 ductors C608 and C609 of the telephone 1ine605.

engages a contact in the associated vertical control contact bank having direct ground potential thereon, whereupon an obvious path is completed for applying ground potential to the test conductor C681 extending to the distributor 680. In the present instance, the first and second wiper sets of the mechanism 6I0 are driven only vertical control wiper 6|9 engages the first contact in the associated vertical control contact bank having ground potential thereon. The application of ground potential to the test conductor C681 causes the distributor 680 to operate; thereby to interrupt the application of ground potential to the vertical conductor 'C686 and to apply ground potential to the rotary conductor C686.

The application of ground potential to the rotary conductor C684 completes the previously mentioned circuit for energizing the rotary magnet M623, this circuit extending from the grounded rotary conductor C684 by way of the contacts 666, 650'and 661 and M623 to battery.

When energized over the above-traced circuit' the rotary magnet M623 operates to drive the first and second wiper sets of the mechanism 610 one step in the rotary direction and to cornplete, at the contacts 624, an obvious path for applying ground potential to the interrupter conductor C685. This application of ground potenupper winding of the switching relay R650, thereby positively to prevent operation of the latter relay at this time. relay R640 interrupts, at the contacts 648, a point in a circuit traced hereinafter for energizing the releasev magnet M625 and completes,

one step in the vertical direction, whereupon the` at the contacts 646, a connection between the rotary conductor C684 and the/guard conductor C683, this connection extending from the rotary conductor C684 by way of the

contacts

666, 650, 646 and 664 to the guard conductor C683. When the rotary conductor C684 isA connected to the guard conductor C683, operation of the distributor 680 to control the local finder switch 600 is arrested, whereupon the distributor 680 operates automatically-,to select for use another idle one of the local links.

Finally, upon operating, the switching relay R660 completes, at the contacts 66|, 643 and 644, connect-ions between the conductors of the trunk 630 extending to the rst wiper set of the mech- Aanism 6I0 and the trunk 615 extending between the local finder switch 600 and the local connector switch 'l00.V When the trunks' 630 and 615 are connected a low resistance circuit is completed for energizing the intermediate winding tial to the interrupter conductor C685 causes the distributor 680 to remove the application of ground potential to the rotary conductor C686, whereupon the rotary magnet M623 restores to interrupt, at the contacts 626, the previously mentioned path for applying ground potential to the interrupter conductor C685. Accordingly, the rotary magnet M623 operates intermittently, thereby to drive the first and second wiper sets of the mechanism 60 step by step in the rotary direction until either the control wiper 6 l 5 or the control wiper 6|8 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 605 is included in the first section of the main contact bank of the mechanism 6I0. Accordingly, when the control wiper 6|5 of the first wiper set of themechanism 6I0 engages the con.

tact of the contact set in the first section of the main contact bank of the mechanism 640 terminating the control conductor C608 of the telephone line 605, a circuit is completed for energizing the upper winding of the switching relay R640. This circuit extends from ground by way of the contacts 694 and 695, the start conductor C691, C698, the vertical control wiper 6l9, C639, the upper winding of R660, the control wiper 6|5, C608,'the contacts 693 and the intermediate winding of R690 to battery. When energized over the above-traced circuit the switching relay R640 operates exceedingly fast, thereby to complete, at the contacts 665, a holding circuit for energizing the intermediate winding thereof, this circuit extending from ground by way of the contacts 662, the control conductor C618 of the trunk 615, the

contacts

651 and 645 and the in'- tacts 649, a point in a circuit for energizing the of the line and cutoi relay R690, this circuit extending from the grounded control conductor C618 of the trunk/615 by way of the contacts 651 and 644, C633, the wiper 6I5, the control conductor C608 of the telephone line 605, the contacts 693 and the intermediate winding of R690 to battery. When the intermediate winding of the line and cutoff relay R690 is thus energized this relay operates completely, thereby to interrupt, at the contacts 696, the previously traced path for applying ground potential to the start conductor C691 extending to the marking network 696 in order to arrest operation of the disj tributor 680. Further the line and cutoff relay R690 interrupts, at the contacts 69! and 692, the previously traced circuit for energizing the windings thereof across the line conductors C606 and C601 of the telephone line 605, thereby to clear the telephone line 605 of impedance elements. At this time ground potential appearing upon the control conductor C608 of the telephone line 605 is applied to the control conductor C609 thereof, thereby to mark the telephone line 605 as busy to the local connector switches and the trunk finder switches having access thereto.

Also it is noted that when the carriage of the mechanism 6|0 is driven one step in the vertical direction the set of switch springs S625 and S621 are actuated. More particularly, the contacts 626 and 621 of the set of switch springs S625 are respectively actuated into disengagement and into engagement; while the contacts '629 and 628 ofthe set of switch springs S621 are respectively actuated into disengagement and into engagement.

Further it is noted that the distributor 680 operates in order to select another idle local link for use only in the event ground potential appears upon the all-link-busy con-ductor C68| and in at least one of the local nder switches, ground potential being removed from the all-link-busy conductor C68l in the local nder switch 600 at this time due to the operated condition of the set of switch springs S625, as previously noted. Also ground potential is applied to the guard conductor C683 in the local nder switch 600, thereby to prevent the distributor 680 from4 Also the switching ,C618 ofv the trunk 615 dueto the busy condition of the local finder switch 600. The path for applying ground potential in the nder switch 600 to the guard conductor C683 extends from ground by way of the contacts 628 of the set of switch -springs S621.and the contacts 665 to the guard conduotor C663, the hold relay R660 being restored at this time. Further it is noted that the hold relay R660 is of the slow-to-release type and restores shortly after the distributor 680 is released. Upon restoring, the hold relay R660 interrupts, at 'the contacts 662, the previously traced path for applying ground potential to the controlconductor C610 of the trunk 615, ground potential being applied to the control conductor in` the local connector switch 100 at this time. Further the hold relay R660 interrupts, at the contacts 663, the previously mentioned multiple circuits for energizing the lower windings of the switching relays R640 and R650, the switching relay R640 being re' tained in its operated position at this. time due to the completed Aholding circuit for energizing theintermediate winding thereof.

thereof in series with the upper winding of the transfer relay R130, this holding circuit extending from 'ground by way of the lower winding of R105, the contacts 106, 10| and 13|, and the upper` winding of R130 to battery. Upon operating, the transfer relay R1|0 prepares, at the i contacts 1| I. a circuit traced hereinafter for energizing in multiple the lower winding thereof and the rotary magnet M191 of the control switchv190; upon operatlng'the transfer relay R120 prepares, at the contacts 125, a circuit Vtraced hereinafter for energizing in vmultiple the lower winding thereof and the vertical magnet M111 of the mechanismy 110; and upon operating, the transfer relay R130 prepares, at the contacts 135, a circuit traced hereinafter'for energizing in multiple the lower winding thereof and the rotary magnet M118 of the mechanism 110. At this time the local connector switch 100 has been rendered responsive to digits to be transmitted thereto from the telephone station TI,

a loop circuit is completed for energizing in' .Y

series the upper and lower windings of the line relay R100 in the local connector switch 100, this circuit extending from ground by way of the lower winding of R100, the line conductor C611 of thetrunk 615, the

contacts

654 and 643, C632 and the wiper 6I4 to the line conductor C601 of the telephone line 605, and from battery by way of the upper winding of R100, the line conductor C616 of the trunk 615, the contacts 65| and 64|, C63| and the wiper 6|3 to the line conductor C606 of the telephone line 605, the line conductors C606 and C601 of the telephone line 605 being connected together by way of the bridge path at the telephone station TI. When the upper and lower windings of the line relay R100 are thus energized this relay operates to complete, at the contacts 102, a circuit for energizing the upper winding of the transfer relay R120, this circuit extending from ground by way of the contacts 102, the contacts 104 of the set of switch springs S182 and the upper winding of R120 to battery. When the upper winding of the transferrelay R120 is thus energized this relay operates to complete, at the contacts 124, an obvious multiple path for applying ground potential to the control conductor C616 of the trunk 615, as previously noted. Also, upon operating, the transfer relay R120 completes, at the contacts 123, a circuit for energizing in series the lower winding of the battery supply relay R105 and the upper winding -of the transfer relay R130,- this circuit extendingv from ground by way of the lower winding of R105, the contacts 123 and the upper winding of R130 to battery. When the lower winding of the battery supplyv relay R105 and the `upper winding fer relay R110, this circuit extending from ground by way of the set of switch springs S191, the

contacts 121 and the upper winding of R1|0 to battery. When the upper winding of the transfer relay R1I0 is thus energized thisrelay opcrates'. Upon operating the battery supply relay R105 completes, at the contacts 106, a holding circuit. for energizing the lower winding In viewer the above description of the op! eration of the local finder switch 600 under the control of the distributor 680 to find the calling telephone line- 605 and the subsequent operation of the local connector switch incident to the seizure of the calling telephone line by the local iinder switch 600, it will be understood that these pieces of apparatus `operate in substantially' the same manner regardless of the one hundred line group including the calling telephone line. In the present example the switching relay R640 in the local finder switch 600 is operated due to the fact that the calling telephone line 605 is included in the first group of one hundred lines accessible to the local finder switch 600. On the other hand, in the event the calling telephone line 605 had been in the second group of one hundred lines the switching relay R650 would have been operated in a similar manner.

The subscriber at the telephone station TI then dials the first digit of the directory number of the called telephone station T2, thereby to transmit a first series of impulses by way of the subscriber loop circuit to the line relay R100 in the local connector switch 100. It is noted that the rst digit of the directory number of any telephone station in the P. A. B. X, either 1 or 2, depending upon which one hundred line group includes the telephone line extending' to the telephone station. In the present example the telephone line 150 extending to the telephone station T2, is included in the-second group of one hundred lines; accordingly, the rst digit dialed is the digit 2. The line relay R100 follows the dialed impulses in the usual manner, restoring each time the loop circuit is interrupted and operating each time the loop circuit is completed. Each time the line relay R100 `restores it interrupts, at the contacts 102, the previously traced circuit for energizing the upper winding of the transfer relay R120 and completes, at the contacts 103, the previously mentioned circuit for energizing in multiple the lower winding of the transfer relay R and therotary magnet M191 of the control switch 190. The circuit for relay R100 operates it interrupts, at the ,contacts 103, the previously traced. circuit for energizing in multiple the lower winding of the transfer relay R110 and the rotary magnet M191, and fcompletes, at the contacts 102, the previously traced circuit for energizing the upper windingA set of switch springs S191 is actuated into disengagement, thereby to interrupt the previously traced circuit for energizing the upper winding of the transfer relay R110; while the set of d switch springs S108 is actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the release magnet M198. In the present instance the first.. digit comprises two impulses, thereby to cause the rotary magnet M191 to drive the wipers noted of the control switch 100 two steps in the counterclockwise direction.

At the conclusion of the rst digit the line relay R100 reoperates, thereby 'to cause' the transfer relay R110 to restore shortly thereafter. Upon restoring the` transfer relay R110 interrupts, at the contacts 1 I 1, a further point in the previously traced circuit for energizing in multiple the lower winding thereof and the rotary magnet M191, and prepares, at the contacts 112, the previously mentioned circuit for energizing in multiple the lower winding of the transfer relay R120 and the verticaLmagnet M111.

The subscriber at the telephoneE station T1 then dials the second digit of the directory number of the called telephone station T2, thereby to transmit a second series of impulses by way of the subscriber loop circuit to the line relay R100 in the local connector switch 100 in the manner previously explained.' As previously' noted the line relay R100 follows the impulses. Each time the line relay R100 restores it completes, at the ontacts103, the previously menfer relay R120 and the vertical magnet M111 extends from ground by way-of the contacts 103, 112 and 125 and the lower winding of R120 to battery, and from the contacts 125 by way of the vertical magnet M111 to battery. On the other hand, each time the line relay R100 operates it interrupts, at thecontacts 103, the previously traced circuit for energizing in multiple the lower winding of the transfer relay .R120 and the vertical. magnet M111. Thus the transfer relay R120 remains operated during impulsing, this relay being of the slow-to-release type. Each time the vertical magnet M111 is energized it operates to drive the first andsecond wiper sets of the mechanism 110 one step in the vertical direction. When the rst and second wiper sets of the mechanism 110 are driven one step in the vertical direction away from their normal positions the sets of switch springs S180, S182 and S185 are actuated. More particularly, the set of swltchsprings S180 is-actuated into engagement, thereby to complete an obvious multiple path for applyingdg'round potential to the control conductor C618 of the trunk 615;

vwhile the set of switch springsS185 is actuated into engagement, thereby to prepare a circuitY traced hereinafter for energizing the release magnet M119. The contacts 184 of the set of switchv springs S182 are actuated into disengagement, thereby to interrupt the previouslyl traced circuit for energizing the upper winding of the transfer relay R120; while the contacts 183 of the set of switch springs S182 are actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the winding of the switching relay R160.

At the conclusion of the second digit the line relay R reoperates, thereby to cause the transfer relay R to restore shortly thereafter. Upon restoring the transfer relay R120 interrupts, at the contacts 125, a further point in the previously traced circuit for energizing in multiple the lower winding thereof and the vertical magnet M111, and prepares, at the'contacts 128, a point in the previously mentioned circuit for energizingin multiple the lower winding ofthe transfer relay R and the rotary magnet M110.

rEhe subscriber at the telephone station TI then dials the third digit of the directory number of the called telephone station T2, thereby to transmit a third series of impulses by way of the subscriber loop circuit tofthe line relay R100 in the local connector switch 100 in the manner previcusly explained. As previously noted the line relay R100 follows the impulses. Each time the line relay R100 restores it completes, at the contacts 103, the previously mentioned circuit for energizing in multiple the lower winding of the transfer relay R130 and the rotary magnet M110. The circuit for energizing in multiple the lower winding of the transfer. relay R130 and the rotary magnet M118 extends from ground by way of the contacts 103, 112, 126 and 135 and the lower winding of R130 to battery, and from the contacts by way of the rotary magnet M118 to battery; On the other hand, each time the line relay R100 operates it interrupts, at the contacts 103, the previously traced circuit for energizing in multiple the lower winding of the transfer relay R130 and the rotary magnet M118. Thus the transfer relay R130 remains operated dur.'

ing irnpulsing, this relay being of the slow-torelease type. Further it is noted that when the line relay R100 restores upon the first impulse of the third digit it interrupts, at the contacts 101, the previously traced holding circuit for energizing in series the lower winding of the battery supply relay R105 and the upper winding ofthe transfer relay R130, the original circuit for energizing in series the lower winding of the battery supply relay R105 and the upper winding of the transfer relay R130 being interrupted at the contacts 123 due to the restored condition of the transfer relay R120 at this time. Also upon restoring, the transfer relay R120 interrupts, at the contacts 124, the previously mentioned path for applying ground potential to the control conductorC618 of the trunk 615, ground potential being applied to the control conductor C618 of the trunk 615 due to the operated condition of the set ofswitch springs S at this time.

Each time the rotary magnet M118 is energized it operates to drive the rst and second wiper sets of the mechanism 110 one step in the rotary direction.

4At the conclusion of the third digit the line circuiting the winding of the busy relay R140.v

relay R100 reoperates, thereby to cause the transfer relay R130 to restore shortly thereafter. Prior to the restoration of the transfer relay R130 and at the conclusion of the third digit the first and second wiper sets of the mechanism 110 engage corresponding lines in the rst and second sections of the main contact bank, Y,whereupon a test circuit for the busy relay R140 is completed. This test circuit extends from battery by way of the winding of R140, the contacts 133, C1|5, the wiper 193 and engaged second contact in the associated contact bank 194 of 'the control switch 190, C149 and the control wiper 116 of the second Wiper set to the control conductor C153 of the telephone line 150 extending to the telephone station T2. In the event the telephone station T2 is busy at this time, ground potential appears upon the control conductor C153 of the telephone line 150, thereby to complete a circuit identical to the test circuit previously traced for energizing the Winding of the busy relay R140, thereby to cause the latter relay to operate. Upon'operating, the busy relay R140 prepares, at the contacts 144, a holding circuit traced hereinafter for `energizing the winding thereof. Upon restoring the transfer relay R130 interrupts, at the contacts'133, the previously traced operating circuit for energizing the winding of the busy relay R140 and completes, at the.

contacts 134, the previously mentioned holding circuit for energizing thewinding of the busy relay R140. The holding circuit for `energizing the winding of the busy relay R140 extends from the grounded control conductor C618 of the trunk 615 by way of the contacts 144 and 134 and the winding of R140 to battery. V'

Also upon operating, the busy relay R140 interrupts, at the contacts 14| and 143, points in a circuit tracedhereinafter for projecting ringing current over the telephone line 150 extending to the calledtelephone station T2. Finally upon operating, the busy relay R140 completes, at vthe contacts 142,/a circuit for returning busy tone current over the loop circuit to the calling telephone station TI, this circuit extending from the ungrounded terminal of a grounded source of busy current by Way of the conductor C104, the

l contacts 12|,142 and 153 and the condenser 108 vbusy tone at this time, thereby to indicate to the subscriber thereat that the connection cannot immediately be had due to the busy condition of the called telephone station T2. f

The subscriber at the calling telephone station T| then releases Athe line circuit 690, the local finder switch 600 and the local connector switch 100 by replacing the receiver ofthe telephone instrument thereat upon its switchhook in a manner more fully described hereinafter.

Accordingly. the busy relay R140 `does not operate at this time. Hence, when the transfer relay R130 restores it interrupts, at the contacts 133,

j the contacts l132, C1|5, vthe `rwiper 193 and enthe previously traced test circuit for the busy relay R140 and completes, at the contacts 132, a path for applying ground potential to the control conductor C153 of the telephone line 1.50 extending to the called telephone station T2, this path extending from ground by way of the wiper 19| and engaged second contact in the associated contact bank 192 of the control switch 190, C1|6,

gaged second contact in the associated contact bank 194 of the control switch 190, C149 and the of the telephone line 150 causes the line circuit individually associated therewith to operate, thereby to mark the telephone line 1.50 extendingto the called telephone station T2 as busy.

Also upon restoring, the transfer relay R130com- 'pletes, at the contacts 131, a circuit for energizing the winding of the switching relay R160, this circuit extending from ground by way. of the contacts 102, the contacts 183 of theset of switch springs S182, C1I3, the contacts` 131, the wiper 195 and engaged second contact in the associated contact bank/196 of the control switch 190 and the winding of R160 to battery. gized over the above-traced circuit the switching relay R160 operates to complete, at the contacts 163,'an obvious alternative path for applying ground potential to the control conductor C153 of the telephone line 1.50 and to interrupt, at the contacts 164, a point in the previously v mentioned circuit for energizing in multiple the the ungrounded terminal of a grounded sourceof ringing current by way of the conductor C101, the contacts 143 and 154, C141, the contacts 162 and the wiper 11.5' to the line conductor C152 of lthe telephone line 150, and from battery by way of the lower winding of the cutoiI relay R150, the contacts 14| and v15|,'C146, the contacts16| and the wiper 114 to the line conductor C15| of the telephone line 150, the ringer at the called telephone station T2 being connected across the line conductors C15| and C152 ofthe telephone line 150. Accordingly, the ringer at the called telephone station T2 is operated at this time,

When the subscriber at the called telephone station` T2 answers the call by removing the receiver of the telephone instrument thereat fromits switchhook av circuit substantially identical to that previously traced lfor projecting ringing current over the telephone line is completed forenergizing the lower lwinding of the cutoif relay R150. When the lower winding of the cutoff relay R150 is thus energized this relay'operates shortly thereafter, this relay be- On the other hand, inthe event the called telephoneJ station T2 'is idle when the local connector switch 106 operates to seize the telephone line 150 extending thereto in the' manner previously explained, battery potential appears upon the control conductor C153 of the telephone line 150, thereby to complete a circuit identical to thetest circuit previously traced for short- 154, the previously traced circuit for projecting When enerringing current over the telephone line 150 ex'- v andl the called telephone station T2. This loop` circuit extends from ground by way of the lower winding of R105, the contacts 122 and 155, C101, l the contacts 162 and the wiper 115,.,to the line conductor` C152 of the telephone line 150 and from battery by way of thel upper winding of R105. the contacts 152, C146, the contacts 16| and the wiper 110 to thel line conductor C15! of the telephone line 150the telephone instrument at the called telephone lstation T2 being connected across the line conductors 015| and C152 of the telephone line 150 at this time. Accordingly, talking battery is supplied to the telephone instrument at the calling telephone station Tl from the line relay R100, while talking battery is supplied to the telephone instrument at the called telephone station T2 from the battery supply relay R105. Finally, it is noted that the loop circuit extending -to the calling telephone station T| is interconnected with a. loop circuit extending to the called telephone station T2 by the condensers 106 and 109, thereby to complete a two-way communication connection between the calling telephone station Tlv and thecalled telephone station T2.

'I'he release of the established connection between the calling telephone station Tl and the called telephone station T2 is primarily under the control of the subscriber at the calling telephone station Ti and when the receiver of the telephone instrument at the calling telephone l station TI is replaced uponVl its switchhook the .previously traced loop circuit for energizing the windings of the line relay R100 is interrupted, thereby'to cause the ,latter relay to restore. Also, when the receiver of the telephone instrument at the called telephone station T2 is replaced upon its switchhook the previously traced loop circuit for energizing the windings of the battery supply relay R105 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the line relay R100 interrupts, at the. contacts 102, the previously traced circuit for energizing the Winding of the switching relay R160, thereby to cause the latter relay to restore shortly thereafter, the latter relay being of the slow-to-release type. Upon restoring, the switching relay R160 completes, at the contacts 169, the previously mentioned circuit for energizing in multiple the release magnet-M119 and the release magnet M198, this circuit extending from ground by way of the contacts 103, 1|2, 126,-136, 169 and 169, the set of switch springsoS185 and the release magnet M119 to battery, and from the contacts 166-by way of the set of switch springs S198 and the release magnet M198 to battery. When thus energized the reiease magnets M119 and yM198 operate.

Upon operating the release `magnet M198 releases the wipers` noted ofthe control switch 190 and causes these" wipers to be returned to their normal positions. When the wipers noted of the control switch 190 are returned to their normal positions the sets of switch springs S191 and S198 are actuated. More particularly, the set of 4 switch springs S191 is actuated into engagement,

thereby to prepare the previously traced circuit for energizing the upper winding of the transfer relay R1I0; while the set of switch springs S198 is actuated into disengagement, thereby to inter rupt the previously traced circuit for energizing the release magnet M198. u

Upon operating, the release magnet M119 releases the rst and second wiper sets of the mechanism 110, thereby to cause these wiper sets to be returned to their normal ,positions When the wiper sets of the mechanism are returned to their normal positions the sets of switch springs S160, S182 and S185 are actuated. More particularly, the set of switch springs S is actuated ito disengagement, thereby to interrupt the previously mentioned path for applying ground potential to the control conductor C618 of the trunk 615; while the set of switch springs S is actuated -into disengagement, thereby to interrupt the previously traced circuit for energizing the release magnet M119. Finally the contacts 163 and 186 of the set o f switch springsy S182 are respectively actuatedinto disengagement and into' engagement, thereby respectivelyV to interrupt a further point in the previously' traced circuit for energizing `the winding of the switching relay R160 andl to prepare a point in the previously traced circuit for energizing the Y upper winding of the transfer relay R120. When the switching relay' R160 restores the previously traced paths for applying ground' potential to the control conductor C159 of the telephone line 150 are interrupted, vthereby to cause the line circuit individually associated with the telephone line 150 to operate in order to mark the telephone line 150 as idle. Also when ground potential is removed from the controlcpnductor C618 of the trunk 615 the previously; traced holding circuit for energizing the intermediate winding o'f the line and cutoff relay R690 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the line and cutoi relay R690 interrupts, at the contacts 693, a further point in the previously traced path for applying ground potential to the control conductor C609 of the telephone line 605 extending to the telephone station TLthereby to mark the telephone line 605 as'idle.

Finally, when ground potential is removed from the control conductor C618 of the trunk A 615 the previously traced holding circuit for energizing the intermediate winding of the switching relay R660 is interrupted, thereby to cause the latter relay to restore, and complete, at the contacts 698, the previously mentioned circuit for energizing the release magnet M625, this circuit extending from ground by way of the vcontacts 66|, the contacts. 621 of the set of switch springs S625, the contacts 65| and 648 and the release magnet M625 to battery. When thus energized the release magnet M625 operates to release the rst and second wiper sets A626 of the set of switch springs S625 are actuated. into engagementl therebyto complete the previously traced path ior applying ground potential to the all-link-busy conductor C681 extending to the distributor 600. Thisapplication of ground potential to the all-lin'k-busy con` ductor C68I- extending to the distributor 680 renders the .distributor 680 operative to preselect for use an idle one of the local links. Also contacts 629 of the set of switch springs S621.

are actuated into engagement, .thereby to connect the control conductorl C618 of the trunk 615 to the guard conductor C683 extending to the distributor 680.

At this time the 1oa1 ander switch son and' the local connector switch 100 of the local link illustrated are completely released, thereby to render this local link available for further use.

vthe contacts 628 of the vset of switch springs lS621 are actuated into disengagement, thereby to Also the line circuit 690 individually associated Y with the telephone line 605 is restored, thereby to-mark the telephone line 605 extending to the telephonestatin Ti as idle. Similarly, the line.

ycircuit individually associated with the telephone line 150 is restored, thereby to mark the telephone line 150 extending to the telephone station T2 as idle. A

Information call from a 4'station to the operator position inthe P. A. B. X

An information call which is to be extended from one of the stations to the operator position in the P. A. B. X is initiated at the-calling station by removing the receiver of the telephone vinstrument thereat from its switchhook'. For

example, in extending an infomation call from the telephone station TI to the operatorposition 800 the call is first initiated at the station -Tl by removing the receiver of the telephone instrument thereat from its switchhook, thereby to cause the line circuit 690 individually associated with the telephone line 605 extending to,the calling telephone station TI to operate as previously explained. Upon operating, the line circuit 690 initiates operation of the distributor 680, whereupon the vdistributor 680 assigns the previously selected local link, such, for example, as the local link illustrated, to the use of the calling telephone station TI and causes the local finder switch 600 of the local link illustrated to seize the telephone line 605 extending to the calling telephone station TI in the previously described manner. After the local finder switch` 600 of the local link illustrated seizes the telephone line 605 extending to the calling telephone station Tl, the distributor 680 operates to preselect anotherone ofthe idle local links to the use of acalling telephone station as. previously explained. Also, when the local nder switch 600 seizesy the telephone line 605 ,extending to the calling telephone station TI, a loop circuit is completed between the line relay R in the local connector switch previously explained, whereupon the local connector switch 100 is rendered responsive to digits transmitted from "the calling telephone sta-'v 100 and the calling telephone station Tl as in the line circuit 690 occupies-its operated position; while the switching relay R640 in the local iinder switch 600 occupies its operated position. Also, in the local connector switch 100 theline relayjR100, the transfer relays R1I0, R120 and yR and the battery'supply relay R105 occupy contacts 102, thel previously traced circuit for energizing the'upper winding of the transfer relay R120 and completes, at the contacts 103,l l the previously traced multiple. circuit for energizing the lower winding of th transfer relay R110 and the rotary magnet M191 of'thefcontrol switch 190. On the `other hand, each time the line relay R100 operates, it interrupts, at the contacts 103, the previously traced .circuit for energizing in multiple the lower, winding or the transfer relay and-the rotary magnet M191 and completes, at the contacts 102, the lpreviouslyI traced circuit for energizing the upper winding of the transfer relay R120.' Thus, during impulsing, the transfer vrelays R1I0 and R120 remain operated.

' fer relay R110 torestore shortly thereafter.

Accordingly, at this time, the rotary magnet M191 is successively energized three times. thereby to cause the wipers noted of the control switch v to be driven in the counterclockwise/direction into engagement with the third contacts in the associated contact banks. Also, when the wipers noted of the control switch 190 are driveri one step in the counterclockwise direction away from their normal positions, the'sets of switch springs S191 and S198 are actuated.I More particularly, the set of switch springs S191 is actuated into f disengagement, thereby to interrupt the previously traced circuit for energizing the upper winding of the transfer relay R110; while the set of switch A springs S198 is actuated into engagement, Ythereby to prepare the previously traced circuit for energizing the release magnet, M198 of the control switch 190.

At the lconclusion of the single digit, the line relay R100 reoperates, thereby to .cause the trans- At this time no further digit-s are dialed at the calling telephone station TI and the operation of the control switch 190 is effective to complete a circuit for energizing the winding of the pilot relay R980 and a path fory applying battery potential to the marking conductor C921 included in a group of conductors extending between the local link illustrated and the operator nder switch 900. The circuit for energizing the winding of the pilot relay R980 extends from ground by way of the wiper 19| and engaged third contactin the associated contact bank 192 of the control switch. 190, C1I0l and the winding of R980l to battery; andthe path for applying battery potential to the marking conductor C921 extends from battery by way of the winding 'of the busy relay R140, the contacts 133, C1I5 and the wiper 193 and engaged third contact in the associatedcontact b ank '|94 of the control switch 190 to the marking conductor C9121. The application of battery potential to the marking conductor C921