US1941085A - Telephone system - Google Patents

Description

`De 26,f'1933.v A. E. HAGUE Er AL 1,941,085

TELEPHONE SYSTEM Filed July 1, 1932 3 Sheets-Sheet l "1. ji I [Ik 0: In 'u l; fe L l H E l, ff QJ A .1. E [|L Q bg Q Q LL IIHII LL LL E Lt .A5/#A605 vv Y /Nl/E/VTOR5.JB.DRAPER v d BV Wwf/m A TTORNE Y we@ 26, i933. A. E, HAGUE Er AL 1,941,085

TELEPHONE SYSTEM Filed July 1, 1952 3 Sheets-Sheet 2 o Il (I) Yi' .dll

.A .E HA GUE /NVENTORSJ B. DRA/DER @Loywwm A TTORNEY Dec. 26, 1933. A. E. HAGUE ET AL TELEPHONE SYSTEM Filed July l, 1932' 3 Sheets-Sheet 3 EHAGUE /NVENTORS.JBDRAPER www@ ATTORNEY Patented Dec.

ismisv TES PAT-ENT QFFICE f1';94 1,o5V i v i l TELEPHONE SYSTEM l Alfred E. Hag'ug'wesvorange; NLJ'., 'and {mh-nk f f B- `DraDel,`BlQ0klyn," N.'Y., assignors'to Bell Telephone yLaiboratories,V Incorporated, New York, N. Ywa@corporatony of'Ne'w York '4 Application Jgiy `11932( serialfNo". 620,468

- sclaims, (o1. ive- 185 fcircuit originating Vin the line finder shown in Fig. 1 and terminatingy in brushes which have access to a called subscribers line in the exchange as shown in `diagrammatic form. f

To showtheembodiments or" the features of this invention in connectionwith thesev drawings,

descriptions will be made' of ya call from a calling subscriber? at A,` through-the callingr subscribersv line'circuit, andithe 'lineffinder LF, shown in Fig. 1, and the selector-connectorvB shown in 65 Figs. 2: and '3 to -a calling-subscriber Vat C, Fig. y3;Vfo1lowed by theoperation of these circuits if theV calling subscriber 'fails-to dial within a cerk tain 'time after they seizure of the selector-con-v nector and if 'the subscriber fails to dial the corn-4 70 plete'n'u'mberutov establish the connection tol thel Y l called: subscriber,y namely, the release' oithe linez finder and the selectors-connector under these circumstances'. V.These descriptions in turn will befollowed :bydescriptions of the' operations of 75 the` circuitswhereby the calling subscriber is pre'- .ventedlffroml seizingan'other' line finder-and establishin'gfav connection until hehas replacedA theV Y receiver on the'f-SWitChh'oOk', whereby, after. the i calling subscriberhashung up his receiver at the Y completion-of the conversation' with the called subscribenalliof the switches used in the connec'" tionare released-arid whereby, if the calledsub'- scriber still has hisf'receiver off the' switchhook, Y his'line"willaimrnediately seize av set of switches, 85 and' hdw allof thesey switches arev released' a' cer'- tain time intervall thereafter providedthe" calledv subscriber takeslno'further actionI withinthisinterval towards-the establishingof anewr connectiongan'dl-how this-called' subscribed'v is thereafter Y. prevented'. fromextending a connection' until after his receiver is replaced on the .switchhook.

Referring n0w"to"a.call from the subscriber `atr A to the subscriber at C a circuit.-is'corr'ipletediv when the-calling;subscriber removesV his receiver from the'switchhook 1to1 cause, the operation of line relay 5,from battery, rrii'ddlewinding of this" relay, lower inner armature and backco'ntact of relay `6,. throughfthe callingsubscribers loopback over .thenpper inner ,armat'ureand backcontact of relay\6,glower windingi-of relay 5f-to; groundik Relay 5' in operating connects"groundf'to'athe c start: lead7i at its lower armature andlfront: contact throughL contacts ,of relays .8',and;-6- .to/start the line finder LFtofconnec't-its brushes 'with'the tere` minals of thislliner circuit and: thuscnnect` the' calling subscribers line to theiselector@connector f B. Relay inoperating alsocon'nects itsuplper winding fro'mbattery through'cbntacts of'y re;

I'tothe'sleevezleadsof the'lineifinder. #110 This invention relates to' telephone systems and particularly to improvements'inlautomatic telephone systems. Y L l 'l An. object of thisinvention is to increase the utility ofthe switching facilities inautomatio' telephone systems., i f I .i

Heretofore, in establishing a connection'` between two subscribers by means off automatic switches, when the calling v'subscriber has failedto actuate said 'switcheseithe'r by failing tod'ial' within a certain time after the seizing of the switches or has failed to complete the desired connection by failureto dialthe complete num-` ber, a signalv has been Aactuatedvai'l an operators `position to permit this operator to clear the con'- nection eitherV by communicating withA the callingssubscriber or releasingthe switchesused-in the attempt rto establish thetconnection..

-It is a feature-#ofthe present'irivention to4 release the automatic switchesseizd'by tliecalling subscriber when hel removesy his re'ceiverl'c iiA the switchhooki-preliminary toA the dialingof' the wanted subscribers numbenif fthe' callings'ubscriber fails' to'dial within a certain tiri-ie" after the seizure of the switchesor the subscriber"A fails to-dialthe complete.nurnber.-l Y Y Another featureof the invention is-an arrangement whereby whenl said'` switches arerelease'd, the callingfsubscriberis prevented fromr seizingV other:Ar switches and.-e`stablishing a connection until he has replaced'the receiver'on thetswitch-y hook.vf

Another feature-is a' timing device common to a plurality'f switches for `controlling therelease,` of seized switches.

Another feature of this invention isa circuit' arrangement whereby if the calling subscriber has hung up his receiver after the 'completion of a conversation with a'c'alled subscriber all7` of I the switches used'in the' connection are released and if the called`-subscriber still has his're'ceiver orf the switchhook his linewill then immediately.' seize a set of switches, but these switches are 'reileased a certainv time interval thereafter provided the called subscriber takes no further laction within this interval towards the est'ablisliing" ofl a new connection andthek called: ysubscriber is thereafter prevented from extending' a' connection or reseizing switches until his receiver is replaced' on the switchhook.

Referring nowt the drawings, Figs.y 1 to.3 may bel connected as shown in Fig'pi.'l Figl'l show/sV a calling subscribers line in a'n'ex'change and a line finder, the latterinfdia'giammatic ,formi Figs l2'and 3" show? 'af"selectoiconnectorY- pulses.

. contact of relay 105.

and lower windings of relay5 from the calling' subscribers line are opened by the operation of relay 6, this relay 5 will be maintained operated through the circuit over its upper winding by theground in the line nder until relay 6 has fully operated when relay 5 releases due to the shunting of the battery connection for relay'5 by the closing of the locking circuit for relay 6 at theV upper outer armature and front contact of relay 6. Relay 6 in operating connects the tip and ring conductors from the calling subscribers line to the tip and ring conductors of the line inder and the selector-connector. The ground connection on the sleeve will now be extended to the multiple sleeve connections terminating in selectorconnectors as indicated at l0. This ground connection extends through the upper outer armatures and back contacts of relays 8 and 6 tomake these multiple connections busy for V incoming calls. rEhe operation of relay 6 will open at this lower armature and back contact the connection to ground for the start lead '7.

for the operation of relay Y through the call- V ingv subscribers loop over these tip and ring conductors, over the tip conductor is connected through contacts of relays 106 and 107, upper winding of relay 105, contacts of relay 108, vertical ,off-,normal contacts 109 to ground, through one winding of the repeating coil 110, the other winding of which is connected to dial tone source, and

over the ring conductor, contacts of relays 108, 106 and 107,-lower winding of relay *105, contact of relay 108 to battery. Relay 105 in operating closes a circuit for relay 111. .This relay Vin turn closes a circuit for relay 112 through the upper winding of relay 112 from ground at the lower inner armature and front contact. Relay 111 also applies this ground at the upper armature and front contact of relay 108 to the sleeve conductor 113 `to the line finder LF to hold thisA switch operated.y Relay 112 in Voperating prepares a pulsing path for the vertical magnet 114 and dial tone is inthe meantime transmitted from the tone sourcethrough repeating coil to thev calling subscriber to indicate that the selectorconnector B is ready for the reception of the first series of impulses. v Y

At each interruption of the dial on 4the sending of the'rst digit impulsesVrelay 105 isreleased. and operates the Vertical magnet 114 in series with relay 115, this latter relay remaining operated during the sending of the first digit im- The pulsing circuit may be -traced from battery through the winding of relay, 115, contact of relay 116, winding ofk vertical magnet 114,.contacts of relay 112, vertical oir-normal contacts 109 to ground at the armature and back After the rst impulse, they .vertical oir-normal contacts. 109 shift the pulsing circuit for the vertical magnet and relay 115 through theupper armature and front contact of relay 115 so that at the end of this series l of impulses when relay 115 releases, the pulsingV circuit may be shifted to the rotary magnet 117. The shifting of the vertical off-normal contact disconnects the dial tone from the calling subscribers line. At the end of this series of il pulses relay 115 releasesand the brushes of the selector-connector have been advanced to the desired level in. which acalled subscribers line is located. On the next digit or series of -dial impulses, relay 105 releases and operates the rotary magnet 117 and relay 118 in series. This circuit may be traced from battery, contact of relay 1l9,winding of relay 118, winding of the vrotary magnetll'?, contacts of relays 120, 122 and 106, upper armature and back contact of relay 115, contactsrof relay 112, vertical oli-normal Vcontacts 109 to ground Aat'the armature and back contact of relay 105. When relay 118 operates thisfcircuit is shiftedjthrough the upper armature and front contact of relay 118 independent of the connection through contacts of relay 122.

Relay 118 remains operated duringthe pulsing due to its slow release characteristics.

At the end of the second series of impulses, the Vbrushes of the selector-connector` B lwill Vbe in connection withthe terminals of the desired subscribers line. When this takes place and the ico line is idle, relay 118 releases and a circuit is thereby completed from battery over the usual cut-01T relay in the line of the called subscriber.,

overthe sleeve connection through contacts of relay 11S, lower winding of relay 120, .contacts of relay 121 and contacts of relay 112 to ground.

This circuit causes relay to be partially operated to close a circuit through its upper inner armature and front contact from battery to. ground at relay 112 to cause the relay 120 to be fully` operated. Relay 120 in operating fully provides a ground for the sleeve circuit at its second upper armature andfrcnt contact from contacts of relay ,112 directly to make the` called subscribers linefbusy. Relay V120`v also prepares a ringingcircuit for thetip and ring conductors to the ycalled subscribers ,line througlithe ringing trip relay 123 from a ringingsource; as hereinafter traced. Before tracing this circuit, howstep therotary off-normal contacts 125-closed a circuitV for the operation of relay 122 from battery, 'Winding of this relay, rotary roff-normal contacts 125, contactsl lcf` relay l*120, to ground at contacts of relay 112. r

Relay 122 closed a locking circuit for itself through its upper inner armatureand front contact through contacts of relays` 106 and 119 to Relay 122 in loperating Y- ever, it should be noted that on the rstrotary '20' a ringing code switch R to yselectarsuitable ringing code. This, the subscriber will now proceed to do by sending a code selecting digit to relay 105. For a single line the codel 1 ishdialed so that vrelay 105 will release once. On the release of relay 105 at this .time a circuit is completed for relay 126 and code switch stepping magnetv 127 in parallel. The circuit for relay 126 extends v from batterythrough the winding of this relay,

contacts of relay 108 to aV point 128 and the-circuit for the stepping magnet 127 extends from battery through the winding of this magnet, contacts l 1,941,081`Y of relay 111 topoint'128'. Fromthis point onther lay 105. `Rela'yi126, in operating, locks itself over its upper. outer armature and front contact to the ground iaturelay 105.`independent lof the uff.-

normall contacts 130 .andcontacts of relay 122. A. circuit is l.also .completed forthe operationaof relayf119lfrom battery, .winding of .relay 119,1contacts of rotary -magnet 117,. contacts .of relay 126,.

oinormal .contacts 130, contacts of relay 122, contacts ofcode .switch start interrupter 131 to ground. This circuit is. closed when vthexinterrdpters .of code switch. Rarel in .apositiontoper- 20'. mit'a. full .code .to be transmitted as is well known in .the art. :Relay 119- opens .at its lower, outer armature and back' contact the.. locking circuit for relay 122 .which nowreleases, and as .nofurther. impulses Yare received relay 126 releases with .thestepping magnet 127. This first impulse lmparts: a rst step to the stepping vmagnet 127 which'the'reupon causes. the brushes ofthe ring? ing lcode switch R to connect with the firstv terminali and thereby close the above mentioned ringing circuit through the windings of the ring.

ing trip relay. 123 for ringingv of the called subscriber.

interrupter 133, right-hand switch bank, first terminal, .and brush of switch R, second upper armature; and. back contact of relay 122, lower outer armature and back contact of relays '123 and. 106, lowerv outer armature and frontcon'.- tact of relay 120 to the ring conductor over the .called :subscribers loop andthe ringer in the subscribers telephone set back over the tip conductor, through the upper outer .armature and frontcontact of relay 120,.upper outer armatures and back contacts ofl relays Y106'ar1d 123,

Athird upperarmature and rback contact of relay 122-,brush and the left-hand `switch bank, rst

terminal, upperY innerarmatureand back contactV of relay 126, upper winding ofjrelay 123 to ground. When the called subscriberB answers z Q relay A123 is operated sufciently over thiscir cuit .to close its locking winding which causesthis relayv to operate fully. The `locking circuit. ymay bextraced from battery, lower` winding .of relay 123 and lower inner armature and front contact torground at contacts of relay 112. .Relay 123 in operating, closes at its upper and lower outer armatures and front contacts a tip and ring connectionto the condensers135 and 136 to complete v' the Vconnection from the calling subscriber to the called subscriber.

This .relay 123 also closes a circuit for relay 107 to;.cause it'to operatev and to close talking battery connections for the called subscribers circuit. The 'talking battery' for ,the called subscribers linemay be tracedfrom battery through-contacts V'of relay 108.upper Winding of relay 107, contacts; of relay 123, contactsof relayslO-and 120 throughthe tip conductor andthe calledV sub-xV scriber.s.loop back over the ring conductor', contactsV of vrelays 120, 106 and 123v through the flower winding of relay 107,. contacts of; relays 123 ands'l to. ground at theupper armature and front contacts ofv relay ,111. Relayr1-07 in4 operating reverses atthe. lowerrarmatures. Aand front ;contacts the connections.. throughsrelay 105-,tor

This .circuit may now be traced fromthe ringingcurrent source 132 throughl thegcodeV the calling subscriber'ss'talking batteri/:supply circuits'for the calling and called Vsubscribers vare now completed through. the condensers 1351and 136, talking battery for both subscribers beingA furnished from the same source, at the third up per .armature and back. contact of relay .108, ground for relay .105.being supplied atthe ver'- tical ofi-normal contacts 1091andgroundffor:

relay V107 .being supplied. at the upper varmatureY atflcontacts. of' relay. 1081fand'groundr at vertical off-normal contacts of ,relay`v 109. The talking.

and front contact .of relay 111. Relay107 in op@ erating also closesran obvious circuit for the op= eration of relay 11,6 and this relay in operating epensl the circuitsfor the delayed release means functioning Aas hereinafter to prevent it from described. y l When. the callingv subscriber disconnects,` relays 105, 111. and 112`are'released in the order named.

The locking circuit forA relaysV 123 and 120 are opened by Vthe release of yrelay 112 causing these relays to release. The release of relay 112 also restores` theA lcode switch R .by energizing its release magnet 138 over a .circuit closed lthrough Y the oifnormal contacts 130 and theV upper outer armature and back contact of relay 112 to ground,

this circuity being opened whenv the code switch! returns to normal at the off-normal contact 130. The release of relay 120 removes the ground connection from the sleeve of the called subscribersline and opens the tip and ring connection thus releasing'relay 107. Relay 120 also causes the energizationof the release magnet 139 of .the selector-connector Bby closing a circuit for this magnet through its third upper armature andback contact, to contacts of relay 112, vertical oir-normal contacts 109 and the ground' at the to normal. ground from the sleeve connection through the line finder thereby causing this line iinder toY releaseand this in turn .causes the release ofy relay 6 in the line circuit of the calling subscribers line to return. the' line circuit to normal. I Y

In order to release the selector-connecter and the line finder in case the callingsubscriber fails. todial after he has removed the receiver from the hook and the selector-connector B hasV been seized, an arrangement is' provided forcausing this release after a certain interval. It will-be noted that when relay 1.12,. operates' after` the l.

Varmature and back contact of relay 105. This lcircuit is opened at the vertical off-normalcon- .tacts when the selector-connector has' returned 115. Relay 111 in releasing v,removesthe seizure of the selector-connectoras hereinbefcre described, a 'circuit will be completedI for the operation of relay vfrom battery throughthe l winding. of this relay, ,the fth lower .armature and front contact of relay 112jand the upper outer armature and back contact of relay 116 to ground, This relay in turn causes an obvious circuit. tobe closed for thepperation ofrelayV 146. Relay 146 -in operating closes a motorcir-v. cuitthat controls an interrupteras shown at 147. `This interrupter in turn .will alternately open and close thecircuit forthe alternate operation and release of relay 148. This lcentrols the stepping y circuit for the stepping magnet149 which controls the switch Vbank 1150 to cause thev brush thereof to step over itsterminals. After the rst step a. circuit isA closedr by the brush of v this switch bank.150 from' ground through the first terminal to close a circuit for vthe operation.

of relay 151 from battery, `winding of this relay,l

lower outer armature and back contact of relay 1.16. upper makefbemrlebreak.amigas Ouder.

151', fourth lower armature and front contact of relay 112, the rst terminal andbrush of bank 150 to ground. Relay 151 operates andcloses a looking circuit for itself from battery through itslwinding, contacts of relay 116, its upper arma-v ture and iront contact to ground at the upper armature and front contact of relay 112. if the calling subscriber fails todialwithin a certain interval, that is, the "time `it takes the brush of bank 150 to travelfrom the iirst ter-v minal to the seventh terminal, a circuit will be completed 'from the ground on this .brush and the seventh terminal foi-'the operation of relay 8 in. the calling subscribers line-circuit. The circuit'for this relay may be traced'from battery through the lower,v winding of relay 8 over the C terminal and brush of the line finder, the second lowerarmature and back contact oi relay 108, the lower armature and front contact ofv relay 2.151, through the seventh terminal and brush of bank 150 to ground.- RelayV 8 in operating closes a locking circuit for itself under control of relay .5 which will operate as heroine..

after described. Ground is connected to the sleeveV leads of the multiple connections to selector-connectorsto make .the line busy and re-V lay 8 opens the locking circuit for relay 6. The

releaseY of relay 6 disconnects the tip and ringconductors from the line nder circuits and thereby causes the releasefof the selector-connector in the manner hereinbefore described when the calling subscriber hangs up his receiver. The relay 6 in releasing also connects the tip and'ring conductorsl to theiupper and lower windings of relay 5 causing this relay to operate to closethe locking circuit for relay S. The calling subscriber will now be unableto eX- tend the connection through another selector-- connector until he has replaced the receiver on the switchh'ook and again removed it to seize an-A other line rlnder and selector-connector. When the selector-connector releases the released niagnet 139 in operating closes a circuit for the release magnet 152 of the switch 150 to causait to.

It will be noted that whenk return to normal.' relay 112 releases relays 145, 146, the nterrupter 147, relay 148 and'stepping magnet .149 are deprived of their operating circuits.

If the called subscriber shouldfhang up prior to the calling subscriber, relay 157 will release.A This permits relay 116 to-,release and` thereby provides the operating circuit for the delayed release timing arrangement to be started, that'. is, thercircuit for relay 145 will'becompleted atA the upperv inner armature and back Contact ofv relayv 116 and thereby cause thefreleasevof the selector-connector and'line nder as rhereinbefore described'. If the calling subscriber fails yto hang up within the timelimit his line `will be removed from service inthe manner asv liereinbeforefdescribed in connection with-failure to-dial. f f" j From the foregoing it follows that if the calle ingV subscriber does not complete the dialingof ,A the desired subscribers number, the delayed rerelease means.

It is evident if the selector-connector isY re-v leased and the called subscriber still has his receiver on the switchhook this will cause his line to seize a linefinder and selector-connector but Now,

as he will fail to takeany further action the time' release means-will operateto disable his line in thesame manner as the calling subscribers lin was disabledon the failure to dial. v f

What .is claimed is:

1. In` a telephone system,- a calling line, a called line, sets of switches, means for establishing a connection betweensaid `calling line and said called line over a setof switches, means responsive to the calling subscriberi replacing his 8K5v receiver-.on the switchhookfor. disconnecting said lines and releasing said switches, means thereafter responsive due to the called subscriber still having his Vreceiver oi the switchhook for seizing a set of switches, and'meansresponsive at a 90 predetermined `time thereafter. if the called subscriber fails to take any further action for ref leasing said set of switches. "I

2. In atelephone system, a calling line, a calledV line,sets of switches, means for establishing af connectionr between said calling line and said called line over a set of switches,1means responsive "to the calling subscriber replacing his. receiver on the switchhook and for disconnecting said lines and releasing said switches, means thereafter responsive due to the called subscriber still having his receiver ofi the switchhook Afor seizing a set of switches, and means responsive at a predetermined time thereafter if the called subscriber fails to take any further action for releasing said set of switches and-for preventing said called lineY from reseizing another set of switches until the called subscriber yhas replaced his receiver on the switchhook.

3. In a telephone system,'a calling line, a called 110;`

associatedwith thecalling line', a timingdevice 12()l common to said sets of switches, means for actuating said timing device when a set of switches isv connectedtothe calling line, means for actu i ating' said relay-by said ing device Vafter-it has j beenl operated a certain'period provided the connection between the'two linesy has not been com-k pletedyine'ans controlled by saidv relay if operatedfor releasing actuated switches Vand for prevent-f ing the calling line from being again connectedV to an idle set of switches as long as the receiver of the calling line remains off the switchhook.

4. In a telephone system, a calling line, sets of switches accessible to said line for establishing connections, meansresponsive tothe calling subscriber removing his receiver' from the switchhoolr for' causing a switch of an idle set of switches to be operated to connect'the calling line with said set, a 'relay associated with said line, a Vtiming device common to said sets of switches; mean'sfor actuating said timing devicel when a 140 set of switches is connected to the calling line, a second relay, means for operating said second relay when said timing device is actuated, means operative a certain'interval after the, actuation. of the timing device and in response to the operation of said second relay for actuating said first relay, a third relay, means for actuatingv said third relay over the calling'subscribers line loop and for releasing said actuated switch in response tov the actuationof said iirst relay, and means 150 Veach comprising a line finder controlled by said third relay for maintaining said first relay operated as long as the calling subscribers line loop is maintained.`

5. In a telephone system, a calling line, sets of switches each comprising a line finder and a selector, means responsive to the calling subscriber removing his receiver from the switchhook for actuating the line iinder of an idle set for associating the calling line terminals with the associated selector, a holding circuit for said line nder closed when said line terminals are associated with said selector, a relayv operating through said holding circuit when closed for connecting the calling line conductorswith said line terminals to said selector, a timing device common to said sets of switches, means for starting the operation of said timing device when the callingline is extended to said selector, a second relay, means for actuating said second relay by said timing device after it has been operated -a certain period provided no impulses have been sent over the calling line to actuate the selector.

within said period, means operative on the actuation of said second relay for releasing said iirst relay to disconnect the calling line from its line terminals and for returning said line'nder to normal. Y Y f f 6. In a telephone system, a calling subscribers line, a called subscribers line, sets of switches and a selector, means responsive tothe calling subscriber removing his receiver from the switchhook'for actu-r ating the line nder of an'idle set for associating the calling line terminals with theasscciated selector, a holding circuit for said line nder closed when said line terminals are associatedwith said selector, a relay operative through said holding circuit when closed for connecting the calling line conductors with said'line terminals to said selector, means for actuating said selector over the calling line conductors to extend thecalling line conductors to said called subscribers line, a'V timing device common to said setsY of switches, means for starting the operation of said timing device when the calling line is extended to said selector, a second relay, means for actuating said second relay by said timing device after it has been operated a certain period provided said selector has not been actuated to l complete the connection to the called subscribers line within said period, means operated on the actuation of said second relay for releasing said first relay to disconnect the calling line from its line terminals and for returning said line nder and selector to normal.

7. In a telephone system, a calling line, a called line,-sets of switches, means for establishing ak connection between said calling line and said called line over a set of switches, means responsive to the calling subscriber replacing his receiver on the switchhook for disconnecting said lines and releasing said switches, means thereafter responsive due to the called subscriber still having his receiver off the switchhook for causing a switch vci an idle set of switches to operate to connect said called line with an idle set of switches, and means responsive at a predetermined time after the connection of the called line to said switch for disconnecting it and restoring it to normal if the called subscriber fails to take any action towards the establishing of a connection through said appropriated set of switches. k y y 8. In a telephone system, a calling line, a called line, sets of switches, means for establishing a connection between `said lines over a set of switches, means responsive to the calling subscriber replacinghis receiver on the switchhook for disconnecting said lines, means thereafter responsive to the called subscribers receiver being oil the switchhook, for causing a switch of an idle set of switches to be operated to connect the called line with said set, a relay associated with 'said called line, a timing device common to said sets of switches, means for actuating said timing device as soon as the called line is connectedto a set of switches, means for'actu-

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