US1798507A - Telephone system - Google Patents

Description

March '371, l1931.

' H. TTzl.

TELEPHONE sysmm oi-iginal Filedl om., v14, 1927' Inuan or' MAN Patented Mar. 31, 1931 ED' STATES HANSYTATZL, oF VIENNA, AUSTRIA, Assienonf To SIEMENS a' H-Ansx'u irxTIniver:senr-.-vv

PATENT oFF-ice SCHFT, OF WEBNERERK,v SIEIiIE1\TSSCIIA/DT,` NEAR BERLIN, GER'M'NY TELEPHONE SYSTEM:

Application tiledE October` 14', 1927?, Serial No..226,054, and in Austriay January 25, 1927; Renewed May 3, 1930.'

This invention relates to telephone systems in generaL-but is'concerned more. particularly with calls between an automatic private' branch exchange and an automatic main exchange.

The object ofthe inventionis topermit a privat-e branch exchange subscriber, after being connected! with a main exchange subscriber, to call another local private branch subscriber and then reestablish connection to the' established main exchange` connection without. releasing the'- main exchange connect-icm The oldest anrangements for this obj ect pronideeach stationfwith two line connec-tions which, however, has the drawback t-'hatboththe set aslwell as the wiring system becomes costly. Thereforait has been proposed toallot the means for bringing about the switching-over to the back\call',.not to the subscriber, but tothe exchange line. By this it is madel possibleA that only one pair ofspeal-ingwines is necessary for the extension stat-ion. The enengization of the switchingv member: allotted; to thefcentral exchange line takes place mostly overalthird: wire or over earth, itY beinga possible to give the impulse for switching: either permanently or temporarily. In any case the call-back-set requires special devices.

rllhe present-invention: relates to acallbacksystem particularly for connecting to automatic. house exchanges or private branch exchanges, wherein, for thel house sets, the exchange sets5, as Well as for the call-fbael sets,t thef same simple type is usedi as is charactenistic for ai system working according tot-he loopr system and the Calif-backdevice'fon private-branch exchanges for switching over toa-bacl-call and also-for switching back totheY exchange call; is released by selecting' impulses or. by. a-4 similar operation; Preferably, af sequence switch carries out thenecessary switching actions.

Fig; l: shows4 an example of' the invention andv indicatesv a system fon automatic trafv fic. Qnly thoseY parts are shown which are essentialfor an understanding of t-he. inventin:

The? automat-ichousef exchange will be assumedi as cateringfor 1,00() subscribers as a maximum'- The impulses are producedby interrupting the loop and the exchangelines are connected tothe top level' of the group. selectors so that the hunting selection off an exchange linetakes place through' the-group selector.V The centraly exchange. isassumedinthe example as being` an automatic exchange for-'10;OOO subscribers.y The call-back devices are, ofcourse, capable ofadaptation to eachexchange.` I

ln the first placca back call without-going trafiic will be described- The subscriberlA takes up=hisreceiver and' thereby in known, manner engages agroup selector such as SEL over his preselector or line finder such as' LS. By dialing ai par'- ticular number, for instance 0,'t'hegroup selector SEL rises to the top level whereinv the office lines are connected.y After the runningdownl ofl the dial switchl the group selector commences to hunt for anidle exchange line".

The engragement of the'exchange line, i; e.,

the setvall'otted tothe exchange line, takes place'over thercfwire; The testing, relayy (not shown) ofthe group selector,haspotentially applied'to it sothat if the groupiselector rests onv thecontact' plate of anidlev setV an testing circuit cany be tracedas follows: potential, testing relayof the4 group selector GWV, relay C' of the exchange set'earth; The testing relay switches through the spealringzlined so that, in the exchange set, the feed relay S70 may function, thus establishing with its con; tact sp1 vthe loop to thecexchangef and for energizing over contact S2911 a slowv acting relay V1. Thev relayl C energizes over' the above tracedcircuit and causes Itheenergization: ofr relayv T over contact en. @ver contactcm'there functions a'relay-X whicliftakes care ofthe switching-through to the central exchange. 'llhe relayl V'l is afsloW actingfrelay andy is-adjusted so that, during: the run# ning downy ofy the dial' switch, it does noteretract, even when itA isf short circuited by the retraction ofspil.

The subscribernow dials. and lets the dial switch rundown; consequently,the feed relay Sp receives the impulses andopens. the loop to theA exchangev throughgthecontact sp1 a correspondingnumber vofvtimes. During the first retraction of the impulse relay Sp, the relay V2 responds in known manner, this also being provided with delayed retraction and the following circuit is established: potential over retracted contact apn, relay V2, contact o1 III, earth. In order to improve the impulses the relay V2 short circuits the choke Drl in the exchange loop over contact o2 I. At the exchange set there is a sequence switch St, which is advanced a step each time the relay V2 operates. In the present case the dial switch is operated four times to send four series of impulses to complete a connection. The sequence switch St has thus been advanced by four steps until it finds itself in a position which may be defined by exchange speaking. In this position the relay F responds over: potential, rotating arm 2 of the sequence switch St contact V2 IV, relay F (winding II), contact o1 III earth. rIhe loop over the main exchange trunkline for holding the main exchange switches now extends by way of contacts fu and choke coil D112. IJVhen the called subscriber A replies, both subscribers are in connection with each other.

In order to maintain a back call within the house, the house subscriber has to advance the sequence switch St by a further step, for which purpose he has to dial once and allow the dial to run down. Preferably only one impulse is given out of course. During the ruiming down of the dial switch, as already mentioned the relay V2 responds, and over contact v2 II advances the sequence switch St the required step.

After the retraction of the relay V2 a circuit for the switching relay U is formed as follows: potential, rotary arm 2 of the sequence switch St, contact o2 III, relay U, back contacts LH, o1 III, earth. 'Ihe relay U holds itself over contact um; it is provided with a slow-acting retraction. Through contact un the relay X is made to retract and thereby brings about the switching of the impulse contact sp1 to the back call terminal. By the opening of the contacts mi and wm the exchange subscriber A is cut off but his loop is still held over the contact u, and choke coil IN2.

The house subscriber A now hears the Vdial toneof the automatic house exchange, and dials the telephone number of subscriber A2 with whom he wishes to conduct the back call. In the present case the house subscriber A2 is to be selected by a three-digit number. The sequence switch is therefore advanced three rotary steps by the time the local switches such as SEL and CONN have completed connections to the line of subscriber A2. In order to return to the main exchange connection, the sequence switch must be advanced again by one step, which may be done by dialing the number l once more.

In order to permit several back calls to be made, it is necessary to again return the sequence switch into the position exchange speaking. This is done in the following manner. As is mentioned, the relay U retracts with a slow action and tierefore it keeps its contact um closed for a moment, even when the rotary arm 2 of the sequence switch has already left the contact plate. Now a temporary circuit for a relay I-I is closed; potential, rotating arm 2 ofthe sequence switch St, relay I-I, contacts un, hu, o, III, earth. The relay I-I holds itself over its contact 7am, and connects the rotary magnet DM of the sequence switch St to a relay interrupter RU so that the sequence switch St is rapidly advanced until the arm of the same comes into the position exchange speaking. In this moment the relay II retracts and stops the rotary switch. rIhe exchange call can now be continued. As the position exchange speaking agrees perfectly with t-he condition before the back call was made, any number of such calls may be made.

Incoming trafic rIhe alternating ringing current from the exchange energizes the calling relay A which holds itself over its winding II and switches on the calling lamp AL. The operator at the private branch exchange operates her listening key allotted to the exchange line in the position central oliice, whereby the operators set is connected in known manner to the exchange line and the relay F is encrgized over winding I. The requirements of the calling main exchange subscriber, such as A', are attended to by means of a plug S and jack .I when a call to a local private branch subscribers line, such A, is made thereby. rIhe jack sleeve of the private branch exchano'e has a potential so that the relay K can respond over the c-wire of the plug S and at the same time, by short circuiting its high resistance winding II, makes the called subscribers line busy in a well known manner.

lVhen the called subscriber A replies the line relay Sp responds over the loop circuit formed by raising the receiver, and atcontact spl again closes the loop to the exchange, because through contact 751, the relay X, which initiated the switching-through to the exchange, is already energized. Line relay SP at contact SI)II again causes the energization of relay VI. The response of the relay Vl causes a circuit to be formed for the relay II as follows potential, rotary arm 2 of the sequence switch St, position O, relay I-I, contact 761, o1 III, earth. The rela-y II over contact hn again connects the rotary magnet DM of the sequence switch S' to the relay interrupter RU. The sequence switch rotates in the manner previously described to exchange speaking position. At this moment, asal-V ready described for the outgoing traiiic, the relay F responds over winding II and again Iwas described forl outgoing trailc.

igvesgsea' The switching over to" a back callnervi talesf place-in exactly the samemanner as The housesubscriberA first dials digit No: 1l and: then the number of the desired house subscriber Whom he: Wishestocall, At the end ofthegconversation'the-returntothe-exchange call is again made by selecting dialingj digit No: Vl, whereby the sequence switch is once moresent1 into the position exchangespeaking byY means of the relay interruptor.l

Release of acaZZ When thev house subscriben A hangs up hisreceiver the feed relay S39 retracts and overcontactspn temporarily'energizes the relay V2, short circuiting, Withfthe samecontactf, therelay V1', which retracts with a delayed motion thereby interruptingalso the circuit for the relayV'g. Through contact nl I the relay interrupter LUI is connectedover the rotaryarmA l ofthe sequence switch St-to the rotary magnet DM Which, inknovvn manner is sent into the 0 position or its normal'i position; The Winding III of the relayIl"lies'iirparallel with therotary magnet DNI; If the call Was an outgoing one therelayy C' would be short circuited by the retraction of4 the contact o1 II ofthe relay Vl and therebytheo-Wire to the groupV selector Wouldbeinterrupted, thus causing release. rSincetherelay T remains energized until the sequenceswitch has returned to the 0 position, the exchange set' remainsl blocked toaresh-calljustv aslong. I' thecall, hon ever, is an incoming-- one, the clearing lamp islit and-the operatorhas-to Withdraw the plug.y

lVhen connect-ion is made to a manual exchangeit is desirable atl the end of a call, further vto block-'the line for about l5Y seconds for the outgoing traic, in order that the central exchange operator mayhave time to cutoff-"the connection; For this purpose also theA sequencelsn'itch St may be used; until\v the returnftotheO'position is-eiected by aslon7` actinginterrupter- LU. Since the relay' T re1nainsenergizedjust as longover `its Winding vIII", thedesired'blocking of the exchange line-isachieved;

What is-claimed is:

l1. In an automatic telephone system, a privateebranoh exchange, a main exchange, a two-Wire trunkcircuit connecting said exchanges, means for vestablishing aA talking connection over said trunk circuiti in either direction,y means controlled by a calling subscriber` in the private branch exchange dialling apredetermined number of digits after beingl connected toV a main exchange-subscriberand Without hanging up hisv receiver orholdingthe connection to the mainY exchange subscriber and for completing afconnectiontoia desi'ned local priivatebranchi exchange subscriber.; saidmainiexchangesub scriber' being excluded. from the talking cir.-l cuit' of: the'la'st mentioned. completed connection between thelocalf subscribers', andmeans responsive to a-i subsequentfdialling openafV tiionwithout the calling subscriber hanging up: his receiver for.' disconnectiingv said other. local subscriben andi for again connecting with said!establishediconnection to said. main exchange subscribers line.. a

2. In a private branch` exchange,l a.tWo.- Wire trunk circuit: extending to a main exchange, meanscontrolledv by: a calling; subs scriber. for establishing a talking connection over said" trun'kicircuit to: a subscriber 'ine the main exchange, aisvvitchinsaiditrunkv circuit operated! oneistep .foreach digitoi 'the called number and? seti in4 main. exchange speaking position at they end; off the. digitimpulses, means responsive to;l subsequentimpulsessent by thev calling subscriber for. moving/'said switch out ot speaking posit-ion',.for holding. the established; connection to: themain: ex-V change subscriber., and*` Vfor completing: a talking connection. to another local? private branchexchange subscribersline,andmeans responsive to a further: subsequent impulse sentby the calling` subscriben for disconnecting said other localsubscniber, .fori reconnect,- ing' with. said'. established connection to the main: exchange subscribers: line,.l and for automatically causingsaidI switch toVV again step to exchange talking; position.

3; Iny a. private branch exchange, a tivos Wire trunk' circuit extendingto' amain ex-A change, means` controlled by;y a calling; sub scriben for establishingfa talking; connection over said tnunkicircuit to a: subscriber inthe main exchange; ai switchl in. said trunk ciricuit operated' one.f step; for; each .digitV ofv the called number andl set: ini main: exchange speaking `positional: thefend` o'the digit-im, pulses-means respoi'isivetol subsequent in,- pul'ses fsent byY ther callingsubscriber for movingsaidlswitchloutof speakingpositiomion holding the. established` connection-to the main. exchange subscriber,` andxfonf completingVL atalkingrconnection to another. local pri; vate branch exchangev subscribersrline, and means responsive to further subsequent impulse sent by the: calling i subscrriberft'or' dis connecting saidV othen local' subscriber, for reconnecting: With-saidrest ablishetl .connection to the main exchange subscribensline, and for' automatically: causingi said? switchto again step to'exchangeftalking position, and means,- controlledaby' said* switchzfor momenh tarily` maintaining said trunk: circuit busy after' the'- release. ofthe-5 establishedI connec; tion.v

46. In a private branch exchange, artwo Wirey trunk circuit extending to @a2 main ex; change, andi' means-insaid trunkf circuit to enable a V callingfprivate branch exchange subscriber to, iirst, call a main exchange subscriber, second, complete a connection to another private branch exchange subscriber without releasing the connection to the main exchange subscriber, and, third, release the connection to the said other local private branch exchange subscriber and reconnect to the established connection to the main `exchange subscriber, said means being controlled by the calling private exchange subscriber dialling predetermined digits without hanging up his receiver.

5. In a private branch exchange, a two wire trunk circuit extending to a main exchange, and means in said trunk circuit to enable a calling private branch exchange subscriber to, iirst, call a main exchange subscriber, second, complete'a connection to another local private branch exchange subscriber without releasing the connection to the main exchange subscriber, and, third, release the connection to the said other local private branch exchange subscriber and reconnect to the established connection to the main exchange subscriber, said means comprising a sequence switch in said trunk circuit which is directively controlled by impulses generated by the calling subscriber.

6. In an automatic telephone system, a trunk line having two branches, means in said trunk line responsive to its seizure for closing a bridge across said trunk line, means responsive to impulses transmitted by a calling subscriber for interrupting said bridge to operate a train of automatic switches over the iirst of said branches to complete a connection to a called line, and means responsive to subsequent impulses transmitted by said calling subscriber for disconnecting said first branch from said trunk line, for holding said switches in operated'position over said first branch, for connecting said trunk line to the second of said branches, and for interrupting said bridge to operate a second train ci' automatic switches over said secondbranch to complete a connection from said calling'line to a. second called line. y

7. In an automatic telephone system, a trunk line having two branches, means in said trunk line responsive to its seizure for closing a bridge across said trunk line, means responsive to impulses transmitted by a calling subscriber for interrupting said bridge to operate a vtrain of automatic switches over the iirst of said branches to complete. a connection to a called line, means'responsive to subsequent impulses transmitted by said calling subscriber for disconnecting said first branch from said trunk line for holding said switches in operated position over said iirst branch, for connecting said trunk line to the second of said branches, and for interrupting said bridge to operate a second train of automatic switches over said second branclrto complete a connection from said calling line to a second called line, and means responsive to further impulses transmitted by the calling subscriber for disconnecting said second branch from said trunk line thereby releasing the second switch train and for reconnecting said trunk line to said iirst branch and said first called line.' i

8. In an automatic telephone system, a

trrmk line, means controlled by a calling subscriber for operating a train of automatic switches over the two conductors of said trunk line in series to complete a connection to a called line, and means responsive to said calling subscriber dialling a predetermined number for opening both conductors of said trunk line and for closing a bridge across said conductors at a point beyond the opened section in order to hold said train of switches in operated position. 9. In an automatic telephone system, a trunk line, means controlled by a calling subscriber for operating a train of automatic switches over the two conductors of said trunk line in series to complete a connection to a called line, means responsive to said calling subscriber dialling a predetermined number for opening both conductors of said trunk line and for closing a bridge across the conductors of the outgoing section in order to hold said train of switches in operated position, and a second train of automatic switches controlled over the conductors of the other section to complete a connection from said calling line Vto a second called line responsive to said dialling operation.

10. In an automatic-telephone system, a trunk line, means controlled by a calling subscriber for operating a train of automatic switches over the two conductors of said trunk line in series to complete a connection to a called line, means responsive to said calling subscriber dialling a predetermined number for opening both conductors of said trunk line and for closing a bridge across the conductors of the outgoing section in orderto hold said train of switches in operated position, a second train of automatic-switches controlled over the conductors of the other section to complete a connection from said calling line to a second called line responsive to said dialling operation, and means responsive to a subsequentdialling operation-by said calling subscriber for disconnecting and releasing said second train of switches from the conductors of said other section and for reconnecting said conductors to said iirst train of switches. l

il. In a telephone system, a trunk line having two branches, means controlled by a calling subscriber over the first of said branches for operating atrain of switches to complete a connection to a called line, and means responsive to a dialling operation by said calling subscriber for operating a second train of switches over the second of said branches to ifa-98,507

15 `completeaconnectionffrom said-calling line `to la second called line, and or disconnecting .the irstbranch from said trunk line Without .releasing said connection tothe iirst called line du-ring the timey the ,connection to Vsaid -zosecond called iline `is maintained, and .means respon-sive to a `subsequent dialling operation by said calling .subscriber for disconnecting and releasing the connection 4to Ythe second .called :line -overthe second .branch `and for reconnecting the :calling line .to .said irst cal-led rlineconnection over the .first branch.

-1-3. In an automatic telephone system, a 'private branch exchange, Va main exchange, :a trunk 5line connecting said fexchanges, means 30 controlled by a -calling branch exchangesub` ,scriber for completing a connectionoversaid ytrunk line .to :a main .exchange Vsubscribers line, means controlled by said callin subscriber ldialling a predetermined .num er of digits without hanging up his .receiver for disconnecting -butnot releasing the1connec'tion 'to-theanain exchange subscriberand dorzcoinvpleting -a .connection vtoa .desired ylocal .private .ibranchlexcharn'ge subscriber@ line.

14,-. In v.an automatic .telephone system, a private branch exchange, a main exchange, a trunk l.line Kconnecting said exchanges, means controlled .by acallingbranch exchange sub- .soriber for completinga connection vover said Strunk fline to a .main exchange subscribers .li-ine, means controlled by said .calling subscriber dialling .a 'predetermined number of digits Without hanging uphis-.receiver fordisconnecting but notreleasing theconnection to .50

,pleting a connection .to a desired local 1private branch exchange subscribers line, and means 4responsive to asubsequent `dialling operation ofsaidcalling subscriber without hanging up 1his receiver for disconnecting vand releasing l the Iconnection to .said .other local subscribers lineland for connecting .the calling line to said .established connection .to the .main exchange .-subscriberis line.

15. In fan .automatic telephone system, a .trunk line, meanscontrolled by acalling sub- .scriber over said tru-nk .line for .operating a train of automatic switches to complete a connection to :afcalled line, means .responsive to T fsaid .calling ysubscriber dialling a ,predeter- -the main yexchange :subscriber and .for comminednumber for operatinga. secondtrainof .automatic switches over said .trunk line Yto complete a connection ,from said-foalling-line `to 1 -second called line, .and .means whereby ysaid iirstand second'tra.in-of:switches aredis- .connected .from .eachiothei'and the .first .train is A*maintained `in `operated position.

16. In l.an automatic `telephone system, .a

/tiunkline, meanscontrolled by aicallingsubvscii'ber over .said trunk yline for voperating `a ytrainof automatic switcaes .to complete aconi nection Yto a .called line, .mea-ns v`responsive .to ysaid `calling subscriber dia-lling .a `predeter- -min-ed number for operating .a `second train yof automatic switches -over .said trunk iline to complete a connection ifrom ,said Acalling line to a .second called line, means whereby said -rst and .second train of .switchesare disconnected :from each other .and the :first -train is maintained iii-operatedpositionyand means responsive toa subsequentdialling.op-

eration by :the .calling .subscriber for `disconnecting ,and releasing the lconne'ction .to Vthe second called lline and .fior reconnecting .said

Icalling .line .to the ,first `sW-itch atrain.

-17 In .a telephone rsystein, vla .main fexchange, a privateebranchexchangeaa two Way trunk line :connecting said exchanges, uneans Y for vcompleting a. connection :between .a .main

exchange subscriberis line and a ,private branch exchange subscriber@ fline in either direction over said trunk line, and means responsive to .a .dialling operation by the '.pr-ivate branch subscriber regardless of whether such subscriber :is :the ica-lling yor the called subscriber in the established connection for disconnecting the branchexchange subscribers line from the main exchange Tsubscribers line Without releasing 'the connection thereto and for completing a connection :ti-tom ,theV

.private branch -subsoribers :line xto ra .second called line.

18. In sa telephone' system, a main exchange, 5a gprivate branch lexchange, a two Way trunk .line connecting :said exchanges, ymeans for completing a connection between a :main exchange subscribers line and a aprivate branch exchange subscribers ,line iin either Vdirection rover lsaid trunk line, .means responsive to a *diatllingvoperation by ythe-private branch subscriberregardless of Whether Vsuch subscriber Vis the calling or the -called subscriber in the establishedconnection for -quent dialling opera-tion by `said private branch subscriber er disconnecting andreleas-ing the connection to ,the .second called line a-nd for reconnecting the ,private branch subscriber to ythe established connection to lthe mnexchan-ge subscriberis line.

19. In a private branch exchange, a trunk line extending to a main exchange, means controlled by a calling subscriber for establishing a talking connection over said trunk line to a subscriber in the main exchange, a register in said trunk line operated one step for each digit of the called main exchange subscribers number, and means responsive to subsequent impulses transmitted by the calling subscriber for operating said register to disconnect the calling subscribers line from the established connection to the main exchange without releasing such connection and for completing a connection between said calling line and a second called line over a branch of said trunk line.

20. In a private branch exchange, a trunk line extending to a main exchange, means controlled by a calling subscriber for establishing a talking connection over said trunk line to a subscriber in the main exchange, a register in said trunk line operated one step for each digit of the called main exchange subscribers number, means responsive to subsequent impulses transmitted by the calling subscriber for operating said register to disconnect the callingsubscribers line from the established connection to the main exchange without releasing such connection and for completing a connection between said calling line and a second called line over a branch of said trunk line, and means thereafter controlled by said register responsive to a subsequent digit for disconnecting and releasing the connection to the second called line and for reconnecting said calling line to the established connection to the main exchange subscribers line.

21. In a telephone system, a trunk line having two branches, means responsive to impulses transmitted to sai-d trunk linel for completing a connection from a Acalling line to a called line overthe first of said branches, a register associated with said trunk line operated one step for each series of impulses transmitted to said trunk line, and means controlled by said register after taking a predetermined number of steps for switching the trunk line from connection with said irst branch to connection with the second of said branches in order to completev a connection from said calling line to a second called line.

22. In a telephone system, a branch exchange in which outgoing trunk connections are completed by means of automatic switches directively controlled by a branch exchange subscriber, and in which incoming trunk connections are completed by an attendant, means responsive to directive impulses transmitted by a branch exchange subscriber en- 1 gaged in either' an incoming or outgoing vtrunk connection for establishing an auxiliary connection to another branch exchange subscriber without releasing the trunk connection, and means responsive to further directive impulses transmitted by the branch exchange subscriber for releasing said auxiliary connection and for reestablishing the trunk connection.

23. InV a telephone system, a branch exchange in which outgoing trunk connections to main-exchange subscribers are completed by means of automatic switches directively controlled by a branch-exchange subscriber and in which incoming trunk connections from main-exchange subscribers are completed by an attendant, means responsive to directive impulses transmitted by a branchexchange subscriber engaged in either an incoming or outgoing trunk connection for establisliing an auxiliary connection to another branch-exchange subscriber from which connection the main-exchange subscriber is excluded, and means responsive to further directive impulses transmitted by the branchexchange subscriber for releasing said auxiliary connection and for reestablishing` the trunk connection.

24. In a telephone system, a trunk line having two branches adapted to be connected to the trunk line alternately, means for transmitting series of digit impulses over the trunk line to establish separate connections t0 called lines over said branches, and an auxiliary switch operated one step for each series of impulses transmitted over the trunk line for controlling the connection of said branches to the trunk line.

25. In a telephone system, a trunk line hav-` ing two branches adapted to be connected up one at a time, means for transmitting groups of digit impulses over the trunk line,'each of said groups representing the digits of a called-subscribers `number followed by an additional digit, means for repeating the called-number digits over the particular branch connected, an auxiliary switch operated one step for each digit transmitted over the trunk line, and means controlled by the switch on operating in response to the additional digit impulses for connecting up the previously-disconnected branch. i

26. In a telephone system, a trunk line having two branches, automatic switches, a line relay controlled over the trunk line for repeating digit impulses over one of said branches to operate certain of said switches to extend a connection to a called line, an auxiliary switch operated one step responsive to each series of impulses representing a digit of acalled number, and means controlled by said switch when operated to a predetermined position Jfor adapting said relay to repeat iinpulses over the other .of said branches to operate certain other of said automatic switches transmitting digit impulses over the trunk line to complete outgoing calls to called subscribers, means for extending incoming calls over the trunk line to subscribers in the e branch exchange, an auxiliary switch associated with the trunk line, a speaking position for said switch to which the wipers of the switch are advanced one step at a time responsive to successive digits transmitted over the trunk line to complete an outgoing call, and circuit connections for automatically advancing the wipers of the switch to speaking position or incoming calls over the trunk line.

28. In a telephone system, a trunk line terminating in a branch exchange, means for transmtiting digit impulses over the trunk line to complete outgoing calls to called subscribers, means for extending incoming calls over the trunk line to subscribers in the branch exchange, an auxiliary switch associated with the trunk line, a home position in which the wipers of the switch normally stand, a speaking position to which the wipers of the switch are advanced one step at a. time in response to the digits of a called number on outgoing calls, circuit connections for automatically advancing the wipers of the switch to speaking position on incoming calls, and circuit connections for returning the wipers of the switch to home position responsive to the termination of either an outgoing or an incoming call.

In witness whereof, I hereunto subscribe my name this 19th `day of September, A. D.

HANS TATZL.

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