US2391389A - Telephone system - Google Patents

Description

Dec. 25, 1945. K, L BURGENER 2,391,389

TELEPHONE SYSTEM Filed Aug. 4, 1944 2 Sheets-Sheefl 1 OmN INVENTOR.

KARL L. BuRer-:NER

ATTORNEY Dec. 25, 1945. K. L.. BURGENER TELEPHONE SYSTEM Filed Aug. 4, 1944 2 Sheets-Sheefl 2 KARL L BURGENER4 ATTORNEY Patented Dec. 25, 1945 U NITE D STATES PAT ENT O F lFl CEl 21,391,389 n TELEPHONE SYSTEM Karl L. Burgener. Villa Park,A lllv., assgnor to Automa-tic Electric Laboratories, Inc., Chicago,r

Ill., a corporation of Delaware Application August 4, 19441,I Serial No. 548,077 e claims. ('olg' 17a-2n This inventiony relates tot telephone systems in general, but is more.V particularly concerned with automatic telephone systems in which both main exchanges and branch exchanges are employed;

and the broad. general object, briefly stated., may f switches, after seizure in the mainv exchange by an. automatic. switch or by anV operator in a manual main exchange. Another method which has been. employed is to bridge across. the trunk a highresistance relay at the branch exchange. A stilLiu-rther method hasl been to connect a re'- lay from one trunk. conductor to groundv at the branch exchange. This. inventionv provides in the branch exchange. a relay which is normaly connected from the ground side. of the trunk to battery 'at the branch.. exchange; However during eachcall over the trunk in either direction, the relay is during certain periods, bridged; across the two trunk conductors and is operated by current. lflowing over the trunk from the main exchange, The relay will operate and perform its functions regardless of the direction of flow of said. current.. n

One. of the objects. of this invention isto provide` improved. means for instantly busying the trunk circuit at the branch exchange when;- a switch in the mainy exchange seizes: the trunk circuit orY when an operator in. a manual exchange seizes the trunk.

Another object of this invention, is to provide means for guarding; the trunk circuit against intrusion. during the period of time between ac*- tual seizure by the main exchange and the start of the ringing period, which followsl seizure, for operating the answering signal: to attract the branch operators. attention.

Another object of this invention is to' provide means for guarding the trunk circuit againstin.- trusion during the period between the` actual completion of the conversation: and the return tof normal of all of' the elements in the trunk circuitl A feature of thisin-vention is the provisionof means for connecting ground to' onef of the trunk conductors to close a circuit: for operating the ling equipment in the main exchange to: cause said.v line; equipment. to seize a. trunkv leading: to an. idle: selector at the main. exchange.

Another feature.- of. this invention is the provisiony of means for preventing the branch exchange subscribers from completing calls to the main exchange numbers in specied. groups by including,r means for opening the trunk circuit, placing ground on one conductor of the main ex.- change section oi the trunk, alternately connect.- ing thehigh resistance relay from battery to the otherV conductor and across the two conductors, to guard the trunk from intrusion until the callingl subscriber abandons the unauthorized V-call. A distinctive tone may be introduced onto. `the calling subscribers line: at. this time by the adapter to remind the. cal-ling party that his line is connected to an unauthorized number.

Another feature of this invention isthe provision of a non-ring-th-rough repeating coil to prelvent ringing current from reaching. the operators receiver in theevent that the answering plug wasv inserted into the jack during. the. ringing period, khowever after the plug hasonce been placed inthejack. in. answering an incoming call or'in-ithe event that` a. patching cord is placed in the jjack toconnect thetrunk direct to. a subscribersi line.. lthe novelv circuit arrangements permits the ringing. current from` the main ex.- changeto by pass the repeating coil. to directly vring a supervisory relay in the. cord circuit. or to ring directly onto'the; line of the called Vsubscriber.. In ringing in. on the supervisory relay the: main exchange. operator can recallthe branch exchange operator. l

The foregoing objects and features together I with others not specifically mentioned will be explained in detail hereinafter, with rreference to thev drawingsv comprising Figures.` 1, 2, 3v and 4. The: drawings show' by theA usual circuit diagrams a, suicient amount. of. the equipment in, a.. telephone system embodying the invention to permit the invention to loereadily explained andun'derstood. Thedrawings should be arranged. horizontally in numerical, order with Fig. 1 atI the left.

The apparatus shown in Fig. 1 is a skeleton key and cord circuitl of a private exchange attendants switchboard. toshow the normal condltionI of a loop across the tip- I-.Bland ring; |62y of thel plug. When. the branch; exchange operator inserts: plug; Pl into'jack J2 a. loop is placed across' the branch exchange section of the. trunk. 2L is the trunk circuit comprising conductors 25T andi '258; They branchV exchange endY has two branches.. one; terminatesthe. jack J-2 which is used mostly' for answering mainA to,4 branch exchange. calls, although it may be used byr the release type.

operator for the purpose of extending special calls from the branch to the main exchange. This jack may also be used with patching cords to extend the trunk line direct to one of the branch exchange subscribers lines, for night service or special cut-through day service. The main exchange end also has two branches, one branch to the regular line equipment for calls incoming to the main exchange from the branch exchange and the other branch to multiple bank contacts for outgoing calls from main to branch exchange. Fig. 4 is a skeleton of the main exchange circuits showing the trunk terminating in a line equipment for the incoming calls and, in multiple switch bank contacts for the outgoing calls from main to branch exchange.

When the trunk circuit is taken into use at the main exchange of the automatic type, a connector seizes the trunk and supplies ground and battery from the ring cut-oi relay to the two sides of the trunk line. Ground, over one side of the trunk from the ring cut-off relay, operates the high resistance relay to place a guarding potential on the selector bank multiple in the branch exchange and to light the busy lamp. Following seizure, ringing current is superimposed on the trunk line to operate an alternating current relay at the branch exchange to signal the operator by lighting the answer lamp. When the branch 'exchange attendant answers the call, the circuit will be closed through a loop in the cord circuit causing the ring cut-off relay to operate and complete the talking circuit from the calling subscriber to the attendant cabinet operator.

As the ringing current is applied intermittingly to thek circuit there is a so called ringing period and a silent period. By providing the high resistance relay connected from battery to the ground side of the trunk line, this relay will operate practically simultaneous with the seizure by vthe connector at the main exchange. Thus the trunk will be guarded from the instant it is seized by the main exchange connector regardless of the condition of the ringing source, as to whether it is in the ringing or the silent period. The windfing of this relay is of such a character that it can operatefrom ground through one winding of the ringcut-oi relay without causing said ring cut- The busy lamp on the atis seized but the answer lamp will not light until `after the ringing current from the connector is superimposed in bridge on the trunk, causing the -alternating current relay to operate and close the circuit to the answering lamp.

After a conversation has been terminated both calling and called parties will open their line circuits by hanging up their receivers and the switch train in the central cnice will restore to normal immediately, if the connector is of the first party This means that the connector will restore before the operator could remove the plug from the jack and means must be provided to guard the main exchange end of the trunk for a period of time until the operator frees the branch j exchange end. This is accomplished by the novel circuit arrangement of the trunk whereby the release of the trunk by the connector in the main exchange, causes a relay in the trunk circuit to operate opening the ground side of the trunk to the attendants switchboard and placing a ground on the battery side of the trunk to the main cnice, thus immediately operating a line equipment in the main office placing a guard on the trunk circuit. When the operator removes the plug from other branch terminating in a regular line switch the jack at the attendants switchboard thus freeing the branch exchange end of the trunk circuit, the line equipment at the main exchange will immediately restore making the trunk available for calls in either direction.

Should the branch exchange operator remove the plug before the release of the connection in the main oice, the branch exchange end of the trunk must be guarded from seizure by a subscriber making an outgoing call, This is accomplished by a novel feature of the circuit which causes the high resistance relay to be bridged across the trunk circuit and held in operated position by direct current from the main exchange which current may be in either direction. rhis relay in turn causes the busy condition to be maintained on the multiple bank contacts of the automatic switches in the branch exchange and also causes the busy lamp to glow to indicate the busy condition to the branch exchange operator. The trunk circuit will remain in this condition until current is removed from the main exchange end of the trunk circuit to allow the high resistance relay to operate to release other relays and restore the trunk circuit to its normal condition and make the circuit available to calls in either direction.

A particular advantage of bridging the high the conditions where calling main exchangeeither automatic or manualhas not released even though the branch exchange has released, is that the main exchange end of the trunk may be attached to a manual switchboard or to any one of several types of automatic systems or to a Toll switchboard, and the various circuits involved are dissimilar. There are instances where the current iiow from the main exchange is in the normal direction of ground on positive line and battery on negative line when the call is iirst established and at a later stage the current flow is in the exact opposite direction. The high resistance relay, when connected as a bridge at the ,branch exchange end, will be energized in either instance and therefore this trunk circuit is more universal in its application than the circuits heretofore used.

Other objects and features of this inventionl are concernedY mainly with circuit details which will be explained hereinafter with reference to the 'accompanying drawings, which show by means of Fig. 1 is a part of the branch exchange attendants cord cord circuit to show the closed loop from the plug tip I6! through one winding |13 of the repeating coil, contact III, relay 120, contact H2, one winding of repeating coil |14 to ring 162 of the plug. Fig. 4 is a portion of the main exchange circuits, indicating that the trunk circuit conductors 463 and 464 have two v branches, one branch terminating in multiple contacts of well known Strowger switch banks through which the main exchange subscribers have access to the trunk line leading to the branch exchange and the equipment through which the branch exchange subscribers have access to the main exchange subscribers. It should be noted that while the line equipment shown is of the well known type, there is a slight change in= the connections, ground has been removed from one spring ot rel'ay/Il with the-result that; when this relay is in its normal position, contact, 4 I I' will not connect with ground,

therefore trunk conductor 461i is'free from ground Should Y when the 'trunk circuit vis normal. trunk termina-te in a manualk main exchange the terminating equipment would have circuit characteristics similarl to those described herein as applying to the automatic system.

Fig. 3 illustrates the discriminating feature, indicating a method of preventing the branch exchange` subscriber from completing, by dialing, a connection through thistrunk circuit` to unauthori'zed numbers, and further means foropening the trunk circuit and connecting the high "resistance relay from'conductor 463 to battery under certain conditions,` andl under other conditions connecting said' relayacross the outgoing section to guard the main exchange end until' the calling branchA exchange subscriber abandons the call. i

It will be noted thatv the branch exchange end of thev trunk circuit also has two branches, one branch terminatingin the multiple bank contacts 251, 258 and 259', through which the branch exe trunks leading to main exchange., it will be assumed that Fig. 2 illustrates one trunk, in such a group; The other branch terminates in a jack on an operators position ina branche. exchange switchboard or attendants cabinet.` `'Ihis branch is` equipped' with the ordinary7 l'amp signals' to indicate incoming calls and busyconditions on` out.- going calls,- and the usualv jack. into which the operator may insert a plug in answering. incoming calls or for establishing outgoing calls to the main exchange, or for a patching cord by which `a subscribersA line maybe connected direct. to a trunkl rornight use or for any other special service. The main exchange may be manual or auto,- matic andi when the latter, the operator completes the call by use ofa dial, which is part of an. operators circuit (not shown).

In connection with the drawings it will. be as.- sumeol that a subscriber inthe automatic main exchange desires to converse witha. subscriber in the branch exchange. It will be assumed further that when the calling. subscriber in the mai-n exchange removes his receiver .and dials the. correctVA digits of the desired number a well known Strowger selector with vertical and rotary motion, seizes. the. rst idle trunk. to thefbranch exchange.

Assuming that the. trunk. linefshown isfthe rst idle trunk` accessible to the selecting. switch, the wipers. of` said switch will then stop. on bank con.- tacts 421, 428 and` 429.` The switching relay 42s!) of the selecting switch willk operate to.. connect the wipers o-f the selector to the bank contact instantly establishing acircuit from ground through, relay 449, contactsv 44| and 42|, bank contact 421-, trunkv conductor. 4.63,. contact 3;I-I, conductor 3.64, contact` k, righ resistance. relay 280, contacts 2.94 and 263-, resistance coili 2141 to battery; Relay 280.Y operates and closesa. circuit to relay 2m.. from ground. contacts-v 28-.I and 2&9', number -2 wind-ing of rel-ay 2M) tobattery;` Reh lay 2 L0 operates, lighting the busy lar-np' 21:15, from ground,v contact 2 [-4, lamp 2'I1` to; battery: Relay 2I9 also closes ground' through contact 219 to leadv 2,59 thus providing guarding potential on the selector bankv contactsy of thev outgoing switch multiple. Relay ZII!V closes anothery contact 2'I'If,

to4 connect; the; tip 225 of the: attendants switch.-

boa-rd jack witlrone conductor of the. trunk` ciry change subscribersv have access tothe group of p cuit. A further contact on. relay 24.9 contact 2'I 5', iis. closed to. prepare a locking circuit toxrelayv 29aandicontact 2I6-1 closes a chain circuit.` This trunk 'circuitI isnow held busy to outgoing callsv even though ringing' current may not as yet have been appliedv bythe main ofl'lce equipment. When the ringing period commences, the A.. Cf., current. is superi-mposedi across the trunk from. the main oli'ce through conductor 4'53-, contact 3I I, conductor, 36'4, condenser 2891, alternating current' relay 2835, contact 21|V to conductor' 365, contact SI2, conductor IlI'4.V Relay 280 remainsv operated but relay 283i operates and releases' in response to the ringingY and silent periodsV ofy the ringing current. During the rst ringing period, relay 283: closes acircuit to operate relay 290,. from battery; two windings of relay 29.9' in series, contactsv 296i, 2:85- and 2-3'8y to ground. These windki-ngsof relay 290. are ofsuchk a nature that Wind-y ing number 2 overpowers winding number Ii su'iiici'einl-y to allow the closure of'Y contact 293 which 'short circuits. winding number I1 and allows relay 299 tooperate fully, closing its own locking circuit, from battery, number 2: wind-ing', contacts 298g 2I1=5 and 223 to ground This relay 290 will remain operated during the subsequent ringing periods and' until itslocking circuit. is`

opened, either at contact 2I5E or contact'.` 223. Another contact on relay290, contact 29d" closes to light the answer lamp, over` a circuit from ground, contacts 292|" and 255, answer' lamp 2-:I8

' to battery; Another contactA 291, on relay 290 closes' a multiple ground' t'othenumber 2 windfingr of relayA 2"!0 and' a further contact 295, closes the circuit to relay 269?, from ground', contact 2`8`Ii, contact 295, number I winding of relay` 260 to battery. Relay 250i' operatesz over` this circuit and closes a part of" its own locking circuit and changes the source of the holding ground of' relay 210, from contact 283i? on relay 28W to contact 215 onrelay 219. During the rstfsilent period which follows the iirstringing period", as well as during all subsequent silent periods; relay 283' will releaseY but relays N9', 260 and 280 will kremain operated under the control of' thev high resistance relay 289, which as previously stated, willl remain operated under the control ofv ground from the main exchange over the trunk" conductor 354i.

The branch exchange operator answers the call by inserting a plug into the-jack J 2. Ground through contact 229? over leadi 3.61, windingnumberY Iz to battery operates relay 320, which through Y contacts '92!v and 322' closes a multiple conneci. tion f'orthe trunk circuit'.

Ground? at jack J12 through- Contact. 229? also furnishes a holding ground? for relay 2III, to-hold relay 2:IIl in operated position for ther period of the plug remain- .ing in. thejack. The closed' loop ofthe plug' circu-i-tfis now across: the tip 226 and ring 225y of the jack J 2 which causesv relay 220i to operate over' theA following circuit: ground, number 2 winding of relay 229, one winding of' repeating coil 2-56, contactA 231;, jackt ring` 225,. plug ring |5624, winding IN of cord circuitirepeating coil', contact IfIZ, both windings of relayA i129- series, contact IISI., winding: |13: of repeating coil; tip I'6I of plug, tip 22:8 of jack JZ, .contacts 2li I1 and 2'34, one winding of repeatingcoil, winding number I of relay 22u', to battery. Relay 2:20 operates and at contact 223.re1noves holding. ground from re.- lay 29D andv through its contact 221.y closes7 a loop across the. trufnlcconductorsf, including` the windfing of relay 249,- over the following circuiti; ground, onev winding;` of relay M95, contacts 44| ual exchange.

and 42|, bank contact 421, trunk conductor 463, contact 3| conductor 364, contacts 262 and 22|, one winding of repeating coil 256, relay 240, a second winding of repeating coil 256, trunk conductor 365, contact 3|2, trunk conductor 464, bank contact 42S, contacts 423 and 444 and, during the silent period, through contact'45l to battery causing relays 246 and 440 to operate. Contact 222 on relay 220 closes ground through winding of relay 256 to battery, operating relay 250. Relay 44!! cuts oii the ringing source and extends the trunk conductors 463 and 464 through contacts 442 and 443 and through the windings of the back bridge relay 416 to ground and battery respectively. Relay 246 operates and at contact 24| completes the locking circuit of relay 266. Relay 256 operates, opens contact 255 to extinguish the answer lamp 2 l S, closes ground through contact 253 to the number 2 winding of relay 2|6 and through contact 254 of the impulsing circuit to the rotary magnet 316 of the adapter which will be referred to in connection with out calls, that is calls from branch exchange subscribers. Another contact 25| disconnects the winding of the high resistance relay 280 from the trunk conductor 364, f

The trunk circuit is now ready for the branch exchange operator to speak with the calling party in the main exchange, which may be an automatic subscriber or an operator in a man- It should be noted that the plug might be inserted into the jack during the ringing period but the only ringing current which' could reach the cord circuit and the operators receiver would be the amount which would be induced between the primary and secondary windings of the repeating coil. Thus, there would be less noise in the operators receiver, should the plug be placed in the jack during the ringing period, than would be the case in many previously designed circuits. The operator cornpletes the connection to the wanted branch subscriber` through the usual circuits, not shown.

After conversation is completed, both parties restore their receivers and the operator at the branch exchange removes the plug, the conditions then existing will depend upon which end of the trunk is released first.

We will assume that the main exchange disconnects rst, which will open the circuit to relay 246. Relay 24|] restores and at Contact 24| opens the locking circuit to relay 260. Relay 269 restores, and at contact 262 opens one side of the trunk circuit and at contact 25| connects ground through relay 24! to conductor 365, I

that is, to the other conductor of the trunk, When one side of the trunk was opened at contact 262, the switch train in the main office restored to normal, after which a line equipment would be seized over the following circuit, busying the main exchange end of the trunk; ground, contacts 26| and 22|, one winding of repeating coil, winding of relay 246, another winding of repeating coil, trunk conductor 365, contact 3|2, conductor 464, contact 4|6, relay 43!! to battery. Relay 436 operates and places guarding potential on the selector bank multiple from ground through contact 43|. Relay 243 again operates over this circuit and at contact 24| closes a circuit to operate relay 266, from battery, relay 260, contacts 24|, 266 and 252, conductor 364, contact 3H, conductor 463, contact 4|2 to ground at the trunk switch which has been seized by the operation of the line equipment. Thus, the

trunk will be guarded until the operator re- P' moves the plug to free the trunk for Vcalls in either direction. Y

' Should the operator remove the plug prior to the trunk being released by the calling party in main exchange, the following would take place; relay 320 in the adapter restores, the cord circuit loop holding relay 2,20 is opened allowing relay 220 to restore and at its Contact 22| opens the trunk loop of the main exchange end giving disconnect supervision to the main exchange, this main exchange loop includes the winding of relay 240 which restores and at its contact 24| opens part of the locking circuit of relay 260. As relay- 260 is being held in voperated position from contact 2`|4 on relay 210, the high resistance relay 280 will now be bridged across trunk conductors 364 and 365 and will operate on current, in either direction, from the main exchange.

This bridge is maintained during the time between the restoring of relay 250 and the iinal release of the slow releasing relay 210. After relay 210 restores ground from contact 214 is removed from the number winding of relay 260, which restores. Relay 286 is now connected to one trunk conductor and operates over the following circuit; battery, resistance coil 241, contacts 263 and 29|, winding of relay 280, contact 25|, trunk conductor 364, contact 3| I, conductor 463 to ground in the main exchange at the trunk switch which is still operated as this end of the trunk has not been released. From ground at contact 28| relay 2|0 is again energized and through its contact 2|3 connects ground to lead 259 which guards the branch exchange end of the trunk until the main exchange end is released to make the trunk free for calls in either direction.

The branch exchange subscribers have access tothe trunk to the main exchange, through the multiple banks of the usual Strowger vertical and rotary type selector and connector switches. The subscriber dials the prearranged number to cause a selector to hunt and connect the calling subscribers line to an idletrunk such as conductors 251 and 258. Conductor 259 is the usual control conductor. Subscribers may dial direct to other branch subscribers or to authorized numbers in the main exchange without assistance from the 4operator, although the operator may supervise such calls. However, should a branch exchange subscriber dial an unauthorized number, the trunk in combination with the adapter will operate to prevent the call reaching a subscriber in the main exchange, or to other unauthorized numbers, and the main exchange endV of the trunk will be guarded until the calling subscriber abandons the call. The dial impulses from the calling subscribers dial are repeated over the .trunk to the main exchange through Contact 22| and are repeated by Contact 223 through contact 254 over conductor 369 to the rotary magnet 31D in the adapter. The wiper assembly of the adapter will step over its bank contacts in response to said impulses and, should an unauthorized number be dialed, relay 3|0 will operate to disconnect the trunk conductors 364 and 365 from leads 463 and 464 thus preventing any further impulses from being received on any main oflice switch. At the same time relay 3H), at contact 3|3 connects ground to the trunk conductor 464 which operates the line equipment in the main exchange to cause this trunk to test busy to outgoing calls from main exchange subscribers. Due .to the action of the weighted spring 3I'l on Vrelay 3|0, there is a perceptible time interval between the opening of contacts 3|| and 3|2 and the moment that relay 313D operates ifully, to connect ground yto conductor :464. During thisftime interval the main .of--V -iice switch train releases, after which ythe line .and through its contact 254, will close `a part .of

the -circuit to relay .210. After the calling subscriber abandons the call, relay 220 will restore and at its contact .223 will complete the -circuit .to relay `210, which will operate, closing ground through contact 2M to energize relay Zli. While relay 2-1-3 is 'being held by itsslow releasing feature vand after relay 250.1estores, the high `resistfancerelay 280 will be bridged across .the .trunk :conductors 64 and v365 and will operate from Vthe current, regardless Vof direction of filow of n .said-:current on these-conductors, from the switch .in the .mai-n exchange which has been seized by .said une equipment. y 281, `closes ground to operate relay .2 if). Relay v2li) immediately operates and through Contact l 2 L3 places guard-ing potential on the bank'A .multiple.V Thus the period during which the bank multiple is .ung-uarded isfurther shortened and when the last slow lreleasing relay has fully 4restored the :trunk will -be free `for calls in either direction.

When -it `is necessary .to :allocate a trunk for .the exclusive yuse of one branch exchange subscriber, for instance for through night service or special .day service, the said subscribers line .is connected .at 'the attendants yswitchboard t0 .a .trunk by a v#patching Ycord, which may 4besimply a -two conductorcord with a switchboard .plug fitted at .each end. Whenthis -is done, the following conditions would prevail; relay V2I-0 will .be .held operated .over the following circuit, ground, contact .1229 .ofvjack J2, number :l winding of relay 210 to'bat- .tery and .-at contact -2I13 4will `connect ground to .lead 259 whichprevents .this particular trunk from v'being :seized by a branch .exchange selector, this same groundis extended to lead in the adapter. lGround through ycontact 244, .lamp ,2.1.1 .to :battery .lights ythe -busy signal yon -the branch exichange operators switchboard. When the vtrunk is seized at `the main exchange, ground lover conv.ductor 3'54 operates relay 280. Followingseizure .ringing current is superimposed intermittingly across the two conductors, .operating relay ,283, "andat `contact 284 ground` from contact 22B is :connected through contact 294 to relay l23il-to sbattery, relay 230 operates ron `each impulse of Jringingcurrent. Theoperation -of relay 2.3i) .closes contact 236 furnishing ground to operate relay `2H) :which-in turn, through vcontact `2.741,operates relay 2.50. Theeoperation of relay .219, opensl at .contact.21| the connection between relay 283 and `the trunk lead `3555 `to allow ,the Yringing current to follow the bypass .circut. 'Thel operation of frelay 2.3.0 completes, ,at-contact 23.3 a partofrthe bypass circuit tor `the ringing-current tothe .sub- `scribers line. During the ringing .period relays 2183, 210, r2li!) .and 230 `are operated, in addition to relay 210 and one ,-path for the ringing current may be traced over the following circuit: conductor 364, contacts 262 and 232, ring 225 ofv through the winding of relay 2.80.

Relay .280, .at its contact jack J2 over one lconductor yof the patching cord one conductor of telephone line, telephone instr-ue ment, other conductor `of telephone line, tip 2.226 -fof jack `vJ2', contacts 2H and 23.5 Itotrunk conductor 3165. Another path for ringing current -is from conductor 364 through 4.condenser 288, winding of relay V283, contact `2 33 to conductor .36.5.Y

Relays '2.83 and 2.30 Iwill operate during the ringi- `ingY period andrelease during the silent period'. However, relay 269 is now being .held .by .a amultiple ground at lContact ,Z8-I through l.contact 268, winding vof relay 260 to battery. v'Ihusrelay 280 is connected in bridge across the tru-nk and is jbeing held vby current Yfrom `the switchboard xat the calling :end of the trunk, which may -be automatic, manual or from a .toll switchboard, also this direct `current may :be 'in either. direction When the called subscriber removes :his receiver to answer 'the' call this places a loop across the circuit and should this occur during the ringing lperiod, the loop wouldoperate :the back bridge `relay in .an automatic exchange or similar circuit at ya tinan- -ual switchboard. Should the called subscribers receiver :be .removed dur-ing :the silent period, the loop would operate relay .22,0 and at lcontact 72.2i .close a circuit to 1connect 'relay .24.0 across the main :exchange end of the trunk to operate the ring cut-oi relay in the calling exchange. When relay `22,0 operates a second contact 222, is 1:closed to operate relay r250, from ground, contact 222, winding of relay 25B to battery. The icallingfand ycalled subscribers are .now connected for .conversation and .the .busy .signal :indicates `to the foperator :of .the branch exchange switchboardthat the' .trunk is busy. .Af-ter conversation is geom- -pleted .both subscribers restore their ,receivers vthus Vcausing the apparatus .to return to normal as previously described. vCalls froma line which .is connected :bya patching `cord to a :trunk fline, will be made in the same .manner as 'previousls described, with the exception athat a fewer number -of digits will be dialed. .As the telephone line `is connected direct with the trunk,.;the removal .of

the receiver lby .a Ybranch -exchangegsubscriber causesa switch in the main exchangeito ',be seized andthe dialed impulse .will `directly operatethe switches -tofcompletethe connection.

'The above completes the ,description :of :the operation vof the invention. VWhatis considered new and is desired to have protected :by Letters 'Patent vis lspeciiically `stated :in the appended claims.

' lWhat 1isvclaimed is:

1.V In a `telephone system, fa two -way v@trunk :extending ffrom a branch y.exchange to :a ,main ,ex-

change) means xfor seizing ythe trunk .and extending kconnections thereover `in .either direction, ,a

relay normally connected to 'one conductor .of

`the .trunk and operatedv when 4the trunk is :Seized at the :main .exchange to busy the trunk at the branch exchange, means responsive to the/,seizure rv.ci .the .trunk at the ,branch Vexchange :-fo'r .disconnecting said relay lfrom said `one lconductor `and for making the trunkrbusy Aat vthe .main Aexchange lend; ,and means responsiveto the :release .of .a

:connection extended over .the trunk yfrom vthe .branch `.exchange for 4connecting said ,relay .to both-conductorsfof the .tr-unkiline to hold the .trunk .busy at y.the branch exchange .until it is cleared fat the .main exchange.

`A 2. In -a telephonesys.tem, a two waytrunk Aextending fromalcranch toa main exchange, means for extending a connection over the trunk Vin .either direction, alre'lay vnormally connected 'to one conductor of the trunk, means responsive to the extension of a connection from the branch to the main exchange for disconnecting the relay from said one conductor, means responsive to the initiation of the release of branch exchange for connecting said relay in bridge of the trunk, said relay controlled thereafter from the main exchange to maintain the branch end of the trunk busy until cleared at main exchange.

3. In a telephone system, a two-way trunk extending from one exchange to another exchange, selector switches in said one exchange and automatic switches in said other exchange, means for operating a selector in said one exchange to seize said trunk and extend a connection thereover to said other exchange, a relay normally connected from battery to one conductor of the other exchange section of the trunk line, means in said trunk responsive to said seizure of said trunk by said selector switch for disconnecting said relay from said one conductor and connecting ground to the other conductor to seize one of said switches in the other exchange and make the other exchange end test busy, means in said trunk responsive to the release by the subscriber in said one exchange for connecting said relay across said trunk conductors to guard said trunk at said other exchange.

4. In a telephone system, a two-way trunk extending from a branch to a main exchange .terminating in an operators position and multiplecontacts at said branch exchange, automatic switches in the main exchange, means controlled by the operator at said position for seizing the trunk and extending a connection thereover from -the branch to the main exchange, a relay normally connected from battery `to one conductor of the main exchange section of said trunk, means in said trunk responsive to the seizure of said trunk by the operator at said position for disconnecting said relay from said one conductor and placing ground on-the other conductor for seizing a switch in said main exchange and guarding the trunk, means in said .trunk responsive to the release of the trunk by said operator for connecting said relay across said trunk circuit to guard said trunk at the branch exchange multiple contacts and for seizing another switchV at the main exchange to guard the main exchange end of the trunk.

5. In a telephone system, a two-way trunk extending from a main to a branch exchange, terminating in automatic switches in the main exchange, in anoperators position and in multiple switch bank contacts at the branch exchange, means including said equipment for seizing the trunk and extending connections thereover in either direction, a high connected from battery to one conductor of said trunk responsive to seizure by a switch at the main exchange, means responsivev to the operation of said relay for busying said trunk at the branch exchange multiple switch bank contacts and for lighting the busy `lamp on the operators switchboard, an alternating current relay in said trunk responsive to ringing current from the main exchange superimposed across bot-h conductors of. said trunk for lighting the answer lamp at said operators position, and means in' said trunk responsive to the operation of said alternating current relay to maintain the high resistance relay connected to one conductor of said trunk until the operator inserts a plug at the switchboard in the jack of the trunk, and means the connection at they resistance relay normally -for preventing an'y further responsive to the removal of said plug for connecting the said high resistance `relay across the trunk to hold trunk busy at the branch exchange until cleared at the main exchange.

6. In a telephone system,V a 4two-way trunk circuit extending froma branch exchange to a main exchange, means for seizing said trunk and extending connections thereover from a subscriber in the branch exchange to the main exchange, a relay normally connected from battery to one conductor of said trunk, an adapter associated with the trunk, means in said trunk, after seizure by a switch at the branch exchange, for operating the stepping switch of the adapter in accordance with the impulse'sent from the calling subscribers dial, means in said adapter responsive to specified groups of imlpulses from the calling subscribers dial for opening both conductors of'said trunk, removing the said relay from one conductor and connecting ground to the main exchange end of the other conductor impulses from passing to the main exchange and for seizing a switch at the main exchange to guard the trunk until the calling subscriber abandons the call.

'7. In a telephone system, a two way trunk extending from a branch toa main exchange having an inductive connection therein, means for seizing the trunk from the main exchange end and means responsive to such seizure to busy the trunk at the branch exchange' end and signal the operator at that end, a cord circuit at times connecting the trunk to a. subscribers line and means responsive to seizure of the trunk at the main exchange, in case said cord is in place, for preventing the operation of said signalling means and for completing a by pass around said inductive connection whereby the ringing circuit is extended to said cord circuit.

8. In a telephone system, a two way trunk extending from a branch to a main exchange having an inductive connection therein, means for seizing the trunk from themain exchange end and means responsive to such seizure to busy the trunk at the branch exchange end and signal the operator at that end, a cord circuit at times connecting the trunk to a subscribers line, means responsive to seizure of the trunk at the main exchange, in case said cord is in fplace, for preventing the operation of said signalling means and for completing a by pass around said inductive connection whereby the ringing circuit is extended to said cord circuit, and means effective when the cord circuit is not in place for preventing any operation of said by passing means.

9. In a telephone system, a two way trunk extending from a branch to a main exchange having an inductive connection therein, means for seizing the trunk from the main exchange end and means responsive to such seizure to busy the trunk at the branch exchange end and signal the operator at that end, Ya cord circuit at times connecting the trunk to a subscribers line, means including a ring down relay operated from the main exchange in case of seizure of the trunk at the main exchange, in case said cord is in place, for preventing the operation of said signalling means and for completing a by pass around said inductive connection whereby the ringing circuit is extended to said cord circuit, and means controlled by said by pass means for causing continued operation of said ring down relay as long as ringing current is applied to said trunk.

KARL L. BURGENER.

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