US853286A - Telephone trunking system. - Google Patents

Description

PATENTED MAY 14, 1907 H. G. WEBSTER.

TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED AUG. 1, 1902.

. To all whom it may concern.

UNITED sures PATENT OFFICE.

HARRY e. WEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

,- TELEPHONE 'TRUNKING SYSTEIVL'V Specification of Letters Patent. I I v Applioatioufi le iAngust l, 1902. S erialNo.117,919.

fPat'e'nted May. 14, 1907;

Be itknown that I, HARRY G. WEBSTER,

a citizen of the United. Statesof-America,

and a resident of Chicago, county of Cook, and State of Illinois, have invented a certain new and useful Improvement in Telephone Trunking Systems, of which the following is Specification. .7

i .My invention relates to tele'phone trunking systems adapted to connect together for conversational purposes telephone lines terminating at. different switchboard sections.

In anapplication filed by William W. Dean, June 28th, 1902, Serial N 0. 113,581, atrunking system is shown extending between different switchboard sections at which terminate subscribers linesof the Dunbar or two My inventionirela'tes to trunk systems designed more particularly for usewithlines of the Dunbar or two-wire type atltlie outgoing. end and lines of the l -fthreei or four wire type at the incoming end.

' In lines of the former type, it is well known, the cut-off relays are actuated over a portion of the talkin circuit, while in lines of the latter type, sue devices areactuated over entirely local circuits.-

Some ofthe novel featuresofmyinvention are capable of use in-various relations and al such uses are contemplated as heingf'withini the limits of myimprovements" e xternal line circuit when the said cut-ofi re lay is-energized. ."g At the central ofiice C, the usual'operator s My invention has for its objects the j' i'ovi Myinvention is i llustrated by the accompan'ying drawings in which Fi ure 11s a diagram of subscribers lines termlnating at difierent central ofiices with a cord circuit at one officeand a trunk extend-' ing between said officesto connect-the lines together for conversation; Fig. 2 is a modification of the outgoin end of the trunk, and" Fig. 3 is also a modi cation of. the outgoing end.

Referrin plurality oi subscribers lines terminating at the central oflice C, said lines beingofthe two-wire" or ,Dunbar type, This line extends in two limbsfl and 3 from the subscriber s station A to the said central emcee or SpI'l to Fig. 1, L designates one of a where itis fittedwith suitable answering and .multiple jacks or connection terminals J, J

of a transmitter, 4, a receiver, 5, a ringer or call hell, 6, and the condenser 7. a The switchhook, 8, is adapted in its normal position and when the receiver is placed thereon, to open the circuit through the transmittere andreceiver 5 andto close it through the call bell G'and condenser 7. A retardation coil 9 is connected at the sub-station when the, ho0k is raised,; in parallel with the receiver 5, and

condenser 7, to provide a path transparent -to-steady currents butopaque to voice currents: The-line conductors 2 and 3 Include respectively the armatures or springs lOand 11 of the cut-off relay R which is" perma nently legged to ground from the sleeve c0ntacts 7' 7' of the jacks J, J The armature gfilO is normally connectedwith ground oughthe conductor 12',- while the [opposite armature 11-, is normally connected with-conductor 13 containing the line'relay R for the-line, said conductor leading tothe live or ungrounded 'poleof the central bat- 'te .B the opposite olefofwhich isground- Gi The line relay 5 The forward contacts 14 and 150i the cut-off r'elay' R are adaptedto connect'the jacks and theswitchboard section OI thelinewiththe cord circuit is provided, said cord circuit hav ing an answering p ug 'andi'awcauifig plug P, each being provided with atip contact 10 controls through its j 'armature= the circuit of the line signal S.

and a sleeve contact p a dapted't o register with like contact surfacsj and 3' in the jacks of. the line when the plug is inserted therein. The'tip contacts of the plugs are connected together by means of the tip strands t'and t of the cord circuit and the interposed con denser 0, while the sleeve contacts are like Wise connected by the sleeve strands sand .9 and-'the interposed, condenser 0 A con-.

'roo

ductor 16 extends from the grounded pole of the batteryflB to the tip strand t and con-- tains the winding of the-tip supervisory relay 1*? associated with the answering plug P, while the live pole of the battery is connected bv means of conductor 17 with the answering sleeve strands and includes the Windingof the sleeve; supervisory relay rte-These relays 1* and-r serveto-control the. circuit of the supervisory lamp S v associatedwith the answering plug P, the former relayserving'to normally close said circuit, ofthe lamp, While {the latter relay normally-iopens 1 "the same. The battery B is associate-dwith the opposite or calling-end of the cord circuit and is connected by conductors 18 and 19With the.

; tip andsleevestrands t and s respectively,

the former conductor including'the Winding of the supervisory relay 1", while the latter conductor includes the similar relay 1' These relays serve in a manner similar to the.

relays'r and T to control the circuit of the supervisory lamp S associated with thecallingplug P .The relays r and 1" are conveniently re ferred to as the tip relays and relays r and r as the sleeve relays, since they are con-' nected with and operated by current flowing when the relay is energized. The back con-- tact 22 of this extra spring is connected over the corresponding strands of the cord circuit. The tip strand t of the callingplug and tes'tingplug P is normally open through the extra 'spr ing or movable contact 20 of the sleeverelay 11 but is adapted to be clo sed by the said spring and its forward contact 21,

" through the medium of conductor 23 with one side of the high resistance and high impedance relay 1", known as the? test relay,

the other side of which is grounded. The armature'of this relay is'likewisegrounded" and its forward contact isconn'ectd with the v primary winding 'of the operators induction coil 25 by means of conductor 24. The

I other end of the'saidr'i primary winding is conedium of conductor 26 nected through the to the live pole of the battery B, a retarda tion coil 27 being included in this circuit The operators transmitter'28 is'joined on one side to conductor 26,-intermediate her primary-coil and the coil 27, andon the other side through conductor '29 to ground. A condenser c is included in the operators local circuit to facilitate talking and is con? nected as shown, The secondary winding of her induction coil 25 is adapted to be included together with her receiver 30 and a condenser c in abridge between the strands of the cord circuit by means of any suitable key and in.-- dicated diagrammatically 'by'k, 7c. Branch connections. 31 and 32 lead from opposite sides of the receiver and secondary-to an ori der key connected-with an order circuit or wire 33leading to'the oflice 0% A grounded alternating current ringing generator '9 is adapted to be connected through a resistance lamp with the tip strand t of the, cord circuit by means of the tip ringing key spring W, the sleeve contact-k of said key-being connected with battery lead 26 through wire 26 and-resistance 26 A trunk circuit-is ShOWnIeXtending between the central oflices C and C said-trunk circuitbeing fitted :at the outgoing end with multiple jacks J ,andJ.

tends inftwo limbs 35 and 36 to the central "oi-lice C where it is provided with suitable This trunk ex means for testingthe' condition of the wanted subscribe'rs line, for ringing the desired sub s'criber and-With signals to enable the operator to properly attend the connection. These trunk conductors 35 and 36-terminate at the' incoming oflice'in windings 'w and w of the repeating coil W and the interposed condenser 0 A trunkrelay 1* of fairly low resistance is connected inf'a conductor, leading from the trunk conductor 36 to the Normally,

spring .81 carrying the back contact 82 of through the medium of conductor 80, s ring 81', contact 84 and conductor 83 and is t erefore operated over the metallic trunk line. The opposite windings 10 and w of. the repeating coilW with an interposed condenser 0 are connected between the tip strand t and the sleeve strand *s of the tlexibleend of" the' trunk circuit, said end-being herein: after-referred to as the trunk cord. These strands, terminate in corresponding contacts 1) and p of the trunk plugl. The tip relay r is located in a conductor 36 leading from.

the tip strand through the battery B to ground; The sleeve relay 1- is legged directly to ground by conductor 41 from the sleeve "strand s of thetru-nk cord. These relays serve to control the signal circuits at theincoming' end of 'thetrunk' so that the operator is enabled to properly attend the connection. These signal circuits comprisethe battery-lead 47 extending from the live pole of the battery, a conductor 85including the ringing lamp S? and extending to the spring contact 51 ofthe-sleeve relay r", the normal contact '86 of which is connected by a conductor -87' to the point 88. A parallel branch of the signal circuit extends from the battery lead 47. over conductor 89 thence through the pilot relay 4? and the disconnect and guard lamp S? andthence' to the spring contact 90 of the trunk relay r which is. normally connected through its contact common conductor 92 leads to the forward contact 93 of the tip relay 1-. An auxiliary branch of the signaling circuit is completed by a conductor 94 from the forward contact 95 of the trunk rela to the back contact 96 of the tip relay. thus be observed :91 with the point 88. From this point 88 a that one parallel branch of the said circuit or circuits includes the ringing lamp S and is controlled through the contacts 51 and'86 of the sleeverelay; while the other parallel parallel branches. The auxiliary branch 94- i is enabled to throw ground upon the parallel branchcontaining the guard and disconnectsignal only when the trunk relay is operated. It will therefore be observed that whenever.

the sleeve relay is operated the ringing lamp circuit is open, that when the trunk relay isoperated the disconnecting lamp circuit is open at the trunk relay 1 but is, ,closed upon the auxiliary branch 94. The operator at thisend of the line is enabled to'connect her telephone with the trunk c'ord by mea-ns of the key -7c,'7c, while the operator at the other exchange is enabled to connect hertelephone with the B operatorby means of. the instruction circuit 33. A, ringing generator 9 is shown connected with the tip'ringing contact k the resistance lamp being in circuit therewith, while the sleeve-key k is grounded as shown. The subscribers .lin'e .Lshown in connection with the ethos C is. ofthe type employing three or four wires andextending throughout the switchboardfor the opera-' tion of the busytest and theycut-ofi relay.

This line includes conductors-2 and 3 eXtending to the subscribers station D, whilethe receiver 5 and transmitter 4"are included in series in the line when the telephone is off the hook, but when the telephoneis up'on' I current will'seek the grounded pole of the the hook',-the tip line conductor 2is connected with the grounded signaling bell '6. In this 4 conductor 47 to the live When the cut-off relay is actuated,-

acksl I the tout-off relay which is grounded through instance the tip spring 10 of the cut-off relay R is normally, grounded while the sleeve spring I 11 normally leads through the line annunciator S7 which is connected by the polelof the battery B however, these springs are connected through their forward contacts 14 and 15 with the tip and sleeve contacts j and i of the connecting A third contact 11 is provided for a resistance coil 11 and the forward contact of which connects by conductor 11? with the test rings 7', ji, of the jacks which are designed insulated from the line even when the plug is inserted in the jack, current from the main battery B flows through the cut-off relay R to operate the same, to disconnect connects the, line signaling device and connect .the line limbs to the main contacts of the jacks.

I J ,;J and J J, are respectively busy back and dont'answer jacks associated with the incoming trunks. comprises an induction coil 67 having its primary in'circuit with the rapidly rotating circuit breaker 68 and, the battery B, this battery being preferably the same as battery B but shown separately for convenience. The secondary of the induction-coil 67 is connected in circuit with the rapidly rotating interruptei169 and the more slowly operating interrupter 701 From interrupter 69 a conduct'or'71 leads to the sleeve'con-tacts ofthe busy back jacks J Jf, through-a 50 ohm resistance coil 72, while interrupter 7 0 is connected byconductor 73 through resistance- .coil 74 to'the sleeves of the dont answer iacks, J J The tips of'both se'ts of jacks are united by conductor 75 with a groundedipole of the battery. The" circuit breaker 68 cause'sinduced currents in the secondary circuits which are interrupted at'short inter- This apparatus vals =by breaker 69and-at longer intervals by breaker 70 to cause distinctive tones in the receiver of the waitingsu'bscriber when the trunk plug-is inserted in'one or the other of the jacks. The circuit breakers 6 9 and 70 serve also to-gmake and break thecircuit of the supervisory relay 1" whereby the supervisory signals at both ends of the trunk are flashed in accorda'ncefwith the interrupted current.

- In tracing the circuits hereinafter, the plan of pointing out th'e'path for current from -the 'live or ungrounded pole of the battery to the ground only will. be followed forl convenience, it being understood that the return permits currentto f lowfrom thebattery B through conductor 13, line relay'R spring 1 1 of cut-0E rlayR, limb '3 of the telephone line, through the retardation coil 9 and transmitter 4 at thesub-station, and thence over limb Zback to the central office and spring 10,. ofcut-orf relay B through conductor 12 to ground. The line relay R is'thus operated and closes the circuit of the signal- .lamp S to ground from the conductor 13.

The opera'tor'upon seeing the line signal exposed inserts the answering plug P into the answeringljack J ofthe subscribers line and er telephone 30 with the cord cir- IIC . cuit by depressing the listening key 7c, It, to

receive the order from the subscriber. insertionof the plugP closes acircuit thron h the cut-off relay'R from the live pole of t e battery B through conductor 17, sleeve supervisory relay 1, sleeve strand 8, sleeve contacts 39 and 7' of I the plug and jack, thence through the winding of the cut-.ofirelay R toground. The operation of this ree lay disconnects the armatureslfl and 11 from the ground wire 12 and from the batterylead 13 and connects themethroughthe circuit of the supervisory signal S which is; associated with the plug P,,but it is prepurposes.

vented from glowi-ngby the operation of the tip supervisory relay 1' which 1s connected in. the conductor 16- and receives currentover' telephone line and the tip strand't of the cord circuit and through the conductor 16 to the grounded 1 )le of the battery B, as soon as the cutrelay R is operated. The su er-- visory signal S therefore remains inert-W 'le the battery B" furnishes ;cur rent':over the' metallic telephone line for the operation 'of the supervisory relays and for conversational The operators transmitter 28 is receivlng current at this time from the bat- 'tery B over the conductor 26 through retardation coil 27, thence through the transmitter 28 and over conductor 29 to ground. When sound waves strike the transmitter 28, the current flowing therethrough is varied which causes a variation of the charge in the condenser and a corresponding surge of current through the primary of her induction coil 25; These induce voice currents in the'secondary which are transmitted to the line and the operator is'therefore able to converse with the calling subscriber. Upon learning that a subscriber in the exchange C is desired, the A operator depresses theorder key to connect her telephone with the order wire or circuit 33, and re eats the number of the wanted subscriber to t e B operator whose head telephone 50 is permanently connected with the said order wire. The latter oper ator designates to the A operator the trunk to .be used for the connection and.

roceeds to. test the condition of the wanted iine with the tip of the plug of the incoming trunk named. If the line is idle, no 4 click will be received, but if busy, the test rings y" of the jacks will be connected to round through the spring 11*- of the cut-o relay and resistance coil 11 to ground.. As before explained the tip of the testing plug is con nected through the tip strand of the trunk cord,.conductor 36?,tip'relay r and battery B to ground. A complete circuit will therefore be established when the tip of the plug is The touchedto the test ring ofthe busydine,

which will-cause a flowof current and willaffect'the receiver of the B operator, which is connected across the trunk cordcircuitby- 'means of theikey k, k, sufficientl to indicate to her that the line is busy. the line idle the plug P is inserted in one of- };he multiple acks of'thewanted subscribers ine.

number of the trunk, to be used inserts the calling. plug P -of her cord circuit in the trunk .jack J at her section at substantially the The A operator-having received the same time that .the trunk .plug is connected with the called line The insertion. of the cord circuit plug 1 closes a circuit from the live pole of the battery'B at the A office through conductor '19 sleeve supervisory relayr sleeve strand 8 of the cord circuit sleeve contact of the plug and jack and over the sleeve' conductor 36 of the trunk to the cen tral ofiice' C thence through conductor 80 and r the trunk relay r over spring 81 and contacts 82 and 42 of the sleeve relay 1' to ground:

Current over this path actuates the sleeve supervisory relay r in the A cord circuit which attracts its armatures and cuts out the test rela r" and completes the tip strand of the cor circuit througharmature 20 and its forward contact 21. The supervisory signal'S associated with the calling plug 1? of the A cord circuit is therefore lighted b current from the live pole of the battery 12 flowing over the conductor 26 and through the signal lamp Stand the armatures of the two supervisory relays to ground. This lamp is therefore lighted and remains lighted until the-re- Ioo' spouse of the called subscriber as hereinafter I explained.

The trunk relay 1 is also operated at this time by current over the path just traced which closes its contacts and and breaks contact 91 and would operate the disconnecting signal S except for the fact that -the tiprelay 1" is now operated by current from .the battery B over conductor 36 a through the said relay, the tip strandfi, the

tip conductor 2 of the subscribers lineland through the grounded signaling bell 6'. This relay therefore operates and closes circuit upon its forward contact 93 and since the sleeve relay 2 is not yet operated, it completes the ground cpnnection of the parallel signaling branches so that the ringing lamp S the continuit of whose circuit is con- 1 trolled by the sleeve relay r", is-now lighted. Ringing current for the subscribers line is furnished by the generator 9 over the ti side ofthelinc and through the bell 6, and s ould the-- subscriber respond during ringing, the

current traverses back to the central office. "over'the sle'eve side of the line andthrough the grounded ringing key is in the sleeve strand of the cord When the subscriber respends a path for current from the battery B over the metallic line is provided through the tip relay and the tip strand of the cord, thence strand of the cordthrough conductor 41, the

' which opens its contacts 4:2,and 82 thus break ing' the grounded trunk-rela y operating cirsame time.

- necting 1am "which indicates to the operator that t e called cuit of ringing lamp S is opened atjcontacts ,51 and 86 of the sleeve relay 7' Whi ch indicates the hook','the supervisory lamp S is lighted, and when the subscriber-D, hangs uphis tele conditions just described and serves to cut- .is lighted. At the same time the ringing draws the-plug Whom the jack of .thesub and a trunk-plug is inserted in the subscrib- .line when a cord circuit is not connected over .the tip line conductor and through the subscribers instruments andf'back over the sleeve conductor of the line and the sleeve sleeve relay rto ground and'the other side of the battery. This current flows in suflicient quantity to also: actuate'the sleeve relay'r cqit and closing contacts 81 and 84 whereby the trunk relayis includedin the metalliecin .cuit of the outgoing end of the trunk and per-'1 mi'ts current to Ifiow from thebattery B of the A cord over the metallic trunk and back to the A office thereby operating the supervisory, relay I -connected with theA cord to open the circuit of the 'superviso signal subscriber has responded. Likewise the cirthe same fact to. the B operator. .The subscribersare now in condition for conversation and all supervisorylamps are extinguished.- When the A subscriber returns his receiver to phone, current is cut-off from the sleeve relay r which permits the re-establishment of the ofl' current from the supervisory relay 1 at the A ofiice whereby-the supervisory signal S? scribers line. This de-energizes the tip relay 7' which disconnects the ground branch from the parallel'signaling branches andretires all signals." f i The disconnect lamp S may be employed. as a guard lampin case a mistake is made ers line or incase the A' operator connects with a wrong trunk. thelatter case, the trunk relay 7' of theline, is operated which closes the auxiliary branch 94 upon the parallel signaling branch containing the disconor guard lamp S which is therefore lig ted together the ilot signal and indlcates the fact of a 'mistalieto the B operator. a

The insertion of the plug P in-a jack of a with the trunk at the opposite end results in establishing the disconnecting j condition heretofore described, that is, the grounded 'branch 92 isclosed upon both of the parallel 'signalingbranches whereby both lamps S and S light.

; 1 la case the wantedsubscribers line is found busy or ifa subscriber having been called does not-respond, the. plug 1 is inserted in the jack J or J and a correspond .ing signal is transmitted to the Waiting subscriber. "Upon the insertion of plug P In one of the busy backordont answer 'acks, for

example, one 0. the jacks-J a pat for ourrent is provided from the battery 13 through the tip strand'of thetrunk cord, theti contacts of the plug andj ack and over con uctor 75 to ground. Q This will serve to operate the t1 relay 1 toiconnect ground upon the pare al el signaling branches. In the rotation of thecircuit breaker 69 a ath 'for current is also rovided from the l ve pole of the battery g over the secondary" of the induction coil 67 and contacts of the circuitbreaker 69 :thence overithe conductor 71' and the sleeve strand of the trunk cord through the sleeve relay 1";to ground. This relay will therefore operate in accordance with the,

interrupted currentto break the grounded circuit of the trunk conductor 1 and complete' 113$; metallic circuit over -both.s ides of the outgoing end of the trunk wherebythe "supervisory; lamp 8- at the A'exchange is flashed in accordance with said interrupted current; The subscriber is simultaneously notified of the condition of the wanted'line by the tone caused by the rapidly interrupted current. r The order circuit 33, as is indicated by the branch lines 33 connects the B operator with several operators either at the same or at diiiereht exchanges. The A o erator is also provided with a plurality of eye Jc to connect herself with several B operators. The busy back or dontanswer apparatus is common to the various sections of the incoming trunklboard, asis indicated by, the I branching lines; v p p Although 'I havedescribed the method of makin connections through the medium of the or er circuit, I do not wish to so confine the invention for it isapparent that. the A operator is able. by means of her testing appa ratus to test the condition of the several .trunks before her until an idle trunk is found, and upon findin j the same,, she may connect the calling plug 15 of her cord circuit {with the trunk, which would operate the trunk relay 1 at the incoming end v and light the lamp S rwhich would then serve as a calling, lamp. The B operator upon seeingthe signal, would depress her listening key k, k, andupon learning the order would make the deslred connection, as hereinbefore described. It

a that subscriber would have been tested in the 7 before the ground circuit is opened,.the sleeve v will also be understood thathad a, A subscriber called for a connectionwith another subscriber in the same exchange, the line of of such coil it would not be necessary for the contacts 81 and 84 at the Bend of the trunk to make contact before breaking contact at points 82 and 42 as is necessary with the arrangement shownin Fig. 1, where, if the me.- tallic circuit of the trunk be not completed supervisory relay in the A cord may become de-energiz'ed. In case of ground currents which may fiow in such strength as to operate the trunk relay when a retardation coil is employedat the outgoing end of the trunk, the device shown in Fig. 3 may be employed in which the retardation coil 34 is connected with a spring 7' of the trunk jack J whichis normally disconnected from the. sleeveconductor, but which, upon the insertion of the connecting plug is lifted by the ti spring into contact with the sleeve side. nder normal. conditions therefore" the retardation coil would be disconnected and earth currents could notaifect the trunk relay. The ground connec-v tions hereinbefore referred to, it will be understood, may be and in practiceusually are one and the same, or they may be the common office feturn, although it is found by ex-. 'perience that it is necessary to place a dead ground upon one side, of the common battery which ground connection may be placed at the opposite pole of the several batteries instead of as shown in the diagram, all of which is apparent to those skilled in the art.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1..The combination with a trunk circuit extending between diflerent switchboard sections and adapted to connect telephone lines together for conversation, of a disconnect signal for the incoming end of the trunk, a

' source of current and a relay'associated with tions and adapted to connect telephone lines. together for-conversation, of a ringing signal for the incomin end of the trunk, a relay actuate'd over the tip side of the talking circuit and ground adapted to direct current through said si al to operate the same when the subscriber i response, and a second relay operated by ouras been called but 'before his rent flowing over a portion of the talking cir-,

cuit but having its coil out of the path of the voice currents, said relay being adapted to deprive said signal of. operating current when the'subs criber responds, substantially as de- I scribed.

. 3. The combinationwith a trunk circuit extending between different twitchboard sections and adapted to connect telephones line together for conversation, of a ringing signal for the incoming end of the trunk, arelay actuated over one'side of the telephone line and through the grounded signaling bell to direct current through said signal to operate the same when the subscriber has been called, *and a second relay at said end adapted to deal of operating current when prive said si the called su scriber responds,'substantially as described.

4. The combination with-a trunk circuit I extendin between diiferentswitchboard sections an adapted to connect lines together for conversation, of a ringing "signal for the incomin end of. the trunk, a relay and a source 0 a current connected with the tip side of the trunk cord, a grounded signaling bell from the tipjside of the subscribers line, said relaybeing actuated by current from said source over the tip. side of a cord and line and through the said grounded bell to cause the operation of said signal when the connection is established with the called line, and a second relay connected with sleeve strand'of the trunk cord and responsive to current in the metallic line when the called subscriber answers, said latter relay serving to render said ringing signalinoperative, substantially as described,

5. The combination with a trunk circuit extending between different switch-board sections and adapted to connect telephone lines together for conversation, of a signal associated with the incoming end of. the

trunk, a relayalso at the incoming end adapted to be operated by current sent over the trunk from the outgoing end, a second relay at said incomin lend adapted to be operated by current owing over o,ne.si de o the called telephone line to the sub-station and ground when the connection is establishe with the said called line, said relays jointly controlling said signal so as to operate the seam to give a guard indication when the connection is established. at the outgoing end of the trunk andv the trunk is discor nected from the called line, or to place said described.

6. The Combination with a trunk circuit extending between different v switchboard sections and adapted to connect telephone lines together for conversation, of a signal associated with the .incoming end of the trunk, a relay also-at the incoming end operated by current over aportion of the tip side of the talking circuit when the connection is established with the called line,'a second relay at the incoming end actuated when. the connection exists at the outgoing end, said relays jointly controlling said signal so as tooperate the same to give a guard indication when the connection is established at theoutgoing end of the trunkand severed at the incoming end, or to place said signal in condition to operate'to give'a disconnect indication when the connection is severed at the outgoing end and is completed at the incoming end, substantially as described.

7. The combination with a trunk circuit extending between different switchboard sections and adapted to connect telephone lines together for conversation, of a guard signal for the incoming end of the trunk, means to actuate said signal by current sent over the trunk when the connection is 1 established at the outgoingend of the trunk,

- the sub-station for rendering said and further means actuated by current sent over a portion oithe talking circuit including one side of the telephone line tog-round at signal inert, substantiallyas described.

8. The combination with a trunk circuit extending between different switchboard sections and adapted to connect-telephone lines together for conversation, of a guard signal for the incoming end ,of the trunk, a relay to place 'said signal in condition to 0perate and actuated by current sent. over the trunk, and a relay actuated by current over a portion of the tip side of the talking circuit when connectionis made with the calledline for rendering said signal inoperative, substantially as described.

9. The combination with a trunk line ex tending between different switchboard sections and adapted to connect telephone lines together for conversation, of a supervisory signal. associated with the outgoing end of the trunk, a relay associated with the incoming end and connected with the sleeve strand ofthe trunk cord and responsive to current in the metallic talking circuit when the trunk is connected with the called line, a source of distinctive signaling current with which the incoming end of the trunk is connected when a subscriber is busy or fails to respond, means for intermittently operating said relay when the trunk is connected with said source, and means operated by said relay to correspondingly operate said supervisory signal, the waiting subscriber being also notified of the condition of the line by the distinctive tone in his receiver, substantially as described. r

10. 'T hecombination with a trunk line extending between different switchboard sections and adapted to connect telephone lines together for conversation, of a supervisory signal associated with the outgoing end of.

the trunk, the outgoing'end of the trunk being open to steady current and one side thereof connected to ground, said signalbeing placed in operative condition by current flowing over said side of the trunk circuit to ground, and a relay at the incoming end connected with the sleeve strand. of the trunk cord actuated when the called subscriber. responds for disconnecting said ground'and connecting the two sides of the trunk'together to permit current to flow over both sides thereof to render the said supervisory signal inoperative, substantially as described.

Signed by me at State of Illinois, this 28 Chicago, county of Cook,

day of July 1902.

, H. G. WEBSTER.

' Witnesses:

ROBERT LEwI-s 'AMn's, F. DUNBAR.

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