US1354891A - Telephone system with automatic ringing and automatic busy - Google Patents

Description

I H. D. CURR'IER AND H. W. BRYCE.

TELEPHONE SYSTEM WITH AUTOMATIC RINGING AND AUTOMATIC BUSY.

' APPLICATION FILED JUNE II. 1915.

5%,891. I Emma @CII 5,1920,

2 SHEETS-SWEET H. D. CUHR-IER AND H. W. BRYCE.

TELEPHONE SYSTEM WITH AUTOMATIC RINGING AND AUTOMATIC BUSY. APPLICATION FILED JUNE H, 1915.

1,354,891 A Patented; 00$. 5, 1920,

Z SHEETSSHEET 2.

EZZQZ TZEQ A A-AA l @WA UNITED-STATES PATENT" OFFICE.

-HIRAM D. CURRIER, 0F CHIUAGO, AND HARRY W. BRYCE,.OF DOWNERS GROVE, ILLI- NOIS, ASSIGNORS TO KELLOGG: SWITCHBOABD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPOBATION OF ILLINOIS.

Specification of Letters Patent.

Patented Oct. 5, 1920.

I Application filed. June 11, 1915. Serial No. 33,628.

To all whom it may concern Be it known that we, HIRAM D. Cunnmn and HARRY W. BRYCE, citizens of the United States of America, residing in Chicago, county of Cook, and Downers Grove, Dupage county, respectively, in the State of Illinois, have invented certain new and useful Improvements in Telephone Systems with Automatic Ringing and Automatic- Busy, of which the following is a specification. Y

Our invention relates to telephone systems and has to do more particularly with manually operated trunk or link circuits which are employed for interconnecting telephone lines, one of the features of our invention being the provision of an improved circuit arrangement by which no preliminary test of the called line is required by the B on trunk operator. To this end, means is provided which automatically adjustsitself to bring about the automatic ringing of the called subscriber if the called line is idle, or if the called line is busy to transmit an audible busy signal to the calling subscriber and at the same time to flash the supervisory lamp at the A operators position to notify her of the busy condition of the called'line.

Another feature of our invention is the provision of means whereby after a connection has been established to the called line, the application of ringing current to the said called line is dependent upon the operative association of the A operators link circuit with the trunk or B operators circuit. While still another feature of our invention is the provision of improved means for flashing the calling supervisory lamp at the A operators position when the trunk or B operator establishes connection with a busy called line, thus eliminating any special operation on the part of the B o erator in transmitting a busy signal'to the or originating operator. These and other objects of our invention will be more articularly pointed out in the ensuing spec' cation and.

in the appended claims.

For a better understanding of our invention, reference may be had to the accompanying drawings in which I Figure 1 illustrates one embodiment of our invention as applied thereto, and

Fig. 2 illustrates another embodiment of our mvention adapted for four party ringl teferring now more in general to our invention as illustrated in the accompanying drawings, and referring to Fig. 1, in which we illustrate our inventlon operating in connection with a single party ringing, we show a calling substation A of a well-known type terminating at the exchange in a twowire common battery line circuit L comprising a line relay LR, a cut-off relay G0, a line signal S and the multiple jacks J.

A cord circuit C is shown associated with the line circuit L, and comprises an answering plug P, and a calling plug P the two plugs being connected by the heavily marked conductors, and having the condensers K and K interposed. The calling plug P is adapted for connecting to multiple jacks of cord circuit comprises a calling tip supervisory relay CT and a calling sleeve supervisory relay CS, the two relays CT and CS controlling the callin supervisory lamp CL. A.listening key L is also shown which when thrown connects the operators set 0 to the cord circuit. An orderwire key OW is provided for connecting the operators set 0 with the trunk operators set 0 at the distant exchange so that the A operator at the cord circuit C may communicate with the operator at the trunk circuit T. The trunk jacks J are located at the A operators position and are connected by the heavily marked conductors 1 and 2 to the trunk circuit T.

The trunk circuit T comprises a calling plug P connected to a repeating coil R. The'repeating coil R having the condensers K and K interposedbetween its windings 3 and 5 and 4: and 6. A relay 7 of high resistance is associated with'the incoming end of the trunk circuit T and energizes when i I wanted substation;

' the trunk circuit T, we show the test control relays TC and TC the relay TC operating each time the plug 2 is inserted into a ack of a called line, and the relay TC automatically adjusts itself depending upon whether the line is in an idle or busy condition. A busy tone generator ET is provided which produces a busy tone that 15 heard by the calling subscriber and also brings about the flashing of the supervisor lamp CL of the A operators cord circuit to notify her of the busy condition of the called line. The tgp and sleeve supervisory relays CT and C 1 are operated upon the response of the called subscriber. The relay CT upon ener izing shunts out the hi h resistance relay which allows the relay T of the cord circuit C to operate to eflace the supervisory signal CL of the said cord circuit to notify the A operator that the called subscriber has answered. A ringing lockout relay BL is provided which operates when the relay 7 restores-and interrupts the circuit of the relay RC which in turn opens the circuit ofrelay RI thereby cutting ofl the ringing generator G. A link control relay trunk circuit T as shown illustrates our in-.

LC is also provided as is also a test control shunt relay TCS. The operation of these relays in conjunction with the other apparatus will be hereinafter more fully described.

The substation D- as shown at the called end of the trunk circuit T is similar to that of the substation A and its associated line circuit L except that it is of the three-wire common battery type. It comprises the usual line relay LE cut-off relay CO multiple 'acks J 2 and the line signal S Re errin now in general to Fig. 2, the

-vention applied to four party ringing. We employ substantially the same apparatus with theaddition of a party line ringing Rey RK and four rin 'ing current generators G G G G of difi erent frequencies for signaling the correspondingly tuned bells at .the substations on the party lines. The apparatus of Fig. 2 bears the same reference numerals as that of Fig. 1, but with difl'erent suflixes added.

Having described in general the apparatus which is embodied in our invention, we will now describe more in detail the operation of at the circuit. as illustrated in Fig. 1.

Assuming that the subscriber at the substation A initiates a call by theremoval of his receiver from its switch-hook an enerizing circuit for theline relay Lllis estabished traced from battery through the winding of said relay, normal contact 8 ofrelay C through the substation to ound at normal contact 9 of relay CO. %pon the energization of relay LR, its alternate contact 10 is closed bringig about the lighting of the line lamp S. e operator noting the lighted'signal S, inserts the plug P into the jack J of the calling line, establishing a series energizing circuit for the cut-0E relay C0 of line circuit L and the answering sleeve supervisory relay AS of the cord circuit C. This circuit extends from battery through the winding of the relay AS, the sleeve contacts of the connected plu and jack, through the winding of the relay 0 to ground. The relay CO upon energizing, opens the circuit of relay LR at contact 8 allowing the relay LR to restore to efi'ace the line signal S. The answering tip supervisory relay AT is also energized over a circuit traced from battery, through the winding of relay AS the sleeve contacts of the connected plug and jack, alternate" contact 8 of relay CC, through the'substation, alternate contact 9 of relay CO, tip contacts of the connected plug and-jack. and through the winding of relay AT to ground. The energization oi relay AT and relay AS prevents the lighting of the answering supervisory lamp AL. The operator now throws the listening key LK to connect her operators set C to the cord circuit and inquires the wants of the calling subscriber. I

Assuming nowthat the calling subscriber at A desires connection with the substation D, the operatordepresses the orderwire key OW leading to the exchange in which the line of substation D terminates, to connect her operators set 0 with that of the operators set 0 associated with the trunk circuit T. The A-operator of the cord circuitC repeats the number of the called subscriber to the operator of the trunk circuit T and the operator at the trunk circuit T then assigns the trunk to be used by the A-operatcr. The A-operator then inserts the plug P into the trunk ack J thus bringing about the energization of the calling sleeve supervisory relay CS over a circuit traced from battery through the winding of the relay CS, sleeve contacts of the plug P and jack J through the impedance coil 11 to ground. The closing of the alternate contact 12 of relay CS brings about the glowing of the calling supervisory lamp CL. The closing of the alternate contact 13 of relay CS establishes an energizing circuit for the high resistance relay 7 of the trunk circuit T, traced from permit sufiicient current flow throughthe relay CT of the cord circuit C to cause it'to energize, thus pern itting the supervisory lamp CL to remain lighted until the called subscribed at the substation D. answers. Upon the energization 0f the relay 7, a circuit for the supervisory relay SR is estab lished, traced from battery, through the winding of the said relay, to ground at alternate contact 14 of relay 7. Upon the energization of the relay SR, its alternate contact 15 is closed, thereby closing a circuit for the supervisory lamp SS, traced from battery through the said lamp SS, the alternate contact 15 of relay SR to ground at normal contact 16 of relay 17. If the trunk operator has not yet plugged into the jack of the called line the lighting of the supervisory signal SS indicates to the trunk operator that the operator at, the originating exchange has plugged into the assigned' trunk jack, while if the operator at the originating exchange has plugged into a trunk jack other than that of jack J (the jack of the as signed trunk), the lamp SS fails to light due to the failure of the relay 7 to energize.

The operator of trunk circuit T having obtained the number of the called subscriber from the A-operator, inserts the trunk plug P 'intothe jack J 2 of the Wanted line, without any preliminary testing, and assuming that the called line is idle, an energizing circuit for the cut-ofi" relay C0 of the line circuit L and the test control relays TC and T0 of the trunk circuit T are established, traced from ground through the winding of the cut-off relay CO the sleeve contacts of the jack J 2 and plug P through the winding of the relay TC and through the upper windin of the relay TC to battery. The relay T upon energizing, closes its alternate contact 18 thereby closing an energizing circuit for the relay 17, traced from battery through the winding of the said relay to ground at alternate contact 18 of relay TC. The closing of alternate contact 18 of relay TC also closes a circuit for relay TCS traced from battery through the winding of said relay, normal contact 28 of relay RC to ground at alternate contact 18, but this operation of relay TCS is only incidental at this time. The opening of normal contact 16 of relay 17 opens the energizing circuit of the supervisory signal SS, bringing about its efiacement. The relay T0 upon energizing, closes its alternate contact 19, thereby establishing a locking circuit for itself, traced from batterv through the lower winding of the said relay, its alternate contact 19 to ground at alternate contact 16 of relay 17. The closin of the alternate contact 20 of the relay TC establishes a circuit for the link control relay LC traced from battery through the winding of said relay to ground at alternate contact 20. The energization of the relay LC'brings about the closing of its alternate contacts 21 and 22, thereby establishing the continuity of the talking strands to allow the ringing current to be sent out over the line to the called substations signal bell. The closing of the alternate contact 16 of relay 17 also establishes an energizing circuit for the relay RC, traced from battery through the winding of the said relay, the normal contact 23 of relay RL, normal contact 36 of relay CS and to ground at alternate contact 16 of relay 17 The closing of the alternate contact 2 1 of relay RC establishes an energizing circuit for the ringing interrupter relay I, traced from battery through the interrupter I, the winding of interrupter relay RI, alternate contact 25 of the relay LC, conductor 26, alternate contact 24 of relay RC to ground at alternate contact 27 of rela SR. The opening of contact 28 of relay 0 opens the circuit of the relay TCS. The relay RI is thus intermittently energized and dele'nergized and opens and closes its alternate contact 29 thereby connecting ringing current from the generator G to the called line, said ringing current being traced from the ungrounded pole of the generator G, alternate contact 29 of relay RI, the alternate contact 21 of relay LC, the tip contacts of the plug 1? and jack J through the condenser and call bell of the called substation, the ring contacts of the connected jack and plug, the alternate contact 22 of relay LC, the alternate contact 30 of RI and through the resistance 31 to ground. An audible tone of the ringing current is also sent out to the calling subscribers substation over-the conductor 32, through the alternate contact 33 of relay RC, winding 4 and winding 6, alternate contact 133, alternate contact 134 of relay TC through the winding of relay CT to ground. The tone is induced into the other winding of R and produces the audible tone to be heardby the calling subscriber. The call bell of the called substation is thus intermittently rung until the called subscriber answers.

'Upon the response of. the called subscriber, an energizing circuit for the relays CS and GT is established, traced from battery through the winding of the relay CS normal contact 30 of relay RI, alternate contact 22 of relay LC, the ring contacts of the connected plug and jack through relay thezsubstation, the tip contacts of the jack and plug, alternate contact 21 of relay LC, normal contact 29 of relay RI, through the winding of relay CT to ground. The 010s ing of the alternate contact 3 1- of relay CT brings about the shunting of the hi h resistance relay 7 allowing the relay T of the cord circuit C to operate through the now closed alternate contact 34 of the relay CT. The relay CT, upon energizing, opens its'normal contact 35 to etlace the supervisory lamp CL, notifying the A operator of the cord circuit 'C that the called subscriber at substation D has answered. The relay 7, restoring to normal due to the said shunt, opens the energizing circuit of the relay SR, and the relay SR upon deenergizing, opens the energizing circuit for the interrupter relay RI at its alternate contact 27, whereupon relay RI restores preventing further application of ringing current to the called line. The restoration of the relay' SR brings about the energization of the relay BL, traced from battery through the winding of the said relay, normal contact 37 of relay SR, alternate contact 36 of relay CS to ground at alternate contact 16 of relay 17. Relay BL upon energizing, establishes a locking circuit for itself traced from battery through its winding, its alternate contact 38 to ground at alternate contact 16 of relay 17. The opening of normal contact 23 of relay RL opens the energizing circuit of control relay RC, and the closing of normal contact 28 ofnRC again establishes the circuit for relay TCS. The subscriber at the calling substation A, and'the subscriber at the called substation D are now in conversational circuit, the

said talking circuit being traced over the heavily marked conductors.

Assuming now that the subscribers have finished conversation, the subscriber at the substation A replacing his receiver upon the switch-hook, opens the circuit of the answering tip supervisory relay AT of the cord circuit C, and allows the relay to again close its normal contact 50 to cause the supervisory lamp AL to glow. The subscriber at the substation replacing his receiver upon the switch-hook opens the circuit of the tip calling supervisory relay GT and the sleeve calling supervisory relay CS of the trunk circuit T. The restoration of the calling tip supervisory relay CT opens the shunt about the hlgh resistance relay 7 due to the opening of contact 34 of relay CT, allowing said relay 7 to again energize. The relay 7 energizing again causes the denergization of the calling ti supervisory relay CT of the cord circuit C thereby causing the glowing of the calling supervisory relay L. (The closin of the alternate contact 14, of: the again closes an energizing circuit neeaeei J ,-the energizing circuit of the high re- 7 sistance relay 7 is interrupted, allowing the said relay to restore to normal. The relay 7 restoring, opens'the circuit of the supervisory relay SR, the said relay restoring again closes the circuit for signal SS through normal contacts 15 of relay SR, 36 of relay CS to ground at contact 16 of relay 17 notifying the trunk operator that the A-operator as withdrawn the plug from the trunk jack. The operator at the trunk circuit T now withdraws the plug P of the jack J of the calledline thereby opening the energizing circuit for the test control relay T The relay TC restoring to normal opens its contact 18 and thereby allows the relay 17 to restore to normal. The relay 17 restoriligLopens the lockin circuits for the relay and the relay C The relay TC restoring opens the.circuit for relay LC. All the apparatus of the trunk circuit T is now in its normal condition as is also that of'the cord circuit C, and therefore the cord circuit C and the trunk circuit T are now available for establishing other connections.

Assuming now that the calling subscriber D is busy the operation of the circuit is the same as previously described up to and including the insertion of the plug P into jack J 2 of the called line. The operator of the trunk circuit T, without any prelinrinary testing, inserts the plug P in the multiple jack of the called line, closing a circuit for the relay TCv traced from ground through the sleeve contacts of the multiple jacks .and the connected plug through the windin of the relay TC, through the relay TC to ttery. The relay TC operates, but sufilcient current does not flow through the winding of the relay. TC to bring about its operation due to the fact that battery is connected through another cord circuit to the sleeve contact of a multiple jack of line D. The closing of the alternate contact 18. of relay TC establishes an energizing circuit for the relay 17 traced from battery through the winding of said relay to round at alternate'contact 18. of relay C, and also closing an energizing circuitfor relay TCS as previously described. The closing of the alternate contact 16 of relay 1'7 closes an energizing circuit for the relay RC, traced from battery through the winding of the relay BC, normal contact 23 of rela RL and normal contact 36 of rela C to round at alternate contact 16 0 relay 17..

nate contact 31. The opening and closing of the said alternate contact 34 opens and closes the shunt about the high resistance relay 7 and this energization and denergization of the relay 7 brings about the energization and denergization of the relay CT,

I of the cord circuit C. The said relay CT opening and closing its normal contact 35 causes the flashing of the calling supervisory lamp CL, thus signaling the A- operator that the called subscriber is busy. The calling subscriber also receives a, busy tone ,which may be traced from battery through busy tone interrupter BT, normal contact 52, alternate contact 133, winding 6 of R, condenser K winding 4 of R, alternate contact 33, through resistance 31 to ground. This tone is induced into the wind ings 3, 5 of the repeating coil R to the waiting calling subscriber which notifies him that the called line is busy. The A-operator noting the flash busy signal, withdraws the plug 1 from the jack J bringing about the deenergization of the relay 7, the said relay deenergizing opens the circuit for the sleeve supervisory relay SR, thereby allowing the relay SR to restore to normal and close the circuit of the supervisory signal SS thus notifying the trunk operator that the A operator has withdrawn the plug P from the jackv J The trunk operator noting the lighted signal SS withdraws the plug P from the connected jack and the apparatus restores as before described.

Should-a local operator test the multiple jack of the called line while conversation is going on, the resulting ground from the test relay of the local cord circuit will assist in holding up the relay T0 of the connected trunk circuit T from the sleeve of the jack and connected plug through the relays TC and TC to battery and not affect the circuit in any way. Again, should a local operator test while a second trunk circuit T is in connection with a multiple jack of a busy line, ground from the test relay of the local cord circuit will flow from the sleeve of the multiple jack through'the tip of the plug of the second connected trunk circuit T through the winding of the relay TC of the secon trunk circuit, at this point the circuit divides one branch extending through the upper winding of relay TC to battery, the other branch extendin through the normal contact 55 of relay OS of the second trunk through the resistance R to battery. The resistance B being lower than the resistance of the upper winding of relay TC suflicient current is shunted away from the relay TC to preventits operative energization, thereby preventin any interference with the trunk circuit that is in a busy condition transmitting a busy tone to the calling subscriber and flashing the A operators supervisory lamps.

Referring now more in detail to Fig. 2, we illustrate a trunk circuit T embodying the features of our invention operating in connection with a four-party ringing sysdition,of the four party ringing ke RK The operation of the trunk circuit 1 as a whole, is practically the same as previously described. The operation of this circuit is practically the same as previously described in connection with Fig. 1, up to and including the act of inserting the trunk plug P of the trunk circuit T into the jack of the called line. The operator 'having inserted the plug P of the trunk circuit T into a multiple jack of the called line, (not shown) a circuit is established for the test control relay TC and the test control relay TC as previously described. The relay 17 is also operated by the actuation of the relay TC The relay TC operating closes a locking circuit for itself through the alternate con tact 16 of the relay 17 The closing of the alternate contact 20 of the relay TC establishes an energizing circuit for the relay LC The operator after having inserted the plug P into the jack of the wanted line, depresses the proper ringing plunger of the partly line ringing key RK to connect theproper generator frequency to ring the call bell of the called substation. When the ringing 'key 'is in its fully depressed position, the end spring contact 60 assumes its alternate position, closing an energizing circuit for the ringing control relay RC traced from battery through the wnding of the said relay, the alternate contact 60 of the end spring of the ringing key RK the normal contact 38 of relay RL to round at alternate contact 16 of relay 17 pon pressure being released from the actuated plunger it assumes its ringing position. The relay RC upon energizing forms a locking circuit for itself traced from battery through its winding, through its alternate contact 24;, normal contact 38 of relay RL to ground at alternate contact 16 of relay 17 An energizin circuit for the ring'm interrupter relay R 1 is established u on t e closure of the alternate contact 7 6 o relay RG traced from battery through the interrupter I through its own winding, alternate contact 25 and alternate contact 76 to round at alternate contact 27 The relay 1 is thus intermittently energized and deenergized by the interrupter I. The call bell of the called subscriber is thus intermittently rung due to the energization and deenergization of the relay R1 whlch alternately connects and disconnects the ringing lead 61 to the alternate contact 29 of relay R1 Upon the response of the called subscriber, the relays (/T and CS operate as previously described bringing about the operation of the relay RL which then closes a locking circuit for itself through its contact 38 to ground at alternate contact 16 The locking circuit for the relay RC is opened allowln it to restore to normal. The opening 0 the alternate contact 7 6 of relay RC interrupts the circuit of the interrupter relay RI thereby preventing further application of the ringing current to the called line. The subscribers having finished conversation replace their receivers and signal for disconnect, the same as hereinbefore described. The restoration of the apparatus of trunk circuit T is the same as that of Fig. 1. The testless features as described in Fig. "1 in which the operator plugs into a called line without making preliminary tests is also incorporated in the trunk T as illustrated.

It is thought that a further description ofthis trunk circuit is unnecessary.

In working out our invention we have shown it operating with a particular form of link circuit but we contem late using it in connection with other circuits than those shown and therefore weaio not desire to be limited to the exact system as shown but aim to cover all such changes and modifications that come within the spirit and scope of the appended claims.

Having described our invention, what we claim as new and desire to secure by United States Letters Patent, is:

l. A telephone system comprisin subscribers lines terminating in multip e terminals at the exchange, a trunk circuit provided with a manual connection terminal for connecting to said lines as called lines, and apparatus responsive to the connection of said terminal to one of said called lines and difi'erently operable according to the busy or idle condition of the called line to automatically connect ringing current to the said called line or to operate a flash supervisory signal according to such idle or busy condition.

2. A telephone system comprising subscribers lines terminating in multiply connected jacks at the exchan e, an operator controlled link circuit provi ed with a plug terminal for connecting" with the jacks of said lines and apparatus difierently operable upon the connection of said plug terminal to one of said jacks according tothe busy or idle condition of the line connected with to connect ringing current to said line or to operate a flash su ervisory signal according to such idle or busy condition.

3. A telephone system comprising subscribers lines terminating in multiply connected jacks at the exchange, an operator controlled link circuit and an operator controlled manual trunk circuit forestablishing connection between the jacks of said lines, a manual terminal for said trunk circuit, a signal for said link circuit, and automatic apparatus including a double-wound test relay automatically operable responsive to circuit and a manual trunk circuit for establishing connection between said jacks of callin and called lines, and apparatus responsive to the connection of said trunk circuit to the 'ack of the called line and difierentl opera le according to the idle or busy con 'tion of the called line whereby ringing current is connected to said line'or a flash supervisory si al is operated according to such idle or nay condition, said apparatus including a double wound test relay.

5. A telephone system comprising sub--- scribers lines terminating in multiply connected jacks at the exchange, a link circuitand a manual trunk circuit for establishing connection, between said jacks of calling and called lines, a visual signal for said link circuit and automatic apparatus responsive to l the connection of said trunk circuit to a jack of the called line and dilferently operable according to the idle or busy condition of the called line whereby ringing current is connected to said line or said signal is operated according to such idle or busy condition,

6. A telephone system including telephone line, a trunk circuit provided with a manually controlled plug terminal for connection thereto, means for automatically ringing a substation on said line'responsive to the connection of said plug to said line, said means being inefl'ective if said .line is busy upon connection made therewith, and means responsive to the busy condition of subscribers line, a trunk circuit provided A with a plug for connection thereto, a pair of relays for said trunk circuit connected to a conductor of said plug, a visual si al for said trunk circuit, means controlle b the energization of said relays for automatlcally associating ringing apparatus with the said called line, said relays being responsive to the connection of said plug with said called subscribers 'line, and means controlled by one of said relays for affecting an operation of said signal.

8. In a telephone system, a link circuit provided with a supervisory signal, a trunk circuit provided with testing means adapted to be manually connected to a called subscribers line, automatic ringing means controlled by said testing means and responsive to the connection of the trunk circuit to the calledsubscribers line for signaling the said called subscriber, means controlled by the called subscriber for operating the said supervisory signal, and means controlled by the said automatic testing means for flashing said supervisory signal if the called subscribers line'is busy.

9. In a telephone system, subscribers lines, an operators link circuit provided with a supervisory lamp and an operators manually controlled trunk circuit for interconnecting said telephone lines, automatic testing means for said operators trunk. circuit for distinguishing between idle and busy called subscribers lines, a manually controllable terminal for said trunk circuit for connecting the trunk circuit to the jack of the called subscribers line, thereby operatively associating said automatic test means with the called subscribers line, ringing means automatically controllable by said testing means and responsive to the connection of said trunk circuit to the called line for signaling said called subscriber, and

means responsive to said automatic testing means for intermittently operating said supervisory lamp if the called subscribers line is busy.

10. In a telephone system the combination of an A-operators link circuit and a B-operators link circuit for establishing connection between telephone lines, automatic testing means for said B-operators link circuit for distinguishing between the idle and the busy condition of a called subscribers line, means responsive to the idle condition of the called subscribers line upon the connection of the B-operators link circuit to the said called subscribers line and to the operative association of the A-operators link circuit with the B-operators link circuit for controlling the application of ringing current to the said called subscribers line, and a visual signal for said A operators link circuit responsive to a busy condition of the called subscribers line.

11. In a telephone system a calling subscribers line and a busy called subscribers line, an A-operators link circuit and a manually controllable trunk circuit rovided with a plug terminal for connectlng said lines, automatic means responsive to the connection of said plug terminal to one of said called lines for ringing the called subscriber, a signal for said A-operators link circuit, automatic testing means for said trunk circuit responsive to the connection of the trunk circuit to the said busy called subscribers line for intermittently operatin the said supervisory signal to-notify' the -operator of the busy condition of the called line.

12. In a telephone system an A-operators link circuit and a B-operators link circuit for extending a call to a called subscribers line, automatic testing means for said B-operators link circuit, signaling apparatus for the B-operators link circuit, means controlled by the operative association of the A and B link circuits and by the said automatic testing means for operatlvely associating the said signaling means with the called subscribers line, said means including a trunk relay, bridged across the strands of said trunk circuit, and subscriber controlled means for denergizing said relay.

13. In a telephone system an A-operators link circuit and a trunk circuit provided with a manually controllable terminal for extending a call to a called subscribers line, a supervisory signal for said A-operators link circuit, automatic testing means for said trunk circuit for operating said supervisory signal or'for associating automatic ringing link circuit and a B-operators trunk circuit for extending a call to a busy called subscribers line, a visual signal for said A-operators link circuit, a relay bridged across the conductors of said trunk circuit, and means responsive to the connection of said trunk circuit to said called subscribers line for shunting said relay whereby said visual signal is intermittently operatedto denote the busy condition of said called subscribers line.

15. A telephone system including a busy called subscribers line, a link circuit and a trunk circuit for extending a call to said subscribers line, a visual signal for said link circuit, a relay bridged across the conductors of said trunk circuit, and means responsive to the connection of said trunk circuit necting circuit, ringing mechanism, and

- maticall 16' apparatus responsive to the connection of said plug terminal to said telephone line and difierently operable according to the busy or idle condition of said line to-either autoconnect said ringing apparatus to said ine or to operate said visual signal according to such idle or busy condition.

- 17. A telephone system including a calling subscribers line and a called subscriberfs line, a link circuit and a trunk circuit for connecting said lines, a visual signal for said link circuit, ringing mechanism for said trunk circuit, apparatus differently operable to automatically connect either said ringing mechanism to said called subscribers line or to operate said visual signalaccordin to the idle or busy condition of the said ca ed subscribers line, and a plug terminal for said trunkcircuit adapted. to be connected to said called subscribers line to operatively associate said apparatus with the called subscribers line.

18. A telephone system including a calling subscribers line and a called subscribers line, a link circuit and a trunk circuit for connecting said lines in conversational circuit, a connection terminal for said trunk circuit for manual connection to said called line, and apparatus associated with said trunk circuit for either signaling the called subscriber or the link circuit operator according to the idle or busy condition-of said called line, said apparatus being operated re-' sponsive to the connection of said terminal to thesaid called line.

Si ned by us at Chicago, county of Cook and tate of Illinois, inthe presence of two witnesses.

HIRAM D. GURRIER.

HARRY W. BRYCE. Witnesses:

Gno. A. YANOCKOWSKI, M. R. ROCKFORD,

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