US1738519A - Signaling system for subscribers' telephone circuits - Google Patents

Description

H. H. ABBOTT 1,738,519

TELEPHONE CIRCUITS Dgc. 10, 1929.

SIGNALING SYSTEM FOR SUBSCRIBERS Filed March 23, 1928 2 Sheets-Sheet l 'L'ce K Maryann! 2 3 s Q i ii 14 A W 52010 release H -i- 1 .5 second Ground .5 Optlru -hzerru,uter

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Jiwa/w 51/ the iz z'mma Zines g Cometuhbe flay second Ida-21w INVENTOR Elf/95bit A TORNEY Dec. 10, 1929. H, ABBOTT 1,738,519

SIGNALING SYSTEM FOR SUBSGRIBERS TELEPHONE CIRCUITS Fil ed March 25, 1928 2 Sheets-Sheet 2 OZZL'ce I [Malena uter- .5 Sec. Gram/m3 .5 u 0 0ew/ INVENTOR ZZZ/4550a ATTORN EY i used on a so-called owl:- at r ABBGTT, GE NEW YORK,

sionarru'e r licaticn flied, March 23, 1928.

This invention relates to a signaling system tor operat circuits, such, for GDZtLIU JlG,

1 'J; as ieiephone cn CllltS. More specllically, the ion relates to signaling system to he foreign exchange sul'- scrihers line.

'lfhe terin foreign e'rchanoe suhscribefis ition. ii foreign e21 chan e subscrii'iers line is one in which the telephone is located in tcle ihcne er:-

ciange area and the circuit appears on the achboarc serving a d' exchange area. By way of example, a suiscriher may he located in one "ity and have i eonoue x L l there, but at the same time ina' for business or other purposes, desire that teephone to appear on. the switchboard in a distant city.

' rune that the subscriber lives in city A and W1 hes his telephone to a )pear on the switchboard in city if. ihe suloscribers line is connected to the central othce oi? city A bit does not appear on the switchboard there. It is merely wired through this otlice, 'oei porrnanently connected to a long cistance line .I 1 x J' 1:4": ft r T) r fir t V T3 a connecting cities .1. ilhcl Jo, and u u y i e 1e lo ace line connected permanently to a wiring circuit which auses the distant subscri ocrs line to appear in the l :r ansteering; ,acli: group for the subscribers h the telephon: xchange or city i3. 'ihus,

when the subscriber in city A rci ores his receiver ironi the switchhooh, no signal is gi en at the central office in city A, but a light )pears under the answering jack associated line in city l3, and the ii. operator B answers the call. in the regular All as though the distant subscriber atcd in city B.

or ureign exchange lines is not to tie c2 so where subscriber in one es his telephone to appear on the i rent city, but also may limited city wise switchhoa d in a di used in the case or a subscriber whose tele phone woulc normally appear on the switchl, iard in excl ange (i, 1062 ted in one part of the city and who wishes that telephone to appear on the switchboard of one iangc area d in a dii'i ierent part of the city. iii-1 l of this latter case would. he where a his oilice at. home in t arrzur cri ics IFE'QR fiYIBSCHIEEH-E TELEPHONE CIRCUITS Serial No. 26 M106.

dentin-l portion of the city, would desire his telephone to appear on the switchboard serving); the business portion of the city.

It can readily be seen that with these foreign exchange lines, signaling between the foreign exchange subscriber and the central office constitutes a much more diliicult problem than is encountered in the case of the usual subscribers circuit, in which the telephone set is loc ted but a short distance from the central otlice. W here the foreign ere change subscriber is located in one city and his t ephone circuit appears in the switchboard in a 0' int city, it frequently happens that the toll line used in conipieting the permanent connection to the distant city is arranged for telegraphic communication in aduition to telephonic communication, in which case all available direct current channels would be taken up by the telegraphic equirnnent. In this case, of course, the usual direct current signalingbetween subscribtr and operator would have to be abandoned. lilven in cases Where the direct current channels are available on such foreign subscribers lines, it might well happen, owing to the extrenie length of many of such lines, teat direct current supervision. between subscriber and operator would not be feasible.

The purpose of the present invention, therefore, is to furnish a method oi signaling; over such foreign exchange suhscribefls lines by utilizing alternating current for this purpose. lilfore specifically, the circuit is arranged to utilize -for this purpose the ordinary ringing current supply which is used for ringing on subscriacrs lines. Direct current supervision is utilized between the foreign exchan suhscrihers telephone t and the local o traloilice, but between the local central otiice and the foreign central oilice the ringing current supply is utilized.

The circuit is so arranged that when the foreign exchange subscriber removes his re ceived from the switchhook it causes the signaling; equipment at the local other: to function in such a manner as to send out ring;- inp; current for zppr :tiniately one second to the foreign oiiice. This ringin cln'rent, incuisin at the foreign cities, or rates th erg aka naling equipment there to cause a steady lighting of the line lamp associated with the answer jack of the foreign exchange line. Furthermore, when the A operator plugs in, the foreign exchange circuit is so arranged as to cause the supervisory apparatus in the A cord circuit to function in a normal manner. Similarly, when the foreign exchange subscriber fiashes or han 's up, suitable pulses of ringing current are transmitted from the local to the foreign ofiice, there to cause the superyisory equipment to function in the same manner as would be the case for a local subscriber.

It is understood, of course, that the signaling current transmitted between the local and the foreign offices need not be the low frequency'ringing current but may be any type of signaling current which is satisfactory for the particular interoflice circuit in question. It is only required that ringing current be used to operate the signaling apparatus at the foreign and local oflices, suit able equipment being installed of courseto transform the low frequency ringing current sent out from one office to the signaling current used on the interoihce circuit and to transform the signaling current back to a low frequency ringing current at the distant end. An example of this occurs where a composite set is used to transform 16-cycle into 135-cycle ringing current for transmission over a toll line, and at the distant end a similar composite set is used to change the signaling current back again to 16 cycles.

The'exact manner in which the'signaling system of the present invention functions, is best obtained from a detailed description of its operation on various types of connections between the foreign exchange subscriber and a distant subscriber. This will now be given. In the drawings, Figure 1 shows a foreign exchange subscribers telephone circuit, the loop connecting such circuit to the local office and the signaling equipment associated with such circuit at the local oflice. Fig. 2 shows the incoming end of the foreign exchange line at the foreign or distant ofiice, and shows the signaling equipment associated with the line at that point. Fig. 3, reading from left to right, shows in order an ordinary interoffice trunk equipped for automate ringing and a portion of an A operators cord circuit, while the dashed line portion of the extreme right shows schematically a connection from the A cord circuit to a subscribers telephone set. Figs. 1, 2, and 3, arranged consecutively from left to right in the order-named, show a complete connection between the foreign exchange subscriber and a distant subscriber, the connection being established over an interoflice trunk. Fig. {i is a chart showing the sequence of operation of relays 1 to 5, inclusive, of Fig. 1 when relay 1 1s connected to the interrupter 22. The functioning of these relays determines the type of signal transmitted from the local office K, Fig. l to the foreign ofiice H, Fig. 2. Fig. 5 shows a chart similar to that of Fig. 1. The chart of Fig. 5 shows the sequence of operation of relays 50 to 54, inclusive, of Fig. 2 when relay 50 is connected to the interrupter lead 68. These relays measure and interpret the signaling impulses incoming from office K to oflice H.

Referring to Fig. 1, the portion to the left of line AA shows the foreign exchange subscribers telephone set. The portion between AA and BB indicates the loop connecting the foreign exchange subscribers telephone set to the local ofiice. The equipment shown between BB and CC shows the signaling circuit of the foreign exchange line located at the local ofiice, which is designated oil ice K. The portion between CC of Fig. 1 and DD of Fig. 2 indicates the telephone circuit connecting the local office K with the foreign office H, at which the foreign exchange subscribers line appears on the switchboard. The portion to the right of DD, Fig. 2, shows the signaling equipment located at ofiiee H associated with the foreign exchange subscribers line. In Fig. 3 the portion to the left of EB shows the signaling equipment associated with the incoming end of an 01- dinary interofiice trunk, the trunk being in this case assumed to terminate at ofiice H. The portion between EE and FF designates the connection over the interoflice trunk be tween the outgoing oflice I and the incoming office H. Between FF and GG jack 10S designates the outgoing end of the interoflice trunk, while 118 designates a portion of an A operators cord circuit. The portion to the right of GG shows in schematic form the connection through intermediate apparatus from the A cord circuit to a calling subscribers circuit.

Circuit operation 01?, cult to foreign arm/1m: 0 subscriber Assume, now, that the subscriber at J, Fig. 3, desires to talk with the foreign exchange subscriber 6, Fig. 1. The subscriber at J i'emoves his receiver from the switchhook in the usual manner, which furnishes a signal to the A operator at ofiice I. The A operator plugs an A cord circuit into the answering jack and takes the called number. She then connects the other end of the A cord to an idle trunk 117, which terminates at ofiice H, where the foreign exchange subscribefis line appears on the switchboard. \Vhen the A operator plugs the cord into jack 108, relay at the incoming end of the trunk operates on battery supplied from the A cord. circuit and closes a circuit from battery through lamp 100, front contact of relay 105, lower back contact of relay 101, through the lower winding of 101 to ground, thus causing lamp 100 to light. llelay 101 does not operon current through its lower Winding. The A cord supervisory relay 110 do s not )oruaic in series With both windings of relay )5 SL106 the upper Winding of this relay is of l slim s only :1 small curline.

connects the plug; 116 oi. trunl: ll? in aclr 0? ol? the foreign exchange subscribefis Current thereupon flows from battery through lamp 100, upper Winding; of relay 101 to the sleeve circuit oil jock 67, Fig. 2, through relay 0% to ground, thereby causing both relays l0l and 04; to operate. The oper: tion o'l-reluy merely preps the for sign eiiichenge line (38 f1 future operation. The operation of relay 101 connects the tip lead. of the trunk through to the ropes coil and connects battery through winding or relay 102, becl; contact oil role i023, burl; conoil relay 104-, lower fron contact of r lay 101, front contact of reloy 1.053, to ground through the upper Winding); of relay 1.01 and. the sleeve circuit of jscl; 0'4. ll1is connects relay in parallel with lamp 100, which reduces the current through lump 100 s; ciently to extinguish it. lbtelsy 1053 operates sud conn cts ringing current to the io 'ei 'n ext-hob e line 08. This circuit is traced tron. the rii' lend 1530 through marginal rels 10 lout over me riu side of the trunk to the ring side ot the ne through the lower boo l; Contact of reluy 00, hi 2, throngs con- 69, rela 62, upper back contact o't rc- 00, to the tip side of the ne and back to ground through the upper fr ,ut contsct of llelsy 10d is niorginel and does nz't operate at this time. Relay 0? of lli g. 2 1 in Syl ClllmllSlll with the ringi g ct pulspplied from the trunk. lateoperated by this ringing current, s oi repeating; co l 06 are -ouch the back contacts of (7 ie operation oi relay 62 connects ogroruul to operutc relay over at circuit from 1 .f st the it bacl; contact oi reluy 58,

1 re -1y 57, front 'ouge h the Winding of ::y 55 thereupon opd connec s mi -neg current across the in: F :foni the foreign oiiice ll ncb llhis ringing current,

on orrivin u p oiiicc ll, flows through relay 1' it to operate in synchronisin with Zlhe operation oi relay ll" l iy directly by means of ground lower fr 1'; contact of relay 1?. 0 furnishes ground to circuit from buttery :uid loft indu through the Winding of 7, upper back contect of relay 8, front contact of relay 16, to ground at the let outer back contact of relay 4. The operation of relay 16 also con nect-s ground to the Winding of relay 8 through the right back contact of relay 11, but relay 8 does not operate ctthis time on battery supplied through resistance 20 as its Winding; is short-circuited by the circuit from the upper lead of t] e vvindinp, oi? 8, back contact oil? relay 0, lower back contact oi? relay 8 to the lower lead oi". the Winding.

The operation of relay '2' connects ringing current rino; the bell of subscribe "s telephone t. The circuit is traced from ringing current supplied over lead 20, through marginal rcluy 9, left back CODtJt-Ct of relay 11, lower tlront contact of relay 7, through the subscribefs set 0, back over the tip side of the line to Fund at the upper trout contact of l". llelsy 9 does not operate at this time, bolus; margin ul.

The subscriber answers by removing the receiver tr the switchliool; which connects e low 1: ce path through the trai'isiniter n coil Winding in parallel with the bell, This allows additional ringing current to flow through relay 0, causing it to operet during' the first ringing interval after the r iceiyer is removed. The operation of relay 9 opens the circuit shunting the Winding oi relay causing relay 8 to operate over e circuit described above. The operstion of relay 8 opens the operzitin circuit at relay ot the upp r buck contact of relay 8. The release of re ay disconnects ringing current from the subscribefis line and hence, causes relay 9 to relec lleloy 8 remains operat Al, however, since the short-circuitiiug path across its Winding is open at the right back contact of 8, due to the operation of this relay. The release of reluy '5 permits reloy 13 to operate from battery through the Winding of over the ring side of the line througl'i the subscribcfs set and baclt to pgroimd through the upper lel't winding of reps-sting coil The operation oi relay 13 prepares u circuit for the operation ot relays 11 and 12 dependent on the condition of relay 16 when the receiver oft subset 6 is removed :rrom the switchhoolt. lit the receiver removed during a silent interval of the ringing; current siiipply relay 16 will be released sud relays 11 end 12 will operate inunediately, the former on buttery through leit Winding, the letter on battery through its Winding, both circuits being traced to ground through the front contact of relay 13, back contact of relay 10 to ground at relay l. H the receiver ol subset 6 is removed during a cnging interval, relay 16 Will be found operated so that relays 11 and 12 Wlll not operate until 16 releases at the end of that particular ringing pulse. liefore the next succeeding; ringing pulse occurs, the signalingapparatus of the foreign eK- is o in ringing current from trunk117 and will thus prevent the further operation of relay 16. The signaling apparatus of the foreign exchange line as will be explained below functions within approximately the first second after relay 12 operates. 'Assuming the automatic ringing supplied from trunk 117 to be alternately two seconds ring and for seconds quiet it will be seen that the signaling equipment of the foreign exchange line will have ample opportunity to function during a silent interval of the ringing current.

. The operation of relay 11 releases relay 8 by openingthe holding circuit for the latterat the right back contact of 11. Relay 7 is prevented from operating again by the open circuit at the front contact of relay 16. The operation ofrelay 11 connects battery through its right Winding to the front contact of relay 16. At the same time battery through the left winding of relay 11 is connected to the back contact of relay 16 through make contact of relay 13. Thus, relay 11, after being operated by relay 13, will remain operated whether relay.16-is operated or released. The purpose of this feature is to permit ringing on the foreign exchange line when the receiver is off the hook, this being a desirable feature on certain long distance calls. It is necessary, in such instances, to insure that relay 11 be operated independently of relay 16 in order to prevent relay 8 from operating and disconcontact of relay 14.-

necting the ringing-current from the subscribers set 6 when the central office operat 1' rings on the circuit with the receiver ofl'the hook.

It will be noted further that when relay 11 operates, it disconnects relay 9 from ringing lead 20 and substitutes therefor, the current limiting lamp 10. This is merely to protect relay 9 from the large current value that would otherwise flow through this relay when ringing occurred while the receiver of subset 6 is off the hook.

Returning now to the operation of relay 1. When this relay operates in the manner described above, it furnishes ground to operat relays 14 and 15, through the back contact of relay 16 to ground at relay 4. Relay 1% is slow to operate and release. Consequently, as soon as relay 12 operates, a. circuit is trace l from battery through the left winding of relay 15, back contact of relay 14, front con right Winding and inner front contact to ground at relay 23. An instant later relay 1 1 operates and locks to ground through the back contact of relay 16 and the right front The operation of relay 15 connects an interrupter 22 to the winding of relay 1. The interrupter'operates to connect the winding of relay 1 alternately to ground one-half secthe chart of Fig. l, where the horizontal lines snow the operated intervals of the relay. The first half-second shows relay 1 operated, the second half-second released, the third open ate-d, the fourth released, and so on. The operation of relay 1 starts the functioning of timing relays 2 to 5, inclusive. The function of these timing relays is to determine the duration of a pulse of ringing currentto be transmitted from office K to oilice H. The length of this pulse determines the manner in which the apparatus at oliice H will function. A one-second interval of ringing current transmitted to if will be interpreted by the apparatus there as a receiver-oli-the-hook signal, wnile a three-second interval of ringcurrent will be interpreted as a receiver- 0! ie-hook signal. Intermittent operation of the switchhook by the foreign exchange escriher will in turn, produce intermittent o eraticn of the signaling apparatus at ofres H through the medium of these timing rclays in a manner to be explained below. The operation of these timing relays will now be taken up in detail.

lVhen relay 1 operates the first time, as shown by the chart in Fig. 4, it closes a circuit to operate relay 3 from battery through the left winding of relay 2, vinding of relay 3, back contact of relay 2, front contact of relay 1, right outer front contact of relay 15 to ground at the left back contact of relay 5. Relay 2 is a marginal relay and does not operate at this time. Upon the release of relay 1 during the second time interval, as shown by the chart of Fig. 4, it opens the operating circuit of relay 3 at the hack contact of relay 1. Relay 3, however, remains operated, due to the fact that current now flows from but tery through the left winding of relay 2, winding of relay 3, right outer front contact of relay 15 to ground at the left front contact of relay 3. Since current now flows through both windings of relay 2, this relay operates. The operation of relay 2 causes relay 5 to operate on a circuit from battery through the left winding of relay 1, winding of relay 5, left inner back contact of relay l, right outer front contact of relay 2, right outer front contact of relay 15 to ground at the left front contact of relay 3. Relay l: is a marginal relay and does not operate at this time. The operation of relay 2 also furnishes ground to operate relays 18 and 23. Both circuits are traced from battery through the windings of the respective relays through the right inner front contact of relay 2 to the common ground at the left front contact of relay 3. l Vhen relay 23 operates, it locks to ground through its ri ht front contact. T he same operation removes the ground from the right windin of relay causing its release. .1 T. .I. 1 .L L 'lhe other operated relays are not affected by the release of relay 15, due to the that r at rei replaces the ground throug the right :tront contact of iii 1: to its i It r ll be notcc mad before the y 15 is ooened, thus operator l relays. cs not disconnect T 1 since the oner prevent The r the in rnpter tion oi relay therefor. The operation of] ringing; current to the torei gn exchange line 1 ion from l t to office H. the third t' interval, as

' clay l opers new operated 2, due to the contact of relay 1 llelay 3 t ieroupon re- .inin operated by the curt Winding. Beginning the fourth interval, relay 1 releases and opens the holding circuit oi relay 2 at the conta oi relay 1. delay 2 there upon releases. Meantime relays and 18 obtain ground on a circuit traced from point 30, WdiCll common to the two relay circo'ts, over lead through the make contact of relay 5 and the hack contact of relay lthe front contact of relay 23.

to ground 1.1L The release of relay 2 opens th holding circuit for rel 5, but this clay reinaii'is operated on a circuit traced from battery through i; the .ei't winding of relay l, Winding of relay 5, right Windin of relay 4i, right inner front contact of relay 5 to ground at relay 23. Re-

iherenpon' operates and opens the hold- 2 circuit for relays 52-3 and 18 at the heel:

contact of relay l. Art the same time, however, the operation of relay 4 closes a circuit from lead 27 through the front contact of relay l to groui'id relay This fornishes an additional ground path for relays and 23, Whicl path, however, is under control oi relay 12. For relay 23 the circuit is traced from battery through. the Winding oi relay 23, over lead 24:, lead r 9, lead 26, lower baclr contact of relay 12, lead 27, front contact 5 oi relay to ground at Z circuit for relay l8 t aced from hatter though relay 38, to point 2-31, and thence the same as for 23. Consequently, it at the moment i 4i operates relay 12 is released, then re- 8 and 23 Will remain operated over fill ti )5 circr't. However, it relay 12 is opera; when relay t operates, then all pos- ..|e interrupter iroin relay 1, causing it also to release. it Will he observed from the above that relay 18 Was operate l for a period of one second, for it operated and released nnder the control of relay 2 which, it Will be seen by referring to the chart of d, was operated for one second. Hence, in this case, ringing current is trans i itted over the toreign exchange line from otiices K to H for a one-second interval.

Referring now to Fig. 2, this one-second interval of ringing current, upon arriving oi'lice H, causes the operatoin of relay Relay 62 is not affected owing to the tact that the right windings of repeating coil 66 are short-circuited under the control of relay (30. The operation of relay 56 furnishes ground through its front contact to operate oi. The operation of relay 57 removes the green d connection for relay at the right inner back contact of relay 5? so that there no possibility of relay 55 being operated to send ringing current hack to oilice K at this time. The operation of relay 57 closesa cir cult to operate relay 59 from battery, throngs the left winding of relay 59, right inner front contact of relay 5? to ground at relay 58. Relay 59 looks to ground under the control of relays (i3 and 58 over a circuit from but tery, through the left Winding; and left inner tront contact of relay 5?), right outer back contact of relay 63, to ground at the right aclt contact of rel y 58. The operation of relay 59 con'iects resistance 61 between the tip and ring leads of the foreign exchange circuit; This circnit is traced from the tip side of the line through the upper back contact of relay (10, through resistance 61, left outer back contact of relay (33, right outer front contact or"? relay 59, through the lower back contact of relay 60 to the ring side of the circuit The connection of resistance 61 between the tip and ring; leads causes ringing current to be disconnected from trunk 117. This is accomplished as follows: As Was explained above, ringing current is being supplied to operate relay 62 oi? circnit 68 through marginal relay IlO l of the inter-otlice trunlt 11?. Vidien, however, resistance 61. is connected in shunt with relay 62 condenser 69, the low resistance path thus introduced, allows an increased current to flow through marginal relay 10 i. its operation. The operation oi relay lO-i opens the shorhcircniting path connected across the winding of relay 103 rol 102 to ground over the sleeve circuit of jack 67, Relay 103 locks up over a circuit from battery through the front contact and winding of relay 103, to ground, as just described.

The battery thus connected to the front contact of relay 103 opposes the further flow of current through relay 102, causing this relay to release. The'release of relay 102 disconn'ects ringing current from the tip and ring leads of the trunk and thus causes the release of relay 10a. The supervisory lamp 100 remains extinguished, being shunted out by the circuit from battery through relay 103, which is connected in parallel with the circuit from battery through lamp 100, these two circuits obtaining a common ground in the sleeve circuit of jack 67 I The release of relay 102 closes the tip and ring leads of trunk 117 through to the repeating coil 107.v This closes a direct current path to operate relay 106, the circuit consisting of battery 119, relay 106 and resistance 61 of Fig. 2. Relay 106 thereupon operates the short-circuits the high resistance winding of relay 105. This increases the current flow through the A cord supervisory relay 110 sufliciently to cause its operation. The operation of relay 110 in turn connects resistance 113 in shunt with the A cord supervisory lamp 111, thus extinguishing the lamp, to inform the A operator that the foreign exchange subscriber has answered the call.

Meantime,while the above is occurring, the

- operation of relay 57, Fig. 2, also connects 'the interrupter lead 74 to relay 50, cansing this relay to be periodically operated and released for half-second intervals in the same manner as was described for relay 1 of Fig. 1. The horizontal dashed lines in the chart of Fig. 5 show the operated intervals of reapparatus located at oflice H. In the present case, as described above, relay 56 is operated for one second. 7

During the first timing interval, as seen :from Fig. 5, relay 50'operates and causes the operation of relay 52 over the circuit from battery, through the left winding of relay 51, winding of relay 52, back contact of re- 7 lay 51, front contact of relay 50, to ground at theleft front contactof relay 57 which is operated while 56 is held up. Relay 52 thereupon operates, relay 51 being marginal does notoperate at this time. The operation of relay 52 in turn causes the operation of relay 54 on a circuit from battery,

' through the left winding of relay 53, winding of relay 54, left back contact of relay 53, right outer front contact of relay 52, to ground at relay 57. Beginning the second timing interval, relay 50 releases and opens the holding circuit for relay 52, which relay, however, remains operated on a circuit from battery through the left winding of relay 51, winding of relay 52, right Winding of relay 51, right inner front contact of relay 52, to ground at relay 5?. Relay 51 now operates. During the third timing interval, relay 50 operates again, and since relay 51 is now operated, relay 52 is shunted out owing to the fact that a circuit is traced from battery, through the left winding and front contact of relay 51, front contact of relay 50 to ground at relay 57. Relay 51 remains operated by this circuit. The release of relay 52 opens the holding circuit for relay 5 1 but this relay remains operated on a circuit from battery through the left winding of relay 53, winding of relay 51, right winding of relay 53, front contact of relay 5a, to ground at relay 5?. Relay 53 thereupon operates. When relay 50 releases during the fourth interval it opens the holding circuit of relay 51, causing it to release, no other change occurring during this interval.

Thus, for an interval of two seconds, the timing relays merely measure the elapsed time without altering in any way the signaling apparatus of circuit 68 at oilicc H. In the meantime, it should be recalled that relay 56 has been operated for approximately a one-second interval only since it was receiving a signaling current corresponding to a receiver-oif-the-hook signal from office K. Hence, some time before relays 51 to 51 inclusive have completed the cycle described above, relay 56 will release, in turn releasing relay 51. The release of relay 57 disconnects the interrupter from relay 50 at the left outer front contact of relay 57 and also removes the ground connection holding the timing relays operated at the left inner front contact of relay 57. Relay 50 and all operated timing relays are thereupon restored to normal.

Meantime, relay 59 remains locked to ground through its left inner front contact to ground at relay 58. The release of relay 5? causes the operation of relay 63 over a circuit from battery through the winding and right.- inner back contact of relay 63, right winding and. left outer front contact of relay '59, right outer back contact of relay 57. front contact of relay 64. to ground at relay 58. As soon as relay 63 operates it locks up through its right inner front contact to ground through the front contact of relay 6% and the back contact of rela 58. The operation of relay 63 releases relay 59 by opening the circuit through the left winding of relay 59 at the right outer back contact of re- Jon filo

li lil rirelay ELK lay 63. The circuit through the right Winding of relay 59 is opcued the right inner hack contact of relay ll ith the operation of rela i1.[l the sulxserpici'it release oil i 1 539 1 stance 61 remains connected across the tip and 111% loads; of circuit l'lil,

clue to the fact that the release of relay 5' and the o 2, of relay 63 transfers lo: ds

l2 and from the cir 1' 1 to the short-cicuithiglead 70. Consequently, relay 106 of F1 remains operated and in turn causes relay 110 in the A cord circuit to remain operated so that the A cord lamp 111 remains ertingruished.

The ophration of relay the circuit to operate relay 69 i i in battery through the winding of relay 60, left iauer front contact oi relay ()3 right outer haclr contact o'l'- relay 57, front contact of relay o l to ground at relay 58. The operation of relay 60 removes the short-circa? leads from around the rig, dings oi repeating coil The circuit now rcaoy -tor conversation between subscribers.

Assume that the call. progresses in the mal manner to completion. Vl hcn the loreiggn exchange subscriber hai :3 up, a receii er-on-the-hoolr signal will he trcuiuuittecl from ollice l: to o'llice l. 1 consist in three-second in .rval oi current which will cause the paratus at illico H to function in such a mauuer as to furnish a oiscounect signal to the A opert tor. l

This accomplished as follows: When tho rcceiy oil the euhscri iers set 6 1 it will open the aoldiug curt on the hoo r for relay 1; release. 10 reloa leases rela 1 arid 12, which were held operatech through the troutcou act of relay 1% to urouud at the malre contact of relay ll, The circuit for relay 1 1 opened by t e l relay 12, but 14-. being slow re remains operated for a short period after l'QlQllmQ relay 12. During; this short interilav 15 operates from battery through its left I o; and the trout contact of relay ll hack contact 01 relay 12 to ground relay llelay 15 immediately locks up through ri winding; and right inner trout contact to ground at the right hack contact of relay 255 The operation of relay 15 connects the interrupter to relay 1 in the manner clescrihcu previously, cursing re ay 1 to start lunatic: r accordance with the chart of The timing relays 2 to 5, incl sive :r with relays and 18 will 111 be operated in the same manner as was previously (lscrihed 111 connection with the rcrciyermfl-the-hcolr signal. ill will he re r 1, car 1;,1 that relay Se of relay 13 in turn. rc-

rourth interval relay 12 was operated so that there are I10 paths closed through which relays 23 and 18 l uld obtain a ground connection. In the present case, however, relay 12 was released upon the subscriber hanging up so that this time, when the fourth timing interval is reach. and relay 2 releases, relays and 18 circuit doright hack contact For relay 23 this circuit was om liJattery through the winding of r 2 1 lead 29 lead 26, lower hack it relay 12, lead 27 right front conelay 1-, which is operated (see chart, to grouuo. at the right front contact 23. llclay 18 remains operated from through the winding of relay 18 to load 26, the emainder ol the circuit being; the same as described above for relay 23. From point on the operation of the timing relays mus he traced to show how the apparai lcd at the end 071 three seconds. the fifth timin interval relay 1 perates, causing relay 3 to operate, as do- :crihcc above, from battery through the left winding oi? 2 winding of relay 3, left haclr contact of relay 2, front contact of relay 1, to wound at relay 23.

l 1 interval relay 1 releases n no: circuit for relay 3. l te 1.1;! 3 howeye romaine operated on the circuit 'tr iu lJil Uu 1 through the left winding or": relay 2, wind 3 of? relay 3., right winding o't relay 2, inner front contact of relay 3 to around at relay 2 Relay 2 thereupon operates ano 111 turn causes relay 5 to reso by shunting; it out, the holding circuit 1- y 4: lacing traced from battery through it winding, rod right inner front contact oil relay l, right outer front contact of relay 2 to ,grroiuid at relay lluriu the seventh tiii'iing; interval relay 1 operates and shu out relay 23, causing}; it to rel arse, the holoin circuit for relay 2 being from battery through the left Winding};

will remain operated oyer tuc scribe l chore through the traccc and left tliro 1t contact o'l relay 2 to ground at relay 23.

During the eighth timing interval relay 1 releases, which opens the holding circuit for relay 2 oausin it to release. .ilhe release of relay 2 opens the holding circuit for relay 4 the right outer trout contact of relay 2, and thus relay l releases *0 hi ch opens the holding circuit for r lays 18 and 2 All timing relays thcrotore released during this i torvch and since all possible paths to ground for 18 and 2?; are opened thou relays now rela a s i 1121* relay 1S Thus it will be seen t a has been operated for an rcrval oi three secofo .s that is, rcterring' the chart TllOllJ the l) grinning of the second liming interval until the he inning of the eighth timing in- -ml. ll h relay 18 is operated it again sends ringi r current from oillce K to ollice H.

Refe ringnow to Fig. 2, it will be recalled from the explanation given above that the receiver-oif-the-hool: signal left relay 63 locked up to ground at the back contact of relay 58. Also, relay 60 was held up through the left inner front contact of relay 63 and the right outer back contact of relay 57 to ground at relay 58. In the inter-office trunk 117,'rel'ays 101, 103, 105, and 106 are still operated, and in the FA cord circuit relay 110 remains operated. The three-second interval of ringing current, upon arriving at office H, operates may 56, which in turn operates relay 57. The operation of relay 57 releases relay 60 and reoperates relay through the right-front contact of 57 to ground at relay 58. The operation of relay 59 opens the lead containing resistance 61 by disconnecting lead 72 from lead 70. The

direct current path between tip and ring leads of circuit 68 is opened by this latter operation, causing the release of relay 106 in trunk 117. The release of relay 106 removes the shunt from the high resistance winding of relay 105, thus causing the release of relay 110 in the A cord circuit to relight theA" cord supervisory lamp 111, and furnish the A operator with a signal that the call is complete.

In addition to the above, the operation of relay 57 connects a ground lead for operating the timing relays and also connects the interrupter to relay 50. The timing relays 51 to 54 will again start to measure olf time in the 'manner described above inconnection with the receiver-oifthe-hook signal. At that time, the operation of these relays was traced over the first four timing intervals, and it was found that during this period they did not affect the operation of the apparatus at oflice in any manner. At the end of the fourth interval relays 53 and 54 were found to be operated. For the receiver-oif-the-hook signal, however, relay 57 was released before the fourth timing interval was reached and all timing relays were restored to normal. In the present case, at the end of the fourth timing interval relay 57 remains operated owing to the fact that relay 56 is operated for three seconds instead of one as formerly. Consequently, relays 53 and 54 are still held up, obtaining ground at the left inner front contact of relay 57 During the fifth timing interval, the chart of Fig. 5 shows that relay 50 is operated, causing the operation of relay 52 again from battery through the left winding of relay 51, Winding of relay 52, back contact of relay 51, front contact of relay 50, to ground at relay 57. The operation of relay 52 shunts out relay 54 which releases, the holding circuit for relay 53 being now traced from battery through the left winding and left front Contact of relay 53, outer front contact of relay 52, to ground at re lay 57. The release of relay 54, together with throu h its left inner front contact.

to operate and lock up followed by the fact that relay 53 remains operated, causes the operation of relay 58 on a circuit frombatterythroughthewinding of relay 58, right front contact of relay 53, back contact of relay 54, to ground at relay Relay 58 immediately locks to ground at relay 57 The operation of relay 58 removes ground from relays 59 and (33, causing both relays to rclease. Hence, the lead containing resistance 61 remains open and no change occurs in the cord circuit 118.

Returning again to the timing re-ays, when relay 58 operates it disconnects the iutcrrupter from relay 50 at the left outer hack contact of relay 58, thus causing relay 50 to release. The release of relay 50 causes the operation of relay 51 from battery through the left winding of relay 51, winding of relay 52, right winding of relay 51, front contact of relay 52, to ground at relay 57 Thus, relays 51, 52 and 53 are now operated, and these relays remain operated until the conclusion of the three second-ringing interval when relay 50 is released. hen this occurs relay releases, removing the ground connection, which releases all operated timing rclays.

lrieantinie, the A operator has noted he steady light on lamp 111, due to the release of relay 110. therefore disconnects plug 109 from jack 108, which in turn causes the release of relay at ofiicc lit. The release of relay 105 opens the holding circuit for rclay 103 at the contact of relay 105. {clay 103 thereupon releases and in so doing rcmovcs the shunt from arouiul lamp l00. Lamp 100 thereupon relights and gives the B operator a signal to disconnect. The B operator thereupon disconnects plug 110 from jack 67, thus opening the circuit for lamp 100, which is extinguished, and removing the battery from relay 04, Fig. 2, which releases. All apparatus involved in the connection is thus returned to its normal condition.

Call from foreign emclzrmgc subscriber When the call originates wiih the foreign exchange subscriber, the apparatus functions as follows:

hen the receiver is removed from the switchhook of subscribcrs set (3, relay 13 at the office K operates. The operation of 13 causes the operation of relays 11 and 12 through the front contact of relay 3 to ground at relay 4. The operation of rcluy l1 removes the relay 9 from the ringing circuit and also opens the operating circuit for relay 8. The operation of relay 12 starts the functioning of the timing relays in the manner described above, first by causing relay 15 the operation of relay 14. The operation of relay 15 connects the interrupter to relay 1, which in tionof relay 6 3, in turn, release.

turn causes timingrelays 2 to 5, inclusive, to function in accordance with the chart of Fig. 1. Since this is the receivcr-off-the-hook condition, relay 18 will be operated for one second to send ringing current from office K to otlice H, as was described above in connection with a call to the foreign exchange subscriber.

The one-second interval of ringing current upon arriving at olliee H operates relay 56 which, in turn, causes the operation of relay 57. The operation of relay 5?, in turn, causes relay 59 to operate through the right, inner, front contact of relay ground at relay 58. Relay 59 immediately locks up through its left, inner front contact and through the right, outer, back contact of relay 63 to ground at relay 58. The operation of relay 59 causes the line lamp to light from but tery through lamp 65, right, inner front con tact of 59, back contact of relay 64; to ground at relay 58. Theoperation of relay 57 also connects the interrupter to relay 50 and connects ground to the timing relay circuits to start the functioningof the timing relays, as was described previously. The operation of relay 59 in addition to lighting; the line lamp 65 also connects the resistance 61 across the tip and ring leads of circuit 66 by connecting; lead "Etc lead I 1. The A operator upon noting the lighted line lamp 65 will connect an A cord circuit, similar to 118, Fig. 3, to ,'rcuit 68 by inserting plug; 10:) into inch 67. As soon as the cord circuit is connected to circuit 68, the A cord supervisory relay 110 will operate over the direct current path through resistance 61, and will. thus prevent the supervisory lamp 111 from lighting. The battery obtained on the sleeve of circuit 68 due to connection offA cord circuit will cause the operation of relay 64. ,.he operation of this relay opens the circuit to extinguish lamp 65. The operation of relay 64: also closes a circuit to operate relay 63 upon the release of relay 5?, through the right windingrand left, outer, front contact of relay 59, right, outer, back contactof relay 5?, front contact of relay or to, relay )und at 58. As soon relay 63 operatemit locks up through its right, front contact. 7 The operarelay 59 by opening the circuits through both windings of this relay at the right, inner and'outcr back contacts of relay 63. The simultaneous release of relay 59 and operation of relay 63,

maintains resistance 61 connected across the tip and ringleads ofcircuit 68 by connecting leads Z3 and 72 to lead 70. The operation of relays 63 furthermore closes the circuit to operate relay 60. The operation of relay 6O removes the short-circuiting' leads from around the right windings of repeating; coil 66, thus preparing; the circuit for talking. When the A operator has obta ned the called number, she proceeds to establish the connection in the usual manner.

lVhen the call is complete and the sub scribers hang up, the apparatus functions in the same manner as was explained above in connection with a call to theforeign exchange subscriber,

Flashing by the foreign exchange subscriber If the foreign exchange subscriber desires the immediate attention of an operator, he will operate his switch-hook intermittently in the usual manner. Assuming that the subscriber has had the receiverolf the hook for few seconds before he commences to flash. relays 11 to 14, inclusive, Fig. 1 will be operated. All other relays will be in the normal condition. When the flashing is started upon first placingthe receiver upon the hook of subset 6, relay 13 releases, causin relay 12 to release. As soon as relay 12 releases and before relay 14c releases, relay 15 will operate through the left, front contact of relay 14 and the left, back contact of relay 12 to ground at relay 4. Relay 15 immediately locks to ground at relay 23 and starts the functioning of the timing relays. Once the timing relays are started in this fashion, at least a one-second interval of ringing current will be transmitted from otlice K to office H. Thisis due to the fact that the only control that the foreign exchange subscriber has over the operation of the timing relays is through the medium of relay 12, and once 12 has function. to start the operation of the timing relays, in the manner described immediately above, these relays will function for the first three timing intervals of the chart of Fig. 4. irrespective of whether relay 12 is operated or not during this period for the reason that, soon as relay 15 operates, it locks to ground at relay 23 and thus the functioning of the timing; relays for the first three timing intervals is independent of relay 12-. Beginning with the fourth timing interval, however, all circuits to ground for relays 23 and 18 are opened except the path through the back contact of relay 12. This condition was ex plaincd above in connection with a call to the foreign exchange subscriber. In the present-case, when the fourth timing interval is reached, assume that the subscriber happens to have the receiver on the hook durthis-interval, relay 12 will be released and relays 23 and 18 will be held up for another three timing intervals; thus, until the end of the seventh interval. At the beginning of the sip, th timing interval, all timing relays are released with the result that there is no possible path to ground to hold relays 23 an d 18 operated, irrespective of the condition of relay Consequently, relays 18 and 23 must release at this time. If, therefore, at]

any time,subsequent to the beginning ofthe eighth interval, the subscr ber removes the receiver from the hook, the operation of the timing relay will start all over again to send a new pulse ofringing current from oiiice K to office H. In the case just described, the ringing pulse transmitted was of three-secondduration. Going back for a moment,

suppose that, at the be inning of the fourth 'intervall A subsequent replacement of the receiver on the switchhook would cause the timing relays to start functioning again since, as soon as relay 12 released, relay 15 would'operate' again through the left, front contact ofrela'y 14 and the back contact of relay 12. The durationof a ringing interval will therefore be of one or three seconds durationdep'endent uponthe operation or nonoperation'of relay 12 at the next succeeding fourth'timing interval. From the above discussion, it will be seen that when the foreign exchange subscriber flashes, ringing pulses of one second or three seconds duration will be transmitted from ofiice' K to oflice H. Whether a'given pulse will be of one second or three seconds, duration will depend not upon the rapidity with which the subscriber flashes but'merely upon whether or not the subscriber has the receiver on or off the hook duringthe fourth timing interval after timing relays start to function. This, of course,

' will be a nie'rematter of chance so that, on the average, if the subscriber flashes continuously fora period, arandom mixture of one-second and'thr'ee-second interval pulses following each other will be transmitted from office K to office H. Y

Assume, now, that train of impulses con- 7 sisting of such a random mixture of one-secend and three-second ringing intervals caused by the flashing of the foreign exchange subscriber arrive at oflice H. If an A cord circuit, similar to 118, is connected to circuit '68; this train of ringing pulses will cause the A supervisor Y lam 3' 111 to flash intermittently. This is accomplished as follows: i

-Relays 56 and 57 operate in synchronism with the incoming ringing pulses.- As soon as relay 57 operates. it causes relay 59 to operate toground at the back-contact of relay 58. With an Acord connected to circuit 68, it will bezremembered that relay 63 is operated so 'thatfwhen relay 59' operates, it opens'the lead containing resistance 61 con nected between the tip and ring leads of circuit 68; This occurs, due to the disconnection oflead 72ffrom lead 70. The disconnection of resistance 61 causes the release of cord circu t'supervisory relay 110 and re-- lights supervisory lamp 111. The'operation V ofrelay 57;,startstiming relays to 54, in

elusive, functioning. If the particular ringing pulse in question is of one-second duration, relay 57 releases before the timing relays affect the circuit in any manner, since the only effect of the timing relays is to operate relay 58 and this does not occur until relay 53 operates and relay 54 is released, which in turn does not occur until the beginning of the fifth timing interval. Therefore, as soon as relay 57 releases, it causes the release of all timing relays, as described above, disconnects the interrupter and also releases relay 59, since the locking circuit of relay 59 through the right, outer, back contact of relay 63 is open due to the operation of this latter relay. The release of relay 59, again connects resistance 61 across the tip and ring leads of circuit 68, causing t-he reoperation of the A cord supervisory relay 110 which extingnishes lamp 111.

Assume that the next ringing pulse is of three-second duration, relays 56 and 57 will again operate, causing the relay 59 to operate and disconnect resistance 61 from across the tip and ring leads of circuit 68 which again causes lamp 111 to relight. At the same time, the operation of relay 57 starts the functioning of the timing relays. In this case, at the beginning of the fifth timing interval, relay 57 will still be operated so that according to the chart of Fig. 5, when relay 54- releases during this interval, relay 53 will be operated. This will cause relay 58 to operate and disconnect the interrupter from relay 50. The opening of the ground lead at the right contact of relay 58 releases relays 59 and 63, which leaves the lead containing resistance 61 open so that lamp 111 remains lighted. Timing relays 51. 52 and 53 remain operated until relay 57 releases at the end of the three-second ringing interval, at which time the disconnection of the ground lead at the left inner contact of relay 57 releases all timing relays and restores that to normal, at the same time releasing relay 58. When the next succeeding ringing pulse arrives, relay 57 upon operating will cause relay 59 to operate and. since, in this case, relay 63 is released, the operation of relay 59 will connect resistance 61 between the tip and ring leads of circuit 68 which will extinguish the A cord supervisory lamp 111. If this ringing pulse is of one-second duration, relay 63 will operate upon the release of relay 57 at the same time releasing relay 59, leaving resistance- 61 connected across the tip and ring leads so that it will require the next succeeding pulse of ringing current to relight the supervisory lamp 111 when relay 59 operates again upon the operation of'relay 57. On the other hand, if the pulse in question were three sec- 7 onds long, relay 58 would operate and re It will thus be seen that regardless of the rapiditywith which the subscriber operates the switchhook of subset 6, a random series of ringing pulses of one-second and three} seconds duration will be transmitted from oitice K to otlice H. These ringing pulses upon arriving at office H will cause the signaling apparatus there to function in such a man. er as to cause an intermittent flashing of the A cord supervisory lamp.

hat is claimed is:

l. in a telephone system in combination a foreign excl'iange subscribefls telephone circuit consisting of a subscril'iers telephone set, a telephone line connected thereto and extending per nanently througl'i a first central oilice and terminating in a second central oflice distant from the first, signaling means at the first oilice controlled by the position of the foreign exchange subscribers switchhook and adapted to transmit ringing current from the first to the second otiice for definite inter vals of time in accordance with changes in the position of the switchhook associated with the foreign exchange set, such ringing can rent being transmitted for one interval of time upon removal of the receiver from the switchhook and for a diiterent interval of time upon replacement oil the receiver upon the switchhook,signaling means at the secnd central. otl'ice associated with the foreign exchange line adapted to receive and interpi'et the ringing currents transmitted from the Mist oilice and thereby to suitably operate suoervisory means associated with the i 01 e1 exchange lineat the secondol'lice in accordance with the position of the switchhool: of the foreign exchange subscribefs set, such signaling means at the second oliice being tturthe adapted upon connection to; the foreirn exchange subscribers line, at thegsecond oilice of a telephone line extending to a distant subscriber to operate signaling means associated with such last mentioned telephone line in accordance with the position of the switchhook of the foreign exchange subscribers set, thus suitably controlling the progress of a call between the foreign ex change subscriber and the distant subscriber, means to apply in ging current to the foreign exchange at" cribers telephone set, under control of ringing current supplied from a telephone circuit connected to thesubscribers line at the second otiice, means to apply such ringi current whether the receiver ison or oil the hookif such ringing is manually op erated from the telephone circuit connected to the foreign exchange line, means to apply such ringing current only when the receiver is on the heel; it automatically operated.

ln a telephone system in combination a rexchange subscribeids telephone cirhnmsting of a subscribers telephoneset, iephone line connected thereto and er:-

ding permanently through a first central oiliee and terminating in a second central ott' lice distant from the first, signaling means at the first oflice controlled by the position of the foreign exchange sul'iscribers switchhook and adapted to transmit ringing current from the first to the second oilice for deli its intervals of time in accordance with changes in the position of the foreign exchan esubscribefis switchhook such ringing current being trimsmitted for a predetermined interval of time upon removal of the receiver from the switchhoolc and for a predetermined interval o'f time different from that first mentioned upon replacement of: the receiver upon the switchhook, signaling means at the second oilice associated with the foreign exchange subscribers line adapted to receive and interpret the pulses of ringing current thus transmitted, such signaling means being adapted upon reception of the signal corresponding to the receiver-olt-thehook to light a lamp associated with such subscrihens line at the second cities and to connect a resistance between the tip and ring leads of such line at that point thereby com pleting a direct current path between such leads which otherwise are provided with means to prevent the flow of direct current between such leads, such signaling means at the second ofiice being adapted to disconnect said resistance and extinguish the subscribers lamp upon reception of the ringing pulse corresponding to the replacement of the receiver upon the switchhook, means to extinguish the subscribers lamp lighted by removal of thereceiver from the switchhook upon connection to the subsc 'ibers line of a telephone trunk or a link circuit, means to apply ringing current to the foreign exchange subscribers set in accordance with ringing current supplied "from a telephone trunk or link circuit connected to the subscribers line at the second oilice.

8. In a telephone system in combination a foreign 'exchar re subscribers telephone circuit eonsistin oi a sulrscribcfs telephone set, a telephone line connei thereto and extending permanently throt' 7b a first central cities and terminating in a second central ofiice distant from the first, signaling means at the first office controlled by the position oil the foreign e chatge suhseribeids switchhook and adapted to transmit ringing current i 'om rst to the second oilice tor definite interim no in. accordance with changes in the position of the :liorcignero change su ribers swmhhool: such ringi current b ad I mined or upon receiver from ti determinedinterval of time different from that ii at mentioned upon replacement of the receiver upon the switchhoolg, signaling means at the second oiii'ce associated with the foreign exchange subscribers line adaptedto or a predetei removal oi the receive and interpret the pulses of ringing current thus transmitted such signaling means being adapted upon reception of the signal corresponding to the receivcr-oti-thehook to light a lamp associated with such subscribers line at the second office, means to exting i said lamp upon reception of the 'inging pulse corresponding to the replace- "lIlGlliiOf the receiver upon the switchhook,

additional means to extinguish said lamp lighted byremoval of the receiver from the switclihookupon connection to the foreign exchange subscribers circuit of a telephone trunk or link circuit, means to apply ringing current to the subscribers set in accordance .with ringing current supplied from a telephone trunk or link circuit connected to the subscribers line at the second ofiice such means being adapted to apply ringing current whether the receiver is on or ofi the .hook it manually. applied from the trunk or of an A cord circuit connected to the outgoing end of atelephone trunk circuit the ncoming end or which 15 connected to the subscribers line, said resistance being adapted further to extinguish the supervisory lamp of an A cord circuit when connected dirctly, to the subscribers line, means at the second oifice to-open the direct current resistance path. between the tip and ring leads of V the subscribers line upon reception of the .signal1ngpulse corresponding to the receiveron-the-hook signal, the disconnection of said resistance being adapted to relight the A cord supervisory lamp in either case mentioned above;

L Ina telephone system in combination a :foreign" exchange subscribers telephone circuit consisting of a subscribers telephone set, a telephone line connected thereto and extending permanently through a first centraloflice and terminating in a second central 'oflice distant from the first, a telephone trunk circuit "equipped for automatic ringing extending from a third central oflice to the second, an A operators cord circuit connected to the trunk circuit at the third oflice, means associated with the subscribers circuit f at the second oflice tonormally prevent the flow of direct current between the tip and ring leads of said circuit, means associated with the 'subscribers circuit at the second office to send ringing current from thesecond to'the first oiiice under control of ringing current supplied from the trunk circuit upon connection of the trunk circuit thereto, means at the first office to apply ringing current to the subscribers set in synchronisin with said ringing pulses received from the second oiiice, means at the first otiice under control oi? the foreign exchange subscribcrs switchhook to send ringing current from the first to the second office for predetermined inter ails of time in accordance with changes in the position of the subscribers switchhooh, one interval of current being transmitted when the receiver is removed from the switchhook and a different interval of current being transmitted when the receiver is replaced upon the switchhook, means at the second ofiice to receive and interpret the ringing pulses thus transmitted and upon reception of the ringing pulse corresponding to the receiver-oil'- the-hook to connect a resistance between the tip and ring leads of the subscribers circuit at the second ofiice such resistance serving to complete a direct current path between said tip and ring leads and causing the ope ation of means in the trunk to disconnect the automatic ringing from the trunk, and extinguish the supervisory lamp of the A cord connected to the trunk at the third o iicc said means associated with the subscribefis line at the second ofiice being further adapted upon reception of the ringing current corresponding to the replacement of the receiver upon the switchhook to open the direct cunrent path between the tip and ring leads oi" the subscribers circuit at the second ofiice and thus cause religliting of the A cord lamp at the third ofiice.

5. In a telephone system in combination a foreign exchange subscribers telephone circuit consisting of a subscribers telephone set, a telephone line connected thereto and extending permanently through a first central office and terminating in a second central ofiice distant from the first, an A. operatoifi; cord circuit at the second ofiicc, means associated with the subscribers circuit at the second oflice to normally prevent the flow of direct current between the tip and ring leads, means at the first oflice under control of the foreign exchange subscribefis switchhook to send ringing currenttfrom the first to the second office for predetermined intervals of time in accordance with changes in the condition of the subscribers switchhook a short pulse of current being transmitted upon removal of the receiver from the switchhooh a longer pulse being transmitted upon replacement of the receiver, means at the second oflice to receive and interpret the ringing pulses thus transmitted and thereby upon reception of the signal corresponding to the receiver-oit-the-hook to light a lamp associated with the subscribers line there and to connect a resistance between the tip and ring leads of such line thus establishing a direct current path between such leads for extinguishing the Al cord supervisory lamp upon connection oi the A cord circuit to the subscribers line, means to extinguish the subscribers lamp upon connection of the A cord to the subscribers line, said interpretive means at thesecond ofiice upon reception of the ringing pulse transmitted upon replacement of the receiver upon the switchhook operating to open the resistance path between the tip and ring leads oi? the subscribers line and thus cause the lighting of the A cord supervisory lamp, said means operating further to open the subscribers lamp circuit at a point distinct from that controlled by the A cord circuit to prevent the relighting of said lamp upon disconnection of the A cord circuit.

6. In a telephone system in con'ibination a foreign exchange subscribers telephone circuit consisting of a subscribers set, a telephoneline connected thereto and extending permanently through a first central oflice and terminating upon the switchboard of a second central oiiice distant from the first, a relay at the second oiii'ce controlled by ringing current supplied from atelephone trunk or link circuit connected to the subscribefis :line at the second o'iiice, said relay being operative to send ringing current over the sub- .scribers line from the second to the first ously and periodically open andclose a circuit for short equal intervals or time and a system of relaysiassociated with said 111terrupter, said signaling means beingoperative upon removal of the receiver from the switchhoolr to send ringing current from the first to the second cities for a short interval of time, and upon replacement oi the receiver upon the switchhook to similarly transmit ringing current from the first to the second oi'iice for a longer interval of time, and upon intermittent operation of the switchhoolr to transmit a series of pulses of ringing current between said oilices, signaling means at the second office consisting of an interrupteh similar to that first mentioned and a system of relays associated therewith said signaling means being adapted to receive and inter iret the pulses of ringing current transmitted from the first oflice, and upon reception of the ringing current transmitted upon removal of the receiver from the switchhook to light a lamp associated with the subscribers line at the second oflice and to connect a resistance between the tip and ring leads oi": said line at said oiiice thereby completing a direct current path between such leads, signaling means consisting of a relay in the sleeve circuit of thesubscribers line operative upon connection of atelephone circuit thereto having battery on the sleeve to extinguish said subscribers lamp, said interpretive signaling means at the secondoilice operative uponreception of the ringing current transmitted from the first oiiice upon replacing the reeeiver upon the switchhook, to open the dircct path between the tipand ring leads or" the subscribers line, and also to open the circuit containing the subscribers lamp at a point distinct from that controlled by the relay in the sleeve circuit to prevent the relightingof said lamp upon disconnection of the telephone circuit from the subscribefs line, said interpretive means at the second oilice being further adapted upon reception of the series of" ringing pulses transmitted from the first oificc upon intermittent operation of the SWltChllOGk, to alternately open and close the direct current. path across the tip and ring leads of the subscribefs line.

7. In a telephone system in combination, a telephope circuit extending from a iii'stito a second point, signaling means, under control of a relay associatedwithsaid telephone circuit at the first point and adapted, upon operation of said relay to transmitringing current from the first to thesecondpoiut over said telephone circuit for a definite interval of time, and upon thesubsequent release of said relay to similarly transmit,ringingcurrent from the firstlto the second point for a definite interval of time diiferent from that first mentioned, signaling meansassociatcd with said telephone circuit at the second point, said signalingmeans-being. adapted to receive and interpret the pulses of ringing current transmitted from the firstpoint and to produce a distinct and unique operation of the signaling means at said second point in ac cordance with the length of the ringing pulse received.

8. In a telephone system incombination, a telepl'ione circuit extend" from a first point through a second point and terminating at a third point, switching means at the first point for connecting adirect current bridge across said telephone circuit at said first point, means inserted in the telephone circuit at the second point for causing the flow of direct current over said circuit be tween the second and first pbints upon connection of said direct current bridge at "the first point, a relay inserted in said direct current path at the second point and operable by said direct current, signaling 11 cans con trolled by said relay and adapted upon operation of said relay to transmit ringing current over said telephone circuit from the secondto the third point for a predetern'iined short interval of time, and upon the subsequent release of said relay to similarly transmit ringing current for a predetermined short interval of time different from that first mentioned, signaling means associated I with said telephone circuit at the third point adapted to receive and interpret said pulses of ringing current and to produce a distinct and unique operation of said signaling means at thethird point for each different length of ringing pulse received.

, 9. In a telephone system in combination, a subscribers telephone set, a telephone circuit connected thereto and extending through a first central oifice and terminating at a second central oflice distant from the first, signaling means at the first oflice under control of the subscribers switchhook and adapted upon removal of the receiver from the switchhook to transmit ringing current from the first to the second ofiice over said telephone circuit for a predetermined short interval of time, and upon the subsequent replacement of the receiver upon the switchhook to similarly transmit ringing current for a predetermined short interval of time diflerent from that first mentioned, signaling means at the second office associated with said telephone circuit adapted to receive and interpret said ringing pulses received there and to cause a distinctan'd unique operation of said signaling means at the second ofiice for each distinct length of ringing current thus received.

' 10. In a telephone system in combination,

Y a sub'scribers telephone set, a telephone circuit connected thereto and extending through a first central oflice and terminatingin a second central oflice, means inserted in the telephone circuit at the first ofl'ice for causing "the-flow of direct current from the first office and over said telephone circuit through the subscribers set upon the removal of the receiver from the switchhook, a relay inserted in said direct current path and operable by determined short interval of time diiferent from that first mentioned, signaling means associated with said telephone circuit at the second ofliee adapted to receive and interpret said ringing currents and to cause a distinct and unique operation of said signaling means at the second ofli'ce for each distinct length of ringing current received.

-' 11. In a'telephone system in combination,

a subscribers telephone set, a telephone circuit connected thereto'and extending through a first central office and terminating'in a second' central oifice distant from the first, means insertedin said telephone circuit at the first 'oflice for causing the flow. of direct current over said c rcuit and through the subscribers setnpon removal of the receiver from the under control of said relay, consisting of an;

interrupter for periodically opening and *closing an electrical circuit and a system of relays, said signaling means being adapted upon removal of the receiver from the switch hook to transmit ringing current over said telephone circuit from the first to the second otfice for a predetermined short interval of time, and upon the subsequent replacement of the receiver upon the switchhook to similarly transmit ringing current to the second ofiice for a predetermined short interval oi time difi erent from that first mentioned, signaling means associated with the telephone circuit at the second office consisting of an interrupter for periodically opening and closing an electrical circuit and a system of relays, said signaling means being adapted to receive and interpret the pulses of ringing current received from the first office and to cause a distinct and unique operation of said signaling means at the second ofiice for each different length of ringing current received.

12. A method of signaling over a telephone circuit which consists in arranging signaling means under control of a relay such that operation of said relay by closing a circuit to cause the flow of current thci'ethrough will cause said signaling means to transmit ringing current over the telephone circuit fora predetermined interval of time, and upon the subsequent release of said relay by opening said circuit will cause said signaling means to transmit ringing current over said telephone circuit for a predetermined interval of time different from that first mentioned, associating signaling means with the far end of such telephone circuit such that each distinct length of ringing current received by said signaling means over said telephone circuit will cause a distinct and unique operation of said signaling means.

In testimony whereof, I have signed my name to this specification this 22nd day of March, 1928.

HENRY H. ABBOTT.

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