US2208765A

US2208765A - Telephone system

Info

Publication number: US2208765A
Application number: US243347A
Authority: US
Inventors: Ralph E King; Ohmer R Miller
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1938-12-01
Filing date: 1938-12-01
Publication date: 1940-07-23
Anticipated expiration: 1957-07-23
Also published as: BE476596A; NL72721C; GB640033A; NL70515C; FR951758A; CH276283A; GB640032A; USRE22440E; FR1031552A; CH286287A; USRE22441E

Description

July 23, 1940. R. E. KING ET AL TELEPHONE SYSTEM Filed Dec. 1, 1938 9 Sheets-Sheet 1 R. E. K/NG uwsA/rons wW/m ATTORNEY July 23, 1940. r R, 5 Km E A v 208,765

TELEPHONE SYSTEM Filed Dec. 1, 1938 9 Sheets-Sheet 2 P01. ARIZED .RE. mva 0. R. M/LLER' ATTORNEY July 23, 1940.

R. E. KING m- AL TELEPHONE SYSTEM Filed Dec. 1, 1958 9 Sheets-Sheet 5 SRO . RE. K/NG Zf 'QRM/LLER ATTORNFV July 23, 1940.

R. E. KING ET AL TELEPHONE SYSTEM Filed Dec. 9 Sheets-Sheet 4 .R. E. mva Zi 'O. R. M/LLER ATTORNEY July 23, 1940. R. E. KING ET AL TELEPHONESY'STEM Filed Dec. 1, 1938 9 Sheets-Sheet 5 INVENTORS:

R. 5. KING By OR. M/LLER July 23, 1940.

'R. E. KING ET AL TELEPHONE SYSTEM 9 Sheets-Sheet 6 NON Filed Dec 1, 1938 R. E. KING /N|/ENTOR$- OR MILLER E ATTORNEY R. E. KING ET AL TELEPHONE SYSTEM July 23, 1940.

Filed Dec.

1, 1938 9 Sheets-Sheet III I Kuu 3k R\ moi $1 WVENTORS- 5 KING 0- R. M/LLER By 7 ATTORNEY July 23, 1940.

R. KING ET AL TELEPHONE SYSTEM Filed Dec. 1, 1938 9 Sheets-Sheets Bk kabkh MH 1E%%LM% MWU . R. E. K/NG MENTOR OR M/LLER ATTORNEY July 23, 1940. R. E. mm: AL,

TELEPHONE SYSTEM Filed Dec. 1, 1938 9 Sheets-Shet 9 R E KING MENTOZ o R MILLER V WW M ATTORNEY Patented July 23, 1946 UNITED, STATES PATENT OFFICE TELEPHONE SYSTEM Ralph E. King, Short Hills, and Ohmer Miller, Morristown, N. J assignors to Bell Telephone Laboratories, Incorporated, New York,

N. Y., a corporation of New York 7 Application December 1, 1938, Serial No. 243,347

21 Claims.

to more efficiently and reliably effect the transmission of directive and supervisory signals to and through the automatic switching means employed in completing desired connections.

This invention is a telephone system comprising toll o-ffices in which automatic switches are provided for routing incoming calls to called toll and local oifices, the talking conductors of one or. more of the trunk. and selector circuits constituting a simplex circuit, the balanced or unbalanced condition of which is effective to control one ormore differential, signaling relays and the resistance of which is efiective to control one or. more marginal, signaling relays. According to. a feature of the invention, a difi'erential signaling relay having one winding connected in series with one conductor; of a simplex signaling circuit and the other winding connected inseries with. the other winding of the simplex circuit is operatively responsive to an unbalance in the simplex circuit. According to another feature, each of two polarized difierential signaling relays hasone winding in series with one conductor of a simplex circuit and another winding in series with the other conductor of the simplex circuit, one of said relays being operatively responsive to an unbalance which causes a stronger current in one side of the simplex circuit and the other of said relays being operatively responsive to an unbalance which causes a stronger current in the other side of the simplex circuit.

Another feature of the invention is a toll system in which the talking conductors of a toll route selector comprise a simplex circuit for transmitting directive impulses from an associated incoming line to the selector, for transmitting directive or supervisory signals to a succeeding selector or trunk used in completing a desired connection, for controlling the transmission efficiency of the associated incoming line, and for controlling the release of the selector.

A further feature of theinventio-n is an arrangement whereby the operators dial, which is automatically disconnected from an outgoing in tertoll trunkupon completion of dialing, may be reassociated with the trunk merely by reoperation of a common dial key without disconnecting the cord from and reconnecting the cord to the outgoing trunk circuit.

Another feature of the invention is a toll'system in which an incoming line may be connected with any one of a plurality of trunks through switching means comprising talking conductors'and a signaling conductor, circuits being closed through the signaling conductor for.

controlling the transmission pads associated with the incoming line while the connection between the incoming line and a desired trunk is. being established, and for transmitting supervisory signals from the connected'trunk line to the incoming line. According to this feature the winding of a marginal relay is connected in circuit with the winding of a normally operated relay and the signaling conductor, the normally operated relay being held operated" while the connection of the incoming line with a desired trunk isbeing established, the marginal relay being. actuated upon connection of the incoming line with v the trunkto shift the control of the transmission pads from the circuit throughthe signaling conductor to a circuit including the talking conductors in paralleL'the answering of the call by an operator or subscriber being effective to open the pad control circuit over the signaling conductor to cause the release of the normally oper atedrelay and thereby connect the signaling conductor to an answering supervisory relay associated with the incoming line,

The invention will be further explained by describing the telephone system illustrated in the drawings which form a part of this specification and in which system 'the invention is embodied. The invention is, of course, not limited in its application to the particular system shown in the drawings.

Referring to the drawings:

Fig. 1 shows anoperators cord Cl circuit POI;

Fig. 2 shows a dial circuit DCI associated with the position circuit PC! of Fig. 1; v

Fig. 3 shows outgoing jacks J I and J 2, answering jacks J 3 and J4, and an outgoing trunk circuit OT! associated with jack J l; v

Fig; 4' shows a two-way trunk circuit TWT'I and a composite signaling circuit CS! connected to one end of. a toll line TI and to the outgoing trunk'circuit CT! of Fig. 3;

Fig; 5 shows a toll route selector TSI associated with the two-way trunk circuit TWTI of Fig. 4, an auxiliary toll route selectorASl and an incoming trunk circuitITl associated with the answering jack J3 of Fig. 3; Fig. 5 also shows and position another two-way trunk circuit TWT l, an outgoing trunk circuit 0T4 and composite signaling circuit CS4, all associated with an intertoll trunk T4;

Fig. 6 shows the composite signaling circuit CS2 and two-way trunk circuit TWT2 connected to the other end of the toll line TI;

Fig. '7 shows a toll route selector T82 and an outgoing trunk circuit 0T2 both associated with the two-way trunk circuit TWT2 of Fig. 6; Fig. '7 also shows another toll route selector TS3;

Fig. 8 shows an operators cord C2 and position circuit PC2, outgoing jacks J 5 and J 6, answering jacks J1 and J 8, an auxiliary toll route selector A52, and an incoming trunk circuit 1T2 connected to jack J I; Fig. 8 also shows an intertoll trunk T3, a composite signaling circuit CS3 and a two-way trunk circuit TWT3 connecting trunk T3 to the selector TS3 of Fig.7 and an outgoing trunk circuit 0T3 connecting this trunk to jack J 5;

Fig. 9 shows a voice frequency signaling circuit S05 and an associated two-Way trunk circuit TWT5 connected to an intertoll trunk T5, the distant end of which is also arranged for voice frequency signaling; and

Fig. 10 shows the relation of each of Figs. 1 to 8, inclusive, to form an operative arrangement.

The system represented in the drawings includes' a plurality of toll offices, each of which comprises a toll board with operators positions and cords for answering calls incoming from local manual or dial offices, from toll subscribers lines, from community dial offices, or from other toll oflices and for extending an incoming call to a switching trunk leading to a called local manual or dial office, to a called toll subscribers line, to a community dial oflice, or to an intertoll trunk. Outgoing jacks such as J I, J2 in one ofiice, and J5 and J 6 in a second oflice, connect to switching trunks, toll lines, trunks to community dial ofiices, and intertoll trunks. Answering jacks such as J3, J4 in the one ofiice, and J l and J 8 in the second office, are directly connected to recording trunks, toll subscribers lines, trunks from community dial offices, and intertoll trunks. The terminals in the banks of incoming or auxiliary toll route selectors such as TSI, TS2, TS3, TS l, ASI and AS2 are also connected to the various lines and trunks other than the recording trunks.

The operators positions PCI and P02 are provided with dials and dialing circuits for controlling the operation of incoming and auxiliary toll route selectors in other toll ofiices and for controlling the operation of the usual toll train in local or community dial offices. The dial circuit DC! and trunk circuit OTl are arranged, as hereinafter described, so that the dial may be reconnected to the impulse receiving relay of the trunk circuit by the reoperation of the position dial key without having'first disconnected the cord from the trunk circuit.

The intertoll trunk TI is a two-way trunk between a first and a second office and is arranged for composite signaling. At one end, trunk TI is connected to the composite signaling circuit CSI, the two-way trunk. circuit TWTI, the outgoing trunk circuit OTl, and the incoming toll route selector TSI; at the other end, trunk TI is connected to the composite signaling circuit CS2, two-way trunk circuit TWT2, outgoing trunk circuit 0T2, and the incoming toll route selector TS2. The two-way trunk circuits TWTI and TWT2 also connect to terminals in the banks of auxiliary toll route selectors ASI and AS2 so that trunk Tl may be seized either by connecting a cord Cl or C2 to outgoing jack Jl or J5 or by the operation of an incoming and an auxiliary toll route selector.

The composite signaling circuits CSI, and CS2, the two-way trunk circuits TWTI and TWT2, the outgoing trunk circuit OTI, the incoming toll route selector T82 and the incoming trunk circuit 1T2 are shown in detail. The outgoing trunk circuit 0T2 which is shown only in part is similar to the outgoing trunk circuit OTI, the incoming toll route selector TSI is similar to the incoming toll route selector TSZ; and the incoming trunk circuit ITI is similar to the incoming trunk circuit 1T2. The auxiliary toll route selectors ASI and AS2 are similar to the toll route selector TSZ.

The intertoll trunk T4 is one of a group between the first ofiice and a third office which is not shown in the drawings; and the intertoll trunk T3 is one of a. group between the second office and a fourth office, not shown in the drawings. The associated composite signaling circuits CS3 and CS4, two-way trunk circuits TWT3 and TWT4, outgoing trunk circuits 0T3 and 0T4, and incoming toll route selectors TS3 and TS4 are similar to the corresponding circuits and selectors associated with intertoll trunks Tl.

The intertoll trunk T5, which is arranged for voice frequency signaling instead of composite signaling, is one of a group between thesecond office and a fifth ofiice which is not shown in the drawings. The associated two-way trunk circuit TWT5 is a modification of the two-way trunk circuit TWT2 of Fig. 6 to function with the voice frequency signaling circuit $05. The associated outgoing trunk circuit and incoming toll route selector are similar to the outgoing trunk circuit 0T2 and incoming toll route selector TS2; and an operative arrangement is formed by placing Fig. 9 adjacent and to the left of Fig. 7 with Fig. 8 adjacent and to the right of Fig. 7. The ref erence characters applied to the relays of trunk circuit TWT5 which correspond to relays of trunk circuit TWT2 of Fig. 6 have like tens and units digits.

The toll route selectors TSI, TS2, TS3 and T84 and auxiliary route selectors AS! and AS2 are of the well-known two-motion step-by-step type. For a description of the structure of such switches reference may be had to pages 57 to 63 of the second edition of Automatic Telephony by Smith and Campbell. The switches TSI, TS3, TS4, AS! and AS2 are each represented by 'a set of brushes and one or more sets of terminals but none of the magnets, relays or other apparatus associated with these switches is shown in the drawings. The bank of the toll route selector TS! is represented by a single set of terminals but this selector is otherwise complete with all magnets, relays and other associated apparatus.

Assume now that a call incoming to the toll board in the first office is answered by connecting the plug RP of cord CI to an answering jack such as J3 or J4. The talking key TK having been operated, and the position circuit being idle, relay in is operated by the energlzationof its left winding. Relay l0 closes a circuit for operating relay 20 of the position circuit and relay 20 closes the locking circuit through the right winding of relay ID. The operator's telephone is connected through the contacts of relay I to the calling line or trunk. To extend the connection, the plug FF is connected to an outgoing jack such as J I or J2; and, if the connected outgoing trunk is arranged for dialing, as is the case if completion of the call includes the selective operation of one or more toll route selectors or the selective operation of a toll train in a local or community dial ofiice, the dial key DK is operated to its Front position. Although the cord and position circuits CI and PCI are arranged so that the dial DI may be connected to either end of the cord, only the relays and connections necessary for dialing over the front plug FP are shown in the drawings. Assume further that on the call in question, plug FP is connected through jack J I to the outgoing trunk circuit OTI. A circuit is closed through the sleeve conductor of plug FP and contacts of key TK for operating relays 2I and 22 of the position circuit and sleeve relay 54 of the outgoing trunk circuit. Relay 2! closes a circuit for operating relay 23 and relay 22 closes a circuit lighting the cord supervisory lamp FL. With the dial key DK operated and relay 23 operated, relay 24 of the dial circuit DC! operates, disconnecting the tip and ring conductors of the plug FP from the operators telephone set and closing a circuit for operating relay 25., Relay 25 closes a circuit for lighting the dial pilot lamp DP and a circuit which includes back contacts of

relays

28, 35, 36, and 3i for operating relay 26. Relay 26 closes a circuit for operating relay 2I. Relay 2! closes a circuit for operating relay 28. Relay 28 looks under control of relays 25, 35, 36 and 3I and opens the operating circuit of relay 26.

In the outgoing trunk circuit OTI, the operation of relay 54 closes a circuit for operating relay 68. Relay 68 looks under control of relay 69 and closes a circuit for operating relay 59. Relay 58 closes a circuit lighting the busy lamps such as BLI associated with jack J l and other jacks connected in multiple with jack J I; closes circuits for operating relays 64 and 69; closes a circuit including the inner lower contact of relay I8 for operatively energizing the upper winding of relay I9; closes a circuit for operating relay I6; connects ground to the sleeve conductor 93 of the two-way trunk circuit TWTI; disconnects the winding of relay 56 from the sleeve conductor 93; connects the winding of the supervisory relay 55 to the front contact of the signaling relay 9!) of the composite signaling circuit CSI; and disconnects the front contact of signaling relay 99 from conductor 95 leading to the windings of relays Il'II)- and IDI of the two-way trunk circuit TWTI. The operation of relay 64 closes circuits for operating relays 60 and 6|, connects ground to .sleeve conductor 93 and connects ground through its middle lower front contact, back contacts of relays I9 and 66, and conductor 52 tothe ring conductors of jack J I and. plug FP. The ground connected to conductor 93 guards against seizureof trunk T by a toll route selector such as 'A'SI and operates relay H5. Relay H locks and disconnects the windings of relays I09 and Ill'I from conductor 95. The operation of relay 69 opens the locking circuit of relay 68, but relay 68' holds under control of relay 54. It is the function of slow-release relay 68 and slowtooperate relay 69 to prevent the release of relay I9; if operated, before the plug FF is fully seated in jack J I. Ihe operation of relay I6 maintains the operative energization of the upper winding of relay ltl independent of relay I8. The armatures' 'of signal relays '99 and I9Il'are normally held. in the position shown in the drawings by trunk Ti, upper windings of retard coils I86,

middle winding of relay H99, retard coil I89, back contact of relay H6, and back contacts of relays 2 l9 and 2I l to ground. The closure of this circuit operates relay 96 and constitutes seizure of The operation. of relay. 16 closes trunk TI to effect guarding of the trunk as busy as hereinafter described. Any Variation in the energization of the middle, operating windings of relays 99 and I99 due to difference in ground potential between the ofilces terminating trunk Tl is compensated by the energization of the lower, biasing windings of these relays in a ground to ground circuit through the lower conductor of trunk TI. The operation of relay 69 closes contacts for holding the busy lamps BLI lighted. Relay 6%! also closes a network comprising resisttors l2, l3 and M, ballast lamp H and the middle, biasing winding of relay 7!). The ballast lamp has a high temperature coeflicient of resistance and variations in its resistance due to variations in the voltage of signaling battery BI affects the energization of the middle winding of relay l'il so as to compensate for changes in the voltage of the signaling battery. The use of the ballast lamp, network of resistors, and biasing winding of relay it to compensate for changes in the voltage of the signaling battery BI is disclosed and claimed. in Patent No. 2,174,006 granted Sept. 26, 1939, to O. Rhlvliller. Relay 6! closes a circuit from battery through resistor 61 and the back contact of relay 66 for holding the normally operated pad control-relay 93. The normally closed circuit for operating relay 83 includes the lower back contact of relay 6E, resistor 62, and back contacts of relays Ill and it! of the two-way trunk circuit TWTI.

When the circuit of slow-to-release relay26 is opened by the operation of relay 28, as hereinbefore described, relay 26 remains operated for an interval long enough for relay E9 of trunk circuit OT I to have been operated, at which time a circuit is closed for holding relay 2l operated and for operating relays 29 and it. This circuit is traced from battery through the winding of relay 21, winding of, relay 29, upper front contact of relay 2?, upper back contact of relay 32, upper front contact of relay 2 t, inner left front contact of relay [8, contacts of ringing key RK, tip conductors of plug PP and jack J I,' conductor 5I, back contact of relay 66, winding of relay I8, to ground at a front contact of relay 69. The operation of relay 29 closes a circuit for operating relay 3|. Relay 3i closes a circuit for operating relay 32, and closes a circuit from battery through resistor 3 1, upper front contact of relay 3i, impulse contacts of the dial DI, winding of relay 35, back contact of relay 26, front contacts of relays 24 and I9, ring conductors of plug FF and jack J I, conductor 52, back contacts'of relays 66 and I9, and through resistor 65 to ground at a front contaotof relay 6d. Relay 32 opens the circuit through the windings of relays 2! and 29 and connects the tip conductor of plug FP through resistor 33 to battery to hold relay I3 operated.

Although relays 21 and 29 release, relay 3I is held The operation of relay I8 closes a circuit for operating relay I9 and opens the circuit through the winding of relay 16. Relay I9 locks under control of relay 69 and connects the operating winding of the impulse relay I0 in series with conductor 52 and the impulse contacts of the dial DI. Since the operation of relay'I8 disconnects the battery at its inner lower back contact from the operating winding of relay I0 and the release of relay I6 disconnects the battery at its front contact from this winding of relay "I0, relay I0 is now ready to respond to impulses created by the operation of dial DI. The lower biasing winding of relay I0 is connected in series with a battery of the same voltage as the dialing battery so as to'compensate for variations in the voltage of this battery.

The required toll route number is dialed and also the local office code and number of the called subscriber if the called subscribers line is in a dial office. The impulse relay I0 repeats the dial impulses over trunk TI to relay I of the composite signaling circuit CS2. Each time the dial is moved off-normal relay 31 operates to hold relays 32 and 3I operated, independent of the dial key. When dialing is completed, key DK is restored and relay 31 releases; relays 32, 3I, 24 and 25 release in succession and the plug FP is thereby reconnected to the operators telephone set. While the talking key TK is operated, supervisory signals are received over the sleeve conductor of plug FP by the marginal relay 22 and relay 22 controls the supervisory lamp FL. When the talking key TX is restored to normal relays I0, 20, 2|, 22 and, 23 are released and the lamp FL is controlled through the sleeve conductor of plug FP by the supervisory relay 55 of the trunk circuit OTI. The release: of relay 32 opens the circuit through resistor 33 and the tip conductor of plug FP to cause the release of relay I8 and thereby reconnect battery through the lower contact of relay I8, to hold relay I0, before the release of relay 3| opens the dialing circuit, relay 3| being slow in releasing. The release of relay I8 closes circuits including a front contact of relay I9 for operating relay 66 and reoperating relay I6. Relay 66 disconnects conductors 5| and 52 from the winding of relay I8 and contacts of relay I9, opens the circuit through resistor 61 and relay 83, and connects conductors 5| and 52 through the windings of retard coil 80, and front contacts of relay 6|, through windings of relays 63 and 11 in parallel, thence through the winding of pad control relay 83 to ground. The pad control relay 83 is thereupon held operated in series with resistors II and I2 of the position circuit PC I as long as the talk key of cord CI is operated. After the talk key is restored and relay I0 releases, the pad control relay 83 is controlled through the tip and ring conductors of the calling line or trunk with which plug RP is connected; if under this condition relay 83 releases, relay 84 operates to short-circuit the transmission pads PI and P2. Relay 66 also opens the normally connected voice frequency repeater termination comprising a resistor and condenser and a back contact of relay 56.

The aforementioned operation of relay I90 upon seizure of the outgoing trunk circuit OTI closes a circuit from ground through the front contact of relay I90, back contacts of relays I58 and I60 of outgoing trunk circuit 0T2, conductor I95, back contact of relay 2I5 of two-way trunk circuit TWT2, back contact of relay 202, to the winding of relay 200. Relay 200 operates, disconnecting relay' 2I5 from ccnductorI93, connecting ground to conductor I93 to guard trunk TI from seizure by a toll route selector such as AS2, and operating relay I56 of the outgoing trunk circuit 0T2. Relay I56 connects battery to the sleeve of the outgoing jacks J5 so as to make these jacks test busy and closes a circuit for operating relay I60. Relay I60 closes a circuit for lighting the busy lamps BL5. Although relay I60 opens the normally closed connection between front contact of relay I90 and conductor I95, relay I56 maintains a connection between the front contact of relay I90 and conductor I95 so as to hold relay 260 operated. Relay 200 also closes a circuit for operating relay 20I of two-way trunk circuit TWT2 and relay 225 of toll route selector T52. This circuit is traced from ground at the front contact of relay I 90, back contact of relay I58, front contact of relay I56, conductor I 95, back contact of relay 2I5, winding of relay 20I, back contact of relay 2I6, winding of marginal relay 206, front contact of relay 200, thence in simplex through both windings of differential relay 205, back contacts of relay I6I, windings of retard coil I80, conductors I8I and I82, front contacts of relay 200, conductors HI and 222, back con tacts of relay 229 of selector T52, and through resistors 23I and 232 to and through resistor 230 and a back contact of relay 229 to the winding of relay 225. Relay 206 does not operate because it is marginal and relay 205 does not operate because its windings are differentially energized. The operation of relay 20I causes the operation of slow-to-release relay 202. After relay 202 operates, relay 200 is held operated through resistor 204 to ground at front contacts of relays 20I and 202. the back contact of relay 2I6 to the sleeve conductor 223 of selector TS2 so as to control the release of this selector as hereinafter described.

Relay 2| 9 is normally operated in series with the upper winding of relay 201 and in series with resistor 203 in parallel with resistor 220 between selector TSZ. The connection of the winding of relay 2I9 and resistor 220 includes a front contact of-relay 2I9, conductor 224, contacts of the 11th rotary step springs, and a back contact of relay 229. Relay 20'! is marginal and is not normally operated. After relay 202 operates, relay 2I9'is held operated in series with resistor 220 until relay 229 operates as hereinafter described. The operation of' relay 225 closes a circuit for operating the slow-to-release relay 226. Relay 226 connects ground to the sleeve conductor 223 and also connects ground through its outer lower front contact to an alarm circuit so that an alarm will be actuated in case no impulses are received by relay 225 within a predetermined interval of time.

When the calling operator dials the first digit of the toll route number, the impulses are repeated by relay I0 of the outgoing trunk circuit OTI over the tip conductor of trunk TI to relay I90 of the composite signaling .set CS2. The release and reoperation of relay I90 in response to each impulse causes a corresponding release and reoperation of relays 20I and 225. Being sloW in releasing, relays 202 and 226 remain operated during the response of relays 20I and 225 to the dial impulses. The release of relay225 in response to the first impulse closes a circuit for operating the vertical stepping magnet 233 and the slowto-release relay 221. Each operation of magnet 233 raises the brushes one' step. The vertical off-normal springs VON are actuated as soon as Relay 202 connects ground from the shaft of the switch moves out of normal position closing a circuit, which includes the front contact of relay 221, for operating relay 228. When relay 225 remains operated after receiving the last impulse of the. series created by the dialing of the first digit of the toll route number, relay 221 releases, opening the operating circuit for relay 228 and closing a circuit for operating the rotary-stepping magnet 234, Relay 228 is held operated through its upper front contact until magnet 234 operates. The operation of magnet 234 steps the brushes into engagement with the first set of terminals in the level selected in response to the dial impulses. The .release of relay 228 causes the release of magnet 234. If this set of terminals is busy, the test brush 231 encounters a ground potential which is effective to cause the reoperation of relay 228, the winding of relay 228 being connected through contacts of the VON springs, the back contact of magnet 234, and a back contact of relay .229 to brush 231. The reoperation of relay 228 causes the reoperation of magnet 234 to step the brushes to the next set of terminals. The operation'of magnet 234 again causes the release of relay 228 and the releaseof relay 228 causes the release of magnet 234. cycle of operations is repeated to, advance the brushes step-by-stepuntil test brush 231. encounters a terminal which is not marked by ground potential connected thereto.

Whereuponrelay 229 is operated by the current in a circuit from battery through the winding of relay v228, cont acts of. the VON springs, back contact of :magnet 234, winding of relay 229, normally closed contact of the 1th rotary step springs,-

to ground on sleeve conductor 223. Being marginal, relay 228 does not operate in series with relay 229. Relay 229 disconnects relay 225 from the conductors 22I and.222 and connects these conductors.throughbrushes 235 and 236 to the line relay, which is not shown in the drawing of the auxiliary toll route selector A82. The ground potential connected through the back contact of relay 2-I3 and upper front contact of relay 202 to sleeve conductor 223 is extended through a front contactof relay 229 to the test brush 231 to mark the selectedauxiliary tollroute selector as busy and thereby prevent its seizure by any other toll route selector having access thereto. Relay 225 releases causing the release of relay 226; and relay 226 disconnects-ground from the alarm circuit. The operation of relay 229 disconnects resistor 228 from conductor 224 and connects conductor 224 through brush 238 to selector circuit AS2 in which there is a connection. through a resistor similar to resistor220 to hold relay 2I9 operated. l

It is assumed that the desired toll route numher is a-two-digit number in which case there are no intermediate selectors between selector TS2 and selector AS2. If a large number of toll routes is required therewill be one or more additional selectors in the train required for selecting a desired toll route; and if one selector is sufficient the-selector TS2 will have direct access to the groups of trunks, which in the system shown, are connected to the'banks of the auxiliary selectors AS2. Upon the dialing of the second digit of the toll route number, the auxiliary toll route selectorAS2 is directively operated to select a desired group of trunks and automatically operated to seize an idle trunk in the selected group. The

selector A82 may have access to. trunks to local incoming trunk circuits such as 1T2 terminating at the positions of a toll board,'and to groups of intertoll dialing trunks, oneof such, groups being represented by trunk TI and another by trunk T3.

Assume that the dialed toll route'number effects the operation of selectors TS2'and AS2 to select the incoming trunk circuit 1T2 terminating in a jack J1 at an operators position comprising a cordCZ and position circuitPC2. Relay 25H of two-way trunk circuit TWT2 isheld operated and relay 25! of the incoming trunk circuit IT2 is operated by the current in a circuit from ground through the front contact of relay I98, back contact of relay I58, front contact of relay I56, conductor I95, back contact of relay 2I5, winding of relay -l, back contact of relay 2H3, winding of relay 286, front contact 'of relay 289, thence in simplex through both windings of relay 285, back contacts of relayltl, both windings of retard coil I89, conductors I BI and I82, front contacts of relay 288, conductors HI and 222, front contacts of relay 229, brushes 235 and 236, through the selector ASZ, conductors 2M and 242, both windings of retard coil 235, and through

resistors

246, 248 and 249 to the winding of relay l. The

resistors

236, 248 and 2 l9-are so chosen that the current through one side. of thesimplex is enough stronger than the current through'the other. side of the simplex to cause theoperation or differential relay'285; but re1ay285 is almost immediately released because the simplex is' balanced as soon as the normally operated relay 21I releases due to the operation of relay 256 as hereinafter described. The current. in the simplex circuit is not strong enough. to operate marginal relay 28 6. Relay 25E closes a circuit for lighting answering lamp AL1, connects the source of ringing current 258 through condenser 215 to talking conductor 262, thereby transmitting rings ing tone to the calling operator to indicatethat an operator is being signaled. At the same time that the simplex circuit is closed for operating.re-

lay 25!, a circuit is closed for holding relay 2I'9;

operated, for operating marginal relay 281. ofthe two-Way trunk circuit TWTZ, and for operating relay 255 of the incoming trunk circuit 1T2; this circuit is traced from ground throughthe upper winding of relay 281; winding and front contact of relay 2I9, conductor 224, back contact .of the 11th rotary step springs of selector TS2,,f r,ont contact of relay 229, brush 238, through selector A82, conductor 244, back contact of'-relay 214 and the lower Winding of relay 255. '"Relay 291 looks through its lower winding and a front con tact of relay 2532. Relay 256. locks through its upper winding to the holding ground connected to conductor 243 from the back contact of relay 2I6 of the two-way trunk circuit TWT2. Normally relay 21I is heldoperated in a

circuit including resistors

266, 261, 258 and .269 and the winding of relay 210 and including the back contact of relay 256. Although relay 21.I is shown as a polarized relay, it may be a sensitive nonpolarized relay. When relay 256 operates, re-

lay 21I releases, thereby opening the short circuit around resistor 241 and closing a short circuit around resistor 248 so as to balance the sim-, plex circuit and cause the release of relay 285. With relay 205 released and relay 281 operated, relay J83 releases. and relay H82 operates shortcircuiting pads Pl and P2. v j

When a plug of a cord C2 is inserted in jack J1 to answer the incoming call, relay 212'is operated since there is battery connected tothe sleeve of the plug, the cord C2 and position circuit PC2 being similar to cord CI and position circuit PCI shown in Fig. 1. Relay 212 closes a circuit for operating relay 213. Relay 213 closes a circuit, which includes a front contact of relay 25I, for operating relay 214. Relay 213 also disconnects the repeater termination comprising condenser 216 and resistor 211 from conductors 26I and 262. This termination, normally connected across these conductors, prevents the voice-current repeater of a connected intertoll trunk from singing prior to answer of a call by an operator. Relay 214 locks to the ground connected to sleeve conductor 243, opens the ringing tone connection, extinguishes lamp AL1, disconnects the supervisory conductor 244 from the operating winding of relay 256,,and connects this conductor in series with a back contact of relay 210 to ground at a front contact of relay 213, thereby causing the release of relay 2I9 of two-way trunk circuit TWT2. The release of relay 2I9 disconnects its winding from conductor 224 and connects this conductor through the upper back contact of relay 2I5, to the winding of the answering supervisory relay 2I I. Relay 2I I operates thereby connecting battery through resistor I15, front contact of relay 2| I, theback contacts of relays 2I0 and I10, and retard coil I89 to the windings of relay I thereby causing the: operation of relay 90 at the other end of trunk TI. Relay 90 closes a circuit for operating supervisory relay 55. Relay 55 opens the circuit through the low-resistance, lower winding of relay 54. Since the upper winding of relay 54 is a high-resistance winding, the current in the circuit through the sleeve conductor of plug FP and lamp FL is reduced to extinguish lamp FL to indicate to the calling operator that the call has been answered.

The pad control relay.21I is held operated in a simplex circuit through the conductors 26I and 262 to battery in the operators position circuit PC2 as long as the talking key of cord C2 is operated. When the connection is extended through the other end of cord C2 to a trunk or line and the talking key of cord C2 is restored to normal, relay 21I is controlled by the trunk or line to which the other end of cord C2 is. connected. If relay 21I releases, it unbalances the simplex circuit to cause the reoperation of relays 205 and I83 and release of relay I84 thereby opening the short circuit around pads P3 and P4. If relay 21I is held operated, the simplex is balanced, relays 205 and I83 are not operated, and relay I84 short-circuitsthe pads P3 and P4.

The calling operator can recall the answering operator by operating the ringing key to the lower position to connect signaling battery to the tip conductor of plug FP, the battery having a high enough voltage, for instance 45 to 50 volts, to operatively energize the winding of relay 63. Relay 63 closes a circuit for operating relay 59 and a circuit for holding relay 10 operated. When the ringing key is restored to normal relay 63 releases. After relay 63 releases and before the slow-to-release relay 59 releases, relay 10 releases thereby temporarily transferring the upper signaling conductor of trunk TI from battery to ground to cause the release and reoperation of relay I90. The release and reoperation of relay I90 causes the release and reoperation of relays 20I and 25I. Being slow in releasing, relay 202 remains operated. The release of relay 25I causes the operation of relay 252. Relay 252 connects the low-resistance winding of relay 254 in parallel with the high-resistance winding of relay 212,

thereby causing the cord supervisory lamp (not shown) to light. Relay 254 operates and locks. When relay 25I reoperates, relay 252 releases and interrupter I is connected to the winding of relay 251. Relay 251 is alternately operatedand'released times a second under the control of interrupter I. Each time relay 251 operates, closes a holding circuit for relay 254 and disconnects the low-resistance winding of relay 254 from the sleeve conductor 263 so that the cord supervisory lamp is extinguished. The cord lamp is thus flashed to signal the operator until the talking key of the cord is operated to answer the recall. When the talking key is operated, marginal relay 254 releases but relay 212 remains operated. The release of relay 254 disconnects the winding of relay 251 from interrupter I.

If the answering operator wishes to signal the calling operator, operation of the ringing key con- I nects battery of a high enough voltage to conductor 26I to operate the marginal relay 210. While the ringing keyand relay 210 are ope'r ated, ground is disconnected from conductor 244 releasing relay 2II. The release of. relay 2II causes the successive release of relays 90 and 5 5 at the calling end of trunk TI. Relay 55 reconnects the low-resistance lower winding of relay 54 in parallel with the high-resistance upper wind: ing to light the lamp FL of cord CI to recall the operator. v I

If the answering operator disconnects cord C2 from trunk circuit 1T2 .while the calling cord CI remains connected with outgoing trunk circuit OTI, relays 212 and 213 release. Relay 213 reconnects condenser 216 and resistor 211 across conductors 26l and 262, disconnectsground from conductor 244 to release relay 2II and thereby signal the calling operator as described in the preceding paragraph, and closes a circuit for operating relay 255. Relay 255 connects battery to both windings of retard coil 245, the current through the winding of marginal relay 206 of the two-way trunk circuit TWT2 being increased sufficiently to cause its operation. Relay 206 closes a circuit for operating relay 2I6; and relay2I6 locks under control of relay 202. The operation of relay 2I6 disconnects ground from conductor 223, thereby causing the release of relay 229 of selector TS2, the release of the corresponding relay in selector A82, and the release of relays '256 and 214 of incoming trunk circuit IT2. The release of relay 229 closes a circuit for operating release magnet 239 and the shaft and brushes are thereupon restored to normal. The opening of the upper contacts of the VON springs, when the shaft reaches normal position, releases the magnet 239. The shaft and brushes of selector AS2 are restored to normal inv like manner. The aforementioned operation of relay 2I6 causes the release of

relays

20I, 205 and 206 but holds relay 200 operated. Relay 2I6 also closes a circuit for holding relay 2I I. The release of relay 20I causes the release of relay 202; and relay 202 releases relays 2I6 and 2II. The release of relay 2II again causes the lighting of lamp FL of cord CI and the release of relay 2I6 recloses the circuit hereinbefore described for operating relays 20I and 205 and relay 225 of selector TS2. Relay 20I again closes the circuit for operating relay 202; and relay 202 reconnects ground from the back contact of relay 2I6 to conductor 223. Thecalling operator may now reconnect the dial to, cord CI and reoperate selector T52 and succeeding switches to complete another call without trunk 'II having been released between calls. 'By rebusy operating the talking key TK, relays I0, 20, 2|, 22 and 23 are reoperated; and by reoperating the dial key DK, relays 24, 25, 26, 21 and 28 are reoperated. The operation of relay 28 causes the.

release of relay 2E5; relay 21 holds and relay 29 operates through the tip conductor of plug ET in series with the windings of

relays

63 and 83. Relay 63 is marginal and does not operate'in this circuit since the voltage of thebattery connectedto the winding of relay 27. is only a 24-volt battery. The operation of relay 29 causes the successive operation of relays 3I and 32 and the release of relay 2'! thereby again connecting battery through resistor 34 to the ring conductor of plug FP, thence through conductor 52, front contact of relay 6%, lower winding of retard coil 80, front contact of relay BI, lower winding of relay I1 and winding of relay 83 to ground. Relay 'II operates and looks through its upper winding under control of relays I9 and I8. The operation of relay 'I'I causes the release of relay 66. Relay 63 again closes the circuit from battery through resistor 33 and the tip conductor of plug FP for operating relay [8. With relay I8 operated, the upper operating winding of relay III is under the operative control of the impulse contacts of the dial DI and the dialing of another toll route number results in the reoperation of selector T82 and an auxiliary selector ASE as above described;

When the calling operator disconnects cord CI from trunk OTI, relay 54 releases. Relay 54 re leases relay 6B. Relay I58 releases relay 58. Relay 58 releases relays i0, 64 and 69 and also relays 55 and I8, if operated. Relay 64 releases relays and SI. Relay 6i! releases relays I9 and also relay it, if operated. The release of relay I0 disconnects signaling battery BI from the upper signaling conductor of trunk TI there by causing the release of relay I99. The release of relay I98 opens the circuit through the winding of relay 29I causing its release, the release of relay 205, if operated, and the release of relay 25I of trunk circuit 1T2, if trunk TI has been extended to trunk 1T2, or the release of relay 225 iftrunk TI is extended only to selector TS2, or the release of the line relay of any other selector, trunk or toll line with which trunk TI is connected. The release of relay 20I causes the release of relay 292. The release of relay 292 causes the release of relay 299, the release of relay 201, if operated, and the reoperation of relay 2I9. Relay 202 also disconnects ground from conductor 223 causing the release of relay 229 of selector TS2, the release of the corresponding relay of selector A82, and therelease of relays 256 and 214 on a connection to trunk circuit 1T2. The release of relay 229 causes the return of selector TS2 to normal as hereinbefore described. Relays 212 and 2'53 remain operated until cord C2 is disconnected from jack J1.

If during the dialing of a toll route number, a toll route selector such as TS2 or ASE or a selector of a toll train in a local dial office to which the connection is extended encounters an all-trunks-busy condition, relay is alternately operated and released to flash lamp FL. Assuming it is selector TS2 which finds all trunks in a selected level, the 11th rotary step springs are actuated, disconnecting the Winding of relay 229 from conductor 223, disconnecting conductor 2% from. resistor 229 to release relay 2I9, and connecting interrupter I to conductor 224 to cause the intermittent operation. of relay 2H. Relay 2.! I causes the, alternate operation and release of relay 9D; and relay 90 in turn causes the alternate operation and release of relay 55 to flash lamp FL. If the selector which encounters an all-trunks-busy condition is arranged to camp on the busy level and wait for a trunk to become idle, relays 90 and 55 are alternately operated and released in similar manner but at a different rate. The operation of relay 55 causes the operation of relay 5! and relay 51 looks through a back contact of relay 66 to ground at a front contact of relay 69. Relay 51 connects battery to the operating winding of relay ill to prevent its further release under control of the impulse contacts of dial D so that further impulses will not be sent out over trunk TI in case another digit. is dialed before the operator takes notice of the camp-on signal. The operator thereupon restores the talking and dial keys to normal causing the release of relay I8 and operation of relays 66 and 76. The operation of relay 6B releases relay 5'! and relay I6 holds relay I9 operated. A selector arranged for campon operation is disclosed in Patent No. 2,097,165, granted to R. L. Stokely October 26, 1937. When a trunk becomes idle, the signal is changed and operation of the talking and dial keys causes the reassociation of the dial with trunk OTI as hereinbefore described. The dialing of the digit 1 will then be effective to send one impulse to the selector in question and thus start its trunk-hunting operation. Any additional digits of the toll route number may then be dialed and relay I0 will repeat the dial impulses.

Since the trunk TI may be seized by toll route selectorssuch as ASI at one end and AS2 at the other end, it is necessary that the two-way trunk circuits TWTI and TWT2 and outgoing trunk circuits OTI and GT2 be arranged to establish the busy conditions which prevent seizure by another selector or by an operator and to establish the required pad control and through signaling conditions. To illustrate these operations, assume that a trunk T3 is seized by a toll operator in a third office. The associated composite signaling circuit CS2, two-way trunk circuit TWT3, outgoing trunk circuit 0T3 and incoming toll route selector T83 are similar to the corresponding circuits CS2, TWT2, 0T2 and TS2 associatedwith trunk TI and the operations resulting from seizure of trunk T3 and dialing are similar to those hereinbeiore described on the call incoming over trunk TI. Assume further that the incoming toll route selector TS3 is operated to select an auxiliary toll route selector ASZ and that the selector ASZ is operated to select the trunk TI. Upon extension of the connection from trunk T3 through the brushes of selector A82 to conductors I9I, I92, I93 and I94, holding ground potential is connected to conductor I93, ground from. the front contact of the signaling relay in the composite signaling circuit CS3 is connected to conductors I9I and I92, and ground through the windings of relays in circuit TWT3 corresponding to relays 2M and 2 I 9 in circuit TWT2 is connected to conductor i9 l all in similar manner to the connection of ground to conductors MI, 242, 243 and 244 of incoming trunk circuit 1T2 on'the call hereinbefore described. The connection of ground potential to conductor I93 closes circuits for operating relay 2I5 of the two-way trunk circuit TWT2 and relay I 56 of the outgoing trunk circuit 0T2. Relay 2I5 locks to conductor I93, connects relay 2I8 to conductor I95 and disconnects. the windings of relays 209 and ZUI from conductor I 95. Relay I 56 connects battery to the sleeve of jack J5 as a busy condition and operates relay I60. Relay I00 closes a circuit for lighting the busy lamps BL5. The connection of ground potential from the front contact of the signaling relay of circuit CS3 through circuits TWT3, T53 and A82 to conductors I9I and I92, is extended through back contacts of relay 200, conductor 123i and I82, windings of retard coil I80, back contacts of relay IISI, windings of relay 205, conductor I86, and back contact of relay 200 to the operating winding of relay 2I0. The connection of ground to conductor I94 causes the operation of relay 2II of two-way trunk circuit TWT2 and relay 2i! looks through its upper winding to the holding'ground on conductor I93. The operation of relay 2I0 disconnects ground from and connects battery through resistor I15 to retard coil I thereby causing the operation of the signaling relay at the other end of trunk TI. The operation of relay 90 connects ground to conductor to cause the operation of relays I00, IOI, I02 and I05 of two-way trunk circuit TWTI and the operation of the line relay (not shown) of selector TSI. Relay I00 connects ground to conductor 93 to guard two-way trunk circuit TWTI from. seizure by an auxiliary toll route selector such as ASI. The connection of ground to conductor 03 also causes the successive operation of relays 56 and '00. Relay 56 connects battery potential to the sleeve of jacks J I to mark this trunk as busy and relay B0 closes the circuit for lighting busy lamps BLI. The connection between ground at the front contact of signaling relay 00 and conductor 35 is maintained by a front contact of relay 56, although the normal connection is opened at the back contact of relay 80. Relay 50 also opens the repeater termination, comprising a condenser and resistor normally connected across conductors BI and 82 to prevent the associated voice frequency repeater which is not shown in the drawing from singing, The operation of toll route selector TSI and an auxiliary selector ASI is similar to that of selector TS2 hereinbefore described. The aforementioned operation of relay 2II causes the release of relay I83 and the operation of relay I84 to short-circuit pads P3 and P4. Answering supervision is received over trunk TI by relay I90. The operation of relay I90 closes a circuit including a front contact of relay 2l5 for operating relay 2I8. Relay 2I8 opens its operating circuit, locks to ground on conductor I93 and opens the operating circuit of relay 2". With relays 2I5 and 2I8 operated, the connection of ground through the front contact-of relay I30 and conductor I95 is extended through conductor I84, selectors A52 and TS3 through back contacts of the relays in two-way trunk circuit TWT3 which correspond to relays 2I9 and 2I5 of circuit TWTZ to the winding of the relay which corresponds to relay 2, thereby transmitting the answering supervisory signal over trunk T3 to the calling operator.

On calls incoming over trunk TI and extended through selectors TS2 and AS2 to a switching trunk leading to a local office, there is no relay in the outgoing trunk circuit of the switching trunk corresponding to relay 256 of incoming trunk circuit 1T2 and therefore relay 2I9 of twoway trunk circuit TWT2 releases as soon as selector AS2 seizes the switching trunk. The release of relay 2I9 connects conductor 224 to the winding of relay 2I I 'to operate this relay when the called subscriber in thelocal office answers. On

such a call, relay 201 is not operated and pad control relay I83 is held operated so that the pads P3 and P4 remain in the talking circuit.

While the two-way trunks TI and T3 are shown and described as being arranged for composite signaling it is of course understood that any type of signaling may be employed. For instance in the arrangement shown in Fig. 9, an intertoll trunk T5 terminates in a signaling circuit S05 arranged for voice frequency signal- :1

ing and the associated two-way trunk circuit TWT5 is provided with two polarized differential relays controlled in a simplex circuit comprising the talking conductors in parallel. One of these two relays is operated by an unbalance of the 1 simplex which causes a larger current in one side to control the transmission pads and the other relay is operated by an unbalance of the simplex which causes a larger current in the other side to control the repeating of the incoming voice 5 frequency impulses in accordance with the type of signaling provided in the outgoing trunk or line to which the connection is extended. In the following description it is assumed that the trunk T5, signaling circuit S05, and two-Way trunk circuit TWT5 are associated with an outgoing trunk circuit and a toll route selector similar to 318 trunk circuit 0T2 and selector TS2 shown in When the trunk T5 is seized at its distant end and voice frequency signaling current is transmitted over trunk T5 as a seizure signal, relay 390 is operated. Relay 390 closes a circuit for operating relay 385. Relay 385 closes a circuit for operating the slow-to-operate relay 386 and closesa circuit from ground at the back contact of relay 386, outer front contact of relay 390, inner upper front contact of relay 385, back contacts of relays I58 and I60 of the associated outgoing trunk circuit, conductor I95, back contacts 4 of relays 3| 5 and 324, lower back contact of relay 302, to the winding of relay 300. The operation of relay 300 opens the normally closed operating circuit through the winding of sloW-to-release relay 320 and closes a circuit for operating relay ;z 30I and relay 225 of the associated toll route selector TS2. The circuit for operating relays 3!" and. 225 is traced from ground at the back contact of relay 386, outer front contact of relay 390, inner upper front contact of relay 385, back 5 contacts of relays I58 and I60, conductor I95, back contacts of relays 3I5 and 324, winding of relay 30I, a back contact of relay 3I6, back contact of relay 324, winding of marginal relay 306, a front contact of relay 300, thence in simplex i5 through resistors 32I and 322, windings of

relays

305 and 323, back contacts of relay IOI, windings of retard coil I80, conductors I 8| and I82, front contacts of relay 300, conductors HI and 222, resistors 23I and 232, and thence through resistor l( 230 and the winding of relay 225. Being marginal, relay 306 does not operate. Relay 30! closes a circuit for operating slow-to-release relay 302. After relay 302 operates, relay 300 is held operated in series with resistor 304 under control of both of relays 30I and 302. The operation of relay 302 closes locking circuit for relay 385 and connects ground at the back contact of relay 3I6 to sleeve conductor 223 of the associated selector TS2 to control the release of this and succeeding =7 selectors. Being slow in operating, relay 386 does not open its back contact until after the seizure signal is ended and relay 390 has released. When relay 390 releases, it connects ground through its back contact and the inner upper front contact 7 of relay 385 to hold relays 20l and 225 operated. Relay 302 also closes a circuit for operating the slow-to-release relay 325; The slow-to-release relay 320 is normally operated, short-circuiting resistor 322 so that at the time relay 30!] operates,

the simplex is unbalanced and the current through the lower windings of the polarized

differential relays

305 and 323 is larger than the current through the upper windings. Relay 305 is thereby energized in a direction to maintain its armature in normal position but relay 323 is en-' ergized in a direction which operates its armature to its alternate position. When relay 320 releases due to the operation of relay 300, the short circuit around resistor 322 is opened causing the release of relay 323. Since relay 323 releases before the slow-to-operate relay 325 has operated, relay 324 also releases. The aforementioned operation of relay 302 also opens a normally closed circuit through resistor 303, the winding of relay 3|9 and the upper winding of relay 301. Relay 3|9 is thus normally operated but relay 301, being marginal, does not operate. After relay 302 operates, relay 3|9 is held operated in series with conductor 224 and resistor 220.

When signaling relay 390 responds to the first train of dial impulses of voice frequency current incoming over trunk T5, relays 30! .and 225 are alternately released and reoperated. .Slow-torelease relay 302 remains operated during the response of relay 30I. The selector TS2 is operated as hereinbefore described to select the desired group and an idle trunk therein whereupon the operation of relay 229 extends the connection to the selected auxiliary toll route selector AS2. The selector AS2 is thereupon con.- trolled by the response of relay 390 to the second train of impulses incoming over trunk T to select a desired trunk group and upon seizure of an idle trunk in the selected group the connection is extended thereto.

If the selected trunk is an incoming trunk circuit such as IT2, the operation is similar to that hereinbefore described on the call incoming over trunk TI to trunk circuit IT2. operated and relay 3|9 held operated in series with the lower winding of relay 255 of trunk circuit IT2. Relay 301 looks under control of relay 302 and opens the normally closed circuit for operating pad control relay 383. When the call is answered the connection of ground to conductor 244 causes the release of relay 3 9 and operation of answering supervisory relay 3| I. Relay 3| closes a circuit for operating relay 301 of the signaling circuit S05. Relay 381 closes a circuit for operating the slow-to-operate relay 388. After relay 381 operates and until relay 388 operates, a circuit is closed for operating relay 339. While relay 389 is operated; the source of signaling current VF is connected to the conductors of trunk T5 to transmit an answering supervisory signal to the calling oifice. If the connection is extended through a cord 02 to a tributary line or trunk, the simplex circuit is unbalanced to cause the operation of the polarized differential relay 305; but if the connection is extended through cord C2 to a toll line, the simplex is balanced and relay 335 does not operate. If relay 305 operates, relay 383 is held operated and the transmission pads remain in the connection; but if relay 305 does not operate; relay 383 releases and relay 3% operates to short-circuit the transmission pads. Rering signals may be transmitted over trunk T5 in both directions. If a rering signal is transmitted from the calling Relay 301 is office, the momentary operation of relay 390 in response thereto causes the momentary release of relays 30| and 25|; but relay 390 releases and relay 3! reoperates before relay 302 releases, and therefore relay 302 holds

relays

385 and 386 operated. If an answering operator transmits a rering signal, the supervisory relay 3| is momentarily released thus effecting the momentary release of relay 381 and momentary operation of relay 339 to connect source VF to trunk T5. Relay 388 is slow in releasing and remains operated; and, when relay 381 reoperates, relay 389 releases. If the answering operator disconnects before the calling operator disconnects, the release of relays 212 and 213 of the trunk circuit IT2 causes the operation of relay 255, thereby connecting battery to both conductors of the simplex to cause the operation of marginal relay 306 of the calling two-way trunk circuit TWT5.

The operation of relay 306 closes a circuit for operating relay 3H5. Relay 3I8 locks under control of relay 302, closes holding circuits for relays 330 and 3| opens the simplex circuit torelease ,relays 30I, 306 and 25l, and disconnects holding ground potential from conductor 223 to cause the release of the associated toll route selector and the release of the auxiliary toll route selector AS2 through which the connection with trunk circuit IT2 was established and to cause the trunk circuit IT2 to be restored to normal. Therelease of relay 30| causes the release of relay 302 and the release of relay 302 causes the release of relays 3l6, 301 and 3| l. The release of relay 3 causes the release of relays 381 and 388 and momentary operation of relay 389 to send a disconnect signal to the calling oflice. The release of relay 3|0 recloses the circuit for operating relay 30| of the trunk circuit and relay 225 of the associated toll route selector. Relay 30| operates relay 302 before relays 325 and 335 have both released so that relay 385 is held operated and the signaling circuit 8C5 is ready to repeat the dial impulses of another called route number to selector T82 and an auxiliary selector ASZ without trunk T5 having been released and reseized by the calling operator. Since relay 380 is slower to release. then to operate, the disconnect signal is of longer duration than a seizure signal. When a disconnect signal is received over trunk T5 from the calling office, relay 390 is operated for a long enough time to cause the release ofrelay 25l and both ofrelays 30! and 302. The release of relay 302 causes the release of

relays

385 and 386, the release of selectors T32 and A82, and the release of the trunk circuit IT2.

If on the call incoming over trunk T5, the selected auxiliary toll route selector AS2 is operated to extend the connection to a two-way intertoll trunk circuit such as TWT2, the operation of circuits TWT5 and S05 are similar to the operations above described on a call to trunk circuit IT2.

Assume next thatthe two-way trunk circuit TWT5 is selected. and seized by an auxiliary toll route selector AS2 on a call incoming over a trunk, such as TI, arranged for composite signaling. In this case, holding ground is connected Relay 3|1 of trunk circuit TWT5 is operated by the current in a circuit from battery through its lower winding, lower back contact of relay 3I8, conductor 394, through selector AS2, brush 238 and conductor 224 of the selector TS2, back contact and winding of relay 2I9 of the two-way trunk circuit TWT2 of the calling trunk TI and through the upper winding of relay 201 to ground. Relay 201 is also operated by the current in this circuit and relay 2I9 is held operated. Relay 3I1 looks through its upper winding to holding ground potential on conductor 393; and relay 201 looks through its lower winding under control of relay 202. With relay 3I1 operated, the circuit for operating relay 383 is opened, relay 383 releases, relay 884 operates and the transmission pads are short circuited. The operation of relay 201 places pad control relay I83 under control of relay 205. Another circuit, closed upon seizure of the trunk circuit TWT5, is traced from battery through the winding of relay 3I0, a back contact of relay 300, thence in simplex through resistors 32I and 322, both windings of the differential and oppositelypoled

polarized relays

305 and 323, through back contacts of relay NH and windings of the retard coil I80 of the outgoing trunk circuit T2 associated with trunk T5, through back contacts of relay 300, conductors 39I and 392, talking conductors of selectors AS2 and TS2, conductors 22I and 222, front contacts of relay 200, conductors IBI and I82, windings of retard coil I80 and back contacts of relay I6I of the outgoing trunk circuit 0T2 associated with the calling trunk, both windings of relay 205, conductor I96, front contact of relay 200, winding of relay 206, back contact of relay 2I6, winding of relay 20!, back contact of relay 2I5, conductor I95, front contact of relay I56, back contact of relay I58, to ground at the front contact of signaling relay I90. Relay 20I is held operated and relay 3I0 is operated by the current in this circuit. At the time this circuit is first closed, the simplex is unbalanced because resistor 322 is short-circuited by the normally operated relay 320; and for this reason relay 323 may be momentarily operated. The momentary operation of relay 323 may cause the operation of relay 324 but relay 324 cannot lock since relay 325 is not operated. When the short circuit around resistor 322 is opened by the release of slow-to-release relay 320, the simplex is balanced and relays 323 and 324 release.

Relays

205 and 305 do not operate because the differential energization of these polarized relays before the simplex is balanced is in a direction to maintain the armatures in normal position. With relay 205 normal and relay 201 operated, pad control relay I83 releases, relay I84 operates and pads P3 and P4 are short-circuited. The aforementioned operation of relay 3I0 upon seizure of trunk circuit TWT5 closes a circuit from battery through resistor I of the associated outgoing trunk circuit, back contact of relay 324, front contact of relay 3I0, back contact of relay I10 of the outgoing trunk circuit, and winding of relay 381. Relay 381 operates closing circuits for operating relays 380 and 389. Relay 389 connects signaling source VF to trunk T5 to transmit a seizure signal. When slow-tooperate relay 388 operates, relay 389 releases. When an answering signal is received over trunk T5, relay 390 operates closing the circuit for operating relay 385. Relay 385 looks to ground at a front contact of relay 3I5 and close a circuit for operating slow-to-operate relay 386. With relays 390 and 385 operated and before relay 386 operates, ground'is connected through a back contact of relay 386, front contacts of relays 390 and 385, a back contact of relay I58 and a front contact of relay I56 of the associated outgoing trunk circuit and through a front contact of relay 3I5 to the winding of relay 3I8. After relay 390 releases at the end of the answer ing signal, ground is connected through a back contact of relay 390 and a front contact of relay 385 thence to the winding of relay 3I8. Relay 3I8 operates and locks to the holding ground connected to conductor 393. With relay 3I8 operated, the supervisory ground connected to conductor 395 is further connected through the lower front contact of relay 3I8, conductor 394, through selectors AS2 and T82 to conductor 224, thereby releasing relay 2I9. The release of relay 2I9 extends the supervisory ground through conductor 224 and a back contact of relay 2I9, to the winding of relay 2. Relay 2II is operated by the current in this circuit to transmit an answering supervisory signal over the calling trunk as hereinbefore described. If a rering signal is received over the calling trunk, the momentary release of relay I90 causes the momentary release of relays I, 3I0 and 381 and relay 389 is momentarily operated to connect source VF to trunk T5 to transmit a rering signal. If a rering signal is received over trunk T5, relay 390 is momentarily operated, causing the momentary release of relay 2H; and relay 2II transmits the rering signal over trunk TI as hereinbefore described. If relay 390 is operated by a disconnect signal incoming over trunk T5, relay 2II is released in like manner to send a disconnect signal over trunk TI. When a disconnect signal is received over the calling trunk TI, the release of relay I90 causes the release of relay 3I0 and the release of both of relays 20I and 202 thereby disconnecting holding ground from conductors 223 and 393 to cause the release switches TS2 and AS2 and return of trunk circuit TWT2 to normal as hereinbefore described. The disconnection of ground from conductor 393 causes the release of relays 3I5 and 3I1, and the release of relay 301, if operated. The release of relay 3I0 causes the release of relays 381 and 388. After relay 381 releases and before the slow-to-release relay 388 releases, relay 389 is momentarily operated to connect source VF to trunk T5 to transmit a disconnect signal.

Assume next that the two-way trunk circuit TWT5 is selected by an auxiliary selector AS2 on a call incoming over another voice frequency intertoll trunk similar to T5, through a signaling circuit and two-way trunk circuit similar to the signaling circuit S05 and trunk circuit TWT5. The signaling and two-way trunk circuits associated with the trunk from the calling toll office are hereinafter referred to as the calling circuits and the signaling and two-way trunk circuits associated with the trunk to the called toll office are referred to as the called circuits. The operations of the calling signaling and two-way trunk circuits are similar to those hereinbefore described on a call incoming over trunk T5 except as hereinafter mentioned; and the operations of the called trunk and signaling circuits are similar to those hereinbefore described when these circuits are seized on a call incoming over a trunk TI except as hereinafter mentioned. Although at the time of seizure of trunk circuit TWT5, the resistor 322 of the calling trunk circuit is not short-circuited, the resistor 322 of the called trunk circuit is short-circuited by a back contact of the normally operated relay 320.

Therefore, the simplex is unbalanced and not only relay 3H3 of the-called trunk circuit operates but relay 323 in each of the connected two-way trunk circuits is operated. The operation of relay 3| 0 of the called trunk circuit causes the operation of relays 381 and 389 to momentarily connect source VF to trunk T5 to transmit a seizure signal. When the normally operated relay 320 of the called trunk circuit releases and opens the short circuit around resistor 322, the simplex is balanced and relay 323 of each trunk circuit releases. The release of relay 323 of the called trunk circuit causes the release of relay 324 since relay 315 is operated on an outgoing call; but in the calling trunk circuit relay 324 is locked to a front contact of the then al-- ready operated relay 325. With relay 324 of the calling trunk circuit operated, the operating circuit of relay 30! is opened but relay 362 is held operated through a front contact of relay 324 and a back contact of relay 3! 5, thence to ground in the associated signaling circuit as hereinbefore traced. Relay 324 of the calling trunk circuit also connects ground through the winding of relay 385 and uppermost front contact of relay 300 to resistors 32! and 322 to maintain closure of the simplex so as to hold relay 3 ill of the called trunk circuit operated. When relay 390 of the called signaling circuit is operated by an answering supervisory signal from the called toll oflice, it causes the operation of relay 3E8 of the called trunk circuit and causes the release of relay EH9 and operation of relay iii! of the calling trunk circuit; but, since relay 324 is operated, the operation of relay SM is ineffective to cause the operation of relays 38'! and 389. The voice frequency answering signal, rering signals, and a disconnect signal from the called office are transmitted through the talking connection to the calling intertoll trunk. The operation of relay 390 of the called signaling circuit in response to rering or disconnect signals from the'called ofiice causes the operation of relay 3!! without causing the operation of relays 381 and 389; Rering signals received from the calling oflice are transmitted through the talking connection to the called intertoll'trunk. The operation of relay 396 of the calling signaling circuit in response to a ringing signal from the calling ofiice, causes the momentary opening of the holding circuit for relay 302 of the calling two-way trunk circuit but relay 302 is slow-in-releasing and remains operated. A disconnect signal from the calling toll office is transmitted through the talking connection to the called toll ofiice and also causes the operation of relay 39!! of the calling signaling circuit for a long enough interval to cause the release of relay 302. The release of relay 382 of the calling trunk circuit causes the release of relay 390 of the calling trunk circuit and release of relay 3!!! of the called trunk circuit. All of the circuits and switches involved in the connection between the calling and called intertoll trunks are thereupon restored to normal.

What is claimed is:

1. In a telephone system, an incoming line, outgoing lines, means including a selector switch for connecting said incoming line to any one of said outgoing lines, a differential relay associated with said incoming line, a simplex circuit including the windings of Said relay and the talking conductors of said selector, signal receiving means for repeating signals from the incoming line over said simplex circuit to a selected outgoing line, and signaling means. associated with said outgoing. line for unbalancing the simplex circuit to operate said differential relay.

2. In a telephone system, an incoming line, outgoing lines, means including a selector switch for connecting said incoming line to any one of said outgoing lines, two polarized difierential relays associated with said incoming line, a simplex circuit including the windings of said relays and the talking conductors of said selector, signal receiving .means .for repeating signals from the incoming line over said simplex circuit to a selected outgoing line, signalingmeans associated with said outgoing line for decreasing the resistance of one side of said simplex circuit to cause the operation of one of said polarized differential relays, and

signaling. means associated with said outgoing line for reducing the resistance of the other side of said simplex circuit to cause the operation of the other of said polarized differential relays.

3. In a telephone system, an incoming line,

ential relay'in series with the talking conductors of said selector, signal receiving means for repeating signals from the incoming line over said simplex circuit to a selectedoutgoing line, signaling means associated with said outgoing line for decreasing the resistance of one side of said simplex circuit to cause the operation of said differential relay, and signaling means associated with said outgoing line for decreasing the resistance of said simplex circuit to cause the operation of said marginal relay.

4. In a telephone system, an incoming line, signal receiving means associated with said line, a route selector comprising talking conductors, a sleeve conductor and a fourth conductor, groups of outgoing lines accessible to said selector, a simplex circuit including said talking conductors for repeating directive signals received by said signal receiving means to said selector, means in said selector responsive to said signals for selecting the desired group of outgoing lines and for selecting an idle line in the selected group, a resistance pad or network connected in the incoming end of said line. a pad control re- I lay for closing and opening a short circuit around said pad, circuit means normally effective to control said pad control relay to open said short circuit, circuit means including said fourth conductor of the selector for controlling said pad control relay upon selection of a line and in acassociated with said incoming line for receiving e signals incoming over said incoming line and repeating said signals to the signal receiving means associated with the connected one of said outgoing lines, the circuit for repeating said signals comprising. said talking conductors con-