US2139800A

US2139800A - Telephone switchboard switching system

Info

Publication number: US2139800A
Application number: US98056A
Authority: US
Inventors: Bonorden Allen Rudolf
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1936-08-26
Filing date: 1936-08-26
Publication date: 1938-12-13
Anticipated expiration: 1955-12-13

Description

Dec. 13, 1938. A. R. BONORDEN 2,139,800 .TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, 1936 v 8 Sheets-Sheet 1' n F/GJ 1 -5/[2 MPG/MAL FIG. /8

F IG. IA

INVENTOR FIG, F/QZ FIG"? BVARBO/YORDEM M ATTORNEY Dec. 13, 1938. A. RIBONORDE N 2,139,800

.TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, 1956 8 SheetsSheet 2 /b0 335 F/G.2

llllllllllll l nun-yum 208 207 (325 mfi b: 2// J 209 I 6% INVENTOR & By ARBONORDEN A TTOR/LIEK Dec. 13, 1938. R BONORDEN 2,139,800

TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, 1936 8 Sheets-Sheet 3 com com CORD CIRCUIT 309 CIRCUIT CIRCUIT A TTORNEV I Dec. 13, '1938. A. R. BONORDEN TELEPHONE SWITCHBOARD SWITCHING SYSTEM 7 Filed AugQ'26, 1 936 1 8 sheets-sheet 4 400 F/G.4

ATTORNEY %c. H, 3938. A. R. BONORDEN 2,139,8fifi TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, l956 8 Sheets-Shet 5 F/G5 5/0 CIRCUIT c090 com 500 CIRCUIT CIRCUIT INVENTOR ARBOA/ORDEN rraeusr Dec. 13, W38. A. R. BONORDEN 2,139,860

TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, 1936 8 Sheets-Sheet 6 F7616 F/a'aA lNl ENT 0R 4. R. BQ/VORDE A TT'ORNEV %c. 13, 1938. A. R. BONORDEN 2,139,800

TELEPHONE SWITCHBOARD SWI TCHING SYSTEM Filed Aug. 26, 1936 8 Sheets-Sheet 7 FIG. 7

CORD C 0R0 C 0R0 CIRCUIT I C/RCU/ 7' CIRCUIT MAINS/MAL W 14 T TOPNEV Dec. 13, 193%. A. R. QBONORDEN 2,139,80G

. TELEPHONE SWITCHBOARD SWITCHING SYSTEM Filed Aug. 26, 1936 8 Sheet-Shet 8 FIG. 8 600 CORD CORD CORD Q/RCU/T CIRCUIT CIRCUIT llll Ill IIHHI HIIHIIi ||||H ullllulllllll I A A A em" OFFICE UNITED STATES PA TELEPHONE SWITCHBOARD SWITCHING SYSTEM Allen Rudolf Bonorden, Fanwood, N. 3., assignor to American Telephone and Telegraph Company, a corporation of New York Application August 26, 1936, Serial No. 98,056 9 Claims. (01. 17948) This invention relates to communication sysondary answering appearance at any position of tems and more particularly to supervising and the multiple type of telephone switchboard.

maintaining private, or order, wire service over Another feature is the provision of having a intercity communication trunk circuits between sequence circuit associated with the trunk cirtelephone test board attendants located in differcuits or the positional keysets. 5 ent cities. Another feature is the provision of recalling the An object of the invention is to permit an atattendant at a primary position after the signal tendant at a telephone switchboard or test board has been transferred to another position and the in one locality to be connected. with any one of a attendant at the latter position has failed to w plurality of attendants at a telephone switchanswer. 10 board or test board in a different locality. Another feature is the provision of a transfer It is essential in telephone test board operation key so that for night operation all signals of dif in telephone systems for attendants at different ferent trunk circuits normally appearing in diflocalities having charge of a particular service at ferent primary positions may be caused to appear 3 5 their respective test boards to obtain direct comat some one position used as a night or light load munication with each other and consequently it position. is desirable to have an arrangement which will A more complete understanding of the invenfacilitate certain direct communication or pertion may be obtained from the accompanying mit of an incoming call being rapidly transferred drawings in which to an attendant responsible for a particular serv- Figures 1, 2 and 3 represent an arrangement of 20 In both 13011 and telephone Practice e the invention when interconnected in accordance fore known the transfer of calls, received over with the block diagram Fig. 1-A, wherein Fig. l certain trunks or line circuits, is possible to a shows two-way communication lines and associvery limited extent, that is, the facilities at presated line equipment, Fig. 2 a control circuit for ent permit the transfer to one or at the most transferring calls, and Fig. 3 answering jacks two points in the ofiice. and lamps, associated busy lamps, position trans- According to the present invention the facilifer keys, position sequence circuit relays and. ties provide for each position or section in a line cord circuits. The cord circuits are shown in deof telephone test boards to become a potential tail by Fig. 1-B. transfer point and in the larger of said oiiices Figs. 4 and 5 represent another arrangement 30 these facilities extend to arrangements for transof the invention, when interconnected in accordferring a call to any one of a plurality of poslance with the block diagram l-A, wherein Fig. i tions or sections. In other words an attendant at shows two-way communication lines and assoc-1 a multiple type of telephone switchboard may ated line equipment including a crossbar switch upon receiving an incoming call over an intercity and Fig. 5 shows answering jacks and lamps, communication trunk circuit, transfer the inbusy lamps, position transfer keys, cord circuits coming call signal to any particular one of a pluof the type shown by Fig. 1-B and a relay type rality of trunk lamps, each of which is located at control circuit. a different position or section. in the switchboard. Figs. 6, '7 and 8 represent still another arrange- The multiple type of switchboard may comprise ment of the invention when interconnected 1n 40 two or more sections, each section having one or accordance with the block diagram 6-A, wherein more operators or attendants positions. Fig. 6 shows two-way communication lines and A feature of the present invention is that it associated line equipment including a crossbar provides a more flexible arrangement than hereswitch and Fig. 7 shows answering jacks and tofore known in that an incoming call signal lamps, busy lamps, position transfer keys, cord may be transferred to a signal lamp at any one circuits of the type shown by Fig. 1-13 and a of even more than twenty positions. different relay type control circuit than that Another feature is that an incoming call signal shown in Fig. 5. may b transferred a p at any one of a Fig. 8 is an alternative arrangement of Fig. '7

plurality of telephone switchboard positions and which uses a control Circuit Consisting f a 50 then again transferred to another lamp at one of tary type Stepping switch the other positions.

Still another feature is that the arrangement may provide by proper cross-connections for any Referring to Figs. 1, 2 and 3, I00 is an inter- 56 trunk circuit to have either a primary or a secoffice line, which terminates in jacks 3G0, 3M and Figures 1, 2 and 3 302 of

positions

1, 2, and 3, respectively. Associated with these jacks are answering lamps 303, 304 and 305 and

busy lamps

306, 301 and 308, respectively. The attendant at each position is provided with a cord circuit, conventionally represented by the

boxes

309, 3! 0 and 3| I and shown in detail by Fig. 1- B. Calls may be answered with plug I03 by plugging into the jack associated with the lighted answering lamp, or originated with plug I04 by plugging into the jack of the line selected for an outgoing call and ringing with key I05. Additional jacks, answering and busy lamps may be provided at additional positions, not shown. As shown in the drawings, position 3 is cross-connected by the conductor 200, so that the associated answering lamp 305 is lighted on an incoming call, that is, position 3 is a primary answering position. Position 2 is not thus cross-connected, its lamp 304 is lighted only on a transferred'call, and is accordingly a' secondary answering position. Position 1 is cross-connected by the conductor 20I so that when night key 3I2 is operated, it is then a socalled night position at which all calls incoming over line I00 and over all other lines with night keys similarly operated, are answered. Under this Condition it is a primary position; when the night keys are not operated it is a secondary position. The night key 362 may be multipled with a number of lines in a predetermined group so that all these grouped lines may be answered at position 1 when said key is operated. It is to be understood that any position in the switchboard line up may be arranged as either a primary or secondary answering position by suitable cross-connection. Any position may also be a night position.

In order to transfer incoming calls from one position to another, line I00 is provided with a rotary type stepping switch, for which 202 is the stepping magnet. This magnet causes the brush arms 203 and 204 to move around the contact banks 205 and 206, respectively.

Each terminal of bank 205 is connected to a conductor leading to an answering lamp at the respective positions whereby each lamp may be selectively lighted as required. Each contact of bank 206 is connected to a conductor to which ground is selectively connected by one of the positional transfer keys as 3I3, 3M, 3I5, which in effecting a transfer identifies the position to which the call is to be transferred. The line being transferred is identified by the insertion of the plug I03 of cord circuit C in the associated line jack and by then operating listening key I06. In order to use a transfer circuit arrangement common to all positions, a so-called sequence circuit is used. This consists of relays SIS, 3I'I, 3I8 and 3I9, 320 and 32I, which are arranged in a manner similar tothe relays of an automatic listening, straightforward trunking system, which is well known in the telephone art. Thus arrangement makes the common transfer equipment available to only one position at a time and thereby avoids the possibility of interference if two'attendants should attempt to transfer calls simultaneously. Another feature of the sequence circuit is the arrangement whereby calls awaiting transfer are handled progressively through the sequence, but not necessarily in the order in which transfers are attempted.

In the description before given, particular reI- erence was made to the line I 00 and its associated apparatus. A similar description also applies to the other lines IN and I02. A more complete understanding of the operation of the arrangement of Figs. 1, 2 and 3 may be obtained from the following detailed description.

Let it be assumed that an attendant at a distant telephone test board desires to communicate with the attendant located at position 2 and selecting the line Q00, applies ringing current thereto. Ringing relay I01 then operates through condenser I08 and the left outer break contacts of cut-01f relay II 0 and closes an obvious circuit through the winding of relay I09, which operates and looks through its inner right contacts to ground on the left inner contacts of relay IIO.

Relay I09, in operating connects battery with its left outer front contacts to conductor I I I, thence through cross-connection 200 and over conductor 343 to ground through lamp 305. The usual audible alarm and auxiliary position pilot lamp may be operated by inserting a low resistive relay between all lamps in a position and this ground. Also, relay I09 connects battery with its right outer front contacts to conductor 322, lighting

busy lamps

306, 307 and 308, and busy lamps at other positions not shown. The attendant at position 3 now responds by inserting the answering plug of a cord circuit which is conventionally represented by a box 3| I, intojack 302. This cord circuit, as before stated, is represented in detail by Fig. 1-B, to which the description now refers. A circuit is closed from battery through the winding of sleeve relay 524 over sleeve conductor of plug I03 and jack 302, over conductor 323, through winding of relay H0 and right winding of marginal relay II2 to ground. arranged for supervision, supervisory relay H3 operates, thereby connecting resistance I I4 in shunt with supervisory lamp H5 which remains dark. If line I 00' is not arranged for supervision, relay II3 does not operate and lamp I I5 is lighted in a circuit from battery through resistance IIB to ground on the contacts of sleeve relay I25, which, operated, when plug I03 was inserted into jack 302. Relay I 50 operates but relay II 2 does not operate at this time. In operating, relay H0 disconnects the circuit of relay I01 from the conductor of line I 00, opens the locking circuit of relay I09 which releases, connects battery with its right inner contacts to conductor 322 thereby maintaining the lighting of the busy lamps. after the release of relay I09, and with its right outer front contacts connects ground to the left inner front contacts of relay H2 so that relay I I2 may lock when it subsequently operates. The release of relay I09 disconnects battery from conductor III, thereby extinguishing lamp 305. The attendant at position 3 now operates listening key I06, thereby establishing communication over line I00 with the attendant at the distant office. Having been informed that communication. with the attendant at position 2 is desired, the attendant at position 3 now transfers the call by operating the position transfer key 3%, which is the key at position 3 assigned to the transfer of calls to position 2. A circuit is now closed from battery.324, through the winding of relay 320, and right operated contacts of key 3M to ground. Sequence circuit relay 320 operates and a circuit is closed from battery through the winding of relay 32!, lower operated front contacts of relay 320 to conductor 325. If neither relay 3I8 or 356 of positions 1 and 2 is operated, due to the previous engagement of the sequence circuit by these positions, the circuit before traced is extended over conductor 325, through lower back contacts of relay 3I8, over conductor 321, through lower If the line is back contacts of relay 3I6, over conductor 326, 75

through winding of relay 2111 to ground 211 on the break contacts of relay 208. Relays 201 and 321 operate in this circuit. Relay 2111 closes a circuit from battery through the winding of slow releasing relay 208 and contacts 239 and 211) to ground. Relay 2118 in operating disconnects ground 211, and the circuit is maintained through contacts 211 of relay 2191 which is locked operated. If either relay 313 or 318 were previously operated, then the circuit through the winding of relay 321 is open at the back contacts of either relay or 318. If relay 316 is operated its winding is connected to battery 324 through the upper inner break contacts of

relays

319 and 321; if relay 318 is operated, battery 324 is connected through the upper inner break contacts of relay 321.

A general description of the operation of the sequence circuit, which as before stated is used in the telephone art for straightforward trunking will now be given. Relay 316 may be said to be in the first, relay 318 in an intermediate and relay 321) in the last position. If

relays

318 and 313 are operated, and lines are awaiting service in the,last and first positions, relay 3211 is opererated but relay 316 is not operated, since its operating path is disconnected by the lower break contacts of relay 318. When relay 318 releases, conductor 321 is transferred from the winding of relay 319 to conductor 325 by the continuity contacts of relay 318, thereby holding relay 231 operated through the lower operated contacts of relay 3211 and the winding of relay 321, which operates. Relay 316 does not operate since its circuit, previously opened at relay 319 is also opened by the upper inner break contacts of relay 321 before relay 319 releases to close its portion of said path.

Relays

311, 319 and 321 are slightly slow to release to assure this feature. When relay 3211 releases, releasing relay 321, the circuit through relay 2111 is opened and this relay releases, releasing in turn slow releasing relay 2118, which after an interval reconnects ground 211. During this open interval, relay 316, and also relay 318, if this relay is again awaiting operation, now operate. Relay 316, however, disconnects conductor 321, so that now relay 311, and not relay 313 or 321, operates. Thus, lines awaiting connection are served by the sequence circuit sequentially in accordance with their numbered position in the sequence, and not in accordance with the order of their call for service. In Fig. 3 only three pairs of sequencerelays are shown corresponding to

positions

1, 2 and 3 respectively. For additional positions, sequence relays may be added establishing the same interconnections between positions as are shown,

battery 324 being connected to the relays of the last position as it is shown connected to

relays

323 and 321.

Relay 321 operating in response to the operation of key 314 and relay 3211 as before described connects ground through its upper outer contacts to conductor 328, thence through the left con tacts of key 314 to conductor 329 and the secend terminal of hunting switch bank 206. This is for the purpose of marking the stopping point for brush arm 234 and associated arm 2113, as will hereinafter be described. Relay 321 in operating also disconnects conductor 344, with its upper inner contacts, from battery 324, thereby preventing the operation of

relays

318 and 316, if a transfer key at positions 1 or 2 should now be operated, and also with its lower inner contacts closes a circuit which is traced from battery through the right and left series connected windings .of relay 212, over conductor 330, through lower inner contacts of relay 321, upper contacts of relay 3211 to ground through the positional release lamp 331. Relay 212 operates in this circuit but lamp 331 does not light because of the high resistance of the right winding of relay 212. Relay 212 in operating closes a circuit from ground through its contacts, left inner back contacts of relay 213, and Winding of slow releasing relay 214 to battery, Relay 214 operates and closes a circuit from battery 215 through resistance 216, left contacts of relay 214, over conductor 332, through lower outer operated contacts of relay 321, to conductor 333, which is also indicated on Fig. 1-B to which reference should now be made. From conductor 333 the circuit continues through the lower outer operated contacts of listening-key 106, over conductor 111, through sleeve conductors of plug 103 and jack 332 and thence over the sleeve circuit before traced. Since battery 215 is of higher voltage than the regular sleeve circuit battery 118 marginal relay 112 now operates through its right winding and looks through its left winding and left inner contacts to ground on the right outer front contacts of sleeve relay 111). Relay 112 in operating closes a circuit from battery through the left outer back contacts of relay 1113, through right front contacts of relay 112, over conductor 211, through winding of relay 218, over conductor 219 to ground on the right outer contacts of relay 1 19. Relay 218 operates and closes a circuit from battery through the winding and break contacts of stepping magnet 2112, right outer contacts of relay 218, over conductor 2211, through right inner contacts of relay 213, back contacts of relay 221 to ground through operated

contacts

222 and 223 of relay 214. Magnet 202 by means of its self-interrupting contacts rotates brush arms 233 and 2134 around their respective contact banks in the direction indicated by the arrows. The brush arms 2113 and 2114 are shown resting normally on bank contacts No. 1; it should be understood, however, that these brush arms may rest normally on any one of the contacts, the position depending on the particular set of contacts required by the last selection. Relay 218 also closes a circuit from battery through the winding of relay 221, over conductor 221, through left contacts of relay 218, over conductor 223 to brush arm 2114. When brush arm 2114 reaches contact 2 of bank 2133 the circuit is continued over the path previously traced to ground on the upper outer operated contact of relay 321. Relay 221 operates opening the operating path of magnet 282 thus causing the selector brush arms 2133 and 206 to remain on contact 2 of their respective banks. Relay 221 operated also, closing a circuit traceable from ground on the operated

contacts

223 and 222 of relay 214, front contacts of relay 221, to battery through the winding of relay 213, which operates and locks through its left inner front contacts to ground on the contacts of relay 212. Relay 213 also opens the circuit of relay 214 which releases after an interval, but before releasing a circuit is closed from ground through contacts 223, right outer contacts of relay 213, over conductor 224, right inner contacts of relay 218, over conductor 225, and through right winding of relay 119 to battery. Relay 113 operates and looks through its left winding and inner contacts to ground on the left outer operated contacts of relay 112. The circuit of relay 2H8 is opened and this relay releases, releasing relay 2.2.1. When relay 213 operated and relay 2I4 released as before described a short-circuit was closed around the right winding of relay 2I2, which is traced from the common terminal of the two windings of relay 2I2, through left outer contacts of relay 2| 3 to battery on the right normally closed contacts of relay 2M. Relay 2I2 now holds on its left winding,

and the resistance of its circuit being reduced lamp 33I is now lighted, which is an indication to the attendant at position 3 that the transferring apparatus has functioned. Key 3M is accordingly released, effecting the release of relays 2I2, 2I3, 329 and 32I, and plug IE3 is withdrawn from jack 3B2. Sleeve relay IIE! now releases also releasing relay II 2. Relay H9, however, remains operated through the right outer back contacts of relay I I5, and with its right inner contacts maintains battery on conductor 322, the busy lamps at all positions remaining lighted. The release ofirelay I I 2 closes a circuit from battery on the left outer contacts of relay I 09, right back contacts of relay II2,left outer front contacts of relay II9, over conductor 225, over brush arm 253, contact 2 of bank 255, over conductor 334 and to ground through answering lamp 336 at position 2.

The attendant at position 2 now responds by inserting into jack 31H the plug of cord circuit 3), thereby operating over the sleeve circuit sleeve relay Ht, but not the marginal relay II 2. The

circuit through the left winding of relay II 9 is opened, and this relay releases opening the circuit, before traced, for lamp 354, which is extinguished. The busy lamps, however, remain lighted, due to battery being reconnected to conductor 322 by the right inner contacts of relay H5. When the listening key of cord circuit SIB is operated, the attendant at position 2 is then in communication with the distant ofiice over the line I59. The flexibility of the transferring fea ture of my invention is such, that now, should the attendant at position 2 desire to transfer the call, this may be done in the same manner as the original call was transferred from position 3 to 2. If, for instance a transfer to position 1 is required, the attendant at position 2 operates key 35!, thereby causing sequence relays M5 and 3I9 to function in connection with the common relays 258, 251, 2I2, 22I, 2M and 2I3 in the same manner as did relays 320 and 32L In this case ground is connected over conductor 342 to terminal No. l of bank 256 and stepping magnetZIlZ rotates brush arm 2% until this grounded terminal is found. Lamp 353 is lighted over conductor 345, terminal No. 1 of bank 255, brush arm 2133, over conductor 226 and the circuit previously traced for lamp 394.

Position 1, (or any position) as before stated may be arranged to be used as a night position. Night key Hi2 is shown associated with line I551, over conductor 335. Other lines may be grouped with line I55 for night answering by connecting conductor 335 to the corresponding conductors of these lines.

In a similar

manner night keys

336 and 331 are associated with lines IGI and I02, over

conductors

338 and 339. When key 312 is operated and relays I01 and I59 operate, as before described, in response to incoming ringing current, a circuit is traced from battery through the contacts of key 3E2, over conductor 335, through left inner operated contacts of relay I09, over conductor 52$ cross-connecter conductor 340 and to ground through lamp 303, which lights. The lamps at the primary positions also light, but

are not answered, since these positions are unattended at this time.

The operation of the arrangement of Figs. 1, 2 and 3 have been described for an incoming call. This arrangement may also be used for outgoing calls. The attendant at position 3, for instance, may originate a call by plugging into jack 302, with calling plug I94 of cord circuit C. Cut-off relay H is operated and the busy lamps at all positions are lighted as before described. The attendant now operates ringing key I05, connecting thereby, ringing current source I2I to the tip conductor and ground I22 to the ring conductor. When the distant attendant answers, communication is established by operating listening key I55, connecting thereby the telephone circuit I23.

Figures 4 and 5 Referring to another arrangement of the invention disclosed by Figs. 4 and 5, in Fig. 4 are shown three intercommunication lines 400, 4M and 462, which are arranged to cooperate with a crossbar switch CB which is of the same general construction as that described in Patent No. 2,021,329, issued November 19, 1935 to J. N. Reynolds, from which patent a complete description may be obtained. The function of switch GB is to cooperate over tional transfer keys, as 536, 531, 538 or 539 of Fig. 5 in order to transfer calls to various posi-- tions in a telephone switchboard line-up. The switch CE is shown with lines G00, 4! and 492 connected to cooperate with verticals 1, 2 and 10, respectively. Intervening verticals, 3, 4, 5, 6, 7

and 8 are omitted as being unnecessary for the purpose of this description, and are symbolized by vertical 9, which is shown unconnected. Only four horizontals are shown, each of which represents positions respectively 1, 2 and 3 of Fig. 5, and position 4, not shown.

Horizontals

5, 6, 7, 8, 9 and 10 are not shown since these are not necessary in describing the invention. By means of the switch CB ten lines, as 400, 4!, 402, etc., may be served, and transferred to any one of ten positions. By using two switches any one of twenty lines-or trunks may be transferred to any one of ten positions, or alternatively, any one of ten lines may be transferred to any one of twenty positions.

When a call is initiated over one of the lines, say line 355, relays 353 and 554 operate so as to light answering lamp 553 at position 3 over conductor 555, and the busy lamps at all positions are lighted over conductor 556. Assuming that the night key 552 is operated, answering lamp 556 at the position will also be lighted. This isin accordance with cross-connections 4 55 and 556. The answering lamps for line 5553 at position 1, when key 555 is not operated and at position 2 are lighted only on transferred calls. Any position may be cross-connected so as to function as either a primary or secondary position. In response to a lighted answering lamp, the attendants plug into the answering jacks 557, 508 or 555 with a

cord circuit

518, 5 or 5I2, conventionally represented by a box but shown in detail by Fig. 1B, thereby extinguishing the lighted answering lamps. In order'to transfer a call from one position to another, a position transfer key, as 536, 537, 538 or 539, corresponding to the position to which the transfer is to be made is operated. This causes the sequence circuit shown at the bottom of Fig. 5 to function, provided it is not already in use at some other position. In operattransfer trunk 500 with posi ing, the sequence circuit causes a horizontal or selecting

magnet

401, 408, 409 or M0, corresponding to the position to which the transfer is to be made, to be energized and then also a vertical or holding magnet 4, M2 or M3, corresponding to the

line

400, 40l or 402, which is to be transferred. The contacts of switch CB, corresponding to the intersection of the operated vertical and horizontal, are now closed. When the transfer apparatus has completed its operation a signal is given to the attendant by the lighting of the positional release lamp 5l3, M or 515. The operated position key is then released, and when the plug of the cord circuit, which was used to answer the call, is withdrawn from the answering jack, the lamp at the position to which the transfer is to be made is lighted. In the description hereinbefore given, particular reference was made to the line 400 and its associated apparatus. A similar description also applies to the other lines MN and 002. A more complete understanding of the operation of the invention may be obtained by tracing the progress of a call as hereinafter described.

Let it be assumed that an attendant at a distant switchboard desires to initiate a call over the line 000 for the attendant located at position 2, which is accessible to line 400 only as a secondary answering position. Relay 403 operates on incoming ringing current through condenser MA and operates relay 404 through an obvious circuit. Relay 404 locks through its right inner contacts to ground on the left contacts of cut-off, or sleeve, relay M0, and connects battery with its right outer contacts to conductor 500, thereby lighting busy lamps H, M8, 5!!) and lamps at other positions not shown. With its left outer front contacts relay 004 connects battery to conductor M0, thence over cross-connecter 405 and conductor 505 to ground through answering lamp 503, which lights at position 3. The attendant thereat answers by inserting the plug of cord circuit 5l2, that is, plug I03 or the cord circuit shown by Fig. 1-B, into jack 500, thereby closing a circuit over the sleeve conductors of plug I03, jack 509 and conductor 520 through the winding of cut-off relay M5 and the right winding of marginal relay 5H. Relay M5 operates but not relay 5. Relay M5 opens the locking circuit of relay 000, which releases, and connects battery with its right inner contacts to conductor 500 maintaining the lighting of the busy lamps. The release of relay 404 removes battery from conductor M6, extinguishing lamp 503. The attendant at position 3 is now in communication with the distant attendant over line 000, when listening key 100 is operated. On being informed that a transfer to position 2 is desired, position transfer key 538 is accordingly operated, closing thereby a circuit from battery 52! through thewinding of sequence relay 522 to ground on the right operated contacts of key 538. Relay 522 operates, and assuming that neither relay 523 nor 524 is operated a circuit is closed from ground 050 through normally closed contacts of slow releasing relay M9, through winding of relay 020, over conductor 525, through normally closed lower contacts of

relays

524 and 523, lower operated front contacts of relay- 522 and winding of relay 526 to battery.

Relays

420 and 525 operate. Relay 420 in operating closes an obvious circuit through the winding of relay M9 and locks to ground on its own contacts. Relay 0 I 9 operates and disconnects ground M 8. Relay 526 disconnects with its upper inner contacts battery 52! from conductor 52?, thereby preventing the operation of

relays

523 or 524, if an attendant at position 1 or 2 should now attempt to transfer a call; connects ground on its upper outer contacts to conductor 528, whence it is extended through the left operated contacts of key 538, over conductor 529 to battery through the winding of horizontal selecting magnet 008, which is energized. Another circuit is closed from ground through lamp 565, over conductor 530, through upper contacts of relay 022, lower inner contacts of relay 520, over conductor 53!, and through the series connected windings of relay 42! to battery. Relay 02! operates but due to the high resistance of its right winding lamp 5l5 is not lighted. Relay lZl closes a circuit from ground through left inner back contacts of relay 422 to battery through the winding of slow release relay 423, which operates and connects with its left contacts battery 024 in series with resistance 425 to conductor 532, thence through lower outer contacts of relay 520 to conductor 333. Referring now to cord circuit C of Fig. 1-13 the circuit continues through lower outer contacts of operated listening key I00 to sleeve conductor H1, thence over the sleeve conductors of plug I03 and jack 500 through the windings of relays M5 and M1 as herein before traced. Due to the higher voltage of battery 020, marginal relay M! now operates and looks from battery through its left winding and inner contacts to ground on the right outer front contacts of relay H5 and connects ground on its right contacts to conductor 420, thence through winding of vertical holding magnet 4l3 over conductor 42'! to battery on theleft outer back contacts of relay 000. Magnet M3 operates and connects ground with its left contacts to conductor 328, whence the circuit continues through left inner back contacts of relay 429 over conductor'030 and through the right winding of relay 022 to battery. Relay 022 operates and locks through its left winding and inner contacts to ground on the operated contacts of relay 42! and releases relay 023. Relay 423 in releasing connects ground through its right inner contacts and right contacts of relay 022 to conductor 43!, thence through left outer break contacts and right winding of relay 029 to battery on the left outer operated front contacts of relay M1. Relay 029 operates and looks through its left winding and inner front contacts to ground on conductor 020. The left outer contacts and left inner front contacts of relay 029 are arranged so that the latter close before the former break, thereby assuring the locking up of relay 429 before its operating circuit is broken.

When relay 423 released as herein before described it closed a circuit from battery through its right outer break contacts, left outer operated contacts of relay 022 to the junction point between the left and right windings of relay 42L This is equivalent to short-circuiting the right winding of relay 02! and lamp 5E5 now lights, relay 02! holding on its left winding. The attendant now knows that the selection has been completed and releases key 530, which releases relays 522, 520, 020, M9, 02!, 022 and magnet 408. The plug N is now withdrawn from jack 509 which releases relays M5 and M1. Because of the right outer continuity contacts of relay M5 ground is connected to conductor 432, before ground is removed from the left locking winding of relay All. Consequently, relay M1 does not release removing ground from conductor 420 until the locking circuit through the right contacts of magnet M3 is established.

With magnets 408 and M3 operated consecutively as herein before described, contacts 433 of the crossbar switch CB are closed and when relay 4H released a circuit was closed from battery on its left outer contacts over conductor 43G, through contacts 433, over conductor 435 to ground through lamp 502, which lights. Battery is connected to conductor 505 by the right contacts of relay 429, thereby maintaining the lighting of the busy lamps. The attendant at position 2 now responds with the answering plug of cord circuit 5, thereby again operating relay 4! 5, but not marginal relay MI. The operation of relay M5 releases magnet M3, opening the switch contacts 433 and extinguishing lamp 582. As in the case of the'arrangement of Figs. 1, 2 and 3 the attendant at position 2 may now, if such is required re-transfer the call to any other position.

Position 1, (or any other position) as before stated, is arranged to be used as a night position. When key 5534 is operated, battery on the contacts of this key is extended over conductor 533 to the left inner contacts of relay 464 so that when this relay operates on an incoming call over line 4430, battery is connected to lamp 59! over conductor 436, cross-connection 426 and conductor 534. Other lines, not shown. in the same group as line 40!! may be multipled with line 468 over conductor 43'! so that their respective lamps are also lighted on incoming calls. when key 594 is operated. In like manner another night key 535 may be arranged to connect for night answering, another group of lines, of which group, lines 4i and 402 are shown. I

The operation of the arrangement of Figs. 4 and 5 has been described for an incoming call. It may also be used for outgoing calls in the same manner as was described for the arrangement of Figs. 1, 2 and 3. 7

Figures 6, 7 and 8 Referring now to another arrangement of the invention as disclosed by Figs. 6, 7 and .8, the comb nation of Figs. 6 and 7 will now be discussed. In Fig. 6 are shown three intercommunication lines 60!], 6M and 602 which are arranged to cooperate with a cross-bar switch CB similar to that of Fig. 4. The function of switch CE isto cooperate over transfer trunk 7 with positional transfer keys. as for instance, I35, 731, 738 or 139, of Fig. '7, to transfer calls to various positions in the switch board line up. The switch CB is shown with lines 600. 6!!! and 682 connected to function with verticals 1, 2 and 10. respectively. Intervening

verticals

3, 4, 5, 6, 7 and 8 are omitted as being unnecessary for the purpose of thisdescription, and are symbolized by a vertical 9. which is shown unconnected. .Only four horizontals are shown. each of which represents positions, respectively, tion 4 not shown.

Horizontals

5, 6, '7, 8, 9 and 10 are not shown since these are not necessary in describing the invention By means of the switch CB ten lines as 5M, SM, 682, etc., may be served and transferred to any one of ten positions.

By using two switches any one of twenty lines may be transferred to any one of ten positions or alternatively, any one of ten lines'may be transferred to any one of twenty positions. Furthermore, by using an N number of cross-bar switches connected together horizontally there is provided space for ten times N number of trunk.

l, 2 and 3 of Fig. 7. and posi-V circuits to ten positions of switchboard; by using M number of cross-bar switches connected together vertically there is provided space for ten trunk circuits to ten times M positions; and by using N number of cross-bar switches connected together horizontally and M number of cross-bar switches connected together vertically there is provided by the joint arrangement ten times N' The answering lamps for line 68!] at positon 1,

when key 704 is not operated and at position 2 are lighted only on transferred calls. Any position may be cross-connected so as to function as either a primary or secondary position. In response to a lighted answering lamp, the attendants plug into the answering jacks I91. 768 or 799, with a cord circuit Hi3, H! or H2, conventionally represented by a box but shown in detail by Fig. l-B, thereby extinguishing the lighted answering lamps. In order to transfer a call from one position to another, a position transfer key such as 136, 13?, 138 or 139, corresponding to the position to which the transfer is to be made, is operated. This causes the relay control circuit, consisting of positional relays l'ls, H4 and H5 H7 and M3 to function, provided it is not already in use. In operating, the control circuit causes a selecting magnet 681, 663, 589 or 6H], corresponding to the position to which the transfer is to be made to be energized and then also a holding magnet 6H, M2 or M3 to the line 6M, 60! or 602 which is to be transferred. The contacts of switch CB corresponding to the intersection of the operated vertical and horizontal are now closed. When the transfer apparatus has completed its operation, a signal is given to the attendant by the lighting of the positional release lamp H5, 729 or 12!, The operated position key is then released, and when the plug of the cord circuit, which was used to answer the call is withdrawn from the answering jack, the lamp at the position to which the transfer is to be made is lighted. A more tacts of cut-off or sleeve relay 6M, connects bat tery with its right outer contacts to conductor m6, thereby lighting busy lamps I22, 123, and 725 and lamps at other positions not shown. With its left outer front contacts relay 6504 connects battery to conductor i323, thence over crossconnection 665 and conductor 185 to ground through answering lamp 103, which lights at position 3. The attendant thereat answersby and common relaysv 1 I 6,'

corresponding plug I03 of the cord circuit shown in Fig. 1-43 into jack H39, thereby closing a circuit to ground over the sleeve conductors of plug H33, jack HR and conductor through the winding of cutoff relay 6M and the right winding of marginal relay 6l5. Relay 6M, but not relay EH5, operates. Relay GIG opens the locking circuit of relay 6%, which releases, and connects battery with its right inner contacts to conductor Hi6, maintaining the lighting of the busy lamps. The release of relay 5% removes battery from conductors 623 and N35 connected in series, thereby extinguishing lamp 183. The attendant at position 3 is now in communication with the distant attendant over line (SE39, when listening key N36 is operated. On being informed that a transfer to position 2 is desired, position transfer key 138 is accordingly operated, closing thereby a circuit from battery, through the winding of marginal relay 1 it, over conductor l26,through serially connected windings of relay M5, to ground through the right operated contacts of key 138. Relay H5 now operates in this circuit, provided relay H3, H4 or another similar relay, at some other position not shown, is not operated. A discussion of the means whereby the control circuit functions so as to avoid interference, when a simultaneous attempt to transfer a call is made, is discussed hereinafter. Relay H5 with its upper inner contacts short circuits its high resistance upper winding which so reduces the resistance of the circuit that marginal relay H6 operates. Relay H5 continues to hold on its lower winding. Relay i it operated; closes a circuit from ground on its left contacts over conductor 721, through upper outer operated make contacts of relay He, left operated contacts of key 138, over conductor 528, and to battery through winding of horizontal selecting magnet 698, which operates. Another circuit is closed from battery through the right contacts of relay HE, winding of relay ill to ground on the left outer break contacts of relay H8. Relay H'l operates relay H8 in a circuit from ground through the winding of relay H8, operated front contacts of relay l l? to battery on the operated right contacts of relay lit, to which relay H8 locks through its left inner cont-acts. Relay H8 in operating, opens the operating path of slow release relay 'i ii and with its right outer contacts connects battery 729, through resistance 13% to conductor 53 i, through lower outer contacts of relay H5 to conductor 333, which is identical with conductor 333 of the cord circuit of Fig. lB. The tracing of the circuit is now continued through lower outer contacts of listen ing key I86 to sleeve conductor ill, thence over the sleeve conductors of plug Hi3 and jack tee, through the windings of relays 6M and 8H? as before traced. Due to the higher voltage of battery 629, marginal relay EH5 now operates and looks from battery through its left winding and inner contacts to ground on the right outer operated front contacts of relay 6M and connects ground on its right contacts to conductor 658, thence through winding of vertical holding magnet 583, over conductor Ell to battery on the left outer back contacts of relay 5M. Magnet 5&3 operates.

When relay H8 operated and slow release relay 'Hl releases, a circuit is closed with the inner right contacts of relay 158 from battery on the right contacts of relay l l 6 through back contacts of relay 'Hl, over conductor 132 through lower 2,139,800 inserting the plug of cord circuit H2, that is,

inner contacts of relay H5, over conductor 133 to ground through release lamp i2 I, which is lighted, indicating to the attendant that the transferring apparatus has functioned. Key H8 is then released, releasing relays H5 and H6 and in turn magnet 6G8 and relay H8. The plug of the cord circuit is now withdrawn from jack m9, thereby opening the sleeve circuit and causing the release of relays 6M and 655. The original operating circuit of magnet 613 is opened by the removal of ground from conductor 6H5 but magnet 6 l3 remains energized from ground on conductor sit through its left contacts and winding to battery over conductor 5. By reason of the continuity contacts of relay 6 i i ground is connected to conductor 8 i8 before ground is removed from conductor 656 by the release of relay M5, thereby assuring the holding of magnet EH3. A circuit is now closed for lighting lamp H32 at position 2, which is traceable from battery on the left back contacts of relay 6 i 5, over conductor Hi9, through operated switch contacts 629, over conductors 62! and 13 through lamp 502 to ground.

If the attendant at position 2 should delay in answering, the attendant at position 3 may be recalled, relays 603 and 6M functioning as before described to light lamp W3. In this case relay EM is adjusted so that battery is connected to conductor H36, by its right outer contacts before battery is removed from conductor fill by its left outer back contacts, magnet 5H3 remaining operated thus maintaining lamp 162 lighted. When either attendant at

position

2 or 3 answers by plugging into jack m8 with the plug of the cord circuit H l, relay GM is operated releasing relay 6E4 thereby extinguishing lamp E03, removing ground from conductor M8 releasing magnet M3, opening contacts 529 and thereby extinguishing lamp N32.

The means whereby interference is avoided if attendants at different positions attempt to transfer calls simultaneously will now be discussed. When key !38 was operated as before described it was assumed that the common control circuit was not then in use. Suppose, however, that the circuit is being used at positionZ, that the associated relay lid is operated and the upper high resistance winding of relay 7 I4 is short-circuited and connected to ground through the operated right contacts of key 535. Under this condition the two serially connected windings of relay 1 l5 are accordingly shunted by the low resistance lower winding of relay H4. Relay 7 i 5 is marginal under this condition and does not operate. Consequently position 2 encounters no interference from position 3. If key should be operated simultaneously with key E38, relays I Hi and H5 would then operate together. If each relay should close its upper inner front contacts simultaneously and short circuit its upper winding then the individual current flow through the respective lower windings of relays lid and H5 would be so small that these relays would immediately release. If now one of the relays, say relay :7 it should release before relay 1 i 5, then the low resistance shunt on the lower winding of relay H5 is removed and relay H5 holds, and at the same time shunts effectively the two serially connected windings of relay 1 Hi, which continues in the released condition.

Referring now to the alternative arrangement in which Fig. 6 cooperates with Fig. 8, trunks 66E, 5M and fitZ are associated with jack and lamp equipment in Fig. 8, identical with that of Fig. 7. Also, the cord circuits BH, M8 and M9, are the 'contacts to battery on conductor 821.

same as in Fig. 7. However, in Fig. 8, instead of a relay type of control circuit, a control circuit of the stepping switch type is used, which consists of a stepping magnet 88B and associated contact banks 352, 883 and 886. In cooperation with the stepping switch are four relays 805, 886, 887 and 888. When one of the positional transfer keys as 889, 850, 8! I, 8l2 is operated, start relay 885 is operated which causes the control circuit to operate and associate itself with the position from which the desired transfer is to be made. The transferring apparatus of Fig. 6 is then caused to function in the same manner as it did in cooperation with Fig. 7. A more complete understanding of this arrangement of the invention may be obtained from the following detailed description.

Let it be assumed that a call over line 608 causes the apparatus of Fig. 6 to function as hereinbefore described, connecting battery to conductors 188 and 185, lighting thereby busy lamps 8M, 8I5, 8H3 and busy lamps at positions not shown, and answering lamp M3 at position 3. The attendant at position 3 responds by inserting the plug of cord circuit 899 into jack 828. Relay 6M operates, but relay 6E5 does not operate. Lamp tit is extinguished and the busy lamps remain lighted as before described. When the listening key 16 of the cord circuit of Fig. 1B, which shows cord circuit M9 in' detail, is operated communication over line 680 is established. Assuming now that the attendant at position 3 is requested to transfer the call, as in the case of the arrangement of Figs. 6 and 7 to position 2, position transfer key SM is accordingly operated, thereby closing a circuit from battery through the winding of relay 885, over conductor 82 I, through right inner contacts of key 8| l to ground. Relay 885 operates and closes a circuit from ground on its contacts, through left outer contacts of relay 896 to battery through the interrupting contacts and winding of magnet 888. Magnet 800 now causes

brush arms

822, 823, 824, 825 to rotate in the direction indicated, beginning the rotation from any terminal on which by chance they may rest as a result of a previous operation. When brush arm 824 makes contact with terminal 3 of bank 883, corresponding to position 3, ground is connected through the right contacts of key 8H over conductor 826, through said terminal 3, over brush 825 to battery through winding of relay 806, which operates and opens the circuit through the winding of stepping magnet 800, thereby stopping the switch with all brush arms resting on the third terminals. If brush arm 824 should happen to rest on the third terminal as a result of a previous operation then relay 806 would operate immediately preventing any movement of the switch. Relay 886 in operating also connects ground with its left inner contacts to brush arm 823, also resting on terminal 3 of its associated bank 882. The circuit is continued over conductor 83!, through left contacts of key Bl I, over conductor E28, and thence through the circuit before traced in connection with the description of the operation of Figs. 6 and 7. Relay 806 also closes a circuit with its right contacts from battery over conductor 82! through the winding of relay 8M to ground on the left outer contacts of slow operating relay 808. Relay 88! operates and closes a circuit from battery on conductor 82'! through the front contacts of relay 801 and winding of relay 888 to ground. Relay 808 operates, releases relay 801, and locks with its left inner Relay 888 in operating also connects battery 828 through resistance 829 and its right outer contacts to brush arm 825, which is resting on terminal 3 of bank 868, which terminal is connected with conductor 333 which corresponds to conductor 333 of the cord circuit C of Fig. 1B. Marginal relay M5 operates over the sleeve circuit, including sleeve conductor 125, as before described in connection with Fig. '7. This is because battery 8'28 has a voltage higher than that of the regular sleeve battery liB'of cord circuit C of Fig. l-B. All apparatus of Fig. 6 now functions as before described, and contacts 629 of switch CB are closed. A circuit is also closed from battery on conductor 82?! through back contacts of relay 881, right inner contacts of relay 888, over conductor 83 and brush arm 822 through terminal 3 of bank 88! and over conductor 835 to ground through position release lamp 832, which lights. The attendant at position 3 is accordingly informed that the transfer has been completed and on removing the plug of the cord circuit from jack 820, the circuit is completed through lamp 833 at position 2, and the invention now functions as before described. When the key 8!! is released, relays 885, 888 and 8118 release, and lamp 832 is extinguished. If the attendant at position 2 should find it necessary to transfer the call to still another position this can be done by operating the proper position transfer key at position 2, the invention then functioning as in the case of an original call.

Position 1 of Fig. 8 is, like position 1 of Fig. 7,

arranged as a night position, so that, when night key 836 is operated, all calls incoming over line 688 cause the lamp 887 to light. Other lines may be grouped with line 680 so that key 838 is eifective for these lines also.

The operating of the arrangement of Figs. 6, 7 and 8 has been discussed on the basis of calls incoming over trunks 680, GM and 882. This arrangement is also equally well adapted to handle outgoing calls, which may be initiated as described for the arrangements of Figs. 1, 2 and 3 and of Figs. 4 and 5.

In all of the above disclosures, it will be noted that after the incoming signal has been transferred, the attendant at the distant end can, by

' is to be considered as being applicable to lines I00, 408 or 680.

What is claimed is:

1. In a manually operated telephone switching system arranged for providing different kinds of service, a telephone switchboard divided into a plurality of sections, a plurality of two-way circuits for incoming and outgoing messages terminating at said switchboard, a primary signal lamp path and a plurality of secondary lamp paths connected to each of said circuits and respectively having appearances at different sections, a signal lamp in each of said paths constituting an appearance, a cord circuit at each of said sections, a telephone set connectable to each of said cord circuits, means associated with each of said transfer of an incoming call signal to a lamp in 75 any desired secondary lamp path, switching means associated with each of said circuits for automatically completing the transfer of an incoming call signal appearing in one Section to any one of the other of said sections.

2. In a manually operated telephone switching system, according to claim 1, wherein the keyset at each of said sections and the switching means individual to each of said circuits comprising auxiliary circuits arranged to transfer an incoming call signal transferred to a secondary signal lamp to one of the other secondary signal lamps at any other of the other of said sections as desired.

3. In a manually operated telephone switching system, according to claim 1, whereby means are provided for cross-connecting each of said circuits so that any one of said plurality of secondary signal lamp appearances may function as a primary signal lamp.

4. In a manually operated telephone switching system arranged to provide different kinds of service, a telephone switchboard divided into a plurality of sections, a plurality of trunk circuits for incoming and outgoing messages, terminating at said switchboard, a primary signal lamp path and a plurality of secondary lamp paths connected to each of said circuits and respectively having appearances at different sections, a lampin each of said paths constituting an appearance,

a cord circuit at each of said sections, a telephone set connectable to each of said cord circuits, means associated with each of said lamps for permitting a connection between said cord circuit and each of said trunk circuits, a keyset at each of said sections comprising means for initiating and completing in response to a request for a particular kind of service the transfer of incoming call signals to any desired secondary signal lamp, and a cross-bar switch common to each group of ten trunk circuits and a group of transfer trunks interconnecting said cross-bar switch and said keysets arranged to transfer an incoming call signal transferred to a secondary signal lamp to one of the other secondary signal lamps at anyof the other of said sections as desired.

5. In a manually operated telephone switching system, according to claim 4, wherein connections are provided between an N number of said cross-bar switches connected together horizontally for transferring when one of said initiating keys is operated, an incoming call signal received over any one of ten times N number of trunk circuits from one of said primary signal lamp appearances respectively associated with said trunk circuits to any one of ten positions of said switchboard.

6. In a manually operated telephone switching system, according to claim 4, wherein connections are provided between an M number of said cross-bar switches connected together vertically for transferring when one of said initiating keys is operated, an incoming call signal received over any one of ten trunk circuits from one of said primary signal lamp appearances respectively associated with said trunk circuits to any one of ten times M number of positions of said switchboard.

7. In a manually operated telephone switching system, according to claim 4, wherein connections are provided between an N number of said cross-bar switches connected together horizontally and an M number of said cross-bar switches connected together vertically for transferring when one of said initiating keys is operated, an incoming call signal received over any one of ten times N number of trunk circuits from any one of said primary signal lamp appearances respectively associated with said trunk circuits to any one of ten times M number of positions of said switchboard.

8. In a manually operated telephone switching system arranged to provide different kinds of service, a telephone switchboard divided into a plurality of primary positions and into a plurality of secondary positions, a plurality of two-way trunk circuits for two-way messages, each trunk circuit having an appearance in said switchboard at each of said primary and each of said secondary answering positions, primary trunk signals individual toeach of said trunk circuits appearing in each of said primary positions, secondary trunk signals individual to each of said trunk circuits appearing in each of said secondary positions, a cord circuit at each of said sections, a telephone set connectable to each of said cord circuits, means associated with each of said lamps for permitting a connection between said cord circuit and each of said trunk circuits, a keyset at each of said positions for transferring in response to a request for a particular kind of service any signal, primary or secondary, to another of said positions, primary or secondary.

9. In a manually operated telephone switching system, a telephone switchboard divided into a plurality of primary positions and into a plurality of secondary positions, a plurality of trunk ircuits for two way messages, each trunk circuit having an appearance at each of said primary and each of said secondary positions of said switchboard, primary trunk signals individual to each of said trunk circuits, appearing at each of said primary positions, secondary trunk signals individual to each of said trunk circuits appearing at each of said secondary positions, means associated with each of said trunk circuits for selectively actuating the associated trunk signal at any one of said primary or secondary positions, transferring means associated with each of said positions for initiating the transfer of a secondary or primary signal to any selected position, and for initiating the transfer of a secondary or primary trunk signal to any selected position and for causing the functioning of the selecting means aforesaid, a transfer trunk circuit common to all trunk circuits and to all switchboard positions interconnecting said selecting means and said transferring means, and means whereby said transfer trunk circuit is effected for the transfer of only one signal at a time thereby avoiding interference between trunk circuits.

ALLEN RUDOLF BONORDEN.