US2405214A - Call distributing system - Google Patents

Description

W 19% D. HOLBROOK ET AL. 2,4053% CALL DISTRIBUTING SYSTEM Filed April 10, 1945 9 SheetsSheet l ss-camm m LIME SWITCHES PRIMARY LIME SWITCHES //0 Flaiz F/aa F/G6 FIG? )NVENTORS B. a HOLBROO/f M ,4. LOGAN ATTORNEY L A T E K O O R B L O H D B .K W H 2 .v R A N t 05 G R 6 I'll! T 0 m M? T. VH A m ,mm C 9 Filed April 10, 1945 B. 0.. HOLBROQK ET AL 29 59 1 CALL DISTRIBUTING SYSTEM Aug. 6, 1945 I 9 Sheets-Sheet 3 m/ NTORS B. 0; HOLE/900K Filed April 10, 1945 M A. LOGAN ATTORNEY Aug. 6, 3946. B. D. HQLQRQOK ET AL- CALL DISTRIBUTING SYSTEM Filed April 10, 1945 S 9 Sheets-Sheet 4 nvvmroks 5; L2 HOLBROOK M A. LOGAN O/WWZQ ATTORNEY B, D. HOLBROOK ET AL CALL DISTRIBUTING SYSTEM Filed April 10, 1945 9 sheets-sheet s inn/5 VTORS HOLROQK LGAN I ATTORNEY r Aug 6, 19% 3,. D. HOLBROOK ETAL CALL DISTRIBUTING SYSTEM Filed April 10, 1945 9 Sheets-Sheet 6' INVENTORS B; 0; HOLBROOK M ,4. LOGAN A TTORNE Y B. D. HOLBROQK EIAL.

CALL DISTRIBUTING SYSTEM 9 Sheets-Sheet 7 Filed April 10, 1945 A'Vl/ENTORS 5. Q. HQLQGK By M ALGA/V A TTORNE Y B. D. HQLBROOK ETAL 9 3 CALL DISTRIBUTING SYSTEM Filed April 10, 1945 9 Sheets-Sheet 8 INVENTORS 0; HOLBROOK M A LQGA/V C. bra/22 A 770E 15 K w I ,B. D. HQLBROOK HAL A$2M= I CALL DISTRIBUTING SYSTEM Filed April 10, 1945 9 Sheets-Sheet 9 I I In Q l Illll INVENTORS B; Q HOLBPOOA By M A. LOGAN 7 CZ/YIQZJ A 7'7'ORNE Y Patented Aug. 6, 1946" OFFICE 2 '1 CALI." DISTRIBUTING SYSTEM Bernard '1). Holbrook, Madison,

and Mason A.

I Application April 10, 1945, Serial No. 587,550

10 Claims. Cl. 179 -18) This invention relates to telephone systems and has for its object increased efiiciency' in call distribution' More specifically, the invention 'con'cerns' the use of -cross bar switches in smalitelephone exchanges designed for use chiefly between members of a business organization and generally known'as private branch exchanges.

' Cross bar switches provide means for connect,- ing any one of a plurality of incoming lines'to any one of a plurality of outgoing lines and are therefore controlled by common control circuits which identify an individual incoming line to be served and an available outgoing line and cause the proper magnets to be operated for connecting the lines together. When the control circuit serves more than one group of incoming lines and a plurality of incoming lines in'aplurality of groups desire service simultaneously, the control circuit first selects a group oflines and then an individual "line to be served, selects an available outgoing line, completes that connection and then serves other lines according to a predetermined arrangement. v

Heretofore control circuits serving a plurality of lines have included one means for identifying the group of lines including a calling line and other means for identifying the line in the group. In accordance with the present invention the same means, comprising a chain of relays, serves to identify the group of lines and the linewithinthe group- The call distributing system embodying the present invention employs primary and secondary switches, with the outgoing lines from one primary switch appearing as incoming lines at the same level of the secondaryswitch. Therefore after the group oflines, inwhich; a callingline is located, has-been determined the select magnet of the secondary switch maybe operated and as soon as the calling line has been located, the select magnet of the primary switch may be operated. Thereafter an idl link between the primary and secondary switches and an idle out- ,going line from the secondary switch may be selected. In accordance with anotherfeatureof the present invention, a check is made to determine that both primary andsecondary switches are ready for operation before selecting an .out-

going line, by including in the circuit, over-which the idle outgoing trunkis seized, contactson the select magnets of both switches.

' In accordance with a further feature of the invention, the outgoing line or trunk is seized by operating the trunk busy relay in the trunk from the control circuit, the trunk busy relay then operating the switch hold magnets to close the switch contacts and connect the calling line with the line relay of th trunk, which upon operating provides an alternate energizing circuit for the trunkbusy relay to place the switches under the control'of the calling line.

f A clearer understanding of the invention may be obtained from a consideration of the following description read in connection with the accompanying drawings in which:

Fig.1 is a diagrammatic showing of the distributing arrangement; Figs. 2 to 9 show the circuits employed in such distribution, Figs. 2 and 3 showing the primary line switch, Figs. 6 and? showing the secondary line switch, and Figs. 4, 5, 8 and 9 showing the control circuits; and

Fig. 10 shows the proper arrangement of Figs. 2 to 9.

Referring first to Fig. 1, the call distributing arrangement shown is designed to serve one hundred'subscribers and to distribute calls from.

.cal' rows the one. hundred lines to twenty trunks or junctors from which calls may be extended by any suitable means. Standard cross bar switches comprise ten horizontal rows of contacts and twenty vertiing connected in multiple. However, in the presentca'se as shown in Fig. 1, the horizontal multiplesare cut so that only five horizontal contacts are connected in multiple. The one hundred lines are divided into ten groups of ten lines eachand the lines are so connected to the horizontal rows that each lin has access to five verticals. To serve ten groups one half standard switch structures are required to constitute the primary line switch. A single switch serves as a secondary switch, its horizontal multiplecut to form five sections, each having fourverticals, The fifty verticals of the primary switch are connected by links to the horizontals of theseconary switch and the-verticals of the secondary'switch are connected to twenty junctors. The arrangement shown in Fig. 1 gives each lineaccessto any junctor. For example, lines I III, I02, etc. are-connected to the horizontal rows of contacts'of the first section of switch structure I00, which may be called th first switch unit and thereforehave accessto links I03 to I01. These links, since they come from the first switch unit, are connected to the first or top level of the units of secondary switchll30, the first link I03 being connected to. the first unit of switch I30, the second link I04 connected to the second of contacts, the contacts in each row beof lines, two and unit andthe junctors 15071413, 154 2, etojanyjone or which may be connected to a calling line. For example line 19! may reach junctor I40 over the first unit of switch 130, link 193, and 7 1311. It may reach junctor l4! over-link I and the third unit of switch [30 and junctor 142 over link and the fifth unit of. switch: I 30. Line I21.

the first unit of switch 1 on the other hand may reach junctor [40 over the.

second unit of switch I20, link I22 and the firstv unit of switch 130, while it may reach junctor I42 over link I23 and the fifth unit of switch I30.

The detailed circuits of Figs. 2 to 9 will now be described. The one hundred lines served by the distributing switches are divided into ten groups often lines each, of which three linesin each of these groups-have been indicated, namely, the first, fifth andlast lines of the first, fifthv and lastgroupsi The. lines have access to fifty links through'aprimary line switch which, as pointed out in connection with Fig. l, is builtup from two and one-half standard twenty vertical switches. The horizontal multiple of the switch is divided to form ten small switch units, each having five sets of. vertical contacts and tensets ofhorizontal contacts, the groups of lines being connected 'to the horizontal sets of contacts and the links being connected to the vertical'sets of contacts. 'However,"the select magnets of the three basic switches are operated simultaneously, creating a unitary fpri'mary switch for serving the entire group of one hundred lines. Three of the small switch units are indicated, including all live verticals but "onlythe three horizontals in which appear the three lines shown.

- As in the case of the primaryswitch, the horizontal multiple of the single secondary switch structure is cut to provide five small switch units, each giving access by means of four verticals to four junctors and accommodating ten links on the ten horizontals. The first, "third'and fifth switch units are indicated, the firstgfifth and tenth levels being shownin each case, thereby showing the termination of the firstythird and fifth link outgoing from the first;fifth and tenth primary swit'chunits. 'All'four junctors of the first, third and fifth groups are indicated.

Assume now that line 200 initiates a. call. When the subscriber removes his receiver from the hook; he establishes "a circuit from battery through themiddle and right windings and contact'4 of relayilfljthrough substation contact 3'and' left winding of relay-2m to ground. RelayZlll whichis atwo-step relay servesas a combined line and cut-off relay, but conventional line and cut-01f relays might be employed instead. Relay 2l0 is energized in the circuit above tracedsuflicie'ntly to take up its'intermediate or "orderi position in" which it closes its front contacts 1- and 6 but-does not open any of the back contacts 2, 3,4 and 5. At contacts 1 and 2, relay-2H! closes a circuit-for identifying the group of lines to which line 200 belongs, while at contacts 5 and 6 relay 2H1 prepares a circuit for identifying-the'position of the line in the group.

For the purpose of locating the calling line, a lock-out chain of test relays 4!!) 'to H9 is provided which is first used to identify thejgroup in whichthe calling line is located and then to loswitch units.

4 cats the position of the line in the group. The group indicating circuit closed by relay 210 may be traced from ground at the back contact of release relay 530, conductor 50!, contact 1 of relay 400, conductor 4M, contacts 2 and 1 of relay 2H3, group conductor 230, contact lei relay 4B2, windingofftest relay 4lll,':;contacts 3 ;'of test relays 414, M9 and the intermediate relays of the series to battery. Relay M0 operates in this circuit,

indicating that the calling. line is in the zero group, andlocking to battery over its contact 4. At its contact 2 it closes a circuit from ground on conductor 50!, contact 3 of relay 4GB, contact 2 of relay A05, contact 2 of relay Mil, contact 2 of relay 402 to the winding of the zero line group relay 4.20 and battery. Relay 42:] operates in this circuit and looks over contact 6 to grounded conductor 501.

With the zero line group relay 420 operated, the zero switch unit 260 in which the calling line appears, has been identified and relay 420 at contacts 1 to 5 closescircuits to test for an idle vertical in that unit. Relay 420 also closes a circuit frorng'rounded conductor 5M, contact '7 ofrelay 420, windingof change-over relay 400 and battery. f v v 7 Relay 400 at contact 1 opens the circuit of relay 4H), causing that relay to release and at contact 3 disconnects ground from the armature of relay 4"), thereby opening the operating circuit for relay 429, which remains operated, being locked directly to conductor 50!. At contact 2, relay M10 closes a circuit from grounded conductor 50!, to'battery through the windings of transfer relays 402, lil3 and 4M in parallel. Relay 402 at contacts l and 2 further opens the operating circuits of relays H0 and 520. When relays 482, 493 and A04 have all operated, a circuit isclosedfrom grounded conductor 50!, contacts 13 of relays 482 and 403, contact 7 of relay 494, conductor 406 to the winding of relay 405 and battery, and over contact 9 of relay 420 and conductor 43!], to the winding of relay 440 and battery.

Relay 440 operates immediately, connecting contacts 6 of the line relays of the first or zero group of lines to the test relays 4 l B to 4 I 9. Since line relay zlll is operated, the operation of relay d-llcompletes a circuit from ground on conductorSBl, extended as above traced to conductor 430, contacts 5 and 6 of relay 2), contact-1 of relay M0, to the winding of test relay M0, contact 3 of the remaining test relays and battery. Relay 4|0 operates and locks to battery over its contact 4, identifying the calling line as the first or .zero line in the group which has be n previduslyidentified as the zero group.

Relay M15 which is slow to operate, does not close its front contacts until after relay MD has operated and locked. When relay 4B5 closes contact 3 it again connects ground to the armature of relay H0; thereby completing a circuit from ground on conductor 50!, contact 3 of relay 495, contact'2 oi relay M0, contact 3'of relay 402 to the windings of select magnets SIG, 320 and 330, to prepare the zero level men of the primary switch-units.

As pointed out in connection with Fig. 1, all of the links outgoing from; one primary switch unit appearin the same level in" the secondary Therefore when line grouprelay 42!) operates it identifies the level which will be used in the secondary switch and it closes a circuit from grounded conductor 501, contact 8 of relay'flfl, conductor 45llto the winding of select magnet 600 and battery, preparing the zero hori-' zontal-in each of the secondary switch units.

It is now necessary to determine which of the links serving the calling line are idle and Whether there is an idle trunk in any of the groups of trunks to which such idle links give access. As previously mentioned, relay 420, when it operated to identify the group of trunks and thereby the switch unit and the group of links serving that group of lines, closed a set of test circuits for that group of links. Whenever a link is busy, the corresponding hold magnet is operated as will be described hereinafter, connecting ground to the associated test circuit. Therefore, when the group relay operates, this grounded test circuit is extended to one of the junctor group test relays 510 to 5M.

Relays M to l4 are two winding relays and provide a simultaneous test of'a group of links and of the trunks to which ,those links have access. The left windings of relays 5) to 5I4 are connected by a line group relay individually to the five test conductors extending to the five primary hold magnets associated with the five link serving the corresponding group of'lines. The right windings of each of the relays 5!!! to 514 are connected directly to a chain circuit extending over front contacts on the hold magnets of the secondary switch unit to which the link circuits tested by their left Winding have access. Therefore a junctor group test relay is operated whenever all of the junctors of the associated group are busy or when it is connected to the test conductor of a busy link having access to that junctor group.

Assume now that the first link 245 is busy with some other line of the group and that all of the junctors 060 to 653 of the third group are busy. With hold magnet 250 operated, when relay 42!! operates, a circuit is closed from ground over the contact of magnet 250, contact 1 of relay 420, conductor 460 to the left winding of relay 5!!) and battery causing relay 5l0 to operate. Whenever the control circuit has been restored to normal, circuits for testing the junctor groups are prepared. Ground on conductor 59! is extended over the normally closed contacts 4 of the junctor test relays 520 to 523 and conductor 502 to the front contacts of the hold magnets of the last junctors in each group. Whenever all of the J'unctors of a group become busy this ground is extended to the right winding of the corresponding junctor group test relay. Under the assumption that all of the junctors appearing in switch 659 are busy, a circuit will be completed from conductor 50! to conductor 502 as above traced and thence over the front contacts of secondary hold magnets 613, 612, 61! and 010, conductor 015 to the right winding of relay 5|2 and battery, causing relay 5|2 to operate. For convenience, assume that relays 5H and M3 are also operated but relay 5 I4 is not operated.

With relays M0 to 513 operated and relay 5M not operated, when relays 402 to 404 are operated subsequent to the operation of relay 420, connecting ground from conductor 50I to conductor 409, a circuit is completed from ground on conductor 406, over the normally closed contacts 8 of the junctor choice relays 800, 802, 904 and the intermediate relays, conductor 900, contacts 2 of relays 5I0, 5| I, M2 and 5l3, contact 1 of relay 5l4, conductor 534 to the winding of junctor choice relay 904 and battery. Relay 904'c1oses a locking circuit for itself over it contact 7 and contacts 8 of relays 802 and 800 and the intermediate junctor choice relays to ground over conductor 406. Thereafter, at its contact 8; relay 904 disconnects the operating circuit for the junctor choice relays from the armature of relay 5l0 so that, if one of the junctor group relays 5|0 to 513 should release because the link or junctor group becomes avail:- able, it cannot be effective to operate another junctor choice relay. At contacts 1 to 5'relay 904 prepares test circuits for the individual junctors of the chosen group and at contacts 9 to 12 prepare circuits for seizing a chosen junctor.

Assuming that junctors H0 and III are busy and thatjunctors H2 and H3 are idle, secondary hold magnets 120 and HI will be operated and magnets 122 and I23 will be unoperated. The operation of relay 904 therefore closes a circuit from ground, connected to conductor 502 over the back contacts of relays 520, to 523 as above traced, "contact 1 of relay 904, to theouter armatures of magnets 120 to 723. Since magnets 120 and ?2l are operated, no circuit will be closed at these magnets but the circuit will be extended over the back contact of magnet 122, contact 4 of relay 994, conductor 542 to the winding of relay 522 and battery and over the back contact of magnet 123, contact 5 of relay 904, conductor 543 to the winding of relay 523 and battery. Relays 522 and 523 look over their contacts 5 to grounded conductor 50! and then disconnect conductor 50! from the above-traced operating circuit, thereby preventing the release of a busy junctor in the chosen group and its associated secondary hold magnet from operating a previously unoperated junctor test relay and interfering with the junctor selection. Relays 522 and 523 also open the junctor group busy circuit controlled by the secondary hold magnet for operating the junctor group relays so that, in the case where only one junctor in a group is idle, the operation of the hold magnet of that juncto-r will not operate the corresponding junctor group relay prematurely.

With the junctor test relays 522 and 523-operalted, a circuit is closed for seizing the first idle junctor. Ihis circuit may be traced from grounded conductor 50l, contacts 4 of relays 520 and 52 I contact 3 of relay 522, conductor 503, contact of operated secondary select magnet 600, contacts of primary select magnets 330, 320 and 310 in series, conductor 340, contacts 1 of relays 520 and 52! contact 2 of relay 522, conductor 552, contact 11 of relay 904, winding of relay 922 and battery.

Relay 922 is the slow-release, junctor busy relay belonging to junctor H2. If the select magnets of both the primary and the secondary switches are operalted, or as soon as they do operate, the circuit above traced is completed and. relay 922 operates. Relay 922 connects ground to the sleeve conductor 732 of junctor H2, in turn operating hold magnet 122. Hold magnet 122 in operating closes cross-point 10L connecting the tip, ring and sleeve conductors of junctor H2 to the corresponding conductors of link 244. The ground which operated secondary hold magnet T22 is extended through the cross-point 101 and over the sleeve conductor of link 244 to the winding of primary hold magnet 254 and battery. Hold magnet 254 operates, closing cross-point 26 l thereby connecting the tip and ring conductors of the link to the calling line 200 and'closing a circuit from battery through the left winding of the junctor line relay 9l2 over the tip conductor of the junctor H2, cross-point'l0l link 244,and cross-point 26d to the substation 200 and back over the ring conductor of the line and contacts 7 of cross-point 261, link 244, cross-point 101 and junctor 11.2 to ground through the right winding of relay 912. Relay 912 closes an obvious holding circuit for relay 922 and originates any operations necessary for extending a connection to a wanted line.

The ground which operated primary hold magnet 254 is extended over cross-point 261 to the sleeve conductor associated with line 200, which is connected to the middle, low resistance, winding of the two-step line and cut-ofi relay 210. The closure of this circuit energizes relay 210 completely, causing it to perform its cut-on function and open its back contacts to disconnect itself from theline. Relay 210 is held operated from the junctor relay 912 which is now held operated under the control of the calling line, relay 912 in turn holding hold magnets T22 and 254 operated. The complete energization of relay 210 opens the circuit of relay 410 permitting that relay to release, in turn releasing select magnets 310, 320 and 330. V

When primary hold magnet 254 operates it closes a circuit from ground at its front contact, contact of relay 420, conductor 404, left winding of relay 514 to battery, since link 244 is now busy. Relay 564 now operates closing a circuit from ground at contact 6 of relay 904, conductor 934, contact 3 of relay 514, winding of release relay 500 to battery. Release relay 500 opens its back contact, removing ground from conductor 501, releasing select magnet 600, relays 420, 440, 400, 402, 403, 404 405, 522, 523, S04 and finally relay 500, which is made slow to release to permit the remaining relays to completely release before reconnectin ground to release conductor 501. Relays 510 to 514 also release, but those which are associated with groups of junctors, all of which are busy, will reoperate as soon as relays 520 to 523 have released.

The foregoing description traced the operation of the control equipment when only a single call required attention. If a lurality of calls are originated at substantially the same time the control circuit will extend them to idle junctors one at a time in a predetermined sequence. For the purpose of describing this sequential operation, assume that calls are simultaneously originated by lines 204, 20 9', 2'10 and 354. Line relays 214, 219, 200 and 38 all operate, each of them closing their front contacts and attempting to complete group identification circuits. Relays 214 and 219 close parallel circuits from grounded conductor 401 to group conductor 230 and the winding of relay 410. duotor 401 to group conductor 234 and the winding of relay 414 and relay 364 connects ground from conductor 401 to roup conductor 319 and the winding of relay 4 I 9. It will be observed that the battery supply for relays 410 and 414 as well as the other intermediate relays is carried over normal contacts Of each of the higher numbered relays. Therefore the operation of a higher numbered relay prevents the subsequent operation of any of the lower numbered relays in the chain, while the operation of a low numbered relay does not prevent the operation of a higher numbered relay. However, the circuit for operating any line group relay is carried over the back contracts of lower numbered relays so (that the subsequent operation of a higher numbered relay does not interfere with the selection of a line group forservice.

Assume then that the group conductors 230, 234 and 319 are grounded very nearly simultaneously Relay 280 connects ground from conbut with sufiicient intervals to permit relays 410,

414 and 419 all to operate and lock; With'relay 410 operated the circuit for relay 420 is closed and relay 420 operates and looks as above described, followed by the operation of relay 400 and relays 402, 403 and 404. The operation of relays 403 and 404 opens the circuits of relays 410, 4 l 4 and 419 and all of these relays release. When relay 440 operates to connect the corresponding group of lines to the test relays, relays 414 and 419 may operate over contacts 5 and 6 of line relays 214 and 219. The operation of relay 405, again connecting ground to the armature of relay 410 completes a circuit over contacts 1 of relay 410 and the intermediate relays, contact 2 of relay 414, contact 3 of relay 403 to the windings of select magnets 314, 324 and 334 in parallel and battery. The operation of selecting an idle link and junctor is the same a previously described after which the release relay 500 is operated and release takes place as previously described. 1A5 soon as relays 420, 400, 402, 403 and 404 release the line group test is repeated, resulting in the extension of line 209 to an idle junctor, after which lines 2'10 and 354 will also be served in turn.

If a subscriber, having initiated a call, abandons it before the line group relay has operated, the line relay and the test relay release and the circuit returns to normal. Since the line group relay locks to grounded conductor 501, means are provided to release the control circuit if the calling subscriber abandons the call after that relay has been operated and before the line has been extended to an idle junctor. For this purpose, when relay 405 operates it prepares'a circuit from battery through the Winding of release relay 500, contact 1 of relay 405 to contact 1 of relay 419. If, because the call has been abandoned, all of the test relays ar in the released condition this circuit extends over contacts 1 of relays 419, 414, 4&0 and the intermediate relays, contact 3 of relay 405 to grounded conductor 501, completing an operating circuit for release rela 500 and restoring the control circuit to normal. If there had been two calls waiting in the group, the abandonment of the one call would permit the second call to be handled and the control circuit to bereleased in the normal manner.

In addition, means are provided to measure a time interval sufficient for the complete operation of the control circuit and to thereupon release the control circuit if necessary, for example, if no idle link and junctor could be found. When a line group relay, for example, relay 420, operates it closes a circuit from ground On conductor 501, contact '7 of relay 420, conductor 401, contact 4 of relay 405, Winding of relay 504 to battery. Relay 504 operates in this circuit, in turn connecting conductor 401 to the winding of relay 505 and battery. Relay 505 operates and locks to grounded conductor 501. When relay 405 operates to initiate the test for an idle link and junctor, it opens the circuit of relay 504 which, however, remains operated for a time because of its slow-to-release character. Normally, relay 500 will be operated, releasing rela 505 before relay 504 closes its back contact. If, however, relay 500 is not operated by one of the above-described methods, relay 504 will finally release and connect ground over its back contact and a front contact of relay 505 to the winding of relay 500, causing that relay to Operate and restore the control circuit to normal. A parallel circuit serves to sound an alarm.

What is claimed is:

1'. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch for each group of lines, a set of select magnets common tosaidprimary switches and a setof hold magnets individual to said switches, a secondary cross bar switch, links connecting said primary switches with said secondary-switch, a plurality of trunks outgoing from said secondary switch, said secondary switch having select magnets and hold magnets, a control circuit common to all said switches, means responsive to the initiation of a call on one of said lines to mark a group conductor and a unit conductor, a set of relays. in said control circuit, means to connect said relays to said group conductors to identify and record the group of the calling line, means to connect said relays to said unit conductor to identify the calling line and tooperate the corresponding primar switch select magnets, means to select an idle link having access to an idle trunk, means to seize said trunk effective only if 7 said select magnets are operated, and means under the control of said seized trunk to operate a hold magnet in said secondary switch and in said primary switch to complete a connection between said callin line and said trunk.

2. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch for each group of lines, a set of select magnets common to said primary switches and a set of hold magnets individual to said switches, a secondary cross bar switch, links connecting said primary switches with said secondary switch, a plurality of trunks outgoing from said secondary switch, said secondary switch having select magnets and hold magnets, a control circuit common to all said switches, means responsive to the initiation of a call on one of said lines to mark a group conductor and a unit conductor, a set of relays in said control circuit, means to connect said relays to said group conductors to identify and record the group of the calling line, means to connect said relays to said unit conductors to identify the calling line and to operate the correspondin primary switch select magnets, means to select an idl link having access to an idle trunk, means to seize said trunk efiective only if said select magnets are operated, means under the control of said seized trunk to operate a hold magnet in said secondar switch and said primary switch to complete a connection between said calling line and said trunk, and means operated by said primary switch hold magnet to release said control circuit.

3. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch, a secondary cros bar switch, a set of select magnets and a set of hold magnets for each of said switches, links connecting said switches, trunks outgoing from said secondary switch, a control circuit common to said switches, means responsive to the initiation of a call on one of said lines to mark a group conductor and a unit conductor, a set of relays in said control circuit, means to connect said relays to said group conductors to identify and record the group of the calling line, means to connect said relays to said unit conductors to identify the calling line, and means under the joint control of said group recording means and said set of relays for operating said switches to connect said calling line with a trunk.

4. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch, a secondary cross bar switch, a set of select magnets and a set of hold magnets for each of said switches, links connecting said switches, trunks outgoing .from said secondary switch, a, control circuit common to said switches, means responsive to theinitiation of a callon one of said lines to mark a group conductor anda unit conductor, a set of relays in said control circuit, means to connect said relays to said group, conductors to identify and record the group of the calling line,-said recording means effective to'operate one of-saidsecondary switch select magnets, means to connect said relays to said unit conductors to identify the calling line, said relays effective to operate one ofsaid primary switch select magnets, and means under the control of said recording means foroperating said switches to connect said callingline with a trunk. 1

5. In a telephone system, a plurality of subscribers lines arranged-in groups, a primarycross bar switch for each group oflines, a set of select magnets common to said primary switches and a set of hold magnets individual to said primary switches, a plurality of trunk'circuits arranged in groups, a secondary cross bar switch for each group of trunks, a set of select magnets common to said secondary switches and -a setof hold magnets individual to said secondary switches,-links connectingeach of said primary switches with each of said secondary switches, a control circuit common to all said switches, means responsive to the initiation of a call on; one of said lines to mark a group conductor and a unit conductor, a set of jrelays in said control circuit, means to connect said relays to said group conductors to identifyand record the group of the calling line, said recording means operating one of said secondary select magnets, means to connect said relays to said unit conductors to identify the calling line and to operate the corresponding set of primary select magnets, said recording'means also efiective to control the operation of said switches to connect said calling line with an idle trunk.

6. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch, a secondary cross bar switch, a set of select magnets and a set of hold magnets for each of said switches, links connecting said switches, trunks outgoing from said secondary switch, a control circuit common to said switches, means responsive to the initiation of a call on one of said links to mark a group conductor and a unit conductor, a set of relays in said control circuit, means to connect said relays to said group conductors to identify and record the group of the calling line, said recording means efiective to operate one of said secondary switch select magnets, means to connect said relays to said unit conductors to identify the calling line, said relays effective to operate one of said primary switch select magnets, means to select an idle link having access to an idle trunk, and means to seize said trunk effective only if said select magnets are operated.

7. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch for each group of lines, a set of select magnets common to said primary switches and a set of hold magnets individual to said primary switches, a plurality of trunk circuits arranged in groups, a secondary cross bar switch for each group of trunks, a set of ,select magnets common to said secondary l1. switches and a set of hold magnets individual to said secondary switches, links connecting each of said primary switches with each of said secondary switches, a control circuit common to all said switches, means responsive to the initiation of a call on one of said lines to mark a group conductor and a unit conductor, a set of relays in said control circuit, means to connect said relays to said group conductors to identify and record the group of the calling line, said recording means operating one of said secondary select magnets, means to connect said relays to said unit conductors to identify the calling line and to operate the corresponding set of primary switch select magnets, means to select an idle link having access to an idle trunk, and means to seize said trunk effective only if said select magnets are operated.

8. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch for each group of lines, a set of select magnets common to said primary switches and a set of hold magnets individual to said primary switches, a plurality of trunk circuits arranged in groups, a secondary cross bar switch for each group of trunks, a set of select magnets common to said secondary switches, and a set of hold magnets individual to said secondary switches, a control circuit common to all said switches, means in said control circuit to identify a calling one of said lines, means to select an idle link having access to an idle trunk, means to seize said trunk, and means under the control of said seized trunk to operate a hold magnet in one of said secondary switches and in one of said primary switches to complete a connection between said calling line and said trunk.

9. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross bar switch for each group of lines, sets of select magnets common to said primary switches and a set of hold magnets individual to said primary switches, a plurality of trunk circuits arranged in groups, a secondary cross bar switch for each group of trunks, a set of select magnets common to said secondary switches, and a set of hold magnets individual to said secondary switches, a control circuit common to all said switches, means in said control circuit to identify a calling one of said lines and to operate one of said sets of primary select magnets and one of said secondary select magnets, means to select an idle link having access to an idle trunk, means to seize said trunk effective only if said select magnets are operated, and means under the control of said seized trunk to operate a hold magnet in said secondary switch and in said primary switch to complete a connection between said calling line and said trunk.

10. In a telephone system, a plurality of subscribers lines arranged in groups, a primary cross loar switch for each group of lines, sets of select magnets common to said primary switches and a set of hold magnets individual to said primary switches, a plurality of trunk circuits arranged in groups, a secondary cross bar switch for each group of trunks, a set of select magnets common to said secondary switches, and a set of hold magnets individual to said secondary switches, a control circuit common to all said switches, means in said control circuit to identify a calling one of said lines and to operate one of said sets of primary select magnets and one of said secondary select magnets, means to select an idle link having access to an idle trunk, means to seize said trunk effective only if said select magnets are operated, means under the control of said seized trunk to operate a hold magnet in said secondary switch and in said primary switch to complete a connection between said calling line and said trunk, and means operated by said primary switch hold magnet to release said control circuits.

BERNARD D. HOLBROOK. MASON A. LOGAN.

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