US2485351A - Automatic telephone system - Google Patents

Description

Oct. 18, 1949. J. l. BELLAMY I 2,485,351

AUTOMATIC TELEPHONE SYSTEM Filed Nov. 2o, 1944 n 1o sheets-sheet 1 1. l. BELLAMY 2,485,351

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AUTOMATIC TELEPHONE SYSTEM Filed Nov. 20, .1944 v l0 Sheets-Sheet 10 Patented Oct. 18, 1949 AUTOMATlG TELEPHONEv SYSTEM John I. Bellamy, Brookfield, Ill., assignor to yKellogg Switchboard and Supply Company, Chicago,.Ill.,.a corporation .of Illinois Application November 20, 1944,.Seral N0. 564,293

30 Claims.

This invention relates to automatic telephone systems. The general Aobject of the invention is the production of a new and improvedline'iinit providing line-finder and connector service for a group of lines, and serving either as a complete telephone exchange or as .one line unit of a telephone exchange employing a desired number of such line units interconnected by one or more selector stages. v

A specific obj ect is to provide new and improve circuit and trunkingarrangements enabling satisfactory service to Ybe afford-ed by the iine unit at a minimum cost in 'control and switching equipment.

Another specific object is to provide afnew` and improved mounting arrangement for the switching and control equipment-of the line unit, enabling all suchequipmentto-be completelypreassembled and interconnected 4on a relatively compact frame 'which can 'be shipped and installed as a unit.

GENERAL DESCRIPTION It has been chosen to illustrate the invention as applied to a uni-t serving one-hundred subscriber lines (including individual lines andtenparty linesiand employing switching equipment and control and trunking arrangements-generally as disclosedin my prior'Paten-t i2,354,660, issued August l, 1944. The switches employedA inthe line unit disclosedi-n this applicationare assumed .however to be of the improved construction .disclosed in my co-pen-din-g application for Automatic telephone switches, Serial No. 524,816, iiled March l, 1944.

THE DRAlZVINGrS- Of the accompanying drawings, Figs. 2l. to 5 are circuit diagramsl showing suflicient of the circuit arrangements -oi the improved 10U-line unit to enable them to be understood;

Fig. 6 is a combined trunking and cabling .diagram showing-the interconnection oi the separate classes 4of apparatus lay-cables carrying the ltrunks and links util-ized in establishing the desired connections to Yand from the lines served by the unit.;

Fig. 7 is a `front view oi the improved 1D0-line unit, showing #the rela-tivelocationsv oiiathezvarious pieces of apparatus mounted .on the front face thereof;

Fig. '8 is a rear viewof .the unit .showing the relative locations of the several pieces of apparatus mounted Yon the rear face thereof.; and

Fig. 9 is a layout. showing the. way. in which the sheets on Whiclif-Figs. l to s5. are'drawn should beassembledl for Ia readyv understanding thereof, f

Figure 1 Fig. l shows one ofthe one hundred lines Y( #I I) served-byy the vunit, together with the individual line `circuit of-such line and vswitching apparatus which may be employed -asline-iinding apparatus toextend such line, When-calling, over a certain one-of several paths to a iincler trunk (FTI). Such finder trunkextends directly to a connector trunk (CTS) when the `unit disclosed serves as the complete exchange. When such unit serves asone unit of a larger exchange employing selectors, the direct connection between the finder trunk and the connector `trunk is removed, and the `finder trunk is extended by way oi" dotted conductors 4Iii-Sto a selector, while the connector trunk is then reached by way 0I dotted conductors i529 incoming fromthe selectors.

The individual linecircuit of the illustrated line #Il includes line. relay IUI, lockout relay I02,.and.cutoffrelay |113. Y A Primary switch IA is one of fty ,line primary switches IA to DE shown in trunking diagram in Fig. 6, and shown locationally in Fig. '7. It is one of ve switches, IA to IE, serving the first- 10- line subgroup, `linesr 11 to l0. Primary switch .IA includes a hold magnet i013 and ten'selectiv-e stackupsof contacts. of which stackupl (through which-the associated line #I I is reached) is one, the nine remaining selective stackups of .the switch being omitted '.for simplicity.

Primary switch IA is accessible .to line-sec-` ondary switch A2, .and others in the same secondary subgroup, by way of the two-way line 'link .LI A. Such link is reached through the illustrated stackup I of secondary A2,` which has nine .otherfselective Istackups, each. ofwhich gives access :to a line link extending to .the .correspondving .one .oi the primary subgroups 2 to Il of Fig. 6.

Fig. l shows also the rst and last of ten subgroups o common .equipment T Gl and TGI). Subgroup 'I'.Gi serves therst ten-line subgroup `(including the illustrated line #.II), while rslibgroup TGll serves the tenth subgroup of lines, including line #00, Fig. 3. The equipment in subgroup TG1 includes subgroup lockout relay I I I, which is operable as hereinafter explained to lock the associated ten lines temporarily out of finder service under -certain conditions; connecting relay I2'I- operable only vduring line-finder action to connect the ten local units leads I.V to, 0 of the iirst ten-linev subgroup to the common units leads UI .to UB connecting relay I 3 I., which is operable both during line-finder action land :during connectorv action to associate the iive primary-:switches serving ythe .associa-ted ten-.line

il subgroup with the line controller of Fig. 5, which controls the operation of the concerned switches during line-finder action and during connector action; and a meter MI which is effective to record traffic data specific to the concerned tenline subgroup.

At this point it may be noted that, for the convenience of manufacture and installation, as well as for the sake of compactness, the equipment illustrated in Fig. 1 as comprising tens subgroup TGI is mounted on a plate shown in Fig. 'l arranged to be mounted opposite the five primary switches lA to IE which serve the associated tenline subgroup, and on which plate are also mounted the three relays IOI to I03 comprising the line circuit of the illustrated line #I I, as well as the nine remaining three-relay groups comprising the line circuits of the nine other lines of the associated ten-line subgroup. The arrangement of each of the remaining tens subd groups TG2 to TG@ is similar.

Fig. 1 also shows the units-select magnets, being the select magnets which control the five primary select shafts 109 (Fig. 7) serving the line primary group of switches. Only the first two and last two (UMI and UM2, UM9 and UMO) of the ten units-select magnets are illustrated in Fig. 1. These ten magnets are controlled over ten units leads UI to U0, by ten units-preference relays UPI to UPU, respectively.

Fig. 1 also shows the first two and the last two of the tens-select magnets TMI to TMll, which control the iive select shafts H0 (Fig. 7) of the secondary group of switches. They are controlled respectively by tens-preference relays l I3I to |40.

Figure 2 Fig. 2, parts 1 and 2, shows the connector CI. to which the connector trunk CTI extends, and

from which the distributor trunk DTI extends 2I2 and 2I3, while the portion of the connector CI shown in part 2 of Fig. 2 includes the tens, units, and party registers TR, UR, and PR.

Of the control relays of connector CI, relay 20| is termed a timer relay, in that it cooperates with the common timer 200 to release the connector Cl at any time when such connector has been held for a predetermined interval (15 seconds, for example) during which no effective use is made thereof, such as dialing or conversation;

Relay 202 is a supervisory relay whose principal function is to reverse the direction of current flow over the incoming talking conductors when the call is answered;

Relay 203 is the line relay, being directly controlled over the calling line in the manner cornmon to connectors;

Relay 200 is the slow-restoring release relay, controlled by line relay 203 to prepare the connector for operation and to maintain the connection;

Relay 205 is the so-called back-bridge relay, being controlled directly over the called line when the call is answered;

Relay 206 is the so-called ringing relay, which is operated under the control of ringing interrupter 24| (Fig. 2, part 2) at the beginning of a ringing cycle to place the connector in ringing condition, and which is restored during the socalled silent interval to permit back-bridge relay 205 to respond when the call is answered;

Relay 201 is the so-called switching relay, being controlled from the line controller of Fig. 5 to effectuate the completion of the connection and to prepare for the ringing of the called line, in the event that the called line has been found to be idle and an idle connection path thereto exists;

Relay 208 is the so-called busy relay, being controlled from the line controller of Fig. 5 to place the connector in busy condition and return a busy-tone signal to the calling line if the called line is busy or if for any reason a connection thereto must be denied;

Relay 209 is the so-called tens-transfer relay, being arranged to operate following the transmission and termination of the impulses constituting the tens digit to prepare for the reception of the units digit;

Relay 2li-l is the so-called units-transfer relay,

, in that it is arranged to operate upon the termination of the units digit to transfer the circuits into condition for the reception of the party digit;

Relay 2li is the so-called chain relay, being included in the preference chain passing through the contacts of similar relays of the other connectors, 1t is arranged to operate at the termination of the party digit to temporarily individualize the connector CI with the line controller of Fig. 5.

Digit registers TR, UR, and PR (part 2 of Fig. 2) are controlled respectively over impulse conductors 223, 224, and 225 to record the tens, units, and party digits in the called number. Each of these registers is preferably an electromagnetic counting device of the type disclosed in my copending application for Electromagnetic counting devices, Serial No. 493,312, led July 2, 1943, now Patent No. 2,441,001, dated May 4, 1948, reissued No. 23,089, March 15, 1949, being illustrated as of the type shown in Figs. 21 to 25 thereof, wherein a single control magnet is provided with a hold winding H, and with an impulse winding I effective to cause the counting contacts to close successively in a wave-like operation responsive to the successive impulses of a series.

Certain features residing in the connector CI of Fig. 2 not brought out hereinbefore include the following:

(1) Release relay 204,: which must be slowacting to enable it to remain operated during successive restorations of line relay 203 pursuant to impulse transmission from the calling line, is rendered capable of remaining operated with a much heavier spring load than it could otherwise carry by virtue of a self-locking circuit therefor through resistor 2I'l, having a resistance sufficiently low to carry substantial current during the time line relay 203 is restored, but insufficient to maintain the relay operated after its momentary slow holding action (residing principally in the diagrammatically illustrated conducting sleeve underlying its windings) has subsided. Additionally, in order to secure a powerful initial energization to give a fast operation, a second winding is provided on relay 204, which is disconnected by contacts E thereof to reduce the holding current for the purpose of economy in power consumption;

(2) As a matter of economy in the number of assenti relays used, tens-transfer relay A 2ll9fiis recperated as-` fa 'party-transfer relay, ipunsuant to which. it is restored: by `contacts 6 of Junits-transfer Vrelay 211.10-,

((3) As a further matter .or economy in the number ofsr-.e'lays used, the units-transfer relay 21|!) is arranged to be restored by hacleebridge relay 205 to act` as a: hingacutol relay, Ato inrevent further operation .oft .ringing relay2' in .the :event that the `called subscriberreplaceshis receiyer ahead of. the calling subscriber;

(4) Further relay economy i-s introduced :by arranging that switching andibcusyfrelays '201 rand 12M, Which are normally operated in the alternative, are -:bothoperated toplace the connect-.Or `in reverting-.call condition, when one :subscriber ion .a panty line -calls anothersubscriber on the fsa-me line;

(5) -rliens`--transfer relay ,2.09 has :a third use. After o'peratingx,.rst as .a tens-transfer relay, and second :as a party-transfer relay, it is employed .asa hang-'up (or ring-start) relay during reverting, calls, restoring upon Vthe replacement of the receiver on th'econcernedline to initiate the rin-ging operation;

(6) Astill further feature is that.; when a reverting call Ais made, no forward connection is ,established :from the connector to the called line, vringing current/being'transmitted .back to the kcalling-:line (Which is then Aalso the called line) over the connection established initially there- :from to thexconnec-tor. This is accomplished by the coopera-tion of busyfrelay 2418 andthe tripleduty tens-transfer relay 2:09 as Will be explained subsequently.. Tins-arrangement makes unnecessary the withdrawing Lof v:a 'further' secondary switchsuch as B l. (Fig. 3.)..and a'turther primary switch such as UB iromserVicewduring theconcerned internal, aswell as insuring :that a reverting-callconnection-will-not fai-l because of a temporary allabusy condition of the terminating trunks .or line links lbetween the connector :and the .called line.

The equipment shownin the lower Vpart fof Fig.

.2, part 2, includes the common .ringing interrupter 24A ,Whichcontrols the 1associ-ated coin ion leads L .and PU and Acontrols the commozione- ,ring and two-ring relays .242 and 24.3. The particular ksystem of party-line ringing illustrated in this applica-tion:A includes live icoinmon'ringing cation `being `made bythe common one-ring relay -242 to the rst i'lve generator leads Gl 4to G15. .Signalling of the la-st ve par-ties on a 10party line `is accomplished by a two-ring application, `by relay 2.43, of the respective frequencies .Fl vto F to the last ve generator leads Gli to G0. A feature of the ringing-interruptor arrangement is that resistors 244 and v245, to which the .ringing lleads Gl to G0 are connected-except during 4actual ,application of ring-ing. current, serve to ldrain the condensers on the called line to prevent `a disagreeable discharge of such condensers into the callingV line upon the subsequent restoration .of ringing relay 206, as will be described more in detail hereinafter. This common arrangement avoids the necessity of provisions individual respectively to `the several connectors, often fused to accomplish the saine result.

Fig. 3 shows switchingapparatus which may be employed to extendl a connection', 'by connector action, from connector C1101 Fig. 2 overa one of several pathsxto one ofthe one hundred lines (#DUL as a calledllne.

The distributor 'DRII of"Fi'g.3\`is onecfthe thirteen distributors DB1 to 'DRlS of Figs. 6V and '1. Each ofthesedistributors is a'three-wire; twenty Apoint switch of the type .disclosed in;imy vpreviously noted application, Serial No."524;816;, having. a circuit` arrangementas shown in Fig.'1"7 of such application. ."lilach such switch has; eleven selectively operable stackups of contacts, lof'vvhich stackups '2 and -II are shovvn in Fig. 3.. For selecting any one ofthe first ten outlets oithe distributoriDEL'the' corresponding one of; its stackupsl to "lis operated Without operation'of stackup '|l.A `When any .one ofthe eleventh to twentieth outlets o the distributor DR'I isfto 'be selected, one oranother stackups lto Il) is actuated, along stackup Il.. For `selection of. the stackup, or stackups, to be operated in one ofthe switches; of the distributor groupe, 'the siX selecting shafts? II of Fig. 'lare provided., "Ihey correspondV respectively tof'the shafts shown in Fig. 1 of thea'bove-noted application (SerialjlNd 52,4;816) .at :Sl-2, Sir-4f, .Si-6, 'Sl-8; ;S9I0, and SI I.

:The distributor lRl has .access to secondary 4switch Bl by way of" terminating trunk TTZ; through its .illustrated stackup 0, secondary switch BI ,has access 'toprimary switch 0B `by.way of the associated line-,link L'UB; and through Aits illustrated stackupv (l, Aprimary .switch UB has access to line #00.

Line, lockout, and.cutoff relays 301.302, andx3`1l3 of the line .circuitassociatedwth line #D0 correspondrespec'tively to relay I 01 to 103' (Fig. .1)

Figure -4 Fig. 4 shows-the twelvedistri'butor select m-a-gnets fDMfl to'DMl 2 which control the select shafts 11H (Fig. 7). MagnetsDMl to IBMIII ycorrespond. respectively to thestacknps l to l0 ofany of the thirteen distributorsi'DRl to 'DRA-3' (Figs. 3, 6, and '7) magnet DM'H corresponds 4to the elevent'lci or switchingstackup of-any one ofthe distributors; andmagnetDMIl is 'an additional magnet employed torotate the sixth selecting" shaft vof the `distributor group lin" the opposite directionA to that in whichA it is rotated lby magnet DMlI. 'Magnet DM'I2 is amagnet not disclosed inmy ,prior application Serial No. 524,816. It :may-be vlocated immediatelyfto the'rightof magnet MII in Fig. 1 of such application, to cause the sixth selecting' tshaft to be `rotatel'lin the' opposite dircction at any *timevvhen selection ofthe eleventh stackup is not to occur.. \".T.he utility of this arrangement. is to secure invariablythe closure of the distributor' olf -normal contacts, DONI l l2, associated With the sixth shaft ol the mechanism. OiT-normalcontactsDONl, 2; DON 3, 4; DONS, 5; DON-1, R; and DONS, 1'0 are associated respectively vvith the first five selectingshafts of the distributor `group.` The off-normal contacts of Fig. 4 `are interwired VWith eachother and with conductors l and 2 in distributor pair DON to cause such-conductors-to be'joined only when one or lanother `of the first veshafts has been ,moved olf-normal, alor-1g Withthe sixth-shaft of the diS- tributor group. v"Thisprovision is utilized in the control of the circuit operations in a mannerto be pointed out subsequently.

Fig.V 4 va1so1=shows` the circuit arrangement of the units-sleeve connector USC and the tenssleeve connector TSC. These two sleeve connect- .ors cooperate during the setting up of a connection from any connector to the called line to connect incoming conductor CLS in cable 552 to the sleeve conductor of the called line, such for example as conductor SII, the sleeve conductor of line` #II (Fig. 1) and conductor S00, the sleeve conductor of line #00 (Fig. 3). The hold magnet of USC is shown at 40|, while the hold magnet of TSC is shown at 402. These magnets are operated over conductor S0 in cable 552 only when the connection being handled by the line controller of Fig. 5 is one involving connector action, as distinguished from one involving linefinder action.

The selective action of sleeve connectors USC andTSC is automatically controlled in accordance with the designation of the called line, for

sleeve connector USC is an additional switch in the line-primary group as shown in Fig. 7, and sleeve connector TSC is an additional switch in the line-secondary group. USC is controlled by select shafts '|09 of the primary group along with primary switches IA to 0E, while TSC is controlled by shafts I I 0 of the secondary group along with secondary switches AI to E5.

enable reverting calls to be handled even though 3 all forward paths be busy between the connector and the called line; and they enable the secondary and distributor switches to be reduced from four-Wire switches to three-wire switches.

Fig. 4 also shows traffic meters 4| to 4 I 9, which are controlled from the line controller of Fig. 5 to record the disposition of each call received by the line controller, according to whether the line controller is called in for nder action or is called in for connector action, and according to whether the received call is disposed of normally or is lost because there is no available path for its completion. record the total calls; 4I3 and 4I4 record the iinder calls; and 4I5 and 4I0 record the connector calls. The rst meter in each pair records the calls received in the concerned category, while the second meter of the pair records the vnumber of such received calls as are lost.

Meters fill to 4I!! are assigned to recording of lost calls, whether finder calls or connector calls, according to the existing trafc condition resulting in the loss, as will be later described.

Figure 5 at which the called number has been completely dialed. It then makes the necessary tests, and directs the extension of a connection to the called line.

The line controller is connected by conductors in cable 55| with the equipment in Fig. 1 and with Of these meters, 4II and 4|2.

the distributor-select magnets of Fig. 4; it is connected through the conductors in cable 552 with the sleeve connectors USC and TSC of Fig. 4; it is connected through conductors in cable 553 with the traffic meters 4II to 4|9 of Fig. 4; it is connected through conductors in cable 554 with each connector, such as CI of Fig. 2; and it is connected, through conductors shown at the top of part 3 of Fig. 5, to each of the twenty-eight line secondary switches shown in Figs. 6 and '7, including secondary A2 of Fig. 1 and secondary BI of Fig. 3.

The line controller of Fig. 5 consists principally of forty-eight relays, 50| to 548. Of these relays, 50| and 502 are employed only for trafficmeter control, relay 50| operating on each call when there is an idle line link in the concerned ten-line subgroup, and relay 502 operating each time there is an idle trunk of the concerned category (under trunk or terminating trunk).

Relays 503 to 501 comprise the connector group, being rendered operative during each connector call, but remaining unaffected during iinder calls. Of these relays, relay 503 tests the busy or idle condition of the called line, over the sleeve conductor thereof to which relay 503 is connected by sleeve connectors USC and TSC (Fig. 4); relay 504 is the so-called idle relay, operated by relay 503 when the called line is found idle; relay 505 is the so-called busy relay, being operated through back contacts of idle relay 504 each time the called line is found busy; relay 506 is the test-cutoff relay, operated each time relay 505 operates; and relay 501 is the transfer relay, which operates in the connector chain to transfer the circuit arrangements of the line controller from under-action condition to connector-action condition.

Relay 508 is the start relay. It operates each time the line controller is called in, whether for finder action or for connector action.

Relays 509 to 5| I comprise a cycle timer, which is operated each time start relay 508 operates. It passes through a timed cycle of operations, which serves to clear out the line controller upon its completion, provided the line controller has not previously cleared out in normal manner.

Relays 5|2 and 5I3 are the clearout and operate relays. Relay 5I3 normally operates to switch the call through. Relay 5I2 normally operates under the control of operate relay 5I3 to clear out the line controller upon the restoration of the latter relay, but operates alternatively from the associated cycle timer or from the connector group of relays under certain conditions.

Relays 5I4 to 5|9 comprise the choice allotter, which responds to each operation of start relay 508 to shift the choice to the next succeeding one of the secondary subgroups A to E. Relay 5l4 is a so-called driver relay, while relays 5I5 to 5I0 are arranged to operate successively in a counting operation as will be subsequently described.

Relays 520 to 525 comprise the matching group. Of these relays, 520 to 524 control the matching in secondary subgroups A to E respectively, subject in each case to there being an idle secondary switch in such subgroup of the concerned category (finder action or connector action), and subject further to there being an idle primary switch in the concerned primary subgroup accessible from Such secondary subgroup. Relay 525 is a so-called reserve-control relay, which operates in a manner to be subsequently explained to permit the use of the last idle Secondary switch in a 9.. 'sibgronpsofthe Vcategorywith` whichthe current call is. 'concerned Relays.' 52I-.tol 530= are. primary test relays,l being controlled? over le adsIPA `to'PElin cable: 55' I I, which leads are connected:I by apparatuses disclosed in Figi. l tothe :respective primary switches A to E intthe primary' subgroup concerned irr any call, finderr action` or connecter'` action..

Relays 53| to 533 are test-control relays.. Ren lay 534i is. operated on each 'finder call: to connect the control leadsot the'fevenenumbered. secondary switches (assigned. to lindern' action.) in. .eachy secondary subgroup to:l respective ones'. of the seconda'ry test relays; relay532 opera-tes on.. each connector' call: to) c'onrrc-ict'theA control. leads.v from the odd-numbered secondary switches (assigned tofconncctor action) respectively tofthe secondary test. relays;` and! relay 53ilffoperates. on each` call to2 disconnect test ground from the secondary test-relays wherr matching hasbeen` elected.

RelaysL 534 13o-5118i are the`I secondary testy relays, eonnectionsto which. are controlled by relays 531- to.533-... Three secondary' tes-t relays. suiice'. for each secondaryv subgroup; inasmuch. asv only three switches of a secondary subgroup are involved? in any one calli. nd'er action ory connector action: as thefcase. may be.. This` arrangement effects' a consid'era'ble.v savii'lg in .secondary test1 relays. as will be appreciated.

Figure* 6 In thezcombined.- trunking and cabling diagram shown inI Eig. 6, it wil ibe: observed that the iif-ty line-primary switches are divided intol ten subgroups of. veswitches each, subgroups I to Il respectively. Eachrsubgroup'of primary switches serves a separatel ten-line subgroup of the 10G- line group served by the disclosed improved line unit.. For. example,.lines II to I0 are served.' by

primary subgroup I.;. lines 2I. to 20: are served by L primary subgroup 2;: and. so forth. The. ten vertical' linesA shownr extending across. the five switches A to. E; of. any primary subgroup repre` sent the ten subscriber lines in the corresponding. teni-line subgroup..

As shown in Fig. 1i, and iniFig, 3,.the conductor pair representing any line maybe attached to the appropriate terminal contacts of theflrst primary switch. in a subgroup', being: connected through the vertically extending. bare-wire bank multiple tothe corresponding: contacts of the other primary switches; yin the same:- subgroup;

Line-linkl cable 501: carries fifty two-way line links: between the respective: primary switches and? the: bank'. multiples of the subgroups A to E into which lthe twenty-eight line-y secondary switches are: divided. There are live. line links for each..primary` subgroup of switches, one such line link for each switch. Theseline links are designated' LILA to LIE- for primary subgroup I; LIZ-Ato L2fEl'for-primary'subgroup 2; and'v s0 forth, to. LQA. to LDE'ior primary subgroup'v 0; The usual primary-secondary spread is employed between'. the primary and secondary switches. Accordingly, th'e ten. links LIA to LGA, extending. to the AP primary' switches. in'. the ten primary sub groups,v :are reached through secondary subgroup the-SterillinelinksLIBto LGB, extending'to the .B switchesin the ten. primary subgroups, are reachedlfvrom. secondary subgroup B.; and so forth; toitheten 'linealinks ILIED to LilE, extending totlfiev E."'switches in theI ten primaryv subgroups, which are reached fromlthe'switches'comprising secondary subgrouirEl Ast noted, each; ofthe primary switches; to'= eethe'r withits associated. line: link', is employed both. .fori n'der actiorr and for-connector action. Onthe other.' hand; each: of th'eisecondary switches is; denitely assigned. to either finder action or connectorfactonr. The: assignment-l arrangement selectedis suchsth'at: the. odd-numbered secondary switches: inl anwsubgroup are employed for con'- nectoif action. while the: even-numbered secondary switchesaref employed for nder action'. The first -ve rlnllerv trunks FTI tol FTE? extend from secondaryfswitclrl' in the: respective subgroups A. to E; 'thezsecon'dzve finder trunks FI'` to FTI'U extend: respectively froml secondary switch- 4 in thef respective secondary subgroups A to E; while the nail three3 finder trunks FTII to FTI-3 extend respectively from secondary switch Iiy in subgroupsvA to\ C?.-

Whenv the unit disclosed. is the complete exchange.; selector cables $06 and 601 are omitted, and local cable: Bilt; is employed to extend iinder trunks .FTP to.: FTIS respectively to connector nectorltrun-k block But, whenl the unit-disclosedis-merelfy one of a-number of similarunits of the exchange, one or more stages of selectors are employedthrough: which originated' callsare routed` to oneor another of. theline units. according. to thel destination of the call... In this event, local. cablev 6.92L is omitted, an'dselector cables 606 and `ISIVI are'installed'.. When used, cable 506 carries theV thirteen lnder trunks FTI to FTl3 to a corresponding number of selectors, while cable ltill, when used, carries thirteen connector trunks, incoming .fromthe vselectors to the connectors by way' of. connector. trunk block CTB.

Instead'V of' a. selector. switching stage as disclosedfinimypreviouslyv noted Patent 21,354,660, the unit. hereini disclosed is particularly adaptedl to cooperatel with". an installation: employing one.l or

f: more'. selector switching. stages of the' improved type. disclosed'in my' co-'pendin'g applicationv for Selector switching; systems, Serial No; 5313949; filed' April 20;.. 1944,. now" Patent No.y 2,400,530; dateds. May 21;. 11946.

From theconnectorA trunk'` block CTB, thirteen connector trunks CTIv to-CTISy extendby way ot cable'rIIlSwto connectors CI= to CI 3, respectively, of which connector CIis shown in detaill in Fig. 2. FromA the co'nnectorsflll to'y CI3g. thirteen disl tribut'or trunksDII-f to DTI132 extend, by way 0l"l cabletmetof distributors DRI to DRI3,frespec tively. Asi-previously' notedeach. of the distributors: is; a tl'iree-wire.` twentybpoint switch, having access to= twenty three-wire outlets. Of the twenty outletsI of the: distributor group, numbers I to I5 are employed, numbers I6 to 20 being unusedi.

The. distributors havel accessv in common to lit-teen terminating. trunks TTI' to TT I5, extending. by' way-"of cable: 605* toy the respective odd-v numbenedi secondary switches. in subgroups A to Theassigmn'ent of the terminating trunks isfsuch) thatthe'irstve terminating trunks TTI to TT5 extendl respectivelyk tot` secondary switches If irr subgroups" A tol E. terminating trunks TTS toaTTlr extend respectively to. secondary switches 3. inifsubgroupsA to: Eg; and terminating trunks TTM4 to" TTI'5: extendl respectively to: secondary switchesY 5 insubgrloupsAi to E.

Itis:to=be1notedathatliteen terminatingr trunksV T'Ill tocy T'I'..I15 are employed.to.4 handle the traiic passing through the thirteen connectors CSI' to (313;. andi the thirteen distributors DR Iu to DRiIS. Consequentlyt. except when.1 one or more' distribu- 'lo tortrunksi maybe temporarily withdrawn from service, as when the secondary switch to which a terminating trunk extends is being repaired, at least two terminating trunks remain idle at a time when the maximum number (13) of connections are established through the connectors CI to CI3. By this arrangement, the likelihood of being able to find an idle path to the called line through one or another of the secondary subgroups and the corresponding primary switch of the called subgroup is greatly increased with a minimum increase in equipment. The only increase in cost represented by an increase in terminating trunks is the cost of the added connector-action secondary switches, switches in subgroups A and E in the illustrated arrangement. It is also clear that the five unused outlets (I6 to 20) of the distributor group can be extended to five additional connector-action secondary switches if desired (one in each secondary subgroup) at a very small cost in equipment, if experience indicates that this is desirable. In this event, the live added connector-action secondary switches would be reached from the dis-V tributor group by way of terminating trunks TTI6 to TT20 (not shown).

Calls extended to the terminating trunks are completed, through the operation of the secondary switches to which such terminating trunks extend, and thence to the respective called lines, by way of line links in cable 60I and primary switches in the concerned subgroups.

Figures 7 and 8 As previously noted, Fig. '7 shows a front View, and Fig. 8 shows a rear View, of an upright frame 100 on which the equipment and wiring comprising the disclosed 10G-line unit are supported. Frame 100 is not shown in complete detail as its specific construction forms no part of this invention. It may be noted that in one physical embodiment of the unit, the frame 100 is of rectangular plan view having overall dimensions: 33 inches in width, 20 inches in depth, and 6 feet, 81A inches in height. Such a frame is conveniently constructed of angle iron sections welded together, with upright members as shown in Fig. 7 providing three columnar spaces for the mounting of face equipment thereon.

The face equipment mounted in the left-hand column of Fig. '7 includes mounting plate 10|, on which the ten units-preference relays UPI to UPB (Fig. 1) are mounted, and ten similar tensgroup mounting plates TGI to TGO, each of which mounts the line-circuit relays and common equipment specific to a subgroup of ten lines.

The layout of the equipment on the rst mounting plate TGI is shown in detail in Fig. 7. Six line-circuit relays are mounted in each of the ve rows provided in plate TGI. The rst three spaces in the uppermost row are occupied by linecircuit relays IOI to |03 of Fig. 1, associated with line #I of the first ten-line subgroup. The three line-circuit relays for the second line of the subgroup may be mounted in the three remaining spaces in the rst row of plate TGI. The second, third, fourth, and fifth horizontal rows on plate TGI may carry the line-circuit relays for the remaining eight lines of the ten-line subgroup. The lowermost row of equipment on plate TGI comprises meter MI and relays I2I, I3I, and III of Fig. 1.

The equipment mounted in the second columnar space in Fig. '1 comprises the primary group of switches, controlled by select shafts 109.

These shafts are supported between rupper and lower brackets 102 and 103, which carry the select magnets and off-normal contacts as disclosed in the previously noted application, Serial No. 524,816. The units sleeve connector USC of Fig. 4 is mounted as the first switch in the group immediately below upper shaft bracket 102, and is followed by the fty line-primary switches IA to 0E.

It will be noted that the ten plates TGI to TGO are each mounted substantially opposite the five primary switches which serve the associated ten-line subgroup, permitting short direct connections from the bank multiples to the respective line circuits, through uniform pre-formed cables.

The equipment mounted in the third column in Fig. 7 includes the secondary group of switches, controlled by the five select shafts 1I0, which extend between upper and lower shaft brackets 104 and 105. Tens sleeve connector TSC of Fig. 4 is mounted as the first switch in the secondary group, immediately below upper shaft bracket 104, and is followed by the twenty-eight secondaryswitches AI to E5.

Immediately below the group of secondary switches, lies the distributor group, `controlled by the six selecting shafts 1II, extending between upper and lower shaft brackets 106 and 101. The thirteen distributor switches DRI to DRI3 are mounted between these shaft brackets.

The remaining portion of the space in the third face-equipment column of Fig. 7 is occupied by fuse panel 108, which carries the required fuses, such as IIO (Fig. 1), through which current is supplied from the ungrounded pole of the exchange battery to the various consuming circuits of the unit.

Connector-trunk block CTB of Fig. 1 is mounted behind the fuse panel 100, as is shown in dotted outline in Fig. 7. This block serves as a xed terminal point for such conductors as extend from csiutside the unit to equipment mounted on gate The equipment mounted at the rear of the frame is shown in Fig. 8. In order to give ready access to the wiring lying between the equipment mounted on the front of the frame (Fig. 7) and the equipment mounted on the rear (Fig. 8), the equipment at the rear of the frame is mounted on the abovenoted gate 800, hinged at 00| and 802 to enable it to be swung out of the way when desired. Connections to the equipment mounted' on the swinging gate 800 include the trunk conductors in cables 603 and 604 of Fig. 6, together with miscellaneous connections such as battery, ground, generator leads, and the like. All such connections are by way of flexible cable conductors.

The uppermost space on gate 800 is occupied by the illustrated mounting plate LC extending entirely across the open space provided by the gate, and carrying principally relays 50| to 548 of the line controller shown in Fig. 5. Of these relays, 50I to 52| are mounted in a row along the top of plate LC; relays 522 to 542 are mounted in a row along the middle of plate LC; and relays 543 to 548 are mounted in the first six spaces along the bottom row on the plate. Immediately following relay 546, ringing interrupter relays 242 and 243 of Fig. 2 are mounted, and these relays are followed in turn by the nine traflic meters 4II to 4I9 of Fig. 4.

The remaining equipment carried on gate 800 comprises the thirteen connectors CI to CI3, of

v13 which CI is shown in Fig. 2. Each connector is mounted on a separate plate, as shown.

The lrelative locations of the relays, talking condensers, and registers of connector CI are shown. Relays 20| to 2|I of Fig. 2 are mounted in the first eleven spaces along the top of the plate, followed by talking 4condensers 2|2 and 2I3. Registers TR, UR, and PR of Fig. 2, part 2, are mounted in a row below devices 20| to 2I3. The arrangement for each of the remaining connectors C2 to CI3 is similar.

The fra-me '|00 as illustrated in Figs. 7 and 8 extends sufficiently to the front and to the rear -to include within its connes all equipment mounted thereon. rSuch a frame may be `fully enclosed vby top and side covers, and by front and rear doors, attached ydirectly thereto.

/I-t -will be observed that the plates on which the yequipment comprising lconnectors CI5 to 'CI3 are ymounted fall -short -of taking up the entire lwidth of gate f800. Where connectors are employed requiring additional equipment, such as a greater number of control relays, Athe length .of the connector'mounting plates may be increased as desired, up to the full width of the gate.

It Awill ybe noted that the unit as disclosed in Figs. '7 and 8 ymalaesno provision for the mounting of common equipment such as timers |42 and 200, ringing interrupter 24|, vgenerators such as 246, ythe current-supply battery, and its charging equipment. It will be understood, of course, that such vequipment is vordinarily provided at a separate location, as on a so-called power board. Where the exchange installation employs a number of 'units such as the one disclosed, and one or more 'groups of selectors, `the power-board equipment is more or less common to all of the units and to the selectors, for which reason it would be an unnecessary duplication to `provide space on .a line unit for such equipment.

DETAILED DESCRIPTION A Idetailed description of the disclosure -wil-l now "be given in conjunction with -a description of -the-operationfo-i the Iapparatus thereof :inestablishing and clearing out connections. For this purpose, it will be assumed that the disclosed unit comprises the entire exchange, in which case selectors are not used, andthe trunks are connected directly with the connector trunks, through a local cable such as `602 (Fig. '6), and as shown at trunk FTI (Fig. 1).

A. Line #11 calls line #00 Operations involved in a ycall from line #Il `as Ashown in Fig. 1 to line #00 as Vshown in Fig. 3 will now 'be described. Each of the illustrated lines #1I and #00 is shown as a party line by the conventionally indicated common connections .extending from the conductors thereof. `One of a possible ten substations on line #II is shown at II5, and one substation on .line is shown at 00|. 'Io make a call, a subscriber at a substation such as on line #II removes his receiver; waits vfor .dial tone; and then .dials the desired three-digit number, .such as number 001.

A1. Marking the calling line When the receiver (not shown) is removed at calling substation I5, :the Ausual direct-current Ibridge is jclosed across the conductors of the calling zline, operating line relay -IOI through contacts of cutoff relay |03. Line relay |0| ygrounds the kassociated sta-rt conductor ST, `common to the ten lines .of the rst subgroup, and it also grounds the associated .units conductor I individual to the calling line.

A2. Tens selection Assuming that the line controller of Fig. 5 is currently idle, the grounding of start conductor ST associated with tens subgroup TGI of Fig. 1, closes a circuit for tens subgroup relays |2| and i3| and start relay 508 in series, as follows: from ground on start conductor ST in tens subgroup TGI, through contacts of relay III, the winding of relay I2 I, lower winding of relay I3I, normally closed contacts of relay I3I, the chained inner-lower contacts of the ten relays to I3I, finder-chain-in conductor F--CH-IN in cable chain contacts 4 of transfer rrelay 501, contacts 2 of clearout relay ,5|2, and thence to battery through the winding of start relay 508. Relays |2I, .|3I, and 500 operate in series over the above-traced circuit. Start relay 508 starts the line controller into operation with results to be hereinafter' described.

At its middle lower armature, relay |3I locks its lower winding directly-t0 conductor F-CH-IN to maintain the above-tracedcircuit intact after the control chain is broken at its inner lower contacts. The chain-end conductor F-CH-END is now isolated to temporarily vpreclude Aoperation cf any further tens subgroup relays, or of relay 501.

Relay ISI connects common control conductors PA to PE in cable 55| to control conductors A to E in tens subgroup TGI, being the respective control conductors of the lprimary switches IA to IE in the nrst primary subgroup. This permits test relays 526 to 530 in the line controller to operate in accordance with the busy or idle condition of the respective concerned primary switches, as will be described hereinafter. Additionally, relay |,3I connects the common meter conductor M to the meter MI pursuant to recordation of the disposition of the initiated finder call.

Finally, at its lower contacts, relay I3| closes a circuit for the associated tens magnet TMI, to effect tens selection in the secondary group of switches, wherein the rst primary subgroup is thereby selected.

A3. Units selection When relay I2| operates over the above traced circuit, it connects the ten units conductors I to 0, associated respectively with the ten lines of the nrst subgroup, to the common units conductors UI to U0, which extend respectively to units-preference relays UPI to UPO. With units conductor I in tens subgroup TGI grounded, units-preference relay UPI is operated .over conductor UI through the illustrated preference chain circuit. Upon operating, relay UPI closes a locking circuit for itself independent of the remaining relays in the chain, and opens the preference chain .to preclude operation of any further relays thereof for the time being. This arrangement prevents two or more units selections from being made in case two or more lines in the same tens subgroup are calling at the same time. At its upper contacts, relay UPI closes a circuit for unitsselect magnet UMI, causing units selection to be accomplished in the primary subgroup of switches, wherein line of the calling subgroup is thereby selected.

A4. Tens and units selections locked The effected tens and units selections are locked in, independent of the continued energization of momentary bridging or grounding of a line.

The tens selection is locked in at the upper contacts of relay |2I, which ground the associated start conductor ST independent of line rclay |I. The units selection is locked in at the inner upper contacts of units-preference relay UPI, which lock the relay to units-lock conductor UL in cable 55|, grounded by contacts 3 of start relay 508.

A5. Finder switch operation As soon as the described tens and units selections have been accomplished, ground is extended to oil-normal conductor PS-ON in cable 55| (through oil-normal contacts SGNI, 2 and PONI, 2) to inform the line controller of Fig. 5 that tens and units selections have been made.

Assuming that primary switch IA and secondary switch A2 shown in Fig. 1 are both idle, these two switches may now be operated by the line controller of Fig. (in a manner to be hereinafter explained) to extend calling line #II to finder trunk FTI. The operating circuit for primary switch IA is from ground applied to conductor PA in cable 55| by the line controller, and thence through contacts of relay I3 I, primary conductor A of subgroup TGI, make-busy contacts |05, and thence to battery through the winding of hold magnet |04 of primary switch IA. Units-select magnet UMI having been operated, the operation of hold magnet |04 results in the closure of the illustrated stackup of switch 5 IA to extend the tip, ring, and sleeve conductors of the calling line to the corresponding conductors of line link LIA. The initial operating ground potential for hold magnet |04 is now applied, through the sleeve contacts of stackup I of primary switch IA, to sleeve conductor S of the multiple associated with the calling line, thereby closing an operating circuit for cutoff relay |03 in series with lockout relay |02. Relays |03 and |02 accordingly operate, whereupon line relay IllI restores because it is disconnected by cutoii` relay |03.

The associated conductors ST and I are thereby ungrounded, but this causes no immediate response, for ground is maintained on each of these conductors (by relays IZI and UPI) by the abovedescribed selection-locking connections.

The operating circuit for hold magnet |335 of secondary switch A2 is as follows: from ground on the associated control conductor CA2 (grounded by the line controller as will be subsequently explained), through make-busy contacts |01, lefthand winding of hold magnet |05, sleeve conductor S of nder trunk FTI and connector trunk CTI, back contact 4 of release relay 204, makebusy contacts 2I4, and thence to battery through the associated resistor. Tens-select magnet TMI having been operated, the operation of hold magnet |06 results in the closure of the illustrated stackup I of switch All, to extend the conductors of line link LIA respectively to the tip, ring, and sleeve conductors of finder trunk FTI and connector trunk CTI.

A moment later, holding ground is placed on the sleeve conductor of the established connection, by the connector CI providing a holding circuit -ior relays |02 and |03, and for magnets |04 and |06. Such holding circuit maintains the connection after the line controller clears out in the manner to be hereinafter described. The

16 clearing out of the line controller causes relays |2I, |3I, and UPI, and magnets TMI and UMI to restore. The holding circuit for secondary switch A2 is from ground on the sleeve conductor of the established connection, through the locking contacts of hold magnet |06 (the so-called offnormal stackup of the switch), the right-hand winding of magnet |06, to battery on lead B of the iinder trunk FTI, supplied through fuse IIO.

A6. Preparing connector C1 for operation The connection has been extended as described, through primary switch IA and secondary switch A2, to connector CI (Fig. 2). In the connector CI, line relay 203 (connected to the incoming tip and ring conductors, through normally closed contacts of busy relay 200 and of supervisory relay 202) operates over the calling line and closes a circuit for both windings of release relay 204 in parallel. Current ow through these two windings provides a powerful initial energization of the release relay, resulting in fast operation thereof.

Upon operating, relay 204 disconnects its upper winding at contact 6 to reduce the holding current. At its contacts 'I, relay 204 applies ground potential to local conductor 2I6, thereby preparing locking circuits for relays 201 to 2I0, closing a holding circuit for registers TR and UR, and establishing an auxiliary circuit for its own lower winding, by way of resistor 2II. At armature 4, relay 204, disconnects the associated idleindicating battery-supply resistor and applies the above-noted holding ground potential to the incoming sleeve conductor S in trunk CTI, such potential being obtained through normally closed contacts of chain relay 2I| and of timer relay 20 I.

At its contacts 8, release relay 204 prepares the impulse circuit for the digit registers, while at its contacts 3, it applies dial tone to the tip talking conductor from the common dial-tone lead DT, by way of contacts of relays 2I0, 209, 201, and 206, and condenser 2|5. The dial-tone signal, thus applied to the calling line, informs the calling subscriber that he may now dial the digits of the desired number.

A7. Setting tens register TR When the calling subscriber operates the dial of his calling device (not shown) in accordance with the iirst digit of the desired number, line relay 203 is restored momentarily a number of times corresponding to the value of the digit. Release relay 204, being slow-restoring, remains operated during dialing. The previously noted auxiliary holding circuit, through resistor 2I'I, is effective to assist the normal holding provisions of relay 204 in maintaining operated the comparatively heavy contact load.

Each time it restores incidental to the dialing of a digit, line relay 203 applies ground potential, through contacts 8 of release relay 204, to impulse conductor 2I'I. During the dialing of the first digit, conductor 2I'I extends through contacts 9 of relay 201, contacts 8 and 1 of relays 2I0 and 209, to branch conductor 223, extending to the impulse winding I of magnet 25| of the tens register TR. Tens register TR accordingly receives from one to ten impulses, depending upon the value of the lrst digit.

In the assumed example, the rst digit is 0, wherefore it is represented by ten impulses. Recording contacts l to 0 of register TR close successively as the impulses arrive, each preceding contact pair opening on the receipt of the next 417 succeeding impulse. Accordingly, contacts of register TR are closed at the end of the first digit 0, contacts I to 9 having reopened successively.

OIT-normal contacts ON of register TR close upon the delivery of the iirst impulse andremain.

closed until the register is cleared out. The closure of contacts ON of register TR occurs with line relay 203 in restored condition during the delivery of the rst impulse of the series. Each time line relay 203 reoperates thereafter during the dialing of the first digit, a circuit is momentarily closed as follows for tens-transfer relay 209: from ground through the left-hand front lcontact of line relay 203, conductor 22|, off-normal contacts ON of register TR, conductor 221, normally closed contacts controlled by armature 6 of relay 209, contacts B of relay 2|0, and thence to battery through the winding of relay 209.

Relay 209 is preferably slow-operating by virtue,

of the comparatively heavy spring load carried thereby, and by virtue of a comparatively inductive Winding. As a result, relay 209 cannot operate during the delivery of series of impulses, for line relay 203 remains operated only momentarily between impulses.

When line relay 203 comes to rest in an operated condition at the conclusion of the dialing of the initial digit (0, in the assumed example), tens-transfer relay 209 operates over the abovetraced circuit. Upon so doing, it closes a local Vlocking circuit for itself at its contacts` 5, at the same time opening its initial circuit to free conductor 22| for further similar control. At its contacts l, relay 209 disconnects dial-tone lead DT so as to terminate the application of the dialtone signal at the termination of the dialing of the rst digit, in accordance with usual practice. At its armature 1, relay 209 disconnects impulse conductor 2|1 from branch conductor 223 of register TR and transfers it to the similar conductor 225 extending to the register UR.

A8. Setting units register UR When the units digit'is dialed, the impulses dclivered to impulse conductor 211 pass over branch conductor 224 (through armature 1 of relay 209 and its front contact), Wherefore units register UR responds as noted in connection with tens register TR to record the units digit 0.

When line relay 203 comes to rest in an operated condition at the termination of the dialing of the units digit, units-transfer relay 2I0 (similar to 209) operates over the following circuit: from ground on conductor 22|, off-normal contacts ON of units register UR, conductor 228, normally closed contacts controlled by armature 1 of relay 2I0, and thence to battery through the Winding of relay 2I0. Upon operating, relay 2I0, vat its armature 1 and associated contacts, locks itself to local conductor 2I6 independent of conductor 228; at armature 8, it disconnects impulse conductor 2|1 from units branch 224 and transfers it to party branch 225, extending to party register PR. At its contacts 9, relay 2li) applies ground potential Ato holdingconductor 226 local to party register PR, registers TR and UR being held over branch 222 of .grounded conductor 2I6. At its contacts E, units-transfer relay 2I0 opencircuits and restoresrthe locked tens-transfer reilay 209, so as to enablethe latter relay to be re- .operated as a party-transfer relay.

A9. Setting the party register PR AWhen the party digit (1) is dialed, `the single .impulse thereof is delivered over branch con- '18 ductor 225 to the party register PR whereat contacts ON and I close.

At the termination of the dialing of the party digit, tens-transier'relay 2-09 is reoperated as a party-transfer relay over 4the following circuit: from ground on conductor 22|, oli-normal contacts ON' of party register PR, conductor 229, and thence to battery through theV winding of relay Upon reoperating, relay 209 does not lock operated, as its locking circuit through its armature Ii and associated contacts has been interrupted at contacts E of relay 2 I0.

A10. Calling in the Zine controller The line control-lier of Fig. 5 is now called in responsive to the closing of a circuit for chain relay 2 ii of the vconnector through contacts 5 of transfer relays and 2li), subject to the line contro-iler being currently in idle condition. This circuit is as follows: from ground, through contacts 5 and i3 of relays 201 and 208, contacts 5 of relays 299 and 2I0, winding of chain relay 2| I, normally closed contacts controlled by armature 5 thereof, chain-end conductor 2 I8 (common to all connectors CI ito vClit), chain contacts on the chain relays of all connectors, including contacts '6 oi' relay 2| I, chain-in conductor CH-IN of cable 550, winding of transfer relay 501 of the line controller, normally closed contacts controlled by armature 5 of relay 501, conductor F-CI-I--END oi' cable 55|, chain contacts of relays such as |40 and I3I, conductor F-CH-IN in cable 55|, chain contacts 4 of transfer relay 501, contacts 2 of clearout relay 5I2, and thence to battery through thewinding of start relay 508. Relays 21|, 501, and `503 operate in series over the above circuit.

At its armature 5 and associated contacts, relay 501 locks itself to the origin point of the chain (through contacts 2 of relay 5I2 and the winding of relay 508) independent of conductors F-CH-END and F-CH-IN in cable 55|, While at its contacts Il, it disconnects conductor F-CH--IN to preclude the operation of any of the finder control relays such as I3I and I2I (Fig. ,1) for the time being.

Relay 501 adapts the line controller for connector action kas will be subsequently described, while start relay 508 initiates the required cycle of operations.

n the connector CI chain relay 2 II, on operating, locks itself .to the associated chain-in conductor .at varmature `5 and its front contact, at the .same .time isolating .its Winding and chain-in conductor CH-'IN from the local chain-end conductor 21B to preclude the operation for the time being of the chain relay in any other connector. At rits contacts L2,.chain relay 2|I locks ground on its yupper winding terminal independent of contacts of relays -205| and y2Ii|1 to insure that relay 2H remains operated until yrestored by the line controller; at its armature .-I and associated contacts, vit disconnects the normally applied source oi holding ground potential from the incoming sleeve conductor vand substitutes ground potential over sleeve lead -SL in cable-554, having to do with the reverting-call `busy test; at its contacts 3 and Ll, it connects switching and busy relaysz201 and;2|l8 respectively: tothe switching and busy lleads ,SW vand BU irl Ycable ,554; and at contacts 1 and 18it`grounds conductors 23| and 232 of the `tens and units register TR and UR, and thereby grounds 'the selected one of the tens conductors 'in cable 241 and the selected one of the units conductors'in cable'243.

19 A11. Tens and units selection In the assumed example, the ground potential applied to conductors 23| and 232 is extended through the closed contacts of tens and units registers TR and UR to tens conductor T0 in cable 241, and to units conductor U0 in cable 248. Units-preference relay UPO operates over conductor U0 to cause the tenth units-select magnet UMO to operate. The upper winding of tenspreference relay |40 is energized over tens conductor T0, wherefore relay |40 is operated without the accompanying operation of relay |30. Relay |40 connects the associated common meter conductor M to the tens group meter M0; it connects common primary control conductors PA to PE to control conductors A to E of the tenth primary subgroup TGI); and at its lower contacts, it closes an operating circuit for the tenth tens-select magnet TMO.

A12. The called Zine is busy If line #00 of Fig. 3 is busy when called, such fact is determined by the line controller of Fig. 5, which thereupon grounds conductor BU in cable 554, closing a circuit through contacts 4 of relay 2|| for busy relay 208. Thereupon, relay 208, at its armature 9, removes ground from holding conductor 222 to permit registers TR and UR to clear out, and closes a self-locking circuit to conductor 2l6, and at its contacts 8, it opens the initial energizing ground connection to chain relay 2| I, leaving such relay locked through its contacts 2.

A moment later, when the line controller opens conductor CH-IN in cable 554 incidental to the clearing out, chain relay 2| I is open-circuited and restored. With contacts 8 of busy relay 208 now open, relay 2| I cannot reoperate when conductor CH-IN is reclosed at the line controller. Since switching relay 201 has not operated, no operating ground potential has been extended to the sleeve conductor S of the distributor trunk DTI, wherefore there has been no forward extension of the connection from the connector CI toward the called line.

At its contacts 2, busy relay 208 connects the common busy-tone lead BT through back contacts I of relay 206, condenser 2I5 and contacts 3 of relay 204 to the tip talking conductor, thereby transmitting a busy signal back to the calling line. The calling subscriber is now expected to replace his receiver to permit the established connection to clear out. Such clearing out is accomplished in a manner similar to that to be hereinafter described.

A13. The called line is idle If the line #00 of Fig. 3 is idle when called, the line controller of Fig. 5 proceeds to match a path thereto from any one of the fifteen terminating trunks such as TT2 and TTIZ of Fig. 3, and to set the distributor select magnets shown in Fig. 4 in accordance with which of the paths has been matched. Assuming that the matched path is by way of terminating trunk TT2 and line link LDB, the distributor selection is such as to cause the illustrated stackup 2 of DRI (Fig. 3) to be selected.

A14. Connector switch operation When the necessary selections have been effected by the line controller,I control conductors CBI and B of the switches BI and 0B (Fig. 3) are grounded along with switching conductor SW in cable 554.

The grounding of conductor B associated with 20 primary switch 0B closes a circuit, through makebusy contacts 300, for holding magnet-301, whereupon the illustrated stackup 0 of such switch is closed, having been selected by magnet UMO (Fig. 1).

Responsive to the placing of ground potential on control conductor CBI, a circuit is closed, through contacts 306, for the hold magnet 305, whereby the illustrated stackup 0 of switch BI is closed, having been selected by magnet UMO (Fig. 1). l

Responsive to the grounding of conductor SW in cable 554, switching relay 201 operates, through contacts 3 of relay 2| I. It closes a selflocking circuit to conductor 2|6 at its contacts 1; it ungrounds conductor 222 at its contacts 8 to permit registers TR and UR to clear out it prepares a circuit for ringing relay 206 at its contacts 6; it opens a point in the initial circuit of chain relay 2II at its back contact 5; and at its contacts 4, it extends the grounded incoming sleeve conductor, through contacts 5 of busy relay 208, to sleeve conductor S in distributor trunk DTI, thereby closing a circuit for hold magnet 304, which includes conductor B (supplied with battery through fuse I I0). Hold magnet 304 now closes the selected stackup 2 of the distributor DRI, thereby extending conductors T, R, and S of trunk DTI, through the back contacts of stackup II and through the three upper pairs of stackup 2 `of the distributor, to the selected terminating trunk TT2, whence the connection extends as illustrated to the called line. The ground potential on sleeve conductor S of distributor trunk DTI is now effective to hold magnets 304, 305, and 301 operated as well as to hold operated cuto and lockout relays 303 and 302 of the called line circuit, such relays having previously been operated over the associated test conductor S00 by the line controller.

A moment later, chain relay 2I| restores responsive to the temporary removal of energizing potential from conductor CH-IN in cable 554, incidental to the clearing out of the line controller. With back contact 5 of relay 201 maintained open, relay 2I| cannot reoperate when conductor CH-IN is subsequently reclosed.

A15. Ringing the called substation Following the described operation of switching relay 201, as soon as the common pick-up lead PU is next grounded momentarily, by ringing interrupter 24| at the beginning of the next ringing cycle, a circuit is closed for ringing relay 206 from lead PU, through contacts 3 of unitstransferrelay 2I0, contacts 6 of busy relay 208, normally closed contacts controlled by armature 4 of relay 206, and contacts 6 of switching relay 201. Upon operating, ringing relay 206 locks itself to locking conductor L in substitution for pick-up lead PU, remaining locked over conductor L throughout the remaining portion of the ringing cycle, at the end of which conductor L is temporarily ungrounded to permit ringing relay 206 to restore temporarily before the next ringing cycle starts. If no response is obtained before the next succeeding ringing cycle begins, ringing relay 20B is operated again when pick-up lead PU next becomes grounded.

As a further result of its operation, ringing relay 206 disconnects conductors T and R in distributor trunk DTI from talking condensers 2I2 and 2I3, and from the windings of back-bridge relay 205, and connects them to the ringing circuit. In this circuit, the tip conductor T is

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