US2386126A

US2386126A - Telephone system

Info

Publication number: US2386126A
Application number: US471684A
Authority: US
Inventors: Clarence E Lomax
Original assignee: Automatic Electric Laboratories Inc
Current assignee: Automatic Electric Laboratories Inc
Priority date: 1943-01-08
Filing date: 1943-01-08
Publication date: 1945-10-02
Anticipated expiration: 1962-10-02

Description

c. E. LoMAx 2,386,126

TELEPHONE SYSTEM Filed Jan, 8, 1943 s sheets-sheet 1 y Y @Sana Y Ew INVEN'ToR. cLARl-:Ncs E. LoMAx i ATTORNEYS Oct.2, 1945. c. E. LoMAx TELEPHONE SYSTEM Filed Jan. 8, 1943 3 Sheets-Sheet 2 cLARf-:Nce E. LoMAx MVM Men, l

` ATTORNEYS Oct.'2, 1945.` c. E'. LoMAx TELEPHONE SYSTEM Filed Jan. 8, 194s 3 Sheets-Sheet 3 INVENTOR. CLARENCE E. LOMAX 82| 47N w l. ,N .vclam E 95m? 555mm l om @0.02. d? Q53, i am ,H ETI ENTI 10m m. 1 .f f .I J 0! Y 4 t l( .1. am P4 SAV Y ,rf f, f. S om 23 SEZS 82 5mm domgm J! 32H SEH J ATTORNEYS Patented Oct. 2, 1945 `'TELEPHONE SYSTEM Clarence E. Lomax, Chicagm'lll., assigner to Automatic Electric Laboratories, Inc., a corporation of Delaware Application January 8, 1948, seria1`No.471,684

19 Claims.

The present invention relates to telephone systems and more particularly to improvements in facilities for providing conference service intelephone systems of the automatic type.

Conference service facilities are usually providF ed in automatic branch exchanges to enable three or` more parties to be telephonically interconnected at the same time. The usual arrangement for this purpose is that in which each party desired in a conference connection is notified, either I by code, calling or separate communications, to call a predetermined conference number at a designated time. If code calling is used to signal the parties desired ina conference, all parties entitled to conference service will join the conference connection by dialing an assigned conference number. On the other hand, if the party calling the conference desires to include therein only'certain of the parties having conference service, only those parties Willbe'notied on an individual basis.

It is an object of the present invention to provide an arrangement of the character described, wherein improved and exceedingly simple provisions are made for permitting only those parties, desired in a given conference connection to gain access to the conference facilities.

It is another object of the invention to provide an improved arrangement of the character described, wherein only certain lines of the system are ever permitted to gain access to the facilities for rendering conference service.

It is a further object of the invention to provide an improved arrangement for rendering conference service wherein provisions are made for positively preventing more than a predetermined number of parties from gaining access to a given conference connection. l

According to still another object of the invention, the facilities for limiting the number of parties to a given conference connection may be preset in advance of the parties entering the conference connection so that, after all authorized parties have joined the connection, further access to the connection is blocked. l i

According to a still further object of the invention the facilities for limiting the number of parties to a given conference connection maybe automatically preset over any line of the system which is arranged for conference service.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figures 1, 2 and, when laid side byside in .the order named, illustrate an automatic telepehone system provided with `facilities for rendering conference service characterized by the `features of the present invention.

Referring now more particularly to the drawings, the telephone "system there illustrated comprises an-v automatic branch exchange at which are terminated'a plurality of `substation lines Ain cluding the lines Ill, Il and I2 serving the substations A, B and C, respectively. Automatic switching apparatus is provided in the exchange for'setting Aup connections between the various substation lines. This apparatus comprises a plurality ofiinder-selector links, including the link I5, and a plurality of groups of connectors, one, of Which includes the illustrated connector I 6.. More specifically, thender-selector links are arranged in groups, each group being adapted to serve a particular group of lines terminating inthe exchange. Each group of links hasassociated therewith a distributor having the function of assigning idle ones of the links to theuse of calling lines in the associated group in a predetermined order. Thus a distributor I3 is pro- `vided for allotting the link I5 and the other links ofthe same group to the use of calling lines in the associatedline group. This distributor is arranged to be controlled over ai start circuit commonly extendingto 'the various line circuits at which the substation lines are individually terminated,` the three illustrated lines I0, II and I2 being shown as extending to the line circuits IDA, I I A and-I2A, respectively. For the purpose of enabling conference connections to be set up between certain of the lines served by the exchange switching equipment, a conference circuit indicated generally at 20 is provided. This circuit may be seized over the first and second contact levels of the exchange selectors in the manner described below.

Theiinder, selector and connector switches of .the exchange, as well as the line circuits and distributors, may be of any desired commercial construction, although, preferably, the enumer- A"at`ed line selectingswitches are of the well-known Strowger type `and the distributors are` of the well-known rotary type. Each nder is provided with a fourth or special service control path there'- throughwhich is utilized to prevent those lines of the -system which areinot arranged forconferenceservice from gaining access to the illustrated conference circuit 20. Thus the nder ISA is shown as including a fourth Wire path |08 whichextends to the wiper |09 and is utilized to indicate to the selector |B those lines which are not permitted to obtain access to the conference circuit 20.

More specifically considered, all selectors of the system are of the open circuit searching type and are of the.identicalarrangement. Theillustrated selector |'5B is shownas comprising atwo-motion switching mechanism of the Strowger type which includes line and private contact banks arranged in ten levels of ten Contact sets each. In order to facilitate the following explanation pertai'l`A ing to the operation of the system, the .first three. levels of contacts in each of `.thelinelgand.private Vbanks, of the selector |5B have"bee'nshownin Fig. 2 of the drawings. It is ypointed out in this regard that direct multiples are usedto' connect corresponding contacts of the selector .banksol all selectors in the exchange, The Strowge` switching .mechanism of this selector further comprises line wipers =2Iland r22 associated with the contacts forming the line bank of the mechamsm; aprivate o'rtestxwiperZ-S associated with the contacts Vforming `the :private bank of the mechanism; a v.vertical .magnet22l4 operative to move the enumerated .wipersvertically to aposition opposite la desired :level .of bank contacts; a rotary magnet125 operativeto rotate the enumerated wipers intoengagement with'the contactsof a desired'contact set in a selected level; alrelease `magnet z26 which, when energized, permits .the enumerated wipers to be returned .to normal; .vertical 'off-normal springs 21 and 28 .which are operatedwhen the enumerated wipers `are molvedoif normal; eleventh'stepfcam springs .29, |53 and v|54 Vwhich are `*operated 4when the `,enumerated `wipersllare rotated to any eleventh rotary off-.normal position thereof; and 'normal 1posi? Springs .which Vare ;o nly. operated into en- .,gagem'entwhen '.the-,enumeratedwipers are moved to the lrstor. second Vertical olf-.normal positions thereof. Ihe .relay .equipment .of this selector comprises aV switching `relayRl 0.0, ailineor pulsing relay BNQ, a .SlQW-itO-.releaselhold.relay RI 20,

.a slow-to-release transfer .relay Rl 30 and. a huntl ,ing VArelay Bildt); Busy fand .dial .tone .signal cur ,rents may be .delivered Yto connections routed'to the selector, through the busy and dial tone transjforrners y|52 and |.-5,|, respectively.

flvrieily considered, the conference circuit .20, as illustrated in Figs. 2 and 3 ofthe drawings, l, comprises a control channel 2.05 which is accessi- -lole to each selector-of ltheexchange through the .lirst set of outlet contacts .in the rst contact ,level thereof. .Inaddition, `the conference circuit v comprises a talking channel which includes the talking leads iemand 205B of the control chan- .nel 205 and is provided with a number `of branches, which respectively include the conduc- `tors 25|. 2,52, 253 and .250 and commonly include the conductor 210, and respectiyelyterminate at :the ten sets of line ,contacts in the second contact level of each -of the exchange selectors. These ten branches Vof the vtalking channel are normally marked as busy to the selectors over the ten guard leadsZSL 262, 263, etc., 260. For the Kpurpose 'of 'selectively` removing the busy markings from `any desired number of the enulInerated guard' leads',"ten'register' relays, includingtlie `four illustrated relays"R300,"R3|0, R320 and R330, are provided. These relays are arranged to' `be selectivelyenergized undery the controllof a register switch 240 of the well-known rminor type. y Briefly, vthis switch comprises ytwo sets of contacts 24| and 246 of ten points each, Wipers 242 and 241, an operating magnet 243 for driving the

wipers

242 and 241 over the contacts of their associated contact sets, a release magnet 5 244 and a set of oi-normal springs 245. In order to impart a predetermined setting to the register switch 240, under the control of impulses received over thetalking leadS of .thecontrol chan@A nel "32.05, arelayfnetworklis provided which comprises the usual line or pulsing relay R200, a slow-to-release hold relay R2 l 0, a switching relay "R220 and a slow-to-release control relay R230. lor'the'lpurpose of restoring the busy markings .to the Aguard leads 26|, 262, etc., as the Various branches of' the .talking channel are seized in settin'gupaconference connection, a group of ten guard relays,Y including the four illustrated relays R'350jR360fR310 and R380, are provided which ,individually correspond to the different branches of the talking channel. These relays are arranged to beenergized yin .series with the windingsof a commonanswerrelayRMU which functions both asa'battery ifeed relay and as a device for holdingthe switching relay R220 operated.

l'Brieilyxto .consider the operation of the system, it vmay be'assumed thata callintended for .the substationB, forexamp1e, is .initiated at the substation A. .To initiate the call, the calling party .at the substation A removes Ythe receiver vprovided `at :this substation lfrom its' supporting .hook or cradle, whereuponfthe usualcalling loop circuit .including theconductors of the line lll is established between @the substation and the line line circuit :IIIA .operates in .the usual manner to `marlr;.the .callinglineinthe vbanks of the nnders having access thereto and .to impress starting :ground .potential upon v:the start lead extending `to Ythe link distributor .1.3. When this lead s grounded, the nder of the previously assigned .link Aoperates in a welleknown manner to seize vthe calling =li ne. Assuming that the illustrated .link ll5 is utilized nsetting up the connection,

the wipers of the finder .|.5A .are rst elevated .to 4amarked position -opposite'the level of bank contacts terminatingtheggroupof ten lines which includes the calling line 0, following which they .are automatically rotated to .a position wherein .they .engage the contacts terminating the conductors of this line. When the calling line |0 is thus seized the calling loop circuit is extended through the finderlA totheselector portion |5B .of the link-ground potential is impressed upon 4the private conductorof the `calling line for the purpose ofguarding this line against seizure, and

Athe-cutoff relay conventionally embodied in the line circuit |0A is operated to .disconnect the distributor start -lead from ground. In response 't0 this pperain.; lthe..dis/tr.butor `I3 functions to .preselect another idle :one of lits Vassociated links for use in Ahandling the -next initiated call.

. When lthe calling 'loop circuit is extended `through the contacts lll-I and lll-2 'and .the cam springs |53 to include the windingsof the line relay Rill) :and ythe lsecondary winding Of the .dial tone transformer 155| ,the line relay closes its contacts Ato completeanobvous circuit for energizing the 4.l'ioldrel'ay R|20, and the usual dial tone signal is'tran'smitted .to the'calling substation. At

.its contacts lf2, the relay RI lopens .a .point in the circuits for transmitting switch directing m- Pllsesfrtofth?-Vltll magnet. 224# The 11016. relay "R120'now'operatesandclosesits contacts |2| to circuit 10A. 'When .this circuit is completed, the

magnet 25.

thus provide locking circuits Yfor the operated rlays ofthe finder |5A and'theulinecircuit |0A.,

is utilized for the purpose of `directing the selector |5B'in its operation to select anidle connector having access to` the desired line More specifically, Vthe line relay RI I `functions to repeat `the impulses of the first digit to the series connected transfer relay R|3|l and vertical magnet 2t over a circuit which includes the contacts Iii?, ||2 and |22. Upon operating in response to therelease of the line relay RI IE) at the `beginning of the open circuit period of the rst impulse, the transfer relay' R|30 closes its contacts I3I to prepare the operating circuit for the hunting relay RI 40, and, at its contacts |32, opens a point in the operating circuit for the rotary magnet 25. Due to the slow-to-releas-e characteristics thereof, the hold relay RIZD andthe transfer relay R|3il remain operated throughout the series of impulses transmitted to the selector I B. Each time a current pulse is delivered to the rvertical magnet 24 through the break contacts `l I2 of the line relay RI I 0, this magnet functions to elevate the wipers 2|, 22 and 23 one step. It will be understood, therefore, that at the end of the digit these wipers are left standing opposite the level of bank contacts in which are terminated the trunksextending to Vconnectors having access to the desired line I|. Incident to the vertical oir-normal movement of the enumerated wipers, the off-normal springs 21 are closed to prepare the operating circuit for the release magnet 26, and the oir-normal springs 28 are closed to complete a circuit through the contacts |3| and |2| for energizing the hunting relay RMU. rIhis relay, in operating, closes its contacts |4| Ato prepare the operating circuit for the rotary `magnet 25. At its contacts |42, the relay RMU completes a path for short-circuiting the winding of the switching relay Rlll, this path-extending from ground by way of the contacts |01 and |42, the cam springs 29, the winding of RIM) land the contacts |2I back to'ground. At its contacts |52, the relay RIM) also completes a locking circuit for itself, this circuit extending from ground by way of the contacts |01, |42 and 25A, the olf-normal springs 28 and the winding of `Rlilll to battery.

IGA-"ismarked by an absence-of any potential thereon. -In operating, the4 magnet 25 also opens its; contacts 25A to deenergizefthe hunting relay Rlil," `This relay now restores and opensl-its contacts TMI `to deenergize the rotarymagnet 25.

At'its contacts M2, the relayRIlI opens another point in its own locking circuit. Assuming rst v that the test conductor of the trunk I 5Ais` mark- 'Shortly after the rst digit is ended and during the interdigit pause separating the dialing` of this digit and the dialing of the second digit, the transfer relay RISE). releases. At its contacts I3I, the relay RI 30 opens the operating circuit for the hunting relay RMD. At its contacts |32, the relay RISO completes a circuit .through the contacts |2| and |4| for energizing the rotary When thus energized, the magnet 25 operates to rotate the wipers 2|, 22 and 23 into engagement with the contacts forming the first contact set of the selected level, whereby the trunk extending to the first connector of the desired group is selected. If this connector, i. e. the connector IS, is busy, the test conductor of the associated incoming trunk I 6A is marked with ground potential.

On the Vother hand, if this Aconnector is idle, the test conductor of the trunk 1'N5 l Y 1o The rst digit' dialed at the calling lsubstation ed with ground potential, the rotary magnet25, upon yclosing its contacts 25A reenergizes the hunting relay RI 40 in a circuit which includes Y the grounded test conductor of the trunk I 6A, the test wiper- 23, the contacts |05, `the cam springs 29, the contacts 25A, and `.the off-normal springs 28. Inthis regard it will benoted that, if the selected rst connector of the group is busy, the winding of the switching relay Rlil is short-circuited'over the trunk test circuit. In reoperating, the hunting rel-ay RMI] again locks to `ground through its contacts |42 and `recloses the` operating circuit for the rotary magnet 25. This magnet, in operating'the second time, opens its' contacts 25A to again deenergize the hunting relay RMB, and advances the wipers 2| 22 and 23 a second step in the rotary direction, whereby the ,trunk extending to the second connector of the group is selected for test. If the secondconnector of the group is also busy, the hunting relayA RMI] and the rotary magnet 25 cooperate in the manner just explained to advance the enumerated wipers a third step, whereby the third connector of the group is selected for test. More generally considered, these two circuit elements continue tomteract for the purpose of driving the wipers 2|, 22 and 23 across thecontacts of the selected level Iuntil an idle connector of the selected group is found or until these Wipers are operated to the eleventh rotary oit-normal posi- 'I 53 are opened to exclude the secondary windingr of the dial tone transformer I 5| from the calling loop circuit and the cam springs |54 areclosed to include the secondary winding of the busy tone transformer |52 in this loop circuit. Thus, the transmission of the dial tone signal to the calling substation A is terminated, and a busy signal is transmitted to this substation to inform the calling party that the desired connection cannot be obtained. The manner in which the link I5 and the line circuit BA are released when 'the calling party disconnects, will be clearly apparent from the following explanation.

As indicated above, if the rst connector I6 ofthe desired group is idle at the time it is selected, the test conductor of` the trunk IGA is disconnected from all sources of potential, whereby the circuit through the test wiper 23 for energizing the hunting relay RIM) and for shortcircuiting the switching lrelay RIB!) is not prea .circuit which `.extends from #ground yby way .of the contacts 121,-the windingof R100, the-cam springs @20, the .contacts 25A, .the olf-normal springs .1.28, andthe winding of R140 to battery. Since the winding .of the switching Lrelay ,R 1 00 .is of relatively high resistance, the hunting relay :RMD-doesnot operate whenenergizedin this circuit. The `relay lR100, however, operates land Aopensitscontacts |05 to interrupt therpreviously traced :test'circuitrand the path over .which .its covvn -yvinding is short-circuited during a trunk hunting-operation. At'its contacts 101, the relay R100 lopens .-a point-in the previously described circuits for energizing therelays R120, R130 and RIAIl and the'magnets .24, 25 and 26. At its contacts and |02,-the relay R100 deenergizes the line relay R110. and openstthe dial' tone signaling circuit. At its-contacts |03 and 104,:the relay R100 extends the -calling loop circuit by way-of ythe wipers .2 Igand 2 2 andthe talking leads of .the -trunk HAto-the windings of the line relay .conventionally embodied'n the connector 16. This line relay, in operating, energizes an associated hold relay having the function, among others, of `connecting .the test lead of the trunk IGA to ground. Whenthis lead .is connected to ground, .the connector |.6is marked as busyV in the banks of all selectors yin the exchange, and locking circuitsincluding the test wiper 23 and the contacts 1.0.15, are'completedior maintaining energized .the

switching v-relay R100 and the operated relaysof the'nder-'ISA andtheline circuit 10A.

.As indicated above, the line relay R110 is deenergized and -releases in response to the oper- `ation vof the switching relay R100. In releasing, this line relay opens its contacts 1-11 further to interrupt the operating circuit for the hold relay R120 .and closes its contacts |12 to prepare the operating circuit for the release magnet 26. The holdrelay R120, -upon'restoring .opens .-its con- .tacts 12,2;furi-,her to interrupt the circuit for transmitting-,current pulsesitothe transferrelay R130 andtlieivertical magnet 24 in series; and .closes .its 4.g'zentacts 2 3 vfurther to Y prepare the operating circui'tfor the release magnet 25. -Atits' contacts i 1-2|,..the relay R12-0 disconnectsthe release conductor i125 from ground -in the .selector |513, whereby the'release of .the Qperated switchtrain transferred -from 'the vselector .15B `to fthe connector L6.

.The second f digit f of the .directory number` designatingthe-.desired substation B andztransmitted .through A. ,operation of the calling -device provided vat ithe `substation A, -is utilized Iin the connector i5 to select the `group of tenilines in -.which .the `called linerll isiincluded, The third .dgit'tof .the directory number .dialed into thisseonnectorirom the -zcalling substation is utilized :t0 rotate the wipers of :this -Cennector into :engagement with the eonta.cts. terminating the conductorsof the line i111. Immediately -after 4:the third .and .vnal 'digit I.of the `directoriT ,number .has been :dialed into the connector 10,the:controlgeguipmentof .this 4.connector 4function-s toft'est the line! for the :purposeoi :determining the idleor i busy .con- .diti'on thereof. 'If theline testsbusyutheuwm busy tto-ne signal :is ltraiisrnitted, to fthe fcalling substation ,A :to inform the fcalling Asubscriber that `the ldesired connection cannot 'fbe v obtained. In this '.case, no 'further v operai-,ion ci 4the switch- .ingapparatus occursluntil the rcall-fisabandoned .at ithe :calling substation. 'If thecall is .aban- .doned, 'either before .completion or .after a :busy

linefisaseleeted, the connector 1.5,:the link 1.5 and thelline acircuit- IDA-are released in substantially the :manner explainedbelow. AIf .the-.called line tests ridi-e, A.the zcontrol equipment :embodied in "the connector f1.6 .is-.operated ato its .ring-ingsetting, wherein 1 -ground potential is applied to the private conductor of `.the line I 1 .to-mark .this line asibus-y; .-thecutoffrelay of the line circuit 11A isoperatedtofdisconnect the windings of its associated fline'relay fromthe conductors of the line .111.; and interrupted ringing current is transmitted over the conductors of theline to energize:the'ringeriprovided at .the called substation A. .The ringing equipment vof .the-connector 16 also lfunctions during -the ringing .operation .to transmitaringing-current over the calling end of the lconnectienffor the purpose of informing the calling subscriber that `the called substationis being rung. Thedesired talking circuit .between lthe .two substations :A and B is completed when the vvGall is :answered at the latter substation. More particularly, whenthe receiver provided at the called substation is removed from-its supiporting'hook or1crad1e, an answering loopcircuit isncompleted :by way of .the line over which the :ring cutoff relay lconventionally embodied in wtheconnector VH .is energized. This relay, in operating,;opens-the ringing current circuits and completes; atalking circuit which extends through the .link -15 and .the-connector Vv15 andconnects thercalling line -l-0 with the called line 1|.

fPreferably,-the arrangement of 'the control apparatus embodied in the connector 13 isrsuch .that .the release .of the connection is entirely 4under the .control of the calling subscriber. As lthus 'arranged, when -.the-.calling fparty replaces .the :receiver provided at theecalling substation A upon lits supporting :hook or cradleto interrupt .thei'loopfcircuitextend-ing to the connector 16, the .contrDIeQuipment-and the switching mechanismrof =thisconnector-are restored to =norma1 ,in a `manner well understood lin'the art. vInci- Aderrt'to the releasefofthecontrol relays embodied in this :connectorfand 4more speciiically, when theghold relay thereof restores, the test Vconductor of the trunk 116A is disconnected from groundtofdeenergizethe switching relay R Aand .the `operated relays of the nder A15A and .the'jline circuit 10A. When-the operatedfswitchthrough relay -of 4the -nder 15A releases, the Strowger switching mechanism of this'nder is restored .to `.normal Yin the usual manner. Incident to-:the release oftheswitching relay R100, theicontacts zl'lareclosed .tocomplete the pre- .pared'operating .circuit through the contacts `|12 .and |123 and vtheol-norrnal `springs'f2'1 for energ'izingzthe:releasermagnet :26. .This magnet, in operating, attracts :zits associated holding pawl, permitting the wipers 2|, 22 and 23 to be returned.to-rotaryand'vertical normal in the usual manner. V:incident `to the vnormalizing of these ,wipers ,r.the ,off-@normal springs 328 are opened fur- ;.therto interrupt the .operating circuit Vfor the :hunting-relayRlA andthe off-normal springs ,2'1 .are .opened .to vdeenergize .the frelease magnet 26. Following .the release .of lthis magnet, the

-selector /15Bis .'fullyzrestored to-normal. In the event an-.all-trunksabusy condition is encountered "inthe selector v["gand thezcallisf abandoned at 'the callingsubstationsA, theline'relay .R1 10 and the hold:relayR120,are-sequentially released in the-order named'incident .to the .interruption of the callingloopicircuit. `In thiscase, the release `.conducto-r .|25 .is .disconnected from ground to .effectlthe releaseiof A.the ndenlSAand the line .circuit 10A .whenthe .holdrelay R120 opens .its

75..contacts 12|- .In.releasing,.this.relay alsocloses its contacts |23 "to energize the release magnet 26, whereby the wipers 2|, 22 and 23 are restored to normal. Incident to the normalizing of these wipers theu off-normal springs 21 and 28 are opened; the cam springs V29 and |53* are closed; and the cam springs |54 are opened. At the offnormal springs 2l', the release magnet 26 is deenergized in an obvious` manner.

In considering the facilities provided for rendering conference service, it is pointed out above that only certain of the substations served by the exchange are permitted to gain access to the conference circuit 20. In the usual branch exchange system, this type of service is limited to the executives and department heads of the organization served by the exchange.v For the purpose of preventing those substations of the system not entitled to conference service from gaining access to the conference circuit 20, special wiring of the line circuits respectively associated therewith is used. In order to explain how this is accomplished, the type of special wiring utilized is shown in conjunction with thel line circuit |A terminating the line l0 for illustrative purposes only. It will be noted that in thisline circuit the special service contact |0d of the contact set at which the conductors of the line I0 are terminated is connected directly to ground, so that when the wipers of the nder |5A, for example, are positioned to engage the contacts of this contact set, the special service path |08'through this iinder is terminated at ground. Inthis regard it will be recalled from the preceding explanation that each time the wipers 2|, 22 and 23 of the selector |5B are elevated to a position opposite-the iirst or second contact levels thereof the normal po-st springs 30 are moved into engagement. Itis also noted that these normal post springs are reopened if the enumerated wipers are positioned opposite any contact level above the second contact level of th'associated bank. With the normal post springs 30 engaged, a circuit including these springs, the, special service path |08, the wiper |09 and the special service contact 0d, is provided for holding the switching relay RI 00 short-circuited and for continuing the energization of the hunting relay RMO, indopendently of the potentials applied tof the test wiper 23 during rotary movement of the wipers 2|, 22 and 23. Accordingly, these wipers will, under the circumstances described,`be rotated to the eleventh ofi-normal positions thereof, regardless of the idle or busy condition of the control channel 205 or the Various branches of the talking channel embodied in the conference circuit 20. When' these Wipers are moved to the eleventh rotary ofi-normal positions thereof, the cam f springs 29 are opened to arrest the 'rotary stepping movement; the cam springs |53 are disengaged t0 terminate the dial tone signal; and the cam springs |54V are moved into engagement to transmit a busy signal to the substation attempting to obtainv access to the conference circuit 20. This signal serves to inform the calling party that the desired connection cannot be obtained.

Aiter receiving this signal, the calling party may release the link in the manner explained above.

In the line circuits which terminate the lines extending to substationsthat are to have conference service,Y the connections between the special service contacts of the finder banks and ground are omitted. Accordingly, when such a substation attempts to seize the conference circuit through one of the links` such, for example, as the link I5, closure of the special servi ice :path at the normal post springs "30is'not effectiveto prevent the' selector of the link from seizingeither the control channel 205 or th various `branches of the talking channel embodied in the conference circuit 20. Thus it will be apparent that, depending upon the Wiring of the lineI circuits individual to the various substations of the system, any desired ones of these substations maybe prevented from obtaining conference service without in any way impairing the ability of the other substations to utilize the conference facilities.,` f i In considering the manner in which conference connections utilizing` the conference circuit 20 may be setup, it may be assumed thatlthe party for whose usethe substation A is provided is entitled to conference service and desires to hold a conference with threeotherpersons, two of Whom are served bythe substations B and C, respectively. In order to inform the desired persons that aconference is to be held at a specied 'ti1ne,. the party at the substation A may utilize the automatic switching equipment of the exchange to call the three desired persons for the purpose of informing them of the time set for theconference. The `manner in which the variousconnections are set up for this purpose is exactly the same as explained above withireference to the routing of a call from the substation A to the substation B. 1 i v Shortly before `the 'time set forthe conference, the person at theV substation A who has called the conference, may seize the conference circuit 20 through one of the links of the exchange over the control trunk 205 and set the register equipmentcomprising the switch 240 and the register relays to indicate the number of substations that are to join the conference connection. Any one of the finder-selector links of the exchangemay be utilized for the purpose of permitting the person who has called the conference to gain access to the conference circuit 20 over the control trunk 205." Assuming that the illustrated link I5 is utilized for this purpose, a single digit of one impulse is dialed into the selector portion I5B of the link by the calling party.` This digit is utilized in `the manner explained above to position the wipers 2|, 22 and `23 on the contacts `terminating the conductorsof the control trunk 205. With the conference circuit 20 idle, the test conductor 205C of this trunk islmarked by an absence of ground potential; whereby 'the switching relay R|00 is permitted to operate and thus effect the switch-through operati'orrof the selector |5B. Incident to'this operation, the calling loop circuitis extended by `way 'of the talking wipers 2| and 22 and the talkingconductors 205A and .205B'of the trunk 205 tothe line terminals of the line relay R200. When the windings of the line relay R200 arethus'included in the calling loop circuit, this relay closes its contacts 202 to complete an obvious circuit forV energizing the slow-to-release hold relay R2|0. 'At its contacts 20|, the Vrelay R200 opens a point in the circuit for transmitting impulses through the series connected windings of the control relay R230 and the magnet 2143.V The hold relay R2|0, upon operating, closes its contacts2|2 to connect the test conductor 205C to ground, whereby the conferenceoircuit is marked as busy in the banks of the exchange selectors, and locking circuits are provided for the operated relays of the selector |5B, the iinder |-5A and the line vcircuit |0A. At its contacts 2| I, the relay R2| 0 opens a point in -the operating circuit for the release magnet 244. At

its contacts2`l3, the relay-R210 prepares the circuitfor transmitting impulsestothe relay YR230 andthe-magnet 243; At its contacts 21|4, the relay R210 completes az path, including the condenser 2.03. and the contacts226; for. transmitting a. special tone signal current over the. calling end` of the; connection. This current as reproduced by thezreceiver provided at the: calling substations servestoinform the calling'partythat the desired connection with the conference circuit 20has-been made.

Upon receiving the special tone signal, the calling partyat the. substation A.. dials into-the conferencecircuit 20a digi-t; the' numerical value ci which, indicates the number of; lines that are to join. the conference connection. In;thepresent case, wherein it isassumed thatthree linesother, thanthe: line` I areto. be. included in; the connection,. theA callingr party will dial the digit 3 as the. second digit.A of; the'v conference. number; The; line relay R200 inreleasingrduringithe opencircuit period of each impulse in thisdigit; func'- tions toransmit threecurrent pulses-tothe series connected; windings of thewcontrol relay R230 and the operating magnet-.2431. Upon operating'at-the beginning, of thef open-circuit period: of. the iirst impulse. in this digit,v the; relay R230. opens its contacts 23|, thereby tmprevent theswitching re.- layRZ-ZD from being prematurely energized. Due to the slow-to-release characteristicsithereof, the relaysR-hl and- R230.: remain; operated throughouttheadigit. Each;timea.current pulse is trans.- mit-ted tmthey magnet 2.43,. this. magnet operates to=advance the wipers 2l42and 24'kone-step.y Accordingly; at therend. of-.thef digit.. the wipers 242 and,V 24?! arei left; standing: in engagement with their associated. third; contacts. Incidentl tothe oir-normal movement.. of; the;` wipers. the. off, normar springs 2.45 are-.moved-int'o;engagement to prepareathe; operating circuit ior the switching relayY R2 20.:

1 Ati thee endy off the.I digit;l the; line; re1ayfR200 is` heldienergizedi iny the. calling? loop circuit, thereby. tofdeenergize-thecontrol relayR-23|)-andftormain.-l tainthe f hold relay- R210 in; itsgoperatedz-,positionz Accordingly, the re1ay-R23liv is. caused to restore shortly-'after the -digit isxended: Inf releasing; .this relay` closes@ itsfcontactsa 2 3-| to.;v complete the -preapared circuit-through the.- of'mormal .springs 2115l` fon'energizing.` the switching relayrR2f20i, This switching; relayupon operating opens; its contacts- 226: toiinterrupt thefcircuitiforf transmitting the:- specialV tonesignal. current .overfthe conne-c.- ticn: tothe, calling.v substation rand thusf terminate. thessignal being transmitted toA the: oalling:party: At itsl contacts 225|-,Y the relay` R220: prepares a loekinggcircuitfon itself.. At its contacts 225, thet relay-R2 20.opens the'circuit fontransmitting cur.- rent pulsesi to: the series` connected: windings of: the relayi R230; and? the: magnet. 243,. thereby-f to prevent. further operation ofthemegisteiV switch` 2.411?.- intheevent the.f calling: device at the;rsub stationA .isz inadvertently.freoperated-ion theihookz on cradlefswitchiseflashed at this substation; At itscontactsg2`2l and. 22.2 therrelay R220fconnects` thee commonportioni of: the talkingchannel prof` videdfin the conference circuitto thebranches Atits contacts 224, the relayfR220, uponv operi ating, completes a circuit for energizing. in series the threeregister relays corresponding to the first three branches of.' they talking channel in the order of their termination in the line contact banks ofi the second levels of the various-selectors. Morer specifically, the relays R300, R3|0 and R320 are, in the present case, energized in rcsponser tothe operation of the switching relay R220; the circuit for energizing these relays extending from ground by way of the contacts 22l|fy the wiper-242 and its engaged third contact, the seriesv connected windings of the. relays R320, R310y and R300, seven units of the resistor R and? the wiper 241? to battery. Each of the three energized register relays,` in` operating; removes guarding ground. potential from its associated guard lead.. Thus the relay R300;A upon operating, opens its contacts 30| to disconnect the guar-d lead. 26.1:Y from. ground` and. thus render the rstrbranchi of' the talking'channel through the-conference circuit 20 accessible to the selec'- tors of; the exchange. Similarly, the-.relays R3|0 and R320, in openingtheir contacts' 3H. and 32| to disconnect' the two guard leads- 262" and 263 from ground, render the second and third branchesof the talking channel accessible to the selectors of the exchange. Following. the operation Otthethree enumerated register relays no further operation of the equipmentV provided in the yconference circuit20- occurs'until connections are extended toi this circuit from the substaticns that are. to-join. the conference connection.

In order for the'persons who have beennotified oi-` the connection to gain. access to the conference cricuit, it is necessary for each such person. to initiate a call athis substationv and dial thef digit 2 intok the selector of the particular link utilized in. handling the call. From a1 consideration of.' theA selector ISB it will be understood-f that; if.' this link isseized from the substation B,. for example. and the digit 2 is l dialed. thereinto; the; Wipers off the selector will beoperated to engage.- the contacts forming the first contact set of. the second'. level. following which thei selector; will'` switch through. This is true for the reason that". guarding; ground' po-v tential. has been removed from. the guard lead 26|` at the contacts 30| ofthe operatedlregister relay R300.. Accordingly, if the rst answering cal1.isoriginated at the'substationB and routed through one of; the links tothe iirst` branch of the-talking channel` provided in the. conference circuit 20, the callingV loopv circuit as setv up through the link in.y use to the conference circuit 20s is extendedbyway offthe conductors'25'l and 2l0tofinclude in seriesthe two windings of the of;y this;channe1r.whichrespectively extend; to. the'.

iirstl tostenth .talking contacts of the= terncontact sets forming the secondleve1;infthe3linerbankzo the.. selector ISB, A's; previously.' indicated; suit-- able multiples are. provided; whereby the; ten' branches; of the; talking channel are aisoirenfdered accessiblea t all? of' the: selectorsf. of: the;

exchange:

answer. relay R390: and. the winding of the guard relay R350. When thus energized the` guard relay.; R350-closes its contacts 35| to connect the guard. 1ead.,26| to ground and thus mark the rstbranch ofr the talking channel as busy in the banksof the exchange-selectors. Also, when this lead is connected to ground,v circuits are `provided for. maintaining energized the operated relays of thelink in` use and the cut-off relay of the linecircuit HA; The answer. relay R390 also operates whenenergizedlin the loop circuit connecting the` substationB with the conference circuit 20, and closes itscontacts 39| to complete the prepared locking circuit for the switching relay R220.

With the first branch ofthe talking channel through the conference circuit 20 occupied with thefansweringicall' as originated at the substavanswer relay R390.

tion B, the call next initiated at the second substation to join the conference will be extended to include the second branch of the talking channel, for reasons clearly apparent from the above explanation. More specifically, with the first branch of this channel marked as busy through the contacts 35| of the guard relay R350, the selector of the j link occupied with the second call will necessarily operate to select the second branch of the talking channel, since this will be the iirst idle branch tested during rotary movement of the selector. When this branch is seized, the guard relay R360 is energized in the calling loop circuit in series with the windings of the In operating,4 this guard relay closes its contacts 36| to `impress guarding ground potential upon the guard lead 262, whereby the second branch of the talking channel is rendered nonaccessible to the exchange selectors and suitable locking circuits are established for maintaining energized the operated relays of the link occupied with the call.

In a manner similar to that just described, the third and only remaining idle branch of the talking channel is seized from the third substation to join the conference through the banks of the selector occupied with the call originating at the third answering substation. Incident to the seizure of this branch of the talking channel, the guard relay R310 is'energized in series with the windings of the answer relay R390 and closes its contacts 31| to impress guarding ground potential upon the third guard lead 263. With the three relays R350, R360 and R310 operated in the guard relay group and only the three relays R300, R3|0 and R320 operated in the register relay group, all ten branches of the talking channel through the conference circuit 20 are marked as busy in the banks of the exchange selectors over the guard leads 26|, 262, 263, etc., 260. Thus, other parties trying to obtain access to the conference circuit for the purpose of eavesdropping are blocked against seizure of any of the branches of the conference talking channel.

As each substation joins the conference connection in the manner explained above, a talking circuit is completed between this substation and the substation A, Thus the common branch of the talking channel as directly connected to the conductors of the line |0 extending to the substation A, includes the talking conductors 205A and 205B of the control trunk 205, the contacts 22| and 222, and the condensers 204 and 206. Talking battery is supplied to this circuit through the windings of the line relay R200. The first branch of the talking channel, i. e. that connected to the first of the called substations to join the conference connection, includes the common conductor 210, the branch conductor 25| and the by-pass condenser 350d shunting the winding of the guard relay R350. The second branch of the talking channel as extended to the second called substation to join the conference connection includes the common conductor 210, the branch conductor 252 and the by-pass condenser 3600i shunting the winding of the guard relay R360. Finally, the third branch 'of the talking channel as connected through one of the links of the exchange to the third called substation to join the conference connection includes the common conductor 210, the branch conductor 253 and the by-pass condenser 310a shunting the .winding of the guard relay R310. Talking battery is supplied to all three of these branches of the talking channel of the conference circuit 20 through the windings of the answer relay R390.

The release of the conference circuit 20 is partially under the control of the calling party at the substation A and partially under the control of the three called parties who joined the conference. Thus itwill be noted that as the three connections extending to the three called substations, includingthe substationsB and C, are released, the corresponding guard relays R350, R360 and R310 are deenergized and restore to disconnect their respective associated guard leads 26|, 262 and 263 from ground. When the last of these connections is cleared out, the answer relay R390 `is also deenergized and releases.` This relay, in restoring, opens its contacts 39| to interrupt the holding circuit for the switching relay R220.

When the connection as extended from the calling substation A to the conference circuit 20 over the control trunk 205 is released at this substation, the line relay R200 and the hold relay R2 l0 are sequentially released in an obvious manner. VThe relay R2|0, `upon restoring, opens its contacts to disconnect the test conductor 205C of the trunk 205 from ground and thus eect the release of the link through which the connection was extended to the control trunk 265 from the calling substation A and the release of the line circuit |0A, all in the exact manner previously explained. At its contacts 2|I, the relay ,RZIO completes a circuit through the contacts223 for energizing the release magnet 244. This magnet, upon operating, attracts its associated holding pawl to permit the

wipers

242 and 241 to be restored to normal. Incident to the release of this switch, the off-normal springs` 245 are opened to interrupt theoperating circuit for the switching relay R220.

From the above explanation it will be understood that the switching relay R220 is only deenergized when the connection extending to the calling substation A and the three connections exstoring, the switching relay R220 'opens its contacts 223 to deenergize the release magnet 244. At its contacts 224, the relay R220 deenergizes the three series connected register relays R300, R3|0 and R320. These three relays, upon restoring, close their contacts 30 3|| and'32l, respectvely, to again impress guarding ground potential upon the three guard leads 26|, 262 and 263respecn tively. Following the release of these three relays the conference circuit 20 is fully restored to normal.

l'rom the above explanation with reference to the operation of the conference circuit 20 it will be apparent that normally, i. e. when this circuit is not occupied with a conference connection, all ten branches of thetalking channel are marked as busy in the banks of the exchange selectors; It will also be apparent thatV the register switch 240 and the ten register relays R300, R3IU, etc., constitute register means which may be present over any calling one of the lines entitled to conference service, to indicate the number of lines that are subsequently to gain access to the talking channel of the circuit. The setting of this register apparatus is determined entirely by the numerical value of the digit transmitted to the conference circuit over the control trunk 205. Thus, if a digit 8 is dialed into this circuit from a calling one of the substations, the register switch 240 will be operated to its eighth off-normal position to effectl the energiz'ation ofeight of the-series connected register relays with the result'thatY the rst eight branches of the talking channel are unguarded and renderedaccessible to the exchange selectors. Similarly, if a digit comprising siximpulses is dialed-intol theconference circuit, the register apparatus functions to unguardfthe'rst six branches of: the talking channel, leaving the remaining four branches guarded'against seizure.

In this connection it is pointedA out that the wiper 241and contact set 246, acting-inconjunction with the resistor R, iunctionto insure the same magnitude of current flow through the series connected windings of the register relays, regardless of the number of relays included in the circuit. To this end, each of the nine sections of the resistor R is chosen of a value equal to the winding resistanceof each register relay. Accordingly, it` only'the winding'of-the-rst registerrelay R3i is included inthe series energizing circuit, all ninesections of the-resistor R are included in the circuit toA limit the magnitude ofk current flow in ,the circuit. Again, if the switch 24U is operated torinclude the windings of'. four. register relays in the series energizing circuit, six sections of the resistorR are included in the circuit to establish the same magnitude of 'current flow in the circuit. By virtue of this arrangement, overheating of the coils of the register relays when only afew or one of these relays is to be energized, is prevented;

It willv yalso be apparentr from the preceding eXplanation'that, as each unguarded branch of the talking channel is seized through one of the exchangev selectors, its associated guard relay operates to return the busy marking to the associated guard` lead. Accordingly, when all of the branches of this channel that have been un'- guardedthrough operation of the register rapparatus have been seizedrthrough the selectors of the exchange, guarding potential is restored to the associatedv guard leads through operation of the respective associated guard relays.

While one embodiment of. the invention has been disclosed, it will be understood that various modifications may be made therein which are within the true spiritv and scope of the invention.

What is claimed is:

f1. In a telephone system, a plurality of lines a group of which are arranged for conference service, apparatusfor providing conference con'- nections between the lines of said group, and prese-ttable means controllable over any line of said group prior to the setting up of' a given conference connection for preventing more than a predetermined number of lines of saidv group from gaining access to said given conference connection.

2. In a telephone system, a plurality -of lines a group of which are arranged for conference service, apparatus for providing conference connections between the lines of said group, presettable means controllable over any line of said group prior to the setting up of a given conference connection for preventing more than a predetermined number ofthe lines` of said group from gaining access to said'given conference connection,v and means whereby all of said' lines other than the lines of said group are at all'times prevented from gaining access to said circuit.

3. In a telephone' system, a plurality of lines a group of which are arranged for conference service, apparatus for providing conference connections between the linesof saidl group, pre'- settable means controllable over any line of' said message group prior totheA 'setting up off a conference connection-'for indicating the number of lines that are togain access to the connection; and meansfffor preventingy more than the indicated number of the lines ofsaid group from gaining access ton the' connection.

4. In a telephone system, a plurality of lines a groupof which are arranged for conference service, apparatus for providing-conference connections between the lines of said group, presettable means controllable over any line of said group prio-r tot the setting up of a conference connection for" indicating the number of lines thatare to gain access to the-connection, means for preventingv morethan the indicated number ofi thelines or` said group from gaining" access to the connection, and means whereby'all or said lines'other than the linesiof said'group are at all timesA prevented fromy gainingaccess to said circuit.

5. In anA automatic telephone system which includes automatic switching apparatus for setting up connections between the lines of the system; a conference circuit including means providing aI talking channel which is accessible through said apparatus tothe lines joining a conference, and' means presettable bef-ore each conferenceV connectionl is established for preventing mo-re than a' predetermined but variable number of lines from' obtaining access to said talking channel through said apparatus.

6. In an automatic telephone system which includes automaticv switching apparatus for setting up connections between the lines of the system; a conference circuit including means providing a talking channel which is accessible through said' apparatus to the lines joining a conference, register means having a plurality of different settingsv designating diierent numbers of` lines that may obtain access'to said talking channel, means controllable throughsaid apparat'us' froma calling point for imparting. a predetermined' setting to said register: means, and means controlledinaccordance with the'setting of said register means for preventing more than the designated number of lines fromV obtaining access toV said talking channel.

7. In a telephone system which includes a plurality of lines and automatic switching apparatus for setting up connections between said'lines, se lectors accessible to'said. lines and provided with outlet contacts arrangedingroups; a conference circuit including a talking channel accessible to said lines through the'contacts of said selectors which form one ot said' groups, and presettable means controlled through contacts in another of said groups for preventing more than a predetermined-but variable number or lines from obtaining access to said talking channel through the selector outlet contacts-of said one group.

Y 8. In a telephone system which includesa plurality of linesI and automatic switching apparatus for. setting up connections between said linesy selectors accessible tosaid lines and provided with ing Vchannel through the selector outlet contacts of said one group.

9. In a telephone system which includes a plurality of lines and automatic switching apparatus l for setting up connections between said lines, a conference circuit including a talking channel provided with a plurality of branches and a control channel, selectors accessible to said lines and provided with outlet contacts which terminate the branches of said talking channel Vand said control channel, the outlet contacts terminating said control channel being designated by a difierent directory number than the outlet contacts terminating said branches, means normally marking all of the branches of said talking channel as busy in the outlet contacts of said selectors, and means controllable over said control channel through one of said selectors from a calling point of the system for removing the busy marking from a number of the branches of said talking channel, thereby to permit certain of said lines to gain access to saidtalking channel through saidselectors, l

- 10. In a telephonesystem which includes a plurality of lines and automatic switching apparatus for setting up connections between saidA lines, a conference circuit including a talking channel provided with a plurality of branches and a co'ntrol channel, selectors accessible to said lines and provided with outlet contacts which terminate the branches of said talking channel and said control channel, the outlet contacts terminating said control channel being designated by a diierent directory number than the outlet contacts terminating said branches, means normally marking al1 of the branches of said talking channel as busy in the outlet contacts of said selectors, and presettable means controllable over said control channel through any one of said selectors from a calling point of the system for removing the busy marking from a predetermined but variable number of the branches of said -talking channel, thereby to permit said predetermined number of said lines to gain access to said talking channel through said selectors.

11. In a telephone system which includes' a plurality of lines and automatic switching apparatus for setting up connections between said lines, a conference circuit including a talking channel provided with a plurality of branches and a control channel, selectors accessible to said lines and provided with outlet contacts which terminate the branches of said talking channel and said control channel, the outlet contacts terminating said control channel being designated by a different directory number than .the outlet contacts terminating said branches, means normally marking al1 of the branches of said talking channel as busy in the outlet contacts of said selectors, means controllable over said control channel through one of said selectors from a calling point of the sys- `tem for removing the busy marking from a number of the branches of said .talking channel, thereby to permit certain of said lines to gain access to said talking channel through said selectors, and means controlled through said selectors for restoring saidbusy markings on an individual basis as the branches of said talking channel are seized through said selectors, whereby only said certain lines are permitted to gain access to said talking channel.

12. In a telephone system which includes a plurality of lines and automatic switching apparatus for setting up connections between said lines, a conference circuit including a talking channel channel.

provided with a plurality of branches and a control channel, selectors accessibleto said lines and provided withI outlet contacts which terminate the branches of said talking channel `and-said control channel, Vthe, outlet contacts terminating said control channel being designated by a different directory number than the outlet contacts terminating said branches, means normally marking ,all of the lbranches of said talking channel as busy in the outlet contacts of said selectors, presettable means controllable over said control channel through any one of said selectors from a calling point of the system for removing the busy marking from a predetermined but variable number of the branches of said talking channel, thereby to permit said predetermined number of said lines to gain access` to said talking channel through said selectors, and means controlled `through said selectors for restoring said busy vmarkings on an individual basis as the branches of Asaid talking channel are seized through selectors, whereby only said predetermined number of lines are permitted to gain access to said talking channel through said selectors.

13. In a conference circuit comprisingla talking channel provided with a number of branches over which said channel may be seized through the apparatus of an automatic telephone system from certain of the lines of the system, means normally marking'all of the branches of said channel as busyin said apparatus, and means controlled from one of said lines for removing' the busy marking from a Variable number of the branches of said talking channel, thereby to permit a variable predetermined number of the lines` of said system to gain access to said talking 14. In a conference circuit comprising a talk- Y ing channel provided with a number of branches over which said channel may be seized through the apparatus of an automatic telephone system from certain of the lines of the system, means normally marking all of the branches of said channel as busy in said apparatus, means controlled from one of said lines for removing the busy marking from a variable number of the branches of said talking channel at will, thereby to permit dierent numbers of the lines of said system to gain access to said talking channel, and means for automatically restoring said busy markings on an individual 'basis as the branches of said talking channel are seized through said apparatus, whereby only said predetermined number of lines are permitted to gain access to said talking channel through said apparatus.

Y 15. In a, conference circuit which comprises a talking channel provided with a' number of branches over which said channel may be seized `through the switching apparatus of an automatic ratus, register means having different settings designating diierent numbers of said lines that may be connected to said talking channel, means controllable through said apparatus over any one of said lines for imparting a predetermined setting to said register` means, and means controlled by said register means when operated to said predetermined setting for removing the busy marking from the number of the branches of said talking channel corresponding to said predetermined setting of said register means, thereby to` permit a corresponding number of said lines to gain access to said talking channel.

thi. usiiseieieraeiratiis fer automatically rester- ,ipg said, iiiisx markings 91,1 an individual basis .as the branches ef. Said'talkingehannelcre seized .e si Seidieiiiiis ehaniielend means entielled f throughsaid. apparatus, whereby only the num- Y Iiecf thsystm for trasrnttng a sgriatl over seiiieiie. lille,K @1191.. means eeiiireiiable. over Said @eine before a 4smieir@niet Qonn'ection is estab- ,iisiiesi ier Preyeniing @reihen a predetermined riAtiiijoreiffthe lines frqm gaining Vaccess to said eireiiii- Y t .t CLARENCE E. LOMAX.