US2317833A - Telephone system - Google Patents

Description

April 27, 1943. J. H. Voss TELEPHONE! SYSTEM Filed July 1l, 1940 14 Sheets-Sheeb-l INVENTOR JOHN H. Voss TTORNEYS April 27, 1943. J. H. Voss TELEPHONE SYSTEM INVENTOR .JOHN H. Voss BY ,zwm/,vy wud 4f/MIL ATTORNEYS mmm 14 Sheets-'Sheet 3 J. H. Voss TELEPHONE SYSTEM Filed July 1l. 1940 avm. IIJll ma. mw

April 27, 1943.

lNvENToR JOHN H. VOSS ATTORNEYS April 27, 1943. J, H; v0.55 2,317,833

' TELEPHONE SYSTEM Filed July 11, 1940 '14 sheets-sheet 4 INVENTOR JOHN H. V055 ATTORNEYS April 27, 1943.

J.-H.,Voss

TELEPHONE SYSTEM Filed July 11, 1940 14 Sheets-Sheet 5 April 27; 1943. L H Voss 2,317,833-

TELEPHONE SYSTEM Filed July 11, 1940 14 Sheets-Sheet 7 INVENTOR JOHN H. Voss ,om L? .am m

' ATTORNEYS C239 C23 C April 27, 1943. J, Voss 2,317,833

TELEPHONE SYSTEM Filed July 11, w46 l14 sheets-sheet 8 l l l, l i 46845 LC84-l $6907 {95/ C//6`8 C8441 C846 -L-l 9 INVENTOR JOHN H. VOSS BY ,0MM by M 'ATTORNEYS April 27,4 1943. J, H, voss- 2,317,333

TELEPHONE SYSTEM INV JOHN H. VOSS ATTORNEYS April 27, 1943.

J. H. VOSS TELEPHONE SYSTEM Filed July 11, 194o 14 Sheets-Sheet 10 nog) V- CIZ/4 INVENTQR v JOHN H. VOSS MMM ATTORN EYS April 27, 1943. J. H. voss' 2,317,833

TELEPHONE SYSTEM Filed July 11, 1940 14 Sheets-Sheet 12 RING/NG /NTERRI/PTER INVENTOR JOHN H. vQss BY I @Ou/mluuwm M ATTORNEYS 'April 27, 1943. L V055 2,317,833

' TELEPHONE SYSTEM n Filed July 11, 1940 I 14 *Sheets-Sheet 13 ICP/400 T0 0T HER GROUP RELA YS ATTORNEYS April27,1943. J H vss y 2,317,833

TELEPHONE SYSTEM ATTORNEYS Patented prj27, 1943 TELEPHONE SYSTEM John H. Voss, Downers Grove, Iii., assignor 'to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application .my 11, 1940, serial No. 344,370

55 claims. (ci. ris-1s) 'I'he present invention relates to automatic telephone systemsv and more particularly to iinprovements in automatic switching apparatus adapted for use in exchanges serving the subscribers of small isolated communities. In exchanges of this type, varied operating requirements must be met, depending upon the location ofthe exchanges' and the grade and type of service desired. A'ccordingly, the present invention has for one of its objects the provision of improved automatic switching equipment which lends itself to the ready adaptation of special service facilities and is so arranged that substantially all service facilities normally required in exchanges of this type may be incorporated therein with a minimum of added equipment.

It is another object of the invention to provide in an automatic telephone system of the character described, an improved and exceedingly simple arrangement for enabling certain telephone stations, such, for example, as toll operators stations, to obtain access to busy lines of the system for the purpose of ascertaining the actual condition of the lines, for the purpose of offering toll .calls to the parties conversingL over the busy lines, and in order to render the other services normally possible when facilities for establishing connections of this character are provided.

vide in an automatic telephone system of the character described, improved automatic switching apparatus which is so arranged that equipment common to'a plurality of switching links is utilized to permit certain subscribers .to obtain' access to the trunks of one or more specified trunk groups and to prevent subscribers for which a different type of service is provided from obtaining access to the trunks of the specified It is a further object 'of the invention to pro- -vide in a telephone system of the character dewhich is so connected and arranged that when a predetermined first digit of impulses is transmitted thereto over a calling line of one group, the switch is conditioned to establish a communication connection to` a busy called line, whereas if the same first digit is transmitted to the switch over a calling line of another predetermined group, the digit is absorbed without producing any effective operation of the control equipment in the switch.

.It is a still further obiect of the invention to provide an impulse-responsive, line-selecting switch of the character described, which is so arranged that the first digit of impulses trans- It is another object of the invention to promitted thereto may also be utilized for trunk group selection, for subscribers line group selection, for the partial selection of the ringing voltage to be applied to a called subscribers line. and for the purpose of determining the type of ringing to be utilized in signaling oveli` a called subscribers line.

It is a further object of the invention to provide in an automatic telephone system of the character described, improved automatic switching equipment which is so arranged that a reverting call connection between two substations served by the same line is set up by the directory number dialing method, and which includes provisions for transmitting a special signal tothe answering substation when the call is answered at one of the substations served by the calling line.

It is another object of the invention to-propositions occupied by one or more group select relays, each having two different operating positions respectively corresponding to the two different groups 'of lines.

It is still another and more specific object of the invention to providean improved automatic telephone system of the characterdescribed wherein the battery reversing relay embodied in one or more of the final numericalrswitches of the system is arrangedselectively i9 be con- .have access to the central ofrlce trunks.

trolled'over an operating circuit which extends through contacts controlled by a preceding nonnumerical switch, whereby the relay is only conditioned for energization in response to calls initiated on certain of the lines of the system.

In the illustrated embodiment of the invention there are provided a plurality of finder-connector links of the all-relay type which, in con- Junction with equipment common to the links and including a link distributor, operate to set up connections between the lines of the system. Each finder and connector switch of the system includes provisions for terminating two groups of lines each including one hundred lines. In accordance with one feature of the present invention, the operating circuits for the connector group select relays of each` link are extended through contacts controlled by a pair of group select relays so that, depending upon the position of the group select relays, the connector group relays are selectively'conditioned for energization. More specifically, the connector group select relays include contacts individual to the operating circuits for the group relays, which are so connected and arranged that when the group select relays occupy non-corresponding positions the operating circuits for one group of the connector group relays are prepared and when the group select relays occupy different non-corresponding positions the operating circuits 'for another group of the connector group relays are prepared. The group select relays are so connected and arranged that when a first digit of impulses is transmitted to the connector portion of the associated link, they will assume positions corresponding to the group of lines designated by the numerical value of the digit.

In accordance with another feature of the invention, the first digit transmitted to the connector portion of a seized link may also be utilized to condition the link to establish a connection to a busy called line accessible thereto. The apparatus provided for this purpose is so arranged that if the predetermined rst digit assigned to this function is transmitted to the link over a calling subscribers line it is absorbed, whereas if it is transmitted to the link over a. calling central olce trunk line, for example, it performs the function assigned thereto. This apparatus is partially controlled lby the auxiliaryl group and unit relays provided in the equipment common to the link, these relays being utilized to identify the character of the calling line and to thus indicate to the connector end of the link whether or not the calling line is entitled to a connection to a bu'sy called line. The auxiliary group and unit relays ofthe common equipment may also be used for the purpose of determining which of the subscribers lines served by the finder-connector links are t These relays, by selectively controlling right-of-Way circuits individual to the various links, serve to indicate to the connector portion of a, seized link whether or not a particular calling line is entitled to free central ofiice trunk service.

In the arrangement illustrated in the drawings and described with particularity hereinafter, reverting call connections between substations served by the same lines are set up by the wellknown directory number dialing method. In accordance with another feature of the invention, apparatus is provided which is operative in response to the answering of a call of the revertive type for transmitting a special signal to the answering substation, thereby to inform the answering party as to the character of the call answered. More specifically, this apparatus comprises a timing device, means operative in response to the answering of a reverting call for initiating operation of the timing device and for transmitting a signal to the answering substation', and means controlled by the timing device for releasing the link occupied with the call, thereby to terminate the signal a predetermined time interval after the call is answered.

In an exchange serving a community of the character mentioned above, wherein lines of several different types, such, for example, as trunk lines, subscribers lines of the metallic and ground return type, and paystation lines may be provided, it is necessary to make provisions for controlling the supervisory or battery reversing relays of the switching links in accordance with the particular character of the line upon which l a call is initiated. Thus, in handling a call initiated on a trunk line, battery reversals for supervisory purposes are essential. Again, in handling calls originating on lines of the paystation type, the reversal of current flow over the calling lines is usually required for coin collect purposes. On the other hand, in handling calls initiated on lines of the local-battery, ground return type, it is desirable to prevent the operation of the battery reversing relays in the links occupied with the calls. In accordance with another feature of the present invention, the selective control of the battery reversing relay embodied in each link is achieved in asimple and reliable manner by extending the operating circuit for the relay through contacts controlled only by the finder group relays which terminate the lines with respect to which operation of the battery reversing relay is required.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. 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 specification taken in connection with the accompanying drawings, in which Figs. 1, 2, 4 to 13, inclusive, 14a and 14b, when combined in the manner indicated in Fig. 3 of the drawings, illustrate an automatic telephone system having incorporated therein the features of the invention briefly outlined above.

type and extends to the substation A, is the fifthv line of the first subgroup of lines in the first line group, whereas the line 2l6, which is of the ground return type and serves the common battery substation B, is 'the sixth line of the same subgroup of lines. Both of these lines are i1- lustrated as being ofthe single party type. The line 2|9, on the other hand, which is the ninth line of the rst subgroup of lines in the first 100- line group, is illustrated as being of the multi- Darty type. serving the substations C and D. This subgroup of lines also includes i'our trunks ofthe well-known ring-down type which extend to a private branch exchange oi' the manual type. The lines of this trunk group are assigned the nrst four unit numbers, namely the numbers l to 4, inclusive, of the subgroup, and are automatically preselected for use through the provision of a, trunk preselect relay group |490.

'Ihe exchange also terminates a group of ten central olce trunks, one of which is indicated at I as extending to the central oiiice l. I'his trunk terminates in the community exchange iny a two-way repeatervS which is connected by a link line to the set of contacts having the directory number 200. In order to preselect idle ones of the central omce trunks as these trunks successively become busy, a second group |490 of trunk preselect relays is provided in association therewith. The two trunk preselect relay groups i490 and I 495 are identical in arrangement and are wired exactly in accordance with the wiring of trunk preselect relays disclosed in Figs. 11 and 13 of applicant's copending application Serial No.

189,121, filed February '1, 1938, and assigned to the the conductors of the ung une m between the twowlink lines 228 and 229. For the'purpose oi` associating the relays or the ilnderswitchy with the common equipment illustrated in Figs.'- 5, il and 'I of the drawings, a pair of connect relays i R280 and R280 are provided.'

The connector portion oi the link is similar to the nnder switch Just described in that twenty group relays, including the two relays Rl400 and RI4I0,. andeach including contacts terminating ten lines of the system, are provided. These relays are 'also preferably of the-construction disclosed and claimed in the above-cited patent to Obergfell. The connector portion o! the link further comprises ten unit relays whichindividually correspond to din'erent linesof each of the ten-line subgroups.` Only three of these relays.

Ri400, Ri400 and RI410. have been illustrated in s the drawings, thesev relays respectively corresponding to the first. ninth and tenth lines of each ten-line subgroup.` As indicated previ-` ously, the lines terminating at the connector switches of the system are divided, into two groups of one hundred lines each.V The connector group relays are likewise divided into` two groups, each comprising ten relays. For the purpose oi' selectively controlling the operating in each ten-line subgroup, and the -lines having directory numbers ending in the units designations 6, '7, 8, 9 and 0 comprise the second smaller subgroup of lines in each ten-line subgroup.

As indicated above, in order to set up connections between the various lines of the system. a plurality of under-connector links of the allrelay type are provided. The details of one of the links are illustrated in Figs. 2. '1, 8. 9, 10, 11, 12,- 13, 14a and 14h of the drawings. The other links included in the exchange are .identical in arrangement with the link illustrated. These links are arranged to be controlled by common equipment which comprises a link distributor. also shown in Fie. 'I of the drawings. a group of distributor control relays illustrated in Fig.' 6 of the ldrawings, and a plurality of guard or auxiliary relays which are illustrated in Fig. 5 of the drawings. Briefly described, the ilnder portion of the illustrated link comprises twenty group relays. two of which are indicated at R200 and R2i0, which respectively .correspond to the different ten-line subgroups. These relays are preferably of the character disclosed and claimed in Patent No. 2,135,832, granted November 11, 1938, to Herbert F. Obergfell, and only two thereof have been shown in the interests of simplifying the disclosure. The finder portion of the link also comprises ve unit relays, each of which corresponds to two lines in each of the ten-line. subgroups.

Thus, the relay R220, for example, is operative in conjunction with any one of the group relays to select the lines having the unit designations of 5 and 0 in each of the twenty different subgroups of lines. It will be undestood that with one of the group relays and any one of the unit relays operated, two lines are selected from theplurality of lines to which the finder switch has access. In order to select one of the two lines thus selected by the group and unit relays, there is provided a subgroup relay R210 which functions to switch circuits oi' these two groups ofv connector. group e relays, two group selectrelays R|350` and are provided in the link illustrated.. l

In order selectively to control the group select relays, the connector group relays, and the connector unit relays to cause the'proper relay operansa ations-for the selection of a'desired called line-y and the selective .signaling-of the substations served by called ones of the multiparty lines ter'- minating at the exchange, an impulse-countingl I chain is provided. 'I'his counting chain is illus trated in Figs 7, 12, and 13 of the drawlngsas comprising ten counting relays'Ri240, RI250,

RI260, Ri210. RI280, RI290,A RI300, Ri3'l0, RI320 and Ri330. and three associated common control relays R150, R and R110.

The control equipment of the link comprises aV switching-through relay R800 which is operative to by-pass the repeating coil 834 in handling central oilice trunk calls routed through the link. a battery reversing relay R8I0, -a pair of line relays R820 and R825, and an impulse-correcting network which includes the two control relays I R830 and R840, a slow-acting control relay R850, and a hold relay R800.

counting chain release relay R810.`

The control equipment embodied in` the con-1 nector portion of the link also includes a pair of link release relays R900 and R9lll, a hack-bridfre R940 and R910, a slow-to-release lineriischarrrc control relay R950, a ring pickup relavR9Sil. and a slow-to-operate ring cut-off relay R98!!v which` may be used yalternatively with the lamp 928 in the ringing circuit of the 1ink.-dependnguponthe type ci' ring cut-oil operation desired.

As illustrated in Fig. 10 ofthe drawings, the'` control apparatus oi the link further cnripriws n.'

ringing transfer relay R|000 which is utilized tc determine the side of a selected line over whch ringing current is to be trol relay RIOIU, la right-of-wav'control. rela alarma line-switching remy Rigas'. a ,bug-v mi; relay Rl040,fanother line-switching relay-H1050,

In orderto control the w i release of the counting chain illustrated inFigs. '7. 12 and 13 oi the drawings, there is provided a projected, a ringing cori, l u

conjunction with the relay R900 to eifect instantaneous ring cut-oif when this feature is incorporated in the link circuit. 'I'he control equipment illustrated in Fig. l1 of the-drawings comprises a verincation relay RI |40 which is utilized in the establishment of communication connections t o busy called lines terminating at the connector end of the link. This equipment also includes three impulse-controlled relays RI |00, RI I50 and RI |50, the last two of which are of the slow-to-release'type, a first digit transfer relay RI I20, a second digit transfer relay RI I I0, and a third digit transfer relay Rl |30.

For the purpose of selecting the type of ringing to be utilized in signaling over a called subscribers line of the multiparty type, of controlling the group select relays RI350 and R|360, and of partially selecting the code of the ringing current to be used in signaling called substations served by the multiparty lines terminating at the exchange, all in response to the impulses comprising a first digit transmitted to the connector lportion of the link.,two relays RI 200 and RI2I0 are provided which are arranged selectively to be controlled by the relays of the impulse-counting chain during the response of this chain to the impulses of a guard or auxiliary relays which individually correspond to the relays embodied in each of the finder switches. More specifically, this .equipment comprises twenty auxiliary group relays, three of which are indicated at R500, R5I0 and R590, which individually correspond to the twenty group relays of the finder switches.v Thus, the two relays R500 and R5I0 are arranged individually to control theiinder group relays R200 and R2I'0 of thellink'illustrated. The seventeen group relays which are not shown yare indicated by the multiple and chain conductors extending between. the contacts er the three illustrated.

auxiliary group relaysv R500, R5'I0 and R590.

Five auxiliary unit relays including the two relays R550 -and` R560 are also provided, which relays vindividually correspond to the .five unit relays of the vvarious nder switches. The auxiliary relay equipment Afurther comprises arpair of vrelays R520 and R530 which function'- to controlv the subgroup relays embodied in the finder switches.

The link distributor or allotter equipment is also" offthe all-relay type, a group of link distributor relays;R100,. R1I0, R130. etc., being provided which individually correspond to the links and operate in `a cyclic manner to assign the respective associated links for use in a predetermined order; These link distributor relaysare arranged to be controlled by a group of control VIrelays which are illustrated in Fig. 6 ofthe draw- "ings as comprising a slow-acting relay RMI for controlling the auxiliary relay startl circuits and the call metering device ill, a group of1 slow-torelease `link transfer and distributor control rea,siv,ass

lays R020, R030, R640 and R050. a slow-acting distributor reset relay R060, and an all-linksbusy relay R810 which is operated only when an all-busy condition of the respective associated links prevails. The relay R610 is also arranged to control an all-busy metering device 032 which functions to register those instances when calls fail due to an all-busy condition of the links. The common equipment further includes a control relay R600 which is provided for the purpose of controlling the trunk call identification circuits referred to above and described with particularity hereinafter in accordance with the operation of the associated auxiliary relays.

For the purpose of initiating the operation of the common equipment just described, each line of the system is terminated in the usual line circuit which conventionally comprises line, cut-oil and lockout relays. Thus, the line 2I5 which extends to the substation Avterminates at the exchange in a line circuit I0, which includes a line relay RI00, a cut-off relay RI I0 and a line lockout relay RI05. Similarly, the line 2I6 which extends to the substation B is terminated at the exchange in a line circuit I5 which includes the line, cut-oil and lockout relays RI20, RI30 and RI25, respectively. The line circuit 25 which is diagrammatically illustrated as terminating the multiparty subscribers line 2I9, is identical in arrangement with the two line circuits I0 and I 5. It will also be observed that the line circuit 20 which is provided in association with the twoway repeater 6 and includes the line, cut-0H and lockout relays RI50, RI60 and RI55, respectively.

is substantially identical in arrangement with the line circuits I0 and I5.

The equipment common to the links also includes the usual ringing apparatus, timing apparatus and tone-generating apparatus. cically, the timing apparatus includes a timing device a, preferably of the all-relay type, which is provided for the purpose of controlling the release of the links after reverting calls routed by way thereof have been successfully completed. A second timing device 120b, also preferablyof the all-relay type, is provided for the purpose of forcibly releasing any link held operated over afaulty line or a line having a permanent calling condition thereon, and of controlling the link release relays of the links for the purpose of timing local call connections established by way of the links. These two timing devices may be of `any well-known construction and arrangement, the operation of which is well understood in the art and, accordingly, the details thereof have not been illustrated. The ringing apparatusprovidedin association with the links includes a ringing current generator, preferably of the pole changer type, and a ringing code interrupter |395. This interrupter is so arranged that it provides on its associated ten interrupter leads ten'sets Iof differently coded ringing control pulses so that ten fundamental ringing codes are produced. The ringing interrupter also includes provisions for preceding each of the ten fundamental codes by a short ringing code pulse so that ten additional codes are effectively produced. This is accomplished by providing an arrangement for selectively controlling the application of the pickup relay oper ating potential to the two pickup leads CI2I5 and Cl 221. More specifically, the arrangement is More speasiasss omitted from the ringing code. whereas if the other pickup lead is utilized as a part of the operating circuit for the ring pickup relay -in the operated link, the short or preliminary ringing interval is included in each of the ten ringing codes. lSince this type of code ringing and the arrangement oi the ringing interrupter whereby it may be achieved are well known in the art, the details of the ringing equipment have not been illustrated in detail.

The tone-generating equipment is illustrated in Fig. 4 oi the drawings as comprising a dial tone generator 435, a busy tone generator 440, and a reverting-call tone generator 415. The dial and busy tone generators are oi identical arrangementand, accordingly, only the details of the busy tone generator have been illustrated in the drawings. Briey described. this generator comprises a start relay R400 which is common to the tone-generating equipment, a buzzer 430, a slow-to-operate start relay R4I0, a control relay R420 and a transformer 662. The reverting-call tone generator 415 includes a pole changing relay R400 which is arranged to be.

controlled by three slow-to-operate, cyclically operating timing relays R650, R660 and R410. These relays are also arranged to control the application of the busy tone potential, generated through operation of the tone generator 660, to the busy tone current lead CI060.

SEIzUnE or THE LINK AND OPERATION or THE FINDER SWITCH upper winding oi RI00, the contacts III, the

conductor 2I5b, the direct current bridge across the conductors of the line 2I5v at the calling substation, the conductor la, the contacts GIZ, and the lower Winding of RI to battery. In operating, the relay RI00 prepares, at its contacts IOI,

a circuit for energizing the auxiliary unit relay- R which corresponds to the line 2I5. At its contacts I03, the relay RI00 connects the private conductor 2I5d to ground, thereby to mark the line 2I5 as busy in the connector switches having access thereto. At its contacts S02, the relay RI00 completes a circuit for energizing the auxiliary group relay R5I0 which corresponds to the first group of ten lines. This circuit extends from ground by way of the contacts I 02 and |01.

the start conductor CI45, the winding of R5I0,

the contacts EIS, C518, the contacts 6I2, C560, the contacts 594, 5I4 and 505, the chain-connected contacts controlled by the other auxiliary group relays, and the resistor 522 to battery. When energized over this circuit the relay R5I0 completes, at its X contacts 5 I 3', anobvious holding circuit for itself, and opens, at its contacts 5I4, a. point in the common portion of the operating circuits for the ten auxiliary group relays. At its contacts SI5, 5I6, 5I1, 5I8 and 5I6, the relay R5I0, in operating, prepares the operating circuits for the ve auxiliary unit relays. In the present case, however, only the auxiliary unit relay R560 is operated, the circuit for energizing this relay extending from ground by way designation 5 of the calling line 2I5. -At its con-l of the contacts `534, the windingoi' R520, CI4I, the contacts |06 and IOI, CI41, the contacts 5I6, the winding of R560, the contacts 566, C511, the contacts 6H, C516, the contacts 564 and 554, similar chain-connected contacts of the other auxiliary unit relays, and the resistor 566 to battery. At its contacts 5II, the relay R5I0 prepares a circuit for energizing the group relay of the assigned link. At its contacts 5I2, the relay R5I0 prepares a circuit for energizing the right-of-way control relay RI340, assuming that the lines of the ten-line group including the line 2I5 are provided with unrestricted trunk' service such that the Y wiring illustrated in Fig. 5

of the drawings is used.

When energized in series with the relay R560 over the above-traced circuit, the slow-to-release relay R520, at its contacts 52|, opens a point in the operating circuit for the relay R560, thereby to prevent operation of the latter relayuntil the call in progress is extended to an assigned link. The auxiliary unit relay R560 also operates when the above- -aced circuit is completed, and upon operating, completes, at its X contacts 565, an obvious locking circuit for itself. After this circuit is completed, the relay R560, at its contacts 564, opens a point in the common portion of the operating circuits for all of the auxiliary unit relays. At its contacts 561, the relay R560 prepares a. circuit for energizing the unit relay of the assigned link which corresponds to the units tacts 562 and 560, the relay R060 prepares two paths for impressing ground potential upon thel trunk call identification lead 066i. At its contacts 56I, the relay R550 completes a circuit for energizing the connect relays of the link previously selected for use by the link distributor relays. Assuming that all of the links are idle, all of the link distributor relays are operated so that the link illustrated is assigned to the use of the calling line 2I5. In such case the relay R560,

4upon operating, completes a circuit for energizextending from ground at the contacts 614 for energizing the call metering device 6I4, whereby the call is registered. At its contacts 6H, the

relay R6I0 opens another point in the coninonl portion of the operating circuits for all of the auxiliary unitrelays. At its contacts 6I2, the relay R6I0 opens another point in the common portion of the operating circuits for all of the auxiliary group relays. Thus, the auxiliary relays are prevented from responding to another call until the finder switch illustrated has completed its operation to seize the calling line 2I5. The relay R260, in operating, prepares, at the contacts controlled thereby, the operatingcircuits for the twenty group relays embodied in the finder switch illustrated. In the case under consideration, only the relay R2I0, which terminates the rst group of ten lines, is energized in response to operation of the relay R280, the operating circuits for the other nineteen group relays being held open at the yrestored contacts of the other auxiliary group relays. More specically, the circuit for energizlngthe relay R2| 0 extends from ground by way of the contacts 5| I, C512, the contacts 28|, and the winding of R2|0 to battery. This relay, in operating, prepares, at its contacts 2|l to 2|3, inclusive, connections between the conductors of the line 2|5 and the conductors of the link line 228, and, at its contacts 241, prepares a holding circuit for itself. Atthe remaining contacts controlled by this group relay, connections are prepared between the other nine lines terminating at these contacts and the twolink lines 228 and 229.

'I'he relay R290, upon operating, prepares the operating circuits for thevilve unit relays of the finder switch. In the case under consideration only the operating circuit for the relay R220 is completed, this circuit extendingfrom ground by way of the contacts 532 and 561, C583, the contacts 295, and the winding of R220 to battery. When energized over this circuit the relay R220 operates to prepare a locking circuit for itself at its contacts 221. At its contacts 22|, 222 and 223, the relay R220 connects the conductors of the calling line 2|5 to the conductors of the link line 228. At its c0ntacts.224, 225 and 225, the relay R220 connects the conductors of the line 2|0 to the other link line 229. At its contacts 293, the relay R290 prepares a circuit for energizing the subgroup relay R210. In the present case wherein the line 2|5 is in the first subgroup of the rst group of lines, the subgroup relay R530 of the common equipment Vis not operated and hence the operating circuit for the subgroup relay R210 is held open at the: contacts 603 of the restored relay R600. Accordingly, the relay R210 remains in its restored position for the duration of the call under consideration. At its contacts'296, the relay R290 prepares alternative operating circuits for the five unitrelays of the finder switch, these alternative circuits being held open at the restored contacts 218 of the subgroup relay R210. At its contacts 292, the 'relay R290 completes a multiple holding circuit for the link distributor relay R100 individual to the link illustrated, this multiple circuit extending from ground by way of the resistor 108, the contacts 106, C232, the contacts 292, C23I, and the winding of R100 to battery. At its contacts 298, the relay R290 prepares a circuit including the trunk call identification lead C68| for energizing the right-of-way control relay R|020.

The relay R290, in operating, also completes a circuit for energizing the two line relays R820 and R82 5, this circuit extending from ground by way of the winding of R825, the winding 835, the contacts 802 and 8| I, the conductor 230a, the contacts 29|, the resistor 283, the conductor 23012, the contacts 8|3 and 804, the winding 836 and the winding of R820 to battery. When energized over this circuit the relay R820 operates to complete, at its contacts 82|, a circuit for energizing the pulsing relay R830, this circuit extending from ground by way of the contacts 9|8', C890, the contacts 84| and 82|, and the winding of R830 to battery.

The relay R825 also operates when energized in series with the relay R820, and, upon operating, prepares, at its contacts 826, the operating circuit for the battery reversing relay R800.

The relay R830, in operating, completes, at its contacts 832, an obvious circuit for energizing the relay R840, At its contacts 834, the relay R830 opens a point in the pulsing circuit traced hereinafter, over which the counting relays illustrated in Figs. 12 and 13 are successively energized during the transmission of impulses to the connector portion of the link. At its contacts 833, the relay R830 completes a locking circuit for itself, this locking circuit extending. from ground by way of the contacts 833, the resistor 823, the contacts 82| and the winding of R830 to battery. At its contacts 83|, the relay R830 completes a circuit for energizing the slow-acting relay R850, this circuit extending from ground by way of the contacts 9|8', C890, the contacts 83| and the winding of R850 to battery. Shortly after this circuit is completed, the relay R840 operates and, in so doing, closes its contacts 842 to shunt the operated contacts 83| and thus complete an obvious multiple circuit for energizing the relay R850. At its contacts 84|, the relay R840 opens a point in the above-traced operating circuit for the pulsing relay R830. The relay R850, in operating, prepares, at its contacts 85| a priming circuit for the line relay R820. At its contacts 852, the relay R850 completes an obvious circuit for energizing the hold relay R860. At its contacts 853, the relay R850 opens a point in the circuit traced hereinafter for energizing the reverting-call relay R940. At its contacts 854, the relay R850 completes a path for impressing ground potential upon the tone apparatus start conductor C895, thereby to energize the tone start relay R400. More specically, this relay is energized over a circuit which extends from ground by Way of the contacts |031, C894, the contacts 854, the tone start lead C895 and the winding of R400 to battery. When energized over this circuit,the relay R400 operates to initiate the operation of the three associated sets of tone apparatus illustrated in Fig. 4 of the drawings. The manner in which this is accomplished is explained in detail hereinafter.

The hold relay R860, in operating, prepares, at its contacts 866,v locking and operating circuits for the relays R8|0 and R|010. At its contacts 869, the relay R860 completes an obvious path for impressing ground potential upon the release conductor C893, thereby to prepare f operating andlocking circuits, traced hereinafter, for certain of the other control relays embodied in the link. At its contacts 861, the

relay R860 completes a path including the con-l tacts 8|8 for impressing ground potential upon the timer start lead C889, thereby to initiate certain of the timing devices embodied in the timing equipment 120. At its contacts 668, the relay R860 prepares a circuit traced hereinafter for energizing the link release relay R900. At its contacts 894, the relay R860 prepares the above-mentioned circuit for transmitting impulses to the relays of the counting chain illustrated in Figs. 12 and 13 of the drawings. At its contacts 863, the relay R860 opens one of the multiple paths included in the normally completed holding circuit for the link distributor relay R100, this circuit now being closed at the engaged contacts 292 of the operated connect relay R290. At its contacts 865, the relay R860 completes the prepared holding circuits for the group and unit relays- R2|0 and R220, respectively. More specically, the holding circuit for the units relay R220 extends from ground by way of the contacts 948, C882, the contacts 865, C235, the contacts 221 and the winding of R220 to battery. The holding circuit for the group relay R2|0 extends by way of the grounded lead C235, the contacts 241 and the winding of R2|0 to battery. At its contacts 86|, the relay R860 completes a path for transmitting dial tone sig-

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