US2333038A - Telephone system - Google Patents

Description

8 Sheets-Sheet 2 mmwu INVENTOR JOHN H voss i' ATTORNEYS J. H. VOSS TELEPHONE SYSTEM Filed April 22, 1940 RS3 @GEQ a winin Oct. 26, 1943.

Oct 26, 1943- I J. H. voss 2,333,038

TELEPHONE SYSTEM Filed April 22. 1940 a Sheets- Sheet 4 T0 LINE 45/\ DIAL TONE ATTORNEYS v Oct. 26, 1943. J. H. voss TELEPHONE SY STEM Filed April 22, 1940 8 Sheets-Sheet 5 INVENTOR JOHN H. VOSS BY M, M, W

ATT-O R N EYS Oct. 26, 1943. J. H. voss TELEPHONE SYSTEM Filed April 22. 1940 8 Sheets-Sheet 8 INVENTOR JOHN HmVOSS ATTORNEYS atented 3943 TELEPHONE SYSTEM John H. Voss, Downers Grove, 111., assignor to AntomaticElectric Laboratories, Inc., a corporation of Delaware Application April 22, 1940, Serial No. 330,975 11 Claims. -(c1. 179-48) The present invention relates to automatic telephone systems and more particularly to improvements in automatic switching apparatus adapted for use in private automatic exchanges.

In private automatic telephone installations serving larg commercial organizations or the like, it is frequently desirable to provide facilities whereby the executives of the organization may obtain access to any line of the system at any time. This form of service has been characterized as executive right-of-way service and involves the provision of apparatus for nabling the executive lines to obtain access to busy called lines of the system. Prior arrangements for providing such facilities are exemplified by the disclosures of Stehlik Patent No. 1,924,661, granted August 29, 1933, and Stehlik Patent No. 1,934,384, granted November 7, 1933. In the arrangements disclosed by these patents, provisions are made respond to different groups of lines of the system, the subgroup relays correspond to a particuon aper line basis for marking the executive lines in a special manner in the banks of the rotary finder switches of the system so that th finderconnector link circuits may be controlled from the executive substations to established dry talking circuits to busy called lines of the system.

It is an object of the present invention to provide, in an automatic telephone system of the character indicated, improved apparatus for enabling the executives served by the system to have right-of-way facilities, which is simple and economical in arrangement, requires a, minimum of special equipment, and is positive and reliable in operation. f

It is a further and more specific object of the invention to provide improved apparatus of the character described, wherein the executive rightof-way facilities ar primarily incorporated in the equipment which is common to the switching links of the system.

In the illustrated embodiment of the invention there are provided a plurality of finder-connector links of theall-relay type, which, in conjunction with equipment common to the links and including a link distributor, operate to set up connections between the lines of the system. In-a'ccordance with the present invention, provisions are made whereby right-of-way facilities are provided for the executive lines of the system under the control of certain of the apparatus embodied in the equipment common to the finder-connector links. More specifically, this common equipment includes auxiliary group, unit and subgroup relays which correspond to the group, unit and subgroup relays provided in each lar subgroup of lines in each line group, and the unit relays respectively correspond to the same lines in each group. These auxiliary relays, as incorporated in the common equipment, are arranged selectively'to control executive rightof-way circuits which extend to the several links, each link being provided with a right-of-way or special service relay which, when energized over its associated right-of-way circuit, operates in conjunction with the busy test relay of the link to establish a talking circuit to a busy called line selected by the connector portion of the link. With this arrangement the executive lines may be connected in the banks of the link-finder switches to have the same unit directory number designations. With these line terminated in this manner, the right-of-way circuits may be connected to be set up by a predetermined one or more of the unit relays operating in conjunction with the tens or group relays respectively corresponding to th line groups which include the executive lines. These circuits are also appropriately controlled by the link distributor and the subgroup relay of the common equipment, so that the right-of-way or special service relay of an assigned link will only be operated when the finder portion of the link operates to seize a calling executiv line arranged for right-of-way service.

Further'features of the invention pertain to the particular arrangement of the circuit elements whereby the above and d i n l p ing features are attained.

Th 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 Figures 1 to 8, inclusive, when combined in the manner illustrated in Fig. 9 of-th drawings, illustrate one link and the common equipment of an all-relay automatic telephone system having incorporated therein the features of the invention briefly outlined above.

Referring. to the drawings, the system there illustrated comprises 'a private automatic exchange at which may be terminated as many as one hundred lines, certain of which have been of the link finders. The group relays also corindicated in the drawings by the directory number designations thereof. More specifically,

2 these lines are divided into groups of ten each, the line H extending to the substation A being the first line of the first group, the line I extending to the substation B being the tenth line of the first group, and the-line 0i, illustrated in Fig. 4 of the drawings, being the first line of the tenth group. For switching purposes, each group of lines is further divided into two subgroups in accordance with the unit designations of the lines therein. Thus, the lines designated by the directory numbers ll, l2, l0, l4 and I5 comprise one subgroup of lines in the first group, and the lines l0, l1, l0, l0 and I0 comprising the second subgroup of lines in the first group.

For the purpose of setting up connections between the various lines of the system, there are provided a plurality of finder-connector links of the all-relay type. one of which is illustrated in Figs. 2, 3, 4, '7 and 8 of the drawings. These links are arranged to be controlled by common equipment which comprises a link distributor, also shown in Fig. '7 of the drawings, a group of distributor control relays illustrated in Fig. 6 of the drawings, and a group of guard or auxiliary relays which are illustrated in Fig. 5 of the drawings. More specifically, the finder portion of the link comprises ten group relays, two of which are indicated at R200 and R2l0, which respectively correspond to the different groups of lines. 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 interest of simplifying the disclosure. The finder portion of the link also comprises flv'e unit relays, each of which corresponds to two lines in each oi,the ten line groups. 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 the selected group of lines. Similarly, the unit relay R200 corresponds to the lines I and 6 in each of the ten different groups of lines. It will be understood that with one of the group relays and one of the unit relays operated, two lines are selected from the plurality 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 group relay R210 which functions to switch the conductors of the link line 200 between the link lines 228 and 220. For the purpose of associating the selectedrelays of the finder switch with the common equipment illustrated in Figs. 5, 6 and 7: there are provided a pair of connect relays R200 and R230. Y

The connector portion of the link is similar to the finder switch just described, in that ten group relays, including the two relays R000 and Rllfl, and each 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 selection of a particular line from a group of lines selected through operation of one of the group relays is accomplished through the operation of a counting relay network which is illustrated in Figs. '1 and 8 of the drawings as comprising ten counting relays R800, R8l0, R020, R030, R040, R850, R000, R810, R000 and R000, three pulse circuit control relays R150, R160 and R110, and a slow-acting pulse controlled relay R100. This counting chain is further utilized for the purpose of selecting the one of the ten group relays to be operated, and the side of a selected line over which ringsubing current is to be projected in signaling a desired called substation.

The control equipment of the link comp a line relay R3l0, a slow-acting hold relay R a right-ofway or special service relay R000, and a battery feed impedance element 000. This apparatus further comprises .a slow-acting ring cutoff relay R300, three ringing control relays R550, R310 and R380, a busy test relay R550, a line switching relay R300, three digit transfer relays R420, R030 and R050, and a slow-to-release test circuit control relay R400.

As indicated above, the equipment common to the several links comprises a plurality of guard or auxiliary relays which individually correspond to the relays embodied in each of the finder switches. More specifically, this equipment comprises two group relays R500 and R5" which individually correspond to the finder group relays R2l0 and R200 of the link illustrated. Eight additional auxiliary group relays are provided, which relays are indicated by the multiple and chain conductors extending between the contacts of the two group relays R500 and R5". Five auxiliary uni-t relays, including the two relays R550 and R550, are provided, which individually correspond to the five unit relays of the various finder switches. The auxiliary relay equipment further comprises a pair of relays R520 and R530 which function to control the subgroup relays embodied in the finder switches.

The link distributor or ailotter equipment is also of the all-relay type, a group of link distributor relays R100, R1l0, R100, 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 relays are arranged to be controlled by a group of control relays which are illustrated in Fig. 6 of the drawings as comprising a slow-acting relay R5l0 for controlling the start circuits and the call metering device 5, a group of slow-to-release link transfer and distributor control relays R020, R530, R500 and R550, a slow-acting distributor reset relay R050, and an all-links-busy relay R510 which is operated only when an all-busy condition of the respective associated links prevails. The relay R510 is arranged to control an all-busy meter 532 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 R500 which is provided for the purpose of controlling the executive right-of-way circuits, referred to above and described with particularity hereinafter, in

aceordance with the operation of the two auxiliary sub-group relays R520 and R500.

For the purpose of initiating the operation of the common equipment just described, each line of the system is terminated in a line circuit which conventionally comprises line and cut-oi! relays. Thus, the line H, which extends to the substation A, terminates at the exchange in a line circuit I05 which includes a line relay RI" and a cut-oif relay RI l0. Similarly, the line II, which extends to the substation B, is terminated at the exchange in a line circuit H5, which includes the line and cut-oi! relays RIM and RI", respectively.

Operation of the system Referring now more particularly to the operation of the apparatus, a call initiated at the substation A and intended for the substation C may be considered by way of example. When the party initiating the call at the substation A re-' moves the receiver provided at this substation from its associated switchhook or cradle, a loop circuit is established which includes the exchange battery and the winding of the line relay RI00. This circuit extends from ground by way of the contacts III, the conductor lie, the direct current bridge across the conductors of the line II at the calling substation, the conductor IIb, the contacts I I2, and the winding of RI 'to battery. In operating, the relay RI 00 prepares, at its contacts IN, a circuit for energizing the auxiliary unit relay R550 which corresponds to the line I I. At its contacts I02, the relay RI00 completes a circuit for energizing the auxiliary group relay R500 which corresponds to the first group of ten lines. This circuit extends from ground by way of the contacts I02, the start conductor CH5, the winding of R500, the contacts 506, C510, the contacts 6I2, C580, the contacts 505 and -I6, the chain-connected contacts controlled by the other auxiliary group relays, and the resistor 522 to battery. When energized over this circuit the relay R500 completes, at its X contacts 504', an obvious holding circuit for itself, and opens, at its contacts 505, a point in the common portion of the operating circuits for the ten auxiliary group relays. At its contacts 505', 506, 501, 508 and 509, the relay R500, in operating, prepares the operating circuits for the five auxiliary unit relays. In the present case, however, only the auxiliary unit relay R550 is operated, the circuit for energizing this relay extending from ground by way of the contacts 534, the winding of R520, CIM, the contacts IOI, CI43, the contacts 506, the winding of R550, the contacts 556, C511, the contacts 6II, C516, the contacts 550 and 569, similar chain-connected contacts of the other auxiliary unit relays, and the resistor 568 to battery. At its contacts 50I, the relay R500 prepares a circuit for energizing the group relay of the assigned link. At its contacts 502 and 503, the relay R500 prepares two of the executive right-of-way control circuits referred to above.

When energized in series with the relay R550 over the above-traced circuit, the slow-to-release relay R520, at its contacts 52I, opens a, point in the operating circuit for the relay R530, thereby to prevent operation of the latter relay until the call in progress is extended to an assigned link. The auxiliary unit relay R550 also operate when the above-traced circuit is completed, and upon operating, completes, at its X contacts 555, an obvious locking circuit for itself. After this circuit is completed, the relay R550, at its contacts 550 opens a point in the common portion of the operating circuits for all of the auxiliary unit relays. At its contacts 551, the relay R550 prepares a circuit for energizing the unit relay of the assigned link which corresponds to the unit designation of the calling line. At its contacts 552 and 553, the relay R550 prepares certain of the executive right-of-way circuits referred to above. At its contacts 55I, 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 II. In such case the relay R550, upon operating, completes a circuit for energizing the two connect relays R280 and R290 in parallel, this circuit extending from ground by way of the contacts 55I, the common start lead C513, the contacts 102, 0234, and the windings of the relays R280 and R290 in parallel to battery. The relay R290, in operating, completes, at its contacts 291, a circuit extending by way of the common guard lead 0682 for energizing the slow-acting relay R6I0. The relay R6I0 now operates to complete, at its.contacts H3, a circuit extending from ground at the contacts 614 for energizing the call metering device 6", whereby the call is registered. At its contacts 6I I, the relay R6I0 opens another point in'the common portion of the operating circuits for all of the auxiliary unit relays. 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 II. The relay R280, in operating, prepares, at the contacts controlled thereby, the operating circuits for the ten group relays embodied in the finder switch illustrated. In the case under consideration, only the relay R2I0, which terminates the first group of ten lines, is energized in response to operation of the relay R280, the operating circuits for the other nine relays being held open at the restored contacts of the other auxiliary group relays. More specifically, the circuit for energizing the relay R2I0 extends from ground by way of the contacts 50I, C51I, the contacts 282, and the winding of R2I0 to battery. This relay, in operating, prepares, at its contacts 2 to 2I3, inclusive, connections between the conductors of the line I I and the conductors of the link line 228, and, at its contacts 2 I1, prepares a holding circuit for itself. At the remaining contacts controlled by this group relay, connections are prepared between the other nine lines terminating at these contacts and the two link lines 220 and 229.

The relay R290, upon operating, prepares the operating circuits for the five unit relays of the finder switch. In the case under consideration only the operating circuit for the relay R260 is completed, this circuit extending from ground by way of the contacts 532 and 551, C584, the contacts 290, and the winding of R260 to battery. When energized over this circuit the relay R260 operates to prepare a locking circuit for itself at its contacts 261. At its contact 26I, 262 and 263, the relay R260 connects the conductors of the calling line II to the conductors of the link line 228. At its contacts 260,265 and 266, the

' relay R260 connects the conductors of the line I6 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 II is in the first subgroup of the first group of lines, the subgroup relay R530 of the common equipment is 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 unit relays 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 R individual to the link illustrated, this multiple circuit extending from ground by way of the resistor 100, the contacts 166, C232, the contacts 292, C23I, and the winding 01' R100 to battery. At its contacts 296, the relay R290 prepares the circuit for energizing the special service or executive right-of-way relay R300.

The relay R290, in operating, also completes a. circuit for energizing the line relay R3I0, this circuit extending from ground by way of the upper winding of R3 I 0, the conductor 230a, the contacts 29I, the resistor 233, the conductor 230b, and the lower winding of mm to battery. When energized over this circuit the relay R3I0 operates to complete, at its contacts 3I2, an obvious circuit for energizing the slow-acting hold relay R320. At its contacts 3| I the relay R3I bridges the windings oi the battery feed impedance element 330 across the associated line conductors. At its contacts 3I3, the relay R3l0 opens a point in the pulsing circuit, traced hereinafter, over which the relays of the counting chain are con trolled.

The relay R320, in operating, completes, at its contacts 324, an obvious path for impressing ground potential upon the release conductor C301, thereby to prepare locking circuits, traced hereinafter, for certain of the other control relays embodied in the link. At its contacts 325, the relay R320 prepares the pulsing circuit to the relays of the counting chain illustrated in Fig. 8 of the drawings. At its contacts 32I, the relay R320 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 operated contacts 292 of the connect relay R290. At its contacts 323, the relay R320 completes the prepared holding circuits for the group and unit relays R2I0 and R260, respectively. More specifically, the holding circuit for the unit relay R260 extends from ground by way of the contacts 323, the finder hold lead C235, the contacts 261 and the winding of R260 to battery The holding circuit for the group relay R2I0 extends by way of the grounded hold lead C235, the contacts 2I1 and the winding of R2I0 to battery. At its contacts 322, the relay R320 prepares a circuit for energizing the ringing control relay R310. At the contacts 322, the relay R320 also completes a path for impressing ground potential upon the private conductor lIc of the calling line II, this path extending from ground by way of the contacts 322, C233, and the contacts 215. 263 and H3, to the conductor I I0.

When the private conductor IIc of the calling line II is grounded, this line is marked as busy in the bank contacts of the various connector switches, and the cut-ofi relay RI I0 is energized over an obvious circuit. The relay RI I0, in operating, disconnects the line conductor Ila from ground and disconnects the upper winding terminal of the line relay RI00 from the conductor IIb, Thus, the line relay RI00 is deenergized and the calling loop circuit is cleared of the impedance represented by the winding of this relay.

When thus deenergized, the relay RI00 restores to open, at its contacts I 0| and I02, the established locking circuits for the operated group and unit relays R500 and R550, respectively. At its contacts IOI, the relay RI00, in releasing, also deenergizes the slow-to-release relay R520. The

relay R500, in releasing, opens, at its contactsv 50I, the above-traced operating circuit for the relay R2I0. At its contacts 502 and 503, the relay R500 opens two of the prepared executive right-of-way circuits. At its contacts 504 and 505, the relay R500 reprepares the operating cirthe relay R500 opens a further point in the abovetraced circuit for energizing the relays R520 and R550 in series. At the remaining contacts controlled by the relay R500, the prepared operating circuits for the other four auxiliary unit relays of the common equipment are interrupted. The relay R520, in releasing, reprepares the operating circuit for the subgroup relay R530. When the auxiliary unit relay R550 restores, it opens, at its contacts 551, the previously traced operating circuit for the unit relay R260. At its contacts 555, the relay R550 opens a further point in its locking circuit. At its contacts 554 and 556, the relay R550 reprepares .the operating circuits for the five auxiliary unit relays. At its contacts-552 and 553, the relay R550 further opens the prepared executive right-of-way circuits referred to above. At its contacts 55l, the relay R550 interrupts the above-traced circuit for energizing the two connect relays R230 and R290 in parallel.

The two connect relays R280 and R290 now restore. The relay R280, in releasing, opens the prepared operating circuit for the ten group relays of the-finder switch. The relay R290, in restoring, opens the prepared operating circuits for the five unit relays and the subgroup relay R210 of the finder switch. At its contacts 291, the relay R290 opens the above-traced operating circuit for the relay R6 I 0, causing the latter relay to release. At its contacts 292, the relay R290 opens the above-traced multiple holding circuit for the link distributor relay R100. The relay R now restores, and at its contacts 102, disconnects the common start lead C513 from the start lead C234 extending to the link illustrated. At its contacts 10I, the relay R100 connects the common start lead C513 through the contacts 1I2 of the second link distributor relay R1I0 to the start lead individual to the second link. At its contacts 106, the relay R100 opens a further point in its locking circuit as traced above. At its contacts 101, the relay R100 prepares an operating circuit for itself. At its contacts 105, the relay R100 prepares a point in the chain circuit for energizing the slow-acting reset relay R660. At its contacts 103 and 104, the relay R100 opens the prepared path for short-circuiting its own winding, and prepares a path extending through the contacts 1 I3 for short-circuiting the winding of the second link distributor relay R1I0. Following the operations just described, the link illustrated is identified as busy in the link distributor relay group, and the relays of this group are in the position required to assign the second link to the use of the next incoming call. Shortly following the release of the relay R100, the slowacting relay R6I0 restores to open, at its contacts M3, the circuit for energizing the metering device 6I4. At its contacts 6 and 6l2, the relay R6I0 reprepares the operating circuits for the auxiliary unit and auxiliary group relays, whereby these relays are conditioned to respond to another call. It will be noted that the operating circuits for these auxiliary relays are held open until all of the other relay operations required incident to the handling of the call in progress are completed, thus positively eliminating the possibility of two calling lines obtaining access to the same link.

As indicated previously, the operation of the common equipment and the finder portion of an assigned link to seize a calling line is diflerent,

depending upon the unit designation of the calling line. The preceding explanation is predicated upon the operation of the apparatus to select a calling line included in the first subgroup of lines of a particular line group. Briefly to consider the operation of the apparatus when a call is initiated upon a line, such, for example as the line included in the second subgroup of a particular line group, it is pointed out that if the line relay R120 individual to this line operates, a circuit is completed for energizing the subgroup relay R530 in series with the auxiliary unit relay R560 corresponding to the line 10. The previously traced operating circuit for the group relay R500 is also completed, at the contacts 122, when the line relay R120 operates. More specifically, the series operating circuit for the two relays R530 and R560 extends from ground by Way of the lower winding of R530, the contacts 521, C162, the contacts 121, C1, the contacts 505', the winding of R560, the contacts 556, C511, the contacts 611, C516, the contacts 5511 and 566, and corresponding chain-connected contacts of the other three unit relays and the resistor 568 to battery. When energized over this circuit, the

I relay R560 is locked up in series with the lower winding of the relay R530 over a circuit including the X contacts 565. At its contacts 564, the relay R560 opens a point in the common portion of the operating circuits for the five auxiliary unit relays. At its contacts 562 and 563, the relay R560 prepares certain of the executive right-of-way circuits referred to above. At its contacts 561, the relay R560 prepares a circuit for energizing the unit relay R220 01 the first link, assuming that the first link has been selected for use by the link distributor relays. At its contacts 561, the relay R560 completes the previously traced circuit for energizing the two connect relays R280 and R290 in parallel. The relay R280, in operating, completes the previously traced operating circuit for the group relay R210. The relay R296, in operating, prepares the operating circint for the unit and subgroup relays of the finder switch. The relay R290 also performs the other functions described above with reference to the call initiated on the line 11. The subgroup relay R530, in operating, opens, at its contacts 532, the previously traced operating circuit for the selected unit relay of the finder switch, and completes, at its contacts 533, an obvious circuit for energizing its upper winding in parallel with its lower winding and in series with the winding of the auxiliary unit relay R560. At its contacts 533, the relay R530 opens a point in the previously traced operating circuit for the slow-acting relay R520. At its contacts 531, the relay R530 completes a circuit extending by way of C581 for energizing the relay R600. The relay R600, in operating, opens, at its contacts 601, certain of the prepared executive right-of-way circuits, and, at its contacts 602, prepares certain others of these circuits. At its contacts 603, the relay R600 completes the prepared operating circuit for the subgroup relay R210 of the assigned link, this circuit extending from ground by way of the contacts 603, C683, the contacts 263 and the winding of R210 to battery. When energized over this circuit the relay R210 operates and prepares a locking circuit for itself at its contacts 211. At its contacts 211 to 216, inclusive, the relay R210 disconnects the conductors of the link line 230 from the conductors of the link line 228, and connects the conductors of the first-mentioned link line to the conductors of the link line 22a in preparation for the selection of a line in the secprepared alternative operating circuit for the relay R220, this circuit extending from' round by way of the contacts 218 and 236, C582, the contacts 561, C583, the contacts 235, 'and'the winding of R220 to battery. When energized over this circuit, the relay R220 operates and prepares a locking circuit for itself at its contacts 221. At its contacts 224, 225 and 226, the relay R220 connects 'the conductors 10a, 10b and of the calling line 10 through to the conductors 230a, 2301) and C233 of the link line 230. At its contacts 221 to 223, inclusive, the relay R220 preparts a connection from the line 15 to the conductors of the link line 230, but since the subgroup relay R210 is operated, this connection is held open at the contacts 211, 213 and 215. Thus, it will be apparent that, depending upon the position of the subgroup relay R210, either of two lines may be selected through operation of any one of the five unit relays embodied in the finder switch.

When the connect relay R290 operates, it also functions to complete the operating circuit for the line relay R810, thereby to cause the sequential operation of this relay and the hold relay R320, in the manner pointed out above. The relay'R320, in operating, completes the prepared holding circuits for the group relay R2l0, the unit relay R220, and the subgroup relay R210, these holding circuits commonly extending by way of the grounded hold conductor C235, and branching through the contacts 211, 221 and 211, respectively, to the windings of the respective enumerated relays. The relay R320, in operating, also completes a path extending by way of the contacts 322, C233, and the contacts 216, 226 and 216 for impressing ground potential upon the private conductor 100 of the calling line 10. Thus, the calling line is marked as busy in the contacts of the connector group relays, and the cut-off relay R130 is caused to operate to disconnect the winding of the line relay R120 from across the conductors of the line 10. When the relay R120 releases, it functions to initiate the releaseof the common equipment. in the manner explained above, it being pointed out that the series holding circuit for the two relays R530 and R560 is interrupted, at the contacts. 121, when the line relay R120 restores. The relay R530, in restoring, reprepares, at its contacts 532, certain of the operating circuits for the finder unit relays, and at its contacts 536, reprepares the operating circuit for the slow-to-release relay R520. At its contacts 531, the relay R530 interrupts the abovetraced operating circuit for the relay R600. The relay R600, in releasing, rearranges the executive right-of-way circuits referred to above, and, at its contacts 603, opens a point in the common portion of the operating circuits for the subgroup relays of the link finder switches.

As indicated above, each time one of the finderconnector links is assigned to the use of a calling line, the link distributor relay corresponding thereto is deenergized and releases. Thus, when the link illustrated is seized, the corresponding distributor relay R100 is caused to restore to extend the control leads C513, C683 and C685 to the contacts of the distributor relay R corresponding to the second link. In a similar manner, when the second link is assigned to the use of a calling line, the relay R1l0 is caused to release to extend the control circuits to the distributor relay corresponding to the third link. This successive assignment of links continues until the last link, namely that corresponding to the distributor relay R130, is assigned to the use of a calling line. In this regard it is pointed out that in the event the second link corresponding to the distributor relay R1I0 is occupied with a call at the time the first distributor relay R100 releases, the control circuits are extended through the restored contacts of the relay R1 i to the distributor relay corresponding to the third link. Further, if this third link is also occupied with a call, the control circuits are extended through the restored contacts of the corresponding distributor relay to the contacts of the distributor relay corresponding to the fourth link. The arrangement of the distributor is such that the relays thereof are not immediately reoperated in response to the release of the respective associated links. Thus, it will be observed that with the relay R100 in its restored position, no circuit is available for energizing this relay regardless of the position of the hold relay R620. When, however, the last link, corresponding to the distributor relay R130, is assigned for use to cause the release of this distributor relay, a chain circuit is completed for energizing the slow-acting reset relay R660. Under these conditions all of the distributor relays are restored regardless of whether or not the respective associated links are occupied with calls. Accordingly. the circuit for energizing the reset relay R660 may be traced as extending from ground by way of the contacts 136, the chain-connected contacts of the distributor relays other than those illustrated, the contacts 1| 6 and 105, C685, and the winding of R660 to battery. When energized over this circuit the relay R660 operates to prepare, at its contacts 66l, a holding circuit for the all-links busy relay R610. At its contacts 662, the relay R660 completes the operating circuits for those of the link distributor relays which are associated with idle links. For example, if the link illustrated has been released prior to the operation of the reset relay R660, the operating circuit for the corresponding link distributor relay R100 is completed, this circuit extending from ground by way of the contacts 662, C681, the contacts 101, C232, the contacts 32!, C231, and the winding of R100 to battery. Obviously, if the link illustrated is still occupied with a call, this circuit is held open at the contacts 321, so that the distributor relay R100 is not energized. In a similar manner, if the second link is idle, an operating circuit for the associated distributor relay R1l0 is completed by way of the grounded conductor C661 and the contacts 1|1. Similar operating circuits are completed for the other distributor relays which correspond to idle links. In the event the distributor relay R100 is energized over the circuit traced above, this relay operates to complete a locking circuit for itself which extends from ground by way of the resistor 106, the contacts 106, C232, the contacts 32I, C23 i, and the winding of R100 to battery. At its remaining contacts the relay R100 arranges the associated control circuits so that the link illustrated will be assigned to the use of the next calling line. The other distributor relays which correspond to idle links ar similarly locked in their respective operated positions. When the distributor relays which correspond to idle links, operate, the chain circuit for energizing the reset relay R660 is broken. The relay R660, accordingly, releases after an interval to open the prepared holding circuit for the relay R610, and to open, at its contacts 662, the respective operating circuits for the distributor relays. 4

Provisions are made in the link distributing apparatus, whereby in the event an assigned link fails to find and seize a calling line within a reasonable time interval, the assigned link is released and a second link is assigned to the use of the calling line. To this end the common equipment is so arranged that each time a call is initiated upon one of the subscribers lines, the

normally energized slow-to-release relay R666 is deenergized. More specifically, the relay R666 is normally energized over a circuit which extends from ground by way of the contacts 616, the winding of R660, the contacts 622, C616, the contacts 666 and 666, the chain-connected contacts of the other unit relays, and the resistor 666 to battery. With the relay R660 energized over this, circuit an obvious circuit for energizing the slowto-release relay R666 is held completed at the contacts 6. With the relay R660 operated, the operating circuit for the overflow meter is prepared at the contacts 66!, a multiple circuit for energizing the relay R666 is completed at the contacts 662, and the operating circuit for the slow-acting relay R660 is held open at the contacts 663. When any one of the five auxiliary unit relays is caused to operate in the manner previously explained. the chain portion of the above-traced circuit for energizing the relay R636 is opened at the contacts 666, 666, or the corresponding contacts of one of the other auxiliary unit relays. After an interval determined by the slow-to-release characteristic of the relay R660, this relay restores to open the completed operating circuit for the relay R660. In the event the assigned finder switch successfully operates to seize the calling line in its intended manner, the line circuit associated with the calling line operates to open the start circuits to the auxiliary group and unit relays, in the manner previously explained, before the relay R660 is released. When these start circuits are opened, the operated one of the auxiliary unit relays is released to recomplete the above-traced operating circuit for the relay R660. This relay, in reoperating, recompletes the operating circuit for the relay R660. Thus, under normal operating conditions the relay-R660 is not released during the time interval required for an assigned finder switch to seize the calling line to which it has been assigned.

If, for any reason, the finder portion of an assigned link fails to seize the line to which it is assigned, thereby to cause the reoperation of the relay R630 before the relay R660 is released, then the assigned link is released and a second new link is assigned to the use of the calling line. Thus, if the operating circuit for the relay R660 is held open for a sufliciently long interval of time, this relay restores to open, at its contacts 66!, the prepared operating circuit for the overflow meter 632, and to open, at the contacts 662, the prepared multiple circuit for energizing the relay R630. At its contacts 666, the relay R660 completes the prepared operating circuit for the slow-acting relay R660, this circuit extending from ground by way of the contacts 616, 626 and 663, and the winding of R660 to battery. The relay R660, in operating, opens, at its contacts "I, the prepared path for short-circuiting the winding of the link distributor relay corresponding to the first assigned link. At its contacts 652, the relay R650 completes an obvious circuit for energizing the slow-acting relay R620. The relay R620, in operating, further prepares, at its contacts 62!, the path for short-circuiting the winding of the distributor relay corresponding to the first assigned link. At its contacts 624, the relay R620 opens the above-traced circuit for energizing the relay R650. At its contacts 622, the relay R620 opens a point in the normally completed circuit for energizing the relay R630. At its contacts 623, the relay R620 completes an alternative circuit for energizing the relay R630, this alternative circuit extending from ground by way of the contacts 613, the winding of R630, the contacts 623, C510, and the resistor 522 to battery. When thus energized, the relay R630 reoperates to complete the operating circuit for the relay R600. The relay R640, in turn, reoperates to reprepare the circuit for energizing the overflow meter 632, to complete a multiple circuit for energizing the relay R630, and to open, at the contacts 643, a further point in the operating circuit for the relay R650. Substantially concurrently with the reoperation of the relay R660, the relay R650 restores to open, at its contacts 652, the operating circuit for the slow-acting relay R620. At its contacts 65!, the relay R650 completes the previously mentioned path for shortcircuiting the winding of the distributor relay corresponding to the first assigned link.

Assuming, for example, that the link illustrated is the first assigned link, and further, that this link has failed to find the calling line to which it was assigned, the link distributor relay R100 is short-circuited when the relay R650 releases in the manner just explained. The path for shortcircuiting this distributor relay extends from the negative terminal of the exchange battery through the resistor 625 and by way of the contacts 62E and 65!, C684, the contacts 103, G232, the contacts 202, 023i, and the winding of R100 back to the negative terminal of the exchange battery. It is noted that the resistance value of the'resistor 625 is relatively small as compared with the resistance value of the resistor 108. More specifically, the resistor 108 has a resistance value of approximately 1,000 ohms, whereas the resistor 625 has a resistance value of only 50 ohms. It will be understood, therefore, that when the above-traced path is completed, the relay R100 is efiectively short-circuited and caused to release. In releasing, the relay R100, at its contacts 102, disconnectsthe common start lead C513 from the start lead C234 individual to the link illustrated, whereby the connect relays R280 and R290 are deenergized and restore. At its contacts the relay R100 extends the common start lead to the link start lead individual to the next available idle link. Thus, if the second link is idle, and the relay R110 is operated,'the common start lead C513 is connected through the contacts 10! and H2 to the start lead individual to the second link. At its contacts 106, the relay R100, in releasing, opens a point in the common portion of its two locking circuits, as traced previously. At its contacts. 101, the relay R100 prepares its own operating circuit. At its contacts 103, the relay R100 opens the path short-circuiting its own winding. At its contacts 104, the relay R100 prepares a path for short-circuiting the winding of the distributor relay corresponding to the next idle link, which, in the case assumed, is the second distributor relay R1l0. At its contacts 105, the relay R100 prepares the above-traced chain circuit for enersizing the reset relay R660. Substantially concurrently with the release of the relay R100, the

relay R620 restores to open, at its contacts 62!, the above-traced path for short-circuiting the winding of the distributor relay R100, and the prepared path for short-circuiting the winding-of the distributor relay corresponding to the second assigned link. At its contacts 624, the relay R620 reprepares the operating circuit for the relay R650. At its contacts 622 and 623, the relay R620 opens the above-traced alternative circuit for energizing the relay R630, and reprepares the initially traced operating circuit for the last-mentioned relay. It will be understood that since one of the auxiliary unit relays illustrated in Fig. 5 of the drawings is at this time still operated, the initially traced operating circuit for the relay R630 is open at the contacts 554, 564, or the corresponding contacts of an operated one of the other auxiliary unit relays. Accordingly, the second timing period is started in response to the release of the relay R620.

When the common start lead C513 is disconnected from the link start lead C234 through the release of the link distributor relay R100, in the manner just explained, the two connect relays R260 and R290 restore to open the operating circuits for the group and unit relays of the finder switch illustrated, and to open the completed operating circuit for the line relay R310. Thus, the line and hold relays R3I0 and R320 are caused sequentially to restore in an obvious manner. At its contacts 291, the relay R290, in releasing, disconnects the conductor' C602 from ground, thereby momentarily to deenergize the relay R6l0. Since, however, ground potential is impressed upon this conductor through operation of the connect relays embodied in the second assigned link substantially concurrently with the release of the two relays R280 and R290, the relay R6l0 is held energized and does not restore. The application of ground potential to the link start lead extending to the second assigned link results in the operation of the finder portion of this link to seize the calling line, assuming that the second assigned link is not also defiective. In such case, the operated ones of the auxiliary group and unit relays, illustrated in Fig. 5 of the drawings, are caused to restore so that the operating circuit for the relay R630 is recompleted before the relay R640 is released. Thus, the normal operation of the distributor equipment is resumed. If, however, the second assigned link is also defective or, for some reason, fails to seize the calling line to cause the operation of the line circuit associated therewith, the cycle of operation of the distributor equipment, as described above, is repeated so that the second assigned link is released and a thirdl-ink is'assigned to the use of the calling line. More specifically, the cyclic operation of the distributor equipment continues until the finder portion of one of the assigned links is successful in its operation to seize the calling line, and thus cause the release of the operated ones of the auxiliary group and unit relays illustrated in Fig. 5 of the drawings.

In the event all of the links embodied in the exchange are busy at the time the relay R130, corresponding to the last link, is released to complete the above-traced chain circuit for energizing the relay R660, none of the distributor relays are immediately energized, although the operating circuits for all of these relays are prepared. Accordingly, the relay R660 remains in its operated position until one of the links is released. With the apparatus in this condition, if a call is initiated upon one 01' the lines terminating at the exchange, the auxiliary unit relay illustrated in Fig. 5 and corresponding to the calling line, operates to impress ground potential upon the common start lead 0613, thereby to complete the operating circuit for the all-links-busy relay R610. This circuit extends by way of the grounded lead C613, the contacts 1, 13l, and the other chain-connected contacts controlled by the distributor relays, C686 and the winding of R6 10.to battery. When thus energized, the relay R610 locks to ground through the contacts 61! and 66!. At its contacts 612, the relay R610 completes a circuit extending by way. of the grounded conductor C686 and the contacts 6 for energizing the overflow meter 632, whereby the all-busy condition of the links is registered. At its contacts 614, the relay R610 opens a point in the previously traced circuit for energizing the call metering device 6, and a pointin the operating circuit for the relay R660. At its contacts 613, the relay A610 opens a point in the multiple operating circuit for the relay R630. Shortly following the initiation of the call, the relays R630-and R640 are caused sequentially to restore in the order named and in the manner previously explained. The relay R640, in releasing, prepares the operating circuit for the relay R650, and opens, at its contacts 6, the circuit for energizing the overflow meter 632. The relay R610 remains in its operated position until the all-busy condition of the links is terminated and one of the links is released. Thus, if the call under consideration is abandoned before one of the links is released, the operated ones of the auxiliary group and unit relays are caused to restore in a manner clearly apparent from the preceding explanation so that ground potential is removed from the common start lead C613 and the operating circuit for the relay R630 is reprepared. Thus, the operating circuit for the all-links-busy relay R610 is opened but this relay remains energized over its locking circuit as traced above. Further, the relay R630 is not caused to operate since its operating circuit is open at the contacts 642 and 613. Accordingly, further calls initiated prior to the release of one of the links to terminate the all-links-busy condition are prevented from causing further operation of the overflow meter 632. It will be own winding. After a time interval determinedv by the slow-to-release characteristic of the relay R660, this relay. restores to open, at its contacts "I, the locking circuit for the relay R010 and to open,at its contacts 602, the prepared operating circuits for the link distributor relays. The relay R610 now releases to open, at its contacts 012, the prepared operating circuit for the overflow meter 632, and to reprepare, at its contacts 613, the operating circuit for the relay R030.- At its contacts 614, the relay R010 completes the previously traced operating circuit for the relay R660. Due to the slow-to-release characteristic of the relay R660 and the slow-to-operate characteristic of the relay R060, the operation of the finder switch illustrated, to seize the calling line and thus cause the operation of the line circuit associated therewith to release the operated auxiliary group and unit relays, is completed before the relay R660 can operate. According y. the relays R630 and R640 are caused sequentially to reoperate before the relay R060 operates in response to the release of the relay R010. Thus, the two relays R620 and R660 are prevented from completing the path for short-circuiting the relay R100. In the event these two relays are operated prior to operation of the relay R640. the completion of the path for short-circuiting the winding of thedistributor relay R100 is without eifect, since, under any circumstances, the finder switch illustrated will complete its operation to seize the calling line before the relay R100 is shortcircuited. Accordingly, the short-circuiting path will be opened at the contacts 262 and 32I of the apparent from the foregoing description that with the relay R660 operated, the operating circuits for all of the link distributor relays are prepared. Accordingly, when one of the links is released, the link distributor relay corresponding thereto is immediately energized. Thus, if all of the linksare busy and the link illustrated is the first link to'be released, the operating circuit for the associated distributor relay R100 is completed in response to the release of the hold relay R320 individual to this link. The relay R100, in reoperating, opens its operating circuit and locks to ground in the manner previously explained. At its contacts 102, the relay R100 connects the common start lead to the link start lead C234 so that if a call is waiting the assignment of a link, the connect relays R260 and R290 are immediately energized to cause the operation of the finder switch illustrated in the manner explained above. At its contacts 106, the relay R100 opens the above-traced operating circuit for the relay R660. 'At its contacts 103, the relay R100 prepares the previously traced path for short-circuiting its relays R290 and R320, respectively, before the relay R650 is caused to restore in response to release of the relay R620. Thus, even though these two relays may operate, such operation is, in the case under consideration, without eflect.

Continuing now with the operation of the link to extend a connection to the called line 0|, it is pointed out that when the hold relay R320 operates to impress ground potential upon the release conductor C301, a circuit is completed for energizing the slow-to-release relay R440, this circuit extending by way of the grounded conductor C301, the contacts 396, C330, and the winding of R440 to battery. Upon operating, the relay R440 completes a path fortransmitting the usual dial tone signal over the calling end of the connectionto inform the calling subscriber that the dialing operation may be started. The path traversed by the dial tone signal current may partially be traced as extending from one terminal of the dial tone current source, not shown, the contacts 45!, 4M and 42I, C320, the contacts 36!, and the condensers 341 and 340, to the negative side of the established loop circuit extending to the calling substation A. After traversing the windings of the receiver provided at this substation, the dial tone current is returned to the opposite terminal of the dial tone source over the positive side of the calling loop circuit, the upper winding of the line relay R3 and ground.

Following the operation of the relay R440, the link circuit apparatus is conditioned to respond to the impulses makingup the first digit of the directory number designating the desired substation 0. In this regard it is pointed out that the link circuit apparatus is so arranged that the first digit is utilized to determine the side of the called line over which ringing current is to be projected, the second digit is utilized to select the group of ten lines including the called line, and the third digit is utilized to select the particuaaaaoas 9 lar called line from the selected group of tan lines. More specifically, .a-first digit of two impulses conditions the link circuit apparatus for the transmission of ringing current over the negative side of the called line. A first digit comprising three impulses, on the other hand, conditions the equipment for the transmission of ringing current over the positive side of the called line. In the present case, since the line 0| is a single party line and the signal device provided at the called substation C is assumed to be bridged across the conductors of this line in series with a condenser, a first digit of either twoor three impulses may be dialed at the calling substation A.

Assuming that a first digit of two impulses is dialed at the calling substation, the relay R3|0 is twice caused to restore and reoperate. When this relay restores at the beginning of the first impulse, the operating circuit for the hold relay R320 is broken at the contacts 3l2. At the contacts 3l3, a circuit is completed for energizing the slow-acting relay R140 in parallel with the first counting relay R800, this circuit extending from ground by way of the contacts M3, 325 and 381' to the conductor C182 where it divides, one

- branch extending through the winding of R140 to battery, and the other branch extending by way of the contacts 154, 164 and 114, C133, and the winding of R800 to battery. The relay R140, upon operating, opens, at its contacts 14! and 142, two points in the operating circuit for the digit transfer relay R430, and a point in the operating circuit for the ringing control relay R350. At its contacts 143, the relay R140 opens a point in the common portion of the operating circuits for certain of the ten group relays embodied in the connector portion of the link. Due to the slow-to-release characteristics thereof, the relays R320 and R140 remain operated during each 40 series of impulses.

The relay R800, upon operating at the beginning of the first impulse, completes, at its contacts 806, a locking circuit for itself, and in so operating circuit for the relay R800. At its contacts 113, the relay R110 further prepares the circuit for energizing the second counting relay R820. At the beginning of the open circuit period of the second impulse, when the line relay mm again restores, the operating circuit for the second counting relay R820 is completed, this circuit extending from ground by way of the contacts 3l3, 325 and 391', C182, the contacts 154, 184 and 113, C182, the contacts 805, and the 15 winding of R820 to battery. When thus energized the relay R820 operates and locks to ground over a path including the contacts 826, C189, the winding of R160, the contacts 152, 018i, the contacts 361, and the release conductor C301. At

its contacts 825, the relay R820 prepares the operating circuit for the third counting relay R840. At its contacts MP the operating circuit for the relay R430 is further prepared. At the remaining contacts controlled by the relay R820,

5 additional circuit control operations. are performed which are of no consequence at the present time. At the end of the open circuit period of the second impulse, when the line relay R310 again reoperates, the path short-circuiting the winding of the second control relay R160 is interrupted, permitting this relay to be energized in series with the second counting relay R820. The relay R160 now operates to open, at its contacts 162, the above-traced series locking circuit for the two relays R110 and R800, causing both of these relays to restore. At its contacts 16!, the relay R160 prepares an obvious multiple point in the operating circuits for the relays R430 and R350. At its contacts 164, the relay R160 opens a point in the'above-traced operating circuit for the second counting relay R820. At its contacts 163, the relay R160 prepares a circuit for energizing the third counting relay R840.

In the case under consideration, wherein a doing completes a path for short-circuiting th first digit of two impulses is dialed at the calling winding of the control relay R110. This locking circuit extends by way of the grounded release conductor C301, the contacts 361, C18l the contacts 162, the winding of R110, C188, the consubstation, no further operation of the counting chain. illustrated in Fig. 8 of the drawings occurs. By way of more completely describing the mode of operation of this chain, it is pointed tacts a", and the winding of R8 to batterm out, however, that in those instances where digits It will be observed that so long as the line relay R3|0 is restored, both winding terminals of the relay R110 are connected to ground, and accordingiy, this relay is short-circuited. At its conother than the digit two are dialed, the counting relays operate in sequence so that at the end of the digit the counting relay which corresponds to the numerical value of the digit remains in tacts 805, the relayR800 prepares a circuit for its operated Position Thus it further impulses.

energizing the second counting relay R820. At its contacts 804, the relay R800 prepares a circuit for energizing the group relay R4l0 em-q bodied in the connector portion. of the link and terminating the first group of ten lines. contacts 803, the relay R800 prepares a circuit for impressing ground potential on the private conductor of a selected called line.v At'its contacts 80| and 802, the relay R800 connects'the conducare transmitted to the line relay R3i0, the operating circuit for the third counting relay R840 is completed at the beginning of the open circuit period of the third impulse, this circuit extend- At its mg byway oi the grounded conductor 0182, the contacts 154 and 163, 019i, the contacts 825, and

the winding of R840 to battery. The relay R840, upon operating, locks to the grounded release conductor C301 over a path including the contors of the link line 321 to the conductors of the ts 846. C189, the winding of R150, the conlink line 480.

At the end of the open circuit period of the first impulse, the line relay R3l0 reoperates to recomplete the circuit for energizing the hold tacts 112, 018i, and the contacts 361. when this path is completed, the relay R150 is obviously short-circuited. At the contacts 845, the relay R840 prepares the operating circuit for the fourth relay R320 and to open the path short-circuiting counting relay R860. At its contacts 84!, the

the winding of the control relay R110. The relay R is thus energized in series with the first counting relay R800 and operates to open, at its contacts 112, a point in the operating circuit relay R840 further prepares the circuit for energizing the relay R350. At the end of the open circuit period of the third impulse, when the line relay R3l0 again reoperates, the path short-cirfor the relay R150. At its contacts 111, the re- 75 cuiting the winding of the relay R is opened,

permitting this control relay to be energized in i w'th the third counting relay R840. The relay R155 now operates to open the series look: ing circuit for the two relays R180 and R820, at its contacts 152, thus causing both of these relays to restore. At its contacts 15!, the relay R150 prepares an obvious multiple path in the operating circuits for the relays R350 and R430. At its contacts 154, the relay R150 opens a further point in the operating circuit for the relay R840. At its contacts 153, the relay R150 further prepares the operating circuit for the fourth counting relay R860.

The last-mentioned circuit is completed at the beginning of the open circuit period of the fourth impulse, and extends by way of the contacts 3!3, 325 and 391', C182, the contacts 153, C180, the contacts 845, and the winding of R860 to battery. When energized over this circuit the relay R860 locks to the grounded release conductor C301 over a path including the contacts 866, C188, the winding of R110, the contacts 162, C18!, and the contacts 381. When this path is completed, the winding of the relay R110 is obviously shortcuited. At its contacts 865, the relay R860 prepares the operating circuit for the fifth counting relay R880. At the end of the open circuit period of the fourth impulse, when the relay R3l0 again operates, the path short-circuiting the winding of the relay R110 is interrupted, permitting this relay to be energized in series with the counting relay R860. The relay R110 now operates to open, at its contacts 112, the series locking circuit for the two relays R150 and R840. At its contacts 113, the relay R110 prepares the operating circuit for the fifth counting relay R880. It is believed that the manner in which the remaining counting relays respond to additional impulses transmitted thereto through operation of the line relay R3|0 will be clearly apparent in view of the preceding explanation. Thus, it will be noted that the relays R8 0, R830, R850, R810 and R890 sequentially respond to the sixth, seventh, eighth, ninth and tenth impulses of a digit in the order named. It will be further noted that the relays R880 and R850 lock to ground over the lead C189 in series with the control relay R160; the relays R8|0 and R810 lock to ground over the lead C189 in series with the third control relay R150; and the relays R830 and R890 lock to ground over the lead C180 in series with the control relay R110. The three enumerated control relays operate sequentially in response to succeeding impulses successively to prepare the operating circuits to the various counting relays and successively to release the previously operated counting relay and its associated control relay.

Shortly following the end of the first digit of two impulses dialed at the calling substation A, the relay R140, which is deenergized through operation of the line relay R3I0, restores to complete the above-mentioned circuit for energizing the relay R430. This circuit extends by way of the grounded release conductor C301, the contacts 142 and 16!, C183, the contacts 426 and 454, C184, the contacts 14!, C185, the contacts 82! C433, and the winding of R430 to battery. Upon operating, the relay R430 locks to the grounded release conductor C301 over a path including the contacts 432 and the winding of R450. When this locking path is completed, the winding of the relay R450 is obviously short-circuited. At its contacts 43!, the relay R430 completes a circuit for energizing the relay R380, this circuit extend -ing by way of the grounded release conductor C301, the contacts 43!, 452 and 424, C33!, and the winding of R380 to battery. The relay R350 now operates to open, at its contacts 381, a point in the common portion of the above-traced locking circuits for the three control relays R150, R and R110, and the ten counting relays illustrated in Fig. 8 of the drawings. In response to this operation the two operated relays R160 and R820 are deenergized and restore. Aside from its function to release the two relays R160 and R820, the operation of the busy test relay R380 is without-effect at this time. When the relays R820 and R restore, the impulse counting chain and associated control equipment is fully released and is prepared to respond to the impulses of the second digit. Further, these two relays, in releasing, open, at the contacts 16! and 82! two points in the path short-circuiting the winding of the digit transfer relay R450. The relay R450 is thus energized in series with the relay R430 over a circuit extending by way of the grounded release conductor C301, the winding of R450, the contacts 432, and the winding of R430 to battery. Upon operating, the relay R450 opens, at its contacts 45!, the above-traced circuit for transmitting dial tone signal current over the calling end of the connection, thereby to terminate the dial tone signal being reproduced by the receiver provided at the calling substation. At its contacts 452, the relay R450 opens the above-traced operating circuit for the busy test relay R360, whereby the latter relay is caused to restore to reprepare, at its contacts 361, the series locking circuits for the counting relays and the associated control relays R150, R150 and R110. At its contacts 454, the relay R450 opens a point in the common portion of the operating circuits for the relays R350 and R430. At its contacts 453, the relay R450 prepares a point in the common portion of the operating circuits for the ten group relays embodied in the connector portion of the link. Following the operation of the relay R450, the connector portion of the link is conditioned to respond to the impulses of the second digit of the directory num-- ber designating the desired line.-

As indicated above, if a first digit of three impulses is dialed, the ringing circuits are rearranged for the transmission of ringing current over the positive side of the called line. In this case it will be recalled from the preceding explanation that the relay R840 is locked energized in series with the control relay R150 at the end of a first digit of three impulses. With these two relays operated, the operating circuit for the ringing control relay R350 is completed in response to the release of the slow-acting relay R140, which occurs shortly following the end of the digit. The circuit for energizing the relay R350 extends by way of the grounded release conductor C301, the contacts 142 and 15!, C183, the contacts 428 and 454, C184, the contacts 84!, C180, and the winding of R350 to battery. When energized over this circuit the relay R350 locks to the grounded release conductor C301 over a path including the contacts 358 and the winding of the digit transfer relay R450. At its contacts 355, the relay R350 completes an alternative circuit for energizing the busy test relay R350, this circuit extending by way of the grounded conductor C301, the contacts 355, C333, the contacts 452 and 424, C33!, and the winding of R380 to battery. At its contacts 35!, 352, 353 and 354, the relay R350 rearranges the ringing circuits for ously explained.

alternative circuit for energizing the busy test.

the transmission of ringing current over the positive side of the called line. The busy test relay R360, in operating, opens, at its contacts 881, the series locking circuit for the two relays R150 and R840, causing both of these relays to restore. Thus, the impulse counting chain and the associatedcontrol relays R150, R160 and R110 are fully released. When the two relays R150 and R840 restore, two points are opened, at the contacts 15l and 84!, respectively, in the path short-cirrelay R360, in releasing,'reprepares the locking circuits for the ten counting relays and their associated control relays,

The impulse counting chain illustrated in Fig. 8 of the drawings, and the associated control relays R150, R160 and R110, respond to the impulses of the second digit in the exact manner described. Further, the slow-acting relay R140 is energized at the beginning of the first impulse of the second digit, and remains operated until shortly after the digit is ended. In the case under consideration, wherein the called line is the first line of the tenth group, the second digit dialed at the calling substation A will necessarily comprise ten impulses. Accordingly, at the end of the digit, the tenth counting relay R890 is energized in series with thecontrol relay R110. Shortly following the end of the digit, the relay R140 restores to complete the prepared operating circuit for the group relay R400, at which are terminated the lines of the tenth group. This circuit extends by way of the grounded release conductor C301, the contacts 142 and 11!, C183, the contacts 426 and 453, C181, the contacts 892, C896, and the winding of the-group relay R400 tobattery. By way of completing the explanation, it is pointed out that the portion of the circuit just traced, which extends to the contacts 892 of the counting relay R890, is common to the operating circuits for all of the even-numbered group relays of the connector portion, of the link. The group relays terminating the lines forming the odd-numbered groups are arranged for energization over a slightly different circuit. Thus,

if the called line to be selected is included in the first group, for example, such that a second digit of one impulse is dialed, the group select relay R410 is energized over a circuit which extends by way of the grounded release conductor C301, the contacts 142 and 1", C183, the contacts 426 and 453, C181, the contacts 143,- C186, the contacts 804, 046i, and the winding of R4i0 to battery. Thus, the odd-numbered group select relays are arranged for energization over a circuit commonly including the conductor C186, and, the select relays corresponding to the even-numbered groups of lines are arranged for energize.- tion over a circuit including the conductor C181.

When the relay R400 is energized over the circuit traced above, it operate and locks to ground over a path including the contacts 402, the winding of the digit transfer relay R420 and the release conductor C301. When this circuit is completed, ground potential is impressed upon both of the winding terminals of the relay R420 in the manner previrelay R360, this circuit extending byway oi the grounded conductor C801, the contacts 4M .and 422,-C33i, and the winding of R360 to battery. At its remaining contacts, the relay R400 connects the conductors of the associated ten lines tothe ten link lines corresponding to and including the two lines-460 and 410. Thus, the conductors of the selected ten lines are extended to the contacts controlled by the ten counting relays; the conductor of the first line in the group being connected over the link line 480 to the contacts 801, 802 and 803 of the first counting relay R800, the contacts of the second line in the group being connected over a similar link line to the contacts of the second counting relay R820, and so on.

The busy test relay R360, upon operating in response to operation of the group select relay R400, opens, at its contacts 361, the series locking circuit for the two relays R110 and R890, causing both of these relays to restore. When these relays release, two points are opened at the contacts Hi and 892, respectively, in the path short-circuiting the winding of the digit transfer relay R420, permitting the latter relay to be energized in series with the group relay R400 over a circuit extending by way of the grounded release conductor, C301, the winding of R420, the contacts 402, and the winding of R400 to battery. The relay R420 now operates to open, at its contacts 422, the above-traced alternative operating circuit for the busy test relay R360. At its contacts 424, the relay R420 opens a further point in the initially completed operating circuit for the busy test relay. At its contacts 426, th relay R420 opens a further point in the common portion of the operating circuits for the ten roup relays embodied in the selector portion of the link. At its contacts 423, the relay R420 prepares alternative operating and locking circuits for the busy test relay. At its contacts 425, the relay R420 prepares a circuit for energizing th line switching and ringing control relay R390. The busy test relay R360, upon restoring in response to the operation of the digit transfer relay R420, reprepares the locking circuits for the impulse counting relays and their associated control relays R150, R160 and R110. Following the release of the busy test relay R360, the connector portion of the link is conditioned to respond to the impulses of the third digit of the directory number designating the calledline 0 I.

The counting relays and their associated control relays operate in the exact manner described above in response to the impulses of the third and final digit. The relay R140 reoperates at the beginning of this digit and remains operated until shortly following the end of the digit. In the present assumed case, wherein the line 0| is the first line of the selected tenth group of lines, the third digit will necessarily comprise only a single impulse, so that the counting relay R800 is locked energized in series with the relay R at the conclusion of the digit. Shortly following the end of the digit, the relay R releases to complete the prepared circuit for energizing the relay R390, this circuit extending by way of the grounded release conductor 0301, the contacts 142 and 1", C183, the contacts 425, C332, and the winding of R390 to battery. The relay R390 now operates further to prepare the desired talking circuit to the selected called line and the circuit for transmitting ringing current over the called line. At its contacts 391, the relay R390 op ns a point in the above-traced pulsing circuit over which impulses are transmitted to the counting relays and the slow-acting relay R140. At its contacts 399, the relay R390 opens the operating circuit for the slow-to-release relay R440. The relay R440 now releases to prepare, at its contacts 442, the operating circuit for the slowto-operate ringing control relay R310. At its contacts 443, the relay R440 opens a point in one of the previously traced operating circuits for the busy test relay R360. At its contacts 398, the relay R390 completes an alternative circuit for maintaining the operated counting relay R800, and its associated control relay R110, energized. This alternative circuit extends by way 01' the groundedrelease conductor C301, the contacts 383, CH", the contacts 162, the winding of R110, C188, the contacts 806, and the winding of R800 to battery. At its contacts 39|, the relay R390 prepares a circuit for transmitting busy. ton current over the calling end of the connection to energize the receiver provided at the calling substation. At its contacts 396, the relay R390 completes a test circuit including the winding of the busy test relay R360 for determining the idle or busy condition of the selected line. In this regard it will be recalled from the preceding explanation that when a line becomes busy. ground potential i impressed upon the private conductor thereof, for the purpose of guarding the line against seizure by the various connector switches oi. the system. On the other hand, if a line is idle, the private conductor thereof is marked with negative battery potential through the winding of the cut-ofi relay embodied in the associated line circuit.

Assuming that the selected is busy, the busy test relay R360 is energized over the test circuit, which circuit extends from groundby way of the contacts 405, the conductor 4600, the contacts 803, C334, the contacts 396, C336, the contacts 443 and 423, C33I, and the winding of R360 to battery. This circuit is completed during the interval between the operation or the relay R390 and the release of the slow-to-release rel'ay R440. It will be noted that the portion of this circuit extending from the contacts 803, and including-the conductor C334 is common to the odd-numbered lines of each ten line group. On the other hand, if an even-numbered line is selected, the idle or busy condition or the line is tested over a slightly diii'erent circuit. More specifically, the common portion of the alternative circuit'individual to the even-numbered lines extends by way of the conductor C335, the contacts391, C336, the contacts 443 and 423, 033i, and the winding of the busy test relay R360 to battery. When energized over the first oi the above-traced circuits, the busy test relay operates to complete a locking circuit for itself. This locking circuit extends by way of the grounded release conductor C301, the contacts 398, 306 and 366, C331, the contacts 423, C33|, and the winding of R360 to battery. Atits contacts 365, the relay R360 opens a point in the operating circuit for the ringing control relay R310. At its contacts 363 and 364, the relay R360 prepares a dry talking circuit to the selected called line. At its contacts 362, the relay R360 completes the above-mentioned circuit for transmitting busy tone current over the calling end 01' the connection to energize the receiver provided at the calling substation. This circuit may partially be traced as extending from one terminal of the busy tone current source by way of the contacts 30!,

native locking circuit traced above.

aasaosa 39| and 362, and the condensers 341 and 348 to the negative side or the established loop circuit extending to the calling substation. The current traversing this circuit is reproduced by the receiver provided at the calling substation to inform the calling subscriber that the desired connection cannot immediately be obtained. At its contacts 361, the relay R360 opens a point in the initially completed series locking circuit for the two relays R110 and R800. These two relays are, however, held energized over the alter- Following the operation of the busy test relay R380, no further operation of the apparatus occurs until the connection is released at the calling substation. The manner in which the link is released when the call is abandoned is described in detail hereinafter.

In the event the selected called line 0| is idle, the busy test relay R360 is short-circuited over the previously traced test circuit and, accordingly, does not operate. Shortly following the end of the third digit, the relay R440 releases, in the manner previously explained, to open the busy test circuit and to complete a circuit for energizing the slow-to-operate ringing control relay R310. In the case under consideration wherein the called line is an odd-numbered line, the circuit for energizing this relay extends from the negative terminal of the exchange battery through the winding of the cut-oil? relay embodied in the line circuit individual to the called line and by way of the contacts 405, the conductor 460e, the contacts 803, C334, the contacts 396, C336, the contacts 442, C329, the contacts 366, the winding 01' R310, and the contacts 322 to the grounded positive terminal of the exchange battery. It will be noted that this operating circuit for the ringing control relay R310, as completed through the cut-off relay associated with any oddnumbered line, includes the conductor C334. On

the other hand, ii an even-numbered called line is selected, the operatin circuit for the ringing control relay R310 is slightly different in that it extends from the conductor C336 by way of the contacts 391, C335, and the operated private contacts of the counting relays which correspond to the called lines. Thus, in the case of an oddnumbered called line, the ringing control relay R310 is energized over an operating circuit including the contacts 396 and the conductor C334, and in the case of an even-numbered called line, this relay is energized over a circuit including the contacts 391 and the conductor C335.

When energized over the above-traced circuit, the relay R310 operates after an interval to complete, at its contacts 31|, an obvious circuit for energizing the relay R380. The relay R380 now operates and locks to the grounded release conductor'C301 through its X contacts 385. At its contacts 383, the relay R380 completes an obvious path for short-circuiting the winding of the relay R310, thereby to render the latter relay slow-torelease and to complete a path for impressing ground potential directly upon the private conductor of the called line 0|, which path includes the conductors and contacts of the above-traced operating circuit for the relay R310. When this path is completed, the cut-off relay embodied in theline circuit individual to this line, operates to clear the line of the impedance represented by the windings of the associated line relay. The application of ground potential to the private conductor of the called line 0| also guards this line against seizure by any of the other connector

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