US2301015A - Telephone system - Google Patents

Description

NOV. 3, 1942. K 'l A J. BUSCH 2,301,015

TELEPHQNE sYsgEM FiledMarch 22, 1940 6 Sheets-Sheet l UNH u er Y ATTORNE V Filed March 221 1940 e sheets-sen 2j khbskl /NVENTOR AJ. BUSCH ATTORNEY r A. J. BUSCH TELEPHONE vsxs'rim Nw.A 3, 1942.

Filed March 22,` 1940 T0 No. n coN/vscran A'E'NDER COA/NE C TOR f llllll 6 Sheets-Sheet 3 AJ. BUSCH 5r AVT rpm/Er Nov. 3, 1942, A. J. BuscH TELEPONE SYSTEM Filed March 22. 1940 6 Sheets-Sheet 4 nooo o o QQ o 00u00 oooo nooo www o mss 0 vo /N VE NTOR ,4. J. BUSCH ATTORNEY Nov. 3, 1942. A. J. BUSCH TELEPHONE SYSTEM Filed March 22, 1940 6 Sheets-Sheet 5 VENTO/Q AJ. BUSCH ATTOWEVv Nav. 3, 1942. A. J. 'BUSCH 2,301,015

TELEPHONE SYSTEM Filed March 22, 1940 6 Sheets-Sheet 6 FIG. 6

/NVENTOR AJ. BUSCH 1 ATTORNEY Patented Nov. 3, '1942 TELEPHGNE SYSTEM Aloysius J. Busch, Madison, N. J., assgnor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application March 22, 1940, serial No. 325,304

22 Claims.

This invention relates to a telephone system and more particularly to a system in which connections are established to certain oilices over a tandem trunk by' selecting the trunk vin response tc the dialing ci one or more of the cnice code digits of the wanted office designation and in which it is necessary to secure a record ci the office code digits dialed for controlling the further extension of a connection from the trunk to the desired office or for other purposes.

in telephone systems of the type in which se lector switches are controlled by a register sender common to all lines of an originating ofce in which both the oice code digits and numerical digits of wanted lines are registered in response to dialing by a calling Subscriber, it is the Wellknown practice when the Wanted line terminates in a distant office to provide intermediate or tandem omces through 'which 'such calls are eX- tended to such distant oilices. Such a tandem office is provided with trunks incoming from originating offices which terminate in seiector switches having' access to trunks outgoing to such distant cnces and with tandem senders accessible from the tandem trunks which are Capable of Controlling selector switches to extend a connection from a tandem trunk to a desired distant oiice and for setting selector switches in the selected distant ofilce to terminate the connection. The tandem trunk is selected by the setting of selector switches in response to the registration of the cnice code digits of a wanted line which terminates in the distant cflice whereupon the tandem trunk seizes an idle tandem sender and the originating sender transfers all of its digit registrations including the oflice code and numerical digit registrations of the Wanted line number to registers of the tandem sender. The tandem sender then proceeds to control selector` switches to extend a connection fromthe tandem trunk to the oce of the wanted line in accordance with the office code digit registrations trans ierred thereto from the originating sender and to control selector switches in the selectedA ofiice in accordance with numerical digit registrations transferred thereto from the originating sender.

yWhen, however, it becomes desirable to provide tandem cnice equipment of the type above described in telephone systems which have no ccmmon senders in the yoriginating oflices Iand in which the selector switches are of the type which 'are controlled in their selective movements directly under the control of a calling subscribers dial, it becomes necessary when a tandem trunk is selected by the setting of such selector switches in response to the dialing of the cnice code digits of a wanted line terminating in a distant cnice to be reached through the tandem omceto provide means at the tandem clice for ascertaining the omce code digits which have been dialed so that the tandem sender may register such digits for use in further extending the connection from the tandem trunk to such wanted olce.

' A specific application of tandem trunking ci this character may be made for example in connection with the extension of short haul toll Connections to oices in the nearby toll area in which the tandem trunks are provided with automatic toll ticketing facilities whereby all such short haul toll connections may be established automatically under the control of a calling subrscribers dial and the toll ticket may be automatically printed. A system of this type is disclosed in the copending application of J. W. Gocderham, Serial No. 325,342, filed concurrently herewith. Since for ticketing purposes the ticket printer must be supplied with the designations of both the kkcalling and wanted lines, it is further essential that the cnice code digits of thewanted line dialed by a calling subscriber to select the tandem trunk be made available for the use of the toll ticket printer. 1t is therefore the object of the present invention to provide facilities at a tandem trunk which may in a simple and accurate manner ascertain any office code digits which a calling subscriber may have dialed in setting up a connection to the tandem trunk and which may make a record of any office code digits dialed subsequentl to the establishment of a connection to the tandem trunk.

As illustrated herein the subscriber desiring a connection to a line terminating in an cfilce of a nearby toll area first removes his receiver from the switchhook whereby an idle line iindcr, paired with a rst selector, is started in search of the calling line and as soon as the line is found the usual dial tone is transmitted. Upon hearing the dial tone the subscriber then proceeds to dial the oflice code and numerical digits of the wanted line number. .In response to the dialing of one or more of the ofice code digits, the selector switches of a switching train including the first selector switch are operated to extend Va connection from the calling line to an idle tandem or automatic ticketing trunk accessible from all lines of the oflice in which the calling line terminates over which trunk a connection may be further extended to the cnice in which the wanted line terminates.

Immediately following the seizure of the trunk an idle sender common to a plurality of such trunks is associated with the seized trunk over a sender-connector switch. The sender is provided with registers for registering the remaining digits of the called line number dialed by a calling subscriber. Since, however, a digit dialed by a calling subscriber might be lost during the time elapsing between the seizure of the trunk and the seizure of an idle sender, the trunk is provided with a digit register for registering the digit dialed following the last code digit dialed to reach the trunk. On calls to certain offices the trunk may be seized by a first selector in response to the dialing of a rst office code digit. On calls to other oinces, the trunk may be seized by a second selector in response to the dialing of two oflce code digits While on calls to st ill other oiiices, the trunk may be seized by a third selector in response to the dialing of three ofce code digits. Since the trunk maybe seized in response .tothe dialing of one, two or three code digits, lthe trunk register may register either the second or third code`digits or the thousands numerical digit. As soon as the first digit has been registered in the sender which digit may be either ,thethird code digit, the thousands digit or the hundreds digit, an idle decoder -is associated with the sender over a decoder-connector and the decoder is associated directly with the trunk over a trunk decoder-connector. Thereupon oiiice code identifying equipment associated with the trunk transfers to registers in the decoder .information concerning the oiiice code digits dialed to .reach .the trunk and if omce code digits have been registered by the trunk register or -by the first register of the sender, such registration or registrations are also .transferred to the decoder whereby the decoder thus receives all of `the information necessary regarding the oince designation of the desired line. This information .may be translated by the decoder if necessary Iand the registered information or-the translated information is then transferred to control registers of the ysender which are instrumental'in cont-rolling f slector switches to extend the connection from the trunk to the oiiice in which the wanted line terminates and in controlling the ticket printer of the `trunk to print the called oice code ydigits on a toll ticket. If the thousands numerical digit has been registered by the trunk register and such registration has been transferred to the decoder, this registration is alsoy transferred to the sender from the decoder. The sender also registers the remaining numerical digits dialed by the calling subscriber and in accordance with its numerical digit registration directs the setting of selector switches in the called oflice, such numerical digit registrations also being effective to control the printer to print such numerical digits on the toll ticket. For controlling the ticket printer in accordance with the code and numerical digit registrations made in the sender, the sender becomes associated with the trunk over a trunk sender-connector.

The sender may also receive digit registrations from calling line identifying equipment associated with the decoder of the type fully disclosed in the application of J. W. Gooderham hereinbefore referred to and control the ticket printer of the trunk to print such identification digits on the toll ticket. The ticket printer may also be controlled following the response of the called subscriber and during the continuance of the conversation to print information on the toll ticket indicative of the duration of the conversational period.

The invention having been described in a general manner, reference may now be had to the following detailed description thereof taken in connection with the accompanying drawings in which:

Fig. 1 shows schematically a calling line, a line nder and a train of first, second and third selector switches for extending a connection from the calling line to a tandem automatic ticketing trunk, branches of the incoming ends of the tandem trunk of Fig. 2, the schematic disclosure of a trunk decoder-connector and one of the oice code digit registers of a decoder;

Fig. 2 shows the remaining portion of the tandem trunk including a step-by-step type digit register, a timing mechanism of the electric clock motor driven type and a toll ticket printer schematicallyV illustrated by the box in the lower right portion of the figure;

Fig. 3 shows in the upper right portion thereof a trunk sender-connector and in the remaining portion thereof a sender-connector and the control circuits therefor whereby an idle sender is associated with a calling tandem trunk;

Fig. 4 shows such portions of a sender as are necessary to an understanding of the invention;

Fig. 5 shows additional registers and relays of a decoder;

Fig. 6 shows other registers of a decoder; and,

Fig. '7 is a diagram showing how the other gures of the drawing should be arranged to completely disclose the invention.

The line finder and the selector switches |02, |63, |04 and |05 may be of the well-known step-by-step type and the selector switches `may be controlled directly by a calling subscribers dial to establish local connections or to establish a connection to an idle automatic ticketing trunk such as is disclosed in Figs. 1 and 2 should the subscriber desire a connection to a subscribers line which terminates in the toll area adjacent to the exchange area in which the calling line terminates. As disclosed the automatic ticketing trunk of Figs. 1 and 2 has branches which terminate in banks of first selectors such as |82, other branches which terminate in banks of second selectors such as |63 and still other branches which terminate in banks of third selectors such as |04 and |95 whereby the trunk may be seized in response to the dialing of the first oflice code digit of certain distant oiiices, in response to the dialing of the rst and second office code digits cf other oflices and in response to the dialing of the three cnice code digits of still .other offices. With the arrangement illustrated to simplify the disclosure, but one group of tandem trunks would be available for serving connections to all offices in the toll area. In the commercial use of the invention, however, a plurality of groups of tandem trunks would be required to handle the toll traflic and therefore some of the groups of trunks would be made accessible only from bank levels of rst selectors, other groups would be made accessible only from bank levels of second selectors and still other groups would be made accessible from bank levels of third selectors. Still other groups might have incoming branches as disclosed accessible from bank levels of different selectors. The trunking scheme may therefore be made quite exible for allocating the trunk groups in accordance with the density of the toll traic to different portions of the toll area.

The register switch 250 associated with the tandem trunk of Fig. 2 may be of the rotarystepby-step type, the brush 25| of which is advanced step by step in response to the operation of its stepping magnet 252 and is restored to normal by the operation of its release magnet 253. The ticket printer 26|) indicated by the boX may be of any Well-known type asfor example a teletypewriter in which the type bars are selected for operation by a plurality' of magnet operated comb bars. The timer 244 for timing the duration of the conversational period is of the elec-v tric clock motor driven type.

The cross-bar sender-connector 30|] of Fig. 3 may be of the general type disclosed in Patent 2,021,329 granted November 19, 1935 to J N. Reynolds. have suilcient cross-point contacts to accommodate all of the control conductors required between a trunk and a sender, an additional trunk sender-connector switch 39|) is provided. rThis latter switch, the trunk decoder-connector |50 of Fig. 1 and the decoder-connector 58D of Fig. 5 are of the multicontact relay type such as are employed in the cross-bar system and as are disclosed, for example, in Patent 2,089,921 granted August 10, 1937 to W. W. Carpenter.

The sender, portions of which are disclosed schematically in Fig. 4, may be ofl a well-known type provided with incoming registers for registering the digits of a wanted line number dialed by a calling subscriber and with pulsing mechanism for controlling the setting of step-by-step selector switches in accordance with such registrations to extend a connection from the seized ticketing trunk to a wanted line. In addition the sender is provided with a printercontrol circuit 480 for controlling the ticket printer of the trunk with which the sender has become associated, which control circuit has relay registers for registering all of the digits of a wanted line number and the identifying digits of the calling line number. The relay registers for registering the called oilice code digits are controlled from the settings of the olce code digit registers of an associated decoder and the relay registers for registering the numerical digits of the called line may be set in accordance with the setting of the incoming registers oi the sender orby such incoming registers in conjunction with a register of the decoder. The called oiiice digit registers of the control circuit are also used by the sender in controlling the setting of selector switches `to terminate the connection. For assisting a sender in controlling the establishment of a desired connection, a plurality of decoders is provided, such portions of one of such decoders as are necessary to an understanding ci the invention being disclosed in Figs. l, 5 and 6. The decoder is associable with a sender over the decoder-connector 583 and with the trunk over trunk decoder-connector |50.

To more clearly set forth the novel features of the invention, it will be assumed that the calling subscriber whose substation is indicated by the numeral |09 initiates a call for a toll connection to a subscribers line terminating in an ofi-ice 'oi the toll area to which the calling subscriber is permitted access by dialing. Upon the `removal of the receiver from the switchhook, an idle line finder having access to the calling line, such as line finder IUI, is started in search of the calling line in a well-known manner. When the line nder has found the calling line, the usual dial tone is transmitted over the calling line to inform the subscriber that his line has been connected Since the sender-connector does not witha first selector |02, paired with the line nder IUI, and that he may therefore commence dialing the digits oi the wanted line number,

It will rst be assumed that the calling subscriber desires a connection with a line Whose directory number is MAR-1000 and that a tandem ticketing trunk over which a connection to this oice may be extended may be reached from the sixth bank level of the rst selector |92. 'I'he calling subscriber upon hearing the dial tone therefore proceeds to dial the oiiice code letters MAR and the numerical digits 1, 0 0 0. In response to the dialing of the first oiiice code letter M, which has a numerical equivalent 6, the rst selector |02 is operated to elevate its brushes to a position opposite the sixth bank level and to then hunt over the terminals of this level in search of an idle tandem trunk. It will be assumed that the trunk disclosed in Figs. l and 2 is idle and that therefore when the test brush of the selector |02 engages the test terminal |36 of this trunk, it'will encounter no busy ground potential thereon and'that therefore the selector switch will seize the trunk and extend a connection from the calling line to the tip and ring conductors 29|! and Z-I of the trunk. A circuit is thereupon established from ground through the upper winding of relay 202, the No. 1 normal contacts of relayY 203, tip conductor 299, through resistance T6 of approximately l0 ohms, branch conductor |08, tip brushes of selector ||J2 and line nder lll! over the calling line loop through substation |90, thence' returning over the ring brushes of line finder lll! and selector |92, branch conductor |59 through resistance RO over conductor 29|, the No."4normalicontacts of relay 203 to battery through the lower winding of relay 292. Relay 2GB thereupon operates closing over its front contact an obvious circuit for slow-to-release relay 294 which operates; connects ground over its upper contacts through the inductive resistance 255 and over sleeve conductor |91 of the trunk to the test terminals of all appearances of the trunk in the banks of selector switches for marking the trunk as busy to other selector switches having `access thereto;` connects ground to conductor 225 over its `inner upper front contacts for furnishing locking ground for other relays of the trunk; at its lower` front contact prepares operating circuits for." relay 296 and stepping magnet 252'of the digit register 250 and at its l upper front contacts establishes a circuit for initiating the association of an idle sender with the trunk. This latter circuit maybe traced from ground over the upper front contacts of relay 204, resistance 255, the inner upper normal contacts of relay 297|, back contact of relay 298, conductor 2638, inner normal contacts of hold magnet 3|!! of one of the two cross-bar switches constituting the" sender-connecter 3M), a hack contact of make-busy relay 392, conductor 303, the No. 3 back contact' of relay 2'33 and conductor 3M through the winding of line relay 33|), individual to the trunk of Fig.l 2 whereupon relay 339 operates. i

A plurality of sender-connectors such as 39|) is provided each `serving two groupsof ten trunks each and all having common access to ten senders. Each sender-connector comprises two crossbar type switches each of lwhich has one hundred sets of cross-point contacts arranged in ten vertical rows alloeated to ten trunks and arranged in tenhorizontal rows allocated to ten senders, any set of cross-point contacts being operable through the conjoint operation of one of the select' magnets, such as- 350, individual to an idle sender and one of the hold magnets, such as 3H), individual to the calling trunk. The two crossbar switches of a connector function as a unit and therefore their corresponding select magnets are multipled together for simultaneous operation and their hold magnets and line relays are arranged in chain lock-out circuits whereby the line relay and hold magnet individual tov but one trunk may be simultaneously operated and the trunks Nos. to 19 are given a preference in the'order named in the selection of an idle sender.

Common to all of the sender-connectors is a chain sender start and lock-out circuit provided with pairs of sender start and busy relays arranged coordinately, Vertical rows of such pairs or relays being allocated tothe several senderconne'ctors and horizontal rows of such pairs of relays being allocated to ten senders. For eX- aniple, the sender busy relay 310 and the associatedY sender start relay 380, allocated to the No. 0 sender 469 disclosed in Fig. 4, the sender busy relay 3'19 and the associated sender start relay allocated to the No. 9 sender 409 indicated by the dot-dash rectangle in Fig. 4 and intervening pairs of such relays (not disclosed) allocated to the Nos. 1 to 8 senders are allocated to the No. 1 sender-connector 309 and sender busy relay 31|]n and the associated sender' start relay 380n allocated to the No. 0 sender 499, the sender busy relay 3'l9n and the associated sender start relay 385i allocated to the No. 9 sender 409 and intervening pairs of such relays (not disclosed) allocated to the Nos. 1 to 8 senders are allocated to the n sender-connector (not shown). Intermediate rows of such relays are similarly allocated to' intermediate sender-connectors. By means of the sender start and lock-out circuit, senders Nos. 0 to 9 are given preference for selection in the order named.

It will be recalled that line relay 330 was operated following the seizure of the trunk of Fig. 2. Relay 330 upon operating prepares over its lower front contact an operating circuit for relay 366'; prepares over its inner upper front contact a locking circuit for itself; prepares over its middle upper iront contact an operating circuit for hold magnet 3l0; disconnects at its inner lower normal contacts operating battery for the succeeding line relays individual to the remaining nineteen trunks served -by the sender-connector 3939 and, assuming that the No. 0 sender is available for use, closes a circuit from ground over the lower back contact of hold magnet 3H), middle lower front contact of relay 330, thence over back contacts of succeeding line relays (not shown) including line relay 349 of the No. 19 trunk and the upper back contact of sender busy relay 3'l0 to battery through the winding of sender start relay 386. Relay 380 thereupon operates, disconnects at its inner lower normal contacts operating battery for succeeding start relays such as 389 allocated to the No. 0 sender and to other sender-connectors to `prevent the seizure of the No. 0 sender by trunks terminating in other sender-connectors; at its lower front contact establishes a circuit for sender make-busy relay 4|!! which may be traced from ground thereover and conductor 391 to battery through the winding of relay 4| 6 and establishes a circuit extending from ground at the upper back contact of relay 38011, over the back contacts of intermediate relays and its own upper front contact through the windings of select magnets 350 and 360 in parallel of the cross-bar switches of the sender-connector 306 to battery, thereby operating said magnets. Sender make-busy relay M0 upon operating closes operating circuits for all sender make-busy relays in the group 379 to 376 allocated to the No. 0 sender with the exception of relay 319, the circuit of relay Slln, for example, being established from ground at the lower back contact of relay 380, over conductor 368, the inner contact of relay 416 and conductor 309 to battery through the upper winding of relay 370. The similar operating circuit for relay 310 is not closed over the outer contacts of relay M9 since it is now open at the lower back contact of relay 38D. With sender make busy relays such as 316 now operated, no trunk served by the other sender-connectors is able to seize the busy No. 0 sender 406.

Should, for example, a trunk served by the No. n sender-connector attempt to seize a sender, the operation of the individual line relay of such trunk, corresponding to line relay 33t, will establish a holding -circuit for relay 31611 from ground over its upper front contact, conductor 394, thence in parallel over the lower back contacts of other sender busy relays such as 379n and over the lower front contact and through the lower winding of relay 316 to battery to prevent the release of relay 370 should the No. 0 sender thereafter become idle. Such line relay will also establish a start circuit from ground over its middle lower front Contact, the middle lower back contacts of succeeding line relays, conductor 395, upper front contact of relay 3161, thence in a chain circuit over the upper front contacts of sender busy relays of other busy senders and the upper back contact of the sender busy relay of the iirst idle sender in the order of preference, for example, relay 319, to battery through the start relay of such sender, for example, relay 389, In the manner previously described the make-busy relay of such sender, corresponding to relay All), will be operated to perform the function previously described in connection with the operation of relay 4H). If it be assumed that the sender start relay 38911 and the sender make-busy relay 4| 9 of the No. 9 sender 469 are operated, the operation of relay 38911 will establish an operating circuit over` conductor 396 for the select magnets of the No. 1L

' sender-connector individual to the No. 9 sender corresponding to magnets 359 and 369.

With line relay 330 and select magnets 359 and 360 operated as previously described, the circuit of relay 396 is completed from ground at the front contact of magnet 356 over the lower front contact of relay 336 and the back contacts of succeeding line relays including relay 349 to battery through the winding of relay 366. Relay 366 upon operating closes a locking circuit for the operated line relay 330 extending from battery through the winding and inner upper front contact of relay 336, thence over the inner upper back Contacts of succeeding line relays including relay 349 to ground at its outer left contact; establishes an operating circuit for hold magnet 3N), individual to the calling trunk of Fig. 2, which may be traced from battery through the winding of magnet 3H), over the middle upper front contact of line relay 330 and the middle upper back contacts of succeeding line relays including line relay 349, to ground at its inner left contacts and at its right contacts connects ground from the front contact of operated select magnet 369 into its own operating circuit whereby it is held operated so long as either select magnet 359 or 366 remains thereby opening the initial operating circuit of hold magnet 3|0 and the locking circuit of line relay 330. The selected cross-point contact set is now held operated by the continued energizaand 350 upon releasingin turn release relay 305 tion of hold magnet 3|0 over its locking circuitul With line relay 330 released, operating battery is now supplied to the operating circuits of the other line relays of the sender-connector and the sender-connector is rendered available to serve another trunk to which it has access. Start relay!A l 380 upon releasing closes a circuit for sender busy relay 310 extending from ground over its lower back contact, conductor 391, outer 4contacts of make-busy relay 4|0 of the seized No. 0 sender upper winding of relay 310 whereupon relay 31|) extends the start conductor from the sender-con nector 300 to the winding of the start relay, such as 309, of a subsequent sender'. Upon the closure magnet 252 of digit register 250 and over the No. 7 back contact of relay 202 through the winding of slow-to-release relay 206 to battery and ground. Magnet 252 operates preparatory to advancing the brush 25| of switch 250 and relay 206 also operates. At the end of the iirst dial impulse with relay 202 reoperated, magnet 252 releases to advance brush 25| one step but relay 206- being slow to release remains operated. Inresponse t0' the next operation and release of relay 202,magnet 252 advances brush 25| a second step. Since no further impulses are transmitted for the second ccde digit series, relay 202 now remains operated whereby the circuit of relay 206 is held open for a suilicient interval to permit its release.

'Relay206 upon releasing closes a circuit from ground over its back contact, the lower contacts of oil-normal switch 2|0, which closed upon the and over conductor 398 to battery through theof the selected set of cross-point contacts, six con-Y Y trol conductors are extended from the calling trunk to the selected sender 400.

It is to be noted that any sender-connector may Y be removed from service by the operation of its individual make-busy relay such as 302 either by the insertion of a short-circuited plug into its associated make-busy jack 399 or over a circuit extending over the middle lower back contacts of `all line relays of the connector and thence serially iirst step advance of brush 25| of register 250, to

ybattery through the winding of relay 203. Relay 203 upon operating `opens at its Nos. 6 and 7 contacts the operating circuits for relay 206 and magnet 252;` prepares at its No. 3 front contact the circuit for denied service relay 2||; extends trunk conductors 200 and 20| over its Nos. 2 and 5 front contacts through condensers 2|2 and 2|3 4to conductors 2 |4 and 2 |5, and at its Nos. 1 and 4 transfer contacts disconnects trunk conductors 200 and 20| from the windings of relay202 and connects such conductors to the windings of the impulse responsive relay 430 of the sender 400.

Relay 430 of thesender now operates over a circuit over the upper fron-t contacts of sender busy re-'7 lays 310 to 310 allocated to the sender-connector to ground should all senders become busy. .When relay 302 operates it opens at its back contacts the operating circuits for all line relays 330 to 349 y and over its front contacts connects ground to conductors 209 of all trunks which that senderconnector serves and thence to the sleeve conductors of the trunks to prevent such trunks from being seized by selector switches. Any sender may also be removed from service and marked as busy by the insertion of a short-circuited plug in the make-busy jack associated with its make-busy relay. Thus if a plug were inserted in the jack 420, relay 4|0 oi"V the No. 0 sender would-be operated to close a circuit through the operating windings of all sender busy relays such as 310 to calling subscriber dialed the second oillce code digit A, which has a numerical digit value of 2,

relay 202 releases in response to the first opening o1 the dial contacts upon the return of the dial vand opens the circuit previously traced for relay 204. Relay 204, however, being slow to release,

` remains operated during the transmission of the remaining impulses of the second code digit series.

With relay 204 operated and relay 202 released, a circuit is closed from ground at the back contact of relay 202 over the lower front contact of relay 204 thence in parallel over the No. 6 back contact vof relay 203 through Vthe `winding of stepping which may be traced from ground through its `right winding, over conductor 43| of cable 432,

No. 5 contacts of the operated cross-point contacts of sender-connector 300, conductor 2|6,

inner upper Vnormal contacts of cut-through relay 2|1, No. 1 alternate contactsv of relay 203 over conductor 200 and the calling line loop, returning over conductor 20|, the No. 4 alternate contacts of relay 203, the inner lower normal conf tacts of` relay 2|1, conductor 2|8, No. 4 contacts of the operated cross-point contacts of senderconnector 300, thence over conductor 433 of cable 432 to battery through the left winding of relay 430. Relay 430 operates and closes an obvious circuit for slow-to-release relay 434 which upon operating connects ground over its left contact, conductor 435 of cable 432, No. 2 contacts of the operated cross-point contacts of sender-connector 300 to conductor 209 for locking hold magnet 3|0 and for supplying busy ground to the trunk sleeve conductor |01.

If following the operation of relay 203, a sender has not been connected to the trunk, the circuit of the denied service relay'2l is completedfrom battery through its winding over the No. 3 front contact of relay 203, conductor 303, back contact of relay 302, inner lower normal contacts of hold magnet 3|0 which will not have operated, conductor 200, back Contact of relay 208, inner upper normal contacts of relay 201, through inductive resistance 255 to ground at the upper contacts of relay 204. Relay 2| upon operating locks over its inner lower front contact to ground on conductor 205 and establishes a circuitfor transmitting an all paths busy tone to the calling line which may be traced from the source of tone current 2 |9 over the inner upper front contact of relay 2| I, trunk conductor 20|, thence over the calling line loop as previously traced and returning over trunk conductor 200, the lower, Vfront contact of relay 2| to ground through the upper winding of relay 202 to inform the subscriber that the call cannot be served and that hershould release the connection.

In response to the dialing of the third code letter R, which has a digit value '7, impulse responsive relay 438 of the sender releases in response to the first opening of the dialing circuit and closes a circuit extending from ground at its back contact, over the right contact of relay 434 which being slow to release does not release upon the momentary releases of relay 438, and thence through the winding of slow-to-release relay 436 to battery and in parallel therewith over brush 431 of steering switch 438 and the first terminal of its bank to battery through stepping magnet 438 of the rst digit register 448. Relay 436 and magnet 438 thereupon operate, magnet 439 preparing to advance the brush 448 of register 44|. At the end of the rst impulse relay 458 reoperates opening the circuits of relay 436 and magnet 438, magnet 439 thereupon releasing to advance the brush 448 one step but relay 466 being slow to release remains operated during the transmission of the succeeding impulses of the third code digit series. In a similar manner relay 458 responds tol the remaining impulses of" the digit series and causes the step-by-step advance of brush 44| through six additional steps. At the end of the digit series relay 438 remains operated for a sufficient interval to permit relay,

, 436 to release, whereupon magnet 442 of the steering switch 438, which operated upon the operation of relay 436, is released to advance its brushes 451 and 455 one step. The brush of the digit register 44| has now beenpositioned on the No. 'l terminal of its bank. In a similar manner in response to the dialing of the numerical digits of the Wanted line number, the digit registers 443, 444, 445 and 446 are operated under the control of their respective stepping magnets 441, 448, y 448 and 458 in successive positions of the brush 481 of steering switch 438. Since as previouslsr assumed the numerical digits of the wanted line are 1, 0, and 0 the brushes 45|, 452, 453 and 454 will be advanced respectively to their Nos. l, 18, and 10 bank terminal positions.

Since in one case to be later described, the nrst digit registered by register 44| may be the third olce code digit, then as soon as this register has been set, indicating that all of the oice code digits have been dialed and registered and, following the registration of this digit, the steering switch 438 has advanced one step from normal, a circuit is established to summon an idle decoder which circuit may be traced from ground over the contacts of oli-normal switch 482 of the steering switch 458 and conductor 456 to battery through the winding of multi-contact relay 58|, individual to the No. 0 sender 488, of the decoder-connector 588. The decoder-connector 568 is provided with a multicontact relay such as 58| individual to each sender and a multicontact relay 582 individual to each decoder and by a lock-out circuit (not shown), the multicontact relay of the first idle decoder is closed by the operated. sender relay 58|. It will be assumed, that in the order of preference the decoder` disclosed in part in Figs. l, 5 and 6 is the first idle decoder and that therefore the operation of sender relay 58| causes the operation of relay 582. The decoder upon being seized then proceeds to associate himself with the calling trunk over either one of two trunk decoder-connectors one of which is disclosed schematically at |58 in Fig. 1.

At this point it should be observed that all groups of trunks are arbitrarily divid'ed into A and B subgroups and that two connectors, such as |58, are provided. All groups of trunks will have their A subgroups served by connector |58 and their B subgroups served by the other connector. This arrangement permits uninterrupted service under trouble conditions or when maintenance conditions arise which make it desirable to remove one of the trunk decoderconnectors from service. To inform the decoder in which subgroup a calling trunk is located and therefore which of the two trunk decoder-connectors is to be used, a signal is transmitted from the trunk to the sender and the sender then signals the decoder. All trunks of the B subgroup are provided with battery connected to one terminal of their relays, corresponding to relay 228, and with ground connected to the upper swing contact of their denied service relays, corresponding to relay 2H, and all trunks of the A subgroup are provided with ground connected to one terminal of their relays, corresponding to relay 228, and with battery connected through a non-inductive winding 22| of their relays, corresponding to relay 2| l, to the upper swing contacts of such relays. The connection of ground or battery to the terminal of relay 228 of any trunk therefore identifies the A or B subgroup in which the trunk is located.

It will now be assumed that the trunk shown in Fig. 2 is in the A subgroup and that therefore following the connection of the trunk to the sender 488, over the sender-connector 388, a circuit is established from ground through the winding of relay 228, upper back contact of relay 222, lower normal contacts of relay 281, conductor 223, No. 3 contacts of the operated crosspoint contacts of the sender-connector 380 and conductor 451 of cable 432, back contact of outpulsing relay 458 of the sender and back contact of relay 458 to battery through the winding of relay 468. Relays 228 and 468 thereupon operate, relay 468 causing relay 46| to operate and lock to off-normal ground. With relay 46| operated as soon as the decoder has been associated with the sender through the connection of ground to conductor 456, a circuit is established from ground on conductor 456 over the right front contact of relay 46|, conductor 462 of cable 464, contacts of relays 58| and 582 of decoderconnector 588, conductor 588 of cable 58| to battery through the Winding of relay 582 of the decoder. Relay 582 upon operating will cause the operation of multicontact relay 5| individual to the seized decoder of the trunk decoder-connectorl |58 over conductor 585 if such connector is available for the use of the decoder. If the calling trunk had been in the B subgroup and consequently battery had been connected to the winding of relay 228, the establishment of the previously traced circuit through the winding of sender relay 468 would not have caused the operation of relay 488 and consequently relay 46| would not have operated. Under this condition upon the connection of ground to conductor 456, a circuit would have been established from conductor 456 over the back Contact of relay 46|, conductor 463 of cable 464, contacts of relays 56| and 582 of the decoder-connector 588, conductor 583 of cable 58| to battery through the winding cf relay 584. Relay 584 upon operating will cause the operation of a multicontact relay, corresponding to relay |5|, individual to the decoder, of the second trunk decoder-connector cause its operation.

if such connector is available for the use of the release relay 204 extending from battery through the winding of relay 204 over such contacts to ground at the upper contacts of relay 204 for holding relay 204 operated during outpulsing and after relay 2li? releases following the operation of relay 203 as previously described.

When relay I5| operates it establishes a circuit frcm battery over its No. 39 contacts, conductor 50E, contacts of relays 582 and 58| of the decoder-connector 580, conductor 501 individual to the No. 0 sender 4530, No. l contacts of the -v operated cross-point contacts of the sender-connector @t0 and conductor 224 to battery through the winding of relay |35 of the calling trunk. Relay |35 operates closing an obvious operating circuit for multicontact relay |52 of the trunk decoder-connector |50, which relay is common to all trunks of the A group in which the calling trunk is assumed to be located; connects ground over conductor |36 to the brush 25| of the trunk register 250 and, following the operation of relay mine the ofce code digits which were dialed by the calling subscriber.

Forl the purpose of enabling the decoder to determine the value of any office code digit dialed to seize the tandem trunk, three groups of low resistances are provided which may, by suitable crcss-connections, be selectively included in the tip and ring conductors of the several incoming branches of the trunk. Resistance R0 is always connected to the ring conductor of every trunk branch which is accessible from a first selector and resistances RI to R0 are connected to ring conductors of the trunk branches which are accessible to either second or third selectors, re-

sistance Ri being connected to the ring conductors of all branches which terminate in the first bank levels of such switches, resistance R2 being connected to the ring conductors of all branches which terminate in the second bank levels of such switches, etc. Resistances T2 to T9 are connected to tip conductors of trunk branches which are accessible from either rst or second selector switches, resistance T2 being connected to the tip conductors of all branches which terminate in the second bank levels of such switches, resistance T3 being connected to the tip conductors of all branches which terminate in the third bank levels of such switches, etc. Resistances TAI to TA are cross-connected as may be required to the tip conductors of all branches which are accessible from third selector switches.

Thus when a connection is established to the .trunk over any one of its branches current will flow through one of the R resistances and through one of either the T or TA resistances and the potential drop across such resistances may be used to inform the decoder as to thecorresponding bank levels of selector switches; which have been employed to establish the con` nection. This will be more apparent if a few( concrete illustrations are considered.

If the first office code digit dialed has a nu-l merical value 6, the first selector Il2 will seize,y the trunk directhr over the branch conductors: |108 and |09 and the decoder must therefore be: informed that the code digit 6 was dialed to reach. the trunk. Therefore the tip conductor |00 is; connected to one terminal of the T6 resistance.y The decoder must also be informed that the second code digit dialed will be registered by the trunk register 250 and therefore the ring conductor is connected to one terminal of the R0, resistance. If the rst code digit dialed has a. numerical value of 7, the first selector |02 will seize the trunk directly over the branch conductors I0 and and the decoder must be informed that the code digit 7 was dialed to reach the trunk. Therefore, the tip conductor` ||0 is connected to one terminal of the T1 resistance and as inthe preceding illustration the ring conductor will be connected to one terminal of the R0 resistance. Thus, whenever a trunk is seized directly over any bank level of a first selector, a T resistance having a number corresponding to the bank level or value of the code digit dialed will be included in the tip branch of the trunk and the R0 resistance will be included in the ring branch of the trunk.

If the first ofcecode digit dialed has the numerical value 3, the first selector will seize an idle second selector such as |03 over its third bank level and the selected second selector will be set in accordance with the value of the second code digit dialed. If the second selector is now set to its eighth bank level, the trunk will be seized thereby over the trunk branch conductors H2 and I I3 and the decoder must therefore be informed that the first code digit dialed to set the rst selector was 3 and that the second code digit dialed to set the second selector was 8. For this purpose the tip conductor ||2 is connected to one terminal of the T3 resistance andthe ring conductor II3 is connected to one terminal of the R8 resistance. Thus whenever aV trunk is seized over a bank level of a second selector, the T resistance having a number corresponding to the bank level of the first selector over which the second selector was seized, will be included in the tip branch of the trunk and an R resistance having a number corresponding to the bank level of the second selector over which the trunk was seized, will be included in the ring branch of the trunk.

If the first selector is set to its third bank level in response to the dialing of the first code digit 3 to select the idle second selector |03 and the second selector is then set to its fourth bank level in response to the dialing of the second code digit 4 to select the idle third selector IE5.

then when the third code digit 5 is dialed, the third selector will be set to its fifth bank level and will seize the trunk over the tip and ring branch conductors II4 and ||5. The decoder must therefore be informed that the first code digit dialed to lset the rst selector was 3, that the second code digit dialed to set the second 75. selector was 4 and that the third code digit dialed to set the third selector was 5. For this purpose tration, if the rst selector is set to its third bank 'f level in response to the dialing of the first code digit 3 to select the idle second selector |03 and the second selector is then set to its iith bank level in response to the dialing of a second code digit 5 to select an idle third selector |04, then when the third code digit 6 is dialed, the third selector will be set to its sixth bank level and will seize the trunk over the tip and ring branches IIS and The decoder must therefore be informed that the first code digit dialed to set the first selector was 3, that the second code digit dialed to set the second selector was 5 and that the third code digit dialed to Set the third selector was 6. For this purpose the tip conductor ||5 is connected to one terminal of the TA4 resistance which, When current flows therethrough, will arbitrarily indicate to the decoder that the rst two digits dialed were 3 and 5 and ring conductor is connectedto one terminal of the R5 resistance whereby when current flows therethrough it will indicate to the decoder1 that the last cf said code digits dialed to reach the trunk was 6.

From the foregoing illustrations it will be noted that current flowing through any T resistance will indicate the corresponding value of the rst code digit dialed to reach the trunk that current flowing through any TA resistance will arbitrarily indicate the values of the first and second code digits dialed when the trunk is seized after dialing three code digits and that current flowing through any R resistance will indicate the value of the last digit dialed to reach the trunk, which if the trunk is reached by dialing only one digit will be resist-ance R and which if the trunk is reached after dialing either two or three code digits will b'e one of resistances Ri to R9.

For registering the oiice code digits dialed to reach the trunk as indicated by current flowing resistances VT2 to T5, respectively, the group '559 of Fig. comprising relays 5|0 to 5|5 which may be bridged around resistances R0 to R9, respectively, and the group 520 comprising relays 52| to 526 which may be bridged around resistances TAI to TAS, respectively. For registering either a second or third oice code digit or the tho-usands numerical digit which may be registered by the trunk register 250, a group 600 of register relays of Fig. 6 is provided comprising ten relays 50| to 5|0, inclusive, which are selectively operable in accordance with the bank terminal upon which the brush of the trunk register 2 50 is positioned, and for registering a third olice codedigit which may be registered by register 05| of the sender, a further group 53!) of register relays is provided comprising ten relays 6| to 625 which are selectively operable in accordance with the bank terminal upon which the brush 540 of register 44| is positioned.

Upon the operationof relays |35, |5| and |52 75 as previously described, the outer terminals of resi/stances R0 to R9 are connected over the Nos. 7 to 16 contacts of relay |35 and the Nos. 29 to 38 contacts of relays |5| and |52 to the upper terminals of the windings of register relays 5|0 to 5'I0, respectively; the outer terminals of resistances T2 to T9 are connected over the Nos. 17 to`2v4 contacts of relay |35 and the Nos. 21 to 28 contacts of relays |5| and |52 to the upper terminals of the lwindings of register relays |22 to |20', respectively; the outer terminals of resistances TAI to TA6 are connected over the Nos. 25 to contacts of Yrelay |35 and the Nos. 15 to 20 contacts of relays I5| and |52 to the upper terminals of the windings of register relays 52| to 526, respectively; the inner terminals of resistances T2 to T9 and TAI to TA6 are connected over tip trunk conductor 200, conductor |30, the No. 5 contacts of relay |35, the No. 13 contacts of relays |5| and ib'and conductor 22| 'to the lower terminals of register relays |22 to |29 and 52| to 520; the inner terminals of resistances R0 to R9 are connected over ring trunk conductor 20|, conductor lill, the No. 4 contacts of relay |35, the No. 12 contacts of relays I5| and |52 and conductor 521 to the lower terminals of register relays 5| 0 to 5IS; the bank terminals to 0 of trunk register 250 are connected over the Nos. 1 to 10 contacts of relays |5| and |52 and conductors of cable 532 to battery through the windings of register relays 60| to 650, respectively; a'circuit is prepared for the denied service relay 2I| of the trunk extending from battery therethrough, over conductor |32, the No. 3 contacts of relay |35 and No. 11 contacts of relays |5I and |52 to conductor 528 of cable 55 I, and a circuit is prepared for the metering relay 225 of the trunk from battery through its winding over conductor 226, the No. 6 contacts of relay and the No. 14 contacts of relays |5I and |52 to conductor 520 of cable 50|.

In the case rst assumed, the trunk was seized over the No. 6 level of the first selector 02 and the dialing circuit previously traced through the windings of impulse responsive relay 430 of the sender, extends through the T6 resistance and through the R0 resistance. With relays |35, I5I and |52 now operated, the winding of relay |26 of the tip register |20 and the Winding of relay 5|0 of the ring register 509 of the decoder are bridged around the T6 and R0 resistances, respectively. The bridging circuit of relay |26 may be traced from the lower terminal of resistance T5 over the No. 21 contact of relay |35, code conductor II8, No. 24 contacts of relays |52 and I5I, conductor ||0 through the winding of registerl relay |25, conductor |2I, No. 13 contacts of relays I5| and |52, No. 5 contacts of relay I35, conductor |30 and conductor 200 to the upper terminal of resistance T6 and the bridging circuit of relay 5|0 may be traced from the lower terminal of resistance R0 over the No. 7 contacts of relay |35, the No. 38 Contact of relays |52 and ,I5|, conductor 508 through the Winding of register relay 5| 0, conductor 521, the No. 12 contacts of relays 5| and |52, the No. 4 contacts of relay |35, conductor |3I and conductor 20| to the upper terminal of resistance R0. Since current is flowing through resistances T6 and R0 as supplied through ythe windings of sender relay (53,0, current will therefore ow in parallel With such resistances through the windings of register relays |26 and 5|()`I thereby causing their operation.'

With relay 5| 0 operated to indicate that no second selector was set by a second dialed code digit to select the trunk and `that therefore the second code digit was registered by the trunk register 250Vand the third code digit was registered by the sender register 44|, a circuit is established from ground at the No. 1 back contact of relay 530 and contacts of register relay to battery through the winding of relay 53|. Relay 53| upon operating associates the contacts of relays 54| to 6|!) of register 600 over conductors of group 52|, the Nos. 11 to 20 contacts of relay 53|, the Nos. 22 to 31 contacts of relays 58| and 552 of the decoder-connector and conductors of group B with the windings of relays of the B code digit register 459 of the sender; associates theA contacts of relays 5|| to 620 of the register 635 over conductors of group 522 over its Nos. 1 to contacts, the Nos. 12 to 21 contacts of relays 58| and 582 and conductors of group C with the windings of relays of the C code digit register 415 of the sender and establishes a circuit from ground over its No. 21 contact, No. 52 contacts of relays 53| and 552 conductor 455 to battery through the winding of multicontact relay 455 of the sender. Relay 455 operates to perform switching operations to be later described.

Register relay |26 upon operating closes a circuit from ground over its contacts, a conductor of cable |33, the No. 35 contacts of relays 58| and 552, a conductor of group A to battery through the windingiof the No. 6 relay (not shown) of the A code digit register 468 of the sender thereby registering in the sender that the first office code digit dialed has anumerical value of 6. It will be recalled that the second code letter dialed was A and that the brush of the trunk circuit 25|) was therefore advanced two steps to its No. 2 bank terminal. A circuit is therefore effective from ground applied by relay over conductor |35 to brush 25|, thence over the No. 2 terminal of its bank, thence over the No. 9 contacts of relays |5| and |52, a conductor of cable 532 to battery through the winding of relay 602 of register 65|). kRelay 652 thereupon operates establishing a circuit from ground over its contacts,

a conductor of the group 62|, the No. 19 contacts of relay 53|, the No. 30 contacts of relays 58| and 582 and a conductor of the B group to register 443 was advanced to its first 4bank terminal in response to the dialing ofthe thousandsdigit 1 and therefore upon the completion of the registration of this digit, at which time brush 455 of steering switch 438 will be in its No. 2 off-normal terminal position, a circuit is established from ground over brush 455 and this bank terminal, brush and the rst terminal of its bank, the No. 11 front contact of relay 456 to battery through the winding of thevNo. 1 relay of the thousands digit register 41|. The brush 452 of register 444 was advanced to its tenth bank terminal in responsie to the dialing of the hundreds digit 0 and therefore upon the 'advance of brush 455 following the setting of register 444 a circuit is established from ground over brush 455 and its No. 3 off-normal bank terminal, brush 452 and its tenth bank terminal, the No. 30 front contact of relay 456 to battery through the winding of the No. 0v relay of the hundreds digit register 412. The brush 453 of register 445 was advanced to its tenth bank terminal in response to the dialing of the tens digit 0 and therefore upon the advance of brush 455 following the setting of register 445, a circuit is established from ground over brush 455 and its No. 4 off-normal bank terminal, brush 453 and its tenth bank terminal, the No. 40 front contact of relay 455 to battery through the winding of the No. 0 relay of the tens digit register 413. The brush 454 of register 445 was advanced to its tenthrbank terminal in response to the dialing of the units digit 0 and therefore upon the advance of brush 455following the setting of register 445, a circuit is established from ground over b-rush 455 andits No. 5 off-normal bank terminal, brush 454 and its tenth bank terminal, the No. 5|) front Contact of relay 456 to battery through the winding of the No. 0 relay of the units digit register 414. All of the called line designationdigits have now been registered by the registers 458 to 414, inclusive of the printer control circuit 48|) of the sender.

battery through the winding of the No. 2 relay of the B code digit register 459 of the sender. It

will be recalled that the brush 445 of the digit register 44| of the sender was advanced into engagement with its No. 7 bank terminal in response to the dialing of the third ofce code let- Vterminal of its bank, the No. '1 front contact of operated` relay 465, thence over a conductor of the group SR, the No. 5 contacts of relays 58| and 552 and a conductor of the group 523 to battery through the winding of relay 6|1 of the decoder register 638. Relay 6|1 thereupon op-l erates and closes a circuit from ground over its contacts, a conductor of the group 622, the No. 4 contacts of relay 53|, the No. 15 contacts of relays 58| and 582 and a conductor of the group C to battery through the winding of the No. 7 relay of the C code digit register 410 of the sender. The sender has now registered the complete information with respect to the three office code digits dialed by the calling subscriber.

1t will be recalled that brush 45| of sender As further illustrative of the functioning of the decoder to register the office code information and to transfer it to the office code registers of the senderQit will beassumed that the callL ing subscriber has dialed an ofiice designation, the letters of which have the numerical equivalents 3, `8, 7 in which case the connection is established to the trunk over the third bank level of the iirst selector |02 and over the eighth bank level of the second selector |83. The third ofice code digit` 7 is registered by the trunk register 25B and the four numerical digits of the wanted line designation are registered by sender registers 44|, 443,444 and 445, respectively. Following the seizure of the sender, current liows over the calling line loop through the tip resistance T3, the ring resistance R8 and the windings of impulse responsive relay 435 of the sender. As soon as a digit has been registered in the sender by register 44| which, in this case will be the thousands digit, the decoder is seized `over the decoder-connector 584 and the decoder is associated with the trunk over the trunk decoder-connector in the manner previously described. With current flowing through resistance T3, relay |23 of the decoder register |24 is now operated. With current iiowing the resistance R8, relay 5|8 of the decoder register f, 555 is also operated and with the trunk register brush 25| positioned upon theNo. 7 terminal of its bank in response to the dialing of the third code digit 7, relay 551 of the decoder register 688 is operated.

With register relay |8 operated, a circuit is vestablished from ground at the No. 1 back contact of relay 538 over the outer front contact of relay 5 i8 to battery through the winding of relay 533 which thereupon operates to connect the front contacts of all relays of register 608 over conductors of group 62|, the Nos. 12 to 21 contacts of decoder-connector relays 58| and 582 and the conductors of the group C to the windings of relays of the C code digit register 416 of the sender. It is to be noted in this connection that relay 533 will operate if any of the relays 5| to 5|9 of the decoder register 559 operate thereby indicating that the trunk has been seized in respense to the dialing of two office code digits and that the third oce code digit dialed has been registered by the trunk register 258, transferred to the decoder register 650, and should be transferred from such decoder register to the C code digit register 410 of the sender.

With register relay |23 operated, a circuit is established from ground over its contacts, a `conductor of cable |33, the No. 38 contacts of relays 58| and 582 and a conductor of the A` group to battery through the winding of the No. 3 relay of the A code digit register 438 of the sender. With register relay 5|3 operated, a circuit is established from ground over the inner front contact of relay 5|8, the No. 33 back contact of relay 538, the No. 23 contacts of relays 58| and 582 and a conductor of the B .group to battery through the winding or the No. 8 relay of the B code digit register 469 of the sender. 533 operated, a circuit is established from ground over the front contacts of relay 631, a conductor of group 82|, the No. 4 contact of relay 533, the No. 15 contacts of relays 58| and 582, and a conductor of the C group to battery through the `winding of the No. 7 relayof the C code digit register 410 of the sender.

Since under the condition assumed neither relay 456 nor 461 of the sender has been operated, the setting of sender register 44|, in accordance with the thousands digit dialed, is not transferred to the decoder register 535 but is transferred over one of the Nos. 1 t0 10 back contacts of relays 466 and 461 to the winding of one of the relays of the thousands digit register 41| of the sender as soon as the steering switch brush 455 reaches its No. 1 off-normal bank terminal following the completion of the setting of register 44| the setting of sender register v443, in accordance with the Yhundreds digit dialed, is transferred over one of the Nos. 11 to 2'0 back contacts of relays 466 and 461 to the winding of one of the relays of the hundreds digit register 412 as soon as the steering switch brush 455 reaches its No. 2 off-normal terminal following the completion of the setting of register 443; the setting of sender register 444, in accordance with the tens digit dialed, is transferred over one of the Nos. 2l to 30 back contacts of relays 455 and 45'! to the winding of one of the relays of the tens digit register 413 of the sender as soon as the steering switch brush 455 reaches its No. 3 off-normal terminal following the completion of the setting of register 444 and the setting of register 445, in accordance with the units digit dialed, is transferred over one of the Nos. 31 to 40 back contacts of relays 455 and 45? to the winding of one of the relays of the units digit register 414 assoon as the steering switch Vbrush 455 reaches its No. 4 off-normal terminal With register relay 68'! and relay following the completion of the setting of register 445.

To further illustrate the manner in which the decoder registers the oice code information and transfers it to the oce code registers of the sender, it will be assumed that the calling subscriber has dialed an oiiice designation, the letters of which have the numerical equivalents 3, 4, 5 in which case the connection is established to the trunk over the third bank level 0f the first selector |02, over the fourth bank level of the second selector |53 and over the fifth bank level of the third selector |55, the thousands numerical digit dialed being registered by the trunk register 258 and the hundreds, tens and units numerical digits being registered by sender registers 44|, 443 and 444, respectively. Following the seizure of the sender, current flows over the calling line loop through the tip resistance TA3, the ring resistance R5, and the windings of impulse responsive relay 435 of the sender. As soon as a digit has been registered in the sender by register 44|, which in this case will be the hundreds digit, the decoder is seized over the decoder-connector 588 and the decoder is associated With the trunk over the trunk decoder-connector |55 in the manner previously described. With current fiowing through resistance TAS, re.. lay 523 of the decoder register 520 is now operated. With current flowing through resistance R5, register relay 5|5 of the decoder register 509 is also operated and with the trunk register brush 25! positioned upon a, terminal of its bank in response to the dialing of the thousands digit, a relay of the decoder register 538 is operated.

With relay 523 of the decoder register 528 operated, an obvious circuit is closed over its outer front contact to battery through the winding of relay 535 which thereupon operates to connect the innergcontacts of relays 5| to 5|9 of register 589, over its Nos. 32 to 40 front contacts, the Nos. 12 to 21 contacts of relays 58| and 582 and conductors of the group C to windings of relays of the C code digit register 416 of the sender; to connect the inner front contacts of relays of decoder register 528, strapped to terminals of terminal block 534 over conductors of the group 535, the Nos. 22 to 31 front contacts of relay 530, the Nos. 32 toll contacts of relays 58| and 582 and conductors of the group A, windings of relays of the A code digit register 468 of the sender and over conductors of the group 535, the Nos. 12 to 21 front eontactsof relay 538, the Nos. 22 to 31 contacts of relays 58| and 532 and conductors of the group B to the windings of the relays of the B code digit register 459 of the sender; to connect contacts of the relays of the decoder register 548 over conductors of the group 62 I, the Nos. 2 to 11 front contacts of relay 538, the Nos. 42 to 51 contacts of relays 58| and 582, and conductors .of the group TH to the windings of the relays of thousands digit register 41| of the sender; at its No. l back contact to open the operating circuit of relay 533 to prevent its operation at this time and to close a circuit extending over its No. 1 front contact, the No. 53 contacts of relays 58| and 532 and conductor 425 to battery through the winding of relay 457 in the sender. Relay 461 thereupon operates to inform the sender that the thousands digit has been registered by the trunk register 25" and that the hundreds, tens and units digits have been registered on the sender registers 44|, 443 and 444.

Register relay 523, since it has been operated to arbitrarily indicate that the rst two code dgits dialed to reach the trunk were 3 and 4, has its inner front contact strapped to terminals on the block 534 to which the third conductor of the group 535 is connected and to which the fourth conductor of the group 536 is connected. Thus when relay 523 operates, a circuit is closed from ground over its inner contact, the No. 3 conductor of the group 535, the No. 29 contact of relay 530, the No. 39 contacts of relays 58| kand 582 and a conductor of group A to battery through the winding ofthe No. 3 relay of the A code digit register 468 of the sender and a circuit is also closed from ground over its inner contact, No. 4 conductor of the group 536, No. 18 Contact of relay 530, the No. 28 contacts of relays 58| and 582 and a conductor of group B to battery through the winding of the No. 4 relay of the B code digit register 469 of the sender. Register relay 5|5 upon operating is not effective to establish the circuit of relay 533since relay 530 is operated,

` but closes a circuit from ground over its inner front contact, the No. 36 front contact of relay 530, the No. 16 contacts of relays 58| and 582 and a conductor of group C to battery through the winding of the No. 5 relay of the C code digit register 410 of the sender. With a relay of the decoder register 60|) operated in accordance with the setting of the trunk register 258 in response to the dialing of the thousands digit, such operated relay closes a circuit from ground over its contact, a conductor of the group 62|, one of the contacts 2 to of relay 530one of the contacts 42 to 5| of relays 58| and 582 and a conductor of the groupTl-I to battery through the winding of one of the relays of the thousands digit register 41| of the sender.

, Since under the condition assumed, relay 463 of the sender is not operated and relay 461 is operated, the setting of sender register 44| in accordance with the hundreds digit dialed is transferred over one of the Nos. l to back contacts of relay 466 and one of the Nos. 1 to 10 front contacts of relay 461 tothe winding of one of the relays of the hundreds .digit register 412 of the sender as soon as the steering switch brush 455 reaches its No. 1 off-normal bank terminal; the setting of sender register 443 in accordance with the tens digit dialed is transferred over one of the Nos. 11 to 20 back ting of the called office code registers 468, 469 and 410 will determine whether the call should be ticketed, whether the message register of the calling line should be operated or whether service on the attempted connection should Vbe denied. If it is determined that the call should be registered, a circuit is established from ground in the send-er, over conductor 416 of cable 464, No. 54 contacts of relays 58| and 582, conductor 529 of cable 56|, No. 14 contacts of relays |5| and |52, No. 6 contacts of relay |35 and conductor 226 to battery through the winding of metering relay 225 whereupon relay 225 will operate and lock over its inner upper front contact to ground on conductor 265 prepara tory to controlling the circuit of relay 221 following the response of the called subscriber. If it is determined that the call should be denied to the calling subscriber, a circuit is established from ground in the sender over conductor 411 of cable 464, the No. contacts of relays 58| and 582, conductor 523 of cable 56|, the No. l1 contacts of relays |5| to |52, the No. 3 contacts of relay |35 and conductor |32 to battery through the winding of denied service relay 2H whereupon relay 2|| will operate, lock over its inner lower front contact to ground on conductor 265 and will transmit an all-paths busy tone signal to the calling line from the source 2|9 as precontacts of relay 466 and one of the Nos. 11 to 20 front contacts of relay 461 to the winding of one of the relays of the tens digit register 413 of the sender as soon as the steering switch brush 455 reaches its No. 2 oil-normal bank terminal and the setting of senderregister 444 i in accordance with the units digit dialed is transferred over one of the Nos. 2l to 30 back contacts of relay 466 and one of the Nos. 21 to 30 front contacts of relay 461 to the Winding of one of the relays of the units digit register The sender now has complete information for extending the connection to the wanted line and to control the printing of thedirectory number of the wanted line on a toll ticket.

While the decoder is obtaining the called ofi viously described.

At the time relay |52 of the trunk decoderconnector operated to connect the decoder with the subgroup of ten trunks in which the calling trunk was located, it established a circuit from ground over the inner contacts of relay |52 and an inner contact of relay |5|, conductor |34 of cable 56|, contacts of relay '58| to 582 and ccnductor 418 of cable 464 to battery through the winding of relay 39| individual to the No. 0 sender which operates and in turn operates the multicontact relay 332 of the trunk sender-connector 396 which has access to the group of vtwenty trunks in which the calling trunk is loselectably operable over conductors such as 418 of cable 415 in accordance with which trunk group relay |52 of the trunk decoder-connector is operated. When all necessary information has been received by the sender, the sender removesground from conductor 456 thereby releasing relay 58| of the decoderconnector 588 individual to the sender whereupon the decoder is released fromits association with the sender by the release of relay 58|, is released from its association with the trunk by the release of the relay |51 and all operated apparatus of the decoder is released. The decoder also releases relay |35 of the trunk. The sender now proceeds to complete its two functions, namely, the transmission of impulses to the trunk to complete the desired connection and printing the necessary information on the toll ticket. These two functions are performedr simultaneously.

To complete the connection from the sender to the calling trunk over the trunk sender-connector 365, the sender when it is ready to start tication register Vrelays of the sender and this class registration in conjunction with the setthe transfer of information from its control reg-k isters to the ticket printer' 268 of the calling trunk, connects battery to conductor 413 cf cable 432 thereby completing a circuit over .the No. 6 contacts of the ope-rated cross-point contacts of sender-connector 388, conductor 228 to ground through the winding of relay 229. Relay 229 thereupon operates closing an obvious circuit for multicontact relay 393 individual to the ten trunks in which the calling trunk is located which relay is located in the trunk sender-connector 399 whereby a plurality of printer control circuits is established from the printer control circuit of the sender 499, indicated by the box 489 and including the calling line identification registers (not shown) and the called line digit registers 458 and 414, to the printer 239 over contacts 2 to 5 of relay 229 and contacts of relays 392 and 393 of the trunk sender-connector 399. The sender then proceeds to control the printer to print on a toll ticket the identification digits of the calling line and the digits of the called line directory nurnber.

For controlling the setting of selector switches in accordance with the oice code and numerical digits registered by the registers 468 to 414, the sender in the well-known manner causes the operation of pulsing relay 459 to transmit series of impulses over the previously traced circuit through the winding of pulsing relay 229 of the trunk. Upon each opening of the pulsing circuit through the winding of relay 229, relay 220 releases to open the outpulsing circuit to the selector switch in which the trunk terminates, to open the locking circuitl of relay 294 which relay being slow to release does not release upon the momentary releases of relay 229 and to close a circuit for relay 230, extending from battery through the Winding thereof, the upper back contact of relay 229 to ground on conductor 295. Relay 239 being slow to release remains operated during the transmission of each impulse series. With relay 230 operated the retard coil 232 and winding of relay 233 are shunted from the outpulsing circuit by a circuit extending over the inner upper front Contact of relay 230 through resistance 23|, and when relay 239 releases at the end of each impulse transmitted from the sender, ground through resistance 234 is connected over the upper alternate contacts of relay 239 and the upper contacts of relay 229 to the tip conductor 235 of the trunk and battery through resistance 236 is connected over the lower alternate contacts of relay 239 and the inner lower contacts of relay 229 to the ring conductor 231 of the trunk to assist the control relay of the selector 'in releasing to thereby increase the pulsing range. In this manner successive selector switches are controlled by the sender to complete the connection to the wanted line.

After the sender has completed its functions, it establishes a circuit from ground over conductor 48|, the outer contacts of relays 392 and 393 of the trunk sender-connector 399, conductor 233 and the No. 6 contacts of relay 229 to battery through the winding of cut-through relay 2|'| which operates and locks to ground on conductor 295; closes an obvious circuit for relay 291; opens at its inner normal contacts the previously traced loop circuit from the calling line through the windings of relay 439 of the sender; closes a circuit for slow-to-release relay 243 extending from ground at its lower front contact over the No. 9 back contact of relay 242, the lower back contact of relay 225 if the call is to be ticketed and relay 225 has not been operated, to battery through the winding of relay 243; and at its inner alternate contacts establishes a supervisory circuit from ground through the upper winding of relay 292, upper normal contacts of relay 221,

upper alternate contacts of relay 2H, No. 1 alternate contacts of relay 293 thence as traced over the calling line loop and returning over the No. 4 alternate contacts of relay 293, the lower alternate contacts of relay 2|?, the lower normal contacts of relay 221, to battery through the lower winding of relay 292. Relay 292 now operates and closes the original operating circuit of slowto-release relay 294. Relay 291 upon operating establishes a holding,r circuit for relay 229 which extends from battery or ground, dependent upon whether the trunk is located in an A or B subgroup, through the winding of relay 229, the upper back Contact of relay 222, the lower alternate contacts of relay 291 to ground or battery over the upper back contact of relay 2| I. This locking circuit is established prior to the opening of the pulsing circuit extending through the winding of relay 229 from the sender. Relay 291 also at its upper normal contacts disconnects the sleeve conductor |91 of the trunk from the previously traced circuit extending over conductor 299 through the sender-connector 395 to ground at the left front contact of relay 434 of the sender and over its upper alternate contacts connects the sleeve conductor |91 to ground at the upper front contacts of relay 204. Upon the opening of the circuit of relay 430 of the sender, relay 433 releases in turn releasing relay 434 and starting the release of all operated apparatus of the sender. Relay 434 upon releasing removes ground from the locking circuit of hold magnet 3 I9 of the sender-connector which thereupon releases to disconnect the sender from trunk at the sender-connector 399. The sender upon releasing also releases relays 229, 39|, 392 and 393 thereby disconnecting the sender from the trunk at the trunk sender-connector 390.

When the called subscriber answers, a battery reversal is received over the trunk conductors 235 and 291 which with relay 229 operated and relay 239 released following the termination of the last digit series of impulses transmitted from the sender, causes the operation of the polarized supervisory relay 233. Relay 239 upon operating closes a circuit from ground at the upper contact of relay 2|1 over its front contact and the lower front contact of relay 225 to battery through the winding of message register control relay 221, if relay 225 has been previously operated, to operate the calling subscribers message register for those calls for which no ticket is required. If relay 221 operates, it reverses the connection of battery and ground supplied through the windings of relay 292 over the calling line loop for the purpose of operating the message register of the calling line in a well-known manner.

Relay 233 also closes a circuit from ground over the upper contact of relay 2|`| and its own front contact to conductor 239 and the cam spring of interrupter 240 whereby when the cam spring engages its lower contact, a circuit is established through the winding of relay 24| to battery thereby operating relay 24| which locks to ground on conductor 239 and prepares a circuit for relay 242. After an interval when the cam spring engages its upper contact, the circuit of relay 242 is completed from ground on conductor 239 over the upper contact of the spring, lower front contact of relay 24|, and the lower normal contacts and winding of relay 242 to battery. Relay 242 thereupon operates and locks over its No. l alternate contacts to ground at the lower front contact of relay 2|1. A delay interval of from two to four seconds is thus in- 425|) is restored to normal.

troduced after the called subscriber has answered before the printer 250 can be operated to print an identification that the called subscriber has answered to prevent charging on half-second trunk reversals for ticketed calls to busy lines and to prevent charging on ticketed calls in which case a momentary reversal may be received when the call is answered by an intercepting operator.

When relay 242 operates, it opens at its No. 9 contacts, the previously traced operating circuit for relay 243, but relay 243 being slow to release remains operated momentarily to close a circuit from ground over the No. 4 contacts of relay 242 and the contacts of relay 243 to the printer 250 to cause the printer to print the trunk number on the toll ticket as an indication that the called subscriber has answered. Relay 242 also connects a source of alternating current over its Nos. '1 and 8 contacts to the motor of the timer 244; connects the winding of relay 24| over its No. 5 contacts directly to conductor 239; prepares a locking circuit for relay 222 over its No. 3 contacts and prepares a circuit for the automatic trunk release circuit enclosed in the dot-dash rectangle 246. The timer 244 starts from its normal position immediately upon the closure of its operating circuit, and at intervals of one minute closes a circuit from ground at the upper iront contacts of relay 201 over the upper back contacts of relay 225, over contacts 245 operated by the timer to the printer 260 to cause the printer to print the trunk number on a toll ticket at one-minute intervals thus recording the number of one minute-intervals of conversation.

When disconnection by the calling subscriber occurs relays 202 and 204 release. Relay 204 upon releasing releases relay 2|1 and relays 2|| and 225, if operated, removes ground from sleeve conductor |01 thereby releasing the connection toward the calling line and with relay 202 released closes the circuit of release magnet 253 of the register 250 which may be traced from yground at the back contact of relay 202, the lower back contact of relay 204 and the upper contacts of off-normal switch 2|0 to battery through the winding of release magnet 253 whereby register When the register reaches its normal position, the off-normal contacts are opened thereby releasing relay 203. Re-

lay 2|1 upon releasing releases relays 201, 24| and 242 and relay 242 upon releasing stops the timer 244 in its normal position. Relay 201 upon releasing releases relay 220 whereupon relay 233 is released and the release of the connection toward the called line is initiated.

` Should the tape or ticket Vsupply become exhausted, the end of tape contact 26| of the print-y er 260 will be clo-sed thereby operating relay 208 which opens at its back contact the circuit for initiating the seizure of an idle sender and which at its front contact connects busy ground to the sleeve conductor |01 of the trunk to prevent the seizure of the trunk. If desired, relay 208 upon operating may close an alarm circuit to indicate to a maintenance man that the ticket printer requires attention.

It is desirable that the connection from the trunk to the tandem office be released automatically after an interval in the event that the called subscriber should disconnect and the calling subscriber fail to disconnect. Thus if relay 233 releases dueto the called subscriber disconnecting and after relay 242 has operated, a circuit is established from ground at the upper front contact of relay 2|1, back contact of relay 233, No.

6 contacts of relay 242 and conductor 241 to battery through the Winding of slow-to-release relay 248 as soon as interrupter contacts 249 close".V Relay 248 upon operating locks over its inner contacts to ground on conductor 241, inde 'ende ent of interrupter co-ntacts 249. Interrupter contacts 25| will close two minutes later and if relays 242 and 248 are then still operated and with relay 24| released, a circuit is closed from battery through the winding and normal contacts of relay 222, back contacts of relay 24|, No. 2 contacts of relay 242, upper contacts of relay 248 to ground at interrupter contacts 254 and relay 222 will lock over its alternate contacts to ground at the No. 3 contacts of relay 242 and will .open at its upper back contacts the circuit of relay 220 which will thereupon release. The release of relay 220 causes the release of all switches toward the called line thereby freeing the called line. When the calling subscriber disconnects, the remaining operated apparatus of the trunk circuit then releases in the manner previously described.

What is claimed is:

1. In a telephone system, a calling line, a plurality of trunks over which connections may be extended to any one of a plurality of ofiices, a train of selector switches responsive to the dialing of one or more of the oiiice code digits of any desired oice for extending a connection from said calling line to an idle one of said trunks, means in each of said trunks for determining the values of the oice code digit or digits dialed to seize said trunk, and means operable in accordance with said determining means for registering the ofiice code digit or digits dialed to seize said trunk.

2. In a telephone system, a calling line, a train' of selector switches, a plurality of trunks certain of which are accessible respectively from different switches of said train and others of which are provided with branches accessible from one or more switches of said train in response to the dialing of one or more of the oice code digits of any desired office, means in each of said trunks for determining the values of the office codel digit or digits dialed to seize said trunk, and means operable in accordance with said determining means for registering the oiiice code digit or digits dialed to seize said trunk.

3. In a telephone system, a trunk having resistance networks, means for selecting said trunk in response to digit impulses and means controlled by said resistance networks for determining the digital values of said impulses.

4. In a telephone system, a calling line, a plurality of trunks over which connections may be extended to any one of a plurality of offices, a train of selector switches responsive to the dialing of one or more of the oflice code digits of any desired oiiice for extending a connection from said calling line to an idle one of said trunks, resistance networks in each of said trunks for determining the values of the oiiice code digit or digits dialed to seize said trunk, and means responsive to said networks for registering the office code digit or digits determined thereby.

5. In a telephone system, a calling line, a train of selector switches, a plurality of trunks certain of which are `accessible respectively from difierent switches of said train and others of which are provided with branches accessible from one or more switches of said train in response to the dialing of one or more of the ofiice code digits of any desired cnice, resistance networks in each of said trunks for determining the values of the ofce code digit or digits dialed to seize said trunks, and means responsive to said networks for registering the oiiice code digit or digits determined thereby.

6. In a telephone system, a calling line, a trunk over which connections may be extended to any one of a plurality of oliices, a train of selector switches responsive to the dialing of one or more of the onice code digits oi any desired oiice for extending a connection from said calling line to said trunk, said trunk having branches terminating in the banks of the several switches of said train, each branch being indicative of the ofiice code digits dialed to extend a connection to said trunk, and means operable in accordance with the particular branch over which said trunk is selected for registering the code digit or digits dialed to selectthat branch.

7. In a telephone system, a calling line, a trunk over which connections may be extended to any one of a plurality of offices, a train of selector switches responsive to the dialing of one or more of the oflice code digits of any desired cnice for extending a connection from said calling line to said trunk, said trunk having branches terminating in the banks of the several switches of said train, means in each branch energizable upon the seizure of the trunk over such branch indicative of the oiiice code digits dialed to seize the trunk, and means operable in accordance with l said means for registering the code digit or digits dialed to select said trunk.

8. In a telephone system, a calling line, a trunk .over which connections rmay be extended to any one of a plurality of oflices, a train of selector switches responsive to the dialing of one or more of the cnice code digits of any desired oflice for extending a connection from said calling line to said trunk, said trunk having a tip conductor provided with as many branches each including a resistance as there are possible values of the first oflice code digit dialed to reach said trunk and having a ring conductor provided with as many branches each including a resistance as there are possible values of a last code digit dialed to reach said trunk, different pairs of said tip and ring branches being accessible from diiierent bank levels of said switches, each pair including Aa tip resistance indicative of the value of the rst code digit and a ring resistance indicative or the value of the last code digit dialed to select the trunk thereover, a 'battery Veffective upon the Seizure of said trunk to cause current to flow through the resistances of the pair of branch conductors over which said trunk was seized, groups of register relays Vand means for bridging the relays of said groups around said tip and said ring resistances whereby a relay of each of said groups vis selectively operable in accordance with the tip and `ring resistances through which current is flowing Yto register the values of the code digits dialed to reach said trunk.

9. `In a telephone system, a calling line, a plurality of trunks over which connections maybe 'extended to any one of a plurality of offices, a

train of selector switches responsive to the dialing of one-or more of the oiiice code digits of any desired oiiice for extending a connection from said calling line to lan idle one of said trunks, each of said trunks having a tip conductor provided with as many branches each including a resistance as there are possible Values of the firstofce code digit dialed to reach said trunk "and having a ring 'conductor provided with as many branches each including a resistance as there are possible values of a last oice code 4digit dialed to reach said trunk, different pairs of said tip and ring branches being accessible from different bank levels of said'svvitches, each pair including a tip resistance indicative of the value of the first code digit and a ring resistance indicative of the value of the last code ,digit dialed to select the trunk thereover, a battery effective upon the seizure of a trunk to cause current to iiow through the resistances of the pair of branch conductors over which said trunk was seized, groups of register relays common to said trunk, and means responsive to the seizure of a trunk for bridging the relays of said groups around the tip and ring resistances of said trunk whereby a relay of each of said groups is selectively operable in a-ccordance with tip and ring resistance through which current is flowing to register the values of the code .digits dialed to reach the idle trunk.

10. In a telephone system, a cailing line, a trunk over which connections may be extended to any one of a plurality of oices, a selector' switch responsive to the dialing of the first office code digit of a desired oflice for extending a connection from said calling line to said trunk, said trunk having a tip conductor provided with as many branches each including a resistance as there are possible values of said first oice code digit, and having a ring conductor provided with a plurality of branches each including a common resistance, different pairs of said tip and ring branches being accessible from different bank levels of said selector switch, each pair including a tip resistance indicative of the value of the code digit dialed to select the trunk thereover and the common ring resistance indicative that no second code digit was dialed to select the trunk, a battery effective upon the seizure of the trunk to cause current to flow through the resistance of the pair of branch conductors over which said trunk was seized, register relays and means for `bridging said relays around said resistances whereby said relays are selectively operable in accordance with the tip and ring resistances through which Vcurrent is flowing to register the value of the single code digit dialed to reach the trunk and to register the fact that but one code digit was dialed to reach the trunk.

1l. In a telephone system, a calling line, a trunk over which connections maybe extended to any one of a plurality of oices, a train of selector switches including first, second and third selector switches responsive to the dialing of the three oiice code digits of any desired office for extending a connection kfrom said calling line to said trunk, said trunk having a tip conductor provided with asrnany branches each including a resistance as there are combinations of values ofiirst and second oilce code digits dialed to reach said trunk, and having a ring conductor provided with as manybranches each including a resistance as there are possible values 'of a third omce code digit dialed to reach said trunk, different pairs of said tip and ring branches'being accessible from different bank levels ofsaid third selector switches, each pair including a ytip Vresistance indicative of the values of the iirst and second code .digits and a ring'resistance indicative of the value of the third code digit dialed to select the trunk thereoven'abattery effective upon the seizure of said trunk to causecurrent to iiow through-the resistances of the vpairoi branch conductors over which said trunk was seized, groups of register relays, and means 'for

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