US2158113A

US2158113A - Teletypewriter trunking system

Info

Publication number: US2158113A
Application number: US93806A
Authority: US
Inventors: Karl F Fitch
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1936-08-01
Filing date: 1936-08-01
Publication date: 1939-05-16
Anticipated expiration: 1956-05-16

Description

Filed Aug. l, 1936 6 Sheets-Sheet l /NVENTOR K, E. F TCH ATTORNEY l May 16, 1939. K, E. FITCH TELETYPEWRITER TRUNKING SYSTEM Filed Aug. l, 1956 6 Sheets-Sheet 2 /NVENTOR KEF/TCH j AHORA/5y May 15, 1939- K. E. FITCH TELETYPEWRITER THUNKING SYSTEM Filed Aug. l, 1936 6 Sheets-Sheet 3 c. Ulhu mmm. Daft.

ATTORNEQ May 16, 1

939. K. E. FITCH TELETYPEWR ITER TRUNKING SYSTEM Filed Aug. n l, 1936 HUNf/NG CONNEC MULTIPLE HUN 7' ING C ONNE C 7 OP 6 Sheets-Sheet 4 www ATTORNEY K. E. FITCH 2,158,113

e sheets-sheet 5 l Filed Aug. 1, 195e TELETYPEWRITER TRUNKING SYSTEM K. E. F TCH By j l ATTORNEY May l 6, 1939.

Patented May 16, 1939 UNITED STATES PATENT OFFICE.

Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application August 1,

6 Claims.

This invention relates to printing telegraph systems, and more particularly to such systems requiring switching arrangements at central offices.

5' The object of the invention resides in a trunking system for completing telegraphic typewriter connections between the telegraphic subscribers associated with a manually operated central office and telegraphic subscribers associated with an automatic switching central ofce or private branch exchange, said trunking system including a central trunking station or central olice adapted for regulation as a through-repeater stav tion and having means for originating connections to either type of subscribers station.

According to one embodiment of the present invention, there is provided a printing telegraph trunking system arranged to selectively interco-nneet lines from manually operated teletypewriter oilces with lines from automatic switching telegraph oflices. The trunk circuits of this trunking system are divided into groups, each group having a sending and receiving printer and a dialing system selectable by any of the trunks in the group. Each trunk circuit in a` group comprises a repeater, a two-position key and a threeposition key, which may be manipulated in various manners for answering and originating connections and signaling apparatus for supervising such connections. The two-position key is provided for the purpose of connecting the local or trunk operators printer set in series with a printer set at either the central office or an automatic office and for associating the dial With the 35 automatic switching system'. The two-position and the three-position keys may be used in various combinations for adusting the trunking system as required for completing and originating calls and for functioning as a through-repeater Fig. l-A illustrates a teletypewriter subscribers stati-on of the type connected with a manual switchboard;

Figs. 1--B,' ZZ-A and 2-B illustrate a line circuit, repeater cord circuit, and a second line circuit, respectively, of a manually operable central oflice of the type for interconnecting teletypewriter stations;

Figs. 3 and 6 illustrate a teletypewriter trunking switchboard With trunks extending in two directions;

Figs. i-A, 4-B, 4-C, and 5-A illustrate a line circuit, line nder, connector, and second line circuit, respectively, for an automatically operated central o'ice;

Fig. 5-B illustrates a teletypewriter subscribcrs station of the type Which is connected with an automatically operated central cnice;

Fig. '7 illustrates the diagrammatic arrangement of the stations and several offices; and

1936, Serial No.v 93,806

Fig. 8 illustrates the arrangement of the drawings for the correct association of the circuit diagrams.

In general, the operation of this system is as follows:

Let it be assumed that an outlying teletypewriter subscriber in a manual exchange district desires a connection to a distant subscriber who is connected to an automatic telephone exchange. The subscriber represented by the apparatus in Fig. l-A initiates a call by operating the start key m2. In response to this operation, electrical circuits are established for starting the teletype- Writer motor 6, establishing a signaling circuit land operating the printer magnet. The signaling circuit is established to a manual exchange represented by the line circuit Fig. l-B, repeater cord circuit Fig. 2-A, and the line circuit Fig. 2-B. The establishment of this circuit operates electrical apparatus and lights lamp H2 associated with the subscribers line jack I I4 for indicating an incoming call to an operator at the manual exchange. Upon observing the light an operator inserts plug 230 into jack H4 and actuates key 245 for associating the cord circuit printer 260 with the subscribers station and establishing a signaling loop'. A signal is printed by the manual operator and transmitted over the established loop to advise the subscriber that signals may now be transmitted by said Subscriber indicating the connection desired. When the signals transmitted by the subscriber are received on the cord circuit printer the manual operator inserts plug 23'! into jack 2I4 of a line connected to a distant trunking office associated with the desired automatic exchange. The insertion of the plug into the trunk jack 2 I4 establishes a loop to a trunk such as shown in Fig. 3. The manual operator rst actuates the ringing key 238 for operating trunk circuit relays and lighting lamp 30| in the selected trunk. The trunk operator responds to the signal by actuating key 366 to the TWX position for associating printer 600 with the signaling loop connected to printer 260. A signal is transmitted from printer 600 advising the manual operator to proceed and in response, signals are vtransmitted by the manual operator by manipulation of her sending keys 262 for operating the trunk position printer 600 giving the station to be called. When these signals have been transmitted, the manual operator` has completed her duties and the cord circuit of Fig. Z-A remains as a through signaling path. As soon as the trunk circuit is selected by the manual operator, circuits are established for operating the trunk finder Fig. 4-A and 4-B in order that no time be lost in completing the connection. The operator at the trunking switchboard uses the apparatus shown in Fig. 3 for operating the switches ofan automatic telephone exchange. The two-position key 336 is moved to the dial position which associates the dial and dial signal with the automatic switches. When the connector switch is associated with the trunk circuit the dialing signal is operated. The signals dialed by the trunk operator set the connector switch Fig. 4 0 for connecting the trunk circuit to a particular teletypewriter subscriber. When the line switch Fig. 5-A is connected to the proper line, an audible signal is sounded at the teletypewriter subscribers station indicating a call for said station. The called subscriber responds by actuating the teletypewriter apparatus for transmitting a code signal to the calling subscriber indicating that the connection .has

been completed. As soon as this signal is received, the calling subscriber Fig. l-A transmits his code message to the selected subscriber Fig. 5-B. After the message has been transmitted, the proper disconnect signals are transmitted, which furnish information to the subscriber stations and indicate by supervisory signals in the trunk switchboard Fig. 3, and manual switchboard Fig. 2-A, that the apparatus used for completing this connection may be restored to normal.

Having briefly discussed the general operation of the system involved in establishing a connection between two distant subscribers, the manner in which this connection is established will now be described in detail. When a subscriber desires to initiate a call the station mechanism is actuated and a sending loop is established by the operation of the start key |02. The operation of the start key associates` the alternating current source 8 with relays |08 and |09, both of which operate. Relay |08 in operating establishes a locking circuit for itself from one side of the-alternating current source through its winding and lower contact, contact of manually operable stop key |03, contactrof automatically operable motor stop key 1 to the opposite side of the alternating current source. The operation of relay |08 further establishes a circuit for the motor 6 `from one side of the alternating current source through its top contact, motor.winding and armature, to the opposite side of the alternating current source. The operation of relay |08 establishes a circuit loop which may be traced fro-rn ground through contact of relay H9, contact of relay H8, line resistance |20, winding of relay H0, contact 4 of key |05, lower winding of relay |01, transmitting contacts of keys |0l, contact of key |05, contact of relay |09, normal contact of key |06, line resistance l2 lower winding of relay l5, contact 3 of relay H3, resistance |24, to positive battery. Resistances |20 and 2| represent a line loop of several miles. The circuit as above traced establishes the operation of relays |01, I I0, H5. rIhe operation of relay |01 establishes a circuit for operating the printer magnet |00. The opera.- tion of relay H0 establishes a contact for replacing the contacts of start key |02 when this key is released. The operation of relay H5 establishes a circuit for relay H9 traced from ground, through the contact of relay H5, contact 2 of relay IIB, Winding of relay H9, to battery. The operation of relay H5 also establishes an obvious circuit for operating relay H6. Relay H6 connects ground to the Atip of jack H4. The operation of relay H9 establishes an obvious circuit for lighting lamp |2 through its contact 3 and a busy circuit through its contact 2, from battery to the upper winding of relay H8 t0 the multipled sleeve of jack H4. The upper con-- tact I of relay H9 connects negative battery tol the loop and disconnects ground.

Upon observing the illumination of the signaling lamp H2, the manual operator inserts a plug such as 230 into the line jack H4. The insertion of this plug in the jack establishes an operating circuit for relays H8 from ground, through its lower Winding, sleeve of jack H4, sleeve of plug 230, resistance 232, to battery. The operation of relay H8 releases relay H9 and closes the path of the signaling loop. This signaling loop is now extended to the cord circuit repeater through contact 3 of relay H8. As soon as plug 230 is inserted in jack H4 the manual operator actuates key 245 for associating the printer 260 with the subscribers station printer l0. The signaling circuit may now be traced from positive 48-volt battery, through the normal contact of repeater relay 248, upper winding of repeater relay 241, lower contact of key 245, contacts 252 and magnet 26| of printer 260, upper contact of key 245, normal contact of ringing key 23|, ring of plug 230 and jack H4, contact 3 of relay H8, lower winding of relay H5, loop resistance |2|, normal contact of key |06, contact of relay E09, contact of key |05, sending keys |0|, lower winding of relay |01, contact 4 of key |05, winding of relay H0, loop resistance |20, contact of relay H8, upper winding of relay H5, resistance |23, to negative battery. Relay ||5 is differentially connected in the loop circuit and therefore current through both windings ras traced causes its release. The release of relay H5 opens the operating circuit for slow operating and releasing relay H6. The manual operator sends a code signal to the calling subscriber by manipulating the keys of printer 260. These signals are sent directly from the printer 260. It will be noted that during the transmission of signals to station A the repeater relay 241 is operated but since no connection has as yet been made over plug 231 the action of repeater relay 241 is not eiective. In response to this signal the calling subscriber manipulates the keys |0| ofrprinter I0 to transmit a code message to the manual operator. This message is recorded on the printer 260 and provides the manual operator with the station and subscrbers line to which the calling subscriber wishes a connection. A record is made on each printer upon the transmission of each message. The manual operator now selects a line extending to a trunk connected to the particular automatic exchange to which the calling subscriber desires a connection. Let it be assumed that the line circuit Fig. 2--B connects to a trunk circuit extending to the desired line. Plug 231 is, therefore, inserted in jack 2|4. A circuit is thus established for the operation of relay 2|8 from ground through its lower winding, sleeve of jack 2|4 and plug 231, resistance 238 to battery. The operation of relay 2|8 establishes a circuit for the operation of relay 2|5 traced from negative battery, through resistance 223, upper Winding of relay 2|5, contact of relay 2|8, toground through contact I of relay 306. The operation of relay 2|5 establishes an obvious circuit for operating relay 2|6 which in turn establishes a circuit for relay 24| from ground through the contact of relay 2| 5, tip of plug 2|4 and jack 231, winding of relay 24| to battery. The operation of relay 24| establishes an obvious circuit for lighting lamp 242. Returning again to relay 2 I8 the operation of this relay further establishes a signaling path from the cord circuit to the trunk circuit Fig. 3. In order to establish connection with the trunk circuit the manual operator actuates the ringing key 238 to associate alternating current from source 230 for operating relay 304 of the trunk circuit. This circuit may be traced from the alternating current source 236, through the contact of key 238, ring of plug 231 and jack 2|4, contact 3 of relay 2|8, lower winding of relay 2|5, resistance 222, resistance 22%, contact 4 of relay 305, condenser 305, winding of relay 304, to ground through contact of relay 300, relay 304 operates in the circuit traced and establishes a circuit for the operation or relay 303 from ground, through contact of relay 303, contact of relay 304, Winding of relay SP3, contact 2 of relay 306, resistance 308, to battery. The current source shown in this trunk circuit is a rectifier which supplies rectified current from the alternating current source 333, as shown, carried through any conventional rectifier diagrammatically shown as 332. The operation of relay 303 establishes an obvious circuit for lamp 30| to indicate that the trunk has been selected. A second circuit is established from ground, through the upper contact of relay 303, Winding of relay 323, resistance 324, to battery source 332. Relay 323 operates in the circuit traced for starting the operation of the trunk iinder switch as hereinafter described and for associating a dial circuit with the outgoing line. The dial 6|5 is common to a group of trunks and, therefore, the circuit paths between the dial and the outgoing line are not completed until the trunk operator has performed other functions. Upon observing the illumination of lamp 305' the trunk operator actuates key 336 to the TWX position for completing the signaling loop between the cord circuit and trunk circuit operators positions. The operation of key 336 establishes a circuit to operate relay 30B from ground, through contact of the TWX key combination, winding of relay 306, resistance 301 torreotied battery current. The operation of relay 30S releases relays 303 and 304 establishes a holding circuit for relay 323 and establishes a signaling path between the trunk circuit printer 600 and the cord circuit printer 260. The holding circuit ior relay 323 may be traced from ground through contact 2 of relay 325, upper winding of relay 323, contact 2 of relay 306, resistance 308 to battery. The signaling path may be traced from positive Liii-volt battery Fig. 2-A, through the contact of relay 241, upper winding of relay 2de, normal contact of key 238, ring of plug 231 and jack 2M, contact 3 of relay EIB, lower winding of relay 2|5, resistance 222, resistance 22|, contact 4 of relay 30B, contact 2-3 of key 336, key :30| of printer 600, key 502, upper winding of relay 603, contact 4 5 of key 336, upper winding of relay 3|1, upper winding of relay 3|5 in multiple with resistance 3|8, armature and contact o relay 3| contact of relay 305, resistance 220, contact of relay 2|8, upper winding of relay 2i5, resistance 223, to negative battery. Relay 2|5 is differentially connected in this loop circuit and therefore current through both windings as traced causes its release. The release of relay 2 l 5 releases relay 2 I6 which in turn releases relay 24| and extinguishes lamp 242. The printer @t0 is common to all trunk circuits of a position and may be associated with other trunks by the operation of the associated trunk keys such as 0H) or 6H. For this purpose a series circuit is extended through the key contacts as shown.

As soon as the foregoing signaling path is established the trunk operator manipulates the keys of the printer 000 to advise the manual'operator Fig. 2-A that code signal impulses may be transmitted to the trunk circuit printer indicating the subscribers station to be called.

These signal impulses are transmitted by the cord circuit printer 260 over a circuit which may be traced from positive L8-volt battery, through contacts of repeater relay 248, upper Winding of repeater relay 241, lower contact of key 245 which is operated, contacts 232 of printer 260, printer magnet 23|, upper contact of key 245, the contact of key 23|, ring of plug 230 and jack H4, contact 3 oi relay H8, lower Winding of relay |45, line resistance |2l, Contact of key |06, contact oi relay |09, contact of key |05, printer keys lili, lower winding of relay |01, contact 4 of key |05, winding of relay ||0, line resistance |20, contact I of relay |i8, upper winding of relay H5, resistance |23 to negative battery. As the signal impulses are transmitted the repeater relay 242 is operated and spacing and marking signal impulses are transmitted to the trunk operators printer 600. The cord circuit repeater relays 241 and 240 are maintained in the position shown when the loop circuit is closed. The current iowing through the upper Winding is approximately twice as great as that flowing through the lower Winding and of the opposite polarity. When the loop is opened by the transmission of signals, the current through the lower winding becomes effective and causes the arma.- ture oi the relays to be attracted toward the inner or upper Contact. This causes a spacing signal to be transmitted since in this case negative battery is connected from the repeater relay to negative battery in the line circuit. The normal loop circuit and the spacing signal circuit may be traced at the same time, the normal loop circuit extending from positive Liii-volt battery through resistance 254 and the spacing signal extended at Llf3-volt negative battery through resistance 253. This extends over` the armature of relay 241, upper winding of relay 243, contact of key 233, ring of plug 231 and jack 2|4, contact 3 of relay 2|8, lower winding of relay 2l5, line resistances 222 and 22|, contact 4 of relay 30S, which relay is operated at this time, contact 2-3 of key 336, which is actuated at this time, co-ntacts 60| and 602, upper winding of relay 003, contact 4-5 of key 33E, upper windings of relays 3|1 and 3|5, contact of relay 3l in multiple onthe contact 2 of key 338, contact of relay 306, line resistance 220, contact i of relay 2|8, upper winding of relay 2|5, resistance 223 to negative battery. It is apparent that as the signal impulses are transmitted by the operator, the open periods will cause the armature of relay 241 to be attract-ed toward the contact connected to the negative 48- volt battery. This causes the spacing signal to be transmitted to the trunk operator from negative to negative battery and transmits the same signal to the subscribers station A by opening the loop at the sending keys 262. Consequently, a record is made in each of the printer stations involved in the connection. Under this condition of sending relay 248 holds its armature against the positive Contact since current is reversed in the lower winding. This completes the duties required of the manual operator and key 225 is, therefore, restored to normal and the cord circuit remains as a through signaling path with the two-Way cord circuit repeater included in the signaling circuits. This signaling path will be traced upon the completion of the connection to the called subscriber Referring again to relay 306, it Will be remembered that a circuit is established through the contacts of this relay for holding the relay 323 operated. When the trunk operator has received the code signal from the manual operator, key 333 is operated to the hold and split position before the TWX key is restored to normal. in the hold and split position of key 330 a locking circuit is established for the aforesaid relay 306 which may be traced from ground, through contact 4 of key 338, contact 3 and winding of relay 306, resistance 301, to battery. Relay 323 is thus held in an operated position until key 338 is restored to its normal position. The trunk operator now operates key 336 to the dial position which energizes relay 32| for associating the dial with the outgoing trunk conductors. Similar relays 5I?! and 6I3 are shown connected with keys I I and 5I l, respectively, for associating the comdial with other trunk circuits. A series circuit carried from ground 360 through the contacts of the keys, as shown, for operating these relays as the individual trunk keys are operated. The circuit for operating relay 32| may be traced from ground 300 through contact oi key 336, winding of relay 321, resistance 322, to battery. The connections from the dial to the line, through the contacts of relay 32|, may be traced as follows: The dial lamp is lighted from ground, through contact 2 of relay 323, contact 3 of relay 325, right contact of relay 6I4, lamp lament, resistance @I1 to battery. The tip conductor of the line is associated with the dial through contact I of relay 325, contact of relay 323, make-beforebreak contact I of relay 32|, contact and armature of relay 6M, left contact of dial, to ground. This circuit may also be traced through the winding oi relay 6I4, right contact of dial, contact 4 of relay 32|, contact 3 of relay 323, contact 4 of relay 325, winding of relay 321, to the ring conductor of the line. The dial contacts are thus eXtencled to the finder switch Fig. 4-A.

At the trunk office the tip and ring line conductcrs 360 and 35| are connected to a terminal set in the trunk or line-finder switch bank herein termed a line nder. Other trunks in the system are respectively connected by means of co-nductor pairs to other terminal sets in the same lineinder switch. The line-lnder switch is of the rotary step-by-step type, which is disclosed in U. S. Patent 815,176 granted to A. E. Heath et al.

on March 13, 1906. The trunk lines may be arranged in one or more groups and subgroups, as fully covered in Patent 1,958,930 to F. J. Singer, May l5, 1934. For each subgroup of lines there is provided a subgroup relay such as relay 405, which operates when a call is initiated. As hereinbefore stated the ground on contact I of relay 32| initiated the operation of the nder switch when relay 323 operated. Upon the operation oi relay 322i this ground was replaced by the dial ground. Obvious circuits are established for the operation of relay 43|, 402 and 405, and as is apparent the finder switch operations hereinafter described are either completed or nearly completed by the time 'the key 333 is operated to the dial position. The operation of the subgroup relay 405 connects ground to a segment on a commutator which is mounted cn a line-finder switch. The commun tator is provided with ten segments to correspond to ten levels o-r subgroups of the switch, there being ten lines in each subgroup. When a call is initiated by the operator a line-finder switch is automatically operated ilrst in an upwardmovement to a particular level and then in a rotary movement to a set of terminals to which the calling line is connected. The upward movement of the brush set is regulated by a brush passing over the segment on the commutator and when the brush reaches a commutator segment to which the calling line has applied ground by means of its associated subgroup relay the upward movement of the line-hder brush set is checked at the level in which the calling line terminal set is located. In this way the level at which the calling line terminates is selected and the line-finder brush is then automatically rotated over the terminal set in a particular level until it nds grounded battery which is connected to the calling line. This prevents further rotary movement 0f the brush set and completes an operating circuit for cutting the conductors through to a connector switch.

The line and connector switches are shown in schematic form since their operation is well understood and since they operate in the system in the same manner as fully described in the aforementioned Patent 1,958,930 to F. J. Singer. As previously stated, the operation of the dial key establishes a circuit for the operation of relay 40| (Fig. 4--A). This circuit may be traced from battery to the winding of relay 40|, normal contact I of relay 400, tip conductor of trunk, normal contact I of relay 325, contact I of relay 323, to ground on contact I of relay 32|, before the dial key and relay 32| are operated. After the operation of this key and relay the circuit is extended through the left contact of relay 6I4, left contact of dial SI5 to ground. The operation of relay 40| establishes an obvious circuit for the operation of relay 402. The operation of relay 402 connects ground to the switchV sleeve terminal and establishes a circuit at this time for operating the line switch relay 405 from battery through the winding of relay 405, contact 3 of relay 402 to ground through contact 4 of relay 400. The operation of relay 405 connects ground to a parn ticular segment on the switch commutator and also establishes a circuit for the switch start relay. It will be assumed that the ground disclosed is connected to the tenth level of the switch, and consequently the operation of relay 405 places a ground upon the tenth commutatorsegment. The operation of the switch start relay establishes circuits for the vertical magnet which elevates the switch in single steps to the tenth level, where it finds ground associated with the commutator. The vertical magnet is then energized to rotate the switch brushes for the selection' of the trunk conductor shown. At the first vertical step the vertical off-normal springs 430 operate to connect ground to conductor 432. This circuit is maintained closed until the dialing of the code number has been completed. When the brushes 404 are associated with trunk terminals 408 a circuit is established for operating the cutoiT relay 400. This circuit may be traced from ground through OIT-normal contact 430, sleeve conductor 432, sleeve brush and terminal of the switch, contact l of relay 502, winding of relay 400 to battery. The circuit traced includes a circuit through the winding of a cut-through relay which is not shown. The cut-through relay associates the trunk conductors with the connector switch (Fig. 4-C) and the sleeve conductor of the finder with the sleeve conductor of the connecto-r Fig. 4 0. A busy condition for the connector .and a eircit for operating the connector relay 449 'is thus established.

When the trunk has been found by the trunk nder and the 'cut-through relay operated, supervisory circuits are Aestablished to advise the trunk operator of the advancement of the connection. A 'circuit is `llrs't 'established for the operation of dial relay 514 over the tip and rin'g conductors which may be traced from negative battery `403 through the upper normal contact of relay M0, lower winding of relay 4H, ring conductor 4733., @brush and terminal of the nder switch, winding of relay 321, contact 4 of relay 325, contact 3 of relay 323, contact 4 of .relay 32|., right contact o'f dial `SI5, winding of relay 614, contact 'l of Arelay 321, contact I of relay 323, contact 4l of relay 325, tip conductor 3611, tip terminal and 'brush of the line-linder switch, conductor 434, upper winding of relay 4l l, lower contact of relay "41'0, upper winding of relay 406, contact of relay 403 .to positive battery. vThe operation of relay El# extinguishes the dial lamp 616 `vto indicate to the trunk operator that the circuit is cut 'through and ready to receive dialing impulses. The dial 61:5 is now actuated by the trunk operator for the selection of the wanted line by causing the connector (Fig. 4 0) to select said line. The connector Fig. 4-C is the same asrjdisclosed and 'described in detail in Patent 1,958,930 to F. J. Singer, May 5, 1934 and therefore only the apparatus which is essential for completing `the Aconnection ris Vshown herein. For the sake of simplicity the apparatus is numbered as in the patent. impulses corresponding to the code number of the called station cause the operation and release of the pulsing relays Vin the connector'iFig. "4;C). The operation of the connector circuit (Fig. 4 0) in response to the dial interruptions is 'the Asame as described in detail in the aforementioned patent to F. J. Singer.

It therefore appears that a general statement of the operation' is suflcient. The first set of impulses transmitted, operates the vertical magnet and 'causes the connector lshait and associated brushes to be elevated to the desired level. Between the r'st 'and second Vseries of dial pulses the pulsing circuit A'is transferred from the vertical magnet to the rotary magnet. Subse quent series o'f pulses Atherefore cause the brushes to rotate for selecting a particular set of terminals 'to Ywhich the desired line is connected. Assuming lthat the selected Astation is idle at the time of the completion of the `dial interruptions, a circuit is 'closed for operating a cut-through relay 4l1 which 'connects the line and sleeve conductors to the called line apparatus. 'Ihe operation oi the cut-"through relay places a ground on the sleeve of the brush shaft for operating the line cut-off relay '5U0. This same ground places va 'busy condition on the sleeve terminal of the `connector multiple bank in order to prevent other connectors 'from seizing this line. The operation of the vcut-through relay 4I1 also establishes a reversal of polarity through the trunk circuit by operating relay M0. 'Relay 449 isoperated at this time and therefore the operation of relay 4I1 establishes obvious operating circuits for relays `420 42| and 4Il1. Relay 4I5 is also in an operated position at this time. This associates lpositive'potenti'al with the tip conductor and'negative potential with the ring conductor over the circuit .previously traced through the Windings'o'f'relaystl l, 321 and 6l4. The reversal of potential causes `the operation of relay 321 in the 'trunk circuit to cause the disconnection of the'trunk conductors 'from the dial circuit and associate `them vwith the'calling station. The current flowing Tin one winding of relay 4H neutralizes the magnetic effect of the current in the other Winding and this relay does not operate. "The operation o'f relay 321 energizes relay 328 'from ground through its Varmature and contact, Winding of relay 328 to battery. The operation of Vrela'y7 328 establishes `an energizing circuit for relay 325 from ground 'through the contact of "relay 321, upper contact of relay 328, Winding of relay 325 to battery. Relay 325 in operating 'establishes a locking circuit for itseli from battery through its Winding and contact 3, to ground through contact 5 of key 338. It will be remembered that the key 338 was placed in 'the hold-and-split position when the dial key A'was'operated At this time the dial key 336 is restored 'to normal which releases relay 321; The 4vkey A338 is now moved 'from the holdand-split position to the through position to actuate 'the le'ft=han'd contacts. The operation of this key does note'stablish any circuits at this time but .prepares a path 'for the disconnect signal and opens two shunt circuits across the repeater Vrelay contacts. The shunt path through the contacts of key 338 is closed except when the key 'is in the through vposition to insure a loop path under lall circumstances when the repeater relays rarenot required in the signal transmission loop. Relay 344 is maintained operated over a circuit Ypreviously traced from ground on contact -4 of .key T338 'through its winding to battery through the contact of relay 312 and resistancef33`4. "Ihe circuit path for the operation of the disconnect vrelay 339 is consequently held open as long as 'the loop circuits are permanently established. Relay '341 is a slow-release relay which prevents its release during the transr'n'ission o'f signals.

Returning now to the operation of the called line apparatus, vlit will be remembered that the cut-'olf 'relaySDD 'was operated when the line was seized. The operation of relay 50B extends the signaling 'conductors from the connector (Fig. 4-C) to Ythe line -circuit (Fig. 5-A) and the called subscribers 'station (Fig. 5-B) The reversal of .polarity on 'the called line is effective over .a circuitl 'traceable from grounded positive .battery '444, front contact and upper armature of relay 4110, ring conductor 445, contact 3 of .relay 441"1, *contact 2 of 'relay 500, winding of polarized vrelay .513, normal contact of key 5I5 to ground on the .back contact of relay 5I6. Relay 513 `'operates and in 'so doing closes an obvious circuit for the operation of relay 5l8. The klatter relay establishes a locking path for itself 'ffrom ground thr'ou'gh the contacts of keys 521 and 52l,.lo"w'er contact and winding of relay 5|,8 to negative battery. The operation of relay 5j|8` establishes a number of operating circuits as rcllows': I

l'. From negative 'battery through the upper contact of .relay .5l8,'lo'wer contact of relay 5I1, buzzer '5l-4 to ground.

2. Frombatte'ry through upper contact of relay 5l8,printer Vmotor'528, contact 529 toground.

3. Battery iis connected through the winding of relay 5`l6to ground and the lower winding of polarized relay 52D 'to ground.

Y'hepolarzed relay 520 may momentarily operate, but as soon as 'relay`5l6 operates the relay 520 is released, since the circuit over the loop extending through the upper winding of relay 520 Aholds the arn'xature against the back contact.

A circuit is therefore established for the printer magnet 526 from ground through its winding, lower Contact of relay 520, resistance 5|9, upper contact of relay 5I8 to negative battery. The buzzer tone is an indication to the subscriber that the line has been called and the motor started and the subscriber upon hearing the buzzer tone operates key 5|5 momentarily, which establishes an obvious operating circuit for relay 5|1 from ground through contact 4 of the key. Relay 5|1 in operating opens the buzzer circuit and establishes a locking circuit for itself from ground to its upper contact, which is maintained until the station disconnects.

The reversal of polarity previously referred to is of short duration. A circuit as shown in Patent 1,958,930 is established for operating relay 4I4 which opens the circuit for relay 4|5 which after a short interval causes the release of relay 4Il. The normal transmitting polarities through the connector repeater relays is thus established. The release of relay 4|0 reverses the polarity over the tip conductor which causes the release of relay 5|3. It will be remembered that a locking circuit was established for relay 5|8 and therefore the foregoing operations in the station circuit Fig. 5-B, recited after the operation of relay 5I8, do not depend in so far as time is concerned upon the interval between reversals beyond the time for operating relay 5|3. As pre- Vviously stated, the signaling loop to the called station is established by the operation of relay 5| 6. 'Ihis loop extends to the repeater in the connector circuit, which is made up of two differential polar duplex repeaters such as

polar relays

405 and 403, arranged to repeat signals from one point to another in opposite directions, but only in one direction at a time. The repeater circuit loop connections for theY called station are traceable from grounded negative battery 409, back contact and upper armature of relay 4|0, ring conductor 445, contact 3 of relay 4|1, brush and terminal of the connector switch contact 2 of relay 500, winding of relay 5|3, contact of key 5| 5, contact ofrelay 5|6,'sending

keys

525 and 523, upper winding of relay 520, contact of relay 500, tip terminal and brush of the connector switch contact 2 of relay 4|1 through the uppermost winding of relay 403, contact of relay 4|4 which is operated, contact of relay 406 to grounded positive battery 46|. The current from battery 45| is simultaneously flowing through the middle winding of relay 403 but in the opposite relation to that in the uppermost winding. The current in the uppermost winding has approximately double the strength and opposite polarity to the current in the middle winding and predominates to hold the armature of the relay in engagement with the back contact.

The signaling circuit extending between the repeater of the connector and the repeater of the trunk circuit may be traced as follows: Grounded negative battery 409, contact of relay 4|0, lower winding of relay 4| I, ring conductor 433, brush and terminal of line-lnder winding of polarized relay 321, contact 4 of relay 225, contact and armature of repeater relay 3|1, upper windings of repeaters 3|2 and 3| I, contacts 1 and I0 of key 336, resistances 361and 368 in multiple, contact of relay 325, tip of line-finder terminal and brush, upper winding of relay 4| I, contact of relay 4I0, upper winding of relay 406, contact of relay 403 to grounded positive battery 401. The currentl from battery 401 is simultaneously ilowing through the lower winding of relay 406 but in opposite relation to that in the upper winding. The current in the upper winding has double the strength and opposite polarity of that in the lower winding and therefore predominates to hold the armature of the relay in engagement with its back contact.

The foregoing circuits traced supply a signaling loop betweenv the called subscriber and the repeater in the connector, also a repeater signaling loop between the connector and the trunk circuit.

For convenience in describing the repeater of the trunk circuit, it may be assumed that the repeater key 338 is operated as previously stated and that the loop circuits are established as previously described. The resistances associated with the repeating relays are for the purpose of proportioning the current flow in the lower windings of relays 3|I, 3|2, 3|5 and 3|1 for causing the repeater action of the relay when signals are transmitted. Current flows through resistances 353, 352, 35| and 350 from ground on`contact 4 of key 338 to battery. This places a negative potential on the terminals of the lower windings of relays 3|2 and 3|5 associated with these resistances. Negative potential connected through resistance 334, contact of relay 3|2, winding of relay 34|, to ground on contact 4 of key 338. Negative potential is also connected through resistance 335, contact of relay 3|5, resistance 3|4 to ground on contact 4 of key 338. The foregoing circuits through the lower windings of the repeater relays create currents known as spacing currents which tend to move the armatures of the relays away from the contacts with which they are associated so that when the signaling circuit is opened in the sending direction, the armature and contacts of one pair of relays are separated. These resistances also estab-A lish a holding current for the alternate pair of repeater relays when signals are transmitted as will be hereinafter described. As previously described, loops are established in each direction and current is flowing through the upper windings of the repeater relays 3| 3|2, 3|5 and 3|1. It may be assumed that the current flowing through the upper windings of these relays is approximately twice as great as the current in the lower windings and has the opposite magnetic effect. This maintains the contacts closed as shown except when signals are transmitted.

When the loop circuit between station A, Fig. l, and the cord circuit, Fig. 2-A, is opened, the repeater in the cord circuit loperates to send a spacing signal between the cord circuit and the trunk circuit, Fig. 3. In this case the armatures of relays 3|5 and 3|1 are opened by the action of the spacing current in the lower windings and a spacing signal is transmitted to station B, Fig. 5-B. This signal is, of course, carried through the repeater of the connector which operates as previously described. The spacing signal of the trunk repeater is transmitted by the opening of the contact of repeater relay 3|1. At the same time the contact of repeater relay 3| 5 is opened for the purpose of opening the circuit path through

resistance

335 and 3|4, which causes a diierence in potential in the lower windings of relays 3| I and 3 I2, with the result that a holding current ilows Vthrough these windings to hold the armatures of relays 3|| and 3|2 against their respective contacts when the loop extendingvto the connector, Fig. 4-C, is opened for the spacing signal. *This same condition exists whena signal is transmitted from station B, Fig. B. The opening of the loop between the connector and the trunk circuit causes the opening of the contacts of relaysy 3|| .and 3|2. The spacing signal is transmitted by relay 3|| and the opening of the contact of relay 2|2 establishes a holding circuit for relays 3|5 and 3|'|.

Signals are transmitted between station A and station B over the circuits and in the manner vdescribed.

Disconnect Upon the completion of the message the line :nder and hunting connector switches are held in place due to the fact Vthat relay 4| is not operated. In order to restore the switches and other appartus to normal the 'subscriber at either station A, Fig, 1-A, or station B, Fig. 5-B, transmits a stop signal, 'usually the upper case H, whereby the mo-tor control contacts 1 at station A and motor control contact 52| at station B are opened, causing 'the release of their respective associated motor start relays |06 and i. The release of relay |08 causes the release of relays |09 and ||0 and also causes the deenergization of the lower winding of the pulse relay 4|07 and the printer magnet |00. Likewise, the release of relay 5|B causes the release of relays 5|6 and Ell and the deenergization of the upper winding of pulse relay 520 and the printer magnet 526. It will be apparent that the release of relays |09 and 5|6 opened their respective transmitting loops. Relay BIS in releasing, connects ground at its armature and back contact causing only one winding of relay 4| to be energized. The release of relay V5|3 allows relay 40B to be operated to the position shown in the drawings. Relay 4| now having only one of its windings energized, operates, thereby causing the release of relay 420, which in turn causes the release of relay 42 The release of relay 42| opens the operating circuit for relay 4|`| and the operating circuit for relay 4|4. The release of relay 4|`| causes the release of the cut-off relay 500 and the operation of relay 403 to the position shown. The release of relays 420, 42| and 4H establishes a circuit for the switch release magnet which allows the switch shaft of the hunting connector switch to return to its normal position. When the hunting connector switch is returned to its normal position, the operating circuit for the release magnet is opened at the contacts and upper spring of the Vertical off-normal springs. Simultaneously with the release of the hunting connector switch the linender switch is released since the release of relay 42| removes ground from the sleeve conductor associated with the line finder. A circuit is now established for the release magnet of the line switch, which operates and allows the line-finder switch shaft to return to normal. When the line-finder switch shaft returns tol its normal position a locking circuit for the cut-off relay 400 is opened and the relay releases, thereby reassociating relay 40| with the ring conductor of the trunk.

When the loop between the trunk circuit, Fig. 3, and the station B is opened, the repeater relays 3| i and 3 2 are energized by the spacing current and the contacts opened. A circuit for relay 34| is thus opened to cause its release. As previously stated this relay is slow to release in order that its release does not take place during the transmission of signaling. The release of relay 34| establishes a circuit for the ultimate operation of relay 339. This circuit may be traced from ground, through contact of key 330, winding of relay 339 and resistance 340 in parallel, contact of relay 34|, thermostat 332, resistance 346, to battery. Relay 339 does not get suiicient current to operate in series with the winding of the thermostat r342. The current flow through the thermostatic relay 342 generates heat therein, which closes its contact after an interval of time. As soon as the contact of the thermostat 342 isclosed, the thermostat winding is shunted, which furnishes sunicient current in the circuit traced for the operation of relay 333. In operating relay 339 alters its holding circuit, which is now carried through its right contact, resistance 345, resistance 346, to battery. The thermostat 342 is thus eliminated from the circuit. 'I'he operatic-n of relay 339 establishes a circuit for the disconnect lamp 343, which may be traced from ground through contact of key 338, left contact of relay 333, filament of lamp 343, resistance 344, to battery. The lighting of lamp 343 is a signal to the trunk operator to restore all keys to normal and in consequence of the restoration of the keys, all of the apparatus of the trunk circuit is restored to normal. Upon the release of trunk relay 306 a circuit is established for the operation of line relay 255 from ground on contact of relay 306 through resistance 220, contact of relay 2|8, upper winding of relay v2|5, resistance 223 to battery. Relay 2i5 establishes an obvious operating path for relay 2|6 and the operation of relay 'M6 establishes a circuit for relay 24| as previously traced. The operation of relay 24| establishes a circuit for lighting the Vsupervisory lamp 242 as a disconnect signal to the manual operator. Ine same supervisory signal is received upon the restoring of the apparatus on the line circuit, Fig. l-B. The manual operator removes plugs 233 and 231 from jacks ||4 and 2|4, respectively, which releases relaysI ||8 and 2|8 which completes the restoring of the apparatus of the system to normal. v

Miscellaneous trunlcing operations Referring again to the trunk position circuit, it will be apparent from the arrangement of the wiring of the key 336 that the printer |500V can be associated with the trunk conductors in either direction by operating the key to the position marked DIAL for one connection and the position marked TWX for the other. In a manner which will be obvious to those skilled in the art Vfrom the description herein calls may be made from station B to the trunk operator 'and extended to the operator at the cord circuit 2--A and thence to a subscriber at station A. AIf two incoming calls are-simultaneously received on the same trunk, one from a station such as A and one from a station such as B, the operator may actuate key 338 tothe hold-and-split position and by operating key 336 'to the desired position, hold communication by the transmission of signals, with one station independently of the second connection. During the communication with either station, the loop in the opposite direction is held over an obvious circuit through resistances 363- 366 or 361-368.

'The trunk operator may originate calls in either direction by the use of key 336, vwith key 338 in the hold-and-split position. In originating a call to station A, key 336 is operated to the left for energizing relay 306 from ground on contact of key 336, through the winding of relay 306,

resistance 30T, to battery. This establishes a circuit for energizing relay 2|5 which may be traced from battery, through resistance 224, contact 3 of relay 228, lower winding of relay 2| 5, line resistances 222 and 22|, contact d oi relay 306, contact 2-3 of key 336, printer iii'iil, contact 4 5 of relay 33S, upper windings of relays 3H and 3I5, armature and contact of relay 3| I, contact I of relay 396, resistance 22|), contact I of relay 2|8, to ground on contact I of relay 2|9. The operation of relay 2i5 establishes a circuit for operating relay 2|9 from ground through the Contact of relay 2|5 contact 2 of relay 2|8, to battery through winding of relay 2 I The operation of relay 2 I9 establishes an obvious circuit for lighting lamp 2|2. The manual operator inserts plug 231 in jack 254 for answering the call from the trunk operator and receives signals as previously described on printer 26d. This operator then inserts plug 23D into a jack such as |I4 associated with the desired subscribers station.

The insertion of the plug in the jack energizes relay |I8 and associates the station apparatus with the cord circuit. Key 23| is actuated by the cord circuit operator for associating ringing potential 236 with the line for energizing the ringer |04. The circuit for ringer |04 is obvious and need not be traced. The apparatus of the subscribers station is manually started by the station operator and the transmission of signals takes place between the trunk positionv and the subscribers station.

A connection may be made by the trunk operator to the automatic private branch exchange, Fig. --B, by the operation of key 336 to the dial position. Key 338 is in this case also placed in the hold-and-split position. The operation of the keys in this manner establishes a circuit for relay 32| from battery, through resistance 222, winding of relay 22|, contact 6 of key 335, to ground 360. A circuit is thus established for the operation of relay 323 from ground through contact 2 of relay 22|, lower winding of relay 223, resistance 224, to battery. The line nder is thus operated as previously described but in this instance the winding of relay 49| is actuated from ground on the left contact of dial SI5. The connector switch, Fig. 4-C, is operated by the transmission of dial impulses as previously described, which associates the station, Fig. 5-B, with the trunk operators position. Signals may now be transmitted in the manner previously described.

What is claimed is:

1. In a trunking system for interconnecting telegraph lines entering central cnice switching systems, teletypewriter subscribers stations connected with different central oces of the manually operable type and automatic switching type, a trunking central office with which said different ofces are connected, trunk circuits in said trunking ofce having a printer set associable therewith, and means in the trunks of said trunking oice including switching apparatus and pulsing apparatus for receiving calls from and interconnecting subscribers stations entering said different offices.

2. In a trunking system for interconnecting telegraph lines entering central office switching systems, teletypewriter subscribers stations connected with different central offices of the manually operable type and automatic switching type, a trunking central oiiice with which said different offices are connected, trunk circuits in said trunking oce having a printer set associable therewith, means in the trunks oi said trunking office including switching apparatus and pulsing apparatus for receiving calls from and interconnecting subscribers stations entering said different oices, and means in said trunks for inserting a through-repeater circuit in between said interconnected stations.

3. In a trunking system for interconnecting telegraph lines entering central oice switching systems, teletypewriter subscribers stations connected with different central ofces of the manually operable type and automatic switching type, a trunking central office with which said diferent oices are connected, trunky circuits in said trunking oice having a printer set associable therewith, and means in the trunks of said trunking oiiice including switching apparatus and pulsing apparatus for originating connections in the trunking oiiice extending to subscribers stations entering said dierent oices.

4. In a trunking system for interconnecting telegraph lines entering central oli-ice switching systems teletypewriter subscribers stations connected with different central oiiices of the manually operable type and automatic switching type, a trunking central ofiice with which said different ofces are connected, trunk circuits in said trunking oflice having a printer set associable therewith, means in the trunks of said trunking office including-switching apparatus and pulsing apparatus for receiving calls from and interconnecting subscribers stations entering said different ofiices, and means in said trunks for splitting said connections for communicating by signals with either type of central oiiice and with subscribers stations entering said oiiices.

5. In a trunking system for interconnecting telegraph lines entering central oiiice switching systems, teletypewriter subscribers stations connected with different central oices of the manually operable type and automatic switching type, a trunking central oice with which said different oiiices are connected, trunk circuits in said trunking oiiice having a printer set associable therewith, means in the trunks of said trunking ofrlce including switching apparatus and pulsing apparatus for receiving calls from and interconnecting subscribers stations. entering said different oices, and means in said trunks for communicating with both said interconnecting stations simultaneously.

6. In a trunking system for interconnecting telegraph lines entering central office switching systems, teletypewriter subscribers stations directly connected with different central oces including the manually operable type and the automatic switching type with trunk finder and connector switches, a trunking central oiiice with which said different oiiices are connected, trunk circuits in said trunking oiiice, means in the trunks of said trunking ofiice for receiving calls from a manual oice and completing a connection for said call from the manual olice to a subscribers station entering an automatic switching oiiice, and means in said trunk circui to cause the operation oi a trunk nder in the distant automatic switching ofce upon the seizure of said trunk circuit at the manual oflice.

KARL E. FITCH.