US2345316A - Through and inward telegraph exchange system - Google Patents

Description

March 28, 1944. R. s. BAILEY THROUGH AND INWARD TELEGRAPH EXCHANGE SYSTEM Filed May 17, 1941 4 sheets-sheet 1` R. S. BAILEY THROUGH AND INWARD TELEGRAPH EXCHANGE SYSTEM Filed May 17, 1941 Sheets-Sheet 2 xxx March 2s, 1'944.

March 28, 1944.4 R` Q BAlLEY 2,345,316

THROUGH AND INWARD TELEGRAPH EXCHANGE SYSTEM Filed May 17, 1941 4 Sheets-Sheet 3 0. ma@ QE. .Tm fl m S v Q E 4 Sheets-Sheet 4 March 28, 1944. R. s. BAILEY THROUGH AND I'NWARD TELEGRAPH EXCHANGE SYSTEM Filed May 17. 1941 Patented Mar. 28, 1944 THROUGH AND INWARD TELEGRAPH EXCHANGE SYSTEM Rand S. Bailey, Glen Ridge, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application May 17, 1941, Serial No. 393,863

35 Claims. (Cl. 178-2) This invention relates to teletypewriter systems and more particularly to automatic switching for establishing and maintaining connections in teletypewriter systems.

This application is in part a continuation of application Serial No. 223,431, filed August 6, 1938, and relates to the subject-matter and system originally disclosed in Figs. 1 to 5, inclusive, thereof, with added subject matter.

`An object of this invention is to provide a system wherewith to establish automaticalltl under control of one operator a connection between subscribers stations over a toll line.

Another object of this invention is to furnish a teletypewriter exchange ofce operator with full supervision of the line of a calling and a called subscriber at the initial toll line exchange center. The teletypewriter toll exchange center will be referred to hereinafter as TWX oilce.

Prior to the present invention numerous types of teletypewriter switching systems have been patented, disclosed in publications or utilized in actual practice to a greater or lesser extent. In general, these fall into two classes, the first of which is the mechanical or selective type in which a calling station by some automatic means under the control of the attendant or operator at the calling station establishes connection with a remote station for one-way communication or for intercommunication. Various technical difficulties are involved in the use of such systems and, in addition, there is the further diiliculty that when a charge must be made for the call some special arrangement must be made for establishing the charge. Another type of system extensively used for the giving oi satisfactory serv ice is one in which all line interconnections and disconnections are made manually by operators using suitable cord or key circuits. A feature of this type of system as generally employed is that a call involves the intervention of an operator at each switching point for setting up and disestablishing a communication circuit. Thus, in a call over a trunk the services of an operator at the calling end o f the trunk as well as another operator at the called end of the trunk are engaged. This has the disadvantage of slowing up the service and also of increasing the cost thereof. In order to expedite the service and, in particular, to reduce the cost by enabling an operating routine in which a call over a single trunk engages the services of one operator only at the outgoing end of the trunk, the system herein disclosed has been devised.

A fundamental operating feature in accordance wtih this invention 'is that a calling Subscribers station is connected automatically by an operator at one TWX office to a desired called subscriber connected to another TWX oice without the intervention of an operator atthe latter oice. The operator `at the originating TWX oiiicehas complete control lof the circuit set up and complete supervision ofthe lines extending to the calling andv called subscribers, the trunk, and the equipment required for automatic switching. Inv addition, the callinitiating with. the TWX operator can at all times ascertain the condition of the subscribers stations and the lines connecting these stations. i

A feature of the invention is'theA use of a trunk which is so terminated that calls may be extended in either direction thereover.

Features of the invention are the provision of trunks terminating both in selectors and in terminals for manual connection of link circuits thereto, such as jack terminals, for example, busy tests or lamps whereby seizureof a trunk by an operator at one end rendersit busy at both ends; a busy. test arrangement whereby -a -subscriber orbranch line connected to. a link circuit tests busy at terminals adapted to seize it for an incoming message; an operators link circuit containing a teletypewriter and a dial of the numerical type for remotely controlling the selec. tion of `a subscriber line; a repeatered'trunk which may be of the differential duplexv type typifying the general case lof a two-way telegraphic impulse transmission channel; a trunk which transmits dial pulses with the same marking and spacing ,elements as used for telegrapl'iic` communication; a trunk normally spacing in the idle condition; a trunk in whicha marking condition is used to indicate a call; a trunkvover which call, mark, space, break, call andri'ecall indications or any oflthem may at appropriate times be transmitted; use 'of break limiting ref' call keys; an operators cordcircuit including a. break limiter; a trunk including a break limiter; a trunk terminating in multiple jacks; andY other useful features. l y l .I

Other objects and features will be readily understood'from the following description and ap-I pended claims when taken in conjunction with the accompanying drawings of which:

Fig. 1 illustrates in block diagram a Iteletypewriter system in which a calling station associated with a rst toll, or TWX, oli'iceis connected by an operator to a called stationassociated with a second toll, or TWX,` olce,1o r viceversa, without the intervention of the operator at the;` toll;

or TWX, oilice nearer the called subscribers station. A subscribers station C is connected by means of a line to the subscribers line equipment at TWX oillce A. The subscribers line equipment is terminated in a jack at the TWX 5 oflice A and is also connected to automatic switching equipment also. located at the TWX oiiice A. Trunk line equipment at the TWX oiiice A is connected to a toll line. The automatic switching equipment is connected to the toll line equip.-` ment and serves as an automatic switching path' from the toll line to the subscribers' stations. connected to TWX oflice A when the subscribers sta'- tions connected to TWX office A are the called stations. T-he toll line equipment atTWX oflice A terminates in a jack. A cord circui-t'atfI'WX olice A serves to connect manually any subsoribers line connected to thatloi'celwith the toll line equipment when the subscribers stations, connected to TWX office A, originate the calls. The toll line connects. to. thev toll?. line; equipmentatv TWX ofiice Bi. One orJ several repeaters; as' required, are interposed in. the' toll line. The tollline may include carrier channels, radio channels or any usual type of duplex telegraph facility. Like the toll-f line equipment at TWX office A, the toll line equipment at TWX' oiii'ce Bl terminates in a jack and is connectedto automaticv switching equipment capable ofV connection with any one of several subscribers line equipments. conneeted to TWX olce BA when the subscribers stations, connected to TWX oflice B, arel the called stations. Y Bothr the toll' linel equipment and TWX oiilce B andA the subscribers line equipments at TWX' oii'ice B'-A are provided with jacks for connection'- between the toll lineI and any subscribers line connected tor central' station B. A` cord circuit at the TWX office B serves to connect manually the tollv line through the-toll. linef equipment withV the subscribers line equipment at TWX ofiice-B, when thesubscri-bers stations connected to rLWX ofiice B originate the calls. subscribers line" as used herein is` a convenient designation for any l-ine to an outlying station; operator is a namev for any person who carries on the switching or other operations to which reference is made. All the parts of the system are indicated by labeled block diagrams in Fig; 1;

Fig. 2 shows the relative positions of Figs. 3, 4 and 5;

Fig. 3- shows in detail" a tel'etypewriter sub-l scribers station set at station C connected to the subscribers line equipment at the TWX oflice A andI an operators cord circuit for connectingthe subscribers line set to the opera-tor's position circuit at TWX oflce A; Fig. 4 shows the toll line equipment at TWX' oiiice A for connecting tothe toll linethe subscribers station equipmentfeither manually by means of the cord circuit, or automatically by means of' automatic switching-V equipment, an intermediate repeater in the-'toll line andk toll line' equipment at TWXofce B; and

Fig. 5 shows an operators cord circuit at TWX oiiicevB for connecting the toll line equipment at thel TWX oiiice B, a subscribers line equipment at TWX oiiice B and a teletypewriter subscribers set at station Dl directly connected to TWX office B. The teletypewriter subscribers station set at 70t stationvv D isV arranged for connection to the toll line'- equipment at TWX office B by'means of the cord circuit shown in Fig. 5, or under thecontrol of the automatic switching equipment shown in Fig'- 4.

Station C initiates a call A call is initiated from station C upon the operation of call. key 309, The operation of this key -energizes motor'35, causing it to operate during the entire timethat the key is in an operated position. Key 339 in being operated also closes a circuit extending from grounded positive battery 3i2, conductor RA, break key 303, transmitting contacts 3l! I, magnet 302, left spring and contact of recall and disconnect key 304,. through the'. winding of slow-release relay 305,y operated. spring and contact of call key 30'9, tip conductor TA, left armature and contact of relay 324, outer armature and contact of relay 3.15,. through the winding of line relay 313 to ground.

Relay 313, in operating, closes an obvious circuit.

for lighting lamp 3l6. The lighting of lamp 3I'6' indicates to the operator' at TWX oiiice A that a call is waiting on this line.

Operator answersl The operator answers Iby inserting a plug such as that designated. 331 into jack 311,. and.' operating the typing key 322.

Assuming that the plug has been insertedy fore the typing. key 322 is operated, two circuits are completed, one from grounded battery 3121. through lamp 320, through the winding of relay 329, sleeve conductors of plug 331 and jack 3|?, through the winding of. cut-off relay 3M, inner armature and Iback contact of relay 315,. to ground. This circuit lights lamp 32H andi opel-'- ates relays 323 and 3M. Relay 3M. in operating.. disconnects at its right armature, relay l315 'from its associated terminal on the lower `bank 421A of a rotary selector switch and applies ground .to that terminalk making the line busy to incoming. calls. At its left armature and front contact, re lay 344, in operating, completesa circuitextending from grounded positiveV battery SI2, through. station C, the left armature and front contact of relay 3M, tip conductors of jack 3H and plug 331, through the winding of relay 332, to ground-.- ed negative battery 30?. Relay 3 32,jin operating, closes an operating circuit for relay 338.. Relay 330 operates and at its inner make-before-break. contact removes grounded negative battery 351' from the subscribers line and replaces it. by grounded negative battery 34B', via4 thecontacts' of relays 329, 333 and 323. Relay 330, in operat-` ing, connects at its left-hand armature and con. tact an interrupter 333, Via the lower and the upper make-before-break contact of relay 33|,y in shunt across lamp 320. At each closure of the interrupter, lamp 323 will be extinguished and on each opening it will light. This flashing of lamp 326 is an indication that key 322 has not been operated.

When the operator operates key 322, which is vassigned to the cord circuit shown in detail, it will operate relay 323. Relay 323, in operating,

will insert the operators teletypewriter set conslsting of magnet 326, transmitting and' receiving tact of relay 330 to grounded battery 32| thereby` applying a permanent shunt across lamp 320.

By shunting lamp 320', the lamp is extinguishedr as long as relays 330 and 33| are operated, andy also after key 322 is released.

If key 322 was operated before plug 331 was inserted into jack 3 I1, relay 33| would have been operated and interrupter 333 would not have been cut in.

The operator may have at her disposal a number of cord circuits, but the operators set can be cut in only on one circuit depending upon which one of keys 322, 321, 328, etc., is operated.

The' operator indicates her answer and presence on the circuit to the calling subscriber C by typing OPR and subscriber C then types the code number of the desired subscribers station which number appears at the operators teletypewriter set.

Operator completes to'a toll line Assuming that the called party is in a distant city, the operator inserts plug 335 into a trunk jack of an idle trunk, such as jack 40|A, which terminates a trunk circuit extending to another TWX oilice to which the called partys station is connected. Repeater relays 403A, 405A, 406A, 401A, 403B, 405B, 406B and 401B are diiierential polar relays and are normally held, in their idle condition, that is, on their spacing contacts, as shown, by current in their lower windings, the voltage polarity and direction of the flow being such as to hold them in the spacing positions.

When plug 335 is inserted in jack MHA, an operating circuit for relays 402A and 338 is closed from ground on back contact and upper armature of relay 4|3A, through the winding of relay 402A, sleeve conductors of plug 335 and jack 40 IA, through the winding of relay 338 to grounded battery, causing relays 338 and 402A to operate. Relay 402A, in operating, closes a circuit from grounded battery, through lamp 339, ring conductors of plug 335 and jack 4UIA, innermost upper armature and Contact of relay 402A, lhack Contact and armature of relay 4|5A, to ground. This latter circuit will cause lamp 339 to light to indicate that the line has been connected through vbut that the answering equipment has not as yet been associated. Relays 338 and 402A, being operated, will extend the communication circuit of the subscribers station C through theV upper winding of relays |||I3A and 405A, armature and spacing, or right, contact of relay 406A and armature and spacing, or right, contact of relay 403A to grounded negative battery. The communication circuit, which has grounded posi. tive battery 3|2 connected to it at station C, will when closed cause relays 403A and 405A to move t their respective marking, or left, contacts. At the left contact of relay 403A, grounded negative battery 45|) will again be established for holding operated relays 403A and 405A, via the upper armature and back contact of relay 404A, through the winding of relay 409A, lower armature and back contact of relay 4|0A to negative grounded battery 450. Relay 409A will operate and maintain open the operating circuit for relay MDA. Relay MDA might have operated previous to this but its operation would not aiect the operation of relays 403A and 405A and upon the operation of relay 409A, relay MUA would release. Relays 409 and 4|0 are brought into use in an established communication circuit so as to reduce the continuanceof long spacing signals received from the direction of the called station over the toll line to one-half second. Relay MUA may be operated inadvertently on a slow plug-in by the initial incoming spacing signal but this is of no moment as relay 409A operates in response to the release of relay 403A, and relay 403A remains released, so as soon as relay 4|0A releases, open signals can be sent from the cord circuit to relays 405A and 403A.

Signal reaches ojice D The operation of relay 405A to its left, or marking, contact applies grounded negative battery to the line via the upper Winding, in series, of relays 406A and 401A, repeater 408, the upper winding, in series, of relays 401B and 406B to meet grounded positive battery on the spacing, or left, contact of relay 405 B, thus causing relays 405B and 401B to move to their respective marking, or right, contacts. Relay 4|5B will operate via a circuit to ground through the lower windings, in series, of relays 403B and 405B.

Relay 4|5B, in operating, will operate relay 404B via the lower armature and contact of relay 402B. Relay 404B will remain operated during break signals, i. e., unless a spacing signal of over one-half second duration is received from oiiice A, that is, a disconnect signal, since both relays 4|5B and 404B are of the slow-to-release type and the time required for these relays to release in succession is such that they will hold 4| 3B operated for any break which the calling subscriber can produce. Relay 404B may be of a very slow-release type.

Relay 404B, in operating, will by its upper armature and front contact apply grounded positive battery to the marking, or right, contact of relay 403B and will also maintain open the operating circuit for relay 409B. At its lower armature and contact, relay 404B will operate relay 4|3B. Relay 4|3B, in operating, will apply at its upper armature and front contact, grounded negative battery to a circuit extending through the winding of relay 402B to the sleeve conductor of jack 40|B, thereby making the sleeve busy, that is, jack 40 |B is'busy to the operator at oice B. Also, relay 4|3B, in operating, will condition at its inner lower armature and contact the dialing circuit which, during dialing, will extend from ground, armature and spacing contact of relay 401B, conductor 434, Contact and inner lower armature of relay 4|3B, conductors 435 and 436, outer lower armature and contact of relay 4|9B, outermost lower armature and back contact of relay 430B, through the winding of relay 4|8B, through the winding of stepping magnet 4|1B of the banks 4|6B and 421B ofl a rotary selector switch at oiiice B, to grounded battery. Also, relay 4! 3B, in operating, will at its middle armature and front contact close an operating circuit for busy lamp 4| IB and maintain open the operating circuit for release magnet 429B, the latter circuit extending over off-normal contacts 428B of the rotary selector switch. Another function of relay 4|3B, when operated, is to close at its lowermost armature and contact the called station loop to grounded positive battery, thereby causing relays 403B and 405B to operate to their respective marking positions due to current now at oice A that the equipment is prepared to receive the dialing pulses. The operator at oflice A could dial with lamp 339 lighted, that is, against the original space signal, since the operated 409A and released relay 4IOA have provided marking instead of spacing battery toward the selected cord circuit at office A in spite of the incoming space Signal received from the toll line;

Dialing Y It is not necessary to give the operator at oflice A a dialing signal since the very fact that the operator has possession of an idle trunk gives her complete control over all required apparatus as no other apparatus need be brought into play. Each trunk is equipped at the receiving teletypewriter exchange ofce with a conventional dial controlled selector switch, a ten point rotary selector switch consisting of banks such as those designated 4l6B and 421B, a stepping magnet such as that designated 4 I TB, an off-normal contact such as that designated 428B and a release magnet such as that designated 429B being illustrated. The operator at ollice A dials by moving her dial 325 off-normal to the number required. The upper contacts of the dialwill operate relay 326 which will split the cord circuit, applying grounded negative battery to the subscribers line andgrounded positive battery to the trunk, thus preventing the dialing pulses from interrupting or affecting the subscribers circuit at station C. Relay 326 will remain operated until the dial returns to normal.

The automatic return of. the dial to normal will cause a train of pulses, consisting of openings and closures, to be transmitted over the trunk thereby operating relays 403A and 405A, in accordance with the pulses. Relay 405A, in operating, in accordance with the pulses causes relays 401B and 406B to operate in accordance with the pulses. Relay 406B, in operating, in accordance with the pulses will not affect relay 4I5B inasmuch as the latter relay is of the slow-torelease type. Relay 4I5B will, therefore, remain operated during the reception of the train of pulses. Thel rst open pulse, causingv relay 401B to go to its spacing, or left-hand, contact, will complete a circuit from ground on the armature of relay 401B in engagement with its left-hand contact, conductor 434', contact and inner lower armature of relay 4I3B, conductors 435 and 436, outer lower armature and contact of busy relay 449B, outermost lower armature and contact of relay 436B, through the winding of relay 4|8B, through the winding of stepping magnet 417B to grounded battery. Relay 4I8B operates in response to the first opened pulse and will, therefore, lock up in a path which shunts the outer lower armature and contact of relay 419B andv .the outermost lower armature and Contact of relay 430B. Relay 4|8B is of the slow-to-release type and will, therefore, hold over for the durationcf the train of pulses. Relay 4|8B, in op- The release of erating, will close an obvious operating circuit for relay 449B, which is alsoof the slow-to-release type and will remain operated for the duration of the train of pulses. Relay 449B, in operating, will open at a secondY point the circuit for operating relay 430B and will condition the circuit for operating busy relay MSB which is. opened at relay 4|8B.

vThe train of pulses will operate stepping magnet 4I1B a successive number of times corresponding in number to the pulses of. each train.v 'I'he successive operation of stepping magnet 4|1B causes the wipers of banks 421B and 415B to rotate one step for each pulse. Now if it is assumed that there is transmitted a train of livey pulses, the wipers of banks 421B and 416B will. be on terminals No. 5 of their respective banks at the end of the train and the final closure ofV the. lineV circuit after the train of pulses has been. transmitted, will cause the armature of dialingrelay 401B to remain engaged to its right-hand contact, thereby opening both the operating and` the holding circuits for relay 4l8B. Slow-re-` lease relay 4|8B after al short time will release thereby opening the operating circuit for relay 449B, which being also slow ,tor release is subsequently released. The line which terminates on terminals No. 5 of switch banks 4|6B and 421B- is multipled, as indicated, to the corresponding terminals of other switch banks, not

shown but respectively associated with other` trunk circuits of the system.

Called line busy v contact and armature of stepping magnet MTB,

contact and lower armature of relay 449B, outer upper armature and contact of relay 418B, contact and next to the outermost lower armature of relay 430B, through the winding of busy relay 4I9B to grounded battery. Busy relay 4I9B, whose function is to cause a busy signal to be sent back to the oiice A, operates and at its contact and inner lower armature closes for itself a locking circuit extending to ground at theouter lower armature and front contact of relay 4l3B.

Busy relay 4| 9B, in operating, connects atv its;

ings, in series, of relays 406BV and40'lB, through the intermediate repeater 408, through the upper windings, in series, of relays 401A and 406A to the armaturek and left contact of relay 405A to grounded negative battery. Relay 406A, uponv operating its armaturev to its right-hand position, closes an operating circuit for relay 409A whichv extends from grounded positive battery at the front contact and lower armature' of relay 4110A,

through the winding of relay 409A, back contact and upper armature of relay 404A, left contact and armature of relay 403A, right contact and armature of relay 406A, through the lower windings, in series, of relays 405A and 403A to ground. Relays 406A and 409A operate for an interval suiciently long, as determined by the cuttings of interrupter 420B, to permit slow-release relays 4IOA and 4I5A to release. These alternate open and closed pulses are greater than one-second duration and are sufficient to release relay 4I5A after each closed pulse. The alternate Operation and release of relay 4I5A causes the alternate opening and closing of the operating circuit for supervisory lamp 339 so that the lamp gives a ashing signal to the operator at ofce A.

This iiashing lamp is an indication to the operator at ofce A that the called subscribers line is busy. The operator then noties the calling subscriber :at station C who, upon receiving such information, will disconnect. The operator then removes plug 335 from jack 401A. The plug may be removed from the jack during either a closure or an opening of the circuit of interrupter 420B. If the line is closed the removal of plug 335 will effect the release of relays 402A and 338. 'Ihe release of relay 338 will close the line circuit extending to subscribers station C and the operator will receive a disconnect signal from the subscriber at calling station C in a manner to be hereinafter described. The release of relay 402A will open the upper winding of relays 403A and 405A whereby relays 403A and 405A will operate to their respective space, or right, positions. The application of grounded positive battery by the varmature 01 relay 405A to the trunk circuit will cause relays 406B and 401B to operate to their respective space, or left, positions. The operation of relay 496B to its space position will cause the release of relay 4I5B which in turn will release relay 494B. Relay 44B, in releasing, will operate relay 469B in a circuit traceable from grounded negative battery, back contact and lower armature of relay 4IOB, through the winding of relay 469B, back contact and upper armature of relay 404B, mark, or right, contact and armature of relay 403B, space, or left, contact and armature of relay 405B, through the upper and lower windings, in parallel, of relays 405B and 403B, the path including the upper windings being extended over conductor 439 to the outer upper armature and back contact of relay 430B, conductor 438, upper armature and contact of relay 4I9B, interrupter 420B to grounded positive battery. The release of relay 4U4B releases relay 4I3B also. Relay 4 I3B, in releasing, removes at its upper armature the grounded battery from jack MIIB which battery had heretofore served as an indication to the operator at oilce B that the trunk circuit shown in Fig. 4 was busy. Also relay 4I3B, in releasing, opens at its outer middle armature and front contact the locking circuit for busy relay 4I9B, which releases to thereby .remove interrupter 42IlB Also relay 4 I3B, in re- ,switch 428B is thereby also restored to normal in which position the contacts are opened. 'I'he re- Vrno'valof interrupter420B, whereby relays 405B and 401B were operated periodically to their spacing positions, 'will result in grounded negative battery being Yapplied to the lower winding of relays 403B and 405B and the latter relays will consequently operate to their respective spacing, or left, positions. The operation of relay 403B to its spacing position will cause the release of relay 409B, The operation of relay 405B to its spacing position causes relays 406A and 401A to operate to their respective spacing, or right, positions, thereby releasing relays 4I5A and 404A. Relay 4 I 3A then releases. Relay 402A, in releasing, extinguishes busy lamp 4I IA and the release of relay 4I3B extinguishes lamp 4I IB. The circuit is now normal.

`If. the line is open when plug 335 is removed from jack` 40IA, the same procedure as just described wil1 be followed except relays 403B and 405B will not have to wait for the removal of interrupter 420B, to operate to their respective spacing, or right, positions.

Called line kidle lIf the called line is idle grounded negative battezy 5I8 will be present on a circuit including the winding of relay 5I5, back contact and left armature of relay 5I4, conductor 540, terminal No. 5 of switch bank 421B at the time the wipers of the rotary'selective switch are operated to their respective No. 5 terminals. When therefore relay 4I3B releases at the end of the train of dialing pulses, busy relay 4I9B will not operate. When relay 449B releases subsequent to the release of relay 4I8B and stepping magnet 4I1B -a circuit is closed extending from ground at the middle lower armature and front contact of relay 4I3B, inner lower armature and back contact of relay MSB, through the lower winding of relay 43B, contact and upper armature of relay 449B, contact and armature of stepping magnet dIlB, wiper in engagement with terminal No. 5 of switchbank 421B, conductor 540, left armature and back contact of relay 5I4 through the winding of relay SI5 to grounded battery. Relay SI5 operates and connects at its front contact and inner left armature grounded negative battery to a circuit extending through winding of cut-oli relay 5M to the sleeve conductor of jack 5I'I. whereby the line circuit of subscribers sta.- tion D is provided with a busy potential upon the sleeve of the jack. Relay 430B operates and closes at its inner upper armature and contact a. locking circuit for itself, which extends to ground at the middle lower armature and front contact of relay 4I3B. Relay 430B, in operating, will at the next to its innermost lower armature and contact apply ground to terminal No. 5 of switch bank 421 thereby making the terminal busy to other calls and serving as a holding ground for oper-ating relay 5I5. The operation of cut-01T relay 5I4 opens the line circuit to line relay 5I3 thereby preventing the lighting of the call lamp for the line of subscribers station D. Also, relay 43B, in operating. will at its innermost lower armature and contact close a circuit extending from ground, interrupter 44IB, innermost lower armature and contact of relay 430, outer lower armature and contact of relay 433B, through th winding of ringing relay 432B to grounded battery. Relay 432B alternately operates and releases in response to interrupter '44.IB and thereby applies .at its armature and contact ringing current to a circuit extending over the Wiper in engagement with terminal No.5 on selector switch bankV 4'I6B, conductor 54|, over the normally ing of relay 433B, outer upper Varmature "and 'liront contact of relay'43'0B, through the upper winding, inseries, of relays 403B and 405B, armatureY and right-hand'contact vof relay 406B, 'tnroughthe Winding or relay 4|5B to grounded negative battery. Relay 433B operates and closes at its inner upper armature and contact a locking circuit for itself, V.extending to ground at the 'outer lower armature of relay 4|3B. Relay 433B, in operatinggwill at its outer lower armature Contact open the operating circuit for ring- "ig 'relay '432Band`th'er'eby cut off the ringing. lThe closing of the subscribers line of station Dftvill 'energize the upper windings "of relays '403B 'and '405B which Will operate to their respective marking, or right, positions, causing in turn, relays 406A and '401A to operate to 'their 'respective marking, or left, positions. Relay MSA, in its marking position, `wil1 operate relay cM515. 'Relay 415A, in operating, opens a circuit lextendingfrom ground, upper armature and'back 'contact of relay 1H 5A, contact and innermost upper armature of vrelay 402A, ring conductors "of jack A401A and 'plug 335, through lamp 339 toA grounded battery and lamp 339 vis therefore extinguished. Relay 1306A, in operating toits marking position, Will at its spacing, or right, fpositiorilopen the operatingicircuit for vrelay 409A. Relay '409A releases and thereby closes at its armature `and contact "the operating circuit for relay YMHA. `Relay 4'|0'A, which is offthe slowtoireleasetypeto the amount'of one-half second, operates. The connection 'is now complete and Ycommunication Ymaytake place from subscriber -Themethod of-'transmission is of Ya well-known typeand Awill notbe'described here, LSubsequent spaces of telegraph code-or subscribers breaks proceeding from rthedirection of oilice B will 'causerelay1499A to release butrelay -4|0A will remain operated to apply positive battery space signals back Vto the direction of station Ar or the calling line-'oi station C. However, a long recall'or disconnect space from the direction ofthe called subscriber of station D will allow relay 410A to release in about one-half second and limit such spacing signals :to one-half second duration toward the calling line. of relay 415A gat tthe vendoi along break signal will light supervisorylamp '339 but the light Will gooutagain on closure of the break and, moreover,-the rela-y may be of a design as slow as desired;

" Telegraphcode and "short break signals from the V'calling subscriber are repeated by relays lilil, -405A,40`|B and 406B, but longer open line signals'employed 'for disconnect or recall coming The release `from the direction of `station C areprevented '75 vfrom continuing on' the trunk circuit beyond vstation lA after one-half second by the release of relay 330 in the cord circuit, which relay releases to close the calling loop toward thetoll line. Relay 330, upon releasing, also removes the shunt path closed at its left-hand armature and contact and permits lamp A320 to light. If the subscriber recalls, the reoperation of lrelay 330 will now shunt lamp 320 intermittently as a recall in the Well-known manner. Relay 33| which cooperates in providing the recall is also slow to release since relay 332 and 'hence relay 330 may be released not only by the calling subscriber but by calledsubscriber Abreak s as well; relay l33| protects the long signal until relay 4|0A has had an opportunity to release and vre close the calling loop. In other Words, if a `break is received from station D upon a call originated lat station C, the releasetime of relay 330 should be longer Athan that o'i relay MUA so that 'upon a 'break proceeding from station D it is limited ,'atrelay 4|-0A 'to a shorter time than it would be limited a't relay A330 so that disconnect lamp 32,0 iis not lighted to give an erroneous indication of 1a disconnect from station C, A desir- `'able but not absolutely essential condition, there- "fore, is that relays 330 and 530 may require more release time by an ample margin than all relays 4110A and 4|0B. Such relative ltimes of one `second and one-half second have vbeen assigned VWhereas'the sum of the releasing'times of relays 1|1|5B and '404B may be above one second.

The relays '409 and v4I0 are not required to func'tion Land do not function to limit breaks on the ,inward end of a toll line, as the relay A.correspending to those designated 332, 532, etc. 'and the 'relay 'corresponding to those designated 33,0, 530, etc. in the cord circuit restrict the duration vof the calling subscribers breaks The 4( lisjconnect signal sent by the ".A operator, that is, the operator Vat the outgoing end of @the connection need not be and is not limited. The operation of the relay corresponding to relays 404A, 404B, etc., therefore, disconnects vthe armatures of relays '410A or 4| 0B, respectively, `janditjs sources of rpotential from the associated 'line Vand 'substitutes positive, Yor spacing, battery for retransmission of all spacing signals received ifi-,om the vtoll line to the called loop subscriber.

Calling subscriber disconnects yThe calling subscriber can disconnect by restoring vkey v309 to normal. The restoration f key 309 toits normal position will open the oper- `a'zting'circuit for motor 306 and remove grounded p ositiye battery 3| 2 from the 'line circuit, whereby "relay-332 isA deenergized after a'time interval of vone second. lRelay 332, in releasing, will open Afthe operating circuit for relay 330 which alsoreleases. Relay 330, in releasing, will split the 'line'at'its right-hand armatures so that the subscribers loop is maintained closed at the inner right make-before-break contact of relay '330'to grounded'negative battery 301 and the tip cond-uctor of the trunk'circuit is maintained closed vat the outer right make-before-break contact of *relayj330 -to grounded positive battery 301. Also, :relay 330,in releasing, opens at its left armature Contact vthe locking circuit for relay 33|, thereby causing lamp y320 to light in a circuit to grounded ynegative battery 32| to lamp 320 through the Awinding of relay 329, sleeve conductors of plug "318 Aand jack 3|1 through the winding of cut- "pif relay vv3|j4 to ground at the inner left armafture and back contact of relay 3|5. The lighting of lamp 320 at this time notifies the operator at oiiice A that the subscriber at station C has disconnected.

Calling subscriber recalls If the subscriber at station C desires to recall the operator at oiiice A before plug 339 is removed from jack 3|'I, the subscriber reoperates l309 and relays 332 and 330 will operate in sequence, as heretofore described, and relay 33| will not reoperate because at this time relay 323 is released and typing key 322 is in its normal position. The operation of relay 330 at a time when relay 33| is released closes a shunt path Aaround lamp 320, said path extending from grounded negative battery 334, interruptor 333, lower make-before-break contact oi relay 33|, contact and left-hand armature of relay 330, upper make-before-break contact of relay 33|, resistance 308 which is of a comparatively low value, through the winding of relay 329, sleeve conductors of plug 331 and jack 3I1, through the winding of relay 3I4 to ground at the inner left armature and back contact of relay 3|5. The shunt path to grounded negative battery 334 extinguishes 1arnp 320 during the intervals of closed circuit eiected by interrupter 333 and lighted -during the open interval thereby causing lamp 320 to flash. The operator at oiiice A observing the flashing of lamp 320 will operate key 322 to close the operating circuit for relay 323. Relay '323, in operating, closes the operating circuit for relay 33| which now operates to extinguish lamp 320 and the subscribers teletypewriter set at station C is connected as heretofore described to the teletypewriter set of the operator at oice A.

Called subscriber disconnects The called subscriber at station D can disconnect by restoring key 509 to normal whereby grounded positive battery 542 is disconnected 'from conductor 54| and a trunk circuit including -the wiper in engagement with terminal No. 5 on switch bank 4I6B, armature and back contact of relay 432B, winding of 433B, front contact and outer upper armature of relay 430B, conductor 439, upper windings, in series, of relays 403B and 405B, armature and right contactl of relay 406B, winding of relay 4I5B, and grounded negative battery. Relays 403B and 405B release to their respective spacing, or left, positions. Relay 405B inv releasing to its left-hand position connects grounded positive battery to a circuit extending over the upper windings, in series, of relays 406B and 401B, intermediate repeater 408, upper windings, in series, of relays 401A and 406A, armature and marking, or left, contact of relay 405A to grounded negative battery. Relays 401A and 406A release to their respective spacing, or right,

positions. Relay 406A closes an operating circuit for relay 409A extending from grounded positive battery 450, front contact and lower armature of relay 4I0 A, through the Winding of relay 409A, back contact and upper armature of relay 404A, marking, or left, contact and armature of relay 403A, spacing, or right, contact and armature of relay 406A, through the biasing windings, in series, of relays 405A and 403A. Relay 409A operates and relay 4|0A releases in about one-half second. Relay 409A, in operating, opens the operating circuit for relay 4 I 0A and the latter relay releases; upon its release it extends marking battery toward the cord circuit of Fig. 3 to prevent relay 330 from releasing at this time,

Relay 406A, in operating to its spacing, or right, posi- 'tion opens the operating circuit for relay 4I5A Called subscriber recalls The called subscriber at station D may reoperate switch 509 or he may have used recall key 504 which restores a marking condition before the operator at oilce A has removed plug 335 from jack 40 IA and thereby connects grounded positive battery 542 through the subscribers teletypewriter apparatus at station D, conductor 54| to the trunk circuit which extends over the armature and back contact of relay 432 through the upper Winding of relay 433, front contact and outer upper armature of relay 430B, conductor 439, through the upper windings, in series, of relays 403B and 405B, armature and marking, or right, contact ,of relay 405B, through the winding of relay 4I5B to grounded negative battery. Relays 403B and 405B operate to their respective marking, or right, positions and subsequently effect the operation of relays 401A and 406A to vtheir respective marking, or left, positions. Re-

operator disconnects The A operator at office A recognizes a disconnect signal by removing plug 335 from jack 40IA. Relays 403A and 405A operate to their respective spacing, or right, positions and, consequently, relays 406B and 401B operate to their respective spacing, or left, positions. The operatie-n of relay 496Bv to its spacing position opens the operating circuit for relay 4I5B which releases. Relay 4I5B, in releasing, opens the operating circuit for relay 404B which in turn releases. Relay 404B, in releasing, opensat its lower armature and contact, the operating circuit or relay 4I3B which releases and causes at vits outer lower armature and iront contact, the Iopening of the locking circuits for relay 430B ,and relay 433B. Relays 430B and 433B are released. Relay 4I3B, upon releasing, closes at its outer lower armature and back contact an operating circuit for release `magnet 429B which, in operating, causes the wipers in engagement with terminals No. 5 on switch bank 4I6B and 421B, respectively, to return to normal. When the wipers of the rotary selective switch return to normal the oli-normal contact 428B automatically closes. Relay 406B upon being released, that is, operated to its spacing, or left, position, closes a circuit extending from grounded negative battery, the back contact and ,lower armature of relay 4|0B, through the winding of relay 409B, back contact and upper armature of relay 404B, spacing, .or rig-ht, contact and armature of relay 4 0 3B, spacing, or left, vcontact yand arma- Jzture of relay 4B SBv through :the lower windings.; Ain

normal.

If the A operator at `oiiice A should, in error, disconnect at the toll line end ofthe cord ycircuit, that is, .by withdrawing plug `335 from jack MIA, the disconnection would b ecome effective yafter an interval of about one-second duration and the called subscribers connection would then be transferred to the A switchboard associated with the called subscribers station-D and appear .as a call by operationof relay `525i-and lighting of lamp 5|6. Jack 5H' represents the calling and answering Jack at A switchboard for subscribersstation D.

A cut-off towards the calling subscriber, that is, by withdrawing plug 331 from jack 3H would f .f

be disp-layed at the originating operating position and could be detected immediately.

Reseizure of toll Zine before previous disconnection. is eective The busy lamp 4l IA at the outgoing end of a toll line will register idle, that is, ,become extinguished, as soon as the cutoir relay 402A and relay 410A have released, usuallyan interval of time of one-second duration after the physical disconnection, while the incoming end of the same toll line will not be free for another second. A reseizure v,during this interval would block the release of the previous connection.

The outgoing jack, such as jack 4MB, which is used only when the call is originating atstation D, is denitely .guarded against intrusion until the toll line equipment at TWX oice A which is in operated condition due to a previous call originating at station C is tfree.

Double seizure at same end of `toll Zine In this case the calling supervisory lamps at the switchboard positions ofthe operators who are establishing calls at opposite ends of the toll line simultaneously would be extinguished instantly and stay extinguished until one or both operators withdrew their respective calling plugs whereupon normal conditions would again prevail. Such should be a rare occurrence because s common practice requires selection of an ridle trunk from the lowest number in a sequence at one terminus and a reverse sequence at the other terminus.

A call originating at station D If the subscriber at station D desires to call and vestablish a connection With a subscribers station C which is connected lto TWX oilice-A,

'the 4'operation of the system is identical to that heretofore described. `In that event., 4 the Querator at V.TVZX ojiice ;B answers :the call by means of a cord circuit shown invFig. 5 whichisjdentical with the cord circuit vshown in Fig. 3. The parts of the cord circuit shown in Fig. 5 and numbered with the preiix W5 correspond 'to and have the same functions as ythose of the -cord -circuitshow-n in fFig. 43 having the prefix 3. If the subscriber at station Dis the calling subscriber, the toll .-line equipment located .at TWX oince B `operates .in the same manner as the Jgtoll line yequipment located at TWX oiIice A i-n the call-heretofore `described in which the subscribers ,station vC .was fthe calling station. The Ytoll line equipment located at T WX oilice B is identical to that located at voiiice A. Similar parts of the vtoll line ,equipment shown in Fig. 5 vhave the same :nu-

merals with a. suffix A or B to correspond gto theTWX oinces A and B, respectively. When'the subscriber at station D calls `the subscriber at station C thecall is established without the in.-

itervention of the operator at TWX office A,;.the

c all ybeing established from TWX oliice 2A -by ymeans of the :automatic switching equipment :as herebefore described fora ycall being established in the Opposite direction when -the automatic :switching equipment at TWX oflice B functions.

Teletypewriters used in a system of this kind `may be of conventional start-stop character. A calling subscriber should not transmit breaks of over one-half second as this would produce a -disconnect indication but breaks generated by :the `recall key 304 .-a-re automatically limited. :No Vbreak lone" enough to disconnect a switch can ypass froma cord `r circuit into a'trunk circuit from ,a calling subscriber because `of the breaklimiting effect of relay 330. Breaks from called subscribers may be of any 'length and will produce recall or disconnect indications but because of `the break limiting Aeffect `of relay v4111A upon signals passing the calling `end of a trunk will not .eiect relay ,3.32 long enough to k'cause ythe release of relay 330. The supervisory operators machine neednot .transmit breaksand no break keythere.- for .is shown. By .special instruction a ,called subscriber `will recognize the .desirabilityof sending :only limited breaks in order to prevent :the production of lfalse supervisory signals. Repeated -short breaks may beused with the Vsame Ageneral effect upon a sending correspondent fas an undesirable and unused 'long break. The system is guarded throughout against initiating the improper disconnectionof a switch bybreaks sent from lbreak keysnormally provided.

What is claimed is:

l. A printing telegraph exchange system ccmprising a plurality-of groups of subscribers telegraph stations, -printing' telegraph signal transmitting and vreceiving mechanism-fatl each of said stations, a plurality of switching oices, vbreak signal limiting means ateach of said offices, a

runk circuit interconnecting said switching ofiices, ka Anormally deenergized line circuitl .connected between each of ,the stations of one V.of said groups and vone of Said switchinggoiiices, :a normally deenergized line circuit connected 'between each of the stations of the otherof said groups and `another Aof said oces, means ,controlled fromeither of said offices for establishing a connection for communication purposes between a station of one of said groups and a `station of the other of `said groups over said trunk circuit, and Ymeans Vat one Vof said switching ofces 'for lthrough supervision, independently of the other nof 'said ollces, yo'f -a connection between a ystation of oneof. said groupsa'nd ai station ofthe other of saidgroups.

2. A printing telegraph exchange system com'- prising a plurality of groups of subscribers telegraph stations, printing telegraph signal transmitting and receiving mechanism at each off saidv stations, means in said mechanisms for sending normal break signa-ls, a plurality of switching offices, a trunk circuit interconnecting said switching onices, a normally deenergized line circuit connected between each ofthe stationsfoi one of said groups and one ofsaid switching oices, a normally deenergized line circuit connected between each of the stations'of the other of said groups and another ofsaid onces, means controlled from either ofsaid ofces for establishing a connection for communicationr purposes between a station of one of said groups and. a station of the other of. said groups over said trunk circuit, means at one of said. switching offices for through supervisioxn independently of the other of said omcesof a connection between a station of one of said groups andV a station of the other of said groups, and break signal limiting means comprising a slow-release relay at each of saidV stations and saidY switching oflices for automatically regulating the duration of an open period in an energizing one ofV said line circuits before disconnectv and recall signals become effective.v

3. A printing telegraph exchange systemic'omprising two switching oices arranged to be used interchangeably for'outward and inward toll'calls, a toll line circuit normally in spacing condition at each terminus interconnecting said oiices, groups of printing telegraph stations, a calling device and a printing telegraph signal transmitting and receiving mechanism' at each of said stations, a pluralityI of line' circuits for respectively connecting said stations of one of said groups to one of said onices, a second` plurality of line circuits for respectively connecting the stations of the other' of said groupsto the other of said oices, a dialing and a printing telegraph signal transmitting and'- receiving mechanism at each oi said switching ofli'ce's; means at each of said switching" oflices fori indicating the peration of said calling device of any one of said" stations of its associated group, means at" each of said switching oflices for interconnecting aline circuitextendingV from any one of the stations of one group' at which' the call originates and' said toll line circuit'whe'reby' said printing telegraph signal transmitting and receiving mechanism at the' calling. station is connected to',` the dialing and printingtelegraph'signal transmitting andreceiving: mechanism at one of said switching ofces conditioned for an outward'call; a switching de'- vice at each of said switching oices, and means included in the switching device at said'switching office conditioned for an inward call,` adapted in response to the operation' of the dialing mechanism at said oice conditioned* for an outward call to complete a connectionfor communication purposes to any one ofthe line circuits extending to a station in said other group.

4a A printing telegraph exchange system comprising two switching oicesarranged to be. used interchangeably for inward and outward toll calls, a normallyI energized-toll line circuit interconnecting said oiices respectively arranged-for inward and-outward tollcalls,- groups of printing telegraphstations; a calling device, and avprinting telegraph signalY transmitting and receiving mechanism at eachof said. stations,- a plurality of normally deenergized line circuits for respectively connecting the stationsA of each of said groups to itsr associated one of said oc'es, manually operated means at one of said offices conditioned for an outward call for' interconnecting any one of said normally deenergized line circuits of one group and said normally energized toll line circuit, an automatically operated switch at said oiice conditionedv for an inward call, said automatically operated switch including means responsive to the operation of the calling device at said office conditioned'for' an outward call for connecting said normally energized toll line cir'- cuit to'one oi said normally deenergized line circuits extending to one ofthe stations-of the other group, and means at one of said offices conditioned for an outward call for supervising: the complete connection between the'two" interconnected stations of different groups. Y

5. A printing telegraph exchangesystem comprising a switching oiiice, a second switching oice, a trunk channelinterconnecting said oices, a group of printing telegraph stations connected to' each of saidswitch'ing offices, means in one of said switching onicesfor establishing a connection between any one of said stations of one group'andany one' of said stations of another group over any one of' said trunk channels, means in one only of said` switching oices for supervisng any one connection'y established `between any two stations o'f differentv groups,- and a break limiting devicev included in a` connected channel' oi transmission between saidstations to prevent thereleaseV of said connection by reak or spacing conditionsv of long duration.

6. A printing telegraphexchange system comprising a toll line switching ofce, a second toll line switching office, toll lines interconnecting said oices, a group of printing telegraph stations connected toeach of saidswitching ofces, manually operable means in-one of said switching oices and automatically operatedmeans control-r lable from said one switching oil-ice but inv the other of saidV switchingv onices' for establishing connections between any oneof said stations of one group and any one of saidl stations ofV the other group over said toll line, and means in one only of said switching oinces'havin'g themanually operable means for. supervising all connections established between any tw'ointerconnected stations of different groups.

7. A printing telegraph exchange system' comprising a switchingoice', a second switching oiidce', said switching omces includ-ing means adapted to interchange said ofncesfor outward and inward toll calls,-an`d equipment responsive to'b'oth inward and outward toll calls in each of said oftices, said equipment' for outgoing calls including a manually 'operated cord circuit and said equipment for incoming' calls` including an automatically operated selector switch, and means in one-onlyof said switching oicesffo'r supervising all connections established upon-outgoing Acalls' between any two interconnecting` stations of different groups: Y

8. A'teletypewriter switching system comprisingtwo central oces with an interconnecting trunk for the transmission of marking' and s'pacingcode impulses and including telegraphic'ir'n-v pulse repeaters-subscriber lines-.terminating at each-of `said. offices, signal means'a'ssociated with each line to notify an operator of a call' upon one I of said lines, and means whereby either' ofv said operatorsmay extend said line over said'trunk to said other office, and means including anue merical code dialing device whereby said operator may transmit over said trunk dial pulses to select a required subscriber line at said other offices and connect it to said trunk thereat for telegraphic transmission between said subscriber lines.

VSl. In a system according to claim 8, a conductor associated with each subscriber line having a normal condition, means for establishing thereupon a busy condition, means controlled by said busy condition whereby the selection of said line as in claim 7 controls the generation of busy indicating pulses, and means for transmitting said impulses over said telegraphic impulse repeaters to the station ofthe calling operator, and a busy signal thereat energizedY by the receipt of said impulses.

10. A telegraphic system having a subscribers line, a jack having a tip, ring and sleeve for connecting a cord circuit to said line, a tip, ring, and sleeve in said cord circuit, a plug for connecting a trunk to said cord circuit, a selector having wipers connected to said trunk and terminals connected to said line, means whereby interconnection of said line to said trunk through said cord circuit for communication is ineffective upon said selectors, a telegraphic impulse repeater in said trunk having marking and spacing conditions, and means for operating said selector from a distant point over said trunk through said impulse repeater to connect said line to said trunk.

11. In a system according to claimr 10, a release means for said selector, means for causing said release means to operate comprising a path controlled by said telegraphic impulse repeater, said means being eiiective upon an element of said repeater assuming a spacing condition fior greater than a predetermined time.

12. A printing telegraph exchange system com- Y prising a two-way trunk equipped for transmission of telegraphic code impulses, said trunk having at each end terminals for the manual connection of a link circuit whereby a call'originating line terminating at one Yend may be associated with said trunk through said link circuit, means in each link circuit for controlling over the trunk at the remote end of the trunk, independently of the link circuit at the remote end thereof, the

^ connection of a line terminating at said remote end to said trunk whereby said lines are connected together for communication bytelegraphic code impulses over said trunk. f f

13. A system for telegraphic switching of the automatic through and inward type comprising a telegraphic trunk channelof transmission, said trunk having associated therewith at each terminus thereof selective means controllable from the remote terminus to select and seize a called channel of transmission to said trunk, and alink circuit at each terminus normally disconnected from but associable'with said trunk, said link circuit containing elements operable to initiate pulses to controlthe actuation of the aforesaid selective means at the remote terminus selectively.

14. A system for telegraphic switching of the automaticV through and inward type comprising a telegraphic trunk channel of transmission, said trunk having associated therewith at Veachy terminus thereof selective means controllable from the remote terminus to select and-seize a called channel of transmission to'l saidV trunk, and a link circuit at eachterminus normally disconnected from but associable with said trunk, said link circuit comprising means for associating a channel of transmission-with'said trunk for in- 75 toy tercommunication independently of Vthe selective means at the trunk terminus adjacent said link circuit, said link circuit containing elements operable to control the actuation of the aforesaid selective means at the remote terminus selectively.

` 15. A system for telegraphic switching of the automatic through and inward type comprising a telegraphic trunk channel of transmission, said trunk having associated therewith at each terminus thereof selective means controllable from the remote terminus to select and connect a called channel of transmission to said trunk, terminals including a test terminal associable with each terminus of said trunk, a link circuit associable with said terminals comprising elements operable to control the actuation of the aforesaid selective means at the remote terminus selectively, and means operable by association of said link circuit with one terminal of said trunk to create a busy condition on said test terminal at the remote terminus of said trunk.

16. A system for telegraphic switching of the automatic through and inward type comprising a telegraphic trunk channel of transmission, said trunk having associated therewith at each terminus thereof selective means controllable from the remote terminus to select and connect a called channel of transmission to said trunk, terminals including a test terminal associable with each terminus of said trunk, a link circuit associable`r with said terminals comprising elements operable'to control the actuation of the aforesaid selective means at the remote terminus selectively, means operable by association of said link circuit with one terminal of said trunk to create a busy condition on said test terminal at the remote terminus of said trunk, and means associated with said called channel of transmission Whereby connection of said link circuit thereto establishes a busy condition individual tovsaid channel whereby the functioning of said selective means to control the selection and seizure of said channel is prevented during the continuance of said busy condition.

I 17. A telegraph station, a telegraph line from said station to an operators position, a telegraphic trunk adapted for the transmission of combinations of impulses constituting codes, said line at the station of said operators position being provided with terminals for manual connection of a link circuit therewith and. `with terminals upon a selector adapted for remote selective control by impulses transmitted over said trunk, and means whereby one of said terminals for manual connection is caused to test busy upon selection of said terminals upon said selector.

l18. A telegraph station, a telegraph line from saidstation to an operators position, a telegraphic trunk adapted for the transmission of combinations of impulses constituting codes, said line at the station `of said operators position being provided with terminals for manual connection of a link circuit therewith and with terminals upon a selector adapted for remote selective control by impulses transmitted over said trunk, and means whereby one of said terminals upon said selector has a busy test condition irnposed thereupon to prevent selection of said line by said selector upon connection of said link circuit to said terminals provided for manual conn nection.

19. A telegraph station, a telegraph line from :acreage 1c said station :to .'an 4:operators rposition, :a ztelegraphic 'trunk adapted ."for the stransmission :of combinations of impulses :constituting lcodes,:said trunk having a marking and a spacingcon'dition as deiined in .teletypewriter :transmission sbu-t f laway-from the terminusof'seizureyupon-seizure, f'

from *spacing to Amarking Icondition, said line -at the locus of said 'operators position fbeingprovided with-terminalsier-manual connection of a link ucircuit therewith iand with terminals upon a selector adapted Vfor 'remote selective control l over said trunk, and means whereby onecf Asaid terminals for manual connection is caused to Vtestibusy upon selection of said terminals upon said selector.

21. A telegraph station, a telegraph line "from said station to an operators position, a 'telegraph trunk having relaying telegraphic repeaters adapted forithe transmission o'f combinations of Aimpulses constituting codes, Ysaid vrepeaters being normally'in spacing condition" but changed in vthe transmission .path 'away 'from the -point of seizure to marking Vcondition u pon seizure, said line at the locus of said ,operatorrsposition being-provided with terminals for manual connection of Ya link rcircuit therewith'and with ses lecto-r terminals vadapted for remote selective control oversaid trunk, and means whereby one of said terminals `for Vmanual connection is caused to test busy upon selection of saidselector 'terminals.

22. In a printing 4telegraph switching system of the through and inward type in which atrunk connects central ,oice A with central .offceB, subscriber lines terminating atcentraloice A, subscriber lines terminating at central oice'B, an operators link circuit at central oilice A'by which vsaid operator may receive telegraphic instructions to and thereupon may vlink.,a subscriber line at station A to said trunk, means operably associable withfsaid linkcircuit whereby theoperator at station Aimaycontrol the selection of an idle `subscriber linefatstationB and connect the same 'to 'said vvtrunk for intercommunication with the linked subscriber line at station A, an voperators link circuit at central office B whereby a subscriber 'line at station'B may be linked to said trunk,'and means operably associated with said ylink circuit at central ofiice `B whereby the operator thereat may 'controllthe selection of an idle subscriberline-atstation A -and connect the same to said trunk ffor `tele- -graphic intercommunication with the linked subscriber line at rstation "B.

23.1111 a printing telegraph switching "system lof the through and-inward type inWhich a'tiunk connects central oice A with central -ofilce B,

f'subscriber lines terminating atcentral loiice A,

-subscriber lines terminating at central oice B, :an,operators'linkfcircuit yat central office A "by @whichsaid operator may-receive telegraphic instructions :to and thereupon may lin-k fea frsubscriber ,line iat i station FA to said atrunk, v:means bperably -associable with said linkxcircuit whereby the operator `atystation Arnayv control :the slection of an idlesubscriber lineatsst-ationl-Bfand connect the same to said trunk for iintercommunication with the linked subscriber line at .station 5A, lan operators 'link icircuit 'at central oliice Bzwherebya ksubscriber line at station B may ;be linked to said trunk, vmeans loperably ,associated with said'linkfcircuit `at centra'lvolice B whereby theoperatorfthereat may controlthe selection-of 1an idle isubscrib'eriline'at station and connect the same :to Ysaid trunk rvfor Vtele- .graphic .intercoinmunication with the -linked subscriber line at station B, and`-busy test-means associated with .Said Itrunk at either lterminus whereby .thescizurethereof by an operator -at 'the one .terminus places a :busy "test vcondition upon said trunk'atftheother terminus.

24. ln -a printing `telegraph switching vsystem Iof the through and inward'type in which a trunk 'connects central foice A withecentral ofliceB, subscriber lines terminating at central office -'A, subscriber lines terminating Vat central office B, anoperators link circuit at centralfofice fA-including meansby which said operator m-ay -receive telegraphic 4instructions to and thereupon maylink a subscriber line at station A-to said trunk, means operably'associable with said -link Vcircuit whereby the operator at station Amay control the selection of an idle subscriber line attestation AB and connect the sameitosaid trunk for yintercommunication with 'the 'linked subscriber line at `--statirm `an voperators"link circuitat central ofceB whereby Va 4-subscriber line -at station 'B-ma-y be `linked yto saidtrunk, means operably associated with saidlink circuit at centraloi'ce 1B whereby the 'operator thereat may control the selection of yan'idle 'subscriber line vat station Aand connect the same to saidtrunk for telegraphic Vintereommunication with vthe linked subscriberlineat station B, vvmeans wherebythe Connectionof a *linking circuit Ato a subscriber lline places la busy condition upon the subscriber line, and means whereby Selection of the terminals of such busied line under control of the remote terminus-of said ltrunkreturns a lbusy indication back *to 'said t'erminus.

'25. -In a printing telegraphswitching system of the through and inward type in which a trunk connects Acentral :office A 4with central oice B, subscriber lines terminating at central oflice A, subscriber lines terminating at central office B, an operators link circuit at central oce Aincluding means by which said operator may receive ltelegraphic instructions to and thereupon may link a subscriber llineat'station .A to said trunk, means operably `associable `with said link circuit whereby the koperator at station A kmay control the selection of an idle subscriber line at station Band connect the same to said trunk for intercommunication with `the linked subscriber lline Iat station A, an operators link circuit at central office B whereby a subscribergline Aat station Bmay 'ce linked to said-trunk, means operably associated withsaidlink circuit at centraloce B whereby I'the operator ythereat may control `the selection of 'an idle subscriber lline at station A and connect'the same to `said trunk for telegraphic `intercomrnunication with the linked subscriberline at station B, means whereby the connection of a'linking circuit 'to a Ysubscriber line places a Abusy :condition lupon :the subscriber line, -means vwhereby selection `of the terminals of such busied line under control of remote terminus of said trunk returns a busy indication back to said terminus, and means for causing said busy signal to be cyclically and repetitiously indicated until the calling operator separates the calling link circuit from the trunk.

Y26. In a printing telegraph switching system of the through and inward type in which a trunk connects central ofiice A with central oiiice B, subscriber lines terminating at central oiice A, subscriber lines terminating at central office B, an operators link circuit at central oice A including means by which said operator may receive telegraphic instructions toand thereupon may link a subscriber line at station A to said trunk, means operably associable with said link circuit whereby the operator at station A may control the selection of an idle subscriber line at station B and connect the same to said trunk for intercommunication with the linked subscriber line at station A, an operators link circuit at central oiiice B whereby a subscriber line at station B may be linked to said trunk, means operably associated with said link circuit at central ofiice B whereby the operator thereat may control the selection of an idle subscriber line at station A and connect the same to said trunk vfor telegraphic intercommunication with the linked subscriber line at station B, means whereby any called subscriber line may create an answering condition, and means whereby said condition creates an indication significant thereof to the operator at the terminus of said trunk remote from the answering subscriber.

2'7.`In a printing telegraph switching system of the through and inward type in which a trunk connects central oii'ice A with central office B, subscriber lines terminating at central oiiice A, subscriber lines terminating at central oflice B, an operators link circuit at central oilice A including means by which said operator may receive telegraphic instructions to and thereupon may link a subscriber line at station A to said trunk, means operably associable with said link circuit whereby the operator at station A may control the selection of an idle subscriber line at station B and connect the sarne to said trunk for intercommunication with the linked subscriber line at station A, an operators link circuit at central office B whereby a subscriber line at station B may be linked to said trunk, means operably associated with said link circuit at central office B whereby the operator thereat may control the selection of an idle subscriber line at station A and connect the same to said trunk for telegraphic intercommunication with the linked subscriber line at station B, means whereby any called subscriber by'creating a disconnect condition at his station causes impulse transmission over the trunk to the far terminus thereof, a signal thereat, and means controlled by the transmitted disconnect condition to produce an indication upon the signal before the operator thereat..

28. In a printing telegraphswitching system of the through and inward type in which a trunk connects central oiiice A with central oilice B, subscriber lines terminating at central oflice A, subscriber lines terminating at central oice B, an operators link circuit at central oiiice A having means associable therewith by which said operator may receive telegraphic instructions to and thereupon may link a subscriber line at station A to said trunk, means -operably associable with said link circuit whereby the operator at station A may control the selection of an idle subscriber line at station B and connect the same to said trunk for intercommunication with the linked subscriber line at station A, an operators link circuit at 4central oiiice B whereby a subscriber line at station B may be linked to said trunk, means operably associated with said link circuit at central office B whereby the operator thereat may control the selection of an idle subscriber line at station A and connect the same to said trunk for telegraphic intercommunication with the linked subscriber line at station B, means whereby any called subscriber by creating a disconnect condition at his station causes the transmission of impulses over the trunk to the far terminus thereof, a signal thereat, means controlled by the transmitted disconnect condition to produce an indication upon the signal before the operator thereat, and means for releasing the selected subscriber line controlled by the unlinking of the link circuit from the trunk.

29. In a printing telegraph switching system of the through and inward type in which a trunk connects central oice A with central ofce B, subscriber lines terminating at central oilice A, subscriber lines terminating at central oice B, an operators link circuit at central office A including means by which said operator may receive telegraphic instructions to and thereupon may link a subscriber line at station A to said trunk, means operably associable with said link circuit whereby the operator at station A may control the selection of an idle subscriber line at station B and connect the same to said trunk for intercommunication with the linked subscriber line at station A, an operators link circuit at central oiiice B whereby a subscriber line at station B may be linked to said trunk, means operably associated with said link circuit at central office B whereby the operator thereat may control the selection of an idle subscriber line at station A and connect the same to said trunk for telegraphic intercommunication with the linked subscriber line at station B, an operable device at a called subscriber station, and means controllable thereby to control over the trunk the production of a recall indication before the operator at the calling terminus of the trunk.

30. In a printing telegraph switching system of the through and inward type in which a trunk connects central oiiice A with central oilice B, subscriber lines terminating at central oflice A, subscriber lines terminating at central oiiice B, an operators link circuit at central oiiice A including means by which said operator may receive telegraphic instructions to and thereupon may link a subscriber line at station A to said trunk, means operably associable with said link circuit whereby the operator at station A may control the selection of an idle subscriber line at station B and connect the same to said trunk for intercommunication with the linked subscriber line at station A, an operators link circuit at central ofl'ice B whereby a subscriber line at station B may be linked to said trunk, means operably associated with said link circuit at central oiiice B whereby the operator thereat may control the selection of an idle subscriber line `at station A and connect the same to said trunk for telegraphic intercommunication with the linked subscriber line at station B, and means whereby upon physical disconnection of a link circuit from a trunk the terminals available to an operator at the distant terminus thereof have applied thereto a guard busy condition until the trunk including the selective means associated there; with are fully freed. Y

31. In a telegraph switching system, a circuit having a source of selective pulses connected with said system at one terminus thereof, circuits to be selected thereby at another terminus, selective devices for accomplishing the selection under control of the pulses, means whereby a prior busy condition may be placed upon one of the circuits, a break limiter device in said circuit for normally limiting spacing conditions sent over said sys'- tem, means for sending back pulses to indicate said busy condition, and means to lock out said break limiter during such sending.

32. A system including a spacing condition limiter, a sender of supervisory signals of duration inconsistent with said limiter, and means for locking out said limiter to permit said signals to be sent.

33. A system in which a channel of telegraphic impulse transmission is established for communication from one station to another, means for sending break signals thereover in a given di'. rection, a break limiter device for limiting break" signals traversing said channel, and an;l other break limiter device between said means and said first break limiter device for limiting breaks from said means to a shorter duration than said rst limiter device.

34. A system in which a channel of telegraphic impulse communication between two points may be established, a device operable by break signals of a certain duration upon said channel but not by normal spacing signals for changing the condition of a supervisory signal device, a means associated with said channel between said device and a potential source of break signals to limit break signals proceeding toward said device to less duration than said certain duration.

35. In a telegraphic impulse transmission system, a numerical dial for setting up connections, said dial being located at one terminus of a main communication path, means for actuating a selective device at a remote terminus of said path by actuation of said dial to extend said path over a selected further path of transmission, means for sending a telegraphic break" signal from said selected path toward the station of said dial, and means controllable over said main path from the locus of said dial to release and disconnect said 25 selected path against and during the continuance of the break.

RAND S. BAILEY.

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