US2345317A - Satellite telegraph switching system - Google Patents

Description

March 28, 1944.

R. s. BAILEY SATELLITE TELEGRAPH SWITCHING SYSTEM Original Filed Aug. 6, 1938 3 Sheets-Sheet 1 .mNd

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SATELLITE TELEGRAPH SWITCHING' SYSTEM original Filed Aug. e, 1938 5 sheets-sheet 2 Ox oo A frog/viv March 28, 1944. R. s. BAILEY 2,345,317

SATELLITE TELEGRAPH SWITCHING SYSTEM Original Filed Aug. 6, 1938 3 Sheets-Sheet 3 /NVEN'R R. s. ,9A/LEV ATTRNEY uw P T mln H NE VIM Wm l J Patented Mar. 28, 1944 SATELLITE TELEGRAPH SWITCHIN G SYSTEM Rand S. Bailey, Glen Ridge, N.. J., assignor to Bell Telephone Laboratories,I Incorporated, New York, N. Y., a corporation oi New York Original application Augustv 6, 1938, Serial No. 223,431. Divided' and this application May 17, 1941, Serial No. 393,864

27 Claims.

This invention relates to teletypewriter systems and more particularly to automatic switching for establishing and maintaining connections in teletypewriter systems.

This is a division of application Serial No. 223,- 431i, led August 6, 1938'.

An object of this invention is to provide a system for giving service to a number of teletypewriter subscribers or branch olilces over a group of trunks, less in number than the number of subscribers, to a central telegraph exchange; this is accomplished in the embodiment disclosed by means of a satellite or automatic switching ofce :between the subscribers lines and the trunks. The expression subscribers station is used in its generic sense of an outlying olice.

Upon a subscribers call the object is accomplished by an allotter circuit which assigns an idle trunk extending to the central ofllce to a subscriber and connects his line thereto whereby a call signal at the central oflice is causedl to-appear in the same manner as in connection with a call upon a line directly terminating at the central oce.

Upon a call to a subscriber the central office operator utilizes a dial to actuate a selector switch at the satellite office to select and test the subscribersl line and connect it to the calling trunk if'the line is idle.

Among the objects of the invention are to accomplish these results by an organization of. simple nature whereby full supervision is possible, trunks may be allotted expeditiously, subscribers lines may be selected accurately over trunks used by a central oiflce operator to make calls, and automatic release under control of the central oice operator may be effectively accomplished.

A speciiic feature of the invention is a break limiter in a cord circuit; another specific feature is a recall key having a break limiter attached thereto.

Anotherl specific feature is that all jacks employed in the system are of the multiple appearance type with multiple busy lampsso that a pluralityf of operators ymay cooperate in setting up and disconnecting communication paths.

Another feature'is that a. conventional numerical dial device is used preferably in series with the operatorsv teletypewriter for sending selecting pulses'to': select subscribers stations; also that the dialing is accomplished over telegraph trunks which may' contain repeaters of standard type, although the invention is not limited to the use of repeatersl When repeaters are used they repeat the dial pulses in the same way as they repeat` telegraphi'c signaling pulses.

The trunk channels are preferably of the di@- ferential duplexl type although two-path polar could Ibe employed and the trunks may include carrier or radio links with any of the usual equipment employed or commonly available for employment therein.

Another feature of the invention is to reduce the duration of telegraphic breaks upon the trunk so that the duration of the recall and the break signal'durations may be correspondingly reduced. Furthermore, disconnect, recall, and break signals may be distinguished.

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

Fig. 1 illustrates in block diagrama teletype'- writer system in which a call is established between a subscribers station connected' to a TWK office F and a subscriber connected to a radial, or a satellite, automatic switchingl oice G.. TWX is' an abbreviation for teletypewriter exchange. Ifa subscriber connected to the TWX office F desires to be connected to a subscriber connected to satellite oflce G, the operator at the TWX ofceV F establishes a connection lby controlling remotely the automatic switching equipment at the satellite oice. When the subscriber connected to the satellite office'G, such as station H, desires to communicate with a subscriber connected to the 'I'WX oflioe F, the. automatic switching equipment: at the satellite office is actuated by the establishment of a calling condition at the subscribers station H to connect the station to the operator at the TWX oflceF. The subscribers stations, TWX oii'ice-and satellite switching office are indicated by labeled block diagrams in the drawings;

Fig. 2 shows the order in which Figs. 3, e and 5 may be connected together to form a complete communication path;

Fig. 3: shows a teletypewriter subscribers station setY at station E connected to the subscribers station equipment at the TWX oflice F and an operators cord circuit' for connectingv the operators position circuit with the subscribers line equipment;

Fig. 4 shows the toll' line. equipment at the TWX oil'lce F connected. by means of a toll line to the automatic switching toll' line equipment at the satellite ofli'ceG; andv Fig. 5 shows a sequence. orv allotter circuit and .subscribers line equipment at the satellite switchequipment at TWX oflice F by tip conductors TE and ring conductor RE. i A

Station E initiates a call A can is initiated by the subscriber at station E upon the operation of call'key 809. The operation of this key energizes the motor 808 causing' subscribers station.

it to operate during the entire `time thatthe v key is operated. Key 809 'also closes a, circuit from grounded positive battery 8| 2, lead RE,

break key 803, transmitting contact 80|,..magnet 802, left spring and contact of recall and disconnect key 804, through the winding of slow-release relay 805, operated spring and vcontact of call key 809, tip conductor TE, upper left armature and contact of relay 8|4, to ground. Relay 8|3 operates closing an obvious circuit for lighting lamp 8 lli.` The lighting of the lamp 8|6 indicates to the operator at TWX oflice F, that a call is waiting on this line.

Operator answers 'I'he operator answers by inserting plug 8 I 9 into jack 8|1, and operating typing key 822. Assuming that the plug has been inserted before typing key 822 is operated, two circuits are completed, one from grounded negative battery 82|, through lamp 820, through the winding of relay 829, sleeve conductors of plug 8|9 and jack 8|1, through the winding of cut-01T relay 8|4 lto ground. This circuit lights lamp 820 and operates relays 829 and 8|4. Relay 8|4, in operating, disconnects ground at its upper armature` and completes in its place the circuit extending from grounded positive battery 8|2, through the equipment at station E, the upper armature and front contact of relay 8 I4, upper winding of relay 8|3, tip conductors of `iack 8I1 and plug 8|9, through the winding oi' relay 832 to grounded negative battery 801. Relay 832 operates thereby operating relay 830. Relay 830, in operating, removes grounded battery 801 and replaces it by grounded battery 840, via contactsof relays 823, 838 and 829. Also, relay 830, in operating, connects at its left-hand armature and contact interrupter 833, via contacts of relays 83| and 830, in a shunt path across lamp 820. At each closure of interrupter 835 the lamp will be extinguished and at each opening it will Ibe lighted. The flashing of lamp 820 is an indication that key 822 has not been operated.

When the operator operates key 822, an obvious operating circuit for relay 823 will be closed. Relay 823, in operating, will insert the operators teletypewrlter set 824 consisting of printer magnet and transmitting contact, and dial 825 in 'series with the subscriber's line in place of resistance 84|. Relay 823, in operating, also closes at its lower armature and contact acircuit extending from ground through the lower winding of relay 83| to grounded battery 82|. Relay 83| operates and at its upper and its lower armature and contact, closes a locking circuit for itself which circuit serves as a permanent shunt across lamp 820 causing the lamp to remain extinguished as long as relay 830 is operated and also after key 822 is released. If key 822 was operated before plug 8|9 was inserted in jack 8|1, relay 83| would have been operated and the interrupter would not have been cut in. The operator may have at her disposal a number of cord circuits, for the operators set can be cut in only on one circuit depending upon which one of keys 822, 821, 828 or any other similar key, not shown, has been operated. The operator indicates her presence to the calling subscriber E by typing OPR and subscriber E types the call of the desired Operator completes to olce G is inserted in jack relays 838 and 902A oper# ate over the sleeve conductors of plug 835 and jack 90|. By inserting plug 835 into jack 90| a circuit will be closed extending from ground' at the right contact and armature of relay 9|4A, conductor ring conductors of jack 90| and plug 835, through lamp 839 to grounded battery. Lamp 839 lights. Relay 902A, in operating, will cut off call lamp 934 and light busy lamp 955. Relay 902A, in operating, also closes a circuit extending through the upper windings of relays 904A and903A to operate the latter relays to their respective marking contacts. The opera# tion of relay 903A to its marking contact will cause the release of relay 905A, which when released connects ground from relay 902A`to a circuit which should extend over the armature and contact of relay 905A, armature and con-V tact of relay 906A, through the winding of relay 901A to grounded battery. However, relay 903A, in operating to its marking contact, closes a circuit extending from grounded positive battery 8| 2 which is connected to the subscribers line extending through station E to the tip conductor of the cord circuit, through the upper windings of relays 904A and 903A, armature and spacing contact of relay 9 3A, armature and marking contact of relay 903A, through the winding of relay 906A, armature and back contact of relay 901A, grounded negative battery, and relay 905A operates to prevent relay 901A from operating. The condition is therefore established for a return signal from'oilice G. Relay 904A, in operating to its marking Contact, operates relay 9|3B to its marking contact.

Signal reaches olce G Relay 9| 3B, in operating to its marking contact, opens the operating circuit for the normally operated relay 905B which now releases, and also operates relay 9|4B from ground, through the lower windings of relays 903B and 904B. Relay 9|4B, in operating, operates relay 909. Relay 909, in operating, operates relay 9|0. Relays 909 and 9|0 are` of the slow-release type so as to remain operated for the duration of the dialing, or selecting, pulses. Relay 9|0, in operating, prepares a circuit to operate relay 9 |5 from the back contact of relay 9|4B. Relay 9|0, in operating, removes ground at the next to its innermost armature and back contact from the operating circuit for release magnet 932 and applies this ground over the associated front contact to armatures of relays 922 and 924 and to the inner aarmaiv 3 lower front contact of. hunting relay 93h The next to the outermostL armature of .relay 910, when operated, connects ground Vto .the outer armature operates, thus making this trunk busy to outgoing calls. The outermost armature and con tact of relay 9I0 prepare to apply ground to a hunting conductor in engagement. with a terminaland wiper oi bank 920 of a rotary selectivei'switchf, after suchswitch completes its selec tion, through the lower winding of hunting relay 93I', through the winding of relay 931, armature and contact of stepping magnet 9I1, conductor 939, to the inner. left armature of relay.

936. The circuit at oflice G is now ready to re-.v

ceive the dialing pulses.

Dialing It is not necessary for the attendant at oilice vGto give the operator at oilce F a dialing signal l since the fact that the operator at oflice F has possession of an idle trunk gives her complete control over all required apparatus. Infact, ofce G is unattached except for the usual maintenance stall, and may at times be entirely unattended. Each trunk at office G is equipped with a rotary selective switch having banks such as those designated 9I-9, 920 and 92|-, a stepping magnet, such as that designated 9I1, off-normal contacts such as those designated 933 and a release magnet such asI that' designated 9.32.

The operator dials by operating her dial 925 tocount by means of its off-normal contact the number of the desiredistation. The upper contact of the dial will operate relay 826 which, in op erating, will split the subscribers line circuit, applying negative battery to the subscribers line and positivebattery to the trunk, thus preventing the. dial pulses from interrupting the telegraph path to the. subscriber at station E. Relay 826 will remain operated until the dial is returned to normalY Relays 904A, 903A, 9I3A, 9-I3B and 914B will' follow the dialing pulses, while relays 909 and 9IItwill remain operated for the duration of the train ofpulses. Upon closure of the. first openY ofv thel pulse train relay 9I3BV will operate to its spacing contact, and will release 9I4B to close its circuit extending from groundat the arma-ture and back contact of relay 9I4B innermost armature and contact of relay 9I0,. through thev winding of relay 9I5, normally closed' contact of the off-normal contacts 933 to grounded battery.. Relay 9I5 operates. Relay 9:!5, in operating, locks up temporarily at its front contact andinner lupper. armature, toground on the back contact of relay 9'I'4B. Relay 915 is also of. the slow-toerelease type and. remains: operated for the duration of the pulse train- Relay SI5.V in operating, operates at` itsl outerv upper armature and. iront contact an operating circuit. for relay 91.6 which is also of the slow-to-release type; Relay SIS', in operating, connects busyA relay 9.22 to the Wiper ofv switch bank 9.1.9 over a make contact of relay 9I6: and a back contact of'relay 92A. The operating circuit. for relay 922. is.,A however, open at the contact of relay SI5 at this time.

Relay 925, in operating, also connects ground at the armature of relay 9 I4Bto a circuit extending through the winding of stepping magnet 9H toy grounded battery. Magnet 9I1 will respond to the train of. pulses andv assuming the train consists of ve pulses, stepping magnet 9 I'1 will step five timesin accordance withthe ve pulses; At thefend of the train,.relay 913B will remain on its marking contact .and relay 9'I4B will `rernainoperated, holding relays: 999 and. 9 I operated when relay .9!5 .release because oil-normal switch 933 has on. the iirst step of the wipers in their respectivebanks 9:I9, 9.29 and 92| opened its contacts.: Relay 916 being of the slow-to-release type remainV operated for a time aiter the y release of relay 9Ie5;

' called Iame busy- I `the `called line which is connected to terminal No. 5 on bank 9I9, is busy, ground will be present. on the fth contact of bank 941 over the fifth contact. ofl onev of the other selectors, the right armature and frontv contact of line relay IDM-which are. ina-multiple. to the line of station H. Thisground will complete the circuit extending over conductor 946 from No. 5 terminal at bank 9! 9 which isyengaged'by its respective wiper, conductor 946, lower armature and front Contact of relayl SIS, contact and next to the innermost lower armature of relay 924, through the Winding of busy relay 922, back contact and outer upper armature of relay 9I5 to grounded negative battery. Relay 922' will operate and when relay 9I6 releases', relay 922 will lock in a circuit extending over the make-before-break contacts of relay 9 I 6, front contact and lower armature of relay 922, front contact and next to the innermost armature of relay SID, to ground. Relay 922, in operating, will open at its lower armature and back contact the circuit including the winding of relayv 924 which will prevent the operation of relay 924'. Relay 922', in operating, connects at its iront Contact and upper armature a grounded interrupter 923 to a circuitV extending. over the armature. and contact of relay 995B, back contact and outer upper armature of relay 92'4, through the upper windings, in series, of relays 993B and 904B-, armature and marking contact of relay 913B, through the winding. of relay 9I4B to grounded battery.` Relays 993B and 994B will follow the interruptions which will cause relay 9.I`3A likewise to follow. The lengths of the open pulses are. made adequately long so as to release theslow-to-release relay 9| 4A upon each pulse. Relay 9I4A operates which will light lamp 839 and a Vsubsequent release will extinguish the lamp. Therefore, lamp 839 will ash in accordance With these interruptions Such flashing is an indioationto the operator at oiiice F that the subscribers station H .is busy, and. therefore the operator so noti'es the calling subscriber at station E who disconnects and the operator removes plug 839 from jack. The plug may be removed from. the. jack. during either a closure or anv opening .of the interruptor 923.

When the line is closed, the removal of the plug will release relays B38 and 992A. The release of relay 83.8 will maintain closed. the subscribers line circuit extending from station E, and the operator will receive a. disconnecty from the call-ing subscriber in a manner to be later described. The release of relay 992A will open the trunk circuit extending through the upper windings of relays 993A and 994A to cause them to operate to their respective spacing contacts. Relay 995A will operate and maintain relay 901A released. Relay 9I3B will operate to its spacing contactV and4 cause the oper-ation of relay 996B which operation will have no function at this time. Relay 913B, in operating to its spacing contact will release relay 9I4B, and in consequence relays 909 and 9I0 will release after an interval. The release of relay 9I0 will release relays 922 and |021, and establish a circuit for the release magnet 932 which will operate and restore the rotary selective switch to normal. The circuit of the release magnet will open when the ofi-normal contacts 933 are restored to normal. The release of relay 922 will cut off the grounded interrupter 923 and cause relays 993B and 994B to operate to their respective spacing contacts. These relays cause relay 9I3A to operate to its spacing contact andthereby releases relay 9| 4A. The release of relay 9I4A extinguishes busy l-amp 955. The circuit is nownormal.

If` the line-'is open at interrupter 923 when plug 835 is removed, the same procedure will followv except relays 903B and 904B will not have to wait for the removal of grounded interruptor 923, to operate to their respective spacing contacts.

` Called line idle If the called line is idleno ground will be on contact No. 5 of bank 9I9 but grounded negative battery will be present Iat the right of cut-olf relay IOI I and therefore connected to a Circuit extended through the winding of cut-01T relay IOII, conductor 941 and the circuit heretofore traced for operating busy relay 922 which circuit will have grounded negative battery at both ends. Now when relayk 9I5 releases, relay 922 will not operate but when relay 9I6 releases, Ia circuit will be provided extending from grounded negative battery at the right armature and back contact of relay IOI2, through the Winding of relay IDI I, conductor 94T, terminal No. 5 of bank 9I9, lower armature and back contact of relay 9I5, through the winding of relay 924, back contact and lower armature of relay 922, to ground at the front contact and next to the innermost armature of relayV 9I0.

Relay I9II will operate to prevent the operation of relay IIII2 and relay 924 will operate. Relay924, in operating, will look through its upper winding under control of relay 9I0, and will conneetV atits outer upper armature and front contact the upper windings ofgrelays 903B and 904B to terminal No. A5 of bank 92|. Relay 924, in operating, applies at its outermost lower armature and contact a solid ground to the multiple of terminals No. 5 on all banks 9I9, and at its innermost lower armature and contact connects grounded interrupter 926 to the Winding of relay 925. Relay 925 will follow the interruptions of the interrupter 926 and apply intermittent ringing current to the ringer IOI0.

Subscriber answers During the non-ringing interval of interrupter 926 Ywhen the subscriber answers by operating switch |009, relay 929 will operate, which in turn will operate relay 930. Relay 930, in operating, will operate relay 93|. Relay 93|, in operating, will at its upper armature and front contact lock under control of realy 930 and at the same armature but at its back contact open the operating circuit for ringing relay 925 thus lstopping the ringing. The closure of the subscribers line circuit will operate relays 903B and 904B to their respective marking contacts. Relay 901B operates in a circuit extending from ground in connection with the outermost lower armature and contact of relay 924, contact and armature ofrelay 995B, through the winding of relay 991B to 'grounded battery, and therefore, inasmuch as relayV 996B is released, provides negative marking battery toward station H. Relay 9III5Bl is maintained released. Relay 903A, in operating to its marking contact, releases relay 905A thus causing relay 901A to operate. Relay 9I3A operates to marking position on marking current from oiiice G. Relay 9IIIA operates and opens at its right armature and contact the operating circuit for lamp 839 whereby the lamp is extinguished. Relay 901A and relay 9I4A are slow to vrelease to the amount of about one-half second or at any rate they are slow but not quite as'slow as-relay 830. The connection is' now complete and communication can take place from the subscriber at station E to the subscriber at station H. 'I'he operator retires by restoring key 822,

Transmission In telegraphy as commonly practiced a line or channel of transmission has two conditions impressed upon it at the signal transmitting terminal with a resultant production of two conditions at a receiving terminal. These two conditions are marking and spacing Ordinarily the circuit line or channel rests in the marking condition and variable combinations of marking and spacing are used for communication. The spacing condition ordinarily does not persist for more than a very short time. Thus in a'system employing a live-unit permutation code and start-stop transmission at a speed of six characters per second, the longest spacing condition employed is approximately 1/6 of a second. When a receiving subscriber or customer wishes to interrupt transmission to him in a system of the present type he ordinarily does this by impressing upon the line a prolonged spacing condition. This is known as a break condition and may persist for several seconds or indefinitely, if nothing is employed to prevent such prolongedV duration. ln the present system break limiters are employed which function to limit the break impressed upon a communication channel to some predetermined maximum time duration, for example, of the orderof 1 second. A break of this length is ordinarily effective to notify the transmitting operator to cease transmission but if it is not so eliective the break condition may be repeated as often as desired, each successive break being limited to a predetermined maximum with an interval of marking condition in between. Any device or arrangement of this kind which limits the time of duration of a break condition is known as a break limiter. Break limiters, although not known to have been previously employed very extensively, are in fact known, but novel and useful applications of them are made in the manner set forth in this specification.

Breaks of length effective to release relay 830 are not admissible during transmission except when a supervisory signal is to be produced at the light 820. Relay 830 should therefore be slow to the extent of one second or longer and breaks from key 8 03 should be shorter than this, although they may be repeated as often as desired. Breaks passing from trunk 9I8 toward the cord circuit of station F during transmission may be limited by relays 906A and 901A to some shorter time such as one-half second or less. Breaks" passing from the trunk 9I8 toward station G are limited by relays 906B and 901B. No break condition during transmission should be allowed to operate relay 9I3B to spacing long enough to release relay 9I0 as such would cause a trunk disconnect; release of relay 929 during telegraphing, if it occurs, will not cause a disconnect or release ductor |025, throughrthecright-hand winding of relay 936'to grounded battery.y 'Relay 936vwil1 operate; Relay 936,- in operating, will prepare for itself a Vlocking circuit Y extending-from grounded battery, throughthe left-hand winding, contact and ,inner left armature and outer lowermost-arniature and contact of relay 9|0, kconduct/M956 toground at the backVv contact and `inner lower armaturecof relay 93|.VV At its right armature and contact relay 936 will open the circuit of therelease magnet 932, 'and will apply at its "outer left armature andV contact grounded battery to a fcircuit extending through the wind- -ingof relayf931, armature and contact of Vstepf ping Imagnet- 9If1, conductors 939 and 956 to ground at aback contact of relay 93|. Relay l931 Ywilloperateand energize stepping magnet wiper'of bank' 920, through the lower winding of relay 93|, conductors 94| and 938, to grounded battery at the outer left armature and contact of relay 936and at its inner lower armature and contact maintainropen' the operating circuit for rvthe 'stepping magnet. All three banks'will be on terminal No'.Y 5 which correspondls'to the calling 'subscribers Astation H. If more than one subscriber' were calling the selector switch would stop on'the'lowest numbered subscribers station terminal. 1 i Y .The wiper .of 'selector' Ybank/9| 9 lreceives grounded negative` battery in acircuit extending from theright of relay and completes the 'circuit -to ground via the back contact of relay `SMB,y lower windingof relay 924, and operated inner lower armature and front rContact of relay 9.31. Therefore, relaysV l|0V|| I and 924 operate. Relay :924, in operating, applies; at itsoutermost lower armature. andcontact a solid. ground to the .wiper 'assciatedfwith 'bank' 9|9, and closes 'at'it's outerupper ,armature and front lcontact the subscribers line, through the Winding of relay 929, to the upper windings of relays 903B and 9343-. .Relay 929,111 operating; Qperates. relay which-docks, relay93| intan operated rposition. vRelays 903BV and,904 B,operate:to their respective marking contacts thereby causingrelay '9|3A to operate to its'inarking contact. Relay 9|3A on itsmarking contact, operates relay 9|4A` which, in turn, ylights line lamp 9,34 indicating to" the operator Y. that a :call Vis waiting.' Relay |04| k|ink operating, releasesrelay `||||2 and consequently relay |032. Operation oiprelayA 930 vcaused the operation oirelay |021,which stays operated so long as relay. 9,30.is;operated, So long as'relay 929 remains operated relay 930 will remainoperated and relayv 93| y will remain operated and release magnet 9,321cannot releasethe selector of this trunk. However, ii` anothercalling line Ihas `causedthe operation 'of relay |032 the'relay |021 willtran'sfer the ground on the armature of relay |032 to the-conductor |025 of thenext trunk and cause it tojbe connected to the neigt calling line. 1

lio

terminal that isI connected to ground at the left armature of relay |0|2. When this occurs relay "93| "will operateVv in a circuit extending'from the Operator answers i The operator answers by inserting plug 83.5 'of the cord circuit shown into jack Relays 938 `and 902A will operate over the sleeve conductors of plug 835 and jack 90|. Relays V838. and 902A, in operating, connect the upper windings ofA relays 903A and 904A through to grounded positive battery 808. Relay 902A extinguishes lamp 934. Relays 903A and 904A operate to their respective' marking contacts. Relay 903A, in operating to its marking contact, releases relay 905A and causes relay 901A to operate thereby applyingthe proper transmitting potential.

The operation of relays 903A and 904A to their respective marking contacts causes relay 9|3B. to

operate to its inarkingfcontact thereby operating ber of the called party. The operator has, of

course, operated key 822 to cut in the operated teletypewriter set into the communication circuit.

Special conditions According to standard operating procedure, if subscribers lines seize trunks in a predetermined order the central oiiice operators will choose trunks in a reverse order beginning at the opposite end of the series of trunks,v Consequently, if enough trunks are provided it will be anexceptional case of reversely directed calls meeting upon the same trunk. However, such situations may occur. If upon a trunk call relay 9|0 operates, a path is closed through relay |021, etc., of the particular trunk whichtransfers the ground at the armature of relay |032 to a relay |036 of some other trunk and a subscribers call which closes the contact on relay |032 subsequently is routed over another trunk. However, if, upon a subscribers call from oilice H therelay 936 of a, trunk becomes operated, the stepping magnet '9|1 steps oi normalyand relay 9|5 remains unoperated. Hence, the dial pulses, if any, sent by the central olce operator do not reach the stepping magnet 9|1 and the magnet steps the selector lto the contact of the calling line; moreover, relay 936 remains operated until vthe calling line' is found because it has a locking path through the lower make contact of relay 9 0 and back contact of relay 93| until the calling line is found which extends the subscribers call to the operator over the trunk. The operator must use a new trunk for her outgoing call'.V

Operator completes `The operator completes a call from a station such as station H to a station E by inserting plug y8|!! into jack 8|1. This'action, as previously described, operates relays 829 and 814. The operation of these relayslights lamp 820 and vas relay 830 is not operated, the ringer 8|0 isthen connected through to grounded battery y801. The operator then operates ringing key 850 which actuates ringer 8|0. The subscriber answers by operating key 809 which causes relay 832 -to operate, thereby operating relay 830. Lamp 820 is extinguished and the subscribers are cut through for communication. The operator retires by releasing key 822.

What is claimed is: i l. YIn a, telegraph system comprising a. central oflice, a satellite oC. subscribers telegraphr lines setting up the connection.

'fand trunks vfrom the central voillce to the satellite oflice, an allotter circuit Aat said satellite oice for 'assigning trunks to' calling subscribers lines in sequence, a selector for connecting one offsaid lines to one of said trunks in response to 'actuation of said selector, a telegraph 'impulse repeater in each trunk, anda-.circuit controlled by a'trans- ,mission condition ofa telegraphimpulse.repeater in a trunk 'connected te aline to vmaintain the connection of. said trunk 'and 'said `line through said selector.

2. In a 4system according to claim 1, wherein lsaid central office comprises means including a dialing device forftransmitting numerical-selecting impulses from said central oiiice to said satellite office, means for applying said impulses over said telegraph repeater Vof a given trunk to said selector, and means controlled thereby to select a line and connectl said line'to said given trunk for telegraphic intercommunication.

3. In a system according to claim 1, wherein said central office rccimprises means including a dialing device for transmittinginumerical selecting impulses fromsaidcentraloice to said satellite cnice, means for applying said impulses over vsaid telegraph repeater .of :a given trunk to said selector, and means controllable overv said trunk from said central oilice through-said trunkkand telegraph repeater to operate a ringeratthe subscribers terminal of said selected subscribers line.

4. A printing telegraph system comprising a central station equipped with a numerical dial device, a plurality of branch stations,V printing telegraph equipment of the current-impulse type at .said stations, a-plurality of signaling channels terminating at .said central station, switching means remotefrom the central station andv responsive to currentimpulsesfior connecting one of said branch stations to any one of said channels, means including thevconnected one of said channels for controlling said switching means fromthe centralstation by impulses originated at said dial device whereby said certain channels are employed for both selecting and signal transmission purposes, other switching means for connecting any idle one of saidsame signalingchannels to calling branch stations, and .means vat the branchstations for controlling'said other switching 4means 'to effect connections between calling 'branch stations and the central station.

' 5. A printing telegraph `system comprising a central station equipped with a'numer'ical dial device, a plurality of branch stations, printing telegraph equipment at said stations, an intermediate switching station,esignaling channels between said switching station and each of the 'other stations, switching means at the switching stationfor connecting any idle one of the central station channels to branch station channels, means for transmitting controlling impulses originated by said numerical dialing device over a lcentral station signaling channel to operate said switching means to connect .a branch station channel tol said `centafal'station channel, means for controlling said switchingmeans `from a calling branch station tov connect the channel eX- tending tosaid branchstation ltoanidle one of vvsaid central station;signalingchannelsland means operative after such connections have been completed at uthe .intermediate switching station for operating theprinting telegraph equipment at the connected stations over the same central station and branch station channel employed for .-.6. A'printing ytelegraphsystem comprising a 'central station lequipped kwith a numerical dial device, a plurality of branch stations, printing telegraph equipment at said stations, an inter.- mediate switching station, signaling channels between said switching station rand each of the other stations, switching means `at the switching station for connecting central station channels to branch station channels, the `channels between the switching station and -the central stationzcon- Ytaining 'telegraphic impulse repeaters, means for ktransmitting controlling impulses originated by said Vnumerical dialing device over a central sta- -tion signaling channel to Voperate said switching means lto connect Ya branch station channel -to VAsaid-central station channel, means for controlling said switching means from 'a calling branch station to connectthe channel extending tosaid branchstation to an 4idle central station signalving channel, and meansoperative'after such connections have been i completed at the vintermediate switching station for operating the printing telegraph equipment at the connected stations over the same central station andibranchstation channel employed for setting up the connection.

7. A printing telegraph system lcomprising .a central station, a plurality of branch stations, printing telegraph equipment at said stations, a V'plurality' ofsignaling channels comprising vduplex `telegraphtrunks including repeaters terminating A'at said central station and commento leach-of said' branch stations, switching means for extending said channels-tothe branch stations, means at the branch stations Vto -control said switching means to connect acalling branch station toan idle channel at the central station, said means comprising a numerical dial.

8. A printing telegraph system comprising a central station, a plurality of branch stations, printing Atelegraph equipment -at said stations, a plurality of signaling channels -including twoway telegraph impulse repeaters terminating at said central station and common to each of said Abranch stations, switching means comprising a numerical dial for extending said channels to the branch stations, and means-at the branch stations to control said -switching means to connect a calling branch station to an idle channel to the central station.

9. A `printing telegraph system comprising a central station, `a plurality of .branch stations, printing telegraph equipment at said stations, a plurality of telegraphic impulse signaling channels terminating at said central station and common to each of said branch stations, switching means for extending any of said channels to any one of the branch stations, said meanscomprising a numerical dial, and means at eachv ofthe branch stations to control said switching means toV connect a calling branch station to any idle of ,said channels extendingto the central station.

l0. Aprinting telegraph system comprising a central station, a plurality of branch stations, printing telegraph-equipmentat saidstations, a plurality of signaling channels terminating -at `said central station and common to each of `said branch stations, switching means comprising -a numerical dial for extending said channels to the branch stations, means at the branch stations to control said switching means to connect a calling branch station to an idle channel to the` central station, means for signaling over an established connection from the branch station tothe central station by means applyingtelegraphic mark- V4,ing and spacing conditions and vbreak conditions, .and means as sociated with; said established .con-

nection to prevent the applying of a prolonged break condition from releasing said established connection.

11. A printing telegraph system comprising a central station, a plurality of branch stations, printing telegraph equipment at said stations, a plurality of signaling channels terminating at said central station and commonto'each of said branch stations, switching means comprising a numerical dialfor extending said channels to the branch stations,pmeans at the branch stations to control, said switching means to connect a calling branch station to an idle channel to, the central station, said channels to the central station terminating'thereat in multiple type jacks for `establishing connections and establishing supervisory conditionsin multiple.

12. Aprinting telegraph system comprising a central station, a'plurality of branch stations, printing telegraph equipmentat said stations, a. plurality of signaling channels terminating at said central station and common to each of said branch stations, switching means controllable by a numerical dial together with a dial for controlling the same for extending said channels to the branch stations, and means at the branch stations to control said switching means to connect a calling branch station to an idle channel to the central station, in combination with a link circuit atsaid central station adapted to extend the call, whether initiated to or by the branch station, :beyond the central olce in a direction away from the branch station.

13. A printing telegraph system comprising a central station, a plurality of branch stations, printing telegraph equipment at said stations, a plurality of signaling channels terminating at said central station and common to each of said branch stations, switching means controllable by a numerical dial together with a dial for controlling the same for extending said channels to the branch stations, and means at the branch stations to control said switching means to connect a calling branch station to an idle channel extending to the central station, in combination with the link circuit at said central` station adapted to extend the call, whether initiated to or from the branch station, beyond the central ofce in a direction away from the branch station, and means whereby after a call has been so extended to a pointbeyond the central office the branch station may place a recall signal for the operator at the central oiiice. 1

14. A printingV telegraph system comprising va central station, a plurality of branch stations, a plurality of trunks or channels terminating at said central station, said channels terminating at said central station including'at least one-telegraphic impulse repeater, switching equipment associated with each of said channels at a point remote from said central station, means at each of said branch stations for controlling said switching equipment from any of said branch vstations to connect the calling branch station to said central station, and means including a numerical impulsing dial forcontrolling from the central station over one of said channels terminating at said central station the selection and connection to said channel of the line of a branch station. v v y 15. A printing telegraph system comprising Va central station, a plurality of branch stations, a trunk or channel terminating at said central station, selective switching equipment associated with'said channel remote from said central sta'- tion, said 'equipment including'means responsive to dial impulses sent from said central station for directively controlling said selecting equipment, printer means for communicating over said trunk or channel, and means whereby impulses from lsaid dial and impulses of telegraphic code sent -from said printer means at saidcentralofce toward a branch station alternate the line of said trunk or channel from marking to spacing in a similar manner but according to their respective codes. .16. A printing telegraph system `comprising a central station, a plurality of branch stations, a plurality of trunks or channels terminating at said central station, switching equipment associated with each of saidvchannels remote from said central station, means for controlling said switching equipment from any of said branch'stations to connect a-calling branch station to said central station, -a numerical dial at said central station, means operative under the control of impulses transmitted by said numerical dial at said central station to control the connection of any of said branch stations to any of said trunks or channels, said trunks or channels being equally available for calls originated by branch stations or by the central station.v

17. In a printing telegraph system, a plurality of outlying oiiices, printing telegraph equipment at each of said oces, aline circuit extending from one of said offices, a selector switch associated with said circuit having a `plurality of bank contacts and a movable switch member for engaging the same, a trunk circuit to a central office terminating at said selector switch, and means for initiatinga call from said central oliice over said trunk circuitfrom said central oice to the printing telegraph equipment at a selected one of the other oiices, means for controlling said selector switch including means for impressing numerical code controlling impulses upon said trunk circuit to control the stepping of said switch by impulses transmitted over said trunk circuit to engage a contact at which a particular line circuit terminates, means'for controlling said selector switch from said oce over said line circuit to connect said trunk circuit to said line'circuit for intercommunication between said olce and said central office over said trunk circuit, said trunk circuit being equally available Yfor establishment of the calls in either direction.

18. A telegraph switching system'comprising a switching oilice, a plurality of lines terminating thereat each provided ata remote point with a teletypewriter set, a plurality of trunks extend-l ing therefrom to a central exchange oiiice, a circuit controlling connection in a predetermined order of the first idlerone of said trunks to a calling line, a numerical dial, and/instrumentalities operative by numerically coded impulses sent over one of said trunks by said dial for controlling the connection of one of said lines to a calling one of saidtrunks in a back and forth intercommunicative relation. s

19. A telegraphic communication system comprising a subscrlbers line extending from a sub.- scribers station to a satellite switching office', a trunk extending from said satellite switching oiiice to a central oiiice, means for controlling the connection in a predetermined order of the rst idle one of said trunks the calling line, numerical dial code controlled instrumentalities controlling the connection of one of said lines to a calling trunk, and means operative on the connection of said line to a calling trunk to impress upon and relay alternating ringing current over said line to actuate a ringer at the subscribers station.

20. In a telegraph switching system, a subscribers station including a teletypewriter with a driving motor connected to a line extending to a remotely controlled. office, a plurality of trunks extending from said ofce to a central office, a switch by operation of which said subscriber may start the motor at his station teletypewriter, means operably controlled by operation of said switch to start said motor to also seize an idle trunk and extend the line of said subscriber to said central oce over said trunk, in combination with numerical code controlled instrumentalities whereby said central oice by remote control may select and connect to said trunk the line from said subscribers station.

21. A telegraph switching system comprising a plurality of trunks, a subscribers line associable with any one of said trunks through a satellite cnice, a calling switch by which a calling subscriber causes his line to be associated with one of said trunks, means whereby numerical code dialing impulses may be transmitted over said trunk to control the connection of the subscribers line with said trunk at said satellite oiiice, a break signal transmitting instrument at said subscribers line, means whereby operation of said break signal instrument for recalling purposes prevents the release of said trunk from the subscribers line connected thereto.

22. In a teletypewriter switching system comprising a plurality of lines and a plurality of trunks, a sequence circuit for assigning any one of said trunks in response to a call on one of said lines, numerical dial code controlled means operable over any one of said trunks for controlling the connection of one of said lines to one of said trunks, a source for producing a series of impulses capable of reception on a teletypewriter of significant information, means for automatically applying impulses from said source to a calling one of said lines when no trunk is available for assignment.

23. In a teletypewriter switching system, a first channel of telegraphic impulse transmission, a second channel of telegraphic impulse transmission, means for maintaining said channels in intercommunicative relationship, slowacting means for causing the disconnecting of said channels from said relationship, circuit varying instruments whereby said slow-acting means is controllable from one of said channels, and other means for timing the control from said channel to prevent such slow-acting means from causing the disconnecting.

24. In a teletypewriter switching system, selective devices for connecting two channels of telegraphic communication together for intercommunication, a numerical dial for remotely actuating said devices to connect said channels, means controlled by a telegraphic impulse condition upon one of said channels to disconnect said channels, and slow-acting instrumentalities for preventing said impulse condition from being applied to said means long enough to cause said disconnection.

25. In a telegraphic switching system, selective devices for associating channels together for intercommunication, a numerical dialfor actuating said devices, means for actuating said devices from one of said channels for disconnecting said channels, and instrumentalities controlled by a telegraphic impulse condition of the other of said channels to determine whether said means shall be effective to disconnect said channels.

26. In a telegraph switching system, means for connecting two telegraph lines together, disconnect means for disconnecting said lines from each other, operable means for controlling said disconnect means from a remote point, and a break limiter locally located With respect to said disconnect means and associated with one of said lines when connected together for preventing disconnection.

27. In a satellite telegraph switching system, trunks and lines, means for connecting one of said trunks to one of said lines, means for impressing a break signal condition upon said interconnected trunk and line, and a telegraphic break limiter operative under a certain condition to limit the duration of the effect of said break condition for preventing disconnection of said trunk and line from each other.

RAND S. BAILEY.

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