US2366733A

US2366733A - Communication system

Info

Publication number: US2366733A
Application number: US408604A
Authority: US
Inventors: Joseph A Krecek; Charles R Walker
Original assignee: American Telephone and Telegraph Co Inc; Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1941-08-28
Filing date: 1941-08-28
Publication date: 1945-01-09
Anticipated expiration: 1962-01-09

Description

Jan. 9, 1945. J. A. KRECEK ET AL 2,366,733

' COMMUNICATION SYSTEM Filed Aug. 28,1941 11 Shqeets-Sheei 1 FIG. 5

POLAR/ZED r/aa I FIG/2 FIG/3 J ,4. mmsx lNVE/VTORS' A TTORNE V FIG. 5

Jan. 9, 1945. J. A. KRECEK ET AL COMMUNICATION SYSTEM Filed Aug. 28, 1941 ll Sheets-Sheet 2 \mm Qkm 3 3 33% khm F6 #8 :3 QHQWT uni. m 6m KW\Q N8 235 MRMM .35 5 8 #35 $833 335 bin a; was 3 mm QR. Ra R8 R3 E .33 358 2 mwm Q :3

3 'JLAKRECEK 'NVENTORS c. R. WALKER ATTORNEY Jan. 9, 1945. J. A. KRECEK ET AL COMMUNICATION SYSTEM Filed Aug. 28, l94l ll Sheets-Sheet 5 'TIT wMaM 35% A T TORNEV Jan. 9, 1945. J. A. KRECEK ETAL I COMMUNICATION SYSTEM 11 Sheets-Sheet 4 Filed Aug. 28, 1941 .1 A. KRECEK" (NVfNTORS c. R. MLKER A TTORNE V Jan. 9, 1945. 'J. A, KRECEK ETAL COMMUNICATION SYSTEM Filed Aug. 28, 1941 ll She ets-Sheet 5 bwk KR Dwk QR lax 4 ATTORNEY Jan, 9, 1945.

v J. A. KRECEK ET L COMMUNICATION SYSTEM Filed Aug. 28, 1941 6 mm km w AR m i S mm .3 n M fii W ATTORNEY Jan. 9, 1945.

Filed Aug. 28, 1941 ll Sheets-Sheet 7 POLARIZED J ,4. KRECEK M/l ENTORS C R ML/(ER m-Maw 2%.

ATTORNEY J. A. KRECEK ET AL 33 COMMUNICATION SYSTEM Filed Aug. 28, 1941 ll Sheets-Sheet 8 C. R. MLKER ATTORNEY Jan. 9, 1945.

I (WE/W095 J A/(RECE/f Jan. 9, 1945. J A, KRECEK ET AL 7 2,366,733

COMMUNICATION SYSTEM Filed Aug. 28, 1941 11 Sheets-Sheet 9 A 7' TORNEV Jan. 9, 1945. J KRECEK ETAL 2,366,733

COMMUNICATION SYSTEM IIIIHI] I \5 1 w a r k I Filed Aug. 28, 1941 ll Sheets-Sheet 10 m0 awl I By C R. ML/(ER ATTORNEY 'Jan. 9, 1945. J. A. KRECEK ET AL COMMUNICATION SYSTEM 11 Sheets-Sheet 11 Filed Aug. 28, 1941 A TTORNE V J. A. KRECEK c R. WALKER IN I/E N TORS any station connected to that particular :party Patented Jan. 9, 1945 UNITED STATES OFFICE ;-12;s6s,7s3 COMMUNICATION. SYSTEM "Joseph A. Ki-cock, New Rochelle, *Y., "and Charles T-R. Walker, Jersey i City, N. IL; "said 'Krecek as'signor to'Bell Telephone Lahoratories,

Incorporated, -New;York, N .Y.,Aa icorporationpf :New :York, and said Walker assignor: to American Telephone and T elegraph Company, aecrimitation of New York 1 I Applicatioh'Augusf28, 19c -serialNo concur (Cl.:1-7i8 4) 21 Claims.

This *invention relates to an 'improved *telegraph transmission switchingsystem and to improved outlying subscriber station circuits connected to party lines extendingto a central switching center.

More particularly, this invention relates to an improved outlying subscriberstation circuit of the type; disclosed" in the -copending application'of Bacon et -al.,Seria1N0. 383,490, filed March 15, 1941-and is-"arrangedto cooperate with the switchingsystemdisclosed in that application.

In accordance with-the present invention, the outlying station circuit switching equipment is arranged so that the same character may be employed to select and" control both the transmitting apparatusat any given station and also the receiving apparatus at the same or any other station connected to any given party line. 1

Another object of this invention relates to an improved conditioning or activating-arrangement which requires the reception "or two "predetermined cod combinations in succession in order to render at leasta portionof the switching equipment responsive "tosucceeding signals 1 and co'de' combinations transmitted overthe sys tem.

Another feature of this invention relates "to a circuit arranged 'for reducing "the "effect "of fals or extraneous currents uponthe-system'-'b*y requiring a specific pattern of 'the succession of predetermined code combinations interposed with other signals of predetermined character and duration to condition at least'certain of the switching equipment.

Anotherfeature of this invention relates to the use of -a single selector for controlling two separate, distinct "and independent groups of switching devices.

Another feature 'of this invention relates "to circuits and apparatus for cancelling the effects of the reception of certainpredetermined characters when they are followed; by. other signals or code combinationsexcept when theyare im- The outlying station circuits and switching equipmentshown in theabove-identified patent application "Bacon .et failed to "respond to or record messages'receiveds at the various sta tionsalong the party line unless" they were preceded by a switching character designating a particular station'served bythe party line indieating the station to-'which themessagewwas directed. When themessages wer properly *ad- 'fdressedthe message would appear and only'at th particular station'to which the-message was designated. However, in the-case of a mutilated or improperly designated or addressed message being transmitted from-the -switching center to a *particular line, the entire message would be losthand'not recorded in any of the stations. In

accordancexwithithe present invention, the-circuits are arrangedto*causesuch messages to berecor'de'd at any one or more'or all of the stations connected to .th party line. Thus, in case a messageis directed to the proper party line but the signal designating the'particular ,stationaonlthe line is. mutilated orlost, themessage will'be received at some one or more of the stations. In .casethe message is received atall of th stations .it .usually can be readily determined from .the .contextcf themessage which .onenof the stations the message should have .been transmitted to. .In this case the message will beidisregarded by all of the otherstations .but=wi-l1 be.considered a messagelfor the-station soaintended.

"In case -"itlisundesirable to record such improperly addressed messages to all of thesta- ,tions, ,the;switchingg equipment located near or, :at the :respective outlying stations may be so a arranged :that such messages are recorded only at ;one :or any :number of :the stations connectedsto .the line; this case, ,the more: lightly loaded or rcentrally located stations will be selected. '.When :such :messages are received. at these: stations; thecproper destination; may usual l-ylbezdeterminedtfromathecontext of the mesmediatelyiollowed by other predetermined 'sig r46 Sageandthe'messageg'retra'nsmittedito thepmper nals of special character and duration "or other specified code combinations. I

Another object of this invention igto provide a switching-equipment at "one or moreof the Outlying. stationstor switchingcenters a party :50 central *swit'chingrcenter. 'I'n: any case, the mesline for recordingall of the messages at oneor more of the stations whenthemessageis :preceded by switching characters "not assigned to line,

station; .Invicase: the :des'tination of the message :cannot the properly determined from the context of 'themessage, :the .message may :be retransmitted to the -originating station or to the sageis; not entirely lost.

Another feature of=this invention relates to an improved'reiay arrangement for cancelling the effect of the nclosure": of ertain contacts 2 of 155 .the selecting equipment unless'theysareL=succeeded by the closure of other specified or predeterminedcontacts of the selecting equipment.

Briefly, in accordance with th specific embodiment of this invention, a plurality of subscriber stations are associated with or connected to party lines extending to a central switching station.

Secondary switching equipment is located at or near various outlying stations of the party line. The secondary switching equipment may be individual to each of the outlying stations or it may be common to a number of outlying stations. The secondary switching equipment includes a selecting device which is permanently connected to the re-ceiving channel of th party line and receives all of the signals transmitted from the central station over the party line. This selecting equipment is provided with contacts which are selectively closed in respons to.

the reception of predetermined signals transmitted over the system.

This selecting equipment is arranged to control two separate, distinct and independent groups of switching devices or equipments. The first group of switching devices is arranged to operatively associate the receiving apparatus atqany of the stations controlled by the, particular secondary switching equipment with the party line. The second group of switching devices is arranged to start the transmitting, apparatus at any of the stations controlled by the particular secondary equipment.

In'general, the receiving equipment at each of the outlying stations comprises a telegraph receiving recorder of which the teletypewriter is a paths have been shown. One path is arranged to transmit signals from the switching center to each of the secondary switching centers located along the party line and thence to the selected controlling the receiving apparatus at the respectypical example. The transmitting apparatus at i each of these stations comprises message storing apparatus such as a keyboard perforator with which the attendant maypunch or perforate a tape in accordance with the message to be transmitted. The stored signals or tape are'then inserted in a telegraph storage or tape controlled transmitter for transmission to the central switching station. Transmission, however, does not immediately take place.

The telegraph'line extending from all of these stations to the central switching station comprises a full duplex telegraph channel capable of transmitting messages simultaneously in both directions without interference. This telegraph transmission system may be of any suitable type and'include any of the low frequency ordirect current telegraph transmission systems including grounded open wire lines, full metallic cable circuits, telegraph channels'of composited telephone and telegraph lines, channels of time division multiplex telegraph systems, telegraph channels of low frequencyor voice frequency carrier current, telegraph channels of high frequency carrier current and radio telegraph, channels and any combination of these Various well understood telegraph communication transmission systems. These telegraph systems may include any suitable type of terminal and intermediate repeat- I ers, regenerative repeaters and the like, as well as gain control apparatus, level compensators, compensating networks and equalizers, all other types of such apparatus and other apparatus sometimes employed in systems of these types. All the respective types of telegraph systems operate in their usual well understood manner so that all of the details of these systems have been shown.

tive outlying stations will be responsive to all but certain predetermined signals transmitted from the central switching station.

As set forth in the above-identified patent application of Bacon et al., each of the messages transmitted over the system is preceded by certain telegraph signals or code combinations designating the particular station to which the succeeding message is directed. Following each of the messages certain predetermined signals are transmitted indicating the completion of that message. The signals preceding each message are employed at the central switching center todirect the message to the proper party line and at the secondary switching centers of that party line, the same or at least certain of the same signals are employed to selectively and operatively associate the receiving equipment at the station to which the message is directed with the party line. The predetermined signals following the message are employed to disestablish the transmission paths and the operative connections employed in the transmission of the preceding mes sage.

Consequently, the first signals transmitted over the receiving channel from the central-station willbe the switching characters preceding each message. The switching equipment at each of the outlying secondary switching centers will respond to these signals and selectively cause the proper receiving equipment to be operatively associated with the receiving channel of the party line. The reception of these switchingcharacters causes the selecting equipment at each of the secondary stations to render the switching equipment for controlling the receiving devices at In case the first signal or code combination transmitted over the receiving channel is not assigned to any of the stations associated with the party line, none of the receiving devices at any of the stations will be operatively associated with the party line and the selecting equipment will not render the switching equipment non-responsive to further signals transmitted over the line.

Normally followin the first directing signals transmitted over the line, a carriage return signal (any other suitable signal may be employed) isusually transmitted preceding thev message proper in order to properly position the carriage of the receiving device for the reception of the following message. The circuits at one or more of the switching centers are arranged to respond to this carriage return signal and cause the receiving equipment at one or more of the stations controlled by the secondary switching centers to be operatively associated with the party line. In

the specific embodiment of the invention shown in the drawings, connections are made so as to caus the receiv ng qu pment at all of the t ions t be iterat vely associated withthe receiving channel of the party line under these circum.- stances. Consequently, the message will betrans- .mitted to all of i the stations of the party line.

The reception of the carriage return signals under these circumstances causes the switching equipment for controlling the receiving apparatus to be rendered non-responsive to any further sig- .ill

centers and cause only one or more but not all of] the receiving devices to. be associated with the receiving channel. Ii; is also, within the scope of this invention to provide'a special receiving device for. receiving such messages. and causing the messages to be recorded only upon thisspew cial receiving device. H

.In the specific embodiment of this linvention shown in the drawings, the figures signal followed by anH signal is employedto indicate the end of each message.

the operative receiving equipment to. be non-responsive to further signalstransmitted over the receiving channel of the party line and further causes the switching equipmentfor controlling the receiving equipment at all of the stationsto be rendered responsive to the succeeding signals transmitting over the receiving channel of the party line. Consequently, the first signals preceding the neXt message which will be transmitted over the receiving channel of the party line will cause the proper receiving apparatus to be operatively associated with the receiving channel.

Thereafter. the circuit will operate in the manner isimilarto that described above.

As indicated above the attendants at each of the outlying s ations will perforate the tape in accordance with the message to be transmitted to the central switching station andthereafter insert the perforated tape in the tape controlled transmitters at each of these stations; Switching signals will be perforated in the tape preceding each message and a figures signal followed by.

an H signal will be perforated in the tape at the end of each message. It is to be understoo'd that suitable signals, such as letters signals, will be perforated in the tape between any of the various switching signals and between the switchin signals or code combinations in the message as may be necessary to provide sufficient time for enablin the switching apparatus to function and establish the necessary transmission paths.

In order to start the transmission from any of the outlying stations, it is necessary that certain predetermined code combinations and signals be transmitted from the central station over the receiving channel. The select ng equipment at each'of the secondary switching centers responds to these signals and causes the switching equipment controlled thereby to start the desired one of the transmitters whereupon the message is transmitted to the central ormain transmitting center.

are started in the specific embodiment of this in- *Vention disclosed herein is briefly as follows.

Any transmission over the receiving channel from the central switching station is first interrupted for a short interval of time following wh ch a blank codeicombination is transmitted from the The reception of the figures sig- H nal immediately followed by an H signal causes I The manner in which the transmitters prises a code combination iii-which all five of the significant selecting impulses are of a spacing.

character. Following the blank code combination a pause of approximately .7 of a second istransmitted from the central station... During this pause the marking condition is applied to the receiving channel of the party line. A predetermined code combination such as thatrepresenting the letterR is then transmitted from the central station and when this signal isreceived it causes any transmitter which may be connected to or transmitting overthe transmission channel to be stopped and disconnected therefrom. Following the letter R. signal, a second pause of approximately, .7 of a second is transmittedfrom the central station following which a selecting code combination is transmitted .whichewill selectively start and operativelycassociate any one of the transmitters with the transmission channel of the party line; Following the transmission of this selecting code combination, transmission from the the central office will be resumed after a slight pause. i i i The circuits at each of the secondary switching centers are so arranged that if. signals are received during the pause in transmission following the blank signal, the eifect of the blank signal is cancelled whereupon the circuits are reestablished as if no blank signal had been received. If following the blank signal no further signals'are received during this .7 second .interVaL'the transmission path extending from the receiving channel to any receiving equipment associated therewith is rendered ineffective so that furthersig:

nals cannot be recorded as part of the message being received. If the letter R signal is not received within apredetermined time of approximately 2 to 5 seconds. the efiects of the blank signal are cancelled. If the selecting code combination is not received withina similar neriodof time ofv approximately 2 to 5 seconds followingv the R. signal, the circuits are restored to'their previous conditions, that is, the transmission pathbetween the receiving channel and the previously selected receiving apparatus is reestablished but none of the transmitters at operative.

The circuits are so arranged that the transmission of messages over the rece ving. channel may be interrupted at any sta e for the transmission of the signals for starting. any of the transmitters and thereafter transmission of the message resumed without adding any characters to the message being transmitted or without deany of the stations will be leting ormutilating any of the switching or mes- Fig 1 shows the manner in which Figs. 5

thrpugh 13, inclusive, are positioned adjacent one i another to form a typical party line circuit arcentral station. A. blank code combination com 75 rangement in accordance with this invention;

Fig. 2 shows the manner in which Figs. 3 and 4 are positioned adjacent each other for showing a suitable central line station;

j Figs. 3 and 4 when positionedas shown in Fig. -2 show. in outline form the various circuitson the central switchingstation; and i i Figs. through 13, inclusive, when arranged as shown in Fig. 1 show the details of the sec- .ondary switching centers and outlying stations associated with a typical party line designed in accordancev with this invention.

Figs. 3 and 4 show in block form the various circuits at a typical central stationsimilar to that disclosed in the above-identified copending patent application of Bacon et a1. and are equivalent to Figs. 3 and 4'of said copending patent application. Figs. 5 through 13 are arranged to cooperate with this switching system and may be placed adjacent to Figs. 3 and 4, in which case the party. line shown in Figs. 5 through 13, inclusive, is shown connected toparty line 200 comprising a receiving channel 204 and transmitting channel205. As maybe well understood by'persons skilled in the art, the party line'shown in Figs. 5 and 13 rnay cooperate equally well with any of the other party lines, such as with the party lines 2M and 202 of the central switching station shown in Fig. 3. It is also apparent that additional party lines may beprovided each of which is provided with equipment similar to that shown in Figs. 5 through 13. It is to be understood that all of these party lines do not necessarily include the same number of'stations or have the stations arranged in the same manner or associated with the same number of secondary switching centers. Instead, the stations and secondary switching centers may be arranged in any manner which may appear tube the most suitable in view of all of the factors in each particular case. These factors include among others geographical selection and separation of the various stations and also the traffic requirements of each of the stations. In general, sufiicient stations are connected to a given party 7 line to insure that it will operate at or near its Figs. 44, 45, 53 and 54 of that application. When these figures are substituted for-any of the groups of figures referred to above comprising party line circuits, they will cooperate with the switching equipment of said copending application in the same manner as the party linesshown described in said application. As will be readily understood by those skilled in the art, the number of stations connected to each of the lines will vary as conditions require. In addition, the apparatus at-the central switchstation, such as the transmitter start circuits and apparatus, may be altered and changed to cooperate with the stations connected to the respective lines. I

It is deemed unnecessary to show all the details and describe the detailed operation of this switching equipment at the central switching station since it operates in substantially the same manner as described in theabove-identified copending patent application of Bacon et a1. and to which reference may. be' made for more detailed description thereof. In the following description it will be assumed that whenthe party line shown in Figs. 5 and 13is connected to the party line 200 of Fig. 3, the central station equipment and circuits have been modified as required by the number of stations connected to the line, and

. crossbar switch that the central switching equipment operates substantially as described in the above-identified cope'nding application. Y

Normally when power is applied to the system, the relays generally assume the position as shown in the drawings. The various motors driving the selecting equipment at the secondary switching centers, as well as motors driving the ceivedeither on a receiving only teletypewriter if they are intended for the central switching 'st'a- V tion or on a typing reperforator if they arcintended for other stations connected to the system. In order to control this equipment an incomingline circuit 3!! is provided in which" the transmitting channel 265 of line 2iilltermina'tes.

The tape 323 from the reperforator 3l8 controls the transmitter 32! Signals recorded in tape '323 together with the'tape transmitter 326', director SH and selector magnet 322 cause the tape transmitter 320 to be "connected through the to the proper outgoing line circuit.

Any suitable type of the crossbar switch may be employed for establishing the connection between the transmitter 326 and the proper outgoingline circuit. The details of the crossbar switch have not been shown in full since switches of this type are well known in the prior art and I the switch incorporated in this invention operates 'in the usual or customary manner. For a more detailed description of the mechanical and electrical features of a typical switch suitable for use in this invention, reference "is madeto United States Patent 2,021,329, granted to Reynolds November 19, 1935. M 1

The outgoing line circuit is provided with two These channels' may be operated simultaneously to record different messages' When the first channel is busy recording another 'message, a,secon d message will be received from the transmitting distributor over the second channel. A typing re- ,perforator is associated with each of these channels. Thus, in Fig. 3, 3M represents the typing reperforator associated with the first channel of the outgoing line circuit 3H5, while 315 represents the typing reperforator associated with the second channel of the outgoing line circuit 3|6.

Assuming that bothohannels areidle and that a message is directed to some station connected tofull duplex line 200, the message will betransmitted over the first channel of. the outgoing line circuit 316 and recorded .by the typing. repertorator 3!! in a tape 324. Tape 324 will .thencontrol the transmitter. 312, causing the message to be transmitted over the receiving channel 204 of transmission system 208 to the desired station.

In addition to thetransmitters M2 and 313 connected to the receiving channel 204 of line we, the transmitter controlcircuit 3H0 andassociated signal code transmitter 31 l'are also connected to the outgoing or receiving channel 204 of the line 200. The transmitter start'circuit-3l0 and the associated transmitter} I I are provided toselectively start the transmitters located at the stations served by thisparty line and' to opera tively associate them. one at a time with the transmitting channel of fullduplex line 260. I The other full duplex lines 29],132 are simi larly provided with terminal equipment at the central switching station. In addition. arrangements are made so that the second channel of" the outgoing line circuit connected to line 20.2 may be d-isasso'ciated with line 202 and employedto receive other messages which are improperly transmitted or for some -reason improperly directed to the correct station. i

Line 203 is provided with similar terminal equipment'at. the central. station, except that" i the transmitter start circuit and its associated transmitter are not provided because only one station is connected to line 293. Consequently, there is no need for selectively starting the transmitter fromthe central station.

- In addition, two local keyboard perforators M8 and 438 are provided at the centralswitching station for perforating tape inraccordance with signalstobe transmitted to other stations of the. system. This tape controls the associated transmitters flfl and 44d. These transmitters are in turn provided wwith directors MI and M1,. re-

spectively', to enable them to 'be connected tothe desired-lines extending torthe proper station. Two intercept circuits lfilli and 49fl are provided for receiving messages which are improperly switched or improperly transmitted over the sys tem. Arrangements are also; provided for direct ing messages intended forany one of thestatio'ns which may be shut down or inoperative due to trouble to either of theseintercept circuits where the messages are recorded by the respective printing reperforators 458 and H8. The tape.

perforated by the typingreperforator 458 is employed to control transmitter 460. With the aid of theassociateddirector 46! this transmitter may be connected to anyof the outgoing line circuitsunder control of'perforationsin the tape.

An interlocking circuit is provided betweemeach of the director circuits to prevent more than one of the director circuits setting up a connection secondary switching center shown in Fig. 7.

. Five outlying stations are shown in Figs. l2 and 13. Theseoutlyingstations are controlled by the secondary switching centers shown in Figs. 8

and 9.. l

i l "It is to be understood that any number of switching centers maybe associated. Withany party line and that any number of stations may be associated with any given secondary switching centers. 1 However, traffic studies indicate. that a maximum of five outlying stations controlled by. one switching center and a maximum often stations connected to a given party line and controlled from. one to ten secondary switchingcenters would adequatelymeet all of the traffic. requirements of any party line likely to. be encountered in commercial. telegraph net works. It. is to be understood, however, that there are no basic limitations: to these numbers. of stations or switching. centers. which. may be associated with any given party line nor are there any limitations regarding the specific number shown in the embodiment of this invention herein described. It will be re'adily understood by those skilled in the art that the switching centers and outlying stations. may bev arranged in. any desirable mannerin accordance with operatingytraffic and geographical considerations. s

It is assumed that in the embodiment of this invention described herein the stations lshownin Fig. 10 are designated by the letters A, B and C, station. shown in Fig; 11 by the letter D, those in Fig. lZ'by E, F and G, and the stations in Fig. 13 by the letters X and Y. Thus when any message transmitted over the receiving channel from the centralswitching station is preceded by any of these letters; the message will be recorded at the proper station.

The receiving channel 2940f the party line 236.

extends through theline windings ofline relays 883,103 and 603 of the respective receiving selectors 91H, l0! and 601 at the secondary switching through the crossbar switch at a given instant of time. The circuits" are arranged, however, so that once the circuit is established through the crossbar switchby one di'rector, other director circuits may establish other connections through the switch withoutdisturbingthe connections already established; Busy-te t arrangements are also provided to indicate whether either or both of the channels of the outgoinglinecircuits are busy, so that .a director willbeunable to connect its associated transmitter to a busy channel of an outgoing. line circuit.

In. the specific embodiment shown in Figs. 5

centers. The receiving channel 204 also extends through the line windings of the repeating relays 9E3; 984, 985, 183 and $83 and 6M .at'the respec tive switching centers. All of these relays follow allof the signals transmitted from the central switching station over thereceiving channel 204 1 of party line 2&0.

Repeatinglrelays

683, 684, 183,

throughv 13,. inclusive, three: secondary switching centers. are. shown. connected to the party line 20!]. Figs. 5 and. 6.- showthe details ofthe. sec? ondaryswitching center rjnost remote fromthe central.switching station... Fig. 7 shows thefdeatails of an intermediate switching center while Figs. 8- and 9 show in. detail the circuitsuand switching equipment rof theswitching center adjacent the centraltswitching. station.

Three outlying stationsare shown in .Fig. 10 to be associated with and controlled by the secondary switching centershown-in Figs. 5 and 6.

The details: of the equipment and the circuits of aisingle outlying. stationrare shown in F'igmll.

. and. 2,154,547, granted toWalker April 18, 1939, "which patents are. hereby made a. part of this application as if fully included herein. The various contacts controlled by the selectors at each of the secondary switching centers are momen tarily operated each time the proper code combination or character is received by the selector ,magnet. However, as described hereinafter.

closure of these contactsis effective to control the switching equipment at each of these stations only under certain circumstances. a 1

The station shown in Fig. 11 is controlled'by the r Selection of an outlying station and the transmission of amessage to the selected station "As pointed out above, each message is preceded by certain significant switching characters each designating the station to which the following message is directed or addressed. Assuming the first message transmitted from the transmitters 3I2 or 3I3 over the receiving channel 204 of the party line 200 is intended for station A, that is,

the left-hand station shown in Fig. 10; this message will be preceded by the letter A. I When the letter A signal is transmitted by one of the trans mitters 3I2 or 3 I3 over the receiving channel 204, it will cause relays 903, I03 and 603 to respond and repeat this character to the respective selecting magnets 902, I02 and 602. These selecting mag nets will in turn cause the selecting equipment in each of these stations which is controlled by them to close the respective contacts 9I0, H and 6 I0. The closure of contacts 9I0 completes a circuit for the operation of relay 929 from ground through the momentarily closed contacts 9I0 the second right-hand break contacts of relay 904 to battery through the winding of relay929. Re-

its outer operated contacts to battery through the winding of relay 904. Relay 904 operates and interrupts the circuits between contacts of the selecting mechanism SM and the switching relays at stations shown in Fig. 9 which control the receiving devices associated with this control station. In other words, further operation of any of these contacts is ineffective to operate any of the switching relays at this point. Consequently,

none of the stations controlled from the secondary switching center shown in Figs. 8 and 9 will receive any of the message signals following this A signal; It is to be noted that the selector magnet 902 will follow all of the signals transmitted over the receiving channel of the party line and cause the corresponding contacts to momentarily close. However, this selector when responding to these signals will not alter the switching circuits until certain predetermined signals have been received as 'will be described hereinafter.

Similarly relay 193 at the intermediate secondary switching center will respond to the letter A signal and repeat it to the selector magnet 102. This magnet causes selector mechanism 'IOI to momentarily close contacts H0 and complete a circuit for the operation of relay I29. Relay I29 in operating completes a circuit for maintaining itself operated under control of relay I31 and also completes a circuit for the operation of relay I04. Relay I04 in operating disconnects the contacts controlled by selector 'IIJI from the switching relays which control the receiving apparatus located at the station shown in Fig. 11. Consequently, the message will not be recorded by this receiving apparatus.

The relay 603 also responds to the letter A signal transmitted from the central switching station and repeats this signalcombination to the selector magnet I302. Selector magnet 602 in responding to this code combination causes contacts flowing in a circuit from battery through the;

winding of relay 630 to ground through the lefthand break contacts of relay 604 and the operated contacts 6I0. Relay 630 in operating completes a circuit for maintaining itself operated from battery through its winding and left-hand inner operated contacts and the left-hand inner break contacts of relay 631 to ground through the rightehand inner operated contacts of relay,630.

Relay 630 in operating completes a circuit for the operation of relay 604'from battery through the winding of-re1ay 604 to ground through the at this station.

Relay 630 in operating also completes a circuit for lighting lamp 650 from ground through the right-hand outer break contacts of relay 68I and the right-hand outer operated contacts of relay 630 to battery through lamp 650. Lamp 650 in lighting indicates to the attendant that the station associated therewith, namely, station A shown in Fig. 10, is operatively associated with or connected to the receiving channel of the party line.

Operation of relay 630 also connects the ar-' mature of the repeating relay 684 to line I 02!.

Consequently, when relay 684 followsthe message signals of the following message it will repeat these signals over the conductor I02I to station A. The transmissionpath from the armature of relay 684 may be traced from they contacts and armature of relay 684, through the outer left-hand break contacts of relay 68I through the outer left-hand operated contacts of relay 630, conductor I02I tostation A and line winding of relay I022 to ground. At station A relay I022 will follow these signals and repeat them to magnet I023. This magnet will cause the signals to be recorded by the receiving device I024 at station A. Thus the signals following the letter A signal will all be received by the receiving device I024 at station A. Following the transmission of the A signal from one or the other of transmitters 3| 2 and 3I3 from. the central switching station one or more letters signals may be transmitted to provide sufiicient time for the operation of the various relays and circuits described above. Normally a carriage return signal, a line'feed signal and another letters signal will be transmitted it is pointed out above, circuits will remain in this condition so long as this message is being transmitted to the station. It'should be noted that the same code combinations which were initially used to control the switching relays and circuits may be transmitted during the message without changing the connections or the switching ap- 'paratus. In the specific example under consideration, the letter A whichwas used to establish arcane the transmission pathut o station A may be transmitted a number or times. during the message without further aifecting the circuits or any of the secondary switching stations. Similarly; characters designating the. other stations connected .to the party line may be transmittedduring the transmission atthe message without at.- fecting the circuits: at or to any of these stag ti'ons.

At the end of this message a figures signal will be transmitted followed: by an H signal. It should be noted that should :a figures signal, .be transmitted during the message which is followed 645. It'should be notedthatthe only possible circuits through the 'l'owervwinding' of relay 546 at thisttime are the circuits which extend through either the figures contacts 625, blank .contacts 621, and the 5H=combination 6H. Theoperation of the circuit wh'en the-particular code combination is a fig-ures code combination is substantially the same as described abovewnen the first figures of the figures signal will be cancelled.

The operation of the circuits under these conditionsis as: follows: Upon the transmission of a figures signal contacts 625 of the selector Bill will momentarily close. Momentary closure car-these contacts completes the circuit for .the operation of/relay G'tifrom ground, through the closed contacts filifigright-hand winding, of relay 645: to battery through the lower winding of relay 54.6. As indicated current flowing through theilower winding of relay 546,, which is'a. polarized relay, is 'in such a direction as to maintain its armature in: its right hand position :as shown :inthe drawings. Relay 6 ,35 in operating completes a circuit for" maintaining itself operated from" battery through its left-hand winding, the left-hand onterxbreak contacts of relay 631., theuleft-hand and right-hand outer operated contacts of relay 64 5 to ground through the right-hand contact and armature of relay546. Operation of relay M5 also completes a circuit fromgroundthroug'h the universal contacts 626 and right-handinner operated contacts of relay 645 to battery through the upper winding of relay 546. Current flowing in this circuit tends to cause the armature of relay 546 to be operated to its left-hand position. However, this current produces an effect upon relay 546 which is weaker than. the. efiiect produced upon relay v546 by the current flowing through the lower winding of this relay. Consequently, relay 546 is maintained-in the position shown on the drawings atthis time.

Contacts 626 are closed once for each code combination received by; the selector mechanism BM. These contacts, howeverydo not close until: after the other contacts close. if the particular code combination received is one that normally controls any of these other contacts. In addition the contact 625 opens before any of the other-contacts open. Consequently, the circuit "through the lowerwinding. .of relay 546 is closed first and maintained closed for ashort interval 1 time'may be traced from ground through the operated universal contacts 626, the right-hand l. inner operated contacts of relay 645 to battery,

through the upper winding of relay 546. Current flowing in this path will cause the armature,

of relay 546 to be operated toits left-hand position and. interrupt the locking circuit of relay code combination was transmitted over the sys: tem. If the particular code combination happens to be a blank code combination, the circuitwill operate as describedhereinafter. If the particular' code combination is an Hcomb ination, the circuit will operate to disconnect the receiving equipment at station A;

Assuming that the code combination following the figures code combination is neither-an I-I code combination nor a blank combination, the oper ation'of relay Ho as described, above interrupts the locking circuit of relay 645 and permits this relay to release. Rel-ease'of relay 64'5 returns the circuit to its preyiousco-ndition and cancels the effectot the reception of the figures code combination in so far asthe switching equipment of the secondary switching center shown in Figs:

5 and 6 is concerned, Thereafteras many upper case characters including the H character or code combination may be transmitted over the system andl recorded by the receiving device shown at station A without affecting the switch- Q ingequipment or the transmission circuits eX tendingto station A. i

The selecting equipment at the intermediate secondaryswitching stations such as shown in Figs? responds in asimilar manner to the transmission ,of theiigure-signal followed by any signa'l otherthan a blank signal or an H signal. Relay 245 will be operated and then later released bythe operation of relay H6.

Likewisere-lay 9ll5 will' beeperated at the first secondary switching center in response to the reception of the figures signal. Thereafter relay Ski-will be-o-pera-tedto its left-hand position in response tothefollowing code combination which under the assumed condition isneither an H signal norablank signal. The operation of relay llfi 'interrupts the locking circuitof relay 945 and thispermits this relay to release and cancel the effect of the figures signal upon the switching: circuits. i

It should be noted that the receiving apparatus conneotedlto thereceiving channel receives and properly responds to the figures signal but the sheets of th-i-s signal upon the receiving apparatusis not cancelled as described above with reterence tothe switching equipment. The effect or'the figures signal upon the receiving .apparatus is cancelled only in -response to a letters signal and sometimes in response to a character spacing or other predetermined signal.

Assuming now that a codecombination immediately following the figures code combination is an H code combination; whenthis code combinaat this timecompletes a circuit through the lower winding of relay 546 for maintaining its armature in theposition shown. This circuit maybe traced from ground through the closed contactsfill, the left-hand inner operated contactsof relay 645; winding of relay 631 to battery through the lower Winding of relay 548. Relay 631 operates due to current fiowing'through this circuit and relay 54B is maintained in the posiinthe position shown where it maintains the loeking circuit for relay 645 and also for relay Relay 631 when operated completes a circuit for maintaining itself operated from battery through the lower winding of relay 546, winding of relay 631, the right-hand inner operated contacts of relay 631, the right-hand and left-hand outer operated contacts of relay 645 to ground through the right-hand contact and armature of relay 546.

Relay 631 in operating interrupts the locking circuit of relay 636 and thus permits this relay to release. The operation of relay 63'! however maintains a circuit through the winding of relay 664 closed and thus maintains relay 664 operated as long as relay 63? remains operated. The operation of relay 631 also interrupts the locking circuit of the figures relay 645 and thus permits this relay to release. Release of relay 645 interrupts both the operating and the locking circuit of relay 637 and permits this relay to release. The release of relays 637 and 645 interrupt the holding circuit of relay 664 and permits this relay to release. switching center shown in Figs. 5 and 6 is returned to the same. condition as it was in beginning and is thus ready to respond to a directing character which will be transmitted preceding the next message transmitted over the receiving channel 204 of partly linev 200.

The circuits at the other secondary switching centers shown in Fig. '7 and Figs. 8 and 9 respond in a similar manner and first cause the operation of relays 745 and 131, the release of relays 129,

Thus the circuit at. the secondary 145, 131, 104 in the order named and thus restore the circuit to its original condition. In a similar manner the circuits at theother secondary switching center shown in Figs. 8 and 9 are also restored to their initial condition in response to the figures code combination immediately followed by an H code combination transmitted at i the endof the message which was transmitted to station A.

Assume now that the switching characters preceding the next message which has been routed by the switching equipment at the central switching station to this line will be preceded by a first character which will not be the letter A, B, C,

I D, E; F, G, X or Y. Under these circumstances -mitted over the receiving channel 204. Consequently, none ofthe switching relays controlled by these contacts will operate to connect any of the receiving devices at any of the receiving stations to the receiving channel. -As pointed out above, following the first signals transmitted over the receiving channel one or more letter signals are usually transmitted in order to provide suf- ,ficient time for the switching circuits to function.

Following the transmission of the letter'signals a carriage return signal and a linefeed signal followed by a letters signal are usually, trans mitted in order to properly position the carriage.

at the receiving instrument at the station to which the message is directed. If none ofthe switching contacts controlled by the selectors at the various stations have been operated when the carriage return signal is transmitted over the system, the selecting equipment at each of the secondary switching centers will respond to this signal and cause the respective contacts 628, I28 and 928 to momentarily closeand complete circuits for the operation of relay 648 atthe most remote secondary switching center, relay 148 at the intermediate switching center, relay 948 at the first switching center. The circuit for the operation of relay 648may be traced from ground through the closed contacts 628, the inner lefthand break contacts of relay 604 to battery through the winding of relay 648. Relay 648 in operating completes a circuit for maintaining itself operated from battery through the winding of relay 648, the right-hand outer break contacts of relay 63'! to ground through the right-hand operatedcontacts of relay 648.- As shown in the drawings the operation of relay 648 will complete circuits for the operation of relays 630, GM and 632 because all of the straps 615 are shown provided between the contacts of relay 648 and the windings of these relays. Consequently,.the operation of relay 648 will cause each of these relays to operate which in turn will cause the receiving equipment at each of the stations, A, B and C to be operatively associated with the receiving channel 284. Consequently, all of these stations will receive the following message transmitted from the central. switching station.

In a similar manner relay .148 completes a circuit for the operation of relay 133 and the relay 133 in turn operatively associates the receiving equipment at the station shown in Fig.

-11 with the receiving channel 264.

Likewise the operation of relay 948 at the first secondary switching center completes circuits for the operation of

relays

934, 935, 936, 943 and 944, the operation of which relays operatively associate the receiving equipment of all of receiving channel of the party line.

The operation ofall of these switching relays at each of the secondary switching centers completes the circuits for. maintaining themselves operated under control of the respective relays 631, 13'! and 931. The message following the carriage return signal will then be recorded by the receiving apparatus of all of the stations associated with the party line. In general this message will be intended for some one of the stations connected to the party line and the attendants at the respective station can usually readily determine from the context of the message the particular station for which it is intended andthe message received in the other stations, will be ignored and the message considered a proper one at the proper station. In case a message is intended for some. other sta 'tion than the one of the stations of thisparty line, the attendants at one or more of the stations may be assigned the duty of transmitting the message either back to the central switching not all of the stations connected to any given party line. In order to accomplish this thestraps the stations shown in Figs. 12 and 13 with the signal followed by the H signal will be transmitted to the circuits ateach of the secondary switching centers which will respond to these signals in the same manner as describedabove and restore the circuits and equipment to its original idle or normal condition.

It is also possible to broadcast any message to all stations of any given party line by transmitting a carriage return signal or, any other specifically designated code combination, which will cause the relays 648, 148 and 948 or relays similar to these relays to operate at each of the secondary switching centers. If these relays are thus operated instead of the: relays individual to each of the stations, they will cause all of the individual relays to be operated as described above and cause the message to be recorded at each of thestations served by the party line. Similarly by suitable connecting contacts on these relays and the individual relays described above any group of the stations associated with the respective party line may be selected for the simultaneous transmission of messages relay 604 to other contacts controlled by the being transmitted from the central switching.

selector mechanism as desired. The contacts of these relays would be connected to the windings of the desired individual relays as described above.

Starting a transmitter At any time during transmission ofa message from the central station to any of the outlying stations it is possible to interrupt the transmission then in progress and send transmitter start signals over the receiving channel 204 of the party line 208.

As pointed out above, the attendants at each of the outlying stations will perforate the tape in accordance with the messages to be transmitted and insert the perforated tapes in the transmitter. Thereafter the message will be transmitted under control of the central station. Normally, the operator at the central switching .station'will control a special circuit so that it will send out a group of. signals interspersed with pauses of predetermined duration constituting a followed by an H signal will be perforated in the tape at the end of the message. The perforated tape is then inserted in the transmitter. The insertion of the tape in the transmitter causes contacts [M5 to close.. The closure of these contacts merely partially prepares a circuit for the operation of relay lll3.

Assume further that a message is in progress of station to the receiving equipment shownat station B. Under these circumstances, if the operator desires to start the transmitter at station D she will operate certain switches or other apparatus at the switching station to initiate the operation of the transmitter start circuit and equipment whereupon the transmission in progress over the receiving channel 204 from the central station to station B is first interrupted by stopping the transmitter at the central switching station. After the transmission has been stopped for a short interval of time of the order of a half of a second or a second, a blank code combinationis transmittedfromthe transmitter start circuit over the system. In the blank code combination the five significant selectin impulses are all spacing. This blank code combination when transmitted over the receiving channel 284 is received by the receiving apparatus at station E.

This apparatus however in. responding to this code combination does not print any character nor does it advance the printingposition a character space or respond in any other manner to this blank code combination. i l

The selector magnets 682, 102 and 982 also respond to this blank code combination and cause their respective selector equipments to momentarily close the respective blank contacts 621, 121 and 921. The closure of contacts 621 completes a circuit for the operation of relay 541 from battery through the lower winding of relay 555, winding of relay 541 to ground through the closed contacts of 621. The operation of relay 541 completes the circuit for the operation of relay 518 which relay in turn completes the circuit for maintaining its-elf operated from battery through through the lower windingof relay 546 and re-.

mains completed through the lower winding of this relay until after the universal contacts 526 lopen, relay 545 is maintained in the position understoodof course, that switching or directing signals will be perforated in the tape prior to the messageand that the figures signal immediately shown. Later when contacts 621 open relay 541 will release and interrupt the circuit through the upper winding of relay 511.

Normally relay 5111's maintained .in the position shown by currentfiowing in a circuit from battery through its upper winding, lower contacts of key 59! to ground through the left-hand break contacts of relay 518. A circuit is also completed through the lower winding of relay of relay 511. The armature of relay 511 does not.