US2407150A - Telephone or like signaling system - Google Patents

Description

Sept. 3, i 946. I c. GILLINGS VEFAL 21 TELEPHONE OR LIKE SIGNALING SYSTEM Filed Sept. 18, 1943 8 Sheets- Sheet 1 mvzn-rons YP CHARLES GILLINGS CHARLES Emuw BEALE TESEO mo DAN'IE TERRONI ATTORNEY Sept. 3, 1946. c. GILLINGS ET AL 2,407,150

TELEPHONE OR. LIKE SIGNALING SiSTEM Filed Sept. 18; 1945 s Sheets-Sheet 2 s m w m CHARLES GILLINGS CHARLES EDMUND BEALE TESEO BRUNO DANTETERRW g VTR CSZ Sept. 3, 1946.

I c. GILLINGS ET AL TELEPHONE OR LIKE SIGNALING SYSTEM Filed Sept. 18, 1943 I I cndl' a Sheets-Sheet s c'nd5 INVENTORS CHARLES sums CHARLES souuuo new:

' TESEO aamoomrsmmm EQRNEY s P c. GILLINGS E AL 2,407,150

TELEPHOiiE OR "LIKE 'SIGNALIEJG 'ISYSTEM FildSebt. lsfie 4s 'ashet -sheet 4 v II CTITI.

" INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE TESEO BRUNO DANTE TERRONI Sept. 3, 1946- c. G|LLINGS ET AL 2,407,150

TELEPHONE 0R LIKE SIGNALING SYSTEM Filed Sept. 18, 1945 8 Sheets Sheet 5 AAAL ' irz YA VSF lfivem'ons CHARLES eumes cums Eouum as:

TESEO BRUM DANTE TERRONI Sept. 3; 1946. c. GILLINGS ETAL 2,407,150 7 TELEPHONE OR LIKE SIGNALING SYSTEM Filed Sept. 18, 1943 8 Sheets-Sheet 6 WR-ZR F1 6 INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE TESEO BRLM DANTE TERRMI ATTORNEY Sept. 3, 1946. c. GILLINGS' ET AL TELEPHONE OR LIKE SIGNALING SYSTEM Filed Sept. 18, 1943 8 Sheets-Sheet 7 mvemons CHARLES GILLINGS CHARLES EMU BEALE TESEO BRUNO DANTE TERROM ATTORNEY.

Sept. 3, 1946.

C. GILLINGS ET AL TELEPHONE 0R LIKE SIGNALING SYSTEM Filed Sept. 18, 1945 8 Sheets-Sheet 8 il llllll llll Ill I6 I 1 l I l l I l l Ill llll l|llll lL I 'INVENTORS CHARLES GILLINGS cums eouuno am: n-zsso anuuo was mam Patented Sept. 3, 1946 UNITEDSTATES PATENT oFricE TTELEPHONE OR'LIKE SIGNALING SYSTEM Charles Gillings, Charles Edmund Beale, and Teseo Bruno Dante Terroni, Liverpool, England, assignors, by mesne assignments, to Automatic Electric Laboratories, Inc., a corporation of Delaware Application September 18, 1943, Serial No. 502,884

- In Great Britain October 15, 1942 7 claims. (o1. 179 27 'May 31, 1943, now Patent No. 2,376,352, dated May 22, 1945.

According to this method of V. F. signaling, the numerical direct current impulses received at the sending end of the trunk are converted into voice frequency coded signals which are transmitted over the trunk and re-converted at the terminal end into' numerical direct current impulses. Furthermore, each voice frequency coded signal is preceded by a prefix signal which is the same for all codes and serves the purposeof testing the incoming equipment and also switching any echo suppressor in the route into the correct direction of transmission preparatory to the sending of the coded signal which is characteristic of the D. C. train of impulses to be transmitted.

This method of signaling gives a good degree of speech immunity in that by reason of their length and combination the signals used rarely if ever occur in speech, In fact the degree of 4 immunity against false operation is so gOOd with this method of signaling that the use of so-called stopper valves which have hitherto been generally used in V. F. systems to prevent the exten- .coming. backwardly over the line to the calling end and accordingly, therefore, any toxic signals received during the setting up of the connection were received quite freely. When the connection was completely set up and the called partly answered, an answer signal was sent backwardly over the trunk to bring about the removal of the stopper .valve at the sending end so that conversation could take place in both directions of transmission. I

Although the use of astopper valve provides a good degree of protection against disturbing currents generated at the sending end interfering with the V. F. receivers, its presence in the line is nevertheless 'undesirablein certainv circumstanceaparticularly-in the case of non-metered calls. Generally speaking this type of call is routed through to an.operator's position and the terminating apparatus issuch that it does not send back an. answering signal so that the operator may talk to the calling party and give him i the information required without metering the call against him. When, however, such a call is originated over] a V. F. trunk including a stopper-valve, itis necessary to arrange the terminating apparatus to send back an answer sigjnalin-order to bring about the removal of the stopper valve to enable conversation to take place. As will be appreciated this is particularly undesirable in the case of automatic calls because a the answer signal brings about automatic metering of the call. against the calling party and it is therefore necessary in such circumstances for the operator tomake out a credit slip for such calls in order thatrthey shall be deducted from the calling subscribers account. From an operating point of view such arrangements are undesirable and it is one of the advantages of the present invention that they have been avoided.

In order to give a gooddegree of speech irnmunity for supervisorysignals which are transmitted over the trunk after the connection has been set up, it is arranged according to the inventionthat the apparatus measures such signals as regards their frequency, their duration and, their spacing. The sequence is such that it is connected in circuit withthe trunk line leading to'a following exchange, said blocking device by introducing considerable attenuation into the speaking circuit preventing the code signal from actuatingflapparatus at said .following exchange.

The invention will be better understood from M the following description of one method of carrying it into effect, reference being bad to the accompanying drawings comprising Figs. 1-9. Of

these drawings, Figs. 1-4 show the circuit arrangements of a sleeve-controlled outgoing relay set, Figs. 5 and 6 show the circuit arrangements of an incoming relay set, Figs. '7 and 8 form a trunking diagram of various combinations of trunk routes to Which the invention maybe usefully applied while Fig. 9 show an alternative circuit arrangement including certain modifications which are necessary if the incoming relay set is required to respond to 'busy flash signals.

Before the detailed circuit .operations are described, a description will be given of .the general method of working with reference to the trunking diagram, Figs. '7 and -8. 'In this diagram exchanges A-H are shown interlinked by V. F. and D. C. trunks. Lik pieces .of apparatus in the various exchanges have been given like designations, for example, MB is manual board, O/G is outgoing relay set, 1/0 is incoming relay set, VF is voice frequency receiver, AA BS is auto-to-auto relay set, while VF. 'TRK and D. C. TRK are voice frequency and direct current inter-exchange trunks respectively.

Assuming that the operator at exchange B plugs into the jack at the manual board MB leading to 'a free outgoing relay set O/G, her supervisory 'lampwill flicker and the 'outgoingrelay set will send a 100 milli-seconds (m. s.) X voice frequencypulse forward over the trunk to the incoming relay set 1/0 at exchange C tobring about the seizure of an associated first selector. The operator now operates the dialling key whereupon the supervisory lamp 'is extinguished and when she dials the required 'subscribers number, the impulses are received and. stored on uniselectors in the outgoing relay -set. Each train of impulses received at the outgoing relay set is re-transmitted over the trunk in coded form made up of a combination of four voicefrequenc'ies, hereinafter referred to as W, X, Y and Z. Each coded digit transmitted is preceded by a preparatory signal comprising all four frequencies, W, X, Y and Z which are effective "in the incoming relay set 170 to prepare the voice frequency receiver thereat for operation. The prepare pulse also takes control of any echo suppressors in the route to turn them .into the correct direction for transmitting. Conveniently the 'W','X Y, Zfrequencies used are of 900, 750, 600 and 500 cycles respectively.

The coded digit comprising not more than three of the frequencies W to Z is decoded at the incoming relay set and converted into a marking on the bank of a uniselector which counts the sending out of a corresponding train of loop impulses to set the automatic switches in exchange C.

.After an interval which is measured in the outgoing relay set and is sufiicient to allow for the setting up and hunting time of the automatic switch in exchange C, the second prepare and code signals are transmitted and are dealt with similarly.

When all digits have been dealt with and the switching equipment at exchange C has been set to connect with the required subscriber, the calling operator will receive ringing tone, busy tone, or iNU tone to denote the state of the called line.

When the called subscriber answers, repeated Y pulses of .140 m. s. duration spaced 36.0 m. s. apart are sent back from th incoming relay set in exchange C to bring about the extinguishing of thesupervisory lamp inthe operators cord circuit at exchange B. Vhen this is done, an acknowledgment signal is transmitted back from the outgoing relay set comprising a single Q40 m. s. pulse of X frequency which serves to terminate the sending of the repeated Y pulses from the incoming relay set. Conversation now takes place and when the called party clears, repeated Y pulses similar to those forming the answer signal are transmitted from the incoming relay set back to the outgoing relay set where they bring about the lighting of the operators supervisory lamp. When the operator clears in response to the clear signal, the outgoing relay set sends forward to the incoming relay set a clear signal comprising a two-seconds X pulse followed by a 300 m. s. Y pulse which causes the incoming relay set to clear down and release the train of automatic switches at exchange C.

In case the operator has to clear in face of ringing, busy or NU tone, the clear signal under these circumstances is lengthened to a six-seconds X 'pulse followed by a 300 m. 5. Y pulse. The object of the long X pulse is to ensure that the clear signal will get through in face of NU tone which is interrupted at the source for one second after the tone has :been transmitted for 'five seconds.

'The proposed voice frequency digit code is as follows:

The proposed voice frequency nal code is as follows:

supervisory sig- As willbe seen from the trunking arrangements of exchange C, the outgoing relay set may be taken into use from any one of three sources, namely, manual board, automatic local subscriber, or incoming relay set from a distant exchange. In the case of seizure from an automatic local subscriber, the operations are substantially similar to those already described for seizure from the manual board, except that resistance battery is connected to the sleeve of the manual board jack to busy the outgoing relay set against seizure from this source.

In caset'he outgoing relay set in exchange C'is taken into use via an incoming relay set in the same exchange, a battery signal over both lines is extended backwardly from the outgoing relay set to the incoming relay set to cause the incoming rela set to switch the lines straight through and cut out ,of circuit the decoding and retransmitting apparatus. At the same time in the outgoing relay set the lines are extended by Way of a repeating coil bridge to the incoming .relay set in exchange D and the storing and code sending apparatus in the outgoing relay set of exchange C is 7 cut outof circuit, Code signaling therefore takes I5 place directly from the outgoing relay set of exchange'B to the incoming relay set of exchange D.

In case the call from exchange C isto be routed over a D. C. trunk to exchange E, access will be had from the incoming selector to theline side of the auto-to-auto relay set A--A RS, thus cutting this relay set out of circuit. lhis arrangement is desirable to avoid two repetitions of the impulses in the same exchange. The incoming rela set extends earth forwardly to hold the automatic switches in exchange C.

If now the call to exchange E is extended over a VF trunk to exchange G, signals passed between th outgoing relay set in exchange E and the incoming relay set in exchange C bring about the setting up of straight through connections and the disabling of the coding and impulsing apparatus. Signaling therefore takes place directly from the outgoing relay set in exchange B to the incoming relay set in exchange G so that the conditions become similar to the VF to VF case already described.

In case the connection from exchange E is extended over a D. C. trunk to exchange F and then over a VF trunk to exchange H, a different set of conditionsarises because an auto-to-auto relay set at exchange E is now interposed in the trunk route. It is therefore now impossible to signal by means of the simplex battery connection between the outgoing relay set of exchange F and the incoming relay set of exchange 0 to cause these sets to switch over to straight-through connections. On the other hand, unless means are provided to prevent it, the VF signals from the outgoing relay set of exchange B can find a circuit 'by way of the condenser bridge in the auto-toauto relay set of exchange E to the incoming relay set of exchange H and this would bring about the generation of two trains of impulses for each train of impulses transmitted from the outgoing relay set in exchange B. To prevent this the incoming relay sets are provided with blocking devices in the line circuit which function almost instantaneously upon reception of the VF prepare signal precedin each code and thus prevent the code signals reaching the incoming'relay set at a dis- &

tant exchange such as exchange H. Thus the sequence of impulsing insofar as setting up of automatic switches in exchange H is concerned is as follows. VF signaling between exchanges B and C; conversion at the incoming relay set of exchange C to D. C. impulses which extend by way of exchange E and the auto-to-auto relay set threat to outgoing relay set of exchange F. Reconversion takes place at exchange F to VF signals which extend to exchange H and are there changed back again to D. C. impulses to set up the automatic switch train in exchange H.

Referring now to the detailed operations involved in setting up a connection over the equipment shown, when the operator plugs into jack JCK, Fig. 1, if the cord circuit speaking key is thrown relay M is operated over the sleeve circuit and in turn operates the relief relay MM, Fig. 4. Relay MM at contacts mm I, Fig. 1, connects flicker earth to the upper low resistance winding of relay M to flash the lamp in the operator's circuit to provide an indication that she is connected to a dialling trunk, and at contacts mm2, Fig. 4, connects earth to the P conductor incoming from selector levels to guard the relay set against seizure over this path and also operates relay SR. Relay SR- at contacts srl causes the switch TS to self-drive from its home position to position l where relay CO is operated over the oil-normal bank TSI and relay FXY is operated over bank.

T84. Relay CO atcontacts e03 disconnects relay SR and also at contacts col and 002, Fig. 2

working the jack points Ill and H are strapped together as shown. For bothway trunk working, however, this strapping is removed and the jack points Ill and ii are cross-connected to the termination in the incoming relay set. Relay FXY in operating, at contacts fang l brings up relay CS and at contacts fats/2 causes the switch TS toselfdrive over its bank TS3 to the third position. During the period that the switch is self-driving over the two strapped contacts, X frequency is applied to transformer VXF via contacts fc2, fxyl and cal and terminatin resistance VTR and then extends via contacts csl and 082 and contacts col and 002 to the trunk line to form a seizing signal to the incoming relay set at the distant exchange. With switch TS in position 3, relay FXY releases to terminate the X pulse after a period of the order of 100 m. s. and at contacts h2g3 operates relay FC which looks and at contacts I03 causes the switch TS to step to position 4-from which it drives to position 6 over bank T and interrupted earth connected to conductor 13. Relay FXY, in releasing, at contacts fan/4 releases relay CS.

When the operator throws the dialling key, battery is connected to both lines and relay RR, Fig. 1, is operated over its upper winding, while at the same time a high resistance isintroduced into the sleeve circuit to extinguishthe calling supervisory lamp. Relay RR at contacts rrl operates relay A which in turn'o-perates relay B, Fig. 3,1;0 prepare certain impulsing circuits and operate relay BR, Fig. 4. Relay BR at contacts brl drops relay RR and at contacts brl and M2 connects relay A to the tip and ring lines extending to the operators dialling circuit and also at contacts 1213 disconnects the flicker earth circuit and connects up relay KR into the sleeve circuit;

this relay however will not operate owing to the high resistance already introduced therein. When the dial isturned off-normal, balanced battery on the lines is replaced by a loop through the dial impulse springs and relay A continues to hold. When the dial is released, relay A responds to the impulses which it repeats at contacts al, Fig. 3, via relay C to the driving magnet DSAM of the first digit storing switch DSA so that wipers of this switch are stepped to a corresponding position. Relays B and C hold operated during the impulsing and the latter at contacts 02, Fig. 4, operates relay OS to prepare the VF signaling circuit at contacts csl and 082, Fig. 2. Relay C also at contacts cl, Fig. '3, energises the driving magnet DDM of the digit distributor switch DD, but as this switch is of the reverse drive type its wipers are not moved at this time.

At the end of the first series of impulses, relay A remains energised and relay C releases after its slow period and at contacts 0! completes a circuit over bank DSAI, Fig. 3, for operating relays CNA and CNR in series. If the digit dialled is 5 or less, relay CNA operates over its left-hand winding and as a result a short interdigital pause is provided between the retransmitted digits as will appear subsequently. Relay CNR at contacts cnr2 advances the: sending control switch SC from its home position to position I where relay ST is operated over its two windings in series. Relay approximately 160 ms. .holds relay CS and at contacts s3, Fig. 2, con- -ST thereupon at :contacts stl short-circuitsits left-hand high resistance winding to self-drive the sending control switch SC to position 4, at contacts 'st2, Fig. 4, maintains relay CS and at contacts Sl38i3 causes a prepare pulse of WXYZ frequency to be connected via the transformer VXF to the trunk line to the distant exchange. When the sending control switch SC reaches contact 4, relay ST releases after its slow period thereby disconnecting the WXYZ prepare pulse and at contacts stl operates relay S 'over its'two windings in series with magnet SCM.

The duration of the prepare pulse is thus meas- .ured by the time takenfor the switch SC to step from contact i to contact '4 plus the slow release period of relay ST which ,gives a total figure of Relay S at contacts s5 nectsthe code pulse to the line, this pulse being dependent for its composition on the setting of the switch DSA as fully described in the previously mentioned specification so that it is thus characteristic of the digit dialled. Relay S also at contact 81 short-circuits its high resistance left-hand winding to self-drive the switch SC to contact :9 where relay Z operates over its high resistance lower winding and at contacts 24 disconnects the code pulse from the trunk line. The

duration of the code pulse is measured by the time taken for switch SC to self-drive from contact 4 to contact 9 which is approximately 100 ms. Relay Z holds relays CNA and CNR at contacts 2] and at contacts 22 causes the switch DSA to self-idrive to its home position where relay Zreleases and at contacts 22 causes the switch SC also to drive to its home position, while at contacts 23 relay-CS is released.

If in the meantime the operator has dialled the second digit on to switch DSB, (notshown) relay CNR will be maintained operated in series with a relay CNB, .not shown, and accordingly when the switch SC comes into its home position it will again self-drive to contact -I where relay ST will re-operate to-send out the prepare pulse of WXYZ frequency followed by the code pulse which .is picked up from the setting of the Wipers of the switch DSB which is assumed to besimilar to the switch DSA already described.

It should be explained here that if, as :has been assumed, the digit dialled was 5, the interdigital pause provided between the two code digits transmitted to line will be measured :by 20 self-driving steps of the switch DSA, say 400 m.s., plus 16 self-driving steps of switch SC, say 320 m.s..giving a total of 720 ms. approximately. During this period five machine-generated pulses are delivered at the distant exchange to the incoming selector after which hunting must take place to select an idle trunk in the level selected. While the selector is hunting, the incoming decoding relays are released to receive the second prepare and code signals which will require a time period of 160 plus 100 ms. giving a total of 260 ms. which may be added to the 720 m.s. already mentioned to give a total of approximately 980 ms. for the complete interdigital pause during which the incoming selector must be set to the required level and perform its hunting operation.

If, however, the first digit dialled had been 6 to 0, a longer interdigital pause would be required to enable the incoming selector to perform its sequence of operations and this is derived as follows. Relay CNA under these conditions would :be operated over its right-hand winding in series with relay CNR so that when relay S operated,

bank and wiper DSAI.

set the cyclic function.

relay EP would operate and lock to earth over Accordingly, when the switch DSA reaches its home position, thus measuring 01f part of the interdigital pause, relay EP will hold during the slow period due to its shortcircuited upper winding and at contacts 6102 will cause the switch DSA to make another revolution. During this revolution relay EP releases but relay Z holds to bring 'about a substantial increase in the interdigitalpause. 'For example, if the digit O had been dialled, the .interdigital pause would be made up as follows: fourteen steps of the switch DSA plusan additional revolution making 39 steps all gives a period of approximately 780 ms. To-this must be added sixteen steps of the switch SC say 320 ms. plus a further 260 ms. representing the transmission time of the prepare and code pulses of the second digit giving a total interdigital pause of approximately 1,360 ms. The object of vthis extra pause period is to ensure that the distant selector has sufficient time to perform its level-selecting function plus its trunk-hunting function before the next decoded digit is transmitted to the succeeding switch.

When all stored digits have been transmitted in code, relay CNR finally releases and at contacts cnrZ opens the kick-on circuit for the sending control switch SC, while at contacts curl, Fig. 4, it brings up relay BS, Fig. 2, which has no functionat this stage.

Although four digit storing switchesDSA-DSD have been provided, it is possible that in practice a lesser number may be found satisfactory depending upon the speed at which storing and retransmitting in code can be accomplished and upon the number of digits to be dialled. As shown the digit storing switches DSADSD are taken into use in cyclic repetition, that is tosa-y, when the fourth digit has been stored on the switch DSD, the switch DSA which will by this time be normal is again taken into use to store the fifth digit and so the storage cycle repeats itself. With the ONA-CND digit storing circuit shown in Fig. 3, however, it is possible that if the fifth digit dialled is received before all the first four digits have been sent out in coded V. F. form, the DSA switch, on which the fifth digit is received, will take precedence and so will up- This trouble may be simply overcome by providing, in the CNR relay individual battery feeding circuits to the three relays CN-A-CNC, break contacts of relay CND which are paralleled by make contacts of each relay concerned. As regards relay CND this will remain directly connected to relay CNR as shown in Fig. 3. With these arrangements the operation in turn of the relays CNACNC is not interfered with and on operating they will lock independently of relay CND, but as soon as relay CND is operated in response to the fourth digit, none of the preceding relays can be operated in response to a fifth and subsequent digits. This condition obtains until the fourth digit has been sent out in coded V. F. form after which the battery feeding circuits of the three relays CNA- CNC are recompleted. If by this time the fifth digit has been dialled, the 'DSA switch will have been already set accordingly and relay CNA will now re-operate to provide for the sending out of this digit. Similar remarks would apply to the sixth and seventhdigits, while the eighth digit would function-on relay CND in the same manner as for the fourth digit. By this means it is contemplated that up to ten digits could be safely handled by the four digit switches DSADSD.

When the operator restores her dialling key at the endof dialling, the current in the'sleeve circuit is increased and the battery applied to the tip and ring conductors is removed shortly afterwards. Relay KR, Fig. l, thereupon operates and locks up at contacts lcrl while at contact lcrZ it releases relay A. Relays B and BR in turn restore after their slow periods and the former at contacts b3 advances thedigit distributors-witch DD to its mid positionpreparatory to the operation of relay AA at a later period. Relay BR at contacts br3 connects the earthed low resistance lower winding of relay RR into the sleeve circuit and though relay RR receives insufiicient currentto operate the supervisory lamp again glows under this condition. Relays M, MM, KR, CO, .FC and BS remain operated and the line condition is now such that the operator may listen to tones and if necessary speak without the necessity for a calledparty answer signalg but no supervision is given.

If the operator restores her cord circuit speaking key the sleeve circuit current is increased. to a value sufficient to operate relay RR and this relay at contacts rr2, Fig. 1, maintains a suitable V. F, termination on the trunk line, in place of the operator's telephoneset.

When the called; party answers, the incoming relay set at the distant exchange transmits 140 m. s. of Y frequency over the trunk followed by a, space period of 360 m. s. and this signal is repeated until acknowledged by the transmission of an X signal from the outgoing relay set. Upon the reception of the Y frequency, relay Y operates in the YF receiver VFR shown schematically as a dotted rectangle in Fig. 2 and opens the circuit to relay BS which releases after a slow period of 80-110 m. s. To release relay BS therefore the Y frequency must be applied for a sufficient period and. when relay BS has released, relays MS and MT are operated inturn and hold for the remainder of'the Y pulse. When the Y pulse is finished, relay BS re-operatesand at contacts bsl opens the circuit for relay MS which has a release timeof 300-400 m. s. Relay MT has a release time of 200-300 m. s. If the break period is of the correct duration, namely 360 In. s.,then thisperiod plus'the 80-110 m. s. release time of relay BS, which releases in response to he next Y pulse, will be. suflic-ient to cause relay MS to release but not relay MT. Hence on the reception of the next Y pulse the "subscriber answer relay SAwill be operated over contacts sy2, sal, sb2, ms], mtl, syl, bsl, ac5, yl and cm! to earth. At the end of the Y pulse, or when relay MT releases, relay SB which has been short-circuited hitherto operates in series with relay SA and locks.

Relay SB operates relay AA, Fig. 3, in the selfdriving circuit of theswitch DD and relay AA at contacts aa2, Fig. 4, reoperates relay CS and at contacts aal, Fig. 2, applies an X pulse acknowledgment signal to the outgoing trunk. The duration of this acknowledgment signal is measured by twelve steps of the switch, DD plus the release time of the relay AA which releases when the DD switch reaches the home position and which in turn releases relay CS. When the Xpulse is received at the distant incoming relay set, the transmission of the Y pulses ceases and relay BS remains operated.

' It should be mentioned that relay SA at contacts sa3, Fig. 1, connects battery via resistances YP and YQ to the ring of the jack for through supervision and alsoatcontacts safi, Fig. 1, removes the short-circuit by way of the lower winding of relay RR from the high resistance winddistant exchange transmits Y pulses of the same typegas for thecalled party answer signal.

At the outgoing end relays M, MM, KR, CO, FC, BS, SA and SB are held operated and the switch TS is in position 6. Accordingly the first m. s. pulse of Y frequency releases relay BS and operates relays MS and MT as already described. During the following 360 m. s. break period relay BS is operated and releases relay MS but not relay MT so that when the next Y pulse is received and relay BS again releases, during the slow release period of relay MT relay SY operates over contacts $172 and at contacts syl completes a locking circuit for itself-for the remainder of the Y pulse. Relay SY also at contact sy3 operates relay SZ and at contacts syZ releases relay SA which at contacts sa3, Fig. 1, disconnects battery fromthering of the jack for backward supervision, and at contacts saB restores earth via the low resistance winding of relay RR to the jack sleeve circuit to re-light the operators calling supervisory lamp. g

As long as the Y pulses persist, relay SY remains held because its release time is 400-450 m. s., i. e. longer than the 360 m. s. breakperiod and consequently if the called subscriber should again remove his receiver, the Y pulses will cease and after its slow period relay SY releases and disconnects relay SZ. During the slow release period of relay SZ relay SA re-operates and locks in series with relay SB to restore the speaking conditions.

When the operator clears by removing the plug from the .jack in response to the clear signal, relays M and M in the sleeve circuit release and the latter releases relay KB. The release of relay MM at contacts mm2, Fig. 4, steps the switch TS from position 6 to position 1 by way of bank TS3, whereupon relay BR operates in series with relay SR over bank TS4. Relay SR on operating at contacts. sr3 re-operates relay CS and these relays together bring about the application of an X frequency pulse forwardly over the trunkby way of contacts sr2, csl and 082. Since relay SB is operated, the switch TS continues to self-drive from position I to position I5 via bank TS3 and contacts sb4 and then steps by means of interruptedearth on lead 13 from position I 5 to position [9 via bank TS5. Relay FXY is then uperated over bank 'I'Sfl, contact l9, and serves to disconnect the X frequency at contacts .fxyl, Fig. 2, after a period of application of two seconds and at the'same contacts to connect up Y frequency to the trunk. When the wiper leaves position ill of bank TS I, relays SR and BR are causedto release after their slow periods and on the release of the latter, earth is extended over bank TS3 to step the switch to position 20. Relay FXY then releases after its slow period and thus terminates the Y signal after a period of application of 300 m. s. and also releases relay CS. Switch TS then steps from position 20 to position 23. via bank TS3 and contacts acl, and then slow -steps from earth on lead l3 over contacts 23 and 24 via bank TS5 to reach its home position where relays CO, FC and SB release. During the forward; application of Y frequency relay BS will have released and at the end ofthe signal relays SY and SZ release in turn. Relay QQ disconnects the busy condition from the sleeve of the jack at contacts 005, Fig. 1, and; as earth is also removed from the P conductor leading to the selector levels when the TS switch reaches its home position the relay set is free for further use.

Consideration must now be given to the condition when the operator clears before receiving the answering signal or in face of any tone (ringing, busy or NU) or on a non-metered call. Any of these conditions are characterised bythe nonoperated condition of relay SB so that when the operator withdraws the plug and releases relays M and MM, the switch TS is caused to slow step from position I to position l9 byway of interrupted earth supplied over lead [3. Accordingly, therefore, the X pulse which precedes the Y pulse is lengthened from 2 to 6 seconds, after which it is followed by the normal 300 m. s. Y pulse.

The object of the long X pulse under these con- 13 ditiOns is to ensure that the clear signal will be received at the distant incoming end when, for example, NU tone is being transmitted backwardly. The NU tone is transmitted for five seconds and disconnected for one second and this :7

arrangement ensures that the clear signal which is being extended forwardly shall be able to break inand register at the incomingrelay set.

When the outgoing relay set is taken into use over the negative, positive and P trunks extending from selector levels, the call may have been originatedeither by a subscriber on the same exchange or via an incoming V. F; relay set from a distant exchange, say 13 In the first case the subscribers dialled impulses are converted by the switche DSA-DSD into VF prepare and code pulses; while in the second case, where through working is required, the outgoing relay set merel transmits the X seizing signal-"to the idstant' incoming VF-relayset afterwhich further prepare and code pulses are. transmitted directly through the outgoing relay set to the distant incoining VF= relay set without modification.

' In the case when the outgoing relay-set is taken into use from asubscriber in the same exchange, earth extended forward overthe private conductor? operates relay-SR, Fig. 4, which causes the switchTS toself-drive over bank TS3 to the first position where'it-operatesrelays CS and Relay C0 operates relay BS; and drops relay SR, while relayFXYextends a 100 m. s. X seizing-pulse forwardly over the trunk to the distant incoming relay set. Relay FXY also causes switch TS to self-drive-to-position 3 where relayFXY isdisconnected and after itsslow period-releases toterminate the X pulse. Relay FC is then operate-d and-locks up and serves'to step TStopositionA from which it slow steps from interrupted earth on conductor; l3; to positionfi Relay FC also brings about-the operation of relay A, Fig. 1, over the calling subscriber s loop-and relay A in turn brings up relaysB- and-BRto prepare the circuitforthe reception of thedialled impulses. From this point thecall proceeds as for an operator call alreadydescribed; that is-to say, relay-A responds to-thedialled-impulses which are stored-via the digit distributor switch-DD on the coding switches DSA--DSD. Subsequently under the control ofthe sending 'sw-itchSC the coded digits-aretra-nsmitted toline in. theform of prepare and code pulsesand are received on decoding apparatus at the incoming relay set in the distant exchange. Relay CO under these, conditions busies the manual board jack by. connecting. resistance battery to the sleeve-cir 1 2 cuit. When the called partyanswer signal is received in the form of repeated 140 m. s. Y? pulses as already described; relays Ms and MT check the length and spacing of the pulsesand ifthese are correct allowrelays SA and SB to operate. Relay SA at contacts saA and sa5, Fig. 1, reverses the A relay connections towards the call-- ing partyfor; supervision, while relay SB operatesrelay AA to cause an X pulse acknowledgment signal to be transmitted forwardly to the distant exchange. This signal lasts fora period measuredby the homing time of the switch DD-via thelow resistance relay plus the slow release period of relay AA which is disconnected when switch DD arrives at its home position. The reception of the X" pulse acknowledgment signal at the distant exchange causes the backward Y" answer signal tobe disconnected and conversation may now takeplace.

In the case of a call via selector levels from an incoming VF relay set, earth is connected toboth the negative andpositive lines and serves to operate relay AG; Fig. 1, while the normal forward earth on the P conductor operates relay-- SR. Relay'AQ at contacts ac2 and ac3'connects the negative andpositive lines from the selector level through to the outgoing-trunk linewhile relay SRsteps switch- TS from the home position to contact I where relays CO, CS and FXY areoperated-a Relay-CO operates-BS, drops SRand' disconnects the trunk line termination TER. Relay FXY extends a 100 m. s. Xseizing pulse for-. ward overthe trunk to the distant exchange and steps the switch Ts to contact 3'. In this position relay- FXY is disconnected and when it re-- leases after-its slow period the X seizing pulse is terminated. Sincerelay AC isoperated, switch TS self-drives-- to position 20 via bank TSZ and remains; there until the end of the call so that as it leaves position l while relay FXY is still'operated, relay F6 is not operated. The incoming- VFprepa-re and code pulses are thus extended directly throughthe outgoing; relay set to the distant exchange; Relay CQ busies thejack by connecting battery to the sleeve circuit, whileswitch TSat bankTSd holdsearth'on the P wire to busy the outgoing; relay set against seizure oventh'e selectorlevels. When-the connection is setup and thecalled party-answers, repeated Y pulses are extended from'the' distant exchange directly through theoutgoing-relay set andare; acknowledgedby-a 440m; s. X acknowledgment signal extendingfrom-the callingend of the connection directly through the outgoing relay set.- It-will benoticedthat the Y relay of the-VF receiver' VFR isoperated from the Y pulse but as relay AC is operated atthis-time theresponse of relays'MS, MT. SA and SB is prevented by contacts1ac5, Fig. 2. When the calling end of the connectioniscleared; earth isremoved from thenegative and positivelines thus releasing relay AC which allows switch TS to self-drive overcontacts 20-23 viabank 'rs3- after which it a slowsteps to its home position.

If the operator inadvertently withdraws the plug while the calledparty is still 'connected and possibly is speaking at rthistime, switch TS will; run homefromposition 6 to extend the clear signal of two seconds'X followed by 300 In, s;,Y'

and release the equipment in the outgoing, relayv set.- If however the called-party is, still talking at this time; any echo suppressor in the connection will be held; against theclearing; signal which may =the refore fail to get throughto the distant end of therconnectionz It is therefore comprising as usual 140 m. s. of Y frequency followed by 360 m. s. space period. The first Y pulse operates relays MS and MT and during the first 360 m. s. break period relay MS releases so that at the commencement of the next 140 m. s. Ypulse relay SA is operated and at contacts 3012, Fig. 4, causes the switch TS to step from its home position to contact I. Relay SB is operated and locked when the Y pulse isfinished and from then on the switch TS makes a complete revolution during which the clearing signal comprising a two-second X pulse followed by a 300 m. s. Y pulse is transmitted to the trunk line to release the distant equipment. It should be mentioned that during the revolution of the switch TS the X seizing pulse is again transmitted while the switch is passing over the early contacts of the bank, but under these circumstances this signal produces no switching function at the distant exchange.

Referring now to the circuit changes produced at the incoming relay set, Figs. and 6, when the 100 m. s. X seizing pulse is received over the trunk line from the outgoing relay set, relay IX, not shown but assumed to be located in the valve receiver IVliRyoperates and in turn brings up the relief relay XR. Relay XR at contacts m3 operates relay K which locks upat contacts kl, at contacts k2 operates relay PY, Fig. 6, and at contacts k4 extends earth forwardly over the P conductor to the incoming selector to busy this switch. At the end of the X seizing pulse, relay IX in the valve receiver releases and in turn drops relay XR which at contacts :rr4 operates relay NN. Relay NN at contacts nnfi further earths the P conductor extending to the incoming selector, at contactsnnl operates relay KK over the negative line in series with one winding of the A relay in the incoming selector and at'contacts nn3 operates relay GX, Fig. 5. Relay GX at contacts 9034, Fig. 6, connects battery by way of a high resistance YF to the centre point of the repeating coil which finds a circuit to earth at the centre point of the transformer which connects the valve receiver IVFR to line. A small current is thus causedto flow by way of various relay contacts connecting with the line circuit which are thus wetted to prevent coherer trouble. No further operations take place at this stage and the incoming selector is now ready to receive the train of impulses.

" When the outgoing relay set transmits the 160 m. saprepare pulse of WXYZ frequency as already described, relays IW, IX, IY and IZ operate in the V. F. receiver and in turn bring up their relief relays WR, XR, YR and ZR. Over the series connected contacts :01'4, yrd, 213 and wr3 relay CA is now operated, whereupon the botliway line termination comprising resistances YB, YC, YJ, YD and YE and condenser QA which normally imposes a loss of the order of 3 db, is converted into a combined line terminationand infinite attenuation loss pad which prevents the passage of signals so that the line is blocked at this point. The purpose of this arrangement will be described later in connection withtandein calls.

-' The prepare pulse, as already described, has

a duration of approximately 160 m. s. and is followed immediatelyby the code pulse which comprises frequencies W, X, Y and Z in suitable combinations having a duration of'lOO m. s. In the example in question the digit 5 comprising the frequencies W and Z is assumed to have been transmitted so that relays IX and IY are released and in turn drop their relief relays XR and YR. The short-circuit is thus removed from relay CB which immediately operates from the earthed contacts M12 in series with relay CA, andat contacts c174 and 0191 looks relays WR and ZR corresponding to the code which has been transmitted. Relays WR to ZR have a pyramid chain of contacts (not shown)v connected to the bank SS2 of the sender switch SS, and since the code relays WR and ZR are operated at this time, earth is connected to the sixth contact of the'bank SS2 in order to terminate the sending after five impulses have been transmitted to the incoming selector as will appear subsequent: 1y. Relay CB also at contacts c225 releases relay GK and operates relays PC and P, the latter looking over its own contacts. Relay PC at contacts pcI operates relay CC which at contacts ccI prepares a circuit for relay IG which operates when the constantly driven impulse springs 66%M next open. Relay IG at contacts z'g2 drops relay K and at contacts igI extends the impulse springs 66%M to the driving magnet SSM of the sender switch. Relay IG also at contacts ig2 transfers the forward, holding loop extending to the selector to the impulse springs 33%M which are closed at this time, since they are out of phase with the magnet impulse springs 56%M'which have just opened to bring about the operation of relay IG. Accordingly, the sending sWitchSS now steps its wipers until they encounter the marking earth connected to the sixth contact of bank SS2 over contacts of the coding relays WR and ZR, while at the same time the impulse springs 33 %M transmit five impulses to the incoming selector as described in the previously mentioned specification. Relay 45 SZ operates when wiper SS2 comes into its sixth position and locks over contacts seI to the homing. bank SSI. Relay SZ also at contacts s22 short-circuits the 33%M springs to terminate the impulses to the selector and at contacts 823 50 releases relays CA and CB which have been held in series. Relay CB at contacts cbt drops relayIG which at con-tacts ig4 causes the sending switch SS to.,-home, while the holding circuit for the selector is again transferred to relay KK 55 which re-operates. Relay CB also re-operates relay GX and releases relays WR and ZR as Well as relay PC after its slow period which is followed by the release of relay CC also after its slow period. Relays K, PY, NN, KK, GX and P 60 remain held.

After a pause long enough to permit the incoming selector to hunt over the selected level, which pause is determined in the outgoing relay set as already described, the next prepare and.

65 code pulse is transmitted and the operation is repeated until all the impulse trains have been transmitted. It will be appreciated that the prepare pulse of WXYZ frequency ensures that any echo suppressors in the connection are switched 70 into the correct direction and provides a test that all the responding relays in the incoming V. F. receiver are operating satisfactorily. If this is not so it will be impossible for a complete connection to be set up and there is no danger of 75 connection being made to the wrong party.

The connection is thus fully set up and the called party is rung. When the called party answers, battery is reversed over the forward trunk so that relay KK releases and relay EE operates. Relay EE at contacts eeZ brings up relay IR which at contacts irZ-ir4 alters the connection to the loss-pad to render it inefiective and at contacts irl drops relay K. Relay K opens the circuit of relay PY and during the slow release period of the latter, relay MA is operated and locks up over contacts mal and gx'l. Relay MA at contacts WW3 and mad, Fig. 5., connects up the secondary winding of the transformer VSF to the backward trunk and at contacts ma2 connects relay FY, Fig. 6, to conductor 14 which extends to interrupted earth having a periodicity of 140 m. s. on and 360 m. s. off. Relay FY therefore pulses to the interrupted earth and extends backward over the trunk repeated 140 m. s. Y pulses with 360 m. s. spacing.

When this signal has been accepted at the outgoing relay set, the latter returns a 440 m. s. X pulse acknowledgment signal which operates relay IX in the valve receiver and in turn the relief relay XR. Relay XR at contacts m3 opens the circuit of relay GX and operates relay GY. Re lay GX' releases after its slow period and at contacts grl drops relay MA which connects the line through for conversation and disconnects the repeated Y signal. Relay GY in operating cuts the earth pulse connection to relay FY. Since the repeated Y signal is measured at the outgoing relay set both for length and spacing, it will be appreciated that this gives the desired degree of irmnunity against false Y signals which may be generated by speech or line noise. Similarly, the X acknowledgment signal is measured against the release time of relay GX (300-400 m. s.) to provide the required degree of immunity against spurious X frequencies on the line. At the conclusion of the acknowledgment signal, relay XR releases, relay G-X re-operates and relay GY releases.

When the called party clears, battery is again reversed over the forward line circuit so that relay KK re-operates and relay EE releases. Relay EE at contacts eeZ drops relay IR to re-introduce the line termination and also operates relay MA. Relay MA connects interrupted earth to relay FY which pulses to send back to the outgoing relay set the clear signal comprising 140 m. s. Y pulses with 360 m. s. spacing. As already explained, in the outgoing relay set this signal results in the release of relay SA which disconnects battery from the ring of the outgoing jack and lights the calling supervisory lamp at the operators position. Relays NN, KK, GX, P and MA remain held,-while relay FY is slowly pulsing;

When the operator clears, the outgoing relay set sends a clear signal comprising a two-seconds X pulse followed by a 300 m. s. Y pulse; The X pulse operates relays 1X, XR and GY in the incoming relay set and the latter opens the circuit for relay F'Y to terminate the transmission of the called party clear signal. Relay XR also opens the circuit of relay GX sufficiently long for it to release whereupon it drops relay MA and operates relay CC over contacts 9333. When the X pulse is finished, relays IX, XR and GY release and relay CC commences to release slowly. The 300 m. s. Y pulse now follows and serves to operate relays IY, YR and CR Relay CR locks to the earthed contacts 172' and transfers the hold ing circuit for relay NN to the Y pulse and also connects earth to the P conductor extending for- Wardly to the automatic switches. When the Y pulse is finished, relay NN releases and drops relays P and K which open the holding circuit for relay CR, The forward holding loop is opened and the earth on the P conductor is removed on the release of relays N and CR thus initiating the release of the operated automatic switches, and the incoming relay set is now free for further use.

In regard to tones which may be encountered during the setting up of the call such as ringing, busy and NH, these are passed back along the trunk line in the normal manner except that the line termination which is in circuit under these conditions imposes a 3 db loss but this does not seriously reduce the tone level. The NU tone is broken at the source for one second in every six to allow the release signal to obtain control of any echo suppressors which may be in circuit and thus get through to its destination. As explained above if the release signal is sent, before the called party has answered, it comprises 6 seconds of X frequency followed by 300 m. s. of Y frequency. This long signal insures a certain break-in during the I second silent period of the NU tone.

Considering now the operation of the incoming relay set under these conditions, since the called party has not answered, relay K will still be operated and hence the X signal operates relay PC which brings up relay CC and from this point the release procedure is identical with that previously described for the normal operator clear.

In case the incoming selector switches through to a short-circuited trunk, arrangements have to be made to prevent this short-circuit masking the VF receiver and so preventing the incoming relay set from accepting the release signal of 6 seconds X followed by 300 m. s. Y. In the face of a short-circuit from the selector, neither of relays KK and EE is operated so that on the release of relays CB, PC and CC in turn relay SC operates over contacts nus, 1001, 003, kkl, eei and p4 and locks up at contacts .901. At contacts s02 and s03, Fig. 6, relay SC disconnects the forward trunk leading to the short-circuit and under these conditions the line termination is maintained since relay IR is not operated and the clearing signals can be satisfactorily received from the outgoing relay set. I

In the case of tandem calls over two VF trunks in series, for instance from exchange B to ex change D, Figs. 7' and 8, the following operations take place. The digits dialled cause the selector to seize an outgoing relay set to another VF channel so that battery is returned from the AC relay in this outgoing relay set over the negative and positive lines to operate both relays EE and KK. Relay EE operates relay IR as already described in connection with. the called subscriber answer condition, and relay IR releases relay K. As relay K is also operated at this time, however, relay PY is held operated and no circuit is completed to operate relay MA and initiate the sending of the repeated Y answer signal backwardly over the trunk. With relay IR operated the loss pad and line termination are removed at contacts ir2-ir4 while any circuit for relay CB is disconnected at contacts 2'15' so that the following VF' signals pass directly through the incoming relay set without any conversion or repetition. Under these conditions before the in-' coming relay set can be releasedr it must receive a long X pulse to drop relay GX followed at the proper interval by a short Y pulse to operate enough to bring about the-release of relay GX.

Furthermore, the 440mm; X pulse acknowledgment signal which is sent from the originating end in response to the called party answer signal will bring about the release of relay GX, but as this is not followed by a Y signal thetemporary release of relay GX brings about no material change in the condition of the incoming relay. set. When the release signal comprising along X pulse followed by a short Y. ulse is received, the incoming relay set releases as already described.

In the case of tandem calls over VF and D. C; trunks in series, for instancefrom exchange B to exchange E, when theD. C. outlet is'seized in the second exchange (C), access i's'had to the outgoing side'of the normal auto-to-auto repeater AA RS, Fig. 7, which is thus cutout of circuit in order to avoid two impulse repetitions in the same exchange. The incoming relay set therefore extends earth forwardly over the P conductor to holdthe selector train in the second exchange (C) and also accepts code signals and transmits forward loop impulses to set up the automatic switch train at the third exchange (E). When the called party connected to the thirdexchange answers, battery is reversed over the line tooperate relay BE in the incoming relay set at the second exchange (C) which thereupon sends repeated Y pulses back to the first exchange (B) as already described. Thefurther operation and release of the incoming relay set are as already described.

In the case'of tandem calls over VF, D. C. and VF trunks inseries for instance from exchange B to exchange G, when connection is made with the outgoing relay set in the third exchange (E), battery over both lines is extended backwardly over the trunk to operate relays'KK and EE in the incoming relay set at the second exchange (C) which thereupon cuts out its repeating apparatus and provides a straight-through pair of trunk as already described. Accordingly, VF signals from the outgoing relay setin the first exchange (B) now pass directly without repetition to the incoming relay set at the fourth exchange (G) which converts them to D. C. im-

In the case of tandem calls over VF, D. 0., D. C.

and VF trunks in series, for instance from exchange B to exchange H, a different set of conditions arises in that an auto-to-auto repeaterwill be taken into use at the third exchange (E) which prevents battery on, both lines from the outgoing relay set in the fourth exchange (F) finding a circuit back to theincoming relay set in the second exchange (C) to cause this to provide a straight through pair of lines as was the. case in the VFD. C.-VF connection. In the absence of any meansto prevent it therefore, there is a danger'that the V.'F.code signals from the originating exchange may be received both at the incoming relay set in the second exchange and the incoming relay set in the fifth exchange (H) and this would result in two train of impulses being delivered for each digit. This explains the necessity for the provision of the infinite attenuation loss pad in the incoming relay set.

Considering now the circuit operations, it will be remembered that when the VF prepare impulse is received at the incoming relay set at the second exchange (C), relay CA operates almost immediately and provides an infinite attenuation loss pad which in effect-short-circuits the trunk across a resistance bridge to prevent the passage of V. F. signals beyond the incoming relay set. However, durin the operate time of relay CA at the incoming relay set in the second exchange (C), relay CA in the incoming relay set at the fifth exchange (H) may operate but will at once release when the CA relay at the first incoming relay set has operated and inserted the loss pad in the trunk. It will be recalled that relays CA and CB lock in series during the reception of the code pulse and while the loop impulses are being transmitted so that neither the prepare nor the code VF signals are transmitted to the incoming relay set in the fifth exchange.

It will be appreciated that the desired block-.

i In the case of non-metered calls which are usually of the enquiry typesuch as service, interception, enquiry or speaking to B operators at manual exchanges, it will be appreciated that with the circuit arrangements as described conversation can take place immediately without the extension of an answer signal and therefore the automatic metering of non-metered calls avoided. It will be seen that a 3 db loss pad remains in the connection-under these conditions owing to the absence of any'battery reversal which would operate relays EE and IR but this does not unduly interfere with speech and furthermore if more than one incoming relay set is included in the connection the loss pad is removed in all incoming relay sets except the one in the terminating exchange where no battery is returned over the negative and positive lines to effect the removal of the pad, and consequently the overall extra loss never exceeds 3 db on this type of call.

Referring now to Fig. 9, this shows the modifications necessary to the incoming relay set to instead of negative, relay TH is operated via the metal rectifier MBA and locks up. Relay IR; is also operated from relay EE and with all four relays operated the line termination and loss pad is disabled and a straight through connection is provided.

In other circumstances where the incoming relay set is the terminating one in the connection, relay KK will be operated while the call is being set up. If a busy line is encountered, busy tone is returned as explained and if this is accompanied by busy flash batteryon the positive line relay EE is also operated. Since however, relay TH is not operated under these conditions since the battery in question is a negative battery, relay IR in operating does not disable the line termination and loss pad, so that balanced conditions are maintained to the line amplifier which is prevented from singing during the busyflashcondition.

What we claim as new and desire to secure by Letters Patent is: 1,. In a telephone system wherein a connection is established to, a called station by automatic switches controlled over a voice frequency signaling trunk including means responsive to a disconnect at the calling end to. transmit a forward signal to release said switches, a source of impulses comprising alternating current ofdetermined voice frequency interrupted at predetermined intervals accessible to the called end of said trunk, means in said trunk responsive to a disconnect at the called station to connect said source of impulses to the trunk as a clearing signal whereby the calling station disconnects and the forward signal is transmitted, and means responsive to said forward signal to disconnect the clearing signals from the trunk before the said switch release is initiated.

2; In a telephone system wherein a connection is extended over a trunk in which the functional operations including superyisory and, releasing Q 'LS l Q 031 8 3 0 2 are cQ ll d y s snals r a plurality of sources of alternating currents of different frequencies, means in said connection to transmit; impulses of said currents of deterin d: f equen y dur tion and spa n over d trunk in accordance with said functional operations'controlled thereover, a signal comprising impulses one of said frequencies repeated at a determined rate to control the supervisory functional operation, a second signal comprising another frequency of determined duration, means in said trunk to transmit said second signal to stop said supervisory signal and means in said connection to transmit a subsequent pulse of said; first signal within a determined spacing, after said stoppage signal is effective to control the functional operation of releasing said connection.

3. In a telephone system, a connection includinga trunk line over which voice frequency signals are transmitted to establish a connection and in which a clearing signal of voice frequency is normally sent tothe calling end when thecalled station hangs up and a release si al of Voice frequency is then transmitted from the calling end to release the connection, the provision of means responsive to a release signal transmitted from the calling end before a. clearing signal. is received for causing the transmission of the clearing signal to act as a release signal to release the connection.

i. In a telephone system, a plurality of voice frequency responsive equipments each associated with a trunk line and each normally responsive to received voice frequency coded signals to translate the same into direct current impulses to operate automatic switches to extend a connection, means in eachyequipment operated only in case a second trunk is seized having such equipment therein in a tandem connection for preventing the translation of received voice frequency signals in the first equipment and causing the transmission of the received signals to the second seized trunk without translation, said meansresponsive only to a flow of current over th two speaking conductors in parallel.

5. In a telephone system, a trunk line, means for transmitting over said line a plurality of coded signals each'comprising impulses of a plurality of different voice frequency sources and a varying number of said frequencies in accordance with received signals and other control signals of varying number of impulses of determined frequency duration and spacing in accordance with other received signals, a plurality of receivers connected successively to said line and responsive to a received signal for translating it to a signal corresponding to said received. signal, a blocking meanscontrolled from each of said receivers to prevent the further passage of said received signal current over said line to the successively connected receivers, means in each receiver effective on certain of said coded signals for translating said signal and operating said blocking device to prevent said other receivers from effectively completing said particular code translation and means in each receiver responsive to other received signals to complete the corresponding translation without operating said blocking means.

6. In a telephone system, a trunk line including voice frequency responsive equipment, means for extending av connection thereto and for transmitting coded digit signals of voice frequency currents thereto to extend a. connection thereover and for transmitting other coded voice frequency signals thereto, a blocking device in said trunk, each digit signal including a portion effective to include the blocking device in the trunk to block further progress of voice frequencies over the connection, and each other signal passing over the connection without blocking.

7. In a telephone system, a voice frequency signaling trunk terminated on a responsive repeater including means for transmitting and receiving over said trunk a signal to seize said repeater and another signal to release said repeater, a. switch operating line controlled from said repeater, means responsive to the seizure of the repeater to connect said line to said trunk, said repeater responsive to other voice frequency Signals received over the trunk to control a connection, and to repeat said release signal thereover, holding equipment in said repeater controlled over said connected line to prevent a false release of said trunk before said line is disconnected, means effective in the event of a short circuit on said line whereby said holding equipment and said other signals are disabled, means insaid repeater effective only when said equipment is disabled to disconnectsaid line from said trunk to permit said release signal to be effective to release said repeater.

CHARLES GILLINGS.

CHARLES: EDMUND BEALE. TESEO BRUNO DAN'I'E TERRONI.

Images