US2355215A

US2355215A - Telephone system

Info

Publication number: US2355215A
Application number: US464811A
Authority: US
Inventors: Myron C Goddard
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1942-11-06
Filing date: 1942-11-06
Publication date: 1944-08-08
Anticipated expiration: 1961-08-08

Description

Aug. 8, 1944. M. c. GoDDARD 2,355,215

TELEPHONE SYSTEM Filed Nov. 6, 1942 5 Sheets-Sheet l Aug. 8, 1944. M. c. GoDDRD TELEPHONE SYSTEM Filed Nov. 6, 1942 5 Sheets-Sheet 2 w .mi

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, rroRA/EV Aug. 8, 1944.

/A/TERCEPT/NG TRUNK CCI J7' M. C. GODDARD TELEPHONE SYSTEM 5 sheets-sheet s 20a j 204ij llo.:

/Nl/EA/TOR By M C. GODDARD Wfnma.

Aug. 8, 1944. M. c. GODDARD TELEPHONE sYsT'EM Filed Nov. 6, 1942 5 Sheets-SheetI 4 i /A/VEA/ TOR M C. GOUDA RD .aut .30%. Exil LYNN@ 150th QL I oww MSN i mm mw AZTOR/VEV Aug. 8, 1944.

M. c. GODDARD TELEPHONE SYSTEM Filed Nov. 6, 1942 5 Sheets-Sheet 5 Evi /NVENTR By M C. GODARD TTRNEV Patented Aug. 8, 194,4

UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Myron C. Goddard, Garden City, N. Y., asslgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York This invention relates to telephone systems and particularly to systems comprising impulse controlled automatic switches for completing connections between calling and called lines.

Objects of the invention are the improvement of call intercepting equipment in automatic telephone systems and the provision of means for intercepting unassigned code calls at the banks of impulse controlled selectors which are used in establishing connections under the control of a registered sender.

It is usual in automatic telephone systems comprising impulse controlled selector and connector switches to connect intercepting trunk circuit equipment to the terminals which are selected in response to the dialing `of unassigned codes and to provide trunk nders for connecting seized intercepting trunks to an operators position in the same or another oiiice. It is also known to so arrange the intercepting equipment and circuits that the signaling of the intercepting operator is effected responsive to ringing current transmitted from the connector on calls intercepted in the banks of connectors, the ringing being tripped at the same time that the calling signal is operated. If now, an impulse controlled selector switch selects a set of terminals connected to an intercepting trunk under the control of impulses being transmitted from another office by a register sender for instance on a call from a -toll operators position at which a key-set is provided for registering the called number, it is necessary to provide means individual to a seized intercepting trunk circuit for absorbing the trains of impulses transmitted by the register sender after the selector has `seized the intercepting trunk and before the connection is extended by a trunk finder to an intercepting operators position. If the selector Which seizes an intercepting trunk is a toll preceding selector, the operation of a trunk finder to extend the connection to an intercepting operators position may be effected responsive to ringing current transmitted by the register sender after the digit impulses have been transmitted, in which case, the operation of the signal at the intercepting position may be effected by ringing current transmitted from the intercepting trunk circuit, the ringing being tripped at the same time that the signal is operated prior to answer of the call by the intercepting operator. If the selector which seizes an intercepting trunk is a toll transmission selector, the operation of a trunk finder to extend the connection to an intercepting operators position may be effected immediately mitted by the register sender, the transmission of ringing current by the intercepting trunk to operate the calling signal at an intercepting operators position being controlled by the selector in the same manner in which the selector controls signed codes in the banks of selectors in a dial oice, which selectors are employed in completing calls including calls established under the control of a register sender, as in the case of calls from a toll operators position equipped with a key-set. A feature of the invention is a trunk circuit arranged to measure oii a predetermined minimum interval of time after seizure before extending the connection, to interrupt the measurement of the interval of time responsive to a train of dial impulses, to start the measurement of a new interval at the end of a train of impulses, and to extend the connection when the measurement of an interval is completed Without interruption.

Another feature of the invention is an intercepting trunk circuit arranged to absorb trains of digit impulses and to effect the extension of the connection to an intercepting operators position in response to ringing current received after the last tra'm of impulses.

A clear and complete understanding of the invention will be facilitated by considering a system in which the invention and its features are embodied, one such system being represented schematically in the drawings which form a part of this specification. The invention is, however, not limited in its applcation to the particular system shown in the drawings, but is generally applicable to automatic telephone systems and the intercepting equipment therein.

Referring to the drawings,

Fig. 1 shows a toll office comprising an operators telephone set and other position equipment, a cord circuit CDI, jacks AJ I and OJ I, outgoing trunk circuit I0, a link circuit 20 and a keypulsing register sender 30; Fig. 1 also shows a dial TPS intercepting trunk circuits ITI, ITZ and ITS; and r after all of the digit impulses have been trans- Fig. 5 shows a trunk nder TFI and a trunk edition of Automatic Telephony by Smith and Campbell for a clear and complete description of the structure and operation of such switches when used as selectors and, connectors. Reference may be had to the .patent to R. L. Stokely No. 1,799,654 of April 7, 1931, for a description of a two-motion step-by-step switch when used as a finder switch. The banks of each of these step-by-step switches is represented in the drawing by two or three sets of terminals. The toll preceding selector circuit 'IPS may be similar to the selector circuit shown in Fig. 3 of the patent to R. L. Stokely No. 1,474,008 of November 13, 1923. 'I'he toll transmission selector circuit TTS shown in Fig. 2 is arranged for immediate ringing; but the intercepting trunk circuits ATZ and' IT2 are also adapted for use with toll transmission selectors which are arranged for delayed ringing under control of the toll operator. Reference may be had to the aforementioned patent to R. L. Stokely for disclosure of a toll transmission selector in which ringing is started by the operation of a ringing key at a calling toll operators position. The plugging up line circuit PL and intercepting trunk circuit IT5 are similar to like designated circuits disclosed in detail in the patent to E. D. Butz, No. 2,021,286, granted November 19, 1935. The intercepting trunk circuit IT2 is similar to the trunk circuit ITI and the auxiliary trunk circuit ATZ is similar to the trunk circuit ATI.

Assume now that an operator in the toll office answers an incoming call by connecting the answering plug API of cord CDI to the answering jack AJ I, that the calling plug CPI is connected to jack OJ I of outgoing trunk circuit I0, that the trunk circuit I0 is connected through a link 20 to a register sender 30, and that the called number is registered by operation of the operators key-set in the register sender, all in the manner described in the aforementioned patent to I. H. Henry. Assume further that the toll preceding selector TPS is operated under the control of the first train of impulses transmitted by the impulse transmitting contact of relay 35 of the register sender to select a corresponding level of the terminal bank and is automatically operated to select a set of terminals therein connected to an idle trunk or idle toll transmission selector, that the selected level corresponds to an unassigned code, and that the selected terminals 44|, which represent such a level, are connected to the auxiliary intercepting trunk circuit ATI.

Operation of the cut-through lrelay (not shown) of selector circuit 'IPS completes a circuit from battery through the llower winding of relay |06, lower back contact of relay |05, conductor |02, -middle terminal of the terminal set 44 and brush 42 of selector TPS, conductor I2 of outgoing trunk circuit I0, conductor 22 of link circuit 20, conductor 32 of register sender 3lll, upper back contact of relay 34, contact of impulse transmitting relay 35, winding of polarized relay 36, lower back contact of relay 34, conductors 3|, 2| and II, brush 4| and engaged terminal of terminal set 44, conductor IOI, upper back contact of relay |05 and upper winding of relay |06, to ground. The line relay |06 is operatively energized by the current in this circuit but polarized relay 36 of the register sender is not operated since the current is not in the operating direction. The operation of relay |06 con-- and relay |08 connects ground to conductor |03 to hold the toll preceding selector TPS in usual manner. The oir-normal springs ||2 are actuated when the brush moves out of normal position. Before brush III reaches the fourth terminal of its bank, relay 35 of register sender 30 starts to send the next train of impulses, lthereby causing the alternate release and reoperation of relay |06. The release of relay |06 in response to the first impulse, closes a circuit for operating relay |09. Relay |09 locks to ground at the upper contact of the oiT-normal springs I I2, opens the circuit for operating relay |05, opens `the circuit for operating the rotaryV stepping magnet |I0 to prevent further advance of the brush I, and closes a circuit through the lower Contact of oli-normal springs I|2 for operating the release magnet I I3 to restore the brush III to normal. Being slow in releasing, relay |09 remains operated until all of the impulses in the train have been received by relay |06. Relay |08 is also slow in releasing so as to remain operated during the response of relay |06 to impulses. When relay |03 releases at the end of the train of impulses, it again closes the circuit for operating the rotary stepping magnet IIO under the control of the interrupter |01; Whereby the brush I I I is again advanced step by step, one step every thirty seconds. When the next train of impulses is transmitted by relay 35 of register sender 30, relay |06 again responds causing the reoperation of relay |09 and the restoration of the brush III to normal. Thus each digit transmitted by the register sender is absorbed by the trunk circuit ATI. When all of the impulses have been transmitted, the advance of brush ||I under the control of the interrupter |01 continues without interruption. When the brush |I| reaches terminal 4, relay |05 operates. Relay |05 locks to conductor |03; disconnects conductors |0| and |02 from the windings of relay |06 to cause the release of relay |06; and connects conductors |0| and |02, through conductors II'I and II8, the left windings of repeating coil I 25 of trunk circuit IT and the back contacts of relay |2I, to the windings of relay |20. Relay |20 operates in series with the contact of impulse transmitting relay 35 and the winding of polarized relay 36 in the register sender 30, the current in this circuit being in a direction to also elect the operation of relay 36. The operation of relay I 20 closes a circuit for operating relay |30. Relay |30 connects ground to conductor |03 to maintain the operation of relay lease .in succession, thereby closing the circuit for operating release magnet I I3 torestore brush and springs ||2 to normal. Since relay |08 is slow in releasing, the release of relay |08 does not occur until after relay |30 has operated; so that the connection of ground` potential to conductor |03 is maintained without interruption upon extension oi.' the connection to trunk circuit IT. The aforementioned operation of relay |30 connects the windings of relay |29, through back contacts of relay |21, right windings of rebetween'conductor |03 and sleeve conductor |63.,

` All of the digit impulses having been transmitted by the register sender, the operation of polarized relay 36 effects the operation of relay 34 as described in the aforementioned patent to I. H. Henry to connect the ringing current generator 31 to conductors 3| and 32 to cause the operation of Arelay |23 of trunkcircuit IT. After a measured interval of time, the ringing generator 31 is disconnected from conductors 3| and 32 and a talking connection is closed through trunk circuit I between the conductors of jack OJI and conductors and I2 in the manner set forth in the aforementioned patent to I. H. Henry. The operation of relay |23 closes a circuit for operating relayv |24. The operation of relay |24 closes a circuit for operating relay |26, closes a holding circuit for relay |30, and connects ground to conductor |03. Relay |26 locks under control of relay |30 and connects ground to conductor |03. Relay releases while ringing current is being received and reoperates after the talking connection is closed through trunk circuit I0. Relays |24 and |25 are slow in releasing so as to prevent the release of relay |30 while relay |20 is released.- The aforementioned operation of relay |26 also closes a circuit for operating relay |21, this circuit being traced from the winding of relay |21, through the upper front contact of relay |26, conductor |34, inner upper back contact of relay |36 of trunk circuit ITI, and conductor |03, to ground at the middle lower iront contact of relay |30. The operation oi relay |21 connects resistor |28, through the right windings of repeating coil |25 and front contacts of relay |30, across conductors |3| and |32 thereby effecting the operation of relay |4| of trunk circuit ITI. The operation of relay |4| closes a circuit for operating relay |39, this circuit being traced from the winding of relay |39, through the continuity back contact of relay |38, a back contact of relay |36, front contact of relay I4! and conductor |03, to ground at a front contact oi' relay 30. The operation of relay |39 closes a circuit for operating relay |38. The operation .contact of relay |30. The operation of relay |30 closes a circuit through its inner upper front contact and the front contact of relay |4| for operating relay` |36. Relay |36 locks to conductor |03, closes a circuit for operating relay |35,

and opens the connection between `conductors |03 and |34 therebycausing the release of relay |21 of trlmk circuit IT and the release of relay |39.

brush I 63 The operation of relay |35 opens the connection 'Il from, and reconnects the windings of relay |23 to, conductors |3| and |32 thereby causing the release of relay |4|. The release of relay |39 causes the release of relay |38. The release of relay |38 connects ground through the outer lower front contact of relay |36 to motor start conductor MS to start the ringing generator and ringing interrupter, if not already in operation; and'closes a circuit at its inner lower back contact for operating relay |46. The operation oi relay |46 closes a circuit tor operating group relay |41, and connects the winding of relay |46 to conductor |53. The operation of group relay |41 connects ground to start conductor |48 to operate the start relay (not shown) of the first idle trunk ilnder having access to trunk circuit ITI; and connects ground to conductor |49 to mark the level of the trunk iinder bank in which the terminals connected to trunk circuit ITI are located. When the brushes of the trunk finder, TFI, thus started in operation, engage the terminals |84, relay |45 is operated by the current in a circuit from battery through its Winding, inner front contact of relay |46, conductor |53, brush |63 of trunk iinder TFI, to ground (not shown) in the trunk iinder circuit. The closure of this circuit is also eilective to stop the further advance of the brushes of the trunk finder, and to effect the operation of the cut-through relay in the usual manner, the cut-through -relay not being shown in the drawing. Relay |45 locks to conductor |53 and opens the operating circuit of relay |46. The release of relay |46 causes the release of group relay |41 unless there is another trunk in the same subgroup awaiting extension to an lnterceptlng operator. The release of relay |46 closes a connection from ground at the middle lower front contact 'of relay |36, through the inner lower back contact of relay |38, lower front contact of relay |46 and back contact of relay 46 to conductor |53. v

|63, conductor |53, back contact of relay |46,v

If' the answering operator disconnects iirst, relays |92 and |99 release. The release of relay |96 causes the release of relay |90; land the release of relay |90 causes the release of relay |95. Relays |63 and |16 are held operated through conductors |13 and |53, back contact of relay |46, lower front contact of relay |45, inner lower back contact of relay |38, to ground at a front contact of relay |36. The release of relay |95 reconnects toll identication tone source |99 to the tip conductor oi' jack RAJ and shortcircuits the left windings of repeating coil RC3. The release of relay |92 opens the short circuit across the high impedance winding of relay |9I to cause the successive release of relays |29 and I2| and reoperation of relay |20.- 'I'he toll operators cord supervisory lamp is thereby lighted as a disconnect signal. If the answering operator again connects an answering cord to jack RAJ, relays |99 and |90 are reoperated and the toll identification tone is given to the answering operator. Operation of the tone removal key eiects the reoperation of relays |92 and |95 to disconnect including a front contact of relay ISI, a back 'j ringconductors of the answering cord, thereby effecting'the operation oi relay |92. Relay |92 closes a circuit for operating relay |95. Relay |95 locks under control of relay |90; disconnects the tone source |99; 'bridges -the talking condenser I93 across the tip andring conductors olf the answering jack; and opens the short circuits across the left windings of repeating coll RCE,

thereby completing the talking connection bethe tone and reestablish the talking connection. If the calling operator disconnects while the answering operator is connected, the switch TPS is restored to normal but trunk circuits ATI, IT,

Assume now that the toll preceding selector TPS selects a level in which the terminals are connected to toll transmission selector circuits and that the terminals 95 representing this level and connected to selector 'ITS are seized by the trunk hunting operation of selector TPS. Upon extension of the connection from conductors II and I2 through brushes 4I and S2 of elector TPS to conductors 5| and 52, the line relay 59 of selector TTS is operated, thewindings of this relay being normally connected through back contacts of relays 58 and 54 to conductors 5I and 52. Relay 59 closes a circuit for operating the slow-to-release relay 9B; and relay 66 connects holding ground potential through conductor 53 to the terminal engaged by brush 93 of selector TPS to hold the selector TPS in operated position. When the next train of impulses is transmitted by impulse relay 35 of the register sender 30, relay 59 is alternately released and reoperated as many times as there are vimpulses in the train. The release of relay 59 in response to the rst impulse closes a circuit from ground through its lower back contact, a

front contact oi relay 66 and a back contact of relay 66, for operatively energizing relay 62 and vertical stepping magnet 33. The operation oi.' stepping magnet 63 advances brushes 1I, 12, 13 and 14 up to the ilrst level of the terminal bank, the vertical oil-normal springs 61 being actuated as soon as the brush shaft moves out of normal position. The operation oi relay 62 closes a circuit for operating relay 51; and relay 61 locks under control o! relay 66 to ground at the inner upper front contact ci' relay 66. With relay 62 operated and the vertical off-normal springs 61 actuated, a circuit is closed for operating relay l 64, this circuit being traced from battery at the back contact o1' release magnet 66 through the upper front contact oi vertical off-normal springs 61, winding of relay 64, and front contact of relay 62 to ground at the 'inner upper front contact of relay 66., Relay 64 locks under control of the rotary stepping magnet 65 to ground at its outer front contact. When relay 59 reoperates at the Aend oi' the ilrst impulse, the vertical stepping magnet 63 releases; but relay 62 is slow in releasing so as to remain operated until after relay 59 has reoperated at the end of the last impulse of the train. Relay 66 is also slow in releasing so as to remain operated during the response of relay 59 to impulses. Each operation of the vertical stepping magnet 63 advances the brushes of the selector one step, thereby selecting the level of the terminal bank correspondingto the number of impulses in the train received from the register sender. When relay 62 releases after all of the impulses in the train have been received, a circuit is closed for operating the rotary stepping magnet t5, this circuit being traced from battery through the Winding of magnet 65, inner upper front contact of relay t4, back contact of relay 62, to ground at a front contact of relay 66. The operation of stepping magnet 65 steps the brushes 1i, t2, 13 and 'it into engagement with the iirst set of terminals in the selected level and opens the circuit for energizing the Winding of relay 64; and the release of relay 64 opens the circuit for energizing the Winding of rotary stepping magnet 65. If the iirst set of terminals in the selected level is connected to a busy trunk, busy selector or busy connector circuit, the terminal engaged by brush 13 is connected to ground, thereby effecting the reoperation of relay 64 in a circuit from battery through the back contact of release magnet tt, upper front contact of vertical c-normal springs 61, winding of relay 66, back contact of rotary stepping magnet 65, inner lower back contact of relay 650 and through brush 'I3 to the engaged grounded test terminal. The reoperation of relay 5t again closes the circuit for operating rotary stepping magnet 65, thereby advancing the brushes to the next set of terminals in the level. Relay t6 and rotary stepping magnet 65 cooperate to advance the brushes step by step until a set of terminals which is not marked by a busy potential are engaged, whereupon relay Bt is operated in a circuit traced from battery through the back contact of release magnet 68, upper contact of vertical oif-normal springs 61, winding of relay 64, back contact of rotary stepping magnet t5, and winding of relay 6I), to ground'at a front contact of relay 66. Being marginal, relay 64 is not operatively energized in series with the winding of relay 60. The operation of relay 60 irnmedi` ately closes a connection from ground at theA inner upper front contact of relay 66, through the outer lower front contact of relay 60, and brush 13, to the sleeve terminal of the selected trunk circuit so as to prevent the selection oi this trunk circuit by any other selector which has access dit thereto. 'I'he operation oi relay 60 connects the locking contact of relay 51 to brush `14 so that the continued operation of relay 51 depends upon the connection of ground potential to the terminal engaged by brush 1I.

Assume that the train of impulses received by relay 69 from the register sender effects the selection of a level representing a non-used code, such a level being represented by the set of terminals 15 connected to intercepting trunk circuit AT2. The trunk circuit ATZ is similar to trunk circuit ATI except that it has an additional conductor which is connected to the terminal engaged by brush 14. The trunk circuit ATZ absorbs the trains of` impulses transmitted by relay 35 of register sender 30 inthe same manner that trunk circuit ATI absorbs trains of impulses as above described. When all trains of impulses have been received, the relay of trunk circuit AT2 which corresponds to relay |05 of trunk circuit ATI is operated to connect conductors 2M and 202 to conductors 2H and ZIB of trunkcircuit IT2. Since trunk circuit TZ is similar to trunk circuit ITI, the operations of trunk circuit IT! involved in starting a trunk finder are similar to those of trunk circuit ITi hereinbefore described. After relay Eli operates, the locking circuit of relay 51 is traced through a front contact 'of relay Et, brush '14 and engaged terminal, conductor '204, continuity back contact of the relay of trunk circuit TZ which corresponds to relay 636 of trunk circuit ITI, conductor mit, terminal and brush 13, and a front contact of relay t0, to ground at a front contact of relay tt. When the relay of trunk circuit ITQ which corresponds to relay |136 of trunk circuit liTl operates, relay release of relay 51 connects ground to conductorv 204. (f the trunk I'Ii were seized by a toll transmission selector arranged for delayed ringing under the control of the toll operator, the connection of ground to conductor 31M in the selector circuit would occur soon enough to prevent the release of the relayv corresponding to relay its; in which case this relay would remain operated until the toll operator rings.) The release of the relay corresponding to relay i3@ causes the release of the relay corresponding to relay I38 to effect the starting of a trunk finder TFI in the manner hereinbefore described on the call through trunk circuit ITG. When a trunk nder TFI extends the connection from trunk circuit IT2 to a trunk circuit T5 terminating at an operators position, the various operations of trunk circuits ITE and T5 are similar to those above described on a call through trunk circuit ITI.

^ When the toll operator releases the connec tion, relay 59 releases, causing the release of relay 66. The release of relay 66 causes the release of relay 60, disconnects ground from conductor 53 to cause the toll preceding selector TPS to restore to normal, disconnects ground from brush 13 to cause the release of the relay of trunk circuit ITZ corresponding to relay |36 of trunk circuit ITI, and closes a circuit for operating releasev magnet 68. The operation of magnet 68 Vallows the brushes of selector TIS to restore to normal; and when the brushes reach normal, the vertical olf-normal springs 67 are restored to normal to eiIect the release of release magnet 58. The trunk circuits ATZ and `T and trunk finder TFI are restored to normal when the answering operator disconnects, in the manner hereinbefore set forth. The trunk circuit IT2 is restored to normal in similar manner to that in which trunk circuit ITI is restored to normal as hereinbefore described.

If the selector 'ITS is operated to select a set of terminals 'l5 connected to a connector Ci, the next two trains of impulses transmitted by relay 350i register sender 3@ e'ect the operation of the connector to select a set of terminals: 85 connected to the called subscribers line L; and, in this case, relay 5'! is held operated until the called line is selected, the transmission of a ringing signal from the register sender being without eiect. The release of relay 57 connects ground 4to brush 14 and connects talking battery through the windings of relay 6| and repeating coil 55 to the talking conductors of connector Cl. Relay 51 is slow in releasing so that there is an interval between the disconnection of ground from conductor ld and the reconnection of ground to conductor 'le by the release of relay 5l. The connector then operates in the usual manner to transmit ringing current to operate the ringer at the called station. When the call is answered, relay 5| operates, causing the operation of relay 5E, whereby the current through conductors 5| and 52 is reversed as an answering supervisory signal. If the called subscriber replaces the receiver, relays 6| and 52 release to again reverse the current as a disconnect signal. When the calling operator disconnects, relay 59 releases, causing the release of relay 66. The release of relay S6 disconnects ground from conductor 53 to cause the toll preceding selector TPS to restore to normal, disconnectsv ground from brush 'I3 to cause the release of relay 60 and to cause the connector C| to restore to normal, and closes 4a circuit for operating release magnet 66 to restore the brushes of selector ITS to normal. When the shaft and brushes of selector 'ITS reach normal, the vertical ofi-normal springs 6l are restored to normal to effect the release of release magnet 5S.

If the connector Cl selects the terminals 8B of a line which is out of order, the plugging up line circuit PL and intercepting trunk circuit IT5 effect the starting ci a trunk finder in the manner described in the aforementioned patent to E. D. Butz, No. 2,021,286. In this case, the normal post springs lid of the trunk ilnder TFI are actuated when the brushes are stepped up to the level in which the terminals |66 are located, thereby connecting ground to conductor |74 to operate relay |81 of trunk circuit TCI. Relay |81 connects the lamp TAL for operation instead of lamp RAL; connects ground from the back contact of relay |83 to conductor |13 to hold the trunk nder until the call is answered;

and connects thermistor |88 in series with the winding of relay |85, in parallel with resistor |89, through a back contact of relay |90, to grounded conductor |13, the temperature of the thermistor being raised by the current therethrough. Relays |8|, l'l'l and |18 are operated in the manner hereinbefore described to eiect the operation of relay to light the lamp TAL. If the call is I5 arredare.

abandoned before relay |85 is operated, relay IBS is operated in series with thermistor |88 as soon as the temperature of the thermistor has been suilciently increased to effect a material decrease in the resistance of the thermistor. When the lamp TAL is lighted and an intercepting operator connects a cord to jack TAJ, relays |96, |90 and |83 are successively operated and the other operations involved on this call are similar to those above described on a call through a set of terminals representing an unassigned number. If the call has been abandoned before the .Operator answers, the operator disconnects from the answering jack and the trunk circuits and trunk iinder are restored to normal.

What is claimed is:

1. In an automatic telephone system, a trunk circuit comprising normally disconnected incoming and outgoing conductors, timing means for measuring a predetermined interval of time,

means responsive to seizure of said incoming conductors for starting the operation of said timing means, means operated at the end of the measurement of said predetermined interval of time by said timing means to interconnect said incoming and outgoing conductors, means eiective in response to a train of impulses received over said incoming conductors prior to completion of the measurement of said interval of time for preventing the interconnection of said conductors, and means effective at the end of va train of impulses received over said incoming conductors to again start the operation of said timing means.

circuit comprising normally disconnected incoming and outgoing conductors, a timing switch, means responsive to seizure of said incoming conductors for starting the operation of said timing switch, means operated when said timing switch reaches a predetermined position to interconnect said incoming and outgoing conductors, and means responsive to a train of impulses received over said incoming conductors prior to the time said switch reaches said position for effecting the return of said timing switch to normal,

said switch being again started in operation at the end of said train of impulses.

4. In an automatic telephone system comprising impulse controlled switches for establishing connections between calling and called lines, a trunk circuit connected to a set of terminals representing an unassigned code in the banks of certain switches, said trunk circuit comprising incoming and outgoing conductors, timing means for measuring a predetermined interval of time, means responsive to seizure of said trunk circuit for starting the operation of said timing means, means for stopping the operation of said timing means in response to the rst impulse of each train of impulses received over said incoming contiming means to measure said predetermined interval of time, and means effective when no impulses are received over said incoming conductors while said interval is being measured for interconnecting said incoming and outgoing conductors.

5. In an automatic telephone system comprising impulse controlled switches and impulse transmitting control means for controlling the operation of said switches to establish desired connections, a trunk circuit connected to a set of terminals representing an unassigned code in the banks of certain of said switches, said trunk circuit comprising incoming and outgoing conductors, timing means for measuring a predetermined interval of time, means responsive to seizure of said incoming conductors for starting the operation of said timing means, means responsive to the rst impulse of a train of impulses received over said incoming conductors for stopping the operation of said timing means, means effective after receipt of the last impulse of a train of impulses received over said incoming conductors for again starting the operation of said timing means, and means effective when said timing means completes the measurement of said predetermined interval of time without interruption to interconnect said incoming and outgoing conductors.

6. In an automatic telephone system comprising impulse controlled switches and impulse transmitting control means for controlling the operation of said switches to establish desired connections, a trunk circuit connected to a set of l terminals representing an unassigned code in the banks of certain of said switches, said trunk circuit comprising incoming and outgoing conductors, means for absorbing trains of impulses received over said incoming conductors, and means for interconnecting said incoming and outgoing conductors a predetermined interval of time after the last train of impulses is received over said incoming conductors. n

'7. In an automatic telephone system, impulse controlled switches, control meanslnffective to transmit trains of impulses to operate said switches to establish desired connections, a trunk circuit connected to a set of terminals representing an unassigned code in the` bank of one of said switches, means in said trunk circuit responsive to a train of impulses transmitted by the control means after seizure of said set of terminals for absorbing said impulses, means in said control means for transmitting a ringing signal after all of the trains of impulses required for the. establishment of a connection have been transmitted, signal receiving means individual to said trunk circuit for responding to a ringing signal, and means effective a predetermined interval 0f time after the last train of impulses transmitted by said control means has been received by said trunk circuit for connecting said signal receiving means to receive said ringing signal.

8. In an automatic telephone system, impulse controlled switches, control means effective to transmit trains of impulses to operate said switches to establish desired connections, a trunk circuit connected to a set of terminals representing an unassigned code in the bank of one of said switches, means in said trunk circuit responsive to the train of impulses transmitted by the control means after seizure of said set of terminals for absorbing said impulses, means in said control means for transmitting a ringing signal after all of the trains of impulses required for the establishment of a connection have been transmitted, signal receiving means individual to said trunk circuit for responding to a ringing signal, means effective a predetermined interval of time after` the last train of impulses transmitted by said of said signal receiving means for effecting the connection of said trunk circuit to said operators position. l

MYRON- C. GODDARD.