US1218806A - Telephone trunking system. - Google Patents

Description

l. G. ROBERTS. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED DEC. 8, |914.

Patented Mar. 13, 1917.

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J. G. ROBERTS. TELEPHONE TRUNKNG SYSTEM. 'APPLICATION mso usc.s.1914.

Patented Mar. 13, 1917.

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JOI-IN G. ROBERTS, OF DOBBS FERRY, YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 WESTERN ELECTRIC CQIVIPANY, IN CORPGRATED, A CORPORATION OF NEW YORK.

TELEPHONE TRUNKING SYSTEM.

Specification of Letters Patent.

Application filed December 8, 1914. Serial No. 876,084.

To all whom it may concern Be it known that I, Jol-IN G. ROBERTS, a citizen of the United States, residing at Dobbs Ferry, in the county of Westchester and State of New York, have invented certain new and useful Improvements in Telephone Trunking Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to trunking and telephone exchanges. It is applicable especially to two-wire trunks between offices, and as so applied its objects are to effect the control of supervisory signals and other devices over the trunks without the use of controlling circuits extending through ground or a third wire between the oilices, and preferably also without the use of marginal controlling devices.

lVhere subscribers lines to be connected terminate in diilierent oltices', it is desirable to provide two-wire interoflice trunks in order to economize in conductors. It is also desirable where the connection extends through such aV trunk, to supply talking current to the calling and called subscribers lines by separate batteries, one at each oiiice, instead of a single battery as usual where the two lines terminate in the same oliice.

lt is furthermore desirable in providing for the necessary signaling operations over an interollice trunk, to avoid the use of controlling circuits which depend upon a ground return path between the otlices, this in view ot' the disturbing effects which sometimes occur in ground circuits due to diftercnces or variations of ground potential between the otlices. ln certain systems, such as manual multi-office, and also in semi-automatic exchanges which provide operators answering equipment and automatic switches under the control of operators senders for completing the connections to wanted lines, it is required that the called subscriber shall have control over the trunk of a supervisory signal at the outgoing end of the trunk, and that the operator shall be able to control at will either the release of the automatic switches at the incoming end of thetrunk, or the restarting of an automatic ringing equipment without requiring for the latter purpose the restoration of the connection and the building of it up again. This invention provides in a telephone exchange system elective means operable over a combined telephonie link and controlling circuit and without marginal controlling devices, for controlling the foregoing or similar operations.

In accordance with another feature of the invention, a differential relay for controlling the called supervisory signal is provided for the called line end of the operators connecting circuit. When this circuit vis used to form the outgoing end of an interottice trunk, the trunk is wholly free from ground or battery connections, at the outgoing end, battery being supplied to the trunk circuit through one winding of the relay from the incoming' end of the trunk, the other winding being included in a local circuit; but when the connecting circuit is directly united to a called line the battery and both windings of the differential relay are switched into the circuit, and current is supplied outwardly to the called line. Whenever the connection is established through an interoflice trunk, the called line supervisory signaling device is controlled by reversals of current at the incoming end under control of ka relay controlled in turnl by current in the called line. By means of compensating resistances included in the various trunk lines at their incoming ends, the total resistances of all trunks may be made equal, thus reducing to a minimum the current margins for controlling the differential relay. Included in the trunk at the incoming end is a relay unaffected versals but responsive to current interruptions. This relay remains in the circuit whether the current is on the trunk in one direction or the other, and is available always for control by the operator to effect or to cause the operation of the disconnect signal or switch restoration.

Itis a' further feature of the invention that this same controlling device or relay at the incoming end of the trunk is adapted by special control from the outgoing end, as by a momentary interruption of current to ca use rei-inging on the called subscribers line.A

The invention will be more fully understood by reference to the accompanying drawings. In Figures l, 2 and 3 is shown a.y system of circuits suitable for a semiautomatic exchange. Fig. 3 represents a line to be called that terminates in the same otlice as the calling line.

Patented Manie, 1917.V

by the current rcf the rering Referring first to the semi-automatic circuits in Figs. 1, 2 and 3, a connection is as sinned to have been established from the calling station 1 to a called station 2 through an interotlice trunk comprising the` two wires 3 and il. Fig. 3 illustrates a three-wire local trunk extending to a called station, and this trunk itself comprising the talking circuit conductors and G andtliird wire 7. The circuit shown in Figs. 1 and 2 is established by way of a plug and jack switch 9 of an operators connecting circuit, the said connecting circuit, the two-wire trunk El, al., contacts 11 and 12 of an automatic switch and contacts 13 and 11 of another automatic switch. Talking current is supplied to the calling line by battery 15 and to the called line by a battery 1G. The latter battery also supplies current at the incoming end of the trunk backwardly to the connecting circuit. lllhen the connection is established, the called subscriber has control over a supervisory signal 17 b means of a supervisory relay 18, one win ing of which is included in the trunk line circuit at the outgoing end. This control is effected bythe operation of a battery reversing relay 19 in a local circuit controlled by the relay 21 in the circuit leading to the called line. An automatic ringing apparatus 22 operates, in the first instance, automatically to ring the bell at the called subscribers station 2 and is tripped and the ringingy current disconnected from the line when the called subscriber answers. If the called subscriber answers and replaces his receiver on the switclihook and the operator desires to start the automatic ringing apparatus again, she may do so by depressing key 23 which produces a momentary interruption in the trunk circuit. This affects relay :24 in such a way as to again place the ringing apparatus into active con'd'tion. To cause switch restoration, a prolonged interruption in the trunk circuit at the outgoing end brings about the energization of a switch restoring magnet 25.

In case the callinO' subscriber is connected to a line which terminates in the same office so that a local trunk circuit 5, 6, 7 would be used instead of the interoliice trunk circuit 3, 4, there is brought into operation a switching relay 2G which connects battery in circuit to the called line.

The foregoing very briefly states the scheme of operation and functions of the principal devices in the system. A more detailed description of the operation still re ferring to Figs. 1, 2 and 3, is as follows:

The apparatus associated with the operators connecting circuit is in part controlled by a sequence switch 27, certain of the resting positions of which as determined by the master contact 28 may be: 11 selection,

1lringing, 1G talking, 18 switch restoring. The apparatus associated with the inconiing end of the trunk may likewise be controlled in part by sequence switch 29, certain of the resting positions of which as determined by its master contact 31 may be; 13 waiting trunk closure, 16 talking and 18 switch restoring. The circuits and apparatusniore directly involved in the operation of selection and the establishment of the circuits up to the point shown in the' diagram, are omitted to avoid confusion. It is assumed, therefore that the sequence switch 27 has reached its position 11 and the sequence switch 29 its position f3. Further progress in the operation of the system is then started by the closingofa contact 32 which is preil'erably effected automatically at the termination of a selecting operation. This closes a circuit-ground 32, 33, 2T, battery, which sends the sequence switch 2TA out of position 11 into its ringing position 1l wherein there is closed a circuit for the ringing lamp 3l as follows: battery 35, 3l, 3G, ground. The function of this ringing lamp is to indicate to the operator that the ringing operation has begun and the lamp remains li glitcd until the subscriber answers. Tn advancing to position 1i, the sequence switch 27 completes at contacts 37 and 38 the trunk line which now forms a combined telephonic link and controlling circuit. Relay 2G is not energized at this time because the third contact 39 of the trunk is free from connections to establish a circuit. The trunk circuit as a combined telephonic link and controlling circuit may be traced as follows: 1c, ai, ii, 42,13, i, 12, i12, es, il, is, i7, is, 37,117,11, 3, i9, 51, ce, ground. This circuit includes the winding of relay 24C and a. single winding i6 of the supervisory control relay 1S. A circuit is also closed foi' the other winding 52 of relay 18 as follows: l5, 53, 5l, ground. The trunk circuit as traced may include the coinpensating resistances 112 and 51, the purpose of which is to render the total resistance of the trunk circuit equal to the resistances of other trunk circuits with which the supervisory relay 18 may be required to operate. That is to say, where the trunklines vary in length, the resistances and 51 would be varied so that the total resistances of the lines themselves plus these compensating resistances would in all trunks be the saine. The resistance in the circuit of the winding 52 ofthe supervisory relay 18 may be provided to cut down the current in this winding. Relay 1S, therefore, has current flowing through windings :elfi and in opposite directions and of equal magnetizing force, so that the relay is notA at this time energized.

Upon the energization of relay 2li 1n the trunk circuit there is closed a circuit ground 29, battery, which sends sequence switch 29 out of its position 13 into its talking position 16. On entering position 14 and continuing to position 16, there is closed a circuit: ground, 56, 58, 59, battery, which energizes the slow release relay 59, so that by the time the sequence switch reaches position 16, relay 59 is energized and its contact 61 is opened. 1n position 16, contacts 62 and 63 are closed which completes the path for current to the called line.

lVhen sequence switch 29 left position 14, it opened at contact 64 the circuit of a holding rela-y 65, resulting in the closing of contact 66 to prepare for the operation of the automatic ringing apparatus 22. Relay was energized in position 12 of the sequence switch 29 over a circuit from ground, bat tery, winding of relty 65, the upper contact of 64, to ground.` The ringing apparatus becomes active as soon as the sequence switch reaches position 16, in which contact 67 is closed. The complete local ringing' control circuit then closed is as follows: ground, 56, 67, 68, 69, 70, 66, battery. Relay 68 is energized, connecting the generator 71 in circuit with the called line as follows: 71, 72, 73, 74, 63, 14, 2, 13, 62, 75, ground. 1V hen the subscriber responds, the current in the line increases, so that relay 72 which is marginal, acts, opening at contact a shunt preexisting about relay 76. This relay 7 6 in turn closes at contact 77 a shunt about relay 68 so that the latter denergizes opening the ringing circuit and closing the battery circuit to the called line, as follows: 1e, 9.1, so, 40, es, 1&1, 2, 1s, 62, 50, 7o, ground. When this circuit is closed, the supervisory control relay 21 is energized, closing a local circuit-battery 78, 19, ground, and relay 19 acts to reverse the connections of the battery 16 to the trunk wires 3 and 4. The rerersely connected circuit for the battery over the trunk line is as follows: 16, 24, 79, a9, a, 11, 117, 37, as, 47, 46, 45, 44, 38, 112, 12, 4, 43, 81, ground. Relay 24 remains in the circuit and is unaffected by the reversal O15-connections, but the direction of current. in winding 46 of the superwisory relay 18 is reversed, so that the currents in the two windings 46 and 52 now assist, and the relay is energized, closing at its contact 83 a circuit- ground 83, 84, 27, battery, which sends the sequence switch 27 out or' its ringing position 14 into its talking position 16. In this latter position, the supervisory signal lamp 17 is brought into a circuit- battery 35, 17, 85, ground, but the lamp is shunted by a path through the resistance 86 by way of contacts 87 and 83 to ground.

Repeated openings and closings of the called subscribers line, by the subscriber replacing and lifting his receiver, will under this condition of the apparatus result in repeated reversals of current in the winding 46 of the supervisory relay 18, thus repeatedly denergizing and energizing this relay and opening and closing the shunt about the supervisory lamp signal 17. The called subscriber thus has effective control over the supervisory signal 17 and, in any condition of the called subscribers line whether opened or closed, relay 24 at the incoming end of the trunk remains unaffected in the circuit.

The control of the automatic ringing apparatus 22 to cause reringing on the called line may be secured by the momentary depression of the rering key 23. This closes at contact 88 a shunt of contact 44 of relay 89, and at contact 91 a circuit for relay 89. The latter opens contact 44. The trunk circuit remains closed, however, at contact 88 until the rering key 23 is restored. Relay 89 is timed to release a moment after its circuit is opened, say in one-tenth of a second. The trunk circuit is thus opened momentarily and then closed again at contact 44. This allows relay 24 to react momentarily, opening at contact 56 the local ringing control circuit and also the circuit through the slow release relay 59. The interruption in the trunk circuit is of such short duration, however, that relay 59 does not have time to react to close contact 61, but the locking-out relay 76 in the local ringing control circuit does react, opens at contact 77 the shunt about the ringing relay 68 and closes at contact 69 the shunt about itself. Ringing is thus again started by the energization of relay 68. If the called subscriber responds again, the operation of tripping the ringing is repeated, the supervisory control relay 21 is again energized, relay 19 is again energized, current from battery 16 is again reversed in the trunk circuit and the supervisory relay 18 is again energized by the reversal of current in its winding 46, so that the supervisory lamp signal 17 again responds.

The control of switch restoring over the trunk line is never taken away from the operator, but may be effected whether the called subscribers telephone is on or oft' the hook, since relay 24 remains continuously in circuit. The operator may thus cause switch restoration at the incoming end of the trunk at any time by a prolonged opening of the trunk circuit in anysuitable manner. The system shown is so organized that when the operator opens the circuit of the calling lino at the plug and jack switch 9 by removing the plug from the jack, the local circuit including the cut-ofi3 relay 93 and cord relay 94 is opened. The latter relay opens at its contact 95 the local circuit of the calling supervisory signal 96 and closes at contact 97 a circuit, ground, 97, 98, 27, battery, which sends sequence switch 27 out ofits talkingY position 16. into its switch restoring position 18, wherein there is closed at contact 99 the circuit oi a switch restoring magnetlOl. This effects the restoration of the automatic switch which had previously closed the trunk circuit at contacts 11 and 12. Then this sequence switch leaves position 16, it opens the trunk circuit at contacts 37 and 38 and relay 24 reacts as before. This time however the trunk circuit is not again closed. Therefore, the slow-release relay 59 has time to react, and closes at contact 61 a circuit, ground, 61, 102, 29, battery, which includes the motor magnet of sequence switch 29, sending it out of its talking position 16 into its switch restoring position 1S, wherein is closed at contact 103 a circuit for the switch restoring` magnet 25. This effects the restoration of the automatic switch which had previously closed at contacts 13 and 14 the circuit to the called line.

It the callingsubscribcr had been calling for connection with a` subscribers line terminating in the same oiiice as that at which the calling line terminates, the connection would be established directly to that line through a local trunk, such as the three-wire trunk, 5, 6, 7 indicated in Fig. 3. The local circuit terminal of conductor 7 in such. a trunk is connected through a resistance 105 to battery, so that when the connection is set up to a local trunk, there is established a circuit for the switching relay 26 as follows: ground, 106, 26, 107, 10S, 109, 7, 105, battery. In this event the relay 26 changes that part of the connecting circuit which leads toward the called line so that current is supplied thereto through repeating coil windings and 46 from battery 15, this circuit being as follows: 15, 52, 111, 46, 45,V

44, as, na, ne, c, iii, s, 115, s, 116, 117, 37, 4S, 11S, ground. The supervisory relay 18 now operates as an ordinary .supervisory relay under the control of the called substation S, its two windings 52 and 46 operating cumulatively in the circuit just traced to Y that station. Each of the windings 52 and 46 of the supervisory relay 18 may be permanently shunted by non-inductive windings 119 and 121 to reduce the impedance to voice currents. These two shunts may be proportioned with respect to the two windings in exactly the same manner as the ordinary non-inductive shunts 122, 123 and 124 of the calling supervisory relay 125, the controlling relay 24 and the called line supervisory control relay 21 respectively.

'Vhat is claimed is:

1. In a. telephone system, a trunk line forming a combinedtelephonic link and controlling circuit, a differential signal controlling device having one winding in said circuit at the outgoing end, means for supplying current to the other winding of said relay, a repeating coil, a source of current connected through the winding oit' said repeating coil in the incoming end ot said circuit, and means for repeatedly reversing the direction of current flow to said outgoingl 2. In a telephone exchange system, a calling subscribers line, a trunk line forming a combined telephonie link and controlling circuit, means for inductively connecting the controlling circuit to said-line, a local circuit, a source of current therein, an electromagnetic signal controlling device having one winding in said local circuit and a second winding in the outgoing end of said controlling circuit, the magnetizing forces exerted by said windings being approximately equal, a source of current in the incoming end of said controlling circuit, and means for reversing the connections oi said source.

3. In a telephone exchange system, a calling subscriber-s line, a trunk line forming a combined telephonie link and controlling circuit, means for inductively connecting the controlling circuit to said line, a signal controlling device responsive to current reversal-s and included in theoutgoing end of said circuit, a source of current in the incoming end of said circuit, means for reversing the connections ot' said source, a controlling device unresponsive to current reversals included in the incoming end of said circuit and unaffected by current reversals responsive-to the openingand closing of said circuit, and a switch for controlling said last mentioned device in the outgoing end of said circuit.

4. In a telephone exchange system, a connecting circuit, a local circuit, a source of current, a super `isory controlling magnet having two windings, and means operable at will for including both of said windings in said connecting circuit or one and the said battery in said connecting circuit and the other in said local circuit.

v5. In a telephone exchange system, trunk line forming a combined telephonie link and controlling circuit, a supervisory signal device at the outgoing end and a ringing device and a disconnecting device at the incoming end of said trunk, the said supervisory signal being responsive to reversals of current, the said ringing apparatus to a momentary interruption of current, and the said disconnecting device to a prolonged interruption of current in said circuit, and means at each end of said trunk for controlling said devices over said circuit.

6. In a telephone exchange system, a calling subscribers line a trunk line forming a combined telephonie link and controlling circuit, means for incluctively connecting the controlling circuit to said line, a supervisory device at the outgoing end of said trunk responsive to reversals of current in said circuit, a disconnecting device at the incoming end of said trunk responsive to an interruption of current in said circuit, and means at each end of said trunk for controlling said devices over said circuit.

7. In a telephone exchange system, a telephone line, a trunk line forming a combined telephoniclink and controlling circuit, means for inductively connecting the controlling circuit to said line, a supervisory relay included in the outgoing end of said trunk responsive to reversals of current therein, a relay included in the incoming end of said trunk and unresponsive to such reversals of current, two devices controllable by the last mentioned relay, one responsive thereto upon a momentary interruption and the other upon a prolonged interruption of current in said circuit, and means at each end of said Copies of this patent may be obtained for ve cents each, by addressing the Commissioner trunk for controlling said relays over said circuit.

8. In a telephone exchange system, a two Wire trunk line forming a combined telephonie link and complete controlling circuit, a local circuit, a source of current therein, an electromagnetic signal controlling device having one Winding in said local circuit and a second Winding in the outgoing end of said controlling circuit, a source of current in the incoming end of said controlling circuit and means for reversing the connections of said source.

In Witness whereof, I hereunto subscribe my name this 7th day of December A. D., 19

JOHN G. ROBERTS. Vitnesses:

E. Emmen,

F. Fnrsrnn.

0f Patents,

Washington, D. C.

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