US1550997A - Telephone-exchange system - Google Patents

Description

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Aug. 25, 1925. 1,550,997

' s. B. WILLIAMS. JR

TELEPHONE EXCHANGE SYSTEM Filed June 18, 1920 3 Sheets-Sheet 1 /nvenf0r Samue/ B. Wi/l/kzms Jr y Affiz Aug. 25, ,1925.

S. B. WILLIAMS. JR

TELEPHONE EXCHANGE SYSTEM Filed June 1 1920 3 Sheets-Sheet 2 W if; i'EEJEPHUi W.

. lnvenfar; Samuel 13. Wi///ams JI."

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Patented Aug. 25, 1925.

UNITED STATES PATENT OFFICE.

SAMUEL B. WILLIAMS, JR., O'F BROOKLYN, NEW YORK, ASSIGNOB TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed June 18, 1920. Serial No. 389,819.

To all whom it may concern:

Be it known that I, SAMUEL B. WVILLrA us, J r., a citizen of the United States, resldmg at Brooklyn, in the county of Kings, State of New York, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and particularly to circuit arrangements for use at a private branch exchange when such an exchange is employed in connection with a central oilice, either of the manual or automatic type.

An object of the invention is to provide novel and improved means for enabling a subscriber of the private branch exchange to extend his line at will, either to the attendant of the private branch exchange, or over an idle one of a plurality of trunks I leading to the central ofiice, the latter conncction being effected without the aid of the operator.

A feature of the invention consists in the provision of a set of relays individual to each subscribers line of the private branch exchange, which respond to the initiation of a call and the sending of a certain predetermined number of impulses from an impulse sender at the calling station to actuate a calling signal at the private branch exchange attendants position, and to the initiation of a call, and the sending of another predetermined number of impulses from an impulse sender at the calling station to automatically extend the calling line over an idle one of a plurality of trunks leading to the central oflice.

The inventive idea involved is capable of receiving a variety of expressions, one of which, for the purpose of illustrating the invention, is shown in the accompanying drawings; but it is to be expressly understood that said drawings are employed only for the purpose of facilitating the description of the invention as a whole, and not to define the limits thereof, reference being had to the appended claims for this purpose.

In the drawings, Figures 1, 2, 3 and 4: with Figure 2 arranged beneath Figure 1 and Figure 3 to the right of Figure 1, illustrate diagrammatically, the circuits em ployed in carrying out the invention.

cordless switchboard as desired with a sufii-' cient number of trunk lines extending from the switchboard to the central office to care for the tratfic. Each subscribers line has an impulse sender associated therewith, and extends through key contacts to a set of re lays individual thereto. The system is so arranged that upon removing the receiver and actuating the dial to send two impulses, certain relays of the set will operate and actuate the line signal at the attendants position, whereas removing the receiver and actuating the dial to send three impulses, additional relays of the set, individual to the calling line, will be actuated to extend the calling line to an idle trunk leading to the central oflice.

Each subscribers line is provided with a row of connecting keys and a ringing key. \Vhen the line signal is actuated, the attendant noting it, will actuate a connecting key and her listening key, and upon learning the number desired by the calling subscriber, will actuate the ringing key of the desired line and then the connecting key associated with that line in the same row with that of the calling subscriber. The lines are then connected for conversation.

Should the calling subscriber desire the attendant to call a subscriber at the central otiice, the attendant will actuate a key individual to a trunk line leading to the central otiice and after having obtained a connection with the central ofiice, actuate a connecting key associated with the trunk in the same row with an actuated key of the calling subscriber.

If the calling subscriber of the private branch exchange desires a central oiiice connection without the aid of the operator, he will dial the digit 3. The line signal will not light, but his line will be automatically extended to an idle outgoing trunk. The trunk circuits are designed for either incoming calls from the central otfice or outgoing calls thereto. If a trunk is taken for use in either direction, a busy signal is dis played at the attendants position. If all trunks are busy, and a subscriber in the private branch exchange dials digit 3 to extend his line to an idle trunk, his line will be automatically extended to the operators position to light a signal thereat. The operator may then inform him that all trunks are busy.

The trunk lines E and D may terminate in a jack such as 107 at a manual switchboard as shown in Figure 3, or in a non-numerical switch such as F at an automatic exchange, as diagrammatically represented in Figure 4.

It is believed that the invention will now be fully understood from the following detailed description of the operation in establishing the various connections. Let it first be assumed that the subscriber at substation A desires to converse with another subscriber within the private branch exchange. Upon the removal of the receiver from its .switchhook, supervisory relay 24 and line relay 20 individual to the subscribers line are energized over a circuit extending from grounded battery, left-hand winding of relay 20, back contact and outer lefthand armature of relay 21, conductor 80, lower and upper left-hand normal contacts of connecting key 22, lower and upper lefthand normal contacts of key 23, through the substation loop, upper right-hand normal contacts of key 23, Winding of supervisory relay 24, lower right-hand normal contacts of key 23, upper and lower right-hand normal contacts of key 22, conductor 81, inner left-hand armature and back contact of relay 21 to ground. Line relay 20 is differentially wound. Suiiicient current does not flow through the righthand winding of relay 20, however, as long as the loop is closed, to deenergize relay 20, due to the short circuit for this winding at the inner armature and back contact of relay 21. WVhen the subscribers loop is interrupted the right-hand winding of relay 20 serves to quickly deenergize said relay. Line relay 20 in operating completes a circuit at its left-hand armature and front contact for slow-to-release relay 25. Relay 25 in operating completes a circuit at its upper armature and front contact for line busy signal 30.

The subscriber at substation A may then operate his impulse sending device S to send two impulses. Upon the first interruption of the substation loop, relay 20 deenergizes, thereby completing a circuit for slowtorelease relay 28, extending from ground, left-hand armature and back contact of relay 20, lower armature and front contact of slow-to-release relay 25, right-hand armature and back contact of relay 26, lower armature and back contact of relay 27, upper normal contacts and winding of relay 28 to grounded battery. Relay 28 operates and locks up through its upper alternate c011- tacts to ground at the left-hand armature and back contact of relay 20. Relay 27 does not operate atthis time, since the upper Winding, through which current flows in parallel with the winding of relay 28 at the time of the first interruption of the calling sub-station loop, is non-inductive. As soon as relay 28 operates, and relay 2O attracts its armature at the end of the first interruption of the line loop, relay 27 operates over a circuit extending from grounded battery, through the non-inductive winding of relay 27, the lower inductive winding of relay 27, front contact and lower armature of relay 28, right-hand armature and back contact of relay 29, inner right-hand normal contacts of relay 21 and front contact and upper armature of relay 25 to ground. Relays 25 and 28 being of the slow-to-release type, do not release their armatures during the sending of a series of impulses.

Upon the second interruption of the line circuit, relay 31 operates over a circuit extending from ground, left-hand armature and back contact of relay 20, lower armature and front contact of relay 25, right-hand armature and back contact of relay 26, lower armature and front contact of relay 27, and winding of relay 31 to grounded battery. Relay 26 is connected to the contact of relay 31 but it will not operate until relay 20 has attracted its armature after the sending of the second impulse due to its being shunted at the normal contacts of relay 20. hen relay 31 is operated and relay 20 attracts its armature at the end of the second interruption of the line loop, relay 26 operates over a circuit extending from grounded battery, winding and contacts of relay 31, winding of relay 26, inner right-hand normal contacts of relay 21, and front contact and upper armature of relay 25 to ground. Relays 31 and 26 are locked up over this circuit.

WVhen the impulses have been sent, relay 20 remains energized and slow-to-release re lay 28 deenergizes due to the opening of the holding circuit therefor at the contacts of relay 20. Relay 28 in releasing opens the circuit for relay 27. lVhen relay 28 releases a circuit for line signal 32 is completed, said circuit extending from grounded battery, winding of line signal 32, front contact and left-hand armature of relay 26, back contact and lower armature of relay 28, back contact and right-hand armature of relay 29, inner right-hand normal contact of relay 21, and front contact and upper armature of relay 25 to ground.

The operator noting the line signal may actuate either the lower contacts of key 23 or the upper or lower contacts of key 22 and then a listening key in a corresponding row to place her telephone set in operative relaltttl tllllll l.

tion with the calling line. Assuming that the attendant actuates the lower contacts of key 23, the circuit for line relay 20 and supervisory relay 24 will be opened, whereupon slow-to-release relay 25 retracts its armatures, thereby opening the circuit for busy signal 30 and causing the release of relays 31, 26 and the deenergization of line signal 32. Supervisory relay 24 is again operated, however, over a circuit extending from grounded battery, left-hand winding of retardation coil 6, inner right-hand normal contacts of keys 59 and 39, lower inner right-hand alternate contacts of key 23, winding of supervisory relay 24, upper right-hand normal contacts of key 23, through the substation loop, upper left-hand normal contacts of key 23, lower left-hand alternate contacts of key 23, inner left-hand normal contacts of keys 39 and 59 and righthand winding of retardation coil 6 to ground. After inquiring the number desired by the calling subscriber the operator will restore the listening key to normal.

Assuming that a line having conductors 1 and 2 leading to another substation (not shown) of the private branch exchange is desired by substation A, the operator may actuate the upper set of contacts of key -13 to project ringing current from a source of current 5 over the conductors 1 and 2 to signal the substation in the well-known inanner. After ringing, the upper set of contacts will be restored to normal and the lower contacts of key 43 will be actuated to connect the calling and called substations for conversation. Battery supply for the substations is fed through retardation coil 6.

Upon completion of conversation and res toration of the receivers to the switchhook of either or both of the calling and called subscribers lines, a circuit including the back contacts of the supervisory relay 2% or 414- and their associated connecting keys will be completed for supervisory signal 33, which in actuating indicates to the operator that conversation is completed. The operator may then restore keys 23 and 13 to normal, whereupon the calling and called lines are ready for the next call.

If the subscriber of station A desires a direct connection with the central oiiice, he would, after removing the receiver from the switchhook, dial digit 3. Line relay 20, supervisory relay 241-, slow-to-release relay 25 and line busy signal 30 would operate in response to the removal of the receiver from the switchhook as heretofore described. Relay 28 will operate in response to the sending of the first impulse and relays 31 and 26 in response to the sending of the second impulse over circuits previously traced. Re lays 28 and 27 will not release at the end of the second impulse, however, and the'line signal 32 will therefore not be actuated, but the third interruption of the line circuit will release relay 20 thereby completing a circuit for relay 29 extending from ground, armature and back contact of relay 20, lower armature and front contact of relay 25, right-hand armature and front contact of relay 26, upper armature and front contact of relay 27, winding of relay 29, back contact and armature of relay 100 to grounded battery. Relay 29 in operating locks up through its right-hand lternate contacts and the inner right-hand normal contacts of relay 21 to ground at the upper contact of relay 25. Relay 29 in operating extends ground from the upper armature and front contact of relay 25 through the inner righthand normal contacts of relay 21, front con tact and inner left-hand armature of relay 29 to the armature and back contact of relay 101, which is common to the trunks leading to the central oiiice and thence over conductor, 94:, armature and back contact of relay 60, if the trunk D with which this relay is associated is idle, and winding of allotter relay 61 to grounded battery. Relay 61 in operating completes a circuit for line linde-r relay 62, said circuit extending from ground, upper armature and front contact of relay 25, enter right-hand normal contact of relay 21, front contact and outer left-hand armature of relay 29, conductor 90, upper intermediate armature and front contact of relay 61, and winding of relay 62 to grounded battery. Relay 62 in operating causes the operation of relays 21 and 60 and extends the calling line through to relays 64-. The circuit for the energization of relays 21 and 60 may be traced from grounded battery, winding of relay 21, conductor S t, front contact and inner left-hand armature of relay 62, and winding of relay 60 to ground. When the calling line is extended through to relay 66%, this relay operates over a. circuit extending from grounded battery, left-hand winding of relay 64:, back contact and outer lower armature of relay 65, intermediate left-hand armature and front contact of relay 62, winding of supervisory relay 24, upper right-hand normal contacts of key 23 through the substation loop, upper left-hand normal contacts of key front contact and outer left-hand armature of relay 62, inner lower armature and back contact of relay 65, and right-hand winding of relay 64 to ground. When relay 60 operated, a circuit was completed at its right-hand contacts for the energization of trunk busy signal 67. At the left-hand normal contact of relay 60 the starter wire circuit to relay 61 was opened whereupon relay 101 will be operated to prevent this trunk from being selected. The circuit for the energization of relay 101 may be traced from grounded battery, winding, front contact and inner lower armature of relay 61, conductor 92, winding of relay 101, inner left-hand armature and front contact of relay 29, and front contact and upper armature of relay 25 to ground. Relay 21 in operating, at its left-hand contacts, opens the circuit for line relay 20 and at its inner right-hand normal contacts, opens the holding circuit for relay 29. Relay 29, and in turn relay 101 and the other operated relays of line A, thereupon release their armatures. The slow to release relay 25 is maintained energized when relay 20 re leases however, over a circuit extending from ground, armature and front contact of supervisory relay 24, conductor 82, and the winding of relay 25 to grounded battery, relay 24 having been energized when the call.- ing line was extended through to relay 64:. hen relay 29 releases, relay 61 of the trunk circuit is maintained energized over a circuit extending from ground, upper armature and front contact of relay 25, inner right-hand alternate contact of relay 21, conductor 88, outer right-hand armature and front contact of relay 62, outer and inner lower contacts of relay 61, and winding of relay 61 to grounded battery. Relay 6 1, in operating, connects ground at its right-hand contacts to conductor 102 of the trunk D leading to the central office, to energize line relay 105 thereat, if the trunk circuit terminates in a jack at a manual exchange as shown in Fig. 3 or to energize line relay 120 of a nonnumerical switch, if the trunk circuit terminates in a non-numerical switch F at an automatic exchange as shown in Fig. a. Relay 64: in operating, through its left-hand contacts, bridges relay 66 across the trunk conductors 102 and 1023. Assuming that the trunk line D is extended to a manual exchange, current for the energization of line relay 105 at the manual exchange will flow over a circuit extending from grounded batte-ry, winding of relay 105, tip contact of jack 107, conductor 102, back contact and upper outer armature of relay 65, and front contact and righthand armature of relay 6-1 to ground as soon as relay 64L operates. Relay 105 in operating completes a circuit for line signal 106.

The operator noting this signal may insert answering plug 108 of a cord circuit G, a portion only of which is shown, into jack 107 thereby disconnecting line relay 105 from the jack and extinguishin the line signal 106. Relay 66 of the trunk circuit will be energized over a circuit extending from grounded battery, upper left-hand winding of repeating coil 109, upper normal contacts of ringing key 110, tips of plug 108 and ack 107, conductor 102, winding of relay 66, front contact and left-hand armature of relay 64, conductor 103, rings of jack 107 and plug 108, lower normal contacts of key 110, winding of supervisory relay 112 and lower left-hand winding of repeating coil 109 to battery. Relay 66 in operating, completes a circuit at its left-hand contact for relay 65 which in operating, locks up over circuit extending from grounded battery, winding and upper inner contact of relay 65, outer right-hand armature and front contact of relay 62, conductor 83, inner right-hand alternate contact of relay 21 and front contact and upper armature of relay 25 to ground. Relay 65 in operating, extends the calling line through to the trunk conductors 102 and 103 and supervisory relay 24: is maintained operated over a circuit extending from grounded battery, upper left-hand winding of repeating coil 109, upper normal contacts of key 110, tips of plug 108 and jack 107, conductor 102, lower inner alternate contacts of relay 65, outer left-hand armature and front contact of relay 62, upper lefthand normal contacts of key 23 through the substation loop, upper right-hand normal contacts of key 23, winding of supervisory relay 24, front contact and inter mediate left-hand armature of relay 62, lower outer alternate contact of relay 65, conductor 103, rings of jack 107 and plug 108, lower normal contacts of key 110, winding of supervisory relay 112 and lower lefthand winding of repeating coil 109 to battery. l Vhen relay 65 operates, relays 66 and 64 are removed from bridged relationship with the trunk.

The operator at the manual exchange may then actuate listening key 111 and inquire the wants of the calling subscriber and after having been informed of the number desired, complete the connection over the other end of the cord circuit (not shown) in the well known manner. Upon completion of conversation and restoration of the receiver to the switchhook at substation A, supervisory relay 24 at the private branch exchange and supervisory relay 112 at the main exchange, will be deprived of current and will, therefore, retract their armatures. Relay 24 in releasing opens the holding circuit for slow-to-release relay 25, which in turn restores all operated relays and busy signal 67 at the private branch exchange to normal. The operator at the private branch exchange noting that the trunk busy signal 67 is no longer actuated, will know that the trunk circuit is no longer in use. Supervisory relay 112 at the main central oflice, may control the usual supervisory signals (not shown) and the operator thereat may remove plug 108 from jack 107 when conversation is completed.

Referring to that part of the description in which it is stated that if trunk D is idle relay 61 is operated, it will be readily seen that if trunk D is busy, the starter wire 9 1 will be extended to relay 70, and relay 71 will be operated. In such case the relays of trunk E will operate in a similar manner to those of trunk D and the calling line will be extended over trunk E to the central office. On incoming calls over a trunk such as D to the private branch exchange, line signal 68 may be actuated by a source of ringing current projected over the conductors 102 and 103, the path therefore being from conductor 102 through the back contact and outer upper armature of relay 65, condenser 69 and signal 68 to conductor 103. The operator noting-the signal, may after removing the receiver 3 from the switchhook 4 actuate a listening key such as to bridge the trunk or the upper set of contacts of key 59 thereby bridging holding coil 58 across the trunk, which will actuate the supervisory signal at the main central oflice in the case of incoming call from a manual exchange, or trip the ringing relay of an automatic switch in the case of an incoming call from an automatic exchange. The operator may after actuating her listening key inquire the wants of the calling subscriber. Actuation of the upper set of contacts of key 59 completes a circuit for relay 60 over a path extending from grounded battery, resistance 14, upper outer right-hand contacts of key 59, and winding of relay 60 to ground. Relay 60 in operating completes a circuit at its righthand contacts for trunk busy signal 67 and its left-hand alternate contact extends the starter wire to the next trunk. Assuming that the subscriber of station A is desired, the operator may then actuate the upper set of contacts of key 23 to project ringing current from a source 5 over the conductors leading to station A to signal said station. The operator will then restore the upper set of contacts of key 23 to normal and operate the lower set of contacts of key 23. As soon as the called subscriber responds, supervisory relay 2% which is in series with retardation coil 6 will operate and supervisory signal 33 will be deenergized, thereby notifyin the operator of the response of the called subscriber. The operator may then restore the upper set of contacts of key 59 to normal and actuate the lower set of contacts of key 59 which disconnects the local battery supply through retardation coil 6 and connects subscriber A through to the trunk conductors 102 and 103 over a path extending from conductor 102, lower left-hand alternate contacts of key 59, left-hand normal contacts of key 39, lower left-hand alternate contacts of key 23, upper left-hand normal contacts of key 23, through the substation loop, upper right-hand normal contacts of key 23, through the winding of relay 24, inner right-hand alternate contacts of key 23, lower right-hand normal contacts of key 39, lower right-hand alternate contacts of key 59 to conductor 103. Battery supply for substation A is obtained from the central oliice. The actuation of a holding key on an incoming call from the central oflice may be dispensed with, if the operator actuates a connecting key such as the lower set of con tacts of key 59, and then the listening key of the corresponding row of keys, such as 55, and remains in on the connection until the called subscriber responds.

Upon completion of conversation and restoration of the receiver of substation A to the switchhook, supervisory relay 24: will be deprived of current and will, therefore, release its armature and complete a circuit for supervisory signal 33, thus indicating to the operator at the private branch exchange that conversation is completed. The operator at the private branch exchange will thereupon restore keys 23 and 59 to nolrimal and the system is ready for the next ca A more detailed description of the operation of the circuit when used in connection with an automatic exchange is not given since such operation will be readily apparent to those skilled in the art.

If all trunks are busy when a subscriber calls, relays 60 and 7 0 will be operated and the starter wire 94 will be extended through the left-hand contacts of relays 60 and 70 over conductor 93 to relay 100. Relay 100 will operate and open the circuit for relay 29 causing relay 29 to release. Relay 29 in releasing opens the holding circuit for relay 28, line signal 32 will thereupon be actuated over the circuit previously traced. The operator on responding thereto may inform the calling subscriber that all trunks are busy.

What is claimed is:

1. In a telephone exchange system, a call- 1ng line, an impulse sender therefor, an attendants position, a line signal thereat individual to said subscribers line, a trunk circuit, and means responsive to one series of impulses from said impulse sender for actuating said line signal, and to another series of impulses to connect said line to said trunk circuit.

2. In a telephone exchange system, a calling line, an impulse sender therefor, an operators position, a line signal thereat individual to said subscribers line, a trunk circuit, and means individual to said line responsive to one series of impulses from said impulse sender for actuating said line signal and to another series of impulses from said impulse sender for connecting said line to said trunk circuit.

3. In a telephone exchange system, a calling line, an impulse. sender therefor, an operators position, a line signal thereat for said subscribers line, a plurality of trunk circuits, means for preselecting said trunk circuits, and means responsive to the initiation of a call and the sending of one series of impulses from said impulse sender to actuate said line signal, and to another series of impulses from said impulse sender for connecting said line to a preselected trunk.

4. In a telephone exchange system, a calling line, an impulse sender therefor, an operators position, a line signal thereat for said subscribers line, a plurality of trunk circuits, means for preselecting idle trunks, and means individual to said calling line, responsive to the initiation of a call, and the sending of one series of impulses from said impulse sender to actuate said line signal and to another series of impulses from said impulse for connecting said line to a preselected trunk circuit.

5. In a telephone exchange system, a calling and a called subscribers line terminating at a first exchange, a trunk line extending from said first to a second exchange, an operators position at said first exchange, a line signal thereat individual to said calling subscribers line, manual means thereat for interconnecting said lines, a dial for each of said subscribers lines, a set of relays individual to each of said subscribers lines, responsive to a predetermined series of impulses transmitted by said dial for actuating the line signal at the operators position and responsive to another predetermined series of impulses transmited by said dial for automatically extending said line to said trunk line.

6. In a telephone exchange system, a subscribers line, an attendants position, a line signal thereat individual to said line, a trunk circuit, means for sending impulses over the two sides of said line in series, and means responsive to one series of impulses over said line to actuate said signal and to another series of impulses to connect said line to said trunk circuit.

7 In a telephone exchange system, a calling subscribers line, an attendants position, a line signal individual to said line, a trunk circuit, an impulse sender for sending impulses over the two sides of said line in series, and relay means responsive to one series of impulses over said line to actuate said signal and to another series of impulses to connect said line to said trunk circuit.

8. In a telephone exchange system, a first exchange, a second exchange, a plurality of trunk lines extending between said exchanges, a plurality of subscribers lines at said first exchange, a line signal at said first exchange for each of said lines, an impulse sender for each of said lines, means responsive to a certain predetermined series of impulses for actuating the line signal of the calling line,-means responsive to another predetermined series of impulses for extending the calling line to an idle trunk circuit, and means operative if all trunks are busy to light the signal of the calling line.

9. In a telephone exchange system, a subscribers line, an attendants position, a line signal for said line, a trunk circuit, an impulse sender for sending impulses over the two sides of said line in series, means responsive to one series of impulses over said line to actuate said signal, means responsive to another series of impulses over said line to connect said line to said trunk circuit, and means operative if all of the trunk circuits are busy to light the signal of the calling line.

In witness whereof, I hereunto subscribe my name this 14th day of June A. D., 1920.

SAMUEL B. WILLIAMS, JR.

/ DISCLAIMER.

1;,550,99T:IS[L7)LU6Z B. 'l Vz'lliams, jia, Brooklyn, N. Y. TLLEPHONE-EXCHANGE SYS- =1 assignce, W estem Eledtmc Uompany, Incorporated.

Hereby enters this disclaimer to the said claims of said Letters Patent which are in the following Words to Wit:

1. In a telephone exchange system, a calling, line, an impulse sender therefor, an attendants position, a line signal thereat individual to said subscribers line, a trunk circuit, and means responsive to one series of impulses fromsaid impulse sender for actuating said line signal, and to another series of impulses to connect said line to said trunk circuit.

2. In a telephone exchange system, acalling line, an impulse sender therefor,

an operators position, a line signal thereat, individual to said subscribers line, a trunk circuit, and means individual to said line responsive to one series of impulses from said impulse sender for actuating said line signal and to anotherseries of impulses from said impulse sender for connecting said line to said trunk circuit.

6. In. a telephone exchange system, a. subscribers line, an attendants position, a. line signal thereat individual to said line, a trunk circuit, means for sending impulses over the two sides of said line in series, and means responsive to one series of impulses over said line to actuate said signal and to another series of impulses to connect said line to said trunk circuit. Y

7. In a telephone exchange system, a calling subscribers line, an attendants position, a line signal individual to said line, a trunk circuit, an impulse sender 'rmr. Patent dated'Au ust 25, 1925. Disclaimer filed May 24, 1928, by the for sending impulses over the two sides of said line in series, and relay means responsive to one series of impulses over said line to actuate said signal and to another series of impulses to connect said hne to said trunk circuit.

[Oyficial Gazette J2me 5, 1.928.]

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