US1763602A - Telephone system - Google Patents

Description

June 10, 1930. c. E. LOMAX TELEPHONE SYSTEM Original Filed Aug. 3, 1925 3 Sheets-Sheet l June 10, 1930. c. E. LOMAX 1,763,602

TELEPHONE SYSTEM Original Filed A g- 1925 I5 Sheets-Sheet 2 June 10, 1930. c. E. LOMAX 1,763,602

TELEPHONE SYSTEM Original Filed Aug. 3, 1925 a Sheetsl-Sheet s H'hiih.

Patented June "10, 1930 UNITED STATES P E T-onion OLARENOE E. LOMA X, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Application filed August 3,1925, Serial 0. 4:7,?30. Renewed February 21, 1929.

' The present inventionrelates in general to improvements in telephone systems, but is tion with an automatic telephone system.

The present disclosure may be considered to be a further development of the circuits disclosed in Patent No. 1,227 ,474issued to T. G. Martin, May 22, 1917, and Patent No. 1,262,843, issued to A. J. Ray, April 16, 1918;

and the object of the inv ntion is to generally improve the operati n, simplify the circuits, and incorporate various novel supervisory and ringing control circuits not covered in thepatents referred to. a

As explained in the previously mentioned patents, long distance calls are usually handled through an operator and it is, of course, desirable that these calls be given preference over local calls. For instance, if

two subscribers are connected in a local connection-and either of these subscribers is desired for atoll connection, it .is desirable that the toll operator be able to inform the desired subscriber that he is. Wanted on a .long distance call. In the previously mentioned Ray patent, the toll operator always sets up the connection to the desired called subscriber ing circuit is-cut through so that the operator can inform the subscriber that he is desired for an incoming toll call. Since all the connector switches are capable of seizing either idle lines or lines busy in local connections, these special features necessarily complicate the connector switches. In the Martin patent, just a sufficient number of special connectors tohandle traflic to busy called lines are provided, but two special types of selectors in addition to the regular switches are required.

In the instant application, the results accomplished are in many respects the same as those described in the Ray and Martin patents, plus special ringing and supervisory features. In the instant case, the manner of ,operation, however, is quiteIdifierent. particularly concerned with means for handling long distance or toll calls in connecoperator. One set of Wipers has access to the regular switch train and the other set has access to switches for extending connections to the special connectors. The operator first sets up'the connection over the regular switch train and only if the called line is busy does she complete the call via the special switch train.

The wipers of the special selector which are ordinari-ly'efl'ective in the instant disclosure are those having access to the regular switch train. If the operator desires that the connection be extended over the other switch train she. operates a key momentarily before dialling.

If it is preferable, the operator may be provided with separate sets of cords instead of the combination cord illustrated under which conditions the route taken will be automatically dependent on the cord used.

The invention is disclosed in the accompanying drawings comprising Figs. 1, 2, and 3. Fig. 1 shows an operators cord circuit. Fig. 2 shows a special selector D whichis structurally of the well known vertical and rotary type, but with'circuits as required by the various features of the invention, while Fig. 3 shows a special connector H which is structurally the same as the selector D of Fig. 2, but the circuits are in accordance with the invention. The line switch C is of the continuous rotary type, while the substation A is of the general type usually found in automatic telephone systems.

In order to make the invention clear, it is believed advisable to describe the manner of operation by explaining first how a connection is established by the operator over a regular switch train and then by explaining the operations which are necessary should the called line be found busy when called over the regular switch train.

It will first be assumed that the toll operator has received a call over the trunk line terminating in jack J and answers this call by inserting the plug P in this jack and operating listening key K. It will further be assumed that the subscriber desired is the subscriber at substation A. in another exchange accessible to the operator over the trunk terminating in jack J. The operator, upon observing the idle condition of busy visual 27, seizes the associated trunk by inserting the plug P in jack J and by then operating her calling device key K. Upon insertion of the plug P into jack J, busy visual signal 27 is operated from ground supplied by spring 21 and its grounded working contact. The operation of the busy visual signal 27 indicates to other operators, at whose position this trunk is multipled, that the trunk is taken into use. The normal conductor 22 is grounded at the same time which serves to protect the trunk from intrusion by subscribers of the exchange in which the cord 0 is located, as will be explained subsequently. Upon the operation of key K, a circuit was closed for sleeve relay 12 of the cord, via springs 20, and sleeve of plug P which has been grounded by spring 21 of jack J. Relay 12, upon operating, at its armature 14 prepares a circuit for polarized relay 11, and at its armature 15 and its working contact completes a circuit for relay 12 independent of the springs controlled by key K.

The operation of key K connected the calling device to the tip and rin conductor of the cord 0. This completes t e loop over a trunk conductor 25, armature 30 and its resting contact, upper winding of differential relay 34, and the upper winding of line relay 36 of the selector D to battery; and from ground over the lower winding of line relay 36, lower winding of differential relay 34, resting contact and armature 33, lower trunk conductor 26 to and through the jack J and plug P, springs of key K and the calling device CD. The line relay 36 energizes over this circuit, completing a circuit for slow release 84. Relay 84, upon operating, at its armature 38 connects ground to holding conductor 85, and at its armature 39 opens a point in the release circuit and closes a point in the operating circuit of relay 42 and vertical magnet 44. The switch D is now in readiness to receive the first series of impulses of the called number. Responsive to an operation of the calling device the circuit of line relay 36 is interrupted a number of times and at each interruption a circuit is completed from grounded resting contact and armature 32, armature 37 and its resting contact, armature 39 and its working contact, winding of relay 42 and vertical magnet 44 to battery.

Due to its slow release characteristics, relay 42 remains energized throughout the series of impulses. Vertical magnet 44, however, is effective in the well known manner to step the wipers 6469, inclusive, opposite the level of bank contacts dependent on the number of impulses transmitted.

Upon the first vertical movement of the switch, off normal springs 48 are closed and a circuit is thereby completed for stepping relay 45. This circuit extends from battery, winding of stepping relay 45, oil normal springs 48, armature 43 and its working contact, conductor 85, and the front contact and rounded armature 38 of the slow release reay 84. Relay 45 operates, at its armature 46 closes a point in the operating circuit of rotary magnet 95, and at its armature 47 completes a locking circuit for itself independent of armature 43. This circuit extends by way of grounded resting contact and armature 32 of the switching relay 92, conductor 89, armature 47 and its working contact resting contact and armature 49 and the 0 normal spring 48.

Following the transmission of the last impulse of the series slow relay 42 restores and, at springs contro led by armature 43, completes a circuit for rotary magnet 95 from the grounded conductor 85, springs controlled by armature 43, working contact'and armature 46 and the winding of magnet 95 to battery. Rotary magnet 95 operates to rotate its wipers into engagement with the first sets of contacts of the level to which they have been positioned and at its armature 49 opens the traced looking circuit for stepping relay 45. Relay 45 accordingly restores and in so doing opens the circuit of rotary magnet 95, which thereupon restores also. Further operation of the selector is dependent on the busy or idle condition of the test contacts en aged by test wiper 66. If the trunk seized is usy, ground potential will be present on test contact 76 and a circuit will again be completed for stepping relay 45 via test wiper 66, conductor 56, resting contact and armature 52, conductor 91, armature 31 and its resting contact, conductor 88, resting contact and armature 49, off normal springs 48 and the winding of stepping relay 45 to battery.

Under these conditions, relay 45 will again operate to close the circuit for rotary magnet 95, which will in turn operate to step the wipers on to the next set of bank contacts and to again open the circuit of stepping relay 45. The alternate operation of stepping relay 45 and rotary magnet 95 will continue until the test wiper 66 finds an idle trunk, which is so designated by the absence of ground on test contact 76.

When an idle trunk is found, the switching relay 92, which has heretofore been short circuited by grounded wiper 66, is operated over a circuit extending from battery, winding of stepping relay 45, off normal springs 48, armature 49 and its resting contact, conductor 88, winding of switching relay 92, conductor 85, and the working contact and grounded armature 38. The resistance of relay 92 is very high compared to that of stepping relay 45 and the latter relay, therefore,

92 operates, however, at its armatures 30 and 33 disconnects the line and differential relays 36 and 34, and at the working contacts of these armatures extends the connection 'via conductors 8687, armatures 51 and 53 and their'resti'ng contacts, wipers 64 and 65, bank contacts 74 and 75 and conductors 61 and 62 to a second selector of the regular switch train. Relay 92 also at its armature 31 prepares a locking circuit for itself and at its armature 32, removes ground from the conductor extending to armature 37 so as to preation of slow release relay 84 which occurs as a result of its circuit being opened at armature 32.

As is customary, the line and release relays of the second selector are operated (not shown) and the release relay connects ground back over conductor 63, test contact 76, wiper 66, conductor 56, resting contact'and armature 52 to' holding conductor 91, to} maintain the switching relay 92 operated" and to prevent the switch from releasing, these operations occurring before the slow release relay 84 has had time to restore.

lhe completion of the connection from this point on is accomplished by the operator dialling the remaining digits, causing the second selector and connector to be positioned on contacts 'multipled with the bank contacts 154, 155, and 156 disclosed in Fig. 3. Now if the subscriber at station A is holding a conversation, the connector will transmit a busy tone to the operator in the same manner as if the line had been called by a subscriber direct. Under these circumstances, the operator will withdraw the plug P from the jack J momentarily, thereby opening the bridge across conductors 25 and 26. This results in the regular switch train being released and I in ground being removed-from test contact 76. The removal of ground from test contact 76 causes the deenergization of switching re-' in Fig. 2 and over the regular switch train.

- The calling end of the cord circuit shown in Fig.1 is however, designed to also permit. establishment of a connection over the special switches shown in Figs. 2 and 3, exclusive of the regular switch train, as is described below.

The operator after having failed to reach the desired party over the regular path, reinserts plug P in'jack J and this time proceeds as before, except that, before dialling any digits, she momentarily operates keyv K causing battery to be momentarily connected via spring 17 of key K, out overtip conductor 25, armature 30 and its resting contact, upper winding of differential relay 34 and the upper winding of relay 36 to battery. This unbalances differential relay 34 momentarily, causing the same to momentarily oper- 1 ate and at its armature 35 and its grounded working contact connect ground over conductor 90 to wiper switching relay 50. Relay 50 operates, at its armature 96 locks up over the grounded conductor 85, at its armature 51, 52,

and 53 switches conductors 86, 87 and 88 from connection with the wipers 64, 65 and 66 into connection with wipers 67, 68 and 69. vent the selector D releasing upon the restor- I The operator proceeds by operating her calling device to position the selector E to line relay 107 is operated, causing the opera- 1 tion of slow release relay 109. Relay 109, upon operating, at its armature 112 applies ground to conductor 83 to maintain the selector E and selector D operated in the usual manner and at its armature 113 closes a point in the control circuit for the connector. The switch is now ready to receive impulses.

Responsive to a n'umberof interruptions in the line circuit, the line relay 107 retracts its armature a plurality of times to cause the wipers 151, 152 and 153 of the connector H to be positioned opposite the level of bank contacts in which the line of substation A terminates. The first impulse may be traced from grounded armature and resting contact of relay 107, armature -113 and its working contact, Off normal springs 116, winding of series relay 119 and the winding of vertical magnet 118 to battery. As soon as the switch'moves ofi' normal this circuit is switched so as to' extend via armature 113 and its working contact and springs controlled by ofi normal springs 116, armature of slow release relay 119 and its working contact, the remainder of the impulse series passing over this circuit.

Shortly following the last interruption of the circuit of line relay 107, slow release relay 119 restores and at its armature and resting contact prepares an operating circuit for slow release relays 133, 147, and the rotary magnet 140. The circuit of slow release relay 147 extends by way of conductor 125, while the circuit for relay 133 and rotary magnet 140, extends by way of this conductor and resting contact and armature 132,

winding of relay 133, armature 141 and its resting contact and the winding of rotary magnet 140 to battery.

The next and final operation of the calling device causes the line relay torepeat impulses to the conductor 125, causing slow release relays 133 and 147 and rotary magnet 140 to operate. The rotary magnet operates in the well known manner to step the wipers 151 to 153 into engagement with the contacts of the called line. Relay 133, upon ion operating at its armature 134, opens a point in the operating circuit of swltching relay 139 and at the front contact of this armature connects test wiper 153 to the winding of test relay 129. Relay 133 also at its armature 135 completes a circuit around armature 132 and its resting contact so as to guard against the rotary ma net circuit being interrupted by operation 0? relay 129 as a result of w1 er 153 passing over busy test contacts. Re ay 147 at its armatures 148 and 150 disconnects the wipers 151 and 162 while the switch is rotating, and at its armature 149 completes the circuit for ring cut-01f relay 121. The circuit ma be traced from grounded armature 111 an its working contact, conductor 136, armature 149 and its working contact and the upper winding of relay 121 to battery. Relay 121 operates at its armature 122 short circuits condenser 110, at its armatures 123 and 127 disconnects generator and ground from con ductors 162 and 163, respectively, and at the working contacts of these armatures connects these conductors to conductors 164 and 165 extending to the upper and lower windings of reversin relay 100; at armature 126 completes a locking circuitfor itself, the circuit extending by way of the armature and resting contact of diiierential relay 106 and ground supplied by armature 111 and its working contact; at armature 124 closes a point in the circuit of the upper winding of relay 100 and at armature 128 and its working contact prepares a talking circuit to the called line, which will be completed immediately upon the slow release relay 147, restorin following the transmission of the last digit of the called number. Following the transmission of the last digit, relays 133 and 147 restore but before this occurs, assuming the called line is still busy, ground will be supplied by way of test contact 156, wiper 153, armature 134 and its working contact to the winding of test relay 129. This relay operates and at its armature 131 prepares a locking circuit for itself independent of armature 134 and its'working contact, at its armature 132 opens one point in the operating circuit of the rotary magnet, and at its armature 130 opens a point in the o erating circuit of the switching relay 139. t will be noted that even though the called line is still busy, the talking circuit has been connected through. As a result of the restoration of slow release relay 147, a circuit for reversing rela 100 is completed from battery, upper winding of said relay, conductor 164, reslstance 117, armature 124 and its working contact, armature 142 and its resting contact, resting contact and armature 149 to grounded conductor 136. Relay 100 operates and reverses the direction of current flow to the polarized relay 11 in the operators cord circuit, causing the lamp L to be extinguished, thereby notifying the operator that the called line is still busy. The operator may therefore operate her listenin key K and inform the called subscriber t at he is desired for a long distance call.

The operator may now follow either of two courses, either operate K momentarily, causing the difli'erential relay 106 to momentarily operate to cause the ring cut-off rela 121 to restore, or she may wait until the ca led line becomes idle and then initiate the ringing by operatin the key K momentarily. If the key K215 operated while the called line is still busy, the rin cut-off relay restores and then as soon as t e called subscriber replaces his receiver, ground will be removed from the test contact, ermitting the test relay 129 to restore. pon relay 129 restoring, a circuit is com leted for switching relay 139 from groun ed working contact and armature 112, conductor 83, resting contact and armature 130, upper Winding of relay 139, resting contact and armature 134, test.

wiper 153, wiper 156, winding of cut-ofi' relay 159, resting contact and armature 160 of the rotary magnet and the windin of said magnet to battery. Due to the big resistance of relay 159 and switching relay 139, the rotary magnet 161 is not operated. Relay 159 is operated, however, to cut off the normal connection ofthe line switch C and the relay 139 is also operated. Relay 139 at its armature 141 opens another point in the operating circuit of rotary magnet 140; at armature 144 and its working contact, completes a locking circuit for itself over its lower winding, conductor 105, conductor 136 and the working contact and grounded armature 111; and at its armature 142 opens the circuit of reversing relay 100, causing the normal current flow to the polarized relay 11 of the operators cord circuit to be restored. This causes the lamp L to be again lighted to notify the operator that the called line has become idle and that the signalling operation is about to begin, the signalling circuit being completed at armatures 145 an 146'and their workin contacts.

Upon response of t e called subscriber, the ring cut-off relay operates in the usual manner, at its armatures 123 and 127 the generator and ground, respectively, are cut oif from the called line and at the working contact of these armatures, the connection is extended through. Relay 100 is now operated in series with the called line to cause the polar relay 11 to be again operated to extinguish lamp L, thereby notifying the operator that the called subscriber has answered.

As previously stated, if the operator s0 desires, she may delay the operation of key K until after t e called line has become idle,

- in which case the operations will be the same as just described exce t that the rin ing will not be started until t e ring cut-o relay is restored to normal by operation of the key K In the foregoifig description, it was assumed that the 0' line called is idle, when the connector H seizes it, relay 129 will not operate and, therefore, the operating circuit of switching relay 139 will be completed upon the restoration of slow release relay 133 over a circuit-similar to that hereinbefore described. Since in this case, the local circuit for reversing relay 100 is opened at armature 142, the lamp L, therefore, continues to glow until the called subscriber responds, it being understood, of course, that the ap lication of ringing current takes place in t e hereinbefore described manner. I

As previously mentioned, thetrunk line terminating in jack J isalso available to subscribers over the normal conductors 22, 23, and 24. The intervenin switches used between a'calling line and the normal conductors 22, 23, and 24 may comprisestandard circuits such, for instance, as the circuits of the line switch associated with substation A, a selector such as selector E shown in the Patent No. 1,540,159, issued to J. I. Bellamy, June 2, 1925. The repeater seized by selector E may be such as disclosed in the patent referred to, or such as the repeater disclosed on page 4:7 of the publication known as Principles of Automatic Telephony by Harry P. Mahoney. The selector E .of Fig. 2 and the regular selector, not shown, may also be like the one shown in the patent.

From the foregoin it will be appreciated that a plicant has esigned improved circuits or completing toll connections in'an economical and efl'icient manner.

What is claimed is:

1. In a telephone system, subscribers lines, means for making any line busy an operators switchboard, automatic switc es, a cord circuit adapted for normally extending talking connections from calling lines to idle called lines via certain of said switches, special operator controlled means associated with said cord circuit for altering the operation of one of said switches to cause certain other of said switches to complete talking connections to busy lines, and a visual signal at the operators switchboard automatically eflective upon a connection being extended to a busy line for notifying the operator that the line called is busy.

2. In a telephone system, subscribers lines, means for making any line busy, an operators switchboard, automatic switches, a cord circuit adapted for normally extending talking connections from callin lines to idle called lines via certain of sai switches, special operator controlled means associated with said cord circuit for altering the operation of one of said switches to cause certain other of said switches to complete talking connections to busy lines, and a visual signal at the operators position for notifying ed line was busy. If the b the operator that the line called is idle, or

3. In a tele hone system, subscribers lines, means for m g any line busy, an operators switchboard, operator controlled means including a train of automatic switches for completing talking connection to busy lines,

means in. one of said switches for transmitting signalin current to the line called, and.

means contro led by the operator for causingsaid signaling current to be applied autordnlztically as soon as the called line becomes 4. In a telephone system, subscribers lines, means for making anyline busy, an

operators switchboard, operator controlled means including a train of automatic switches for completing talking connections to busy lines, means in one of said switches for transmitting signalin current to the line called,

and means opera le by the operator for causing said signaling current to be applied in- I stantly upon the called line becoming idle, or for causing the application of signaling current at any time afterwards.

5. In a telephone system, calling lines of two classes, trunk lines, automatic switches of two classes, the automatic switches of only one class being available to one class of calling lines to establish connections to the same class of called lines, while the automatic switches of both classes are available for use by lines of the other class, another automatic switch available to both classes of calling lines, said switch having access to switches of either class only when seized by a particular class of calling line.

6. In a telephone system, subscribers lines, an operators switchboard, automatic switches for establishing talking connections to other lines from the said switchboard or from the said subscribers lines, and other automatic switches available to one of said first switches to complete connections to said subscribers lines only when the connections are extended from the operators switchboard.

7. In a telephone system, an operators switchboard, a trunk line having one end terminating in a-jack at saidswitchboard and the other end terminating in an auto-. matic switch at a distant point, a plurality of sets of wipers for said switch, each set having access to a difierent train of automatic switches for use in extending connections, operator controlled means in said switch for predeterminin which wiper set will be effective, subscr1 ers lines, and means rendering said switch operable only to extend calls via one of said wiper sets if seized by subscribers lines.

8. In a telephone system, calling stations of two classes, an automatic switch accessible to said stations and'provided with a plurality of sets of wipers, each set having access to a different train of automatic switches for use i in extending connections from calling to called stations, means for rendering said switch operable to extend calls only-via one 'of said sets of wipers if seized by a calling station of one class, and means in said switch for redetermining which wiper set is to be use if said switch is seized by a calling station-of the other class.

9. In a telephone system, calling stations of two classes, an automatic switch accessible to said stations and provided with a plurality. of sets of wipers each set having access to a different train of in extending connections from calling to called stations, means for rendering said switch operable to extend calls only-via one of said sets of wipers if seized by a calling station of one class, and station controlle means in said switch for (predeterminin which wiper set is to be use if said switc is seized by a calling station of the other class.

10. In a telephone system, calling stations of two classes, an automatic directively controlled step by ste switch common to both classes and accessib e thereto, said switch having access to called stations over two different paths each involving a separate train of switches, means in said switch responsive to a call from a calling station of one class for extending a call over a predetermined path to a called station, and means responsive to'the conditions of a calling station of the other class for rendering said switch operable to extend a call over either of the two paths at the choice of the calling station.

11. In a telephone system, calling stations of two classes, an automatic switch common to both classes accessible thereto, said switch having access to called stations over two different paths, one of said paths being predetermined for serving calling stations of one class and adapted to establish a talkin connection between a calling and a calle station only if said called station is idle, said other path being predetermined for servin calling stations of the other class and adapted to establish a talking connection re ardless of the idle or busy conditions of a ca led station, and means 1n said switch for effecting the switching operations in accordance to the class of a callin station.

12. In a telep one system, calling stations of two classes, an automatic switch common to both classes and accessible thereto, said switch having access to called stations over two different paths, one of said paths being adapted when used in the extension of a call to establish a talking connection between a calling and a called station only if said called station is idle, and said other paths being adapted to establish a talking connection regardless of the busy or idle conditions of 9. called station, only the first of said paths being accessible to calling stations of one class and both of said aths bein accessible-to calling stations of t e other e ass.

13. In a telephone system,.calling stations of two classes, an automatic switch common to both classes and accessible thereto, said switch having access to called stations over two different paths,,one of said paths being adapted when used in the extension of a call to establish a talking connection between a calling and a called station onlyif'said called station is idle, said other paths being ada ted to establish a talking connection regar less automatic switches for use of the busy or idle conditions of a called station, only the first of said paths being accessible to calling stations of one class and both of said paths being accessible to calling stations of the other class, and switching means in said switch responsive to the conditions of calling stations for determining the path to be taken in the extension of a call.

14. In a telephone system, calling stations,

automatic switches of two classes, called stations accessible to said switches, the switches of one class being adapted when used in the extension of a call from a calling to a called station to complete a talking connection only if said called station is idle, and the switches of the other class being adapted to complete a talking connection regardless of the busy or idle conditions of a called station, and common switching means accessible to said calling stations and havin access to said switches for determining t e switch to be taken into use in the extension of a call. 15. In a telephone system, calling stations, automatic switches of two classes, called stations accessible to said switches, the switches of one class being adapted when used in the extension of a call from a calling to a called station to complete a talking connection only if said called station is idle, and the switches of the other class being adapted to complete a talking connection regardless of the bus or idle conditions of a called station, and rommon switching means accessible to said calling stations, directively controlled therefrom, and having access to said switches for determing the switch to be taken into use in the extension of a call.

16. In a telephone system, calling and called stations, an automatic switch for establishing'a talking connection between a calling station and :1 called station while said called station is engaged in another call, means automatically operable upon said called station being seized for notifying said calling station of the busy condition of said station, a relay in said switch for causing ringing current to be applied to an idle called station, and means controlled by said calling station for rendering said relay effective at will, said relay also effective upon response of the called station to disconnect ringing current and to complete the talking circuit.

17 In a telephone system, calling and called stations, an automatic switch accessible only to certain calling stations for establishing a talking connection with a called station regardless whether said called station is idle or busy, a relay in said switch for applying ringing current to said called station it said station is idle, means for preventing the application of ringing current if said station is busy, and means controlled by said calling station for rendering said relay efiective at will. 1

18. In a telephone system, calling and called stations, an automatic switch accessible only to certain calling stations for establishing a talking connection with a called station regardless whether said called station is idle or busy, means automatically operable upon said switch seizing said called station for notifying. the calling station whether said called station is busy or idle, a relay in said switch'for applying ringing current to said called station if said station is idle, means for preventin the application of ringing current if sai station is busy, and means controlled by said calling station for rendering said relay effective at will.

19. In a telephone system, calling and calledstations an automatic switch accessible only to certain calling stations for establishing a talking connection with a called station regardless whether said called station is idle or busy, means automatically operable upon said switch seizing said called station for notifying the calling station whether said called station is busy or idle, a relay in said switch for applying ringing current to said called station if said station is idle, means for pre- .venting' the application of ringing current if said station is busy, and means controlled by said calling station for rendering said relay efiective at will, said relay also efi'ective upon response of the called station to disconnect ringing current and to complete the talking circuit.

20. In a telephone system, a calling station, a called station, an automatic switch for connecting said' calling station with said called station, a relay in said switch for applying ringing current to said called station, means for preventing the operation of said relay when the called station is busy and permitting its operation when the called station becomes idle, a ring-cut-ofi relay in said switch having means for preventing the operation of said other relay from applying ringing current to the called station, and calling station controlled means for operating said ring-cut-ofl relay while said switch is connected to a busy called station to permit aultomatic ringing when the station becomes id e.

21. In a telephonesystem, a calling station and a called station, an automatic switch for connecting said calling station with said called station, a relay in said switch operative to close a circuit to apply ringing current to the. called stations, means for preventing the operation of said relay when the called station is busy, a ring-cut-ofi relay in said circuit having means for opening said circuit, means for energizing said ring-cutoif relay before the other relay energizes to I prevent said other relay from applying ringing current to the called station when said other relay energizes, and means controlled from the calling station fordeenergizing said ring-cut-ofi relay while the called station is busy to permit automatic ringing when said called station becomes idle.

22. In a telephone system, a calling station, an automatic switch having two sets of wipers for routing calls over diflerent switch trains, a trunk line terminating in said switch and accessible to said station, means associated with said station for seizing said trunk, means at said station for operating said switch to route a call over one set of said wipers and oneswitch train, means at said station for releasing that switch train without releasing said trunk, and means for routing another call over the other set of Wipers and a different switch train. I

23. In a telephone system, a calling station, a trunk line terminating in an automatic switch .having two sets of wipers, means aserative to close a circuit to apply ringing current to the called station, means for preventing the operation of said relay when the called station is'busy, a ring-cut-ofi' relay in said'circuit having means for opening said circuit, means for energizing said ring-cutolf relay before the other relay energizes to prevent the said other relay from applying ringing current to the called station when said other relay energizes, and means alternatively controlled -from the calling station for either deenergizing said ringscut-ofl' relay while the called station is busy to permit automatic ringing when the station becomes idle, or deenergizing said ring-cut-ofi relay after the called station has become idle to prevent ringing at will.

In witness whereof, I hereunto subscribe my name this 31st day of July, A. D. 1925.

CLARENCE E. LOMAX.

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