US1537306A

US1537306A - Automatic telephone system

Info

Publication number: US1537306A
Application number: US376501A
Authority: US
Inventors: Jacobsen Emil
Original assignee: Automatic Electric Co
Current assignee: Automatic Electric Co
Priority date: 1920-04-26
Filing date: 1920-04-26
Publication date: 1925-05-12
Anticipated expiration: 1942-05-12
Also published as: DE406219C; GB177172A

Description

' maria-192's. 1537,306

E. JA COBS EN AUTOMATIC TELEPHONE; SYSTEM Filed April 26, 1920 mam-f Emfl Jacubssn Patented May 12, 1925.

UNITED STATES PATENT OFFICE.

EMIL JACOBSEN, PORT WASHINGTON, NEW YORK, ASSIGNOR TO AUTOMATIC ELEC- TRIO COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed April 26, 1920. Serial No. 376,501.

To all whom it may concern:

Be it known that I, EMIL JAcoBsEN, a citizen of the United States of America, and a resident of Port WVashington, Nassau County, and State of New York, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

My invention relates in general to automatic telephone systems, but more articularly to such systems as comprise mam and branch exchanges; and the object of the invention is to provide a new and improved method for completing branch exchange connections locally, branch to main and main to branch trunk lines not being used for such connections, without departing from or in any way modifying the standard numbering arrangement.

Systems in which this result is accomplished have been designed before, notably in the following U. S. Patents which are referred to as indicating the state of the art: Lubberger, No. 1,295,181, Feb. 25, 1919. \Villis and Martin, No. 1,306,825, June 17,1919.

Hershey, No. 1,283,182, Oct. 29, 1918. The present invention provides a number of circuit improvements and other refinements, especially in the switching selector rcpeaters' at the branch exchange, these being the switching mechanisms used to eliminate the interexchange' trunk lines on local calls. Other new features of improvement have to do with the use of rotary secondary line switches in connection with the switchingselector repeaters for selecting main exchange trunk lines, together with special means for indicatingto a calling branch subscriber the condition of all trunks busy. These and other features willbe pointed out and explained fully in the course of the general description of the invention which will now he proceeded with. p i

- Although the invention is applicable to systems of different size, it will be assumed for convenience that we are. dealing with asystem of 10,000 lines, of which'one thousand, the second thousand, are in the branch exchange; while the remaining thousands may be in the a main exchange. The general trunking arrangement is not novel and consequently is not shown, the single drawing shoiving only the improved switching selector repeater and associated mechanism in the branch exchange. It is believed that a brief explanation of this figure will serve to give a general idea of how this apparatus is related to the system as a whole, and this is all that is necessary.

Referring to the drawing, the substation A is an ordinary automatic substation and is one of a thousand similar substations which as before stated terminate in the branch exchange. Each substation line may terminate at the branch exchange in a rotary line switch or trunk selector of the usual type, the line switch in which the line or substation A terminates being indicated by the reference character C. The lines and associated line switches are preferably divided into groups of one hundred each, cor responding to the capacity of a connector switch of standard construction, and the line switches of each group have common access to a group of switching selector repeaters. One of these latter is shown in the drawing and is indicated by the reference character D. It is understood that the repeated D is one of a group of perhaps ten repeaters which are accessible to a group of one hundred line switches one of which is the line switch 0. a

The switching selector repeater D is a vertical and rotary switch of the usual Strowge-r type so faras mechanical construction is concerned, having special relays and circuits added, however, which enable it to function as a repeater. Being directly accessible to the line switches it will be apprehended that the selector functions which the switch performs will be those of a so called first selector, which as is well understood is the switch which selects the thousand group, it being understood of course that a 10,000 line system is referred to. This is in fact the case, for the switch, when'seized by a calling line,.responds to the first digit of the called number and raises its shaft accordingly to select the-proper level or thousand group after which thewipers may be automaticallyrotated in the usual manner. This function of the selectoris made use of, however, only in completing calls which are local within the branch exchange one which corresponds to the thousand group of lines terminating in the branch exchange are left dead. According to the previous assumption, this is the second thousand and therefore the second level of these switches is the only level which is wired. The bank contact sets in the second level are terminals of trunk lines extending to local second selectors (not shown), and these local second selectors have access to groups of connectors, which in turn have acceSs to the local lines such as the line of substation A, all according to the well known percentage trunking system. In the draw- 1ng there is shown one set of bank contacts in the first level and one set of bank contacts in the second level. The first set is left dead, that is, not wired, as are all other contact sets in this level and all the remaining levels except the second level. The other set of contacts, being the first set in the second level, and" comprising contacts 94 97, inclusive, is the terminal of a trunkline leading to a local second selector, the conductors leading off from bank contacts 94, 95,and 97 being the usual line and release trunk conductors. Bank contact 96 is per manently grounded asare all the adjacent contacts of the second level which are engaged by the wiper 92.

Having described briefly the a paratus having to do with the establishment of local connections, the apparatus used in branch to main connections will be briefly considered. To handle these calls each of the switching selector repeaters is provided with a secondary line switch, and all of these secondary line switches have access in common to a group of trunk lines extending to the main exchange and there terminating in first selector switches. The secondary line switch which is associated with the switching selector repeater D is shown in the upper right hand part of the sheet and is indicated by reference character C. One of the trunk lines to the main exchange to which the line to the brank exchange where they terminate in so called incoming second selectors, which have access to the several groups of connectors in common with the local second selectors.

These The foregoing paragraphs will serve to give a general understanding of the character of the apparatus and the system of trunking which is employed. The new improvements, however, and the precise circuits used in accomplishing the objects of the invention, cannot be readily understood without a more detailed explanation of the operation, and such explanation will now be given. For this purpose it will first be as sumed that the subscriber at substation A desires to obtain connec'ion with another subscriber Whose telephone number is #2555, and whose line therefore terminates in the branch exchange.

When the receiver is removed from the hook at substation A, a circuit is completed over' the line conductors 11 and 12 for the line relay 14 of the line switch C. Upon energizing, the line relay completes a circuit extending through the switching relay 13 and the stepping magnet 15 in series at its armature 20, and at its armature 19 connects the test wiper 26 to the above circuit at. a point midway between the switching relay and the said stepping magnet. The operation now depends upon whether the test contact with which the test wiper 26 is in engagement is busy or is not busy. If this test contact is busy it will have a ground potential upon it, the switching relay 13 will be short cireuited, and the stepping magnet 15, which interrupts its own circuit, will operate as a buzzer to advance the switch wipers 25-27, inclusive, step by step in search of an idle trunk line. This operation will continue as long as the test wiper 26 engages" ground or busy test contacts. 7 How-- ever, we may assume that in the present case when the call is initiated. the switching selector repeater D is idle and the test contact 31 therefore is not grounded. Under these circumstances, when the line relay ll is energized, the switching relay 13 is energized immediately afterwards, with the result that the line conductors 11 and 12 are disconnected from the winding of the line relay 14 and from ground, respectively, and are extended by means of armatures 16 and 18, wipers 25 and 27, bank contacts 30 and 32, armatul'es 64 and 67 and their resting contacts and normally closed contacts of reversing relay '51 to the upperand lower windings of the line relay 52 of switching selector repeater D.

Immediately upon the extension of the line as above described the line relay 52 will be energized over the line circuit and will close the circuit of the slow acting release relay 53. Upon energizing, relay 53 prepares the circuits of the switch for the vertical operation in the usual manner, at its armature 72, and at armature 5S completes a holding circuit extending back to the line switch C over the following path: Ground Hill at G, working contact of armature 71 and the said armature, conductor 33, test contact 31, test wiper 26, armature 17 and its working contact, winding of theswitching relay 13, and the'winding of the stepping magnet 15 to battery. It is understood that the above circuit is established before the slow acting line relay 14 has had time to deenergize. By a ground potential on test contact 31 and its multiples this holding circuit also serves to render the switching selector repeater D busy to the other hne switches; and the busy potential also extends by way of private normal conductor 34 to multiple test contacts in the banks of the connectors having access to the line of substation A, thereby protecting the line against intrusion in the usual manner.

Returnin to the switching selector repeater D, w 1en the release relay 53 energized it also closed at its armature 70 a circuit extending from ground (it to the polarizing winding of the electro-polariz'ed relay 56, a branch of which circuit may be traced by way of off normal springs 53 to the relay 58.

, Upon energizing, relay 58 establishesa locking circuit for itself at its armature 79, prepares a circuit for the rotary stepping relay 57 at armature 80, andat armature 81 prepares the circuit of the vertical magnet 61.

The switch D is now ready to operate responsive to the calling of the first digit in the desired number, but before proceeding with this it will be necessary to consider circuits which were closed for the secondary line switch C immediately upon the seizure of the switch D by the line switch C.

When the line relay 52 .is energized a bridge is closed across the branch trunk line conductors 111 and 112 which is effective to energize the line relay 102 of the secondary line switch, the circuit being as follows:

Grounded conductor 133, resting contact of armature 107 and the said armature, conductor 112, working contact of armature 69 and the said armature, lower windin of the electro-polarized relay 56, lower winding of busy relay 55, resting contact of armature 73 and the said armature, conductor 111, armature 104 and its resting contact, and the winding of the line relay 102 to battery. The above is the circuit through the bridge. It will be noticed that the upper conductor of the trunk incoming to the switch D connects with conductor 111 by way of the upper condenser and armature 73, while the lower trunk conductor connects with conductor 112 by way of the lowerv condenser and armature 69; To proceed, an. instant after the bridge across conductors 111 and 112 is closed by relay 52, conductor 110 is grounded at armature 70 of relay 53. This takes place by the time the line relay 102 has energized and obviously results in the closure'of the usualcircuitfor the switching relay 101 in series with the stepping magnet 103. Line relay 102 having energized, it will be seen that the test wiper 122 has been connected to the above circuit between the switching relay and stepping magnet. These circuit conditions are substantially the same as were described in the case of the line switch C, and it will necessarily follow that the secondary switch C will operate as a trunk selector to select an idle trunk line to the main exchange. Assuming that the trunk line comprising conductors 140 and 141 is the first idle trunk line, when the test wiper 122 arrives at test contact 126 the rotary movement will cease, no ground potential being found, and the switching rclay 101 will be energized. As a result the branch conductors 111 and 112 are disconnected from the winding of the line relay 102 and from ground conductor 133, respectively, and are extended by way of

armatures

104 and 107 and their working contacts, wipers 120 and 123, bank contacts 124 and 127, and trunk conductors 140 and 141 to the line relay -of a first selector (not shown) in the main exchange. Therebeing a bridge closed across the trunk conductors 140 and 141 at the switching selector repeater D, as already explained, the line relay of the distant selector is energized and the se lector is made-ready for operation in the usual manner.

Certain circuit details in the secondary switch G will now be considered. lVhen the switching relay 101 was energized the original energizing circuit oftheline relay 102 was broken, but this relay is maintained energized by a locking circuit previously closed at its armature 115. Relay 101 also disconnects the test wiper 122 at armature 106, and at armature 105 closes a circuit for relay 130. Relay 130, upon energizing, grounds the testcontact 126 and its multiples in'the banks of the other secondary switches in order to make the selected trunk line busy; and at its armature 132 breaks one of the multiple ground connections to the common conductor 133. It will be convenient to explain at this time that there is a relay similar to relay 130 for each of the trunk lilies to the main exchange, and each of these relays controls a multiple ground connection toconductor 133 as is shown in the case of relay 130. This arrangement is provided for the purpose of giving a calling branch exchange subscriber the busy signal in case all the main exchange trunk lines are in use. In case all the trunk lines are busy, all the relays similar to relay 130 will be energized, common conductor 133 will be entirely disconnected from ground, and since all the secondary line switches are sup lied with ground from this conductor exact as is shown in the case of line switch C, it will be impossible to energize the line relay of any secondary switch which it is attempted to operate. Suppose that all the trunk lines had been busy when the connection being described was initiated. Under these circumstances, when the bridge is closed across conductors 111 and 112 the line relay 102 is not energized, and the grounding of conductor 110 results in the immediate energization of switching relay 101, this relay being operated only about half way, however, due to the interlocking of its armature with the armature of the line relay in the well understood manner, so that the connection is-not extended through to the line switch wipers. Since there is no flow of current in the bridge at the switching selector' repeater D, the relay 55 included therein will not energize and the calling subscriber will be given a busy signal by the inductive action between the two windings of the said relay 55, the upper winding of the relay being in a closed circuit including the transformer secondary winding of the busy signalling machine Q. Under ordinary conditions, when trunk lines areavailable and one is selected as described in the preceding paragraphs, relay 55 is energized as soon as the bridge is closed and disconnects the busy signalling machine at armature 75.

The explanation may now he proceeded with. The calling line has been extended to the switching selector repeater D and a branch from the said switch has been extended by way of the secondary line switch C to a first selector in the main exchange; With these facts in mind the results ensuing from the calling of the first digit will be readily grasped. The first digit to be called is the digit 2 and when the calling device S at substation A is operated, two interruptions are produced in the circuit of the line relay 52. The line relay is accordingly twice deenergized momentarily and at each deenergization sends an impulse of current through the vertical magnet 61 as follows: Ground at G, armature 68 and its resting contact, resting contact of armature 66 and the said armature, armature 72 and its working contact, working contact of armature 81 and the said armature, and the winding of the vertical magnet 61 to battery. By the operation of the vertical magnet responsive to these impulses the switch shaft is raised two steps until wipers 9093, inclusive, stand opposite the second level of bank contacts. The slow acting relay 54 is "energized in parallel with the vertical magnet,'maintainmg its armatures attracted during the vertical movement of the switch, and at the first upward movement of the switch shaft this relay closes at its armature 74 an initial energizing circuit for the stepping relay 57, this circuit being readily traceable by way of off-normal springs 62. Upon energizing, relay 57 prepares a circuit for the rotary magnet 59 at its armature 77, and at its armature 78 establishes a locking circuit for itself in the usual manner.

Returning now for a moment to the line relay 52, the deenergizations of this relay not only brings about the operation of the vertical magnet 61 as described, but also produce interruptions in the bridge across branch trunk conductors 111 and 112, these interruptions being produced atarmature 69. As a result the line relay of the distant selec tor in the main exchange is also deenergized twice and the wipers of such selector are also raised to the second level. In brief, the line relay repeats the impulses or interruptions received into the circuit of the distant selector and as a result the switch D and the distant first selector are operated simultaneo-usly, or practically so. It will be noticed that while impulses are being repeated the relay 54 is energized, resulting in the closure of the-bridge across conductors 111 and 112 over a path excluding the windings of relays 55 and 56. This is the usual expedient made use of to obtain a first class switch control circuit.

At the end of the vertical movement of the switch D, the slow acting relay 54 is deenergized and at its armature 74 closes the circuit of the rotary magnet 59. The rotary magnet is accordingly energized and 0perates to rotate the switch wipers 90-93, inclusive, into engagement with the first set of hanlr contacts in the second level, being the contacts 9497, inclusive. At its right hand interrupter contact the rotary magnet breaks the locking circuit of relay 58, but since wiper 92 is now in engagement with bank contact 96, a new locking circuit has been established and relay 58 remains energized. At its left hand interrupter contact the rotary magnet breaks the locking circuit of the stepping relay 57 which'relay therefore deenergizes and breaks the rotary magnet circuit, the rotary magnet thereupon deenergizing in turn and again closing its interrupter contacts. The operation now depends upon whether the first trunk line terminating in the second level is busy or idle. If this trunk line is busy the test contact 95 associated therewith will have a ground potential upon it and the stepping relay 57 will be energized again over a circuit which includes the test wiper 91, armature 65 and its resting contact, the left hand interrupter contact of the rotary magnet, off normal springs 62, and the contact closed by armature 80' of relay 58. Upon energizing, relay 57 again closes the rotary magnet circuit and the switch wipers will be advanced into engagement with the next set of bank contacts. Evidently the rotation of the wipers will be continued by the alternate operation of the stepping relay and rotary magnet as long as test wiper 91 continues to engage grounded test contacts. However, in the present case it may be assumed that the first trunk line is idle, iniwhich case the test contact 95 will not be grounded. Under these circumstances, when the rotary magnet deenergizes after the first rotary step, the stepping relay 57 will not again be operated, but instead the switching relay 50, which heretofore has been short-circuited, is energized over a circuit extending as 'follows: Grounded-conductor .33, winding of switching relay 50, left hand interrupter contact of the rotary magnet, ofi' normal springs 62, working contact of armature 80 and the said armature, and the winding of the stepping relay 57 to battery. Relay 50 is of such high resistance that relay 57 is not operated. Upon energizing, relay 50 opens the release magnet circuit at its armature 66, connects the test wiper 91 toconductor 33 by way of its armature 65, and by means of its armatures 64 and 67 disconnects the'incoming line conductors from the windings of the line relay 52 ar d, extends them by way of line wipers 90 an?! 93, and bank contacts 94 and 97 to the trunk line conductors 98 and 99, which conductors are understood to extend to and terminate in the line relay of a local second selector switch, as previously explained. The line relay of this second selector is accordingly energized and closes the circuit of its associated slow acting release relay, and the latter relay then places a ground potential upon the release trunk or holding con- 4 ductor 85. By the latter operation the conductor 33 is maintained grounded after relay 53 of the switching selector repeater has deenergized and relays 13 and 50 are main tained energized to retain switches C and D in o erated position.

As to the secondary switch C and the first selector in the main exchange, the latter switch is released by the permanent deenergization of the line relay 52 following the operation of the switching relay 50. The slow acting relay 53 deenergizes soon after relay 52 and disconnects ground from conductor 110 thereby breaking the circuit of

relay

101, 102, and 130. Since the latter two relays are slow acting, relay 101 will deenergize first, thus closing a circuit for the stepping magnet 103 at armature 106. The stepping magnet is therefore energized and advances the wipers of the line switch into engagement with the next set of bank contacts. The circuit of the stepping magnet is broken when wiper 122 leaves test contact 126 and this insures that only one step will be taken by the wipers. The object of stepping the wipers ahead one step upon the release of the switch is not only to secure a better distribution'ot the calls, but also to prevent the tying up of a call by a defective trunk line. Suppose the trunk comprising conductors 140 and 141 is defective for some reason, one of the conductors perhaps being open or grounded or the distant first selector being out of order. In such case a party might try repeatedly to get a main exchange number without success, for on each attempt he might get the same defective trunk line. With the arrangement shown, however, the first attempt would be unsuccessful, if the connection was attempted via the defective trunk line, but when the calling party disconnected to try the number over again he would get a new trunk line, and ultimate success would be assured, even if it should be necessary to try all the trunks available.

The connection under consideration has now been extended to a local second selector in the branch exchange and the trunk line to the main exchange, which was tentatively connected with at the start, has been restored to conunon use by the release of the secondary switch 0'. The calling subscriber can now go ahead and call the remaining three digits in the desired number, with the result that the local second selector and a connector accessible thereto are operated to comlete the connection to the desired called ine. This part of the operation is old and need not be further considered.

I will now explain briefly what happens when a connection is extended from the branch exchange to the main exchange. Assuming again that the calling party is the subscriber at substation A, and that the desired number is #1555, which is a main exchange telephone number, when the receiveris removed the line switch C is operated as before explained to connect with an idle switching selector repeater. Assuming that the switching selector repeater D is the one connected with, the secondary line switch C will be operated to connect with an idle trunk line to the main exchange, the trunk line comprising conductors 140 and 141, for example. The calling subscriber will now operate his calling device in accordance with the first digit of the desired number, which is the digit 1. As a result, both the switching selector repeater D and the first selector in the main exchange are operated to raise their wipers to the first level, and the latter switch is thereafter operated automatically in the usual manner to select a trunk line extending to an idle main exchange second selector. The rotation of the switching selector repeater D is also initiated the same as in the previous case and the wipers are rotated into engagement with the first set of bank contacts in the first level. But when the rotary magnet 59 energizes to produce this result, it breaks the locking circuit of relay 58, and since the wiper 92 is now in engagement with a dead bank contact, the said relay is at once deenergized. Relay 58, upon deenergizing, breaks its own circuit at armature 79 so that it cannot again pull up, breaks the vertical magnet circuit at armature 81, and at armature 80 breaks the circuit of the stepping relay 57. The latter operation puts an end to further rotary movement and also prevents the energization of the switching relay 50. From now on the switch D operates as a repeater. The interruptions produced by the subsequent operations of the calling device are repeated in the circuit ofthe main exchange trunk line by the line relay 52, and bring about the operation of the selected second selector in the main exchange and a connector switch accessible thereto to complete the desired connection.

It will be unnecessary to explain the releasing operations in detail, as these circuits follow standard practice. The switching selector repeater is restored by the release magnet 60, the circuit of which is closed by the deenergization of relay 50 at the termination of a local connection, and by the relay 53 at the termination of a branch to main exchange connection. Line switch O is of course restored by the deenergization of relay 13 upon the removal of ground from conductor 33 at the termination of either kind of connection, the line switch wipers being always kept standing onthe trunk line last used. One other standardprovision in the switching selector repeater D may be mentioned, although it has nothing to do with the invention. This is the reversing relay 51 which reverses the direction of current flow in the calling line when a called subscriber in the main exchange answers. tro-polarized relay 56 which in turn is controlled by the usual reversing relay on the main exchange connector. On local calls the reversal of current is taken care of by the reversing relay of the branch exchange connector.

This completes the explanation. It will be understood of course that any other level in the switching selector repeaters provided by my invention may be used for local switching as well as the second level, and it will be clear also that two or more levels may be wired for local switching where the size of the branch exchange makes this necessary. Other modifications are considered to be within the scope of the invention and I do not therefore wish to be restricted to the precise form shown herein, but

What I claim as my invention is:

1. In a telephone system, main and branch exchanges, means including a switching selector repeater for connecting a calling branch exchange subscribe-r with a called subscriber 1n the same exchange, a rotary Relay 51 is controlled by the elec-' line switch permanently associtaed with said selector repeater, trunk lines to the main exchange accessible to' said line switch, means for operating said line switch to select an idle trunk whenever the said selector repeater is taken for use, and means for giving the calling subscriber a busy signal only in case all of said trunk lines are busy.

2. In a telephone system, main and branch exchanges, means including a switching selector repeater for connecting a calling branch exchange subscriber with a called subscriber in the same exchange, a rotary line switch permanently associated with said selector repeater, trunk lines to the main exchange accessible to said line switch, means for operating said line switch to select an idle trunk line whenever the .said selector repeater is taken for use, a relay associated with each of said trunk lines, and circuit connections such that said relays cooperate when all the trunk lines are busy to prevent the operation of said line switch and give the calling subscriber a busy signal. 3. In a telephone system, main and branch exchanges, branch to main exchange trunk lines, switching selector repeaters in the branch exchange, means responsive to the initiation of a call in the branch exchange for connecting the calling line with an idle switching selector repeater, automatic switch mechanism for connecting the -calling line with an idle trunk line at the same time,

and means for preventing the operation of said mechanism and for giving the calling subscriber a busy signal if all of said trunk lines are in use. I

4. In a branch exchange,- a switching selector repeater, means for operating said selector repeater primarily to select a group of trunks and for initiating its secondary trunk selecting movement, means for continuing the secondary movement if a group of local trunks has been selected, a relay for determining whether. the secondary movement is to continue or, 'not, a circuit for ener gizing said relay, means for breaking said circuit, a locking circuit for preventing the deenergization of said relaywhen the first circuit is broken, said locking circuit broken when the secondary movement is initiated, and a second locking circuit for said relay completed by a wiper. of said switch.

5. In a branch exchange, a switching selector repeater, means for operating said selector repeater primarily to select a group of trunks and for initiating its secondary trunk selecting movement, a locking relay for determining whether the secondary movement is to continue or not, means for closing a self locking circuit for said relay, means for always opening said self locking locking circuit in case a group of local trunks has been selected.

6. In a branch exchange, a switching selector repeater, means for operating said selector repeater primarily to select a group of trunks and for initiating its secondary trunk selecting movement, a relay fordetermining whether the secondary movement is to continue or not, means for energizing said relay prior to the initiation of the secondary movement; and circuit connections whereby the continued energization of the said relay is controlled jointly by the secondary operating magnet and by a wiper of said switch. I

7. In a telephone system, main and branch exchanges, means including a switching se-.,

lector repeater for connecting a calling bran'ch exchange subscriber with a called subscriber in either exchange, primary and secondary operating magnets for said selector repeater and a stepping relay .for the secondary magnet, a switching relay for extending the calling line through to a local trunk line in case a branch exchange subscriber is being called, and means for energizing said switching relay in series with.

said stepping relay.

8. In a telephone system, means including serially related primary and secondary rotary line switches for completing a connection between a calling and called line, movable wipers in said switches through which the connection is extended. means for releasing the connection and restoring said switches to normal without moving the wipers of said primary switch, and means operated automatically. when the connection is released for advancing the wipers of said secondary switch and-for bringing them to rest in engagement with another trunk line.

9. In a telephone system, a subscribers line, means including a rotary line or trunk selecting switch for extending said line when calling into connection with an idle one of a plurality of trunk lines, movable wipers in said switch having no normal position as regards the said trunk lines, and means for automatically advancing the said wipers into connection with the next trunk line when the connection is released.

10. In' a telephone system, a group of trunk lines and sets of fixed connective terminals therefor, a rotary line switch having the fixed terminals engaged thereby are busy, and means for automatically operating said switch to advance said movable terminals when the connection is released.

11. In a telephone system, a group of trunklines and sets of fixed connective terminals therefor, a rotary line switch having movable terminals normally inengagement with a set of said fixed terminals, means for operating said switch to connect a calling line with an idle trunk line without advancing the said movable terminals unless the fixed terminals engaged thereby are busy, and means controlled automatically during the release of the connection for operating said switch to advance said movable terminals into engagement with another set of fixed terminals.

12. In a telephone system, a rotary line switch having movable wipers and a group oftrunk lines accessible thereto, an individual stepping magnet for said switch, means for extending a connection through said switch to an idle trunk line without advancing said wipers, and means for automatically operating said magnet to advance said wipers responsive to the release of the connection.

13. In a telephone system, a group of trunks, an automatic switch, a line, means for connecting said linewith said switch, a second switch associated with the said first switch adapted to select an idle trunk of said group, said second switch having a line relay, a relay in first said switch r'or preventing theapplication of a busy tone to said line by energizing, a circuit including both of said relays, means for closing said circuit when the said line is connected with first said switchyand means for preventing said circuit from being closed in case the said group of trunks is busy.

14. In a telephone system, a group of trunks, an automatic switch. a line, means for connecting said line with said switch, a second switch associated with the first said switch adapted to select an idle trunk of said group, said second switch having a line relay, a relay in first said switch for pre- 'venting the application of a busy tone to being closed in case the said group of trunks is busy, and means. for renderingllast said means inoperative when a trunk of said group becomes idle.

15. In a telephone system, a line, an automatic switch, means for connecting said line therewith, a group of trunks inaccessible to said switch, a relay in said switch for applying a busy tone tosaid line when all of said trunks are busy, and a second relay in said switch for removing said busy tone when a trunk in said group becomes idle.

16. In atelephone system, an automatic switch, a line, means for connecting said line with said switch, a second switch, a group of trunks accessible thereto but inaccessible to said first switch, and means in said first switch independent of the second switch for applying a busy tone to said line when all of said trunks are busy.

17. In a telephone system, an automatic switch, a line, means for connecting said lme with said switch, a second switch, a

group of trunks accessible thereto but inapplying a busy tone to said line when allof said trunks are busy.

19. In a telephone system, a line, an automatic switch, means for connecting said line therewith, a second switch individual to said first switch, a group of trunks accessible thereto but inaccessible to said first switch, a relay in said first switch for applying a busy tone to said line when all of said trunks are busy, and a second relay for removing said busy tone When a trunk in said group becomes idle. a

. 20.'In a telephone system, main and branch exchanges, means including a switchng selector repeater for connecting a call: mg branch exchange subscriber witlia called subscriber in the same exchange, a rotary line switch permanently associated with said selector repeater, trunk lines to the main exchange accessible to said line switch, means for operating said line switch to select an idle trunk whenever the said-selector repeater is taken for use, and means for in-' dicating to the calling subscriber that all the trunks are busy before the said line switch is operated.

21. In a telephone system, main and branch exchanges, means including a switchng selector repeater for connecting a, calling branch exchange subscriber with 21. called subscriber in the same exchange, a rotary line switch permanently associated with said selector repeater, trunk lines to the main exchange accessible to said line switch, means for operating said line switch to se- -lect an idle trunk whenever the said selector repeater is taken for use, and means for indicating to the calling subscriber that all the trunks are busy before they have all been tested. v

22. In a telephone system, main and branch exchanges, means i eluding a switchmg SQlQL tor repeater for onnecting a calling branch exchange subscriber with a called subscriber in the same exchange, a rotary line switch permanently associated with said selector repeater, trunk lines to the mam exchange accessible to said line switch, means for operating said line switch to select an idle trunk whenever the said selector repeater is taken for use, and means for indicating to the calling subscriber upon the seizure of said selector repeater that all of said trunks are busy.

23. In a branch exchange, a side-switchless switching selector repeater having wipers and groups of contacts accessible thereto, an outgoing trunk line extending to the main exchange, meansior seizing said repeater, means responsive thereto for closing. a switch control circuit over said outgoing trunk line, means responsive to the dialling of a digit in a telephone number for bringing said wipers into engagement with the first set of contacts in one of said groups and for transmitting impulses over said control circuit, and means responsive to this operation for opening the said control circuit and for extending a connection through said wipers only in case the group f contacts with which the wipers are assoclated represent a group of trunk lines local to the branch exchange.

24. In a branch exchange, a switching selector repeater, means for operating sald selector repeater primarily to select a group of trunks and for initiating its secondary trunk selecting movement, a switching relay for extending the calling line through to a local trunk line in case'a branch exchange subscriber is being called, a control relay for determining whether the switching relay is to energize or not, a circuit for energizing said control relay, means for breaking said circuit, a locking circuit for preventing the deenergization of said relay when the first circuit is broken, said locking circuit broken when the secondary movement is initiated, and a second locking circuit for said relay completed by a wiper of said switch.-

25. In a branch exchange, a switching selector repeater, means for operating said switching selector repeater primarily to se- 'lect a group of trunks and for initiating its secondary trunk selecting movement, means .for continuing the trunk selecting movement until an idle trunk is found in case a. group of local trunks has been selected, a switching relay for extending the calling line through to an idle local trunk line in case one is selected, and a control relay energized to complete the circuit of the switching relay only in case the primary movement imparted to said repeater is such as to pro-determine that a local'subscriber is being called.

26. In a branch exchange, a switching selector repeater, means for operating said switching selector repeater primarily to select a group of trunks and for initiating its secondary trunk selecting movement, means for continuing the trunk selecting movement until an idle trunk is found in case a group re eater, and meansrespcnsiye only in case of local trunks has been selected, a switcha coal trunk line is selected for closing said ing relay for extendin the calling line circuit.

through to the idle loca trunk line in case Signed by me at New York, New York one is selected, a circuit for energizin said County, New York, this 21st day of April, relay, said circuit being entirely in epe 1920. dent of the wipers and bank contacts of said ELDL JACOBSEN.