US2271878A - Telephone system - Google Patents

Description

Feb. 3, 1942.

P. w. wADfswoRTH' TELEPHONE'SYSTEM Filed 0G12. 25, 1940 .moine Il .o E Il Patented Feb. 3, 1942 TELEPHONE SYSTEM Paul W. Wadsworth, Garden City, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a, corporation of New York Application October 25, 1940, Serial No. 362,771

23 Claims.

This invention relates to telephone systems and particularly to systems comprising impulse controlled switching mechanism for establishing connections between calling and called stations.

Objects of the invention are an increase in the flexibility, adaptability and efficiency of group selector switches and the trunking arrangements of telephone systems comprising such switches.

This invention is a selector switch having a primary group selecting movement and a secondary, trunk hunting movement arranged to absorb a rst digit of any desired numerical value, arranged to absorb a second digit of any desired numerical value after absorbing a iirst digit, arranged to transmit a busy tone to a connected calling station if the level selected in response to the rst digit is a level which is not used or is one on which service is restricted, and arrangedto transmit a busy tone ii the level selected in response to a second digit is a level which is not used or is one on which service is restricted. According to a feature of the invention a selector is provided with six sets of shaft operated springs, each set independently operable on any desired level or levels. The actuation of a first set of springs effects the return of the brushes to absorb a rst digit, the actuation of a second set of springs eiects the return of the brushes to absorb a second digit, the actuation of a third set eiects the advance of the brushes to the eleventh rotary position in a selected level to transmit a busy tone if the level is selected in response to a first digit, the actuation of a fourth set eiTects the advance of the brushes to the eleventh rotary position in a selected level to transmit a busy tone if the level is selected in response to a second digit, the actuation of a fth set of springs eiTects the advance of the brushes to the eleventh rotary position and transmission of a busy tone if the call is from a restricted service subscribers station and the level is selected in response to a rst digit, and the actuation of the sixth set of springs effects the advance of the brushes to the eleventh rotary position and transmission of a busy tone if the call is from a restricted service subscribers station and the level is selected in response to a second digit.

Another feature cf the invention is a digit absorbing selector arranged to absorb two digits, each of any numerical value, by a return of theA brushes to normal after a primary movement of the shaft and brushes. A further feature of the invention is a two-motion group selector arranged to advance to the eleventh rotary position in an unused level when selected either in response to a rst or a second digit and to advance to the eleventh rotary position upon selection of a restricted level in response to either a first or a second digit on calls from restricted service subscribers.

A clear and complete understanding of the invention will be facilitated by considering a system and selector in which the invention is embodied, one such system and selector being shown schematically in the drawing which forms a part of `this specification. The invention is not limited in its application to the system vand selector shown in the drawing but is generally applicable to impulse controlled group selectors.

The drawing, which consists of a single figure,

shows subscribers stations A and B, lines LI and.A

L2 and line circuits LC! and LCZ, line nders LFI and LFZ, selector Sl, connectors Cl and C2, and timing apparatus TA.

While only one selector is shown in a connection between a calling and a called line, it is understood that intermediate selectors may be provided, the total number of switches required for establishing connections between calling and called lines depending upon the trunking arrangement and number of subscribers in the system.

The subscribers stations A and B may be of known type, each comprising a dial or other impulse sender for controlling the operation of the switches through which connections are established with called lines. Each of the line finder, selector and connector switches are of the wellknown two-motion step-by-step type. Reference may be had to pages 53 to 65, inclusive, of the second edition oi Automatic Telephony by Smith and Campbell for a description of the structure of such switches and their operation when used as selectors and connectors. Reference may be had to the patent to T. L. Dimond, No. 2,210,068 of August 6, 1940, for a description of the operation of a subscribers line circuit and the operation of a step-by-step line nder switch in connecting a calling line to a rst selector. Each of the line nder and connector switches are represented in the drawing by a set of brushes and a single set of terminals, all operating magnets, relays and other associated apparatus being omitted. The line finder LFI is further represented by shaft operated level or normal post springs 24 and 2t, vertical off-normal springs 28 and .release magnet 29.

The selector SI, which is shown in detail, comprises a set of brushes 4I, 42, 43 and 44, a bank of termin-als consisting of ten levels, each level consisting of ten sets of four terminals each, a vertical stepping magnet 41, a rotary stepping magnet 4B, a release magnet 49, vertical 01T- normal springs 45, eleventh rotary step springs 46, shaft operated level or normal post springs 5I, 52, 53, 54, 55 and 56, a line relay 3|, a release relay 32, rotary stepping relay 35, cut-through relay 39, and other control relays 33, 34, 36, 31 and 38. Reference may be had to the patent to I-I. Sengebusch, No. 1,888,700, November 22, 1932, for ,a description of the shaft operated level or normal post springs 5| to 56, inclusive, and the manner in which they are adjusted for operation when the brushes are on any desired level or levels. Although the-selector SI is shown as a first selector connected directly to a line finder LFI, the invention is applicable to selectors other than first selectors. The bank of selector SI is represented by five sets of terminals 6I to 65, inclusive. Terminals 6| represent the irst level in which the terminals are connected to auxiliary first selectors; terminals 62 represent a level in which the terminals are connected to second selectors (not shown) or directly to connectors C2; terminals 63 represent a level which is not used; terminals 64 represent a level in which the terminals are connected to outgoing trunk circuits T2 associated with trunks to another oflice; and terminals 65 represent the tenth level in which the terminals are connected to 'outgoing trunk circuits OTI associated with trunks to an operator. The outgoing trunk -circuits 0T2 associated with inter-oce trunks may be similar to that shown in Fig. 67 and described on pages 70 to '12 of the aforementioned second edition of Automatic Telephony. The outgoing trunk circuits OTI associated with trunks to an operator may be similar to that disclosed in Fig. of the patent to R. B. Buchanan et al., No. 2,233,282 granted Feb. 25, 1941.

The timing apparatus TA, which is common to all of the first selectors in the oihce, comprises slow-to-operate relays I3 and |4 and slow-torelease relay I5. When these relays are normal, ground is connected to conductors I6 and I1. As soon as ground is connected to start conductor I8, relay I3 is operatively energized. Relay I3 disconnects ground from conductor I6 and closes a circuit for energizing relay I4. Relay I4 operates from two to four minutes after its operating circuit is closed, thereby closing a circuit for operating relay I5. Relay I5 disconnects ground from conductor I1 and disconnects relay I3 from start conductor I8 to release relay I3. The release of relay I3 causes the release of relay I4 and the release of relay I4 opens the operating circuit of relay I5. Relay I5 is slow in releasing so that ground is disconnected from conductor I1 for not less than a desired interval; and relay I3 isl slow in operating so that ground is connected to conductor I6 for not less than a desired interval. Relays I3, I4 and I5 repeat their cycle of operations, as long as ground is connected to start conductor I8, to control the release of selectors when connected to subscribers lines on which a permanent signal condition exists, as hereinafter described.

Assume now that a call is initiated at station A and that the line LI is connected by a line finder LFI to the selector SI. The line relay 3| is thereupon operated by the current in a circuit from battery through the lower winding of relay 3|, outer lower back contact of relay 39, brush 22 of line nder LFI, conductor I2 of line LI,

through station A and the dial thereat, conductor of line LI, brush 2| of line finder LFI, outer upper back contact of relay 39, upper winding of relay 3|, upper back contact of eleventh rotary step springs 46, outer lower back contact of relay 38, and through the left winding of dial tone transformer 51 to ground. Dial tone is transmitted in this circuit to the calling subscriber. Relay 3| closes a circuit for operating relay 32 in series with relay I9, relay I9 being common to a plurality of rst selectors. Relay 32 connects ground to conductor 30 to hold the line nder LFI in usual manner. Relay I9 connects ground to start conductor I8 of the common timing apparatus TA, to start its operation if not already in operation. As soon after relay 3| operates as ground is connected to conductor I6, the upper winding of relay 31 is operatively energized. Relay 31 locks through its lower winding under control of relay 32 and connects conductor 30 to timing conductor I1, to enable the automatic release of the selector, as hereinafter described, in case the selector has not completed the connection of the calling line to a succeeding switch or trunk within an interval of from two to four minutes after relay 31 is operated.

When the calling subscriber dials the first digit of the number of a subscribers station with which connection is desired, relay 3| is alternately released and reoperated as many times as there are units in the digit dialed. The release of relay 3| in response to the first impulse of the train closes a circuit including the outer upper front contact of relay 32 for energizing relay 33 and vertical stepping magnet 41 in series. The operation 'of magnet 41 steps the brushes 4|, 42, 43 and 44 up to the rst level of the bank. When the shaft carrying the brushes moves out of normal position, vertical off-normal springs 45 are actuated, thereby closing a circuit including the lower contact of eleventh rotary step springs 46, upper contact of springs 45, and the lower front contact of relay 33 for operating relay 35. Relay 35 locks under control of springs 45 and 46, and under control of the rotary stepping magnet 48, to ground at a front contact of relay 32. The reoperation of relay 3| at the end of the rst impulse opens the circuit through the windings yof relay 33 and magnet 41. The stepping magnet 41 releases but relay 33 is slow in releasing and remains operated while relay 3| is responding to succeeding impulses in the train. Relay 32 is slow in releasing and is operatively unaffected by the response of relay 3| to dial impulses. Each succeeding release and reoperation of relay 3| in response to the impulses in the train created by the dialing of the first digit effects the operation and release of vertical stepping magnet 41, thereby stepping the brushes up to the level corresponding to the digit dialed. If the level selected in response to the first digit is a level requiring trunk hunting and if this level is not a restricted level or a vacant level, none of the normal post springs 5|, 52 or 55 are operated. Assume the selected level to be the tenth level, to which trunks to an operator are connected, this level being represented by terminals connected to trunk circuit OTI. In this case, the release of relay 33, after all of the impulses in the train created by the dialing of the digit 0 have been received, closes a circuit including the back contact of springs 5|, back contacts of relays 38 and 36, and a front contact of relay 35 for operating the rotary stepping magnet 48. .The operation of magnet 48 rotates the brushes into engagement with the first set of terminals in the selected level and opens the locking circuit of relay 35. Relay 35 releases, in turn opening the operating circuit of magnet 48. If the first set of terminals is connected to a busy trunk, the terminal engaged by brush 43 will be connected to ground potential to Yguard against seizure of this set of terminals. This ground potential is further connected through brush 43 and the middle lower back contact of relay 39 to conductor 53; and when magnet 48 releases, it connects the winding of relay 35, through the upper back contact of release magnet 43 to conductor 50, thereby causing the reoperation of relay 35. Relay 35 again closes the circuit for operating rotary stepping magnet 48; the operation of magnet 48 steps the brushes to the next set of terminals and opens the operating circuit of relay 35; and the release of relay 35 causes the release of magnet 48. Relay 35 rand magnet 48 are in this manner eective to advance the brushes step by step until the brushes engage an ungu'arded set of terminals; whereupon, relay 39 is operated by the current in a circuit from battery through the winding of relay 35, lower back contact of springs 45, upper Contact of springs 45, back contact of magnet 48, upper back contact of magnet 49, conductor 50, winding of relay 39, to ground at a front contact of relay 32. Being marginal, relay 35 does not operate in series with relay 39. Relay 39 disconnects the windings of relay 3l from the calling line and connects the calling line, through brushes 4I' and v42, to the selected trunk OTI. Relay 39 also temporarily connects ground potential from the inner upper front contact of relay 32, through the inner lower front contact of relay 39, to test brush 43 to guard the selected trunk against seizure by another selector until the trunk circuit has operated in the usual manner to connect a holding and guarding ground potential to the terminal engaged by brush 43. Relay 3| releases and causes the successive release of relays 32 and 31. After relay 32 releases, relay 39 and the line finder LFI are held through brush 43 to ground potential in the trunk circuit. Relay 39 connects conductor 25 to brush 44 so that the trunk circuit OTI may receive an indication of the class of the calling line under control of level springs 24 of the line nder, as described in the aforementioned patent to R. B. Buchanan et al. The connection is held under the joint control olf the calling subscriber and the answering operator. When holding ground potential is disconnected from the terminal engaged by brush 43, relay 39 releases. 'I'he release of relay 39 connects ground to conductor 40 to effect the operation of release magnet 49, so as to restore the brushes to normal. When the shaft reaches normal, springs 45 are restored to normal, opening the circuit for operating magnet 49. The connection of ground to conductor 4l] also causes the operation of release magnet 29 of line iinder LF! to restore the brushes of the line finder to normal. When the shaft of the line finder reaches normal, springs 28 are restored to normal, opening the circuit for operating magnet 29.v

If, when the brushes of selector Sl are hunte ing in a level, all of the sets of terminals in the level are guarded against seizure, the brushes are advanced by an eleventh rotary step to an over'- ilow position in which springs 46 are actuated to open the circuit for operating relay 35 and to connect the right winding of busy tone transformer 58 to the upper Winding of relay 3l to transmit a busy tone to the calling subscriber. When the calling subscriber restores the telephone set to normal, relay 3| releases. The release of relay 3l causes the release of relays 32 and 3l and return of the selector and line finder to normal, as above described.

Assume next that the level selected in response to the first digit is one having trunks to another oiiice connected thereto. The terminals 64 represent such a level; and normal post springs are actuated upon selection of this level. If the calling station is not a restricted service station, the brushes are advanced in the manner hereinbefore described to hunt for and seize an idle outgoing trunk circuit connected to a trunk to the called office; the operation of relay 39, upon nding an unguarded set of terminals, disconnects relay 3l and connects the calling line to an outgoing trunk circuit 0T2; and the connection is held under the control of the calling subscriber and release is effected as above described. If, however, the calling station is a restricted service station, the level springs 26 of the line nder are operated and ground is connected through springs 25, conductor 21, a back contact of relay 33, springs 55 and a back contact of relay 39 to conductor 50, thereby simulating an all-trunksbusy condition which eiects the repeated operation of relay 35 and stepping magnet 48 to advance the brushes to the eleventh rotary position, a busy tone being thereupon transmitted to the calling station. When the connection is released, the selector SI and line finder LFI are restored to normal.

Assume next that; the level selected in response to the rst digit is a vacant level, that is, one which represents numbers not assigned to subscribers stations or a level restricted to all stations having access to the selector SI, such a level being represented by terminals 53. Level springs 52 are actuated upon selection of this level; and ground is connected from the back contact, of timing relay I5 through conductor I1, upper front contact of relay 3l, lower back contact of relay 35, outer upper back contact 01' relay 38, through springs 52, and a back contact of relay 39 to conductor 50 to effect the advance of the brushes to the eleventh rotary position; and a busy tone is transmitted to the calling station until the connection is released thereat.v

If the rst digit dialed is one which is to be absorbed, the brushes are advanced to the corresponding level to eiect the operation of normal post springs 5l. When relay 33 releases, after receipt of the last impulse of the train, a circuit for operating release magnet 49 is closed from battery through the Winding of magnet 49, lower contact of springs 45, front contact of springs 5l, back contacts of relays 38 and 36, upper front contact of relay 35, back contact of relay 33, to ground at the lower back contact of magnet 49. The release magnet locks under control of vertical o-normal springs 45, opens its operating circuit, prevents operation of rotary stepping magnet 48, closes a circuit for operating relay 36, and causes the shaft and brushes to be restored to normal. The circuit for operating relay 38 is traced from battery, through the winding and inner upper back contact of relay 38, upper front contact of magnet 49, lower 'front contact of relay 35, to ground at a front contact of relay 32. Relay 33 locks under the sole control of relay 32; opens its operating circuit; disconnects the dial tone transformer from, and connects ground to, the upper winding of relay 3l; and transfers connections from contacts of springs 5I, 52, and 55 to contacts of springs 53, 54 and 56 respectively. When the shaft reaches normal, springs 45 are restored to normal, releasing relay 35 and magnet 49.

When a second digit is dialed, switch SI having been restored to normal to absorb the first digit, the brushes are advanced to the level corresponding to the digit dialed in the same manner that the brushes were advanced responsive to the rst digit. When relay 33 operates in series with vertical stepping magnet 41 in response to the first impulse of the train, it closes a circuit including the middle lower front contact of relay 38 for operating relay 34. Relay 34 opens its operating circuit and locks under the sole control of relay 32. If the level selected in response to the second digit is not a restricted level or a vacant level and is a level in which it is desired that the brushes be advanced to select an unguarded set of terminals, none of the normal post springs 53, 54 and 55 are operated; and, when relay 33' releases at the end of the train of impulses, the brushes are advanced in the selected level to hunt for and seize an unguarded set of terminals in the manner hereinbefore described, the circuit for operating magnet 48 including the back contact of springs 53. Ii the level selected in response to the second digit is a restricted level, level springs 56 are actuated; and, if the call is from a restricted service station, ground is connected through level springs 26 of line nder LFI, conductor 21, front contact of relay 33, springs 55, and a back contact of relay 39 to conductor 53 to effect the advance of the brushes to the eleventh rotary position and transmission of a busy tone to the calling station. If the level selected in response to the second digit is a vacant level or is denied to all subscribers having access to selecter SI,

springs 54 are actuated to connect ground to.

conductor 55 and effect the advance of the brushes to the eleventh rotary position.

If, after absorbing the first digit, the second digit dialed is one which is to be absorbed, the level springs 53 are actuated upon selection of the level corresponding to the second digit. When relay 33 releases, at the end of the train of impulses, a circuit for operating release magnet 49 is closed through the lower contact of springs 45, springs 53, a front contact of relay 38, inner upper back contact of relay 35, upper front contact of relay 35, and back contact of relay 33, to ground at a back contact of magnet 49. Magnet 49 locks under control of springs 45, opens its operating circuit, prevents the operation of rotary stepping magnet 48, closes a circuit for operating relay 36, and causes the return of the brushes to normal. The circuit for operating relay 35 includes the lower front contact of relay 34, upper front contact of magnet 49, lower front contact of relay 35, and a front contact of relay 32. Relay 35 locks under the sole control of relay 32, opens its operating circuit, connects ground to contacts of springs 55 and 55, and connects the rotary magnet for operation at the end of any third digit. When the shaft reaches normal, springs 45 are restored to normal opening the operating circuit of magnet 49.

When the third digit is dialed, the brushes of switch SI having been restored to normal to absorb the second digit, the brushes are advanced to the corresponding level. The operation of any of normal post springs 5|, 52, 53 and 54 does not affect the` further operation of the selector. When relay 33 releases at the end of the train of impulses, a circuit is closed for operating the rotary stepping magnet 48 to step the brushes into engagement with the iirst set of terminals in the selected level. If this level is a restricted level, normal post springs 55 or 5G are operated to connect ground through the inner lower back contact of relay 39 to conductor 50 to effect the advance of the brushes to the eleventh rotary position, thereby preventing selection of a trunk in a restricted level by the dialing of a third digit of the same value as that of a rst digit or a second digit which eiiects selection of a restricted level. If neither of springs 55 or 56 is operated, the brushes are advanced to select an unguarded set of terminals whereupon relay 39 is operated to connect the calling line thereto. Upon selection of a set of terminals, such as 62, leading to another selector or a connector, holding ground potential is connected to the terminal engaged by brush 43 to hold relay 39 and to hold the line nder in usual manner.

Upon connection of the calling line through terminals 62, either directly or through an intermediate selector, to a connector C2, the line relay 1| of the connector is operated. Relay 1I closes a circuit for operating relay 12; and relay 12 connects holding ground potential to conductor 10 to hold the intermediate selectors, if any, and to hold the selector SI and line nder LFI. Relay 1I responds to the impulses created by the dialing of the last two digits of the called subscribers number to control the operation of the connector whereby connection is established with the called line L2. The called station B is signaled in the usual manner and the talking connection is under the control of the calling station A. When the telephone set at station A is restored to normal, relays 1I and 12 release in succession. The release of relay 12 disconnects holding ground potential from conductor 10; and all of the selectors and the line nder are restored to normal. When both the calling and called stations have restored their telephone sets to normal, the lconnector C2 is restored to normal in the usual manner.

If, after connection of a calling line to the selector SI and after relay 31 has operated in the manner hereinbefore described to connect the ground at the back contact of timing relay I5 to conductor 3D to hold the line nder LFI, the selective operation of the selector SI is not completed and relay 39 operated before the two to four minute interval measured by timing relays I3, I4 and I5 has elapsed, the disconnection of ground potential from conductor I1, by the operation of relay I5, causes the release of the line finder LFI, and the operation of a line lock-out relay (not shown) if the line circuit LCI includes such a relay, in the manner described in the aforementioned patent to T. L. Dimond. Upon return of the line nder to normal, relays 3l, 32 and 31 release in succession. The release of relay 3l causes the momentary operation of relay 33 and vertical stepping magnet 41, the brushes being thereby stepped up to the first level. When relay 32 releases, it closes the circuit for operating release magnet 49 restoring the brushes to normal, the circuit for operating magnet 49 being opened by springs 45 when the shaft reaches normal.

What is claimed is: A

1. In a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, and means for advancing the brushes in any level to select an unguarded set of terminals, a set of contact springs actuated upon selection of a particular level, means comprising said set of contact springs for returning the brushes to normal upon selection of the level with which the springs are operatively associated in response to a rst train of impulses, another set of contact springs actuated upon selection of a particular level, and means comprising said other set of contact springs for returning the brushes to normal after selection contact springs actuated upon selection of a particular level, means comprisingsaid set of contact springs for returning the brushes to normal upon selection of the level With which the springs are operatively associated in response to a rst train of impulses, another set of contact springs' actuated upon selection ofa particular level, `and means comprising said other set of contact springs eiective, upon selection of the level with which said other contacty springs are operatively associated in response tov a second train of impulses incoming to the selector, ,to ad- Vance the brushes to an all-trunks-busyposition irrespective of whether there is or is not an unguarded set of terminals in the level. i.

5. In a telephone system, lines connected to re- Y stricted service subscribersfstations, other lines,

of the level With which said other springs are a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive imv pulses incomingto saidselector, and means for level, means comprising said set of contact springs for returning the brushes-to normal `upon selection of the level with which the springs are operatively associated in response to a first train of impulses, another set of contact springs actuated upon selection of a particular level, and means comprising said other set of contact springs effective upon selection oi the level with which said other contact springs are operatively associated in response to-a rst train of impulses incoming to the selector to advance the brushes to an alltrunks-busy position irrespective of Whether there is or is notan unguarded set of terminals in the level.

3. In a telephone system, lines connected to restricted service subscribers stations, other lines,

a two-motion step-by-step selector comprising a Vset of brushes, a terminal bank divided'into levels, means for advancing the brushes to selectv any level, said means controlled by directive impulses incoming to said selector, and means for advancing the brushes in any level to select an unguarded set of terminals, means connecting a calling line to said sele-ctor, a set of `contact springs actuated upon selection of a particular level, means comprising said set of contact springs for returning the brushes to normal upon selection of the level withwhich the springs are operatively associated in response to a rst train of impulses, another set of contact springs actuated upon selection of a particular level, 'and means comprising said other set of contact springs effective, upon slection of the level with which said other contact springs are operatively associated in response to a rst train ofimpulses incoming to the selector, only if the connected calling line is a restricted service line to vGO advancing the brushes in any level to selectA anv unguarded set of terminals, means connecting' a calling line to said selector, va set of contact springs actuated upon selection of a particular level, means comprising lsaid set of contact springs for returning the brushes to normal upon selection of the level with Which the springs are operatively associated-in. response to a rst train of impulses, anotherset of contact springs actuated upon selection of a particular level, and means comprising said lother set of contact springs effective, uponv selection of the level With which said other contact springs are operatively associated in responseto a second .trainl ofimpulses incoming to the selector,r only if the connected calling line is a restricted service line to advance the brushes to an all-trunks-busy posi- .tion irrespective of Whether there isf or is not an unguarded set of terminals in the level. A

6. In a telephone system, lines connected to ref stricted service subscribers stations, other'lines, l

any level, said means controlled by directive impulse'sincoming v*to said selector, and means for advancing the brushes in any level to select an unguarded set of terminals, means connecting a calling'line to saidA selector, a set of contact springs actuated upon selection of a particular level, vmeans comprising-'said set of contact springs effective upon selection of the level with which said contact springs are operatively associated in response to a first train of impulses incoming to the selector to advance the brushes to an all-trunks-busy vposition Whether there is or isnot an unguarded set of terminalsin the level, another set` of kcontact springs actuated `upon selection of 'a particular level', and means comprising said yother 'set of contact springs effective, upon selection ofthe level with Which saidy other set of contact springs is operatively associated in response to a rst train` of impulses incoming to the selector, only if the rConnected calling line is a restricted service line to advance the brushesto an all-trunksbusy position irrespective of Whether there is `or is not -an unguarded set of terminals in the level.

7. In a telephone system, lines connected to restricted servicev subscribers stations, Aother lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the (brushes to irrespective of select any-level, said meanscontro'lled by directiveimpulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means' for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one ofV said sets is operable being the same or different from the particular level or levels on which rmy other of said sets is operable, means connecting a calling line to said selector, means comprising a irst one of said sets of contact springs for returning the brushes to normal upon selection of a `level vvith which said first set of springs is operatively associated in response to a rst train of 'impulses incoming to the selector, means comprising a second one of said sets of contact springs for advancing the brushesin a level With which said second set of contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to the selectorto an all-trunks-busy position irrespective of Whether there is or is not an unguarded set ofterminals in the level, and means comprising means actuated only if the calling line is a restricted service line and comprising-a third one of said sets of Contact springs for advancing the brushes, in a level with which said third set of contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to the selector, to an all-trunks-busy position irrespective of vWhether there is or is not an unguarded set of terminals in the level.

8. Ina telephone system, a two-motion stepby-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, ysaid means controlled by directive impulses incoming to said selector, means for advancing the brushes in'any level to select an unguarded setoterminals, va plurality of sets of contact springs, and individual operating means for each set of springs, eachY operating means adapted to operate the associated set of springs upon selectionof a particular level or any one of a plurality-of particular levels, the. particular level or levels on Which any one of said sets is operable being the same Vor difierent from the particular level or levelson which any other of said sets is operable, means comprising a first one 'ofv vsaid. sets of contact springs for returning the brushes to normal upon selection of a level with which said rst set of springs is operatively associated in response to a irst train of impulses incoming to the selector, means comprising a second one lof said sets of contact springs for advancing the brushes, in a level with Which said second set of contact springsis operatively associated upon selection-of the level in response `to afirst train of impulses incoming to the selector,

toan all-'trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and means comprising a third one of said sets oi contact springs for returning the brushes to normal upon selection of a levelivvith which said third set of contact springs is operatively associated, in response to a second train of impulses incoming to the selector.

9. In a telephone system, a two-motion stepby-step' selector comprising a set of brushes, a "terminal bank dividedA into levels, means for ad- 'restricted service subscribers ythe Vsame or different from the particular level or levels onwhich any otherof said sets if operable, means comprising a first one, of said sets of contact springs for returning the brushes to normal upon selection of a level with which said first set of springs is operatively associated in response to a rst train of impulses incoming to the selector, means comprising a second one of said setsof contact springs forV advancing the brushes, in a level with which said second. set

of contact springs is operatively associated upon selection of the level in response to a first train cf impulses incoming to the selector, to an all trunks-busy position irrespective of whether there is, or is not an unguarded set of terminals in the level, and means comprising a third one of said sets of contact springs for advancing the brushes in a level With Which said third set of contact springs is operatively associated upon selection of the level in response to a second train ol impulses incoming to the selector, to an alltrunks-busy position irrespective of whether there is or is not an unguarded set of terminals in the level.

10. In a telephone system, llines connected to stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said meanscontrolled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets isoperable being the same or different from the particular level or levels on which any V,other of said sets is operable, means connecting `a calling line to said selector, means comp-rising a rst `one of said sets of` contact springs for l atively associated upon selection of the level in `response to a rst train of impulses incoming tc the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and means comprising means actuated only if the Vcalling line is a restricted service line andcomprising a third one of said sets of contact springs for advancing the brushes, in a level With which said third set ofcontact `springs is operatively 'associated upon selection of the level in response to a second train of impulses incoming to the selector,- to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

l1. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or dilerent from the particular level or levels on which any other of said sets is operable, means connecting a calling line to said selector, means comprising a first one of said sets of contact springs for returning the brushes to normal upon selection of a level With whi-ch said first set of springs is operatively associated in response to a first train of impulses incoming to the selector, means comprising means actuated only if the calling line is a restricted service line and -comprising a second one of said sets of contact springs for advancing the brushes, in a level With which said second set of contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to the selector, to an all-trunks-busy position irrespective oi whether there is or is not an unguarded set of terminals in the level, and means Icomprising a third one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said third set of contact springs is operatively associated in response to a second train of impulses incoming to the selector.

12. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for ea-ch set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or f levels on Which any one of said sets is operable being the same or different from the particular level or levels on Which any other of said sets is operable, means connecting a calling line to said selector, means comprising a rst one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said first set of springs is operatively associated in response to a first train of impulses incoming to the selector, means comprising means actuated only'if the calling line is a restricted s-ervice line and comprising a second one of said sets of contact springs for advancing the brushes in a level with which said second set of Contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to thel selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and

-contact springs for advancing the brushes in a level with Which said third set of contact springs isr operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

13. In a telephone system, a two-motion stepby-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or different from the particular level or levels on which any other of said sets is operable, means comprising a first one of said sets of contact springs for returning the brushes to normal upon selection of a level with Which said rst set of springs is operatively associated in response to means comprising a third one of said sets of a rst train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said second set of contact springs is operatively associated in response to a second train of impulses incoming to the selector, and means comprising a third one of said s-ets of contact springs for advancing the brushes in a level with Whi-ch said third set of Contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

ll. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select `any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, vand individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or different from the particular level or levels oh which any other of said sets is operable, means connecting a calling line to said selector, means comprising a rst one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said first set of springs is operatively associated in response to a first train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said second set of contact springs is operatively. associated in response to a second train of impulses incoming to the selector, and means comprising means actuated only if the calling line is a restricted service line and comprising a third one of said sets of contact springs for advancing. the brushes, in a level With which said third set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector, to an alltrunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

15. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on Which any one of said sets is operable being the same or different from the particular level or levels on which any other of said sets is operable, means connecting a calling line to said selector, means comprising a iirst one of said sets of contact springs for returning the brushes to normal upon selection of a level With which said rst set of springs is operatively associated in response to a iirst train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for advancing the brushes in a level with which said second set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and means comprising means actuated only if the calling line is a restricted service line and comprising a third one of said sets of contact springs for advancing the brushes in a level with which `said third set of Contact springs is operatively vassociated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

16. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select `any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any leval to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or different from the particular level or levels on which any other of said sets is operable, means connecting a calling line to said selector, means comprising a rst one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said rst set of springs is operatively associated in response to a rst train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for returning the brushes to normal upon selection of a level on which said second set of contact springs is actuated in response toa second train' of impulses incoming to the selector, means comprising a third one of said sets of contact springs for advancing the brushes in a level With which said third set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective oi Whether there is or is not an unguarded set o terminals in the level, and means comprising means actuated only if the calling line is a restricted service line and comprising a fourth one of said sets of contact springs for advancing the brushes in a level With which said fourth set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

17. In a telephone system, a-two-motion stepby-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level 'to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or different from the particular level or levels on which any other of said sets is operable, means comprising a lirst one of said sets of contact springs for returning the brushes to normal upon selection of a level With which said rst set of springs is operatively associated in response to a first train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for advancing the brushes in a level With which said second set of contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to the selector to an all-trunks-busy position irrespective of whether there is or is not an unguarded set of terminals in the level, means comprising a third one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said third set of contact springs is operatively associated in response to a second train of impulses incoming to the selector, and means comprising a fourth one of said sets of contact springs for advancing the brushes in a level with which said fourth set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an alltrunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

18. In a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs'upon selection of al-particular level or any associated in response -to a first train of impulses incoming Ato ythe selector, means comprising a second onejofvsaid'lsets Vof contact springs for advancing the brushes in a level with Which said 'secondset of contact springs is operatively associated upon selection of the level in response to a first train of impulses incoming to the selector toanv` all-trunks-'busy position irrespective of whether there isor is not an unguarded set'of .terminals in the level, means comprising means actuated only if Ethe calling liner is a restricted service line and comprising a third one of said sets-o`f contact springs foradvancing the brushes in a level With which said third set of contact springs is 'operativelyv associated upon selection of 'the level in response to a rst train of impulses incoming to the selector to an all-trunksbusy position .irrespective of whether there is or is not `an unguarded set of vter'nii-nals in the level, means comprising vai'our-th one of said sets of Contact springs for'returning the brushes to nor-y mal upon selection of a level with which said fourth set of contact springs is operately associated in response to a second train of impulses incoming to the selector, means comprising a fifth one of said sets of Contact springs for advancing the brushes in a level with which said fth set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and means comprising means actuated only if the calling line is a restricted service line and comprising a sixth one of said sets of contact springs for advancing the brushes in a level with Which said sixth set of contact springs is operatively associated upon selection of the level in response to a second train of impulses incoming to the selector to an :'1

all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

19. In a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushesy to `select any level, said means controlled by directive impulses incoming to said selector, and means for advancing the brushes in any level to select an unguarded set of terminals, a set lof contact springs actuated upon selection of a particular level, means comprising said set of Contact springs for returning the brushes to normal upon selection of the level with which the springs are operatively associated in response to a rst train of impulses, another set of contact springs actuated upon selection of a particular level, and means comprising said other set of contact springs for returning the brushes to normal after selection of the level with which, said other springs are operatively associated in response to a second train of impulses incoming to said selector, said brushes being advanced responsive to a third train of impulses to select an idle set of terminals in the level corresponding to vsaid third train ofimpulses. A v

20. In a telephonefsystem, lines connected to restricted service subscribers stations, other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to saidv selector,` means for advancing the brushes in any level ito select an ung'uarded set of terminals,` a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated setoif springs upon selec-tion of` a' particular level or any one of a plurality of patricular levels, the particular level or 'levels on Which any one of said `sets is operable being the same or different from l the particular llevel or levels on which any other of saidA setsA is' operable, means connecting a calling line to said selector, means comprising a rs-t one of said l'sets of Ycontact springs for returning the brushes to normal'upon selection o'f a level with which said iirst set of springs is operatively associated in response to a rst train of impulses incoming to the selector, means cornprising means actuated only if the calling line is a restricted service line and comprising al s'ec ond one of said sets of contact springs for advancing the brushes in a level Withwhich said second set of contactsprings `is operatively associated upon selection of the level in response either to a first or to a third train of impulses incoming to the selector to an 'all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level, and means comprising a third one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said third set of contact springs is operatively associated in response to a second train of impulses incoming to the selector.

2l. In a telephone system, lines connected to restricted service subscribers stations, other other lines, a two-motion step-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for advancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level or levels on which any one of said sets is operable being the same or-different from the particular level or levels on which any other of said sets is operable, means connecting a calling line to said selector, means comprising a first one of said sets of contact springs for returning the brushes to normal upon selection of a level With which said irst set of springs is operatively associated in response to a first train of impulses incoming to the selector, means comprising a second one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said second set of contact springs is operatively associated in response to a second train of impulses incoming to the selector, and means comprising means actuated only if the calling line is a restricted service line and comprising a third one of said sets of contact springs for advancing the brushes in a level with which said third set of Contact springs is operatively associated upon selection of the level in response either to a second or to a third train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

22. In'a telephone system, lines connected to restricted service subscribers stations, other lines, a two-motion stey-by-step selector comprising a set of brushes, a terminal bank divided into levels, means for advancing the brushes to select any level, said means controlled by directive impulses incoming to said selector, means for Yadvancing the brushes in any level to select an unguarded set of terminals, a plurality of sets of Contact springs, and individual operating means for each set of springs, each operating means adapted to operate the associated set of springs upon selection of a particular level or any one of a plurality of particular levels, the particular level orlevels on which any one of said sets is operable being the same or different from the particular level or levels on which any other of said sets is operable, means connecting a calling line to said selector, means comprising a first one of said sets of contact springs for returning the brushes to normal upon selection of a level with which said first set of springs is operatively associated in response to a rst train of impulses incoming to the selector, means comprising means actuated only if the calling line is a restricted service line and comprising a second one of said sets of contact springs for advancing the brushes in a level with which said second set of contact springs is operatively associated upon selection of the level in Vresponse either to a first or to a third train of impulses incoming to the selector to an all-trunksbusy position irrespective of Whether there is or is not an unguarded set of terminals in the level, means comprising a third one of saidsets of contact springs for returning the brushes to normal upon selection of a level with which said third set of contact springs is operatively associated in response to a second train of impulses incoming to the selector, and means comprising means actuated only if the calling line is a restricted service line and comprising a fourth one of said sets of contact springs for advancing the brushes in a level with which said fourth set of contact springs is operatively associated upon selection vof the level in response either to a second or to a third train of impulses incoming to the selector to an all-trunks-busy position irrespective of Whether there is or is not an unguarded set of terminals in the level.

23. In a telephone system according to claim 18, means automatically eiective if the selection of an unguarded set of terminals in a selected level is not completed Within a predetermined interval of time to effect the disconnection of said line and return of said selector to normal.

PAUL W. WADSWORTH.

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