US2347107A - Switching system - Google Patents

Description

April 18, 1944. HUBBARD 2,347,107

SWITCHING SYSTEM Filed Aug. 22, 1942 6 Sheets-Sheet l 1.7 DISTRICT LINK FRAME A aFF/cE LINK FRAME a DISTRICT OFFICE OFFICE ND LINKS JUNCTORS sFco ARY OUT LINKS 2o sync/ 25; PAIRS TRUNK-F DIS TR/C T DISTRICT FIG. 2.

DISTRICT LINK FRAME A V OFF/CE LINK FRAME f J'ECONDARY PRIMARY /9 n-m-s 2/.9 /9 259 PRMMRY IQ l8 [Hag 3329 /8-7 -a-/a| 2/5 ,8 se'awomy 25a\ /4 /5 a-/ 22/ /-7 H7 A-l-S i 1 DISTRICT 20/ l JUNCTOR 250 24/ JILK 240 220 04 0 A-0-5 200 L f O //v l/EN T0}? FA. HUBBARD A T TORNEV April 18, 1944. HUBBARD 2,347,107

' .SWITCHING SYSTEM Filed 22, 1942 6 Sheets-Sheet 3 INVEN TOR V EAHUBBARD A T TORNEV April 1944- F. A. HUBBARD 2,347,107

SWITCHING SYSTEM Filed Aug. 22, 1 942 6 Sheets-Sheet 4 FIG 6 FIG. 8.

FIG. 5.

FIG 7 [Imam- 41 I INVENTOR' EA. HUBBARD QQM A T TORNEV April 18, 1944. F. A. HUBBARD 2, 0

SWITCHING SYSTEM Filed Aug. 22, 1942 6 Sheets-Sheet 5 INV EN 70/5 FA. HUBBA PD A T TORNEV April 18, 1944.

F. A.- HUBBARD 2,347,107

SWITCHING SYSTEM Filed Aug.. 22, 1942 e Sheets-Sht e n v 8 M m E i\\ u 'q Q l 5 8 8. N g g 1 I g k g a; W :2 2 #3 z 5% INVENTOR HAM/APO EW' f? s ,1

Patented Apr. 18, 1944 SWITCHING SISTEM Francis A. Hubbard, Ma'plewood, N. 1., assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application August 22, 1942, Serial No. 455,739

13 Claims I ployed in the telephone .system known as the crossbar system, only a small number of choices is required at each switch and the time consumed in establishing a connection is considerably reduced over the time required when hunting switches are used.

By applying such a symmetrical arrangement to movable switches, such as panel type switches, smaller trunk and link groups maybe used, thus reducing the travel of the switches, and trunk hunting may be largely eliminated.

The present invention provides a multistage, marker controlled telephone system in which a multistage busy test can be made at a single point by means of a moving switch. More specifically, after the identity of a calling line and a called line has been determined, a series of traveling switches are arbitrarily positioned to select a plurality of links by which the calling line and the called line may be interconnected, after which the switch to whichthe calling line has been extended hunts for an idle channel made up of a set of idle links.

The invention will be more clearly understood from a consideration of the following description in connection with the drawings in which:

Fig. 1 shows a typical symmetrical arrangement suitable for the crossbar system;

Fig. 2 shows a similar arrangement applied to panel type switches;

Fig. 3 is a diagrammatic showing of details of a primary and a secondary panel switch frame;

Fig. 4 shows a suitable arrangement for brushes to be used on the frames of Fig. 3;

Figs. 5 to 8 show parts of the circuits of a marker and district iunctor circuit suitable for proper arrangement of generally used in such a system. The switches of the four stages are shown as conventional line grids each grid having the dimensions indicated at the top of each stage where the horizontal dimension is given first, followed by the vertical dimension. The grids of the primary district stage have ten inlets and twenty outlets, while the grids of the other stages each have ten inlets and ten outlets, there being ten grids in the first stage and twenty grids in each of the remaimng stages. In this figure the inlets are shown along the bottom of each grid, the outlets along the vertical side, with the direction or trailic indicated by the arrows. This figure, therefore, represents an idealized pattern for an omce having a capacity of I vidually all of the grids of a stage or all of the inlets and outlets of any one grid. However, in each case the grids are numbered from 0 to 9 or from 0 to 19 and the outlets of each grid are similarly numbered. Each outlet is marked with two fingers, the first the number of the grid and the second the number of the terminal. For .example, the nineteenth terminal of district primary grid No. 0 is designated 0-19. Onthe secondary grid the outlet numbers are preceded by a letter representing the frame on which the grid is located. Therefore, the oflice junctor connected to the ninth terminal of secondary grid No. 19 on district frame A is designated A-199.

The designation on the inlet terminal along the horizontal side of each grid indicates the output terminal of the preceding stage to which the input terminal is connected. Thus the No. 0 vertical on the nineteenth district secondary grid is marked 0-19 to show that it is connected to the nineteenth terminal of primary grid No. 0. This particular connection is indicated by the dotted line I00 but no attempt has been made to show the interconnections completely since this would lead to very complicated drawings. Examination of the designations will show, however, that the basic pattern of the link is extremely simple. The twenty outlets from any given primary grid go to twenty different secondary grids and on No. 19 to vertical No. on secondary grid No. 19, etc. Similarly, primary outlet 9-0 goes to vertical No. 9 on secondary grid No. 0, etc.

To follow the pattern of the office junctors on .the outlets of the district secondary grids is somewhat more difficult because the ten outlets of 7 each grid are connected to ten different omce link frames. For this reason there is marked on each of these Junctors the destination to which it is routed. Thus it will be'seen that oflice junctor A-00 goes to primary vertical 0-0 on oflice frame a while iunctor A--05 goes to the corresponding point on oiilce frame and junctor A09 to'omce frame j. Similarly, the junctors on grid No.1 go to vertical l0 on the ten different oiilce frames. The eflect can be seen on the vertical of the oiiice primary grids which are marked to indicate the district secondary outlets from which they come. Thus it will be observed that all the first verticals of the ofllceprimary come from district frame A, all of the verticals No. 5 from district frame F, and all verticals No. 9 from district frame J. The dotted line IIlI indieates one such connection.

The office link pattern is practically the same as thatof the district links except that in this case the primary-secondary conditions are reversed, the outlets from the secondary grids bethese connections. If the dotted lines IIID- to I02 are traced through, they will be found to provide a path from any one of the ten district junctors-'(A-00 to A-O-Q) to any of the ten outgoing trunks (A-0 0 to A-0-9). There are twenty such paths that could be traced, all

completely independent, each using a different district seondary grid and a different ofllce primary grid.

From the foregoing, it will be apparent that 4 all of the district links, such as link I00, from a particular primary grid, appear in the same to level No. 5. They will represent all the available district links. In Fig. 2 it has been assumed that district link 2I9 is busy with another call, which will have been directed to it from some other district junctor on district primary grid No. 3. District links 208, 2III and 2I8 are reprgsented as idle and have been driven to level No.

Similarly, since the call originates on. district frame A, it must be served by one of the omce primary verticals in row No. 0, and, since the chosen outgoing trunk is on secondary grids I4, I5 which constitute pair No. 7, the primary omce switches must go to level No. 7. In Fig. 2

' it has been assumed that the office junctor 220 is busy on another.call from district frame A but ofiice junctors 22I, 238 and239 have been driven to level No. 7." [Also the ofllce link 2 is represented as busy on another call while the verticals, to which the oifice links 240, 258 and 259, etc., are connected, have been driven to level No. 3 and rest on the chosen outgoing trunk.

If, now, a hunting operation is instituted by the district junctor 260, as the vertical starts upward it. first encounters district. link- 200 which is idle. However, the secondary vertical on the secondary grid No. 0, to which this link 200 is connected, is resting on ofiice junctor 220 which is busy on the ofllce primary grid No. 0. Hence there is a busy condition on oflice junctor 220 which will be extended over the'district secondary switch and appear on the test terminal of the district primary. The primary switch recognizes this busy condition when it tests district link 200 and passes on. District link 2III is idle and office junctor 22I to which it is connected is idle also, but the oilice secondary vertical to which connection is made over oflice link 2 is shown as busy on the oflice secondary so that a busy position on the district secondary grids, that is,

they occupy the same vertical row. Further, all of the office lunctors, such as iunctor IIII from a particular district frame appear in the same vertical row on the-oflice primary grid. 0n the other hand, all of the office junctors of a par-v ticular oflic'e frame appear on thesame levels of the district secondary grid and all of the office links, such asllnk III2, leading ,to a particular office secondary grid, appear in the same level of all ofilce primary grids.

In place of the crossbar switch assumed to form the grids of Fig. 1, there may be substituted switches having a. horizontal fixed multiple with vertical moving switches similar to the wellknown panel type switch but having accessto only ten sets of multiples. Such an arrangement is indicated in Fig. 2. In this figure it has been assumed that a call is incoming ondis-- trict jrmctor A-3- -4 and that outgoing trunk condition will appear from this point on district link 20I at the district primary switch where 'thedistrict junctor switch will test it and pass on. At level No. 18 it encounters district link 2I8zwhich is connected to oflice iunctor 238 and in turn to oflice link 258, all of which are idle so that the path is idle throughout and the district junctor switch may stop thereon and estabhsh the connection over this path.

Figs. 3 and 4, in a diagrammatic way, show a possible type of switch which could be used to realize the system above described. Fundamentally, the switch is of the panel type such as is disclosed in Patent 1,103,623 to J. N.- Reynolds, July 14, 1914. The basic unit 3H), 3, etc., is of the panel multiple type comprising thirty multiple strips eachwith side projections on front mary frame 300 and a secondary frame 30I each including ten such basic units 3I0, 3| I, 320, 32I, etc. Such a unitwouldbe approximately 1 inches high and each unit is independently secured to the frame so that variations in terminal positions are not cumulative. The equipment shown in Fig. 3 represents half of a frame, a second similar unit being mounted above or beside it. Since the'contact terminals project on the front and rear oi, the terminal strips, 9. second set of switches, such as 330, 3 3,I, etc., serves the rear of the frame, and one terminal unit with the ten switches-corresponds to one 10 x 10 grid of Figs. 1 and 2. Switches 330 and 325 are connected in multiple to the district Junctor so that the frame has ten groups of ten district junctors, each of which has access to twenty district links and thereby to twenty disof the secondary unit 30l representing the office iunctors are cabled to the primary switches of the oflice link frame. For convenience, a cross connection frame would probably be interposed between the district link frame and the office link frame. The switch unit comprises a vertical drive rod 310, driving means 350 arranged to raise the rod 310 through ten vertical steps, and ten brush carriages 330, 335, etc., one for each terminal unit. Electrical connections to the brush carriages 330, 335, etc., are made by flexible leads from the vertical cable 31!. The use of such flexible leads is possible because of the limited travel of the brush carriages. In the circuit shown in Figs. 5 to 8, it has been assumed that the driving means 350, 35l, etc., is of the power drive type controlled by revertive pulses from a commutator. Only a slow up-drive isv necessary, since both rod and brush carriage may be returned by gravity. It is, of course, obvious that a suitable step-by-step mechanism controlled by directive pulses could readily be designed.

Fig. 4 is a diagrammatic showing of a suitable form of brush carriage. It consists of three principal brushes 40!, 402 and 403 mounted ii. s y convenient manner to be movable before the multiple terminal bank. The sleeve brush 403 is of the bridging type andis always in contact with a sleeve terminal such as terminal 406. The tip and ring brushes 4M and 402 are normally spaced away from the bank terminals to which they have access, such as terminals 404 and 405, and are brought into contact with them by means of an operating magnet 401. The brush carriage is moved upwards by means of-a driving rod like rod 408 to which is fixed a pin 409 which engages a latch 4 on the brush carriage. This latch may be fastened directly to the tip brush as at 4 or may be separately mounted as at but in either case is movable with the brush so that, when magnet 401 or magnet 452 is operated, the latch is withdrawn frem pin permitting the driving rod 408 to be withdrawn and later to operate again Without disturbing the established connection. With the magnet oper ated, the tip and ring brushes hold the brush carriage in position. The circuit of magnet 401, for example, extends from battery, through resistance 4l3 over a normal contact 414 controlled by ring brush 402 through the winding of magnet A 401 to the sleeve brush 403. Resistance 3 is sufilcient to prevent the operation of magnet 401 when brush 403 passes over or rests on a grounded terminal. When magnet 401 is operated'drawing the ring brush 402 to the left, contact 4 is opened and contact 5 closed, short-circuiting resistance 3. With resistance 4l3 shortcircuited magnet 401 will remain operated with brush 403 connected to ground.

It will be noted that the primary tip and ring brushes are connected in pairs, each pair ex-' tending to a district junctor while the secondary switches are connected individually to different district links. This is in agreement with the arrangement of Figs. 1 and 2, since each district junctor is given access to twenty district links, while each district link has access to ten omce junctors. At the same time this arrangement permits the use of the same multiple units and brush structures on all framesv and limits the switch movement to a distance of 1 inches in all cases. The twenty district links which are accessible to the group of district junctors all appear as secondary switches in' the same vertical row, ten on each half of the secondary frame.

Thus each of these twenty district links can reach ten different offlce junctors so that everydistrict junctor can reach all of the two hundred oflice junctors.

In general, the operation of such a system takes place as follows: when the marker has chosen an outgoing trunk on a particular oflice frame it the driving means of one of the two ver which are accessible to the district junctor that is being used and operates this driving means by a' number of pulses corresponding to the ofllce frame on which the chosen trunk is located.- All idle brush carriages .in this vertical row are engaged by their drive rods and are driven upwards to the level on which the ofllce junctors of the chosen ofiice frame appear. The sleeve brushes rest on sleeve terminals but the tip and ring circuits remainopen, even if the office Junctor is busy since the holding magnet will not operate to ground. These office junctors appear on the ofiice frame primary as brush carriages all inthe same vertical row corresponding to the district frame from which they come. The marker seizes the drive elements belonging to this vertical row and applies a number of pulses corresponding to the secondary bank on which the chosen trunk is located. Thus all available paths will be extended from the primary bank of the district. frame to the brushes of the ofilce secondary bank wherethe trunk islocated. Those paths which are busy at any point produce ground on the corresponding sleeve terminals of V the district primary bank.

The marker then operates the drive mechanism of the district primary, making a busy test of a' sleeve terminal at each step. As soon as a non-grounded sleeve is 'found the 'drive is stopped. thus selecting a path which is idle throughout. Reverse battery is now applied to the sleeve circuit at the district junctor to operate the hold magnets of the brush units which are in contact with the sleeve conductor thus cutting through the tip and ring conductors to the omce link and short-circu'iting theresistance such as resistance M3 on each brush carriage and identifying that link'to the marker or oflice frame connector. The ofllce secondary brush which forms the final step in this path is now driven to the chosen trunk completing the sleeve circuit from the-district junctor to the trunk.

Ground from the supervisory relay is now applied to the sleeve, operating the magnet of the oflice,

secondary switch and the connection will remain held until the supervisory ground is removed. Operation of the magnets disengages the latches from the driving rods and returns the latter to normal.

Figs. 5 to 8 show circuits, for performing these operations, inmore detail. H pwever, only such circuits as are necessary to understand the present invention have been shown, re'ference being hereby made tothe above-identified Carpenter patent for a complete disclosure of a marker for use in the crossbar system, many of the functions of which would be incorporated in a system embodying the present invention. In addition,

1 units of the district secondary switchesv connector is ready for selections.

reference is made to Ijatent No. 1,862,549 to R. Raymond et al., June 14, 1932, for a complete telephone system employing panel type switches.

A call incoming to district junotor 500 will be extended in the manner described in the above-identified Carpenter patent through sender link to an idle subscriber sender 100 where the designation of the wanted line will be re corded. As soon as the designation of the office in which the wanted line is located has been recorded, the sender operates the marker connector to seize an idle marker which includes the equipment shown in Figs. 7 and 8. The

number of the frame on which the district junctor 508 is located is recorded on the frame register I02 which operates the district frame connector to associate the marker with the district frame of Fig. 5 by closing a circuit for operating multicontact relay 550.

The designation of the wanted oflice is transferred to the code registers I03 which in turn operate translator relays I04 to bring about the operation of a route relay I05. Route relay I05 identifies the group of trunks leading to thewanted office and closes a circuit over conductor I05 for operating the multicontact relay 800 which completes a connection between the marks er and the ofllce frame of Fig. 6 on which the trunks leading to the wanted oifice are located. Both relays 550 and 600 are controlled through 'a preference circuit by which it is determined that one and only one marker can be connected with a frame at a time.

With relay 800 operated the route relay I05 closes a circuit over conductor I01 to the winding of trunk group relay 502 which operates to extend the sleeve conductors of the selected group of trunks to the chain of test relays 802, 803, etc. Busy trunks are characterized by ground on the sleeve conductor and the corresponding relays 802, 803, operate. Thereupon a circuit is closed over the contacts of relays 802, 803, etc., which extends over the back contact of the first non-operated test relayto the corresponding trunk selecting relay. Assuming that trunk 603,.

whose sleeve conductor 504 extends over the contacts of relay 502 to conductor 805 and the winding of relay 802, is idle, relay 802 is not operated and the trunk selecting circuit above mentioned is extended over the back contact of relay 802, through the winding of relay 812 and battery. Relay 8l2 operates and closes a circuit from ground over its contact, conductor 820, contact of relay 500 to the winding of relay 868 and battery. Since the identification of the trunk also identifies the group of oilice links having access thereto and thereby the set of switches and the driving elevator controlling them, relay 806 prepares the circuits for controlling the selection of the primary ofllce switch but these circuits are not effective at this time.

However, relay 508 in operating closes a circuit from ground over its inner right contacts and a contact of relay 500 to conductor 50l, back contact of relay 800, through the winding of relay 80! and battery to indicate that the omee frame Relay 80! closes a circuit at m ground over its left contact, conductor 2 through the marker connector, sender and sender link, through the winding of relay 502 to battery. Relay 502 operates and closes an obvious circuit for relay 55! in the district frame connector to identify the group of district links which serve district junctor 500. With relay 55I operated, relay 502 extends its operating ground over conductor 503, contact ofrelay 55l, contact of relay 550, conductor 552 through the winding of relay 800 to battery. Re-

lay 800 looks to ground over the back contact of relay H3. This ground also serves to hold relay 502 operated when relay 80I releases due to the opening of its circuit by the operation of relay 800. These circuits lock the marker to of relay H0 to ground but relay H4 cannot operate, being shunted by the operating circuit of relay I24 until relay 80I releases.

Relay is individual to the group of district iunctors including the iunctor 500 and therefore identifies the group of districtlinks and the switches in which they terminate. Relay 55I therefore associates these switches with the .control equipment in the district frame connector and in the.marker. When relay "4 operates, it closes a circuit for controlling the operation of the district secondary switches. This circuit is closedfrom battery through the winding of relay 553, back contact .of relay 554, contact of relay 550, conductor 555, front contact of relay H4, back contact of relay I40,'front contact of normally operated relay I3l, back contact of relay I32 and the winding of stepping relay: I33 to ground. Relays 553 and I33 operate in this circuit. Relay I33 closes a circuit from ground at its front contact, inner upper contact of relay Il4, contact of ,i-elay I05 to conductor I35. Since route relay I05 identifies the frame on which the trunk 503 is located it therefore identifies the level to which the district secondary switch must be advanced. Therefore conductor I35 is cross-connected to one of the counting relays of Fig. 7 to control the operation of magnet 542.

Relay 553 in operating closes a circuit from ground at its outer right front contact, back contact of relay 555, back contact of relay 588,

:1 .front contact of relay 55I and the winding of with a segment of commutator 544 thereby closing a circuit over the contact of relay 55I, inner back contact of relay 558 to the front contact and winding of relay 553 and battery. Relay 553 is held operated but the stepping relay 1331s released. Assuming that conductor I35 was connected as shown, the circuit closed by relay I33 above traced to conductor I35 extends over the back'contact of relay I4l, winding of relay 'I5l to battery. Relay I5l operates and closes a locking circuit for itself through the winding of relay HI and the front contact of relay I5l to .ground at the contact of normally operated relay I3l. However, relay I cannot operate When now-relayil33 is releaed by the action of the commutator, relay Ill operates and extends the conductor I36 over the front contact of relay 'I4l to the winding of relay I50 and battery. When. the brush 543 moves off the first conducting segment of commutator 544, relay I33 reoperates in turn operating lrelay I50 which locks'through the windings of relays I39, and I40, the latter relays remaining unoperated. Contact with the second conducting segment by brush 543 again releases relay I33 permitting relays I33 and I40 to operate. Relay I40 in ow crating opens the circuit of relay 553 which now releases, in turn releasing magnet 542, and leaving the brush rod elevated to hold switches etc., opposite the second o'filce junctor in each case. At this time the brush rod is maintained in its elevated position by means of a latching mechanism of the type shown in the aboveidentifled Reynolds patent.

Relay I33 in operating closes a circuit from ground at its contact, over the back contact of relays H3, H2, Ill and H0 to the winding of relay I20 and battery. Relay I20 closes a locking circuit for iteslf through the winding of relay Il0, upper front contact of relay I20, lower back contact of relay III to ground. Relay 120 also closes a circuit from ground at the back contact of relay "2, front contact ofrelay H4,

front contact of relay I20 to battery through the winding of relay I32. Relay I32 opens the circuit of relays I33 and 553 at another point and also opens the circuit of relay I3I causing that relay to release, further opening the circuit of relay I33 and also releasing the counting relays. The release of the counting relays opens the operating circuit for. relay I20 and permits relay IIO to operate. The operation of relay H0 releases relays H4 and I24. The-release of relay "4 opens the circuit of relay I32 and that relay releases, restoring the circuit of relay 'I3I which reoperates.

With relays H0 and 120 operated, the circuits for operating the primary oflice switches are established. The circuit of stepping relay I33 may be traced from ground through the winding of relay I33, back contact of relay I32, front contact of relay I3l, back contact of relay I40, lower front contact of relay IIO, conductor I35, contact of relay 600, winding of relay 601 to battery.v Relay 601 closes a circuit from ground at its front contact, over the back contact 'of relay 606, back contact of relay 660, front conrevertive pulses from commutator brush 624 terminate the operation ofthe office primary switches. As before, relay I40 opens the circuit of relay I33, releasing that relay and relay 601, relay 601 in" turn releasing magnet 620. Relay I39 operates relay I2l which locks through the winding of relay III to ground over the, back contact of relay "2, but relay Ill does not opcrate at this time being shunted by the operating circuit for relay I2I.

tact to ground at the lower front contact of relay H0, operating relay I32 to release the I33 as in the case of the district secondary switch.

With relay "0 operated, the counting relay circuit is'controlled by relay 8l2 which, in identifying the position of the idle trunk, also identifies the position to which the primary ofllce switches must be advanced. The counting relay circuit may be traced from the front contact of. relay I33, inner upper contact of relay 1I0, conductor I34, front contact of relay 812, conductor 023 which is cross-connected to the counting relays, for example as shown, so that the circuit extends over the back contact of relay I42, winding of relay I52 to battery. Therefore, three counting relays and prepare for the next operation. The release of the counting relays opens the operating circuit of relay I2! permitting relay III to operate. Relay III opens the locking circuit for relays H0 and I20 and these relays release, thereby releasing relay I32 reclose the pulsing circuit.

When relay I2I operates, it closes a circuit from ground at its contact over conductor I3I,

contacts of relays 550, 55!, winding of relay556 and battery. Relay 556 transfers the control of relay. 553 from the secondarydistrict switch to the primary district switch.

When relay Ill operates, the circuit of relay 553 is closed and relay 553 operates and establishes a holding circuit for itself over its front contact and the front contact of relay 556, back contact of relay 580, contact of relay 55L contact of relay 502, conductor 526 to sleeve brush Since only the district secondary switches associated with drive magnet 542 have been positioned, only those district-links which terminate therein need be tested. At its left contact relay 553 closes a circuit for relay 554 which operates, opening the operating circuit for relay 553, leaving that relay dependent upon its holding circuit. Relay 553 also closes a circuit over its front contact, front contact of relay 556, front contact of relay 502 through the winding of updrive magnet 560 and battery. As brush 56! moves upward it tests not only the condition of the district links 563, etc., but over these links the condition of the ofilce junctors 545, etc., and the ofilce links 621, etc., that is, it tests for an idle channel by which the connectionmay be extended tothe selected trunk. I

When brush 56I reaches an idle channel, re-

1ay'553 releases to stop the up-drive magnet 560 and bring the brush carriage to rest. Relay 553, in releasing, opens the circuit of relay 554 but relay 554 is slow to release and a circuit is closed during the releasing time of that relay from high potential positive battery 510, through resistance 5'", front contact of relay 554, back contact of relay 553, front contact of relay 556, back contact of relay 580, front contact of relay 55!, front contact of relay 502, conductor.

526, through the winding of hold magnet 565, normal contact of magnet 565, resistance 566 to the negative central office battery and ground. Magnet 565 operates, drawing the tip and ring brushes into contact with the tip and ring multiple terminals, disconnecting resistance 566 at its front contact and connecting battery to release magnet 569 to restore the brush rod of the selector to normal. The high potential battery'extends over brush 56l to the sleeve conductor of district link 563 and thence to magnet 541 which functions in a manner similar to magnet 565. The positive battery also extends over the sleeve brush 548 and the sleeve conductor of ofllce junctor 545 to magnet 628. Magnet 626 Relay 'I2I closes a circuit for relay I32 over its lower front conoperates, drawing up the tip and ring brushes tohold the switch 622 in position and operating release magnet 62! to restore the drive rod. The high potential battery also extends over brush 626 toi the sleeve conductor of the associated 'of oiilce links, the tubes are connected to the sleeve conductors of the group of office links.

When relay 166 operated in series with relay 666, prior to the operation of the. district prima'ryiswitch, a counting relay circuit was closed. \over the front contact of relay 1 to conductor 166 and thence through the winding of the No. counting relay 166 to battery. Relay 166 locks through the windings of relays 166 and 166 as before but the latter relays do not operate. When relay 666 established the holding circuit above described, ground over this holding circuit completed a shunt around the winding of relay 166 and that relay released so that relays 166 and 166 operated. Relay 166 opened the pulsing circuit as before. Relay 166 closed a circuit over the back contacts of relay H6 and H 2, front contact of relay 1", winding of relay 122 and battery. Relay 122 looked through the winding of relay 1l2 which did not operate at that time. Relay 122 operated relay 162 to bring about. the release of the counting relays and to permit relay 1|: to operate. Relay 122 also connected ground to conductor 166 which completed a circuit over the front contact of relay 666, winding of relay 666 to battery. Relay 666 transferred the driving and revertive pulse circuits from the oflice primary switch to the omce secondary switch. In addition it prepared an operating circuit for the trigger tubes 666 to 666. Relay "2 closed a circuit from battery through the winding of relay 661, front contact of relay 666, conductor 166, front contact of relay "2, back contact of relay 166, front contact of relay 16l, back contact of relay 162 through the winding of relay 166 and ground. Relay 661 prepared an operating circuit for the up-drive magnet of one of the oiilce secondary switches and a revertive pulse circuit to the commutator of that switch. However, these circuits do not become effective until the positive battery applied to the selected channel causes the operation of one of the trigger tubes 666 to 666. Since battery was connected as above described to the sleeve of ofllce link 621, tube 666 will become conducting, causing the operation of relay 666. With relay 666 operated, the circuit of up-drive magnet 66l is closed, advancing brush carriage 662. A circuit is also closed from-ground on brush 666, commutator 666. over a front contact of relay 666, contact ofrelay 666, front contact of relay 666 to the front contact and winding of relay 661 and battery, thereby transmitting revertive pulses to shunt relay 166 in the marker.

With relay "2 operated, steppin relay 166 closes a circuit from ground at its front contact. front contact of relay "2, conductor16l, front contact of trunk relay "-2 to conductor 662 which will be cross-connected to the counting relays in accordance with the position of the trlmk in the secondary oillce switch. The counting relays will be operated under the control of the revertive pulses. resulting in the operation of relays 166 and 166 to open the circuit of elay 661 to bring the switch to rest. Relay .661 in releasing closes a circuit over its back contact, front contaEt of relay 666, winding of relay 666 to battery. Relay 666 closes the sleeve conductors of the ofllce links having access to the group of trunks to which relay 666 is individual to the normal contacts and windings of magnets 666, etc., preparatory to operating magnet 666. Relay 166 operates relay 126 which in turn operates relay 162 to release the counting relays. Relay 123 looks through the winding of relay 113 which operates when .the counting relays have been released. Relay 6 at its outer lower contact disconnects ground from the holding circuit of relay 666 which in tum'permits relay 662 to release. Relay 1" also initiates the. further operation oi the marker.

With relay 662 released the district junctor is disconnected from the district frame connector. In response to the release of the marker the sender 66I operates relay 626 which connects the incoming tip and ring conductors through to the windings of relay 62L If the receiver is still oil the hook at the calling substation, relay 62! operates in turn operating relay 622. Relay 6,22 connects a bridge through retard coil 626 across the tip and ring conductors leading toward the wanted oflice to initiate the operation of the equipment at that office to complete the call. Relay 622 also connects ground to conductor 626 thereby providing a holding circuit for relay 626 andtransmitting a signal over the operating circuit of relay 626 to the sender 66l which causes the sender to send a release signal to the marker. Ground on conductor 626 through resistance 626 holds the line switches operated. Conductor 626 is also connected over the normal contact of relay 662 to the sleeve conductor 626-and brush 66l of the district primary switch. Magnet 666 is held operated as are magnets 661 and 626 under the control of relay 62! and thereby of the call-. ing subscriber. This ground extends. over the sleeve of oince link 621, front contacts of relays 666 and 666, normal contact and winding of magnets 656 to battery. -Ma t 666 operates, locking over its alternate cont t directly to the sleeve conductor of ofllce-link 621. The circuits of oflice secondary magnet 666, etc, do not include the resistances included in the circuits of the other switches so that they will operate from ground. However, since the magnets are disconnected from the sleeve brush until the switch is in position, the magnets cannot operate falsely in passing over busy terminals.

It is to be understood that these circuits are illustrative only and that other circuits might be substituted for those shown without departing from the spirit of the invention. One modiflcationcontemplated is to terminate the outgoing trunk before-the oillce primary switches thereby eliminating the last selection and permitting the district'junctor to select an idle trunk as well as an idle channel.

' What is claimed is:

1. In a telephone system, a district junctor, a plurality of trunk circuits, a plurality of channels, each comprising a plurality of switch-ended links by which said iunctor may be connected to said trunk circuit, means for identifying an idle trunk, means under the control of saididentifying means to position the switches of idle links included in the channels having access to said trunk, and means in said district junctor for selecting an idle channel.

2. In a telephone system, a district iunctor, a

plurality of trurk circuits, a plurality of serially .related switch-ended links for connecting said junctor with one of said trunk circuits, means for positioning said switches to prepare a plurality of connections, and means in said district iunctor for selecting an idle series of links and an idle trunk' 3.- In a telephone system, a switch-ended district junctor, a plurality of trunk circuits, a'plurality of serially related switch-ended links for connecting said junctor with one of said trunk circuits, means for positioning said link switches to prepare a plurality of connections, and means to operate said district junctor switch to simultaneously select an idle series of links and an idle trunk.

4. In a telephone system, a, district junctor, a plurality of trunk circuits, a plurality of serially related switch-ended links for connecting said junctor with one of said trunk circuits, means for positioning said switches to prepare a plurality of connections, and means in said district junctor for selecting an idle series of links leading to an idle trunk.

5. In a telephone system, a switch-ended in-' coming circuit, outgoing circuits, a. plurality of channels for. connectin said incoming circuit to said outgoing circuits comprising a plurality of serially related switch-ended links, and means for establishinga connection between said incoming circuit and one of said outgoing circuits comprising means for positioning idle ones of said switches, and means for operating said incoming circuit switch to select a channel in which all of the links are idle.

6. In a telephone system, an incoming circuit, outgoing circuits, a plurality of channels for connecting said incoming circuit to said outgoing circuits comprising a plurality of serially related switch-ended links, and means for establishing a connection between said incoming circuit and one of said outgoing circuits comprising means for positioning idle ones of said switches, and means for testing sets of said links in series for selecting an idle channel.

'7. In a telephone system, an incoming circuit, a plurality of'outgoing circuits a plurality of serially related switch-ended links for connecting said incoming circuit with one of said outgoing circuits, means for positioning said switches to prepare a plurality of links, and means in said incoming circuit for selecting an idle series of links leading to an idle outgoing circuit.

8. In a telephone system, a switch-ended incoming circuit, a plurality of outgoing circuits, a, plurality of serially related switch-ended links for connecting said incoming circuit with one of said outgoing circuits, common control means, means in said control means for identifying a wanted outgoing circuit, means under the control of said identifying means for positioning idle ones of said link switchesto prepare a plurality of connections between said incoming circuit and said wanted outgoing circuit, means to operate the switch of said incoming circuit to select an idle connection between said incoming circuit and said outgoing circuit. means in said control means for completing said connection, and means in said incoming circuit for maintaining said connection independent of said control means.

9. In a telephone system, a switch-ended incoming circuit, a plurality of outgoing circuits, a plurality of channels comprising primary, secondary and tertiary switch-ended links for connecting said incoming circuit with said outgoing circuits, common control means, means in said control means for identifying an idle wanted out going circuit, means under the control of said identifying means for positioning the switches of the idle ones of said primary and secondary links, means to operate said incoming circuit switch to select a channel the primary, secondary and tertiary links of which are all idle, and means to operate the switch of the tertiary link of said selected channel to complete the connection between said incoming circuit and said outgoing circuit.

' 10. In a telephone system, a switch-ended incoming circuit, a plurality of outgoing circuits, a plurality of channels comprising primary, secondary and tertiary switch-ended links for connecting said incoming circuit with said outgoing circuits, common control means, means in said control means for identifying an idle wanted outoing circuit, means under the control of said identifying means for positioning the switches of the idle ones of said primary and secondary links, means to operate said incoming circuit switch to select a channel the primary,'secondary and tertiary links'of which are all idle, means to identify the selected channel, and means under the control of said channel identifying means to operate the switch of the associated tertiary link to complete the connection between said incoming circuit and said outgoing circuit.

11. In a telephone system, an incoming frame, a switch-ended incoming circuit on said incoming frame, an outgoing circuit on said outgoing frame, a plurality of channels for connecting said incoming circuit with said outgoing circuit comprising a plurality of switch-ended primary links on said incoming frame to which said incoming circuit switch has access and all of which have access to the same outgoing frame in the same position, a plurality of switch-ended secondary links and a plurality of switch-ended tertiary links on said outgoing frame, said tertiary link switches all having access to the same trunk in the same position, and said secondary link switches having access to said pluralit of tertiary links in the same position, a common control circuit, means-for connecting said control circuit with said incoming frame, means for connecting said control circuit with said outgoing frame, means in said control circuit for identifyin said outgoing circuit, means under the control of said identifying means for positioning said primary link switches and said secondary link switches, means for operating said incoming circuit switch to select an idle channel, means for identifying said selected channel at said outgoing frame, means in said control circuit to prepare the opcrating, circuit for a tertiary link switch, and means under the control of said channel identifylng mean for extending said prepared circuit to the tertiary link of said selected channel.

12. In a telephone system, an incoming frame, a switch-ended incoming circuit on said incoming frame, an outgoing frame, an outgoing circuit on said outgoing frame, a plurality of channels for connecting said incoming circuit with said outgoing circuit comprising a plurality of switch-ended primary links on said incoming frame to which said incoming circuit switch has access and all of which have access to the same outgoing frame in the same position, a plurality of switch-ended secondary links and a plurality of switch-ended tertiary links on said outgoing frame, said tertiary link switches all having access to the same trunk in the same position, and

said secondary link switches having access to said plurality of tertiary links in the same position, a common control circuit, means for connecting said control circuit with said incoming frame, means for connecting said control circuit with said outgoing frame, means in said control circult for identifying said outgoing circuit, means under the control of said identifying means for positioning said primary link switches and said secondary link switches, means for operating said incoming circuit switch to select an idle channel, vacuum tube means for identifying said selected channel at said outgoing frame, means in said control circuit to prepare the operating circuit for a tertiary link switch, and means under the control of said vacuum tube means for extending said prepared circuit t the tertiary link of said selected channel.

. l3. In a telephone system, an incoming frame, a switch-ended incoming circuit on said incoming frame, an outgoing circuit on said outgoing frame, a. plurality of channels for connecting said incoming circuit with said outgoing circuit comprising a plurality of switch-ended primary links on said incoming frame to which said incoming circuit switch has access and all of which have access to the same outgoing frame in the same position, a plurality of switch-ended secondary links and a plurality of switch-ended tertiary links on said outgoing frame, said tertiary links all having access to the same trunk in the same position, and said secondary links having access to said plurality of tertiary links in the same pozition, a common control circuit, means for connecting said control circuit with said outgoing frame, means in said control circuit-for identifying said outgoing circuit, means under the control of said identifying means for positioning said primary link switches and said secondary link switches, means for operatin said incoming circuitswitch to select an idle channel, means for identifying said selected channel at said outgoing frame, means in said control circuit to prepare the operating circuit for a tertiary link switch, means under the control of said channel identifying means for extending said prepared circuit to thetertiary link of said selected channel, and means under the control of said incomin circuit for holding the switches of said selected channel operated and for restoring the remain,- ing switches and said control circuit to normal. FRANCIS A. HUBBARD.

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