US2136620A

US2136620A - Telephone system

Info

Publication number: US2136620A
Application number: US27675A
Authority: US
Inventors: Gerald V King
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1935-06-21
Filing date: 1935-06-21
Publication date: 1938-11-15
Anticipated expiration: 1955-11-15
Also published as: CH240076A

Description

Nev. 15, 1938. GJV. KING TELEPHONE SYSTEM 11 Sheets-Sheet 1 Filed June 21, 1935 65E amt 9mm 5%. 3E nut v 95 95 Not GR Q Um INVENTOR c.- v. mwa @m A T TOR/V5 V Nov. 15, 1938. G v Km 2,136,620

TELEPHONE SYSTEM Filed June 21. 1935 ll Shaets-Sheec 2 lNl ENTOR G. V. KING am A ATTORNE V Nov. 15, 1938 FIG. 3

SECOND L/NK G. V: KING TELEPHONE SYSTEM 'Filed June 21, 1935 11 Sheets-Sheet 3 F /F TH LINK FIRST LINK INVENTOP By G. 1 K/NG ATTORNEY Nov. 15, 1938. G. v. KING TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 4 Q g /NVENTOR (I. 1 KING ATTORNEY G. V. KING Nov. 15, 1938.

TELEPHONE SYSTEM 11 Stieets-Sheet 5 Filed June 21, 1935 mNm QQm INVENTOF? G. 1/. KING @gm ATTORNEY Nov. 15,1938. G. v. KING 2,136,620

TELEPHONE SYSTEM Filed June 21. 1935 ll Sheets-Sheet 6 //V VE N 0/? a. V. KING A TTOR/VE) G. V. KING Nov. 15, 193.

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 7 ATTORNEY Nov. 15, 1938. v K 2,136,620

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 8 55mm LINK.

S/XTHLINK lNl/EN 8V 6. 1 KING A TTORNE V Nov. 15, 1938. G v, KING 2,136,620

TELEPHONE SYSTEM Filed June 2l, 1935 11 Sheets-sheaf, 9

INVENTOR G. l/. KING BY waeem'w ATTORNEY Nov. 15, 1938. G. v. KING 2,136,520

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 10 NW9 h P 1 A 7' TORNE V Nov. 15, 1938. a. v. KING TELEPHONE SYSTEM Filed Jun 21, 1955 ll Sheets-Sheet ll W3 xvi INVENTOR By a. l K/ NG 696M A T TOR/V5 V Patented Nov. 15, 1938 PATENT OFFICE TELEPHONE SYSTEM Gerald V. King, Chatham,'N. J., assignor to Bell Telephone Laboratories Incorporated, New York, N. Y., a corporation of New York Application June 21,

9 Claims.

This invention relates to telephone systems and particularly to systems involving the use of automatic equipment for establishing conversational connections.

The object of the invention is to improve small automatic telephone systems, such as satellite systems, by performing the various local and interoffice switching connections with a unitary and compact arrangement of switch structure and circuits.

A feature of the invention is the use of a crossbar switch unit per group of local lines which combines in a ingle structure the functions of a line finder and a connector in relation to a group of links common to all switching units. Each switch unit is provided with horizontal line contacts and vertical link contacts coordinated in relation to each other into one cross-point Whereby the operation of one horizontal and one vertical magnet in the proper combination closes said contacts or cross-point of a calling line through an allotted link, and the operation of another horizontal and vertical magnet in proper combination closes the defining cross-point of the called line or outgoing trunk through said allotted link. All the lines in each switching unit are accessible to one end of all the common links when calling and all the lines and trunks are accessible to the other end of said links when said lines or trunks are called.

Another feature of the invention resides in the allocation of a plurality of cross-points on one or more of said switch units for the use of outgoing trunks which may extend to a main central office and which may be reached by a calling subscriber by dialing a predetermined digit which serves to extend his connection to the trunk cross-point level and to the operated cross-points of an idle trunk in that level.

The nature of the invention will be more clearly understood from the following description of one embodiment thereof and of possible modifications thereto with reference to the accompanying drawings in which;

Figs. 1 to 10, inclusive, when arranged as shown in Fig. 13, disclose a number of link circuits accessible to groups of subscribers lines and trunks shown in Figs. 2 and 6 for the purpose of completing connections between said lines or between said lines and trunks;

Fig. 11, arranged below Fig. 10, as shown in Fig. 13, is the timing, ringing and alarm circuit which serves all links;

Fig. 12 is a diagrammatic presentation of the 1935, Serial No. 27,675

arrangement between lines, links, and switching units contemplated by the invention.

Before discussing the details of operation, attention is directed to Fig. 12. In this layout of three cross-bar switching units, identified as

frames

1, 2 and 3, twenty lines are shown, ten on frame 1 and ten on frame 2. Ordinarily, each frame iscapable of holding five links, each of which can be connected to any two lines on different horizontal levels through the appropriate cross-points. pacity of the exchange is greater than ten lines, say twenty lines, and the traflic originating from said lines does not warrant the use of more than five links, the additional ten lines can be located on a second frame, as for instance on frame 2, and the five links accessible to frame 1 can be extended so as to be available to the additional ten lines on frame 2. In this manner, the number of lines which can be included in one exchange unit limited to five links can be extended, in groups of ten, almost indefinitely, although the circuits of the present invention, being designed primarily for application in rural districts, limits the total number of lines to a maximum of fifty lines, that is five switching units of ten lines each. Moreover, while the number of lines can be increased with respect to a definite number of links, conversely, my invention makes it possible to increase the number of links with respect to a definite number of lines. If, for instance, the quantity of trafiic which originates in an exchange of twenty lines is greater than that which can be handled successfully by five links and two additional links are needed, said links may be accommodated on a separate or third switching unit to one half of whose horizontal cross-points may be multipled the lines from the first switching unit and to the other half the lines from the second switching" unit with the two links extendingto both halves of the third switching unit. In Fig. 12, an exchange of twenty lines is illustrated as needing seven links to handle the trafiic successfully. Consequently a third switching .unit is supplied, frame 3, to the left half of whose horizontal cross-points the lines appearing on frame 1 are extended and to the right half of whose horizontal cross-points the lines appearing on frame 2 are extended and the two additional links, namely,

links

6 and 7 are extended to both halves of frame 3. Obviously, if ten links were needed to serve the twenty lines, then a fourth switching unit would be required and the third and fourth switching units could be arranged so that the lines appearing on frame 1 would ex- On the other hand, if the catend clear across frame 3 and the lines appearing on frame 2 would extend clear across frame 4 with the five additional links accessible to each of the twenty lines through

frames

3 and 4.

Inasmuch as the preferred embodiment of this invention is disclosed with respect to its application to a rural telephone system in which a plurality of telephone stations may be located in the same pair of line conductors, as for instance, five stations on the tip and five stations on the ring, and which makes it necessary to provide code ringing to identify each station and to make it possible for one station to call another station on the same line, the more detailed description of this invention will include the operations required to establish a connection between a station on one line and a station on another line, a connection between two stations on the same line and (3) a connection between a station and an outgoing trunk, three of which occupy the first three horizontal cross-points, respectively, on frame 1 and the left half of frame 3.

It must be understood, however, that the invention herein set forth and claimed is not limited to any such arrangement but can be readily applied by any one skilled in the art to an exchange having individual lines or to any other arrangement of lines and stations that suggest themselves by the character of the service to be rendered as, for instance, two or four party line service or single party service.

When any one of the group of subscribers in the group shown in Fig. 6, say subscriber 624, initiates a call, line relay B is operated over a circuit extending from grounded battery through the left winding of said relay, outer contacts of cut-off relay 60I, the subscribers line loop, inner contacts of relay 60I, right winding of relay 600 to ground. Relay 600 operates and completes a circuit for selective magnet 2I2 which extends from ground through the contacts of relay 600, left back contacts of relay 602, conductor 633, upper No. 4 contact-set of relay 206, conductor 2I4, right winding of selective magnet 2I2, conductor 2I5, lower normal contacts of relay 20B, conductor 2I6, left contacts of relay I02, right outer contacts of relay I03, right contacts of relay IOI, to battery and ground. Magnet 2I2 operates and locks in a circuit completed from operating ground as traced to its left winding, through its left front contacts, left back contacts of selective magnets 2II, 2I0 and 209, conductor 2", winding of relay I02, right inner contacts of relay I03, right contacts of relay IN, to battery and ground. Relay I02 operates in the locking circuit of magnet 2I2, closes an obvious circuit for slow-operate relay I04 over its right front contacts and opens the operating circuit of magnet 2I2 at its left contacts.

In the usual construction of the cross-bar switch, the so-called 100 point switch preferably has one selecting magnet for ten horizontal cross-points, thus making it possible to provide five links to the frame, each link having one calling cross-point and one called crosspoint; that is, one set of contacts through which the link gains access to the calling line and another set of contacts through which it gains access to the called line. However, where the link capacity is greater than five, and other switch frames have to be provided to accommodate additional links, the number of frames is, of course, determined by the number of links. Where, as in the case being illustrated according to Fig. 1

seven links are provided for twenty lines, an additional frame (frame 3) is split in two and the two additional links accommodated thereon as already described. Under such circumstances, when a subscriber, such as subscriber 624, initiates a call and the selecting magnet 2I2, on the main frame for the horizontal level of the calling line is operated, it also becomes necessary to operate the selecting magnet for the same level on the additional frame since the idle link to be selected and attached to the calling line may be either in the main frame or the auxiliary frame. In the drawings, Fig. 4 represents the auxiliary frame, while its selecting magnets 306 to 3I0 are shown on Fig. 3 and of which selecting magnet 309controls the continuation, on the auxiliary frame, of the level controlled by selecting magnet 2I2 on the main frame. Consequently when relay I04 operates, it completes a circuit which extends from ground through its contacts, conductor I06, conductor GIT right contacts of magnet 2I2, conductor 2I8, right winding of selective magnet 309 to battery and ground. Magnet 309 operates and then extends its operating ground through its right contacts, conductor 3II, top outer contacts of relay 208, winding of relay 2I9 to battery and ground. Relay 2I9 operates and completes a circuit for relay I008, which circuit extends from ground on the left contacts of relay 2I9, conductor 224, left normal contacts of link make-busy key III, left back contacts of relay H0 (if the first link is idle), conductor H2, No. 8 contact-set of relay I0I5 winding of relay I008, to battery and ground. Relay I008 operates and, through its right sets of contacts, connects ground to conductors 3I2 and 3I3 respectively, the former of which extends to the operating winding of the holding magnet 300 on the crossbar frame 1 while the latter extends to the operating winding of the holding magnet 100 on the lower cross-bar frame 2. Inasmuch as the calling line 624 appears in the upper frame and the origination of the call therefrom has resulted in the operation of relay 2 I9, the circuit of holding magnet 300 of the first link, if idle, is completed over conductor 3| 2, winding of magnet 300 conductor 320, right contacts of relay' 2I9 to battery and ground. Magnet 300 operates, looks from battery through its lower winding and contacts, conductor 3I5, right back contact of relay IOI0, conductor IOI6 to ground over the No. 2 contacts of relay IOI5 and, since horizontal selecting magnet 2I2 is also operated, the combination of the operated selecting magnet 2I2 and the operated holding magnet 300 serves to operate contact-set 3| 4 on the first link and thereby extend conductors 609, SH and (H2 of the calling line 624 to the first link. As soon as cross-point 3I4 is operated, then, by virtue of succeeding operations in the link which result in the operation of relay I0I5 as described hereinafter, a circuit is completed for relay 602 which extends from ground and battery, through the right winding of said relay, conductor 6I2, third set of contacts on cross-point 3I4, conductor IOI6, to ground on the No. 2 contact-set of relay I0I5 Relay 602 operates and performs functions described hereinafter.

If the calling line had been located on frame 2, and in the corresponding fourth horizontal position on the frame as line 624 is located on frame 1, say line 634 (not shown), with its extension to the fourth horizontal position on the right of frame 3, then after the operation of the proper selecting magnet on frame 2, instead of closing the circuit of holding magnet 300 the circuit of holding magnet I00 on frame 2 would have been completed from ground and battery through the right contacts of relay 606, conductor 628, upper winding of holding magnet T60 conductor 3 I3, right inner contacts of relay H108 to ground. In this way, only the holding magnet of the chosen link in the frame in which the calling line belongs is operated.

Before proceeding with the further operations which follow the connection of a link to the calling line, it is necessary to observe those circuit operations which, prior to this connection, take place to insure that, in the event that more than one line calls at the same time, links, if available, are connected to each of said lines in a definite order of preference and only after each link has been connected; to a line.

Suppose that subscriber 624, whose line according to Fig. 12, is located on cross-bar frame 1 and on the fourth level thereof and that subscriber 63L whose line appears on cross-bar frame 2 and on the first level thereof, simultaneously initiate calls by removing their respective receivers off their hooks, line 624 will cause the operation of line relay 600 as already described while line 63H will cause the operation of line relay fiIZ by the closure of an obvious circuit similar to that for line relay 600.

It will be recalled that the operation of relay 690 resulted in the operation of horizontal selecting magnets H2 and 309 controlling those cross-points on the link frames to which the line I524 is extended. In a similar manner, the operation of relay EH2 causes the operation of horizontal selecting magnets 601 and 306 of those cross-points in the link frames to which line 63I extends. Accordingly, when relay 6I2 operates, a circuit is completed which extends from. ground on the contacts of relay BI2, left normal contacts of relay 6M, conductor BIS, No. I contact set of relay 603, right winding of selective magnet 60?, left normal contacts of relay 605, conductor EIE, conductor 2I6, left contacts of relay I02, right outer contacts of relay I03, right contacts of relay IilI, to battery and ground. It will be recalled that the circuit of horizontal selecting magnet 2 I2 was similarly completed to conductor 2m and thence to battery and ground on the back contacts of relay IOI. Assuming that the circuit of each of the selective magnets 2I2 and till is closed simultaneously then, when. magnet 60'! operates, a circuit path is partially completed for selective magnet 306 which extends from ground and battery through its left winding, conductor 3 I1, right contacts'of magnet 601, conductor GI'I, conductor Illfi, to the contact of relay I64. However, each of the selecting magnets 2I2 and Gill, on operating, closes a locking path through their respective left windings and front contacts, the left back contacts of the selecting magnet immediately ahead of them in preference, to conductor 2|! and thence to battery and ground on the back contacts of relay IOI through the winding of relay I02. Inasmuch as the operation'of magnet 212, which is ahead of magnet 5431, by opening its back contacts breaks the locking path of magnet 691, only magnet 2I2 whose locking path is not broken, can lock. Hence, when relay I02 operates as before described, the operating circuit of magnets 60'! and 2I2 is opened at its back contacts and since magnet 2 I2 is now locked and magnet 60] is not, magnet Bill releases and further opens the previously described path for magnet 306. In virtue of the operations already described, the first link, if idle, becomes attached, therefore, to line 624.

Should the first link be busy, this condition causes the mechanical locking of relay H0 in the manner described hereinafter, and the ground connected to conductor 224 is advanced over the left front contact of relay H0 back contact of relay H0 of the second link, if idle, the No. 8 contact-set of relay I0I5 of said link, to the winding of the start relay corresponding to relay I003 in said second link. Further, if the second link is also busy and, therefore, relay H0 is mechanically locked in an operated position, the ground on conductor 224 is advanced over the left front contact of relay H0 to the armature of relay "H0 (not shown) in the third link and from thence either over the back contact of this relay, if the link is idle or over the front contact if the link is busy, to the contacts of relay H0 (not shown) of the fourth link; the circuit path being extended over an operated relay H0 in each busy link until an idle one is found, after which operations will take place similar to those already described. Should all links be busy at the time a subscriber initiates a call, relay H0 in each link will be locked in an operated position, whereupon a circuit is completed which extends from ground on the right front contacts of each relay I'Iil up to and including relay H0 of the seventh link, conductor I, winding of relay N16, to ground and battery. Relay I00 operates and closes an obvious circuit for relay IOI which operates and opens the battery connection to the operating circuits of the horizontal selecting magnets, thus making it impossible to operate any of them if no link is available. Relay IOI further completes a circuit which extends from ground through its left contacts, conductor I07, winding of magnets 109 -109 in parallel, to battery and ground. Each of these magnets operates and unlocks its companion relay 1 I 0 409 So long as each of the links is busy, then, inasmuch as relay I008 in each of said links releases immediately after the horizontal selecting magnets are operated, as more completely described hereinafter, each of the separate make-busy relays HU -Hi1 will remain operated over a path which, for relay H0 extends from ground and battery through its right winding, conductor I08, left contacts of relay I006, No. 2 contact-set of relay M5 to ground; relay I0I5 in each of the busy links having been operated as described hereinafter. link becomes idle, relay I0I5 releases, the corresponding make-busy relay II 0 releases and the link is made available for service. Also, when a link becomes idle and its make-busy relay H0 releases, the circuit of relay I06 is broken, causing the release of relay ml, the consequent release of all locking magnets 'IEl9 'I09 and the restoration of battery to the start circuit of the horizontal selecting magnets.

Returning, now, to the allotment of an idle link to the subscriber on line 63I on the assumption that said subscriber has started the call at the same time as the subscriber on line 624, and assuming that, due to the preferential arrangement of line 624 ahead of line 63 I, a link has been connected to line 624, it will be recalled that the: horizontal selecting magnets 601 and 306, corresponding to the position of line 63I on the link frames, could not remain operated once the locking circuit of magnet Bill was opened by the operation of magnet 3I2. However, as soon as the link is allotted to line 624 and relay 602 has On the other hand, as soon as a operated, cut-01f relay I operates over a circuit completed through the right locking contact of relay 602 to a previously traced ground on conductor GIZ, whereupon line relay 600 releases and opens the locking circuit of horizontal selecting magnet 2I2 the release of which, in turn, opens the locking circuit of the corresponding selecting magnet 309 on the third link frame. Once the locking circuit of the horizontal magnet 2I2 is opened, relay I02 releases and restores the operating and locking battery for all of the horizontal selecting magnets. The horizontal magnet 60? and also consequently, horizontal magnet 306 can now operate and lock and cause the allotment of an idle link to line 63L Having shown how each one of two idle links may be connected to each one of two calling lines on which calls are initiated simultaneously, the operations which follow the connection of the first link to a line on which a subscrihers station, say station 624, is located, will now be described. It will be assumed that the subscriber 624 wishes to establish a connection with another subscribers station, say station 63I whose line, according to Fig. 12, is located on the first horizontal level of frame 2 and that, in order to establish said connection, subscriber 624 dials the number 319. The first two digits of this number identify the position of the line on the frame on which it is located while the last digit identifies the ringing code assigned to station 63L When the cross-point 3I4 is closed, a circuit is completed for relays IOI2, IOI3 and IOI4 over the line loop which may be traced from ground and battery through the winding of relay IOI2, bottom outer back contacts of relay IO0I, bottom outer contacts of relay I000, conductor IOIl, second contact from the top of cross-point 3I4, conductor 6II, loop of subscribers line 024, conductor 609, top contact of cross-point 3, conductor 3I6, top outer back contacts of relay I000, top outer contacts of relay IO0I, winding of relay IOI3, conductor IOI8, left normal contacts of relay III I, left normal contacts of relay 906, conductor 9I5, left winding of transformer I I3I to ground. Relays IOI2 and IOI3 operate closing obvious parallel circuits to the winding of relay i0 which operates. Relay IOI4 causes the operation of relay I0I5 which, on operating connects: (1) ground through its No. I contact-set to conductor IOI9 which extends to the No. I contact-set of relay I0I5 of the second link and from thence through corresponding contact sets of relay I0I5 -I0I5 of all'the seven links, from the last relay of which, that is relay I0I5 it extends by way of conductor 800, to the winding of register I which, on the other side of its winding, is connected to battery and ground. If, when the first link is taken into use, as abovedescribed, and relay I 0 I 5 operates, the remaining six links are busy, each of their corresponding relays IOI5 is operated and the circuit to register I 05. is completed to indicate an all-busy condition of the links; (2) through its No. 2 contact-set,

- relay I0I5 connects ground to conductor IOI6 which completes previously described circuits to the right winding of relay 602 and to the locking winding of holding magnet 300 (3) over its No. 3 contact-set relay I0IIi extends ground through the bottom inner back contacts of relay IBIH and thence to the No. 4 contact of relay i009; (4) over its No. 4 contact-set ground is connected to conductor I020 and, through the bottom outer contacts of relay I002, to conductor I020, both of which conductors provide locking paths to the various relays shown in Figs. 5 and 9, as explained hereinafter; (5) over its No. 5 contact-set, ground is connected to conductor I02I which, over the right middle contacts of relay 9| I, extends as conductor M4 to resistance II32, contacts of relay II2I, left winding of relay I I2I to battery and ground. Relay I I2I operates over this self-interrupted circuit and induces currents at each interruption in the closed inductive path extending from ground through the right winding of relay II2I, right winding of coil II3I to ground. Inasmuch as the left winding of said coil comprises an element in the circuit of relays I M2 and IOI3, which circuit extends over the subscribers loop, said interruptions are repeated over said loop as dial tone which is heard by the subscriber as an instruction that he may proceed to dial the wanted number; (6) over the No. 6 contact-set of relay I0I5 a circuit is completed over the left outer contacts of relay I009 and conductor I 023 through the left winding of relay I I00 to battery and ground, which relay functions are described hereinafter; (7) over its No. I contact-set, relay I0I5 closes a partial path for relay IOII which extends from battery through the winding of said relay, conductor I022, right outer contacts of relay III I, conductor 9I3, No. I contact-set of relay I0I5 normal contacts of relay IOII to conductor I02I. The manner in which conductor I02I is completed to ground will become evident hereinafter from a consideration of the operation of the miscellaneous signaling circuits in Fig. 11, which begins to function as soon as relay I I00 operates at the time ground is connected to conductor I023; (8) over its No. 8 contact-set, relay I0I5 opens the previously described circuit of relay I008, causing said relay to release. In releasing, relay I008 disconnects ground from conductors 3I2 and 3I3 and, since the holding magnet 300 is now locked through its lower winding, ground on these respective conductors is no longer necessary while over its left contacts relay I008 completes a circuit for the link make-busy relay H0 which extends from grounded battery through the right winding of said relay, conductor I08, left contacts of relay I008, No. 2 contact-set of relay I0I5 to ground. Relay H0 is now held operated as long as the link is busy.

Relay II00, on operating, looks over the right winding and right inner contacts to ground on conductor 9M, causes ground to be connected to locking conductor I I33 which extends to various parts of the circuit of Fig. 11, and further completes a circuit for relay Hill which extends from. ground on the left outer contacts of relay H00, contacts of relay II03, winding of relay IIOI to battery and ground. Relay IIOI operates and closes an obvious circuit for relay II02 which causes it to operate and to further close an obvious circuit for relay H03. Relay II02 further completes a circuit for relay II I6 extending from ground through its right contacts, conductor I I38, normal contacts of relay I I I6, winding of relay III6, resistance H34 to battery and, in parallel therewith through the left outer back contacts of relay III5, resistance H35 to battery. It will be observed that the winding of relay III5 is short-circuited by the operating ground for relay III6 by the connection of said ground to one side of its winding at its left outer back contacts and to the other side of its winding at the normal contacts of relay III6. Relay III6 operates, locks to ground on conductor H33 .of relay IH5 through its front contacts.

In the meanwhile, the operation of relay H03 opens the circuit of relay IIIlI which, after an interval, releases, in turn opening the circuit of relay H02 which releases after an interval and in turn, opening the circuit of relay H03 which also releases after an interval and reestablishes the circuit for relay HOI to repeat the cycle of operations ofrelays HOI, H02 and H03. Relay H02, on releasing, further disconnects ground from the left terminal of relay III5 at the left outer back contact of said relay, after which said relay operates in a circuit which extends from ground and battery, resistance H35, winding of relay Hi5, front contacts of relay HIE to ground on conductor H33. Relay IH5 operates and establishes a circuit for relay IIII extending from ground on its right outer contacts, left inner normal contacts of relay III'I, winding of relay I I I1, resistance I I3! to battery and ground. Relay HIT operates and establishes a short circuit for the winding of relay HM by connecting ground on conductor H33 through its left inner contacts to the left terminal of the winding of said relay, ground having been already connected to its other terminal in a path extending from ground on the right outer contacts of relay HI5, right outer back contacts of relay IIM to the right side of its winding.

On the next operation of relay H02 ground is again connected to conductor II 38 and since relay I I I5 is operated, said ground is extended to resistance H34 thereby short-circuiting relay I I I and causing it to release. Relay I I I5, however, does not release since it is now held in an operated position by the ground on conductor H38 extended through the normal contacts of relay HIE. On the subsequent release of relay H02 and the removal of ground from conductor H38, relay IH releases, the short-circuiting ground for relay HM is disconnected and this relay now operates in a circuit extending from ground and battery through resistance H36, winding of relay I I I4, left inner contacts of relay III] to ground on conductor H33.

Upon the next operation of relay H02, relay IH6 operates again over a previously described path, locks as before and again shortcircuits the winding of relay HI5. When relay releases, relay III5 operates in parallel with relay HIS and establishes a short circuit for relay III'I which circuit may be traced from ground on the right outer contacts of relay II I5, right front contacts of relay HM, resistance H31. Relay III'I releases and completes a circuit for relay HI8 which may be traced from ground and battery, resistance H40, winding of relay IH8, left inner normal contacts of relay III8, left middle contacts of relay HI'I, left inner front contacts of relay IIM to ground.

Relay III8 operates and establishes a short circuit for relay H3 by connecting ground on conductor I I33 through its left inner front contacts to the left terminal of the winding of relay I I I3 while ground is connected to the right terminal of its winding through its own right back contacts, through the left middle contacts of relay III! as already traced.

When relay H02 operates again, relay HIS releases in the manner already described and, when it releases, relay III5 also releases. Inasmuch as relay HM is held through the normal contacts of relay HH and the right outer contacts of relay III5, then, with the release of relay HI5, relay IIM'releases. Further, since the winding of relay III3 is held short-circuited by ground through its right back contact and extending over a previously traced path to. the left inner front contacts of relay I I M, then, when said relay releases, the short circuit is removed and relay III3 operates over a circuit which extends from grounded battery, resistance IM'I, left inner front contacts of relay I I I8 to ground on conductor H33.

Thus, after relay H02 has operated and released four consecutive times, relays III3 and III8 are operated and locked while the two previous pairs of counting relays, namely HI5 and HI6, HM and HH are released.

In the same Way it can be shown that after eight consecutive operations and releases of relay H02, relays III2 and HI9 will be operated and locked; that after twelve consecutive operations, relays I I i0 and H20 will be operated and locked, that after twenty-four consecutive operations, relays H09 and H05 will be operated and locked, and that after forty-eight consecutive operations relays H09 and H05 will be released. In all cases, all preceding pairs of counting relays will be released.

Thus in the circuit of Fig. 11, six pairs of counting relays are provided which function to count time through the operating cycle of relays IIOI, H02 and H03, which cycle can be made as long or as short as desired by appropriate means. During the interval that a link is connected to the calling line the counting relay circuit of Fig. 11 provides the proper intervals for giving the appropriate signals usually given when calls are not completed in a given length of time and further provides for operating the five ringing relays .I I22-I I26,.inclusive, in the proper interval called for by the ringing code of each of five stations located on each of the line conductors. Inasmuch as code ringing is well established in the art and can be carried out by any Well-known means which provides for the closure of the ringing circuit path in accordance with the code called for by the Wanted station, it is not thought necessary tounduly lengthen this specification by the detailed description of all the functions of the circuit shown in Fig. 11 except in so far as they are necessary to. a complete disclosure and understanding of the operation of the link circuit and the manner in which it is used to establish a talking connection between two stations.

Returning, now, to the operation of the link circuit and the fact that the calling station has been given dial tone, let it be assumed that the subscriber does not dial for the time interval measured from the instant relay H02 operates to the time that relay II I0 operates. If the link has not released during this interval, which means among other things, that the subscriber has not dialed, a circuit is completed over a previously described path to conductor I02I and thence over the inner right back contact of relay H20 and the left front contact of relay HIO as soon as the timing circuit hasadvanced to operate relay HIO. Relay IOH operates, locks over conductor I022, outer back contact of relay 9I I, conductor 9I3, No. 1 contacts of relay I0I5 to ground at its left front contacts and, over its right contacts, extends the winding of relay IOI0 to conductor I024. When the timing circuit has advanced, in the manner previously described, to the point where relay H09 is operated and relay H05 is released, ground is connected to conductor I024 over a path which extends through the left front contacts of relay H09 and right contacts of relay II05, causing the operation of relay IOI0 which locks to ground over conductor I022, right outer contacts of relay 9! I, conductor 9I3, No. I contact-set of relay I0I5 left contacts of relay IOI I, ground. Relay IOI0 disconnects ground from conductor 3I5 over which holding magnet 300 has locked. Magnet 300 releases and frees the subscribers line at the cross-bar contact-set 3I4. The restoration of the link equipment to normal thereafter is the same as that which will be described subsequently for the disconnection of a completed connection.

Now if the subscriber 024 still has his receiver off the hook after the link is freed, or if the line is crossed, the line relay 600 will reoperate over the line loop since, with the release of the crossbar point, ground is disconnected from conductor 6 I2 causing the cut-off relay 60I to release, thereby again connecting relay 600 over the line. Relay 602 being slow-release, does not release immediately and before it can release, the reoperation of relay 600 will cause it to remain locked, which condition will prevent the reconnection of the ground to conductor 609 and thereby prevent the seizure of another link during the time that the line is locked out of service.

Assuming, however, that the subscriber does not delay dialing until the operation of relay I0l0 but that, on hearing dial tone, proceeds to dial the tens digit 3, then on the interruption of the line which follows the first pulse, relays IOI2 and IOI3 release, but relay IOI4, being slow to release, remains operated during pulse interruptions. A circuit, therefore, is completed which extends from ground on the left back contacts of relay IOI3, left inner contacts of relay IOI4, conductor I025, winding of relay 905 to battery and ground. Relay 905 operates and closes an obvious circuit for relay 904 which also operates. Another circuit is also completed which extends from ground through the No. 4 contact-set of relay I0I5 conductor I020, lower back contacts of relay I002, conductor I026, backcontact of No. 4 contact-set I of relay 9I0, conductor 9I6, right back contacts of relay IOI3, conductor I021, left back contacts of relay I, contacts of relay 902, winding of relay 903 to battery and ground. Relay 903 operates and the ground through the left back contacts of relay 90I is now extended through the left inner contacts of relay 903 to one side of the right winding of relay 90I, the other side of which is also connected to ground through the left front contacts of relay 994. Relay 903 further completes a circuit for relay 50I which extends from ground through the right front contacts of relay 903, left back contacts of relay 900, conductor 9I'I, winding of relay 50I to battery and ground. Relay 50I operates but performs no useful function at this time.

When relay IOI3 reoperates on the closure of the line after the interruption thereof by the first pulse, the circuit which caused the operation of relay 903 is opened while neither relays 905 nor 904 release during the pulse interruption since both of them have slow releasing characteristics. Moreover, and due to the fact that relay 904 does not release, relay 903 does not release either, but holds in a circuit which extends from ground through the left front contacts of relay 904, right winding of relay 90!, left inner contacts of relay 903, contacts of relay 902, winding of relay 903 to battery and ground. Relay 90I operates in this locking circuit and, on operating, extends ground to conductor 9 I8 which looks relay 50I through its top inner contacts, closes an obvious circuit for relay 900 through the left winding of said relay, causing the operation of said relay which further locks over its right winding and right outer contact to ground on the left front contacts of relay 904.

When the line is opened again by the interruption of the second pulse and relay IOI3 consequently releases, the ground previously traced through the right back contacts of relay I 0I3, left armature of relay 90I to conductor I021, is now extended over the left front contacts and left winding of relay 90I, winding of relay 902 to battery and ground, causing relay 902 to operate,

whereupon relay 903 releases and relays 90I and j 902 hold in the circuit of relay 902 just traced. With relay 993 released, a circuit is completed for relay 502 which extends from ground on the right back contacts of relay 903, conductor 9I9, top outer contacts of relay 50I, winding of relay 502 to battery and ground. Relay 592 operates and completes I a circuit which extends from ground through the right outer front contacts of relay 905, conductor 92!, top outer contacts of relay 502, conductor 5I9, normal contacts of relay 909, winding of relay 909, resistance 922, to battery and ground. Relay 909 operates while relay 908 remains short-circuited by ground on the battery side of its winding extended thereto over conductor 5I9. On the reoperation of relay !0I3 following the closure of the line on the termination of the second pulse, the holding circuit for relays SM and 902 is opened causing said relays to release, but relay 900 being locked to ground on the contacts of relay 904, which relay does not release during the transmission of the pulses of a digit, remains locked, whereupon relay 50I is released by the opening of the contacts of relay SM and relay 502 is locked in a circuit which extends from ground and battery through the winding of relay 502, top inner contacts of said relay, conductor 5I8, left outer back contacts of relay 903, right inner contacts of relay 900 to ground on the left front contacts of relay 904.

On the release of relay I9I3 when the line is opened by the interruption of the third pulse, relay 903 operates again as it did for the interruption of the first pulse, and since relay 900 is operated at this time, a circuit is completed for relay 503 which extends from ground through the right front contacts of relay 903, left front contacts of relay 900, conductor 920, top middle contacts of relay 502, winding of relay 503 to battery and ground. Relay 503 operates. On the reoperation of the relay IOI 3 when the line is closed after the third pulse, relay 90I operates while relay 992 does not as before described. However, since the third pulse is the last of the series of pulses for the first digit 3, no more pulses will be forthcoming for the interval required by the subscriber to wind up the dial, an interval sufficiently long to cause the release of

relays

904 and 905. However, due to the operation of relay 9! prior to the release of

relays

905 and 904, relay 502 is released, whereupon the short circuit to the battery side of the winding of relay 903 is removed and this relay now operates in parallel with relay 909 in a circuit which extends from ground and battery through resistance 924, winding of relay 908, front contacts of relay 009, to ground on conductor 923. When relay 908 operates and, as soon thereafter as relay 905 releases, a circuit is completed for relay 906 which extends from ground and battery through the left winding of relay 9%, left front contacts of relay 908 to ground on the right outer back contacts of relay 905. Relay 906 o-p-. crates and locks over'its right winding and right inner contacts. to ground on conductor 923. Now, due to the operation of relay 905 and the prior release of relay 905, relay 503 does not release because of a holding circuit which extends from battery through its winding and top inner contacts, conductor 520, left outer contacts of relay 995, left inner contacts of relay 996, conductor 925, bottom outer contacts of each of the relays 5H3, BIZ and 5| I, to ground. A circuitis now completed for relay 5I2 which extends from ground on the left back contacts of relay 996, right middle contacts of relay 906, right outer back contacts of relay 90'I, conductor 92%, bottom middle con tacts of relay 503, top winding of relay 5B2, to battery and ground. Relay 5I2 operates over its top winding and locks overits lower winding and bottom inner contacts to ground on conductor 923. The operation of relay 5I2 registers the tens digit 3 and unlocks relay 593 which releases.

The subscriber now dials the second or units digit which, under our assumption is the digit 1. When relay I I it releases on the line interruption, relays 904 and 905 operate as before described and the previously traced pulsing ground causes the operation of relay 903, after which a previously described circuit path is completed for operating relay 50I which further looks over conductor 9! to ground on the right middle contacts of relay 90L When relay 995 operates at the beginning of the pulse a shunting circuit is completed for relay 909-which extends from ground on the right outer front contacts of relay 905, left outer contacts of relay 99%, right front contacts of relay 909, to resistance 922. Relay 909 releases but relay 903 continues to hold through the right normal contacts of relay 909 to ground, as traced, on the right outer front con tacts of relay 995. On the reoperation of relay IOI3, at the termination of the pulse, relay 99i operates in series with relay 903 followed by the operation of relay 909 and, after an interval, relays 905 and. 994 release, causing the release of relays Bill and 903 after which relay re leases. Further, with the release of relay 995, the

holding circuit for relay- 909 is broken and this relay releases. Thereupon, a circuit is completed for relay 901 which extends from ground and battery through the winding of said relay, right outer contacts of relay 909, left back contacts of re lay 908, right outer back contacts of relay 935 to ground. Relay 9-01 operates and locks to ground on conductor 923.

Now if the units digit of the wanted subscribers number had been any other digit than the digit 1, say the digit 6, then six pulses would have been dialed and would have resulted in the opera tion of relay 506 by circuit operations similar to those described for the hundreds digit 3. When,-

in this assumed series of six pulses, relay 55 2 crates on the second pulse, ground is connected to resistance 922 over a path extending from the right outer front contacts of relay 905, conductor 92!, top outer contacts of relay 592, conductor 5l9, right front contacts. of relay 908 to resistance 922. This causes relay 999 to be shunted and released, causing relay 908 to be held locally so long as relay 905 remains operated; that is, until all the six pulses of the digit are received, at which time it releases and completes the operating circuit of relay 901, already described. A circuit is now completed for relay 5M which extends from ground and battery through the lower winding of relay 5M, No. 3 contact-set of other frames as required.

relay 506, conductor 52I, No. I contact-set of relay 9I0, right outer front contacts. of relay 991, right middle contacts of relay 900 to ground on the left back contacts of relay 994. Another circuit is also completed for relay 5i 5 which extends from ground and battery through the lower winding of relay 5I5, No. 0 contact-set of. relay 5% to ground as traced on conductor 52%. Both of these relays operate and then look over their re spective top windings. and top inner contacts to ground on conductor 923.

The reason why, in the case of any units digit higher than 1, it is necessary to operate one or more of the four relays 5I4-5I'I is the fact that, for each digit including 1, a record of the digit must be preserved for the future operation of the proper selecting magnet in the link for reaching the wanted line. Each of the first two digits of the Wanted number represents a specific function which must be performed to reach the wanted line. Referring to Fig. 12, it is evident that the first, or tens digit, represents the particular link frame on which the wanted line terminates. Since the invention can accommodate a maximum of fifty lines with ten lines to the frame, it is obvious that the lines on the first frame will have a tens digit which will identify the frame, and inasmuch as the digit 1 is not used as the tens digit, all the lines located on the first frame will have a digit 2 for the tens digit while those on the second frame will have a digit 3. I have chosen to illustrate my invention as adapted to twenty lines, spread over two frames with an additional split frame to accommodate two more links that could not be accommodated on the first two frames, so that the lines terminating on the first frame all have a 2 as a tens digit and those terminating on the second frame have a 3 as a tens digit. In other groups of ten lines each were to be added to the office up to a maxi mum of fifty lines, then each of these groups would have a 4, a 5 and a 6, respectively, as the tens digit.

Hence, so far as the operation of the invention is concerned, the tens digit is used to identify the frame on which the wanted line is located, and this fact is recorded on the operation of one or more of the three relays 5 to 5I3, inclusive, by the connection of ground to one of the five conductors that identify each of the frames accommodating a group of ten lines. Since the illustration of the operation of the invention has been limited to twenty lines, ten on each frame, only two of these conductors, namely 522 and 523, are used and connected to such parts of the circuit as are controlled over these conductors; the remaining three being bracketed and labeled to Since, in the call being illustrated, the wanted subscriber is located on the second frame and therefore involves the digit 3 as the first digit, the relay operated on the tens digit 3 was relay 5I2 to make conductor 523 effective at the proper time.

The relationship between the operation of the relays 5| I--5I2 and each of the tens digit which ten lines to the frame is as follows:

Digit Relays operated The seconds or units digit of the subscribers line is that which identifies the horizontal level in the frame on which the line terminates, and this fact is recorded in the four register relays 5I4 to 5H, inclusive, in order to eventually prepare a circuit for operating the horizontal magnet involved for reaching the wanted line. These relays are operated or non-operated in particular combinations by the operated relay in the group of relays 50I to 5I0 which is responsive to the digit dialed. In the case of the call being used to illustrate the operation of the invention and which has the digit 1 as its units digit, none of these relays was operated following the operation of relay 50I. If the wanted line had had the digit 6, as assumed for detailing the function of relays 5 to 5I'I, then relays 5M and 5I5 would have been operated as described. The relationship between the units digit dialed and the relays operated is as follows:

Digit Relays operated Returning, now, to the number being dialed by station 624; that is number 3I9, and remembering that the dialing of the units digit 1 resulted in the non-operation of the relays 5M to 5, as well as the release of relays 908 and 909 and also the release of relay 50I, the subscriber is now ready to dial the last or the ringing digit 9. Each of the pulses of the digit causes the operation of relays 900, MI, 902 and 903 in the manner described, followed by the successive operation and release of relays 50I-509. It will be recalled, however, that during the dialing of the units digit and as a result of the operation of relay 905 at the beginning of the digit and its release at the end of the digit, relays 908 and 909 were released. However, when the second pulse has been received and relay 502 has operated in consequence, a previously described circuit path is closed for relay 909, causing said relay to operate. When relay 502 releases, relay 908 is operated in parallel with relay 909, as before described. On the ninth or last pulse, relay 509 is operated and held over its locking contacts to ground on conductor 520 so long as the pulsing relay 903 remains operated. However, at termination of the pulse, the release of relay 905 causes a circuit to be closed extending from ground through the right outer back contacts of relay 905, left front contacts of relay 908, left outer contacts of relay 901, left winding of relay 9I0 to battery and ground. Relay 9I0 operates, locks over its right winding and No. 4 front contacts, conductor I026, bottom outer contacts of relay I002 to ground on the No. 4 contact-set of relay II5 and extends ground over its No. 5 contacts to the right winding of relay 90I, causing the pulsing relays 900, 90I, 902 and 903 to hold after the release of relay 904 following the termination of the last pulse of the ringing digit. With

relays

903 and 900 remaining operated, relay 509, instead of releasing as it would have done if it had operated on a 9 units digit, remains locked to ground on the N0. 5 contacts of relay 9I0. Relay 9I0 further causes relay 904 to be held over its No. 8 contact-set to ground on conductor 923 in preparation for making the busy test of the wanted line as explained hereinafter.

The operation of relay 9I0 further causes a circuit to be completed which extends from ground on the left outer back contacts of relay 9| I, No 2 contacts of relay 9I0, conductor 928, right winding of relay I00'I conductor I028, left contacts of relay I03, right back contacts of relay I02, battery and ground. Relay I00! operates and completes a locking path extending from ground on conductor 928, left winding of relay I00'I and left inner front contacts, conductor I029, Winding of relay I03, right back contacts of relay I02, to battery and ground. Relay I03 operates in this locking circuit, opens the operating circuit of relay I00! at the left contacts of relay I03 and also the operating circuit of relay I001 in every link. The locking circuit of each of said relays is likewise opened by the operation of relay I00'I since said locking circuit is controlled over conductor I030 which extends over the back contacts of each of relays I001 in a chain arrangement, so that once relay I001 of one link is locked, corresponding relays in other links cannot operate, thereby looking out other links which may be seeking access to the frame containing the wanted line.

Relay I00'I on operating, closes an obvious circuit for relay I006 which, on operating, causes a circuit to be completed for relay 9II extending from ground through the right outer contacts of relay I906, conductor I03I, winding of relay 9| I, to battery and ground. Relay 9 operates and looks over its right inner front contacts to ground on conductor I020. In the meanwhile, the operation of relay I001 causes the connection of ground to conductor I032 which extends to the top armature of relay 5. Inasmuch as relay 5I2 has been operated for the tens digit 3, said ground is extended to complete a circuit over the top back contact of relay 5II, top outer front contacts of relay 5l2, top inner back contacts of relay 5I3, conductor 523, winding of relay 605 to battery and ground; winding of relay 604 to battery and ground and winding of relay 603 to battery and ground. Relay 603 operates and opens the path of each horizontal selecting magnet on the second frame, each of which extends back to a corresponding line relay of a subscribers line on this frame; relay 604 operates and extends the operating winding of each of said magnets to each of the ten conductors extending to the contacts of relays 5I4-5I1, while relay 505, over its left front contacts, connects ground and battery to each of the operating windings of said horizontal magnets while over its right inner contacts it extends ground to conductor 62I which is connected to the operating windings of all link holding magnets 10 I -101 Since the units digit of the wanted subscribers number is 1, and since the impulse of this digit resulted in the operation and locking of none of the relays in the group of relays 5I4-5Il inclusive, a circuit is completed which extends from ground on the right inner contacts of relay I00'I conductor I033, left outer contacts of relay 500, bottom outer back contacts of relays 5I4-5II inclusive, conductor 524, No. I contacts of relay 604, right winding of horizontal selecting magnet 601, left contacts of relay 605, to battery and ground. Magnet 60! operates and prepares the horizontal cross-points for contact with the vertical at the link attached to the crosspoint of the calling line. In the meanwhile, the

ground connected to conductor 62I completes a II circuit through the top winding of. holdingmage net llll of the first link, conductor. 102, left contacts of relay I006 to battery and ground. Hold: ing magnet 'I0I operates over its top winding and then looks over its lower winding and contacts in a previously described circuit. Since the circuit of horizontal selecting magnet 601. was closed ahead of that of holding magnet 'I0I by the fact that the former circuit is completed by relay 1001 and that of the latter by relay lime which is slow-operate, the cross point contacts controlled by magnet 601 are set for lockingunder control of magnet 'I0I in advance of the opera tion of said magnet, as required for the proper operation of across-bar switch. a

When relay 9H operatesit opens the circuit of relay I'I which, on releasing, further releases relay I000 disconnects ground from conductor 023 which latter causes the release of all relays locked to said conductor including relay 904, connects ground to conductor IOI8 which extends to the winding of relay [M3 to replace ground supplied from conductor 9I5, andif the wanted line is idle after testing it in the manner to be described hereinafter completesa circuit which extends from ground through the i left inner back contacts of re1ay500, conductor 525,

left middle contacts of relay 9| I right outer con tacts of relay 904, conductor 929, right outer contacts of relay I009, winding of relay I005, to battery and ground. l V

.If the wanted line'is busy, relay 6I4 of said line is operated and as soon as cross-point, I03 is operated and before relay 9| I shall have had time to operate and, therefore, remove ground from conductor 923,,a path is completedfor relay I000v which extends from ground. and battery through the winding of said relay, conductor I045, right inner contacts of relay 904, conductor I039, third contact of cross-point I03, conductor 625, right outer front contacts of relay 6 I4 to ground. Relay I009 operates, locks to ground onthe No. 3 contact-set of relay IllI5 under the control of the bottom inner back contacts of relay IO0I, cuts off the operating circuit of relay I005, opens the circuit of relay I I00 which, however, does not release at this time because it is held up over another ground to its right winding extending over conductor II43, bottom inner contacts of relay i005, No. 1 front contacts of relay I009, to ground through the No. fi contacts ofrelay I0I5 and completes a busy tone circuit for the calling line which extends from ground through the right winding of inductioncoil I:I3I, left inner front contacts of relay III5, condenser H44, conductorv H46, No. 6 contacts of relay I009, top outer back contacts of relay I005, top outer back contacts of re1ayl004, upper winding of relay I002, to ground and,-in parallel therewith through condenser I044, bottom outer con tacts of relay IO0I, bottom outer back contactsof relay I000, conductor IOI'I, second contact of cross-point 3I4, conductor BI I, subscribers loop 624, conductor 609, first contact of cross-point 3I4, conductor 3I6, top outerback contacts of relay I000, top outer contacts of relay IO0I, condenser I034, lower winding of relay I002 to battery and ground and, in parallel therewith, bottom back contacts of relay I004, bottom outer back contacts of relay I005, No. 5 contacts of relay I009,conductor H41, condenser H45, right inner contacts of relay I I I5 to ground. The subscriber hears thetone which isinterrupted at regular intervals by the operationand release of relay? I I I5 asbeforedescribed. He is by this means notified that the called line is busy and restores his receiver to the switchhook.

If the, wanted line is not busy, relay GM is normal, relay I009 does not operate and the circuit of relay I005 is completed as before described. Relay I005 operates and looks over its operating path to ground on conductor .929. It further completes a circuit for operating the called line cut-off relay 6I3 which extends from ground through the bottom middle contacts of relay I005, conductor I039, fourth contact of cross-point J03, conductor 025, right outer back contacts of relay 6I4, winding of cut-off relay M3 to battery and ground. Relay 6I3 operates, removes the line relay 6I2 from the line and prevents the subscriber from initiating a call.

As soon as relay I005 is operated, the wanted line is out throughtto the calling line preparatory to the closure of the ringing circuit over a path hereinafter described.

It will be recalled that, when the link is seized, the alarm circuit shown in Fig. 11 begins to function as soon as ground is connected to conductor I023, and that the pairs of counting relays like relay I I I5 and IIIO operate and release to count off time in the manner described. As soon as relay III'I operates, ground is connected to conductor H39 through the left middle back contacts of relay I I I9, right middle back contacts of relay III8, right inner front contacts of relay III'I to conductor H39 which further extends through theright middle back contacts of relay I009, top inner continuity contacts of relay I004, conductor I036, left inner contacts of relay 9| I, conductor 930, conductor I031, winding of relay I004 to battery and ground. Relay I004 operates and looks over its top inner front contacts, conductor I038, to ground through the left outer back contacts of relay III2 which is normal at this time.

During the period in which relay I004 is operated, the called subscribers station is being rung, and this period is measured from the first release of relay H02 to the operation of relay IlI2 on the eighth consecutive release of relay H02, as already described.

The operation of relay I 004 completes the ringing circuit to the called subscribers line and in theproper ringing code combination determined by the last digit of the wanted number which, in this case, is determined by the digit 9 and, therefore, by the operation of relay 509. Inasmuch as the operation of the invention is being disclosed with respect to a rural exchange having five stations on the tip conductor of the line and five stations on the ring conductor, the different stations must be rung by a code individual to each station although the invention is not limited to a plurality of stations on one line or even to a single station. Under these circumstances, relays I I23 to H26 each provide a different ringing code for each of the five stations on one of the line conductors and the circuit for operating each of 1 said relays is controlled in the appropriate order and for the required length of time by the pairs of counting relays shown in Fig. 11. Inasmuch as this part of the circuit is ancillary to the operation of the invention in that ringing code relays and the manner of their control are well established in the art, it is not deemed necessary to describe the various operating circuits for the relays H23 to H26 except to mention the fact that relay II22 provides a code of two medium rings per cycle; relay H23 three short rings; relay H24 four short rings; relay