US2092465A

US2092465A - Telephone system

Info

Publication number: US2092465A
Application number: US27889A
Authority: US
Inventors: William H Matthies
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1935-06-22
Filing date: 1935-06-22
Publication date: 1937-09-07
Anticipated expiration: 1954-09-07

Description

Sept. 7, 1937. w. H. MATTHIES TELEPHONE SYSTEM Filed June 22, 1955 9 Sheets-Sheet l sept. 7, 1937.

-W. H. MATTHIES TELEPHONE SYSTEM 9 Sheets-Sheet 2 Filed June 22, 1935 VEN TOR nf. H. MA r TH/Es ATTO/QN y LAST F/RS 7' LINK Sept. 7, 1937. W, MATTHlEs 2,092,465

TELEPHONE SYSTEM vFiled June 22, 1935 9 Sheets-Sheet 3 RE G/S TE R /A/z/E/v TOR W H. MA 7' TH/ES ATTORNEY Sept. 7, 1937. w. H. MATTHIES 2,092,455

TELEPHONE SYSTEM Filed June 22, 1955 9 sheets-sheet 4 POLAR/Z50 MA/N EXCHANGE ops/1A r//va TRU/vk /N VEN TOR w. H. MA r TH/Es ATTORNEY Sept. 7, 1937. w. H. MATTI-"Es TELEPHONE SYSTEM Filed June 22, 1955 9 Sheets-Sheet 5 /NVENTOR By yW H. MATTH/ES ATTORNEY N @Px Sept. 7, 1937. w. H. MATTHlEs TELEPHONE SYSTEM Filed June 22, 1935 9 Sheets-Sheet 6 /N VEN T 0R By WH. MATTH/ES A TTORNEV Sept. 7, 1937. w. H. MATTHIES TELEPHONE SYSTEM 9 Sheets-Sheet '7 /NVENTOR W H. MATTH/ES (fw ATTORNEY Sept. 7, 1937. w. H. MATTI-"Es TELEPHONE SYSTEM Filed June 22, 1935 9 Sheets-Sheet 8 /A/l/E/v TOR By WH, MATTH/Es ATTORNEY Sept. 7, 1937. w. H. MATTHxEs TELEPHONE SYSTEM Filed June 22, 1955 9 Sheets-Sheet 9 /Nl/E/VTOR B WH. MATrH/Es ATTORNEY Patented Sept. 7, 1937 PATENT OFFICE 2,092,465 v TELEPHONE SYSTEM William H. Matthies, Hackensack, N. J., assignor to Bell Telephone Laboratories, Incorporated, NewYork, N. Y., a corporation of New York Applicaties June z2, 1935, serial No. 27,899 f 6 Claims.

This invention relates to telephone systems and particularly to those in which connections in a local exchange are established by automatic switches under the control of a distant main office. n

Objects of the invention are to improve and simplify the equipment needed at the local exchange by making use of a common switch controlling register for setting up both local and trunk calls; to enable the registration of the switch controlling designation over an operating trunk from the main office when one type of connection is required and the registration of such designation lover a conversational trunk when another type of connection is required; to enable the use of a more simple and eilicient form of selective switch at the local exchange;

and to otherwise improve the construction and operation of systems of the foregoing character. It has been proposed heretofore to complete both local and trunk calls in a small rural exchange by means of automatic switches under the control of an operators dial at the main .exchange. For this purpose an operating trunk4 is provided between the main and local exchanges over which the local subscriber orally requests the number he desires, and over which the operator sends the designation impulses to complete the connection at the local exchange. In some of these prior systems, Aswitches of the step-bystep type are used and in others relay switches are employed. Where relay switches are used, it is necessary to provide some form of register mechanism for receiving Ithe designation impulses.

According to the present invention advantages are secured over these prior systems by using cross-bar switches at the local exchange for establishing both local and trunk connections and providing a digit receiving register common to all switches and link circuits at the local exchange. When a local subscriber calls, his line is automatically connected through a cross-bar switch to one end of an idle link, and the link is automatically connected to the common register and to the operating trunk leading to the distant operators position. The operator receives the number from the subscriber and dials back over the operating trunk to set the register which thereupon connects the other end of the link either to a local subscribers line or to a conversational trunk according to whether the call `is a local one or one to the central ofllce.

Another feature is an arrangement in a system of the character above described in which pulses sent over-the operating trunk fromthe main office when a call is to be completed between two local subscribers or when the local subscriber is calling the main omce, and in which the register is set by impulses sent over the conversational trunk when a call is being extended from the central office to a subscriber in the local oilce.

These and other features of the invention will be more fully described in the following detailed specication 'which should be taken in conjunction with the accompanying drawings.

Referring to the drawings:

Fig. 1 is a schematic of the telephone system including a remote control rural exchange and part of a main exchange;

Fig. 2 is a diagram showing how Figs. 4 to 10. inclusive, should be arranged to disclose one embodiment of the invention;

Fig. 3 is a diagram showing how Figs. 4 to 8, inclusive, and Figs. 10 and 11 should be arranged t? disclose a second embodiment of the inven- Fig. 4 shows a plurality of rural exchange'subscribers' lines and line circuits, which are associialtd with the group equipment shown at the rg Fig, 5 shows in the upper portion thereof the link allotter equipment and in the lower part thereof registering and control equipment common to the links and to the interoice trunks and responsive to dial impulses from the main exchange to effect the selective operation of the cross-bar switches of Figs. 8 and 10;

Fig. 6 in theleft portion thereof shows the main exchange end of both the operating trunk and the conversational trunk. The right portion of this figure shows the rural exchange equipmentfor the operating trunk;

Fig. 7 in the right portion thereof shows a link circuit and in the left portion thereof shows a relay for associating said link circuit with the registering equipment of Fig. 5 and with the rural6 exchange end of the operating trunk of Fig.

Fig. 8 shows a portion of a switch of the crossbar ype which is associated with the link equipmen Fig. 9 in the right portion thereof shows one arrangement of the rural exchange end of the conversational trunk and in the left portion thereof shows a relay for associating said trunk with the rural exchange end of the operating trunk of Fig. 6 and with the registering equipment of Fig. 5;

Fig. shows a portion of a switch of the cross-bar type 'which is associated with the rural oflice end of the conversational trunk of Fig. 9 or Fig. 11;

Fig. 1l in the right portion thereof shows a second arrangement of the rural exchange end of the conversational trunk and in the left portion thereof shows a relay for associating said trunk with the rural exchange end of the operating trunk of Fig. 6 and with the registering equipment of Fig;` 5.

Referring more particularly to Fig. 1,"an exchange system including a remote control rural exchange and part of a main exchange is schematically illustrated. The rural exchange is equipped with selectors SWI, SW2, and SW3 of the cross-bar type, links LKI and LK2, one for cach selector, an operating trunk OT extending to an operators position in the main exchange and a conversational trunk CT, individual to selector SW3, appearing in selectors SWI and SW2 and extending to the main exchange, and a register REG common to all of said links and trunks. The main exchange is indicated at the right of the drawings and comprises two operators cord circuits C and CI and the trunk circuits which form the main exchange ends of the aforementioned trunks at the rural exchange.

Each subscribers line, such as A or B, appears at two cross-points in each of local selector switches SWI and SW2; one of the vertical rows of contacts, associated with said cross-points, is provided to extend said lines to the nder end F of the associated link on originating calls; and the other vertical row of contacts is provided for extending the connector end C of said link to said subscribers lines for completing local calls. The conversational trunk CT, extending to the main exchange also appears at a cross-point associated with the connector end C of SWI and SW2, for the completion of outgoing trunk connections. In addition to the aforementioned local switches SWI and SW2 there is provided an additional switch SW3 which is used only for the completion of incoming connections from the main exchange. Each subscribers line appears at a cross-point of this switch and the vertical rows of contacts, associated with said crosspoints, are provided for extending the conversational trunk CT to the subscribers lines. Relays Rl and R2 are provided to associate the links LKI and LK2 with the operating trunk OT and with the register REG; relay R3 is provided to associate the conversational trunk CT with the register REG and with the operating trunk OT.

If a call is initiated by a subscriber at station A for a subscriber at station B, for example, a connection is established through selector SWI nder end F of link LKI, relay RI, operating trunk OT, thence to the main exchange. A signal at the latter oilce apprises the operator of a waiting call. The operator answers by means of cord circuit C, and determines the number of the called subscribers line, whereupon a second cord CI is inserted into a dial jack associated with the operating trunk OT, and the called subscribers number is dialed. The dial pulses are recorded in the register REG, which in turn associates the connector end C of the link LKI, through contacts of the selector SWI, with the called subscribers line B. 'Ihe operator then rings the called station and when the subscriber at said station responds the operator at the main exchange disconnects, thereby releasing relay Ri b v which the register REG and operating trunk OT were associated with the link LKI. The operating trunk is restored to normal and may be used for other calls.

If a trunk call is initiated by a subscriber at station A, for example, the connection is extended to the main exchange over the operating trunk OT as described for a local call. In this case it is necessary to connect the line associated with station A with the conversational trunk CT; this connection is effected by the operator at the main oilice who dials the conversational trunk code, an operation which causes the connector end C of the link LKI to be associated with said conversational trunk at the contacts of selector SWi. Thus the connection is extended to the main oillce over the conversational trunk CT and may be completed by means of another cord circuit. The operating trunk OT is released when the operator at the main office removes the' cords from the jacks of said trunk.

Calls incoming from the main exchange to stations in the rural exchange may be completed by either of two methods, depending upon whether or not the conversational trunk CT is arranged for dialing. For example, assume that said trunk is not arranged for dialing. The main oilice operator extends the connection to the conversational trunk by means of a cord circuit C. Relay R3 extends the connection to operating trunk OT and thence back to the main exchange thereby causing a signal to be displayed before the same or a diierent operator. In either case the operator associates a cord circuit with the associated trunk jack, dials the called subscribers line number, whereupon the dial pulses are recorded in register REG which in turn actuates the selector SW3 to connect the called subscribers line to conversational trunk CT. The dialing operator then signals the called station and when the subscriber responds the dialing operator disconnects from the operating trunk thereby releasing said trunk as aforementioned. If the conversational trunk is arranged for dialing the main exchange operator, after having extended the connection thereto, dials the called subscribers line number directly over said trunk. The dial pulses are recorded in register REG which in turn actuates the switch SW3 to connect the called subscribers line to the conversational trunk as aforementioned. The called subscriber is signaled in the usual manner.

All of the switches disclosed in this system comprise briefly, a plurality of horizontal selecting members, one for each horizontal row of contacts for preparing said contacts for operation. In addition, there is provided a plurality of vertical operating bars, each individual to one of the ver-y tical rows of contacts for operating said contacts to establish connections. For a more detailed explanation of the construction and operation of these switches, reference may be had to patent application of J. N. Reynolds, Serial No. 702,453, led December 15, 1933, granted as Patent No. 2,021,329, Nov. 19, 1935.

Having described the trunking schematic of the exchanges in general, and having described generally the various connections which can be established within the system, the operation of the circuits will now be described in detail, rst with the drawings placed together in accordance with Fig. 2, and then with the drawings placed moval of the receiver from the receiver hook associated with line 4|| causes the operation of the associated line relay 400` in an obvious circuit, Relay 400 operates group relay 40|, which is common toall of the subscribers lines associated with the uppermost level of contacts of selector switch 825, and is equipped with an individual set of contact springs for each subscribers line appearing in said level. 'I'he circuit for operating relay 40| may be traced from ground at the lower outer front contacts of relay 400, left winding of relay 40| and through back contact of relay 402 to battery. Relay 40| operated locks through its right winding and right inner front contact to battery through the winding of relay 402. Relay 402, which is common to all of the group relays such as 40|, 403 and 404 operates in the aforementioned circuit. Relay 402 operated opens the initial operating circuit for relays 40|, 403 and 404 to prevent the operation of another of said relays at this time. The circuit is arranged that in case two or more group relays operated simultaneously only one would lock due to the series locking circuit which extends through the back contacts of said group relays. Group relay 40| also closes a circuit for the operation of relay 100 which is associated with the particular link allotted for completing the call. This circuit may be traced from ground at'the right outer front contact of relay 40|, conductor 405, closed contact of key 500, back contact of allotter relay 50|, associated with the irst link, and through the winding of relay 100 to battery. Relay 100 operated causes theoperation of selecting magnet 800 of selector switch 825. This magnet is associated with the uppermost level of contacts in which line 4|| appears. This circuit is traced from ground at the right middle front contact of relay 40|, upper seventeenth front contact from the top of relay 100 and through the winding of magnet 800 to battery. Magnet 800 operates the selecting members associated with the horizontal row of contacts in which the line 4|| appears, thus preparing these contacts for operation. Relay 100 also operates relay 406 in a circuit from ground at upper outer front contact of relay 100, winding of relay 406 and through front contact of aforementioned operated relay 402 to battery. Relay 406 operated extends its operating ground, through its front contact, left inner front contact of relay 40|, lower inner front contact of relay 400, upper next to outer front contact of relay 100 and through the winding of selector holding magnet 803 to battery. Magnet 803 operates the bar associated with the vertical row of contacts thus engaging the contacts at cross-point 802 and extending the conductors 4|1, 4|8 and 4|0 of line 4|| to

conductors

804, 805 and 806 respectively of the link. Due to the fact that relay 406 is slow in operating it does not close its front contact, to operate the aforementioned holding magnet 803, until suiicient time has elapsed for the operation of the aforementioned selecting magnet 800. The association of the line 4|| with the link closes a circuit for operating relay which may be traced from ground through upper winding of relay 10|, conductor 804, contactof cross-point 802 of selector switch 825, conductor 4|1, through subscribers set of line 4H, conductor 4|8, contact of cross-point 802 of selector switch 825, conductor 805 and through the lower winding of relay 10| to battery. Relay 10| operates slow-torelease relay 104 in an obvious circuit. Relay 104 operated, operates cut-oil relay 4|9 from ground at lower middle front contact of relay 104, sleeve conductor 806, contact of crosspoint 802 of selector switch 825, conductor 4|0 and through the winding of relay 4I9 to battery. The sleeve conductor 806 also appears ln the connector end of the selector switch 825 and the ground connected thereto guards the calling line from seizure by another link. 'Ihe operation of relay 104 furnishes a holding ground for relays 100 and 402 and holding magnet 803. 'Ihe holding circuit for relay 100 is traced from lower inner front contact of relay 104, upper back contact of relay 102 and thence through the winding of relay 100 to battery; and the holding circuit for relay 402 and magnet 803 is traced from ground at lower outer front contact of relay 104, thence in parallel one path extending through back contact of relay 103, 4front contact and winding of hold magnet 803 to battery; and the other extending over conductor 822, seventh from top front contact of relay 100 and thence through the winding of relay 402 to battery. The operation of cut-oil relay 4 I9 disconnects the line relay 400 from the line 4|| and the latter relay releases. Relay 400 released, releases 'group relay 40| thereby releasing the selecting magnet 800. With the selecting magnet 800 released the connection through the contacts of cross-point 802` of selector switch 825 is maintained by the energization of the holding magnet 803.

Relay 100 operated as aforementioned closes a circuit to operate the line relay 600 and thereby signal the operator at the main exchange. This circuit is traced from ground through the upper winding of relay 600, upper outer back contacts` of

relays

603, 604, 605, 606 and 601, winding of polarized relay 602, lower inner front contact of relay 100, lower outer back contacts of

relays

601, 606, 605, 604 and 603 and through the lower winding of relay 600 to battery. Line relay 600 operates in this circuit but relay 602, which is of the polarized type, does not operate due to the battery polarity. Relay 600 operated lights lamp 60| to apprise the main exchange operator of a waiting call. The operator responds by associating a cord circuit (not shown) with jack 608 thereby operating relay 603 and causing the release of relay 600 and the subsequent effacement of lamp 60|. There is now established a talking connection from subscribers line 4|| to the operator at the main exchange. This connection was partially traced from the subscribers line 4| to the tip and ring condensers 105 of the link. From the latter condensers, the tip and ring conductors extend through contacts of relay 100, talking condensers 101, upper and lower outer back contacts of

relays

601, 606, 605 and 604, respectively, tip and ring springs of jack 608 and thence to the cord circuit. The talking connection thus established enables the calling subscriber to inform the operator at the main exchange as to the details of the desired connection.

Assume that the call is for a station associated with subscribers line 4|5 and that the operator at the main exchange has associated a second cord circuit (not shown) with the dialing and ringing jack 609 associated with the operating trunk,

thereby operating relay '604. Relay 604 disconnects the tip and ring conductors of the operating 'trunk from jack 608 and connects the tip and ring conductors from the dialing and ringing jack 609 thereto in a manner so that the polarity of the current through polarized relay 602 is in the proper direction to cause the operation of said relay. Relay 602 operated operates slow-to-release relay 6I0 which in turn operates relay 601 in an obvious circuit. Relay 601 operated dis. connects the tip and ring conductors, associated with the main oflce portion of the operating trunk, from the tip and ring conductors extending to the calling subscribers line, and connects the pulsing relay 502, of the register, thereto. Pulsing relay 502 operates from the dialing cord and operates slow-to-release relay 503, which provides a locking ground for relay 601 in a circuit traced from ground at left outer front contact of relay 503 and through lower inner front contact and winding of relay 601 to battery. Relay 601 operated, also releases aforementioned relay 602 thereby releasing relay '6I0. Relay 6I0 aforementioned is slow-to-release in order to maintain relay 601 energized until relay 503 provides relay 601 with an independent holding ground. The two rotary switches 504 and 505 associated with the register circuit are set by impulses, caused by the operator's dial at the main exchange, and cause the operation of a selector switch such as 825 to effect a connection with the called subscribers line. The rst train of impulses causes the rotary switch 504 to be positioned for operating a selecting magnet in the switch level in which the called subscribers line terminates, and the second impulse train positions the rotary switch '505 for operating the hold magnet to associate the connector portion of the link with that particular set of line terminals. From inspection it is obvious that the called subscribers line 4I5 appears in the selector level of switch 825 with which selecting magnet 8I2 is associated and that the particular terminals in that level may be associated with the link by the operation of holding magnet 8I0.

When the operator at the main exchange transmits the rst or tens series of pulses the pulsing relay 502 is released upon the opening of the line circuit for the first pulse. Relay 502 released closes a circuit for slow-to-release relay 5I! from ground at back contact of relay 502, front contact of relay 503, normally closed contact of off-normal springs. 506 and thence in parallel one path extending through stepping magnet 5I0 to battery and the other extending through relay 5I2 to battery.. The operation of the stepping magnet 5I0 advances the brush of switch 504 to terminal I thereby operating the off-normal springs 506. Relay 5I2, which is slowto-release, remains energized through its right front contact and the middle closed contact of off-normal springs 506 until the series of pulses has been transmitted. Relay 503 also being slowto-release remains operated during the transmission of impulses. For each successive opening and closure of the line, the brush of switch 504 is advanced one step until it reaches the 9th terminal. After an interval has elapsed, following the series of impulses, relay 5I2 releases thereby closing a circuit for the operation of selecting magnet 8I2.l This circuit is traced from ground 5 at left inner front contact of relay 503, left back contact of relay 5I2, brush and terminal 8 of switch 504, ninth contact from the top of relay 100 and through the winding of selecting magnet 8l2 to battery. Magnet 8I2 operates the selecting bar associated with the horizontal row of contacts in which subscribers line 4I5 appears, thus preparing these contacts for operation.

The transmission of the units digit releases pulsing relay 502 upon the opening of the line circuit for the first pulse thereby operating stepping magnet 5I I and relay 5|3. This circuit may be traced from ground at back contact of relay 502, front contact of relay 503, middle closed contacts of off-normal springs 506, right back contact of relay 5I2, normally closed contact of oif-normal springs 501, thence in parallel, one path extending through the winding of stepping magnet 5II to battery and the other extending through the winding of relay 5I3 to battery. The operation of the stepping magnet 5II advances the brush of switch 505 to terminal I thereby operating the oif-normal springs 501. Relay 5I3, which is slow-to-release, remains energized through its right inner front contact and lower closed contact of olf-normal springs 501 until the series of pulses has been transmitted. Relay 5I3 also operates slow-to-release relay 6II in an obvious circuit. For each successive opening and closure of the line, the brush of switch 505 is advanced one step until it reaches the 5th terminal. After an interval has elapsed, following the series of impulses relay 5I3 releases thereby closing a circuit for the operation of holding magnet 8I0 of selector 825. This circuit is traced from ground at the left inner front contact of relay 503, back contact of relay 5I3, brush and terminal 5 of switch 505, eighteenth from the top front contact of relay 100 and thence through the winding of holding magnet 8I0 to battery. Magnet 8I0 operates in the above traced circuit and actuates the associated bar, thus engaging the contacts at cross point 809 and extending the conductors 801, 808 and 8I2 of the link to conductors 8I3, 8I4 and 4I3, respectively, of line 4I5. Holding magnet 8I0 also locks to ground at the lower outer front contact of relay 104. The aforementioned relay 6II which is slow-torelease remains operated. following the release of relay 5I3 after the unit". train of impulses has been transmitted, for a sunicient length of time to test the called subscribers line 4 I 5. If the said line is idle relays 606 and 4I2 operate in a circuit traced from battery through the winding of cutoff relay 4I2 associated with line 4I5, conductor 4I3, contact at cross-point 809 of switch 825, conductor 8I2, lower next to inner front contact of relay 100, conductor 106, right outer front contact of relay 6I I, upper winding of relay 606, and through upper twenty-third front contact from top of relay 100 to ground. Relay 606 operated locks in a circuit from battery through its lower winding and its upper next to inner front contact to its aforementioned operating ground; and connects said operating ground at upper inner front contact of relay 606 to conductor 106 for maintaining the operation of cut-oil relay 4I2. When slow-to-release relay 6II releases the initial operating circuit for relays 4I2 and 606 is opened.

If the called subscribers line 4I5 is busy its associated sleeve conductor 4I3 is grounded thereby preventing the aforementoned operatori of relay 606 due to ground at both terminals of its upper winding. In this case the release of relay 6II closes a circuit for the operation of relay 6I2 in a circuit traced from battery through winding of relay 6I2, left back contact of relay 6H, lower inne'r back contact of relay 606, to ground at lower closed contact of olf-normal springs 506. Relay 6 I 2 operated connects a source of busy tone BT to the ring conductor of the operating trunk and also to the ring conductor of the link thereby apprising both the operator and the calling subscriber of a busy line.

Let it be assumed that the called line 4I5 is idle in which case relays 4I2 and 606 are operated as aforementioned. Relay 4| 2 disconnects the line relay 4I6 from the tip and ring conductors of line 4|5. Relay 606 opens the operating circuit for the busy tonerelay SI2 thereby pre- 5 venting said relay from operating, operates relay S|3 in an obvious circuit, disconnects the pulsing relay 502 from the tip and ring conductors of the operating trunk and connects relays S|4 and 6| 5 thereto. Relay 502 releases and causes the release of relay.503, thereby releasing relay S01. Relay 503 released causes the

release magnets

508 and 509 to energize and restore register switches 504 and 505 to normal. Relay 503 also removes ground from the brush of switch 504 thereby causing the release of selecting magnet 8|2. Polarized relay S|4 operates in a circuit traced from ground on tip conductor of dial and ring cord (not shown) tip of jack S09, lower inner front contact of relay 604, lower back contact of relay S05, lower outer front contact of relay 606, through winding of relay 6|4, upper outer front contact of relay S06, upper back contact of relay S05, upper front contact of relay 604, contact and ring conductor of jack S09 to battery on ring conductor of dial and ring cord.

Relay S|4 operated operates relay 6I8 in an obvious circuit. Relay S|3 aforementioned is slowto-operate and does not close its front contact until relay SIS has operated thereby preventing a premature operation of relay 102 as will be described presently.

The called subscriber is signaled by the operator at the main exchange by the manual application of ringing current to the tip and ring conductors of the operating trunk. The circuit for 'projecting ringing current to the subscribers line 4I5 follows: ring spring and contact of jack 609 to upper outer front contact of relay 60S in an aforementioned circuit, through condenser SIS, wind- 40 ing of relay SI5, lower outer front contact of relay 606 and thence to the tip spring of jack 609 in an aforementioned circuit. Relay SI5 operates in the above circuit 'and provides a holding circuit for relay SI8 as well as an obvious operating circuit for relay 6I9. Relay 6I9 extends the ringing circuit to the called subscribers line 4|5. This circuit extends from condenser SIS through left front contact of relay S| 9, conductor S20, lower fourth from bottom front contact of relay 100, conductor 801, contact of cross-point 809 of switch 025, conductor 8|3, over subscribers line 4I5 to conductor 8|4, through contact of cross-point 809 of switch 825 to conductor 808, lower fifth from bottom front contact of relay 100 to conductor 62|, right front contact of relay SIS, and thence to the winding of relay SI5. Condensers 109 are provided in the link to furnish the calling subscriber with the usual revertive ringing signal. After each application of ringing current tothe line, relays SI5, and S|9 release. The release of relay S I 9 connects the windings of relay 622 to the aforementioned conductors which extend to the called subscribers line so that when the receiver is removed from the switchhook at the called station relay S22 will operate. The operation of relay 622 operates relay 102 in a circuit from ground at the front contact of relay S22, conductor 623, lower third from bottom front contact of relay 100 and through the winding of relay 102 to batteiy. Relay 102 operated, connects ground through its lower inner front contact to aforementioned conductor8| 2 to maintain the operation of cut-oil relay 4 I 2; connects the winding of relay 1 I 0 to the tip and ring conductors 801 and 808 which extend to the called subscribers line; opens the the calling subscribers line 4|I.

holding circuit for relay thereby causing its release; and closes a locking circuit through its upper inner front contact to ground at the inner front contact of relay 104. The condensers complete a talking connection between the calling 5 and called subscribers lines. The release of relay 100 opens all connectionsbetween thelink and operating trunk and between the link and the register thereby releasing

relays

402 and 406 and disconnecting relay S02 from across the tip and 10 ring conductors of the operating trunk. 'I'he release of relay 402 reestablishes the operating circuit for group relays 40|, 403 and 404 and the release or relay S02 causes the supervisory lamp associated with the operators dial and ring" 15 cord to light as a disconnect signal. Whereupon the operator removes the cords from the jacks 608 and S09 thereby restoring the operating trunk apparatus to normal. Relay 1I0 aforementioned operates in series with the Vcalled subscribers line 20 and closes a second holding circuit for relay 104.

Thusthe connection is controlled lointly by the calling and called subscribers.

The aforementioned release of relay 406 closes a circuit for theoperation of allotter relay 50| 25 in a circuit traced from battery at back contact of relay 406, winding of relay 50|, conductor 822 to ground at the lower outer front contact of relay 104. Relay 50| operated locks mechanically under control of relay 5I4 and preselects 30 the link for use on the next cell by associating the common start lead 405 with said link. When -all links have been allotted relays 50|, 5I5 and 5|S will have operated and locked mechanically thereby causing the operation of slow-to-release 35 relay 520 in a circuit from ground at right front contact of relay 50|, right front contact of relay 5I5, right front contact of relay 5I6 and through winding of relay 520 to battery. Relayv 520 operated operates slow-to-operate relay 5I9 which, 4o in turn, operates release relays 5I4, 5I1, and 5I8 thereby mechanically releasing relays 50|, 5I5, and 5IS, respectively, for another link allotment cycle. The release of any relay in the chain consisting of relays 50|, 5I5 or 5IS opens the 45 circuit for relay 5 20 causing the release of said relay which, in turn, releases relay 5I9 to restore relays 5I4, 5I1, and 5I8. The combination of slow-to-release relay 520 and slow-to-operate relay 5I9 insures that release relays 5I4, 5I1, and 50 5I8 have suflcient time to energize and release allotter relays 50|, 5I5, and 5IS, respectively, before relays 520 and 5I9 are released by the release of any one of said allotter relays. Each link is provided with a key such as 500, 52|, and 522 so 55 that any link may be taken out of service by the operation of its associated key.

When both subscribers disconnect.. relays 10| and 1I0 release thereby releasing relay 104. Relay 104 released releases relay 102 thereby re- 60 leasing cut-off relay 4|2 associated with the called subscribers line. Relay 104 also releases the cutoi relay 4|9 associated with the calling subscriber's line and also causes the release of the holding

magnets

803 and 8|0 associated with se- 65 lector switch 825. The circuits are thus restored to normal.

The operation of the system will now be described wherein the called subscriber is a party on Assume that 70 the call has been extended to the main exchange as hereinbefore described and that the operator at said exchange has dialed the called subscribers number. When the selecting magnet 800 and the holding magnet 8 I 5 have operated the selector 75 bar engages the contacts at cross-points 6|1 to associate the conductors 001, 003, and I2 of the link with the conductors 4|1, 4I8 and 4I0, respectively, associated with line 4|I. Due to a 5 ground on sleeve conductor 4|0, relay 808 is prevented from operating, thereby causing the operation of relay 5I2 in an aforementioned circuit. Relay 8|! operated returns a busy tone to both the calling subscriber and the operator as aforelo mentioned. 'I'he subscriber recognizing the busy tone as originating from a revertive call condition i will restore the receiver on the switchhook and the operator also knowing that the call is a revertive one will ignore the busy tone.

When the calling subscriber restores the receiver on the switchhook relay 10| releases thereby opening the circuit for relay 104 and closing a circuit from ground at back contact of relay 10|, conductor 0I6, contacts of selector crosspoint 002, contacts of selector cross-point 8|1,

conductor 8|8 and through relay 103 to battery.

Relay 103 operated locks to ground at the lower next to outer front contact of relay 100, opens the holding circuit for holding magnet 803 and closes a holding circuit for slowtorelease relay 104 in a circuit traced from ground at lower back contact of relay 102, left inner front contact of relay 103 and through the winding of relay 104 to battery. Relay 103 also closes an operating circuit for relay 008 in a circuit from ground at left outer front contact of relay 103, lower outer front contact of relay 100 and through the lower winding of relay 606 to battery. Relay 606 operated releases the busy tone relay 6 I 2 and otherwise functions as aforementioned. The release of the aforementioned holding magnet 803, disengages the contacts at selector cross-point 802 thereby disconnecting the finder portion of the link from the subscribers line. The cut-off relay 4|9 does not release when holding magnet 803 releases since said relay is now held in a circuit traced from ground at the left outer front contact of relay 103, lower outer front contact of relay 100, upper inner contacts of relay 606, conductor 106, lower next to inner front contact of relay 100, conductor 8|2, contacts of selector cross-point 6|1, conductor 4|0 and through the winding of cut-off relay 4|9 to battery. Ringing current is applied to the line in an aforementioned manner and when either the called or calling subscriber removes the receiver from the switchhook relay 622 operates causing the operation of relay 102 as aforementioned. Relay 102 operated causes the release of relay 100 together with all other operated relays required for establishing the connection as aforementioned. Relay 102 operated also closes an aforementioned operating circuit for relay 1|0. Relay 1|0 operated provides a holding circuit for relay 104.

When both the calling and called subscribers disconnect, following a completed connection, relay 1|0 releases followed by the release of relay 104 thereby restoring the circuits to normal in an aforementioned manner.

In the event that neither the calling nor called subscriber responds the operator will disconnect in the usual manner thereby causing the release of relay 6 I4 followed by the release of 6 I8. Relay 6|8 released closes a circuit from ground at the 70 front contact of relay 6|3, back contact of relay 6|8, conductor 623, lower third from outer front contact of relay 100 and through the winding of relay 102 to battery. Relay 102 operates in this circuit and releases all operated relays thereby restoring the circuit to normal.

Assume now that a subscriber associated with line 4|| desires a connection with a subscriber in the main exchange, that the call has been extended to the main exchange in a manner previously set forth and that the operator has responded. The operator upon learning the details of the call dials a code which causes the selector 825 to associate the calling subscribers line 4| I, with a conversational trunk to the main exchange and extending to selector 825 over conductors |004, |005 and 02|. In order to associate the calling subscribers line with the conversational trunk it is necessary for the main exchange operator to dial a code so that the register will4 be positioned to operate a selecting magnet anda holding magnet of selector 825 that will cause the engagement ofl contacts at crosspoint 00| since the subscribers line and conversational trunk are associated with said crosspoint. Assume then that the operator has dialed the proper code and that the register has been positioned to operate select magnet 820 and holding magnet 0 I 5, in order to cause the engagement of contacts at cross-point 00|. Magnet 820 operates in a circuit traced from battery through its winding, upper eight contact from top of relay 100, terminal 0 and brush of register switch 504, back contact of relay 5I2 to ground at left inner front contact of relay 503. Magnet SI5 operates in a, circuit from battery through winding of said magnet, upper twenty-second contact from top of relay 100, terminall and brush of switch 505, left back contact of relay 5I3 to ground at left inner front contact of relay 503. The operation of the aforementioned magnets engages the contacts at cross-point 00| thereby extending the conductors of line 4II with the conductors of the conversational trunk extending to the main exchange. Magnet 8|5 operated locks to ground at the lower outer front contact of relay 104. Cut-off relay 900, in the conversational trunk, and relay 606, in the operating trunk, operate in a. circuit traced from ground at upper twenty-third contact from top of relay 100, upper winding of relay 606, front contact of relay 6II, conductor 106, lower next to inner front contact of relay 100, conductor 8I2, closed contact at cross-point of switch 825, conductor 82|, upper outer back contact of relay 90| and through winding of relay 900 to battery. Relay 900 operated disconnects the line relay 902 from the tip and ring conductors |005 and |004, respectively, of the conversational trunk. Relay 606 operated functions as aforementioned. The operator at the main exchange applies ringing current to the operating trunk in a manner similar to that described for a local call thereby causing the operation of ringing relay 624 associated with the conversational trunk at the main exchange. This circuit extends from the operators cord (not shown) to the switch 825 via conductors 801 and 800 as previously set forth and thence through the contacts of switch 825 at cross-point 80|, conductors |005 and |004 of the conversational trunk; the condenser 625 and lower winding of relay 624 completing the circuit. Relay 624 operated locks in an obvious circuit and also lights lamp 626. The same or another operator at the main exchange, depending on the position at which the conversational trunk terminates, responds to the lighted lamp by inserting a cord (not shown) into the jack 621 thereby causing the operation of relay 628 and connecting battery and ground to the conductors |004 and I 005, respectively, of the conversational trunk.

Relay 628 operated releases relay 624 and disconnects the lower winding of relay 624 from the trunk conductors |004 and |005. Relay 624 released extinguishes the lamp 626. When battery and ground are applied to the conductors of 004 and |005 two circuits are closed for the operation of relay 622. One of these circuits may be traced from ground on the tip conductor of operator's cord, tip conductor of jack 621, conductor |005. closed contact of switch 825, at

cross-point 80|, conductor 808 and thence to battery through the left winding of relay 622 as previously set forth; and the other circuit may be traced from battery on the -ring conductor of l5 the operators cord, ring conductor of jack 621, conductor |004, closed contact of switch 825, at cross-point 80|, conductor 801 and thence to ground through the right Winding of relay 622 as previously set forth. Relay 622 operated causes the operation of relay '|02 in the link thereby causing the release of the register and operating trunk apparatus as aforementioned for a local call. The originating operator or the calling subscriber then passes the details of the call to the completing operator who completes the call in the usual manner. The originating operator then disconnects from the operating trunk jacks 608 and 609 thereby restoring the operating' trunk apparatus to normal at both the main and rural exchanges.

When both the calling and called subscribers disconnect the circuits are restored to normal as previously set forth.

A call incoming from the main exchange to a subscriber at the rural exchange will now be described in detail. This circuit arrangement emvbodies a conversational trunk between the main and the rural exchange wherein incoming calls to the rural exchange are completed by dialing over the conductors of said trunk.

The main exchange operator, upon learning that a connection is desired with a subscriber at the rural exchange, inserts a cord (not shown) into jack 621 associated with the conversational trunk thereby operating relay 628 and closing two circuits for the operation of line relay 902. One of these circuits extends from ground on the tip conductor of the operators cord, tip conductor of jack 621, conductor |005, upper back contact of relay 900 and thence to battery through the upper winding of relay 902; and the other extending from battery on the ring conductor of the operators cord, ring conductor of jack 621, conductor |004, lower back contact of relay 900 and thence to ground through the lower winding of relay 902. Sleeve relay 628 operated functions as aforementioned and relay 902 operated closes an obvious circuit for the operation of slow-to-release relay 90|. Relay 90| operated connects ground to the sleeve conductor 82| of the conversational trunk thereby guarding said trunk against a subsequent seizure by a link. Relay 90| also closes a. circuit for the operation of relay 903 from ground at the lower back contact of relay 904, lower inner front contact of relay 90|, left Winding of relay 903, conductor 629 to battery at the back contact of relay 402. Relay 903 operated closes a circuit through its right winding and front contact, conback contact of relay 403, right back contact of relay 40|, to battery through the winding of relay 402. Relay 903 locks and relay 402 operates in the above circuit. The operation of relay 402 prevents any other group relays, such as 40 I, 403

ductor 1| I, right back contact of relay 404, right or 404, from being energized at this time by removing the source of battery from their respective windings. Relay 903 operated also closes a circuit for the operation of relay 906, which associates the conductors of the conversational trunk with the conductors of the dial register and with the conductors of the operating trunk. 'I'he circuit for operating relay 906 is traced from ground at the lower outer front contact of relay upper back contact of relay 904, front contact of relay 903, and through the winding of relay `906 to battery. Relay 906 operated closes a circuit for the operation of pulsing relay 502 associated with the register. This circuit is traced from ground at the upper outer front contact of relay 902, upper inner front contact of slow-to-release relay 90|, lower sixth contact from bottom of relay 906 and through the left winding of relay 502 to battery.- Relay 502 operated operates relay 503.as aforementioned.

The operator at the main exchange now dials the called subscribers number and the interruptions of the line, caused by the dial, alternately release and operate relay 902 in turn alternately releasing and operating relay 502. The register is thus positioned as aforementioned for operating the selecting and holding magnets of the switch |000 for associating the conversational trunk with the called subscribers line. Assume that the called subscriber is associated with line 4|I, which extends to switch |000 via conductors 4 |1, 4| 8, and 4|0. In order to associate the conversational trunk conductors |005, |004 and 82| with the conductors of said line it is obvious that the contacts at cross-point |003 must be engaged. This cross-point is common to selecting magnet |00I and holding magnet |002. Magnet |00| operates in a circuit from battery through winding of said magnet, upper eleventh contact from the top of relay 906, terminal and brush of switch 504, back contact of relay 5|2 to ground at left inner front contact of relay 503. Magnet |002 operates in a circuit from battery through Winding of said magnet, upper twelfth contact from top of relay 906, terminal 5 and brush of switch 505, back cont-act of relay 5|3 to ground at left inner front contact of relay 503. Holding magnet |002 operated engages the contacts at cross-point |003 and locks to ground at the lower outer front contact of relay 90|. The cut-off relay 4|9 associated with the called subscribers line operates in a circuit from ground at the lower seventh-from bottom contact of relay 906, upper winding of relay 606, right outer front contact of relay 6| I, conductor 106, lower inner front contact of relay 906, conductor |001, contact of cross-point |003 of switch 000, conductor 4|0 and thence to battery through the winding of relay 4|9 to battery. Relay 606 also operates in the above circuit and extends a ground to maintain the' operation of relay H9 and to guard the line against seizure in a circuit from aforementioned ground at upper inner armature and front contacts of relay 606, to conductor 106 and thence to the winding of relay M9 in an aforementioned circuit. Other functions of relay 606 are the same as previously set forth. When relay 5|3 releases following the dialing of the final digit,

relay

605 and 900 operate in a circuit traced from ground at the back contact of relay 513, right inner front Contact of relay 6| lower fifth contact from bottom of relay 906 thence in paralle] one path extending through the winding of relay 900 to battery: and the other extending through lower fourth contact from bottom of relay 906 and through winding of relay 605 to battery. Relay 605 operated opens the tip and ring conductors of the operating trunk, extending to the main exchange, and locks to ground at the lower seventh from bottom contact of relay 906. Relay 900 operated, disconnects relay 902 from conductors |004 and |005 of the conversational trunk and connects relay 6|4 associated with the tip and ring conductors of the 1g operating trunk thereto. This circuit extends from tip conductor |005 extending to the main exchange, upper front contact of relay 900, lower second from bottom contact of relay 906, lower front contact of relay 606, winding of relay l5 6|4, upper outer front contact of relay 606, lower third from bottom contact of relay 906, lower front contact of relay 900 to the ring conductor |004 extending to the main exchange. Battery and ground from the operators cord causes the operation of polarized relay 6|4 thereby causing the operation of relay 6|8 as aforementioned. Relay 6|8 operated closes a circuit for maintain- -ing the operation of relay 90| which otherwise would release due to the release of relay 902 when relay 900 operated as aforementioned. This circuit may be traced from ground at the front contact of relay 6|8, lower outer front contact of relay 906 and thence through the winding of relay 90| to battery.

The main exchange operator projects ringing current to the operating trunk thereby operating relays 6|5 and 6|9 in order to signal the called subscriber as hereinbefore described'for the completion of a local call. When the called subscriber answers, relay 622 operates in a circuit closed by the removal of the subscribers receiver from the switchhook. Relay 622 operated closes a circuit for operating relay 904 from ground at front contact of relay 622, conductor 623, upper outer front contact of relay 906 and through the winding of relay 904 to battery. Relay 904 operated locks in an obvious circuit, releases relays 903, 402 and 906, and connects a ground to sleeve conductor |001 for maintaining the operation of cut-off relay 4|9. Relay 906 released disconnects the register and operating trunk from the conversational trunk thereby restoring the register and operating trunk apparatus to normal as aforementioned. Relay 906 released also releases relay 900 thereby extending the tip and ring conductors |005 and |004,

respectively, of the conversational trunk to the tip and ring conductors associated with subscribers line 4| Relay 902 reoperates over the conversational trunk conductors and a talking cc .ectif n is established by means of condensers 901. battery for the called subscriber line is furnished through the windings of relay 905.

When the operator at the main exchange disconnects relay 902 and 620 release. Relay 628 restores the main exchange end of the conversational trunk to normal and relay 902 causes the release of 90|. Relay 90| released releases relay 904 and holding magnet |002 thereby restoring the circuits to normal.

The operation of the system will now be described in detail with the drawings placed together in accordance with Fig. 3. The system as shown by the drawings of Fig. 3 differs from 70 the system as shown by the drawings of Fig. 2 only with respectA to the conversational trunk equipment at the rural exchange shown by Fig. 11. Since the equipment of Fig. 11 is required only for the completion of calls incoming from 75 the main to the rural exchange the operation of the system will be described only for this class of connection.

Assume that an operator at the main exchange desires to complete a connection to a subscriber associated with line 4|| at the rural exchange and that a cord circuit (not shown) has been associated with jack 621 for the completion of said connection. Battery and ground from the cord circuit is connected to the ring and tip conductors |004 and |005, respectively, as aforementioned and is extended through the back contacts of relay |00, lower and upper windings of relay ||02 to ground and battery respectively thereby operating relay H02. Sleeve relay 626 associated with jack 621 operates as aforementioned. The operation of relay ||02 operates slow-to-release relay ||0| in an obvious circuit. Relay ||0| disconnects relay ||00 from aforementioned sleeve conductor 02| and connects ground thereto to guard the trunk against subsequent seizure by a link. Relay ||0| also closes a circuit for the operation of relay ||03 from ground at the lower back contact of relay ||04, lower inner front contact of relay ||0|, left winding of relay H03, conductor 629 and thence to battery at the back contact of relay 402. Relay |03 operated locks through its right winding and front contact, conductor 1|| and through the Winding of relay 402 to battery in an aforementioned circuit. Relay 402 operates in the above circuit and disconnects battery from the operating windings of all group relays to prevent double connections in the event that two or more group relays are energized at the same time. Relay ||03 operated also operates relay |06 in a circuit from ground at the lower outer front contact of relay ||0|, upper back contact of relay ||04, left front contact of relay ||03 and through the winding of relay ||06 to battery. Relay ||06 operated associates the equipment of the conversational trunk at the rural exchange with the common register equipment and the equipment of the operating trunk at the rural exchange. Relay ||06 specically connects the winding of polarized relay 602 across the tip and ring conductors of the operating trunk extending to jack 608 at the main exchange. This circuit is closed at the lower inner contact of relay ||06 and extends to the main exchange in a manner previously set forth.

The operation of the circuit at this point is exactly the same as aforementioned for the completion of a local call. A signal is displayed before the same or another main exchange operator who, after inserting a cord into jack 608, obtains the details of the call. A second cord is then associated with jack 609, the called subscribers line is dialed and the associated station is signaled in an aforementioned manner. When the called subscriber answers relay 622 operates thereby operating relay |04 in a circuit traced from ground at the front contact of relay 622, conductor 623, upper outer contact of relay ||06 and thence to battery through the winding of relay ||04. Relay ||04 operated locks to ground at the lower outer front contact of relay ||0| and connects ground to sleeve conductor |001 for maintaining the operation of the cut-off relay 4|9. Relay ||04 operated also releases relay ||03, 402 and relay H06. Relay 402 released connects battery to all group relays so that said relays may operate on other calls; and relay |06 released disconnects the conversational trunk apparatus from the register and operating trunk apparatus. The operator at the main exchange disconnects the cords from

jacks

608 and 609 thereby restoring the operating trunk apparatus to normal. The holding magnet 002, associated with switch |000 by which connection was established with the caller subscribers line 4H,

is held from ground through the lower outer front contact of relay ||0|. Relay H04 operated connects the tip and ring conductors of the called subscriber line to the tip and ring conductors |005 and |004, respectively, of the operating trunk, the talking connection being established through condensers ||0'|.

When the operator at the main oice disconnects from jack 521 relay ||02 releases thereby `releasing relay ||0|. Relay ||0| disconnects ground from the holding magnet |002, by which the trunk was associated with the called subscribers line, thereby disconnecting said line from the conversational trunk. Relay ||0| released also releases relay ||0|| thereby restoring the conversational trunk to normal ready for use on another connection.

What is claimed is:

1. In a telephone system, a main oflice, a local exchange having subscribers lines terminating therein, automatic switches and link circuits in said local exchange, a register device in said local exchange common to said switches and link circuits, an operating trunk interconnecting the main ofiice and the local exchange, means for operating one of said switches to connect a calling subscribers line to a particular one of said link circuits, means for connecting said link to the register device and to said operating trunk, means controlled over the operating trunk for setting said register device according to the called designation, and circuit means controlled by said register and extending through said connecting means for operating one of said switches to con-l nect said link circuit to the called subscribers line.

2. In a telephone system, a main exchange, a local exchange, automatic switches in said local exchange, subscribers lines multipled to appear 45 in the terminals of said automatic switches, link circuits, one for each of said automatic switches,

a number receiving register common to all of said link circuits, an operating circuit interconnecting the main ofce and the local exchange, 50 means responsive to a` call on one of said subscribers lines for operating a particular one of said switches to connect the calling line to the link circuit individual to such switch, means for connecting said link circuit to said operating circuit, 55 means controlled from the main office over said operating circuit for setting said register in accordance with the called designation, and means controlled by said register for operating said switch to connect said link circuit to the called subscribers line.

3. In a telephone system, a main oce and a local exchange, a number of cross-bar selector switches in said local exchange, subscribers lines multipled to appear in al1 of said selector switches,

link circuits, one for each of said selector switches, a digit receiving register in said local exchange common to all of said link circuits, an operating trunk interconnecting the main office and the local exchange, means for allotting an idle link circuit for use, means responsive to a call on one of said' lines for operating the selector switch individual to th(` allotted link circuit for connecting the calling line to such link, means for sending designation impulses over said operating trunk from the main oflice to set said register, and means for operating said switch in accord ance with the setting of the register to connect the allotted link circuit to a called subscribers line.

4. In a telephone system, a central oice and a local exchange, automatic switches in said local exchange, subscribers lines appearing in said automatic switches, a trunk line appearing in said automatic'switches, a register common to said switches, an operating circuit interconnecting the central oice and the local exchange, means responsive to 'a call on one of said lines for operating one of said switches to connect the calling line to said operating circuit, means for setting said register by impulses transmitted over said operating circuit from the central oflice, and means controlled by said register for establishing a connection either to a called subscribers line or to said trunk line according to the setting of said register.

5. In a telephone system, a main office, and a local exchange, subscribers lines in said local exchange, automatic switches in said local exchange, a register common to said automatic switches, a conversational trunk interconnecting the main office and the local exchange, an operating trunk interconnecting the main office and the local exchange, vmeans responsive to a call on one of said lines for operating one of said switches to connect the calling line to said operating trunk, means for setting said register by impulses transmitted over said operating trunk, means controlled by the register in accordance with such setting for establishing a connection between the calling line and a called line in said local exchange, means for setting said register by impulses transmitted over said conversationaltrunk when a call is extended from the main oflice to the'local exchange, and means for operating one of said switches in accordance with such setting to connect said conversational trunk to the called subscribers line in the local exchange.

6. In a telephone system. a main ofiice and a local exchange, a plurality of selector switches in the local exchange, link circuits, one for each of said switches, subscribers lines appearing in said selector switches. a conversational trunk extending from the main oflice and appearing in said selector switches in thc local exchange, a trunk switch at the local exchange in which said conversational trunk also appears, 'a register common to said link circuits. means responsive to a call on one of said subscribers lines for operating a particular selector switch to connect such line to the link circuit individual to such switch. an operating trunk interconnecting the main ofce and the local exchange, means for setting said register by impulses transmitted over the operating trunk from the main otlice, means for operating said particular selector switch in accordance with the setting of the register to connect said link circuit either to a called subscribers line in the local exchange or to said conversational trunk extending to the main ofllce, means for setting said register by impulses transmitted over said conversational trunk on an incoming call from the main office to a called line in the local exchange, and means controlled by the register in accordance with such setting for operating said trunk switch to connect the conversational trunk to the called subscribers line in the local exchange.

WILLIAM H. MATTHIES.