US2042828A - Telephone system - Google Patents

Description

June 2 319%. R B. BUCHANAN ET AL TELEPHONE SYSTEM F ile d March 7, 1935 3 Sheets-Sheet 1 R. B. BUCHANAN INVENTORS L A. K/LLE BVJ ATTORNEY Junie 1936- R. B. BUCHANAN ET AL 1 TELEPHONE SYSTEM Filed March '7, 1955 3 Sheets-Sheet 2 FIG-2 RB. BUCHANAN lNl/ENTORS LAW/ALE A TTO RNEV June 2, 1936- R. B. BUCHANAN ET AL TELEPHONE SYSTEM 3 Sheets-Sheet 3 Filed March 7, 1935 RB. BUCHANAN LAK/LLE mwm in HM.

A 7'TORNEV Patented June 2, 1936 UNITED STATS PATENT OFFICE TELEPHGNE SYSTEM Bell Eelephone Laboratories,

Incorporated,

New York, N. Y., a corporation or" New York Appiication March '7, 1935, Serial No. 9,728

17 Claims.

This invention relates to telephone systems and particularly to improvements in the means for completing toll connections. It is in the nature of an improvement over known trunking arrangements and contemplates the use of means where by a single trunk between the originating ofiice and the toll office is employed for recording as well as for completing the toll connection.

An object of the invention is an arrangement Whereby'a trunk used for recording and completing in one direction may be used as an ordinary toll switching trunk for calls in the opposite direction, said trunk terminating at one end in a trunking operators board and an A operators board while at the other end it terminates in a trunking operators board. A considerable saving in cost in handling toll trafiic is therefore effected.

Another object of the invention is an arrangement whereby a trunk used for recording and completing a call in one direction may also be used as an ordinary B trunk in completing a local interofiice call in the same direction as, for instance, in those cases where lines terminate in a local board located in the toll oifice; said trunk for this purpose, further appearing in a special jack at the originating A board and terminating in a special jack at the local B board of the toll oifice. By means of this arrangement the use of local interofiice trunks to complete ordinary interoffice connections is avoided.

One feature of the invention is the use of a novel signaling circuit comprising a high-low relay in combination with a marginal relay and a source of high voltage current at one time and the use of another relay and a source of low voltage in combination with said high-low relay at another time whereby a plurality of signals are transmitted in either direction over the trunk to operate signals and control circuit operations at the three terminal outlets of the trunk in the most economical and eflicient manner.

The method and means of handling toll connections in accordance with this invention may, in general, be outlined as follows: When an A operator receives a request for a long distance toll connection, she plugs the calling plug of an A cord into a jack of a combined recording and completing trunk designed in accordance with this invention. This connects the A operator with a toll operator at the recording-completing board, and the latter is advised of the call completing information, after which she momentarily depresses a key associated with this trunk to cause a lamp associated with the trunk at the toll switching position to light as an indication that a call is awaiting thereon. The toll switching operator at the originating oflice, and before whom one of the three branches of the trunk terminates in the form of a cord plug, then connects her telephone head-set to the trunk and receives the number of the subscriber from the recording-completing operator, after which the plug of the switching trunk is inserted into a multiple jack of the calling line and the calling supervisory signal of the A cord is caused to light to apprise the A operator that the A cord may now be removed from the connection since the calling line is now extended to the toll completing position via the toll switching branch of the trunk. After the toll switching operator has connected the trunk to the calling subscriber's line and the A operators position cord is removed from the connection, the recording-completing operator at the toll ofiice has complete supervision of the call. Should the calling subscriber have restored his receiver in the meanwhile, the fact is made known to the toll operator by the lighting of a ring and guard lamp in the toll cord then connected to the trunk. The operator may then rering the subscriber by operating the ringing key associated with the cord. When the calling subscriber restores his receiver and the recording-completing operator receives the disconnect signal to this effect, the connection is taken down by removing the toll cord from the trunk whereupon the toll switching operator receives a disconnect signal and removes the plug of the trunk from the calling subscribers jack.

As outlined above, therefore, means are provided for recording and completing toll calls over a single trunk and the A operators work, relating to the extension of such a toll call, remains the same as in present practice; that is, her functions in this respect are practically the same as when she extends a connection between two local lines.

A clearer conception of the scope and purpose of the invention may be obtained from a consideration of the following description and appended claims taken in connection with the attached three drawings placed in their consecutive numerical order. These drawings, taken together, show a toll trunk which extends between a local ofiice, where it has outgoing outlets such as jacks I06 and I49 at the A board and one incoming completing trunk plug I31 at the B board, as disclosed in Fig. l, and a toll oflice where it terminates, as disclosed in Fig. 3, in jacks such as-396 for the extension of toll or long distance connections and in jacks such as 323 for the completion of calls within an area which is local to the toll center.

Referring now to the illustration of the invention as applied to the establishment of a call from an originating A board to the toll office for completion therefrom to a toll subscriber beyond, the extension of a connection over the trunk for this purpose may be described as follows: A subscriber at substation I calls an A operator in the usual manner. The operator, in answering the call, inserts plug IOI of the cord A into jack I03 of line I02 and connects her telephone head-set I04 to the cord by the usual means. The subscriber I00 asks :for a toll connection by saying long distance. 'The A operator will then insert plug I05 of the A cord into jack I00 of the combined recording and completing trunk. It should be understood, of course, that a plurality of such trunks are available to the A operator and that she first tests for and locates an idle trunk.

The above connection between the A cord and the trunk jack I06 causes the calling supervisory lamp M0 to light in a circuit which is completed from battery through lamp II 0, resistance I58, sleeve of jack I06, resistance III to ground. A circuit is also completed for relay 200 extending from ground through its upper and lower windings in series, right winding of retard coil 2I2, ring conductor I01, ring of jack I00, ring of the A cord, winding of calling supervisory relay I08, right lower winding of repeating coil II2, battery to ground. Relay 200 operates and closes an obviouscircuit for relay I which operates and then completes a circuit for relay 202 extending from ground through its lower inner contacts, bottom inner contacts of relay 2I3, winding of relay 202 to battery. Relay 202 operates, transfers the trunk conductors extending to the left windings of repeating coil 2 to the local trunk conductors I09 and I01 and therefrom to the tip and ring conductors of the A cord, opens its bottom inner contact in the circuit path of the winding of relay 203 in order to prevent the winding of this relay from shunting, and thereby interfering with, the proper operation of the calling supervisory relay I08 in the A cord, and closes a circuit for operating relay 204 which extends from ground through the bottom middle contacts of relay 202, top outer contacts of relay 2I0, winding of relay 204 to battery. Relay 204 operates and disconnects the outward supervisory bridge consisting of the winding of polarized relay 206 and both windings of relay 205 from the trunk conductors 201 and 208, connects ground to conductor 201 over the upper back contacts of relay 2I4, the top front contacts of relay 204 and right upper winding of repeating coil 2I I, and further connects battery through resistance 209, over the bottom inner back contacts of relay 2 I4, bottom inner front contacts of relay 204, right lower winding of repeating coil 2 to trunk conductor 208. The connection of ground and battery to the trunk conductors serves to operate a signal at the toll end of the trunk to the effect that a call is waiting thereon, as more clearly explained hereinafter. Relay 204 further closes an obvious circuit for relay 223 which operates and opens another contact in the circuit path of the calling supervisory bridge while through its bottom contacts relay 223 closes an obvious circuit to operate relay 2I0 which, on operating, looks through its top inner contacts to ground on the upperinner contacts of relay 20L Relay 2I0 further connects supplementary ground to the circuit of relay 202 while over its top inner contacts it opens the circuit of relay 204 which, on releasing after an interval, opens the circuit of relay 223 which also releases after an interval and opens the circuit of relay 2 I 0. Relay 2I0, however, does not release since at this time it is held locked under the control of relay 2!. With relay 204 released, battery and ground are removed from the tip and ring conductors 201 and 208, while on the release of relay 223 the supervisory bridge consisting of the windings of relays 206 and 205 is again connected across the trunk conductors.

In the meanwhile and at the time ground and battery were connected to conductors 201 and 1 208, a circuit was completed for relay 300 extending from ground on conductor 201 as previously traced, left upper winding of repeating coil 3I3, resistance 3 I4, top back contacts of relay 3 I5, top

outer back contacts of relay 3 I 0, upper winding of 2 relay 300, top back contacts of relay 305, winding of polarized relay I, bottom inner back contacts of relay 305, lower winding of relay 300, bottom outer back contacts of relay 3I6, bottom back contacts of relay 3I5, resistance 3I1, left lower winding of repeating coil 3I3, conductor 208 to battery through resistance 200 as previously traced. Relay 300 operates in this circuit, but relay 30 I, being polarized, operates only when the current is in the reverse direction. Relay 300 00 now closes an obvious circuit for relay 302 which operates and then locks in a circuit which extends from ground on its bottom outer contacts, top contacts of relay 304, bottom middle back contacts of relay 305 to the winding of relay 302.

Relay 302, on operating, connects battery through resistance 321, upper inner contacts of relay 3I0, top front contacts of relay 302 to one side of the L (low resistance) winding of relay 308 to establish a busy test condition at every position to which the trunk is multipled and particularly to guard the trunk against seizure at those positions where it is available for completing calls in the opposite direction only; closes a circuit for trunk lamp 303 at every toll or CLR answering position at which the trunk appears, said circuit extending from battery through the bottom inner front contacts of relay 302, contacts of relay 3I2, bottom back contacts of relay 320, lamp 303, to ground, lighting said lamp to indicate to the operator that a call is awaiting on the trunk.

It will be recalled that the circuit for relay 300 is maintained only during the period during which relay 204 is operated, a period measured from the time said relay is operated until it is released by the operation of relay 2I0. This period is measured by the time taken to operate relay 223, the time taken to operate relay 2i 0 and the time taken to release relay 204 which, being slow-release, takes an interval long enough to insure the operation of relay 300, the operation of relay 302 and the consequent lighting of lamp 303 at the distant end. Hence when relay 204 releases and the supervisory loop consisting of relays 205 and 206 is reconnected to the trunk conductors 201 and 208 subsequent to the release of relay 223, sufiicient time will have been allowed to operate relay 302 and light trunk lamp 303 so that, upon the release of relay 300 which follows the release of relay 204, relay 302 will have been locked in and lamp 303 will remain lighted.

The toll operator, upon seeing the lamp 303 lighted, plugs the answering end of a regular toll cord 301 into the trunk jack 300 and connects her telephone circuit across the cord in the wellknown manner. A circuit is now completed for relay 308 which extends from battery through cord lamp 328, the sleeve of the cord, sleeve of jack 306, lower winding of relay 308 to ground. Relay 308 operates and closes an obvious circuit for relay 300 which, on operating, closes an obvious circuit for relay 3I0. Relay 3I0 operates and closes a circuit for operating relay 3i I which extends from ground on the bottom contacts of relay 304, bottom inner contacts of relay 3I0, winding of relay 3| I to battery, and further closes an obvious circuit for relay 3| 2. Relay 3, on operating, looks over its bottom contacts to ground on the lower outer front contacts of relay 302, closes an obvious circuit for operating relay 3 I l, and further closes another obvious circuit for operating relay 305. Relay 3|! causes the operation of relay 304. Relay 304 opens the locking circuit of relay 302 which releases, and further opens the operating circuit of relay 3I I; but the last-mentioned relay does not release since it is locked to ground on the bottom outer contacts of relay 3I0. Relay 3I2, on operating, opens the circuit of lamp 303 thereby extinguishing it while relay 302, in releasing, connects ground through the top inner contacts of relay H3 and its own top back contacts to the upper winding of relay 008 which, in combination with the battery supplied from the sleeve of the toll cord and the ground through the H (high resistance) winding of relay 308, supplies the same busy test potential to the sleeve of the trunk jacks that was previously maintained by battery through resistance 321, which latter was removed by the operation of relay 3I0 and further causes the cord lamp to light.

At the time relay 305 operated as already described, it disconnected relay 30I from the trunk conductors 201 and 208 and connected ground and high voltage battery to said conductors through its inner front contacts and thereby completed a circuit which extends from ground through the top front contacts of relay 305, upper winding of relay 300, top cuter back contacts of relay 3I0, top back contacts of relay 345, resistance 3 I4, upper left winding of repeating coil 3I3, conductor 20?, right upper winding of repeating coil 2, top back contacts of relay 200, winding of relay 206, (L) winding of relay 205, top back contacts of relay 2I3, top outer contacts of relay 20L top contacts of relay 223, bottom inner back contacts of relay 204, right lower winding of repeating coil 2| I, conductor 200, left lower winding of repeating coil 3I3, resistance 3I'l, bottom outer back contacts of relay 3I5, bottom outer back contacts of relay SIS, lower winding of relay 300, bottom inner front contacts of relay 305 to high voltage battery. It will be observed that the (H) or high resistance winding of relay 205 is, at this time, short-circuited. The quantity of current flowing through the circuit, therefore, is such as to cause both relay 205 and relay 300 to operate. Relay 200 does not operate because it is polarized in the opposite direction. Relay 300, in operating, causes the operation of relay 302 which, in turn, removes ground from the (L) winding of relay 308 through the toll cord lamp. Said toll cord lamp is now in series with the high resistance (H) winding of this relay and is extinguished because the quantity of current is below its luminosity level. Relay 205, in operating, closes an obvious circuit for relay 226 which, on operating, provides an additional holding circuit for relay 2!!) over its top outer contact, and closes an obvious relay for relay 2I5. Relay 2I5,

in operating, connects ground fromthe top outer back contacts of relay 2I1, top outer contacts of relay 2I5 to the mid-point of the two windings of relay 200 and thereby short-circuits the upper high resistance winding. As a result, the current flowing through the circuit extending from ground through the lower winding of relay 200, the right winding of retard coil 2I2, conductor I01, relay H58 in the A cord to battery is now sufiicient to cause the operation of relay I08, whereupon battery through resistance II5 is connected in shunt of lamp IIO which is thereby extinguished to indicate to the A operator that the distant toll operator has connected her telephone set through a toll cord to the trunk and that a talking connection now exists between the operators telephone circuit I04 over the tip and ring I09 and E01, respectively, of the trunk, the top front and bottom outer front contacts of relay 202 to the left windings of the repeating coil 2I I. The talking circuit to the toll operator is then completed from her telephone set connected to the toll cord 30? inductively through the windings of repeating coil 3I3, tip and ring conductors 20! and 200, respectively, and the right windings of repeating coil 2| I. Relay 2I5 further connects ground to the mid-point of the windings of relay 224 which is identical with relay 200 but, inasmuch as relay 22 i is not used on this type of a call, it performs no function at this time.

The A operator now passes the details of the call to the toll operator who will, from the information received, complete the connection to the distant subscriber through the calling portion of the toll cord 30'! and then extend the connection back to the calling subscriber by way of the trunk extension to the B board.

When the toll operator has extended the con nection to the called subscriber or even before she has done so, she operates key 3H3 of which 1 there is one associated with the trunk at every position to which the trunk is multipled for completing toll connections. As a result of the operation of key 3I8, a circuit is completed for relay 3I5 which, on operating, reverses the direction of current flowing over the circuit that includes relays 300, 205 and 200 previously traced, the effect of which is to operate polarized relay 205 and hold relays 300 and 205 operated. Relay 200 closes a circuit to operate relay 2H5 which, on operating, completes a circuit for relay 2 I3 which extends from ground on the bottom outer contacts of relay 2M, lower contacts of relay ZIS, lower winding of relay 2I3 to battery. Relay 2 i 3, on operating, releases relay 202, and transfers the path for short-circuiting the lower (H) winding of relay 205 from the top outer contacts of relay 205 to the back contacts of relay 203 by way of the bottom inner contacts of relay 2E5.

Relay 202, upon releasing, transfers the talking conductors of the trunk from conductors I09 and till, which extend to the A cord, to conductors H3 and H4 which extend to the plug extension of the trunk at the B board, and further connects relay 203 across the trunk conductors H3 and H4 in a circuit which may be traced from battery through the lower winding of relay H5, resistance IIS, lower normal contacts of relay H5, right lower winding of repeating coil H9,

conductor II, bottom outer back contacts of relay 202, left lower winding of repeating coil 2II, bottom inner contacts of relay 202, bottom middle contacts of relay 2I5, winding of relay 203, upper left winding of repeating coil 2! I, top

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back contacts of relay 202, conductor H3, right 75 upper winding of repeating coil H9, top contacts of relay I I6, upper Winding of relay I I to ground. Both relays 203 and H5 operate in this circuit. However, relay 203 is only operated momentarily since, with the operation of relay H5, a circuit is closed to operate relay I I5 which extends from ground on the contacts of relay H5, lower winding of relay H6, conductor I20, bottom outer contacts of relay 215, conductor 2 I9, bottom inner contacts of relay I2I to battery and in parallel therewith, winding of relay H1 to battery, both of which relays operate. With the operation of relay H6, battery and ground is removed from conductors H4 and H3, respectively, causing relay 203 to release if it has operated while relays H5, H5 and H1 are held locally, relay H5 in a circuit through its lower winding to ground on the bottom contacts of relay H5, and relays I56 and I I1 in parallel circuits to ground on the contacts of relay H5.

Relay I H, on operating, closes a circuit to light guard and disconnect lamp 24 to signal the B operator that the trunk identified by said lamp has been taken up at the CLR toll position. The circuit for the lamp extends from battery through lamp I24, resistance I23, bottom outer back contacts of relay I2I, to ground on the top front contacts of relay H1. Relay H1 further connects ground to conductor I28 to close another circuit for relay 2E3 over its upper winding to insure its operated condition when the original operating circuit of said relay is opened by the release of relay 206, which happens when the operator releases key 3? and thereby causes the release of relay 3I5 and the consequent reversal in the direction of current flowing through the circuit which includes relay 206. Relay I 51 further provides a locking circuit for relays I25, Hi5 and I21 when these relays operate as described hereinafter.

All of the trunks appearing at the B position are arranged for operation on an automatic listening basis; that is, the operators telephone circuit I50 is automatically attached to each of the trunks in succession in a defined order of preference regardless of the time and order in which the trunks are taken into use at the CLR board. This feature is, of course, old in the telephone art and the control circuit by which the order of preference is carried out is not disclosed except as to such parts of it as relate to the operation of the trunk herein being described. It is understood, however, that the features of the invention which are claimed hereunder are not limited to any particular kind of a trunk or in the manner in which the operators telephone circuit is connected thereto, but is applicable to any organization of signal circuits wherein signals are transmitted in both directions over a marginal-polarized circuit consisting of relays 353, 3I5, 205 and 205 or their equivalent.

A pair of cut-in relays is provided for each trunk appearing at the B position and arranged to operate in the prescribed order for the connection of the operators telephone circuit to the preferred trunk if two or more should happen to be taken into use at different CLR boards at the same time. Relays MI and I5I are shown connected to the trunk of Fig. l which is further assumed to be the first trunk in the order of selection, relays I52 and I53 are associated with an intermediate trunk while relays I54 and I55 are associated with the last trunk in the order of selection. Consequently when relay H1 operates,

a circuit is completed for relay I4I, extending from ground on its top front contacts, top outer back contacts of relay I21, lower contacts of relay ,I I1, bottom back contacts of relay I25, winding of relay I4I, through the chain of contacts which extends through other relays similar to relay I5I associated with the other trunks appearing at the position, to battery. Relay I4I operates and closes a circuit for relay I5I extending from battery through the winding of said relay, lower front contacts of relay I4I to ground. Relay I5I, when operated, completes a circuit for operating relay I22, which extends from ground through the top contacts of relay I4I, top inner front contacts of relay I5I, winding of relay I22, top inner back contacts of relay I25 to battery; closes a circuit for flashing lamp I24 by completing a low resistance battery path through resistance I30, contacts of relay I23, which is continuously flashing-under the influence of interrupter I32, top outer contacts of relay I 5|, resistance I23, lamp I24 to battery and further causes a circuit to be closed for lighting lamp I33 which extends from battery through said lamp, bottom outer contacts of relay I4I to ground. Relay I22 operates, looks over its top inner contacts to a ground in the common control circuit (not shown), connects the talking conductors of the operators telephone circuit to the trunk conductors I55 and I51, and further extends the party ringing keys common to the position to relays I25, I26 and I21. The flashing of lamp I24 indicates to the operator that her telephone set and the common ringing keys have been connected to the trunk, the connection of which to the calling subscribers line must be disposed of before said control circuit can operate to cause the lighting of a similar lamp I24 on other trunks which may have been seized for completing purposes at the distant toll positions.

With relay I22 operated, the operators telephone circuit I50 is connected directly across the trunk conductors I55 and I51 over which an inductive talking circuit is established back to the toll operators cord 301 and the telephone circuit connected thereto by way of repeating coils I I9, 2H, and. 313. It is not believed necessary to trace this circuit since, with relay 202 normal, said circuit is perfectly evident by following the talking conductors drawn in heavy line across Figs. 1, 2 and 3.

The toll operator now communicates the details of the call to the B operator by telling her the calling line number together with the particular party designation.

The next function of the B operator is to depress the particular ringing key for signaling the callingsubscribers station. In the disclosure of this application, it is assumed that the subscribers substation I00 may be one of the usual four party line substations connected to the line I02 and that it becomes necessary, therefore, to depress the key which characterizes the kind of ringing current which has to be transmitted over the line to ring the correct subscriber. If, for instance, substation I00 is the so-called party M, then ringing key I 33 is operated whereupon a circuit is completed for relay I25 extending from the right contacts of said key, bottom middle contacts of-relay I22, lower winding of relay I25, bottom contacts of relay I40 to battery, while at the same time two other circuits are completed over the left contacts of said key: one through the bottom inner conacts of relay I22, winding of relay I26 to battery, and the other over the top middle contacts of relay I22, winding of relay I27 to battery. All three relays operate, relay I25 locking over its top inner front contacts to ground on the contacts of relay I I], while relays I26 and I2? also lock to ground on the front contacts of relay III as previously traced. If, on the other hand, the party is the so-called party J, the operator will momentarily depress key I34 whereupon only relays I25 and I2! are operated. For party R, relays I25 and I26 are operated, whereas for party W, key I36 is operated in which case only relay I25 responds. Thus, as soon as the operator knows the calling station to which the call is to be completed, the particular ringing key is depressed and the ringing combination as determined by relays I25, I26 and I2? is set up in preparation for ringing the subscriber as described hereinafter.

The operation of relay I25 opens the locking circuit of relay I22 which, in releasing, disconmeets the ringing keys and the operators telephone circuit I50 from the trunk in preparation for connection with any other trunk which may have been waiting, or which may have been subsequently seized, and further opens the circuit of relay MI, followed by the subsequent release of relay I5I. The release of relay I4I restores the path for operating any other relay, such as relay I53 or I55, of the pairs of relays associated with other waiting trunks, opens the original operating circuit of relay I22, and further disconnects the grounds originally connected to lamp I 24. The release of relay I 5! disconnects the flashing circuit for lamp I24 and reestablishes the series battery connection for operating any of the relays I4I I53 I55 of a waiting trunk in the chain of preference.

The B operator now inserts the plug of the trunk into the jack of the calling line I02. As a result, a circuit is completed for relay I2I extending from battery through the winding of said relay, sleeve of plug I31, sleeve of jack I42 to ground, through the winding of the line cut-01f relay. The operation of relay I2I opens another pair of contacts in the circuit of trunk lamp I24, removes battery from conductor 2I9 which, through the bottom outer contacts of relay 2I5 and conductor I20 removes it from relay IIS and causes said relay to release if the subscriber has disconnected in the meanwhile as described hereinafter, connects battery to relays I39 and I40, while it further connects battery to conductor I4! which completes the circuit for relay 2I'I, causing said relay to operate.

If the calling subscriber has restored his receiver in the meanwhile, the holding circuit for relay I I6 is released as already described, whereupon battery and ground through relay H5 is again connected to the trunk conductors H3 and I I4 as a result of which a circuit is completed for relay 203 extending from battery on conductor I I4, bottom inner back contacts of relay 202, left lower winding of repeating coil 2! I, bottom inner contacts of relay 2532, bottom middle contacts of relay 2 I5, winding of relay 263, left upper winding of repeating coil 2| I, top back contacts of relay 202, conductor II3 through the upper winding of relay I I5 to ground. Relay 203 operates and removes the short circuit from around the high resistance (H) winding of relay 205 which in turn causes the release of relay 360, the release of relay 302, the connection of ground to the low resistance (L) winding of relay 3% and the consequent lighting of the toll cord lamp 328 due to the increase in current now flowing therethrough. The lighting of the lamp indicates to the toll operator that the calling subscriber has restored his receiver and must be rerung. The application of battery to conductor I4I causes the operation of relay 2I'I. As said before, it removes the short circuit from around the high resistance winding of relay 200 whereupon the current for relay I08 in the A cord is increased, said relay operating and lighting lamp I I as a signal to the A operator that the connection has been taken up at the B board and that she may now take down the A cord which connects the calling line with the A branch of the trunk. In removing plug I from the trunk jack I06, the operator disrupts the circuit of relay 200 whereupon said relay releases followed by the release of relay 20 I.

When the toll operator depresses the ringing key (not shown) of the toll cord 301, battery is connected to the tip side of the trunk whereupon a circuit is completed from battery (not shown) on the tip of the cord and tip of the trunk, right upper winding of repeating coil 3I3, winding of relay 3| 3 to ground, Relay 3I3 operates, opens the ground to the (L) winding of relay 308 and thereby causes the toll cord lamp to be extinguished, closes an obvious circuit for relay 3I5 which, on operating, reverses the current direction of the supervisory circuit which includes relays 300 and 206 and 205 and thereby causes the operation of polarized relay 206 as on a previous trunk reversal. Relay 206, on operating, causes the operation of relay 2I6 which, on operating, connects ground through its upper contacts, the contacts of relay 22I to conductor 220 and completes thereby a circuit through the winding of relay I43 and the winding of relay I39 to battery on the top inner contacts of relay I2I Relay I39 operates and connects the tip and ring conductors of the trunk which extend to the calling line to the contacts of the ringing relay combination as determined by the operation of relays I21, I25, and I26 as called for by the ringing key which was depressed at the time the B operator was notified of the calling station to which the call had to be completed. The operation of relay I43 closes the circuit from ground on its lower contacts to the upper winding of relay I I 6 to battery, causing said relay to operate which, in turn, closes the holding circuit for relay I I5 and removes battery and ground through said relay II5 from the trunk. As a result, relays 203 and 2I8 release, reestablishing the short circuit around the (H) winding of relay 205, causing the reoperation of relay 300, the consequent operation of relay 302 and the removal of ground from the upper winding of relay 308, which then causes the cord lamp to remain extinguished as evidence that ringing current is being applied to the line during the time that the toll operator keeps the ringing key depressed. Relay I43 further connects ground from the ringing circuit, through its upper contacts and then through the lower inner front contacts of relay I21 it operated, bottom front contacts of relay I39 to the ring of the trunk plug I31, or through the top inner back contacts of said relay if not operated, and thence through the top front contacts of relay I39 to the tip of the trunk plug I31. In either case, the ground is carried through the. subscribers substation loop and completed either to the ringing source on conductor I41 or another ringing source on conductor I48 depending upon whether relay I26 has or has not been operated as called for by the ringing key that was depressed. In this manner the particular station I is rung. When the toll operator restores the ringing key relay 206 releases in consequence of which both relays I39 and I43 release. With the release of relay I43, relay H9 is released and battery and ground are again connected to the trunk, reoperating relays 203 and 2I8, removing the short circuit from around the high resistance winding of relay 205, in consequence of which relay 300 releases followed by the release of relay 302, the connection of ground to the high resistance winding of relay 308, and the lighting of the toll cord lamp as already described.

It has been shown that if, at the time the B operator inserts the trunk plug into the subscribers jack, the subscriber has restored the receiver, the toll operator receives a ringing signal by the lighting of the toll cord lamp, and that this signal was the result of the release of relay IIB, the reconnection of battery and ground to the trunk conductors H4 and H3, respectively, and the consequent release of relay 302 following the release of relay 300 in virtue of the removal of the short circuit around the high resistance (H) winding of relay 205. However, if the subscriber should happen to have the receiver off the hook, a circuit is completed for relay I44 over a path which extends from ground through ballast lamp I45. upper winding of relay I44, left upper winding of repeating coil I I9, conductor I 56, top back contacts of relay I39, top outer front contacts of relay I2I, tip of plug I37, tip of jack I42, subscribers loop, ring of jack I42, ring of plug I31, bottom back contacts of relay I39, left lower winding of repeating coil H9, lower winding of relay I44, ballast lamp I49, to battery. Relay I44 operates and completes a holding circuit for relay IIB which extends from ground on the contacts of relay II5, contacts of relay I44, upper winding of relay IIB to battery. Relay H3 thus remains operated, prevents battery and ground from being connected to the trunk conductors H4 and H3, respectively, and thereby prevents the operation of previously described circuits which result in the lighting of the toll cord lamp. The failure to light the lamp indicates to the operator that the subscriber is already on the line and may be communicated with without ringing.

When the subscriber answers, relay I44 operates over the circuit above described and further closes the above described circuit for relay IIB. Relay II6 operates, holds relay I I5, removes battery and ground from trunk conductors H4 and H3, respectively, causes the release of relays 203 and 218 as previously described and initiates the operation of the circuits which result in extinguishing the toll cord to indicate that the subscriber has answered.

In case the toll operator finds it necessary to rering while the subscribers receiver is off the switch-hook,relays I39 and I43 are reoperated as already described. The operation of relay I39 releases relay I44 and applies to the called line the same ringing current as that previously set up by the operation of relays I25, I26 and I2'I as called for by the operation of the proper ringing key. The operation of relay I43 holds relay ||6 operated after relay I44 releases and connects ringing ground to the contacts of relay I2I. When the toll operator finds it necessary to rering after the receiver has been placed on the switch-hook at thecalling station, relays I39, I43 and H6 reoperate and ringing current is applied to the line as on an original call. When the toll operator restores the ringing'key, relays I39 and I43 release. Relay I33 removes the ringing current from the line and closes the tip and ring of the trunk cord through the repeating coil I I9. Relay I43, on releasing, opens the holding circuit for relay H6 and opens the ringing current circuit. Relay I44 now reoperates if the receiver is off the switch-hook and holds relay IIB operated, thus keeping the toll operators cord lamp unlighted.

When the conversation is over and subscriber I00 restores his receiver, relay I44 releases, in turn causing the release of relay H6 and the reapplication of battery and ground to the trunk which, as in previous operations, results in the operation of relays 203 and 2|8, whereupon the high resistance winding of relay 205 is again short-circuited and relay 300 is operated in consequence thereof. The operation of relay 300 is followed by the operation of relay 302 which in turn connects ground to the upper winding of sleeve relay 308 as before described and causes the lighting of the toll cord supervisory lamp 328 as a disconnect signal to the operator.

Upon the toll operator removing the plug of toll cord 30'! from the trunk jack 306, relay 308 releases followed by the release of relay 309, in turn by the release of relay 3I0. Relay 3| 0 causes the release of relay 3| 2, connects battery through resistance 321 to the (L) winding of relay 308 by way of the top front contacts of relay 302 to establish the busy potential on all CLRjacks which has been removed by the disconnection of cord sleeve battery from the sleeve of the trunk jack, and further causes the release of relay 3| I. The release of relay 3I2 reestablishes the circuit for trunk lamp 303. This, however, is only momentary because the release of relay 3| I causes the release of relay 305 which, in turn, disconnects battery and ground from the signal loop that includes relay 300 and causes this relay to release. The release of relay 3| I is further followed by the release of relay 3 I I and that of relay 304. However, relay 3|! is slow release, so that while relay 305 releases before relay 300 and thereby establishes a locking circuit for relay 302, this locking circuit is ineffective at this time since it depends upon the normal condition of relay 304 which, depending upon slow-release relay 3 I I, is operated at the time relay 305 releases and thereby will notbe successful in causing relay 302 to remain locked which, upon releasing, causes trunk lamp 303 to be extinguished.

The removal of battery and ground from the trunk loop by the release of relay 305 further causes the release of relay 205 which, in turn, causes the release of relay 226. Relay 226 upon releasing, unlocks relay 2!!) and releases relay 2|5. With the release of relay 2 5, the previously described circuit which includes relays 203 and I I is now opened, whereupon relay |I5 releases and causes the release of relay II? which, upon releasing, unlocks relay |25 as well as relays I 23 and I2? if operated. It further causes a circuit to be established for relay I40 extending from ground on the top normal contacts of relay Ill, winding of relay I40, top inner contacts of relay |2I to battery. Relay I40 operates, locks to ground on its own top inner contacts, but under the control of relay I2I, and establishes a steady lighting circuit for lamp I24 extending from ground on the-top inner contacts of relay I 40, bottom outer front contacts of relay I2I, resistance I23, lamp I24 to battery. The lighting of the lamp is a signal to the B operator to take down the connection. The disconnection of trunk plug I31 from line jack I42 causes the release of relay I2I, which in turn causes lamp I24 to be extinguished and unlocks relay I40 which, upon releasing, restores the trunk to normal.

In case the plug of the toll cord 30'! is withdrawn from the trunk jack 306 before the calling subscriber has disconnected, relay 308 releases, in turn, releasing relay 309. Relay 309 causes the release of relay 3I0. Relay 3! I, however, which would normally release after the release of relay 3), does not release at this time since it is held locked to ground on the lower outer contacts of relay 302 which, in turn, is held operated to the contacts of relay 300, the latter being held operated over the trunk loop in series with relays 205 and 200 from battery and ground supplied through the contacts of relay 305. Relay 205, it will be remembered, has its high resistance winding short-circuited by virtue of the fact that relays 203 and 2I8 are released because of the absence of battery and ground through relay I'I5, since relay H3 is locally held by relay I44 which, in turn, is held over calling line loop. Relay 309, on releasing, completes a circuit for relay 3I3 which extends from ground on its top contacts, bottom outer contacts of relay 305, winding of relay 3I5 to battery. Relay 3I6 operates, disconnects the loop circuit which includes relay 300 and battery and ground thereto, closes an obvious circuit for relay 320 which operates, connects ground through the upper winding of polarized relay M9 to the tip conductor 201 by way of the top outer front contacts of relay 3l3, top back contacts of relay 3I5, resistance 3M, left upper winding of repeating coil 3I3 to conductor 201, connects a definite potential determined by battery through resistance 32! and ground through resistance 322 through the lower winding of polarized relay 3I9, bottom outer contacts of relay 3I9, bottom back contacts of relay 3 I 5, resistance 3 I I, left lower winding of repeating coil 3 I 3 to conductor 203. The battery and ground thus supplied to the trunk replaces the high voltage and ground supplied through relay 305 and is, therefore, in series with relays 205 and 2&6. Inasmuch as the polarity of the current is the same in both cases, relay 206 remains unaifected by the substitution of relay 3I9 in the circuit for relay 300. Relay 3I9, however, operates and maintains ground to hold relay 302 operated to replace the ground which was disconnected from the circuit of the relay by the release of relay 300. By maintaining relay 302 operated, the circuit for lamp 303 is closed, the lighting of which apprises the operator that the calling subscriber has not yet restored while the connection of resistance 327 to the (L) winding of relay 308 causes busy test potential to be connected to each of the sleeves of the trunk at the various positions at which it appears to prevent its seizure. The effect of reducing the voltage on conductor 208 causes the release of relay 205 which, in turn, releases relay 226. The release of relay 226, in turn, releases relay 2I0, if operated, and further releases relay 2I5. Beyond this, the release of relay 205 serves no useful function at this time.

However if, at the time the connection has been extended to the CLR position from the originating A board, and the operator at said CLR position has taken up the connection by inserting the plug of cord 30! into the trunk and thereafter failed to extend the connection back to the B position of the calling office by depressing key 358, but wished to flash the A operator before doing so,

or otherwise wished to abandon the connection. the Withdrawal of the plug of cord 30? would cause the circuit operations above described to take place. In this case, however, the release of relay 205, and the consequent release of relay 2 l 5 would remove the short circuit around the high resistance winding of relay 200, cause thereby the release of relay I08 in the A cord as a result of which lamp H will light. If the CLR operator fails to reinsert the plug of cord 30': into the trunk jack, the steady lighting of lamp H0 serves as a disconnect signal to the A operator. On the other hand if the CLR operator repeatedly withdraws and reinserts the cord plug, lamp II 0 is flashed to call the A operators attention to the fact that the CLR operator wants to communicate with her.

N 0 further operations occur until the subscriber disconnects since relays 203 and 2I8 are already released at this time due to the fact that relay H6 is held from the contacts of relay I44 and battery and ground thereby disconnected from the trunk. These relays, when normal, maintain a short circuit around the high resistance winding of relay 205 which thus holds the connection at the toll end of the switchboard by causing relay 3I9 to remain operated. The subscriber, therefore, is enabled to hold the connection and make the fact known to the toll operator.

When the subscriber restores his receiver, relay IM releases which further releases relay II 6. Ground and battery are again connected to conductors H3 and II 4, respectively, through relay H5 as a result of which the short circuit around the (H) winding of relay 205 is removed. Due to the increase of the resistance in the circuit including relays 205 and 3I9, relay 3I9 is released, in turn, followed by the release of relay 302, in turn, releasing all the operated relays, restoring the trunk to normal, and extinguishing lamp 303.

If the subscriber does not disconnect, and the plug of the toll cord is reinserted in the trunk jack, relays 308, 309, SH] and 3I2 reoperate, removing the busy test potential from the winding of relay 300 which is now replaced by battery from the toll cord sleeve, extinguishing lamp 303 and disconnecting ground from the circuit of relay 3I6, causing it thereby to release, remove relay 3I9 from the trunk and reconnect the high voltage through relay 300, allowing the trunk signaling apparatus to function as previously described.

In case the toll operator disconnects after the operation of the transfer key 3I8 but before the toll switching trunk plug I3! is plugged into the calling line jack I42, relays 308, 309, 3I0 and 3I2 will release and function as before to protect the trunk against selection at other toll positions. The disconnect condition passed back over the trunk by the operation of relays 3I6 and 320 causes the release of relays 205, 226 and 2I5 as before described. The release of relay 2I5 opens the circuit of' relay I I6 the effect of which is the opening of the steady lighting circuit of lamp I24 and the release of relay 2I3. The release of relay 2I3 disconnects the short circuit around the high resistance (H) winding of relay 205, thus permitting the apparatus at the toll switchboard end of the trunk to restore to normal.

In case the toll switching operator at the B beard completes the call to the wrong subscribers line, the toll operator will instruct the subscriber to disregard the call and disconnect. When the subscriber disconnects, the circuit operations initiated by the release of relay I44 results in the consequent release of relay 302 by those circuit operations which have already been described and by which the toll cord lamp is lighted as an indication that the subscriber has restored. The toll operator may then reconnect the trunk to the distant A operators cord circuit, providing that said operator has not yet disconnected, by withdrawing the plug of the toll cord and reinserting it into the trunk jack. The withdrawal of the toll cord plug causes the release of relays 309, 3I0, 3| I, 3I'I, 3I2 and 304 as previously described, giving a, disconnect signal to the B operator. However, due to the fact that the distant A operator has not yet disconnected, the connection will automatically be transferred back to the A operators cord circuit by Virtue of the fact that the release of relay 205 as previously described results in the subsequent release of relay 2 I5, the removal of short circuiting ground from the high resistance winding of relay 200, the release of relay I03 in the A cord and the consequent lighting of cord lamp I I0. When the plug of the toll cord is reinserted in the jack, relay 300 operates, operating relay 309. The operation of relay 309 causes the operation of relay 3I0 which, in turn, causes the operation of relay 3I I. The operation of relay 3| I now causes supervision to be passed back over the trunk as previously described, that is, by causing the operation of relay 205 and the extinguishing of the A cperators calling cord lamp I I0 as a signal that the toll operators cord is reconnected to the trunk. The toll operator will ask the A operator for the calling subscribers number and may then transfer the connection back to the toll switching trunk by the operation of transfer key 3I8 as already described. In case the plug of the toll switch trunk has not yet been disconnected from the incorrect line, relay 302 will be released, which will cause the lighting of the toll supervisory lamp as previously described. When the plug of the toll switching trunk is withdrawn from the jack of the wrong line, relay 302 will reoperate and extinguish the toll cord supervisory lamp. The call may then be completed to the correct line, as already described.

Having described the use of the trunk in extending a connection from a local ofijce to the toll switching point, its use in a connection which extends in the opposite direction will now be described, that is, on a toll inward call which is to be completed by way of the trunk to a called line in some distant local oflice, such as, for instance, subscriber I00 located on line I02.

When the plug of a toll cord is inserted in the multiple jack of this circuit, such as, for instance jack 300, relay 308 operates. Relay 308, on operating, operates relay 309, which causes,

in turn, the operation of relay 3I0. The operation of relay 3I0 in turn causes the operation of relays 3H and 3I2, as already described.

The operation of relay 3 causes the operation of relay 305 which, in turn, connects high voltage battery and ground to the signaling loop including relays 300, 205 and polarized relay 206. As a result, relay 205 operates, in turn causing the operation of relays 226 and 2I5, whereupon the signaling loop including relays 203 and H5 is closed and results in the operation of relays IE5 and 203, the former of which operates, as already described, to light trunk lamp I24 as an indication that a call is waiting upon the line, while the relay 203 causes the operation of relay 2I8. The operation of relay II5 further causes the operation of relay IIB which looks relay H5 and releases relay 203, and connects ground to conductor I28 causing the operation of relay 2I3. Relay 2I3 opens the operating circuit of relay 202 and short-circuits the high resistance (H) winding of relay 205 through the contacts of relay 203 which is now deenergized. The effect of this is to cause the operation of relays 300 and 302 and the extinguishment of the toll cord lamp if it lighted the momentary interval during which relay 300 was operated prior to the short circuiting of the (H) winding of relay 205. Relay 3H further causes the operation of relays 3H and 304 as already described and the latter, on operating, opens the operating circuit of relay 3! I. Relay 3! I, however, remains locked through its own contacts and the contacts of relay 3 I0 to ground. The operation of relay 204 also opens the locking circuit of relay 302 so that this relay remains under the direct control of relay 300.

When the B operators telephone set I50 is connected to the trunk at the distant end, order tone is passed over the trunk conductors to the toll operator as in the previous type of call. When the details of the call are passed to the B operator and the plug of the toll switching trunk E31 is inserted in the idle line jack of line I02, relay 300 releases, followed by the release of relay 302 as previously described, and the connection of ground to the toll cord sleeve through the low resistance winding of relay 308. This ground lights the toll cord supervisory lamp as a ringing signal, whereupon the toll operator will then ring out over the trunk to call the subscriber in the manner previously described. It is obvious, however, from the circuit operations already described, that if the toll operator should disconnect the toll plug from the trunk before the toll switching operator connects plug I31 to the called subscribers jack, the release of relay 205 will extinguish lamp I24 at the toll switching position as an indication that the call has been abandoned. In all other respects, disconnection is identical to that described for the previous type of call.

This trunk may also be used in completing calls between two oflices within the local area immediately contiguous to the toll point. For this purpose an extra pair of jacks is provided at the A terminus of the trunk such as, for instance, jack I49. This jack differs from the jack I00 only in the fact that the talking conductors I01 and I09 are reversed. When a call is initiated by a line, such as subscriber I00 on line I02, for some called subscriber whose line terminates in an ofiice within the toll oflice area, the operator inserts plug I05 of a regular A cord into jack I 49. Since the trunk conductors are reversed, A cord battery is connected to conductor I09 whereupon a circuit is completed through the left winding of retard coil 2! 2 and both windings of relay 224 in series to ground. Relay 224 closes an obvious circuit for relay 2I4 which, on operating, cornpletes an obvious circuit for relay 20i, and reverses the battery and ground connection to conductors 20'! and 200, causing battery through resistance 225 to be connected to conductor Ziil and ground to be connected to conductor 208. At the same time, relay 204 operates as a result of the operation of relay 202, which follows in consequence of the operation of relay 20!, as in the previous use of the trunk in establishing a toll connection from line I02 to the CLR position. This battery and ground connection is in the circuit of relays 300 and 30I, but inasmuch as the direction of current flow has been reversed by the operation of relay 214, and inasmuch as the value of resistance 225 is such as to limit the quantity of current to a value below that which will operate relay .300, only relay 30! will operate. Relay 30L on operating, closes a circuit for relay 326 which extends from ground on the contacts of relay 30!, lower winding of .relay 326, bottom inner back contacts of relay 302 to battery. Relay 326 operates, and through its top outer contacts closes a circuit for operating relay 302, and then locks over its top winding and top inner contacts to ground on the bottom outer contacts of relay 302 when operated. A circuit is thereafter completed for lamp 324 at the inward local position, extending from ground through said lamp, bottom front contacts of relay 326, contacts of relay 3l2, bottom inner contacts of relay 302 to battery, lighting said lamp as a signal to the operator at the inward position that a call is waiting thereon, while the operation of relay 302 further establishes busy test potential to the sleeve of the trunk jacks at other positions in the manner already described. The operator then plugs the calling cord 325 into the jack 323, after which operations proceed as before described except that, since there is no transfer key 3|8 to be operated in this instance, relay 202 at the originating end will remain operated under the control of relay l. The trunk connection therefore will extend from the inward position to the calling subscriber over the front contacts of relay 202 and through the' A cord to the subscribers line. All other operations are then the same as previously described for a toll connection.

What is claimed is: V a

1. In a toll switching system, a trunk comprising one outgoing end and two incoming ends, meansresponsiveto a connection to said outgoing end for establishing a talking and signaling connection between said outgoing end and one of said incoming ends, and means controllable after the establishment of said connection for establishing a talking and signaling connection between said incoming end and said other incoming end.

2. In a telephone system including subscribers telephone lines, a trunk for use in connecting said lines terminating at its one end in an A operators board and in a first B operators board and at its opposite end in a second B operators board, a signal at said A board associable with said trunk, a signal for said trunk at said first B board, a signal at said second B operators board associated with said trunk, and a circuit to control said signals including a first relay, a second relay and a third relay, means responsive to a first operation at said second B board for operating said first and third'relays to afiect the signals at said A board and at said second B board respectively and means responsive to a second operation at said second B board for operating said second relay to affect said signal at said first B board.

3. In a telephone system including subscribers telephone lines, a trunk for use in connecting said lines terminating at its one end in an A operators board and in a first B operators board and at its opposite end in a second B operators board, a key for said trunk at said second B operators' board, a signal at said A board associable with said trunk, a signal for said trunk at said first B board, a signal at said second B operators board associated with said trunk, a circuit to control said signals including a first relay, a second polarized relay and a third relay, means responsive to an operation at said second B board for operating said first and third relays to affect the signals at said A board and at said second B board and means responsive to the operation of said key for operating said second polarized relay to afiect said signal at said first B board.

4. In a telephone system including a calling telephone line, a trunk terminating at one end in an A operators board and in a first B operators board and at its opposite end in a second B operator's board, means at said A board for extending said calling line over said trunk to said second B board, means for extending said trunk to said calling line at said first B board, a signal for said trunk at each of said boards, and a circuit to control said signals including a first relay having a high resistance winding and a low resistance winding and a second relay, means responsive to the extension of said connection at said second B board for operating both of said relays to light said signal at said first B board and to extinguish the signal at said second B board, and means responsive to the restoration of said calling line for short-circuiting the high resistance winding of said first relay for releasing said second relay to light said signal at said second B board in the event that said connection at said second B board has been disrupted.

5. In a telephone system including a calling telephone line, a trunk terminating at one end in an A operators board and in a first B operators board, and at the other end in a second B operators board, a source of ringing current in said trunk, means at said A board for extending said calling line over said trunk to said second B board, means for extending said trunk to said telephone line at said first B board, a signal for said trunk at each of said boards and a circuit to control said signals including a first relay having a high resistance winding and a low resistance winding, said high resistance winding being normally short-circuited, a second polarized relay and a third relay, means responsive to a first operation at said second B board for operating said first relay and said third relay for operating said signal at said first B board and keeping nonoperated said signal at said second B board, means responsive to the extension of said trunk to said telephone line at said first B board for removing said short circuit around the high resistance winding of said first relay to release said third relay to operate said signal at said second B board, means responsive to a second operation at said second B board for operating said second polarized relay to connect said ringing source to said line over said trunk at said first B board, and other means responsive to the operation of said second polarized relay for short-circuiting said high resistance winding of said first relay for operating said third relay to render said signal at said second board non-operative.

6. In a telephone system including a calling telephone line, a trunk terminating at one end in an A operators board and in a first B operators board and at the other end in a second B operators board, signals associated with said trunk at said A board and at said first B board and a first and second signal associated with said trunk at said second B board, means for controlling the operation of each of said signals comprising a first relay having a high resistance winding and a low resistance winding, said high resistance winding being normally short-circuited, a second polarized relay and a third relay, means responsive to the extension of said telephone line to said second'B board over said A board for operating said third relay to operate said first signal at said second B board, means effective after the operation of said signal for connecting said three relays in a series current path for placing said second signal under the control of said third relay for operating said first relay to aiTect the signal at said A board and to operate said third relay to extinguish said first signal at said second B board, means responsive to a second operation at said B board for operating said second relay to affect the signal at said first B board, means responsive to the extension of said trunk to said telephone line over said first B board for removing the short circuit around the winding of said first relay to effect the release of said third relay, and means responsive to the restoration of said calling line to short-circuit said high resistance winding for reoperating said third relay and effeet the operation of said second signal at said second B board.

'7. In a telephone system, a toll trunk for extending a calling line from an A board to a toll board, a signal for said trunk at said A board, a first and second signal for said trunk at said toll board, and a circuit for controlling the operation of each of said signals comprising a relay having a high resistance winding and a low resistance winding, said high resistance winding being normally short-circuited, a second relay, a third relay, means responsive to the extension of said calling line to said toll board for connecting said first and said third relay in series and for operating them to render said signal at said A board and said first signal at said toll board non-operative, means responsive to an operation at said toll board prior to the disconnection of said calling line for disconnecting said third relay from said first relay and connecting said second relay with said first relay and operating said second relay to affect said second signal at said toll board, and means responsive to the restoration of said calling line for removing said short circuit around the winding of said first relay to release said second relay and restore said second signal.

8. In a signaling system, a trunk having three terminal ends, a signal for each of said terminal ends, and a signaling circuit for controlling the operation of all of said signals comprising a relay with a high and low resistance winding, a

polarized relay, a marginal relay, sources of potential, means for reversing the current direction in said circuit, and means for short-circuiting the high resistance winding of said high-low relay whereby upon the application of one of said sources of potential said high-low relay operates to control one of said signals and said marginal relay operates or non-operates to control another of said signals depending upon whether said shortcircuiting means are operated or non-operated respectively, and whereby when said current reversal means are operated said polarized relay is operated to control the last of said signals.

9. In a telephone system, a trunk terminating at one end upon a trunking operators board and having its opposite end divided into parallel branch circuits terminating upon different operators boards, a calling signal for said trunk located upon one of said last boards, a supervisory signal for said trunk located upon another of said last boards, means for operating said calling signal to denote a call and other means for operating said supervisory signal to show that the call has been completed at the board where said calling signal is operated.

10. A telephone system comprising subscribers telephone lines, a trunk for interconnecting said lines, one end of said trunk appearing upon a trunking operators board and the opposite end of said trunk having parallel branches appearing upon different operators boards, a signal for each parallel branch of said trunk circuit and means controllable by the trunking operator for operating said signals in a definite order or sequence.

11. A telephone system comprising subscribers lines, a trunk for interconnecting said lines, one end of said trunk circuit terminating upon a trunking operators board and the opposite end of said trunk circuit being divided into two parallel branches which appear upon a trunking operators board and a local operators board, a signal for each parallel branch of said circuit, and means controlled by said first trunking operator for operating one of said signals on one type of connection and both of said signals on another type of connection.

12. In a telephone system, a trunk terminating at one end in an originating operators board and in a terminating operators board and at the other end in another terminating operators board, means for establishing a talking connection over said trunk between said originating operator's board and said last-mentioned terminating operators board, and manually controlled means at said last-mentioned terminating operators board for disrupting said talking connection and establishing another talking connection between said first terminating operators board and said last-mentioned terminating operators board.

13. In a telephone system, a trunk terminating at one end in an originating operators board, and at the other end in a trunking operator's board, a link for connection at either end of said truck, a signal in each of said links, and means in said trunk for operating said'signals comprising a first relay having a high resistance winding and a low resistance winding, a second marginal relay in series with said first relay and a source of potential, means responsive to the connection of one of said links to the originating end of said trunk for short-circuiting said high resistance winding of said first relay, means responsive to the connection of said other link to the terminating end of said trunk for applying said source of potential to both of said relays, means responsive to the operation of said first relay to operate the link signal at said originating board, means responsive to the operation of said second relay to cause the link signal at said terminating board to remain non-operative, and means responsive to the disconnection of said first link from said trunk for removing the short circuit around the high resistance winding of said first relay to cause 1 the release of said marginal relay to operate said link signal at said terminating board.

14. In a signaling system having three separate signals, means for controlling each of said signals comprising a first marginal relay, a second polarized relay, and athird relay having a high resistance winding and a low resistance winding, a current path extending through'all of said relays in series, means for short-circuiting said high resistance winding, means for reversing said current path, and a source of potential connectible to said current path.

15. In a telephone system, a trunk having three outlets, a signal at each outlet, and means in said trunk for controlling each of said signals comprising a first relay having a high resistance winding and a low resistance winding forcontrolling a signal at the first outlet, a second polarized relay for controlling a signal at the second outlet and a marginal relay for controlling the signal at the third outlet, a serial circuit path for all of said relays, a source of potential connectible to said path for operating said first and third relays, means for reversing said circuit path for operating said second relay and means for short-circuiting the high resistance of said first relay to efiect the release of said third relay.

16. In a telephone system including subscribers telephone lines, a trunk for use in connecting said lines terminating at its one end in an A operators board and at its other ends in two different B operators boards, a signal for each branch of said trunk, and means to control each of said signals comprising a first relay having a high resistance winding and a low resistance winding normally short-circuited, a second relay connected to a source of potential, 2, third relay connected to a different source of potential, means for connecting said second relay to said first relay for operating said first relay to selectively operate said signal at said A board and said signal at one of said B boards and for operating said second relay to hold said signal at the other of said B boards non-operated, means for removing said short circuit to release said second relay for operating said signal at the other of said B boards and means for disconnecting said second relay and connecting said third relay to said first relay to release said first relay and operate said third relay for extinguishing said signals at said A board and one of said B boards and maintaining operated said signal at other of said B boards.

17. In a signaling system having five signals, a circuit for controlling the operation of each of said signals comprising a first relay having a high resistance winding and a low resistance winding, said high resistance winding being normally short-circuited, a secondpolarized relay, a third marginal relay, a fourth relay and a fifth relay, means for effecting a series connection between said first, second and third relay foroperating said first and said third relays to control a first and second signal, means for reversing said connection to operate said second relay to control a third signal, means for removing said short circuit around the high resistance winding of said first relay to release said third relay to control a fourth signal, means for disconnecting said third relay from said connection and for connecting said fourth relay thereto for releasing said first relay with its high resistance winding short-circuited and for operating said fourth relay to operate said second signal, means for releasing said fourth relay when said short circuit is removed to control said second signal, and means for disconnecting said fourth relay from said connection and for connecting said fifth relay thereto for operating said fifth relay to control a fifth signal.

RUSSELL B. BUCHANAN. LINDLEY A. KILLE.

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