US2295372A

US2295372A - Telephone system

Info

Publication number: US2295372A
Application number: US350465A
Authority: US
Inventors: John H Voss
Original assignee: Associated Electric Laboratories Inc
Current assignee: Associated Electric Laboratories Inc
Priority date: 1940-08-03
Filing date: 1940-08-03
Publication date: 1942-09-08
Anticipated expiration: 1959-09-08

Description

Sept. 8, 1942. J. H. voss' TELEPHONE SYSTEM 2 Sheets-Sheet 1 Filed Aug. 3, 1940 Qm. hm

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INVENTOR .JOHN H. v'oss ATTORNEYS sept. s, 1942.

4. H. voss TELEPHONE SYSTEM Filed Apg, 3, 1940` 2 sheets-sheet 2 w w ..w MSS mmw m SS m@ lNvENToR JOHN H. Voss ATTORNEYS Patented Sept. 8, 1942 UNITED STTES PTENT FFICE TELEPHONE SYSTEM Application August 3, 1940, Serial No. 350,465

15 Claims.

The present invention relates to telephone systems and more particularly to improvements in trunk circuit apparatus of the character utilized in terminating inter-exchange trunks in an exchange of the automatic type.

In small community automatic exchanges, commonly known as C. A. Xs, the character of the automatic switching equipment is frequently such that the outlet contacts of the iinder and connector switches utilized are arranged in sets for subscriber line termination, and the corresponding contacts of the contact sets having the same directory number designations are conductively connected together. This line multiple arrangement, wherein the private or control contacts as well as the talking contacts of the corresponding contact sets are conductively connected, is known as a straight multiple. While this type of outlet contact multiple is entirely adaptable to subscriber line termination, it is not Well adapted for use in conjunction with the conventional trunk circuits now used to terminate inter-exchange trunks. More specically, conventional trunk circuit arrangements require, for proper operation, a separation of the control leads eX- tending to the nder switches from the control leads extending to the connector switches.

It is an object of the present invention, therefore, to provide in a system of the character described, an improved trunk circuit, which is so arranged that it may be directly substituted for a subscriber line circuit without in any way altering the multiple wiring of the finder and connector switches or the equipment common to these switches.

It is another object of the invention to provide an improved trunk circuit of the character noted, which is equipped to provide supervisory and trunk lockout facilities, and is extremely simple in arrangement.

It is a further object of the invention to provide in a telephone system of the character described, an improved trunk circuit arrangement wherein two trunk circuits, each adapted for use with trunks individual thereto, are cooperatively used in conjunction with a single trunk and two 'sets of outlet contacts of the associated finder and connector switches, so that the trunk may be seized by a connector switch as a first choice trunk for one type of call and as a second choice trunk for another type of call.

In the illustrated embodiment of the invention there is provided a small community exchange which is connected with a central exchange of the manual type by means of inter-oice trunks of two types, namely, toll and free service trunks.V

The community exchange is of the automatic type, finder-connector links and common equipment including a link distributor being provided therein for setting up connections between the lines terminating at the exchange. Straight line multiples between the outlet contacts of the link nder and connector switches are used, so that a subscriber line connection may be made by connecting the subscriber line equipment, i. e., the line, cut-off and lockout relays directly to the private and talking leads of a particular multiple having the desired directory number designation. Each of the trunks utilized solely for toll service and free service are terminated in the C. A. X in trunk circuits individual thereto, these trunk circuits being so connected and arranged that they may be directly connected to a subscriber line multiple individual thereto. Each of these trunk circuits is so connected and arranged that by disconnecting a set of subscriber line relay equipment from a line multiple the talking and private leads of the trunk circuit may be directly connected to the talking and private leads of the selected multiple. These trunk circuits individually comprise line, lockout and cut-off relays which are so arranged that the associated trunk is locked out of service when a permanent calling condition exists thereon. Each trunk circuit further includes a supervisory relay which is controllable over the private lead of an associated line multiple to transmit on-hook and oi-hock supervisory signals over the associated trunk through the expedient of reversely connecting the talking conductors of the associated trunk to the talking conductors of the associated line multiple.

One of the trunks connecting the C. A. X with the manual oince is used as a combination toll and free service trunk. More specically, this trunk is normally used as a iirst choice, free service trunk, but provisions are made whereby it may be used as a second choice toll trunk on calls routed from the substations served by the C. A. X to the central exchange. The provisions whereby these combined service facilities are obtained include a combination of two of the trunk circuits normally used for individual trunk termination. More specifically, the switchboard trunk sections of these two trunk circuits are individually connected to line multiples having different directory number designations, one of these designations representing the rst choice free service directory number, and the other designation representing the second choice toll trunk designation. Both of the two trunk circuits are equipped with line, cut-off, lockout and supervisory relays, whereby the facilities mentioned above are provided regardless of which trunk circuit is taken for use in seizing the singleassociated trunk. In addition, provisions are made in the circuit arrangement formed by the combination of the two trunk circuits, whereby when either trunk circuit is seized the other trunk circuit is marked against seizure. Provisions are also made for selectively switching the associated inter-office trunk between the two trunk circuits, depending upon the type of call being handled.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings, in which Figures 1 and 2, considered together, illustrate a telephone system havingincorporated therein the features oi' the 'invention as briefly outlinedabove.

Referring now more particularly to the drawings the system there illustrated comprises a manual oiicev 5 and a C. A. X I0, each of which is arranged for subscriber line termination. These two exchangesA are inter-connected by means of a group of toll trunks including the trunk andV a-group of free service trunks. An additional trunkA 9| is provided which, in the arrangement illustrated, is utilized as a rst choice free service trunk and 'as a second class toll trunk. These trunks terminate in the central exchange at different operators positions of an operators switchboard 6 which may be entirely conventional in arrangement.

The automatic switching apparatus provided in the C. A. X I0 is preferably of the character disclosedand claimed in applicants copending application, Serial No. 189,121, filed February '7, 1938. -Briefly described, this apparatus comprises a plurality of finder-connector links, one of which is indicated at I5 as including the nder switch 25 and the connector switch 30, and common equipment 20. The finder and connector switches are of the all-relay type, group and unit relays arranged in a novel manner being Vprovided in each switch for performing .the required lineselecting functions.. Each of the finder switches is fully selective in character, auxiliary group and unit :relays being provided in the common equipment20 for causing the instantaneous operation of the corresponding relays in anassigned nder switch in response ,to the initiation of a call on oneof the lines accessible to the links. The links are successively assigned for use in a predetermined order through the provision of a link distributor which is also of the all-relay type. Straightline multiples are utilized to connect the corresponding contacts of the link finder and connector switches. Thus, the outlet contacts formingthe ,contact set IIf of the finder switch 25 are conductively connected by means of two talking leads and a private lead directly to the outlet contacts forming thecontact set ||c of the connector switch 3.0. This multiple is also extended to the contact sets having the directory number. designation XI IX of the other link nder and connector switches. In a similar manner, the nder outlet contacts .0If are directly multipled to the connector outlet contacts 0| c; the finder outlet contacts 02 f are .directly multipled to the connector outlet contacts 020; and the The invention, both as Vtion of the two trunk circuits.

iinder outlet contacts 9|, are directly multipled to the connector outlet contacts 9|c. These line multiples are carried to a distributing frame at which connections are made to the subscriber line equipment. Thus, the line circuit I2, which is provided in association with the subscriber line II serving the substation A, may be connected to the line multiple having any desired directory number designation by making three connections at the distributing frame. In the arrangement illustrated, this line circuit is connected to the line multiple having the directory number designation XI IX.

Each of the inner-ofce trunks inter-connecting the C. A. X I0 and the central exchange 5 is terminated in a trunk circuit which is connected and arranged in accordance with the present invention. Thus, the toll trunk 0| extends to a trunk circuit 35 having a trunk section which is connected to the outlet contact multiple having the directory number designation 0|. The arrangement of the trunk circuit 35 is identical with the arrangement of the trunk circuit 40,

which may either be used to terminate a second toll trunk 02 illustrated in dotted lines, or may be used in conjunction with the trunk circuit 45 to terminate the combination toll and free service trunk 9|. Each of the trunk circuits which terminates a toll or free service trunk individual thereto is identical in arrangement with the trunk circuit 40. Briefly described, this trunk circuit comprises a line relay RI 0, a cut-01T relay R|20, a slow-acting lockout relay R|00, a supervisory relay R|30 and circuit connections therebetween which are described more fully in the following portion of the specification dealing with the operation of the system. The trunk circuit 45 is substantially similar in arrangement with the trunk circuit 40. More specifically, the trunk circuit 45 comprises a line relay R2|0, a cut-olf relay R220, a lockout relay R200 of the slow-acting type, a supervisory relay R230, a line-,switching relay R240 and a guard control relay R250. The two last-mentioned relays are provided for the purpose of correlating the opera- In this regard it will be noted that the trunk 9| may be seized through the trunk circuit 45 directly over the trunk section |56 having the directory number designation 9|, or may be seized through the trunk circuit 40 over the trunk section |49 having the directory number designation 02. If more than one toll trunk is required between the central exchange 5 and the C. A. X |0, the switchboard side of the trunk circuit 40 is connected to the outlet contact multiple having the largest directory number. Thus, if three such trunks, in addition to a combination trunk, are required, the associated trunk circuits are connected-to the line multiples having the directory number designations 0I, 02 and 03, and the trunk circuit 40 is connected to the line multiple having the directory number designation 04. In any case where more than one toll trunk is provided, it is necessary to make provisions for automatic trunk selection. To this end there is associated with the finder-connector links of the C. A. X I0 a set of trunk preselect relays 50 which are of the character disclosed in Figs. 11 and 13 of the abovementioned copending application Serial No. 189,-

121 now U. S. Patent 2,252,309, granted August 12, 1941. Briefly described, these relays are so arranged that when the first trunk of a group, such, for example, as the trunk 0|, becomes busy, it is marked as busy in all of the finder and connector switches, and the second trunk, namely, the trunk 02, is immediately allotted for use. If the second trunk is also busy at the time the first trunk is taken for use, the third trunk, if idle, is allotted for use. Further, the arrangement of this relay group is such that the trunk having the lowest directory number designation is assigned for use in preference to the other trunks. so long as it is not occupied with a call.

The operation of the trunk circuits 35, 4|), etc., individually terminating the toll and free service trunks, in handling calls incoming to the C. A. X I0, may best be understood by considering the trunk circuit 40 as being used to terminate the toll trunk 02. In such case, the conductors C2 I5,

C2|6, C2I'| and C2I8 are disconnected from the terminals |68, |09, II'| and II 8, respectively, the talking conductors of the toll trunk |32 are connected to the terminals .|28 and lili), and the terminals II'| and IIB are strapped or otherwise conductively connected. With this wiring arrangement, if one of the operators attending the switchboard 6 inserts the calling plug of one of her cord circuits in the jack terminating the toll trunk U2, a direct current path is bridged across the talking conductors of this trunk to complete a circuit including the conductors CI I5 and CI I6, and the contacts |2| and |25 for energizing the line relay Rim). In operating7 the relay RII!! closes its contacts I I I to prepare a locking circuit for the lockout relay R509, and moves its contacts I|2 out of engagement to open apoint in the operating circuit for the supervisory relay RISO, At its contacts H3, the relay RIIG completes an obvious path for impressing ground potential upon the group select lead CIM. At its contacts I I4, the relay RI I connects the unit select lead CIB? through the contacts to the start lead C208. When the group select lead CIBG is grounded, and the leads CID? and C228 are connected together, the auxiliary relays of the common equipment 213 operate to cause the operation of the corresponding relays in the finder switch of the assigned link. Assuming that the link I5 is assigned to handle the call,

the tenth group relay and the second unit relay of the finder switch operate to extend a connection from the trunk section |59 to the connector portion of the link. Incident to the operation of the relay equipment embodied in the f finder switch 25, a circuit is completed for energizing the line relay of the connector switch 3Q, whereby the line, hold and impulse-correcting relays of this connector switch are caused to operate. mentarily to impress ground potential upon the conductor CIE!! and to impress ground potential upon the control conductor Ci52 for the duration of the call. When the control Aconductor C!.52 is grounded, the trunk preselect relays 553 operate to mark the trunk 02 against seizure in all of the link connector switches. When the positive talking conductor Cl! is grounded, a circuit including the contacts |32 and i213 is coinpleted for energizing the upper winding of the cut-off relay RIZG. The relay R522 now operates and locks to ground over a path including the contacts |23 and |35, the strapped terminals EI? and IIB, and the grounded conductor CI52. After this locking circuit is completed, the relay RI20 opens its operating circuit at the contacts |24. At its contacts |26, the relay R422 completes an obvious circuit for energizing the slowacting lockout relay RIii, At its contacts |21, the relay RIZU opens another point in the oper- These relays, in operating, function moating circuit for the supervisory relay RI30. At

its contacts |2| and |25, the relay Rl2ll opens two points in the above-traced operating circuit for the line relay RIIiI and, in so doing, clearsV the trunk G2 of the impedance represented by the windings of theA line relay. At its contacts |22, the relay RIZ extends the calling loop through the contacts |32 and |37, and the contacts of the operated relays in the finder switch 25 to the connector portion of the link I5, thus establishing a pulsing circuit for the line relay of the connector switch 3l).

The line relay RI I0, upon restoring, closes its contacts II2 to reprepare the operating circuit for the supervisory relay RI3S, and opens its contacts I I3 to disconnect the group select lead CIUB from ground. At its contacts II I, the relay RI I0 opens a point in the locking circuit for the lockout relay Rlilil. At its contacts IIll, the relay RI Il) disconnects the units select lead CIIl'l from the start lead C298. The lockout relay Rlll, upon operating, prepares its locking circuit at the contacts IBI, and closes its contacts |02 to prepare another path for impressing ground potential upon the control conductor CI52. At its contacts |93, the relay RIM opens another point in the operating circuit for the supervisory relay RIBB. At its contacts |04, the relay RIDE) opens another point in the path for grounding the group select lead Clil. At its contacts H35y the relay Rieti opens a further point in the path for connecting the units select lead Cl'l to the start lead C298.

When the units select lead CIM is disconnected from the start lead C208, and the group select lead CIli is disconnected from ground, the operated auxiliary relays embodied in the common equipment 2B are deenergized and restore, Incident to the operation of the relay equipment embodied in the link I5, the link distributor relays forming a part of the common equipment 20 are caused to operate to select another idle link, and the link I5 is marked against seizure. Thus, the common equipment 20 is freed for use in handling another call which may be waiting or which may be subsequently initiated.

Following the extension of the connection to the connector portion of the link I5 in the manner explained above, the operator handling the call at the operators switchboard 6 in the central exchange 5, may extend the connection to the desired line, and cause ringing current of the frequency or code designating the desired substation to be projected over this line by dialing a four digit directory number. The rst digit is utilized to determine the type of ringing to be employed in signaling over the called line, i. e., bridged or divided ringing and partially to select the ringing code or frequency of the ringing current. The second digit is utilized for the purpose of causing the operation of the connector group relay which terminates the group of ten lines including the called line. Thus, if the substation A, served by the line II, is called, the dialing of the second digit will result in the operation of the first group relay of the connector switch 30. The third digit dialed at the calling operatcrs position 6 in the manual exchange 5 is utilized for the purpose of causing the operation of the connector unit relays which correspond to the particular desired line. In the case under consideration, the first unit relay of the connector switch 3G will be operated in response to the dialing of the third digit. The fourth digit dialed is used to complete the selection of the particular 'code or -frequency of the ringing current to be projected over the selected line II. Immediately after the called line II is selected it is tested to determine the idle or busy condition thereof. In the event the line is busy, the usual busy tone signal is transmitted over the trunk 02 to inform the calling operator that the desired connection cannot be obtained, and the ringing circuits are held open to prevent the transmission of ringing current over the selected line. AOn the other hand, if the called line is idle, ringing current of the selected code or frequency i-s projected thereover for the purpose of energizing f vided at certain of the other substations served by this line but the coded character of the signals produced indicates that only the substation A is being called. The desired conversational circuit is established when the call is answered at the called substation A. In response to this operation, the back-bridge relay embodied in the connector switch 3i) operates to reverse the direction of current flow over the conductors of the trunk 92 in the usual manner. This current reversal causes the operation of a polarized supervisory relay embodied in the trunk circuit terminating the toll trunk 02 at the operators switchboard 6, whereby an oit-hook supervisory signal is produced at the calling operators position of this switchboard, indicating that the call has been answered. The back-bridge relay of the connector switch 30 also follows the connection release and the call answering operations which may subsequently be performed by manipulation of the switchhook provided at the substation A, so that the usual` flashing recall and disconnect signals are produced by the supervisory lamp associated with the connection at the calling operators position in the central exchange 5. Thus, the operator handling the call may be informed that she is being recalled by the calledparty and is also informed when the connection is released at the called substation. The release of `the connection is entirely under the control of the operator handling the callv at the switchboard 6 in the central exchange 5. More specifically, when a disconnect or on-hook supervisory signal is transmitted to the calling operator, indicating that the connection has been releasedl at the called substation, the operator may initiate the release of the Iswitch train by withdrawing the calling plug of the cord circuit included in the connection from the jack termiu nating the trunk 02. In response to this operation, the loop circuit extending from the calling operators position to the connector switch 3D is interrupted to cause the deenergization and release of the line and hold relays embodied in this switch. When the hold relay of the connector switch 3Q restores, the finder and connector switches 25 and 30, respectively, andthe line circuit I2 are restored to normal in the manner explained in detail in the above-mentioned copending application. During the release of the link I5, the link is marked as idle in the distributor relays of the common equipment 2li, and ground potential is removed from the control conductor CI 52 of the trunk section M9. When this control conductor is disconnected from ground, the cutoff relay RIZ() is deenergized and restores to open,

fat its contactsll26, the operating circuit for thev i. lockout relay RfIlJII.- Following therelease of fthe lockout relay R100, vthe trunk'circuit 40 is fully energized and restores.

f restored to normal Aand is marked as idle in the trunk preselect relaygroup 50.

As indicated in the introductory portion of the specication, provisions are kmade in the trunk circuit 4U for locking this-circuit and the associated trunk 02, if used, out of servicev when a permanent calling conditionoccasioned by a fault or the like is present on this trunk. Under these circumstances, the link I5, for example, may be seized in the manner explained above, but, following seizure thereof, no dial' pulses are transmitted to the connector switch 30. When the link I5 is seized, a timing ldevice common to the links of the exchange is conditioned forcibly to release the link after the expiration' of a predetermined time interval in Ithe event a talking circuit is not established by Way of :the link before the predetermined time interval expires. Should this contingency be met', the control equipment of the link I5, in releasing,` disconnects the control conductor CI 52 from ground, whereby the operated cut-oi relay-RIZ!) is de- This relay, in releasing, reconnects the windings of the line relay RIIU to the conductors of the trunk 02 upon which the calling condition is still present. Accordingly, the line relay RI I0 reoperates to complete, at its contacts III, the prepared locking circuit for the still operated lockout relay RI I!J. Thus, the line and lockout relays R'I I0 and Rll), respectively, are locked energized. With the vrelay Ri operated, and the cut-off` relay R'I2 in its restored position, an auxiliary path,v including the contacts |32 and I2'I is completed-for maintaining ground potential upon the control conductor CI52; whereby the trunk circuitfsdll is guarded against seizure by one of the connector switches provided in the C. A. X; With the lockout relay RIQO operated, the start circuits described above, and including the group select lead CIBG, the units select lead CI'I and the start lead CIIIS, are held open to prevent the finder portion of an assigned link from operating to seize the trunk section M9. It will be `obvious that the two relays RIIU and VRlll remain in their respective operated positions until the permanent calling condition present on `the toll trunk 02 is cleared. When the fault responsible for this condition is corrected, the line relay RI I0 is deenergized and restores to cause the release of the lockout relay Rl in an obvious manner. With these two relays restored, the trunk circuit 40 is fully released, and this circuit is `marked 5as idle in the relays of the trunk preseiect group The manner in which the trunk circuit- 45 operates in the extension of a call from the' operators switchboard 6 by Way of the' trunk 9| and the link I5, for example, to the subscriberA line II, for example, is substantially similar to the mode of operation of the trunk circuit' SE1 as described above. In this regard it will be understood from the preceding explanation that 'the trunk circuit 45 is in all cases used in conjunction with the trunk circuit 4@ or the equivalent thereof, and terminates a combination toll'and free service trunk. More specifically, if one of the operators having access to the trunk 9| at the operators switchboard 6 inserts the calling plug of one of her cord circuits in the jack terminating the conductors of this trunk to establish a direct current path between the talking conductors of the trunk, the line relay R2 I is energized and operates. Upon operating, the relay R2|0 closes its contacts 2|3 to impress ground potential upon the group select lead C200, and closes its contacts 2|4 to connect the units select lead C201 to the start lead C208. In response to these operations, the finder portion of the assigned link, such, for example, as the link l5, is caused to operate to seize the trunk circuit 45 over the trunk section |56 in the manner described above. 'I'he line relay R2|0, in operating, also opens, at its contacts 2|2, a point in the operating circuit for the supervisory relay R230. At its contacts 2||, the relay R2|0 completes an obvious circuit for energizing the guard control relay R250. The relay R250, upon operating, closes its contacts 252 to complete an obvious path for impressing ground potential upon the connected control conductors C2|8 and Ci52, whereby the trunk circuit 40 is marked against seizure over the trunk section |49 by one of the connector switches provided in the C. A. X I0. At its contacts 25|, the relay R250 opens a point in the operating circuit for the switching relay R240.

When the finder switch 25 of the assigned link |5 operates to extend the connection from the trunk section |50 to the connector switch 30, the control relays of the connector switch operate momentarily to impress ground potential upon the positive talking conductor C|53, thereby to cause the energization of the cut-off relay R220 over a circuit including this talking conductor and the

contacts

222 and 224. Coincident, with the energization of the relay R220, ground potential is impressed upon the control conductor CI 54 by the control relays of the connector switch 30, whereby the trunk circuit 45 is marked against seizure by another of the connector switches. The cut-off relay R220, upon operating, locks to the grounded control conductor C| 55 over a path including the contacts 223, 236 and 240. relay R220 opens its contacts 224 to interrupt its operating circuit. At its contacts 22| and 225, the relay R220 disconnects the windings of the line relay R2 I0 from the conductors of the trunk 9|. At its contacts 222, the relay R220 extends the calling loop circuit to the connector portion of the link. At its contacts 220, the relay R220 completes an obvious operating circuit for the slow-acting lockout relay R200. At its contacts 221, the relay R220 opens a point in the operating circuit for the supervisory relay R230. 'Ihe line relay R2l0, upon restoring in response to operation of the cut-off relay R220, opens its contacts 2|3 and 2|4 included in the start circuits extending to the common equipment 20, whereby the operated relays of this equipment are deenergized and restore to condition the common equipment for use in handling another call. At its contacts 2|2, the relay R2|0 prepares the operating circuit for the relay R230. The lockout relay R200, upon operating, opens its

contacts

204 and 205 further to interrupt the start circuits extending to the common equipment 20. At its contacts 203, the relay R200 opens another point in the operating circuit for the supervisory relay R230. At its contacts 202, the relay R200 prepares an alternative path for impressing ground potential upon the control conductor C|55. At its contacts 20|, the relay R200 prepares a locking circuit for itself, and completes a locking circuit for the guard control relay R250, the latter circuit extending from ground by way of the

contacts

226 and 20|, and the winding of R250 to battery.

After this locking circuit is completed, the

After the connection has been extended through the trunk circuit 45 to the connector switch 30, it may be forwarded to the substation A, for example, served by the line in the exact manner described above with reference to the call routed through the trunk circuit 40. Supervision of the call is under the control of the backbridge relay embodied in the connector switch 30, this relay being arranged to follow the connection release and call answering operations performed at the called substation A to transmit corresponding supervisory signals to the position ci the operator handling the call at the operators switchboard 6 in the central exchange 5. The release of the connection is also accomplished in a manner similar to that described above with reference to the trunk circuit 40. Thus, when the operator receives a disconnect signal and withdraws the calling plug of the cord circuit included in the connection from the plug terminating the conductors of the trunk 9|, the operated relays of the link |5 are caused to rele-ase, the line circuit I2 is released, and the link |5 is marked as idle in the distributor relays of the common equipment 20. During the release of the link l5, ground potential is removed from the control conductor C|55 to cause the deenergization and release of the cut-01T relay R220. 'Ihis relay, upon restoring, opens the operating circuit for the lockout relay R200, and the locking circuit for the guard control relay R250. When the two last-mentioned relays restore, the trunk circuit 45 is fully released, and both this circuit and the trunk circuit 40 are marked as idle.

The manner in which the four relays R220, R2| 0, R200 and R250 cooperate to lock the trunk 9| and the two

trunk circuits

40 and 45 out of service when a permanent calling condition is present on the trunk 9| is substantially similar to the mode of operation of the relays R|20, Rl I0 and R|00 to accomplish this end, and will be clearly apparent from Ithe foregoing explanation of the operation of the three latter relays to lock to the trunk 02 and the trunk circuit 40 out of service when a permanent calling condition exists on the trunk 02.

As indicated above, the toll trunks 0| and 02 may be used for routing toll calls from the substations served by the C. A. X |0 to the toll operators position provided at the switchboard 6 in the central exchange 5. If desired, provisions may be made whereby these toll trunks are use-d in handling C. A. X subscriber calls to the central exchange subscribers when the calls are initiated at substations serving subscribers who pay only for local exchange service and are to be charged for central office calls. In such case, the other C. A. X subscribers, namely, those paying a higher rate for both local and central exchange service, are permitted to have access to the free service trunks and to the combination toll and free service trunk 9|.

Assuming that a call initiated at the substation A is to be routed to the toll operators position at the switchboard 6 and, further, that the link I5 is assigned to the use of the call, the calling subscriber, after initiating the call in the usual manner to cause the seizure of the line by the finder switch 25, dials the four digits necessary to cause the connector switch 30 to seize the trunk section |49 terminating at the contact set having the 02 directory number designation. It will be understood that if the rst trunk 0| is idle, the trunk circuit 35 is seized, and the trunk 0| is utilized in forwarding the On the other hand, if the toll trunkthe call is initiated, the trunk preselectY relays 50 1 f occupy a position such that the connector switch 30 automatically seizes the trunk circuit 40. Incident to the seizure` of this trunk circuit, the control equipment of the connector switch 30 functions to complete a loop circuit between the connector switch 30 and the trunk circuit 40, and to impress ground potential upon the control conductor CI52.v When the conductor CI52 is connected to ground, the relay RIB is energized over a circuit including this conductor, the strapped terminals I|8 and II'I, and the contacts |21, |03 and I|2. Upon operating, the relay R|3IJ locks to the grounded control conductor CI52 over a path including its contacts |36, "and opens, at its contacts |35, a point in the above-traced locking circuit for the cut-off relayV RI20.'l `At its contacts |33, the relay RI3|J completes an obvious circuit for energizing the lower winding of the cut-off relay RI20. The relay RI2Il, upon operating, completes the operating circuit for the lockout relay Rl, disconnects the windings of the line relay RIIO from-the conductors of the trunk 02, and connects the trunk conductor CI I to the talking conductor CI5I of the trunk section |49.` In this regard it will be apparent that when the relay RISIl operates, it prepares, at its contacts |3I, |32, |34 and |31, paths for reversely connecting the conductors Cl |5 and CIIISY to the conductors Cl5 and CI5I, whereby an orf-hook supervisory signal is produced at the toll operators position of the switchboard 6 when the call is answered.

'Ihe lockout relay RIGD, upon operating, opens its contacts |03 to interrupt the above-traced operating circuit for the relay R|30. At its contacts |04 and |05, the relay RIDD further opens the start circuits extending to the common equipment 20. At its contacts IGI, the relay R| 00 prepares its locking circuit, and, at its contacts |02, prepares one of the previously traced paths for impressing ground potential upon the control conductor CI52. Following the operation of the relay RIIJU, no further operation of the relay equipment embodied in the trunk circuit 40 occurs, until the connection is released at the calling substation A. After the relay RI operates reversely to connect the talking conductors of the trunk 02 to the talking conductors of the trung section |49, the ringing control equipment converse with the calling subscriber at the sub-J station A to ascertain the identity of the desired substation or party, and may forward the'connection to the desired substation in a manner well understood in the art.

The release of the connection extending between the substation A and the toll operators position at the switchboard 6, is entirely under the control of the calling subscriber. Thus, when the connectionis released at the substation A, the line circuit I2 and the link lI5 are caused.V

to release. in the manner briey vdescribed labove l 'l and pointedout withlparticularity in the previ-1"*- ously referred to copending. application; During-Hy the-release of the link |5,groundpotential-is rel moved from the control conductor CI52 to cause I- the deenergizationof the relay-RI30.f1 Thisrelay,

upon restoring its contactsy |3I', |32, |34 and-|31- to normal, reversesthe directionof current flow over the conductors -of the trunk v 02,3 whereby: the r usual disconnect signal is producedfby ythesuper- A visoryfsignal lamp associated with this vtrunk-at the toll operators position of therswitchboardl-G. f-

In releasing, the relay RI30 also opens the operf ating circuit for? the relay RI 23.5 The relay.' RI20 `Isf- 'now restores lto bridgethe windings of the line: relay RI I0 across the conductors of the trunk.|l2.i1

In the event the connection hasnot beencleared out at the toll operatorsposition-of ythe switchboard 6 prior:` to the release of the connection.: at the substation A, the `conductors of the trunk" 02 areconnectedltogether overA a direct currenti.l

path extending through the operators `cord lcir-1'` cuit in use at the toll operators position. 1Ac' cordingly, the line relay RI II) is energized when its windings .arebridged across theconductors of thetrunk 02,"and operates to complete the= f locking circuit for the lockout relay RIOI'L The' `v two relays RI I0 and R-Il are thus held operated until theconnection is cleared out at the toll operators position of the switchboard 6.

With

these two relays operated and :the -two relays R|20 and RISI) restored, the previously traced path including the contacts |02 and |21 is completed for impressing ground potential uponthe f Vcontrol conductor CI52, thereby to guard the'.l

hand, the connection is cleared out at the tollI operators position of the switchboard 6 prior kto l its release at the calling substation A, the line relay RI I0 is not energized in response to the -re lease of the cut-oi relay `IRIZI).` Accordingly;

the three relays R|30,.R|20 andvRI sequen- Y tiallyrestore in the order named and .in a manner clearly apparent from the Iabove explanation when the control equipment of the link I5 functions to disconnect the control conductor CI52 from ground.

Assuming that the trunk circuit 40 is used in conjunction with the trunk circuit 45 to terminate the combination toll and freeservice trunk 9I,the relay operations -which occur incident to the extension of the'above-described call to the trunk circuit 40, are substantially the same as describedabove. howeventhe switching relay R240 is energized lin parallel with the supervisory relay R|3 when i With the latter arrangement,

the control equipment of the connectorv switchv 30 operates to impress ground potential upon the control conductor CI52. vThe circuit for energizing these two relays in parallel extends by way of the grounded conductor CI52 and the contacts 25| to theconductor C2|1 where it divides, one' branch extending through the winding of R240 to battery, and the other branch extending by way of the contacts |21, |03 and |I2, and the winding of RISO to battery. The relay R240, upon operating, opens its

contacts

242 and 244 to disconnect the conductors of the trunk 9| frornthe .trunk circuit 45, and closes its contacts 24| and L,

243 to connect these conductors to the conductors C2|5 and C2|5 which extend to the trunk circuit 40. Accordingly, the ringing current which is transmitted by the connector switch 30 over the trunk section |09 following seizure of the trunk circuit 00, is projected over the trunk 9| to energize the incoming call signal device provided in association with this trunk at the op eratcrs switchboard in the central exchange 5. At its contacts 242, the relay R240 opens a point in the operating circuit for the relay R230.

At its contacts 265, the relay R220 completes an obvious path for impressing ground potential upon the control conductor C|55, thereby to guard the trunk circuit 45 against seizure by the connector switches of the C. A. X l0. In handling a call of this character, the other relays of the trunk circuit 40, namely, the relays R|00, Rl l0 and R|20 operate in the exact manner described above with reference to the call routed to the toll operators position of the switchboard over the trunk 02. It will be observed that the switching relay R200 is held energized over a circuit including the connected control conductors C2i 1, C2|8 and C|52 until the connection is cleared out at both the calling substation A and the position of the operator handling the call at the switchboard 6 in the central exchange 5.

Since the trunk 0| is primarily provided for free service calls tothe central exchange subscribers, it will normally be seized by the connector switches of the C. A. X l0 through the trunk circuit 45. Assuming, for example, that the above-described call originating at the substation A is routed through the finder-connector link l to th-e trunk circuit 45 at a time when the trunk 0| is idle, the connector switch 30, upon operating to its ringing position, impresses ground potential upon the control conductor Ci 55 of the trunk section |56 to energize the supervisory relay R230 over a circuit including this control conductor and the

contacts

246, 22T, 203 and 212. Upon operating, the relay R230 completes an obvious circuit for energizing the lower winding of the cut-off relay R220, and locks to the grounded control conductor Ci55 over a path including its contacts 231 and the contacts 24%. At the contacts 222, 23|, 232, 23d and 235, the two relays R220 and R230, in operating, reversely connect the conductors of the trunk 9| to the talking conductors C153 and C|54 of the trunk section |56, whereby the proper ofi-hook supervisory signal is produced by the signal lamp associated with the trunk 9i after the call is answered at the operators position of the switchboard 6 at which the trunk 0| is terminated. In operating, the relay R220 also opens its contacts 22| and 225 to disconnect the windings of the line relay R2|0 from the conductors of the trunk 0|. At its contacts 221, the relay R220 opens a point in the above-traced operating circuit for the supervisory relay R230. At its contacts 222, the relay R220 completes an obvious circuit for energizing the lockout relay R200. The relay R200, upon operating, closes its contacts 20| to prepare the previously described locking circuit for itself, and to complete the previously traced operating circuit for the guard control relay R250. At its contacts 202, the relay R200 prepares an alternative path for impressing ground potential upon the control conductor C|55. At its contacts 203, the relay R200 opens another point in the operating circuit for the supervisory relay R230. At its

contacts

204 and 205, the relay R200 opens further points in the start circuits individual to the trunk circuit and extending to the common equipment 20. The guard control relay R250, upon operating, closes its 'contacts 252 to impress ground potential upon the control conductor C|52 and thus guard the trunk circuit 40 against seizure for the duration of the call. At its contacts 25|, the relay R250 opens a point in the previously traced circuit for energizing the relays R240 and R|30 in parallel.

After the call, as routed through the trunk circuit 45 and over the trunk 4| to the operators switchboard 6, is answered at the position of the operator where this trunk is terminated, the answering operator may converse with the calling subscriber and ascertain the identity of the party desired or the directory number of the substation desired, and may extend the connection to the desired substation in a manner well understood in the art.

The release of the finder-connector link I5 is in this case also entirely under the control of the calling subscriber at the substation A. During the release of this link, which occurs when the calling subscriber restores the receiver provided at the substation A to its supporting hook or cradle, the control conductor C 55 is disconnected from ground in the connector switch 30, thereby to deenergize the supervisory relay R230. Upon restoring, the relay R230, at its contacts 23|, 232, 234 and 235 reverses the direction of current flow over the trunk 3|, whereby a disconnect signal is produced at the position of the operator handling the call in the central exchange 5. Upon restoring, the relay R230 also opens its contacts 233 to deenergize the cut-off relay R220. In the event the connection has not previously been cleared out at the position of the operator handling the call in the central exchange 5, the cutoff relay R220, upon restoring, completes the operating circuit for the line relay R2 i0. The relay RZiii, upon operating, closes its contacts 2|| to complete the locking circuits for the guard control relay R250 and the lockout relay R200. Thus, the three relays R2|0, R200 and R250 are held operated until the connection is cleared out at the position of the operator handling the call in the central exchange 5. With the lockout relay R200 operated, and the cut-off relay R220 in its restored position, the control conductor C|55 is connected to ground over a path including the

contacts

200, 221 and 202. Thus, the trunk circuit 5 is guarded against seizure by the connector switches of the C. A. X I0. With the guard control relay R250 operated, ground potential is also impressed upon the control conductor C|52 over a path including the contacts 252 to guard the trunk circuit 40 against seizure. When the connection is cleared out at the position of the operator handling the call in the central exchange 5, the line relay R2i0 is deenergized and restores in the manner previously explained. This relay, upon restoring, causes the sequential release of the relays R250 and R220 in an obvious manner. Thus, the trunk circuit 45 is fully restored to normal, and the two

trunk circuits

40 and 45 are marked as idle. In the event the connection is cleared out at the position of the operator handling the call in the central exchange 5 prior to the release of the connection at the calling substation A, the relays R230, R220, R250 and R200 are caused sequentially to restore in the order named and in a manner clearly apparent from the above explanation. iihen these relays restore, the trunk circuit 45 is fully released and both'thisV circuitfand the trunk circuit i4!) are marked as idle.

While there has been described whatfis at pres-v ent considered to be the preferred-.embodiment of the invention, it will befunderstood that various-modications may be made'` therein,l and vit is contemplated to cover in the appended claims all-such modifications as fall within the trueconnected `and being arranged in sets for subscriber line termination, a pairof trunk circuits respectively including trunk sections terminated at sets of said outlet contacts having different` directory number designations, a second exchange, a trunk extending from said second exchange to said trunk circuits, and means controllable through said connector switches for selectively connecting said trunk to one or the other of said trunk circuits.

2. In a telephone system, an exchange includingl automatic finder and connector switches for setting up connections between the lines of the system,- the corresponding outlet contacts of said iinder and connector switches being conductively connected and being arranged in sets for subscriber line termination, a pair of trunk circuits respectively including trunk sections terminated at =-s'ets of said outlet contacts having different director number designations, a second exchange, a trunk extending from said second exchange` to said trunk circuits, and means comprising a relay controlled over a circuit including one of the contacts of one of said pair of contact sets for selectively connecting said trunk to one or the other of said trunk circuits.

3. In a telephone system, an exchange including vautomatic nder and connector switches for setting up connections between the lines of the system, the corresponding outlet contacts of said finder and connector switches being conductively connected and being arranged in sets for subscriber line termination, a pairoi trunk circuits respectively including trunk sections terminated at -sets ofsaid outlet contacts having diierent directory number designations, a second exchange, a trunk normally connected to one of said trunk circuits and extending to said second exchange, and switching means operative to disconnect said trunk from said one trunk circuit and to connect said trunk to the other of said tru'nk'circuits.

4. In a telephone system, an exchange including automatic finder and connector switches for setting up connections between the lines of the system, the corresponding' outlet contacts of said nderand connector switches being eonductively connected and being arranged in sets for subscriberline termination, a pair of trunk circuits respectively including trunk sections terminated at sets of said outlet contacts having different directory number designations, a second exchange, a trunk normally connected to one of said trunk circuits and extending to said second exchange, and means comprising a relay controlled over a circuit including one of the contacts of the contact set terminating the trunk section of the other of said trunk circuits for disconnecting said trunk from said one trunk circuit and .for connectingfsaid trunk to the other of said trunk circuits.

5. In a telephone system, an exchange. including automatic finder and connector switches for set ting up connections between the lines or the syscircuits, means controlled over the control conductor of one of said trunk sections for selectively connecting said trunk to said trunk circuits, and means controlled over the control conductors of said trunk sections for marking both of said trunkcircuits busy when either trunk circuit is occupiedw vl with a call.l

6. In -a telephone system, an exchange including 1;.' :automatic finder and connectorswitches for setting up connections between the lines of the system, the corresponding outlet 'contacts of said finder and connector switches being conductively connected and said contacts being arranged in a control contact, a pair of trunk circuits respectively including trunk sections terminated at setswv of said outlet contacts having different directory 1 number designations, each of said trunk sectionsY including 'a pair of talking conductors and a control conductor, a second exchange, a trunk extending from said second exchange to said trunk circuits, means .controlled over the control conductor of one of said trunk sections for selectivelyz f'connecting said trunk to said trunk circuits, and

means responsive to the seizure or either of saidf trunk circuits by one of said connector switches for reversely connecting the talking conductors-ffof said trunk to the talking vconductors of the v' trunk section individual to the seizedtrunk cir-l l cuit.

'7. In a telephone system, an exchange including automatic finder and connector switches for setting up connections between the lines of the sysif litem, the corresponding outlet contacts of lsaid nder and connector switches being conductively connected and said lcontacts being arranged in sets each including a pair of talking contacts and a control contact, a ipair of trunk circuits respec-' ,tively including trunk sections terminated at sets of said outlet contacts having diierent directory number designations, each of said trunk sections f including a pair of talking conductors and a'control conductor, a second exchange, a trunk extend-l A .ling fromisaid second exchange to said trunk cir-.-

cuits, means controlled over' the control conductor o" of one orf said trunk sections for selectively con-I' y necting said trunk to said trunk circuits, "and means individual to said trunk circuits and lcon-mn trolled over the control conductors of the associated trunk sections for reversely connecting the talking conductors of said trunk to the talkingv`l`- conductors off the respective associated trunk sections.

8. In a telephone system, an exchange including automatic nder yand connector switches for setting up connections betweenlthe lines of the systern, the corresponding outlet contacts of said" r nder and connector switches being conductivelyf f lconnected and' said contacts being arranged in sets each including a pair of talking contacts and .f

sets each including a pair of talking contacts and a control contact, a pair of trunk circuits respectively including trunk sections terminated at sets of said outlet contacts having dierent directory number designations, each of said trunk sections including a pair of talking conductors and a control conductor, a second exchange, a trunk extending from said second exchange to said trunk circuits, means icontrolled over the control conductor of one of said trunk sections for selectively connecting said trunk to said trunk circuits, means controlled over the control conductors of said trunk sections for marking both of said trunk circuits busy when either trunk circuit is occupied with a call, and means responsive to the seizure of either of said trunk circuits by one of said connector switches for reversely connecting the talking yconductors of said trunk to the talking conductors of the trunk section individual to the seized trunk circuit.

9. In la telephone system, an exchange including automatic finder and connector switches for setting up connections between the lines of the system, the corresponding outlet contacts of said nder and connector switches being conductively connected and said contacts being arranged in sets each including a pair of talking contacts and a control contact, a pair of trunk circuits respectively including trunk sections terminated at sets of said outlet :contacts having different directory number designations, each of said trunk sections including a pair of talking conductors and a control conductor, a second exchange, a trunk extending rom said second exchange to said trunk circuits, means controlled over the control conductor of one of said trunk sections for selectively .connecting said trunk to said trunk circuits, means controlled over the control conductors of said trunk sections for marking both of said trunk circuits busy when either trunk circuit is occupied with a call, and means individual to said trunk circuits and controlled over the control conductors of the associated trunk sections for reversely connecting the talking conductors of said trunk to the talking conductors of the respective associated trunk sections.

10. In a telephone system, an exchange including automatic finder and connector switches for setting up connections between the lines of the system, the outlet contacts of said switches being arranged in sets each including a control contact and a pair of talking contacts, multiple conductors providing unbroken connections between the corresponding talking and control contacts of said contact sets, a trunk circuit comprising a trunk section including talking and control conductors terminating at the control and talking multiple conductors interconnecting the contacts of the contact sets having a predetermined directory number designation, a second exchange, a trunk interconnecting said trunk circuit and .said second exchange, and means in said trunk circuit controllable over said trunk section for transmitting supervisory signals over said trunk.

11. In a telephone system, an exchange including automatic finder and connector switches for setting up connections between the lines of the system, the outlet contacts of said switches being arranged in sets each including a control contact and a pair of talking contacts, multiple ccnductors providing unbroken connections between the corresponding talking and control contacts of said contact sets, a trunk circuit comprising a trunk section including talking and control conductors terminating at the control and talking multiple conductors interconnecting the contacts of the contact sets having a predetermined directory number designation, a second exchange, a trunk interconnecting said trunk circuit and said second exchange, and means comprising a supervisory relay controllable over the control con- 7Vductor of said trunk section for transmitting supervisory signals over said trunk.

12. In a telephone system, an exchange including automatic nder and connector switches for setting up connections between the lines oi the system, the outlet contacts of said switches being arranged in sets each including a control contact and a pair of talking contacts, multiple conductors providing unbroken connections between the corresponding talking and control contacts of said contact sets, a trunk circuit comprising a trunk section including talking and control conductors terminating at the control and talking multiple conductors interconnecting the contacts of the contact sets having a predetermined directory number designation, a second exchange, a trunk interconnecting said trunk circuit and said second exchange, and means comprising coacting line and lockout relays included in said trunk circuit for locking said trunk and said trunk circuit out of service when a permanent calling condition exists on said trunk.

13. In a telephone system, an exchange including a plurality of nder-connector links for setting up connections between the lines of the system, equipment common to said links and including finder start circuits, the outlet contacts of the finder and connector portions of said links being arranged in sets each including a control contact and a pair of talking contacts for subscriber line termination, multiple conductors providing unbroken connections between the corresponding talking and control contacts of said contact sets, a trunk circuit comprising a trunk section including` talking and control conductors terminating at the control and talking multiple conductors interconnecting the contacts of the contact sets having a predetermined directory number designation, a trunk extending to said trunk circuit, and means comprising line and cut-0E relays included in said trunk circuit and respectively controlled over said trunk and said trunk section for controlling said inder start circuits.

14. In a telephone system, an exchange including a plurality of lnder-connector links for setting up connections between the lines of the system, equipment common to said links and including finder start circuits, the outlet contacts of the Iinder and connector portions of said links being arranged in sets each including a control contact and a pair of talking contacts for subscriber line termination, multiple conductors providing unbroken connections between the corresponding talking and control contacts of said contact sets, a trunk circuit comprising a trunk section including talking and control conductors terminating at the control and talking multiple conductors interconnecting the contacts of the contact sets having a predetermined directory number designation, a trunk extending to said trunk circuit, means comprising line and cut-off relays included in said trunk circuit and respectively controlled over said trunk and said trunk section for controlling said finder start circuits, and meansr comprising a lockout relay coacting with said line relay for locking said trunk circuit and said trunk out of service when a permanent calling condition exists on said trunk.

terminating at lthe control and talking multiple conductors interconnecting the contacts .of the Contact 'sets having a predetermined directory number designation, a trunk extending to s'aid trunk circuit, means comprising line and .cut-'onf relays included in said trunk circuit and respeta tively controlled over said trunk and said trunk section for controlling said finder start circuits, and means comprising a supervisory relay 'con'- trollable over said trunk section for transmitting supervisory signals over said trunk.

JOHN H. VOSS.