US2037221A - Telephone system - Google Patents

Description

April 14, 1935.

j H. e. EVERS TELEPHONE SYSTEM Filed April 27, 1932 6 Sheets-Sheet l InuEnEr'- HEF%E. Euer'e H. G. EVERS TELEPHONE SYSTEM Filed April 27, 1932 A ril 14, 1936.

6 Sheets-Sheet 2 Inuen cr- Har E5. ELJETE;

A ril 14, 1936. H. G. EVERS TELEPHONE SYSTEM Filed April 27, 1932 6 Sheets-Sheet 3 April 14, 1936. H. G. EVERS TELEPHONE SYSTEM Filed April 27, 1932 6 Sheets-Sheet 4 Wm g @LW v Q mm April 14, 1936 H. s. EVERS TELEPHONE-SYSTEM Filed April 27, 1932 6 Sheets-Sheet 5 o 0 l o vo April 14, 1936. H, e, EVERS TELEPHONE SYSTEM Filed April 27, 1932 6 Sheets-Sheet 6 E. Euars Patented Apr. 14, 1936 T ES UNITED ST .ATENT OFFICE TELEPHONE SYSTEM Ware Application April '27-, 1932, Serial No. 607,814

35 Claims.

This invention relates to telephone systems in general and particularly to telephone systems in which connections are completed through the medium of automatic switches. The object of the invention is the provision of new and'improved circuits and apparatus for use in systems of the above type for supplying telephone service to small groups of stations.

General description Separate exchanges or central ofiices commonly known as sub or satellite ofiices are usually installed to supply telephone service to small groups of stations, when for economic or other reasons, it is impractical to connect the stations individually with the nearest main office. With the equipment heretofore available for installation in such offices, it has been found that the average cost per line of the equipment tends to increase greatly as the number of station's served by the office decrease. This increased cost is due, largely, to the necessity of installing a complete set of power equipment including, for example, ringing current and tone generators, battery charging equipment, etc., regardless of the size of the office.

Arrangements have been suggested whereby the power equipment at a main office could be made to serve a sub-office as well. So far as applicant is aware, prior systems employing this arrangement have not been entirely satisfactory due to their inability to provide service of a quality acceptable for general use. In order to have a general application a system must be able to handle more than one call at a time and prior systems of the type under consideration have not been able to do this. It is also desirable that connections be guarded against intnusioln by other subscribers and this has not been possible in prior systems as far as subscribers in the same sub-office are concerned.

The present invention is designed to eliminatethe objectionable features of the prior systems. Switching apparatus is provided at the suboffice for handling a plurality of simultaneous calls. The switching apparatus, which consists, mainly, of simple stepping switches, operates on low voltage current supplied by a storage battery at the sub-office. This storage battery is the only item of power equipment required at the sub-'oflice. Ringing current and tone'cu-rrent as well as charging current are supplied from the main office to which the sub-office is connected. The arrangement for handling simultaneous calls in a system of the above type constitutes one of the main features of the invention.

Another feature of the invention resides in the arrangement for simultaneously operating a switch in the sub-office and a switch in the main l0 o'ffice under control of impulse generating apparatus located at the main ofiice. The firstmentioned switch hunts for a calling sub-oflice line and the latter "switch identifies the line for metering and guarding purposes.

Another feature of the invention consists in the provision of a selective switch which is adapted to cooperate with either of several finder switches to complete connections between sub' office subscribers lines. This switch is adapted to be controlled indirectly by a calling subscriber through the medium'of registering and impulse sending means located at the main olfi'ce.

Another feature of the invention relates to the arrangement whereby the testing for the idle or busy condition of sub-cffice lines is carried out by equipment located at the main office. An incidental feature is the further arrangement whereby the test for an idle sub-office switch is carried out by equipment at the, main office in the case of attempted connections between two sub-office subscribers lines.

There are various other features relating to the novel circuit organizations employed in carrying out the functions of the different pieces of apparatus constituting the invention. These features and others not specifically mentioned will be described in detail hereinafter, reference being had to the accompanying drawings.

Description of drawings The accompanying drawings comprising Figs. 1 to 6, inclusive, show representative circuits of a telephone system comprising a main office and a sub office embodying the features of the invention. The system disclosed is designed to supply telephone service'to a group of ten stations and to handle two simultaneous calls. It will be appreciated, however, that this particular system is shown to merely illustrate the features of the invention and that these features may be readily applied to systems supplying telephone service to larger groups of lines and adapted to handle any reasonable number of simultaneous calls.

Referring now to the drawings, Figs. 1 and 2 show switching apparatuslocated at a sub-office. Figs. 3, 3A, 4, and 5 show apparatus located at a main office and cooperating with the apparatus shown in Figs. 1 and 2. Fig. 6 is a layout diagram showing the manner in which the various sheets of drawings are to be arranged to illustrate the inter-relationship of the various circuits.

In Fig. 1 there is shown a finder-connector switch FC which operates as a line finder for calls originating on sub-office lines and a connector for calls incoming to such lines. This switch is of the well-known rotary type whose wipers move in one direction only. A contact bank consisting of eleven contact sets is provided. Ten contact sets are assigned to the ten sub-office lines and the eleventh set serves as the normal or home position of the switch wipers. The switch terminates one of the two trunks connecting the sub-office with the main oifice. Associated with this switch is a revertive connector shown in Fig. 2 over which connections are completed to called lines which terminate in the same sub-oflice as the calling line. The connections to this latter switch are shown in the lower right-hand corner of the drawings.

Two of the ten sub-'oflice lines accessible to switch FC have been shown in Fig. 1, namely, the lines extending to stations T3 and T7. These lines terminate, respectively, in the third and seventh contact setsoi the bank of switch FC. The lines for the other substations terminate in other bank positions. Associated with each line is an individual cut-oif relay of the relay group LR shown in the upper left-hand corner of the drawings. A distributor relay group DR is common to all of the sub-office lines and controls the allotm nt of calls to the trunks and associated finder connectors.

Fig, 2 shows the revertive connector RC previously referred to. This switch is mechanically similar to switch FC and has access to the various sub-office lines in corresponding positions of its bank. The circuit connections for the finderconnector associated with the second main office trunk are shown immediately above switch RC. The finder-connector has not been shown, as it is exactly the same as the finder-connector FC and the circuit connections will be readily understood by referring to Fig. 1.

Figs. 3 and 3A show the relay equipment comprising the repeater associated with the first trunk connecting the main office and sub-ofiice. The trunk in the sub-office terminates at the left side of Fig. 3. An outgoing trunk extends from the right of Fig. 3A to a line switch LSW. Included in the repeater are a group of impulse generating relays and a group of counting relays which will be described in detail hereinafter.

The lineswitch LSWshown in Fig. 3A may be of any well-known and suitable type and has access to the regular switch train at the main ofiice. The switch trainhas not been shown as it may be of any well-known type, for example, such as that disclosed in the co-pending application of J. Wicks, Serial No. 395,882, filed April 16. 1931.

Referring now to Fig. 4, auxiliary switches ASI and A82 are associated with repeater R; These switches are of the rotary type provided with eleven position banks of which ten positions are assigned to sub-omce lines and the eleventh position serves as a normal or home position for the wipers. Both of these switches are operated under control of impulse generating relays of repeater R. Switch ASI operates in synchronism with the finder-connector FC at the sub-ofiice and serves to locate and identify a calling line. Switch A82 operates in synchronism with revertive connector RC in local calls between sub-office subscribers and in synchronism with finder-connector FC in incoming calls to the sub-ofiice.

Fig. 5 shows an auxiliary switch A83 which is associated with repeater R and the auxiliary switches shown in Fig. 4. This switch is mechanically similar to the first-mentioned auxiliary switches. The switch operates as a counting and marking switch at different stages of a'connection. For example, during the establishment of a connection it controls certain counting relays in repeater R which determine the routing of a call. After a call has been definitely identified as for a sub-ofiice subscriber for example, the switch then tests for the busy or idle condition of a revertive connector RC at the sub-ofiice over which connections between the sub-ofiice subscribers are completed in calls of this type.

In Fig. 5' there is also shown a group of line relays LRI and a portion of a contact bank accessible to local and tool connectors of the main office. The line relays are associated individually with the various sub-ofiice lines. A set of contacts in the connector bank is assigned to each sub-office line, these contacts appearing in the same order as the lines terminate in the bank of the finder-connectors at the sub-oflice.

. In the upper-left-hand corner of Fig. 5 the repeater and auxiliary switches associated with the second trunk connected in the main and sub ofiice have been shown diagrammatically. The circuits of this equipment are exactly the same as shown in Figs. 3, 3A, 4, and 5, except for the starting chain circuit. A sufficient amount of the latter circuit has been shown to permit the arrangement to be readily understood. The connection to the banks of the auxiliary switches which for convenience have been designed ZASI, 2AS2, and 2AS3 are shown in the left-hand portion of Fig. 4.

Brie 1 description The layout of the system disclosed is generally similar to that ordinarily used in sub-ofiice systems. The sub-office lines are assigned a block of ten consecutive numbers in one of the main office hundred groups. As the instant system is a five digit system, it is apparent that there will be some main ofiice lines with numbers whose first three digits are the same as corresponding digits of the sub-office numbers. Provision is, therefore, made for releasing the'branch connection set up over the main office switches only after a fourth digit has been dialled and definitely identifies the call as for a sub-oflice line. In the case of calls to main ofiice subscribers, such calls may be identified by any one or more of the first four digits. No further digits are registered after a call is definitely identified as for a main ofiice line.

In the particular system shown, the sub-oflice lines are assigned numbers 24511 to 24510. In the case of calls originating in the sub-office, the digits 2451 are registered to identify the call as for a sub-ofiice line and the final digit is then registered to identify the particular line wanted.

Main office subscribers dial the complete subofiice line number thereby setting the connector on a set of contacts assigned to the wanted line. The calling subscriber does not dial over the sub office trunk. The setting of the main ofiice connector marks the wanted line and apparatus associated with the trunk transmits impulse to set the sub-ofllce switch accordingly.

The operations involved in establishing various connections in the system under consideration will now be described briefly. Upon the initiation of a call on a sub-ofiice line, the distributing relayv equipment will operate to allot the call to one of the finder connectors, for example, finder connector FC. The impulse generating. apparatus at' the main ofiice will be started in operation and will transmit impulses to the finder connector and the auxiliary switch ASI associated with the trunk at the main ofiice. These two switches operate in synchronism until the wipers of the finder connector engage the contacts of the calling line. The impulsing'is then stopped and the repeater is prepared for the receipt of dialled impulse. A connection is now extended over the outgoing trunk and line switch LSW to an idle first selector in the main ofiice. This selector returns the dial tone to the calling subscriber to indicate that the equipment is in readiness to respond to dialling. The subscriber then dials the number of the wanted line. If the called subscriber is a main ofiice subscriber, the associated apparatus for com pleting the call in the sub-ofiice will be temporarily disabled and the impulses will be transmitted to the main ofiice switch train. The manner in which the destination of the call is identified is generally similar to that employed in the so-called switching selector repeater circuit. The auxiliary switch ASS responds to each series of impulses until a series is received which definitely indicates that the call is for a main office subscriber. Each series of impulses registered on switch A83 operates either one of the counting relays of the repeater or the switch through relay which controls the switching through of the connection to the main ofiice. In the case of a call to another sub-office subscriber, switch A83 brings about the operation of the counting relay necessary to release the main office connection and to prepare the switch in the sub-ofilce to complete the connection therein. The impulse generating relays reoperate and transmit impulses over the trunk to set switch RC in accordance with the setting of switch AS3. Switch ASZ operates in synchronism with switch RC, stops the impulsing when the proper line has been found, and proceeds to test the line for its idle or busy condition. In case the line is idle,

ringing current is sent out from repeater B. When the called subscriber answers a connection is completed between the calling and called subscriber over the local equipment at the sub-office. Upon the subscribers hanging up at the termination of a connection, the finder-connector will be restored to normal under control of the impulse generating relays. Auxiliary switches AS! and AS2 will also restore tonormal in synchronism with the sub-office switches. Auxiliary switch ASS and switch RC will restore to normal under a self-controlled circuit.

In the case of calls from a main office subscriber to a sub-ofiice subscriber, a connection will be extended over the regular main ofiice switch train including a connector to the set of bank contacts associated with the wanted suboflice line. The impulse generating relays of the repeater will function and operate finder-connector FC and auxiliary switch A82 in synchronism until the latter switch finds the contacts marked in the connector banks. This brings both switches to rest on the contacts associated with the wanted sub-oflice line which is then signalled in the usual way by ringing current from the calling connector. At the termination of the connection the switches are restored to normal as in the preceding call.

Toll calls may be extended tosub-office subscribers over a toll switch train in substantially the same manner as local calls. In this case, however, if the called line is busy, the toll connector will return either a local or toll busy tone to the operator in the usual manner. If the called line is locally busy, the operator may cause the connector to establish a temporary talking connection with the wanted subscriber. The operator may request the wanted subscriber to terminate the local connection whereupon the toll connection can be established in the well-known manner. In case no switches are available for establishing a connection to the sub-ofiice and the wanted subscriber is not engaged in one of the connections which are employing these switches, the calling toll operator will receive the busy tone in the usual manner. On attempting to cut-in on the connection, and offer the call to the sub-orifice subscriber, the operator will be given an all-trunks busy tone. Upon receiving this tone the operator may either release the connector or may wait until such time as an idle sub-ofiice switch and trunk is available whereupon the connection may be established without further operations on the part of the calling operator.

With the foregoing brief description in mind the operations of the various circuits will now be described in detail.

Initiation of a\ call by a sub-office subscriber.

. By way of illustration it will be assumed that the subscriber at station T3 initiates a call with the apparatus in normal condition as illustrated. When the, receiver is lifted at the calling station, relay it operates over a circuit which may be traced from battery, winding of the relay, contacts l9 and 32, line conductor l, through the loop at the station, line conductor 2, and contacts I! to ground. Relay i4 closes a circuit for the upper winding of two-step relay to by way of contacts 2!) and 22. Relay E5 operates in its first step and closes the contacts designated by the Roman numeral I. The other contacts of the relay are not operated at this time. Av circuit for the lower winding of the relay is completed at contactsZ-t but is ineffective to operate the relay at this time as the winding is short-circuited by the ground applied via contacts Relay l 5 also completes a circuit from ground, contacts 26 which do not open, contacts 25 which close, conductor 32, contacts 133, uppercontacts of relay vMil, winding of relay E83 to battery. Relay 558 operates, completes a locking circuit for itself at contacts I49 and completes an obwlous circuit for relay Hi3. Relay i539 disconnects the battery B from trunk conductor 55! by opening its upper contacts, by closing its lower contacts it connects ground via contacts it! and conductor 36 to relay i3. Relay 53 operates and at contacts i8, i9, etc. disconnects relay i lfrom the various subscribers lines. Relay l4 opens the original energizing circuit of relay I at contacts 20 and the relay now operates in its second step due to the removal of the short circuit from its lower winding. Relay 5%: prepares circuits for relay H3 at contacts 2| and 23 and at contacts 26 opens the original energizing circuit of relay I538. Relay 508 now remains energized over the home contact of the bank which is normally engaged by wiper I I8.

Referring now to the repeater (Figs. 3 and 3A) it will be seen that relay 393 which has been energized over a circuit extending from 48-volt battery BI, winding of the relay, upper contacts of relay 302, contacts 3H3, 345, and 34I, trunk conductor I55, upper contacts of relay I39, resistance to 12-volt battery B at the sub-office will deenergize upon the initiation of the call as above-described. Relay 393 completes a circuit from ground, contacts 623 (Fig. 3A), contacts 625, conductor 383, lower contacts of relay 303, contacts 3%, conductor 384, lower contacts of relay 635, winding of relay 6G! to battery. It may be noted at this point that relays 605, 606, and 6 .11 constitute an impulse-generating relay group. Relay 381 is slightly slow-to-operate due to the slug on its upper, or armature end and operates a short time after a circuit is closed. as just described. Relay til! completes an obvious circuit for relay 606 which energizes slowly due to the resistance shunted across its winding. Relay E55 completes an obvious circuit for relay G35 which operates after a short delay and opens the circuit of relay till. Relay 6t? accordingly releases and opens the circuit of relay 696 and that relay in turn opens the circuit of relay 605. The relays accordingly restore and the latter relay again completes a circuit for relay 6t! which reoperates to initiate the second cycle of operation. Relay 58!, it may be noted, completes a locking circuit for itself over contact 625 to insure a' complete cycle of operation regardless of the condition of the original energizing circuit after the cycle has started. Each time relay 601 energizes an impulse is transmitted from ground on the lower armature of the relay, conductor 381, lower contacts of relay 305, contacts 32'! and 322, conductor 368, winding of stepping magnet 4% (Fig. 4) to battery. The magnet accordingly energizes and steps the wipers of switch ASI ahead to the next set of contacts. As the wipers leave normal position, off-normal contacts 402 close and ground is applied over conductor 363 to operate relay 39!. Relay 3M prepares the stopping circuit by closing contacts 3I'I; connects starting conductor 383 to starting conductor 394 by way of contacts 323 and 3:3; completes a circuit for the upper winding of relay 305 at contacts 3H1; and completes a second point in the stopping circuit at its lower contacts. Relay 305 which is a two-step relay operates in its first step, closing only its contacts designated by the Roman numeral I to prepare a circuit for its two windings in series. Upon each energization of relay 636 a circuit is completed from battery, resistance M3, contacts 62, trunk conductor thence to the finder-connector at the sub-office, contacts I52! and i255, winding of relay I04 to ground. Relay 934 on each energization completes'a circuit from ground at contacts l3i, upper contacts of relay I04, winding of relay use, contacts I23, winding of stepping magnet I I 3 to battery. The sub-ofiice switch is accordingly advanced step-bystep in synchronisrn with the switch ASI at the main ofiice.

The switch continues to step under control of the impulsing relay at the main exchange and when the wipers engage the contacts in which the calling line terminates, a circuit is completed, from battery, resistance 652 (Fig. 3A) contacts BIB, conductor 3'56, contacts 3, 345, and 34!, trunk conductor ii'ai, winding of relay I95, upper contacts of relay lei, wiper In, line conductor I, through the loop at the calling station, line conductor 2, wiper I25, lower contacts of relay IBI, contacts I23 and I39 to ground. Relay I533 of the selector operates, opens the stepping circuit at contacts 533 and at contacts I3I completes the circuit for relay H15. Relay I05 operates, disconnects relay I35 and ground from the lower trunk conductor by opening contacts I23 and by closing contacts I2! extends the lower side of the calling loop by way of contacts I 53, conductor I52, contacts 625, conductor 39I, contacts 33?, lower contacts of relays I 0, lower contacts of relay 33L conductor 369, lower winding of relay 604 to ground. Relay 634 operates in series with relay I66, opens the circuit of impulsing relay Bill at contacts 623 and closes an obvious circuit for relay 6G3. Relay EH3 operates, applies ground to holding conductor 318 at contacts 653, and connects the upper winding of relay 634 to the upper trunk conductor in place of battery through resistance M2 by closing contacts'tii? and opening contacts 618. The finder connector and the auxiliary switch AS! are, therefore, brought to rest on contacts individual to the line on which the call originated. The switch ASI by means of its wiper 4&5 connects up a meter associated with this line so that the call may be registered against the calling subscriber. The operation of relay 634 results in the further extension or a connection over the lineswitch LSW to a local first selector of the main exchange, due to the completion of a loop circuit at the lower contacts of relay 604. The two windings of im pedance fiElI are included this loop circuit over which the line relay of the lineswitch and the line relay of the first selector operate in the usual manner.

It may be noted that with each of the magnet of the selector a circuit is closedr'romthemagnet contacts for relay mi and in parallel therewith by way of contacts Hill and I25, wiper H9, and the release trunk conductors of the various lines for the cut-oil. relays I, 8, etc. The relays operate successively although this is without effect until the relay associated with the calling line is operated. Relay it? operates at each step of the switch and at its upper and lower contacts disconnects the talking wipers of the switch. This prevents interference with the operation of the equipmentas the wipers pass over the contacts of lines engaged in other connections. The ground on the test contacts of such lines maintains relay Iill operated when magnet II3 releases between impulses. When relay I 93 deenergizes upon the calling line being connected with, the cut-off relay of the calling line is connected over contacts !36 to ground through the lower winding of relay Ill'i. Relay I01 operates, completes a locking circuit forits upper winding at contacts I35, prepares a circuit to relay Hi3 at contacts I34, applies direct ground to the test wiper II9 at contacts 35, and at contacts 537 opens the circuit of relay I3. Further, starting conductors 32 and are now connected at contacts I 32 and starting relay E93, switch FC is disconnected. Any call coming in at this time will, therefore, be to the other selector regardless of the position of the distributor relays as will be apparent later on. Relay I3 now restores and reconnects relay l4 to the various line conductors so that new calls can be made by sub-oflice subscribers.

. In case a new call should be initiated at this time, relay !4 operates as in the preceding case and relay l remains operated over its two windings in series. Relay l4 completes a circuit by way of'contacts 26 and 22 for two-step relay I6. Relay 16 operates in its first step, completes a circuit for its upper winding by way of contacts 2| and 21, and at contacts 29 applies ground to starting conductor 33 which extends to the starting relay of the other finder-connector. Relay l6 operates only in its first step at this time, closes the contacts designated by the Roman numeral I and when ground is returned on conductor 34 by the finder-connector, relay [3 will reoperate and disconnect relay I4. Relay [4 removes the short-circuit from the upper winding of relay l6 which thereupon operates in a second step and completes a circuit for relay !1. Relay l1 operates and opens the circuit of relay [5 which restores and in turn opens the circuit of relay l6. Relay l6 restores and prepares the distributor relays for grounding conductor 32 upon the initiation of another call.

When the connection has been established as above described, the terminals assigned to the calling line in the connector banks is marked busy by ground on conductor 368, wiper 404, third contact of the bank engaged by the wiper, conductor 411, lower winding of relay 552 to battery. Relay 552 operates and at contacts 56!! connects ground to test contact 561.

Dialling The general operation resulting from dialling the digits of a called number will now be described. As previously stated, the sub-ofiice is identified by the digits 2, 4, 5, 1 and a particular line of the sub-office is selected by an additional digit which follows the four identifying digits. Main ofiice lines are identified by five digit numbers of which one or more of the first four digits differ from the corresponding digit or digits of sub-office numbers. The subscriber dials a digit of .a wantednumber, interrupting the circuit of line relay 606 of repeater R and that relay responds. When relay 604 restores a circuit is closed from ground, contacts 623, 6I9, lower winding of relay 662, conductor 383, contacts 356, conductor 38!, winding of magnet 56! of auxiliary switch A83 to battery. The magnet advances the wipers 563-436 one step for each impulse transmitted by the impulse relay. The loop circuit over line switch LWS to the first selector is interrupted at the lower contacts of relay 604 and the first selector is stepped to the level indicated .by the digit dialled. Relay 602 operates response to the first impulse, short circuits its upper winding, completes. a circuit for relay 3l5 at contacts 616, removes the high resistance upper winding in impedance 66! from the loop circuitto the switch ahead at contacts 6M and connects the low resistance winding in this circuit at contacts 655; At its lower contacts, relay 632 opens the circuit to wiper 506 of switch A83. The operation of relay 3&5 is without efiect until the final digit of a sub-ofiice number is dialled. Shortly after the last impulseof the series, relay .662 restores and completes a circuit over wiper 506 of switch A83, the efiect of which will depend upon the value of the digit dialled as will be explained subsequently. v

First digit 1 In case the first digit dialled is the digit 1, the

wipers of switch A83 come to rest on the first contacts of the bank and upon the release of relay 662 a circuit is closed from ground, contacts 62!, lower contacts of relay 602, conductor 5M, wiper 536, first bank contact, conductor 519, contacts 666, to conductor 311; for the digits 3 and 60 the ground on wiper 536 is applied directly to conductor 311; for the digit 4, ground is applied over conductor 52| and contacts 653 to conductor 311; and for the digit5 ground is applied over conductor 520 and contacts 646 to conductor 311. These digits indicate that the called subscribers line is outside of the suboffice. The ground on conductor 311 operates relay 3| 4 which locks the ground on conductor 318, prepares the busy tone circuit at contacts 352, disconnects the stepping magnet of the switch A83 at contacts 356 and at contacts 355' connects battery through a resistance to relay 602. The switch A83 accordingly remains in its operated position throughout the remainder of the-call as it will receive no more impulses and its restoring circuit is opened at contacts 622. The further extension of the call will be described in later paragraphs.

In case the first digit dialled is the digit 2 indicating that the line called may be a sub-office line, ground is applied over wiper 536, conductor 522, contacts 65! winding of relay 6i l, resistance 662 to battery. The first step of the switch wipers also results in the closure of the circuit from ground, resistance 528, wiper 563, conductor 558, contacts 656, resistance 652 to battery. Relay GM is, therefore, partially short-circuited by the ground through resistance 523. When the circuit is completed over wiper 506, relay 61! operates in its first step, closing only the contacts designated by the Roman numeral I. The normally closed contacts are not opened at this time. The closing of the lower contacts of the relay results in the completion of the circuit from ground, contacts 651, conductor 5l5, elf-normal contacts 562, interrupter contacts of magnet 50! winding of the magnet to battery. The magnet accordingly operates in its self-interrupting circuit until the wipers are in normal position whereupon contacts 562 open and stop the stepping action. With the wipers in normal position the shunt is removed from relay 6 and that relay now operates in its second step over an obvious circuit including its upper contacts to ground on conductor 318. Relay 6!! disconnects itself from conductor 522 at contacts 65l and at contacts 652 connects this conductor to conductor 311 so that a subsequent digit 2 will bring about the energization of relay 3M. Conductor 521 is disconnected from conductor 311, at contact 653 and at contacts 654 is connected by way of contacts 644 to relay 6), so that the second digit if it is the digit 4 will operate relay 6H! instead of relay 314 as was the case with a first digit 4. The circuit over which the shunt was applied to relay 6 is transferred to relay 6H1 by way of contacts 655 and 649. The homing circuit for the switch A83 which was completed over the lower contacts of relay 6ll as previously stated, is opened at contacts 651. The removal of ground from conductor 5I5, now permits switch A83 to operate and release under control of relay 6H].

Second digit 7 Relay 6B4 responds to the second digit in the same manner as for the first digit, transmits impulses to the stepping magnet of the switch AS3 and interrupts the loop to the main ofiice switches as before. If the second digit dialled is any other than the digit 4, ground will be applied over Wiper 506 and the circuits previously traced to conductor 311 to operate relay 3M and prevent further operation of the switch AS3. If the second digit is the digit 4, which is the second digit of sub-office numbers, a circuit will be closed over wiper 506, conductor 52L contacts 654 and 644 winding of relay 6|0, resistance 66| to battery. Relay GM is partially shunted by ground applied over wiper 563 and at this time operates in its first step to close the contacts designated by the Roman numeral I. The restoring circuit of switch A83 is closed by way of contacts 659 and the lower contacts of the relay and the switch wipers are restoredto normal position as in the previous instance. Upon the removal of the shunt from relay 6), the relay operates in its second step transferring conductor 521 from its connection to the relay to connection with conductor 311 at contacts 645, so that a subsequent digit 4 will operate relay 3M. Conductor 650 is disconnected from conductor 311 at contacts 646 and connected by way of contacts 641 and 638 to relay 609. The circuit over which relay 6l0 was partially shunted is transferred by way of contacts 648 and 642 torelay 609.

Third digit In case the third digit is any other than the digit 5 ground is applied over wiper 506 to conductor 311 to bring about the operation of relay 3l4. The connection will then be extended over the main o-flice switches in the usual way. In case the digit 5 is dialled, ground is applied over wiper 506, conductor 520, contacts 641 and 638, winding of relay 609, resistance 660 to battery. Relay 660 is partially shunted by ground through resistance 528 and operates in its first step at this time, closing the contacts designated by the Roman numeral I. Relay 609 in addition to preparing a circuit for operating in its second step completes the restoring circuit for switch AS3 by way of contacts 643 and the lower contacts of the relay. Switch AS3 returns to normal position as in the previous instances and the shunt is removed from relay 609. Relay 609 then operates in its second step, disconnects itself from conductor 620 at contacts 636 and connects this conductor through to conductor 311 at contacts 631 so that a fourth digit 5 will operate relay 3l4. Conductor 519 is disconnected from conductor 311 at contacts 640 and connected by way of contacts 639 and 631 to relay 608. The circuit for shunting relay 669 is transferred to relay 608 by way of contacts 64! and 632.

Fourth digit If the fourthdigit is of any other value than 1, ground will be applied over wiper 566 to conductor 311 to operate relay 314. The connection will then be extended over the main ofiice switch train.

In case the fourth digit is the digit 1, ground is applied over wiper 506, conductor 5I9, contacts 639 and 63!, winding of relay 698, resistance 659 to battery. Reiay 608 is shunted by the ground through resistance 528 and operates in its first step at this time closing the contacts designated by the Roman numeral I. These contacts com plete the usual operating circuit for the relay and the restoring circuit for switch A83. Upon the restoration of the auxiliary switch to normal position the shunt is removed from relay 608 and that relay operates in its second step, disconnects conductor 5l9 fromthe relay and connects it by way of contacts 630 to conductor 311. Conductor 315 is connected by way of contacts 629 to conductor 524 for purposes to be explained subsequently. The loop circuit for the main exchange switch train is opened at contacts 621 and the lower contacts of relay 608. A busy-tone circuit is prepared at contacts 628.

Test for idle sub-ofiice revertive connector Proceeding with the description of the connection it will be assumed that the calling subscriber has dialled the digits 2, 4, 5, 1 which indicate that the called subscriber is located in the sub-office. The test for an idle revertive connector switch is made upon the return of auxiliary switch AS3 to normal. Wiper 504 engages its home contact which is connected by way of con ductor 396' to repeater 2B. In case a local call in the sub-office is in progress on the second repeater at this time, ground will be applied to conductor 396' in a manner to be explained subsequently. This ground by way of wiper 504, conductor 524, contacts 629, conductor 315, contacts 351 and 354, winding of relay 3I3 to battery energizes relay 3l4. Relay 3M on operating opens the impLL singcircuit for switch A83 and prepares the busy-tone circuit as in the previous instances.-

The calling subscriber may dial the final digit of the number although this would be without eifect since the circuit for stepping magnet 50! is open at contacts 356 and the loop circuit of the main oflice switch train is open at the upper and lower contacts of relay 608. A busy tone will now be returned to the calling subscriber by way of the conductor designated busy, contacts 352, upper contacts of relay 3| l, conductor 314, contacts 628 and 6M, conductor 313, through the talking condenser, contacts 33! through conductor |5| and thence through the calling subscribers loop and back to ground through the lower winding of relay 604. The tone will inform the calling subscriber that the connection cannot be established at this time and he is expected to hang up and release the connection as will be explained subsequently.

Idle revertive connector available In case there is no other call in the sub-exchange in progress following the dialling of the fourth digit as above described, wiper 504 of switch AS3 will find no ground on its home contact and relay M4 is not energized. The calling subscriber then dials the final digit of the called number which for convenience may be assumed to be the digit '1. Relay 604 will respond in the usual way and transmit a series of seven impulses over the previously traced circuit to stepping magnet Bill of switch AS3. The wipers of the switch are stepped to the seventh set of contacts which correspond to the wanted line.

Called line busy The called line is tested for its busy or idle condition prior to the release of relays 602 and 3| 5 which remain operated a short interval after the last impulse of the series is received. The test circuit may be traced from conductor 4l5, seventh contact of the bank engaged by wiper 504, conductor 524, contacts 629, conductor 315, contacts 319, winding of relay 3|3 to battery. If the called line is engaged in an incoming or outgoing call the associated line relay in this case relay 553 will be operated and contacts 555 will be closed by applying ground to conductor M5. This ground, of course, will be applied over the wiper 404 of the auxiliary switch ZASi associated with the second repeater. Relay 3I3 accordingly operates, opens the circuit of relay 3!! and prepares a locking circuit for itself. When relays 602 and H5 restore, the circuit for initially operating relay M5 is transferred by way of contacts and 354 to relay 3M which operates. Relay 3 Hi completes the busy tone circuit at contacts 352 and the busy tone is returned to the calling subscriber exactly as in the preceding instance.

Called Zine idle In case the called line is idle wiper 504 of switch ASS wil'l find no ground on the test contact and relay 1H3 does not operate. Upon the release of relay 602, a circuit is closed by way of contacts 62!, lower contacts of relay 602, conductor 5! 4, wiper 586, seventh contact of the bank engaged by this wiper, conductor 3', winding of relay 3H4 to battery. Relay 3M operates, prepares the busy-tone circuit, and opens the impulsing circuit as in the previous instance. A circuit is now completed for relay 3 from ground at contacts 633, conductor 382, winding of the relay, upper contacts of the relay 3 l3, contacts 353 and 351', conductor 3'55, contacts 629, conductor 524, wiper 503, seventh contact of the bank engaged by the wiper, conductor M5, lower winding of relay 553 to battery. Both relays 3H and 553 operate in this circuit. The latter relay opens the starting circuit at contacts 564, and applies ground to the test contact 510 in the connector banks at contacts 565. Relay 3| l on operating opens the busy-tone circuit, at its upper contacts, completes an obvious circuit for relay SW, and at contacts 39'! applies ground by way of conductor 396 to the home contact of the bank engaged by wiper 504 of the auxiliary switch 2AS3 associated with repeater 2R. This auxiliary switch corresponds to switch ASS associated with repeater R and the wiper 50% corresponds to wiper 504. It will be apparent that an attempt to establish a call between subscribers in the sub-office over the other trunk and repeater 2R will result in the calling subscriber receiving the busy indication as was described previously. As a further result of the operation of relay 3! l a marking ground is applied by way of contacts 391, lower contacts of relay 305, conductor 388, wiper 505, seventh contact in the bank engaged by this wiper, conductor i i 4 tothe seventh contact in the bank of switch ASE. This ground serves to mark the calling line for purposes which will be apparent as the description proceeds. As a result of the operation of relay am a holding circuit is completed for relay 604 extending from ground, upper contacts of relay 312, upper contacts of relay 3l0, contacts 3, conductor 316, contacts 5H, upper winding of relay 604 to battery. Trunk conductor I5! is disconnected from the upper winding of relay 604 at contacts 345 and extended by way of contacts 346 to the upper winding of relay 3938. Trunk conductor I52, which as previously explained was connected to the lower winding of relay 504 is now opened at the lower contacts of relay 3E0.

Referring now to the switch FC in the suboffice it will be recalled that relay Q00 has bee-n maintained in its operated position in series with relay 5.04 of the repeater at the main ofiice. Upon the disconnection of the latter relayas explained above, relay W6 will release, thereby extending the lower talking conductor of the switch by way of contacts 522 and 533 through the winding of high resistance relay iii to ground. It will be recalled that battery through relay 308 is connected to conductor l5l at the main ofiice and this battery by way of the winding of relay 58%, upper contacts of relay NH, wiper iii, over the. loop circuit of the calling line, back over wiper lZt, lower contacts of relay iti and the lower talking conductor of the switch operates relay 5 l l. Relay 308 also operates in series with relay H I but due to the high resistance of the latter relay, relay 9% does not operate. uelay 308 completes a new holding circuit for the upper winding of relay 600 at its upper contacts, and completes a new circuit for impulse generating relay 601 by connecting ground to conductor 383 at contacts 338. erate to transmit impulses in exactly the same manner as when the connection was being established, as was described in detail in preceding paragraphs. The impulses generated at this time,

however, operate different switches than in the impulses generated at the lower contacts of relay 3 603 are, therefore, applied over conductor 38?, lower contacts of relay 305, contacts 321 and 32! conductor 36?, winding of magnetAfi'i of switch ASE to battery. The wipers of this switch. are

accordingly advanced step-by-step until the called line is reached. Impulses are also transmitted from battery through resistance 6 i3, contacts 624, conductor 552, contacts M9, conductor E55, offnormal contacts 209 (Fig. 2), winding of relay 202 to ground. Relay 2&2 operates in response to each of these impulses and transmits an impulse by way of the stepping magnet interrupter contacts, winding of the magnet, to battery. The stepping magnet on operating opens its interrupter contacts and slow-releasing relay 201 is thereupon connected in series with the magnet. Relay 20! operates and completes a new circuit for relay 202 independent of off-normal contacts 209. The wipers of the switch are advanced one step whereupon the cit-normal contacts open. Subsequent impulses are transmitted to relay22 by way of contacts 2%. Relay 20! remains operated throughout the series of impulses and in addition to maintaining the impulsing circuit, opens the test circuit of its upper contacts. It should be noted at this time that relay 5 i l on operating as previously described completed a circuit by way of contacts i i-8, conductor E56, winding of relay 2% to battery. Relay 204- on operating connects the upper winding of relay 205 to the test wiper at its upper contacts, opens the re storing circuit of the switch at contacts 2 l5, and prepares the ringcut-off circuit at contacts 2H. Switch R0 at the sub-ofiice and auxiliary switch ASZ at the main ofiice are stepped in synchronism until the wipers of both switches reach their seventh set of contacts which correspond to the called line which was marked responsive to the digit dialled by the calling subscriber. When wipers of the switch A82 engage their seventh set of contacts, a circuit is closed from ground at contacts 391, lower contacts of relay 300, conductor 3B8, wiper 5E5 of switch AS3 which is standing on the seventh set of contacts of its The impulse relays 505, 606, and 601 opbank, conductor 4 I4, seventh contact of the bank engaged by wiper 4i i, said wiper, conductor 335, contacts 335, winding of relay 335 to battery. Relay 3% operates, opens the circuit of the impulse generating relay at contacts 330 to prevent further impulsing, completes a locking circuit for itself by way of contacts 328, conductor 364, wiper 4 I 0, seventh contact of the bank engaged by that wiper, conductor 4I5, seventh contact of the bank engaged by wiper 53 i, conductor 524, contacts 629, conductor 3J5, contacts 351, 353, upper contacts of relay 313, winding of relay 3, conductor 382 to ground at contacts 683. Relay 306 also completes a circuit for relay 331, prepares the ringing circuit at contacts 323 and disconnects ground from conductor 333. At the subofiice relay 232 remains normal after the cessation of impulses and relay 23I restores after a slight delay. A circuit is now completed from battery through the winding of cut-on" relay 8 associated with the called line T1, conductor 6, wiper 2 which is engaging the seventh contact of its bank, upper contacts of relays 20! and 204, upper winding of relay 255 to ground. Relay 205 operates, closes points in the talking circuit of its upper and lower contacts, applies direct ground to the test wiper at contacts 29, completes an obvious locking circuit for its lower winding over conductor E53, and completes the ringing circuit at contacts 220. Ringing current is now sent out to the called line from the generator lead GEN, lower winding of relay 309, contacts 329, lower winding of relay 338 and condenser 335 in parallel, contacts 346, and 34I, trunk conductor I5I, upper contacts of relay 205 of switch RC, wiper 2), line conductor 4, through the bell and condenser at the called station, line conductor 5, Wiper 2I3, lower winding of relay 233 and the condenser in parallel, contacts 251, 223, 222, and 221 to ground. The bell at the called substation rings intermittently to notify the subscriber of the call. A small quantity of the ringing current is transmitted to the calling line by way of conductor I5I, winding of relay I 35 and the condenser in parallel, upper contacts of relay IGI, wiper I I1 over the loop of the calling line, wiper I20, lower contacts of relay Ifil, contacts I28 and I38, winding of high resistance relay III toground. The amount of ringing current flowing in this circuit is relatively small due to the very high resistance in relay III. Further, the resistance to this relay is so great that relay 309 is prevented from operating over the direct current path afforded therethrough. When the called subscriber answers a direct current bridge is closed over the calling line and a low resistance path is completed for relays 283 and 309 and these relays accordingly operate. Relay 309 opens the ringing circuit at contacts 3%, and extends trunk conductor I5! through to the upper winding of relay 50 and battery by way of contacts 343. Relay 333 also completes a locking circuit for its upper winding at contacts 344 and closes a further point of the talking circuit at its lower contacts. Relay 203 completes a locking circuit for its upper winding at contacts 2I5, and at its upper contacts connects ground by way of conductor I56 and the lower contacts of the relay III to the lower talking conductor of the switch FC. Relay III is shunted by this direct ground and restores, and relay I35 now operates and completes the circuit for relay I05. Relay I05 operates and connects the lower talking conductors of the switch through to trunk conductor I52 by way of contacts I50. The release of relay I I I removes ground from conductor I54 and relay 204 of switch RC restores to complete the talking circuit. Relay 338 of repeater R releases responsive to the operation of relay 300, and trunk conductor "32 is thereby connected by way of contacts 625, conductor 39I, contacts 335, lower contacts of relays 309 and 30I, conductor 333, lower winding of relay 504 to ground. Both subscribers are now connected to trunk conductors I5I and I52. and ground are supplied through the windings of line relay 604.

Release after a completed connection At the termination of a connection as above described both parties will restore their receivers, thereby opening the direct current loops at their respective stations. Relay 604 of repeater R accordingly restores and opens the circuit of relay 503. Relay 603 on restoring removes ground from holding conductor 318 thereby permitting relays 309, 3l2, 3M, and 608-6 to restore. A circuit is again closed for the impulse generating relay group comprising relays 605301 and these relays operate as in the preceding instances to transmit ground and battery impulses. Relays 3i and 302 of the repeater remain energized over circuits including the ofi-normal contacts of auxiliary switches ASI and AS2, respectively. Relay 303 remains in normal position and relay 305 remains operated in its first step with the contacts designated by the Roman numeral I closed. Impulses are all transmitted from ground at the lower contacts of relay 301, conductor 381, lower contacts of relay 305, contacts 321 and 32I, conductor 361, winding of magnet 431 to battery. Magnet 401 operates and advances the wipers of switch A82 step-by-step until the home position is reached whereupon off-normal contacts 408 open and permit relay 302 to restore. Relay 302 transfers the impulsing circuit by way of contacts 322 and conductor 338 to magnet 40I of switch ASI This switch is then advanced stepby-step until the wipers return to normal position, whereupon off-normal contacts 402 open and permit relay 30! to restore. Relay 30I reconnects relay 302 to the upper trunk conductor and disconnects ground from the upper winding of relay 305 and from relay 301. Relay 301 restores. Relay 305 now operates in its second step over a circuit including .a contact of relay 333 which has not been i e-operated unless the sub-oilice switches have reached normal position.

Relay 305 remains operated while the sub-office switches are returning to normal position and maintains the stepping circuits of the auxiliary switches open at its lower'contacts.

In the sub-oflice, relay Hi5 releases responsive to the calling subscriber hanging up and opens the circuit of relay E55. Relay I35 restores and connects relay Hi4 direct to the lower trunk conductor. The impulse relay group at the main exchange transmits battery impulses over trunk conductor I52 in the same manner as for the original setting of the switches FC and RC. Relay HM responds and transmits a ground impulse through the winding of relay I03 to battery through resistance E1 6. Relay I33 operates in response to the first impulse and again shortcircuits the upper winding of relay I33, thereby causing "hat relay to release from its second step and connect stepping magnet H3 in series with relay I03. Subsequent impulses operate the magnet H3 to restore the switch wipers to nor- Talking battery 145 and the upper contacts of rel'ay'l08 to ground at contacts'l46 completes acircuitfor relay I I Relay IOI :operates and opens the'talking conductors of theswitchduring'the release of the wipers. When the wipers reach normalor home position the holding circuit of relay'l09is openedclue to wiper H9 leaving the last contact'ofthe bank relay and I09 restores. Battery is connected "to trunk conductor I! at the upper contacts of relay I09 and energizes relay 303 which has been reconnected to the trunk, assuming that the auxiliary switches at the main office have "been restored to normal as above described. 'Relay 303 opens the holding circuit of relay 305 which releases. Relay 303 stops the operationof the impulse generating relays by opening its lower contacts and relay305restoresthe local impulsing'circuit to normal. .At the sub-ofii'ce relay I04 no longer receives impulses and relay I03 releases after a short interval. The circuits of relays I02 and H0 are opened and these relays restore.

Referring now to revertive connector BC, the release of relay I02 of switchFC as above described removes ground from conductor I53 .thereby permitting relay 205 of the switch RC to release. Relay 204 having previously released upon therestorationo-f relay III, relay 205 now completes the restoring circuit of the switchby closing contacts 22!. This restoring circuit includes contacts '22lj222,22l, and2l6, oil-normal contacts. engaged by wiper 2I2, and-the interrupter contacts of the stepping magnet. The magnet operates in its self-interrupting circuit to restore the switch to normal position, whereupon the impulsing circuit is opened by wiper'2l2 leaving the lastvbank contact and relay-202 is .again connected to .the control conductor I55 by closure of .ofimormal contact 209.

Auxiliaryswitch AS3 at the main ofiice returns to normal upon the release of relay 603 which completes a circuit-by way of .contacts622, conductor 5 I 5, oft-normal contacts 5 02, interrupter contacts of the magnet, winding of the magnet to battery. Whenthe wipers reach normal position, the restoring ecircuit isopenedat the offnormal contacts. 'All switches have nowreturned to normaland-the apparatus is-in condition to respond to the next call.

Release after attempted local call with reverting call switch busy Release in this case is substantially the same as that for a completed call. 'The calling subscribed on hanging up releases relays 004 and 603 and counting relays 6085II also restore. The starting circuit for the impulse generating relay group is completed by relays 604 and 603 and these relays transmitimpulses to restore auxiliary switch ASI and the sub-ofiice switch FC to normal. 'Since the final digit has not been dialled, auxiliary switches A82 or ASS have not been operated and consequently there is'no necessity of restoring them. 'Upon the "return of the sub-'office switchto normal, battery is re-applied to the upper trunk conductor and relay 303 operates to stop the impulse. generating relays and to permit the equipment to. assume its normal position.

Release after attempted callto a busy' line The release in this case is the same as that for the preceding case, except that switch AS3 will have been operated to the contacts of the called line. Upon the release of relays 604 and 603 the usual restoring circuit will be. completed for the stepping magnet '50I ofthe switch A83.

Switch ASI .and the sub-olfice selector switch S restore in the usual way upon the release of relay 603 which removesground from holding conductor..3l8. Relay 604 opens the loop to the main oflice switch train and these switches release in the usual manner.

Incoming call to a sub-office subscriber The operations involved in establishing a connection to a sub-oflice subscriber from a subscriber in the main ofiice will now be described. The calling party will dial the number assigned to a wanted sub-.oflice line which for convenience will be assumedto be the number.2451'7 assigned to sub-office line T7. The dialled digits will operate theautomatic switches at the main office in the usual manner and a connector willset its wipers on contacts '5l0512 which are assigned to-the wanted sub-oilice line. The connector will test the line in the usual manner, that .is by applying ground through the low resistance winding of the switching relay to the test wiper. This ground byway of contact .510, upper winding of relay 553, contacts 564, resistance 514,. conductor 393, contacts 324,.winding of relay 304 to battery will energizerelay 304. Relay 553 and the switching relay of the connector do not energizeat this time due to resistance-5T4 and to .the relatively high resistance of relay..304 which cuts-down the current flow in the circuit. Relay 304 on operating completes a circuit for the impulsegenerating relays at contacts 325 and at contacts 326 connects .impulsing conductor 38'! to the motor magnet of auxiliary switch A82. The ground applied to the test contact of the connector bankwill be extended in a parallel circuit by wayof .contacts 514.and 558,.and conductor 4| 4 to the seventh. contact of the bank engaged by wiper 4H of auxiliary switch ASZ. This will mark the wanted sub-oliice lineand determine the numberof impulses to be transmitted tothe finder connector at thesub-o-flice.

The impulse generating relays transmitimpulses to the auxiliary switch A82 in the usual manner advancing the wipers of this switch stepby-step. 'Impulses will .be transmitted simultaneously over. a circuit .from battery, resistance 6I3, contacts 624,.trunk conductor I52, contacts I50 and I29, winding of relay I04 to. ground. Relayl04 responds, transmits aseries of impulses through relay I03 to steppingv magnet ll.3 .of.the Lswitc'h FC. Relay I03 remainsoperated during the series of impulsesand-completes acircuit for relay H0 which also operates. ..Relay H0 disconnects starting relay 108 from the incoming starting conductor, completes a circuit for relay I I2 at contacts I44 which is efiective at this time since relay I09 is unoperated and completes the circuit for relay IOI. Relay IOI operates and opens the talking conductors of the switch so that there will be no testing of the calling lines passed over during the operation of the switch. Relay I I2 operates, prepares a locking circuit for itself to holding conductor I53, and prepares a point in the ringing circuit at its lower contacts.

After seven impulses have been transmitted by the impulse generating relays, the wipers of the switch FC will engage the contacts associated with the called line and the wipers of auxiliary switch AS2 will be in a similar position. When wiper 4II encounters the ground on the seventh contact of its bank, a circuit is completed over conductor 365, contact 335, winding of relay 306 to battery. Relay 306 operates, opens the circuit of the impulse generating relays at contacts330 and completes a circuit for relay 301 at its upper contacts. The stepping of switch AS2 from its normal position results in the closure of off-normal contacts 408 and ground over conductor 366, energizes relay 302. Relay 302 disconnects starting relay 303 from the upper trunk conductor and completes a holding circuit for relay 301. Relay 306 has a relatively low resistance and permits relay 553 and the switching relay of the connector to operate at this time. The switching relay of the connector completes the usual ringing circuit over the talking wipers of the connector and relay 553 looks over its lower winding to ground on the test contact. This ground is also extended by way of conductor M5, wiper 4I0 of auxiliary switch AS2, conductor 364, contacts 328 to hold relay 308 operated. In the sub-office, relay I09 operates as soon as the wipers of the switch leave their home position. The normalbattery connection to conductor I5I is opened at the upper contacts of the relay, ground is applied to holding conductor I53 at contacts MI, and a circuit is completed for relay I3 ,at the lower contacts of the relay to prevent the starting apparatus from functioning in case a call should originate in the sub-ofiice at this time. As soon as the wipers of the switch engage the contacts associated with the called line, cut-off relay 8 of the called line operatesin series with the lower winding of relay I01. conductor I53 and transfers the incoming starting conductor 32 of thesecond finder-connector switch at the sub-oflice by way of outgoing starting conductor 33 and contacts I32.

A connection has now been established with the called line and ringing current'is transmitted by the connector in the usual manner. The circuit for this ringing current may be traced from the upper talking wiper of the connector, contact 51 I, conductor 420, wiper 409 of auxiliary switch AS2, conductor 36I contacts 332, trunk conductor I5I winding of relay I06 and the condenser in parallel, upper contacts of relay IOI which restores at the end of the impulsing, wiper I.I1, line conductor 4 through the bell and condenser at the called station, line conductor 5, wiper I20, lower contacts of relay IOI, contacts I28 and I38, lower contacts of relay II2 toground. Neither'relay 106 nor. the ring-cut-ofi relay of the connector operate at this time as no direct current flows over the circuit. The bell at the called station rings intermittently to advise the subscriber of the incoming call. When the subscriber answers the call a direct current bridge is closed at the Relay I01 operates and locks to holding called station which permits relay I06 and. the

ring-cut-off relay of the connector to operate. The ring-cut-off relay of the connector stops the ringing and connects up the battery feed relay in the usual manner. Relay I06 completes an obvious circuit for relay I05 which operates and connects the lower talking conductor of the switch FC through to trunk conductor I52 by way of contacts I21 and. I50. Conductor I52 is connected by way of contacts 625, conductor 39I, contacts 336 and 340, conductor 369, wiper II2 of switch AS2, seventh bank contact, and conductor 42I to the bank contact 512 which is engaged by the lower talking wiper of the connector. The talking battery for the called subscriber is fed through the back-bridge relay of the connector in the usual manner and the calling and called subscriber may converse over the circuit above traced.

Release The release of the connection is brought about by both subscribers hanging up. The calling subscriber in hanging up first will release the line relay of the connector but the back-bridge relay is energized over the called subscribers loop and will prevent the switch from releasing at this time. When the called subscriber hangs up, the back-bridge relay of the connector releases and'permits the switch to restore in the usual manner. Relay I06 releases and opens the circuit of relay I05. The removal of ground from the test contact of the connector bank permits relays 553 and 306 to restore. Relay 302 is held up over the off-normal contacts of switch AS2. Relay 303 will be in normal position and the release of relay 306 will complete a circuit at contacts 330 for the impulse generating relays. These relays transmit impulses in the usual manner to restore switch FC at the sub-office and auxiliary switch AS2 at the main office. The circuit for restoring switch AS2 is the same as that over which the switch was initially set. The circuit for restoring switch F0 is also the same as that over which it was previously set. In this case, however, the first impulse serves to restore relay I02 far enough to close contacts I23 and open its upper contacts. When the switch AS2 reaches its normal position, off-normal contacts 608 open and the relay 302 restores and reconnects relay 303 to the trunk conductor I5I. In case the sub-office switch has not yet reached normal position relay 303 will be normal and upon the release of relay 302, relay 305 will operate in its second step and open the impulsing circuit for switch AS2 at its lower contacts. The impulses will continue to go out to the sub-oflice until switch FC reaches normal position. Upon the sub-office switch reaching normal position, wiper II8 opens the circuit of relay I09 and that relay restores and applies battery to trunk conductor I5I to operate relay 303. Relay 303 on operating opens the impulsing circuit at its lower contacts and opens the circuit of relay 305 which restores. The release of relay I09 removes ground from holding conductor I 53 and relay II2 to restore. All of the apparatus has now returned to normal condition and is ready for the next call.

Incoming call with all trunks busy It will be recalled that a starting circuit for repeater R was completed over conductor 393 when the repeater was idle at the time a connection was extended. In case this repeater is in calling and called lines, respectively.

zaosrz za-i use when the call arrives, the second repeater, if not in use will be'started, as conductor 393 is connected by way of contacts 3|.8 or 333 to :outgoing starting conductor 394 which goes to repeater 2R. Conductor 394 corresponds to conductor 393 of repeater R as far as connections in repeater 2B are concerned. A relay in repeater 2R corresponding to relay 304 :of repeater R Willoperate in response to the incoming call provided the repeater is idle at this time and the connection will be completed over the'second trunk exactly as was described for the connection-over the first trunk.

If the second trunk should also be'busy when the call arrives, starting conductor 394 will be connected to conductor 394 instead of to the starting relay. This conductor instead of go- .ing to the starting relay of a third repeater is,

in the instant case, connected to all-trunks busy Relay 556 and the busy test relay of The connector Relay 556 has special functions .to perform in toll calls and its-operation will be described hereinafter.

Toll ofiering Since the present system maybe used in systems provided with a toll switch train equipped for .so-called toll offering service it is, -.of course,

necessary to make provisions for'the' extension of toll calls to sub-ofiice lines busy in local connections. In case the line is busy in a local connection with another subscriber in the sub-oflice'the connector terminal will be grounded to give the busy indication and switches ASI and A62 -will be engaged with contacts corresponding to the When-Va calling operator now extends a connection to one of the lines engaged in this connectionover the usual toll switch train, the connector will return the usual busy supervision to notify the operator of the condition of the line. The-operatorimay 'now cause the connector to cut in on theline and establish a temporary talking connection. This talking connection will extend over the upper talking wiper of the connector, conductor 4H3, wiper 4090f switch AS2, conductor 36 l,*contacts 332 to :upper trunk conductor 151; or over-conductor- 4l8, wiper 403 of switch ASLconductor 36!], .upper contacts of relay 3l-4 "to trunk conductor I5 I. A circuit also'extends'from the'lower talking wiper of the connector, conductor 4l'9,

wiper -4l2 of switch 'AS2, conductor 369,contacts 340and336, conductor 39!, contacts16-25to trunk conductor I52, or over conductor' '4'l9, wiper 486 of switch ASI, conductor3'l0, and lower-contacts of relay '3l4 to trunk conductor I52. :Both the calling and. called subscribers are connected to the trunk, the calling operator can obviously converse with them and ofier the toll call. Should the call .be accepted the'unwanted :party :may

withdraw from the connection :and the tollcall can-be established over the path just described. A toll offering connection can be completedas above described even though both sub-.office trunks are busy as long as the called line itself is engaged in a connection. If the called line is idle, howevenand both sub-ofiice trunks'are busy 'as'longas the called line itself is engaged in a connection. If the called line is idle, however,

and both sub-oflice trunks are busy, the connectioncannot beestablished and the toll operator" is given an all trunks busy tone when she-at- ;temptstto :offer the call. 'When theconnector engages :thecoritactsassociatedwith the wanted .line, for -example .line T1, :the .test circuit of the 1connector is iextendedoverbank contact 5.10, up-

perwinding of relay 553, contacts 564, resistance I .514, conductor 393, and the .chainedstarting circuit-tothe two repeaters which, as previously described, znow returns on conductor 394' from re- 1peater'R2,"winding of relay-5'56 to ground. Relay 550 .operatesiin' series with the busy test relay" 0f the connector, completes :a holding circuit "for itself by connecting battery through resistance k! to conductor 3.93 at contacts 523, and con- ;nects-aH-trunks busy tone to the talking conductors .associatedwith the various line contact sets on all lines which are not engaged in other'lcon- :nections. The :busy test .relay of the connector returns the usual busy tone to the operator. In case .the operator attempts to set .up an offering connection the busy tone is disconnectedin the :connectorand a temporary connection isiset up :overxtheatallking wipers of the switch. A circuit then extends over the upper talking wiper of the :connector, :contact 51], conductor 420, contacts 563 and"5.66, 'through the condenser to the -.alltrunks busy tone generator. This tone, which will ordinarily .be .diiferent from the .usual busy tone, notifies the operator that :the connection cannot :be completed-due to alltrunks tojthesub- "office being busy. The operator 'may wait untilsuch time as .a trunk is available or release the connection. .JIf'she elects to wait, when :a .trunk :becomes'idle the chain circuit will :be 'open'eclin .the repeater associated with the now i'dle'rtrunk and *relay- 5.56 will restore and remove the all itrunkslousy :tone from "the line. The chain circuit'willbe-connected'throughito the starting re lay vand the. repeater and ;the apparatus will then operate as previously described for an incoming call 'to' an idle line-and the connectionwill be completed in the usual manner.

What .isiol'aimed is:

1. .In a telephonesystem, two .offices connected by a trunk line, two switches associatedwith the trunk line at -'one office, a registering device as- :sociated with the trunk line at the other ofiiceyza .joalling'line and a called line at said one office, :means including one of said switches for. extending :the calling. lineito :said registering device via said trunk line-means controlled over the callingline for registering'ithe'number of the called line in said device, :andimea-ns controlledby said :device ioroperatingthe otherof said switches .in accordance with the number registered to extend ;a connection :to the called-line.

2. In a telephone system, two'ofiicesconnected zbysa trunk line, two switcheszassociated with the trunk i line" at one :ofiice, a registeringdevice associatedWiththe trunkline at the other ofiice,=a calling line-and aicalled line at said one 'office, meansincIuding-One ofsaid switches for extend- ;ing the calling ;line "to said registering :device 'via said trunk dine, means controlled-over the call- ;ing line for'registering the number of'thecalled line in said device, means'controlledby said-device for operating the otherof .said switches in accordancewith the number registered to extend 1a connection "tothe called line, and means assotciated with said device for transmitting signalling current over .the trunk :line to'signal the :called line.

'3. .In atelephone system, two officesconnected by a'trunk line, two" switches associated'with the trunk line at one office, a registering device as :sociated with the trunk line at'the .otherpo'ffice, a

calling line and a called line at said one ofiice, means including one of said switches for extending the calling line to said device via the trunk line, means controlled by the calling party for setting said device in accordance with the number of the called line, means controlled by said device for operating the other of said switches to extend the connection to the called line, and means for supplying talking current to both parties to the connection over the trunk line.

4. A telephone system as claimed in claim 2 in which part of the signalling current transmitted over the trunk line to signal the called line is permitted to flow over the calling line to inform the calling party that the called line is being signalled.

5. In a telephone system, two oilices connected by a trunk line, a switch associated with the trunk line at ,each oflice, subscribers lines accessible to the switch at one office, call registers individual to said lines accessible to the switch at the other office, and means responsive to the initiation of a call on one of said lines for simultaneously operating said switches to connect with the calling line and the call register associated with that line, respectively.

6. In a telephone system, two oiices connected by a trunk line, a switch associated with the trunk in each ofiice, lines accessible to the switch at one office, call registers individual to said lines accessible to the switch at the other oifice, an impulse sender at said other oflice, meansresponsive to the initiation of a call on one of said lines for causing said sender to transmit impulses to both of said switches to set the switch at said one oifice into engagement with the calling line and to set the switch at the other oifice into engagement with the call register individual to the calling line.

7. A telephone system as claimed in claim 6 in which the impulse sender re-operates upon the termination of the call and transmits impulses to both switches to restore them to their normal positions.

8. In a telephone system, two offices connected by a trunk line, two switches associated with the trunk line at each office, lines accessible to the switches at one office, contacts individual to the lines accessible to the switches at the other office, means for simultaneouslyoperating one of the switches in each ofiice to connect respectively with a calling line and a contact individual thereto, and means for simultaneously operating the other of the switches in the two oflices to connect respectively with a called line and a contact individual thereto.

9. In a telephone system, two ofilces connected by a trunk line, two switches associated with the trunk line at each office, lines accessible to the switches at one office, contacts individual to the lines accessible to the switches at the other office,

means responsive to a call on one of said lines for simultaneously operating one of the switches in each oflice to connect, respectively, with the calling line and a contact individual thereto, means controlled over the calling line for designating a called line, and means for simultaneously operating the other switches in the two oflices to connect, respectively with the line designated and a contact individual thereto.

10. A telephone system as claimed in claim 9 in which the operation of the various switches is controlled by an impulse sender at one of the oilices.

11. In a telephone system, a group of lines, two

' switcheshaving access to said lines, means for operating one of the switches to connect with a line on which a callhas been initiated or with a line which is being called from a line outside of the group, means for operating the other switch to connect with a line which is being called by another line in the group, and means for temporarily connecting said switches to complete a talking connection between calling and called lines in the group.

12. In a telephone system, a main office and a sub-oflice, a calling line and a called line at the sub-ofl'ice, a switch at the sub-office having access to the called line, registering apparatus at the main ofiice for registering the number of the called line under control'of the calling party, and means at the main office responsive to the registration of part of the called line number for testing for the idle or busy condition of said switch.

13. In a'telephone system, two offices connected by a trunk, calling and called lines at one office, means for extending the calling line to the other oifice, means at said other office for registering the number of the called line, a switch at said one ofiice adapted to be directively operated under control of said last means to extend the connection to the called line, and means for preventing the directive operation of said switch in case the called line is busy.

14. In a telephone system, two oflices, a calling line and a called line at one ofiice, means for extending the calling line to the other ofiice, means at the other officefor registering the number of the called line, and means at the other oifice controlled by said registering means for determining the idle or busy condition of the called line.

15. In a telephone system, two ofiices, a calling line and a called line at one ofiice, means for extending the calling line to the other oilice, means at the other office for registering the number of the called line, means at the other office for determining the idle or busy condition of the called line, and means efiective provided the called line is idle for directively operating switching mechanism in accordance with the number registered to extend a connection to the called line.

16. In a telephone system, a main oflice and a sub-office, calling and called lines at the suboffice, means for extending a calling line to the main ofiice, registering means at the main ofiice controlled over the calling line for registering the. digits of the called number, a switching device at the sub-ofiice for extending a connection to the called line, means associated with said registering means for testing for the idle or busy condition of said device prior to the registration of the last digit of the called number, and means associated with said registering means for testing for the idle or busy condition of the called line after the registration of the last digit of the called number and prior to the operation of said device.

1'7. A telephone system as claimed in claim 16 in which a busy tone is returned to the calling party in case either the switching device at the sub-of'nce or the called line is found busy.

18. In a telephone system, two oflices connected by a trunk line, a plurality of lines at one ofl'lce, a switch terminating the trunk at said one oflice and having access to said lines, a set of terminals for each of said lines at the other office, a second switch associated with the trunk at said other office and having access to said contact sets, means for extending a connection to one of said terminal sets, means responsive to the connection for causing said second: switch to hunt for and connect with said one terminal .set,. and means.

for simultaneously operating the. first switch to take up a position corresponding to that of the second switch and to extend a connection to the line corresponding: to the terminal set..,

19. In a telephonesystem, two offices connected' by a. trunk line, a, pluralityof lines at one oflice, a, switch at said one ofiice having access tov said lines, a set of terminalsfor each lineat the other oflice, a secondswitch at said other office having access to saidterminal sets, an impulse sender at said other ofiice, means for extending a, connection to. one of said terminal sets, means responsive to the connection for causing said. senderzto nected to said. second relay and accessible to said.

switch, a second contact normallyconnected-to said first relay and accessible to said switch, means for operating the switch to connect with said first contact to operate said second relay, and means controlled by said second relay for disconnecting itself from saicl first contact, for connecting the contact to said first relay, for disconnecting said second contact from said first relay, and for connecting the. second contact to said third relay.

21. In a telephone system, a main ofiice and a sub-office, trunks connecting the offices, subscribers lines at the sub-office, a set of terminals at the main oifice for each of said lines, means responsive to the extension of a toll connection to one of said terminals for further extending the connection to a wanted line provided the same is busy, means for giving the calling toll operator a busy signal without extending the connection thereto in case the line is busy, means for giving the calling toll operator a busy signal without extending the connection thereto in case the line is idle and all of said trunks are busy, and means for giving the calling toll operator an all-trunks busy signal in case the operator attempts to offer the toll call to the wanted line when the line is idle and all of said trunks are busy.

22. In a, telephone system, two offices connected by a trunk line, two switches associated with the trunk line at one office, a registering device associated with the trunk line at the other ofiice, a calling line and a called line at said one ofiice, means including one of said switches for extending the calling line to said registering device via the trunk line, means controlled over the calling line for setting said device in accordance with the number of the called line, means controlled by said device for operating the other of said switches in accordance with the. setting of the device to extend a connection to the called line, a source of signalling current and means in said device for connecting it to the trunk line to signal the called line, and means responsive to the called subscriber answering for disconnecting said current source from the trunk line.

23. In a telephone system, two oifices connected by a trunk line, two switches associated with the trunk line at one ofiice, a registering device associated with the trunk line at the other office, a calling line and a called line at said one ofilce, means including one of said switches for extending the calling line to said registering device, via thetrunk line, means controlled over the callin line. for setting said device in accordance with tha'number. of the called line, means controlled by said device for operating the other of said switches; in accordance with the setting of the device to extend a connection to the called line, a source of signalling current and meansin said device for-connecting it to the trunk line to signal the called line,,a sourceof talkingcurrent, and means controlled. over the; called line for disconnecting said first current source from the trunk line and for connecting said second current source to the trunk line.

24. In a telephone system, two ofiices connected by a trunk line, a switch associated with the trunk line at each ofiice, subscribers lines accessible to the line at each office, subscribers lines accessible tothe switch at oneofiice, call registers and test contacts individual to said lines and accessible to the switch at the other ofiice, means responsive to the initiation of a call on one of said lines for operating the switchat said one office to connect with the calling line, and means for simultaneously operating the switch at the other ofiice to connect with the call register and test contact individual to the calling line.

25. In a telephone system, a group of lines, two switches having access to said lines, means for operating saicl switches to connect with any of said lines as calling or called lines, a third switch having access to said lines, means for operating said third switch to connect with any of said lines as called line, and means for temporarily associating said third switch with either one of said first two switches to complete a connection between two lines in the group.

26. In a telephone system, a main ofiice and a sub-ofiice, a calling line at the sub-ofiice, switches at the sub-oifice, means including one of said switches for extending the calling lineto the main office, subscriber controlled means at the main ofiice for registering the digits of a called line number, and means responsive to the registration of suflicient digits to indicate that the called line is in the sub-office for causing said last means to test for an idle sub-office switch over which to complete the connection.

27. In a telephone system, a main ofiice and a sub-ofiice, a calling line at the sub-ofice, means for extending the calling line to the main ofiice, a registering device at the main office, means controlled by the calling subscriber for setting said registering means in accordance with certain digits of a called line number, and means responsive to the setting of said registering means to mdicate a call to another sub-ofiice line for rendering the registering means effective to register a subsequent digit of the called number.

28. A telephone system as claimed in claim 16, in which means is provided for returning a busy tone to the calling party in case the switching device at the sub-office tests busy, and in which the registration of the last digit of the called number is prevented under these conditions.

29. In a telephone system, two ofiices connected by a trunk line, a plurality of lines at one office, a switch having access to said lines, a set of terminals for each of said lines at the other office, a second switch having access to said terminal sets, an impulse sender at the other ofiice, means for extending a connection to one of said terminal sets, means responsive to the connection for causing said sender to transmit impulses to both switches to stop them simultaneously, and means minal set to which the connection was extended for disabling said sender and thereby stop the first switch in position to connect with the line associated With said one terminal set.

30. In a telephone system, a sub-exchange, a trunk line extending from said sub-exchange to a main exchange, two switches terminating said trunk in the sub-exchange, means for operating the first switch as a finder to extend a calling sub-exchange line to the main exchange, means for operating said first switch as a connector to complete a call from the main exchange to a subexchange line, and means controlled from the main exchange for operating said second switch 7 as a connector to complete a call to a sub-exchange line provided the calling line is also a subexchange line.

31. In a telephone system, a main exchange, a sub-exchange, a trunk line connecting said exchanges, a switch terminating said trunk in the sub-exchange, an impulse sender in the main exchange, and means responsive to a call on a line in the sub-exchange for operating said sender to send impulses over said trunk line to said switch to operate the same to find the calling line.

32. A telephone system as set forth in claim 31, in which impulses are transmitted over one conductor only and in which means in the switch is provided for stopping the sending operation over the other conductor.

33. A telephone system as set forth in claim 31, in which the said switch is provided with a responsive to said second switch engaging the tertest relay controlled over the two sides of the calling line in series to stop the sending operation.

34. In a telephone system, a main exchange, a sub-exchange, a trunk line connecting said exchanges, a switch terminating said trunk in the sub-exchange, said switch having access to the lines in the sub-exchange, means for operating said switch as a finder to connect with a calling line or as a connector to connect with a called line, two auxiliary switches in the main exchange, an impulse sender in the main exchange for transmitting the necessary impulses over the trunk line to the first switch to operate the same in either case, and arrangements whereby said impulse sender when transmitting impulses over said trunk line, also transmits impulses to one or the other of said auxiliary switches depending on whether the first switch is being operated as a finder or as a connector.

35. In a telephone system, a calling and a called line, means for connecting said lines, a common conductor connected to one conductor of the calling line and to one conductor of the called

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