US2057864A - Telephone system - Google Patents

Description

Oct. 20, 1936. .1 H. Voss TELEPHONE SYSTEM 62m UU IJHHMM HH-- -I il-.. Al--. -i U@ .-b |16 N2 nai, W .41 LN. www n H1@ Nlulllnmom 2 all? Oct. 20, 1936. .1. H. Voss TELEPHONE SYSTEM Filed July 5, 1935 4 Sheets-Sheet 2 Oow INVENTOR.

JOHN H. VOSS OmOO w2 mmh-LO A TTORNEY.

Oct. 20, 1936. J. H. Voss TELEPHONE SYSTEM Filed July 5, 1935 4 Sheets-Sheet 3 A TTORNE Y.

Oct. 20, 1936. J. H. Voss TELEPHONE SYSTEM Filed July 5, 1955 4 Sheets-Sheet 4 A TTORNEY,

Patented Oct. 20, A1936 UNITED' STATES PATENT oFFlcE TELEPHONE SYSTEM Application July 5, 1935, Serial No. 29,863

14 Claims.

This invention relates to' telephone systems.

It is concerned particularly with telephone systems including a main exchange and a private branch exchange in which the local calls and calls outgoing from branch exchange subscribers are handled through automatic switches, while calls incoming to the branch exchange are intercepted and completed under the control of an attendant operator. The main object of the invention is concerned with the production of new and improved features of operation which enable the inter-exchange service to be handled more satisfactorily by means of a minimum of relatively simple equipment. j l5 GENERAL DESCRIPTION As is well known, local service ina private automatic branch exchange is handled through dial-controlled automatic switches; calls from branch exchange lines to the main exchange are handled over inter-exchange trunk lines Seized by the automatic switching apparatus in the branch exchange responsive to the dialling of the main-exchange designation; while calls incoming from the main exchange to the branch exchange are intercepted by the branch exchange operator, who directs them to the appropriate or desired branch exchange lines.

From the standpoint of handling incoming calls, attended private automatic branch exchanges may be divided into two classes: (l) private automatic branch exchanges in which the incoming calls are completed through automatic switching apparatus controlled by the 3 branch-exchange attendant or operator, and (2) private automatic branch exchanges in which incoming calls are extended manually through a manual switchboard presided over by the branch exchange operator. The present dis- 40 closure has to do with a private automatic branch exchange of the Second of the above-mentioned classes.

The private automatic branch exchange disclosed herein contains desirable features, including the following:

1. In order to insure the secrecy of conversation against accidental or intentional invasion or eavesdropping by the branch-exchange operator, arrangements are provided such that a 50 warning tone-signal is transmitted over a connection established through the operators switchboard in the event that the operator throws the talking key of a cord circuit overwhich a conversation is taking place, this ar- 55 rangement being controlled through the answering supervisory relay and contacts of the associated talking key.

2. In order to prevent the operator from plugging in to the manual-switchboard multiple of the local subscribers line and overbearing a con- 5 versation in progress, and also to prevent the operator from inadvertently interfering with a dialling operation in progress in the event that she makes connection with a busy local line, the tip and ring conductors of the local plug of each 10 of the cord circuits are maintained normally disconnected from the main part of the cord circuit, and the connecting up of the normally disconnected talking conductors is made dependent upon the operation of an idle-test relay over the sleeve conductor of an idle subscribers line. By this arrangement,the operator may insert her plug in the jack of a busy line and still be unable to hear the conversation over the line and be prevented from interfering with the progress of a 2 partially completed connection, because the tip and ring strands of the local plug of the cord circuit are maintained open.

3. In order to prevent the operator from defeating the arrangement set forth in the preceding paragraph by employing the trunk plug of a cord to listen in on a busy connection, contacts controlled jointly by the sleeve-connected trunk supervisory relay and the talking key of the cord circuit bring about the transmission of the aforementioned warning tone-signal to the operators headset conductors and thus to the line being intruded upon thereby notifying the operator that her intended intrusion is not going unnoticed, and notifying the two Subscribers of the busy connection that the secrecy of their conversation is being invaded.

4. In order to provide for the making of a more reliable busy test through the bringing of the tip and the plug into engagement with the sleeve of the jack, circuit arrangements have been provided to respond to the operation of a busy-test relay (over the tip of the plug from guarding potential encountered on the sleeve of the jack of a busy line) to bring about the application of a tone signal to the operators headset conductors. By this simple provision, the operator need only make sure that the tip of plug makes rm contact with the sleeve of the jack. Under this condition, the absence of a tone signal in the operators receiver indicates that the line is idle. This same arrangement operates in conjunction with a previously mentioned feature to secure correct performance in the event that the operator inadvertently or intentionally fails to make the tip-sleeve busy test and inserts the plug into the jack of a busy line. The above busytest relay then operates over the tip conductor of the busy line to cause the application of a busy-tone signal to the operators headset conductors, while the tip and ring conductors of the plug are maintained disconnected from talking conductors of the cord because of the absence of an idle-indicating potential on the sleeve element of the jack. The busy-test relay is preferably of high impedance, so that its connection to the tip contact of a jack will not interfere with the progress of a connection being set up automatically under the control of a dial. f

5. In order to provide the branch exchange `operator with a ready means of making connecbranch exchange has CII tion with bus'y branch-exchange lines for'the purpose of offering incoming calls, an offering cord and plug are attached to the operators headset conductors, through which the operator may extend connection to any local line multipled into the manual switchboard. But, the above mentioned warning tone-signal arrangement is associated also with the offering cord so that the insertion of the offering cord into the jack of the local line results in the application of warning tone-current to the operators headset conductors and to the conductors ofthe local line connected with so as to warn the subscribers that the operator is telephonically connected with the connection.

6. In order to enable a local subscriber engaged in an inter-exchange conversation to obtain additional information, for example, each of the inter-exchange trunk lines terminating at the a branch connection extending to the automatic switchboard, together with switching means controllable at will over a localline to switch the local line temporarily into connection with the automatic switchboard so that the subscriber may set up a local connection automatically to another local line and then later switch the connection back to the inter-exchange trunk line.

7. An additional desirable feature is found in the arrangement controlled partly through a local cord and partly from an inter-exchange trunk circuit for disconnecting both plugs of a local cord when the local subscriber involved in a call incoming from the main exchange replaces his receiver, thereby freeing the branch-exchange end of the trunk line immediately as well as immediately freeing the local line for further use, pending the taking down of the local cord by the branch exchange operator.

8. In order to render completely eiective the aforementioned arrangement for preventing the operator from either eavesdropping or interfering unintentionally with the progress of calls being set up automatically from local substations, a cut-oir relay has been added to each of the two-way inter-exchange trunk lines, which relay operates when the two-way trunk line is seized automatically in the branch exchange to cut off the switchboard extension of the trunk line so that the corresponding jack at the operators switchboard is telephonically disconnected.

Description of drawings Referring now to the accompanying drawings, comprising Figs. 1 Yto 4, they show by means of the usual circuit diagrams a suicient amount of the equipment involved in a telephone system embodying the invention to enable the invention to be underst0od.`

as the cord circuit CC, Fig. 1), together with l the offering cord which terminates in the offering vplug OP;

Fig. 3 shows the one-way outgoing trunk line TI and the associated trunk circuit TCI; and

Fig. 4 shows the two-way interexchange trunk line T2 and associated trunk circuit TC2.

In Fig. 1, the lines from the automatic substations A and B extend as indicated to the line switches LSZ and LSI, respectively. These line switches may be of any desired construction, being indicated only diagrammatically in the drawings, as are the similar line switches LS3 and LSI.

The line switches LSILS4 have common access to selectors, of which the selector SI is one. The selector SI may be of the usual Vertical and rotary type, having its back contacts arranged in horizontal rows or levels. The selector SI has access by way of one of its levels of bank contacts to the connector CI, which is one of a group of connectors through which connection may be extended to the 10U-line group containing the line of substation B. On another of its levels, the selector SI has access to the trunk lines of Figs. 3 and 4. The one-Way trlmk line of Fig. 3 is indicated as being a first-choice trunk line, while the two-way trunk line of Fig. 4 is indicated as being taken into use only after the first-choice trunk lines have been tested and found to be busy. This is inaccordance with the usual practice of reserving the more expensive two-way trunk lines until all of the less expensive one-way trunk lines have been taken for use.

It is to be noted that the line jack LJ I is a manual-switchboard multiple of the called multiple of the line of substation A at the automatic switchboard, while the line jack LJ2 is a similar multiple of the called multiple of the line of substation B. It will be noted further that the trunk jack TJ is a manual-switchboard extension of the trunk T2, Fig. 4, by way of the trunk circuit TG2, and that the line switches LS3 and LS4 are associated respectively with the trunk circuits TCI and TC2. It may be mentioned at this point that it is through line switches such as LS3 and LS4 that transfer service is made available to local subscribers involved in inter-exchange conversation, as will be pointed out more in detail hereinafter.

At the cord circuit CC, Fig. 1, the trunk plug 'I'P is the one designed to be inserted into trunk jacks such as TJ, while the local plug LP is the one to be inserted into a local jack, or line jack, such as LJ I and LJ2. The cable 200 is a multiple cable which multiples the common conductors 22I230l (associated with the position equipment of Fig. 2) with the various cord circuits, of which the cord circuit CC, Fig. 1, is one.

Detail description The disclosure havingbeen described generally, a detailed description of the operations involved in setting up and handling the several kinds of connections will now be given. For this purpose it will be assumed rst that the subscriber at subchange subscriber, removes his receiver and dials the designation of the main exchange.

Outgoing call over a one-way trunk When the receiver (not shown) is removed at substation A, the line switch LS2 operates in the usual manner to select an idle selector, the' selector SI, for example. Upon the seizure of the selector SI the automatic switchboard equipment is in readiness for the subscriber at substation A to dial the designation of the main exchange.

When the designation of the main exchange (the digit 0, for instance) is dialled, the selector SI raises its wipers opposite the level of bank contacts containing the main-exchange trunk lines, whereupon the wipers are rotated over the bank contacts in search of an idle trunk line. Under the assumption that the trunk line TI, Fig. 2, is idle, the wipers of the selectors SI come to rest on the bank contacts from which the conductors 309, 3I0, and 3II extend to the trunk circuit TCI, associated with the trunk line TI,

Fig. 3.

Upon the seizure of the trunk circuit TCI, line relay 304 thereof, which is connected to conductors 309 and 3I0 through the right-hand windings of repeating coil 303 and the windings of the differential transfer-control relay 308, energizes over the line of substation A. Upon energizing, line relay 304 places a bridge across the conductors of the trunk line TI at its upper contacts through the left-hand windings of repeating coil 303 and the resistor 3I5, which is shunted around the talking condenser associated with the lefthand repeating-coil windings. The closure of this bridge prepares automatic switching apparatus in the main exchange for further dialling operations in the event that the main exchange is an automatic exchange, while, if instead the main exchange is a manual exchange, the bridging of the trunk line TI results in the lighting of the usual line lamp at the operators switchboard.

As a further result of its energization, line relay 304 closes a circuit for release relay 306 at its inner armature, whereupon relay 306 operates and prepares a locking circuit for transfer relay 305 at its lower armature, at the same time applying a holding potential to conductor 3II at its upper armature. The holding potential thus applied to conductor 3H is effective to maintain the selector SI and the line switch LS2, Fig. 1, operated until the receiver is replaced at the calling substation A.

When the connection over the trunk line TI has been set up through the main exchange switchboard to the desired line and an answer has been secured, conversation may take place between the line of substation A and the called line through the line switch LS2, the selector SI, the trunk circuit TCI, and the trunk line TI.

When the conversation is finished, the subscriber at substation A replaces his receiver, whereupon line relay 304 restores and opens the bridge across the conductors of the trunk TI at its upper contacts, thereby bringing about the release of the automatic switching equipment in the main exchange in the event that the main exchange is an automatic exchange, or bringing about the lighting of the usual disconnect lamp at the manual switchboard in the main exchange, provided the main exchange is a manual exchange.

The deenergization of line relay 304 brings about the deenergization of relay 306, whereupon holding potential is removed from'conductor 3| I, permitting the release ot the selector SI and line switch LS2 to take place.

Transfer service through the one-way tmnk circuit TCI Let us assume now that the subscriber at substation A has set up an outgoing connection by way of the lineswitch LSI and the selector SI over the trunk circuit TCI and the trunk TI, and

that during the conversation the subscriber at substation A desires to converse momentarily with another local branch exchange subscriber, to obtain additional information, for example. For this purpose, the subscriber at substation A after requesting the main exchange subscriber to hold the line for a moment, momentarily depresses his grounding transfer-control push button PI, thereby applying ground potential momentarily to one of the conductors of his line. .This momentary application of ground potential to a conductor of the line of substation A unbalances the current-flow through the two windings of the differential transfer-control relay 308 suiciently to cause an operation of relay 300. Upon operating, relay 308 closes a circuit for the inefficient upper Winding of the two-step transfer relay 305, whereupon relay 305 energizes just suflciently to close its lightly adjusted first-step contacts, the inner lower contacts of the relay. The actuation of these contacts closes a locking circuit for both windings of relay 305 in series, through contacts controlled by the armature of unlock relay 301 and the lower contacts of 'release relay 30G. No current, however, flows through the lower winding of relay 305 for the time being because the initial circuit for the upper winding of relay 305 is an effective shunt around the lower winding of the relay.

When the push-button PI is released, transfercontrol relay 308 restores responsive to the restoration of the normal balanced condition of current flow through its windings. The initial circuit for the lower winding of relay 305 is thereby opened, whereupon the locking circuit for both windings of the relay in series becomes effective, and relay 305 operates fully to seize the lineswitch LS3, Fig. l, by way of conductors 3I2-3 I 4. At its upper armature, transfer relay 305 places a shunt around the upper contacts of the line relay 304 so as to maintain the trunk line TI continuously bridged, and at its lower armature it shifts the contacts of transfer control relay 308 from its own winding to the winding of unlock relay 301.

The line switch LS3 operates over the calling line (A) and over conductors 3I2 and 3I3 in the usual manner to select an idle selector, similar to the selector SI. Ground potential is placed on conductor 3I4 of the line switch LS3 by the seized selector to close a holding circuit over conductor 3I4 and through the inner upper contacts of transfer relay 305 for release relay 306, thereby maintaining this relay operated after line relay 304 has fallen back, which it does upon being dis-v connected at the transfer contacts of relay 305.

The subscriber at substation A now proceeds to dial the number of the desired local line, whereupon the connection is extended through the automatic switchboard to the desired line and called local'subscriber, he again momentarily depresses the'push button PI, again bringing about ture to the locking circuit of transfer relay 305,

at the same time disconnecting the locking circuit of transfer relay 305 from ground potential at the lower contacts of release relay 306. Then, when transfer-control relay 308 restoresV (when PI is released). it opens the circuit of relay 301 and the locking circuit of relay 301. Relay 305, being slow-acting, remains operated for a short interval after the circuit is opened, so that transfer relay 305 is permitted to fall back and open a point in its locking circuit before relay 301 restores.

Upon restoring, transfer relay 305 disconnects conductors 3|2, 3|3, and 3|4, permitting the con- 'nection set up through the lineswitch LS3 to clear out.

Line relay 304 now operates again over the line of substation A and again takes over the control of release relay 306 and the control over the bridge established across the outgoing trunk line TI. A moment later, the slow-releasing unlock relay 301 restores. Relay 301, it is noted, maintains the trunk line TI bridged during the transition period following the restoration of relay `305 and the resulting reoperation of line relay 304.

The interrupted conversation between the subscriber at substation A and the main exchange subscriber reached over the outgoing trunk line .Tl may now be resumed.

It will be appreciated, of course, that the subscriber at substation A may, if he so desires, again interrupt the conversation with the main exchange subscriber and again transfer his connection over to the line switch LS3 for the purpose of setting up another local inquiry connection in the manner described hereinbefore.

When the conversation is completed the subscriber at substation A replaces his receiver, whereupon the interexchange connection is cleared out as before explained.

An outgoing call over a two-way trunk For the purpose of explaining the operation of the trunk circuit TC2, Fig. 4, when it is seized in the branch exchange in an outgoing call, it will be assumed that the subscriber at substation A makes an outgoing call by way of the selector Sl, for example, at a time when all of the one-way trunk lines, such as the one shown in Fig. 3, are in use and that the trunk line T2, Fig. 4 is the rst one found to be idle by the selector SI as it rotates over the trunk-line contacts. That being the case, the trunk circuit TC2, Fig. 4, is seized by the selector SI over conductors 42l-423, whereupon line relay 404 of the trunk circuitTCZ energizes over the line of substation A and over conductors 42| and 422. At its upper contacts, line relay 404 bridges the conductors of the trunk line T2 through the left-hand windings of repeating coil 403 and resistor 4|3, while at its lower armature it closes a circuit for release relay 405. Release relay 405 thereupon operates and places ground potential on conductor 423 at its upper armature, thereby providing a holding circuit for the selector SI and the line switch LS2. Release relay 405 also disconnects the ring-up relay 405 from in bridge of the conductors of the trunk line T2, while at its inner upper'armature it prepares a locking circuit for transfer relay 4|0.

At the lower armature of release relay 405, a. circuit is closed over 421 for busy lamp |23 to notify the operator that the trunk is in use.

Jack-cut-off relay 4|2, whose lower winding is normally in series with conductor 42|, energizes over conductor 42| and over the calling line,` in series with line relay 404. Upon energizing, relay 4|2 closes a locking circuit for its upper Winding to the grounded release while at its upper and lower armatures it disconnects conductors 424 and 425 which lead to the trunk jack TJ. The trunk jack TJ is therefore no longer in multiple of the trunk circuit TC2, and will be maintained disconnected for the duration of the call.

The lower Winding of jack-cut-oi relay 4| 2 is by-passed at the lower armature of the relay, so as to alord a better talking and dialling circuit.

The desired connection is completed in the main exchange, either manually or responsive to further dialling on the part of the subscriber at substation A, depending upon whether the main exchange is a manual exchange or an automatic exchange. In the event that the main exchange is an automatic exchange, the dialling impulses are repeated by line relay 404 at its upper contacts, as in the case of line relay 304 of trunk circuit TCI, Fig. 3.

Transfer service through the two-way trunk Circuit TCZ trunk conductor 423,'

is to be noted that the transfer connection in this case is over conductors 4|3-4 5 to the line switch LS4, Fig. 1.

It is to be noted further that relays 409 and 4 I0 cooperate at their upper contacts to maintain the trunk T2 bridged during the time the connection is transferred away from the trunk T2 and pending the reoperation of line relay 404.

When the receiver is replaced at substation A at the end of the inter-exchange conversation, line and release relays 404 and 405 restore, whereupon the removal of ground potential from conductor 423 at the upper contacts of release relay 405 results in the clearing out of the automatic switches LSZ and SI.

Handling an incoming call For the purpose of `describing how incoming calls are handled, it will be assumed that the trunk line T2, Fig. 4, is seized in the main exchange in a call for a subscriber of the branch exchange.

When the trunk line T2 is seized in the main exchange, ringing current is projected thereover in the usual manner, operating ring-up relay 406 which is bridged across the conductors of the trunk line T2 lthrough the associated condenser. Relay 406 closes a circuit for call relay 401, which relay responds and closes a locking circuit at its inner upper armature through contacts of release relay 405. Call relay 401 also prepares a circuit for hold relay 408 at its inner lower armature, while at its upper armature it places ground po- 'tential on conductor 423 so as to mark the trunk line engaged immediately at the selectors such as Sl Fig. 1.

Relay 401, at its inner lower armature, closes a circuit over conductor 421 for busy lamp |23 at the trunk jack TJ, while at its lower armature it closes a circuit over conductor 428 for the call lamp |24, thereby notifying the operator that a call has been received from the main exchange.

The branch exchange operator responds to the lighted condition of the call lamp |24 by inserting the trunk plug of a cord circuit, trunk plug TP of cord circuit CC, for example, into the trunk jack TJ.

When the trunk plug TP is inserted into the jack TJ, the strands of the cord circuit CC are bridged across conductors 424 and 425 operating the line relay 404 in the trunk circuit TC2 over the supervisory bridge in the cord circuit CC, which bridge includes contacts controlled by the lower armature of connecting relay |06, contacts of the answering supervisory relay |05, and resistor |4. Upon operating through the cord circuit CC, line relay 404 at its lower armature removes ground potential from sleeve conductor 426 of the trunk jack TJ, thereby preventing false operation of the supervisory and release timer relay |08 in the cord circuit CC. Line relay 404 also closes a direct current bridge across the conductors of the trunk T2 at its upper contacts, thereby causing the ringing condition to be terminated in the main exchange and giving answering supervision.

Hold relay 408 operates through the lower contacts of the operated relays 404 and 401 to bridge the trunk line T2 at its upper contacts independent of the upper contacts of line relay 404.

Release relay 405 responds to the operation of line relay 404 and disconnects ring-up relay 406 at its inner lower armature; makes an additional application of ground potential to conductor 421 at its lower armature; makes an additional application of ground potential to release trunk conductor 423 at its upper armature; and at its inner upper armature it opens the locking circuit of call relay 401, at the same time closing a locking circuit for the upper winding'of the operated hold relay `408 and preparing a locking circuit for transfer relay 4|0. Relay 408 is therefore maintained operated throughout the remaining time of the incoming connection under the control of release relay 405 so as to maintain the state of answered supervision over the trunk line T2 at its upper contacts. Y Upon-the falling back of call relay 401, the call lamp |24 at the trunk jack TJ is extinguished at the lower contacts of the relay, but conductors 423 and 421 remain grounded at contact of release relay 405, thereby maintaining the trunk circuit TC2 guarded at the automatic switchboard and maintaining busy lamp |23 lighted at the trunk jack TJ.

In order to converse with the calling subscriber, the operator now throws her key Kl of the cord circuit CC into talking position, thereby operating the right-hand contacts of the key. The tone lead 225 is connected up at the upper contacts or' the talking key; the hold lead 222 is connected up at the lower contacts of the talking key, While at the middle contacts of the talking key the test lead 22| is brought into connection with the lower winding of connect relay |06. The test conductor 22| is normally grounded at the upper contacts of guardv relay 20|. Assuming guard relay 20| to be in normal position at this time, the upper winding of connect relay |06 of the cord circuit CC is energized over conductor test 22|, whereupon connect relay |06 operates and closes a holding circuit for its lower winding at its inner lower contacts, through the lower contacts of the talking key, and over hold conductor 222 in series with guard relay 20|, Fig. 2. Guard relay 20| thereupon operates in series with the lower winding of connecting relay |06 and removes ground potential at its upper contacts from test conductor 22| to insure that no further connect relay such as |06, Fig. 1, is operated until the operator restores the key KI and permits connect relay |06 and guard relay 20| to restore.

As further results of its operation, connect relay |00 connects the tip and ring conductors 223 and 224 of position equipment PE with the corresponding conductors'of the cord circuit CC; it connects the busy-test lead 221 to the tip of the local plug LP; it connects the split conductor 228 to split relay |01 of the cord circuit; and it connects the ring-start lead 226 to ring-start relay |04. At the normally closed contacts controlled by the lower armature of relay |06, the bridge across the strands of the cord circuit CC by way of resistor ||4 is opened, and the strands on the cord are now bridged only by the common tip and ring conductors 223 and 224, contacts of feed relay 203, secondary windings of the induction coil IC. and the articial line AL. The line relay 404 of the trunk circuit TC2 is held operated for the time being through the bridge just traced.

The operator may now converse with the calling main-exchange subscriber over the cord circuit CC and the trunk line T2 and ascertain with whom connection is desired.

It is to be noted that the operators receiver R, instead of being directly associated with the secondary windings of the induction coil C (in the usual anti-sidetone arrangement involving the artificial line AL), is replaced in this circuit by the primary windingof repeating coil RC, whose secondary winding leads to the receiver R. The primary winding of the repeating coil RC is shunted by a full-wave dry-disc rectifier 2|0, which is so proportioned with respect to the voltages normally applied to it during conversation that it acts as a high-resistance shunt normally, but acts as a low resistance shunt in the event of the momentary application of a high voltage surge. The operator is thus protected in a large measure from loud, disagreeable noises which are otherwise produced occasionally in her receiver.

It may be pointed out that the transmitter T obtains its energizing current from the condenser-shunted retard coil 209, and is in circuit with the primary winding of the induction coil Assuming that the operator learns that the calling subscriber desires to be connected with the subscriber at substation B, accessible by way of the line jack LJ2, the operator may follow either of two procedures, depending upon the operating instructions which she has received:

(l) She may forego the usual voluntary busy test and insert the local plug LP straightway into the line jack LJ2 of the line of the subscriber at substation B; or

(2) She may first make a busy test by touching the tip of the local plug LP to the sleeve of the line jack LJ2.

Testing the called Zine It is to be noted that busy-test relay 206 has one terminal thereof connected to the negative or grounded pole of the exchange battery, While y heard by the calling subscriber.

the other terminal thereof is connected by way of busy-test conductor 221, contacts of the operated connect relay |06, and contacts of switching relay |02, to the tip of the local plug LP of the cord circuit CC. In the event that the operator is instruceted to make a tip busy-test, she places the tip of the plug LP in contact with the exposed portion of the sleeve of the line jack LJ2. In the event that the' line of substation B is idle at this time the test or sleeve conductor |2| thereof has a negative potential thereon, through the usual cut-off relay (not shown), and busy-test relay 206 therefore does not operate. On the other hand, if the line of substation B is engaged, there is a ground potential on sleeve conductor |2| thereof with the result that busytest relay 206 operates over sleeve conductor l2 I. At its inner contacts, relay 206 closes a circuit for the ticker relay 205, while at its lower armature it places a shunt around the resistor 201 so as to increase the amplitude of the signalling tone at this time. When ticket relay 205 operates (in series with resistor 2| I), it closes a shunt around its winding at its inner armature, which brings about a deenergization of the relay. Relay 205 therefore operates somewhat after the fashion of a buzzer, but less rapidly because its operation is delayed by the lpresence of .the copper collar around the armature end of its core and the indicated copper sleeve over the entire part of the core beneath the Winding, while its restoration vis further delayed by the retarding eiect of its winding when short circuited at the inner lower contacts of the relay.

The intermittent operation of relay 205 while its circuit is maintained closed at the inner lower contacts of busy test relay 206, results in the intermittent closure of a circuit at the lower contact of relay 205 through the lower contacts of relay 206 and resistor 208 for the tertiary Winding of the induction coil IC. The current-flow induced in the secondary winding of the induction coil IC by this intermittent closure of the circuit through the tertiary Winding of the coil, results in the application of a tone signal to the operators receiver, which tone signal may also be This tone signal is interpreted as an indication that the line of substation C is in use.

When the tip of the plug LP is removed from the sleeve of the jack LJ2, busy test relay 206 restores and terminates the intermittent operation of the ticker relay 205.

Assume now'that the operator is instructed to LJ2 without previously determining Whether the connected line is busy or idle. Nevertheless, the operator does not establish a telephonic connection with the line (when it is busy), for the tip and ring strands of the plug LP are open at contacts of switching relay |02, and the controlling, idle-test relay having its lower terminal connected to ground through contacts of cut-off relay |09, requires an idle-indicating potential on the sleeve conductor |2| of the jack LJ 2 for its operation. Therefore, busy-test relay 206 remains connected to the tip of the plug LP. Since the line of substation B is in use at this time, the potential applied to either of the talking conductors thereof is somewhere between the potentials existing at the two poles of the exchange battery (due to the bridged condition of the line and the potential l jack LJ2, the operator is drop in the usual battery-feed bridge (not shown) As a result, busy-test relay 206 is operated over the tip of the line jack LJ 2 and causes the busy tone to be applied by bringing about an operation of ticker relay 205, as above described. The operator is therefore notified that the line of substation B is in use and that she should remove the plug LP from the jack LJ 2.

It may be pointed out at this time that the impedance of the busy test relay 206 is made very high with respect .to the impedances normally obtaining in connection with subscribers lines, whereby a dialling operation, if occurring at this time over the busy line, is not interfered with, and the automatic switching mechanism being operated continues to operate without interference.

When the plug LP is withdrawn from the jack LJ2, busy test relay 206 restores and ticker relay 205 ceases to operate.

Oering an incoming call to a busy line In the event that the operator desires to make a talking connection with the line of substation B and inquire of the subscriber at substation B whether or not he cares to abandon the local connection in which is engaged and accept the incoming call, the operator restores her talking key KI of the cord circuit ing plug OP to make connection with the desired busy line through the line jack LJ 2.

When the talking key KI is, restored, connecting relay |06 restores and reestablishes the supervisory bridge through resistor I 4. The guard relay 20| in the position equipment PE, which has also maintained the talking conductors of the offering plug OP disconnected, restores and reconnects these conductors to the operators headset conductors.

When the offering plug OP is inserted into the placed in telephonic communication with the line of substation B through the tip and ring conductors of the plug OP and the corresponding conductors of the line jack LJ 2. The lower winding of tone relay 202 is energized at this time over the grounded sleeve conductor |2| of the line jack LJ 2 to operate the ticker relay 205 and thereby apply the tone signal to the operators receiver and to the operators headset conductors, thereby warning the subscriber at substation B immediately that his conversation may now be heard by the branch-exchange operator. 'Ihe tone produced at this time by the above described operation of ticker relay 205, although noticeable, is suiiiciently mild that conversation is not materially interfered with. Therefore, the branch exchange operator can now converse with the subscriber at substation B and inform him that she is holding an incoming call for him.

In the event that the two local subscribers to the conversation replace their receivers and the operator withdraws the offering plug OP from the local jack LJ2, tone relay 202 restores and ticker relay 205 ceases operating when vthe offering plug OP is removed from the jack PJ. Moreover, the line of substation B is freed and brought to its normal idle condition responsive to the receivers being replaced at substation B and the other substation included in the previously established connection.

The. operator now inserts the local plug LP of the card CC into trunk jack TJ, whereupon idletest relay |0| is operated over Athe sleeve of the jack LJ2, conductor |2|, and the usual cut-of! CC and employs the olerrelay (not shown) to the negative pole of the exchange battery. The line of substation B is caused to test busy to the automatic .switches having access to it by the ground potential applied thereto through the winding of idle test relay |I. Relay |0| operates switching relay |02 to close the talking circuit to the line of substation B and to disconnect the busy test conductor from the tip conductor of the plug LP. Switching relay |02 also closes a lighting circuit through contacts of .answering supervisory relay for supervisory lamp |26, while at its inner upper armature rt 'prepares a circuit by way of contacts of relay |08 for cut-off relay |09.

The operator now operates thetalking key Kl again, again operating connect relay |06 along with guard relay 20|, thereby again associating the position equipment PE lwith the cord circuit CC and again bringing the operator into telephonic communication with the calling mainexchange subscriber.

In order to signal the subscriber at substation- B, the operator momentarily actuates the common ring start-key K2, thereby applying ground potential to ring-start conductor 226, closingA a circuit through contacts of connect relay |06 for the lower winding of individual ring-start relay |04. Ring-start relay |04 locks itself through its upper winding by way of contacts of relays |03 and |02, and contacts of the key KI. At its upper and lower armatures, ring-start relay |04 opens the talking strands and connects the ringing circuit through the plug LP to the called line. The tip conductor is now connected to the ringing-current-supply conductor ||0', while the ring conductor is connected through the winding of ring-trip relay |03 to the ungrounded negative pole of the exchange battery. Ringing current is now applied intermittently in the usual manner to the line of substation B. The condenser |25, shunted around the upper armature and resting contact of ring-start relay |04, is of suicient size to permit a small amount of ringing current to pass back to the right-hand end of the cord circuit CC, serving as an indication both to the calling subscriber and to the operator that the called subscriber is being signalled.

The operator is expected to restore her key KI as soon as she has started the ringing operation and has heard the ringing-tone indication above mentioned. This brings about the restoration of connect relay |06 and guard relay 20|.

When the subscriber at substation B responds to the applications of ringing current by removing his receiver, the direct-current bridge thereby closed across the conductors of his line results in the operation of ring-trip relay |03. The locking circuit of ring-start relay |04 is opened by relay |03, whereupon relay |04 restores thereby opening the ringing circuit and reclosing the talking strands of the cord. Answering-supervisory relay |05, whose lower winding is connected in series with the lower talking conductor of the cord circuit CC, now operates over the line of substation B in series with line relay 404 in the trunk circuit TC2 and in shunt of the supervisory-bridge resistor ||4. At its inner upper armature, relay |05 closes a locking circuit for itself through contacts of key KI, and contacts of the operated switching relay |02. At its lower armature, relay |05 shunts its lower winding to provide a better talking circuit, while at its upper armature it disconnects supervisory lamp |26. Answering supervisory relay |05 opens the previously existing supervisory bridge through resistor ||4, .thereby placing line relay 404 of the trunk circuit TC2 under. the direct control of the called line.

The two subscribers may now converse with each other as desired. I

Transfer service during an incoming' call In order to explain how the transfer service operates during an incoming call, it will be assurned that the subscriber at substation B desires to obtain further information on some point under discussion before completing his conversation with the calling main exchange subscriber. In this event. the subscriber at substation B momentarily operates his push button P2, thereby momentarily applying ground potential to one of the conductors of his line to bring about a momentary unbalanced current fiow through the windings of the diierenital transfer-control relay 4| I. As a result, transfer relay 4|0 is operated through its first step when the push button PI is pushed and is operated through its second step when push button P2 is released. 'I'he line of substation B is thereupon transferred from the trunk T2 and over conductors 4|3-4I5 to the line switch LS4, which line switch operates in the usual manner to seize an idle selector such as SI. The subscriber at substation B now proceeds to set up the desired connection and obtain the desired information.

After the information has been obtained the local subscriber again operates the push button Pl momentarily, whereupon transfer-control relay 4|| in the trunk circuit TC2 is again momentarily actuated. By the resulting operation of unlock relay 409 at this time, transfer relay 4|0 is restored and relay 409 restores shortly thereafter. The connection between the subscriber at substation B and the calling main exchange subscriber is thus reestablished, while the line switch LS4 is disconnected.

Transferring an incoming call to another local line In the event that the subscriber (at substation B) to whom the incoming call has been directed decides that some other branch exchange subscriber (the subscriber at A, for instance) should take over the call, he may signal the branch exchange operator and request her to transfer the incoming call.

In order to signal the branch exchange operator, the subscriber at substation B operates his calling device, preferably in accordance with some digit greater than 5. As a result, a number of interruptions are produced in the circuit of line relay 404 of the trunk circuit TG2. Each time its circuit is interrupted, relay 404 restores and applies ground potential to conductor 426 but it does not interrupt the answering bridge across the conductors of the trunk T2, for hold relay 408 (operated because this is an incoming call) holds the bridge closed. Each time it applies ground potential to conductors 426, line relay 404 closes a circuit through the sleeve of the trunk jack TJ and the sleeve of trunk plug TP for the supervisory and release-timer relay |08. Relay |08 operates the first time its circuit is closed. When it does so it closes a local circuit for its upper winding, rendering itself slow-releasing. Therefore, relay |08 is maintained operated throughout the dial-produced series of deenergizations of relay 404, by the slow-acting effect produced by the local circulating current in the upper winding of the relay. The somewhat momentary operation of relay |08 (during the transmission oi' the series of impulses) results in the corresponding closure of a circuit for supervisory lamp |26 at armature |29. Lamp |26 therefore becomes lighted for a moment to attract the operators attention.

The weighted spring |21 is struck by the associated armature, but the contact produced by this action is an unsteady vibrating contact pref, erably for a period of substantially more than a second, with the result that the vibrating spring |21 does not come to rest (to thereby allow the upper winding of relay |09 to become energized) during the somewhat momentary interval that relay |08 is held operated responsive to the succeeding impulses of the recall series. Relay |09 is somewhat slow to operate, as indicated, for which reason it does not respond in any event to the operation of relay |08 until the vibration of the weighted spring |21 has substantially ceased.

When relay |08 restores, upon the cessation of the impulses, lamp |26 becomes extinguished.

The above signalling operation may be repeated as often as desired, or until the operator responds.

The operator responds to the above lighting of supervisory lamp |26 by throwing her key KI to talking position, bringing about the reoperation of connect relay |06 and guard relay 20|. The operator may converse with the local subscriber and discover to whom the call should be transferred, which transfer operation is carried out by removing the plug LP from the local jack and by proceeding to make connection with the line of substation A through jack LJ l. When the plug LP is removed from the jack LJ2, idle-test relay switching relay |02, and answering supervisory relay restore successively, placing the cord circuit in condition for making a new connection. Line relay 404 is held operated, during the transfer of the plug LP, through the oper- Aators headset conductors, and resistor H4 is Clearing out the incoming connection When the inter-exchange conversation is completed, the calling main exchange subscriber and the local branch-exchange subscriber replace their receivers. When thereceiver is replaced at substation A, line relay 404 in the trunk circuit TC2 restores and opens the circuit of release relay 405, permitting relay 405 to restore after a slight interval. Hold relay 408 is unlocked by release relay 405. Disconnect supervision is given to the main exchange at the upper contacts of hold relay 408. With release relay 405 restored, conductor 423 is ungrounded to mark the trunk T2 idle at the selectors such as SI.

Line relay 404 also applies ground potential to sleeve conductor 426, thereby closing a circuit through the sleeve of the jack TJ of the plug TP for supervisory relay |08. Relay |00 operates and at armature |29 closes a circuit for supervisory inner upper armature of switching relay |02, and' contacts of key KI. Cut-oil? relay |09 is therefore operated after an interval of somewhat more than one second has elapsed, during which interval the weighted spring of contact |21 goes through its period -of vibration. Upon operating, relay |09 locks its lower winding to the sleeve of the plug PT, at the same time opening the talking strands of the plug TP. At contacts controlled by the middle lower armature, relay |09 removes'ground potential from one terminal of idle-test relay |0| thereby freeing the line of substation B and permitting idle-test relay |0| and switching relay |02 to restore. At its upper armature, switching relay |02 opens the initial circuit of cut-oi relay |09, but cut-off relay |09 is now maintained operated in the locking circuit including its lower winding and the sleeve conductor of the plug and jack. Answering supervisory relay |05 is also restored by the opening of the inner upper contacts of relay |02.

Answering supervisory relay |05, at its lower armature, again bridges the resistor ||4 across the strands of the cord circuit CC, but'this does not result in a reoperation of line relay I 04 of the trunk circuit TG2, because the tip and ring conductors of the trunk plug TP are disconnected at contacts of cut-oli relay |09.

It is to be particularly noted that both the line of substation B and the trunk circuit TCZ are freed for furtherA use, even though the operator permits the plugs LP and TP of the cord circuit CC to remain in the jacks LJ 2 and TJ indefinitely.

When the operator removes the plugs LP and TP, relays |00 and |09 in the cord circuit CC restore, returning the cord circuit to normal condition, supervisory lamp |26 being extinguished at armature |29 of relay |08.

In the event that the trunk line T2 is seized at the automatic switchboard in an outgoing call while the plug TP is still in the trunk jack TJ, and the local plug LP is still in the local jack LJ2, jack-cut-off relay 4| 2, upon operating in series with conductor 42| upon the seizure of trunk circuit TC2, places ground potential directly on conductor 426 at its lower armature so as to maintain relay |09 of the cord circuit CC actuated' after line relay 404 has operated responsive to the seizure.

Conductor 426 is thus maintained grounded at jack-cut-ofi relay 4 2 for the duration of the outgoing call, and ground potential is reapplied to this conductor by line relay 404 at the termination of the call before jack-cut-oi relay M2 is permitted to restore.

In the event that an incoming call is received over the two-way trunk T2 while the trunk plug TP still is in the trunk jack TJ and the local plug LP is still in a local jack, the call lamp |24 at the jack TJ is lighted in the usual manner over conductor 428 when call relay 401 responds to the actuation of ring-up relay 406. Upon noting the lighted condition of the call lamp |24, the operator iirst removes the local plug LP from the local jack and then momentarily removes the trunk plug TP from the trunk jack TJ, again inserting the plug in the jack. The momentary removal of the trunk plug TP from the jack TJ, permits relays |08 and |09 to restore, and relay |09 is thus permitted to again connect up the talking conductors of the plug TP to the cord. TherelOering an incoming call to an idle line Since the VcordCC is a dry cord`(it contains no current-supply bridge) special arrangements must be made to furnish talking current to the called local line in the event that the operator desires to converse with thelocal called sub- -scriber without the knowledge of the calling main exchange subscriber, ordinarily for the purposeo-determining whether or not the tentatively selected local subscriber is the one to take the call.

1n order to spia the cord cc, the operator (with the talking key K! and connecting relay |06 in the cord operated, together with guard relay 20| of position equipment PE) operates the common key K2 to split position, in which position the left-hand contacts of the key are actuated. The

` lower contacts 'of the split key place ground potential on split conductor 228, closing a circuit through contacts of operated relay |06 for split relayf |01 in the cord circuit. Relay |01 bridges the dial conductors 229 and 230 across the tip and ring conductors of the trunk plug TP, to hold the line relay of the connected trunk in operated condition. At the same time, the talking strands of the cord circuit are separated at the contacts of relay |01, whereby the telephonie connection with the calling main-exchange line is severed.

The local line reached through the plug LP ls now deprived of its previous supply of energizing current for the transmitter. Therefore in the position equipment PE contacts of the split key K2 operate the feed relay 203 to connect the retard bridge 204 across the operators tip and ring conductors 220 and 223 `as a transmittersupply bridge for the local line, at the same time inserting condensers between conductors 223 and 220 and the operators telephone equipment, it

being unnecessary to send transmitter current through the secondary winding of the induction l The operator now proceeds to converse with the local subscriber and determine whether or not he is the one to take the incoming call. It is to be noted that the upper contactsof the split key K|2 disconnect the upper winding of tone relay 202 from tone conductor 225, so that this tone relay is not operated at this time to place a warning tone on the operators headset conductors and the conductors of 'the called local line. This warning tone is obviously unnecessary now, as the conversation is Vonly between the operator and the local subscriber.I

Assuming that the called local subscriber is the one to take the call, the operator restores the talking key Kl ,and split key K2. Feed relay 203 in the position equipment PE restores, as does split relay |01 in the cord circuit CC. e

The twosubscribers may now converse through the cord circuit CC.

Putting through a delayed cazz The way in which a delayed outgoing call is handled by the branch exchange operator will now be explained. For this'purpose it will be assumed that the subscriber at substation A, being unable to ,reach a desired main exchange subscriber, requests the switchboard operator to make an attemptto set up the connection for him, such a call being termed a delayed call. To complete the delayed call, the branch exchange opthe trunk plug TP of the cord circuit CC, for example, into a trunk jack, such as TJ, associated with a two-way trunk which is idle, the

busy or idle condition being indicated by the lighted or unlighted condition of the busy lamp erator inserts. the trunk plug o( an idle cord,

as previously pointed out, in series with resistor l I4 bridged across the strands of the cord circuit CC. Releasel relayr 405 applies ground potential to conductor 423 to guard the trunk circuit TG2 against seizure at the automatic switchboard. At its upper contacts line relay 404 closes a bridge across the conductors of the trunk T2 through the left-hand windings of repeating coil 403 and resistor 413, thereby signalling the main -exchange operator in the event the main exchange is a manual exchange, or taking a first selector for usein the main exchange in the event that it is an automatic exchange. The throwing of the key KI into talking position associates the position equipment PE with the cord circuit CC, so that the branch exchange operator may converse with themain exchange operator and request the number she wants. f

Setting up the delayed connection when the main exchange is an automatic exchange For the purpose of explaining the dialling feature oi' the position equipment PE, the cord circuit CC, and the trunk circuit TC2, it will be assumed now that the main exchange is an automatic exchange, in which event the operator must control the transmission of dialling impulses to bring about the setting of the automatic switching apparatus on the terminals of the desired main exchange line.

With the key KI operated in CC, the operator actuates the key K2, Fig. 2, to split position, thereby placing ground potential on split conductor 228. As a result split relay |01 in the cord circuit CC is operated through contacts of connect relay |06. In addition to disconnecting the lower winding of supervisory relay |08, relay |01 connects dial-tip and dial- ring conductors 229 and 230 to the tip and ring conductors of the trunk plug TP, at the same time disconnecting the two p lugs of the cord from each other to prevent dialling interference from the local plug in the event that the operator has already made connection to' the 'local line. The line relay 404 of the connected trunk circuit TC2 is now held operated over the dial-,tip and dialring conductors 229 and 230, through contacts of the actuated split relay |01, resistor 235 in the position equipment PE,'.and impulse contacts 232 of the calling device 23|.

When the operator actuates the dial (not shown) of the vcalling device 23| from its normal position pursuant to the dialling of the first digit, off- normal contacts 233 and 234 close. Oil-normal contacts 233 shunt the associated resistor 235 so as to form a better dialling" circuit for relay 404 in the trunk circuit TC2, while cifnormal contacts 234 apply ground potential at a ,second point to split conductor 228, so as to inthe cord circuit variably maintain the split relay |01 operated until the calling device reaches normal position. This' latter feature is of utility in the event that the operator, upon the dialling of the final digit, restores her split key before the calling device completes the transmission o f the nal digit.

As the calling device 23| returns to normal, the impulses are transmitted by the predetermined number of momentary separations of impulse contacts 232, which contacts are shuntedl by the usual spark suppressor condenser and associated resistor, as shown.

After she has completed dialling the desired umber, the operator restores the key K2, bringing about the restoration of split relay |01 to ter# minate the split condition of the cord circuit CC.

Assuming now that the desired main exchange subscriber responds, the operator may request him to wait a moment while she gets in touch with the subscriber at substation A. 'I'his she does by inserting the local plug! LP ,in the line jack LJ2 and momentarily operating the ringstart key K2 to bring about the operation of ringstart relay |04. Relays |0| and |02 operate responsive to the insertion of the plug LP'into the jack LJ 2 to prepare the talking circuit, while the ring-start relay |04 starts the operation. From this point the operations are as hereinbei'ore described.

Night service In order to provide for the reception of calls incoming to the branch exchange by such subscribers as are on duty at night or at other times when the branch-exchange switchboard is unattended,the trunk T2 may be extended directly to a branch-exchange line, the line ofsubstation B, for example. This extension is made through a cord circuit, the cord circuit CC,'for example. In this event, the key KI is actuated to night position and the trunk plug TP is inserted into the night jack NJ, Fig. 4, while the local plug LP is inserted into the jack LJ2.

The upper contacts of jack NJ ground conductor 423 to guard the trunk-against seizure at the automatic switchboard. With the plug LP in jack LJ2, idle test and switching relays I 0| and |02 are actuated, as in a standard call to the local line. Moreover, answering supervisory relay |05 is held continuously operated at contacts of the night' ke whereby the resistor I|4 isl not in bridge of the talking strands of the cord, andlamp |26 is maintained extinguished.

Henceforth, each time an incoming call is received over trunk T2, ringing current passes through jacks NJ and LJ2 by way of cord circuit CC to the line of substation B. such incoming calls, therefore, may be answered directly at B. Moreover, when h e desires to do so, the subseriber at B may make an outgoing call directly over the trunk T2, which has been rendered individual to his line as above described.

When desired, the operator may inform the subscriber at substation B when his line is about to be converted to' thenight condition. For this purpose, before placing the plug 'I'P into the jack NJ, the operator places the plug LP into the jack LJ 2; operates the talking key; momentarily operates common key K2 to ring-start position to start the ringing operation and then operates K2' to split position to cause feed relay 20.3 vto operate and connect up retard 204 as a transmitter-supply bridge foruse when the called subscriber responds.

After the subscriber responds and acknowledges the information, the operator restores K2; actuates Kl to night position; and inserts plug LP into night jack N 'Ihe upper contacts of the night section of key KI open the lockingcircuit of ring-start relay |04 to restore this relay in the event that the subscriber at substation B does not. respond, while the middle contacts of the key separate the circuits of relays |05 and |04 to prevent the operating potential applied to the upper winding of relay |05 lfrom driving a holding current through relay |05.

What is claimed is:

1. In a telephone system, lineswitches terminating subscriber lines, respectively, other lineswitches, links accessible to all said lineswitches, means responsive to the removal of the receiver on a subscriber line'for operating the associated lineswitch to take one of the links for use, means for extending a connection from the seized link to a desired called line, a transfer link included in the extended connection or not depending upon the line called, one of said other lineswitches being individual to said' transfer link, and means controlled at will over the line of the calling subscriber in the event -that the extended connection includes said transfer link for severing the distant end of the transfer link and for operating the associated lineswitch to extend the calling line by way of the near end of the transfer link and the associated individual lineswitch to another one of the first named links.

2. In a telephone system, lineswitches terminating subscriber lines, respectively, other lineswitches, links accessible to all said lineswitches, means responsive to the removal of the receiver on a subscriber link for operating the associated lineswitch to take one of the links for use, means for extending a connection from the seized' link to a desired called line, a transferlink included in the extended connection or not depending upon the line called, one of said other lineswitches being individual to said transfer link, means controlled at will over the line of the calling subscriber in the event that the extended I connection includes said transfer link for severing the distant end of the transfer link and for operating the associated lineswitch to extend the calling line by way of the near end of the transfer link and the associated individual lineswitch to another one of the first named links, and means subsequently controlled at the will of the calling subscriber for freeing the link taken for use by way of the last-named lineswitch and for reconnecting the severed portion of the transfer link.

3. In a telephone system, two groups of serially related link circuits for use in setting up telephone connections betweenl subscriber lines, a group of subscriber lines, each line extending to a lineswitch having access'to links of the rst vgroup, switching apparatus for extending a seized link of the rst group to a link of the second group, each linky of the second group having a normally connected branch and a normally disconnected branch, each of said normally disconnected branches extending to a lineswitch having access to links of the first group, and means controlled at will over the line of a calling subscriber when a connection has been set up therefore through one of the links of the second group for disconnecting the normally connected branch and for connecting the normally disconnected branch to cause the `associ-- ated lineswitch to operate and extend the calling line to a second link in the rst group.

4. In' a telephone system, a trunk line extend- 1 ing from a rst exchange 'to a second exchange,

to said trunk line by way of the first branch, an

automatic switch terminating the second branch, andmeans controlled at will over the subscriber line for substituting the second branch for the trunk line to extend the subscriber line to said automatic switch and subsequently controlled at will over the calling line for substituting the trunk line for the said second branch.

5. In a telephone system, a trunk line extending from a first exchange to a second exchange. said trunk line having rst, second, and third branches in the iirst exchange, switching means in the rst exchange for connecting a subscriber -line with the trunk line by way of the iirst branch, switching means for connecting a subscriber line with the trunk line by way of the second branch, an automatic switch terminating the first branch and means controlled at the will of the subscriber on a line connected with the trunk line by way of either the first branch or the second branch for substituting the third branch forthe trunk line to connect such subscriber line with the automatic switch, and subsequently controlled at will for substituting the trunk line for the said third branch.

6.. In a telephonesystem, a trunk line having a first branch and a second branch at one end thereof, means for connecting a subscriber line with said trunk line by way of the first of said branches, a supply bridgeV in said trunk line for supplying transmitter current to the connected subscriber line, a differential control relay in the iirst branch non-responsive to the normal balanced ow of current over the subscriber line, means at the substation on the subscriber line for temporarily unbalancing the flow of transmitter current to bring about an operation of said control relay, means responsive thereto for substituting the second branch for the said trunk line,

. means in the second branch for supplying a ow of transmitter current, and means responsive to a further operation of said control relay in the event that the ilow of transmitter current therethrough from the second branch is subsequently unbalanced at the station on the subscriber line for substituting the trunk line for the said second branch.

Ameans controllable by the '7. In a branch telephone exchange trunk-connected with a main exchange, an automatic switchboard and a manual switchboard, means at the automatic switchboard connections and for setting up connections to the main exchange by way of the trunk lines, means at the manual switchboard for completing incoming connections from the trunk lines 'to the local lines, meanseiective in the event of a connection incoming from the main exchange or of 'a connection outgoing to the main exchange for enabling the local subscriber at will to transfer the connection temporarily from the main exchange to another local line, and subsequently back to the main exchange again, and operatorl through lthe manual switchboard responsive to a signal from the local subscriber for transferring an incomfor completing local interconnecting 1 ing connection from the local line originally connected with to a desired other local line.

8. In a combined automatic and manual branch exchange trunk-connected to the main exchange, means including a cord circuit at the manual switchboard for interconnecting an incoming trunk line with a local line to complete an incoming connection, a transfer relay in the trunk line, a supervisory relay and a cut-off relay in the cord circuit, and means selectively controlled over the called line for actuating the said relays.

9. In a branch exchange trunk-connected with` a main exchange through two-way 'trunk lines, an automatic switchboard through which local connections may be made and connections through which outgoing to the main exchange over said trunk lines may be made, a manual switchboard, an extension from each two-way including a double-plug cord circuit at the many ual switchboard for interconnecting a subscriber line with a trunk line, and means automatically eective when the subscriber on the interconnected line replaces his receiver after the termination of a conversation for disconnecting both plugs of said cord circuit to thereby free the subscriber lineior further use and to free the trunk line for further use while the plugs of the cord circuit remain in place.

11. In a telephone system, a manual switchboard having cord circ 'ts through which desired connections are extended, the talking strands of the calling plug of each cord circuit being normally open, means dependent upon the called line being in an idle condition for closing the calling strands of the cord circuit, and means including an offering cord and plug forming an extension of the operator's headset conductors for enabling the operator to make connection with a busy line to oier a call.

12. In a telephone system, a plug ending cord having the tip and ring conductors normally open, a busy-test relay normally connected to the tip of the plug, and relay apparatus operable over the sleeve of a 'jack into which the plug is inserted for disconnecting the busy-test relay and for closing the tip and ring conductors, depending upon an idle condition of the line associated with the said jack.

13. In a telephone system, a plug ending cord having the tip and ring conductors normally open, a busy-test relay normally connected to the tip of thel plug, relay apparatus operable over the sleeve of a jack into which the plug is inserted for disconnecting the busy-test relay and for closing the tip and ring conductors, depending upon an idle condition of the line associated with the said jack, and means controlled by the busytest relay when the line associated'with the jack with which the plug is brought into engagement is busy for placing a busy-tone potential on the cord.

14. In a combined automatic and manual branch exchange trunk-connected to the main exchange by two-way trunks appearing both at the automatic switchboard and at the manual when the operator plugs into one of said lines and when she plugs into one of said trunks for preventing intrusion upon a busy connection if one is taking place and for preventing interference with the transmission of switch settling impulses in the event that an automatic connection is being 'set up.

JOHN H. VOSS.

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