US1811444A - Toll service trunking system - Google Patents

Description

June 23, 1931. v. s. THARP I TOLL SERVICE TRUNKING SYSTEM Filed April 19, 1930 2 Sheets-Sheet 1 QREWNEMQQ UiE'ZH" ELThaP June 23, 1931. v. s. THARP TOLL SERVICE TRUNKING SYSTEM 2 Sheets-Sheet 2 Filed April 19, 1930 v UI'ETH- EThax-F Patented June 23, 1931 l 'UNETED stares PATENT seer ca vrorons. rHAnP, or nL'MnURsT, rumors, ASSIGNOR T0 n-nsnnvn HOLDING COM- PANY, or cmceec, rumors, A CORPORATION or DELAWARE TOLL SERVICE TRUNKING SYSTEM Application filed April 19,

This invention relates to telephone systems generally, and particularly to toll-service trunking apparatus and equipment for automatic telephone systems.

In modern automatic telephone systems, it is the usual practice to provide a separate train of automatic switches for use by the toll operator in completing connections to sub scribers lines. These switches are of the same general type as the switches used for localoservice, except that they are designed to provide greater transmission eiiicie'ncy and more complete supervision. This switch train includes, essentially, a toll-transmission selector repeater and atoll or combination localand-toll connector. One or more intermediate selectors may be interposed between the selector repeater and the connector.

A toll switch train of the above general type is disclosed in United States patent to Wicks No. 1,633,149, of June 21, 1927. It will be noted, that, in this case, the connector on seizing a line reverses the direction of current flow over the incoming trunk to initiate the switchover operation of the toll-transmission selector. A later andniore etlicient type of toll switch train is disclosed in the copending application of Tharp and l/Vicks, SerialNo. 225,063, filed October 1c, 1927, on

which, incidentally, the present invention may-be considered as an improvement; In the latter case, the connector disconnects ts line relay from the trunk to initiate the switchover operation of the toll-transmission selector. Line-seizure supervision is given to the toll operator in both cases following the switchover operation, and the apparatus is placed in waiting condition. Due to this difference in effecting the switchover, the transmission selectors of the two systems cannot be used interchangeably. In making additions to exchanges employing the older type of equipment, it has, therefore, been impractical in the past to install the newer type of toll-transmission selectors.

It may be further noted that the requirements for line-busy supervision are not uniform throughout the telephone industry. In some telephone systems an audible busy tone is used t6 notify the'operator of an all-trunks- 1930. SerialNo. 445,570.

busy condition or a busy called 'line. In other systems, a lamp associated with the operators cord circuit is flashed under these conditions. It has, therefore, been customary to build a separate type of switch train to meet each condition.

One of the features of the invention is the provision of a toll-transmission selector which will operate equally well with connectors employing either of the previously-dcscribed methods of effecting the switchover.

Another feature is the provision of a toll switch train which can be used without alterations in'systems employing either of the previously-referred-to methods of line-busy supervision.

A still further feature is the arrangement whereby the operator receives no line-seizure supervision when an all-trunksbusy condi tion is encountered or a busy line is connected with. lVith this arrangement, the operator may proceed with setting up the connection without listening for busy tone as soon as the supervisory lamp lights.

The foregoing features, together with others not specifically mentioned, will be described in detail, reference being bad to the accompanying drawings comprising" Figs. 1 and 2.

Referring now to the drawings, in Fig. l is shown the calling end of a regular tollcord circuit 0. This cord circuit may be of the usual type provided with a polarized relay for controlling the supervisory signal. The toll-transmission selector S terminates the trunk line extending from the toll board to an automatic exchange. This switch is of the well-known Strowger type. having directive vertical motion and automatic rotary motion.

In Fig. 2 is shown, in skeleton form, an intermediate selector S1 and a toll connector C. The intermediate selector may be of any well-known type provided with a fourth wiper for extending a ring-control conductor. The connector shown, is arranged only for toll operation, although similar connectors arranged for both local and tell operations may be used if desired.

In order that the features of the invention may be fully appreciated, the operations involved in setting up'a tollconnection to the substation T will now be described 1n detail.

It will first be assumed that a toll call for substation T has come into the toll board over a toll line (not shown), and that the operator has answered this call by connecting the answering end of the cord O to the toll line. After determining that the call is for the subscriber at substation T, the operator will insert the calling plug P of the cord circuit into the jack of an idle toll-service trunk, for example, the jack J terminating the trunk comprising conductors 1 and 2. Key K will then be actuated to the right, thereby bridging the calling device CD across the talking conductors of the trunk. Line relay 11 of transmission selector S has its lower windin g normally connected to trunk conductor 2 by way of T normally-closed contacts of relays 6. and 4,

and this relay now operates over the loop through the cord c rcuit to ground at normally-closed lower contacts of relay 4. Relay device.

11 closes a circuit for release relay 12 which operates and prepares the holding circuit and impulsing circuits for the switch.

7 After connecting with an idle toll-service trunk and actuating the dialling key, the operator will proceed to dial the number of the called subscribers line. At-the completion of the dialling, the operator will restore the key to normal, thereby bridging polarized supervisory relay 3 across the talking strands of the cord in place of the calling The calling device interrupts the loop over which relay 11 is operated, and that relay responds in the usual way. Responsive S to the first digit dialled, relay 11 transmits a corresponding series of impulses to vertical magnet 16, which operates to step the wipers oi the switch to the called level. Slow-to-v the series, and maintains its armatures actuated throughout the series of impulses. Re-

lay 13, on operating, short circuits a winding of the repeating coil to. improve impulsing,

and also prepares a circuit for relay 15. This circuit is completed at oil-normal contacts 22 which close on the first vertical step of the wipers. Relay15 operates, completes a locking circuit for itself through the interrupter contacts of rotary magnet 17 and prepares a circuit for magnet 17. Shortly after the last impulse of the series, relay 13 restores and completes a circuit for rotary magnet 17 which operates to step the wipers in on the first set of contacts of the called level. Ma gnet 17 opens the circuit of relay 15 at the interrupter contacts, and the relay'restores and in turn opens the circuit of the rotary magnet. In case the trunk terminating in the first set of contacts is busy, the test wiper of the switch will encounter agrounded contact and relay 15 will reoperate and again i close the circuit of rotary magnet 17 Magnet 17 will operate to step the wipers to the next set of contacts, and will open the circuit of relay 15 as in the previous instance. This testing and stepping operation will be repeated as often as the test wiper encounters grounded contacts. When an idle trunk is found, which may be, for example, the trunk comprising conductors 2528, the test wiper of the switch will not find a ground and ,relay 14 will operate in series with relay 15. Relay 14 was prevented from operating before, since its winding was shunted by the ground on the test wiper. Relay 15 does not operate in series with relay 14, which has a relatively high resistance. Relay 14 switches the connection of the test wiper from its lower terminal to its upper terminal to complete a holding circuit and to prevent the reoperation of relay 15, disconnects the vertical magnet from the impulsing circuit, connects the talking and control conductors through to the wipers, and completes a circuit for the lower winding of differential ing of relay 4 upon the operation of relay 14.

Relay 4 is so constructed that, when its lower winding alone is energized, or when its upper and lower windings are energized so that they cooperate, the armatures of the relay are actuated. At this time, however, the current How in the upper winding is in such a direction that the windings oppose each oth r and the relay is prevented from operating.

The second series of impulses is now dialled and relayll responds, as in theprevious instance, and repeats the impulses over the loops to relay 41 of selector S1. Relay 13 again operates during the series of impulses, 1

its only function at this time being to short circuit a winding of the repeating coilto improve impulsing. The line relay of selector S1 responds in the usual way, and the wipers of this switch are raised to the called level, whereon the switch operates to select an idle trunk, for example, the trunk comprising conductors 4447.

Selector S1 on switching through extends the control loop through to line relay 52 0f connector G. Relay 52 operatesover the loop and completes a circuit for relay 58 which operates and locks to groundon control conductor 45. Referring back to transmission selector S, relay 4 is still prevented from operating since the two windings oppose each other. It will be noted also that during the transmission of the second series of impulses,

"relay i1 opened the circuits for both the upper and lower windings of this relay responsive to each impulse to prevent the relay from ra-i'se the wipers of the switch to the called level. Relay 54: operates in response to the first impulse of the series, and maintains its armatures actuated throughout the series of impulses, thereby maintaining the circuit of the vertical magnet after oil-normal contacts 62' open on" the first vertical step of the wipers. Shortly after the'last impulse of the series, relay 54 restores and prepares a circuit for the rotary magnet at its back contact.

Relay 11 oftransmission selector S and relay 520i connector respond to the last series of impulses, the latter relay transmitting corresponding impulses to rotary magnet 59 which is connected in series with slowto-release relay 56 Relay 56 energizes in response to the first impulse of the series and maintains its armatures actuated throughout the series of impulses, closing an auxiliary impulsing'cireuit independent of the normally-closed contacts of busy relay 55, and also preparing the busy test circuit by connecting the test wiper through to busy test relay by wayof normally-closed contacts of switching-through relay 57.

It will be assumed at this time that the called line'is idle, and that the busy test wiper, therefore, does not encounter ground on the test contact of the line. WVhen relay 56 restores shortly after the last impulse of the series, the test wiper is again connected through the upper winding of relay 57 to ground on'the' release trunk conductor 46. Relay 57 operates over this circuit from battery through'the cut-oii relay of the line switch associated with the called line. Relay 57 on operating connects the talking conductors through to the wipers of the switch, separate the control and release-trunk conductors and connects the test wiper to the latter conductor, completes a locking circuit for itself to the'release-trunk'conductor,and

opens the circuit of the busy test relay and the rotary magnet; v p

The-operation ofrelay 57 completes a circuit for relay '51, which operates and locks to ground on conductor 46. Relay'51 disconnects the'talking conductors to the switch from line-relay"'52.and' extends them through to the wipers, andalso'opens a point in the original energizing circuit of relay 53.

Returning now to the transmission selector S, the disconnection of the line relay of the connector from the talkingconductors of the trunk destroys the circuit of the upper winding of relay 4 which now operates its armatures under the influence of its lower winding alone. Relay 4 locks to ground through oii-normal contacts 19, bridges alternating current responsive to relay 7 across the conductors of the trunk, and also bridges both windings of line relay 11 across the trunk, reversing the connections, however, so that the current flow over the trunk is now in the reverse direction.

After dialling the last digit, the operator restores the dialling key to normal as previously mentioned, thereby bridging polarized relay 3 across the talking strands of the cord. Since the direction of current flow over the trunk has now been reversed, relay 3 will operate and complete the circuit oi supervisory lamp L. Lamp L lights to give the line-seizure supervision.

A connection has now been established with the wanted line, but no ringing current has been sent out due to the fact that ring-cut-oil relay 53 has been locked up to control conductor-(t5. hen the operator is ready to signal the called subscriber, key K of the cord circuit will be actuated to the left, thereby applying ringing current to the toll-service trunk to operate relay 7 of transmission selector S. Relay 7 completes a circuit for relay 8 which operates, closes a temporary holding circuit for line relay 11 of the transmission selector, and removes ground from the control conductor by opening contacts 29. Relay 53 of the connector now restores and completes the ringing circuit which includes its own upper winding. Ringing current with superimposed battery is intermittently connected to the ringing circuit by ringing interrupter RI to signal the called subscriber.

A ring-back tone is transmitted to the operator through condenser 67 and the normallyclosed upper contacts of relay 53.

When the called subscriber answers, a direct current loop is closed over which relay 53 energizes and again locks to the control conductor, to which, incidentally, ground has been reconnected following the restoration of the cord circuit ringing key. Relay 53 on operating extends the loop from the called subscribers line, back over the talking conductor of the intermediate selector and interconnecting trunks, to battery-feed relay 5, which was connected up responsive to the operation of relay 4. Relay 5 feeds battery to the called subscriber and operates over the called subscribers loop to close a circuit for relay 6. Relay 6 on operating, connects ground to the control conductor to prevent reapplication of ringing current to the called line as long as the called suhscribers receiver is 05 the hook, disconnects line relay 11 of the transmission selector from the talking conductors of the toll-service. trunk, and closes.

a holding circuit for that relay. The disconnection of the line relay of the transm1s-- sion selector opens the ClI'CHllJOf the supervisory relay of the cord circuit, and that relay' restores and extinguishes the supervisory lamp to give the answering supervision. Conversation may now take place in the usual way. 5

When the called subscriber hangs up, the operating loop of relay 5 is opened and that relay restores and opens the circuit of relay scriber by again operating ringing key K to apply ringing current to the toll-service trunk as in the previous instance;

' To release the connection the operator withdraws the plug of the cord from the jack thereby opening the circuit of relay 11 which restores and in turn opens the circuit of relay 12." Relay 12 restores, removes ground from the release-trunk conductor, and completes a circuit for release magnet 18 including offnormalcontacts 23 which closed on the first vertical step ofthe wipers. The release magnet operates in the usual way to restore the wipers of the switch to normal position. When the wipers reached normal position, the locking circuit of relay 4 is opened at off-normal contacts 19 and that relay restores thereby placing the transmission selector in condition to receive the next call. The intermediate selector S1 will release in the usual way following theremoval of ground from release-trunk conductor 27. Relays 51 and 57 of connector C were-also held operated over the release trunk conductor and restore following the removal of ground from that conductor. Relay 53 will restore assoon as the control conductor is opened following the release'of relay 14 of the transmission selector. Relays 51 and 53 complete a circuit for release magnet 60 of the connector, this circuit including off-normal contacts '61, which openwhen the wipers reach normal position. All apparatus is now returned to normal condition and is in readiness to receive the'next call.

It will be recalled that the switchover op eration, that is the operation of relay 1, was initiated by the disconnection of the line relay of the connector when an idle line was connected with. In the event that'transmission selector S is used to extend'a connection by way of'a connector such as that disclosed in the previously-mentioned WVicks patent,

the operation will be somewhat different. Referring to the patent, it willbe noted that when a called line is connected with, the connection of the line relay; tothe trunkis reversed. In this case, the reversal of current flow over the trunk line will cause the two windingsof relay 4 to cooperate, whereon the relay will energize and complete the switch over operation exactly as in the previouslydescribed connection.

I/Vhen a connection, such as hasjust been described, is extended to a private branch exchange, it is often desirable to recall the branch-exchange operator after the branchexchange subscriber has hung up, but before the branch-exchange operator has pulled down the connection. In this case, the toll operator will actuate the ringing key of her cord circuit, thereby applying ringing current to the toll-service trunk to operate relay 7. Relay 7 will close a circuit for relay 8 which will operate in the usual way, and since the connection has not been pulled down at the branch exchange, relays 5 and 6 will be operated and alternating current will beapplied directly to the talking conductors at the transmission selector. This current willoperate a ring-down relay in the branch-exchange cord circuit, which inturn will operate the recall signal associated therewith.

In case the called-line had been a paystation line, it would. be necessaryv for the toll operator to either refund or collect the coin deposited to pay for the-connection. To do this, the operator wouldfirst actuate the collect-and-refund key K1 either to the leftor right depending upon whether the coin was to be returned or collected, and would then operate ringing key K to apply high-potential current to the talking conductors of the trunk. Relay 9, which has a very high resist ance, operates from this current and completes a circuit for relay 10. Relay 1O operates and connects a bridge across the outgoing conductors of the switch and also connects the bridgeto the trunk conductor towhich the high-potential current is connected. This current is thereby extended over the two talking conductors of the interconnecting trunks andthe called line, and actuates the control relay at the paystation line.

lar system involved. Consider first the type r of system using tone supervision, in which case the busy-tone transformer BT will be connected'to the tone conductor 32 at contacts of terminal 33. Referring back to the description of the transmissionselector S, it will be recalled that rotary magnet 17 and control relay 15 alternately operated and released until an idle trunk was found. In case no idle trunk is available, this stepping operation will continue until the wipers of the switch are rotated to eleventh position whereon the test wiper will leave the last grounded contact and remove the shunt from relay 14.

Relay 14 will operate, close a point in the up- 7 contacts 24 also close when the wipers reach eleventh position, and the busy tone is applied to the upper talking conductor of the switch and through the repeating coil to the operators set. Relay 4 will not operate since the circuits of both its windings are open.

' The current flow over the trunk will not be reversed and consequently no line-seizure supervision will be given. The failure of the supervisory lamp to light will indicate to the operator that the called line has not been connectedwith and she will, therefore, actuate her listening key, whereon the busy tone will inform her that a busy condition has been encountered. Selector S1 on encountering an all-trunks-busy condition, will operate in substantially the same manner as the transmission selector to return a busy tone to the operator.

.It will be recalled that when connector C has responded to the last series of impulses, relay 56 energized in parallel with the rotary magnet and connected busy test relay 55 to the test wiper. In case the line connected with is busy, relay 55 will operate over a circuit extending through the test wiper to the grounded test contact engaged, and when relay 56 restores, shortly after the last impulse of the series, relay 55 looks to ground on the release-trunk conductor. Busy-tone conductor 32 is thereby connected through the normally-closed contacts of relay 56 and front contacts of relay 55 to the upper talking conductor of the switch by way of condenser 68. Relay 51 does notoperate since its circuit is opened at contacts of relay 57, therefore, the line-seizure supervision is not given. The operator will again actuate her listening key and be advised by the busy tone that the called line is engaged.

It will be noted' that only one busy-tone machine has been shown for the exchange, although, obviously, ifdesired, separate machines can be used for each rank of switches, for instance, to give one tone for an alltrunks-busy condition and a different tone for. a line-busy condition.

In the event that the flash-busy supervision is. desired, terminal 33 will be connected to interrupter I1 instead of to busy-tone transformer BT. When the transmission selector S encounters an all-trunks-busy condition as previously described, relay 4 will operate from the first ground impulse applied to conductor 32 over a circuit extending through rotary oif-nor1nal contacts 21. Relay 4 will lock up in the usual way and connect up battery-feed relay 5. The connection of line relay 11 to the toll-service trunk will be reversed, as previously described, and polarized relay 3 of the cord circuit will operate as before. Ground impulses from the interrupter will now cause relay 5 to operate intermittently over a circuit including rotary offnormal contacts 24, front contacts of relay 14, back contacts of relays 8 and 10, front contacts of relay 4, and the upper winding of relay 5. Relay 5 on operating will disconnect relay 11 from the trunk, thereby opening the circuit of relay 3 which will restore and open the circuit of the supervisory lamp. This operation will be repeated at intervals depending on the rate at which interrupter I1 applies ground impulses to conductor 32, and lamp L will consequently flash to give the operator busy supervision.

Selector S1 in encountering an all-trunksbusy condition will rotate to the eleventh position, whereon the circuit of the upper winding of the relay 4 of the transmission selector will be opened, and that relay will operate. Ground impulses will then be applied to the upper talking conductor by way of rotary ottnormal contacts 43 which close when the switch is in eleventh position and the supervisory lamp of the cord circuit will be flashed as in the previous case.

When connector C encounters a busy line, busy relay 55 will operate as described in the previous connection, and when relay 56 restores, shortly after the last impulse of the final series, the busy-tone conductor 32 will be extended to relay 51 by way of back contacts of relay 56 and front contacts of relays 55 and 52. Relay 51 will operate from the first ground impulse on the busy-tone lead and will lock to ground on the release trunk, disconnecting the line relay in the usual way, and connecting the talking conductors through. Relay 4 of the transmission selector will operate responsive to the disconnection of line relay 52 of the connector, and

will reverse battery over the toll-service trunk in the usual way. The ground impulses from conductor 32. will now be applied to the upper talking conductor of the connector, and over the interconnecting trunks to intermittently operate relay 5 which causes the supervisory lampto flash as previously described.

The release of the apparatus when a busy condition is encountered, is substantially the same as that described for a connection to an idle line.

What is claimed is:

1. In a telephone system wherein calls are extended to subscribers lines via a switch train comprising a plurality of automatic switches, a double-wound relay in the first switch of the train, circuits closed responsive to the completion of the operation of said first switch for difierentially energizing the two windings of said relay to maintain the same unoperated, means for temporarily Opening said circuits during the operation of succeeding switches of the train, and means for altering the circuit of one of said windings to operate said relay responsive to the completion of the operation of the last switch of the train.

2; In a telephone system wherein calls are extended to subscribers lines via a switch train comprising a plurality of automatic switches, a switchover relay in the first switch of the train, an operating winding and an auxiliary winding for said relay, a circuitfor said operating winding closedresponsive to the completion of the operation of said first switch, a circuit including said auxiliary winding for energizing the same to oppose said operating winding closed responsive to the completionof the operation of said first switch, and means responsive to the completion of the operation of the last switch of the train for altering said second circuit to permit said relay to operate over said first circuit.

3. In a telephone system, a toll selector, toll connectors, a double-wound sw tchover relay in the selector, means for operating said selector to seize an idle one of said connectors,

' circuits completed responsive to the seizure of an idle connector for differentially energizing the two windings of said relay whereby the magnetic flux of the two windings substantially balance each other, and means in the connector for openingone of said circuits to upset the balanced condition of the relay and permit the same to operate.

4. In a telephonesystem, a toll switch train comprising a plurality of automatic switches adapted'to be successively operated to extend a connection, a double-wound relay in t-he first switch, a local circuit for energizing 'one of said windings closed responsive to the completion of the operation of the first switch, a circuit for energizing the other winding of the relay to oppose said first winding, said circuit extending to successive switches of the train, and means in the last switch of the train for opening said last. circuit topermit said relay to operate. 7 I I 5. In a telephone system, two automatic switches, a differentially-wound relay in the first switch, a double-wound line relay in the second switch, means for operating the first switch to extend a connection to the second switch, a circuit including one winding of said difierential relay and the two windings of said line relay in series closed responsive to the completionof theoperation of the first switch, a local circuit for the other winding of said difierential relayclosed simultaneously with the closureof said first circuit, means pletionof the operation of the selector for difierentially energizing the two windings of said relay,'means in the connector responsive to the completion of the operation thereof for opening one of said circuits to permit said relay to operate, and means controlled by said relay for reversing the direction of current fiow over the trunk line.

7 In a telephone system wherein connections are extended from atollswitchboard to subscribers lines via atoll-service trunk line and. a toll switch train comprising a plurality of automatic switches, a double-wound switchover relay in the first switch of the train maintained unoperated during the setting up ofa connection by having its two windings difi'erentially energized, means for opening the circuit of one winding of therelay responsive to the connection being extended to a subscribers line, and a supervisory signal at the switchboard controlled by said relay. V

8. In atelephone system wherein connections are extended from a toll switchboard to subscribers lines via a toll-service trunk line and a toll switch train comprising a plurality of automatic switches, a double-wound switchover relay in the first switch of the train maintainedunoperated during the setting up of a connection by having its two windings difierentially energized, means for opening the circuit of one winding responsive to the connection being extended to a subscribers line, and a battery-feed bridge in the first switch connected up by said relay to feed talking current to the called line. I

9. In a toll transmission selector adapted to cooperate with connectors which either open or reverse the direction of current flow over a control circuit whena called line is connected with, a control circuit over which a current How is maintained during the setting up of a connection, and a switchover relay operative responsive to either the opening of or the reversal of current flow over said control circuit. I r a W 10. In a toll transmission selector adapted to cooperate with toll connectors which either open or reverse the direction of current flow over a control circuit when a called line is connected with, a control circuit over which a current flow is maintained while the selector is in operating condition, and a relay operated responsive either to the opening of or the reversal of current flow over said control circuit for switching over the selector from operating condition to talking condition.

11. In a toll transmission selector adapted to cooperate with toll connectors which either open or reverse the direction of current flow over a control circuit when a called line is connected with, a control circuit over which a current flow from an external feeding bridge is maintained during the setting up of a connection, a local current feeding bridge, and a switchover relay operated responsive to the opening of or the reversal of current flow over the control circuit for connecting said local bridge to said circuit.

12. A toll selector, a signal-control relay and a battery-feed relay for the selector, a busy signal terminal, a source of tone and a source of interrupted current either of which may be connected to said terminal, means for operating theselector to hunt for an idle trunk, means responsive when no idle trunk is available for applying a tone to a talking conductor of the switch provided said tone source is connected to said terminal, and means for operating and locking said signal control relay and for intermittently operating said battery-feed relay provided said second current source is connected to said terminal.

13. In a tool selector, incoming trunk conductors, a battery-feed relay, a signal terminal, two sources of busy signalling current either of which may be connected to said terminal, means for operating the selector, and means responsive when the selector encounters an all-trunks-busy condition for applying a characteristic tone to one of said trunk conductors provided said first current source is connected to said terminal and for intermittently operating said relay provided saidsecond tone source is connected to said terminal.

14. In a telephone system, a trunk line terminating in a toll selector, a line relay for the selector bridged across the talking conductors of the trunk, a signal terminal, two

sources of current either of which may be connected to said terminal, means for applying a characteristic tone to said trunk line provided said first current source is connected to said terminal, and means for intermittently disconnecting said relay from the trunk line providing said second current source is connected to said terminal.

15. In a toll connector, incoming trunk conductors, a signal controlrelay, a signal terminal, two sources of signal current either of which may be connected to said terminal, means for operating said connector to extend a connection to a called line, and means re-

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