US1700473A - Telephone-exchange system - Google Patents

Description

Jan. 29, 1929.

J. B. DRAP'ER TELEPHONE EXOHANGE SYSTEM Filed March 22, 1924 /m/e/ffar. Jo/m 15. Draper Patented Jan. 29, 1929.

siren STATESg PATENT OFFICE.

JOHN B. DRAPER, OF BROOKLYN, NEW' YORK, ASSIGNOR TO WESTERN ELECTRIC (301W-k PANY, INCORPORATED, OF NEW' YORK, l\l`. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

This invention relates to machine switch-v ing telephone systems and more particularly,

to such systems wherein the trunk circuits between otiices are accessible at more than one polnt.

Heretofore in systems of this general type,

it sometimes happens that the trunk is again seized by another mechanical switch which happens to be in the trunk huntingposition.

The object of this invention is to permit the switching mechanism to release while at the same time preventing the trunk'ifrom being again seized until it is fully restored to normal. Y

Tn accordance with this invention means are provided inthe trunk to cooperate with the switching` mechanism seizing the trunk whereby the trunk is caused to test busy, the means aforesaid allowing the switching mechanism to regulate its own release, but causing the trunk to testbusy again instantly thereafter and to remain busy until it is restored to normal. More specilically, a relay is retained inoperative due to a circuit condition im pressed upon the trunk test terminal by the switching mechanism the circuit condition changing the instant switching mechanism releases, whereby the relay previously held inoperative is allowed to operate and cause the trunk to again test busy, the unguarded interval at the test terminal being reduced to the time required to operate the relay in question, which in practice, is a negligible length oi' time, virtually eliminating the possibility of a double trunk seizure.

in vthe drawing comprising but a single sheet, the invention is diagran'nnatically shown applied to a toll telephone system employing mechanical switches. The designation llT'C indicates a distant toll center having access over a toll line TL to the repeater R, thence by way of the toll selector switch (T) to the trunk circuit. At the lett is shown a toll cord TC at the toll switchboard (T. S. B.)

Dur-v ing the unguarded interval which thus occurs,

of ar second toll center, the trunk circuit appearing before the toll operator at the second toll center in a trunk jack. The trunk eX tends ST to a neighboring ohce wherein connections are established by means of mechanical switches, the trunk terminating thereat in anincoming selector IS. The re maining switches required to build up a typi cal connection to the called station 24 are a transmission selector (TS), a third selector' (Si-3) and a connectorr (C). Y'

It is believed that the invention will be more readily understood from the detailed description of the progress of a typical call from either the distant toll center DTC or the second toll center 'which follows:

CALL FROM Dis'rANT TOLL CENTER.

I mftz'atz'ag call.

vprogresses over the toll line TL to operate the repeater R which may be of any of the well.- known types, commonly used in the art. The toll selector (T) functions in a manner (not shown) to extend the connection by way of the brushes 4, and 6 and the terminals 7, 8

vand 9 to the switching trunk ST. With the brush 6 resting on the terminal 9 a circuit is closed to operate relay 49 as follows: battery, winding of relay 49, 99, 98, 9, 6, to ground. Relay 49 operated locks in series with relay to ground at armature 75 of' relay 40 and connects battery at its armature 100 to the test sleeve 38 of the jack 35 and all multiples thereof at the toll switchboard TSB, causing the trunk circuit to test busy at the ytoll switchboard. The relay 45 does not operate at thistime because it is short-circuited by the ground at the test brush 6 of the toll selector The dial l at the distanttoll center DTC is new operated and released in accordance with the various digits comprising the number of the called line 24 and the relay 2 responds to the impulses produced by the dial 1.

The bridge through the winding of the relay is opened each time the relay 2 operates, thus repeating the impulses by Way of the toll selector (T) and the switching trunk ST to the selector switches IS, TS, S-3 and the connector (l in succession, whereby the connection is extended to the called line 24. The switches IS, TS, S-3 and the connecn tor C may be of any well known type, but for convenience it will be assumed that these switches are of the Strowger type so well known in the art, in which case, the connection will be established as described in the patent to Ray Stokely, 1,553,337 dated Sept. 11,5, 1925. Signaling and supervision will occur and conversation will take place substantially in the manner disclosed and described in the application cited.

Disconnectz'on.

When disconnection takes place at the distant toll center DTC, the toll selector (T) releases in the manner well-known in the art and the brushes 4, 5 and 6 are restored to normal removing the ground from the test ter minal 9 of the trunk circuit. The moment ground is removed from the test terminal 9 relay 45 operates in series with the winding of relay 49. Relay 45 operated connects solid ground to the test terminal 9 by way of 98, 99 and 97, thus providing a busy test condition at the test terminal 9 to prevent any other selector switch in the trunk hunting position from seizing this trunk.` So long as t-he receiver is'removed from the switchhook at the station of the called line 24, the supervisory relay 17 will remain operated retaining the relay operated over an obvious circuit. So long as relay 15 remains operated the battery and ground supplied to the switching trunk ST through the windings of relay 16 will be disconnected from the trunk circuit. T he operation of relay 45 connected the winding of relay in bridge across the conductors of the switching trunk ST over the following circuit: brush 10, switching trunk ST, 87, 96, 95, 94, winding of relay 40, 83, switching trunk ST to brush 11. As long' as relay 15 remains operated relay 40 will not operate, hence, relays 49 and 45 will remain locked in series to ground at the armature 75 of relay 40. When the receiver is replaced on the switchhook at the stat-ion of the called line 24,

relays 17 and 15 vwill release in sequence and battery and ground will be again connected by way of the windings of relay 16 and the incoming selector TS to the switching trunk ST. Relay 40 will operate in series with the windings of relay 16, opening at 75 the locking circuit previously traced for relays and 49 which release. Relay 49 released, removes the busy condition from the test sleeve 38 of the ack 35 and all multiples thereof at the toll switchboard TSB and relay 45 released removes ground at its contact 97 from the test terminal 9 causing the trunk circuit to test idle at the multiple bank of the toll selector Relay 45 released, also opens at- 94 and 95 the bridge previously established through the winding of relay 40 across the switching trunk ST, releasing relay 40 and restoring the circuit to normal.

CALL rnou SECOND TOLL CENTER.

Initiating call.

Then it is desired to establish a connection with the toll line 24 from the toll switchboard TSB, the plug 34 of the toll cord TC is inserted in the jack 35 or any multiple thereof of the trunk circuit at the toll switchboard TSB. Relay 46 now operates over a circuit as follows: battery, winding of relay 33, 38, winding of relay 46 to ground. A circuit is likewise established to operate relay 51 as follows: battery, resistance 53, left winding of relay 51, 54, 55, 37, 59, 58, winding of relay 31, 60, 61, 36, 56, 57,. windingl of relay 47 to ground. Relays 31 and47 do not operate at this time due to the high resistance of the winding of relay 51 .and of the resistance 53 in series with them. Relay 46 operated closes at its armature 103 an obvious circuit to operate relay 14. Relay 14 operated, connects solid ground by way of its armature 98 to the test terminal 9 of the toll selector (T) at the multiple bank causing the trunk circuit to test busy to all toll selector switches. Relay 51 operated locks through its right winding over the following circuit: ground in the incoming selector IS (not shown) switching trunk ST, 87, 96, 86, winding of relay 50, 85, 84, right winding of relay 51, 79, winding of relay 40, 83, switching trunk ST to battery (not shown) in the incoming selectorl TS. Relay 40 operates over the circuit previously traced in series with relay 51, but relay which is polarized does not operate at this time.

Dialing' the 7mm-ber.

The dial 25 is now operated and released in accordance with the various digits comprising the number of the called line 24. TWhen the dial is operated contact springs 28 and 29 of the dial 25 are closed, operating relay 30 over an obvious circuit. Relay 30 operated substitutes a path by way of the impulse springs 26 and 27 of the dial 25 for the winding of relay 31, normally bridged across the toll cord TC. The series circuit previously traced through the left hand winding of rclay 51, winding of relay 31, winding of relay lUU 47 is opened, but relay 51 remains locked up through its right hand winding in series with relays 40 and 50. A circuit is now closed to operate 'the impulse relay 47 as follows: battery, impulse springs 27 and 26 of the dial 25, 62, 61, 36, 56, 57, winding of impulse relay 47 to ground. Relay 47 operated closes at 71 a path to short circuit the right winding of relay 51 and the winding of relay 50 releasing relay 51. Relay 40 is now bridged operates through its left hand winding directly across the conductors of the switching trunk STl over the following circuit: switching trunk ST, 83, winding of relay 40, 79, 71, 87 to the switching trunlrST. The impulse relay 47 operated also closes a. circuit to operate relay 42 as follows: battery, armature 63 of relay 44, 64, resistance 65, 66, 67, 68, 69, winding ot relay 42, 70 to ground. Relay 42 operated closes a circuit to operate relay 48 as follows: battery, winding ci rclay 48, 72, 73, 63 to ground. Relay 48 operated locks by way of 78 and 74 to ground at 63, thus providing a substitute path to retain relay 42 operated after the impulse relay 47 releases as follows: battery, armature 63 of relay 44, 64, resistance 65, 69, winding ol' relay 42, 70 to ground. Relay operated connects the interrupter 41 in series with the winding ot' the relay 52 and relay 52 operates and releases under control or' the interrupter 41, but performs no useful function at this the impulse springs 26 and 27 of the dial are closed and releases each time these impulse springs are opened. VThe impulse circuit torV setting the incoming selector IS is controlled at the armature 71 of the impulse relay 47. iience, the incoming selector TS is set under control oit' the impulse relay 47. The relay 30 in the toll cord TC is designed to be slow to release so that it will not release immediately at the end of each train ot impulses corresponding to a particular digit, hence, the circuit including the winding ot' the inipulse relayv 47 and the impulse springs 26 and 27 ot the dial 25 will not be permanently opened until all the digits comprising the number of the called line have been dialed. The various selector switches IS, TS, S-3 and the connector C will be set in accordance with the digits dialed and the connection will be established with the called line which we will assume to be the line 24.

`Called Ziele busy.

Assuming the called line 24 is busy, the battery and ground supplied through the windings ot the relay 16 oi the transmission selector TS will remain connected to the circuit (in the manner shown in the drawing after dialing is completed. lVith the dial 25 iii the normal position. contact springs 28 and will be separated and atteia reasonable interval of time` relay 30 will release, reconnecting the winding of relay 31 across the springs 36 and 37 of the jack 35. The left iaiid windingof relay 51, the winding of relay 31 and the winding ot relay 47 will once more be connected in series Aover the circuit previously traced but relays 31 and 47 will.

not operate, due to the high resistance of the left hand winding of relay 51 and of the resistance 53 in series with them. Relay 51 in series with the windings of relays 31 and 47 and establishes a bridge across the conductors of the switching trunk ST through the winding of relay 50 over the following circuit:

brush 10 of the selector 1S, switching trunk ST, 87, 06, 86 winding ot relay 50, 85, 84, right hand winding of relay 51, 79,. winding olf relay 40, 83, switching trunk ST to brush 11 ot the selector IS. The relay50 is polarized and will not operate so long as battery through the right hand winding ot relay 16 is connected to the terminal 13 of the selectoi IS. Relay 42 which was operated and locked up during the dialing period connected the interrupter 41 in series with the winding of relay 52 which operates and releases under control of the interrupter 41. Each time relay 52 operates battery is connected to its armature 82, thus short circuitingv resistance in series with the left hand winding of relay 51. Relay 31 will operate under this con dition thus closing an obvious circuit to light the supervisory lamp 32 indicating to the operator at the toll switchboard that thel called line is busy.

Called Zine seized.

Assuming, however, that the called line is idle, it will be seized by the connector C and' relay 104 will be released and cause relay 105 to be operated to ground on the back contact of relay 106 to reverse the position of the battei-y and ground supplied over the conductors of the switching trunk ST through the windings of relay 16, thus reversing the direction of the current flowing over the trunk conductors. A complete description of the method of reversing thel position of the battery and ground through the windings ot' relay 16 is given in the pate-nt to Ray Stokely, 1,553,337 dated Sept. 15, 1925. Then relay 30 releases in the manner previously described under called line busy relay 51 will reoperate and relay 47 will release, thus establishing the bridge through the windings ot relays and 50 and the left hand winding of relay 51 in series across the conductors of the switching trunk ST. Relay 50 which is polarized now operates under controlof the reversed. battery and `ground supplied through the vwindings of relay 16 and closes an obvious circuit to operate relay 39. Relay 39 operated, locks by way of 76 and its arinature 91; opens at y the circuit through the winding of relay which releases; extends by way of its armatures 101 and 102 and contacts 56 and 55 the toll cord circuit TC to the switching trunk ST and the called line 24, The release of relay 42 closes a circuit to operate relay 44 as follows: battery, winding of relay 44, 77, 72, 78, 74, 63 to ground. The called station 24 is signaled and responds in a manner not shown but which is fully described in the art cited, closing an obvious circuit, to operate relay 17 which in turn operates relay 15 over an obvious circuit thus disconnecting relay 16 from the switching trunk. Relays 40 and 50 now release. Relay 40 released, provides a locking path for relays 48 and 44 to prevent them trom releasing when relay 46 releases as hereinafter described. This circuit is traced as follows: for relay 48, battery, winding otl relay 48, 78, 74, 92, 93, to ground; for relay 44, battery, winding of relay 44,77, 72, 78, 74, 92, 93, 75 to ground.

Disconnect.

Assuming that the called station 24 disconnects betere the toll cord T C is removed Jfrom the jack 35 at the toll switchboard TSB, relays 17 and 15 release in sequence recon necting battery and ground through thev windings ol relay 16 to the switching trunk ST. A circuit is now closed to operate relay 31 as follows: battery, right hand winding of relay 16, 13, 11, 101, 56, 36, 61, 60, winding of relay 31, 58, 59, 37, 55, 102, 10, 12, lett hand winding of relay 16 to ground. Relay 31 operated, lights the supervisory lamp 32 as a disconnect signal to the toll operator. When the plug 34 of the toll cord TC is removed from, thejack 35, relay 46, releases. A circuit is now closed to supply a busy condition to the jack sleeve 38 until the trunk circuit is restored to normal as follows: battery, armature 63 ot relay 44, 88, resistance 89, 90 to the jack sleeve 38. Relay 40 is now bridged across the switching trunk ST over the tollowing circuit: brush 10, switching trunk ST, 87, 96, 79, winding ot relay 40, 83, switching trunk ST to brush 11. Relay 40 operates in series with the windings of relay 16, thus opening at 75 the locking circuits tor relays 14, 44 and 48 which release. The release oi relay 48 opens at 76 the locking circuit tor relay 39 which releases. The release of relay 44 opens at 79 the bridge across the trunk through the winding of relay 40 which releases, thus restoring` the circuitto normal. It is evident from this description that a busy test condition is retained at the test terminal 9 and the jack sleeve 38 until the trunk circuit is fully restored to normal.

Assuming that the toll operator removes the plug 34 ot the toll cord TC trom the ack 35 betere the called line 24 disconnects, relay 46 will release and the busy condition will be removed from the jack sleeve 38 during the releasing time of relay 46. Relay 46 released,- closes at its armature 90 a substitute path to provide a busy condition at the jack sleeve 38 until the circuit is restored to normal as hereinafter described. Relay 14 which was operated under control oit relay 46 will not release at this time as it is locked up by way of 92, 93 and 75 to ground under control of relay 4() which is not operated at this time. Relay 40 is now bridged across the conductors of the switching trunk over the vfollowing circuit: brush 1() of the selector TS, switching trunk ST, 87, 96, 79, winding ot relay 40, 83, switching trunk ST to brush 11 of the selector TS. As long as the called station remains on the line, relays 17 'and 15 will remain operated and battery and ground through the windings oit relay 16 will be removed from the conductors ot the switching trunk ST, hence relay 40 will not operate and the trunk circuit will continue to test busy at the test terminal 9 and the jack sleeve 38, thus preventing the re-Seizure ot the trunk circuit.

l/Vhen the receiver is placed on the switchhook at the called station 24, relays 17 and 15 release in sequence and battery andground through the windings ot relay 16 are reconnected to the conductors of the switching trunk ST.- Relay 40 is now operated in series with relay 16 opening at 75 the locking circuits tcr relays 14, 44 and 48 which release. The release oi' relay 48 opens at 76 the locking circuit tor relay 39 which releases. The release of relay 44 opens at 79 the. bridge circuitthrough the winding of relay 40 which releases and restores the circuit to normal.

AZZ tran/es busy.

Assuming that during dialing the incoming selector 1S encounters an all trunks busy condition, the circuit through the winding of relay 40 will be momentarily opened (in a manner not shown) and relay 40 will release. Relay 40 released, connects a ground by way of 75, 67, 66 and 69 to the winding of relay 42, thus short-circuiting the relay, which releases. The release of relay 42 closes a circuit to operate relay 44 as follows: battery, winding ot relay 44, 77, 72, 78, 74, 63 to ground. Relay 44 operated, connects the interrupter 43 in series with the winding of relay 52 which operates and releases under control of the interrupter. lVhen relay 30 releases at the end ot the dialing period, relays 47 and 31 are once more connected in series with the lett winding o1' relay 51. Under this condition, each time relay 52 operates and shortcircuits resistance 53 in series with the lett winding of relay 51 relay 31 is operated, and the supervisory lamp 32 is lighted, thus supplying a distinctive flashing signal to the toll operator, indicating that all trunks are busy.

llt should be observed that the flashing signal provided under control of the interrupter 41 when the called line is busy is different from that produced under control ot the interrupter 43 when all trunks are busy so that no confusion between the signals need occur.

ililhat claimed is:

1. 1n a telephone system, a telephone line, a manual switch, a mechanical switch, means 'lor linking each switch to the line, means individual to each switch for imposing a busy condition directly upon the test terminal or sleeve ot the lineat the linking point used, means included in the line and controlled by the particular switch used for imposing a busy condition upon the test terminal or sleeve of the line at the other linking point, means includedin the line operated when the switch is disassociated therefrom `ior substituting a self-imposed busy condition upon the test terminal or sleeve for the busy condition .previously supplied by the switch while maintaining the busy conditionupon the test terminal or sleeve at the other linking point, and means for removing the busy condition from each test terminal or sleeve when the line is again ready for use.

2. In a telephone system, a mechanical switch, a trunk circuit accessible thereto, means included in the mechanical switch t'or imposing a busy condition upon the test terminal ofthe trunk when seized by the switch, and relay means included in the trunk circuit and energized by the mechanical switchv in releasing for maintaining a busy condition upon the test terminal of the trunk until said trunk is restored to normal.

3. In a telephone exchange system, a mes chanical switch, a cord circuit, a trunk circuit directly accessible to either the switch or the cord circuit,means included in the mechanical switch for imposing a busy'condition upon the test terminal of the trunk when seized by the switch, and means included in the trunk circuit and set by the mechanical switch in releasing for maintaining a busy condition upon the test terminal of the trunk until it is restored to normal.

. 4:. ln a telephone exchange system, a mechanical switch, a cord circuit, a trunk circuit directly accessible to either the switch or the cord circuit, means included in the mechanical switch for imposing a busy condition at the switch bank upon the test terminal of the trunk when seized by the switch, and means included in the trunk circuit and set by the mechanical switch in releasing for maintaining a busy condition upon the test terminal of the trunk at the switchbank until the trunk is restored to normal.

5. ln a telephone exchangey system, a cord circuit, a mechanical switch, a trunk circuit directlyaccessible to either the switch or the cord circuit, means controlled by the cord circuit when used tor placing a busy condition upon every test terminal or sleeve of the trunk, means included in the mechanical switch for imposing a busy condition at the svitch bank upon the test terminal oit' the trunk when seized by the switch, and means included in the trunk circuit and set by the mechanical switch in releasing for maintaining a busy condition upon the test terminal of the trunk at the switch bank until the trunk is restored to normal.

6. In a telephone exchange system, a trunk circuit accessible to both manual and mechanical switching devices, means controlled by the manual switching device when used for placing a busy condition upon the test terminal or sleeve of the trunk at each point o access, means included in the mechanical switch for directly imposing a busy condition upon the test terminal of the trunk at the point of mechanical switch access and indirectly'imposing a busy condition upon the test terminal or sleeve of the trunk at the point of manual switch access, and means included in the trunkcircuit and set by the mechanical switch in releasing for maintaininga busy condition upon the test terminal or sleeve of the trunk at every point oi access until the trunk is restored to normal. c

7. In a telephone exchange system,a trunk circuit directly accessible to both manual and mechanical twitching devices, means controlled by the manual switching device when used ior placing a busy condition upon the test terminal or sleeve of the trunk at each point of access, means includedin the mechanical switch` for imposing a busy condition upon the test terminal of the trunk at .the point oi" mechanical switch access, means operated by the mechanical switch for imposing a busy condition upon the test terminal or sleeve ot the trunk at the point of manual switch access until the trunk circuit is restored to normal, and means includedinthe trunk circuit and set by the mechanical switch in releasing for maintaining a busy condition uponV the test terminal of the trunk at the peint of mechanical switch access until the Ytrunk circuit is restored to normal.,

8. in a telephone exchange system, a trunk circuit directly accessible to both manual and mechanical switching devices, means con# trolled by the manual switching crevice when used for placing a busy condition upon the test terminal or Lsleeve of the trunk at each point of access, means included in the mechanical switch for imposing a busy condition upon the test terminal of tl e trunk at the peint oi mechanical switch access, means operate( by the mechanical switch for iniposing a busy condition upon the test terminal orr sleeve of theV trunk at the point of manual switch access which busy condition niaintained. thereon until the trunk is restored to normal, means included in the trunk circuit and set by the mechanical switch in releasing tor maintaining a busy condition upon the test terminal of the trunk at the point of mechanical switch access until the trunk circuit is restored to normal, and means ter restoring the trunk circuit to normal.

9.' ln a telephone exchange system, a mechanical switch, a cord circuit, a trunk circuit accessible to the switch via a terminal bank and to the cord circuit via a trunk ack, means included. in the cord circuit for imposing a busy condition upon the sleeve of the trunk jack, means operated by the cord circuit for imposing a busy condition upon the test terminal at lthe terminal bank, means nov included in the mechanicalswitch for imposing a busy Ycondition upon the test terminal at the terminal bank, means operated by the mechanical switch for imposing a busy condition upon they sleeve of the trunk jack, and means included in the trunk circuit and set when the trunk is released by either the switch or cord for maintaining a busy condition upon the test terminal and jack sleeve of the trunk until it is fully restored to normal.

10. In a telephone exchange system, a mechanical switch, a cord circuit, a trunk circuit accessible to the switch via a terminal bank and to the cord circuit via a trunk jack,

r means included in the cord circuit :tor imposing a busy condition upon t-he sleeve oit the trunk jack, means operated by the cord circuit for imposino a busy condition upon the test terminal at the terminal bank, means in`- eluded in the mechanical switch for imposing a busy condition upon the test terminal at the terminal bank, means operated by the mechanical switch for imposing` a busy condition upon the sleeve of the trunk jack, means included in the trunk circuit set when the cord is removed from the trunk jack 'jor maintaining the busy condition at the trunk jack sleeve and upon the test terminal at the terminal bank until the trunk is restored to normal, and means included in the trunk circuit set when the mechanical switch releases or maintaining a busy condition upon the test terminal at the terminal bank and at the trunk jack sleeve until the trunk circuit is restored to normal.

l1. In a telephone exchange system, a mechanical switch, a cord circuit, a trunk circuit accessible to the switch via. a terminal bank and to the cord circuit via a trunk jack, means included in the cord circuit for imposing a busy condition upon the sleeve of the trunk jack, means operated by the cord circuit or imposing a busy condition upon the test terminal at the terminal bank, means included in the mechanical switch for imposing a busy condition upon the test terminal at the terminal bank, means operated by the mechanical switch for imposing a busy con dition upon the sleeve of the trunk jack means included in the trunk circuit set when the cord is removed from the trunk jack for maintaining a busy condition at the trunk jack sleeve and upon the test terminal at the terminal bank, means included in the trunk circuit set when the mechanical switch re leases for maintaining a busy condition yupon the test terminal at the terminal bank and at the trunk jack sleeve, and means for re-` trunk is used thereat, means included in then trunk and controlled by the cord over they jack sleeve for imposing a busy condition upon the test terminal at the terminal bank,

means included in the trunk circuit ellectiveA when the cord is removed from the jack for substituting a self-imposed busy condition upon the jack sleeve while maintaining the busy condition upon the test terminal at the terminal bank until the trunk is again normal, means included in the mechanical switch effective when the trunk is seized for imposing a busy condition directly upon the test terminal at the terminal bank, means included in the trunk and controlled by the mechanical switch over the test terminal for imposingl a busy condition upon the jack sleevemeans included in the trunk circuit effective when the mechanical switch releases for substituting a self-imposed busy condition upon the test terminal at the terminal bank while maintaining the busy condition upon the jack sleeve until the trunk is again normal, and means included in the trunk circuit for restoring the trunk circuit tonormal.

In witness whereof, l hereunto subscribe my name this 19th day of March, A. D. 1924.

.man B. Daarna.

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