US1990437A

US1990437A - Telephone system

Info

Publication number: US1990437A
Application number: US687870A
Authority: US
Inventors: Dwight L Moody; Neal D Newby
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1933-09-01
Filing date: 1933-09-01
Publication date: 1935-02-05
Anticipated expiration: 1952-02-05

Description

Feb. 5, 1935.

k a I H N 2 D. L. MOODY ETAL TELEPHONE SYSTEM Filed Sept 1, 1933 4 Sheets+$het 1 VERTICAL E 1: w l I g INVENTORS D. L. MOODY IV; 0. NEWS) Feb. 5, 1935. MOODY r AL 1,990,437

TELEPHONE SYSTEM Filed Sept. 1, 1935 4 Sheets-Sheet 2 D. L. MOODY N. D. NE'WBY A T7DRNEY IN NTOR$'- Feb. 5, 1935. M DY ET AL 1,990,437

' TELEPHONE SYSTEM Q Filed Sept. 1, 1933 4 Sheets-Sheet 3 MARE/N M4 RGINA L w l EN TOPS 0. L. M0 00) N. 0. NEWBY ATTOENEY Feb. 5, 1935. D. 1.. MOODY ET AL 1,990,437

' TELEPHONE SYSTEM Filed Sept. 1, 1953 4 Sheets-Sheet 4 INVENTORS D. L. MOODY N. 0. NEWBV Patented Feb. 5, 1935 umrso stares TELEPHONE SYSTEM Dwight L. Moody, Hempstead, N. n, and Neal D. Newby, Woodridge, N 5., assignors to American Telephone and Telegraph Company, a corporation of New York Application september 1, 1933, Serial No. 687,870

' 15 Claims.

This invention relates to telephone exchange systems and more particularly to trunking circuits for extending connections from calling lines in cfiices employing dial switching apparatus to operators positions.

The objects of the invention are to simplify trunk circuits for trunking calls to an operators position and to distribute incoming calls to operators positions in such a manner that the work of operators is lessened and the speed with which connections are established is materially increased.

Heretofore it has been the practice, for example, in trunking calls from a dial switching office to a toll operators position to provide a group of trunks terminating in a terminal bank of a selector switch in the dial switching oflice and terminating at the toll switchboard in jacks to which the toll operator has access, each trunk being provided at the toll switchboard with a calling lamp. To establish a call for toll service, the calling subscriber dials a number, thus setting the selector to select the group of trunks extending to the toll switchboard. The selector then hunts and seizes an idle trunk, the trunk seized being indicated to the toll operator by the lighting of the calling lamp of such trunk. The toll operator to answer the call then plugs an idle cord circuit of her position into the jack of the-calling trunk.

In accordance with the present invention, however, it is proposed to make all toll trunks extending to the toll operators position normally busy to selector switches having access thereto until such time as the toll operator at the toll position in which the trunks are incoming is free to answer a call. When an operator is free to answer a call she will thenplug an idle cord circuit into the jack of one of thegroup of trunks which is not in use thereby removing the busy test from the test terminal of that trunk appearing in the banks of selector swiches at the dial switching oifice so that the next toll call will cause that particular trunk to be seized. Since at that time the toll operator's cord is already connected to that trunk, an immediate response of the toll operator is possible. The trunk thus functions to distribute calls to idle operators. As soon as the trunk has been seized by a selector, it is at once made busy to all other selectors having access thereto. Upon the termination of the call, the selector switches may be released either under the sole control of the toll operator or jointly under the control of the operator and calling subscriber as found most desirable, the trunk then being rendered again busy until such time as it is again plugged up to an idle toll cord circuit.

In accordancewth another feature of themvention overflow trunks may be provided extending from the selector banks in the dial switching ofiioe to the toll switchboard termihating thereat in answering jacks and provided with calling lamps. Thus each group of toll trunks would comprise a number of call distributing trunks and a number of overflow trunks, the overflow trunks being second choice trunks. With thisarrangement of trunks if no idle operators are available when a call is originated as indicated by the busy condition of all of the call distributing trunks, the selector switch will hunt for an idle overflow trunk. The call distributing and overflow trunks are multipled before the same group of operators at the toll switchboard so that when one of the operators becomes idle, she will plug into the jack of the overflow trunk upon which the lighted trunk lamp indicates that a call is waiting rather than into one of the call distributing trunks. Thus whenever a calling lamp of an overflow trunk is lighted, the operators are given an indication of a waiting call and in accordance with the number of overflow trunk lamps lighted an indication of the number of calls waiting. If desired, the overflow trunks may be multipled not only before the operators positions which normally handle the calls on the corresponding call distributing trunks of the same group, but also before other groups of operators, thus increasing the speed of answer during peaks of traffic due to the fact that while all operators of the assigned group may be busy, other groups of operators normally assigned for answering calls on other groups of trunks .may have one or more idle operators available to answer calls.

It will, of course, be obvious that the trunks may terminate in calling jacks at an originating manual ofiice rather than in the banks of selector switches of the dial switching oflice and function in substantially the same manneru For a clearer understanding of the invention reference may had to the accompanying drawings taken in connection with the following detailed description. Referring to the drawings:

Figure 1 shows schematically a calling subscribers line and the brushes of a line finder having access thereto, a first selector switch for extending a connection from the calling line to the outgoing end of a toll trunk shown in the lower right portion of the figure, or to the outgoing end of an overflow trunk shown in the upper right portion of the figure;

Fig. 2 shows in the upper portion thereof the distant end of the overflow trunk, in the central portion thereof the distant end of a toll trunk and in the lower portion thereof a modified form of the toll trunk;

Fig. 3shows a cord circuit of a toll recording and completing operators position having access to the trunk jacks of Fig. 2 together with control relays and keys of the operators position;

and

Fig. 4 shows the telephone set of the operators position.

For a complete disclosure of the circuits appertaining to the invention, Fig. 2 should be placed at the right of Fig. 1, Fig. 3 should be placed at the right of Fig. 2 and Fig. 4 should be placed beneath Fig. 3.

The line finder schematically indicated at 101 may be ofthewell-known step-by-step type similar to that shown, for example, in Patent No. 1,711,682, granted May 7, 1929 to H. Hovland. Thefirst selector switch 102 is of the well-known Strowger" type having a step-by-step vertical movement to select a desired trunk group and a step-by-step rotary hunting movement to select an idle trunk in the selected group of trunks. For the purposes of this description it will be assumed that to establish a connection from the calling line to the toll operators position the first selector switch is directed by the subscribers dial to position its brushes opposite its upper or tenth bank level and is then caused to hunt over. theterminal sets of this level to find a trunk which is available for use. The first nine terminal sets of this bank level are connected to the outgoing ends of nine toll trunks one of which is shown in the lower right portion of Fig. 1, connected to the second terminal set. The tenth terminal set of the bank level is connected to the outgoing end of the overflow trunk shown in the upper right portion of Fig. 1.

It will be assumed that the calling subscriber at substation I00 desires a toll connection and to initiate the connection, removes his receiver from the switchhook. In response to the initiation of the call the line finder 101 is started to find the calling line terminal whereupon a circuit is established from battery, left winding of relay 103, inner upper back contact of relay 104, brush 1050f line finder 101, thence over the calling line loop returning over brush 106 of line finder 101, upper back contact of relay 104, right winding of relay 103, upper normal contacts of the eleventh rotary step springs 107 to ground through the right winding of dial tonecoil 108. Relay 103 operates over this circuit and a dial tone is also transmitted to the calling substation indicating to the calling subscriber that he has become connected to the first selector 102 and that he may therefore commence dialing. Relay 103 upon operating closes an operating circuit for slow-to-release relay 109 extending from battery, winding of relay 109, front contact of relay 103 to ground at the lower back contact of relay 104.

In response to the operation of the substation dial relay 103 follows the dial impulses and upon its first deenergization closes a stepping circuit extending from ground at the lower back contact of relay 104, back contact of relay 103, right front contact of relay 109, winding of slow-torelease relay 110 to battery through the winding of the vertical stepping magnet 111. Relay 110 and magnet 111 operate, magnet 111 stepping the switch shaft one step vertically, whereupon the vertical off-normal springs 112 close and the circuit of relay 113 is established from battery,

winding of relay 113, lower contacts of off-normal springs 112, alternate contacts of relay 110 to ground at theleft contact of relay 109. Upon the next energization of relay 103 the circuit through the windings of relay 110 and magnet 111 is opened and magnet 111 releases, but relay 110 being slow to release maintains the circuit of relay 113 closed. It being assumed that the calling subscriber dialed zero, the magnet 111 is intermittently operated through the successive deenergizations and energization of relay 103 to step the selector switch shaft to position the shaft brushes opposite the tenth bank level. When the dial returns to normal relay 103 remains steadily energized thereby holding the circuit traced through the windings of relay 110 and magnet 111 open for a sufificient time to permit relay 110 to release, relay 113 being now held operated in a circuit extending from battery, through its winding, the lower contacts of offnormal springs 112, the back contact of rotary magnet 114, the outer contact of relay 113 to ground at the lower back contact of relay 104 preparatory to initiating therotary hunting movement of the selector switch102.

The toll trunk to which theselector switch 102 has access may be made busy in two ways: First, each trunk, although idle in the sense that no selector has seized it in the establishment of a toll connection,-is rendered normally busy to all selector switches until such time as'a toll operator is free to handle an incoming call and indicates that she is free byplugging a toll cord circuit into the jack of the trunk at the distant end thereof; further, a toll trunk will also test busy if it has previously been seized by another selector switch. To remove the normal busy condition from the testterminal of a toll trunk, the toll operator if free to handle an incoming call, plugs the plug 300 of one of her cord circuits into jack 200 thereby establishing a circuit from ground at the back contact of relay 206, through the upper low resistance winding of sleeve relay 201, in parallel with the lower high resistance winding of relay 201, sleeves of jack 200 and plug 300, right normal contacts of relay 303 to battery in parallel through resistance 302 and lamp 301. Relay 201 operates and lamp 301 lights. Relay 201 closes an obvious operating circuit for relay 202 which establishes a circuit extending from battery, upper winding of relay 115, upper back contact of relay 116, lower right winding of repeating coil 117, trunk conductor 203, lower back contact of relay 204, lower left winding of repeating coil 205, left contact of relay 202, winding of polarized relay 206, upper left winding of repeating coil 205, upper back contact of relay 204, trunk conductor 209, upper right winding of'repeating coil 11'], lower back contact of relay. 116 to ground through the lower winding of relay 11 5. Relay operates in this circuit, but the direction of the current flowing is not such as to operate polarized relay 206. At its right contactrelay202 also bridges the condenser 207 between the inner terminals of the left windings of repeating coil 205 to establish a talking circuit.

Relay 115 upon operating closes an obvious circuit for relay 118 which operates, in turn closing a circuit from ground. at its left contact to battery through the winding of relay 119 and in parallel therewith over the back contact, of relay 120, resistance 121 to battery through the winding of relay 122. Relays 119 and 122 operate. With relay 119 operated busy groundwhich is normally connected to sleeve terminal 124 over the right back contact of relay 119 and the normal contacts of relay 123 is removed thus rendering the trunk selectable.

Returning now to the operation of selector switch 102, with relay 113 operated and relay released, a circuit is established for the rotary magnet 114 extending from battery through the winding of magnet 114, inner contact of relay 113, normal contacts of relay 110 to ground at the left contact of relay 109. Magnet 114 operates stepping the brushes of the selector switch one step in a rotary direction into engagement with the first set of terminals of its tenth bank level, and opening the circuit of relay 113 which now .releases opening the circuit of magnet 114. It will be assumed that the toll trunk which isconnected to the first terminal set of thetenth bank level of selector switch 102 has not been associated with a toll operators cord circuit and therefore tests busy. When, therefore, the brushes of the selector switch engage the first terminal set a cir cuit is established from ground, normal contacts of the relay of the trunk similar to relay 123, right back contact of a relay similar to relay 119, test terminal 125, sleeve brush 126, inner lower back contact of relay 104, back contact of rotary magnet 114, lower contacts of the off-normal springs 112, winding of relay 113 to battery. A branch of this circuit extends from brush 126 over the inner lower back contact and winding of relay 104, lower normal contacts of springs 107, to ground at the left contact of relay 109, but relay 104 being shunted by ground encountered by brush 126 on terminal does not operate.

Relay 113 operates and closes a holding circuit for itself extending from battery through its winding, thence as first traced over the back contact of magnet 114, the outer contact of relay 113 to ground at the lower back contact of relay 104, and closes a circuit for operating the rotary magnet 114 which may be traced from battery, winding of magnet 114, inner contact of relay 113, normal contacts of relay 110 to ground at the left contact of relay 109. Magnet 114 energizes stepping the brushes of the selector switch to the next set of terminals in the tenth bank level and opening the circuit of relay 113 which thereupon releases in turn opening the circuit of magnet 114. If the sleeve brush 126 now engages the test terminal of a toll trunk which also tests busy, relay 113 will reoperate and cause magnet 114 to step the brushes another step. This action will continue until the test brush encounters a sleeve terminal which is ungrounded when, relay 104 no longer being shunted, will operate in a circuit extending from battery, winding of relay 113, lower contacts of off-normal springs 112, back contact of magnet 114, winding of relay 104, lower normal contacts of springs 107 to ground at the left contact of relay 109. Due to the resistance of the winding of relay 104 relay 113 does not operate in this circuit. Relay 104 upon operating disconnects the windings of relay 103 from the calling line and extends the calling line over its upper front contacts to brushes 127 and 128. Relay 103 now deenergizes in turn releasing relay 109.

t will be assumed, however, that the toll trunk shown in the lower portion of Fig. 1 has been previously connected with by a toll operators cord circuit and that therefore ground has been removed from the sleeve terminal 124 in the manner previously described and that the selector switch 102 is therefore arrested with its brushes in engagement with the terminals of this trunk. When, as previously described, relay 104 operates a circuit is established from battery, lower winding of relay 129, lower left winding of repeating coil 117, lower back contact of relay 130, ring terminal 131, brush 128, inner upper front contact of relay 104, brush' 105 over the calling line loop, brush 106, upper front contact of relay 104, brush .127, tip terminal 132, upper back contact of relay 130, upper left winding of repeating coil 117, upper winding of relay 129 to ground. Relay129 operates and closes a circuit from ground at its contact through the winding of reversing relay 116 to battery at the inner left contact of relay 119. Relay 116 upon operating establishes an operating circuit for relay 123 extending from battery, innerleft contact of relay 119, winding of relay 1'23, lower front contact of relay 116 to ground at the normal contacts of relay 123.- Relay 123 operates and locks independently of relay 116 in a circuit from'battery, inner left contact of relay 119, winding and alternate contacts of relay 123 toground. With relays 119 and 123 now both operated busy ground is applied to terminal'124 from ground over the alternate contacts of relay 123, right front contact of relay 119, terminal 124 and thence over brush 126, inner lower front contact of relay 104 to conductor 133 thus furnishing holding ground for the line finder 101 and over the lower contacts of springs 107,

winding of relay 104 thence as traced to battery for holding relay 104 operated to replace holding ground supplied to conductor 133 and relay 104 over the lower normal contacts of spring 107 and the left front contact of relays 109 which is removed as soon .as slow-to-release relay 109 "releases following the release of relay 103. The

busy ground applied to terminal 124 and multiples thereof also makes the trunk busy to all other selector switches having access thereto.

Relay 116 also upon operating reverses the connection of battery and ground to

trunk conductors

203 and 209 whereupon polarized relay 206 operates removing ground from the upper winding of relay 201. Since now only the lower high resistance winding of relay 201 is included in the sleeve circuit previously traced to battery through the supervisory lamp 301 of the connected toll cord circuit, the lamp is extinguished as a signal to the operator that a call has come in on her connected cord circuit. The calling subscriber may flash the cord lamp 301 by manipulating the switchhook thereby intermittently releasing and operating

relays

129, 116 and 206, relay 206 thus following the switchhook to vary the resistance of the sleeve circuit through the windings of relay 201 andthe cord supervisory lamp 301.

In response to the extinguishing of lamp 301 the toll operator throws her talking key 304 to the right or talking position. A circuit is thereby olosed from battery through the left windings of relays 305 and 303 in parallel, upper right alternate contacts of key 304 to ground at the nor- 'mal contacts of relay 307. It is to be noted in this connection that all apparatus below the dot and dash line in Fig. 3 and all apparatus of Fig. 4 is positional apparatus common to all cord cir- 'cuits of the operators position, one such cord circuit being disclosed in the upper portion of ,Fig. 3. Relay 303 upon operating transfers the circuit previously traced over the sleeve of plug 300 from battery through lamp 301 to battery through the windings of marginal relay 309 and relay 310 in series. Relay 310 now operates in series with relay 201, but relay 309 does not. Relay 310 in turn closes an obvious circuit for operating relay 311. Lamp 301 is now connected into a circuit extending over the inner right frontcontact of relay 303, throughhigh resistance 312 to ground at the left front contact of relay 311. Due .to the high resistance 312, lamp 301 remains extinguished. At its inner left contact relay 303 similarly transfers the sleeve conductor of plug 308' from connection with lamp 313 and resistance 314 to the windings of relays 315 and 316 and transfers the circuit of lamp 313 in parallel with resistance 314 to the inner left contact of relay 317 through high resistance 318. With relays 305 and 303 both operated a circuit is closed for operating relays 307 and 319 which may be traced from batterythrough the windings of these relays in parallel, outer left contacts of relays 303 and 305 to ground at the-lower right alternate contacts of key 304. With relay 307 operated the initial operating circuit of relays 305 and 303 is opened and a holding circuit for them is closed through their right windings in parallel, the inner right front contact of relay 305 to ground at the alternate contacts of relay 307.

Relay 305 upon operating, at its, outer right and inner left contacts opens the talking'conductors normally extending from the tip of plug 300 to the tip of plug 308 and from the ring of plug 300 to the ring of plug 308 and with relay 311 operated establishes a talking circuit which may be traced from the upper right winding of repeating coil 205 over the tips of jack 200 and plug 300, inner lower right normal contacts of ringing key 320, outer right alternate contacts of relay 305, upper right normal contacts of key 321, right front contact of relay 311, conductor 322, left windings of repeating coil 400, conductor 323, inner upper left normal and upper right normal contacts of key 324, lower inner right normal contacts of key 321, inner left alternate'contacts of relay 305, rings of plug 300 and jack 200 to the lower right winding of repeating coil 205. With her headset 401 plugged up the talking circuit just traced is inductively connected over the right winding of repeating coil 400. Since the left windings of repeating coil 205 are connected into a talking circuit previously described over

trunk conductors

203 and 209 through the right windings of repeating coil 117, and the left windings of repeating coil 117 are connected tothe subscribers line loop, as previously described, the operator is now enabled to talk with the calling subscriber to receive information for completing the connection. The operator then proceeds to complete the desired connection in the wellknown manner.

Should it become necessary for the operator to recall the calling subscriber she may do so by operating the ringing key 320 to the right thereby establishing a circuit from battery, resistance 402, winding of relay 403, winding of relay 404, conductor 405, inner lower right alternate contacts of key 320, tips of plug 300'and jack 200, upper right winding of repeating coil 205 to ground through the winding of ring-back relay 204.

Relays

403, 404 and 204 operate, relay 403 closing a circuit from battery, winding of slowto-release'relay 407, contact of relay 403, conductor 406, lower right contacts of key 320 to ground atthe lower right alternate contacts of key 304. Relay 404 upon operating completes a circuit in multiple with the contacts of relay 407 for shortcircuiting resistance 408 inthe operators receiver circuit. Relay 407 upon operating, following the operation of

relays

403 and 404, opens one short-circuiting path, but relay 404 being operated retains the other short-circuiting path. When the ringing key 320 is restored, relays 403, 404 and 204 release, relay 407 opening one short circuit around resistance 408 before relay 407 has time'to releaseto restore the other short-circuiting path. Thus, during the releasing time of slow-to-release relay 407 the resistance 408 is included in the operator's receiver circuit for a surficient' time to discharge'thereceiver before it is restored to its normal efiiciency, and thus to reduce the clicks incident to the operation of theringing key 320. 1

Relay 204 upon operating opens the talking circuit extending to the left windings of repeating coil 205 thereby releasing relay 206, and establishes a ringing circuit from the source of ringing current 208, lower front contact of relay 204, trunk conductor 203, lower right winding of repeating coil 117, windings of alternating current relay 120, upper right winding of repeating coil 117, trunk conductor 209, upper front contact of relay 204 to ground. Relay 120 responds to the ringing current and opens at its back contact the circuit of slow-to-release relay 122, which, after an interval releases and establishes a circuit extending from ground, winding of ring-back relay 130, back contact of relay 122 to battery at the outer left contact of relay 119. Relay 115 releases upon the opening of the direct current circuit overthe trunk by the operation of relay 204 releasing relay 118, and'relay129 releases upon the operation of ring-back relay 130 thereby releasing relay 116. Relay 119, however,'does not release following the release of relay 118 since it is held operated following the operation of relay 130 in a circuit extending from battery through the winding of relay 119 to ground at the inner upper front contact of relay 130. Relay 130 also establishes a ringing circuit extending from the source of ringing current 134, lower front contact ofrelay 130, thence as traced over the calling line loop to ground at the upper front contact of relay 130. During the ringing operation with relay 206 released, the lower high resistance Winding of sleeve relay 201 is shunted by the upper low resistance winding thereby increasing the current flowing over the sleeve conductor of the cord circuit to such an extent as to cause marginal relay-309 to operate. Relay 309 connects low resistance 327 in parallel with high resistance 312 in the circuit previously traced through lamp 301 whereupon lamp 301 lights. After the calling subscriber responds the operator restores the ringing key 320 whereupon relays 403, 404, 407, 204 and 120 release and relay 122reoperates to release relay 130. The source of ringing current 134 is now disconnected from the calling line. Relays 129, 116,115, 118 and 206 then reoperate restoring the toll trunk to the condition in which it was prior to the ring-back operation. With relay 206 now reoperated, relay 309 releases and lamp 301 is again extinguished.

When the toll connection has been completely established and it is no longer necessary for the operator to" listen in on the established connection she restores the talking key 304, whereupon relays 303, '305, 319 and 307 release and the talking circuit is established over the talking conductors of the cord circuit from the tip of plug 300 to the tip of plug 308 and from'the ring of plug 300 to the ring of plug 308. With relay 303 released, the cord lamps 301 and 313 are then connected directly to the sleeve conductors of the cord circuit. I

When the call is terminated the toll operator may release the toll trunk, with the calling subscribers receiver either on or off the switchhook, by removing plug 300 from the trunk jack 200. The removal of plug 300 releases sleeve relay 201 and relay 202. With relay 202 released the circuit over

trunk conductors

203 and 209 extending through the windings of

relays

206 and 115 is opened and these relays release, relay 115 in turn releasing relays 118, 119 and 122. Relay 119 upon releasing, releases relay 123 and if relay 116 is still operated because the subscriber has his receiver on the switchhook, it is also released. Since relay 123 is of the slow-to-release type, a slight interval will elapse between the release of relay 119 and its release, during which the holding ground from the alternate contacts of relay 123 over the front contact of relay 119 to sleeve terminal 124 is removed by relay 119 opening its right front contact, thereby causing the release of relay 104 of the selector switch 102 to initiate the release of the selector switch and the removal of ground from conductor 133 to initiate the release of the line finder 101. When'relay 123 finally releases the normal busy condition of the trunk is reestablished by groundvapplied from the normal contacts of relay 123 over the right back contact of relay 119 to sleeve terminal 124.

Relay 104 uponreleasing opens the connection between the subscribers line and the windings of relay 129 whereupon relay 129 releases. The toll trunk is now fully restored to normal. Relay 104'upon releasing closes a circuit from ground at its lower .back contact, back contacts of relays 103 and 109, upper contactsof off-normal springs 112 to battery through the winding of release magnet 135. Magnet 135 causes the restoration of the brush shaft of selector switch 102 in the well-known manner, the circuit of magnet 135 being opened at the off-normal springs 112 when the shaft reaches its normal position. The line finder is restored in the well-known manner.

Should it be desired to place the release of the selector switches under the joint control of the calling subscriber and toll operator, the outgoing end of the toll trunk would be equipped with strap 136 to afford an additional holding circuit for relay 118 and relay 115 would be made marginal with respect to the polarized relay in the distant end of the trunk. Also the distant end of the trunk would be wired as shown in the lower por-'- tion of Fig.2. In this case,,when the toll trunk is normal, a circuit is closed from battery through the upper winding of relay 115, upper back contact of relay 116, lower right winding of repeating coil 117, trunk conductor 203, joined to conductor 213, lower back contact of relay 214, lower left winding of repeating coil 215, both windings of polarized relay 216 in series, upper left winding of repeating coil 215, upper back contact of relay 214, conductor 219, joined to conductor 209, upper right winding of repeating coil 117, lower back contact of relay 116, to ground through the lower winding of relay 115. Relay 115 being marginal does not operate because of the resistance of both windings of relay 216 and polarized relay 216 does not receive current in the proper direction to operate. When the toll operator is free and plugs the cord plug 300 into jack 210, relays. 211.and

212 operate, relay 212 establishing the talking circuit through its right contact and condenser 217,

short-circuiting the lower high resistance winding of relay 216 and opening at its back contact the operating circuit of relay 220. With the lower winding of relay 216 short circuited, marginal relay 115 now operates and relays 118, 119 and 122 operate as previously described to remove the normal busy condition'from the sleeve terminal 124 of the trunk. I

When a selector switch seizes the trunk at the outgoing end, relays 129,, 116' and 123 operate in the manner previously described, relay 116 reversing the direction of the current flowing through the upper winding of polarized relay 216 to cause it to operate and to control supervision in the connected cord circuit as previously described. Relay 116 in addition closes a holding circuit for relay 118 extending fromground at its intermediate lower front contact overstrap 1136 to battery through the winding of relay 118 so that relay 118 is now under the joint control of both

relays

115 and 116. The trunk now functions in the manner previously described up to the point when release is initiated.

If now the toll operator removes the cord plug 300 from jack 210 prior to the restoration of the calling subscribers receiver to the switchhook, relay 211 will release in turn releasing relay 212. Relay 212 upon releasing will remove the short circuit from the lower winding of relay 216, thereby increasing the resistance of the trunk loop to such an extent that marginal relay 115 will release opening one circuit for relay 118. Relay .118 will not releaseghowever, since with the calling subscribers'receiver ofi the switchhook, relays 129 and llfiwillflbe energized and relay 116 will hold relay 118"operate'd. Relay 212 upon releasing withrelay 216 still operated, will close the circuit of 'relay 220, extending from ground, front contact of relay 216, back contact of relay 212, to battery through the winding of relay 220. Relay '220 therefore operates and closes an obvious circuit fortrunk la1np 221. The

calling subscriber may now flash lamp 221if he wishes to recall the operator. 'If the calling subscriber restores his receiver, however, relays 129, 116, 118, 216 and 220 will release, relay 220 extinguishing lamp 221 and relay 118 causing the release of relays 119, 122, and 123 and the consequent release of line finder 101 andselectorswitch 102 in the manner previously described.

Should all toll trunks such as the one shown in the lower portion of Fig. 1 be marked busy either because an. operator has no toll cord'circuit available for connection therewith or because of prior seizure in the establishment of other toll connections, the selector switch 102 will upon'the initiation of a call by the calling subscriberhunt over the terminals of these trunks to the last set of terminals of its tenth level which isconnected to the outgoing end of an overflow trunk shown in the. upper portions of Figs. 11 and 2. This trunk will test busy only when in use on a pre-established toll call. Itwill be assumed that when the selector test brush 126 engages the test terminal'of this trunk,.the trunk is idle'and that therefore no ground potential is present on the sleeve terminal 137. The selector switch 102 will thereforeseize the trunk and relay 104 will opcrate to cut the calling line through to the trunk, establishing a circuit from battery, lower Windjing of'relay 138, lower left winding of repeating coil 139, lower back contact of relay 140, terminal 141, brush 128, inner upper front contact of V operating circuit for slow-to-release relay 144, a

circuit extending from ground at its outer right front contact, over the back'contact of relay 145, resistance 146 to battery through the winding of relay 147, and in parallel to battery through the winding of relay 148, and connects ground to sleeve terminal 137 for holding the selector switch 102 and line finder 101'and to mark the trunk busy to other selector switches;

Relays

144, 147 and 148 operate, relay 144 connecting holding round to sleeve terminal 137 and to the windings of relays 147 and 148'. Relay 147 performs no useful function at this time and relay 148 establishes a ringing tone circuit extending from the source of ringing current 149, inner 'upper front contact of relay 148, left back contact of relay 150, lower back contact of relay 140, thence as traced over the subscribers line loop, returning over the upper back contact of relay upper left winding of repeating coil 139, upper winding of relay 138 to ground. This ringing tone persists until the toll operator answers.

Relay 148 also establishes a circuit from bat tery, left winding of marginal relay 151, left front contact of relay 143, lower contact of relay 148, lower right winding of repeating coil 139, trunk conductor 233, lower back contact of relay 234, lower leftwinding of repeating coil 235, both windings of polarized relay 236 in series, upper left winding of repeating coil 235, upper back contact of relay 234, trunk conductor 239, upper right winding of repeating coil 139, upper front contact of relay,148,'in ner right front contact of relay 143, to ground through the right winding of relay 151. Polarized relay 236 operates in this circuit, but due to the resistance of the windings of relay 236, marginal relay 151 does not operate. 1 Relay 236 upon operating closes the circuit of relay 240 extending from ground, front contact of relay 236, back contact of relay 232, to battery through the winding of relay 240. Relay 240' operates closing the circuit of lamp 241, which lights as a call signal. 7,

When the toll operator becomes free, seeing the lighted trunk lamp 241, she plugs the plug 300 of r a cord circuit of her position into the trunk jack 230 thereby establishing the previously described supervisory circuit from battery throughthe cord lamp 301 to ground through the lower high resistance winding of relay 231. Relay'231' operates but the cord lamp does not light. Relay 231 in turn causes the operation of relay 232 which opens the circuit of relay 2'40 thereby extinguishing the trunk lamp 241, switches the condenser.

237 between the left windings of repeating coil 235 to establish the talking circuit over the trunk, and short circuits the lower high resistance winding of relay 236. 'Ihe'current'now flowing over the trunk is sufficient to permit marginal relay 151 to operate thereby establishing an operating circuit for relay 150, extending. from ground, front contact of relay 151, right normal contacts and winding of relay 150 to battery. Relay 150', upon operating looks over its right alternate contacts to ground atthe front contact of relay 144, discontinues'the application of ringing tone from the source 149 to the calling line as'a signal that the operator has answered, and at its left front contact connects the condenser 152 between the inner right windings of repeating coil 139 to ringing current from the source 238 to the

trunk conductors

233 and 239 thereby operating alternating current relay and opening the direct current circuit over the trunk extending through the windings of

relays

236 and 151. These relays thereupon release. Relay 145 upon operating opens the circuit of relay 147 which releases and since at this time, relay is held operated over its locking circuit extending from ground at the front contact of slow-to-release relay'144, a circuit is established from battery, outer front right contact of relay 150, back contact of relay 147, winding of relay 140 to ground. Relay 140 upon operating opens the connection between the calling line loop" and the windings of relay 138 which thereupon releases if it is operated, in

turn releasing relays

143 and 144. Relay 140 also applies ringing current from the source 153 to the calling line and closes holding ground to the windings of relays 148 and 150. When the operator stops ringing, relays 234 and'145 release, relay 145 upon releasing permitting relay 147 to reoperate thereby releasing relay 140. With relay 140 released, the source of ringing'current 153 is disconnected and the talking circuit is reestablished'and relays 138,143, 151 and 236 recperate.

The connection over the overflow trunk is held until the calling subscriber has restored his receiver and the toll operatorhas disconnected her cord circuit from the trunk jack 230. As long as the toll operatorlhas her cord circuit connected, relay 151 is held operated in turn holding relay 144 operated 'ina circuit from battery through its winding, the inner right front contact ofrelay 150,to ground at the front contact of relay 151. Relay 144 is also held operated by relay 143 which in turn is maintained'operated by relay 138 so long as the calling subscriber has his receiver ofi the switchhook. Thus until both

relays

143 and 151 release after the calling subscriber has restored his receiver and the operator has disconnected, relay 144 remains operated in turn holding relays 147,148 and 150 operated. When the calling subscriber restores his receiver before the operator disconnects, relays 138 and 143 release, relay '143 upon releasing, reversing the direction of current flowing over the trunk circuit to cause the release of polarized relay 236. Relay 236 upon releasing shunts the lower high resistance winding of relay 231 by the upper low resistance winding thereby'reducing the resistance of the cord sleeve circuit to such an extent as to permit the lamp 301 to light as a disconnect signal. The operator seeing the disconnect signal removes the cord plug 300 from jack 230 thereby releasing relays 231 and'232. With relay 232 released, the 'shunt'around the lower high resistance winding of relay 236 is removed and marginal relay 151 does'not now receive sufficient current and releases. Relay 151 upon releasing opens one circuit of relay l44and since relay 143 is not now energized, relay 144

releases releasing relays

147, 148 and 150 and removing holding ground from sleeve terminal 137 to initiate the release of selector switch 102 and line finder .101. The apparatus used in extending the connection is now normal.

Although it has been assumed that the selector switch 102 has access over its tenth bank level to nine toll trunks such as is disclosed in the lower portion of Fig. l and to one overflow trunk, it will be obvious that the ratio between the number of toll trunks and overflow trunks may be varied as the service requires. It will also be obvious that the toll trunk and overflow trunk may be multipled at the toll office before as many toll operators positions as may be desired.

From the foregoing description it will be apparent that so long as any toll operators of a team of operators are free to handle incoming toll calls and have preconnected cord circuits of their positions to the distant ends of the toll trunks, toll calls originated thereafter by calling subscribers will be automatically distributed to the free operators positions and that the toll calls will, because of the preconnection of the toll op- U erators cord circuits with the toll trunks receive fast and efiicient attention. When, however, at periods of peak load allof the regular toll trunks are either busy on established toll connections or the operators are not immediately free to handle additional toll calls, such additional toll calls will be routed over overflow trunksand all operators of the team will be apprised of waiting calls by the lighting of thetrunk lamps of the overflow trunks so that as soon as any operators become free the waiting calls maybe answered.

What is claimed is:

1. The method of extending calls from an originating ofiice to a manual switchboard having an operators position equipped with a plurality of cord circuit which consists in first preallotting idle cord circuits ahead of calls to be answered by the connection of the answering plugs of idle cord circuits to answering jacks appearing'in the face of said switchboard and subsequently upon the initiation of calls at the originating ohice trunking such calls to the jacks to which cord circuits have been previously connected.

2. In a telephone exchange system, a manual.

switchboard, operators positions at said switchboard, answering jacks on said switchboard, cord circuits for connection to said jacks, trunk circuits extending from an originating office toward said switchboard, and switching means for extending connections over said trunk circuits to said answering jacks only when idle cord circuits have been previously connected to said jacks.

In a telephone exchange system, a group of trunk circuits, means for connecting with the distant ends of said trunk circuits, means for connecting with the outgoing ends of said trunk circuits, and means for normally rendering each of said trunk circuits busy at the outgoing end thereof to the connecting means having access thereto until a connection has been made therewith by connecting means at the distant end thereof.

4,. In a telephone exchange system, a group of trunk circuits, means for connecting with the distant ends of said trunk circuits, means for connecting with the outgoing ends of said trunk circuits, means for normally rendering each of said trunk circuits busy at the outgoing end thereof to the connecting means having access thereto, means operable upon the seizure of a trunk circuit at the distant end thereof for removing the busy condition from the'outgoing end thereof thereby rendering said trunk circuit selectable at its outgoing end, and means operable upon the subsequent seizure of said trunk circuit at its outgoing end to again render it busy r to other connecting means having access to the outgoing end thereof.

' 5. In a telephone exchange system, a manual switchboard, operators positions onsaid switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said position for connection to the incoming ends of said trunk circuits, means for connecting with the outgoing ends of said trunk circuits, and means for normally rendering said trunk circuits busy to. said connecting means until cord circuits have been connected'therewith at the incoming ends thereof.

6. In a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said positions for connection to the incoming ends of said trunk circuits, means for connecting with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits busy to said connecting means until cord circuits have been connected therewith at the incoming ends thereof, and means operable upon the seizure of a trunk circuit by a connecting means for again rendering said trunk circuit busy to other connecting means having access thereto.

'7. In a telephone'exchange system, a manual switchboard, operators" positions on said switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said positions for connection to the incoming ends of said trunk circuits, means for connecting with the outgoing ends of said trunk. circuits, means for normally rendering said trunk circuits busy to said connecting means, means operable upon the connection of a cord circuit to the incoming end of a trunk circuit for removing the busy condition from' the outgoing end of said circuit, thereby rendering said trunk circuit selectable to said connecting means, and means operable upon the subsequent seizure of said trunk circuit by a connecting means to again render said trunk circuit busy to other connecting means having access thereto. 8. In a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said positions for connection to the incoming ends of said trunk circuits, selector switches for connecting with the outgoing ends of said trunk circuits, and means for normally rendering said trunk circuits unselectable to said selector switches until cord circuits have been connected therewith at the incoming ends thereof.

' 9.111 a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said positions for connection to the incoming ends of said trunk circuits, selector switches for connecting with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits unse-v lectable to said selector switches, means operable upon the connection of a cord circuit to the incoming end of a trunk circuit for rendering said trunk circuit selectable to said selector switches, and means operable upon the subsequent seizure of said trunk circuit by a selector switch to again render said trunk circuit unselectable to other selector switches.

10. In a telephone exchange system, a. group of trunk circuits, means for connecting with the distant ends of said trunk circuits, selector switches for connecting with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits unselectable to said selector switches, means operable upon the seizure of a trunk circuit at its distant end for rendering said trunk circuit selectable to said selector switches, means operable upon the subsequent seizure of said trunk circuit by a selector switch to again render said trunk circuit unselectable to other selector switches, and means operable upon the disconnection of the connecting means from the distant end of said trunk circuit for releasing said selector switch and for reestablishing the normal unselectable condition of said trunk circuit.

11. In a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group of trunk circuits incoming to said switchboard, cord circuits at said positions for connecting to the incoming ends of said trunk circuits, selector switches for connecting with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits unselectable to said selectorswitches, means operable upon the connection of a cord circuit to the incoming end of a trunk circuit for render: ing said trunk circuit selectable to said selector switches, means operable upon the subsequent seizure of said trunk circuit by a selector switch to again render said trunk circuit unselectable to other selector switches, and means operable upon the disconnection of the cord circuit from the incoming end of said trunk circuit for releasing said selector switch and for reestablishing the normal unselectable condition of said trunk circuit.

12. In a telephone exchange system, a group of trunk circuits, means for connecting with the distant ends of said trunk circuits, selector switches for connecting with the outgoing ends of said trunk circuits, said trunk circuits normally being unselectable to said selector switches by busy potential applied to the test terminals thereof appearing in the terminal banks of said switches, a first relay for each of said trunk circuits in the outgoing end thereof operable upon the seizure of said trunk circuit at'the distant end thereof for removing said busy potential to render said trunk selectable, a second slow releasing relay associatedwith the outgoing end of said trunk circuit and operable upon the subsequent seizure of said trunk circuit by a selector switch to again apply said busy potential to render said trunk circuit unselectable to other selector switches, and a locking circuit for said second relay controlled by said first relay, said relays both releasing upon the disconnection of the connecting means from-the distant end of said trunk circuit, said first relay upon releasing removing said busy potential thereby releasing said selector switch, and said second relay upon releasing again applying said busy potential to reestablish the normal unselectable condition of said trunk circuit.

13. In a telephone exchange system, a group of trunk circuits, means for connecting with the distant ends of said trunk circuits, calling lines, selector switches for connecting said lines with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits unselectable to; saidselector switches, meansoperable upon the seizure of a trunk circuit at its distant end for rendering said trunk circuit selectable to said selector switches, means operable upon the subsequent seizure of said trunk circuit by a selector switch to again render said trunk circuits unselectable to other selector switches, and means operable upon the disconnection of the connecting means from the distant end of said trunk circuit; and the restoration of the receiver of the calling line for releasing saidselector switch and for reestablishing the normal unselectable condition of said trunk circuit. V

14. In a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group .of trunk circuits incoming to said switchboard, cord circuits at said positions for connection to'the incoming ends of said trunk circuits, calling subscribers lines, selector switches controllablefrom said lines for connecting with the outgoing ends of said trunk circuits, means for normally rendering said trunk circuits unselectable to said selector switches, means operable upon the connection of a cord circuit to the incoming end of a trunk circuit for rendering said trunk circuit selectable to said selector switches, means operableupon the subsequent seizure of said trunk circuit by a selector switch to again render said trunk circuit unselectable to other selector switches, and means operable upon the disconnection of the cord. circuit from the incoming end of "said trunk circuit and the restoration of the receiver of the calling line for releasing said selector switch and for reestablishing the normal unselectable condition of said trunk circuit. 7

1-5. In a telephone exchange system, a manual switchboard, operators positions on said switchboard, a group of trunk circuits incoming to said switchboard; said group of trunk circuits being divided into a first and a second subgroup, the trunks of the second subgroup serving as overflow trunks and having trunk lamps associated with their incoming ends, cord circuits at said positions for connecting with any trunk circuit or said groups of trunkcircuits, selector switches having first choice access to the outgoing ends of the trunk circuits of said first subgroup and second choice access to the outgoing ends of the trunk circuits of said second subgroup, and means for normally rendering the trunk circuits of said first subgroup unselectable to said selector switches until cord circuits have been connected therewith at the incoming ends thereof, whereby if no cord circuit is available for connection to a trunk circuit of said first subgroup a selector switch will upon its operation select an idle trunk circuit of said second group and light the trunk lamp of such trunk circuit.