US2377314A - Telephone system - Google Patents

Abstract

552,765. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., CHRISTIAN, D. A., and DIBBEN, W. H. J. Jan. 7, 1942, No. 252. [Class 40 (iv)] In a satellite system, a local selector, after responding to a discriminating digit, is released completely, the next digit being taken by another selector of the same group. The switch giving access to these selectors may be of the double-hunting type. Circuit arrangements. When the circuit is seized, line and release relays A, B and relays AA, BA and J pull up and the switch JH hunts for a junction under control of KJ. With the arrangement shown in Fig. 1, SH hunts in a similar way under control of KS for a local first selector. Relay A repeats the digits over the junction, to discriminator. magnet DSM and to AA which repeats them to the local selector. JG is operated by the first impulse and locks up. When it is determined that a call is local, LD pulls upon the relapse of dialling relay C, energizes LE and causes the release of KJ and the junction and when it is determined that the call is an outgoing one, JD releases KS and the local selector. Assuming that the first two digits do not determine the destination of the call, DA pulls up after the first and DB after the second, the discriminator proceeding to its next home position in each case and OA pulling up in the second home position and OB in the third. Operation of DA or DB drops KS to start SH in search of another selector. CT, an instant later provides a test circuit for KS until the operation of OA or OB. The circuit provides for metering with the aid of relays MD which pulls up on the called party's reply and V which is released by MD. An operator can hold the connection by holding I to prevent release of BA. The double-hunting switch giving access to local selectors is shown in Fig. 2, the apparatus shown in this Figure replacing that shown in the rectangle in broken lines in Fig. 1. When the circuit is seized; the switch moves off unless it is standing on the terminals of an idle selector. In this case, or when such terminals are reached, TA pulls up if the selector tested by wiper SH3A is idle and TB if only that tested by SH3B is idle. TA energizes KSA and TB KSB to cut the drive. When the destination of the call is not determined at the end of a digit, DA or DB drops KSA or KSB. The test relay TA or TB is momentarily shunted by ground from the releasing selector ahead but if the other selector available in this position is idle, the other test relay pulls up to initiate its seizure and prevent the switch from driving off. Otherwise the switch hunts as before. If it reaches the second half of its bank, OF is energized and locks up so that on reaching contact 12 for the second time the switch is stopped. If all the junctions are busy, the switch JH stops in an overflow position, supervisory relay I is not energized and, if relay JD is operated, an overflow meter is operated and busy tone goes back.. If the switch SH fails to find a local selector there is no circuit for operating I if LO is operated and the relapse of JG, which follows that of KJ, connects up the busy tone.

Description

June 5, 1945. D. A. CHRISTIAN ETAL 2,377,314

TELEPHONE SYSTEM Filed Nov. 50, 1942 3 Sheets-Sheet 2 JH/ /(contd). I i 03 5 a2 L15 d2 I L 5a} 3918 Attorney Vdb/ ' v s Inventors.

H- 05 DAVID ADAM CHRISTIAN I I .7 wuum 11mm JUSEHI o/Bam June 1945- D. A. CHRISTIAN ETAL 2,377,314

TELEPHONE SYSTEM Filed Nov. 30, 1942 3 Sheets-Sheet 3 Inventors DAVID ADAM CHRISTIAN WILLIAM HENRY JOSEPH DIBBEN N QR Attorney Patented June 5, 1945 UNITED STATES PATENT OFFICE TELEBHONE David Adam Christian, Batley; amf William Henry IosephDibben, Dewsbury; England; as-

si'gnors to Siemens Brothers & co, Iiimited; Westminster; I lon'd'on, England! a British. com- D i y (CL. Hit-I 8):

1 2'- @l'aims:

The present; invention. relates to telephone. systems and more particularly to automatic sys terms in which there are maintexchanges and;sat'-. ellite or sub-exchanges and in which calls, from a satellite or: sub-exchange tobe completed. local. Iy or in an. adjacent exchange are. made without passing through themain exchange In aisystem ofthis kind. ajunction. to the. main exchangev is automatically taken intousewhenever av call is originated at a. satellite exchange anddiscriminating apparatus is employed the function of whichis to determine the destination of. the call as soon, as possible and release any route that has been seized or prepared. but, willnot be required for use. onthe call.

In order, that. acall. to a subscriber connectedto.

a satellite. exchange. may be. set. up. from any a station. by always dialling, the same number it is: usual. when; the calling, station is. connected. to the samesatelliteexchange as the called-line or to anadjacentexchangeto absorb one or more digits as the full number of digits will not normally be required. for the setting up) of. sucha call. Ase.- lector, therefore, having respondedto a. digit, that is to be. absorhedvis requiredto releaseandibein a condition to. respond to another digit before the expiry of. the inter-train pausev Withisome; types of two-motion switches,., for instance those that are releasedby acontinued rotary motionfollowa ed by a vertical and. then a backward. rotary movement the inter-train pause may not belongenough to ensure complete release of. the switch in allcases during the time available.

The present invention is directed to means whereby this disadvantage may be. overcome; with a View to. a, more certain operation of the selecting, switch. Accordingly, in this. invention ase'-- lector. whichhas beentaken into use ands hasre-- sponded' to a digit which is to be, absorbed is allowed, to release its own time, the next digit being. taken by another selector of the same. group and operating. on the samemultiple. The selectors for. local calls. are connected. upby ahunting, switch which is conveniently operated at. the. same time-as the junctionhunting switch and a, digit which is to be absorbed causes. the hunt.- ing switch to advance in; search of a further local selector; advance automaticallyreleasing the first seized local selector from the connection The normal speed of a: single motion hunting switch being greater than the rotary speed of a two motion selecting switch the'former' can easily sea-rchthemunberof outletsusuallyprovid'ed ata normal numerical switching stage in the inter-- train: pause. The chance of" a call being" lost due to the hunting switch beingvunable to findianr other free. sel'ector need therefore never exceed the smallvaluegenerall'y permitted at any'normal switching stage andmay'in fact be. less than this; Iiidesired', the hunting switch. maybe; of the kind in. which simultaneous search; is carried out over two sets. of'wipers. The control ofthe' hunting switch may be bya high speed. test'rel'ay or'rel'ays; By the arrangements of the present invention. all the group: selecting switches, inthe lo'cal' excl'iange may be of the same type, i; e; ordinary group; selectors.

The; discriminating arrangements maycom- V search of another selectorof' the same group and the originally seized" selector releases its own time. Discriminationwmaybe-efiected'onanydigit I bythe connection in a suitable manner'ofdiscrinr' inati'ng' relays to contacts of a digit switch. It preferred that each digitreceived. results in a connection over' a diiferentwiper of the digit switch andthat the digit switch steps a subnormal positiorr after each digit that does-not determine the destination of-thecall'. I

If the" calf is to be coinpleted over the junction, thelocal selector will be released as' soon as (18.- terminatiorr has b en made; In each case the-discri'minator' is cut out of circuit as soon as'determ-ihaticn is=completed-.-

For the release from the connection of a se- Iect'or' following a-digit that is to be absorbed and the: seizure of a further selectorto take the next digitthe arrangements may provide" for thetemporary opening;- of the testing circuit of the: selector hunting switch; thereby initiating the release of the selector; thetest relay circuit being restored before the removal of: the busy potential? from the test bank' contact by the selector whereby the test relay; is prevented from re:- operatmgand a stepping: circuit for the selector hunting switch is' completed. The hunting; switch may be ofthe' dual testing type in which test is made simultaneously over. two. Wipers andb'anks, inwhich case high speed test relays are preferabh employed and on the restoration of the test" relay circuit the selector connected to the outlet in the other bank corresponding to that over which the released selector is connected may be seized, if free, without stepping action taking place.

Arrangements may be provided whereby the giving of a busy signal is delayed if congestion is met with at any stage until is has been determined that such congestion will prevent the completion of the connection. Thus failure to find a free junction does not prejudice the completion of a local call and in such case while a busy signal circuit and overflow metering circuit may be prepared they will only be completed when it has been determined that the call is to be extended over the junction. Similar conditions apply to the selector hunting switch. Furthermore failure by a local selector to find a free outlet in response to a digit to be absorbed is no bar to the successful completion of the call and trans--' mission of busy signal is delayed until it has been determined that the setting of the selector is necessary for extension of the connection. An overflow meter may be provided for the selector hunting switch and the arrangements may be such that its circuit is not completed after the initial search or if the digit which would normally cause its operation is to be absorbed. These arrangements provide for the stepping of the hunting switch from an overflow position after unsuccessful search following a digit that is to be absorbed.

Reference will now be had to the accompanying drawings which show by way of example discriminating arrangements suitable for use at a satellite exchange. Fig. 1 of the drawings shows a discriminating repeater including 25,-point single motion stepping switches as junction hunter and selector hunter, both switches being of the direct drive type and of the kind in which each outlet is tested in turn as the switch is stepped. Fig. 2 shows a modification of that part of Fig. l enclosed in a broken line rectangle in which the selector hunter is of the kind in which outlets are tested in pairs.

The circuits shown in Fig. 1 will first be described after which reference will be made to the modification shown in Fig. 2. The discriminating repeater of Fig. 1 may be considered as being situated'at a satellite exchange and connected to outlets from a subscribers preselector. It is also suitable for use at an exchange in which calls are received from a sub-satellite exchange. The repeater includes a transmission bridge with the usual impulse receiving relay A connected to the incoming side thereof and supervisory relays I and D bridged across the outgoing side thereof. The outgoing wires extend to a junction hunter which has outlets connected to junctions, the switch having a stepping magnet JHM and four wipers designated JHl-JH4. The outgoing wires from the bridge also extend to a -point selector hunter which has its outlets commoned in pairs so that the first 12 outlets numbered I to l2 are connected to local first selectors and the next 12 outlets numbered l3 to 24 are connected to the same local selectors as are outlets numbered I to [2. The switch has a stepping magnet SHM and four wipers designated SHl-SH4. All the local selectors connected to the selector hunter are in the same group so that a call for any local subscriber may be extended over any one of them. The 25th contact in each hunter is an overflow contact over which access is had to an overflow meter. There is also a 25-point reverse drive digit switch the contacts of which are also commoned in pairs, contacts 2 to II being commoned to contacts l3 to 22 respectively and connected as required to discriminating relays. The digit switch has a stepping magnet DSM and five wipers designated DSl-DS5. The switch has normal positions on the 1st and 12th contacts. The discriminating relays are designated DA, DB, LD and JD. Relays DA and DB by their operation at the end of a digit determine that the digit is to be absorbed, relay LD by its operation determines that the call is to be completed over the local selector and relay JD by its operation determines that the call is to be completed over a junction to the main exchange. The principal relays are the release relay B with its relief relay BA, metering relay J, all of the slow releasing type; dialling relay C, metering delay relay MD of the slow to operate type, the test relays KJ for the junction hunter and KS for the selector hunter and the auxiliary impulse repeating relay AA. The functions of the other relays will be apparent from the description as it proceeds.

The general operation of the repeater is as follows. When the repeater is taken into use, the junction and selector hunters search for and seize a free junction to the main exchange and a free local selector respectively. The first digit received at the repeater is repeated over the junction and to the local selector and is also registered by the digit switch. If this digit is such as to determine the route to be taken, one of the relays JD and ID will be operated and further impulses will be repeated directly over that route and the other route will be dropped and the digit switch out out of circuit. If the digit does-not determine the route, relay DA will be operated. The junction will be held but the seized selector will be released and the selector hunter will search for a further free local selector. The second digit is received and repeated in a similar manner to the first. If a third digit should be necessary to determine the route, relay DB will have been operated at the end of the second digit. The local selector seized as a result of the discriminating action in respect of the second digit is dropped and another seized and at the end of the impulse train of the third digit one or other route is dropped and further digits are transmitted over the route that is retained. Supervision and metering is effected in either case under control of the bridged relays D and I. v

Up to the time that the digit that finally determines the route is received several possibilities of encountering an engaged condition exist. So that the existence of an engaged condition encountered during this time may not be prejudicial to the completion of the'connection no busy signal is given until it is finally determined that it is not possible to extend the call over the required route. The conditions which may arise and which permit the delay and the final giving of an engaged signal if necessary will be made clear in the course of the detailed circuit description which now follows.

The repeater tests free by reason of the absence of earth from the incoming test wire p. When the repeater is taken into use, relay A operates over a preceding loop, in the example over the loop closed by the calling subscriber. Contact al closes operating circuits for relays B and AA and contact a2 closes in the wires outgoing from the feeding bridge. Relay B operates and at contact bl connects earth to the incoms ing wire p to mark the circuit engaged. Contact b2 operates relay BA, contact b3 connects relays I and D to the outgoing side of the bridge and contact b4 prepares the circuit of magnet DSM of the digit switch to receive impulses. Re-

. lay AA operates and at contact no! closes a point in a loop circuit over resistance YE in the circuit for the local selector when seized. Relay BA operates and at contact bcl connects earth to the incoming 22 wire to substantiate that over contact bl. Contact ba2 connects earth to a who over which many of the relays are p rated and held, con act but connects earth to one side of relay K contact but connects the junction point of relay KJand magnet JHM to wiper JH3, contact ut connects the junction.

the magnet will be disconnected from wiper JH3 at contact hi2. If, however, the wipers of the junction hunter are resting on contacts connected to a junction already engaged in a connection, earth will be present on the contact in the bank of wiper JH3 and relay KJ will be shortscircuited. Magnet JHM will operate in a circuit from this earth over wiper JH33fcon tacts 1 7612, had, y'hm, and the magnet to battery and by the interruption of its own circuit at contact y'hm the magnet will step the switch until contacts connected to a free junction are reached whereupon there bein no earth over wiper JH3 magnet JHM will not re-operate but relay KJ will operate, disconnect the magnet at contact 7012 and at the same contact apply earth to wiper J H3 to guard the junction against seizure by another testing. switch. Contact is? I opens the homing circuit of the junction hunter and contacts M3 and kid. switch the speaking wires through to the junction over Wipers JI-Il and J H2.

A similar operation takes place at the selector hunter. On the changeeover of contact 12115, a driving circuit for magnet SHM is prepared and if the contacts on which the wipers are standlog are connected to an en aged ou le he driving circuit will be completed over wiper 61-13 to earth on the bank contact of engaged outlets. The switch will he stepped un il a free outlet is encountered whereupon. there being no earth on the bank contact of. Wiper 8H3, the magnet will not be energised. Relay KS which during stepping is short-circuited by the busy earth now operates from earth over contacts b112, dad and id! in series with magnet Sl-IM and at contact ksZ opens the stepping circuit and applies earth to the test wiper SH3 to engage the outlet. Contacts ks3 and ks4 switch the speaking wires through to the seized. selector over wipers SHI and 51-12 and a loop to the selector is closed over contactaal an resistance YE.

When both hunting switches have found free outlets and relays KJ and KS are both operated, dial tone is connected over wireDT, contacts Iss5,

15., 3, 593 and. the right-hand winding of relay 1 w nce it is related by induction to the incoming speaking wires. Meanwhile relay J has operated in a circuit from earth over contacts ba2, 9d3, lel and mdl. At contact ii relay'J looks up, at contact 52 the metering circuit is prepared and at contact 13 the supervisory lamp SL is lit over contacts 1 72, it and le2 and a battery connected alarm relay. Also, consequent on the seizure of a junction, relay I is operated over the junction and at contact il connects a holding earth to relayBA andat contact i2 opens a point in the busy tone circuit over wire BT.

It may here be convenient to refer to busy conditions that may be encountered at this stage. Should either of the hunting switches fail to find a free outlet they are stepped to their 25th contacts where, there being no connection at this time they are brought to restand relays KJ and KS are operated. These contacts in the bank of wipers JH! and JH2 are not connected so that relay I will not be operated. The bridge is, at this stage, disconnected from the selector hunter at contacts of. relay LD. As neither relay. JD nor LE is as yet operated busy tone over wire BT and contact i2 will not reachthe caller,

The caller having heard dialling tone may now commence to dial the wanted number. Thelmpulses of the first digit are received by relay A and are repeated at contact al to relay AA, and magnet DSM and at contact a2 over the junction, if a free junction has been seized as will be assumed. At the first release of relay A, relay AA will release and repeat the impulse to the T seized local selector at contact aal, (it will be assumed that a local selector has been seized) a loop existing over resistance YE. At the 'back contact al, a circuit'is now closedfrom earth-over contacts al, 124, led, :idfi, magnet DSM to battery and the magnet is energised. A parallel circuit is also closed over contacts at, 54 andjgl for relay JG. This relay operates and locksovercontacts y'gI, Icy'fi and M2. At contact 7'92 it opens the circuit of lamp SL and at contact 7'93 it opens the dial tone circuit. In another parallel circuit relay C operates and short-circuits its low resistance winding at contact cl to render the relay slow to release sothat it holds up during impulse transmission. Contact 02 opens to guard against a false operation of a discriminating relay and contact 03 closes a low impedance bridge across the outgoing speaking wires. On the re-operation of relay A, relay AA re-operates and the circuit of magnet DSMbeing opened the digit switch is stepped to its first contacts. Subsequent impulses are repeated in a like manner over the junction and to the local selector and digit switch. After the last impulse, relay A remains steadily operated and relay C releases. Contact 02 closing, a circuit is closed from earth over contacts 1M2, ld5, 1:12, 02, da2, wiper DS3.for one of the discriminating relays. Relay I is operated over the junction. If this digit determines the route then the other route seized is dropped and the digit switch out out of circuit. If it does not determine the route then thedigit switch responds to a subsequent digit. If the call is to proceed over a junction it will probably be determined by the first digit but the arrangements provide for its determination by any of the first three digits.

Assuming that the first digit determinesthe call to be one for completion over the junction to the main exchange, the circuit closed over wiper BS3 will include relay -JD and that relay will be operated and will lock up over contacts y'dl and M12. Contact 1112 opens the circuit over the digit switch wiper toprevent operation oi hunter, contact ids disconnects magnet DSM from the impulse repeating circuit and connects it in a homing circuit over contact dsm and wiper DSI, contact id! releases relay KS thereby releasing the seized local selector and contact ad8 connects the 25th contact in the bank of wiper JH3 to an overflow meter for the operation of the latter should no junction have been seized by the junction hunter in its search. As a consequence of the release of relay KS, the speaking wire circuit over wipers SHI and H2 i opened to initiate the release of the seized local selector and until the release relay of the selector releases the earth on the test bank contactapplied by it is extended back over wiper SE3, contacts Iss2, ba5, shm and magnet SHM. The magnet operates and steps the selector hunter to the next contacts. If these contacts are busy the selector hunter will step and continue stepping until free contacts are found or the last contacts reached. These movements are however without eifect as the circuit of relay KS being open at contacts id"! the contacts on which the switch rests will not be engaged by it.

Further impulse trains from the subscriber's dial are repeated over the junction at contact a2 until the connection has been completely set up.

If the first digit does not determine the route,

relay DA will be operated instead of relay JD as r:

described above and will lock up over contacts dai and M2. over wiper DS3 for the discriminating relays, contact da3 closes the homing circuit for the digit switch over wiper DSl, contacts dsm and OM and magnet DSM, contact da4 closes an operating circuit over contact oa3 for relay CT, which is slow to operate to give time for the release of relay KS, and releases relay KS and contact da5 connects the right hand winding of relay 0A to the normal contacts in the bank of wiper DS2. The digit switch drives to its next normal position in which relay 0A is operated in the above described circuit. Relay CT on operating re-connects relay KS at contact oil. When relay KS released the local selector was released and the selector hunter stepped on as described in connection with the operation taking place when the first digit denotes a junction call but in this case when a free outlet is encountered, relay KS re-operates over contacts ctl and M2, (relay JD being unoperated) and engages the outlet and switches the speaking circuit through. Before coming to rest on the th contact position if no free selector has been found the selector hunter will test all the outlets, that is the remainder of those numbered 1 to 12 and all of those numbered 13 to 24. No busy signal is given in the last contact position as relay LE has not been operated and relay JG is operated and the final route of the call has not yet been determined. When relay 0A operates, it locks over contacts cal and b112, at contacts 0112 connects wiper D34 to the discriminating circuit, at contact 0413 releases relay CT and holds relay KS over contacts dbl and dad, at contacts '0a4 opens the homing circuit and at contact 0415 connects a circuit for relay OB;

The second digit is repeated like the first over the Junction, to a local selector and to the digit Contact da2 opens in the circuit.

a the normal contacts in the bank of wiper DSZ to switch which is set accordingly, relay C being operated during the impulse train. At the end of the impulse train, relay C releases and at contact 02 extends earth over wiper DS4 to the discriminating relay connected up by the digit switch. If this digit does not determine the route to be taken, relay DB will be operated and looked over contact dbl. Contact (1112 opens the circuit over wiper D84, contact db3 closes a homing circuit for the digit switch, contact db4 releases relay KS and closes a circuit for relay CI over contacts ob3, M3 and du l and contact (1225 connects the left-hand winding of relay OB over contacts oa5 to the normal contacts in the bank of wiper DS2. The digit switch homes, the magnet circuit being over contacts OM and 11133 and relay KS is released thereby releasing the local selector and closing the stepping circuit for the magnet SHM in the manner described earlier. When the digit switch reaches a normal position, relay OB is operated by means of its left-hand winding and locks up over its right-hand winding and contacts chi and ba2. Contact 0122 connects up wiper DS5 in the discriminating circuit, contact 0133 releases relay CT and re-connects relay KS over contacts dbl, 0113 and dad and contact 0124 opens the homing circuit of the digit switch. Relay KS operates when the selector hunter has found a free selector to respond to the third digit.

The arrangements of the present example are provided for discrimination on any one of three digits so that since no determination of route has been eiiected by either of the first two digits, such determination must be made at the end of the third digit. If the call is to be completed over the local selector, relay ID will be operated over wiper DS5 at the end of the third impulse train and will lock up over contact ldl. The operations which follow are the same whether relay LD is operated by the third or any earlier digit except that in one case relays DA and 0A with or withoutsDB and OB are operated and in the other case they are not. When relay LD operates, it closes the circuit of relay LE at contact Zd2, connects wipers SH! and SH2 to the feeding bridge and disconnects resistance YE at contacts M3 and Zdl, opens the operating circuit for the discriminating relays at contact M5 and holds relay AA operated at contact ld6. Relay LE operates; at contact lel opens a point in the operating circuit for relay J, at contact ZeZ opens a further point in the circuit for lamp SL, at contact le3 prepares a circuit for the transmission of busy tone, at contacts le4 disconnects magnet DSM from the impulse repeatin circuit and closes the homing circuit of the digit switch, at contact le5 releases relay KJ and at contact Zeli maintains the engaged marking of the junction and holds open the operating circuit of magnet JHM. Contact Zel connects the last contacts in the bank of wiper SH3 to an overflow meter this circuit being completed should no free selector have been found by the selector hunter to take the third or other digit. In this latter event the overflow meter will be operated and on the release of relay JG the and M4. Further impulses for the setting 01 local selector switches are repeated at contact a2 over theflpop closed over contacts 03 and the selector hunter wipers, contact can remaining closed by reason of relay AA being held over contact ldfi.

It may be noticedthat relays LE and JD perform similar functions for a local and junction call respectively. If the second or third digit had caused operation of relay JD, the subsequent operations would have been the same as those described earlier in the case of the first digit determining that the call was to proceed over the junction to the main exchange.

Whenthe called subscriber replies, relay D is operated either over the junction or over the local selector as the case may be and at contact vdl operates relay MD. Contact d2 in conjunction with contacts 9'5 guards the outgoing circuit against a flick of relay A during the subsequent reversalof current through relay A for the repetition of the answering supervisory signal which would be necessary if the call had been received :frcm a sub-satellite or adjacentexchange. Con- :tactmdl disconnects relay J initiating its release, contact mdZ disconnects the direct earth from the incoming test wire 22, contact md3 applies positive battery thereto for metering purpose during the release period of relay J, contacts md4 and md5 reverse the direction of current over the incoming wires for the supervision and metering of the call should it have come from anotherexchange and connect a ballast resistance ER in the incoming line circuit and contact mdS opens to guard against lighting of the supervisory lamps .SL on the subsequent release of relay J. .Afteran interval relay J releases, terminates the metering pulse at contact 9'2 and at contact 7'5 removes the 1 guard circuit-from contact a i.

At the end of the conversation the caller will clear-and relay A will release. Relays JG and'C 'will operate over contact al but without efiectand the outgoing circuit will be opened at contact (:2.

Shortly after, relay B will release and in turn will release relayBA. Relay BA on releasing disconnects the holding earths for all the relays now held and they will release in their own time.- By the relapse of contact ba l the homing circuit of the junction hunter is closed from earth over commoned elf-normal contacts and wiper JH4, contacts lei l, ba l, ihm and magnet JHM and the hunteris restored to its first contact position in which it will rest with its wipers on the first contacts connected to outgoing junctions. At con-- 'tact 'ba5 a similarhoming circuit will be closed over wiper 8H4, contacts ks! b115, shm and mag-' net SHM and the selector'hunter is restored to its first contact position in which its wipers rest on contacts connected to a local first selector. Re-

lays I -and D release consequent on the opening of contact a2 and the other relays consequent on the opening of contact bat. Contacts bl and-bu! disconnectthe engaging earth from the incoming test wire p. If the called subscriber clears first,

relays D and I'willrelease. Release of relay D releases relayMD-at contact d! and consequent n the relapse of contact mdB, lamp SL will glow sition, the .caller may clear afterhe has been answered andzin that case ;.a steady battery conrelays A and B released and the negative junction Wire wasopened at contact a2. Relay I is however held from earth over contacts 9'4 .and b3 to battery on the positive wire and relay BA remains held and-the busymarking of the circuit maintained by earth over contact bal to wire p and the callers ,line is held. Release follows when the operator clearsand ,the battery potential is disconnected from the positive wire. :Relay I releases, releasing relay BA and release of the other relays follows in the manner described earlier.

Reference will now be made to Fig. 2. The figure shows aselector hunterarranged .fordual testing and :the circuits shown therein should be substituted .for those enclosed in the broken line rectangle in ;Fig. 1:to .form a complete repeater. However, as the circuits of Fig. 1 have been fully described itris thought that a descriptionof the; modified operations due tothe chan e of selector hunter will be sulficient for the ,understanding of the modification. The selector hunterof,Fig.,2 is shown as a ,25-pointstepping switch with two setsof '4 wipers and contact banks the contacts :I to J0 and 1 3 =to522 in each bank being commoned to the same set of outlets so that ,20 outlets are actually available. :Only-the testing and homing wipers of the switch :are shown and these are designated SI-13A and'SI-HB and 8H4 to correspond -to WipersSHS and 5H4 of Fig. 1. There is also an additional wiper 5H5. and bankv of contacts for dealing with congestion conditions. It is to be .iunderstood that there will be1two pairs of speaking wire :wipers connected to the feeding bridge over suitably spo ed contact DI the switchin relays KSA and K513 ;in place of pcntacts 70.8.3 and *lcsfl .10) Fig. 1, their contact banks being connected :to

.local ,first selectors from contacts 4 ;to it? and ls -to 22in the; manner shown for the outlet connections from the banks of wipers .SI-IfiA land ,SH3B. The-stepping magnet is designated SHM and associated with the switch are two-highspeed test relays TA and the former for :testing the outlets over wiper T SHtA and the latter zfpr testing the outlets over wiper {SI-13B. .-In :the

.bank of wiper-,SI-RA contacts H, ;2.3 and 12A :are earthed and contacts 12 and .25 are last contact or overflow positions. ;I n the bank, of wiper SHSB contacts 11,12, 23, 2,4 and'25 are -earthed, a relay ,0? .is provided for connecting contact :12 in the bank of wiper SH3A to the overflow .meter when necessary and for --stepping the hunter from the 12th contact overflow position. Ad-

ditional contacts of 'relays -B, BA, and LD, DA

andDB of Fig. .1 are hown and itis to be understood thatcontacts of ,relays KSA and-gKSB will be connected'in place of contactsrlos5zin l ig. 1.

The operations when the,discriminatoristaken into useare as follows. When relays Band gBA operate, earth is-connectedgovercontact id! and contacts ksb4 and kswl to relays "IA; and FIiBrespectively. .-Contacts ba 5 and ibail will also :be

closedso that if the outlets n-winch the switch is standing,,.that is, the first cutlets as shown in the drawings, are both engaged, earth .;potential will be present .on the contacts and relays TA and will not operate. If-onlyone-of the contacts isearthed, then the relay connected to the unearthed contact-willoperate torthe locally connected battery. If neither contact is earthed, -both -rela-ys will enerate but. CDHIIEtCtltG/l will con- ;nect delay KSA-to earth over contact id! and .dis-

connect the circuit for relay KSB over the front. 'contact tbi so that relay KSB will not be operated. The operation of relay KSA opens the circuit for relay TB at contact ksa4 so that relay TB is released. In this way preference is given to the outlet in the A banks if like outlets from both banks are free. Let it be assumed that the first outlets are both engaged. When contacts b and M2 (Fig. 2) are operated, a circuit is completed from earth over contacts y'd'l, tal, tbl, b5, shm, and magnet SHM to battery. The magnet energizes, steps the wipers to the second contacts, opens its driving circuit at contact shm and releases. If the second contacts are both engaged, neither relay TA nor relay TB will be operated and the magnet operates to step the wipers to the third contacts. Stepping continues in this manner until a free contact in one of the pairs of banks is encountered. If a free outlet is found in the A bank and the'corresponding outlet in the B bank is engaged, relay TA operates and at contact ta! opens the magnet circuit and closes the circuit for relay KSA. Relay KSA operates. At contact ksal the homing circuit is opened, at contact ksalrelay TA is disconnected from wiper SH3A and earth is connected thereto to engage the outlet, at contact ksa3 relay TB is disconnected from Wiper SHSB, at contact local relay TB is disconnected from the earth over contact id! and other contacts connect the speaking wire wipers to the transmission bridge and close in the dial tone circuit. Had the free outlet been found in the B bank and the corresponding outlet in the A bank was engaged, relay TB would have operated to open the magnet circuit and connect up relay KSB. Relay KSB on operating performs similar functions to relay KSA, engaging the outlet over contact ksb2 and disconnecting relay TA at contacts ksb3 and ksbl.

It the first digit received at the repeater does not determine the route, relay DA (Fig. 1) is operated and relay KSA or KSB as the case may be is released and the selector impulse relay releases. For convenience of description it will be assumed that the selector was connected to the A bank. The earth applied to the test bank contact by the selector release relay is maintained during the release lag of that relay and relay TA is released. If the corresponding outlet in the B bank is free, relay TB will operate and the selector connected to the outlets in the B bank will be se zed and engaged and relay KSB will be operated. Should, however, this outlet be also engaged the magnet circuit will be re-closed on the release of relay TA and search for a free selector to take the second digit will be made. If the second digit does not determine the route to be taken, relay DB (Fig. 1) will operate and the selector hunter test relay and the seized selector will be released and the selector hunter will hunt for, it necessary, a further selector totake the third dig t. If the third or either preceding digit determines that the call is to be completed over a Junction, relay JD (Fig. 1) will be operated and contact id! opens the circuits of the operated test and switching relays releasing the local selector, leaving the selector hunter on the contacts to which it was last set. If, during its search for a tree selector, contacts ll, 23 or 2-4 are reached the hunter is stepped on as for a busy outlet to contacts l2 or as the case may be. Closure of contact dafi or dbS will complete a stepping circuit for the magnet to step the switch to contacts !3 or I respectively. In'the bank or wiper SH5 contacts !3 to 25 are connected together and to relay OF so that when the switch is stepped to any of these contacts relay OF is operated and locked up over contact of! to earth over contact ba2 (Fig. 1).

In the case of the preliminary seizure, search will continue in the normal manner and if congestion is encountered the switch will be stopped on contacts [2 by the operation of relay TA owing to absence of earth over wiper SH3A. If the first digit is to be absorbed failure to record the digit on a selector will be of no consequence. When the first digit has been received, contact dai will be changed over if the digit is to be absorbed. TA will be released due to the disconnection of earth over contact id! and when this earth is subsequently re-applied, relay TA will be short-circuited over wiper SH3A, contact 12 and contacts of2 and daB and search will commence for a free selector over contacts I3 to 22. Should a state of congestion be encountered at this stage the switch will be stopped on contacts 25 and ii the second digit is to be absorbed, contact db6 will be changed over to prevent re-operation of relay TA after the earth over contact ad! has been re-applied following its removal by the operation of relay DB (Fig. 1). The switch will then search for a selector to take the third digit. When the switch reached contacts l3, relay OF was operated so that when it again reaches contact I 2 it is stopped owing to the absence of earth on this contact in the bank of wiper SHSA due to contact of! in its front position. If this search had started from one of the contacts !3 to 22 it would have continued over contact 25 earthed over contact dbB until the 12th contacts were reached. When it is determined that the call is to proceed over a, local selector, relay LD (Fig. 1') will be'operated and if the selector hunter has failed to find a free selector to take the route determining digit, it will be standing on contacts 25 or l2 and a circuit for the overflow meter will be closed over contacts ksa2, ba5, wiper SH3A,

contact dbfi or 012, contact Id! and overflow meter to battery and the congested condition will be recorded. The caller will receive busy tone as described in connection with Fig. 1. When the connection is finally cleared, the disconnection of earth from contact id! releases the operated test and switch ng relays and the locking circuit of relay OF is also opened and that relay released if it has been previously operated. Relays B and BA (Fig. 1) being now released the homing circuit for the selector hunter is closed from .earth over the homing bank and wiper 5H4, contacts ksbl, ksal, b5, shm, magnet SHM and the magnet steps the switch by self-drive action to its first contact position which is unconnected in the homing bank and the hunter is brought to rest.

What we claim as new and desire to secure by Letters Patent is:

1. In a digit absorbing repeater, a plurality of outgoing lines, means operated responsive to the seizure of said repeater for seizing an idle one of said lines, means for receiving impulses indicative of any value of digit, means for repeating said impulses over the seized line, and means operated responsive to the completion of said reception and repetition of impulses, if the digit indicated thereby is of a predetermined value, to release said seized line and automatically seize another idle one of said lines.

2. In a digit absorbing repeater, a plurality'of lines, a switch having access to said lines, means operated responsive to the seizure of said repeater for causing' said. switch to search for and seize any idle one of said lines, means for receiving impulses indicative of any value of digit, means for repeating said impulses over the seized line, and means effective after saidreception and repetition of impulses, if the digit indicated thereby is of a predetermined value, for causing said switch to automatically release said one line and to search for and seize any other idle one of said lines, said third means then effective to repeat over said other line impulses subsequently received by said second means.

3. In a discriminating unit, means for receiving a particular order of digit in a multi-digit number, two groups of lines, means for seizing an idle line in each of said groups before. said; first means has completed its reception of said particular order of digit, and means controlled by said digit when its reception is complete, if said digit is of a predetermined value, for releasing one of the seized lines without releasing the other and seizing another idle line in the same group as the releasedline.

4. In an automatic telephone system wherein, during the extension of a connection through a plurality of successive switching stages, a repeater at one of said stages receives a succession of digits and normally repeats them to one of a plurality of switches which make up a single subsequent switching stage, means in said repeater operated after the reception and repetition of one of said digits, if that digit is of a predetermined value, to release said one switch and condition another one of said switches to receive digits, said repeater then effective to repeat at least part the remainder of said succession of digits, when received, to said other switch.

5. In a telephone system wherein, during the extension of a call, a discriminating unit at a particular stage of the connection receives call directing impulses and determines therefrom whether the call is a local call or an outgoing call, and wherein said unit, until it completes such determination, repeats said impulses to one of a, plurality of local switches making up the next switching stage and also repeats them over an outgoing trunk line, means in said unit controlled by the received call directing impulses at times to release the local switch to which it has been repeating said impulses, said means effective at such times to cause said unit thereafter to repeat call directing impulses subsequently received during the extension of the same call to a different one of said local switches.

6. In a telephone system, a repeater in one exchange having access to a trunk line outgoing to another exchange and also having access to a plurality of local trunk lines, means in said repeater for seizing said outgoing trunk line and one of said local trunk lines, said repeater then effective to receive call directing impulses and repeat them over both of the seized trunk lines, means controlled by said impulses for causing said repeater to release said outgoing trunk line if the impulses are indicative of a call to said one exchange and to release the seized local trunk line if the impulses are indicative of a call to said other exchange, means at times controlled by said impulses for causing said repeater to release the seized local trunk line without releasing, the

outgoing trunk line and immediately to seize another local trunk line, said repeater thereafter effective to repeat the received impulses over said outgoing trunk line and said other local trunk line.

7.. In adigit' absorbing-repeater, a plurallti of lines, .aswitchhavingaccess to said lines and also to an overflow position, means operated responsive to the seizure. of said repeater for causing said. switch to search for an 'idleone of said lines, saidswitch effective. to move to-said overflow position if no idle line is found, means effective when said switch occupies said ovterfiowposition for'receiving impulses indicative of any'digit, means operated after .said receptionxof impulses, if the digit indicated thereby is of a predetermined value, to cause. said switch to leave said overflow position and again search for an idle one of said lines, means effective if an idle line is found on said last search .toseize such idle line, and means for repeating impulses subsequently received by said second; means over the seizedline.

8. In a digit absorbing repeater, a plurality of lines, a switch having access to said lines and also to an overflow position, means operated responsive to the seizure of said repeater for causing said switch to search for an idle. one of said lines, said switch effective to move to said overflow position if noidle line is found, means effective when said switch occupies said overflow position for receiving impulses indicative of any digit, means operated after said reception of impulses, if the digitindicated thereby is of a predetermined value, to transmit a busy signal, other means operated aftersaid reception of impulses, if the digit indicated thereby is of a dif-. ferent predetermined value, to cause said switch to leave said overflow position and again search for an idle one of said lines, means effective if an idle line is found on said last search to seize such idle line, and means for repeating impulses subsequently received by said second means over the seized line.

9. In a telephone system, a trunk line outgoing from one exchange to another, a plurality of trunk lines local to said one exchange, a switch having access to said local trunk lines, discriminating apparatus in said one exchange, means responsive to a seizure of said apparatus for seizing said outgoing line-and for causing said switch to search for an idle local line, means for seizing any idle local line found by said switch, means in said apparatus for receiving impulses and determining whether they are indicative of a desired connection local to said one exchange or a desired connection outgoing from said one exchange to said other exchange, means in said apparatus at times controlled by said impulses before said determinationis complete for causing said switch to repeat its search for an idle local line, andmeans in said apparatus effective at such times responsive to the completion of said determination if same reveals that the received impulses are indicative of a desired local connection for transmitting a busy signal only if said switch has failed to find an idle local line on its last search before the completion of said determination.

10. In a telephone system, two switches each having access to a different group of lines, ap-

paratus for receiving impulses indicative of de-' sired connections over both of said groups, means responsive to a seizure of said apparatus for operating each of said switches to search for and seize an idle line in its respective group, means in said apparatus for identifying, from the impulses thereafter received, the group over which a connection is desired, means in said apparatus at times controlled by said impulse before said identification is complete'to cause one of said switches to search a second time for an idle line in the group accessible to it and to seize any idle line found during said second search, means effective upon conclusion of said identification for causing the one of said switches having access to the group over which a connection is not desired to release the line which at that time is seized by it, and other means effective upon conclusion of said identification to transmit a busy signal only if the one of said switches having access to the group over which a connection is desired has failed to find an idle line in that group.

11. In a telephone system, two switches each having access to a different group of lines, apparatus for receiving impulses indicative of desired connections over both of said groups, means responsive to a seizure of said apparatus for operating each of said switches to search for and seize an idle line in its respective group, means in said apparatus for identifying, from the impulses thereafter received, the group over which a connection is desired, means effective upon conclusion of such identification for causing the switch having access to the group over which a connection is not desired to release the line seized by it, and other means efiective upon conclusion of such identification to transmit a busy signal only if the one of said switches having access to the group over which a connection is desired has failed to find an idle line in that group.

12. In a telephone system wherein each of a plurality of lines becomes characterized as busy responsive to its seizure and becomes characterized as idle responsive to its release, a switch having access to all of said lines, means for causing said switch to start searching for an idle one of said lines, means in said switch for testing each of-said lines in turn during said search, said testing means effective to control said switch in accordance with the characterization of each line tested whereby said search is continued in response to each test of a line characterized as busy and is halted in response to the test of any line characterized as idle, means for seizing any idle line which causes said search to be halted, means for preventing said testing means from causing said switch to resume its search when the seized line becomes characterized as busy responsive to such seizure, means for subsequently releasing the seized line, said last means effective to disable said preventing means before the released line becomes characterized as idle responsive to such release, whereby said testing means is efiective to control said switch to resume its search in accordance with the temporary characterization of said released line as busy.

DAVID ADAM CHRISTIAN. WILLIAM HENRY JOSEPH DIBBEN.

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