US1974159A - Telephone system - Google Patents

Description

9 Sheets-Sheet l TELEPHONE SYSTEM Ha. IA.

W. G. PATTERSON ET AL Filed March 31, 1933 2 a 5 MH 5 Sept. 18, 1934.

Sept. 18, 1934.

W. G. PATTERSON ET AL TELEPHONE SYSTEM Filed March 31. 1953 9 Sheets-Sheet 2 Swan 118, 1934. w. G. PATTERSQN El AL 1,974,159

TELEPHONE SYSTEM Filed March 31, 1933 9 Sheets-Sheet 3 Sept. 18, 1934. w. G. PATTERSON El AL 1,974,159

TELEPHONE SYSTEM 25 Sheets-Sheet 4 Filed March 51. 1953 M'- MI Sept. 18, 1934.

TELEPHONE SYSTEM 9 Sheets-Sheet 5 Filed March 31, 1933 s 5 3 WT w H m K s m MT J M T W D rm F u k ol? w j i w E w K00 rm lw m m 9n 2 m I JQMM W m m m x m :3 M WIL E p 1934- w. G. PATTERSON ET AL 1,974,159

TELEPHONE SYSTEM Filed March 31, 1933 9 Sfieets-Sheet 6 SPW cRoss comsem v Hm GROUP MnRKma Y m T MM 1; u.

Sept- 18 1934- w. s. PATTERSON ET AL 1,974,159

' TELEPHONE SYSTEM Filed March 31, 1933 9 Sheets-Sheet 7 56.4. &

usON2 malml m, MHDM w. G. PATTERSON ET AL 1,974,159

TELEPHONE SYSTEM Filed March 31, 19:55 9 Sheets- Sheet 8 Sept 18, 1934. w. a. PATTERSON ET/AL 399743159 TELEPHONE SYSTEM Filed March 31, 19-33 9 Sheets-Sheet 9' @atentecl Sept. 18, 1 934 I omr 'sr si PATENT rice 7 1,974,159 TELEPHONE sYs 'rEM William George Patterson, Mottingham, London} and Douglas Percy Long, Chislehurs't, England; assigimlrs to Siemens' Brothers? & (Eompany; Limited ilion'don, England i Application March- 3-1, 1933, Serial No. 663,842-

- In Great-Britain April- 4,1932

' 16 "claims (el 179 119;)"

' 5 change may proceed over direct junctions" to the required exchange or may have to be routed over a tandem exchange.

In areas in which subscriber numbers consist of an exchange code followed by a line number, it is usual to register the code and numerical digits'in a register translator and to transmit the translated code and the untranslated numerical digits j from the register translator to set code and nu' merical selectors. All calls are dealt with by register translators and the numerical digits'fare registered. This method of working is not the most economical and especially in systems in which direct inter-exchange junctions are gener-' ally available. I u v I One variation of the method of working mentioned which avoids the storing of numerical digits, except where a tandem exchange is in ques-.

tion, is described in British patent specification No. 220,364 in which the exchange code is used" -in a by-path route to select a junction in a required direction.

It has also been proposed in multiexchange areas to route 'a call which'would normally proceed over a direct junction, over an intermediate exchange or exchanges if the direct'junctions are all engaged. In this case it may well be economical to provide a lesser number of direct junctions which are consequently more frequently occupied and send part of the traffic over the tandem route.

To some extent the routing arrangements'of the present invention are based upon considerations of junction occupation. If a group of outlets is straight multipled over a number of selecting switches, the earlier choices work substantially at maximum capacity, in intermediate choices utilization falls oif rapidly'and last choices are little used.

By the arrangements of the present invention'a saving in apparatus is effected, this saving resulting from the fact that all switches for outgoing groups (i. e. both first selectors and auxiliary selectors) are efficiently used, since they ares-in general, used for carrying traffic for all or a con- A further saving of 5 apparatus results from the fact that numerical storage and machine impulsing are obviated; in

siderable number of groups.

the case of a call routed over a direct outlet of a first selector.

According to the present invention, in a mu1- ti-oiifice automatic telephone system, an exchange is-connected to a number oi other exchanges by" direct junctions and: a. routing system is provided wherein, at such anexchange, first selectors have, in g'e neral, access to apart of each group, or to a part of some groups, of direct junctions to other exchanges, and are provided with a common group of overflow outlets over which access is had to auxiliary selectors in the banks of which ap pear further andrdifferent junctions of the groups. j One of the'groups' of direct junctions referred to above as those by which an exchange may be connected to other exchanges may be the links leading to local niunerical selectors situated at the exchange under consideration and being those over which local connections are set up and it may be that one of the groups of further and-different junctions is so connected.

The auxiliary selectors have in general access to thesame-other exchanges, such access being had over the further and diiferent junctions which represent later choice junctions, and to other junction outlets leading totandem exchanges through which calls are passed either" because they normally pass therethrough, that is there are no direct junctions, or because the tandem exchanges provide alternative routes forcalls which normally pass over the direct junctions or, failing an idle such, over the, further and different junctions' JllIlCtlOl1S '0l"1illkS to a manual board preferably though not necessarily, appear in the first selectors. l i

The junction multiple of the first selectors may be 'common to all first sel'ectors in the exchange or may be dividedt'o give access to separate groups of early choices as may be best. Similarly there may be only one group of auxiliary selectors or more than one group. 7

The auxiliary group of selectors has available to it apparatus forsendi-ng out tandem trains and for-storing and repeating numerical impulses.

The information as to the group of outlets required in an auxiliary selector is conveyed to the control apparatus ofthe auxiliary selectors from the like operators'iof the first selectors, for instance by means of atrain or trains of impulses sent forward over one speaking wire.

It may-be that the junctions to tandem exchange'sappear in the banks of the first, instead of in those ofthe auxiliary selectors in which case apparatus similar to that available to the auxiliary-group of selectors may then be associated with the junctions. As this apparatus, which would have testers and to repeat numerical digits and tosend tandem trains, may be similar to that available to the auxiliary group of selectors, it has not been thought necessary to describe it herein. The necessary modifications could be made by those skilled in the art and to whom this specification is directed.

The selectors may be of the rotary one motion type and may be steered to the required group of outlets by a marking or markings applied from the control apparatus.

First selectors may be permanently associated with call finders and tandem call finders may be employed.

The feeding bridges used in a talking connection can be situated at a first selector or at the outgoing end of a junction in all cases or, alternatively, at the outgoing end of junctions as regards first selectors or at the auxiliary selector if one is called in. As these matters do not form part of the invention they will not be further referred to herein.

The term tandem exchange or tandem centre used herein is not to be understood as being applied to an exchange or centre serving exclusively as a tandem exchange or centre. It may be that the exchange or centre serves in that capacity only incidentally. Moreover, it may be possible to route a tandem connection preferably to one tandem exchange and, if no outlet thereto is idle, secondarily to another exchange, and so on. The manner of effecting this will be apparent from a study of the following description and such an arrangement is to be understood to be within the terms of the claims, the word tandem centre or tandem exchange being understood to include the plural form.

The invention will now be described with reference to Figs. 1-5 of the accompanying drawings in which it is illustrated by way of example.

Of the figures, Figs. 1A, 13, 2A and 2B illustrate a first junction selector which may be referred to as FJ S, and common controlling apparatus by which, in common with other selectors FJS, it is served. The first junction selector and its individual apparatus is shown in the upper part of Fig. 1 and the common control apparatus, which may be referred to as FCC, in the lower part of Fig. 1 and in Fig. 2.

Figs. 3A, 3B, 4, 5A and 5B illustrate a second junction selector, which may be referred to as SJ L, and common controlling apparatus by which,

in common with other selectors SJL, it is served. The second junction selector and its individual apparatus is shown in the upper part of Fig. 3 and the common apparatus, which may be referred to as SCC in the lower part of Fig. 3 and in Figs. 4 and 5.

The selectors FJS and SJL, as well as switch FMS in FCC and MA in SCC are represented diagrammatically as of the type described in British patent specification No. 388,173. In the common controlling apparatus, in addition to switches FMA and MA respectively, which are marking switches, there are a number of switches as AS, BS, CS in FCC, and ASA, BSA, CSA, MS, HS, TS and US in SCC which act as registers to register the several trains of impulses as they are received. Of these switches AS, BS and CS register the ABC code in response to impulses delivered from the calling line switches. ASA, BSA, CSA register this code, if the connection has to be routed over switch SJL in response to impulses delivered from the FCC switches, and switches MS, HS, TS and US register the numerical part of the called number if the connection has to be routed over switch SJL. Impulses for setting switches I-IS, TS and US are delivered to these switches directly from the calling line. As, however, apparatus SCC may not be ready to receive the thousands digit, that is the digit which should be registered on switch MS, by the time the caller is ready to send in that digit, it is arranged that the thousands digit shall be received on switch AS in FCC and transferred to MS in SCC after the ABC code digits have been transferred to their respective switches ASA, BSA, CSA. In order that switch AS may be in a position to receive the thousands digits it transfers its setting which resulted from the A digit, to certain relays W.X.Y.

The first junction selector FJS may be associated with a calling line in any convenient mann r, as by being connected back-to-back with a line finder.

The second junction selector SJL is associated with a calling line by having the calling line extended to it over FJS by way of overflow links, if all direct junctions on FJS are busy and the call is one which can be reached by way of second choice junctions as described. If all direct junctions are busy and the call is one which cannot be so reached, busy signal is given to the caller.

Selectors as FJS, SJL, FMS, MA have two sets of wipers and two sets of bank contacts shown respectively in full and dotted lines. The switches are arranged such that the wipers operate successively over their respective banks.

Switches like AS, etc., are provided with a number of wipers each of which operates over a bank of contacts. The normal contact will be referred to as N and the succeeding ones as 1 to 24. A wiper will be referred to as in N or in 1 etc., meaning that it is in position N or position 1 etc.

The FJS which is to be used is determined by an allotter which in allotting an FJ S for service, takes note of its busy or idle condition. The allotter is not shown and its manner of operation is not described herein as it forms no part of the invention and may be of any convenient type.

The idle condition of an FJ S is indicated to the allotter by negative or wire P. The circuit for this negative is from battery over wipers BS5 and CS3, Fig. 2, in N, wire 1 Figs. 2 and 1 through various off-normal contacts, contact jbl, offnormal contact fy'sonZ to wire P.

When the line finder associated with FJ S picks up a calling line, relay A operates in a circuit from earth by way of contacts Zcl Fig. 2, and $11 at rest, and so forth as may be easily seen.

Relay A has two contacts a1 and a2 this fact being indicated by the numeral 2 beneath its code letter. Of these, contact a1 serves for repeating subscriber-delivered impulses to FCC and contact :12 serves for repeating such impulses to SCC if necessary. For the present contact a2 may be disregarded entirely as it is rendered inefifective in a manner which will later appear.

Contact al, Fig. 2, when first operated closes a circuit for relay B which operates and remains operated in the well-known manner, until relay A shall remain released for a prolonged period.

Relay B prepares circuits as follows: at contact b1, Fig. 1, for holding relay K when eventually that relay shall operate; and at contact b2 for relay C and magnets of the various switches which circuit will be completed when impulsing shall be in progress. It closes a circuit at contact M for relay JB which operates. The effects of the operations of'other contacts of relay B will be referred to in due time.

circuits may be completed thereover:

contact c3, Fig. 1, places a short circuit around contact a2 for the purpose referred to above;

' Relay JB operates and opens all its contacts jbl to y'bfi whereby all the first junction selectors served by FCC are rendered busy and the relay K of the FJS which is at present under consideration is operated in the test circuit already described.

Relay K operates and at contact kl closes the holding circuit alreadyprepared by contact bl; at contact 2 connects earthto wire P to mark the FJ S busyyand at its various other contacts couples the first junction selector circuit to the first common control. 7

Everything is now in order for the caller to commence dialling and this fact may be indicated to him by dialling tone in any convenient manner which need not be described herein.

The caller now dials andin response thereto relay A releases and re-operates. At the first release of relay A, contact (11 closes the already prepared circuit for relay C as follows: earth, contacts (11, b2, relayC, i503 and E3 at rest, wiper A81 in N, and magnet ASDM which is the driving magnet of digit switch AS, to negative battery.

Relay Cand magnet ASDM operate this circuit and relay C (which will remain operated until relay A shall be held operated during the inter-digital pause) at contact 01 closes an alternative circuit for magnet ASDM, over which (alternative circuit subsequent impulses will be delivered to that magnet: at contact 02 isolates wipers AS2, BS3 and BS4 oicthe AB digit switches so that, whilst those switches are in motion (only switch AS is at present under consideration), no and at Contact 04 will be referred to in due time.

As relay A reoperates, and subsequently releases and reoperates, switch AS is driven stepof impulses delivered to magnet 1, any number above 1 and less and at contact 821 connects NU tone to the caller,

the circuit being NU, sZl, wire 2 and so on through relay A.

Ten impulses as a first train usually denote an call, that is a call to an operator. Thus, when relay C releases after the delivery of ten impulses, and the resultant stepping of switch AS into position 10, a circuit is completed from earth, over contacts 274, t06, c2, wiper A82 in l0, winding (1) of relay TM to negative. Relay TM operates and may, at contact tml, Fig. 1, cause the operation of relay WS if 0" calls are to be completed over the second wiper of switch JS. At contact tm2, relay TM closes a circuit from earth over contacts tol, tbl, tdl, tal, all at rest, tm2 and k8 operate, for unlatch magnet FLM. Contact tm3 has no eliect in an 0 call. Switch AS, at wiper AS in 10 effects the marking of the group of contacts in'bank PG (or FGl) in which lines to the operator are situated.

Unlatch magnet FLMis the unlatch magnet of.

as a first train, is not recognized switch FJS, and theefiect of its operation is to unlatch'the switch and to close, at its contact flml the circuit of the driving motor FDM of the switch FJS.

In response to the closing of the circuit of motorFDM, switch FJ S is driven to find an idle outlet to the operators position. As soon as it moves off normal it opens off-normal contact fy'sonZ whereby the test circuit over which FJ S was tested is opened at a second place (it was opened at contact ason2 as soon as switch AS moved ofi normal). Selector FJS continues to rotate until its wiper FG (or FGl) reaches the marked group of lines and until its wiper FF (or FPl) reaches an idle line within the group leading to the operator. When this happens a circuit is completed from earth through rectifier R, winding of quick acting relay TA, wiper A in 10, wiper (say) FG, contacts 21135, 707, ws, wiper FP, to negative on the test wire FPW of the idle operator-circuit.

Relay TA operates and, at its contact tal, opens the circuit of unlatch magnet FLM and closes a circuit for winding (I) of relay TD, this circuit being from earth over contacts to-l, tbl, tell at rest tal operated, winding (I) of relay TD, wiper ASS in 10 and then as forrelay TA to negative on closes a holding circuit for itself, at contact i022,

closes a second holding circuit for itself from earth over contacts b7, td2, winding (II) of relay TD,

resistance ml to battery, and at contact td3 closes a circuit from earth over contacts td3, and 703, and relay H to negative.

Relay H operates and at contact hl closes a holding circuit for itself, at contacts b2 and 71.3 connects incoming wires W+ W- to wipers F+, F, at contacts hl extends wire P through to wiper FP whereby earth is reverted, in'a manner not necessary to be described, from wire FPW to maintain the busy condition on wire P, and at contact h5 closes a holding circuit for relay V/Sif that relay should be operated. The calling line is now through to the idle operator circuit.

As a further resultof the operation of relay H, the circuit of relay A is opened and this relay releases. Relay A, at its contact al, Fig. 2 opens the circuit of relay B which releases. Relay B at contact b1, Fig. 1,.opens the circuit of relay K, at contact b2 (Fig. 2), opens the circuit of relayC,

atcontact 224 opens the circuit of relay TM and a at contact 223 closes a homingv circuit for switch AS. This homing circuit is as follows: earth, contact b3, wiper BS1 in N o-fi normal contacts csonl at rest, and asonl operated, interrupter contact ascZm of switch AS, contact gSat rest to magnet ASDM.

As soon as switch AS reaches its home position,

it opens contacts csonl and thus opens its own drive circuit.

Any number of impulses, other than 1 or 10, has a first train, denotes that a B and perhaps a C, digit should follow. Thus, when relay C releases, after the delivery of the A digit impulsesand the resultant stepping of switch AS into a position which may be any of the positions 2-9 inclusive,

a circuit is completed from earth over contacts.

b4, to6, c2, wiper AS2 in.2-' (-9), contact elwinding (I) of relay E to negative. Relay E operates with results to be described.

As switch AS was moving tothe desired position,

wiper AS4 encountered, in turn, contacts 2-9 and in 3-9 of these positions caused a relay, or a combination of relays W, X, Y to operate in a circuit from earth at contact b5, over contact 29: at rest, and wiper ASQ in its successive positions. These relays operate in accordance with the following table.

Digit gg Relays or windings 2 2 None. 3 3 W 1, 4 Y 5 5 W (II) Y 6 6 X 7 7 X (I) Y (II). 8 8 W (III) X 9 9 w (Ill) X 1 Y (III) Although these relays operate as wiper AS4 passes through the successive positions, they re lease as soon as the wiper leaves the positions'on the way to that one at Which it shall stop.

When, eventually, wiper AS i comes to rest, the relay or combination of relays W, X, Y appropriate to the stopping position is not released.

Now to return to relay E and the effect of its operation. At contact e1 it closes a holding circuit for itself. At contact 02 it opens the circuit of relay TM so that when eventually switch AS may move to or through position 10, this relay will not operate. At contact c3 it switches the impulse repeating circuit (contact (11) from magnet ASDM to magnet BSDM. At contact e7 (bottom left quarter of Fig. 2) it closes a circuit from earth over contacts b6, e7, 11, for the unlatch magnet MLM of marking switch FMS. At contact e9 it closes a holding circuit for which ver relay, or combination of relays W, X, Y is operated, this circuit including a contact wl, $1 or 111, and winding (I) of the relevant relay (8). Other contacts of relay E have no present effect.

Magnet MLM removes the latch from switch FMS (which is a marking switch and which is represented in Figs. 1 and 2 by various wipers and banks FMS and by its motor MDM) and at mlml closes the circuit of motor MDM.

Motor MDM drives wipers FMS until wiper FMSl arrives at a contact which is cross-connected to the contact marked by wiper AS3, when a circuit is closed from earth over contact b5, through quick relay T, wiper FMSl in marked, wiper ASS in marking (that is 2-9) resistance 102, to negative. 7 Relay T operates and opens the circuit of unlatch magnet MLM which releases and latches switch FMS in the position to which it has been driven, the position-being the beginning of a group of contacts appropriate to the A digit.

The operation of switch FMS is completed be fore impulses representing; the B digit arrive.

Impulses representing the B digit are directed to magnet BSDM which drives its wipers to an appropriate position, the circuit being from earth over contacts a1, b2, operated, and f2 at rest, BSDM, to negative. In addition to eiiecting the drive of switch BS, the impulses cause the operation of relay C which remains operated until the end of the train of impulses. Contacts c2 and 03 have the same effect as previously. Contact 01 closes a circuit from earth over contacts to8, e LjZ, cl, through magnet ASDM to negative. Magnet ASDM therefore energizes and remains energized during the reception of the B train of impulses.

Selector BS will be driven into one of its positions 2 to 10 in response to a B digit 2-0; Digit relay C, contacts t03, e3

1 is not used as a 13- digit. When switch BS ar rives at, or passes through position 2 a circuit is completed from earth over contact 123, wiper BS2 in 2, wiper CS1 in N, contact cadm, and magnet CSDM to negative. Magnet CSDM operates, opens contacts csdm, releases, and as a result goes into a false normal shown as 0 where it rests. If the B digit be more than 5, as soon as the BS selector reaches position 6, the circuit for magnet CSDM is again completed the circuit now including wiper BS2 in 6-10 and CS1 in 0 to 11. Switch CS consequently self drives to position 12. The reason for driving switch CS during the setting of switch BS will be referred to later.

At the end of the train of impulses representing the B digit, relay C releases and, at contact 01, opens the circuit of magnet ASDM. The AS switch is thus moved to the position next to that to which it was set in response to the impulses, representing the A digit. One effect or" this movement of AS is, at ASS, to open the circuit of relay T, which releases. Other effects will be referred to later.

Further effects of the operation of relay C are, at contact 02 a circuit is closed from earth over contacts 124, to6, c2, wiper BS4 in 2l0, winding (1') of relay F, to negative.

Relay F closes, at contact f1 a holding circuit for itself; at contact f2 switches the impulse repeating circuit from magnet BSDM to magnet CSDM: at contact f3 opens the circuit in which magnet ASDM was induced to take its extra step; at contact f5 connects winding (Ii) of relay SL to wiper ASS: at contact f6 closes a marking circuit to wiper BS6: and at contact f7 prepares a circuit for winding (I) of prepositionin relay PP. The function of relay PP will be referred to anon.

Relay T, which, as stated, released, closes at contact t1 a circuit for unlatch magnet MLM which removes the latch from marking switch FMS and closes the circuit of motor MDlVl of that switch. The marking switch therefore moves rapidly to find a contact within the group at the beginning of which its wiper F1581 is standing, marked over wiper BS5.

When wiper FMSl reaches the contact, which is the first contact of a sub-group of contacts within the group to the beginning of which it was moved in response to the marking over wiper AS3, relay T again operates "and releases latch magnet MLM whereby switch FMS is brought to rest.

mined by the combined setting of switches AS and BS, that is by the A and B digits. This position may be one, that is the A, B digits may be such that the second (dotted) wipers and bank contacts of switch FJS have to be utilized for routing the connection. In such cases there will he a cross-connection from the contact in bar Flt 2S3, appropriate to the A, B digits, to relay PP.

When, therefore, switch FMS comes to rest, as a further result of the operation of relay T, a circuit will be completed from earth over contacts b, 67, Z1, 95, f7, wiper FMSB in a position determined by the AS, BS marking, winding l of relay PP, to negative. Relay PP operates with results to be explained. a

If a non-existent AB. combination shall have been dialled there will be no connection from wiper BS6 in marking to the contact bank served by wiper FMSl, and as a result, relay T will find no circuit. Wiper FMSl will therefore Switch FMS is now in a position which is deter-'- cuit.

continue in rotation until it reaches the last contact of the group to which it was set in response to the setting of wiper ASB. This last contact is, in fact, the first'contact of the next group but this fact is immaterial. This last contact is marked by wiper ASS, which, it will be recalled, took an extra step after the release of relay -C. In this last contact position a circuit is completed for relay T, and in series therewith, for winding (11) of relaySL over contactf5. Relay SL op-' pares a circuit for stopping selector FJS at the first contact of the arcs of contacts shown dotted. Magnet FLM removes the latch from selector "F and closes the circuit of its motor FDM whereby the selector is driven rapidly to find the first contact above mentioned.

As soon as the first-contact of the arcs of contacts shown dotted is reached, a circuit is closed '1 from earth through rectifier R, relay TA, contact 12103, first dotted contact and dotted wiper FG,

contacts ws5, k7, ws4, wiper dotted PP and first dotted contact, resistance w3 to negative.

Relay TA operates and at contact tal opens the Icircuit for the unlatch magnet which releasesto open the motor circuit and latch the selector.

Meantime the caller is transmittingimpulses representative of the C digit. These are effective on magnet CSDM and cause switch CS to be driven to an appropriate position. This position will be one of the positions 2-10 or 14 22 it being recalled that switch CS has already been driven to one of the positions false normal 0 or- 12, and it being noted that 1 is not used as a C digit.

" During the reception of the train of impulses,

relay C is operated, and at the conclusion of this reception relay C releases.

When relay" C releases, a circuit is closed, from earth over contacts be, too, 02, wiper BS3 in "2-5 or 6-10, wiper CS2 in 2l0 or 14-22, contacts 91, winding (1) of relay G to negative. Relay G operates and at contact g1 closes a holding circuit for'itself; at contact 92 switches the impulsing circuit from magnet CSDM to magnet 'ASDM for apurpose to be explained later; at

contact 93 prepares a self driving circuit for magnet ASDM; at contact g4 opens the circuit, which 7 passed over wiper BS6, of relay T, which relcases; at contact 9'5 prepares a circuit for winding (II) of relay TM: and at contact 97, Fig. 1,

connects windingiII) of relay PP into the circuit previously traced over wipers PG and F]? of the ore-positioned selector FJ S. Since the two windings of relay 'PP -are in opposition, this relay releases and opens the circuit of relay TA which releases. 7

Relay T, on its release, closes the circuit of unlatch magnet MLM which, as before, unlatches marking switch PMS and closes the motor cir- F iSZ encounters a marked contactwhen a circuit is completed as follows: earth over contacts ing or CS3, CS4, CS5, CS6 01' CS7 in high. B

digits.

The marking switch rotates until its wiper marking, wiper BS5 in distributing, which depends on the value of the Bdigit and may be 2-10, resistance w t, to negative. Relay T operates in this circuit and, at contact 151, opens the circuit of the unlatch magnet and closes a circuit for winding (II) of relay TM.

Relay TM operates and at contact tml, Fig. 1 connects earth to wiper FMS4 whereby, if the outlet is to'be found over the auxiliary wipers of selector FJ S, relay WS is operated; at contact tm2, closesa circuit for selector unlatch magnet ELM which removes the latch from selector FJ S and closes a circuit for its motor FDM, and at contact tm3, Fig. 2 closes the already prepared self drive circuit for magnet ASDM.

Selector AS self-drives in the, circuit from various movements, been brought to a position where it can mark a contact in its bank FMSG which is appropriate to a group of outlets from selector FJS which corresponds to the A. B. C. This contact is cross connected to a group of contacts appropriate to the required group of outlets in bank FG' (either full or dotted) or bank FGl (either full or dotted). If the outlet is reached over bank FG or FGl dotted, selector FJS is prepositioned and if it is reached over bank FGl either full or dotted a corresponding contact in bank FMS4 is cross connected to relay WS. Moreovenif the'destination to which the group of outlets lead is one which can be reached over an alternative route by way of second selector SJL, a corresponding contact in bank FMSS is cross-connected to a group of contacts in bank FG or bank-FGI which is appropriate to a common group of overflow outlets.

There may, ormay not be an idle outlet in the marked group, and if not, it may or may not be possible to complete the connection to an alternative route. a

Let it first be assumed that there is an idle outlet. When the latch was removed from selector FJS,'this selector rotated rapidly from its normal position, or from its prepositioned positionon the firstcontact of the arcs shown dotted, until it arrives at the group of marked contacts and until it arrives at the first idle outlet-in that group. When itreaches this position a circuit is completed from earth through rectifier'R, winding of relay TA, wiper FMSS in marking, a group of marked contacts in bank FG (or bank FGl, say FG), wiper FG, contacts ws5, 707, 1084, wiper FP, the test wire of the first idle outlet (which maybe considered to be wire FPW) to negative at the. next stage.

Relay TA operates in this circuit and at tal opens the circuit of the latch magnet FLM, whereby the selector is brought to rest, and closes a circuit from earth over contacts to l, tbl, tdl, tal, operated, winding (I) of relay TD and then as above. I v

Relay TD operates and, at contact tdl closes a holding circuit for itself. The resistances of relays TA and TD-in parallel are sufficiently low to mark the outlet busy. Relay TD, at contact td2 closes analternative holding circuit for itself from earth, over contact 12"], through winding (ID-ofv relay TD,-resistance ml, to negative and, at contact td3 closes a circuit for relay H which operates and at contact hl closes a holding cir-i llllil to wire P so that earth, eventuallyfed back fromthe next selector, may ireplace that at present provided by contact k2; and at contact 715 closes a holding circuit for relay WS if that relay is operated. Relay H at contacts 7L2 and k3 also opens the circuit of relay A which releases.

The result of the release of relay A is as described at the end of the description below, of" discharge from FCC of theA. B.'C. digits and first. 7

impulsing contact 02 to wire W+ so' that subsenumerical digit.

The connection will have been extended to the next stage, that is to the first numerical selector before the subscriber will haveebeen able to dial the first numerical digit. The impulses representative of this digit will be received at that numerical selector.

When the connection is' to be cleared, earth is removed from: wire FPW in a manner not forming part of'this invention, and being any suitable one of the known manners, not being described herein. The removal of thisearth allows relay -I-I to. release and relay I-I, at its contact h-5 opens theflcircuit of relay WS and closes a circuit from' earth over contact k5, ofi normal contact fisonl contact k8, unlatch magnet FLM to negative. As soon as selector FJS reaches its home position it opens contacts #80121 and so brings itself to rest by releasing unlatch magnet FLM and motor FDM.

Let it be assumed now that there is no idle outlet in the marked group and the connection is not one which can be routed over an alternative route. In this condition there will be no circuit completed over wiper FMSG, for relay TA, and consequently the circuit for magnet FLM will be maintained. Due to this, switch FJ S will continue to rotate until its wipers reach the last contact 7 in the arcs shown dotted whether the selector was prepositioned or not. Thereupon a circuit will be completed for rapid relay TA, from earth throughrectifier R, relay TA, contact p103 at rest, last dotted contact of bank FG (or bank FGl) the associated dotted wiper, contacts 1085, I07, and we l, dotted wiper FP 'or wiper FPl), the last dotted contact in the associated bank winding (II) or" relay TD and relay LC, to negative. Relays TA and LC operate but relay TD does not since upon the operation of relay TA, its two windings are in opposition, the circuit of winding (I) being completed at contact tal as soon as re lay TA operates. Relay LC, at contact (ZcL'Fig. 2 connects busy tone to the caller and, as soon as he clears down, relay A releases and restores all apparatusto normal. i

Let it be assumed now, that there is no idle outlet in the marked group, and that the connection is one that can be completed over an alternative route. For this purpose selector FJS to rotate until its wipers reach a group of overflow outlets leading to a group of'secon'd junction selectors. Its continuing to rotate is, as in the immediately preceding paragraph, due to its wiper PP or FPl not being able to complete a' circuit for relay TAlin the marked group. When,

however, wiper FGI arrives at the group of over flow links and wiper FPl arrives at the contact of an idle such link, a circuit is completed from Relay TB operates and closes a circuit from earth over contacts tol, tbl, winding (I) of relay TO and then as above.

Relay TO operates and, at contact tol closes a holding circuit for itself; at contact Z02 Fig. 2,

prepares an impulse circuit which will be more fully explained anon.

purpose to be described; at contact to l, Fig. 1 provides an alternative circuit for relay WS, if that relay shouldbe ciperatedagainst the eventual release of relay TM; at contact r05, connects quent numerical impulses may be repeated to the second junction selector, as later described; at contact to6, Fig. 2 provides an alternative holding circuit for itself through its own winding (II); and at contacts to? and to8 prepares operations which need not here be considered. The alternativeholding circuit for relay TO is'to guard against itsrelease when, due to earth being fed back over wire FPW, its winding (I) is short circuited. n

Had there been no idle overflow link, relay TB and relay TO would not have operated, and selector JFS would have rotated to its last dotted contact and relays TA and TD would have operated, all in the manner described for the case in which there was no direct outlet and alternative routing was not provided.

Certain differences should here be notedu- When an idle direct outlet was found relay TD operated and led to the operation of relay H which switched the calling line through to the next stage, at. which the first numerical train of impulses was' merical impulses are received on relay A,

' An ov erfiow outlet having been found, it is necessary to transfer the A. B. C. digits to the second common control SCC. This operation commences as soon as SCC is ready to receive the relevant impulses. The dialing of the first numerical digit is, however, in no way under the control of SCC and the caller may (through not necessarily would) commence this operation before, even with the very rapid selectors such as FJS, the SCC'is ready to receive the impulses. For th s reason it is arranged that when an overflow link and selector SJL is to be used, the first numerical digit shall always be received in the first common con trol apparatus and shall subsequently be transferred to SCC. This'first numerical digit is received on switch AS, and it was for this reason that the A digit was cleared out of switch AS and stored on relays W.X.Y.'

There are a number of concurrent operations that may take place at this stage, namely the first numerical digit may be received in FCC during the time that the A. B. C. code is being discharged; the A. B. C. code and first numerical digit will be, of course, discharged from FCC at the same time that it is being received in SCC, and. the second, third and final numerical digits may e in course of reception by SCC during the time that SCC is receiving from FCC the A. B. C. code and first numerical digit. As it is difiicult and, in any case, unsatisfactory to treat these concurrent operations concurrently, they will be treated sep- At contact i023 connects the al impulse circuit directly, to switch AS for aaratel'y in the order: reception of first numerical by FCC; discharge of A. B. C. code andfirst numerical digit from FCC; reception of A. B. C. code and first numerical digit by .800; and temp tion of "second etc., digits by SCC.

impulses from contacts N1 are of impulses to W- As the caller transmits the first numerical digit; relay A responds and, at contact a1 repeats these impulses to magnet ASDM, the circuit being. by way of contacts e3, f2, 92, until relay TO operates when the circuit is by way of contact to3. The first impulse is by way of wiper ASl in 13 and subsequent impulses are by way of contact 01. As, when relay TO operates, contact a2 is connected to wire vithis contact is short circuited during the repetition of the first numerical impulses, first by Wiper ASS in 13 and later by contact 03. In response to the train of impulses representing the first numerical digit, switch AS is set into one of its positions 14-23. At the. end or the train of impulses, relay C releases and cannot again operate, as in positions 14-24 there is no circuit for it. Consequently there will, for subsequent trains of impulses, be no short circuit across contact a2.

The manner in which dischargedis as follows, it being recalled that a relay or combination of relays W X Y is operated whereby the A digit is stored; wipers BS, and in particular wiper BS7, are in a position 2-10,

wipers CS and particularly wiper CS8, are in a position 2-10 or 14-22; and that wipers AS and particularly wiper. AS'l, will soon be in a position 14-23.

As soon as relay TO operated as the finding of an idle overflow link, a circuit is completed from earth over machine interrupter contact Ml, contacts t02 and c6, wiper SS1 in N to driving magnet SSDM whereby sending switch SS is driven out of position N. Successive delivered directly, that is not over contact c6, to magnet SSDM whereby this switch continues to stop until stopped at the conclusion of the transference of the A. B. C. digits.

When switch SS reaches position 1 a circuit is COlllDlStSdTlOlll earth over contact b8, wiper SS3 in l, winding (I) of relay S2, to negative. Relay SZ operates and, at contact 521, closes a. holding circuit for itself; at contact 522 closes a circuit from earth over machine interrupter contacts M2, over wire 3 to wire W- whereby impulses are repeated to SCC; and at contact s23 -emoves a short circuit from its winding (11'). Contacts M1 andMZ interrupt their respective a result of circuits in synchronism with the result that for each step or switch SS, an impulse is delivered to wire W- as long as contact cs2 is closed.

When switch SS has made a number ofsteps corresponding to the A digit stored on a relay or relay combination WXY. a circuit is completed from earth over contacts b8, 65.7%, g6, through winding (II) of relay G, over appropriate con tacts w, at, y, an appropriate counting wire CW, wiper SS2 in 3-11, winding (ID'oi relay SZ, resistance 1.05 to negative. Relays G and SZ. release due to the completion of this circuit as their respective windings (I) and (II) are in opposition.

Due to the release of relay SZ, the delivery is interrupted. Relay G, atcontact g5 releases relay TM and at contact 95,

switches out relay W.X.Y. and substitutes wiper Switch SS continues to drive, the circuit for taking it through position 12 being over contact e8 and wiper SS1 in 12. In position 13 a circuit is again completed for winding (1) of relay'SZ over wiper SS3 in 13.

The pause between the A and B pulses is provided as switch SS passes from the the A. B. digits are Nbeing over contact 66 and wiper SS1 in N.

In position 1 a circuit is again completed for winding (1) of relays SZ. over wiper SS3 in 1.

The pause between the B and C trains of impulses is provided' as switch SS passes from the marked contact to'position 2.

vEventually wiper SS2 encounters a marked contact 3-11 and a circuit is completed from earth over windings (II) of relays E and SZ. These relays release and relay SZ interrupts the delivery of impulses to wire 1 V Relay E, at contact c5, switches out wiper CS8 and switches in wiper AS'Y; at contact c8 opens the circuit over which switch SS was driven through position 12; at contact c6 prepares a circuit for relay CO; and at contact e9 opens the holding circuit of relays W.X.Y.

Switch SS continues to drive until it reaches position 12. Whether it shall drive through positionv 12 or not will depend on whether the caller has commenced and finished to dial the first numerical digit. Assuming that he has commenced, switch AS will have left position 13, and assuming that he has finished, relay C will be released. In this case the driving circuit for switch SS is from earth over contacts M1, to2, c4, wiper ASS in 14-23, contact c8 at rest, wiper SS1 in 12, magnet SSDM 'to negative.

Eventua ly wiper SS2 encounters a marked.

be driven as its circuit is open at contact 06.

this position, a'circuit is completed from earth through relay CO, over contacts to? and e, wiper SS1 in N and magnet SSDlVi to battery. Relay CO operates but magnet SSDM does not do so.

Relay CO, at its contact col, Fig. 1, closes a circuit for. relay l-ll whichoperates and connects the caller through to thesecond junction selector and cuts out relay Relay A releases and causes the release of relay B whereby relay JBv is released to short-circuit relay K, and the holding circuit of relay K is opened.

Switch BS is self-driven home in a circuit from earthover contact 133, wiper BS1 in 1-24, interrupter'contact' bsdm, magnet BSDM, to negative. When wiper BS1 is in N, a circuit is completed from earth over contact b3,.wiper BS1 in N, offfrom earth over contact 113, wiper B81 in N, offnormal contacts csoni at rest, asonl, interrupter N contact asdm, contact g3, magnet ASDM, to nega- Switch AS is thusflself driven to normal.

pleted a circuit from earth over b6, off-normal MLM to negative.

a Relay'B, when it released also at contact b6 com- I trains of imco'ntact jms'on unlatch magnet Magnet MLM unlatches marking switch FMS and closes a circuit for motor MDM whereby the marking switch is driven to its home position where it opens the circuit of the unlatch magnet MLM. The common control apparatus is now in its normal condition and is, due to the release of relay dissociated with the junction selector F58.

The operation of second junction selector SJL and of the second common control apparatus SCC and particularly the reception of the A. B. C. digits will now be described. A few notions must, however, be carried forward from the preceding description (1) earth through rectifier R, relay TB to wiper FMS5, and over contact tol, relay TO to wiperFMSB, is extended by way of wiper FG (or FG'l) contacts ws5, 767, we l, wiper FP (or FPl), to wire FPW (or FPW 1) which is continued in Fig. 3 as FPW; (2) as soon as relay TO operated, on the finding of an idle second junction selector SJL, ne ative was connected to wiper F+ (or F+1 and thus to wire WA+ (or WA-I-l) which is continued in Fig. 3 as WA; (3) the negative referred to in (2) will eventually be interrupted (impulsed) at contacts a2 by the caller for the second to final numerical digits; (4) each time relay SZ (winding I) operated, earth impu ses for the A. B. C. digits, and first numerical digit, were transmitted over wiper F (or F--1) and thus to wire WA- (or WA-l) passes over contacts $730122, a'al, a series of offncrinal contacts, wipers CSAZ in N Fig. 4 and BSAS in N, resistance 01, to negative. This is the circuit over which the outlet was tested. The earth on wire WA- passes over contact no.3, through relay AA, to negative. Relays AS and AA operate, and the former, at contact asl, Fig. 5 closes a circuit for relay BA which operates.

Relay BA, at contact bal, prepares a circuit which will be referred to later; at contact 19002, closes circuits from earth over contact ba2, through auxiliary winding (I) of relay D to negative, and from earth over contact ba2 over wiper BSA5 in N, through relay JA to negative; at contact ba3, Fig. prepares a circuit which will be referred to later; at contact but, Fig. 3, prepares a holding circuit for relay KA, not yet operated; and at contacts M5 and bat) prepares circuits.

Relay JA removes the short circuit from relay KA, whereby that relay-operates and, at contact an closes its own holding circuit. Relay KA, also, at contact lca2 reverts earth to the preceding selector, and at its other contacts couples the junction to the second common controller SCC.

impulses representing the A, B, C and first niunerical digit, and consisting of interrupted earth on wire WA-, cause relay AA to release and re-operate. Relay AA consequently at its contact cal, Fig. 5, repeats the trains of impulses to magnets ASAM, BSAM, CSAM and MSAM, the circuit including wiper MSl, which acts as a distributor to distribute the successive trains of impulses to the appropriate magnet. The impulsin circuit also includes relay CC which operates during the iinpulsing, and releases between trains. Relay CC, at contact 001, therefore brings about, by alternately closing and opening the circuit of magnet MSAM, the stepping of switch MS whilst that switch is acting as a distributor. The stepping circuit for stepping switch MS from N to 1, from 1 to 2, and from 2 to 3 is from earth over contact ba2, wiper MSZ in N, l and 2 respectively, contact 001, and magnet MSAM to negative. The circuit for stepping switch MS from position 3 to i, in response to the first digit of the first numerical train is from earth, over contact cal relay CC, wiper MSI in 3, and MSAM, and for stepping it for subsequent impulses of the same train is over wiper M81 in 4-13 and contact 001. Relay CO, at contact 002 isolates wiper MS l, so that during the setting of this switch for the first numerical digit, no circuit shall be completed over wiper BSA i, etc.

It is thought that a description ofthe operation of switches HS, TS and US, in response to the hundreds, tens and units impulses respectively, which are received on relay AS, it may be concurrently with the receipt of the A. B. C. digits and thousands digit, is not necessary as it is similar in every way to the operation of switches ASA, BSA, CSA and MS. Wiper U1 acts first as a distributor and then as a register in the same manner as did wiper MSl.

During the setting of switches ASA, BSA, CSA in response to the transferred A. B. C. digits, certain operations have taken place automatically. Thus when, in its course of being set in response to the B digit, switch BSA passes through position 1, a circuit is completed from earth over contacts 002, tf2, wiper BSA2 in 1, wiper CSAl in N, driving contact csam, magnet CSAM to negative. Switch CSA therefore self-drives from position N to false normal position. If the B digit is more than 5, a circuit similar to the above is completed to cause switch CSA to self drive from position 0 to position 12. The reason for this is similar to that for the corresponding switch CS in FCC. When switch MS steps from position 2, after the recording of the C digit, to position 3 for the recording by transfer from FCC of the first numerical digit, a circuit is completed from earth over contact ba2, wiper MS2 in 3, contact tel, unlatch magnet MALM to negative. Magnet MALM operates, and unlatches marking switch MA and closes a circuit at contact malml, Fig. l, for motor MADM. Motor MADlVi drives the marking switch until that switch occupies a position appropriate to the A. B. C. digits. When this position is reached, a circuit is closed from earth over contact baB, quick relay TE, wiper ASAZ in A group marking, MAI in A group marked MAZ in C contact marked, one of the wipers CSA in 0 contact and B sub-group marking, wiper BSAS in a B sub-group marking, resistance ()1, tonegative. Relay TE operates and at contact tel opens the circuit of unlatch magnet MALM whereby switch MA is stopped. As soon as switch MA goes 01? normal, it closes at contact mac-11,1, a circuit which is independent of wiper M32. This is because wiper MSZ may soon be driven in response to the first numerical digit.

Relay TE, in addition to opening at contact tel the circuit of magnet MALM closes a circuit for relay TF. Relay TF, at contact I' l closes a holding circuit for relay TE.

As the A. B. C. digits are now recorded on switch MA switches ASA, and BSA are relieved for other functions, ASA acting as a counting switch, and BSA as a distributing switch. Thus, when relay TE operated it closed at contact 1512, a circuit from earth at contact 002, over contact 2312, wiper ASAl which may be in any position 2-8 (or in position 9 in which position the circuit will not be closed), driving contact ascm, magnet mitted over wipers 8+ and S.

" dotted arc of contacts.

ASAM, to negative. In this circuit, switch ASA drives to position 9. Relay TF also; at contact tfZ closes a circuit over wiper BSAl in 2-10, contact bsaon operated, drive contact beam, magnet BSAM, whereby switch BS self-drives to position 11. Relay 'IF, at contact tj3, Fig. 3, closes a circuit from earth, over contact tgl, thl, ttl, tlcl, U3, kaS unlatch magnet SLM, to negative. Magnet SLM operates and in the now well understood manner causes the selector SJL to rotate in search of a free outlet in the desired direction. The group of outlets may be marked in either of the banks SG orSGL. In the former case, relay WAS is not to be operated, and in the latter it is to be operated. Further there may or may not be a free direct outlet, and the destination may be one which can be reached directly from SJL only, or directly preferably, and via a tandem exchange if there are no'direct outlets.

Let it be assumed that the operation of relay WAS is not required and that there is a free outlet. There will be an appropriate cross connec tion from wiper MA3, in the position to which it has been set, to a group of contacts in bank SG. When a free outlet is found, a circuit will be completed from earth through rectifier RA, rapid relay TH, wiper MAS in marking, wiper SG in marked, contacts was5, lca'l, was l, wiper SP to wire SI-W which is the test wire of the idle outlet. Relay TI-I, operates, and at contact thl, opens the circuit of the unlatch magnet and closes a circuit for relay winding (I) of TG. Relay TG operates and, at contact tgl, closes a "j holding circuit; at contact i112, closes an alternative holding circuit for itself over winding (II); contact tgS Fig. closes a self-drive circuit for advancing switch BSA from position 11 to position 16: and at contacts tg and W5, Fig. 3, closes i a loop across the wipers 5+ and S, this loop including wiper ASA5 in 9, and winding (11) of shunt field relay D.

At this stage, if the thousands digits have been received by switch MS, impulses would be trans- It is convenient, however, to reserve the consideration of the manner in which this is effected, and to consider what happens if all outlets were busy; what happens if the outlets are in a bank which requires the i operation of relay WAS: what happens if all outlets there are busy; and how a tandem outlet is reached. I

If wiper SP finds no free outlet at the same time that wiper SG is moving over a marked group of contacts, or if wiper SG encounters no marked group (by reason of the group being marked in bank SGl) there will be no circuit for relay TI-I until switch SJ L is driven to such a position that its dotted wipers reach the last contact in the In this position a circuit will be completed from earth, over rectifier RA, winding (I) of relay TI-I, wiper SG in last dotted, contacts was5, 7ca7, was, wiper SF in last dotted, winding (II) of relay TG, and winding (I) of relay 5 to negative. Relay TH operates at contact thl opens the circuit of unlatch magnet SLM and closes a circuit for winding (I) of relay TG. The two windings of relay TG are now in opposition so that this relay I does not operate, but relay S does and, at conact sl closes a holding circuit for itself through its winding (II) Fig. 5. It also at contact .82, i ig. 3, closes a circuit for relay WAS. Relay WAS operates, and at contact wasl prepares a holding circuit for itself; and at contacts was.2--

was5, switches over the wipers of selector SJL. By the changeover of contacts was4 and was5, the circuit of relay TH is opened, and this relay releases.

Now, although wipers SP1 and SGI are in last dotted, yet no circuit is completed for relay TK, since this relay must be understood to be connected to the last but one dotted con-tact of arc SGL' When, therefore, relay TH releases, the circuit .for unlatch magnet SLM is reclosed and selector SJL is driven in search of a free outlet in marked group. v

If this drive is being effected because, although a group was marked in bank SG, no free outlet was found, selector SJL will not find a marked group of direct junctions but will find a mark on a group of contacts appropriate to a tandem route. In this case it will be to find an idle outlet to the tandem centre over which the alternative route can be set up. If the drive is being effected for the purpose of finding an idle outlet in a direct group that is marked, not in banks SG, but in bank SGl, the drive will continue until such outlet is found, if one exists. If no free outlet exists the drive will continue to find a free -outlet to the tandem centre. If no idle outlet to the tandem apparatus -eXists,-the drive will be a restoring drive.

Let it be assumed that an idle outlet exists in a group or direct outlets, marked in bank SGl. In this case, as soon as the first idle outlet is reached by wiper SP1, a circuit is completed from earth. over rectifier RA, relay TH, and so on as before, to wire SPWl. The selector is consequently brought to rest in association with the selected outlet and relay TG operates with the results already described.

Now let it be assumed that there is no idle direct outlet. There will be, in addition to the marking of the direct group, a marking of a common group of outlets leading to the tandem centre. As soon as an idle tandem outlet is found, a circuit will be completed from earth through rectifier RA, rapid relay TK, cross connection from terminal TN to the .group of contacts in bank SGl appropriate to the tandem route, wiper SGI, contacts was5, lca7, vwasel, wiper SP1, to a test wire similar to 'SPWI. Relay 'IK operates and at its contact tlcl releases the unlatch magnet and closes a circuit for winding (I) of relay TT which operates. Relay TT, at contact .ttl closes a holding circuit for itself; at contact ttZ closes an alternative holding circuit from earth, over contacts M15, #62, winding (II) of relay TT, resistance S2, to negative; at contact tt3 prepares a circuit for causing the transmission of tandem impulses as will be described, and at contacts tie and tt5 places a loop across the outlet, this loop including winding (II) or" shunt field relayD.

If there were no idle tandem outlet, relays TE. and TT would not find a circuit as selector SJL went through the tandem group, and the switch would continue to drive until dotted wiper SGI reached the last but one dotted contact. In this position, selector SJL completes a circuit from earth, through rectifier RA, relay TK last but one dotted contact of wipers SGl and SP, winding (II) of relay TT, and relay LC. Relays TX and LC operate but relay TT does not do so, as upon the operation of relay TK, the two windings of relay TT are connected differentially. Relay TK causes selector SJ L to come to rest and relay LC at contact 101 reverts busy tone to the caller. The caller should replace his receiver whereby relays AA and AS will release with results described later.

Assuming that there is an idle outlet, the transmission of impulses from SCC, to operate the next selector, now takes place. One or other of two conditions may exist, either the connection was extended over a direct outlet and relay TG was operated, or it was extended over a tandem outlet and relay TT was operated. In the former case impulses for operating the numerical selectors are transmitted immediatelyy'in the latter, impulses for operating up to five code selectors at the tandem centre, or, if more than one tandem exchange is involved, centres are. transmitted followed by the impulses for. operating the numeral selectors.

Considering the former case first; when, due to the operation of relay IG, contact tgS, Fig. 5,

closed and caused switch BSA to self-drive to position 16; and when either zthereafter or al ready selector ASA goes to position 9 following the setting of marking switch MA, and when, moreover, the first numerical digit has been received' on switch MS and relay CC has released,

all as already described, a circuit will be completed from earth over contacts ba2, cc2, wipers MS4 in 4-13, BSA4 in 16, ASA3 in 9, contact 011 (relay D being unoperated if the numerical selector to which the connection is so far extended is ready to receive impulses and is therefore reverting current in the correct direction to wind ing (II) of relay D, winding (I) of relay SZA to negative. Relay SZA operates, and at contact seal, closes; a holding circuit for itself (earth at contact ba2).

Relay SZA, at contact seaZ, connects winding (II) of relay SZA to wiper ASA4; at contact sea3, Fig. 3, short circuits winding (II) of relay D and removes a loop from across the outlet (an alternative loop, however, exists over wiper ASAS in 9): at contact 82054, Fig. 5, closes a driving circuit from earth, over contacts 002, tf2, sza i, impulsing contacts M3, for magnet ASAM; at contact sza5, opens the self driving circuit'which exists over ASAl in 10-20; and at contact sea6 closes a circuit for magnet BSAM.

Switch ASA is driven in response to impulses from contact M3,.and when it moves from posi,: tion 9 it removes the short circuit which existed over wiper ASA5. so that'impulsing contacts M4, which operate synchronously with contacts M3,, transmit impulses over the loop. As wiper ASA4 rotates it searches for a contact marked in accordance with the setting of wiper MS3 that is in accordance with the value of the thousands digit. When such a contact is found, "a circuit is completed from earth, over contacts b112, wipers BSA5 in 16, MS3 in marking, ASA4 in marked, contact sza2, winding (II) of relay SZA to battery. The two windings of relay SZA being in opposition, this relay releases and, at contact s2a3 short circuits impulsing contacts M4; at contacts szcui opens the impulsing circuit for switch ASA; at seat: connects magnet ASAM into a self-drive circuit to take switch ASA to position 21; and at contact 52116 opens the circuit of magnet BSAM so that this switch goes to position 17.

Switch ASA is impulse driven from position 21 to N, and self-driven from N to 9 where, if, or as soon as the hundreds numerical selector to which the connection is now extended is ready to receive impulses and is reverting current in the correct direction and relay D is therefore still (or again) released, and if the tens digit has been dialled by the caller, a circuit is completed from earth, over contacts 1x12, wiper T81 of the tens switch in 1-10, BSA4 in 17, ASA3 in 9, contact d1, relay SZA, to negative. Relay SZA again operates. and permits the transmission of the hundreds digit in the same manner as the thousands were transmitted, wiper;HS1 in marking being involved.

' At the end of this transmission, switch ASA is again driven to position 9 and switch BSA is driven to position 18. If the units digit has been received and relay D is again unoperated, the circuit for relay SZA is again completed, this time over wiper US2 in 3-12. Relay SZA again operates and permits the transmission of the tone impulses.

Atthe end of this transmission, switch ASA is again driven to position 9 and switch BSA is driven to position 19. Theunits digit having been received, relay. SZA again operates and permits the transmission of the units digit.

At the end of the units transmission, relay SZA releases as before, and at contact sea6, drive switch BSA into position 20. When switch ASA, on its way from position 21 to N, reaches position 24, a circuit is completed, from earth at contact b112, over wiper ASA3 in 24, wiper BSA4 in 2G, relays CO to negative. Relay CO operates, and at contact col, Fig. 3, closes a circuit for relay HA whereby the connection between the caller and the numerical selectors is completed and the circuit for relays AS and AA is broken. These relays release and cause the release and restoration to normal of SCC., Contact e02 opens the stepping circuit of switch ASAM which rests awhile in 24.

The manner in which, if a tandem route is involved, impulses representing the A. B. C. digits are transmitted is as follows, it being, of course, understood that the number of impulses transmitted or number of trains need bear no numerical relationship to those received.

Owing to the non-operation of relay TG, Fig. 3, contact tg3, Fig. 5, isnot closed and therefore switch BSA does not immediately self drive from position 11 to position 16 but, instead, rest in 11 for the present. Owing to the operation of relay 'IT instead of relay TG, contact #3 is closed and provides a circuit fromearth, over contacts :22, #3. wiper BSA4 in 11 and ASA3 in 9, for relay SZA which operates and sets switch ASA into motion as above described. 7

Relay SZA releases when wiper ASA4 reaches a contact marked from earth, over wiper BSA5 in i1, wiper MA4 of the marking switch in marking, cross connecting field CF and so on. The release of relay SZA causes all the effects al ready described, including the stepping of switch BSAfrom position 11 into position 1 2.

This process continues until all the trains of digits representing the translated A. B. C, code have been transmitted when switch BSA will be in position 16, the position from which numerical transmission commences. If the translated A. B. 0. codes does nct involve the transmission of five trains of impulses the marked contact in one of the banks MA4 to MAS will be crossconnected to relay SD. When, therefore, wiper BSA5 reaches a position which leads to the MA wiper thus cross-connected, relay SD operates,

'vidual groups of junction-"lines connecting said It'maybe that, after the setting of one selector in response to impulses transmitted from impulse contact M4, a succeeding-"switch is not ready for response to a succeeding train of impulses. To guard against the premature transmission of impulses, it is arranged that, until a switch is ready, battery is fed back over wipers S-}- and S- "(or 8+1 and 57-1) is in reverse direction whereloy shunt field relay D operated. Thus when wiper ASA3- is in 9, the operation of relay SZA is delayed until relay D shall release due to the correction of the direction of the cur-rent fed back. 1 Sequential restoration of the switches is effected as soon as relay BA releases,the circuit being from earth over contact 21112 and the various off normal and self-drive contacts such as hsonl, \hsam; tsonl, tsam; usonfusam; monl, mam; csonl, csann; and soon. The drive for switch MA is from earth, over contact ma'on, contact tel, magnet MALM, to negative, relay TE releasing due to the release of contact -ba3.

1. In a multi-office telephone system, a main exchange, a plurality of other exchanges, groups of junction lines directly connecting each exchange with said main exchange, a first selector in said main exchange having access to a part of each grcup of said junction lines, overflow junction lines accessible to -said first selector, auxiliary selectors in said main'exchange connected to said overflow junction lines, and additional junction lines of said first junction groups accessible to said auxiliary selectors.

' 2. In a multi-ofiice telephone system, a main exchange, a plurality of other exchanges, groups of junction lines directly connecting each exchange with said main exchange, a first selector in said main exchange having access to a part of some groups of saidjunc'tion lines, a group of common overfiow junction lines accessible tosaid first selector, auxiliary selectors in said main exchange connected to said overflow junction lines, and different junction lines of said first groups of junction lines accessible to said auxiliary selectors. V

" In a multi-otfi'ce'telephone system, a main exchange, a plurality of other exchanges, individual groups of junction lines connecting said exchanges with said main exchange, first selectors in said main exchange having access as an early choice to said individual groups-oi junction lines, a group of common overflow junction'li-nes accessible to saidfirst selector,--'auxiliary selectors in said ma-in exchange connected to said overflow junction lines, and a group of later choice junction lines of said individual groups of junction lines accessible tosaid auxiliary selectors.

4. In a rn-ulti-olfi'ce telephone system, a main exchange, a tandem exchangeaplural i ty of other exchanges, individual groups of junction lines connecting said other exchanges with said main exchange, first selectors in said main exchange having access to a first choice of said individual groups of junction lines, a group of overflow junction lines accessible to said first selector, auxiliary selectors in said main exchange connected to said overflow junction lines, a group of second choice junction lines of said individual junction groups accessible to said auxiliaryselectors and a group of tandem junction lines extending to said tandem exchange also accessible to said auxiliary selectors;

5.In a multi-ofiice telephone system, a main exchange, "a plurality of other exchanges, "ind-iother exchange with said main exchange, first selectors insaid main exchange having access to a first choice of said individual groups of junction lines, a group of overflow. junction lines accessible to said first selector, auxiliary selectors in said main exchange connected to said overflow junction lines, a group of second 'choiceljunction lines of said individual junction groups accessible to said'auxiliary selectors, said first selectors operatedin accordance with a plurality of digits designating an exchange'to select an idle first choice junction line leading to .suchexchange, and means for transferring and utilizing said code routing designation to selectively operate-said auxiliary selectors 'toselect an idle second choice junction line. l, x.-

6-. In a inulti office telephone system, a main exchange, a plurality of other exchanges, groups of junction lines connecting each exchange with said main exchange, first selectors in said main exchange having access-11:0 a :firstchoice of said groups of junction lines, .a group of common overflow junction lines accessible to said first selec'tors, auxiliary selectors in said main exchange connected to said overflow junction-lines, a group of second choice lines of said first junction group accessible to said auxiliary selectors, common control apparatus for operating said first selectors in accordance with the registration of-la set of con-trolling digits to select an idle first choice junction line or an idle one of said common overfiow junction lines, and means operated in :case the overflow junction line is used for transferring the controlling digits from said common control apparatus over said overflow junction line to control said auxiliary selectors to select an idle one of said second choice junction lines; 7

7. In a multi-ofilce telephone system, a main exchange, a plurality of other exchanges, groups of junction lines connecting each exchange with said main exchange, first selectors in said main exchange having access to a first choice of said groups of junction lines, a group of common overflow junction lines accessible to said firstselectors, auxiliary selectors in said main exchange connected to said overflow junction lines, a group of second choice'lin'es of said first junction group accessible to said auxiliary selectors, common control apparatus for operating said first selectors in accordance with the registration of a set of controlling 'digits to select an idle first choice junction line or an idle one or" saidcommon overfiow junction lines, means operated in case the overflow junction line is used for transferring the controlling digits from said common control apparatus over said 'overfiowijunction line, and other common control apparatus operated responsive to said controlling digits from said over fiow junction line for controlling said auxiliary selectors to select an idle one of said second choice unction lines.

8. In a multi-ofiice telephone system, a main exchange, aplurality of other exchanges, groups of junction lines connecting each exchange with said main exchange, first selectors in said main exchange having access to a first choice of said groups of junction lines, groups of common overflow junction lines accessible to said first selectors, auxiliary selectors in said main exchange connected to said overflow junction lines, groups of second choice junction lines accessible to said auxiliary selectors, common control apparatus for operating said first selectorsto 'selec't'an idle first choice junction line, other-common con-

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