US2272464A - Telephone system - Google Patents

Description

'Feb.10,1942. I B. A. HENSLER' 2',272 ,4s4

TELEPHONE SYSTEM Filed Nov. 18, 1939 8 Sheets-Sheet l ro W RZLA vs /L 0B3 m x RELAYS I J Z 70 r RELAYS Fla! 005] 370 z RELAYS Feb. 10, 1942. a. A. HENSLER 2,272,464

TELEPHONE SYSTEM Filed Nov. 18, 1939 8 Sheets-Sheet 2 INVEN'MR BE ANTHONY HEHS R BY .Z.

IITTORNE Y Feb. 10, 1942. B. A. HENSLER TELEPHONE SYSTEM Filed NOV. 18, 1939 8 Sheets-Sheet 3 em i Q 3. 4 Y u a:

IN VE N TOR can! ANTHONY nmsgn BY ATTORNEY Feb."10,1942. B. A. HENSLER- 2,272,464

TELEPHONE SYSTEM INVENTOR BERNA D ANTHONY HENSLER av .Z.

ATTORNEY Feb. 10, 1942. B. A. HENSLER 2,272,464

TELEPHONE SYSTEM Filed Nov. 18, 1959 8 Sheets-Sheet 5 &

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' H 'INVENTOR n'rronne Feb. 10, 1942. B. A. HENSLER 2,272,464

TELEPHONE .SYSTEM Filed Nov. 18, 1959 s Sheets-Sheet s (I) 6 d g m 3; 0,5 (2 5; 5'04 ,7 7711.?

1 MH g F INVENTOR ATTORNEY Feb. 10, 1942; B. A; HENSLER 2,272,464

TELEPHONE SYSTEM Filed Nov. 18, 1939 8 Sheets-Sheet 7 INVENTOR BERNARD ANTHONY HENSLE waz ATTORNEY Feb. 10, 1942. H s R 2,272,464

TELEPHONE SYSTEM Filed Nov. 18, 1939 8 Sheets-Sheet 8 8 R80 ANTHONY HENSLER EZZZM IATTORNE Patented Feb. 10, 1942 rem" orrlc TELEPHONE SYSTEM Application November 18, 1939, Serial No. 305,146 In Great Britain November 18, 1938 12 Claims.

This invention relates to telephone systems and more particularly to systems in which calls between exchanges are set up over automatic switches by operators.

In such systems a register sender is usually employed which registers the digits transmitted to it by the operator, the digits in one form of system being in the form of a code transmitted from a key strip, and transmits digits which may be the same as or different from those received for the setting up of the desired connection. The register sender is usually available in common to a number of operators positions and may include a number of registers sufficient for the registration of the whole of the number to be transmitted for the setting up of the required connection or arrangements may be employed whereby a less number of registers is required. The digits to be transmitted from the register sender may be either in code form or impulse form. As a rule coded digits would only be used for setting switches in the same or in an adjacent exchange where more than two signalling wires may readily be provided, impulses being used for transmission over junctions and trunks to distant exchanges and to local switches which are available to subscribers and are arranged for the reception of impulses.

In the selection of a route which a call is to take consideration may be given to the state of traffic over the normal route and the sender may embody arrangements whereby if all the direct trunks in the desired direction are engaged an alternative route is selected. These arrangements may embody group control circuits associated with the trunk groups and operating on translating arrangements whereby in response to the transmission to the register sender of digits denoting the trunk required two translations may be made or prepared one for the direct route and the other for an alternative route to be taken if the direct route is congested.

Furthermore in a trunk switching system it may be desirable to transmit impulses over the trunks in the form of impulses of voice frequency alternating current.

In the present invention the register sender is adapted to send out impulses of voice frequency alternating current. At the same time ordinary D. C. impulses may be sent out from the sender so that at all times the type of impulsing may be suited to the selecting arrangements which may be met with. With this dual form of impulsing arrangements may be provided at a suitable circuit, where the nature of the distant selecting arrangements may be determined, whereby the undesired form of impulses is suppressed, only the desired form being allowed to go forward. Arrangements may be provided in the sender itself whereby in some cases the nature of the impulses to be sent can be determined and only impulses of one form are sent out.

The sender may be arranged so that normally impulses to be sent out are D. C. impulses. The sending of voice frequency A. C. impulses may be brought about in response to particular cross connections in the translating field or in response to a signal from the operators position or a trunk selected or outgoing repeater circuit. It may be convenient in the transmission of voicefrequency A. C. impulses to permit the transmission of D. C. impulses simultaneously these being suppressed at some convenient point.

As regards the digits received by the sender some of these maybe translated or be otherwise utilised and others may be re-transmitted unchanged. In the setting up of a trunk connection it may be sufficient in most cases to transmit coded digits in response to a received code for the setting of trunk selectors to select the desired trunk route which may and usually would terminate at a manual trunk position at the distant exchange. The sender may then release itself automatically or be released by the operator. If the trunk or outlet from the trunk selector terminates in an automatic switch over a two wire circuit it will be necessary to transmit impulses for the setting of this switch and possibly succeeding switches.

Accordingly for the same digits received by the sender the sender may be arranged to send out different digits depending on the state of the route indicated by the received digits. Thus in the case of an alternative route through an exchange at which the trunk is terminated on an automatic switch an additional digit may be interpolated for the setting of this automatic switch and the additional digit may be transmitted as a train of A. C. impulses of voice-irequency. In this case if a state of congestion is encountered at the intermediate exchange a voice-frequency signal may be reverted over the trunk and transformed into a D. C. signal to the sender to cause it to dispose of the call in some other manner which may require a different number of digits.

As regards the provision of alternative routes these may in general be the same as direct routes to some other exchanges but the arrangements of the sender provide for groups of trunks which are not direct routes to any exchange but exist solely as alternative routes if the direct route to which they provide an alternative are busy. The translation effected by the sender for the selection of a solely alternative route may be one in which the digits for the setting of the trunk selectors are digits which cannot be obtained directly by keying by the operator. The operator is generally provided with digit keys on a decimal basis since numerical designations are required to be transmitted but the translated digits may be on a non-decimal basis. To make full use of the availability of the trunk selectors these may be of the uniselector type set by the marking method whereby the number of groups and their size may be provided to suit requirements since the type of switch is not limited to operation on the decimal system. The alternative route trunks referred to are conveniently taken from a special group of trunk selectors and since the translation to reach this group cannot be had at the will of an operator their reservation as an overflow route is assured.

Reference has already been made to arrangements in which the number of registers is less than the number of digits to be sent. It may happen that after an association of the sender with trunk selecting switches and the selection of a desired route a number of digits greater than the number of the remaining registers may be required to be sent or after the sender has been released it may be desired to transmit further digits. In such an event a re-association of the sender with the route already set up may be made and a signal transmitted to the sender as a consequence of such connection to bring about the sending of subsequent impulse trains as trains of voice frequency impulses. At the same time D. C. impulse trains are transmitted so that the form of impulses may suit the selecting arrangements provided. The form of impulses not required may be suppressed or ignored at a suitable point.

The sender may also be provided with arrangements whereby the probable period of delay, if any on a trunk route may be signalled to the operator.

The nature of the invention and the means for carrying it into efiect will be better appreciated from a consideration of the following detailed description taken in conjunction with the annexed drawings. These relate to a specific embodiment of the invention and are given by way of example. The drawings, comprising Figs. 1, 1a, 2, 2a, 3, 3a, 4, 4a show circuits of a register sender which is adapted to receive keyed up digits in code form and to transmit digits in code form or as impulses for the setting of selecting switches. The sender is of a kind for use at a trunk exchange and means are provided whereby impulses may be transmitted as D. C. leg impulses or as voice frequency impulses or both. The arrangements also provide for suitable translations of some or all of the received digits to be made and for the selection of an alternative route if the direct routes in the direction of the wanted subscribers exchange are all busy. The sender is adapted to deal with different types of trunk calls and local calls.

The principal parts of the sender are the coupling switches CSA and CS3 for connecting the sender to an operators position for the purpose of setting up a call, register relays comprising 7 sets of 4 relays each, the sets being designated AW, AX, AY, AZ, BW-BZ, and so on to GW--GZ. To avoid overcrowding the drawing relays OK to CZ and EX to FZ have been omitted but these relays are similar to the other register relays shown, their operating windings being connected to contacts in the banks DDZ, DD3, D134 and DDS of a digit distributor and their locking windings being connected to contact ba5 of relay BA in a similar manner to that shown for the registering relays AW-AZ and so on. A digit distributor comprising a pawl and ratchet driven stepping switch with 8 banks of contacts designated DDl--DD8, and stepping magnet DDM provides for the routing of successive digits to the several registers in turn, the switch being controlled for this purpose by relay DS which is connected in series with the several parallel connected-operating windings of the register relays. A controller comprising a pawl and ratchet driven stepping switch with 8 wipers designated SDISD8 and stepping magnet SDM provides for the connection of the several registers in turn to the out-sending wires, W, X, Y, Z or to an impulse counter. It also provides connection to relays RL, RS and CN to determine whether re-search or re-routing is required.

There are three latch-controlled motor-driven translating switches the motors of which are represented by their latch magnets MUC, MUD, and MUE respectively. The first two of these switches have each 15 wipers and 50 point contact banks and switch MUE has 8 wipers and point contact banks. Switches MUC and MUD are the main translating switches and their banks are cross connected as follows. Terminals l to 9 marked by contacts of the relays of the A and D registers are connected each to a maximum 10 contacts in the banks of wipers 12 of either or both switches. These switch contacts need not be consecutive but may be so chosen that if the switch has to drive from marked contacts to other marked contacts for the purpose of effecting a translation for an alternative route, the search for the new marking may be a short one. If the two routes are alternative to one another this latter provision cannot well be made. Similiarly terminals H to 20 marked by contacts of the relays of the B and E registers are each connected to a maximum of i0 contacts in the banks of wipers Id of one or both of the switches but care must be taken that the several contacts connected to a terminal of the series [I to 20 appear only once in the corresponding positions in the banks of wipers 12. As the registration of the numeral 0 as a first digit or the registration of the numeral 9 as the first and second digits does not cause the switches MUC and MUD to leave normal only 89 contacts will be taken up by the above mentioned cross connections to the banks of wipers 12. The terminals are cross connected in a similar fashion to contacts in the banks of wipers 6 and I of switch MUE and considering the bank associated with each of these wipers as the equivalent of the corresponding banks of the switches MUC and MUD the terminals may be connected to switch MUE in positions corresponding to those to which they are connected in switches MUC and MUD. The switches MUC and MUD are not used on minor trunk calls whereas switch MUE is used on such calls. Accordingly positions on switch MUE used for minor trunk calls may correspond to uncon nected positions on switches MUC and MUD Terminals corresponding to the numbers of minor trunks, that is the 4th and 5th digits as will hereinafter appear are cross connected to any available positions on switch MUE. Terminals of numbers in the group and the number 99 are also cross connected to any available position on switch MUE.

Besides its use on minor trunk calls switch MUE is mainly concerned with alternative routing. The switch is set normally in accordance with the digits indicative of a direct trunk group and cross connections are made between contacts in the bank of wiper 8 of the switch MUE and contacts in the banks of wiper I3 of switch MUC or MUD. Normally the alternative route for one group of trunks will be the direct route for another group of trunks. Arrangements may however be provided wherein a route may be provided with a group of alternative route trunks which are not direct trunks for any other group even though the trunk se lectors are fully occupied by direct route and special trunks are connected in a special group of 2nd trunk selectors. As the number of contacts on switches MUC and MUD devoted to direct routes is limited to 89 and the first contacts are used for another purpose there remains 10 contacts available for cross connection to switch MUE for these special alternative route trunks. It will be obvious from this that switches lVIUC. and MUD cannot be set to these positions by depression of the decimal keys in the operators digit strip but can only reach these positions by reason of the marking applied over the wipers of switch MUE. The translating switches have a combined capacity of 100 outlets and of these one is required for their tandem connection, leaving 99 available outlets. As 88 outlets are required for translating purposes in response to digit key operation there remains 10 outlets available for the special alternative route trunks. The 1st trunk selector must be capable of accommodating at least 12 groups of outlets so that a uniselector for this purpose is imperative if complicated arrangements are to be avoided. Moreover decimal setting is also inadmissable. It will be clear therefore that no combination of digits to be had by decimal key operation will effect the setting of the translating switches to these 10 special positions and that the trunks which are selected corresponding to these positions cannot be reached at will by an operator.

In the banks of the translating switches not previously referred to those in the banks of wipers I to 8 of switches MUC and MUD are connected to earthed terminals, the contacts so connected being those which will provide the required translation. The translation for the first digit to be transmitted is made over the odd numbered wipers and that for the second digit over the even numbered wipers. Contacts in the banks of wipers I to 4 of switch MUE are also connected to earthed terminals as required to provide a marking to determine the number of voice frequency impulses that are to be counted for the setting of an automatic selecting switch in an intermediate exchange in an alternative route. The contacts in the banks of wipers 9 of switches MUC and LEUD are connected to arrangements for signalling the period of delay likely to be experienced in main trunk calls and contacts in the bank of wiper of switch MUE are similarly connected for minor trunk calls. Contacts in the banks of wipers I0 and It of switches MUC and MUD are connected; to contacts of group control relays for the direct. and alternative trunk routes respectively. Contacts in the banks of wipers I5 of switches MUC and MUD are likewise connected to earthed terminals, the contacts being those in positions corresponding to trunk groups for which alternative routes are available, such alternative routes requiring the transmission of a train of voice frequency impulses for the completion of the connection to the wanted exchange.

There are no connections to switches MUC and MUD on dead numbers.

The normal contacts in the banks of wipers I, 3, 5, I of switch MUC are cross connected in a manner which will cause the setting of a 2nd trunk selector to an outlet to a 3rd trunk selector on minor trunk calls.

The impulse counting device comprisesthe relays CA, CB, CC, CD and X and the impulse generating relay A. By means of cross connections between terminals I I to 2B and terminals FI relay FD can be operated on some digits to vary the capacity connected in the circuit of relay A for the purpose of increasing the speed of impulsing. The impulse generating and counting device is substantially similar to that described in British Patent Specification No. 471,987. AR and AS are impulse repeating relays.

Of the relays shown PY and SY are concerned with translations for the direct and alternative routes in a desired direction and VF, N and AD are concerned with the transmission of voice-frequency switch setting impulses. Relays TC, IT, MT, MS and LC are concerned with the different types of call that may be set up, relays S, SN, S0, S5, ST, S2 and SR are concerned with impulse transmission and relays VA,

VB, and V0 are concerned with determination of the intertrain pause. The purpose and function of the other relays will be clear from the detailed description which follows.

The trunk exchange includes three ranks of trunk selectors over two or three of which all outgoing calls are set up. For calls over main trunks and special trunks two ranks of selectors suffice but minor trunks and local selectors are connected to 3rd trunk selectors. The 2nd trunk selectors are set by two digits, the first determining the group of trunks over which a connection is required, the second determining whether the whole group shall be searched or an individual trunk selected. The 2nd trunk se-,

lector is provided with outlets to storage equipment for storing calls that cannot be completed immediately but if the selector is employed in a connection which is to take an alternative route the second digit is modified to prevent the selector routing the call to an outlet to a storage position and to bring the selector to rest in a position in which a signal may be returned to the register sender to cause it to re-route the call over the direct route so that it is stored in the storage equipment appropriate to the direct route.

The different types of connection that can be set up and their characteristic features will now be set out.

(1) M ain trunk calla-These are calls over the main groups of trunks to distant exchanges. These trunks are reached by the operator keying up three digits, the third of which is 0. The numeral 0 for the first and second digits is excluded as is the combination 99. The third digit 0 (code WX) is used to indicate to the 2nd trunk selector that a trunk group i to be searched. The first two digits are translated but the third digit is sent out untranslated. If the call is routed by the sender to an alternative route the digit is not transmited but a special digit (code WXY) is transmitted to prevent the call being stored if by the time the storage position on the trunk selector is reached the last available trunk has been already taken into use. If the exchange to which a trunk becomes connected in a call via an alternative route is one in which the switching is automatic the sender will interpolate a train of voice frequency impulses for setting switches in the exchange in the alternative route for advancing the connection to an exchange in the direct route. A call may be routed to a particular trunk in a group by keying one of the digits 1 to 9 as the third digit.

(2) Minor trunk caZZs.--These trunks are trunks associated with routes of lesser importance and are connected in the bank of 3rd trunk selectors. To reach one of these trunks five digits are keyed up, the first three being 990 which select a free outlet to a 3rd trunk selector. The 4th and 5th digits take effect at the 3rd trunk selector to select the desired trunk or one in a desired group.

Trim-7c calls requiring the keying of additional digits The sender when first taken into use associated itself with a free 1st trunk selector and a trunk route is set up in response to keyed up digits and the sender thereupon releases. If the operator now has to send further digits she takes a sender into use and this can associate itself with the same 1st trunk selector even though it is busy and in consequence of this association with a busy selector impulses sent out are voice frequency impulses. Up to seven trains of such impulses can be sent out.

(3) Special trunk calls-Calls between certain important centres are set up over a special group of trunks. To set up such a connection a special key is operated the code (WXY) of which is translated into a code WXZ not provided by the decimal keys. The second digit selects the trunk group and the third digit would normally be 0 to initiate a search in the selected trunk group. Individual trunks may be selected by keying up a third digit other than 0.

(4) Local caZZs.These may be from 2 to 7 calls consisting of from 2 to 7 digits, the first digit being 0. The first two digits are translated and re-transmitted in code form to set the 1st trunk selector and the first local selector, subsequent digits being transmitted as impulses.

The means by which calls of the several types referred to may be set up and the arrangements for alternative routing, re-searching and signalling the period of delay to which a call is likely to be subjected will be clear from the detailed description that will now be given. In the drawing points indicated by like numerals in circles are to be taken as being joined together.

The coupling switches CSA and CSB are latchcontrolled motor-driven switches having l6 wipers each, each wiper being associated with a 50 point bank. Thus, the sender may connect itself to any one of 100 operator's positions. The switch motors are represented by their latch magnets designated MUA and MUB.

The senders are connected to a chain start circuit. There are actually two such circuits one for positions connected to switch CSA and the other for positions connected to switch CSB, re-

lays SA and SB being the starting relays for the corresponding coupling switches. Relay C is normally operated in a circuit extending over contacts m3 and b2, upper springs of the test jack TJ to earth. The chain start circuit is extended over contacts cl and 02 to relay SA and SB respectively. Since the functions performed by these two relays are similar it will be assumed for the sake of example that a demand for a sender is received from a position connected to switch CSB. Such a demand is made by an operator pressing a key earthing the wire marked In B. Relay SB thereupon operates and at contact sbl closes a circuit for relay C independently of contact 1113, at contact .9212 connects earth over contact ml to magnet MUB thereby completing the magnet circuit which includes relay RA, at contact sb3 connects earth to test relay TA, at contact sb4 lights the pilot lamp PL which thereupon glows steadily and at contact 8175 extends wire In A to wire Out A so that a demand from a position connected to switch CSA will be extended to the next sender along the chain. The latch magnet MUB and relay RA operate, the former connecting up the motor which thereupon rotates the switch at high speed in search of the position that created the demand. Relay RA operates its contacts which at contact ml connects earth to a delayed release alarm device, at contact m2 connects the pilot lamp PL over wire IE to earth, the connection being intermittently interrupted, and at contact m3 opens the original operating circuit for relay C. The position creating the demand is marked by battery potential on the wire con nected to the banks of wiper l3 of the coupling switch and when the marked contact is reached relay TA operates and at contact tal short circuits its right hand winding and removes a short circuit from relay B. The resistance in the circuit of magnet MUB is now too high for the magnet to remain held so the latter falls and stops the motor. Relay B operates. Contact bl connects battery over a resistance to relay B to hold the relay and opens a point in the circuit of magnet MUB. Contact b2 disconnects earth from relay C and connects earth to lamp PL, contact m2 now being back since relay RA released with the magnet MUB, and lamp PL continues to glow steadily, contacts b3, b4, b5 and b6 connect wipers DDZ-DDS of the digit distributor to wipers l-4 of switch CSA and thence to the corresponding wipers of switch CSB in readiness for digit reception and contacts bl and b8 connect earth to a number of circuits including one to relay BA. Relay C releases, extends the In start wire to the Out start wires and releases relay SB. During the time relay 0 is operated relay CO cannot be operated as the only possible circuit for the latter relay at this time is over contact 03. Relay BA operates. Contact bal disconnects earth from the homing circuits for the motordriven coupling switches and connects earth to wiper l6 of switch CSB to light a lamp at the position to indicate that a sender has been taken into use. Contact M2 is without useful effect at the moment, contact bail connects a termination consisting of a 600 ohm resistance and a 2 microfarad condenser to wipers 9 and I0 and thus across the X and W out-sending wires, contact ba l connects relay F to wiper 1 in preparation for a signal denoting that keying up has finished, contact bail disconnects earth from the homing circuit for the digit distributor and connects earth to the holding wire for the register relays and closes a self stepping circuit over the first contact, contact ddm of the magnet DDM and the magnet in which the digit distributor is stepped to its second position, contact bafi connects contact I in the bank of wiper S135 with the commoned contacts of the bank, and contact ba1 connects relay ZS to wire SP of a 30 second pulsing device. Reference to this arrangement will be made later. The position is now connected to the sender and the sender is in a condition to receive the first digit of the route designation.

Main trunk caZZ.-Such a call is indicated by the registration of 3 coded digits in the sender, the first digit being any numeral but and the first and second digits not being the combination 99, the third digit being 0.

It may here be remarked that the reception of the digit 0 results in the operation of the W and X relays in the sets of register relays and the digit 9 in the operation of the X and Y relays. Relay TC is operated in this class of call to bring about translation of the first two registered digits, the third digit being re-transrnitted untranslated.

The digits are transmitted from the key strip by the application of earth to one or more of the wires connected to the banks of wipers I to 4 of the coupling switches. On the first digit key being pressed the appropriate relay or relays in register A are operated in series with relay DS. Contacts of the register relays in tree formaticn mark a contact in the banks of wipers 12 of the translating switches MUG and MUD and in the bank of wiper 6 of the translating switch MUE. The operated relays lock up over their contacts I and contact bat. Relay DS operates and at contact dsl closes an operated circuit for magnet DDm, contact dsZ connects winding (II) of relay VF to wipers 5 of the coupling switches, contact ds3 disconects earth from wiper DDB and contact dls l is without useful effect at the moment. Magnet DDM operates and when thekey is released relay DS releases and the magnet armature falls back stepping the distributor to the 3rd position. In this position the second digit is recorded on. the register relay set BW-BZ and the distributor is stepped as before to its 4th position. The relays AX, AY, BX, BY not having been operated a circuit exists in this position after the release of relay DS as follows: earth, contacts 178, r55, vii, 1133, contact a203, or (m3, wiper DDB, contact z't3 one or more of the contacts (1x2, a115, em, b115, relay TO to battery. Relay TC operates and locks up over contact to! and starts the hunting of the translation switches. The controller now commences to step by self-interruption until the 17th position is reached. The circuit is from earth over contacts bl, rll and wiper SD! thence over bank contacts I, 2, or 3, contacts tc2, r82, sdm magnet SDM to battery. The magnet operates, interrupts its own circuit at its armature operated contact sdm and steps the wipers. Over bank contacts 4 and 5 the magnet circuit continues over contacts sat and dcl: over bank contacts 6 and I the circuit is the same as that over contacts l to 3: over bank contacts 8 and it it is over contacts loft and tc2; over contact 9 it is over contact dcl; over contacts H it is over contacts lc i and dot; over contacts 32 to it it is over contacts Z02 and 02. Contact 1503 prepares a circuit for relay ST to be completed when wiper SD4 reaches its 17th position. Contacts 1504 and tc5 close circuits for the translating switches MIUE and MUG, contact tcfi prepares a homing circuit for switch MUD to home this switch should it be off-normal and contact to! prepares a circuit for relay F, to be completed after the reception of the third digit. The circuit for magnet MUE is from earth over contacts 198, tdl, tc4, magnet MUE, relay RA to battery and that for magnet MUC is from earth over contacts b8, tbl, sw3, 1565, c155, cs2, magnet MUC, relay RA to battery.

The motors are started and the switches ,commence to hunt for markings applied to their banks in accordance with the register relays operated. Relay RA operates to close the delayed release alarm circuit and to connect intermittent earth to the pilot lamp PL. When the marked contact in the bank of switch MUE is encountered the folowing circuit is closed; earth over contacts b8, msfi, contact tree of the B register relays, bank contact and wiper I of switch MUE, relay TD, wiper 6 of switch MUE, bank contact and cross-connection to the contacts in the contact tree of register relays A, contact ms5 to I battery. Relay TD operates, releases the latch magnet at contact tdl thereby stopping the switch and operates relay ET. Similarly switch MUC is stopped on a marked contact in a similar circuit over wiper I4, relay TB, contact sy5 and wiper l2.

If the marking is on switch MUD instead of MUC the latter switch continues to rotate until its last contacts are reached whereupon the following circuit for relay TB is closed; earth over contact b8, last contact and wiper l4, relay TB, contact sy5, wiper I2 and last contact, shunt around left hand winding of relay SW to battery. Relay'TB operates followed immediately after by relay SW. Contact swl prepares a throw out circuit for the differentially connected right hand winding of relay SW, contact swZ holds relay SW to earth over contact 138, contact sw3 connects magnet MIUD in place of magnet MUC, contact swfl closes a homing circuit over oilnormal contact mucom' for switch MUC and contact swS opens the homing circuit for switch MUD. Swith MIUC homes and relay TB releases and at contact tbl connects up magnet MUD and switch MIUD hunts for the applied marking, and when it is found relay TB operates over wipers M and I2 of switch MUD to stop the switch.

The period during which relay TB is operated over last contacts of switch MUC, is so short, as the switch is moved ofi these contacts very shortly afterwards by the operation of relay SW, that relay CT will not be operated if relay ET should have been already operated. Even if relay CT does operate it will be immediately released again without producing any circuit changes. The operation of relay ET closes a circuit over contacts tbl and etZ for relay CT, opens the homing circuit of switch MUE at contact eti and prepares circuits for the delay working signalling relay DA at contacts 6753 and aid. Relay CT operates and prepares a holding circuit for itself over its winding (ID at contact ctl. Contact 0152 connects relays DA to wiper 9 of switch MUD, which if in its normal position extends the connection to wiper 9 of switch MUC, to determine if there is any period of delay on the trunk group marked. Contacts ct3 and ctfl prepare circuits for relays PY and SY, contacts c and cit open in the hunting circuits for magnets MUC and MUD, contact ct! prepares a circuit for stopping switch MUE on last contacts and contact ct8 connects relay N to wiper l5 of switch MUC or MUD for alternative routing purposes.

Meanwhile the third digit will have been registered resulting in the operation of relays CW and OK and the stepping of switch DD to its th contacts. The register relays lock up over their contacts I and at contacts 0102' and 011:2 close circuits including contact d2 for slow to operate relay CS, Contacts cw3, 0x3 and 0204, c334 connect relays PY and SY to wipers I0 and l I of switches MUC and MUD for the purpose of determining whether a direct or alternative route is to be taken. Contacts 5 of relays CW and CK prepare circuits for the transmission of the digit 0 to the 2nd trunk selector when it has been set by the second transmitted digit contacts 6 open in a possible circuit for relay CO and contacts i prepare a holding circuit for relay SS. As a result of the stepping of the distributor to its fifth position after the receipt of the 3rd digit, relay F is operated and this relay locks up over contacts fl and 178. Contact f2 prepares a circuit for relay CO to be completed when the controller reaches its 23rd position, contact 3 opens in a locking circuit for relay SR over winding (II) of that relay and contact 4 opens to prevent further operation of the register relays and relay DS. If a direct route is to be taken relay PY operates over its upper winding and locks up over its lower winding and contact pyl. Contact 12112 opens to prevent relay SY operating, relay SY being slow to operate so that PY can operate first, contact 12 13 opens in a circuit in parallel with contact ct'l now closed,

and contact py4 disconnects winding (II) 'of relay RS and connects winding (I) of relay CN in its place. The route to be taken, whether direct or alternative is determined by a group marking relay which maintains earth on the contacts in the banks of wipers ID and H of switches MUC and MUD so long as a free route is available. If the direct trunks of a group are all busy no earth will be present over wipers I0 and if an alternative route is available free earth will be found over wipers II and relay SY will be operated. Contacts syl and 8112 perform similar functions to contact pyl and p112, contact sy3 opens the battery connection to the last contact in the bank of wiper MUEB, contact 31 4 prevents the relay PY operating when relay CS is operated, contact s1/5 releases relay TB, contact syfi in conjunction with contact sy5 prepares an alternative circuit for relay TB, contact sy'l prepares a circuit for relay AF and contact sy8 closes in the circuit over which the 3rd digit is transmitted to give a different signal to the 2nd trunk selector which prevents this selector or routing the call to a storage equipment if the last alternative route trunk should have become engaged in the meantime.

If an alternative route is to be taken then on the release of relay TB relay CT releases and the translating switch MUC or MUD as the case may be continues to drive until a further marking is found or last contacts are reached. If switch MUC reaches last contacts relay TB operates over wiper l4 and the left hand winding of relay SW. Relay SW transfers the drive to switch MUD and homes switch MUC as before described and switch MUD hunts for the marking. When this is found relay TB operates to stop further drive. If switch MUD had found the original marking and the alternative route is marked on switch MUC then MUD would be driven to last contacts. Relay SW would have been operated and when last contacts are reached the right hand winding of relay SW is energised over wiper l3 and relay TB and relay SW is released by difierential action to transfer the drive to switch MUC and home switch MUD. Relay TB operates when the marked contact is found over wiper l3, bank contact and wiper 8 of switch MUE to battery and relay CT is re-operated. The operation of relay CS has the following results: contact csl locks the relay, contacts 082 and 083 open in the driving circuits of magnets MUC and MUD, contact cs4 operates relay PY if this relay or relay SY is not already operated and contacts 035 to 058 connect the relays of the G register set to wipers l, 3, 5, and 1 of the translation switch MUC or MUD. The contacts in the banks of these wipers are earthed in accordance with the code of the first digit to be sent out and the contacts in the banks of wipers 2, 4, 6, 8 are earthed in accordance with the second digit to be sent out. Accordingly one or more of the relays of the G register set are operated.

When the controller reaches its llth position relay ST was operated, the circuit being from earth over contacts T83, b1, wiper SD l, contacts tc3, 1Z3, right hand winding of Relay ST to battery. Relay ST locks up over its left hand winding, contacts stl, rll, b1, and rs3. Contacts st2, st3, st5 and stfi extend the out-sending signalling wires over wipers l0, 9, 8 and 6 of the coupling switch to wipers SD'I, SD3, SD2, and SDG in preparation for the transmission of the digits for setting the trunk selectors and disconnect the terminating impedance, and contact stl completes the out-sending circuit. It will be assumed here that the route to be taken is a direct route and that relay PY has been operated. The first translated digit is transmitted depending on the relays of register G operated over the odd numbered wiper of switch MUC. The out-sending circuit is from battery over contact tti, high speed relay TS, relay TT, contact stl, contacts 2 of one or more of the relays GW, GX, GY, GZ Ilth contacts in the banks of the controller, the corresponding Wipers, the out-sending wires to earth over code receiving relays in the 1st trunk selector. Relays TT and TS operate in this circuit, contact tsl maintaining the circuit after operation of relay TT. When the first trunk selector has been set earth is disconnected thereat from the digit transmission circuit and relay TS releases. Relay DC operates over contacts i152 and tsl during the release of relay TT which follows that of relay TS and at contact dcl closes a self-stepping circuit for switch SD which steps to contacts is and on the subsequent release of relay DC following the release of relay TT steps over the bank contact dcl to the 19th contact position. Contact dc2 closes a circuit for relay DE but the operation of this relay is without useful effect in the type of call under consideration. The relays of register G are released at contacts (103 to dcB. In position [8 of switch SD relay FD operated over wiper SDd and is maintained operated in position IQ of the switch. Contacts M2 to fdb disconnect wipers l, 3, 5, l of switch MUD and substitute wipers 2, 4, 6, 8 so that when relay DC releases the relays of the G register are connected to these latter wipers over which a translation for the second digit is found which brings about the re-operation of one or more of these relays. This second digit is transmitted in a similar manner to the first and sets the 2nd trunk selector to the beginning of the desired trunk group. Re-

lays TS, TT and DC operate as before described and switch SD steps to position 2!, relay FD being released in position 20, in preparation for the transmission of the 3rd digit which in the present example is represented by the operation of relays CW and OK. This digit is transmitted in a similar manner to the 1st and 2nd digits and the circuit includes contacts 0105, 0x5 and Wipers SD! and SD3. This digit causes the 2nd trunk selector to hunt in the marked group and when relay DC subsequently operates switch SD is stepped to contacts 23. In this position of switch SD a circuit is closed from earth over wiper SDtl, contacts ads, wiper DD? in position t, contacts rmii, f2, syl, 0112, relay CO to battery. Relay CO operates and locks up over contact col. Contact 002 applies earth over contact bafi to wiper l l of switch CS to bring about at the position circuit the opening of holding circuit and the release of relay TS, contact 003, opens to prevent operation of relay C whilst release of the register sender is taking place, contact co l connects the intermittent earth wire to lamp PL when relay RA is not operated, contact 005 earths wiper SDB until relay B has released, and contact 008 closes the delayed alarm circuit. Following the release of relay TA relay B is short circuited and released and earth is disconnected from the principal relay circuits at contacts b! and b8. Relay BA releases and at contact bal closes the homing circuit for the switches MUA and M'UB over their off-normal contacts muaonl or mabonl as the case may be and extinguishes the lamp at the operators position.

As a result of the opening of contact bl relays ST, DE release and as a result of the opening of contact b3 relays TC, TB, TD, F, ET, CT, CS and SW if operated and FY release. The homing circuit for switches MUS, MUD and MUE are closed over contacts muconl, mudonl and mueonl respectively and these switches are driven rapidly to their normal position. Following on the release of relay BA the homing circuit for the distributor is closed over contact b115, wiper DD! and self-interrupting contact ddm, and that for the controller over wiper SD5, con tacts rsl, but and self-interrupting contact sol'm and these two switches are homecl by self-interruption of their magnet circuits. When all the switches have reached their normal position a short circuit for relay CO is closed over contacts e05, 303, wiper SDll, contacts f2. rmt, wiper DDl' storing the register sender to a condition for further use by the closure of contact 003. Relay C thereupon operates and connects relays SA and SE to the chain start circuit.

If an alternative route is to be taken relay SY will be operated instead of relay l-Y and switch MUC or MUD hunts for the alternative route marking in the manner previously described. The 3rd digit in this case is transmitted as W, X, Y, contact syli closing in the out-sending circuit over wiper S132 in its 21st position. The effect of this code is to set the 2nd trunk selector searching and to prevent its routing the call to a storage position.

With contact syl in its front position relay Al operates when wiper SDft is stepped to its 23rd operator may now press a cancel key which' brings about the release of relay TA and by connecting earth to the contact in the bank of wiper M of the coupling switch operates relay CO'via contact 03 and points (1) and release of the register sender takes place.

If there is not an alternative to the direct route or no alternative route is available neither relay PY nor relay SY will be operated over the wipers of the translating switch but on the operation of relay CS relay PY will be operated over contacts sy i and cs l and the 2nd trunk selector will store the call.

If the last free alternative route trunk becomes busy while the 2nd trunk selector is hunting the selector will be stopped in a group busy position in which battery will be applied to the Z signalling wire resulting in the operation of relay RS over the Z signalling wire, wiper SD? in position 22, contacts 17 .1% and 4 and winding (II) of relay RS. Contact rsl disconnects contact l! in the bank of wiper SD5 and connects earth over the wiper and commoned contact to magnet SDM and over contact rs2 to winding (I) of relay RS to hold the relay. Switch SD now self-steps over the above traced circuit until position I1 is reached, contact baG being included in the circuit in position I of the switch and contact sol in position 4. Contact rsSopens to prevent operation of relay AF in position 23 and releases relay ST. Contact 1'54 operates relay PY which thereupon locks up over contact pyl and releases relay SY, and contact r56 connects earth to wiper 5 of the coupling switch to transmit a signal to bring about the release of the trunk selector. In position i! of the switch SD relay RS is released. Relay SY having been released the translating switch drives off in search ofthe direct route marking. The digits for setting the trunk selector to a trunk in a direct route are transmitted and the call is stored by the 2nd trunk selector.

If the alternative route taken leads to an automatic exchange it will be necessary to set switches in that exchange for completing the connection to the desired exchange. Alternative routes that require the transmission of an additional digit are marked by an additional marking on switches MUC and MUD so that relay N is operated over contact ct8 and wiper l5 of the translating switch. Relay N locks up over its left hand winding and contact 12! and b8, at contact 112 prepares a circuit for the possible operation of relay RS over its winding (I) and at contact n3 closes a circuit for relay AD over contacts syl and pyl. Relay AD operates and at contacts coil to add connects the relays of the D register to wipers l to 4 of switch MUE. Contact (1115 removes a short circuit from winding (I) of relay S0 to allow that relay to operate after the 3rd digit has been transmitted contact adl disconnects relay AF and prepares an alternative circuit for the operation of relay CO and contact aclt opens to prevent operation of relay CO in position 23 of the controller. One of more of the relays of the D register are operated according to the marking found on the bank contacts of wipers i to 4 of the switch MUE. After the 3rd digit (CW, CX, SY) has been transmitted the controller is stepped from position 2| and in position 22 the following circuit is completed: earth over contacts r33, bl, TZl, wiper SDI in position 22, winding (I) of relay SO, contacts dcl, r52, sdm, magnet SDM to battery. Relay SO operates and at contact sol connects winding (II) of relay SO in a circuit for magnet SDM over commoned contacts and wiper SD and the controller is stepped until position 4 is reached where the stepping circuit is found open at contact sol. Relay SO releases. Consequent on the operation of relay SO contact 802 closes an operating circuit for relay SS over its left hand winding, contact s03 opens the releasing circuit to prevent operation of relay CO while the controller is in position and contact 804 closes a circuit for winding (I) of relay VF over contacts m5 and b8. Relays SS and VF operate and contact cs6 locks relay SS over its left hand winding and in conjunction with contact of! locks relay ST independently of contact rll. Contacts ssl to ss4 disconnect the outsending wires from the wipers of the controller and connect them as follows. Wires W and X over contacts ss4 and s53, W4 and M5 to a source of voice frequency current dependent on closure of contact arl, wire Y over contacts ssZ and M2 to battery dependent on contact asl. Contact ss5 prepares a stepping circuit for the controller in position II, contacts of? short circuits relay VA and connects a termination consisting of a condenser and resistance in series in the voice frequency current supply circuit and contact vjfi closes an operating circuit over contact 302 for relay S. At contact 82 earth over contacts rs3, b! and TI! is extended over contacts 011.3,

006, $13, (1103, and 1203 to winding (I) of relay SN which operates and at contact sn! closes a circuit over contacts sn! and s! for relay A. Contacts s4, s5 and s6 connect relay SZ to wipers SDZ, SD3, and SD!, the connection to wiper SDG being made over contact ssl and contact s! closes in the connection to the first contact in the bank of wiper SD'I. Contact sn! closes an 7 operating circuit for DQ over its right hand winding and a circuit for relay X over the back contact of armature (12, contact S'IL3 prepares locking circuits for the counting relays and contact snfl prepares an operating circuit for relay CO. Relay X operates. Relay A is an impulse generating relay and the circuit for one of its windings includes a make-before-break contact controlled by relay A itself and the other winding is connected in parallel with the first over a condenser or condensers, the condensers connected depending upon rate of impulsing required. The relay on operating opens its operating circuit at contact a! and connects earth over contacts ml and s! to relays AR and AS and at contact a2 extends earth over relay X and contact 1:! to the counting relays. Contacts er! and as! close signalling circuits as follows: contact a1! completes the voice frequency signalling loop for the transmission of voice frequency impulses over the trunk to the intermediate exchange in the connection and contact as! connects battery over contact $22 to wire Y for the transmission of D. C. leg impulses. The distant switches will respond to the voice frequency impulses brought about by release and operation of relay AR and the D. C. impulses will be without efiect as they will be suppressed at an outgoing repeater. At contact a: a circuit is closed in series with relay X over contacts 0112, e02, 003, cb2, c193, ca2, cb l for the right hand winding of relay CA. Relay CA locks up over contacts cal and S112 short circuiting relay X, and at contact caZ disconnects its operating circuit and connects up relay CB over contacts cc4. Before this occurs relay X which is quick to operate and release has released. Contact ca3 connects relay SZ to wiper SD'l. In

position 4 of the controller earth over contact 22:15 and one or more of the locking contacts dwl, dxl, dyl, dz! is connected to the 4th contacts in the banks of wipers SDS, SD2, SD3, SDI. If only one impulse is to be transmitted relay SZ will operate over wiper SD! and contact dz! to terminate impulse transmission. If more than one impulse is to be transmitted relay SZ will be short circuited over one or more of the contacts cd l, cc5, or c and the relevant locking contacts of the register relays and succeeding impulses generated by the continued operation and release of relay A will cause relays CB and so on to be operated in turn and at the same time impulses will be transmitted at contact arl. When no short circuit for relay SZ exists that relay operates from earth over the relevant register relay locking contact or contacts, front contacts of the counting relay or relays, contact asl, to battery. A more detailed description of the operation of the impulse generating and counting arrangement is given in British Patent Specifications Nos. 462,773 and 471,987. Relay SZ locks up over contacts v02, 32!, b! and rs3 and at contact s22 opens the D. C. leg signalling circuit and prepares for the possible operation of relay RS, and at contacts s23, opens the voice frequency impulsing loop and connects the condenser and resistance formerly included in the circuit over the wire W across the trunk as a termination. Relay SR operates in the locking circuit of relay SZ and at contact sr3 releases relay SN. contact sr l opens the operating circuit for relay SZ. contact 8T5 prepares a holding circuit for relay VC and contact srB prepares an operating circuit for relay DP. Contact sn! opens the circuit for relays A, AR, and AS, contact sn2 releases relay DQ and contact s1t3 releases the operated counting relays. Release of relay DQ closes a circuit over contacts b8, arG, dq! and tip! for winding (I) of relay DP. Relay DP operates and locks up over contact dpl. Contact dp3 recloses the circuit for relay SN over the front of contact sr3. Relays SN, DQ and A re-operate and relay A generates impulses for measuring ofi a pause to permit of a reverted signal being received before the register sender is released. Contact dpd permits a different capacity being connected to relay A to alter the speed of impulsing. Operation of relays AR and AS is ineffective because the impulse repeating circuits are open at contacts of relay SZ. The counting relays allow 10 impulses to be counted whereupon relays CA, CB and CC being operated a circuit is closed over contacts 173, dpZ, cbfi, cot and ca l for the left hand winding of relay VC. Relay VC operates and locks up over contacts vcl and sr5. Contact 2102 prepares for the release of relay SZ by leaving that relay dependent on continued closure of contact dql, contact 003 releases relay SN. Relay DQ releases and releases relays SZ and SR, and relays DP and VC thereupon release. The counting relays are released. Relay VC is slow to release and after the release of relay SR a circuit is closed from earth over contact 8T2. winding (II) of relay DP, contact vc4, magnet SDM to battery. The magnet operates and on the release of relay VC steps the controller to its 5th position. In this position earth over wiper SDS is extended over contact a118, 5th contact in the bank of wiper DD! contacts rmfi, f2, syl, ad'l, 017.2 to relay CO. Relay CO operates and the register sender is released.

If the distant selector encounters congestion a signal of voice frequency current is reverted and at an outgoing repeater in the trunk exchange or other convenient circuit is converted into a D. C. signal in the form of earth applied to wire Y. This signal is received during the measured pause after the transmission of the voice frequency impulses and operates relay RS, the circuit being over wire Y, contacts st5, ssZ, M2, s22, n2 and winding (I) of relay RS. Relay RS locks up over this winding, contacts rs2, rsl,

sol and wiper SD5 in position 4 and the controller is stepped to position I! where it is stopped by reason of the connection to the 17th contact in the bank of the wiper SD5 in the switch magnet stepping circuit being open at contact rsl. Relay RS holds during the stepping of the controller in the manner previously described. Contact rs4 operates relay PY which releases relays SY and AD at contact syl. The connection is released consequent on the closure of contact rs6 and the switches in the trunk exchange are set to store the call in the manner before described.

If the operator wishes to route the call via a direct route irrespective of whether this route is congested or not she presses a special key instead of the key for the 3rd digit. This results in the operation of relays CW, CX and CY. Relay PY is thereupon operated by means of its upper winding over contacts sy2, 0:03, cw3, ct3 and 0113 independently of the translating switches and the call is routed via the direct route or stored as the case may be.

If in the setting up of a connection over either a direct or an alternative route the 1st trunk selector encounters congestion relay RL is operated. In the type of call under consideration this occurs in position iii of the controller. The congestion signal is the application of battery to the Z wire and this effects the operation of relay RL over wiper SDB, contacts sn5, rmfi and winding (I) of the relay. The relays locks up in series with winding (11) of relay DC over contacts rm and-rll. Relay DC being held the self-stepping of the controller is prevented. Contact r23 prepares a circuit for relay RM. At contact rll relay ST is released and a circuit is closed over contacts sl and al for relay A which commences to generate impulses. The speed of impulsing is controlled by contact 122 which nullifies the effect of the change over of contact fdl. Contact 124 connects earth over contacts rll, sl and al to magnet SDM so that this magnet is operated at each release of relay A whereby the wipers of switch SD are stepped slowly round their banks to measure 01f a time interval. Contact 715 removes a short circuit from winding (I) of relay DC to ensure that this relay releases before relay RL. Earth is applied to wiper 5 of the coupling switch over contact 116 to bring about the re-setting of the 1st trunk selector to its normal position. The controller is stepped until contact I1 is again reached whereupon relay RM is operated over wiper SD4, contacts tc3, 1'13, and the right hand winding of the relay. The relay locks up over contact ml and at contact rm5 releases relays RL and DC and stops further impulse generation by relay A. Contact rm substitutes winding (I) of relay CN for winding (I) of relay RL in the connection to contact l8 in the bank of Wiper SDG, contact rm3 prepares a circuit for the left hand winding of relay RM over contact 23 in the bank of wiper SD4 and contact rmfi opens in the circuit over wiper DD! for relay CD. Release of relay RL operates relay ST at contact 113 and the locking circuit for relay ST is Ire-prepared at contact TN. The first digit is again transmitted and if the first trunk selector is able to find a free outlet in the required group the remainder of the digits are transmitted as before described and when switch SD reaches position 23 the left hand winding of relay RM is energised to release the relay by differential action. If, on the contrary, congestion is still encountered relay CN operates over the Z wire and locks up over its winding (II) and contact cnl. I

Contact 0114 applies earth to wiper l2 of the coupling switch which is extended to the position circuit to light a lamp thereat indicating a state of congestion. The operator presses the cancel key operating relay CO to initiate release of the register sender.

If a dead number is keyed no cross connection will be present to the banks of switches MUC and MUD. Switch MUE tests on the contacts marked by the A and B registers or if no contact is marked it drives to a last contact position in which relay TD operates in a circuit from earth over contact b8, last contact and wiper I of switch MUE, relay TD, wiper 6 and last contact, contacts sy3 and 3 to battery. Relay ET operates. Switch MUC drives to last contacts where it is stopped by the operation of relay TB in a circuit from earth over contact b8, last contact and wiper M of switch MUC, relay TB, contact sy5, wiper I2 and last contact, left hand winding of relay SW to battery. Relay SW operates and locks up over contact swZ. Contact sw4 closes the homing circuit for switch MUC which is driven to normal. Relay TB releases. Earth over contacts tbl and sw3 is now extended to magnet MUD and switch MUD drives to its penultimate contacts whereupon relay TB reoperates from earth over contacts b8, penultimate contact and wiper M of switch MUD, relay TB, contact 51 5, wiper l2 and penultimate contact, contacts sy3 and 101113 to battery. Relay CT operates and a circuit is closed from earth over winding (II) of relay SN, penultimate contact and wiper 15 of switch MUD, contact 0228, right hand winding of relay N to battery. Relay SN operates but relay N does not. Contact ct! holds relay TD against the operation of relay PY which is about to take place. After the third digit has been registered relay CS is operated and contact 054 closes a circuit in which relay PY operates. Meanwhile the controller has reached position I! and relays ST and F have been operated. The relays of the G register are connected by contacts cs5 to cs8 to wipers I, 3, 5, 1 of switch MUD and the penultimate contacts on the banks of these wipers are cross connected to bring about the operation of relays GW, GK and GY. The out-sending circuit is now closed over relays TS and TT, contacts 2 of relays GW, GK and GY and the 1st trunk selector is set to contacts associated with a source of NU tone which is thereupon transmitted to the operator. On the release of relay TS relay DC operates and switch SD is stepped to position I8 in which winding (I) of relay CN is connected over contact to wire Z. In the N. U. tone position of the 1st trunk selector battery is connected to wire Z resulting in the operation of relay CN. Relay CN locks up over its winding (II) and contact cnl, contact cn2 closes a circuit over contact ml for relay CO, contact c'n3 releases relay SN, contact 0114 connects earth over wiper I2 of the coupling switch to light a lamp in the position circuit and contact 0115 prepares a connection to an overflow meter which is ineffective in the present case. The operation of relay CO brings about the release of the register sender. The aforementioned operations presuppose contacts available on the 1st trunk selector for N. U. T. purposes and the utilisation of the code W, X, Y for this purpose. If for any reason these facilities are not available, and the code W, X, Y effects the'setting of the 1st trunk selector to a free 2nd trunk selector, a second digit must be transmitted to set the 2nd trunk selector to N. U. T. contacts. This is taken care of by suitable cross connections to the penultimate contacts in the banks of wipers I, 3, 5, I of switch MUD. After the transmission of the first digit switch SD steps to position I8 in which relay FD is operated and then to position IS in which relay FD is held. Contacts 2 to 5 of relay FD connect the G register relays to wipers 2, 4, B, 8 of switch MUD, and a translation provided by means of cross connections to these contacts causes the 2nd trunk selector to drive to the contacts connected to the source of NU tone which is thereupon transmitted to the operator. Relay CN operates as before to initiate the release of the register sender.

If a connection is to be made to an individual trunk the 3rd digit will not be but one of the digits 1 to 9. In this case relays CW and CK will not be operated so that relays PY and SY cannot operate over the group control connections. After the third digit has been received relay CS operates and at contact cs4 closes an operating circuit for FY and the call is set up as previously described for a call via a direct route with the exception that the third digit, which is untranslated is a number other than 0.

If, under any of the conditions before referred to delay working on a group of trunks is in force a distinguishing potential will be present on the relevant contacts in the banks of wipers 9 of switches MUC and MUD for main trunk groups and in the bank of wiper 5 of switch MUE for minor trunks. After the second digit has been registered and switch MUE has found the contact marked by the relays of the A and B registers relays ET and CT are operated. Contacts et3 and e154 connect the two windings of relay DA in series and their mid-point to Wiper 9 of switch MUD over contacts (14 and 0252. If no potential is present on the bank contact relay DA is not operated because its windings are connected in opposition. If delay working is in force the bank I contact will have one of three potentials applied to it; either (i) flicker earth and battery (ii) interrupted earth and battery or (iii) steady earth. In any of these cases relay DA will operate on one or other of its windings and at its contact daI will connect relay D over contacts dbl and b8 to earth. Relay D operates and locks up over contact dI. Contact d2 opens to prevent operation of relay CS, contact d3 connects winding (II) of relay DB to wiper 1 of the coupling switch, contact d4 disconnects relay DA and extends the connection over wiper 9 of switch MUD to wiper I5 of the coupling switch over points (3) and contact 3% and contact d5 holds relay CT over its winding (II) and contacts ctI, cs4 and 728. The delay signa1 is thereby repeated to the position circuit where a lamp is flickered, flashed or caused to glow steadily to indicate one of three periods of delay to which calls over the group of trunks in question will be subject. The

register sender is released without any digits being transmitted by the depression of the cancel key by the operator whereby relay CO is operated over wiper I 4 of the coupling switch.

Minor trunk calls Calls to these trunks are made by keying the numerals 990 which efiect the setting of the 1st and 2nd trunk selectors leading to the 3rd trunk selectors to which minor trunks are connected. Two more digits are then keyed to select the minor trunk group required. In a call of this kind switches MUC and MUD are not driven in search of a marking as relay TC, the operation of which is necessary for the starting of switch MUC, will not be operated in position 4 of the distributor as its connection to the bank of wiper DD8 will be open at contacts of the A and B register relays. The numeral 9 is represented by the code XY so that relays AX, AY, BX, BY will be operated by the first two digits and contacts of each of these relays will open the only possible operating circuit for relay TC. In the C register relays CW and CK will be operated and after receipt of this digit which DD will be stepped to position 5. The 4th digit will be received on the relays of the D register and the 5th digit on the E register after which the distributor will be stepped to its 7th position. In this position earth is connected over contacts b8, rs5, ofl, ds3, aw3, wiper DD8, relay MS, contact ztI, to relay MT and relays MS and MT operate. Contact msI closes an operating circuit for relay F, contact ms2 connects up magnet MUE over the back contact of armature 1504, contact ms3 prepares the circuit for relay CT in the place of contact tbI since relay TB will not be operated and contacts ms5 and ms6 disconnect the marking contacts of the A and B registers and connect contacts of the relays of the D and E registers to the marking terminals which are cross connected to the marking switches. Contact 1nt2 holds relays MS and MT independently of switch DD, contact mt5 closes a circuit for stepping switch SD to position I! similar to that closed by relay TC, contact mt I prepares a circuit for relay ST similar to that closed at contact 1503, contact mt5 connects wind ing (I) of relay RL in place of winding (II) of relay RS and contact mt6 closes in the delay signalling wire for minor trunks over wiper 5 of switch MUE. Switch MUE is driven in search of the contacts marked by the D and E register relays and is stopped by the operation of relay TD as in the case of a main trunk call. Relays ET, CT and CS are operated. Contact cs4 operates relay PY and contacts cs5 to cs8 connect the relays of the G register to wipers I, 3, 5, I, of switch MUD. In position I! of the controller relay ST is operated and locked and the out-sending wires are connected by switch SD to battery over contacts of the operated relays of the G register and relays TT and TS. The normal contacts in the banks of wipers I to 8 of switch MUD are marked in a manner which will bring about the setting of the 1st and 2nd trunk selector to an outlet to a free 3rd trunk selector and the first digit transmitted will be in code form and in accordance with the operation of the relays of the G register operated by the marking provided over wipers I, 3, 5, I of switch MUD. After the digit has been transmitted the relays of the G register are released and switch SD is stepped to position I9 and in passing position I8 relay FD is operated to connect the relays of the G register to wipers 2, 4.

6, 8, of switch MUD whereby the. second translated digit is transmitted. After thetran'sm'ission of this digit the relays of the G register are released and the controller is stepped to position 2|, relay FD releasing in position .20.

In position 2| the code WXY is sent out consequent on the closure of contacts 0105, x5, and msl, to prevent the call-being stored if congestion is encountered by the 2nd trunk selector after which switch SD steps to position 23. Since wiper DD! is not resting in position but in position I no circuit is made for reIayCO and wipers SDS, SD2, SD3 and SD! are connected over those contacts d103, (111:4, dy5, dyB of the relays of the D register which havebeen operated and the 4th digit transmitted is in accordance with the 4th registered digit. Switch SD is then stepped to position 25 in which the digit transmission circuit is completed over those contacts e203, ew l, ew5, ewt of the relay of register E which have been operated. After this digit has been transmitted and relay DC has been operated, earth over wiper SDI is extended over relay MC and contact dcl to magnet SDM. Relay MC operates and at contacts I to 4 opens the out-sending circuit and at contact mc5 operates relay CO which brings about the release of the register sender.

' In calls of this type the 2nd trunk selector gives access to 3rd trunk selectors and relay MT is operated and locked. In congestion is encountered by the 1st trunk selector the action is as described in connection with a main trunk call.

If congestion is encountered by a 2nd trunk selector the selector will drive to an overflow position in which a circuit will be completed for relay RL over wire Z, wiper SD6 in position 22, i. e. after the controller has stepped on after the transmission of the 3rd digit, contacts mt5, rmd, and winding (I) of the relay. The controller is stepped round to'position I1 and action thereupon takes place as described for a main trunk call. If congestion is encountered a second time relay CN is operated and with wiper SD4 in position 22 an overflow meter is operated over that wiper and contact 0115. v

If a dead number is keyed the 3rd trunk selector is driven to a position in accordance with the 4th and 5th digits keyed and the relevant contacts in this trunk selector will be connected to a source of N. U. tone.

If a number other than 0 be keyed for the 3rd other than 0 setting trunk selectors of the lattergroup to an individual trunk in a selector group. Release of the register-sender in the case of a wrong 3rd digit takes place by the operation of relay CO in position 22 of switch SD over wiper SDB and contacts ms t and cw6 or 0936.

If delay working is in force relay DA will be operated over contacts mtfi and wiper 5 of switch MUE and the appropriate signal will be transmitted to the operator, relay D operating andpreventing operation of relay CS whereby digit transmission is prevented. If, instead of depressing the cancel key to operate relay CO and release the register sender the operator presses a finish key, earth is connected over the contact in the bank of wiper 5 of switch CS and relay BB is operated by means of its winding (I) and relay F is held. Relay DB locks up over its winding (II) and contact dbL'releasing relay D thereby permitting digit transmission to proceed.

Trunk calls requiring the keying of additional digits When the register sender is taken into use a 1st trunk selector is seized and after the trans-, mission of the first three code digits the sender is automatically released. If, however, the operator should have to transmit furtherdigits the Y sender can be caused to re-associate itself with the position and the 1st trunk selector even though it is busy and the further digits, up to 7 in number can be keyed up and registered in the register sender. These digits are sent out as trains of voice frequency loop impulses. the register sender has become connected to the 1st trunk selector the distributor is stepped to position} and the first additional digit isregistered on the A registen, Relay DS operates and at contact dsZ connects winding (II) of relay VF to wiper 5 of switch CS. In the engaged condition of the 1st trunk selector earth is connected. to the contact in the bank of wiper 5 of the cou-.

pling switch and relay VF operates and locks up over its winding (I). The change over of contact of! prevents operation of relay TC and consequent translation of the keyed up digits.

Closure of contact 11]6 operates relays S and SS and following on the operation of relay SS,

and closure of contact s86 relayST operates over contact of! and the left hand winding, of the relay. Relays VF and SS connect the W and X Wires to the source of Voice frequency current, the circuit including the contact art, and con-' tact s3 closes in a circuit over contact 8 in the bank of wiper SD8. Relay SN is operated at contact 82 to operate relay A to start impulse generation and counting, relay AR operating at each release of relay A to close the voice frequency impulsing loop. At the same time a leg.- circuit is closed over contact as! and wire Y but these impulses are without effect: either they, are ignored at the outgoing repeater or are suppressed. The impulse counting relays are operated in succession until relay SZ operates consequent on earth being found overone or more of the operated contacts 0:13, 0735, 005, ed t and absence of earth overthe unoperated contacts, the earth being applied over'the locking contacts of the relays of the A register and wipers of the controller in position I. The operation of relay SZ terminates the impulse train by opening the loop and operating relay SR which efiects release of relays SN and DQ and the timing of the inter-train pause.

At the end of the pause which is measured by the time taken to generate 8 impulses relay'VC' is operated and relay SR released whereupon:

magnet SDM is operated over contact $11,. winding (ID- of relay DP and contact not during the slow release of relay VC. When relay VC releases the controller steps to position 2 and relay DP releases to reclose the circuit for relay SN all the keyed digits have been transmitted. After:

the operator has keyed the last digit she presses the .finish key and relay F is operated by means of its winding (II). When the last digit has been transmitted the circuit for relay CO is nowcom pleted over wiper SDB in position 8, contact '83 After By this time other digits will and wiper DB! in position 9 and the register sender is released.

Special trunk calls Special trunks are trunks between important centres and calls to be made over them are set up by keying a special digit as a first digit, any of the numbers 1 to as the second digit and 0 as the third digit. The special digit is represented by the code WXY and this is translated to the code WXZ for transmission to the 1st trunk selector.

After the registration of this digit and the operation of relays AW, AX, AY the distributor is stepped to position 3. Relay IT is operated in a circuit from earth over contacts b8, rs5, oil, ds3, asc3, awZ, ay6, left hand winding of relay IT to battery. Relay IT locks up over contact itl and relay MT. Contact it2 closes to maintain earth on wiper DD8, contact it3 opens the operating circuit for relay TC and contacts it5, it! and it8 connect earth over contacts (Z92, de4, and 1165 to operate relays GW, GX and GZ. Consequent on the operation of relay MT and closure of contact mt3 switch SD steps to position I! in which position relay ST is operated and locked up. The digit transmission circuit is closed and the code WXZ is transmitted for the setting of the 1st trunk selector and the controller is stepped to position [9. During the time relay-DC is operated after the transmission of the special first digit a circuit is closed for relay DE from earth over contacts T83, b1, rll, i754, dc2 relay DE to battery. Relay DE operates and locks up over contact del and at contacts deZ to de connects the relays of the G register after release of relay DC, over the locking contacts of relays BW, BX, BY and B2 and contact bail to earth.

By this time the second digit has been recorded and relays GW to G2 are operated according to the digit received over the locking contacts of the operated relays of the B register and contacts of relays DC, IT and DE to close circuits over the appropriate out-sending wires for the setting of the 2nd trunk selector. After the second trunk selector has been set relay DC is operated the relays of the G register are released and switch SD stepped to position 2 l. The 3rd digit is registered by relays CW and CX but relays CS and CT are not operated. The 3rd digit, like the second is transmitted without translation but the out-sending wires are marked by closure of contacts owl and 0x5. After registration of the 3rd digit the distributor is stepped to position 5 and after transmission of this digit switch SD is stepped to position 23. A circuit is now closed from earth over wiper SDB, contact ad8, and wiper DD! for relay CO, relay F being operated in position 5 of the distributor over contact it2, wiper DDS and contact mtl. Relay CO operates and release of the register sender takes place.

Congestion encountered by the 1st trunk selector results in the operation of relay RL as in the case of a main trunk call and congestion encountered by the 2nd trunk selector results in the call being stored.

Local calls Calls to be completed locally are made by prefixing the directory number with the numeral 0." The first digit 0 effects the setting of the first trunk selector and the second digit effects the setting of the first local selector. Any further digits are transmitted as impulses and set numerical selecting switches in the usual manner.

If the call is to a manual exchange in the area only two digits are keyed followed by the depression of the finish key. The first key pressed is the 0 key and results in the operation of relays AW and AX. The digit switch is then stepped to position 3 on the release of relay DS Where a circuit is closed over contacts b8, rs5, vii, ds3, a503, aw2 and ay6 for relay LC. The relay operates and locks up over contact 10!. Contact 202 closes a stepping circuit for switch SD which steps to its 8th position in which the stepping circuit will be found open at contact 103. Contact lc4 removes a short circuit from winding (III) of relay SS, contact closes an operating circuit over wiper SD4 in position 8 for relay ST and contacts 106, lo! and Z08 prepare circuits for winding (II) of relay FD which are completed over cross connections to marking terminals II to 20 as required for cutting out some of the condensers and shunting a resistance across the condensers which have been cut out to increase the rate of impulsing. The second code digit is received on the B register and the distributor is stepped to position 4 but as contacts aw3 and ax3 in the circuit over wiper DD8 are both open relay TC is not operated. Following the operation of relay ST the out-sending circuit is closed and the first digit 0 is transmitted over wipers SD'I, SD3 and wires W and X and after this digit has been received by the 1st trunk selector relay TS is released and relay DC is operated. At contact do! a circuit is closed for stepping switch SD to position In. In position ID the 2nd digit is transmitted untranslated by the closure of one or more of the contacts bw4, M6, by'!, be! and the 1st local selector is set. Switch SD then steps to position H whereupon relay SS operates over its winding (III) and locks up over its winding (II) and contact cs6. Contact ss5 short circuits winding (III) of relay SS and the magnet SDM operates and by itself release steps the controller to position [2. Relay SS prepares the circuits for impulsing and relay FD operates over wiper SD4 and contact rm2 to prepare for fast impulse transmission. As, however, in the call under consideration only two digits are necessary the operator depresses the finish key and relay F operates over its winding (II) and wiper 1 of the coupling switch. The following circuit is then completed; earth over contacts rs3, b1, rll, e05, 803, wiper SDB, 4th contact and wiper DDI, contacts rmG, f2, sy'l, 0122, relay CO to battery. Relay CO operates and contact col connects battery over a resistance to wire Y to switch in a bridge in the 1st local selector. Release of the register sender takes place as before described.

If the call is to be set up wholly by automatic selecting switches further digits up to 7 in all are keyed and these are registered on the C, D, E, F, G registers or as many of them as may be necessary. In this case relay F will not be operated after the 2nd digit has been registered. Relay FD is operated in position I2 of the controller and may lock up over its winding (II) if the cross connections permit to cut out one or more of the condensers from the circuit of the right hand winding of relay A to increase the speed of impulse transmission. Following the operation of the relays of the C register one of the contacts 0201, 0x1, 0114, cad will be closed and relay S will be operated. Contact 52 extends earth to relay SN and this relay operates and at contact snl closes the circuit of relay A. Contact snZ operates relays DQ and X and contact .9113 prepares a locking circuit for the counting

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