US1951134A

US1951134A - Telephone system

Info

Publication number: US1951134A
Application number: US583051A
Authority: US
Inventors: Dixon Reginald Griffith
Original assignee: Siemens Brothers and Co Ltd
Current assignee: Siemens Brothers and Co Ltd
Priority date: 1930-12-24
Filing date: 1931-12-24
Publication date: 1934-03-13
Anticipated expiration: 1951-03-13
Also published as: GB366669A

Description

arch E3, 1934, R. ca. DIXON TELEPHONE SYSTEM Filed Dec. 24. 1931 3 Sheets-Sheet l f n. w .5 6 m Y W J l l H m I. E v d6 I QIRWM% L11??? fi T E 5 W Y a 2m. flmm fig E E MMMM E m L/ Eg 5 W E w 5 -M EQ 2/ @222. 5 E, gi: Eff

Mamh 13, W34. R. G. DIXON TELEPHONE SYSTEM Filed Dec. 24, 1931. 3 Sheets-Sheet 2 Inuan :11- Eaainald Er'TmTh Dixon March 13, 1934. R. e. DIXON 1199119134 TELEPHONE SYSTEM Filed Dec. 24, 1931 s Sheets-Sheet s TY i tzl v '17 .lmmi b \{fiE-EIHIF Y Z BTl:

ITLUET'LtCII" Patented Mar. 13, 1934 PATENT CFIQE.

TELEPHONE SYSTEM Reginald Griffith Dixon, London, England, as-

signor to Siemens Brothers & Company Limited,

London, England Application December 24, 1931, Serial No. 583,051 In Great Britain December 24, 1930 14 Claims. (Cl. 17918) The present invention relates to automatic telephone systems and is especially suitable for systems employing line finders.

In this invention a switch has its outlets grouped, each group being connected to a difierent multiple, the multiples being associated with diiferent switching stages, and the switch operates as a backward hunting or forward selecting switch as required, the group of outlets in which the switch performs its himting or selecting movements being determined by the function of the switch, i. e. whether it is operating in a backward hunting or forward selecting capacity.

Two such switches may be connected to the ends of a link circuit, the link circuit being connected to the switch wipers, and either switch may operate as a backward hunting switch as required, the other then operating as a forward selecting switch.

As regards the outlets of a switching stage these may be divided into groups, one group being accessible to one switch of the pair and the other group to the other switch of the pair.

For co-operating with the outlets of the two switching stages, a switch may be provided with two wiper sets, one set being used when the switch operates as a backward hunting switch, the other set being used when the switch operates as a forward selecting switch.

The determination as to which switch of a linked pair is to operate as a backward hunting switch and which as a forward selecting switch may be made in a control circuit common to a group of linked switches, and the association of a control circuit with a particular link may be effected by a hunting switch. The control circuit preferably comprises the necessary arrangements for stepping the switches, and for the control of the forward selecting switches, is preferably provided with impulse receiving and repeating arrangements.

A pair of linked switches according to the invention may be employed as a line finder and group selector, incoming lines being divided into two groups, one group appearing as outlets in one switch and the other group as outlets in the other switch, outlets to a succeeding switching stage being similarly connected so that the two switches may operate on different groups. The switches are conveni ntly 200 point switches having two banks of 109 outlets each, and two switching relays only are required.

For the better understanding of the invention reference will now be had to the accompanying drawings which show byway of example an embodiment of the invention. In the drawings Fig. 1 shows a link circuit comprising two switches either of which may act as a, call finder, the other acting as a group selector, and Figs. 2a and 21) show a control circuit associable with any one of a number of link circuits for controlling the operation of the switches of a link circuit.

The link circuit shown in Fig. 1 comprises two switches A and B, the former represented by the wipers AFl, AF2, AF3, ASl, ASZ, A53 and magnets AV, AR, and AZ and the latter by the wipers BFl, BFZ, BF3, BS1, BS2, BS3 and the magnets BV, BR and BZ. Each switch has included in it a set of level marking contacts ANP, BNP which are engaged by a wiper having movement in a vertical direction only and vertical off normal contacts denoted by the letters an and 1m with a numerical sufiix and rotary off normal contacts curl and bnrl. Each vertical and rotary magnet has an armature operated contact designated at, be and a1, br respectively while as and bs are contacts which are closed when the wipers of switches A and B are stepped respectively to the 11th contacts in a level. Two switching relays HA and HB are provided, one for each switch, the relay operated being that corresponding to the switch used as a group selector in a connection.

Each switch has 6 wipers and corresponding banks. Wipers AFl-AF3 engage banks connected to one group of 100 subscribers lines and wipers BF1BF3 engage banks connected to another group of 100 subscribers lines, while wipers AS1AS3 and BSl-BSB engage banks connected to 2 groups of 100 outlets each. The incoming subscribers lines of one group which will for convenience be termed group A are connected to switch A while the incoming lines of the other group, group B, are connected to switch B.

The lines of a group are connected in levels of 10 contacts each in the usual manner and a common starting wire from the line circuit is provided for each level of lines. These starting wires are connected to the level marking contacts in the banks of the respective switches, the contacts being multipled over a number of switches, and also over suitable resistances to a start relay A in a control circuit, there being a start relay A for each group of lines, the start relays being in different control circuits.

A control circuit is shown in Figs. 2a and 2b and it will be seen that the start wires SWA associated with group A of incoming lines are normally connected to relay A but should the control circuit shown be in use when a call is made the start circuit is extended to a start relay B in the alternative control circuit, viz. that normally associated with group B of incoming lines. Similarly a call originating in group B normally causes the operation of the start relay A in the alternative control circuit shown in Fig. 2a, but if this circuit is busy the start circuit is directed to relay B of the control circuit shown fully. The two control circuits are similar and the operations concerned with the circuit shown only will be described.

Associated with the control circuit for the purpose of connecting it to a free link circuit are two single motion switches denoted by the wipers PAl-PA8 and PB1-PB8, the switch magnets being denoted respectively by PADM and PBDM;

of these switches, the bank contacts of wipers PA2PA8 and PB2PB8 are multipled over the switches of the two control circuits while the bank contacts of wipers PAl and PBl are not so multipled. Besides the relays mentioned the following are the principal relays: AS and BS are discriminating relays for determining which switch is to be used as a call finder and which as ,a group selector, RD is used to determine when the level in which a line is calling has been reached by the call finder, H is the line test relay for the calling line, AC the impulse relay, 'CC 2. dialling relay, HC the test relay for the group selector, G an interacting relay for effecting stepping of both switches and PX a relay controlling the aligning of switch PB with switch PA. Switches PA and PB are normally resting with their wipers on contacts connected to a free link circuit and when they are stepped on to such a circuit the switches A and B of that link circuit which after use are left in the positions in which they were last used are restored to their normal positions. For the purpose of description of the operation of the circuits shown this will be taken as a starting point and relay PX will be operated and held over its winding (I) and contacts p921 and sp i. In this condition the circuit of relay ET is open at contact 10532 and a point in a circuit for relay T is closed at contact p003.

It will now be assumed that the control circuit is free and in the above condition and a call is originated in group A. Earth is connected to the start wire SWA corresponding to the level in which the calling line is situated consequent on the operation of the line relay and the appropriate contact in the bank ANP is marked. The earth on the start wire also operates relay A '-over the resistance in the starting wire circuit,

contact M of relay B in the alternative control circuit, contact hfi of the control circuit shown and windings (I) and (II) of relay A to battery. Relay A locks up over its winding (II) contacts a1 and 1202 and opens contact cal to prevent operation of relay B in the alternative control circuit, when the calling line is found. Contact a2 prepares for engaging the link circuit, contact a3 prepares a circuit for discriminating relay AS and contact a5 closes a circuit for relay T. Relay T operates and at contact t1 connects earth for the operation and holding of many of the relays and completes the circuit of relay AS which operates and locks up over its contact asl independently of relay A. Contacts t2 and t3 disconnect relay SP and in conjunction with contacts 112 and (132 connect earth to the test wires of the link circuit to mark the latter engaged. Contact t4 connects winding (I) of relay G to wiper PA2, contact 156 connects winding (II) of relay G over contacts m2 and 7356 to wiper PBB and contact t5 closes a point in the circuit of vertical magnet BV of switch B which in the case of a call origi nating in the group A of incoming lines will serve as a group selector. The operation of relay AS closes at contact cs5 a circuit for vertical magnet AV of switch A which will act as a call finder and at contact cs4 prepares a circuit for the rotary magnet AR of the same switch. Contact 1133 closes a point in a circuit over the left hand winding of relay AC, wiper PBS and wiper AFl of switch A and contact cs6 disconnects relay B to prevent interference should a call be extended thereto consequent on the alternative control circuit being engaged in which case the overflow meter OM would be operated. Vertical magnet AV now operates in the following circuit, earth over contacts g1, n13, cs5, wiper PAS, rotary off normal contact anrl of switch A, magnet AV to battery. The magnet attracts its armature and closes contact at thereby operating relay G over wiper PAZ and winding (1) of the relay. Contact g1 opens releasing the magnet which thereupon opens its contact at releasing relay G. Contact g1 recloses and again completes the magnet circuit. This interaction between the vertical magnet and relay G continues until switch A is stepped to the level in which the calling line is connected. When the switch takes its first step the vertical off normal contacts are operated, contact cml connecting the release magnet AZ to the contact in the bank of wiper PAB and contacts (m2 connecting the test wiper BS3 to contact br operated by the armature of rotary magnet BR for the purpose of effecting rotation of switch B as a group selector over busy outlets. Contact an3 performs no useful function in this connection but should the call have reached the link from group B it would have closed a point in the testing circuit over wiper AS3, switch A in that event, being used as the group selector.

When switch A reaches the level containing the calling line a circuit is closed from earth onthe level marking contact AVP over the vertical wiper co-acting therewith, contact Zm3, wiper P138, contacts 1136, to, M2 winding (II) of relay G to battery. Relay G therefore remains held over this circuit after the vertical magnet releases and at contact g2 allows relay RD, which is too slow in operation to operate during the stepping of the vertical magnet, to operate. Relay RD locks up over contacts rdl and t1 and disconnects winding (II) of relay G at contact r022 connecting winding (I) of relay EC to wiper P138. Contact n13 opens the call finder vertical magnet circuit and prepares the rotary magnet circuit, contact m4 closes but contact g3 is not closed long enough to effect release of relay A which is short circuited by it.

Consequent on the change over of contact r112 relay G releases and at contact cl completes the following circuit: earth over contacts 91, r033, h5, cs4, wiper PA4= rotary magnet AR to battery. The magnet operates and closes its contact ar thereby operating relay G in a circuit over its winding (I) and wiper PA2 and relay G and magnet AR interact with one another to effect rotation of the wipers of switch A. At the first rotary step rotary off normal contact arnl is operated to disconnect magnet AV and prepare a circuit for relay HR. The calling line is marked in the test bank of the call finder by battery potential over the winding of the out off relay and when the wipers reach the contact connected to this line a circuit is closed from this battery connection over wipers AFB, PA'Z, contact 22, 272, (282, left hand winding of relay E to earth. Relay H operates and locks up over contacts hl and t1 and opens the magnet circuit at contact h5.

Contact k2 connects direct earth to operate the line out off relay and contacts b3 and he connect the incoming speaking wires over contacts hb3, hb i, wipers P333, PBS, contacts (283, and Z133, b3 and ha, 004 and 1:22 in parallel to earth and battery over both windings of relay AC. When the calling line is switched through by the cut-oii relay, relay AC operates over the calling loop.

Contact acl closes circuits for relays BC and CC. Relay BC operating disconnects earth from the locking circuit of relays A and B, releasing the operated relay at contacts i902 and closes a holding circuit for relay T at contact bcl independently of relay A. Relay CC operating, contact cci prepares the impulsing circuit to the vertical magnet of the group selector, and contact cc2 opens a point a circuit for the rotary magnets AB, and ER. Contact 003 prepares a circuit for relay TY of a timing device for the forced release of the control circuit should no impulse be received within a predetermined time and contact 004 opens to render contact 1522 of relay T2 in the timing device efiective. The common start wire is extended by contact 726 over contact (14 to the alternative control circuit, earth being dis-- connected from the start wire if no other line is calling by the operation of the line cut-oh" relay.

The caller now receives dialling tone over wire DTL and contacts M3, 723, cs3 and wiper P33 and commences to dial the wanted number. The impulses for settig the group selector of the link circuit are received by relay AC and are repeated at contact acl in a circuit over contacts 001, bs5, t5, wiper PA6, contact lmrl to vertical magnet BV of switch. B. Relay CD operates in a parallel circuit and locks up over its make-before-break contact cdl and contact ti and at contact 0112 makes relay CC dependent for continued energization on the back of contact col. Contact 0613 loses a point in a circuit for the group selector rotary magnet, contact :14 prepares a circuit for relay BT which circuit is closed effectively if no free outlet is encountered by the group selector contact cd opens in the circuit of winding (Ii) of relay ET. On the first vertical step of switch B the vertical. normal contacts are operated, contact bnl connecting the release magnet to the contact n the bank of wiper PA3, contact 12123 disconnecting the contact in the bank of wiper PBS from the vertical marking bank ANP and connecting it to the test wiper BS3. Contact is without effect in this connection but in a connection which ,witch B is used as a call finder it connects the test wiper A53 to contact or for the automatic stepping of switch A in search of a free outlet.

At the end of the impulse train. relay AC remains steadily operated and relay CC releases closing the following circuit, earth over contacts 91, M3, cs2, 7102, bed, wiper PBZ, rotary magnet BR to battery. The rotary magnet operates, steps the wipers of switch B into the bank and closes its contact 131" thereby connecting the test wiper BS3 over contact c122 and wiper PA2 to relay G. If the outlet is busy the test bank contact will be at earth potential and relay G will operate and open the magnet circuit. The magnet releases and opens the circuit of relay G which releases and re-closes the magnet circuit, magnet BR and relay G interacting with one another to step the Wipers around the level so long as busy outlets are encountered. If no free outlet is encountered the wipers are stepped on to the last contacts in the level whereupon shaft contacts bs are closed maintaining relay G energized and thereby bringing the switch to rest. A circuit is now held closed for relay BT over its winding (I), contacts cd l, spl and g3 and relay BT which is slugged at its armature and is energized for sufficient time to permit it to operate.

Contact btl closes but is without efiect as contact cd5 is open and contact hi3 connects the busy tone over wire BTL and wiper PB3 to the calling line and the caller hearing the tone replaces his receiver and clears the connection. If, however, the wipers of switch B as a group selector find a free outlet battery potential will be found on the test bank contact. Relay G will not operate but relay HC will in a circuit from earth over its winding (I), contact rci2, t6, bs6, wiper PBS, contact Zm3 and wiper BS3. Relay HC locks up over its winding (II), contacts hcl, rdl and i1 and opens the rotary magnet circuit at contact 7102, connects earth over contacts 7103, cs5, wiper PAS and contact anrl to switching relay EB and at contact he l opens a point in the connection of relay G to armature contact pad/m. of magnet PADM. Relay HE operates and connects itself to the test wire at contact hbl, the relay holding over the test wiper BS3 to earth connected to the test wire in the succeeding circuit after the connection has been switched through at contacts 71b2, M13 and M74. The link circuit remains in this condition during the conversation and on its conclusion relay I-iB releases and the switches A and B remain with their wipers on the contacts on which they were last used until the circuit is again picked up by switch PA. Relay AC is now disconnected and releases, contact acl falling back opening the circuit of relay BC which releases after a short interval. Contact 1302 reconnects the holding earth for relays A and B, contact Z201 releases relay T which in turn releases relays HC, CD and RD. On the release of relay T a circuit is closed over back contact t1, contacts boil and r035 for the right hand winding of relay SP which operates and on the release of relay HC closes a circuit from earth over contacts padm, sp2 and he l for winding (1) of relay G. Contact sp l releases relay PX, contact 3393 opens to guard relay BT (winding (1)) against closure of contact p502, a possible circuit for this winding being opened at contact 0:14 and contact spl, closes in a circuit for magnet PADM which is closed by the operation of relay G. The magnet operates and steps the switch PA and when relay RD releases relay SP is left dependent for continued operation on earth from busy link circuits connected over the test wires and wipers PA"! and PAS. Operation of magnet PADM opens the circuit of relay G and the magnet and relay G interact with one another to step the wipers of switch PA in search of a free link circuit. When such a circuit is encounterd relay SP releases, releases relay G at contact sp2 and at contact 5103 closes a circuit for winding (1) of relay BT. Relay BT operates, connects earth over contacts U62 and pbdm to magnet PBDM and at contact bt'l connects earth over low resistance winding (II) of relay BT, contact cd5, wiper PA3, contacts cml and bnl to release magnets AZ and BIZ f the link circuit found. The magnets operate and release the switches or" the link circuit.

The bank contacts of wipers PAl and FBI are connected together, the contacts in the bank of wiper PBl being connected to contacts one ahead in the direction of rotation of the wipers in the bank of wiper PAl. Switch PA having been stepped from the position in which it was last used and switch PB not having been stepped there is no circuit over wipers PAl and P131 for winding (11) of relay PX consequently on the closure of contact hi2 magnet PBDM operates and the switch self steps until wiper PBl rests on contacts connected to those on which wiper PAl is resting whereupon relay PX operates over its winding (II) and holds magnet PBDM operated and consequently contact pbdm open and locks up over its winding (1), contacts p901 and spa and releases relay ET at contact 37032. Relay BT releasing allows magnet PBDM to release and.

advance its wipers one step whereby switches PA and PB are brought into alignment and rest with their wipers on contacts connected to the same link circuit. Relay PX remains operated over its high resistance winding (1) and all the other relays in the control circuit are in their un-energized condition.

When the calling line was found by the call finder and was switched through to the link circuit relays AC and CO were operated and contact 003 closed a point in the circuit of relay TY. Relays TY and T2 are part of a timing device and a continuously rotating cam applies earth periodically to wire Y and after the elapse of a predetermined interval after every such application applies earth mom ntarily to wire Z. The first application of earth to wire Y after the operation of relay (30 operates relay TY which looks up over its make-before-break contact tyl and connects relay T2 to wire Z at contact i112. If a train of impulses has not been received by the time earth is applied to wire Z relay 'IZ operates and locks up over make-before-break contact tel and at contact m2 opens the loop for relay AC, contact ce l, being open, and this relay releases and contact t'z3 opens no release relay CC,

' relay CD operating due to the release of relay AC.

consequent on this operation an impulse is transmitted to the vertical magnet of roup selector in the link circuit, which is stepped to the first level. This level may have no outlets connected to it and the test bank contacts with the exception of the last contacts may be earthed so that the wipers are rotated to the last contacts in the level where the shaft contacts are operated and relay G held energized. Relay BT then operates as previously described and busy tone is connected to the calling line.

Should the calling subscriber clear before the call finder has found the line should there be -no line in the group calling the earth on the level markin bani: will be disconnected and if the level has not yet been reached the call finder will continue to step until the last level is reached. The marking contact corresponding to this level is permanently earthed so as to stop the switch in this level. Relay G then operates and operates relay ED. Then and also in the case where the subscriber clears during rotary search the wipers are rotated to the last contacts where relay G is held over shaft contacts. A short circuit now closed over contacts g3, spl, ads, wi l for the start relay operated and this releases, releasing relay '1 and the discriminating relay and relay RD. During the release period of relay RD relay SP operates to initiate stepping of switch PA to a further free link circuit in the manner descr'bed.

If when the call was initiated the control circuit shown was already engaged and the call finder had found the calling line relay H would be operated and the earth on the start wire SWA would be extended over contact be of start relay B in the alternative control circuit, supposing this to be free, contacts R6, at of the control circuit shown, contact cs6 of relay AS in the alternative control circuit to relay B therein and the call would have been set up under the control of the alternative control circuit. a

If, however, a call is initiated in the group B of incoming lines and the alternative control circuit is in use so that either relay A or relay H therein is already operated the earth on start wires SWB will be extended after the operation of relay H and release of relay A over contacts be of relay 3 the control circuit shown, contacts hi; and as in the alternative control circuit, contact 2186 to relay B. Relay B operates and locks up and operates relay T by closing contacts b5. After the operation of relay '1 relay BS operates over contact b3 and locks up over contact lz-sl. Relay BS performs similar functions to relay AS and its operation determines that switch B which has access to incoming lines in group B over its wipers BF1BF3 is used a call finder and switch A which has outlets to a subsequent circuit connected to the can :s associated with wipers K lsi-ASE is used as a group selector. The earth on the st wire SW13 marks the level in the group of contacts ENP corresponding to that in which the calling line is situated. Relay at contact closes the circuit for operating magnet BV to step switch B in search of the marked level. Magnet BV and relay G interacting by means of contacts c1 and be connected in the relevant circuits. The earth on the contact of the set BN1? is extended when the switch B reaches the marked level over wiper PB? and contact (236 to hold relay G and relay RD op crates. Contact 12122 connects the test wiper A33 to contact or for stepping switch A over busy outlets. The rotary magnet is then operated to rotate the wipers over the level in search of the calling line, the magnet circuit being from earth over contacts g1, T523, 715 back of contact (134 and wiper P132. Contacts hr and g1 effect interaction to step the switch. Belay El operates when the line is found and when the latter has been switched through contact cs3 being unoperated and contact beg operated relay AC is operated over wipers and P36, contacts Iss3 and ha l, wipers BFl and BFE and the calling loop. linpulses for stepping the group selector are repeated by relay AC over contacts col, ccl, i735 front; wiper PA5 to magnet AV and at the end of the train relay CC releases and rotary magnet AB is stepped by interaction with relay the magnet circuit being over contacts 91, M3, 7L5, e02, cal-3, hcZ, b34- front and wiper PAel. Relay I-IC operates over contacts M22, 156, I236 and wiper PET, contacts ans and wiper A83 to battery on the test hank contact of a free link and operates relay HA over contacts Imrl, wiper PAS, contacts t5, E982 and hog and the connection is switched through over contacts Iii/,2, 72:23 and has.

Consequent on the operation of start relay B, contact be connects the start wire directly to relay B so that should the alternative control circuit becoine free the later calling line is found release of relay H in the alternative control circuit will not bring about operation of relay A therein until the later calling line has been found whereupon, relay B being released earth continuing on the start wire due to initiation of a further call will operate relay A and the alter native control circuit will be taken into use for the control of the switches of another link circuit.

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

1. In a telephone system, a link circuit comprising two selecting switches, groups of lines accessible to the first of said switches, different groups of lines accessible to the second of said switches, means for operating the first switch as a finder to find a line in one of said first groups of lines and for thereafter operating the second switch as a group selector to select an idle line in one of said diiierent groups of lines to extend a telephone connection, and means for operating the second switch as a finder to find a line in another of said different groups of lines and for thereafter operating the first switch as a group selector to select an idle line in another of said first groups of lines to extend another telephone connection.

2. In a telephone system, two groups of lines, each group of lines being associated with a difierent switching stage in establishing telephone connections, a selecting switch having access to both groups of lines, means for seizing said switch for establishing a telephone connection, and means for operating said switch in a backward hunting movement over one of said groups of lines or for operating said switch in a forward selecting movement over the other of said groups of lines dependent upon the switching stage said seized switch is to be used in.

3. In a telephone system, subscribers lines, trunk lines, a switch having access to said subscribers lines and said trunk lines, means for seizing said switch for establishing a telephone connection, and means for operating said switch as a finder to find a calling subscribers line or for operating said switch as a selector to select an idle one of said trunk lines dependent upon whether a subscribers line is initiating a call at the time of the switch seizure or is thereafter further extending a telephone connection after the switch seizure.

l. In a telephone system, subscribers lines, trunk lines, a switch having access to said subscribers lines and said trunk lines, and means for operating said switch in a backward hunting movement to connect with a calling subscribers line in response to a call on said line or for operating said switch in a forward selecting movement to connect with an idle one of said trunk lines in case said switch is connected to a subscribers line by another switch.

5. In a telephone system, subscribers lines, trunk lines, a first and a second switch, wipers in said switches having access to said subscribers lines and said trunk lines, a link circuit connecting the wipers of the first switch to the wipers of the second switch, means for operating the wipers of either one of said switches in a backward hunting movement to connect said link circuit to a calling subscribers line in relines and to the second sub-group of subscribers lines, a link circuit connecting the wipers of said first switch to the wipers of said second switch, means for operating the wipers of the first switch in response to a call by a calling subscriber in the first sub-group or the wipers of the second switch in response to a call by a calling subscriber in the second sub-group in a backward hunting movement to connect said link circuit to the calling line, and means for then operating the wipers of the remaining one of said switches in a forward selecting movement to select an idle one of said trunk lines and connect said link circuit thereto.

'7. In a telephone system, subscribers lines, trunk lines, a first and a second switch, a first set of wipers in each switch having access to said subscribers lines, a second set of wipers in each switch having access to said trunk lines,

a link circuit connecting the first set of wipers the wipers of either one of said switches in a backward hunting movement to connect the first set of wipers to a calling subscribers line in response to a call on such line, and means for thereafter operating the wipers of the remaining switch in a forward selecting movement to select an idle one of said trunk lines over the second set of wipers and connect said link circuit thereto.

8. In a telephone system, subscribers lines, trunk lines, a switch, a first set of wipers in said switch having access to said subscribers lines,

a second set of wipers in said switch having access to said trunk lines, and means for operating said switch as a finder to connect said first set of wipers with a calling subscribers line or as a selector to connect said second set of wipers with I15 an idle one of said trunk lines dependent upon whether a subscribers line is initiating a call or is further extending a call after being connected to said switch by another switch.

9. In a telephone system, subscribers lines,

the second switch, means responsive to the initiation of a call on one of said subscribers lines for initiating the operation of the wipers of either one of said switches in a backward hunting movement, means for automatically continuing the hunting movement, means responsive to the wipers of the operated switch finding the calling line for stopping said hunting movement with the said wipers in engagement with the calling line, means for thereafter transmitting impulses over said calling line and the wipers in engagement therewith, and means for operating the wipers of the remaining one of said switches in a forward selecting movement in response to said transmitted impulses to select an idle one of said trunk lines and connect said link circuit thereto.

10. In a telephone system, trunk lines, a group of subscribers lines divided into sub-groups, a plurality of link circuits, a first and a second switch in each link circuit, each first switch having access to one of said sub-groups of lines and to said trunk lines, each second switch having access to another of said sub-groups of lines and to said trunk lines, control apparatus common to said plurality of link circuits, a different path for each sub-group of lines connecting such lines to said common apparatus, means responsive to a call on one of said suhscrioers lines for seizing said common apparatus over the path associated with the sub-group containing the caliing line, and means dependent upon the path over which said common apparatus is seized for operating either the first or the second switch in an idle one of said link circuits as a finder to find the calling line and then the remaining switch in said link circuit as a selector to select an idle trunk line.

11. In a'telephone system, subscribers lines, trunk lines, a first and a second switch each having wipers, a link circuit, two switching relays in said link circuit, means for operating the wipers of either one of said switches in a'primary and a secondary movement to connect said link circuit to a calling suhscrihers line in response to a call on said line, means for thereafter operating the wipers or" the remaining one of said switches in a primary and secondary movement to connect said link circuit to an idle one of said trunk lines, and means for operating only the first of said switching relaysin case the wipers of said first switch are connected to said calling line or for operating only the second of said switching relays in case the'wipers of the second switch are connected to said calling line to extend the connection from the calling line to said trunk line.

12. In a telephone system, trunk lines, a group of subscribers" lines divided into sub-groupaa plurality of link circuits, a first and a second switch in each link circuit, each first switch having access to one of said sub-groups of lines and said trunk lines, each second switch having ac cess to another of said sub-groups of lines and to said trunk lines, control apparatus common to said plurality of link'circuits, a hunting switch associated with said common apparatus, means for operating said hunting switch to maintain said common apparatus in connection with an idle one of said link circuits, a start circuit "for each sub-group of lines connected to said common'apparatns, means responsive to a call on one of said subscribers lines for seizing said common apparatus over the start circuit associated with the sub-group containing the calling line, and means dependent upon the start circuit over which said'common apparatus is seized for operating either the first or the second of said switches in said selected idle link circuit as a finder to find the calling line and then the remaining switch in said link circuit as a selector to select an idle trunk line.

13. In a telephone system, a group of subscribers lines divided into a first and a second sub group, trunk lines, a first and a second link circuit, a first and a second switch in each link circuit, the first switch in the first link circuit and the second switch in the second link circuit having access to said first sub-groups of lines and said trunk lines, the second switch in the first link circuit and the first switch in the second link circuit having access to the second subgroup of lines and said trunk lines, a first and a second control apparatus for said link circuits, a first and a second start relay in each control apparatus, a start circuit for each subgroup of lines, said start circuits normally connected to the first start relays in said apparatuses, means responsive to a call on one of said subscribers lines for operating the first start relay in one of said control apparatuses if idle or if said one control apparatus is busy for operating the second start relay in the other of said control apparatuses over the start circuit associated with the subgroup containing'the said calling line, and means for operating the first switch as a finder to find the calling line and the second switch as a selector to select an idle trunk in one of said link circuits in case the first start relay in one of the apparatuses is operated or for operating the second switch as a finder to find the calling line and the rst switch as a selector to select an idle trunk line in the other link circuit in case the second start relay in the other apparatus is operated.

14. In a telephone system, trunk lines, a group of subscribers lines divided" into sub-groups, a plurality of link circuits, ai'first and a second switch in each link circuit, each link circuit comprising only the operating magnets or" said switches and only two switching relays, control apparatus commonito said plurality of link cirouits, means for operating said common apparatus to select an idle link circuit, means responsive to a call on one of said subscribers lines for seizing said common apparatus, means in said common apparatus responsive to its seizure for operating the operating magnets of either the first switch or the secondswitch of the selected link circuit dependent upon the sub-group the calling line is in to operate'said switch as a finder to find the calling line, means in said common apparatus for thereafter operating the operating magnets of the remaining switch in said selected link circuit as a selector to select an idle one of said trunk lines, and means, in said c'ommon apparatus for thereafter operating only one of said switching relays, the relay operated being dependentiupon the functions performed by the respective switches in the said link circuitl REGINALD GRIFFITH DIXON.