US1675310A - Telephone system - Google Patents

Description

June 26, 1928. 4 1,675,310

W. SAVILLE TELEPHONE SYSTEI Filed June v, 1926 Y 2 Sheets-Sheet 1 M11115 Samlle WET? June'26, 1928.

W. SAVILLE TELEPHONE SYSTBI 2 Sheets-Sheet 2 Filed June 7, 1926 -IITEfiEF-+ M11115 Sauz'lle Patented June 26 19 28.

UNITED STATES PATENT OFFICE.

WILLIE sAvILLE, or LIvEnrooL, nNeLANnnssIeNon '10 AUTOMATIC ELECTRIC Inc, or CHICAGO, ILLINOIS, A coaronnrron or DELAWARE.

TELEPHONE SYSTEM.

Application filed rune 7, 1926, Serial No. 114,072, and in Great Britain August 31, 1925.

The present invention relates to telephone systems and is more particularly concerned with the operation of small exchanges on What is known as the satellite principle, that I is to say, the exchange contains only suffici-ent switches for completing local connections, the first selectors being located in a main exchange situated nearby. The prob lem that always arises in these circumstances is that in case a connection is to be set up' between two subscribers both connected to the satellite exchange, it is not desirable that a trunk line should be taken to the main exchange and another one back again to the satellite, althotwh it willnot be decided until a considerable proportion of the number has already been dialled. that the call. is to be entirely local. Consequently it is necessary to provide some means on a local call for releasing the switches which have been operated in the main exchange and also the trunk lines taken into use. The problembecomes additionally diflicult case it is desirable, as may sometimes happen, to provide facilities for direct V trunking to a manual exchange for toll calls or the like and in some cases satellite'e'xf changes are themselves provided with subexchanges' in another building. The object of the present invention is to provide service'in a simple and economical manner for i all the foregoing cases.

' of its setting to control the routing of the I According to one feature of the invention, 1n a system including satellite exchanges a number IBCOI'CllIlgxdGVlCG at ai satelhte ex change is adapted to be set in responseqto each exchange selecting digit and by virtue call.

Another feature of the invention is that in a system including satellite exchanges, connections extended from a satellite .ex-

change by way of the main exchange are completed over one set of w pers-of an auto matic switch while local connections are completed over another set of wipers of the same switch.

A further featureof the invention is that in a system including satellite exchanges the first numerical switches associated with a satellite exchangeare located in a main exchange while a number recording device adapted to respond to certain digits of a called number is located in a third exchange.

These and other features not specifically mentioned at this point will be better appreciated from the following description of one embodiment of the invention, taken in conjunction with the accompanying drawings comprising Figs. 1 and 2, which when the call may be completed with the minimum employment of switches and of trunk lines. Two line switches are provided for giving four directions oi access, each of these switches being of what may be termed the on and oil type, that is to say, its bank contains twice as many levels as there are wipers in use at any one time and'two sets of wipers are provided which project in diametrically opposite directions. It is arranged that for all calls both switches are started up and hunt over the first portions of their banks to select idle trunks, but only theline leading to the main exchange is connected up and the impulses dialled are repeated over this line to operate switches in the main exchange.- They are also recorded on the discriminator and it they are of a certain critical value, they may produce the furtheroperation of one or both switches to the other portion of its bank and subsequently the release of the one not required.

In order that no impulses shall be lost it is essential that in case the call to be switched locally, that is to say either to the satellite therefore that from the first half of the bank of the first switch trunks extend to the main exchange while from the first half of the bank of the second switch, access is obtained to local switches. Since both these switches are operated initially, they set in good time before impulses can possibly be required to be tI'HDSlIllttGCl thereover. The trunks to the sub-exchange are outgoing from the second half of the bank of the first switch and this switch may be caused to hunt again (which involves releasing the trunk to the main exchange) as soon as it is definitely determined that the call for either the satellite or its sub-exchange. Access to a manual operators position for the completion of toll calls is had from the second half of the bank of the second switch and since after the subscriber has dialled enough digits to indicate that the toll operators p0- vsition is required no more will be sent, it is not necessary that the second line switch shall have found an idle line leading to the operators position by the time all the digits have been dialled. The discriminator for recording the first digits consists of a ten point switch of the known type which is released after each train of impulses as soon as it has been set and by its setting serves to operate one or more relays.

Referring now to the drawings, it will be seen that all calls are initially extended to the main exchange and arrangements are made for switching in three other directions, that is to say, locally, to a sub-exchange, and to a toll operators position, and it will be assumed that the digits, or the numerical equivalents of the letters, for determining local trunking are 234., these indicating the sub-exchange are 2347, and those for obtaining connection to the toll operator are. 235. Access 18 then obtained over the wipers lV to the main exchange, over the wipers W which rotate with W to the sub-exchange, while over wipers local switches are reached and over the wipers V which rotate with access is obtained to the toll operators position.

The case will first be considered in.-which a subscriber in the satellite desires connection with a subscriber who is reached by way of the inain exchange, and for convenience it will be assumed that the first two digits of each subscribers number are 25. The repeater and associated apparatus shown may be reached over the subscribers individual line switch in the usual way. Hence when connection from such a switch is completed to the'repeatcr, a circuit is completed over leads 1 and 2 and the calling partys loop for the line relay A, which accordingly operates and at its armature 5 completes a circuit for slow relay B, and its armature 6 prepares a loop to a first selector switch in the main exchange. Relay B upon operating, at armature 7 connects earth to release trunk eon ductor 3 so as to hold the line switch operated, at armature 8 prepares the impulsing circuit, and at armature 9 prepares locking and switching circuits which will be de scribed fully in due course. The connection of earth to lead 3 completes a circuit for the left-hand winding of the polarized relay D and is also extended over back contact and armature 1S, armature Q5 and its back contact, lead 58, armature 77 and its back contact,norinall y closed springs controlled by armature 7%, winding of relay L resistance 80 to battery. It will be assumed that the wipers V are in their normal or home position at this time and consequently relay L energizes and at armature 60 completes a circuit t'or relay K and rotary magnet M in series, and at armature 67 connects test wiper 109 by way of armature 73 and its back contact to the junction of relay K and magnet M Since the contact on which wiper 109 is standing is connected to earth, relay K is short-circuited and magnet M is operated. The switch S therefore starts to hunt in the usual manner and this continues until wiper 109 engages a contact which is not connected to earth, whereupon relay K energizes and at armature 7b connects earth to test wiper 109, at armature H opens the circuit of relay L and completes a locking circuit for itself at armature 75 opens a point in a circuit for shorting relay L and at armature 76 opens a point in the homing circuit for magnet M Moreover at arn'iatures 71 and 72 the speaking conductors are connected through, whereupon the line relay oi the switch at the distant end of the seized trunk is energized to prepare the switch for operation in the usual manner. The earth on lead 3 is also extended by way of back contact and armature 16, armature 33 and its back contact, lead 63, armature 99 and itsback contact, normally closed springs controlled by arma ture 96, winding ot relay L and resistance to battery. The consequent operation of relay L starts the hunting operation of the switch S comprising the two sets of wipers and XV, and this continues until wipers TV" connect with a trunk leading to an idle local switch. This switch however, is not operated at the present time since there is no bridge connected across conductors 5.5

and 62.

The subscriber will now dial the first digit in the wanted number, in the present case the digit 2; consequently two interruptions are produced in the circuit of relay A, and these are repeated at armature 6 to the line relay of the seized first selector. Upon each de-energization of relay A, a circuit is also completed from earth, armature 5 and its back contact, armature 8 and its front contact, winding of relay C to battery, and parallel thereto by way of back contact and V armature 15, winding of magnet DM to battery. .Relay C is slow and remains energized throughout each train of impulses and upon energizing at its armature 10 shortlip-male circuits relay D and impedance I so as to improve the impulsing circuit, and at armature 11 re'movesearth from lead 40 so 'as'to prevent circuits being completed over the wipers 41, 42, and 43 of the discriminating switch before it has been completely set. By the operation of magnet DM, wipers 41, 42 and 43 are advanced into engagement with the second contacts of their respective banks and when relay C de-e'nergizes at the end of the train of impulses, earth is connected to lead40 and is extended over wiper 42 and the second contact in its bank, back contact and armature 52, lower winding of relay DA to battery. Relay DA is a twostep relay and at this time only operates sufficiently to close its light armature 51 to prepare a locking circuit for itself. When the original earth is removed by the release of wiper 42', relay DA operates fully and at armature 52' opens its initial energizing cir cuit and at armature 53 prepares a circuit for relay DB. The earth on lead 40 is also extended over wiper 43 to release magnet RM upon the operation of which the dis' criminating switch is restored to normal.

When the next digit is dialled, five 1mpulsesare repeated to the main exchange at armature 6 in the manner previously de-' scribed and the wipers of the discriminat ing switch are advanced five steps. When rel'a C de-energizes, earth is extended from lea 40 by way of armature 45' and its back contact to the fifth contact in the bank of wiper'41 and thence over the wiper to the ture' opens a point in the circuit of mag-;

net DM so as to prevent the discriminating switchbeing operated again, and at armature 16 opens the locking circuit for relay K. This latter operation is permissible since it has now been definitely determined that the call is to be completed by way of the main exchange, and it is therefore unnecessary to j retain the switch seized over the wipers W Upon the release of relay K a circuit is completed from the earthed homing plate 111, wiper 112, back contact and armature 92,

back contact and armature 98, back contact and armature 106, and byway of the inter rupter contact to battery through the winding' of magnet M. Magnet M therefore operates to rotate thewipers W and W of the switch S until the set W are clear of the bank and the set W are engaging with the first contacts in their respective banks. A circuit is now completed from earth, armature 91'and its bank contact, back contact and armature 101, contact 114, homing wiper 113' of the set. W, armatures 92, 98. 106 and their back contacts, to magnet M Thus' M operates to advance the wipers a further step and earthis then supp in known manner.

ied from the W of the switch S continue to rotate until wipers W engage the first set of contacts when no further circuit is completed for ma net M g it ie subsequent digits dialled by the calling party are repeated as before by armature 6 to operate switches in the main exchange When the called party replies, current is reversed back over loads 54 and 57' and is then in such a direction as to cause the operation of relay D, which at armature 12 connects earth to metering conductor 4 so as to register the call against the calling subscriber. When the calling party replaces his receiver all the operated equipment is released owing to the release of relay A and the subsequentrelease of re l ay B. i 1

The case will now be considered in which acall is to be set up to a subscriber in the satellite exchange, so that as mentioned above the first three digits dialled will be 284. The operations when the repeater is taken into use are the same as those previously described, namely, that atrunk to the main exchange is seized over the wipers W oi? the switch S and a local switchover the wipers lV of the switch The dialling of the digit 2 also produces results identical with those in the previous case, namely, that in consequence of the operation of the discriminating switch relay DA is operated and lockedup. When thencxt digit 3 is dialled, however, wipers 41, 42 and-43 are advanced into engagement with their respective third ban-k contacts and when they come to rest a circuit is completed from earth onlead 40,

wiper 42,1.rontcontact and armature 53, back'eont-act and armature 4'1 for the two step relay DB, which is similar to the relay DA and only operates fully when the initial earth is removed, thereupon at armatures 48 and 49 preparing circuits for relays. H and in the repeater. A circuit is also completed over wiper 43 for release magnet BM in the usual manner sothat the discriminating switch wipers are restored to normal in readiness to record the next digitf The next digit in this case is 4-, and when; the discriminating switch has been setin re sponse to this-digit, a circuit is completed over wiper 42, front contact and armature 48 for relay HA. Relay HA upon operating, at armature removes the shunt round armature 17, at armature 26 shunts armature 16, at armature 29completes a locking circuit foritself, at armatures 27 and opens the loop to the main exchange, thereby. releasing the opera-ted switches therein, and completes the loop to the seizedlocal switch so as to prepare this in readiness to respondto the next digit, and at armature 28-completes a now determined that the call is not destined for the main exchange but it is still possible that it may be intended for the sub-exchange, the set of wipers will now come into 0 eration to select a trunk leading to the su exchange. This is effected by the operation of the relay H which at armature 77 removes the locking earth for relay K so that this relay de-energizes, and at armatures 71 and 7 2 opens the loop to the main exchange thereby effecting the release of the operated switches therein. Moreover a homing cir- ,cuit is completed for magnet M by way of the homing wiper of the set W and armatures 70, 76 and 85 and their back contacts, so that the magnet M operates until the wipers W are clear of the bank. Though the earth on lead 58 is extended to relay L over the normal contacts controlled by armature 82 upon the operation of relay H relay L cannot operate for the present since it is short circuited over armatures 68, 75 and 84 and their back contacts. hen the homing wiper leaves the earthed homing plate, however, this shortcircuit is removed and relay L then operates to initiate a hunting movement under the control of the wipers W Moreover by the operation of armature 7S, relay KA has been connected up in place by relay K while at armature 79 earth is disconnected from normal contact 116 so as to permit the switch to stop in this position if the trunk extending therefrom should be idle. Accordingly the wipers are advanced over their bank contacts until they come into engagement with an idle'trunk extending to the sub-exchange. When such a trunk is found, relay KA is no longer short circuited and operates; at armatures 86 and 87 connects up the speaking leads, at armature 81 connects earth forward to the test wiper of the set V and at armatures 82 and 83 completes a locking circuit for itself, at the 1 same time opening the circuit of relay L whereupon this relay de-energizes.

The calling party will now dial the fourth digit of the wanted number and since it has been assumed that the call is to be completed locally within the satellite, this digit may be anything except 7 Supposing therefore,

' that it is 5, five interruptions are produced in the circuit of line relay A and these are repeated over leads and 62 and wipers to operate the local switch in the satellite. Moreover, as in the previous case, the wipers 41, 42 and 43 of the discriminating switch are advanced in accordance with the impulses sent, hence when relay C de-energizes, a circuit is completed from earth at armature 9, lead 40, armature 38 and its front. contact, fifth contact in the bank of wiper 41 and said wiper, winding of relay PCO to battery. Relay PCO therefore now operates and locks up as before at armature 14, and at armature 15 opens the circuit to the magnet DM so as to prevent the discriminating switch being operated by the remaining impulses dialled by the calling party. Moreover at armature 17 the locking circuit for the relay KN is opened, whereupon the trunk line to the sub-exchange is released and the switch S restores to normal in a manner similar to that above described for the switch S The operation of armature 16 is without effect at this time since it has previouslybeen shunted by armature 26. The speaking connection is completed in known manner and when the subscribers have finished conversing release takes place as described above.

Consider now the third case in which a connection is desired with a subscriber in the sub-exchange, in accordance with which the first 4 digits dialled will be 2347. The effect of dialling the digits 234 will be the same as in the case previously described, the result being that the trunk line to the main exchange initially seized over the wipers has been released, a lineto the sub-exchange has been seized over wipers while over wipers V a local switch has been prepared for operation. lVhen the fourth digit 7 now dialled, the local switch is operated to the seventh level and hunts in known manner. lVipers 41, 42 and 43 are also advanced into engagement with the seventh contacts in their respective banks and when relay C (lo-energizes earth is connected to lead 40 and extended over wiper 42 and the seventh contact in its bank, armature 39 and its front contact, winding of relay HB to battery. Relay HE is thereupon operated; at armature 31 shunts armature 17 so as to secure the continued operation of the switch S after relay PCO subsequently operates to disconnect the discriminating switch, at armature 34 completes a locking circuit for itself, at the same time opening the previ ous locking circuit. of relay HA. at armature 33 completes a new locking. circuit of relays HA and H at the same time removing earth from lead 63. and at armatures 32 and 36 connects up leads 36 and in place of leads 56 and 61 so that the operated local switch is released and the connection is extended over' the trunk line to the sub-exchange. Moreover at armature 35 a circuit is completed for the cut-off relay PCO- v upon the operation of which the discriminating switch is cut-off inthe usual manner. The subsequent completion of the connection is effected in a manner which will be readily understood from what has already been said.

One further case must be considered, namely, that in which the calling party desires to set up a long-distance all and hence wishes to obtain connection with the toll operator: in this case he will dial only the digits 235. Assuming that the repeater shown is again used, when it is taken into use, a trunk line is seized over the wipers and a switch at the distant end is prepared toroperation and in additiona local switch isse zed over the wipers WV \Vhen the digits 23 are dialled, the switch in the main .e zchange is operated accordingly and alled, wipers 41.,42and 43 are advanced,

five steps and upon the connection of earth to lead a circuit. is completed over wiper 42 and the fifth contact in its bank, front contacttand armature 49 and back contact and armature 30" i',or.relay H, whileover wiper 43 the usual. release circuit for the discriminator-Wis completed. Relay H u on operating-at armature 21 completes a ocking circuit for itself and at armature 22 completes a circuit for relay PCO which operates to ,driscoimect thc discriminator. The operation of armautre l8 'opensthediolding circuit QEOI relay K whereupon the release I o'tthe switch S is brought about, but since armature 19 places a shunt round armature 16, earth isnot removed from lead 63 and the subsequent operation of the switch S is possible, Moreover at armatures' 20 and 23 the speaking. leads are connected through to leads, and v65 extending to the wipers W and, the connection to the local switch is released, whileat armature 24 a circuitis completed for relay H The effect of the operation of relay H? is similar to that of relay H and brings aboutthe de-energ ization -ot relayK and the initiation of a homing operation under the control of wipersWt. When this has beencompleted, huntingpta kes place for a trunk line to the toll operators position under the control of wipersW and when such, alineis found relay KA operates to switch through. When this takes place a circuit i-s completed for a visual indicator at th'e operators position and when the operator plugs in, the calling party makes his wants known to her. The release of the o erated apparatus takes place when the calling party hangs up in the usual manner.

It should be mentioned that'the relay 0 is provided to give what is known as operators holdup; It a connection is extended.

to anoperator, battery is connected to the lower -speaking lead; consequently, when the \callingparty hangs up and relay A deenergizes, this battery connection is. extended over armature 6 and its back contact andwindingof relay 0 to earth. Relay 0, therefore operates and at armature .13 completes an auxiliary circuit for release relay B; hence. the connection remains set up'unti'l the operator removes her plug or otherwise initiate'sthe release, It will be understood that the arrangement described above is given by way of exampe only and that various modifications to the circuits shown might be made by those skilled in the art without exceeding the scope of the invention. ,For instance, it might be desirable to arrange for the discriminating switches to be accessible in common to a number of repeaters over non-numerical switches and clearly 5 also, fewer thanl three separate switch-over operations could be catered for. Moreover the discriminating switch need not release after the receipt of each series of impulses or a separate switch might be provided for recording each digit. An a r-- rangement could also be adopted, particularly if the satellite had no associated subexchange and hence switching was 0111 requiredin two directions, which emp oyed switching selector repeaters of the two-directional type. The mode of operation would thenbe that when the switching repeater is taken into use it receives a preliminary impulse and is raised to the first level and hunts to find a free discriminator. If the call is going to the main exchan e, itis completed over the first half of the ank of the outgoing secondary as in the previous arrangement whileif it is going tothe manual operatofls position it is completed over the second portion of the bank. In case, however, it is to be completed locally the switching repeater is operated and access is hadto local switches from its bank.

Having now particularly described and ascertained the nature of my said invention and in whatmanner the same is to be per formed, what I claim is 1. In an automatic telephone exchange,an

impulse repeater, three groups of trunks accessible to the repeater, means in the repeater for transmitting groups of digit impulses, the-first groups of impulses being transmitted over a trunk in one of said groups of trunks, means associated with the repeater for counting the digit impulses transmitted, means efiective if certain roups of digit impulses are of certain value or releasing the trunk over which the digits were transmitted and transmitting the subsequent digit impulses over a trunk in a ditferentgroup, and means effective if the subsequent digit impulses are of certain value for releasing the last named trunk and transmitting the remaining impulses over a trunk in the third group.

2; In an automatic telephone exchange, animpulse repeater, three groups of trunks accessible to theimpulse repeater, means for extending connections to the repeater from a calling line, means responsive to the extension oi': the connection to the repeater for seizing an idle trunk in each of two of the groups, meanstor transmitting groups of digit impulses from the repeater over one of said seized trunks, means associated with the. repeater for counting thedigit impulses transmitted, means efiective if certain groups of digit impulses are of certain value for releasing the trunk over which the impulses were transmitted and transmitting the subsequent digit impulses over the other seized trunk and for seizing an idle trunk in the third group of trunks, and means effective if the subsequent digit impulses transmitted over the second trunk are of certain value for releasing the second trunk and for transmitting the remaining digit impulses over the third seized trunk.

3.111 an automatic telephone system, an impulse repeater, an automatic switch, two groups of trunk lines accessible to said automatic switch, means responsive to the seizure of the repeater for causing the automatic switch to hunt for and seize an idle trunk in one of said groups of trunks, means in the repeater for transmitting groups of digit impulses over the seized trunk, and means effective if the digits transmitted are of certain value for releasing the seized trunk and for causing the automatic switch to hunt for and seize an idle trunk in the other group of trunks accessible thereto.

4. In an automatic telephone system, an impulse repeater, a first and a second choice automatic switch, each of said switches having accessible thereto two groups of trunk lines, means responsive to the seizure of the repeater for causing each of these switches to hunt for and seize an idle trunk in one of the groups accessible thereto, means in the repeater for transmitting groups of the dig it impulses over the trunk seized by the first choice switch, means effective if the groups of digit impulses transmitted are of certain value for releasing that lastmentioned trunk and for transmitting the subsequent digit impulses over the trunk seized by the second choice switch, and for causing the first choice switch to hunt for and seize an idle trunk in the other group of trunks accessible thereto, and means effective if the subsequent digit impulses transmitted are of a certain value for releasing the trunk seized by the second choice switch and trans mitting the remaining digit impulses over the last seized trunk of the first choice switch or over one of the trunks in the other group accessible to the second choice switch.

5. A structure such as defined in claim 4 characterized in this, that the two groups of trunks accessible to the first choice switch are accessible over two different sets of wipers on said switch.

6. In an automatic telephone system, a main exchange, a satellite exchange, a subexchange associated with the satellite exchange, an impulse repeater in the satellite exchange, means for extending a connection to the repeater from a calling line in either the satellite exchange or the sub-exchange, trunks extending to the main exchange and trunks extending to the sub-exchange accessible to the repeater, automatic switches of the local switch train in the satellite exchange accessible to the repeater, means for extending the call over a trunk extending to the main exchange, means effective if certain digits of the called telephone number are of certain values for releasing the trunk over which the call was extended and for extending the call over a switch in the local switch train, and means effective if the following digits of the called number are of certain value for releasing the local switches and for completing the call over a trunk extending to the sub-exchange.

7. In an automatic telephone system, a main exchange, a satellite exchange, a subexchange-associated with the satellite exchange, an impulse repeater inthe satellite exchange, means for extending a connection to the repeater from a calling line in either the satellite exchange or the sub-exchange, trunks extending to the main exchange and to the sub-exchange accessible to the repeater, automatic switches of a local switch train in the satellite exchange accessible to the repeater, means for transmitting groups of digit impulses from the repeater, the first group being transmitted over a trunk extending to the main exchange, means at the satellite exchange for counting the digit impulses transmitted, means effective if certain groups of digit impulses are of certain values for releasing the trunk over which the di its were transmitted and transmitting the subsequent digit impulses to a switch in the local switch train, and means effective if the subseguentdigit im ulses are of certain value or releasing t e local switches and transmitting the remaining di it impulses over a trunk extending to t e subexchange.

8. In an automatic'telephone system, a

main exchange, a satellite exchange, a subexchange associated with the satellite exchange, an impulse repeater in the satellite exchange, means for extending a connection to the repeater from a calling line in either the satellite exchange or the sub-exchange,

trunks extending tothe main exchange and to the sub-exchange accessible to the repeater, automatic switches of the local switch train in the satellite exchange ac cessible to the repeater, means responsive to the seizure of the repeater for seizing an idle trunk extending to the main exchange and for seizing an automatic switch, means for transmitting groups of digit impulses from the repeater, the first group being transmitted over the seized trunk, means at the satellite exchange for counting the digit impulses transmitted, means effective if certain groups of digit impulses are of certain values for releasing the trunk over which the digits were transmitted and transmitting the subsequent digit impulses to the seized switch, and means effective if the subsequent digit impulses are of certain value for releasing the local switches and transmitting the remaining digit impulses over a trunk extending to the sub-exchange.

9. In an automatic telephone system, a

main exchange, a'satellite exchange, a sub exchange associated with the satellite exchange, an impulse repeater in the satellite exchange, means for extending a connection to the repeater from a calling line in either the satellite exchange or the sub-exchange, trunks extending to the main exchan e and to the sub-exchange accessible to tie repeater, automatic switches of the local switch train in the satellite exchange accessible. to the repeater, means responsive to the seizure of the repeater i'or seizing an idle trunk extending to the main exchange and for seizing an automatic switch, means for transmitting groups of digit impulses from the repeater, the first group being transmitted over the seized trunk, means at the satellite exchange for counting the digit impulses transnntted, means effective if certain groups of digit impulses are of certain value for releasing the trunk seized, for

seizing an idle trunk extending to the subexchange, and for transmitting the subsequent digit impulses to the seized switch, and means effective if the subsequent digit impulses are of certain value for releasing the seized switch and transmitting the remaining digit impulses over the seized trunk extending to the sub-exchange.

10. A structure such as defined in claim 9 characterized in this, that the means for seizing the trunk extending to the main exchange and the means for seizing the trunk extending to the sub-exchange consists of a single automatic switch which seizes the said trunks by successive operations.

11. A structure such as defined in claim 9characterized in this, that the means for seizing the trunk extending to the main exchange and the means for seizing the trunk extending to the sub-exchange consists of a single automatic switch having two sets of wipers, which seizes the trunks over the respective wipers.

In witness whereof, I hereunto subscribe my name this 20th day of May, A. D. 1926.

WILLIE SAVILLE.

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