US2305968A - Telephone trunking system - Google Patents

Description

22, i2. G., KlNER y I 2,305,968

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l, G. KINER TELEPHNE TRUNKING SYSTEM s sheets-sheet 2 Filed `May 5. 1941 y nus-7 1? ar Elem? ff'zhen' TNSSS 3 IV *$5 .En

Dec. 22, 1942.

G. KINER.

' TELEPHONE 'IRUNKING- SYSTEM Filed May 5, 1941 :s sheets-shet 3 l ES I.. n I l I s I l l L zur# az". glenn/finer:

Patented Dec. 22, 1942 UNlTED STATES EEATENT OFFlCE 2,305,968 TELEPHONE TRUNKING SYSTEM Application May 5, 19411, Serial No. 391,823

10 Claims.

The present invention relates to telephone trunking systems, being concerned more particularly with telephone trunking systems used in automatic telephone systems employing line iinders.

One object of the invention is the provision of a simple circuit arrangement for allotting idle finders for use.

A further object is the production oi' a new and improved finder allotter for allotting nders associated with two-way trunks only when all of the nders associated with one-way trunks are in use.

A feature of the invention is that, even though the allotter relays of the finders associated with they two-way trunks are in a position to cause the two-way-trunk nnders to be allotted, the allotment thereof is prevented by a group relay as long as any nder associated with a one-way trunk is idle.

A further feature is that arrangements are provided for actuating and locking all the allotter relays associated with idle finders, and for unlocking and restoring them successively as the finders are taken for use.

Other objects and features of the invention will appear as the description progresses.

GENERAL DESCRIPTION lines are provided to extend connections from 2,.

the main exchange to the satellite exchange.

In the satellite exchange, switching equipment is automatically responsive to the removal of the 'receiver at any calling substation thereof to exm tend a connection from the calling line to a trunk line leading from the satellite exchange to the main exchange. When line finders are employed in the satellite exchange, this extension of the connection is accomplished by a line nnder linked with a trunk line leading from the satellite `exchange to the main exchange.

In order to reduce to a minimum the number of trunks required between the satellite exchange and the main exchange for handling calls in the two directions, it is desirable that some of the trunks between the two exchanges be arranged for two-way operation. 'The overall trunking eiciency is increased greatly when the two-way trunks are used at either exchange only when all of the one-way trunks leading from that exway trunks, that a finder linked to a two-Way trunk is used in extending a connection to the main exchange only when all of the nders linked to the one-way trunks are in use.

The drawings Referring now to the accompanying drawings, comprising Figures 1 to 3, they illustrate suflicient of the equipment included in an automatic telephone system embodying the invention to enable the invention to be understood.

Figure l is a trunking diagram illustrating the paths taken by connections set up through the main and satellite exchanges; and

Figures 2 and 3 are circuit drawings of the portion of the switching equipment with which the invention is concerned.

The trunkzng layout The trunking layout shown in Figure 1 will now be described. The main exchange has a nominal capacity of one thousand lines, with one of the hundreds groups (the sixth) served by the satellite exchange. The portion to the right of the vertical broken line represents equipment of the main exchange, While the portion to the left of the vertical broken line represents equipment in the satellite exchange. These two exchanges are interconnected by trunk lines indicated at TI T2, and T3. In the example illustrated, the trunk Tl is one of a group of iive one-way satellite-tomain, trunks; the trunk T3 is one of five one-Way, main-to-satellite, trunks; and the trunk T2 is one of ve two-way trunks. With the ifteen trunks arranged in this manner, there can be amaximum of ten connections established in one direction (and five in the other direction) at any one given time.

Of the main exchange subscriber linesthe lines of substations C and D (telephone numbers 255 and 245) are illustrated, being two lines 55 and 45, respectively, of the second hundreds group. These lines are provided with individual line circuits LC-S and LC-ll, associated withthe control relays CR-Z. The control relays CR-2 control the iinder allotter FA-Z, associated with a group of finders, including F3, having access to the hundred-line group including the lines of substations C and D. It will be understood, of course, that a separate group of inders may be provided lfor each hundred-line group.

The finder F3 is linked with the hundreds selector S3, each of the finders being similarly linked to a separate selector.

The selector S3 has access to groups of connectors corresponding respectively to the assigned hundreds digits. The selector terminals through which the separate connector groups are reached are indicated under the rectangle representing the selector S3 by a heavy horizontal line section. The lowermost such line section indicates the trunk group reached when the digit 1 v is dialed; the next higher one indicates the trunk group reached when the digit 2 is dialed; etc., to the uppermost one, which indicates the trunk group reached when the digit is dialed. In the usual construction, a selector has ten choices in any trunk group. Accordingly, each of the said heavy horizontal line sections may be taken to indicate the terminals of ten trunks accessible to the selector. The fainter lines interconnecting the trunk terminals of the selector S3 with the corresponding ones of the selector S2 are intended to indicate multipling between the trunk terminals of the selectors S2 and S3, and the same holds true for the conductors extending hori-` zontally between the trunk terminals of the selectors Sl and S2. It Will be understood, of course, that the same multiple may extend to the other selectors, in accordance with the usual practice.

It is common practice to leave unassigned all telephone numbers beginning with the digit 1, because of the frequency with which a false or preliminary impulse is delivered during the removal of the receiver. ing of the word dead opposite the digit-1 group of selector contacts.

The second group of selector contacts is indicated as containing a trunk extending to the connector C3, the latter being one connector of the group having access to the second hundreds group, including lines 255 and 245. In the connector C3, each of the short horizontal lines shown thereunder indicates a group of ten lines, each reached responsive to the dialing of a separate one of the tens digits l to 0. These short horizontal lines are joined by fainter horizontal vlines to those of the finder F3, indicating the usual finder-connector multiple between the finders and connectors having access to the same v lines.

The short faint lines extending to the right .from the heavy lines indicative of other hundreds groups accessible from the selector S3 are intended to represent conductors extending to the connectors in the hundreds groups 3, 4, and 5 and 7, 8, 9, and 0. It will be observed that the sixth trunk group of the selectors SI `to S3 is illustrated somewhat dierently from the other trunk groups. The sixth hundreds group is the one located in the satellite exchange, and reached from the main exchange over the oneway and two-way trunks including `T2 and T3. The showing at the selectors SI to S3 with respect to the sixth trunk group is intended to indicate that the rst five choices of any one of the selectors are trunk conductors leading by way of repeaters, such as R4, to the ve one-way main-to-satellite trunks, of which the trunk T3 is one, and to indicate that the last ve choices of any one of the selectors are trunk conductors leading through repeaters, such as R3, to the five two-way trunks, of which the trunk T2 is one.

The selector SI is an incoming selector normally connected with the main-exchange end This explains the plac- Y (the irst and the sixth) included of the trunk T2, which trunk is capable of being switched over to the repeater R3 when the repeater is seized to complete a call over the trunk T2 from the main exchange to the satellite exchange. The selector S2 is an incoming selector in which the trunk TI terminates. It will be understood, of course, that there are ten incoming selectors in all, one for each of the five one-way incoming trunks illustrated by the trunk TI, and one for each of the ve two-way trunks illustrated by the trunk T2.

In the satellite exchange, the lines of substations A and B are shown, to which telephone numbers 601 and 606 are respectively assigned. These lines have the line circuits LC-l and LC-2 associated respectively therewith t0 exercise control over the control relays CR-l, in turn controlling the finder allotter FA-I. In the illustrated example the nder allotter has access to ten iinders, including finders Fl and F2. The finders F! and F2, along with the other eight finders, have access to all of the subscriber lines of the satellite exchange in multiple with the contacts through which the connectors CI and C2 have access to these lines.

As in the case of the switches described in the main exchange, each of the short horizontal lines below the rectangle indicating any of the nders and connectors in the satellite exchange, indicates a group of ten contacts. Since lines 601 and 606 are in the 0 group of the sixth hundred, these lines are indicated as coming out of the tenth or uppermost contact group of the illustratednders and connectors. It will be un'- derstood that these are only two of the lines in the tenth contact group.

The finder Fl is linked with the one-way repeater RI, individual to the trunk Tl leading from the satellite exchange to the main exchange. It will be understood that there 'are four other finders similarly linked, through other repeaters, to the four other one-way trunks lin'- cluded in the same group with the trunk TI.A

The nder F2 is linked through the repeater R2, which, upon seizure, may be connected with the two-way trunk T2. There are four other finders similarly linked through repeaters such as R2 to the other four two-way trunks.

The connector C2 terminates the incoming one-way trunk T3, and is one of ve connectors reached by way of the live one-way incoming trunks. The connector CI is one of five connectors normally connected with the two-way trunks, of which the trunk T2 is one.

Extending Connections Y With further reference to the trunking'diagram shown in Figure 1, a few examples will'be given of how connections are extended between the subscriber lines.

Assuming that the subscriber at substation D (telephone number 245) in the main exchange desires to call the subscriber at substation C (telephone number 255), the line circuit LC-I operates upon the removal of the receiver to cause a nder allotted by the nder FA--2 t0 make connection with the calling line. Assuming that the finder F3 is the one allotted, this finder is the one used, thereby placing the selector S3 under the control of the calling line.

When the first digit 2 of the desired number is dialed, the selector S3 associates itself with the connectors in the second hundred group, including the connector C3, and selects the iirst idle one of them found. Assuming that the selected one is connector C3, the calling line is now extended to the connector C3, 4

Responsive to the dialing of the second digit 5 in the desired number, the connector C3 associates itself with the fifth tens group of contacts, and it makes connection with the fifth line in the selected fifth tens group when the final digit 5 is dialed. The usual ringing operation follows, and the conversation may ensue when the subscriber at the called substation C (telephone number 255) removes his receiver. The switches included in this connection (between the lines of substations D and C) are the finder F3, the hundreds selector S3, and the connector C3.

In a similar way, a connection can be extended from any line in the main exchange t0 any other line therein.

Let it be assumed that the subscriber at substation D desires to converse with the subscriber at substation A (telephone number 601) in the satellite exchange, and that the iinder F3 is the one which makes connection with the calling line. In this case the selector S3 is under the control of the calling line, and it responds to the rst digit 6 in the desired number to associate itself with the sixth'h'undreds group of trunks accessible thereto and proceeds to select the rst idle one found. If any one of the first ve trunks is idle, one of the five one-way trunks is selected. It may be assumed that the one-way trunk T3 is selected, in which case the connection is extended from the selector S3, by way of the repeater R4 and the trunk T3, to the con nector C2 in the satellite exchange.

In this event, the connector C2 responds to the tens digit 0 to associate itself with the tenth group of lines accessible thereto, and it responds to the iinal digit l to make connection with the e first line in the group.

In the event that all of the one-way trunks leading from the main exchange to the satellite exchange are in use when a selector is searching in the sixth group, a connection may then be completed over one of the two-way trunks (such as by way of the repeater RS, and the two-way trunk T2, to the connector CI) in the satellite exchange. The connector in the satellite exchange then responds, as explained before, to the tens and units digits in the number to complete the connection to the called line.

In case the subscriber at substation A, for example, in the satellite exchange desires to converse with the subscriber at substation D, for example, in the main exchange (telephone number 245), the removal of the receiver at the calling sub-station in the satellite exchange results in the operation of one of the nders (Fi, for example) to extend a connection to a selector in the main exchange. This operatic-n results from a control being exercised over the control relays CRP-B, through the calling line circuit LC-l, to cause the finder Fl to rnake connection with the calling line. A connection is thereby extended from the line of substation A, through the finder Fi, and the repeater Ri, and over the one-way trunk Ti, to the incoming selector S2 in the main exchange.

The selector S2 responds to the dialing of the hundreds digit 2 by selecting the corresponding hundreds group, and by then selecting and connecting with the nrst idle connector found in that group. It may be assumed. that the connector C3 is the first one found to be idle, in

which case the connection is extended from the selector S2 to the connector C3. The connector C3 may then respond to the tens and units digits (4 and 5) in the called number to complete the connection to the line of substation D.

In the event that a call is made in the satellite exchange at the time all of the finders, such as Fi, associated with the one-way satellite-to-main exchange trunks are in use, the finder allotter FA-I allcts the rst idle one of the finders (F2, for example). associated with the two-way trunks, rI he finder F2 is thereby caused to make connection with the calling line, and to extend this line through the repeater R2, and thence by way of the two-way inter-exchange trunk T2 to the incoming selector Si in the main exchange. The selector Sl then responds to the dialed hundreds digit to extend the connection to an idle connector in th'e desired hundreds group, following which the connection is completed to the called line responsive to the dialing of the tens and units digits With respect to the completion of connections between two lines of the satellite exchange, it may be pointed out that in the trunking diagram as herein given each such connection reouires a trunk from the satellite exchange to the main exchange and another trunk from the main exchange back to the satellite exchange. It will be understood, of course, that well-known switching devices may be used for freeing both of the inter-exchange trunks and completing the connection looaily, when the calling and called lines both terminate in the satellite exchange. This ieature. however, has nothing to do with the present invention and has not been illustrated herein.

The circuit drawings Referring now particularly to Figures 2 and 3, equipment indicated by the circuit diagrams will be described generally. The equipment in Figure 3 to the right of the generally vertical broken` line is located in the main exchange, While the equipment in Figure 3 to the left of this line, together with all the equipment in Figure 2, is in the satellite exchange.

The satellite-exchange finder Fi of Figure l is indicated in the circuit diagram in Figure 2 by the equipment inside the broken-line enclosure. The finder Fl includes ten tens relays, associated respectively with the tens groups l to 9 and Q. convenience only the O-group tens relay T-llis shown. The conductors to the right, of the contacts of relay T- are multi.- plied to the similar contacts of each of the other tens relays. Additionally, while each tens relay has ten sets of contacts, each set including three Contact pairs, only four such sets have been indicated on the tens relays T-Li in order to conserve rawing space.

The finder Fl also has ve units relays, of which the units relays Ul and U2 are shown. The unitsv relays U3 to U5 are assumed to be located below the relay U2. With the exception of the series operating-chain contacts, a pair of which is shown below each of the relays Ul and U2, the contacts of units relays are connected in multiple to the two sets of conductors incoming thereto :from the units switching relay US. The units switching reiay US is arranged to be operated, or not, depending upon whether the units digit is from l to 5 or from 6 to 0. is the usual arrangement employed in order to. reduce the number of units relays from ten to Iive. Each set of conductors controlled by a units relay leads to a separate contact set of each of the tens relays, as indicated.

Each of the finders has a connecting relay associated therewith which is operated under the control of the finder allotter to place the nder under the control of the group control relays when connection is to be made with a calling line. The connecting relay I2 is the one associated with the iinder FI. The connecting relay I2', Figure 3, is similarly associated with the finder F2, whose circuits are not shown because they are similar to those of the nder FI.

The line circuits LC-I and LC-Z of Figure 1 are shown in detail in Figure 2. The line circuit LC-I includes line relay 2 and cutoff relay 3, while the line circuit LC-Z includes line and cutoi relays 4 and 5. Each of the line relays is arranged, when operated, to ground a marking conductor and a start conductor when energized, whereby the currently allotted inder is controlled to make connection with the calling line. Line relay 2 being associated with line till, the iirst line in the group, grounds the O-group mark conductor I, 6, common to lines 1 and 6 of the 0 group, and it grounds the 0-group start conductor I-5, common to lines 1 to 5 in the 0 group.

Line relay 4 of the line circuit LC-Z, being associated with line 60E, the sixth line in the 0 group, is arranged, when operated, to ground the mark conductor I, 6 (common to lines l and 6 in the same tens group) and to ground the start conductor G-IJ common to lines 6 to 9 and 0 in the same tens group.

For each group of tens lines there are two start conductors, such as the start conductors I--5 and 6 0 for the O group, and there are ve mark conductors, such as the mark conductors I, 6; 2, 1; 3, 8; 4, 9; and 5, l) of the 0 group.

The control relays CR--I of Figure 1 are illustrated in Figure 2. Each group of ten lines has three control relays assigned thereto, the control relays for the 0 group of lines being the illustrated relays A--0, B-ll, and C-I). Relay C-U is the guard relay, and it operates to disconnect the corresponding relays associated with the other tens groups when there is a calling condition in the associated tens group of lines. The operating circuit for the relays A-II to C-, ltherefore, includes chain contacts on relay C-IJ, as well as on the other similar relays associated with the other tens groups. Relay C-I, assoelated with the l tens group is illustrated, in order that the chain-contact arrangement may 'be shown more fully. The tens-group guard relays CkZ to C-9 are not shown,l but are interconnected in the chain circuit between the relays C-I and C--IJ at the portion thereof indicated by the dotted lines.

It is to be noted that cable CA-I contains a number of conductors extending from the control relay CR-I and multiplied to contacts of the connecting relays (such as I2) of the finders, and that the cable CA--2 carries ten conductors associated respectively with the contacts of the C relays (such as C-Il of the tenth tens group and C--I of the first tens group) to other contacts of the finder-connecting relays, such as relay I2 of the nder FI.

The nder allotter FA-I of Figure 1 is shown in circuit diagram in Figure 2. This allotter includes ten allotter relays indicated as relays AI to AIO, each of which is associated with a separate one of the ten iinders, including nders FI and F2. Relays A3 and A4 and A8 and A9 have been omitted from the drawings to conserve drawing space, as these relays are similar to the respective preceding and succeeding relays.

The allotter relays AI to A5 are associated respectively with the velinders, such as nder FI, which are associated with the one-way trunks, such as TI, extending from the satellite exchange to the main exchange. The allotter relays A6 to AIU are associated, respectively, with the ve finders (of which the finder F2, Figures 1 and 3, is one) associated respectively with the ve two-way trunks extending between the satellite and main exchanges.

The iinder allotter FA--I includes also the group relay IIJ, common to the ve one-way trunks and normally operated, as indicated, yto insure that no nder associated with a two-Way trunk is allotted as long as there is at least one idle finder associated with a one-way trunk. The nder allotter also includes pick-up relay II which serves to transmit energizing pulses at the proper times to the allotter relays AI to A5 and A6 to AIIJ.

The repeater RI of Figure 1 is shown in Fig- V ure 2. This repeater has four conductors, a to d, linking it with the nder FI, and it includes the line and release relays 22 and 2|, as well as the high-resistance trunk relay 23, normally energized over the outgoing conductors a and b of the trunk TI in series, whereby this relay is restored at any time the trunk vTI is in use or is out of order.

'Ihe two-way trunk T2 of Figure 1 is shown in Figure 3 as a twoconductor inter-exchange trunk, comprising the usual a and b talking conductors. These conductors normally extend at the satellite exchange to ground and battery through normally closed contacts of transfer relay 29, and the upper and lower windings of line relay 24 in the connector CI. The conductors of the trunk TI normally extend in the main exchange to ground and battery, through contacts of transfer relay 32 and the upper and lower windings of line relay 3| of the connector SI. The circuit arrangements of the connector CI and the selector SI are only fragmentarily shown, for they may be of any well-known, suitable type.

The circuits of the repeaters R2 and R3, associated with the trunk T2 in the satellite exchange and in the main exchange respectively, are shown and will be described hereinafter.

It is to be noted that the a, b, and c conductors of the lines of substations A and B, Figure 2, in addition to extending to contacts of the illustrated tens relay T-IJ of the finder FI, are shown as multiplied to the finder F2 and to the connector CI of Figure 3. As indicated by the notation at the top part of Figure 3, these conductors are multiplied to the other finders and connectors. It will be understood, of course, that the same arrangement applies to each of the other subscriber ylines in the satellite exchange.

DETAILED DESCRIPTION The invention having been described generally, a detailed description of the operation of the apparatus shown will now be given.

A calling B Let it be assumed now that the subscriber at substation A, whose telephone number is 601, de-

sires to converse with the subscriber at substation B, Whose telephone number is 606. Both of the lines concerned terminate in the satellite exchange.

When the receiver (not shown) is removed at substation A, line relay 2, Figure 2, operates over the calling line through contacts of cutoi relay 3. Upon operating, relay 2 places ground potential on the I, 6 marking conductor of the associated group, and also places ground potential on the start conductor |-5 of the associated 0 group. The grounding of the marking conductor I, 6 has no immediate eiect, but the grounding of start conductor I-5 extends ground potential to the junction of the windings of the A-U and the B-ll relays. Assuming that no call is being initiated in another one of the tens groups, all of the ten C relays, such as C-ll and C-I, are in normal condition at the time. Under this condition, the placing of ground potential on the start conductor I-5 completes a circuit through mark-control conductor B-, through guard relay C--IL and the innermost armature and resting contact of relay C-, to the common guard conductor I3. From thence, under the condition of all of the C relays being restored, the circuit extends through normally closed chained contacts controlled by the armatures of the C relays, and thence to battery through normally closed contacts controlled by t.

the armatuer of'the slow-operating recycle relay 5, by way of resistor l. Relays B- and C-Il operate over the above circuit. Relay B- connects the ve mark conductors (I, 5; 2, 1; 3, 8;

, 9; and 5, 0) of the 0 group to conductors I ,1

to 5, respectively, of the cable CA-I. As is indicated by the conductors extending a short way to the right of the contacts of relay B-U, the conductors 1 to 5 of the cable CA-I extend to similar contacts of the B relays (not shown) in the other tens groups.

When relay7 C-Q operates it locks itself to the battery-supply chain, at the same time opening the chain and also disconnecting its winding from guard conductor i3. Battery potential is now removed from guard conductor I3 but guard relay C- is now disconnected from this guard conductor and is locked up independently thereof. In this way the operation of any of the ten C relays results in the removal of battery potential from guard conductor I3 to prevent an operation of a further C relay, and consequently the operation of any other A and B relay, as long as the operated C (guard) relay remains in operated condition.

At its lowermost armature, relay C-ll grounds conductor it of the cab-le CA-2, preparatory to operating the D tens relay in the finder allotted to make connection with the calling line. Additionally, relay C- places ground potential on the allotter-start conductor I9.

Let it be assumed that in the allotter AI the relays Ai to A5 are in the indicated restored :condition at the time allotter-start conductor I9 is grounded by relay C--5, and that group relay i@ is in the indicated energized condition, because one or more of the one-way satellite-to-inain trunks are idle. Under this condition, the ground potential on conductor I9 is extended through normally closed contacts of relays AI to A5, and the lower armature of the actuated group relay il), to the winding of the slow-operating pick-up relay EI. When relay H operates and extends ground potential, through contacts of the operated group relay It, to pick-up conductor I5.

Conductor I5 is associated with the allotterrelays Al to A5, associated respectively with the one-way trunks. Each of the relays AI to A5 whose associated one-way trunk is not in use at the moment operates when conductor I5 is thus grounded. The circuit for operating relay AI is ironi ground on conductor i5, through normally closed contacts controlled by the inner armature of relay Ai, through the winding of relay AI and thence to battery through the middle armature of the high resistance, normally energized trunk relay 23. This circuit is closed unless the trunk Ti is in use or is out of order, in which case relay 23 in a restored condition. Assuming that the trunk Ti is idle, relay 23 is operated, and the circuit for the relay AI is closed as above Upon the closure of the above circuit, relay Ai operates and locks itself to ground through its innermost armature, at the same time disconnecting its winding from conductor I5 in order to avoid making an additional ground connection to pick-up conductor I5. Each of the other relays to A5 whose associated trunk is idle operates with similar results.

Upon the operation of any one of the relays to A5, the chain circuit for pick-up relay it is broken, permitting relay Il to restore after a slight interval and remove ground potential irorn pick-up conductor I5.

Upon the operation of allotter relay AI, the grounded allotter-start conductor I9 is transferred to the rst conductor of the cable CA-3, thereby allotting the nder FI by operating connecting relay I2 associated therewith. A branch holding circuit for the upper winding of relay Al is closed at the same time. Upon the operation of relay I2, the conductors in cables CA-I and (JA-2 are connected respectively with conductors of the finder FI.

Battery potential, through resistor 9, and contacts of relay I2, is now applied to the a conductor in the link between the nder FI and the repeater Rl, thereby closing a circuit to ground, through the upper left-hand repeating coil winding, and the upper winding of line relay 22. Line relay 22 thereupon operates and closes'an operating loop across the conductors a and b of the trunk Tl, through the right-hand repeating coil windings in series, thereby operating the line relay (not shown) of the selector S2, Figure l, which line relay is unable to operate in series with the high resistance trunk relay 23. The selector S2 in the main exchange is thereby prepared for operation in the usual manner.

Line relay 22 also closes a circuit at its upper armature for slow-acting release relay 2i. Release relay El now operates, and it disconnects the high-resistance trunk relay 23 at its inner armature, while at its lower` armature it applies a ground potential to the associated c and d leads. Trunk relay 23 now restores. At its lower armature relay 2,3 opens one point in the circuit of group relay I5, but relay I remains operated as long as the relay corresponding to 23 is operated in any other repeater associated with a one-Way outgoing trunk. At its inner armature, relay 23 disconnects battery potential from the` lower winding of the relay AI, thereby deenergizing such lower winding. Relay AI however, remains operated for the time being because the upper winding thereof is energized in parallel with the winding of connecting relay I2, as previously pointed out. In this way, the allotter is maintained in association with the finder FI until the finder has completed its operation.

When ground potential is applied to the hold lead d by the above-mentioned operation of release relay 2I, a circuit is closed, through the outermost .contacts of the operated connecting relay I2, and thence over conductor 'I of the cable CA-I, for the slow-operating recycle relay 6. Relay 6 does not have time to operate during normal finder operation, but is provided to open the battery connection to the associated group relays to restore them to permit recycling oi' the group relays, and the transfer of the allotter to the next finder, in case there are overlapping calls in the same group.

With the tenth conductor in cable CA--2 grounded, at the lower contacts of relay C-, the operation of connecting relay I2 closes a circuit through contacts thereof for the tens relay T-- of the finder FI. Relay T- thereupon operates and locks itself to the associated common locking conductor, connected by way of resistor 8 to the associated d lead, grounded at the lower armature of release relay 2l.

With the grounded I, 6 mark conductor associated with the line circuits LC-I and LC'-2 connected through the upper contacts of relay B- to the i'lrst conductor in the cable CA-I, the operation of relay I2 results in the closure of a circuit through contacts thereof, for the first units relay UI of the nder FI. Relay Ui now operates and locks itself to the associated d lead, at the same time removing battery potential from the succeeding units relays so as to prevent simultaneous operation of two of the units relays in the event that a further line in the 0 tens group is simultaneously calling, and has grounded a further one of the work conductors 2, 'I to 5, 0.

The units switching relay US, although connected with the sixth conductor in the cable CA-I by contacts of the operated connecting relay I2, is not operated at this time because the calling line is one whose start conductor goes directly to the winding of relay B-Q and has not, therefore, operated relay A-, wherefore the sixth conductor in the cable CA-I is not grounded.

With the units switching relay US not operated, and with relays UI and T-El operated, the a, b, and c leads of the line of substation A are now extended through contacts of the relays T-U, UI, and US to the a, b, and c leads linking the nder FI with the repeater Rl. The ground potential placed on the associated c lead by release relay 2| is effective at this time to apply a guarding potential to the c lead of the line circuit LC-I, to guard the calling line against intrusion, and to operate cuto relay 3. Cutoff relay 3 disconnects ground potential and the winding of line relay 2 from the associated a and b conductors of the calling line, whereupon the line relay 2 restores.

When line relay 2 restores it removes ground potential from the mark conductor I, 6, thereby opening the initial circuit of units relay UI, but relay UI remains operated in its described locking circuit, including the grounded hold lead d and the lower armature of the operated release relay 2|.

Relay 2 also removes ground potential from the I-5 start lead thereby permitting relays B- and C-El to restore, unless a call has been origi- B-ll and C-D to remain operated. In the latter event, the control relays CR-I are not cleared out responsive to the restoration of the line relay 2 and the described circuit for the slow-operating unlock relay 6 remains established sufficiently long for relay 6 to operate. Upon operating,` relay 6 opens the battery connection to relays C-I to C El, whereupon relays B--l and C-Il restore.

When relay C- restores, whether from the remcval of ground potential from start lead I-5 by the restoration of line relay 2, or from the abovementioned operation of unlock relay 6, it removes ground potential from the 10th conductor in cable CA-2, thereby opening the initial circuit of the operated tens relay T-IL Relay T-0, however. remains operated in its described locking circuit, including the lower armature of the relay, current limiting resistor 8, and the grounded Vhold lead d.

Relay C-i) also removes ground potential from the allotterstart conductor I9, thereby opening the circuit of the finder-connecting relay I2 and the circuit of the upper winding of allotter relay AI. Relays l2 and AI thereupon restore, the lower winding of relay AI having been opened by the described restoration of relay 23. The restoration of relay I2 disconnects the conductors of the cables CA-I and CA-2 from the now-operated nder FI. When this occurs the circuit for recycle relay 6 is opened at the outermost armature of relay I2, permitting relay E (if operated) to restore after an interval to permit a further operation of the control relays to cause the next calling line to be connected With by another nder.

When allotter relay AI restores, at its inner armature it opens a further point in the previously existing locking circuit for its lower winding, and at its lower armature it disconnects the now ungrounded allotter-start conductor from its own upper winding and the winding of relay I2 and extends it through the illustrated allotter chain circuit, and through the armature of the next operated one of the relays A2 to A5 to the associated finder-connecting relay, such as relays I2 and I2', Figures 2 and 3.

With cutoff relay 3 operated, and with resistor 9 having been disconnected from the a lead between the nder FI and the repeater RI, by the restoration of relay I2, the line relay 22 in the repeater RI is now held operated over the calling line and in series with the substation telephone A.

The calling subscriber at substation A may now operate his calling device in accordance with the digits (6, 0, and 6) in the number of the desired substation B.

As a result of the operation of the calling device (not shown) at substation A in accordance with the rst digit 6 of the desired number, the line relay 22 of the repeater RI is restored momentarily six times. Each time it restores, line relay 22 opens the circuit of the associated slow-acting release relay 2l, but relay 2i remains operated throughout the series of restorations. Also, each time it restores, line relay 2l opens the bridge across the conductors of the trunk TI at its lower armature. As a result, the selector S2, Figure 1,v

with the repeater RI to close a loop across the conductors of the trunk T3 to prepare the connector C2, shown in Figure l, for operation.

When the second digit in the desired number is dialed, line relay 22 of the repeater Rl restores `ten times momentarily, thereby interrupting the bridge across the outgoing conducto-rs of the trunk Tl ten times. With the connection having been extended by way of the selector Rl to the repeater R4, Figure l, the ten interruptions are repeated by the repeater R4, to the connector C2 in the satellite exchange, causing the connector C2 to select the tenth associated group.

When the final digit 6 is dialed, the resulting series of six interruptions is repeated by the repeated Ri, Figures 2 and l, to the repeater Ril, Figure l, and thence to the connector C2, to cause the connector to select the sixth line in the tenth group, being the line of substation B, Figures 1 yand 2. In Figures 2 and 3, the connection is extended to the line by way of the vertical multiple between the nders and connectors, bearing the label -at the top thereof, Mult to other finders and connectors.

When connection is extended to the called line, the line of sub-station B, a guarding ground potential is applied by the calling connector to the c lead thereof, resulting in the energization of cutoi relay to clear the called line for ringing and talking purposes.

When the subscriber at substation A replaces his receiver, line relay 22 opens the control circuit established through the selector Si, Figure l, to the repeater R4, whereupon the line relay (not shown) in the repeater R4 resto-res and opens the control circuit extending over the trunk T3 to the connector C2, permitting the `connector C2 to clear out and free the line of substation B. When the line is freed, cutoff relay 5 restores.

The selector S! in the main exchange is released when the release relay (not shown) in the repeater R4 restores and removes ground potential from the associated c lead.

In the repeater RI, rel-ease relay 2| restores shortly after the restoration of line relay 22. When it does so, it again bridges the high-resistance trunk relay 23 across the conductors a and b of the trunk Tl, permitting relay 23 to reoperate. The releasing operation in the -m-ain exchange is not interfered with because of the high resistance of relay 23. Upon reoperating, relay 23 again closes a point in the multiple operating -circuit of the normally energized group relay ID, and it reapplies battery potential to the l upper terminal of the lower winding of the allotter relay A! Relay A! does not r-eoperate responsive to this operation, but waits until the circuit of the lower winding is closed by an operation of pick-up relay Ii, as previously described. In this way, the nder FI is not again allotted until each of the finders associated with allotter relays A2 to A5 has had its turn.

Release relay 2i of the repeater RI yalso disconnects ground potential from the associated leads c and d. When lead c is ungrounded, cutoff relay 3 in the line relay LC-i restores and again connects up the line relay 2 for operation. The removal of ground potential from the hold lead d opens the locking circuit of the operate-d relaysr Ul and T0 in nder Fl, whereupon these relays restore, clearing out the nder Fl and breaking the connection between the line of substation A and the repeater RI B calls Let it be assumed that the subscriber at substation `B desires .to make a call `and accordingly removes his receiver (not shown). Let it be assumed further that the call is originated as the next call following the one previously described which used the finder Fl and the repeater Ri, and resulted in the restoration of allotter relay Ai, leaving the allotter relays A2 to A5 operated as the result of having been operated as previously explained responsive to the initiation of the call over the line of substation A.

When line relay fi operates over the line of substation B upon the removal of the receiver thereat, it grounds `the mark conductor I, Ea, as the case of line relay 2. The start conductor grounded by line relay t, however, is the start conductor @-9 common to the 6th and 10th lines in the il group. As a result, relay A-il energizes in circuit with relays B-Il and C--IL Relay A-O grounds the associated sixth conductor in the cable CA-L Relays B-ll and C-El operate with the previously described results. The grounding of the allotter-start conductor I8 at this time does not result in an operation of relay It, because allotter relays A2 and A5 are still operated under the conditions now assumed. A circuit is, therefore, closed, through the lower armature of the restored relay Al, and through the lower armature of the operated relay A2, for the upper winding of the relay A2 to hold this relay operated until the associated nder has completed its operation. At the same time, a parallel circuit is closed through the second conductor in the cable CA-S for the connecting relay (similar to relay I2) of the finder associated wi-th relay A2. This connecting relay thereupon operates to connect the conductors of cables CA-I and CA-Z to such finder, resulting in the operation of the 0 tens relay .therein (similar to relay T-ED and in the operation of the first units relay therein (similar to relay Ui). At this time, since the sixth conductor in cable CA-l has been grounded by the operation of relay A-i), a circuit is closed for the units switching relay (similar to units switching relay US of the finder FI) in the now active finder.. As a result, the finder makes connection with the line of substation B through contacts of the operated relays corresponding to US, Ui, and T-Il of the iinder Fi. This connection is made over the previously mentioned vertical multiple shown extending from Figure l across Figure 2.

When this connection is made, cutoff relay 5 is operated to disconnect and restore the line relay 4.

After the connection has been made and the relays A-0, B-0, and C-ll have cleared out as previously explained, the removal of ground potential from conductor i9 permits relay A2 to restore and extend the control to the A3 relay (not shown) of the allotter FA-l. The restoration of relay A2 takes place at this time because the circuit of the lower winding thereof has been opened by the restoration of the relay similar to relay 23 associated with the nder and repeater with which relay A2 is associated.

The further operations in connection with a call from substation B may be similar to those described in connection with the call from substation A.

Picking up idle allotter relays Let it be assumed now that other calls have been initiated suficient to cause each of the live one-way outgoing trunks (such as TI, Figures l and 2) to -be taken for use in turn. Let it be assumed further that these calls are suciently separated that one or more of the trunks ilrst used have become idle by the time the last one has been taken for use. It may be assumed that the trunk TI is one of those which has become idle, in which case trunk relay 23, Figure 2, has reoperated as pointed out. Under this condition, group relay I has not been restored. Then, when the next call is initiated in the satellite exchange, the resultant grounding of allotter-start conductor I9 results in the closure of a circuit, through the lower armatures of the restored relays AI to A5, and the lower armature of the operated group relay I9, for pick-up relay Il. Relay II again grounds conductor I5, through the armature of the operated group relay I9. The placing of ground potential on conductor I completes a circuit for the lower winding of each of the relays AI to A5 which is associated with an idle nder and repeater. 'I'he circuit for the lower winding of relay AI includes the normally closed contacts controlled by the inner armature of relay AI, the said lower winding, and the inner armature of the operated trunk relay 23. Relay AI now operates and locks the lower winding energized independent of the conductor I5, at the same time disconnecting the lower winding from this conductor. Relay II restores as a result of the operation of relay AI and of any other ones of the relays AI to A5, and again removes ground potential from conductor I5, leaving the operated ones of the relays AI to A5 in their operated and locked condition.

The ground potential on start conductor I9 is now extended to the upper winding of relay AI, and also through the No. 1 conductor in cable CA-3 to the winding of lnder-connecting relay I2, causing relay I2 to operate, and relay AI to remain operated, as previously described.

From the foregoing, it will be seen that the relays AI to A5 are operated over and over to reallot the associated iinders and one-way outgoing trunks, with no calls being transferred to the nders and two-way trunks associated with allotter relays A6 to AI, so long as at least one one-way outgoing trunk remains idle, and group relay I0 consequently remains operated.

Using the two-way trunks for .satellite-ifo-main calls Let it be assumed now that all of the i'lve oneway trunks, including the trunk TI Figures l and 2, are in use. At the same time, all of the allotter relays AI to A5 will have been restored as a result of the restoration of all of the trunk relays, such as 23, associated with the repeater RI. Additionally, with all of the one-way trunks from the satellite exchange to the mainy exchange in use, and all of the relays, such as 23, in restored condition, the multiple circuit is open at all -points for the group relay I0, causing this relay to restore.

Under the above conditions, when the next -call is originated in the satellite exchange, the resultant grounding of allotter-start conductor I9 completes a circuit, through the lower armatures of the restored relays AI to A5, and thence by way of the lower armature of the now-restored group relay I0, and through contacts of the unoperated relays A5 to AII), for pick-up relay II. Relay II now operates and extends ground through the inner armature and resting contact of the restored group relay I 0 to conductor I5, thereby completing a circuit through the lower winding of each of the relays A6 to AIU (associated with the two-way trunks) provided in each case that the two-way trunk associated there` with is idle. In the case of relay A5, if the twoway trunk T2 is not in use in a call incoming to the satellite exchange the connector CI, Figures 1 and 3, is not in use, and the release relay 25 therein is restored. Also, if the trunk .T2 is not in use in completing a call from the satellite exchange to the main exchange, the repeater R2, Figures 1 and 3, is idle and transfer relay 29 therein is restored. Under this condition, the application of ground potential to conductor I4 results in the closure of a circuit through the nor. mally closed contacts associated with the inner armature of relay A6 for the lower winding of the relay, over conductor I8, and through the lower contacts of relays 29 and 25 to battery. Relay A6 thereupon operates and closes a locking circuit for itself at its lower armature independent of the continued grounded condition of conductor E 4, at the same time disconnecting its lower winding from conductor I4. Each other one of the allotter relays Al to AII) (relays A8 and A9 not being illustrated) which operates similarly closes a local locking circuit for its lower winding.

With relay I9 in a restored condition, the operation of relay A6 extends the ground potential incoming over conductor I9 to the upper winding of relay A6 to hold this relay operated until the associated nder F2, Figure 3, has been operated to connect the calling line with the repeater R2. At the same time, a branch circuit is extended over conductor 6 of the cable CA-3, and thence by way of conductor I6 to the finderconnecting relay I2 of the finder F2, whereupon' relay l2 operates-to connect the control oonductors in cables CA-I and CA-2 with the finder F2, to cause this finder to be operated as explained in connection with the finder FI.

Upon the operation of any one of the allotter relays A6 to Al, the extended circuit of pick-up relay il is now broken because the circuit of relay ii includes contacts of relays A6 to AIO when group relay I0 is in restored condition. Relay II restores shortly thereafter and again removes ground potential from operating conductor I4.

With further reference to the finder F2 and the repeater R2, the upper winding of line relay 2S of the repeater R2 is energized, rst in a local circuit through contacts of finder-connecting relay 52 as previously explained in connection with the finder FI and the repeater RI, and then over the calling line after the finder F2 has made connection therewith. Upon energizing, line relay 23 operates the associated slow-acting release relay 2l, and relay 2'I grounds the associated c and d leads with results in the nder F2v as previously pointed out in connection with the finder FI. In the repeater R2, the grounding of the c lead has the further elect of closing an energizing circuit for transfer relay 29. When relay 29 operates, it transfers the a and b leads of the trunk T2 from the corresponding leads of the connector CI to the outgoing a and b leads of the repeater R2. When this results, a loop circuit is closed across the a and b leads of the trunk T2, by way of the right-hand windings of the repeating coil of the repeater R2, and the lower contacts of operated line relay 28. This results in the operation of the line relay 3| in the selector SI in the main exchange. When line relay 3l operates it closes a circuit for the associated release relay 30. Release relay 30 disconnects the associated c lead of the repeater R3 from transfer relay 32 and connects it to ground, thereby guarding the repeater R3 and the trunkV T2 against seizure in the main exchange. By the operation of line and release relays 3l and 30 of the selector Si, the selector SI is prepared for operation in the usual manner to extend the connection when the calling subscriber dials the rst digit in the desired number.

A further result of the operation of transfer relay 29 in the repeater R2 is the opening of the previously established circuit over conductor I8 for the lower winding of the 4associated allotter relay A6. As a result, relay A@ restores along with relay I2' when the finder F2, Figure 3, has made connection with the calling line.

When the calling subscriber subsequently replaces his receiver (after having dialed to cause the connection to be extended as desired) the resultant restoration of line relay 28 of the repeater R2 results in the opening of the loop across the conductors of the trunk T2 at the lower contacts of the relay, permitting the operated switching equipment in the main exchange to clear out in the usual manner. The restoration of relay 2lil also permits release relay 21 to restore and remove ground potential from the associated c and d leads to permit the finder F2 to clear out and free the called line. The removal of ground potential from the c lead permits transfer relay 29 to restore and again connect the conductors of the trunk T2 with the connector CI. Relay 2S also again prepares a circuit over conductor I8 for reenergizing the lower winding of allotter relay A6 the next time pick-up conductor I4 becomes grounded.

Assuming that the one-way trunks all remain busy for a time and that 'another call is initiated in the satellite exchange during this time, the consequent grounding of allotter-start conductor I9 results in the closure of a circuit through the contacts of the restored relays AI to A5, through the contacts of the restored relays I0 and A6,

and thence by way of the remaining portion of the allotter chain circuit to the upper winding of the next one of the relays A1 and AI@ which is in operated condition, thereby causing this relay to be held and the associated finder-connecting I relay (similar to I2) to be operated.

As soon as one of the one-way trunks outgoing from the satellite exchange to the main exchange becomes idle, group relay Il! is again operated,

when its circuit is closed at the rst one of the I trunk relays (such as relay 23 of the repeater RI, Figure 2) to reoperate. Upon reoperating, group relay IG again prepares for the allotting of any one of the ve finders associated with the oneway outgoing trunks and respectively with the alotter relays Al to A5, as previously explained.

The next time all of the one-way trunks become busy and relay IIJ restores as a result thereof. it may well be that one or more of the relays A6 to All) associated respectively with the twoway trunks, are still in operated condition. Under this condition, the grounding of the allotter-start conductor I9 does not cause a reoperaton of allotter-control relay II but closes the chain circuit through contacts of any restored ones of the relays A6 to AIO and through the lower `arn'iature of the rst operated one of such relays for the upper winding of the relay and a parallel circuit for the associated finder-connecting relay, to cause the finder to be operated as previously pointed out. The finders associated with the two-way trunks are, therefore, taken for use in turn.

Using the two-way trunks for main-to-satellz'te calls 'Figure l, is one, are the choices 6 to 10 of the selectors in the main exchange.

Let it be assumed that all of the one-way trunks leading from the main exchange to the satellite exchange are in use, and that one of the selectors (the selector S3, Figure l, for example) is operated in accordance with the hundreds digit 6, in a call from the main exchange to the satellite exchange. Under this condition, the searching operation of the selector S3 continues until all of the five busy one-way trunks have been tested and the two-way trunks are reached. It may be assumed that the two-way trunk T2 is idle and that this is the one selected. The trunk T2 is shown also in Figure 3. Referring particularly to Figure 3, the trunk T2 is accessible in the main exchange by way of the a, b, and c leads of the repeater R3. The testing of the trunk T2 in the main exchange occurs over the c lead of the repeater R2, which lead is in an ungrounded condition when the trunk is idle. When the repeater R3 is seized by the selector in the main exchange, ground potential is applied temporarily by the seizing selector to the c lead to render the trunk busy in the local selector multiple. The ground potential thus applied closes an operating circuit for transfer relay 32 of the repeater R2, which includes the lower armature and resting contact of release relay 3Q of the selector SI. When transfer relay 32 operates it disconnects the a and b conductors of the trunk T2 from the selector SI and transfers them to the outgoing conductors of the repeater R3.

As a further result of the seizure of the repeater R3, the calling subscribers loop is extended to the incoming conductors o, and b thereof, thereby closing a circuit for line relay 33. Line relay 33 actuates the slow-acting release relay SIII to ground and maintain grounded the associated c lead at the repeater. Additionally, line relay 33 bridges the left-hand windings of the associated repeating coil across the associated outgoing talking conductors, thereby closing a loop across the now transferred c and 7J leads of the trunk T2, establishing a circuitJ through contacts of the unoperated transfer relay 29 of the repeater R2, for the line relay 253 of the connector CI in the satellite exchange.

Line relay 24 now operates and closes a circuit for release relay 25. Release relay i5 operates to prepare the connector for the usuel operation in response to the further dialing on the part of the calling subscriber. Additionally, relay Z5 disconnects battery potential rcn conductor I8, normally applied thereto through contacts of transfer relay 29. The circuit or" the lower wind-` ing of relay allotter A@ is thereby opened at one point, preventing operation of relay Al in theV event that pick-up conductor Ill becomes grounded as previously described while the trunk T2 is in use, or restoring relay A6 if currently locked up and held over conductor I8.

When the calling subscriber dials the two remaining digits in the desired number, the connector CI of Figure 3 operates in the usual manner to extend the connection to the desired line. The dial pulses are repeated by line relay 33 of the repeater R3 to line relay 24 of the connector CI for this purpose. The slow-acting release relays 34 and 25, of course, do not restore during the dialing operation.

When the calling subscriber replaces his receiver, the resultant restoration of line relay 33 permits line relay 24 of the connector CI to re-l store. Release relay 23 restores shortly thereafter and again replaces battery potential through contacts of transfer relay 29 on conductor I8 to prepare a circuit for relay A6 in the allotter FA-I, thereby rendering the two-way trunk T2 accessible again from the satellite exchange, subject to the previously described condition of all of the one-way trunks being in use to bring about the restoration of group relay IB.

In the main exchange, release relay 34 shortly restores responsive to the restoration of line relay 33, thereby removing ground potential from the associated c lead to restore transfer relay 32. Transfer relay 32 transfers the a and b conductors of the trunk T2 back to the corresponding conductors of the incoming selector SI. The removal of ground potential from the c lead of the repeater R3 marks associated trunk multiple as idle in the banks of the selectors having access thereto.

What is claimed is:

1. In a telephone system, a first telephone exchange and a second telephone exchange, a group of one-way trunk lines extending from the first exchange to the second exchange, a group of two-way trunk lines interconnecting said exchanges and available in each exchange for ex` tending connections to the other, two groups of finders in the first exchange, the finders of the first group being linked respectively to the said one-way trunk lines extending from the first exchange to the second, the finders of the second group being linked respectively to the firstexchange end of said two-way trunk lines, lines of the first exchange accessible to all said finders, a finder allotter associated with said finders and effective to allot idle ones of said finders successively for use to extend calling ones of said lines to the second exchange, and means for causing said allotter to allot an idle finder of the second group only in the event all of the trunks to which the nders of the first group are linked are in use.-

2. In a telephone system, a first telephone exchange and a second telephone exchange, a group of one-way trunk lines extending from the first exchange to the second. exchange, a group of two-way trunk lines interconnecting said exchanges and available in each exchange for extending connections to the other, two groups of finders in the first exchange, the finders of the first group being linked respectively to the said one-way trunk lines extending from the rst exchange to the second, the finders of the second group being linked respectively to the first-exchange end of said two-way trunk lines, lines of the first exchange accessible to all said finders, a finder allotter associated with said finders and effective to allot idle ones of said nders successively for use to extend calling ones of said lines to the second exchange, and means for causing said allotter to allot an idle finder of the second group only in the event all of the trunks to which the finders of the first group are linked are in use, said means'including a group relay controlled according to the busy or idle condition of each of said one-Way trunks.

3. In a trunking system,'two groups of finders, lines directly accessible to all said finders', Vany of said finders being operable when in idle condition and when allotted to extend any calling one of said lines, an allotter associated With said finders and operable to allot any idle one -of them to extend the next calling line, means for con'- trolling said allotter to allot an idle finder in the second group only in case all ofthe finders in the first group are in use, said means including a group relay and means for actuating it directly responsive to thevcondition of all finders in the first group being in use. v v

4. In a switching system, two groups of finders, lines accessible to all said finders, an allotter comprising a series of relays,` means for causing said relays to respond successively to allot idle ones of said finders, the first relays .in the series being associated respectively with the finders of the first group, the remaining relays in the series being associated respectively with the finders of the second group, and means including a group relay responsive to the condition of all finders in the first group being busy for rendering the said relays of the series associated with the second group of finders initially responsivev to allot finders in the second group.

5. In a switching system, two groups of finders, lines accessible to all said finders, two series of allotter relays associated respectively with said groups of finders, the first series of relays being normally operative to allot idle finders in the first group, and means responsive to the condition of all finders in the first group being busy for joinl ing the second series of allotter relays to the first, the relays in the second series being thereupon rendered effective to allo-t idle finders in the second group.

6. In a switching system, a group of line finders, normally closed control contacts individual respectively to said finders, lines accessible in common to all said finders, a series of allotter relays, said relays being individual respectively to said finders, means including a starting chain circuit extending through contacts of said relays for allotting the finder associated with the rst operated relay, such operated relaybeing held operated in a self-locking circuit including the said control contact individual to the associated finder, and means effective when the allotted finder is taken for use for opening the said individual contact to unlock and restore the said operated relay to thereby allot the finder asso` ciated with the next succeeding operated one of said relays.

'7. In a switching system, a group of line finders, normally closed control contacts individual respectively to said finders, lines accessible in common to all said finders, a series of allotter relays, said relays being individual respectively to said finders, means including a starting chain circuit extending through contacts of said relays for alloting the finder associated with the first operated relay, such operated relay being held operated in a self-locking circuit including the said control contact individual to the associated finder, means effective when the allotted finder is taken for use for opening the said individual contact to unlock and restore the said operated relay to thereby allot the finder associated with the next succeeding operated one of said relays, the said control contactindividual to anynder becoming closed again when the iinder again becomes idle, a pick-up relay associated with said allotter relays and means for operating it over the said chain circuit when all of said allotter relays are in restored condition, said pick-up relay being eiective when operated to reoperate all of said relays whose associated iinders are in idle condition, whereby such relays again become self-locked.

8. In a switching system, a group of line nders, normally closed control contacts individual respectively to said nders, vlines accessible in common to all said nders, a series of alloter relays, said relays being individual respectively to said finders, means including a starting chain circuit extending through contacts of said relays for allotting the nder associated with the rst operated relay, such operated relay being held operated in a self-locking circuit including the said control contact individual to the associated nder, means effective when the allotted nder is taken for use for opening the said individual contact to unlock and restore the said operated relay to thereby allot the nder associated with the next succeeding operated one of said relays, and independent means controlled over the said starting chain circuit for maintaining operated the allotter relay associated with the currently allotted finder after the opening of the said unlocking contacts until the nder has completed its operation.

9. In a switching system, a group of line finders, normally closed control contacts individual respectively to said nders, lines accessible in common to all said finders, a series of allotter relays, said relays being individual respectively to said nders, means including a starting chain circuit extending through contacts of said relays for allotting the nder associated with the first i operated relay, such operated relay being held r ciated iinder, each of said relays having also a second winding thereon, and means effective when an allotted iinder is being operated to connect with a, calling line for energizing the second winding of the operated allotter relay associated with the currently allotted nder to thereby maintain such relay operated after the said individual control contacts have been opened and until the operation of the associated iinder has been completed.

10. In an inter-exchange trunking system, twoway trunk lines extending between a first exchange and a second exchange, each of said trunk lines having an incoming branch and an outgoing branch in the first exchange, line finders in the first exchange linked respectively to said outgoing branches, a separate allotter relay assigned to each of said nders, and a separate control circuit for each of said relays including two contacts individual respectively to the said branches of the associated trunk.

GLENN KINER.

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