US1536464A - Telephone system - Google Patents

Description

S. B. WILLIAMS, ,JR

May 5, 1925.

TELEPHONE SYSTEM Filed June 6, 1922 5 Sheets-Sheet 1 hue/72hr I Samue/ 5. l W/wmJz awn-3.,

5 's; B. WILLIAMS, JR 1536464 TELEPHONE SYSTEM Filed June 6, 1922 :s sheets-sheet 2 May 5, 1925.

S- B. WILLIAMS, JR

TELEPHONE SYSTEM Filed June 6, 192; 3 Sheets-Sheet s hven/on- Samue/ 5. VW/fams J/r Patented May 5, 1925.

UNITED STATES SAMUEL B. WILLIAMS, JB., OF BROOKLYN,

PATENT OFFICE.

NEW YORK, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed. June 6,

To all whom it may concern Be it known that I, SAMUEL B. VVILLIAMs, J12, a citizen of the United States, residing at Brooklyn, in the county of Kings, State of New York, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to improvements in machine switching systems and has particular reference to telephone exchange systems.

It has heretofore been proposed to provide a switching system wherein a plurality of coexisting connections may be established at contacts controlled by a single switching member of a switching mechanism which comprises a plurality of cooperating switch ing members, each controlling a plurality of said contacts. In order to secure the advan tages incident to such a system, it has been found preferable to arrange the subscribers lines having access to said mechanism intogroups, each of which is served by one of said switching members which cooperates with other switching members to extend a subscriber's line appearing in the particular group served by the first named switching member to an idle trunk.

An object of the present invention is to utilize a. switching system of the above character in such manner that when calls appearing on lines in various groups are initiated sin'iultaneously, or substantially so, a call in each of said groups will be extended before a second call in any particular one of said groups is satisfied. 7

Another object is to prevent the extension of more than one line in any particular group of lines provided a line is calling in any other group.

A further object is to employ switching mechanism of the above mentioned character to successively extend a plurality of calling lines, each in a different group, in the order of the appearance of said groups.

The above and other objects will appear more clearly from the following detailed description when taken in connection with the accompanying drawings, wherein Figs. 1 to 3, when arranged in accordance with the lines extending to the margins of the draw- 1922. Serial No. 566,312.

ings, illustrate a preferred embodiment of the inventive idea.

In carrying out the invention the subscriberslines are preferably divided into vertical groups, three of which are indicated by the characters A, B and C. It will be understood, of course, that the number of these groups will depend upon the number of subscribers lines which have access to the exchange at which the switching mechanism is located. A plurality of outgoing trunks 202 or lines are adapted for connection to said subscribers lines to extend the same. To accomplish these connectionsthe invention contemplates the use of a coordinate switching mechanism such as illustrated in the British Patent N0..183,438 issued to l Vestern Electric Company, Limited, ac cepted September 6, 1923, to which reference is hereinafter made in connection with the operation of switching elements which control sets of contacts utilized to connect subscribers lines through link circuits to the outgoing trunks.

The subscribers lines may further be said to be divided into horizontal subgroups, each of which is provided with a plurality of link circuits common to the lines of the subgroup.- Lines 100, 106 and 112 comprise one subgroup and have links 206 and 217 common thereto. Although only two links are shown as serving each subgroup, it will be understood that as many links may be pro vided for each subgroup as are found necessary to properly handle the traflic.

In order that more than one line in any particular group of lines is prevented from being extended to a trunk pro-vided another line in some other group is also calling and to accomplish the successive extension of a plurality of calling lines in different groups in the order of the appearance of said groups, a switching arrangement (Fig. 3) is provided. This switching arrangement includes, in addition to apparatus which is common to all of the subscribers lines, a plurality of relay groups each of which is individual to a particular group of lines, these groups of relays being separated by the vertical broken lines appearing in said figure. Thus, relays 300, 301 and 303 form a group which is individual to the lines of group A, the relays 315, 316 and 319 form another group individual to the lines ot group B, and so on. Relays 30% and 30'? are common to all the groups of lines and groups of relays and cooperate to prevent a second operationot any particular group of relays it any other group of relays is waiting to extend a calling line in the group to which it is individual. A switch D, which may be of any desired type, is also provided and operates, each time a subscribers line in any group has been extended to an idle trunk, to preselect another idle trunk for the extension of a succeeding call in any group.

It is thought that the invention will now be fully understood from the following detailed description of the operation.

It will first be assumed that all of the apparatus of the various figures ot the drawings is in normal condition and that a subscriber on the telephone line 100 appearing in group A initiates a call by removing his receiver from the switchhoolt. an ohvious circuit is thereupon established for line relay 101 individual to said line and upon energization of said relay, the operation of a group of relays ot the common mechanism shown in Fig. 3 is initiated. Since the calling subscribers line appears in the group of lines served by the group of relays of the common mechanism of Fig. '3 shown at the left, the energization of relay 101 and closure of its le'tt-hand contact establishes a circuit extending from grounded batter through the winding o't relay 300, the normal contact of relay 301, conductor 302, lett-hand contact of relay 101 and from thence to ground over the conduct-or 102 which is common to all ot the groups of subscribers lines. Relay 300 cuergizes in this circuit and in closing its alternate contacts simultaneously establishes circuits for group relay 303 and relay Stlt which is connnon to all. of the various groups of lines and which is energized during the time that any one of the lines is in the process of being extended. The circuit "for operating relay 303 extends from grounded battery through the upper winding of said relay, the upper alternate contact of relay 300, the normal contact of relay 305 common to the Various groups of relays and from thence to ground through the outer left-hand normal contact 0t relay 306. The circuit for energizing relay 80-; extends from grounded battery through the winding of relay 30a and the lower contact of relay 300 to the grounded conductor 102. Relay 304i prepares a circuit for slow-torelease relay 807 which controls the operation of the various groups of relays of the common mechanism in such manner that when calls are initiated simultaneously in different groups of lines, the ditlereut groups of relays associated with said groups of lines are all operated to extend said calls before a second call appearing in any particular one oi. said group of lines is extended. Relay 307 is not energized at this time since the normal contact ot the relay 300 is open. Upon the closure of its inner lower alternate contact, relay Z303 establishes a locking circuit for itself extending from grounded battery through its lower winding and inner lower alternate contact, winding of relay 305 and the left-hand outer normal contact of relay 300 to ground. lay 305 energizes in this locking circuit and thereby establishes an operating circuit tor the slow-to-i'elease relay 2-508 extending from grounded battery, through the winding of relay 308, the inner right-hand contact ot relay 305 and the inner left-hand normal contact ot relay 306 to groimd. The opening of the normal contact o't' relay $305 breaks the original energizing circuit tor relay 303,'but relay 303 remains energized in its lockin circuit. liy closing its uppermost alternate contact, relay 303 establishes an obvious energizing circuit for relay 30 which thereupon locks through its winding and lower contact, the leift-hand outer contact of relay 30% and the contact of relay 307 to ground. The energization of relay 301 also opens the energizing circuit for relay 300 which thereupon releases to open the original energizing circuit for relay 3-0-1, but this relay now remains energized over a ci':- cuit extending from grounded battery through its winding, upper alternate contact oi relay 301, conductor 302 and from thence to ground over the original energizing circuit tor relay 300. The release of relay 300 closes the bleak in the operating circuit prepared tor relay 307 previously reterred to. but this relay Still remains in its normal condition due to the operation of relay Ale- Pull). In addition to the results d scribed as being effected by the energization of relays 303 and 30.3, the operation of these relays also 'auses the actuation of members preferably secured to the armatures of line and trunk magnets 200 and 201, the latter of which ix: associated with an idle outgoing trunk 202 which has been preselected in a manner to presently appear by the rotary switch D (Fig. 3). The circuit for magnet 200 (no tends from grounded battery thrt'iugh the winding of said magnet, the inner upper alternate contact of relay 303, the leit-hai'n'l alternate contact of relay 305 and from thence to ground either through the contact of relay 308 or the outer lett-hand normal contact of relay 300. The circuit for niagnet 201 is traceable from grounded battery through the winding of said magnet, the wiper 309 of switch I) and the terminal engaged thereby, the contact of slow-to-relcase relay 310, the right-hand contact of relay and the outer right-hand contact of relay 305 to ground. In operating, magnet lilo 201 establishes a locking circuit for itself extending through its winding and letthand contact, winding of relay 306 and the outer right-hand contact of relay 305 to ground. Relay 306 is momentarily shortcircuited through the contact of relay 310 and does not, therefore, immediately operate to open the holding circuit for slow-torelease relay 308, thus providing an ample time interval for magnets200 and 201 to perform their respective functions as set forth. in the above mentioned application. The closure of the right-hand contact of magnet 201 establishes an obvious operating circuit for relay 203 associated with the seized trunk. The operation of relay 203 now establishes a circuit extending from grounded battery through the winding of slow-to-release relay 310, the winding and contact of stepping magnet 311, wiper 312 of switch D and the terminal engaged there by, the left-hand contact of relay 203 and the right-hand contact of magnet 201 to ground. Relay 310 and stepping magnet 311 energize in this circuit, the former removing the short circuit from around the relay 306 which now energizes in the locking circuit for magnet 201. The operation of the stepping magnet 311 steps the wiper. 309 and 312 of switch D oil? the terminals individual to the seized trunk 202 and continues to step said wipers until the wiper 312 engages a terminal free from ground, whereupon the stepping circuit for magnet 311 will be permanently opened and said wipers brought to rest upon the terminals individual to an idle trunk. The operation of relay 306, as previously described, now opens the holding circuit forslow-to-release relay 308 which thereupon restores to open the holding circuit for relays 303 and 305. Relay 308 is made sutliciently slow in releasing to permit of the connection of the calling subscriber to the seized trunk before the contact of said relay is opened.

.UpOn the energization of magnet 200 ground is extended from its contact through the normal contact of relay 313, the lowermost alternate contact of relay 303, conductor 31 1, the right-hand contact of relay 10.1. and the left-hand winding of relay 204: to grounded battery. Relay 204?, which is common to the lines appearing in the first horizontal subgroup including lines 100*, 106 and 112, is energized in this circuit and locks through its right-hand winding and inner alternate contact, winding of relay 313 and the contact of magnet 200 to ground. Relay 313 operates in this circuit to open the original energizing circuit for relay 2041:. lWhen relay 204: closes its outer alternate contact, a circuit is established for the magnet 205 associated with the idle link 206 extending from grounded battery, through the winding of magnet 205,

normal contact of relay 207, the outer alternate contact of relay 1, the alternate contacts of relays 313 and 306 to ground. Magnet 205 is energized in this circuit and, as explained in the above mentioned patent, operates the switching elements or cards 208, 209, which have been previously selected for operation by the energization of magnets 200 and 201, to connect the subscribers line 100 through the idle link 206 to the trunk 202. A circuit is now estab lished for the supervisory relay 210 of the trunk 202 extending from grounded battery through the lower left-hand winding of the repeating coil 211, winding of relay 210, the middle switching contact of element 209 and the conductor of the link e11- gaged by said contact, the middle switching contact of element 208, thence through the subscribefis line loop and back over the upper switching contacts of elements 208 and 209 to ground through the upper left-hand winding of repeating coil 211. Relay 210 energizes in this circuit and establishes an obvious operating circuit for slow-to-release relay 212, which in closing its contact, pr0- vides an obvious locking circuit for relay 203' The energization of relay 212 also establishes a holding circuit formagnet 205 extending from grounded battery through the winding of said magnet, the winding of relay 207, the lowermost contacts of elements 208 and 200, the left-hand contact of relay 203 and the contact of relay 2 12 to ground. Relay 207 also energizes in this circuit and in closing its alternate contact preselects the next idle link serving the subgroup in which lines 100, 106 and 112 appear, so that the next call initiated in that subgroup will be taken care of through said idle link, provided the link 206 has not, in the meantime, become idle. The energization of relay 212 also closes an operating circuit for cut-oil relay 103 of line 100, said circuit being traceable from grounded battery through the winding of relay 103 and from thence over the holding circuit for the magnet 205 to ground at the contact of relay 212. The operation of relay 103 causes the release of line relay 101 followed by the deenergization of relay st, and finally of the relay 301 which was locked through the lett-hand contact of relay 30 1. It will be understood that this action of releasing the relay 30 1 takes place provided only that no other call has been initiated in any ot' the groups which fact would prevent relay 304: from releasin Following the connection of the subscribers line to the trunk 202, the contact of relay 308 is opened to release relays 303 and 305, whereupon the holding and locking circuits for magnets 200 and 201 will be opened and these magnets then restored to normal. Magnet 200may new be utilized inthe eX- tension of another call initiated in group A, as explained in the previously mentioned application. Relay 306, which is held energized in the locking circuit for magnet 201,is also released. Release of magnet 200 opens the holding circuit for relays 204 and 313, whereupon these relays release. The common mechanism of Fig. 3 .is again in its normal condition.

lVhen the subscriber on line replaces his receiver at the termination of the con versation, supervisory relay 210 is released and opens the circuit for relay 212 which, after an interval, opens its contact to disconnect ground from the locking circuit of relay 2-03 and the holding circuits of magnet 205, relay 207 and cut-off relay 103. Relays 103, 203, 207 and magnet 205 thereupon release and the apparatus including link 206, which has been employed during the establishment of the connection, is now restored to normal.

The manner in which substantially simultaneous calls occurring in the same and different groups of lines are taken care of will now be explained. It will first be assumed that two calls are initiated simultaneously on lines 100 and 104 which appear in the same vertical group of lines A. as will be understood from the previous description, line relays 101 and are operated whereupon relay 300 is energized through the lefthand contact of either of said line relays. The energization of relay 300 initiates the operation of the common mechanism of Fig. 3 in the manner previously set forth which results in the energization of magnets 200 and 201. Since the present arrangement provides that a call on line 100 shall have permanent preference over lines 104, and other similar lines in group A, it will be obvious that when relays 204 and 213 operate in response to the energization of magnet 200, a circuit for magnet 205 will be established through the outer alternate contact of relay 204, but magnet 214 of the first idle link circuit serving the lines of the subgroup in which line 104 appears, or any other magnet of link circuits assigned to said subgroup, will fail to operate as the circuit therefor will be opened at the outer normal contact of relay 204. Therefore, line 100 of group A will be extended to the idle preselected trunk 202 and line 104 must await such extension before being connected through to another idle trunk which is preselected by switch D. The connection of line 104 to the preselected trunk is then effected in the following manner. When relay 306 energizes in response to the removal of the short circuit around this relay, which removal occurs upon the operation of relay 310 when switch D preselects the next idle trunk, the circuit for relay 308 is opened and this relay, after an. interval, releases.

It is during this interval that magnet 205 is operated to extend line 100 and energize cutoff relay 103. hen relay 308 opens its contact, the holding circuit for relays 303 and 305 'is opened and these relays re lease. It is also at this time that magnets 200 and 201 release, the circuit for the latter extending through the winding of relay 300 and the outer right-hand contact of relay 305. Relay 306 also releases whereupon a circuit is established from grounded battery through the winding of relay 307, the inner contact of relay 304 (which is now held energized through the upper alternate contact of relay 301 and the left-hand contact of relay 105) the normal contacts of relays 317, 315, 300 and 305 in series, and the outer left-hand normal contact of relay 306 to ground. Relay 307 energizes to open the locking circuit of relay 301 which then restores to normal. The opening of the upper alternate contact of relay 301 causes the release of relay 304 followed by the restoration of relay 307 which is slightly slow in releasing. Now, with line relay 105 operated a circuit is again established for relay 300 which energizes to again initiate the operation of the common mechanism of F 3 to effect the energization of magnet 200 and a magnet of the preselected idle trunk similar to magnet 201. It is here noted that the magnet 200 is again employed in establishing another connection in group A so that by means of a single switching member such as magnet 200 coexisting calls in the same group of lines may be established. Assuming the first link serving the lines in the subgroup in which line 104 appears, to be idle, magnet 214 is now energized to extend line 104 to the preselected trunk in a manner now believed to be well understood, the circuit for magnet 214 being traceable through the outer normal contact of relay 204 which is released at this time.

If two calls are initiated substantially at the same time in diiferent groups of lines, that is, for example, on lines 100 and 100 of groups A and B, or lines 100 and 114 of groups A and C, line 100 will be given preference, in each instance, over the other lines. lVhen calls are initiated simultaneously on lines 100 and 100, line relays 101 and 108 are energized followed by the operation of relays 300 and 315. The opera tion of either of these latter relays causes the energization of relay 304-. Relay 303 is also energized by the operation of relay 300 with the results before described, but relay 310 will fail to operate, first, due to the energization of relay 300 and, later, to the operation of relay 305. Line 100 must, therefore, await the extension of line 100 to an idle trunk and the consequent release of relays 305 and 306. \Vhen relay 305 re loo leases in this instance a circuit is not established for relay 307 since relay 315 is held operated by the energization of line relay 108 during the extension of line 100 and continues to remain in its operated condition after said line is extended. Hence, relay 30 1 also remains operated through the lower contact of relay 315. The release of relays 305 and 306 causes the operation of relay 316 through the upper alternate contact of relay 315, whereupon magnet 215 and a magnet similar to 201 are operated in response to the operation of relays in the common mechanism of Fig. 3, as hereinbefore described. The operation of the last mentioned magnets is followed by the energization of a magnet, suchas 216 associated with an idle link serving the subgroup of lines including line 106, so as to extend line 106 to an idle preselected trunk.

In the same manner, if the calls are initiated simultaneously on lines 100 and 11 1 in different groups of lines, line relays 101 and 117 are energized to cause the operation of relays 300 and 317. Again, the line 100 has preference and is extended before line 114 can be connected to a trunk by the operation of a magnet such as 219.

It will now be assumed that two calls in group A and one each in groups B and C are initiated simultaneously or in such rapid succession that before the first line making a call in group A is extended to an idle trunk, the second call in said group is initiated and before the latter call is extended, a call in group B is initiated, and soon throughout the groups In this instance, a call in group A is taken care of and thenthe calls in the other groups are satisfied before the second call in group A is extended. Taking lines 100 and 10 1 in group A, 106 in group B, and 112 in group C for example, it will be obvious that when the receivers at the substations of these lines are removed at the same instant, line relays 101, 105, 108 and 115 are energized whereupon relays 300, 315 and 317 of the common mechanism are operated. The lines of group A having preference over those in groups B and C, and the lines appearing in the lowermost subgroup of lines having a permanent preference over those of the other subgroups, it follows that line 100, which appears in the lowermost subgroup is the first to be extended. hen the connection for this line has been completed, as previously described, relay 307. is not energized due to the coexisting calls in groups B and C which maintain relays 315 and 317 operated. Relay 304: is, therefore, held energized through the lower contacts of either of the relays, 315 and 317. Hence, it follows that relay 301, which was energized and locked during the extension of line 100, is prevented from releasing so that a circuit cannot at this time be establish-ed for relay 300, which, if now operated, would permit of the operation of relay 303 and the consequent extension of the call on line 10% which also appears in group A and which, according to the present arrangement, is the last of the four lines to be extended. The line 106 appearing in group B now has preference since relay 318, individual to group C, cannot energize because of the opening of the normal contact of the relay 315. Therefore, relay 316, individual to group B, operates through the upper alternate contact of relay 315 and normal contact of relay 300 as soon as relays 305 and 306 are released at the termination of the extension of line 1.00. The operation of relay 316 now controls the extension of line 106 through the next idle link 217 which serves the horizontal subgroup of lines in which lines 100, 106 and 112 appear. In the operation of extending the connection for the line 106, magnets 215 and 216 and a magnet similar to 201 and individual to the trunk preselected by switch D are operated in a manner which is now thought to be obvious. Magnet 216 remains operated during the establishment of this connection while the other two magnets are released. Following the connection of line 106 to a trunk, relays 308, 305, 306 and 316 release, but relay 30 1 still remains operated through the lower contact of relay 317, the open normal contact of which prevent the energization of relay 307. Relay 319, which operated and locked during the extension of line 106 is, therefore, held energized and thus prevents the operation of relays 315 and 316 should another call be initiated in group B before the one in group C has been satisfied. With the release of relays 305 and 306, an obvious circuit is now established. for relay 318 which operates to energize relay 320. The operation of relay 320 provides a temporary holding circuit for relay 304 through the upper alternate contactof relay 320 and left-hand contact of line relay 115, which circuit is opened when relay 115 releases in response to the energization of cutoflf relay 116. The energization of relay 318 controls the operation of magnet 218 which energizes simultaneously with a magnet similar to 201 of another preselected trunk. These magnets control their respective switching elements similar to elements 208 and 209, so that when the magnet of the next idle link (not shown) serving the lowermost subgroup of lines, similar to magnets 205 and 216, is operated, the line 112, upon which the call in group C was initiated, is extended to the trunk preselected by the switch D. After the extension of line 112, relays 308, 305, 306 and 318 release, as will be understood from the previous description, and upon the deenergization of relays 305 and 306 the previously described circuit for relay 307 is established. Relay 307 energizes to release relays 301, 319 and 320, following which relay 30 i releases to open the circuit for relay 307, which then deenergizes. The calls in groups B and C having been extended the other simultaneous call on line 104: of group A is now connected to an idle trunk. Upon the release of relay 301, relay 300 again energizes through the lefthand contact of line relay 105, whereupon the extension of line 10% to a preselected trunk is initiated in the same manner as previously described in connection with line 100. It will be obvious from the foregoing description that if other calls are initiated in groups of lines (not shown) succeeding group C, in the order of their appearance before the one in said group C is extended, these other calls will be successively satisfied before the call on line 101 appearing in group A. It will also be obvious that if a call is initiated in group B and before being extended, other calls should be simultaneously initiated in groups C and A, the line appearing in group C will first be extended before that appearing in group A. Thus, by means of the common mechanism of Fig. 3, one and only one call appearing in each of the groups substantially at the same time will be extended before a second call appearing in any one or more of said groups is satisfied.

lVhat is claimed is:

1. In a switching system, a plurality of groups of lines, coordinate switches serving said lines, a relay individual to each group of lines, means responsive to the initiation of a call on a line in any particular group for operating one of said switches to extend said line and for operating the relay individual to the group in which said line appears, and another relay common to said groups of lines for maintaining the first named relay operated to render all remaining lines in said group ineffective to operate one of said switches until a calling line in another group has been extended.

2. Ina switching system, a plurality of groups of lines, coordinate switches serving said lines, a plurality of trunks, a relay individual to each group of lines, means responsive to the initiation of a call on a line in any particular group for operating one of said switches to extend said line to an idle trunk and for operating the relay individual to said group, another switch responsive to the operation of the first named switch for preselecting another idle trunk, and a relay common to said groups of lines for maintaining the first named relay operated to render all remaining lines in said particular group ineffectiveto opcrate one ofsaid switches until a line calling simultaneously in. another group has been extended.

8. In a switching system, a plurality of groups of lines, contact sets, switching members cooperating with each other and each serving a plurality of contact sets, means responsive to lines in any particular group for operating switching members to establish coexisting calls at contact sets served by a single switching member, and means operable when a. plurality of lines are simultaneously calling in different groups for rendering all but one of the lines in: a particular group ineffective to operate said switching. members until a simultaneously calling line in each of the other groups has been extended.

4. In a switching system, a plurality of groups of lines, contact sets, switching members cooperating with each other and each serving a plurality of contact sets, means responsive to lines in any particular group for operating switching members to establish coexisting calls at contactsets served by a single switching member, and means common to said groups of lines and operable when a plurality of lines are simultaneously calling in difierent groups for. rendering all but one of the lines in a particular group ineffective to operate said switching members until a simultaneously calling line in each of the other groups has been extended.

5. In a switching system, a plurality of groups of lines, contact sets, switching members cooperating with each other and each serving a plurality of contact sets, means responsive to lines in any particular group for operating switching members to establish coexisting calls at contact sets served by a single switching member, and means for controlling the extension of a line in a different group cal-ling simultaneously with one of the lines in said particulargroup before another line in said particular group is extended.

6. In combinationa plurality of incoming lines arranged in groups, outgoing trunks, a plurality of link circuits for interconnecting said lines and trunks, vertical rows of contacts in which the linesofa group terminate, other vertical'rowsofcontacts in which trunks terminate, a plurality of switchingmembers, each individual to a group of lines, means, responsive to the initiation of a call in any group of lines for operating. a corresponding switching member, and means-rendered effective upon the actuation of said corresponding switching member to render the remaining lines of the associated group ineffective to actuate said corresponding switching member if a line in any otheiugroup'is awaiting extension.

7. In combination a plurality of incoming lines arranged in groups, outgoing trunks, a plurality of link circuits for interconnecting said lines and trunks, vertical rows of contacts in which the lines of a group terminate, other vertical rows of contacts in which trunks terminate, a plurality of switching members, each individual to a group of lines, means responsive to the in itiation of a call in a particular group of lines for actuating a corresponding switching member, and means for controlling the extension of calls on lines appearing in succeeding groups simultaneously with the first named call before another line calling in the first named group is extended.

8. In combination incoming lines, link circuits for extending said lines, switching devices having permanently paired primary and secondary contacts for connecting said lines to said link circuits, coordinately arranged operating members, certain of said operating membersbeing each individual to a group of lines, means responsive to the initiation of a call in a particular group for operating a plurality of operating members to extend the calling line, and means for successively controlling the extension of calls on lines in succeeding groups in the order of the appearance of groups before another call occurring on another line in the first named group is extended.

9. In combination incoming lines, link circuits for extending said lines, switching devices having permanently paired primary and secondary contacts for connecting said lines to said link circuits, coordinately arranged operating members, certain of said operating members being each individual to a group of lines, means responsive to the initiation of a call in a particular group for operating a plurality of operating members to extend the calling line, a switch responsive to the extension of said line for preselecting an idle trunk, and means operable when a plurality of lines are simultaneously calling in different groups for rendering the remaining lines in any particular group ineffective to operate said operating members until all the simultaneous calling lines in other groups have been extended.

I11 witness whereof, I hereunto subscribe my name this th day of J une, A. 1)., 1922.

SAMUEL B. WILLIAMS, JR.

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