US2030412A - Telephone exchange system - Google Patents

Description

3 SheetsfSheet l Feb. 11, 1936. F. A. STEARN TELEPHONE EXCHANGE SYSTEM Filed Oct, 24, 1954 F A. STER/V BV ATTORNEY Feb.' M, 1936. F A, STEARN www TELEPHONE EXCHANGE SYSTEM Filed Oct. 24, 1934 3 Sheets-Sheet 2 /NVENTOR B E A. STEARN Feb, El, 1936. F A. STEARN 2,930,412

TELEPHONE EXCHANGE SYSTEM Filed Oct. 24, 1934 3 Sheets-Sheet 5 OS Q l] -D [l o 12W IIIHIIIIIUUDUD U l] UUUUI] U -D UHU [IUI] U UI] UD B FRAME llllll ff m /NVENTOR FA. STEARN ATTORNEY Patented Feb. 11, 1936 UNITD STATES PATENT OFFICE TELEPHONE EXCHANGE SYSTEM Franklin A. Steam, Westfield, N. J., assigner to 4leii Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application ctober 24, 1934, Serial No. 749,710 4 Claims. (Cl. 179-18) This invention relates to telephone exchange oince and numerical designations of a desired v-systems and more particularly to systems in line dialed by a calling subscriber and for zcon- :which connections between subscribers lines tertrolling the setting of a district and an cnice-,seminating in different ofces of the exchange area lector to extend a connection to ythe oiiice in 5 .are established by automatic switching mechwhich the line terminates and for controlling .5 anisms over groups o'f interoiice trunks. other apparatus in the selected oice for complet- .1n exchange areas having a large number oi' ing the connection. local offices, it is not economical to provide direct Each sender is provided with a translator groups of trunks for interconnecting each office switch which is set in accordance with thedialed 1o .with every other ofce, particularly when `the ohice code `registration of any of two `hundred Y10 Ioiices are widely separated and the traffic load routes. The translator switches of part of the islheavy. In some exchange areas, therefore, it senders of the office are mounted on an A -irame 'is :more economical to route traic between cerand the translator switches of the remaining Ytain oiiices through a tandem office .which serves senders are mounted on a B frame. Common l5 as a common intermediate distributingV point. to all translator switches of the A frame ,there 15 It has heretofore been proposed to render more are provided as many A synchronizing .circuits eflicient the trunks in a group directly interconas there are trunk groups whichV the A trans- -necting any two oices by limiting the number lator switches serve. Also common to al1 transof direct trunks to the maximum required for lator switches of the B frame there are pro- 20 handling normal traic between such oices and vided as many similar B synchronizing cir- 20 by automatically rerouting the abnormal or overcuits as there are trunk groups. CommonV to `all flow trafc between such offices to a tandem or the translator switches ofthe A frame there office where it may be directly routed to thedeis provided apulse machine drum having a plusired office. This proposal also enables existing rality of sending drums anda plurality of receiv- 25 direct trunks between oiiices to be employed withing drums. A similar pulse machine drum com- 25 out the addition of further trunks thereto when mon to all of the translator switchesof the B traino-loads increase beyond the capacity of such frame is also provided. The pulse machine drums trunk groups by rerouting calls through a tanare instrumental in setting secondary registerso'f dem oce. To accomplish the rerouting of calls any sender in accordance with the settingoithe .-30 .to a tandem @mee in systems employing central translator switch of the s ender. The secondary 30 "office senders which control the setting `of selectregisters in turn control the brush and group ing switches to establish connections, the sender selection movements of a district selector and of must receive av signal when ali trunks of a. direct an office selector to select the trunk` group intrunk group extending t0 an Ofce are busy in dicated by the office code dialed by the calling order that the sender may take the necessary Subscriber, steps to reroute the next connection for that Inrorder that a sender of this type maybe trunk group over a different trunk group extendlcaused to reroute a connection through aftandem ing to the tandem once which has direct trunks office when all trunks of the groupvextendingdi- Vto the desired ofce. This signal depends upon rectly to the oice indicated by the oice code .the closure of a chain circuit controlled by the dialed are busy, it is necessary to. preparegall-O trunks of the direct trunk group when all trunks senders of the originating ofce so that :when the ofthe group become busy. translator switch of any oi the senders is set In systems of the type disclosed in Patent to route a connection directly toadesired-oflice, 1,395,977, granted November l, 1921, to' F.v A. it will cause the pulse machine to set the .sec- L Stearn and F. J. Scudder, the establishment of ondary registers of the sender vwhich has beenv/D connections, from an originating office to any taken or use to control lthe selective movements other cnice of the exchange area, is made possible ofthe district and oflice selectors to select a-,trunk "by district and oice selectors which are set to extending to the tandem ofce rather than to-se- Yselect an idle trunk of the group of trunks exlect a trunk extending directly to the desired ""U tending to the ofce in which a desired subscriboice. ers line terminates by a sender common to all It is further necessary to guard against changsubscribers lines of the originating oflice. A ing of the routing during the time that the pulse plurality of senders, any o'ne of which may be machine may be setting up a routing on the vsec.- taken for use by a calling line, is provided,.l.each ondary registers of a sender toprevent the muti- '05 sender having registers for, registering both the lation of any call. It is, therefore, the objectfof g55 selector |01, sender selector |63, sender 75- the invention to enable the more efcient use of trunking facilities by rerouting calls through tandem ofces during heavy peaks of trafc in systems of the type employing translator switches and pulse machines.

In accordance with the invention, each trunk group extending from one oiiice to another oflice to which it is desirable to apply alternate routing through a tandem oce is provided with a chain circuit having relays associated therewith one of which operates only when all but one of the trunks of the group are busy and another of which operates when all trunks of the group are busy. A synchronizing circuit which is individualized to a trunk group and to which it is desirable to apply the rerouting feature, is provided having a reroute relay and a group of synchronizing relays.

lf it be assumed that a direct trunk group extending between two oices becomes loaded to such an extent that but one trunk in the group is idle, then the chain circuit controlled by relays of the trunks of that group becomes altered in such a manner that one of the relays associated with the chain circuit indicates to the synchronizing circuit common to all senders and allocated to that particular trunk group that there is but one available idle trunk in that trunk group. The synchronizing relays of the synchronizing circuit then function from the pulse machine to insure that no calls to this particular trunk group, which are at the time being routed thereto by the action of the pulse machine, will be mutilated and that as soon as the pulse machine has completed its cycle, the last call which may be routed to the trunk group is counted and the reroute relay is operated preparatory to routing the next call by way of a tandem oflice. When the last trunk of the direct group is taken for use by a selector switch, the chain circuit associated with the trunk group is further altered to operate the second relay associated with the chain circuit which holds the reroute relay operated until a trunk of the group becomes idle.

For a clearer understanding of the invention reference may be had to the following detailed description read in connection with the accompanying drawings of which:

Fig. 1 shows schematically a calling subscribers line, a line switch, district selector, o'ice selector, sender selector and a portion of one sender of an originating office; a subscribers line, incoming selector and nal selector of a distant office; a group of direct trunks extending between the oices; and a tandem oiice indicated by the full line rectangle through which connections may also be established between the originating and distant offices;

Fig. 2 shows schematically two translator switches of the A translator frame, one of which is the translator of the sender of Fig. l and the other the translator of another sender, the A drum of a pulse machine common to all translator switches of the A frame and the A synchronizing circuit individual to the direct trunk group of Fig. l; and

Fig. 3 shows schematically two translator switches of the B translator frame individual to other senders, the B drum of the pulse machine common to all translator switches of the B frame and the B synchronizing circuits individual to the direct trunk group of Fig. l.

The line switch IBI, district selector |2, ofce |55, translator switches 20B, 295, 300 and 39|! and the pulse machine drums 250 and 35|) being of the well-known type and functioning in the Wellknown manner have, in order to simplify the drawings, been disclosed schematically herein. For a complete disclosure and description thereof, reference may be had to Patent No. 1,395,977 granted November l, 1921 to F. A. Stearn and F. J. Scudder, hereinbefore referred to. The tandem oce equipment indicated by the rectangle |58 of Fig. 1 is of the type fully disclosed in Patent No. 1,840,132, granted January 5, 1932 to T. H. Roberts. The incoming selector switches |59 to H2, inclusive, and the final selector ||3 schematically shown, are also of the well-known type `disclosed in the patent to Stearn et al. above referred to.

Each sender of the originating cnice is provided with a translator switch, the translator switches of all of the senders being mounted on two frames approximately one half on each frame. The translator switch of sender |05 mounted on the A frame is shown at 200 and the translator of a second sender mounted on the same frame is indicated at 290. Two translator switches of two other senders are indicated at 300 and 39D and mounted on the B frame. Each translator switch has access to two hundred sets of bank terminals each set corresponding to a diierent trunking group or code point over which a connection may be extended in the originating ofce. It is thus possible for any translator switch to be set in accordance with the oflice code digits registered in the sender with which it is associated to determine which of two hundred routes will be employed to route a desired connection.

Some of these routes are employed in the establishment of local connections within the originating oflice such as connections to local lines and to service operators positions. used in the establishment of connections to other nearby offices, others to more distant oiiices and still others to tandem olices through which connections may be further extended to distant ofiices. Obviously on calls which are local to the originating oice, the provision rof alternative routing to a tandem office is not necessary and there would be slight, if any, economy in the provision of alternative routing on such routes as handle short haul tralic to nearby oces. It is therefore proposed to provide alternative routing only for such routes as handle long haul tramo to distant omces. In accordance with the present invention this is accomplished by providing for each of such groups two synchronizing circuits, one of which is termed the A synchronizing circuit and is associated with the multiplied terminal sets of all translator switches of the A frame allocated to that particular group and the other of which is termed the B synchronizing circuit and is associated with the multipled terminal sets of all translator switches of the B frame allocated to that particular group. The dot-dash rectangles 20| of Fig. 2 and 30| of Fig. 3, show the A and B synchronizing circuits of one such route or the route including the group of direct interoflice trunks shown in Fig. l.

Each A synchronizing circuit such as 29| is provided with a group of relays 239 to 2lll,"inl

elusive, and a reroute relay 245 and similarly each B synchronizing circuit such as 30| is provided with a group of relays 339 to 344, inclusive, and a reroute relay 345. 'I'hese relays function in cooperation with the ktranslator Some are switches and pulse machine drums 250 and 350 in the manner hereinafter described.

In order to distribute the traiicload, a pulse machine having two synchronously driven drums is provided. The A drum of the pulse machine disclosed at 250 serves all of the translator switches of the A frame and the B drum, disclosed at 350, serves all of the translator-switches of the B frame. To better disclose these drums, portions of them have been shown as developed in a single plane. Each drum is made of insulating material in which a plurality of circumferential rows of contact segments are embedded, these segments being all connected to a common-slip ring-to which battery potential is applied by means of a brush. On pulse machine drum 255 this slip ring is indicated at 25| and the cooperating brush at 252 and on drum 350, the slip ring is indicated at and the cooperating brush at 352. For contacting 'with the `rows of contact segments on each drum, a plurality of other brushes is provided.

In the sender |05 only the seco-ndary register control relays |30 to |35, inclusive, and the corresponding auriliary control relays |40 to |45, inclusive, have been disclosed, the relays of the secondary registers having been omitted to simplify the drawings. For a disclosure of the secondary registers reference may be had to the Steam et al. patent herenbefore referred to. The relays of the secondary registers are operated over the indicated contacts of relays |40 to |45, inclusive, from the pulse machine drum 250 in accordance with the translated oiiice code for registering the class, district brush and group, office brush and group and talking selection information required by the sender in establishing any desired connection. The circuits for control relays |30 to |35, inclusive, are associable over the brushes of translator Iswitch 20E! with any set of terminals upon which the translator switch may be positioned and thence either directly to terminals on the lower side of the cross-connecting rack 280 if the translator brushes are positioned on the terminal set appertaining to a route that is not provided with the rerouting feature, or indirectly to the cross-connecting rack through the front or back contacts of a reroute relay of a synchronizing circuit such as 20| if the translator brushes are positioned on the terminal set appertaining toa route that is provided with the rerouting feature. The terminals on the upper side of the cross-connecting rack 280 are connected, respectively, to the forty sending brushes such as 254, 256, 258, 261 and 263 which cooperate with the forty rows of sending segments of pulse machine drum 250. By the use of jumpers between the terminals on the two sides of the cross-connecting rack the circuits of relays |30 to |35, inclusive, may thus be selectively completed during the rotation of the pulse machine drum 250. The circuits of relays of the secondary registers are completed over contacts of relays |40 to |45, inclusive, to six receiving brushes such as 259, 25|, 263 and 255 cooperating with siX rows of receiving segments on drum 250. In a similar manner, the corresponding control relays of the senders associated with the translator switches 300 and 390 are connected over the cross-connecting rack 380 either directly or over contacts of the route relay of a B synchronizing circuit, such as 30|, to the send- -ing brushes of the pulse machine drum 350.

`Each-trunk Vof a directtrunk group to which alternative routing is applied, as disclosedin Fig.A l, is provided with a sleeve relay, such as relays ||8 and H9, which becomes operated whenv the trunk is seized. Associated with each sleeve relay is a resistance, the resistances associated with relays v| I1, ||8 and ||9 being disclosedat |20, |2| and |22, respectively. Each resistance is providedwith a normally open shunt extending over the contacts of the associated sleeve relay and all of the resistances, when all trunks of the group are idle, are normally connected inl ay chain circuit extending from grounded battery therethrough in series to conductor |23 and then in series through the lower operating winding of relay |24 and the winding of relay |25 to ground. Relay |24 is a polarized relay, electrically biased by the circuit through its upper winding, and -so adjusted that it will operate in series with one of the resistances, but will not operate or will release in series with two or more of the resistances. Relay |25 is margined to operate only when all of resistances have been excluded from the chain circuit. It will thus be apparent that as each trunk of the group is taken for use, one ofthe serially connected resistances will become shunted by the operation of the sleeve relay of that trunk and that when all but one of the trunks of the group have been seized, all but one of the resistances will become shunted and relay |24 vwill therefore operate and, that when all trunks become busy and all oi the resistances become shunted, marginal relay |25 will operate. The operation of relay |24 is therefore indicative that there is but one available or free trunk in the group and the operation of relay |25 is indicative that all trunks of the group are busy. Itwill, Iof course, be obvious that it is not necessary that the trunks be taken for use in-any denite order.

in order that the invention may be more-clearly understood, it will be assumed that the -subscriber at substation |00 of an originating oflice of an exchange area desires to establish a connection with a subscribers line ii 4 which terminates at a distant ofce of the same exchange area and, upon removing the receiver from the switchhook obtains a connection with an idle `sender in the originating office through the operation of line switch |5i and sender connector |03 and then dials the oihce code letters and'numei-ical digits of the directory number of the wanted line H4.

In response to dialing, the ofce code and numerical designations are registered in the sender.l in the well-known manner and following the reg-v istration of the letters of the office'code designar tion, the translator switch 200 is set in accordance therewith. VIt will be assumed that the ofiice code dialed indicates that the distant oiice may be reached over the group of direct trunks shown in Fig. l and that the brushes of tra-nslator switch 255 are therefore positioned on the set of terminals illustrated, which set of terminals correspond to the synchronizing `circuit 20| individual to the direct trunk group of Fig. l. It will further be assumed that at the time 'the call is initiated, there are two idle trunks'||5 and I5 in this trunk and that, therefore, neither relay |24 nor relay |25 is operated and consequently none of the relays of the associated-synchronizing circuits 20| and 30| are operated.

With the reroute relay 245 unoperated, as the pulse machine drum 250 rotates, three impulses are transmitted from grounded batteryover brush 252 and 'slip ring 25|,l the segments 253, brush '254, jumper -oncross-connection rack 280, outer right back contact of reroute relay 245, terminal 208 and brush 209 of translator switch 200, conductor 2|0 to ground through the winding of class register control relay |30. Similarly, two impulses are transmitted over segments 255, brush 256, jumper on the cross-connection rack 280, middle right back contact of relay 245, back contact of relay 24|, terminal 2|| and brush 2|2 of translator switch 250, conductor 2 I3 to ground through the winding of district brush control relay I3 I Two: impulses are transmittedover segments 255, brush 256, jumper on cross-connection rack 280, inner right back contact of relay 245, terminal 2 I4 and brush 2I5 of translator switch 200, conductor 2|6 to ground through the winding of oce brush register control relay |32. In a similar manner two impulses are transmitted over segments 251, brush 253, jumper on cross-connection rack 280, inner left back contact of relay 245, terminal 2I1 and brush ZIS of translator switch 200, conductor 2|9 to ground through the winding of district group register control relay |33. The circuit of the oiice group register control relay |34 is twice completed in a similar manner over segments 255, brush 256, jumper on crossconnecting rack 280, middle left back contact of reroute relay 245, terminal 228 and brush 22| of translator switch 20D, conductor 222 to ground through the winding of relay |34. The talking selection control relay |35 is also twice operated over a circuit extending from battery on segments 255, brush 256, jumper on cross-connection rack 289, outer left back contact of relay 245, terminal 223 and brush 224 of translator switch 200, conductor 225 to ground through the winding of relay |35.

Control relay I30 upon operating closes the circuit of relay |40 and thus relay |40 operates each time that the pulse machine brush 254 engages one of the segments 253. At the time brush 254 engages the iirst segment 253, the brush 259 also engages segment 268 thereby establishing a circuit from battery over brush 252, slip ring 25|, segment 260, brush 259, conductor 226, inner right contact of relay |49 to the .winding of the third relay of the class register. Again when brush 254 engages the next segment 253, brush 26| will engage segment 262 thereby establishing a circuit from battery over segment 262 and brush 26|, conductor 221, inner left front contact of relay |40 to the winding of the fourth relay of the class register. When brush 254 engages the next segment 253, brush 265 will engage segment 266 and will apply battery thereover to conductor 229, thence over the middle left contact of relay |40, but since there is no class register relay connected to this contact of relay |40, the establishment of this circuit is without effect at this time.

Control relay |3| upon operating closes the circuit of relay I4| and thus relay |4| operates each time that the pulse machine brush 256 engages one of the segments 255 and, since at the time brush 256 engages the first segment 255, brush .266 and will apply battery thereover to conductor 229, thence over the middle left contact of relay y *|4I, but since there is no district brush register .relay connected to this contact o f relay 4| the establishment of this circuit is without effect at this time.

When control relay |32 operates it closes the circuit of relay |42 and thus relay |42 operates each time that the pulse machine brush 256 engages one of the segments 255 and, since at the time brush 256 engages the first segment 255, brush 259 engages segment 260, a circuit is established as previously traced to conductor 226 and thence over the inner right contact of relay |42, to the winding of the third relay of the oce brush register. Again when brush 256 engages the second segment 255, the brush 265 will engage segment 266 and applies battery over conductor 229 and the middle left contact lor" relay |42, but since there is no oiiice brush register relay connected to this contact of relay |42, the establishment of this circuit is without effect at this time.

When control relay |33 operates it closes the circuit of relay |43 and thus relay |43 operates each time that the pulse machine brush 258 engages one of the segments 251 and, since at the time brush 258 engages the first segment 251, the brush 263 engages segment 264, a circuit is established from grounded battery over brush 252, slip ring 25|, segment 264, brush 263, conductor 228, outer right contact of relay |43 to the winding of the rst relay of the district group register. Also when brush 258 engages the second segment 251, brush 265 will engage segment 266 and apply battery over conductor 229 and the middle left Contact of relay |43, but since there is no district group relay connected to this contact of relay |43, the establishment of this circuit is without effect.

Control relay |34 upon operating closes the circuit of relay |44 and thus relay |44 operates each time that the pulse machine brush 256 engages one of the segments 255 and, since at the time brush 256 engages the first segment 255, brush 259 engages segment 269, a circuit is established from battery as traced to conductor 226, thence over the inner right contact of relay |44 towinding of the third relay of the oflice group register. Also when brush 256 engages the second segment 255, brush 265 will engage segment 266 and will apply battery over conductor 229 and the middle left contact of relay |44, but without effect as there is no register relay connected to this contact of relay |44.

When control relay |35 operates it closes the circuit of relay |45 and thus relay |45 operates each time that the pulse machine brush 256 en# gages one of the segments 255 and, since at the time brush 256 engages the first segment 255, b-rush 259 engages segment 260, a circuit is established over conductor 226 and the inner right contact of relay |45 to the winding of the third relay of the talking selection register. When brush 256 engages the second segment 255, brush 265 will engage segment 266 and will apply battery over conductor 229 and the middle left contact of relay 45, but without eiiect as there is no register relay connected to this contact of relay |45. f v

All of the information required by the sender, as translated from the dialed ofhce code designation, has now been registered by the secondary registers of the sender and the sender will then proceed to control the setting of the district selector |02 and oiiice selector |61 in accordance therewith to select the group of direct interoiiice trunks extending to the oiice in which the wanted line ||4 terminates. It has been assumed vthat all but the last two trunks H and IE6 of this group are busy. The oiiice selector will therefore hunt over the terminals of the busy trunks and will seize the rst of the idle trunks or trunk I I5. The sender will then proceed to control the setting of the incoming selector I I I in which the trunk H5 terminates and the final selector |53 in accordance with the numerical designations of the call as registered in the senr er to complete the connection to the line I|4. Following the completion o1" its controlling functions, the sender is dismissed in the usual manner.

Upon the seizure of trunk ||5 its sleeve relay IIB is operated to shunt resistance |2l. Since now all but one of the trunks of the group are busy and therefore only one resistance |22 associated with the sleeve relay ||9 of the only remaining free trunk |16 remains connected in the previously traced chain circuit through the windings of relays |24 and |25, relay |24 operates, but relay |25 does not. Relay |24 upon operating closes an obvious circuit for relay |29 which also operates to prepare at its lower and upper contacts the operating circuit of relay |28 which is employed to count the last call which may be established over the trunk group, and to close a circuit extending from ground at its inner upper front contact over conductor |36 to battery through the windings of relays 239 and 349 in parallel, individual respectively, to the A and B synchronizing circuits allocated to the direct trunk group of Fig. 1.

Relay 239 upon operating establishes a circuit for the group of relays including relays 23|! and 23| as soon as the pulse machine drum in its continuous rotation has rotated to the position in which brush 235 engages segment 235. This circuit may be traced from grounded battery, brush 252, slip ring 25|, segment 233, brush 255, windings of relays 233, 23| to ground at the inner left Contact of relay 239. As many relays such as 23|? and 23| are provided as are necessary to control the operating circuits for the relays 24| of all A synchronizing circuits. A similar circuit is also established by relay 339 for relays 330 and 33| over brush 355 and segment 366 of the B pulse machine drum 35i). As many relays such as 335 and 33| are provided as are necessary to control the operating circuits for the relays 34| of all B synchronizing circuits.

The circuit of relay 24| may be traced from battery at the inner right contact of relay 232, winding of relay 24| to ground at the outer left contact of relay 239 and the circuit of relay 34| may be traced from battery at the inner right contact of relay 33S, winding of relay 34| to ground at the outer left contact of relay 333. It is thus apparent that whenever the pulse machine drums 252 and 35S rotate into the position in which brush 365 engages segment 255, or brush 255 engages segment 355, the relays such as 24| and 34| of all synchronizing circuits of the trunk groups in which there is but one available or free trunk will operate.

Relay 24| upon operating closes a circuit from battery over brush 252, slip ring 25|, segment 255, brush 252, middle right back contact of reroute relay 245, outer right iront contact of relay 24|, winding of relay 244 to ground thus operating relay 244 during the time the drum 253 is in the position in which the circuits are closed over the segments266 and 255. Relay 24| also opens the short circuit from the winding of relay 243.

It will rst be assumed that at the time relay 24| operates to remove the short circuit from the winding of relay 243, there is a translator switch, for example 29B, standing on the code point or terminal set allocated to the trunk group of Fig. 1 and that, therefore, a translation is being effected and registered on the secondary registers of the sender to which such translator switch belongs for routing a call to the trunk group of Fig. 1. When the sending circuits for effecting this translation are established over the brushes of translator 290 the sending circuit over brush 292 will, when the pulse machine reaches the position to close the previously traced circuits of relays 230 and 23 I, be established from ground through the ofce group register control relay corresponding to relay |34, over brush 292, terminal 29|, winding of relay 243, middle right back contact of reroute relay 245, jumper on cross-connecting rack 233, brush 255, last terminal 255, slip ring 255, brush 252 to battery. Relay 243 will therefore operate and since relay 24| is also simultaneously operated as previously described, a circuit will be established from battery, inner front contact of relay 24|, front contact of relay 243, conductor |21, upper front contact of relay |23, winding of relay |28, lower contact of relay |29 to ground at the back contact of relay |25. Relay |28 will therefore operate, lock in a circuit from battery over its upper contact and winding, lower contact of relay |29 to ground at the back contact of relay |25 and at its lower contact connect ground to conductor |26. While relays 24|, 243 and 244 are operated, the operating circuit for relay 242 from battery over the inner contact of relay 24|, the back contact of relay 243, and the left contact of relay 244 is not effective since it is open at the back contact of relay 243.

As soon as the pulse machine drum 252 rotates further it breaks the circuit previously traced over the sending segment 255 and brush 25S and relay 243 releases in turn releasing relay 244 and .024 second later, breaks the circuit previously traced over its receiving segment 263, brush 265 thus releasing relays 230 and 23| in turn releasing relay 24|. The last call which the direct trunk group of Fig. 1 can handle has thus been counted and the sender upon receiving the routing information will proceed toset district and ofce selectors to select this group oi' trunks. If a sender having a translator switch such as 303 and 39|] had positioned its translator switch on the code point of the trunk group of Fig. l instead of the translator switch 233, as previously described, then the relays of synchronizing circuit 30| would have functioned in conjunction with pulse machine drum 350 in a similar manner.

If additional senders set their translator switches of frame A on this code point after drum 25|) advances beyond the position in which the receiving segment 263 breaks contact with brush 265, but before the next reclosure over this segment, the above described cycle of relay operations will be repeated on each closure as long as sender translator switches are connected to the code point. Similarly, if additional senders whose translator switches are on frame B set their translator switches on this code point after the drum 35|! advances beyond the position in which the receiving segment 36E breaks contact such senders will be lost as there will be no trunk of the trunk group available.

When the pulse machine 250 rotates to the position in which its receiving segment 266 and sending segment 255 again contact with brushes 265 and 256, respectively, after the last call to the trunk group of Fig. 1 has been counted as previously described and no sender has positioned its translator switch on the code point corresponding to this trunk group, relays 230, 24| and 244 will operate as previously described, but since there is no register control relay connected to the previously traced circuit over brush 255 and segment 255 through the winding of relay 243, relay 243 will notl operate. With relays 24| and 244 operated and relay 243 not operated, a circuit is now closed for rela-y 242 extending from battery, inner contact of relay 24|, back contact of 'relay 243, left contact of relay 244, winding of relay 242 to ground. Relay 242 will therefore operate and lock in a circuit through its winding and left contact, back contact of relay 243 to battery at the inner contact of relay 24|. As soon as the pulse machine rotates to break the circuit over its sending segment 255, relay 244 will release and close a circuit from battery in parallel through the windings of relay 240 and reroute relay 245, back contact of relay 244, right front contact of relay 242, right contact of relay 239, conductor |26 to ground at the lower contact of relay |28. Shortly after the circuit over sending segment 255 is broken or in .024 second, the circuit over receiving segment 266 is also broken thereby releasing relays 230, 24| and 242. Relays 240 and 245 are no-w locked over a circuit extending from ground, back contact of relay 242, left contact of relay 240 and thence to battery in parallel through the windings of relays 240 and 245.

When the last call has reached the trunk group of Fig. 1 relay |25 will operate indicating that all trunks of the group are busy and will cause the release of relay |28. Relay |28 upon releasing removes ground from conductor |26, but relay |25 has upon its operation connected ground to this conductor so that should relays 242 and 244 subsequently operate in the manner previously described, relays 240 and 245 will still be maintained operated from ground on conductor 26 so long as all trunks of the group remain busy.

With reroute relay 245 operated, the sending circuits from the code point or multiple terminal set of the A frame corresponding to the trunk group of Fig. 1 will be transferred from the sending brushes 254, 256 and 258 to other sending brushes in accordance with the translation necessary for rerouting any calls directed to this code point for the distant office of Fig. 1 to a group of indirect trunks extending to a tandem oice through which a call may be extended to the same distant office. It will be assumed that the registrations which must be set up on the secondary registers of any sender are the same as previously described with the exception of the class and oiiice group registrations. Ii, for example, the sender |05 is now seized for a call to the distant office of Fig. l and the translator switch 200 is set on the code point corresponding to this office, the sending circuit from the class register control relay |30 will be extended as previously traced to terminal 208, thence over the outer right front contact of reroute relay 245, jumper on cross-connecting rack 280 to sending brush 261 of the pulse machine drum 250. The

sending circuit for the district brush, ofce brush and district group register control relays |3|, |32 and |33 will be extended over the middle right, inner right and inner left front contacts of relay 245 tothe cross-connecting rack 280, thence by jumper connections, as previously traced, to sending brushes 256 and 258. The sending circuit from the oice group register control relay |34 will be extended as previously traced to translator switch terminal 220, middle left front contact of reroute relay 245, jumper connection on crossconncction rack 280, thence to the sending brush 268, and the sending circuit for the talking selection control relay |35 will be extended as previously traced to translator terminal 223, thence over the outer left front contact of reroute relay 245, jumper on cross-connection rack 280 to sending brush 256.

In the manner previously described, the sender will register on its secondary registers the necessary routing information and will then proceed to set the district selector |02 and oice selector |01 to select an idle trunk extending to the tandem oice |08. The sender will then transmit the necessary routing information to the sender of the tandem oice whereby the connection may be further extended to the distant oiiice. The connection is then completed in the distant office under the control of the tandem sender, for example, over the incoming selector |08 and the nal selector l I3. All subsequent calls to the distant oice of Fig. 1 will be rerouted in this manner so long as all trunks of the direct route remain busy and reroute relay 245 is thus maintained operated.

Should any trunk in the direct route now become idle, relay |25 will release thus removing ground from conductor |26 to open one holding circuit for reroute relay 245. Relay 245 will not, however, immediately release at this time since it will be held operated over the back contact of relay 242 or the front contact of relay 244. It can only release at such times as the synchronizing circuit 20| reaches the point in its cycle of operations when relay 244 is released and relay 242 is operated. This provision is made so that relay 245 will not be released to change the routing from tandem routing back to direct routing if any tandem routing is at the time being set up in an associated sender thus preventing mutilation of the routing. Assuming that the sender |05 is receiving such a tandem routing at the time a trunk in the direct route of Fig. 1 becomes free, when the segment 266 closes with brush 265, the

circuit of relay 230 will be completed as prei viously described in turn causing the operation of relay 24|. Relay 24| will establish the previous traced circuit for relay 244 over the sending segment 255 and remove the shunt from the winding of relay 243 which will operate since the sender translator switch 200 is still standing on the code point of the trunk group of Fig. l. With relays 24| and 243 both operated, relay |28 will reoperate, lock and reconnect ground to conductor 26, but since relay 244 is operated, this ground is not effective to hold relays 240 and 245 operated. However, these relays are maintained operated from ground supplied over the right front contact of relay 244 and the back contact of relay 242. As soon as the pulse machine drum rotates to iirst open the circuit over its sending segment 255, relays 243 and 244 will release. Shortly thereafter the circuit over the receiving segment 266 will be opened and relays 230 and 24| will release.

When thereafter the pulsemachine `drum 250 Arotates to the position in which receiving segment '266 is again closed and relays 235! and`24| .again operate and the sender 65 employed in establishing the previous standard call has been Thereafter relay 244 will release when the circuit over segment 255 Vis opened. With relay 25d released and 242 now operated, there will be no holding circuit'for relays 249 and 265 and these relays will release,

relay 245 changing the routing from tandem .routing back to direct routing so that any subse- .quent calls to the distant office of Fig. 1 will be routed directly thereto over the trunk of the direct. route which has become idle.

It will now be assumed that at the time all but one of the trunks of the direct trunk group of Fig. 1 are busy and relays |24, |29, 239 and 339 are operated, there are no senders having translator switches standing on the code point of the trunk group. When, therefore, the pulse machine drum 255 rotates to the position in which circuits are closed over its receiving segment 266 and its sending segment 255, relays 230, 24| and 244 will operate as previously described, but relay 243 will not operate. A circuit will therefore be established from battery, inner contact of relay 24|, back contact of relay 243, left contact of relay 244, winding of relay 242 to ground and relay 242 will operate and lock under the control of relay 24|. When thereafter the pulse machine drum 255 rotates to first break the circuit over the sending segment 255, relay 244V will release, but serves no useful purpose since neither relay |25 nor |28 is operated to furnish operating ground over conductor |26 for operating relays 255 and 245. When the pulse machine rotates further to break the circuit over its receiving segment 255 which occurs .024 second after the opening of the circuit over the sending segment 255, relays 239, 24| and 242 are released in cascade without function. Thus, relays 230, 24|, 242 and 2445 will continue to operate and release so long as relay |24 remains operated and there are no sender translator switches positioned on the code point corresponding to the trunk group.

The synchronizing circuit and pulse machine drum 35i! function on calls from sender translator switches over the B frame in the manner previously described in connection with synchronizing circuit 25| and pulse machine drum 25! on calls from sender translator switches over the A frame.

What is claimed is:

l. In a telephore exchange system, a calling office, called offices, an intermediate olce, switching mechanism located in said calling oiice, a

' group of direct extending from said switching mechanism to each of said called offices, a group of indirect paths extending from said switching mechanism through said intermediate oflice to each called oflice, a register sender for recording office code designations of wanted lines and for controlling said switching mechanism to select a path to the called office in which a wanted line terminates, a translating means ncluding a pulse machine for translating ofce code registrations to enable said sender to control said switchingmechanism, reroute relaysainV said translating means corresponding vto *the groups of direct paths, each of said reroute re- .lays 1being operable to change vthe translation normally effective for routing a call to the corresponding group of direct paths toa Atranslation effective for routing the call to said groupof vindirect paths, and means effective for operating the reroute relay corresponding to a particular group of direct paths when all but-onefof that group oi paths are` actually busy andsaid emachine has completed a cycle to route `a can to the last idle path of that group.

2. In a telephone exchange system, a calling oflice, called offices, an intermediate oflice, switching mechanism located in said calling officeV-a group ofdirect paths extending from said switchingmechansm to each of said called oiflceaffa group of indirect paths extending from said switching mechanism through said intermediate office to-each called pince, a register sender Jfor recording oiiice code designations of wanted lines and for controlling said switching mechanism to select a path to the called oihce in which a wanted line terminates, a translating means including a pulse machine for translating office code registrations to enable said sender to control said switching mechanism, reroute relays and associated synchronizing relays in said translating means corresponding to the groups of direct paths, each of said reroute relays being operable to change the translation normally effective for routing a call to the corresponding group of direct paths to a translation effective for routing the call to said group of indirect paths, a group relay for each group of direct paths operable when all but one of the paths of the group are busy, means for operating the synchronizing relays appertaining to a group of direct paths under the joint control of said pulse machine and the corresponding group relay to determine when said pulse machine has completed a cycle to route a call to the last path of said group and a circuit for the reroute relay corresponding to said group thereupon controlled by said group relay and said synchronizing relays.

3. In a telephone exchange system, a calling office, called offices, an intermediate office, switching mechanism located in said calling oflice, a group of direct paths extending from said switching mechanism to each of said called offices, a group of indirect paths extending from said switching mechanism through said intermediate office to each called oflice, a register sender for recording office code designations of wanted lines and for controlling said switching mechanism to select a path to the called office in which a wanted line terminates, a translating means including a pulse machine for translating ofce code registrations to enable said sender to control said switching mechanism, reroute relays in said translating means corresponding to groups of direct paths, each of said reroute relays being operable to change the translation normally effective for routing a call to the corresponding group of direct paths to a translation effective for routing the call to said group of indirect paths, means effective for operating the reroute relay corresponding to a particular group of direct paths when all but one of that group of paths are actually busy and said pulsing means has completed a cycle to route a call to the last idle path of that group, and means to hold said reroute relay operated should an idle direct path become free until said pulse machine has completed its fcycle in routing any call intended for said parfticular group of direct paths by Way of said group of indirect paths.

4. In a telephone exchange system, a calling oice, called offices, an intermediate office, switching mechanism located in said calling oice, a

group of direct paths extending from said switching mechanism to each of said called offices, a

group of indirect paths extending from said switching mechanism through said intermediate oice to each called oice, a register sender for recording office code designations of Wanted lines and for controlling said switching mechanism to i select a path to the called oice in which a Wanted line terminates, a translating means including a pulse machine for translating oice code registrations to enable said sender to control said v switching mechanism, reroute relays and associated synchronizing relays in said translating means corresponding to the groups of direct paths, each of said reroute relays being operable to change the translation normally effective for routing a call to the corresponding group of direct paths to a translation effective for routing the call to said group of indirect paths, a group relay for each group of direct paths operable :L5

when all but one of the paths of the group are busy, means for operating the synchronizing relays appertaining to a group of direct paths under the joint control of said pulse machine and the corresponding group relay to determine Whenqv said pulse machine has completed a cycle to route a call to the last path in said group, a circuit for the reroute relay corresponding to said group thereupon controlled by said route relay and said synchronizing relays, and a locking circuit for'1' said reroute relay maintained by said synchronizing relays until said pulse machine has completed its cycle in routing any call intended for said particular group of direct paths by Way of said group of indirect paths.

FRANKLIN A. STEARN.

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