US2467457A - Distributor switching apparatus - Google Patents

Description

April 19, 1949.

Filed June 4, 1945 TRUNKS H. w. BALZER 2,467,457

DISTRIBUTOR SWITCHING APPARATUS 8 Sheets-Sheet 1' FIG.IQ

REPT.

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- INVENTOR. HARVEY w. BALZER ATTORNEY April 19, 1949. H. w. BALZER 2,467,457

DISTRIBUTOR SWITCHING APPARATUS Filed June 4, 1945 8 Sheets-Sheet 2 INVENTORL gnome! HARIEY W.BALZER 2 v I 0 m N K 1 F n m m mm m. .w 3 N M M .w m 2 me x 3 m 3 4 4 4 L G RT m ll 0 m G s a 2 \l lb F l 2 LR 6F 8 8 H N 2 2 mm W FIG. 4

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DISTRIBUTOR SWITCHING APPARATUS Filed June 4, 1945 8 Sheets-Sheet 5 LINK VTMl

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INVENTOR. HARVEY w. BALZER BY z ' ATTORNEY T0 TONE SOURCE April 19, 1949.

Filed June '4, 1945 TEST-1%" s l ELL-0.9: 602

hcns Aw. m .7 m mLh 5 2 .H m T L MuL ksYl TO OTHER LINK KEYS April 19, 1949. w, BALZER 2,467,457

DISTRIBUTOR SWITCHING APPARATUS Filed June 4, 1945 8 Sheets-Sheet 5- IND FIG.7

POSITION EQUIPMENT E m.) .780 I ELl-oJ INVENTOR. HARVEY W. BALZER ATTORN EY TO OTHER POSITIONS Aprii 19, 1949. H. w. BALZER DISTRIBUTOR SWITCHING APPARATUS 8 Shets-Sheet '7 Filed June 4, 1945 F I G. IO

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INVENTOR. HARVEY W. BALZER ATTORNEY April 1949. H. w. BALZER DISTRIBUTOR SWITCHING APPARATUS 8 Sheets-Sheet 8 Filed June 4, 1945 "A" POS. DIST.

"B" Pos. DIST.

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INVENTOR. HARVEI' W. BALZER POSITION DISTRIBUTORS ATTORNEY Patented Apr. 19, 1949 NlTE-D STATES PATENT OFFICE i -e e a. V DISTLBIBUT'OR'SWITCHINGAPPARATUS liarvey; Balz er; bowners uGlovevllL, .assignor 'j-toeAiitoinaticl'Eleetric Laboratories, Ina, Chicago,lll. ,'a corporation'of Delaware Y W 'AilplicationJ-une 4, 1945, Serial No. 597,461 is cans. (01.179 27) The present invention relates in general to telephone systems and more particularly to improved switching apparatus, for distributing calls tova plurality of operator positions in a cordless proposed that adistributorbe :used which would marka,batch of callingones of the lines to idle ones of the links, and which wouldprevent marking of lines over which callsgare subsequentlyreceive d until-all callinglines in themarkedbatch had been s eized by the idle links. n; has also been proposedthat a distributor beused which would mark severalgroupsoi-calling ones of the lines to idle ones of the linksvcausin h m to seize said calling lines roup by agroup and which would prevent -further markingof calling lines in a group, aiter all initialand subsequently received calls overlines in saidone group had been answered, until callingjines in all "other groups a be n eiz d- W en u th li es a e d ide in s l c a s an'dicerta o i a e llea ed to an w r-aparticu r la s c us ve y th t et od has the d sadv nta e o ot a tins any calls to saidce ainpositio a er-th calls of said particularifilass .havebeen-answered, until the calls got all otherclasses inthe same at ha eb en answ r h he her it onsh jectio s ergeme n he con th d by using .separatedistributors ioreach class of en'tly; which will cause idle links in positions'allocated to any one or onore classes toseize the marked calling ones of said lines in the corresponding, classes, and which will mark .a new batch of calling lines in each class when the prepreceding obiectf wherein certain positions are allocated to -answerwcalls in two .or more classes, in which means} individual to .eachflposition are provided to .prevent further answering of calls .in oneof said classes by said certain positions, when all calls'of that one class includedinanbatch have been exhausted, until-the callsof each other clas s included 'in-a batch have been exhausted.

ervice. How ve as t is s conideme e a A still further'gobjectof the invention is to provide a call. distributing. arrangement as stated in thej 'precedirig.objects wherein other positions are'allooated to receive only one of. the classes-0f calls, allocatedto saidcertainI positions, in which said fineans individual to each position will permit a new batch of .cansxw be ansW'eredLby said other positions when the previous batch of callsof the class allocated ith'erto has, been exhausted, regardless of whether or not batches of calls in the other .classes' h'ave'been exhausted by said certain positions. a I ,v

hno'ther'objec'tlof the' invention is to provide means causing simultaneous calls. in. difierent classes to be given afdesired order of preference at'af position which 'is difierent than the order in jwhich corresponding marking .circuits are scanned by the links in searching for a calling line, p ,t

.St'i1l anothernobjctf is to provide means for removing; a marking corresponding ,to a group of lines in casefalink attempts vto find a calling line in saidgroup but fails .to doso, thereby preventing aifalse. marking .of any line in the group fromlolockingother groups of lines.

Another object is 1170 provide means for markingnew batches of .callingflinesin all classes in case, afllink attemptst'o lfindla calling lineinthe last choice group of the last choice class but fails Qt'odo so, .thereby preventing a false group marking fro'mlblocking all calls. I

. A further object is to provide animproved link and control circuit therefor'wherein certain con ductors are marked by the control circuit to identify asub-group ofcalling lines toa link when said link is searching. for a calling line in said sub-group,-,and "wherein said certain conductors are marked'by the link when a line has call by an associated link identifies the class of call being answered.

Other objects of the invention will appear upon a further perusal of the specification taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic trunking diagram showing the general arrangement of a telephone system embodying the present invention;

Figs. 2, 3 and 4 show conventional trunk circults adapted for use with a call distributor incorporating the invention;

Fig. 5 is a schematic diagram of an improved link circuit;

Figs. 6 and 7 taken together comprise a schematic diagram of an operator's position equipment and novel link control circuits associated therewith;

Figs. 8 and 9 taken together comprise a schematic diagram of a novel call distributor constructed in accordance with the invention;

Fig. 10 shows a supervisor's equipment;

Fig. 11 shows conventional distributors for routing calls to idle operators positions; and

Fig. 12 illustrates the mode of combining Figs. 2 to 11, inclusive, in order to form a unified system.

A brief description of the invention will first be given and will be followed by a detailed description of the illustrated embodiment thereof. As previously noted, a system embodying the invention comprises a plurality of lines or trunks of several different classes, a plurality of operators positions each having a number of links having access to the lines or trunks, and a common call distributor for causing idle links to seize calling ones of the lines. As in prior circuits where calling lines are marked batch by batch, a pair of conductors extend from the trunk circuits to the common call distributor and each trunk is provided with a relay Whose operating circuit includes a normally open point individual to the trunk, one of said conductors, and a normally closed point in the call distributor common to a number of such relays. When a call is received over a trunk, the normally open point in the operating circuit of the relay associated therewith is closed, thereby operating the relay to mark the trunk and to extend a start signal to the call distributor over the remaining conductor of said pair. The call distributor opens said common point in response to the start signal to thereby prevent the operation of other such relays in response to the reception of calls over other trunks, and directs an idle link to find the marked trunk. Upon seizure of the marked trunk by a link the start signal is removed, thereby causing the call distributor to reclose said common point to permit operation of the relays associated with trunks over which calls have subsequently been received. In accordance with the present invention, a pair of conductors is provided for each class of trunks, a normally closed point in the call distributor common to all of the trunk marking relays in each class being provided and being connected in series therewith over one conductor of the correspondingpair. In response to a start signal over the other conductor .4 of any pair, the call distributor opens the common point in the operating circuits of the corresponding class of trunk marking relays, thus preventing subsequent marking of other trunks in that class independently of the remaining classes. Thus independent batches of calling lines are marked in each class. Now if all operators positions are to answer all classes of calls and each position gives preference to the different classes in the same order, it is apparent that no calls in the last choice classes would be answered if calls continued to be received in the first choice classes since each is marked in independent batches. In order to prevent a call included in a second batch of a first choice class from being answered prior to a call included in a first batch of a last choice class, at a position allocated to answer both classes, a further call distributing arrangementdndividual to each position is provided. This individual distributing arrangement prevents further answering of calls in a first choice class at the associated position, once a batch thereof has been exhausted, until all marked calls in corresponding batches of later choice classes have been answered. However, new batches of calls may be answered at other positions allocated to answer any one choice class exclusively. For example, assume that there are three classes of trunks A, B and C, and that thereare four positions, one of which answers calls in any of the three classes and the other three of which each answer a particular class exclusively. The trunks will be marked in separate and independent batches at varying intervals of time depending upon the calling rate and answering time prevailing for each class. There is thus no true correspondence between batches of marked trunks in different classes. Each of the positions answering a particular class will act independently of the other two. However, the one position that is answering calls in all three classes is automatically caused to assist any one of the other three positions which is overloaded, or to assist all three other positions equally, by the distributing arrangement individual to said one position. Assuming that the other three positions are equally loaded, at a given instant when the one position starts to answer calls in class A there will be a batch of marked lines in each of the three classes A, B and C. These three batches are referred to as corresponding batches, it being understood that when one of these batches is exhausted and a new batch is marked in that'class that this new batch does not correspond to the other two batches even though they overlap in time. Said one position will now answer calls in all three classes, thereby assisting the other three operators, until a batch of one class has been exhausted. If the batch of class A calls is the first to be exhausted a new batch thereof will be marked and answered by the other operator allocated thereto exclusively, but said one operator will be prevented from answering any more class A call, class B and C calls being answered thereby instead thus further assisting the other operators allocated exclusively thereto. When one of the corresponding batches of these last two classes has been exhausted, say class C for example, a new batch thereof will be marked and answered by the other operator allocated exclusively thereto, said one operator being prevented from answering any more class C calls until the remaining batch of class B calls is exhausted. Thus the greatest assistance is given to the heaviest loaded one of the other operators by said one operator. When the remaining batch of class B calls has been exhausted, three new corresponding batches of calls are shared by said one operator with the other three operators. The individual distributing arrangement is further arranged so as to permit ready disablement thereof for any one or more of the several classes so as to provide preference to particular classes at certain operators positions. The manner in which these results are accomplished will best be understood from the following detailed description.

Preparing an operator's position to receive calls When the operators position shown in Figs. 6 and 7 is occupied the plug 'III of the operators headset Till is inserted into jack I12 thereby completing a circuit to relay I in series with the transmitter of the headset. Relay I00 opcrates, connects lamps AN, BN, and CN to leads AL, BL, and CL, respectively, at contacts 102, m3, and 704 in series with contacts on the class of service keys 130, I40 and I50 corresponding to each lamp. The letters A, B, and C represent the three classes of service into which the various types of calls are subdivided. These letters have been prefixed to the reference characters of all leads and relays associated with a particular class of service to facilitate a clear understanding of the invention. The leads AL, BL, and CL extend through a cable to the call distributor (Fig. 9). Relay I00 also completes a circuit to relay 680 at contacts 105 and prepares circuits to relays AP, BP, and CP from leads APG, BPG, and CPG, respectively, through contacts of the corresponding class of service keys at contacts I06, I01, and m8. The APG, BPG, and CPG leads also extend through a cable to the call distributor (Fig. 9). Relay 68!! operates and further prepares the circuits to relays AP, BP, and CP at contacts 68I, $82, and 683, respectively. It will be noted that terminals are provided so as to permit ready strap-ping of any of these latter contacts, of which the first is shown strapped. For the moment this strap will be ignored.

When the operator at the position shown is ready to receive calls she will operate a link key, such as LKI (Fig. 6), to its locking position (i. e. to the left) thereby completing an operating circuit to the lower winding of relay 560 (Fig. of the corresponding link from ground at contracts IIlI, through contacts 62I and LKIZ to relay 560 over lead OGI. Relay 56!] operates and closes a circuit to its upper winding at contacts 569 over lead HGI, through contacts LKII and relay 626 to ground. Relay 620 operates, opens the operating circuit to relay 560 and closes a circuit to relay 610 at contacts 62!. Relay 560 remains operated due to the energization of its upper winding in series with relay 620. It should he understood that a similar key LK2 and corresponding leads 0G2 and I-IG2 are provided for the second link, and so on. Relay 610 operates; removes ground from guard leads AGDI, BGDI, and CGDI at contacts 61!, 612, and 613, respectively; and closes ground from contacts 684, 685, and (-386, through contacts EM, 615, and 618 and contacts of the corresponding class of service keys to position distributor start leads ADS, BDS, and CD8, respectively. The distributor start and guard leads for each of the three classes of service extend over a cable to the position distributors (Fig. 11).

Only one position distributor has been shown in detail in Fig. 11 since they are all identical.

Each distributor has a common distributor start lead, such as CDS, extending therefrom to all operators positions, and a pair of individual guard and start leads, such as CGDI and CSTI, extending to a particular position corresponding ,to the suffix number. As long as any occupied position allocated to receive class C calls has a link key of an idle link thrown, the CDS lead will be grounded. When this lead is grounded initially, the lower winding of relay IIZU is energized thereover in series with contacts II II.

Relay H20 operates, closes a holding circuit through its upper winding in series with relay Hill and contacts II3I at contacts II22; connects lead CGDI to the lower winding of relay I I30 in series with contacts I I5I at contacts H23; and extends lead CSTI to lead CST at contacts H25. Relay IIII] operates and opens the operating circuit to relay IIZI'I at contacts IIII. Since it has been assumed that the position equipment shown in Figs. 6 and '7 represents the first position and is now prepared to receive calls, there will be no ground on the guard lead CGDI and consequently the lower windingof relay I I36 will not be energized at this time. Each of the other distributors operates in a similar manner to extend leads ASTI and BSTI coming from position I (Fig. '7) to the leads AST and BST, respectively, extending from the call distributor (Fig. 9) to the corresponding position distributors.

Answering a class A call Referring now to Fig. 1, three incoming trunks are shown terminating in a toll selector, a suburban selector, and a toll information trunk circuit. The toll selector is employed by toll operators at a distant ofiice to extend toll calls to local subscribers over a toll switch train which is not shown, or via the repeater and toll selector intercepting trunk circuit shown to an information operator through the cordless switchboard. The suburban selector is employed by subscribers of nearby oflices to complete connections to local subscribers over the local switch train, or via the suburban information trunk to an information operator through the switchboard. A similar local information trunk is accessible from the local selector to permit local subscribers to call an information operator through the switchboard. The toll information trunk is employed by toll operators at a manual toll switchboard to call an information operator through the switchboard. Since the switch trains follow conventional practice they have been omitted in the detailed circuit diagrams The trunk circuits have been shown in detail although they differ from conventional practice only in the adaption thereof to suit the novel call distributor.

The toll selector intercepting trunk circuit shown in Fig, 2 is seized over conductors 28I and 282 when ringing current is transmitted thereover from a preceding repeater under the control of a toll operator. The ringing current flows through condenser 283 and relay 200 in series causing this relay to operate and complete a circuit to relay 23D. Relay 23c operates, closes its locking circuit at contacts 232, connects relay 220 to conductor AH at contacts 233, and rounds lead 284 to light a call waiting lamp not shown. For convenience, calls received over the trunk circuits of Figs. 2, 3, and 4 are hereinafter referred to as class A, B, and C calls, respectively. As previously noted, all conductors and relays associated. with a particular class of service have been prefixed with the corresponding letter A, B, or C. Thus the AH lead to which relay 220 has been connected is associated with the class A trunk circuits. If there are no unanswered class A calls this lead will be grounded at contacts AG3 in Fig, 8, but if a batch of class A trunks have previously been marked there will be no ground on lead AH until all of the marked trunks have been seized by idle links. In either case, when ground is present on lead AH relay 220 operates; closes its locking circuit and opens its operating circuit at contacts 224; closes a multiple locking ground to relay 230 at contacts 22!; at contacts 222 connects relay 258 to lead 285, which is multiplecl to corresponding bank contacts of all links to mark the trunk circuit; and grounds lead AS to extend a start signal to the call distributor (Fig. 8) at its contacts 223. The class A trunks may be divided into a number of groups, each corresponding to a particular level of bank contacts oi the links. In the present instance it is assumed that the class A trunks appear on two different levels of the links and therefor two AS leads are provided. to relay AI and is multipled to all of the class A trunks in one group, while lead AS?! is connected to a similar relay A2 (not shown) and is multipled to all of the class A trunks in the second group. Assuming that lead ASI was grounded by relay 220, relay AI operates in series with contacts AGI, closes its holding circuit at contacts Al I, grounds lead VAI at contacts AI3, and closes a circuit to relay AD of Fig. 9 at contacts Al i, Relay AD operates, grounds lead AL at contacts ADI to light the corresponding class of service lamps, such as All (Fig. '7) at all occupied operators positions allocated to receive class A calls and in the supervisors circuit (Fig. 10), opens the circuit to normally operated relay AG and grounds lead AST at contacts A133, and grounds lead APG at contacts ADE. Relay AG releases after a brief delay and opens the operating circuits to relays AI and A2 at contacts AGI and AGE, respectively; and removes ground from the AH lead to prevent marking of class A trunks over which calls may subsequently be received. Relay .AI remains operated due to the shunting of contacts AGI by contacts AI I.

The ground placed on lead APG by relay AD completes a previously traced circuit to relay AP (Fig. 6), and to corresponding relays of other coupled positions allocated to receive class A calls. Relay AP operates, opens the circuit to relay 58%) at contacts API, shunts contacts 68I at contacts APB, closes a multiple ground to the ADS lead at contacts AP I, and closes a circuit to relay AR from ground at contacts AD3 (Fig, 9), over lead AST, through contacts such as I I25 of the A position distributor (Fig. 11) over lead ASTI, through contacts 63! (Fig. 6), contacts A1 5 and Hill, through relay AR and contacts ARB, CR5, BRIO,.and ARd to negative battery. Relay AR operates, closes its locking circuit through its preliminary make contacts AR'I, opens points in its operating circuit at contacts ARG and ARE, closes a circuit to relay Slit at contacts ARI, transfers lead All. from the identity lamp AEL to ground at contacts AR3, and connects leads VAI and VA2 to leads LI and L2, respectively, at contacts AR& and ARA, thereby marking level I to the link since the VAI lead was grounded by relay AI in the call distributor (Fig. 3). The LI to L9 leads extend over a cable to a set of vertical marking contacts of the link (Fig. 5)'

Lead ASI is connected I and are multipled to: all. links associated with the.

first position.

Relay 683 restores after a brief delay, opens the operating circuit to relay AP at contacts 68I, grounds the BGDI and CGDI leads at contacts 684 through contacts BP3 and CP3, respectively, and removes ground from the BDS and CD8 leads at contacts 685 and 68%, respectively. If other positions are occupied the B133 and CD8 leads will be grounded thereby and the ground placed on the BGDI and CGDI leads will cause the corresponding position distributors to advance to the next idle position. The ground on CGDI energizes the lower winding of relay H38 (Fig. 11) through contacts H23 and II5I. Relay H30 operates, closes a locking circuit to its upper winding at contacts I I32 through contacts IHI and relay I I II) to ground over the CDS lead, opens the locking circuit to relay H23 at contacts SI, and extends the CST lead to lead CST2 at contacts H35. Relay IIZEI restores, opens the operating circuit to relay H39 at contacts H23, connects the CGDZ lead to the lower winding of relay I M6 at contacts I I 24 through contacts H34, and disconnects lead CST from lead CSTI at contacts I I25. If the second position is busy the CGD2 lead will be grounded and the chain will continue to advance until an idle position is reached. If all positions are busy there will be no ground on the CDS lead and all relays will then restore to normal. The B position distributor operates in the same manner to extend theBST lead to an idle position,

Relay 66!) operates in response to the operation of relay AR and closes a circuit from ground through contacts 66 I, through the low resistance upper winding of relay 650, through contacts GI I, over lead ST to the link (Fig. 5) thence tln-ough contacts 561,. SRI I, and 533 to the high resistance lower winding of relay 540. Relay 65!) does not operate over the above traced circuit due to the high resistance of the lower winding of relay 549. Relay 54!) operates and closes a circuit from ground through contacts 5, 521, 54-3, 51!, and 583 to the vertical magnet VTM. VTM operates to advance the link wipers WI to W5 to the first level, and closes a circuit to relay 510 at contacts VTMI.v The advancement of wiper W5 to the first level marking contact completes a circuit from ground on lead Ll over wiper W5, through the upper winding of relay 580, and through contacts 584 and 531 to relay 510 in multiple with the circuit completed thereto by contacts VTMI. Relay 570 operates and opens the circuit to VTM at contacts 5H. When VTM restores it removes a short circuit from the upper winding of relay 58!] thereby energizing this winding in series with relay 510. causing relay 580 to operate its preliminary make contacts 585 which complete a circuit to its lower winding. Relay 580 then operates completely, connects the low resistance upper winding of relay 54!! in parallel with its lower winding at contacts 58I, grounds lead LB! at contacts 582 tolight the first link busy lamp LBIL (Fig. 6), opens a second point in the operating circuit to VTM and prepares a circuit to the rotary magnet ROM at contacts 583, and opens the circuit to relay 510 through the upper winding of relay 580 at contacts 584. Relay 578 rostores. andv closes the circuit to ROM at contacts 5'. ROM operates to rotate the wipers WI to W4 to the first set of bank contacts in the first level and to disengage wiper W5 from the set of vertical marking contacts, and closes a circuit to relay 510 at contacts ROMI. Relay 510 operates and opens the circuit to ROM at contacts 51!. ROM restores and opens the circuit to relay 516 at contacts ROMI. Relay 516 restores and recloses the circuit to ROM. ROM reoperates, advances wipers W! to W4 to the second set of contacts in the first level, and recloses the circuit to relay 516. This cycle of operations continues until Wiper W3 engages the contact connected to lead 285 which has been marked by the connection of negative battery thereto through relay 266 (Fig. 2) When this contact is reached a circuit is completed from negative battery over lead 285, through wiper W3, contacts 523, relay l6, con tacts 532, wiper W4, and over an E lead common to all of the link bank contacts associated with class A trunks (i. e. lead AE) to ground through contacts AR3 (Fig. 6). Relays 5!6 and 266 operate over the above traced circuit and relay 5!6 opens the circuit to ROM to prevent further rotary stepping and closes a circuit to relay 526 at contacts 5!!. Relay 266 operates, closes a circuit to relay H6 at contacts 262, closes its looking circuit at contacts 263, and opens the circuit to relay 226 at contacts 264. Relay 2l'6 operates, opens the circuit to relay 266 and connects resistance ground through windings of impedance coil 246 to conductors 28! and 282 to operate a ring trip relay in the preceding repeater at contacts 2!! and 2!2, and removes ground from start lead AS at contacts 2l4. Returning now to Fig. 5, relay 526 operates in response to the operation of relay 5!6; transfers wiper W3 from ground through relay 5l6 to ground through relay 566 at contacts 523, extends leads 286 and 281 through wipers W! and W2 to leads R! and R2 through contacts 563 and 564, condensers 563 and 564, and contacts 59! and 592, at contacts 52! and 522, respectively, connects ground to wiper W4 through contacts 532, 524, and 54!, opens its operating circuit and closes its locking circuit to contacts 582 at contacts 525, and closes a circuit from ground through contacts 526, 566, over lead RS to relay 6!!! (Fig. 6). Relay 566 operates in series with relay 266 (Fig. 2). Relay 5!6 restores.

It will be recalled that when relay 586 operated it connected the low resistance upper winding of relay 546 in parallel with its lower winding, thus lowering the resistance in series with the upper winding of relay 656. Relay 656 operates, transfers the end terminals of the secondary winding of the operators induction coil IND from leads R! and R2 to ground through condenser 622, and through contacts AR2 and condenser 623 to a source of tone current not shown at contacts 652 and 65!, respectively, and closes a circuit to its lower winding through resistance 624 in multiple with relay 646 at contacts 653. Relay 646 operates after a brief delay, closes a multiple circuit to itself and the lower winding of relay 656 from ground through contacts 66! at contacts 642, and closes a circuit to relay 636 at contacts 643. Relay 636 operates after a brief delay and shortcircuits the upper and lower windings of relay 656 at contacts 633 and 634, respectively. Relay 656 restores and reconnects the secondary winding of IND to leads RI and R2 at contacts 65! and 652. Relays 636 and 646 remain locked to ground from contacts 66!. During the time that relay 656 was operated, a continuous tone is transmitted from the tone source to the secondary winding of IND. The center portion of this winding is connected to the receiver of the operators headset 116 causing a single long audible tone to be given to the operator to inform her '16 of the acceptance of a class A call by an idle link associated with her position. In the event that a class B or C call was being accepted, relays BR or CR would have been operated in place of relay AR as will presently be described. In this event the tone current would have been transmitted through condenser 623, contacts 64! and contacts after relay 656 operated until relay 646 operated to interrupt the tone current path at contacts 64!. The subsequent operation of relay 636 would then close a second tone path through contacts 64! at contacts 632. The subsequent release of relay 656, after a brief delay caused by the slugging effect of its short-circuited windings, would then interrupt the tone path a second time at contacts 65!. Thus when a class B or C call is accepted the operator receives two short audible tone signals.

Relay 6l6 operates from the ground placed on lead RS by relay 526 (Fig. 5), connects direct ground to lead ST at contacts 6! and opens the circuit to relay 616 at contacts 6l2. Relay 616 restores, grounds the AGD! lead at contacts 61! to cause the A position distributor to advance to the next idle position in the manner previously described, removes ground from the ADS lead at contacts 614 to restore the A position distributor to normal in case there are no other idle positions, and opens the circuit to relay AR at contacts 611. Relay AR restores and transfers lead AE from ground to lamp AEL which lights due to the ground placed on lead AE over wiper W3 of the link (Fig. 5) thereby indicating to the operator that a class A trunk has been seized. Relay AR in restoring also opens the circuit to relay 666 which restores and opens multiple holding circuits to relays 636 and 646 at contacts 66! thus permitting these relays to restore.

When the trunk circuit of Fig. 2 was seized,

' relay 2!!) operated and removed ground from the at contacts ADI to extinguish all class A call waiting lamps, such as AN (Fig. '7), removes ground from the APG lead at contacts AD2 to release all operated position grouping relays, such asrelay AP (Fig. 7), and removes ground from the AST lead and closes a circuit to relay AG (Fig. 8) at contacts AD3. Relay AG operates and grounds the AH lead.

When the trunk circuit of Fig. 2 was seized the circuit to relay 226 was opened at contacts 264. After a brief delay relay 226 restores and opens the locking circuit to relay 236 at contacts 22!. Relay 236 restores, connects relay 216 across leads 286 and 261 at contacts 23!, and opens the circuit to the call waiting lamp not shown at contacts 234. All of the common equipment has now been freed and a talking circuit is established between the distant toll operator and the information operator over conductors 28! and 282 through condensers 283 and 288, over leads 286 and 261, through wipers W! and W2, contacts 52! and 522, 59! and 562, condensers 563 and 564, contacts 563 and 564, over leads R! and R2, and through contacts 662 and 663, 635, 65! and 652 to the secondary winding of the induction coil IND. The center portion of this secondary winding is wound with resistance wire to balance the impedance of the line connected across the whole secondary winding, this being a well known antisidetone circuit. Speech currents received over the line are therefore reproduced by the receiver of the operators headset "0, whereas speech currents produced by the transmitter of the operators headset flowing through the primary winding of IND induce corresponding voltages in the several sections of the secondary winding which are connected so as to produce speech currents in the line but not in the operators receiver. When operating practice or circuit requirements necessitate acknowledgement of the answering of a call the operator may operate the flash key 180 (Fig. 7) momentarily, thereby grounding the FL lead which extends over a cable to the link (Fig. 5) thence through contacts 544 to relay 590 which operates and transfers wipers WI and W2 to negative battery and ground, respectively, at contacts 59l and 592. A circuit is thus completed to relay 210 (Fig. 2) which operates and closes a circuit to relay'250 at contacts 212. Relay 250 operates, closes its locking circuit to ground through contacts 262 at contacts 253, and transfers leads 28! and 282 from resistance ground to a loop circuit through contacts 2' at contacts 25! and 252. The low resistance loop circuit operates a back-bridge relay in the preceding toll selector which reverses battery to the distant ofiice. When the flash key 180 is released relay 590 restores and releases relay 210 which restores and opens the loop circuit to leads 28l and 282 at contacts 2', and opens the operating circuit to relay 250 at contacts 212. Relay 252 remains locked to contacts 262. Opening the loop again causes battery to be reversed to the distant ofiice in the preceding toll selector.

Releasing the connection After the distant operator has obtained the desired information from the information operator, the latter momentarily operates a common release key H (Fig. '7) thereby grounding the RSC lead which extends over a cable to the link (Fig. thence through contacts 55 I to relay 530. Relay 53B operates, opens the circuit to relay 540 at contacts 533, and opens the locking circuit for relay 580 and closes a locking circuit to itself through contacts of the vertical oil-normal springs VON at contacts 536. Relay 54D restores. Relay 580 restores and at contacts 582, opens the locking circuit to relay 520, opens the circuit to link busy lamp LBIL over lead LBI, and closes a circuit to the release magnet RLM through contacts 534 and contacts of VON. Relay 520 restores and opens the circuits to wipers WI, W2 and W3 at contacts 521, 522, and 523, thus opening the circuit to relay 500 in series with relay 2% (Fig. 2) over lead 285. Relay 500 restores. The release magnet RLM operates to release the link switching mechanism which restores'and opens the vertical off-normal springs VON, thereby opening the locking circuit to relay 530 which restores, opens the circuit to RLM atcontacts 534 and opens the circuit to relay 6H] (Fig. 6) over lead RS and through contacts 568 at contacts 535. The release magnet RLM restores. Relay 6H1 restores and recloses the circuit to relay 610 at contacts 6| 2. Relay 610 reoperates to prepare the position to receive another call. All of the equipment in Figs. 5, 6, and 7 is now restored to the condition existing at the time the position was first prepared to receive a call by the operation of the link key LKI.

Relay 260 (Fig. 2) releases in response to the opening of lead 285 at contacts 523 (Fig. 5) and opens the circuits to relays 2H) and 250 which 12 restore. All relays in the trunk circuit have now been restored.

Answering class B calls In Fig. 1 both a local and a suburban information trunk circuit have been shown, the first being accessible to local subscribers from a local selector, and the second being accessible to sub urban subscribers from a suburban selector. Actually only one type of trunk circuit is required for either use, the only difference being in the interconnection of the trunks with the cordless switchboard. Calls over either of these trunks are classified as class B calls, but it is desirable that the operator be informed whether the call is coming from a local or a suburban subscriber.

Only one trunk circuit has been shown in Fig.

3, the difierences in connections for the two types of calls being described hereinafter.

The trunk circuit of Fig. 3 is seized by the closure of a loop circuit thereto over leads 356 and 35l from the preceding selector. The release trunk 352 is normally connected to resistance battery in case the preceding selector is the battery searching type. Closure of the loop energizes relay 3H3 which operates and closes a circuit to relay 338 at contacts 3| 2. Relay 330 operates, connects a source of ring back tone not shown through condenser 353, contacts 331 and 30! to lead 356, connects relay 345 through contacts 332, 323, 345, and 392 to lead BH, closes a circuit to a call waiting lamp not shown through contacts 333 and 303, and over lead 354, and connects ground to lead 352 to mark the trunk busy at contacts 331.

It was previously assumed that the class A trunks were divided into two groups occupying the first and second levels on the banks of the links. It will now be further assumed that there 40 are insufficient class A trunks to fill the second level, the unoccupied contacts being connected to class B trunks, and that the next five levels, i. e. levels 3 through 1, are filled with class B trunks. The class B trunks are further divided into two groups, local and suburban, but this latter grouping need bear no relation to the level grouping thereof. Due to this grouping by levels, six BS leads extend from the call. distributor (Fig. 8) to the class B trunk, the particular BS lead which is associated with a trunk being dependent on the level of the link on which that trunk appears. However, the BH lead is not so subdivided but instead is common to all class B trunks. Therefore, if or when there are no marked class B trunks waiting to be answered, the BH lead will be grounded energizing relay 34B. Relay 340 operates, connects the lower winding of relay 320 to lead 355 to mark the trunk to the link (Fig. 5) at contacts 343, grounds the BS lead (I to 6) corresponding to the level of the link on which the trunk appears at contacts 3M, and closes its locking circuit independent of the BH lead at contacts 345. Assuming that the call being considered is over a trunk connected to the second level of the links, lead will havebeen grounded to energiz the upper winding of relay Bl through contacts BGI. Relay Bl'operates, closes its holding circuit at contacts Bl l, grounds leadVBl at contacts BB,

operate position grouping relays, such as BP (Fig. 6) at all operators positions allocated to receive class B calls, and opens the circuit to relay BG (Fig. 8) and grounds lead EST at contacts BD3. Relay BG restores after a short delay and opens points in the operating circuits to relays B! to B6 at contacts BG! to BG6, respectively, and removes ground from lead BH at contacts BG! to prevent marking of class B trunks over which calls are subsequently received. The BST lead grounded by contacts BD3 (Fig. 9) extends through the 13 position distributor (Fig. 11) to the corresponding start lead of an idle operators position, which will be assumed to be the position illustrated, in which case lead BST is extended to lead EST! and results in the operation of relay BR (Fig. 6). Relay BR extends leads VB! through VB6 (corresponding to relays B! to B6, respectively) to leads L2 through L'l (corresponding to the levels on which the trunks associated with relays B! to B6 appear), at contacts BR9 through BR4, thus marking lead L2 from ground at contacts BI3 over lead VBI, transfers leads BE! and BEZ from the corresponding identity lamps BEIL and BE2L to ground at contacts BRZ and BR3, and closes a circuit to relay 660 at contacts BRI. The link is now operated to the second level and rotated to the marked trunk in the same manner as previously described. In case the class A trunks appear on the first contacts of the second level and the class B trunks appear last, and in case any of these class A trunks have been marked to the link by the operation of a relay such as 220 (Fig. 2) the link will pass over such trunks since the E leads corresponding thereto, which are encountered by wiper W4 during the rotary trunk hunting movement of the link, will be connected to battery through lamp AEL rather than ground at contacts AR3. However, the E leads corresponding to the class B trunk are grounded at contacts BR2 and BR3 thus completing a circuit to relay 5I0 when the marked class B trunk is encountered by wiper W3. When this occurs relay 320 is energized in series with relay 5!0 through contacts 343, over lead 355, through wiper W3, contacts 523, relays 5!0, contacts 532, thence through wiper W4 to ground at contacts BB2 or BR3. Subsequent operations of the link relays are the same as previously described. When the W4 wiper is grounded by the operation of relay 520, and when relay BR restores, lamp BEIL or BEZL is energized over lead BE! or BEZ to identify the type of class B call which has been seized by the link.

Relay 320 operates over the above traced circuit, closes a multiple circuit to relay 330 and removes ground from the BS lead at contacts 322, opens the circuit to relay 340 at contacts 323, closes its locking circuit at contacts 32!, and closes a circuit to relay 300 at contacts 324, Relay 300 operates, closes its locking circuit to contacts 333 and opens the circuit to the call waiting lamp not shown over lead 354 at contacts 303, and disconnects the source of ring back tone from lead 350 at contacts 30!. Relay 340 restores after a brief delay and extends a talking circuit from leads 350 and 35! through contacts 34! and 342, over leads 356 and 351, through wipers W! and W2 and over the previously traced circuits to the operators induction coil IND (Fig. 7).

The removal of ground from the start lead, BS! in this case, releases relay B! which restores causing relay BD to restore and relay BG to be reoperated in a manner similar to that previously described for the class A call.

Extending the call to a local subscriber Although the equipment shown is intended primarily for information service, occasionally it is necessary for an information operator to extend a connection to a local subscriber. In such an event, the operator operates the dial ke 604 (Fig. 6) thereby closing a circuit to relay 600 which operates and closes a circuit from ground, through contacts 60!, over lead LD, through contacts 56! (Fig. 5) and 53! to relay 550, and opens leads R! and R2 at contacts 602 and 603. Relay 550 operates, locks to ground on the DH lead from contacts 63! (Fig. 6) through contacts 562, 55!, and 53!, and closes a loop circuit to a local line circuit not shown over leads 505 and 506 through contacts 552 and 553, 565 and 566, over lead-s F! and F2, through contacts 65!, the secondary winding of IND, contacts 652, 635, and impulsing contacts 19! of dial 190. The local line circuit has not been shown since it may be any of the well known circuits usually connected to a local subscribers line. When a selector switch has been associated with leads 505 and 506, either by a plunger lineswitch, rotary lineswitch, or finder switch, the operator operates the dial to direct the local switch train in the well known manner. Whenever the dial 190 is rotated off normal the contacts 192 are closed, short-circuiting the operator's receiver to avoid clicks therein, and short-circuiting the two lower portions of the secondary winding of IND to reduce the impedance thereof so as not to interfere with proper impulsing of the local switches. After the connection to the called local subscribers line has been established dial key 604 may be restored to release relay 600 which opens the operating circuit to relay 550 at contacts 60!, reconnects leads RI and F! at contacts 602, and reconnects leads R2 and F2 through impulsing contacts 19! at contacts 603, thus connecting the calling partys talking circuit across the called line in multiple with the secondary of IND. The operator may retire from the connection by restoring the link key LKI thus opening the holding circuit to relay 560 through relay 620 at contacts LK! l. Relay 560 restores, substitutes direct ground for ground over lead DH for the locking circuit of relay 550 at contacts 562; disconnects the local line leads 505 and 506 from the position relays and connects them directly to the talking conductors of the link at contacts 563 thrpugh 566, opens the circuit to relay 540 at contacts 561, and opens the circuit to relay 6! 0 at contacts 568. A holding loop is now closed to the local line through impedance coil 501. Relay 6!!! restores and opens the circuit to relay 540 over lead ST at contacts 6! Relay 540 restores and removes ground from wiper W4 at contacts 54! to extinguish the trunk group identity lamp BEIL or BEZL. Relay 620 restores. The operator may now operate another link key like LK! to prepare for the reception of another call in the same manner as described previously.

Recalling the operator or releasing the connectz'on The link circuit is arranged so that it is readily adaptable to either release the connection under the control of the calling subscriber or to permit recall of the operator by the calling subscriber. In the first case strap X (Fig. 5) is used while in the latter case this strap is omitted. In either case, when the Icalli-ng-subscribers loop is opened rela '3") (Fig. 3) is released thereby removing a short circuit from the high resistance upper winding of relay 320 at contacts 3| I. Relay 320 is now held with its two windings in series over lead 355 and wiper W3 to ground through relay 500. The increased resistance of this circuit permits relay 500 to restore. When relay 500 restores it short-circuits itself at contacts 50! to provide locked in supervision, and closes ground throughcontacts H, 52?, and 502 to lead SYI thereby lighting the supervisory lamp SYIL. If strap X is omitted no further operation takes place. If desired, the connection between contacts SM and 541 may be omitted to permit flashing of lamp SYIL by the calling party. When the operator observes the lighted lamp SYIL she operates key LKI to connect the position relays with the link, as previously described, to ascertain'whether the call-- ing party desires further assistance. If not, key LKI is restored and momentarily operated to its non-locking position (i. e. to the right) thereby grounding lead RSI Relay 530 operates and brings about the release of the link as previously described with the additional function of opening the locking circuit to relay 550 at contacts 53I. Relay 5'50 restores and opens the local line circuit at contacts 552 and 553 to release the local switch train. When the link is released by the operator the circuit to relay 320 is opened at contacts 523 causing relay 320 to restore and open the circuit to relay 330 at contacts 322. Relay 330 restores,

opens the locking circuit to relay 300 at con-, 3

tacts 333, and replaces the ground on lead 352 with battery to release the local switch train and mark the trunk idle. Relay 390 restores.

When strap X is used in Fig, 5, opening of the calling subscribefs loop causes the release of.

relay 530 as just described, but in this case when relay 5053 restores a circuit is closed to relay 53:! in multiple with lamp SYIL. The'operation of relay 5% releases the link and trunk as just described. Lamp SYIL will be energized in multiple with relay 530 until the locking circuit thereto is opened by contacts on VON upon restoration of the link switching mechanism to normal.

When the operator first extended a connection over the local line she may have made an error in dialling, or for some other reason it may be necessary to release the local switch "train and again set up a connection thereover without .releasing the link. In thi event the key 605 is momentarily ope-rated causing relay 530 to operate and open the loop to the local line at contacts 635. The locking circuit to relay 550 will also be opened at contacts 63I but without effect since the operating circuit thereto remains closed at contacts 50L When key 555 is released relay 53G restores and recloses the loop to the local .line causing it to be reseized. A connection mayagain be set up over the local switch train. If the operator desires to release the local switch train and not reseize the local line circuit to establish a second connection, the dial key 5634 is first restored causing relay 5:70 torestore and open the operating circuit to relay 550 at contacts 60L after which key 605 is operated momentarily causing relay 530 to operate and open the locking circuit to relay 553 at contacts 631. Relay 550 then restores and opens the local line circuit at contacts 552 and 553 to release the local "switch train. I

l6 Extending the call to the supervisor instead of extending the call received over the local or suburban trunk circuit over the local switch train, it may at times be necessary to connect the calling party with, the supervisor. To do this the operatorfirst notes whether the supervisors circuit is idle or busy as indicated by the lighting of lamp SBL' (Fig. '7). If or when this lamp is extinguished the operator throws key I20 to the left momentarily, thereby grounding the supervisor call lead SC and the supervisor's signal lead SSE. These leads extend over a cable to the .link (Fig. 5) Where a circuit is closed to relay SRI from ground over lead SC, through contacts .502, 538, relay SRI, contacts SRI3, .SRS I, SRZI', andSRII' to negative battery. Relay SRI operates, closes its locking circuit to negative battery through its preliminary make contacts SRIZ' and to ground on lead SR at contacts SRIQ, extends leads FI and F2 through contacts SRI I and SRI5 to leads SI and S2, grounds lead SE at contacts SRI 6 to operate relay I080 (Fig. 10) and to light the supervisor busy lamps, such as 'SBL (Fig. '7) at all operator's positions, extends ground over lead SSI to lead SS at contacts SRI8, and opens a point in the operating circuits of relays SR2 and SR3 at contacts SR! I. It might here he noted that relays SR2 and SR3 represent relays corresponding to :SRI but which are associated with links 2 and 3, respectively. Relay limo operates and extends ground over lead SS and through contacts IO0I and Hill to buzzer 5833, which operates as long as key 720 is held operated, to signal the supervisor, closes a circuit to a signal lamp I034 through contacts EOI2 at contacts I002, and closes ground from contacts I02I through contacts I003, over lead SP, through contacts SRI'I, and over lead SPI to the supervisor pilot lamp SPL (Fig. 7). When the supervisor answers the call by inserting the plug 103i of her headset I030 into jack I032, a circuit is completed to relay I023 through the transmitter of the headset I030. Relay I020 operates and closesa circuit to relay I0 I 0 and opens the circuit to lamp SPL over lead SP at contacts m2 I. i Relay IiIIlJ operates and opens the circuits to buzzer I033 and lamp I034 at contacts I0 and IOI2, respectively. Either the information operator or the calling party may now converse with the supervisor. If desired, the information operator may retire from the connection by restoring the link key LKI, relay SRI remaininglocked to ground on lead SR. In this case the supervisors talking conductors SI and S2 will be connected directly to the link talking conductors at contacts .563 and .564 through contacts SR and SRI5 when relayv 580 restores. When the supervisor subsequently withdraws plug I03I from jack M32 relay I020 restores, releases relay "H0 and recloses a circuit to lamp SPL over lead SP at contacts 102 I. The information operator may then release the supervisors circuit by momentarily operating key to the right, thus removing ground from lead SR and opening the locking circuit to relay SRI (Fig. 5) which restores and removes ground from the SB lead to release relay I000 and to extinguish the busy lamp-s, such as SBL. If the calling party has also disconnected, this fact will be indicated by the lighting of lamp SYI and the operator may then release both the link and the supervisors circuit by operating the corresponding link key LKI to the right momentarily instead of operating key 120 to the right. Relay 530 is then operated and areal-er brings'about' the release or the link as reviously the link busy lamp LBlL at contacts SRZFZ;

grounds lead RS at contacts SE13 to operate relay Bill and thereby cause the release of 610" to mark the position-busy to'th'e positiondistri bu tors, and opens a point in the circuit to relay 546 at contacts SRH to prevent the subsequent operation of relay tl-fi from operating the link switching mechanism. The supervisors circuit operates as just described and is released'dn the same manner.

Answering class C calls The toll information trunk circuit showniii' Fig. serves a manual toll board located near the cordless switchboard. The three conductors ied, 5M, and 452 terminates'in ring, tip, and

sleeve terminals of jacks on the manual tollboard. When an operator at the manual bo'a'rd' calls the information operator by inserting a plug into'one of these jacks, battery is connected to the sleeve of the jack thus completing acircuit to relay 4% over lead 452. Relay 1% operates, grounds lead 458 through contacts 413' at contacts M2 to light a call waiting lamp not shown, and connects relay 440 to lead through contacts M4, M3; and 433 atccntact's 403. If or when ground is present on'lead CH,

relay i iii operates, grounds lead CS at contacts 452 through contactsdslconnects relayfltil to lead 455fat contacts M1 to mark the'trunk to'the link, and closes its'locking circuit independent of lead CH at contac'ts'Mt'. The class" C trunks are divided into groups corresponding to the levels of the links on which they appear just as the othertrunks were. Thus there are three leads CSI, CS2, and CS3 corresponding to levels 8, 9, andtl of the links. Assuming that the callbeing considered'isover a trunk which'appearson'the eighth level of the links, lead CS! will be grounded causing relay Cl to operate and ground leadfVCI.

The subsequent operationsof relays CD, CP, and" CR, and release of relay'CG should be apparent from the foregoing description and therefore need not ha described in detail. When relay CR (Fig, 6) operates it extends the ground over lead VCI to lead L8 to mark the eighth level to the link.

It may here be noted that no VC3'lead need be provided since level 3 corresponding thereto is.

permanently marked in the link. The position relays and link operate as previously described toconnect wipers WI, W2, and W3 to leads "456 457, and 455, respectively. When the trunk is seized by the link, relay 43fl--is energized in series? manner described previously. Relay 4| operates,

removes resistance battery from conductors 4 50' and E! at contacts 4| I and M2 to extend answersupervision to the calling operator, and closes it'sdocki'rigcifiiitand" I M lit'e to'e'xtineuisnthe can waiting-lamp not shown at co'iitf'aets @131 Relay Mflre's'tores; The in formationoperator may extend negative battery and groundoveii leads 456 and 451 by operating her flash key rat-as previously described for a cl'as's'Acall. When' -this is done relay 520 is operated'and recohnects resistance battery to leads -i5ila'nd45 l contactsAZ'I' and i'22 to'si'gnalthe calliiig' operator. 'When the "calling operator removes the plug from the jack connected to this trunk", relay the restores and removes a short circuit from the high resistance lower winding" of rela str atcoritaets mil. Thischang'e intesistance over lead causes relay 5% to restorea'ndlightdamp SYIL and also release the link if strap X is used.

Distribution of calls Now that the operation of the invention has been described in some detail considering only onecall at a timein each'of thethreeclas'sesfithe maiiner in which simultaneous or overlapping calls in all three classes are distributed may be described in more general terms, omitting" such details as have beencovered by the preceding description.

Firstassum'e that all positions are allocatedto' answer all three classes of calls. Now when 'a' number ofcalls in all three classes are received simultaneously, or Within a short time-interval dete'rminedby the release times of relay AG, BG, and CG in the call distributor, a number of relays, such' as AI, will be" operated to markthe corresponding vertical marking leads, 's'ii'ch"as VAI, and the trunks over which the calls are received wili'be marked to the'links bythe operationor relays in the trunk circuits, such as relay 44B. Relays AD,-BD, and CD'will'be oprated and relays AG, BG, and CG will restore to prevent further markingof trunks. The'position group"- ing relays AP, BP, and CP will be operated in all positions and will release're'lay sense as to'preventreoper'atio'n' of any of the rel'ays'AP, BP,or CP, after they arereleased, until all three'have been released; The threestar't leadsAST,-BST,- and CST will be extended through theircorre spending position distributors to" the correspond ing start leads of one of the'po'sitions;sa'yposition one) The grounds thus'e'xtended' over=lea1dsASII, BSTL-an'dCSTl' will energize the corresponding relays AR, BRg' and CR; All threeof' theserelays will operate momentarily but only on'e'will' remain operated. The one which wil1"remain operated isdetermined'by the'strapping between terminals Tl to T7; With the strapping indicated changing the strapping any desired alter preference maybe obtained: For example, if

the order oi-preference desired is BR; AR; CR}

negative battery; or ii tliejorder of preference ei-' rate Ts; ana'rz to 'riegativeha'ttery; The of preference rieedhot be he-samend I positions. Ifthefirst positionhasthe stra time indicated andthe sec'ond and thirdpositiohs'haye the strapping giveri n the above' twoj ei ia1np1'es'; respectively; then the first position wnraiiswer can readily be varied to meet changing trafllc requirements.

Calls in all three classes will continue to be answered in accordance with the preference given the various classes by the positions as they are successively associated with the call distributor by the position distributors. The class of service in which a marked batch of calls will first be exhausted will be that class in which 20 the number of calls included in the batch thereof divided by the number of positions giving preference thereto is the least. Assuming that the batch of class B calls is the first to be exhausted, when the last marked class B trunk is seized the last of the relays BI to B6 will be released causing relay BD to restore and reoperate relay BG. As soon as relay BG reoperates all of the trunks over which calls have been received during the time that relay BG was restored will be marked to the links and will reoperate the corresponding relays BI to B6. Relay BD is then reoperated and relay BG released to prevent further marking of class B trunks. During the interval when relay ED is restored the class B position grouping relays, such as HP, will all be released. The circuits to these relays will be open at contacts such as 682 thereby preventing reoperation thereof when relay BD reoperates. Therefore the class B level marking relays, such as BR, are prevented from operating so that only the marked class A and calls may be answered at all positions. Also with all relays such as BP and 680 restored there Will be no ground on the B position distributor start lead BDS thus causing this distributor to be inactive. When one of the remaining batches of either class A or C calls is exhausted a new batch thereof will be marked in a similar manner and all positions will then answer calls in the remaining batch. When this remaining batch is exhausted a new batch thereof will be marked, relays such as 680 will be operated in all positions causing relays such as AP, BP, and GP to be reoperated (assuming that there are calls waiting to be answered in all three classes) and the same cycle of operations will be repeated.

Giving preference to particular classes of service The mode of operation described in the preceding section tends to equalize the waiting time for all calls. In some instances it may be desirable to give preference to a particular class of serviceso as to provide a shorter average waiting time therefor. This is readily accomplished by strapping the contacts of relays such as 680 which are included in the operating circuits of the position grouping relays corresponding to the class of service which is to have preference. For example, in Fig. 6 a strap is shown connected across contacts 68I whereby relay AP is nabled to operate from ground over lead APG independently of relays BP and CP. The terminals TI to T1 of 'the positions thus strapped should be wired so that the corresponding relay AR, BR, or CR 20 will have first choice. In this case relay AB is given first choice since contacts BBI which are associated with relay AP have been strapped. Now when a batch of class A calls is exhausted 5 and a new batch marked, relays such as AP will earlier.

be reoperated in all positions thus strapped to permit such positions to answer class A calls in the new batch despite the fact that there may be class B or C calls waiting which were marked Since the relays such as AR have first choice in the positions thus strapped, class B or C calls will be excluded therefrom as long as any class A calls are waiting to be answered. The

other positions will operate as previously described. Several classes of calls may be given preference either in the same or in different positions in like manner.

Blocking a position to particular classes of service When it is desired that a particular position shall answer one or two, but not all, of the different classes of calls, the class of service keys corresponding to those classes which are to be excluded from the position are operated. For example, if position I is to answer class A calls exclusively keys I40 and 150 are operated, thereby opening points in the circuits to lamps BN and CN, to the corresponding position distributor start leads BDS and CD8, to the position grouping relays BP and CP from leads BPG and CPG,

and grounding leads BGDI and CGDI to mark this position busy to the B and C position distributors. Relays BP, CP, BR, and CR are thus prevented from operating to exclude class B and C calls from the position. Under this condition of operation the position distributors will not advance over the positions in step with one another as they do when all positions are allowed to answer all classes of calls. For example, if the 40, three position distributors are in step when they leave the last position, the A distributor will stop on position I but the B and C distributors will advance to position 2 since position I is marked busy thereto. Position I will therefore answer a class A call at the same time that position 2 is answering a class B or C call, depending on the preference given therein. Because the position distributors are thus thrown out of step, a position allocated to receive all classes of calls ,but strapped so as to give preference to a particular class of call will not necessarily receive calls in that particular class exclusively, although that position will receive more calls in that particular class than it would if the preference strapping 5 5 were omitted. Under heavy traffic conditions only one position will become idle at a time. The preference strapping will then be effective to cause a preferred class to be answered to the exclusion of other classes, as long as calls in the ,preferred class are waiting, at positions strapped so as to give preference thereto because all three position distributors will start from normal and will reach the position thus strapped at the same time whenever that position becomes free.

Preventing false markings from blocking calls If one of the start leads to the call distributor is grounded but no marking is extended to the links on the corresponding level thereof, all calls in succeeding levels included in the same class of service would normally be blocked. Such a condition may arise as a result of a false ground on a start lead, such as BSI, or due to a contact failure in a trunk circuit. For example, suppose contacts 343 (Fig. 3) failed to complete a circuit between relay 320,,and lead 355 *whemrelay' 340 is operated. If this trunk appears on the, second;

level of the links lead BS1 will be grounded causing relay Bl to operate and'cause an idle link in a position1allocated to answer class B calls to search for a marked trunk, in the, second level. Since no trunk in that level is marked to the link it,will rotate to the eleventh step wherethe cam springs CAM of the link (Fig. 5) close a circuit to relay 53flvthrough contactsof VON, and connect ground to wiper W4, The contacts encountered by wipers Wl to W3 on the eleventh step areleft disconnected, but thoseencountered by wiper W4. extend over a cable and terminate in contacts such as M2 on relays associated with corresponding levels of the link. Thus lead EAl is connected to the eleventh contact of the first.

level,- leads EA2 and EB! to the eleventh contact oi the second level, lead EBZ to-the eleventh contact of the third level, etc. The ground placed on wiper W lby the cam springs is thus extended overlead E3! to the lower winding of relay 13!. The relays such as Bl are differentially wound. Relay Bl therefore restoresand opens circuits to both of its windings at contacts Bit and B52.

'I'heop-eration of relay 530 in the link causes it. to restore as previously described. Ifthere are.

sition, thus blocking all class B callsappea-ring on higher levels.

A second type of false marking which might normally block all calls is an open circuit inone of the vertical marking leads, such as might be caused by a failure of contacts AI3 to ground lead VAI when relay Al is operated. In this case no link would stop on the first level, and consequently the marked trunk appearing thereon could not be seized. Relay AI would-then continue to hold relay AD operated which would in turn hold all of the position grouping relays such as AP operated thereby, preventing relays such as 680 from reoperating after all marked trunks, other than those appearing on the first level, had been seized and relays such as B]? and.

on lower levels, it is connected to relay 9% through contacts 834. The link is released; by

the operation of relay 530 as previously described.

The momentary ground placed on lead ECS by this link causes relay 900 to operate, open points in the.circuits to all position grouping relays such as AP over leads APG, BPG, and CPG at contacts 90!, 902, and 993, close a locking circuitto its lower winding at contacts 904 .through contacts 835 to contacts AG3, and close a circuit to relay AG at contacts 905. Relay AG reoperates and opens the locking circuit to. relay 960.; Relay 9910,; restoresand vrecloses the pointsin the operating circuits vto the .positiongrouping relays. During; he-timet at avflflfl 1 i. perated the relays.

such as-AP release to'reclose the circuits to relays such as 680 which reoperate and prepare circuits to --all of the associated position grouping;

relays. A-new batch of-class A calls and'the pre: viously markedbut inaccessiblebatches of class B andC callsare thus admitted to the switchboard. The calls waiting onthe first level are still inaccessible butblocking of other calls has been prevented.

Transfer t'o alternatecalldistributor When either of the two types of failures dis-.-

one operator will beaware of the failuresince she will receive anacceptance tone but will receive no call over the link which rotates to the eleventh step. The operator may then operate the emergency start key which closes a circuit to relay 69E! and grounds lead EMS which ex-.

tends over a cable to the call distributor and thence through contacts 836, the two windings of. relay 820 in multiple, jack points 3Dl, 2D2, and i132, and fuse FD2 to negative battery. Relays Slfl and 828 are differential relays arranged to operate when the circuits thereto are opened, rather than when closed, as fully described in Patent No. 2,152,524. The two windings. of relay. 829 are now energized in series opposition causing the relay to remain inactive for the moment. Relay 69E! operates and closes circuits to relays AR, BR, and CR at contacts 69L 692, and 693,

respectively, through contacts AP5, BP5, and

0P5, of the relays AP, BP, and CP which are operated. The position relays and an idle link then operate to seize a marked trunk in the previously described manner.

event of a failure therein. This bypass will be; effective only if the call distributor is functioning properly. After the link which is operated in;

response to the operation of key 160 has either seized a trunk (which. would occur if a failure had occurred in the position distributors) or rotated to the eleventh step of any level (which would occur in the case of either oneof the types, of failures described in the preceding section) key 760 is released opening the circuit to relay 82E). Relay 82!] operates, closes its locking circuit from battery on jack point 3Dl, through its; two windings in series aiding relation, and through contacts 82E and 802 to ground, and

opens the circuit to relay 830. from ground through contacts 802 at contacts 822.

AG, BG, and CG at contacts 83!, 832, and 833, respectively, and closes a circuit. to its corre sponding relay 81min, the alternate call distribu tor at contacts83'l. Relay 800 operates and opens.

the lockin circuit to relay 829 at contacts'802; Relay 820 restores. The alternate call distributor is identical to the one shown so that itis apparent that the operation of relay Bllllwill close circuits to the relays therein correspondingto The purpose of relayv 696 is to bypass the position distributors in the:

Relay s30] restores, opens pointsin the circuits to relays preferably jack mounted to permit ready removal I from the switchboard for repair or replacement. Only those jack points involved in the arrangements for preventing transfer in the event that the alternate distributor is out of service are shown. All of the negative battery and ground connections within the first call distributor DI are obtained from jack points IDI and SDI, excepting that negative battery for relay 820 is obtained from jack point SDI through fuse FDZ of the second distributor. Similarly, all of the battery and ground connections within the second call distributor D2 are obtained from jack points ID2 and 6D2, excepting that negative battery for relay BIO is obtained from jack point 3D2 through fuse FDI of the first distributor. Thus if fuse F132 is blown relay 820 cannot be operated to transfer control to the second distributor. When the second call distributor is removed from the switchboard the connection between jack points ID2 and 2D2 will be opened which also prevents operation of relay 820. The jacks are constructed so that the fifth and sixth jack points will make contact when a switch is removed so as to maintain ground on the fifth jack point to hold relay 830 in switch DI, or 806 in switch D2.

If the first distributor DI is in use and the corresponding fuse FDI blows for any reason, relay 830 will restore and close the circuit to relay 1800 at contacts 83'! causing the second distributor D2 to take over the functions of distributor DI. The operators cannot return control to the first distributor as long as fuse FDI is open since relay 8I0 cannot be energized. If the first distributor DI is removed from its mounting while it is in service jack point SDI contacts jack point 5DI thereby operating relay 800 to place the alternate distributor D2 in service. Relay 8IIl is disabled by the removal of the connection between jack points EDI and ID! in this case.

It should be understood that numerous modifications may be incorporated in the invention without departing from the true spirit and scope thereof as defined in the appended claims.

What is claimed is:

1. In a telephone system, a plurality of groups of lines, a marking relay associated with each of said lines operated in response to calls received thereover, a plurality of links having access to said lines, a first means individual to each of said groups of lines operated in response to the operation of marking relays associated with calling ones of said lines in the corresponding group to cause idle ones of said links to seize marked ones of said calling lines, and a second means individual to each of said groups operated in response to the operation of said first means to prevent further operation of said marking relays in response to calls subsequently received over lines included in said corresponding group until all marked lines included therein have been seized by idle links.

2. In a telephone system, a plurality of groups of lines, a marking relay associated with each of said lines operated in response to calls received thereover, a plurality of links having access to said lines, and means individual to each of said groups of lines operated in response to the operation of marking relays associated with calling ones of said lines in the corresponding group to cause idle ones of said links to seize marked ones of said calling lines and to prevent further operation of said marking relays in response to calls subsequently received overlines included in said corresponding group until all marked lines iii-' cluded therein have been seized by idle links.

3. In a telephone system, a plurality of lines divided into two or more classes, a plurality of operators positions each allocated to answer calls over lines in one or more of said classes, a plurality of links associated with each of said positions having access to said lines, a marking relay associated with each of said lines operated in response to calls received thereover to mark the associated line to said links, a first means corresponding to each of said classes operatedin response to the operation of marking relays associated with lines in the corresponding class to cause idle links in said operators positions, al-

located to answer said corresponding class, to seize the marked lines included therein, and asecond means corresponding to each of said classes operated in response to the operation of said first means to prevent further operation of marking relays associated with lines included in said corresponding class until all marked lines included therein are seized by idle links. i

4. In a telephone system, a plurality of lines divided into two or more classes, a plurality of operators positions each allocated to answer calls over lines in one or more of said classes, a plurality of links associated with each of said positions having access to said lines, a marking relay associated with each of said lines operated in response to calls received thereover to mark the associated line to said links, and means corresponding to each of said classes operated in response to the operation of marking relays associated with lines in the corresponding class to cause idle links in operators positions allocated to answer said corresponding class to seize the marked lines included therein and to prevent further operation of marking relays associated with lines 40 included in said corresponding class until all marked lines included therein are seized by idle links.

5. In a telephone system, a plurality of groups 7 of lines, a plurality of marking relays individually associated with said lines, a plurality of links having access to said lines, means responsive to the operation of the marking relay associated with any one of said lines for causing an idle one of said links to seize said one line, means responsive to the receipt of a call over any one of said lines for closing a point in the operating circuit of the associated marking relay, and

means individual to each of said groups of lines operated in response to the operation of said l marking relay to open a common point in the operating circuits of the marking relays associated with lines in said corresponding group until all marked lines included therein are seized by idle links, whereby independent batches of calling lines in each of said groups are marked to said links.

6. In a telephone system, a plurality of groups of lines, a plurality of marking relays individually associated with said lines, a plurality of links. having access to said lines, means responsive to the receipt of a call over any one of said lines for closing a point in the operating circuit of the associated marking relay, and means individual to each of said groups of lines operated in response to the operation of the marking relay associated with any one of the lines in the cor-

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