US2112549A - Telephone system - Google Patents

Description

March 29, 1938- E. P. G. WRIGHT ET AL 2,112,549

TELEPHONE SYSTEM Filed June 11, 1936 4 SheetsSheet l 'K kzE'l lkar'l l AK5 v ERG. WRIGHT AKGQ I 'WENTORS GZCIHARTLB ATTORNEY March 29,. 193 8. E. P. G. WRIGHT a? AL TELEPHONE SYSTEM 4 Sheets-Sheet 4 ERGWR/GHT By G.C.HAR7ZEV wge ua Filed June 11, 1936 ATTORNEY Patented Mar. 29, 1938 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application June 11, 1936, Serial No. 84,640 In Great Britain June 21, 1935 15 Claims.

This invention relates to telephone systems and more particularly, though not exclusively, to equipment for use in setting up long-distance or toll connections.

The nature of the invention will be understood from the following description of certain embodiments thereof.

It is intended to provide a combined line and recording (C. L. R.) toll service entirely without plugs and cords. Each position is equipped with links having talking and monitoring keys and supervisory lamps, but the usual plugs are replaced by automatic switching apparatus. The switching apparatus can be controlled either by dials on the operators positions or by key sender equipment. Access is provided by means of the automatic switches to all toll routes, to the local exchange equipment, and to miscellaneous circuits such as test desk information and enquiry positions, etc.

Types of positions There are two principal types of positions, namely inward and outward. The link circuits of the inward positions are connected at one end to trunk line finders which can search for and pick up incoming calls, and at the other end to toll first selectors which are the first switches in the automatic switch train giving access to the various toll routes and the local exchanges. Each operator has up to fifteen inward links on her position, each one having a listening key and monitoring key, calling and called supervisory lamps, and a busy lamp. The associated position circuit contains the various keys required to control the completion and supervision of the connection, including keys for ringing both ways, splitting and releasing either way, together with the digit keys required to control the key senders.

The outward positions are arranged to provide C. L. R. outward services, and also to act as toll or point-to-point positions. They are fitted with two types of link circuits; the first is connected to a finder at one end, which searches for incoming calls on the record circuits, and at the other end to a toll first selector; while the second kind of link is connected at both ends to toll first selectors via selector finders which are introduced to cut down the number of first selectors required.

The C. L. R. links have a special feature whereby the first level of the finder is connected, not to incoming record circuits, but to toll first selectors. Normally, the finder will not search over this level but can be made to do so under control of a key in the operator's position circuit so that, when required, the link may be used for point-to-point Work, or for the establishment of delayed calls. It is likely that this facility will be of considerable use in enabling the operator to release the calling side of the link and reverse the call should the 5 calling party for any reason have become disconnected during the time in which the operator has been waiting for the forward connection.

Method of operation Apart from the delayed search facility described later on, the method of operation on various classes of call is as follows:

(A). Inward calZs.-An inward call arriving on a toll line circuit establishes a calling condition to 15 the.allotters which control the movement of the trunk line finders. These allotters will select a suitable link circuit for handling the call, and will cause the associated finder to search for and seize the toll line circuit. The principle of distribution '20 governing the movement of the allottersis that calls shall be distributed to the various positions in rotation, except in so far as this is rendered impossible either by reason of there being no free links on a given position or if the position due to 25 receive the next call is still testing busy owing to the operator not having cleared the sender from the preceding call. This latter condition may, of course, arise if the operator has difliculty in dealing with a call such, for instance, as a. per- 30 sonal call in which difliculty is experienced in locating the wanted party.

When the inward link seizes a toll line circuit, a flicker condition is established on the calling supervisory lamp. The operator will answer by throwing her listening key, and this process will cause the sender finder associated with the position to pick up a free sender. At the same time, the link circuit is connected to the operators position circuit. The operator will ascertain the particulars of the required connection, and will immediately set up the required digits on her key strip. The sender will then transmit the required digits to the automatic selecting equipment, and in the case of a call terminating locally in an automatic exchange, this will actually give connection to the wanted subscriber. In the case of a through call to another toll line, the automatic switchgear will simply select the toll line andthe subsequent ringing and supervisory work will be as for standard toll practice.

During the time that the sender is transmittin the required digits, it connects itself direct to the link via a by-path circuit so that the position circuit is rendered available for the monitoring and the appropriate keys of the position circuit. To

release an established connection, the link circuit listening key is thrown, followed by the link re' lease key, it being assumed that the normal routine for clearing the tolljline to the other operator has previously been carried out. The toll line signal is received as a' flicker signal on the supervisory lamp and this flicker condition in the toll line circuit is automatica-ll-y'removed by the throwing of the associated listening key. In

order to enable the operator to correct errors, or 1 to re-route calls in cases of difliculty, a forward release key isprovided whichre'leases the forward train but not the entire link; the operator may then; throw a key tore-introduce the sender and establish the call afresh. '(-B)-. Outward callS'.--The operating procedure on outward calls is essentially'the same except that' the operator will be required tof perform the customary 'docket'ing and'timing operations, and will in consequence be unable to handle the same amount of trafilc. As a consequence of this, the distribution scheme difiers from that'ifor inwardcallsin that an perat r will signify her willingness to accept a call by throwing the key whereupon thelallotters will steer the calls to the positions thus indicated: The C L. R. links are fitted with a device to enable them to be used as point-to-point links and, in' consequence, the position is provided with back and front release keys as well as a key 'torelease the entire link. The operator can, therefore, when required, releasev the finder from a record circuit and by throwing a; special key cause the finder to select a toll first selector, and by the use of her key sender can reverse the call to any desired term n n 1. (C'). Point-to-point calla-'I'hs-are delayed calls built up in accordance with dockets, and they .will normally use the double ended links provided for this purpose. The operator will connecther key sender to the back, and front ends of the cord in turn, and will establish thereby a connection to the wanted parties or distant operators as the case may be.

Group display lamps Both classes of positions are provided with a group of lamps to indicate the groupor route of the incoming call. These lamps are lighted from an. additional bank of the line flnder, and,in order to avoid excessive splitting of the multiple, this bank is multipled over a number of positions. This would normally result in confusion between the indications required by. the various positions, and to avoid this a flickerindication is given, the various positions being connected in turn, each for a'short period. The lighting of these lamps is controlled by. the keys on the position, so that the flicker control relaysneed not operate except when the operator requires the display.

Delayed search Oneofthe major difliculties in securing emcient working of a .C. L. B, toll board is due to the time taken by the operators in making repeated attempts to establish connections on a congested route. This difliculty is avoided by special arrangements for the group selector circuits which search for a free toll line. The selec tors of these circuits are fitted with an additional wiper, the bank contacts associated with which aretaken to a group congestion circuit and when a toll line. selector arrivesat the beginning of a group, before commencing a search it makes a test on this outlet for the special condition from the congestion circuit. If no toll line is available, this. condition will not be forthcoming, and the selector will refuse to, search, but will issue busy flash to the operator. The operator may now restore her listening key in order to carry on with further calls. The busy flash will stop, but the link busy lamp will remain alight. When a toll line becomes free, the appropriate test condition is restored to the control bank contacts, and this will cause the group selector to transmit a flicker signal to the operator. If she decides to avail herself of the opportunity to complete the connection, she will throw the listening key and this will cause the toll line selector to search over the group and select a free line. Special double test arrangements aremade so that in the event of two operators simultaneously attempting to seize the only available, junction, only one selector will commence to search and the other will proceed to transmit the flicker waiting signal again. Delayed Search may be provided on a non-numerical forwardly hunting switch accessible from a group selector instead of on the group selector itself. The group congestion circuit which con t'rols this operation is arranged for. special signaling on both-way routes so that when. calls are Waiting on toll line selectors at each end of a both-way group, the congestion circuits will allow them to be released in rotation in a sequence dependent on the time for which calls have been waiting at each end.

Special arrangement of senders The sender circuits are arranged to accept the necessary code digits for the selection of an outgoing route, and also the numerical digits required for establishing aflocal connection, or connection toa route which employs through dialing. The sender will normally send the complete storage, but in the event ,of the toll line selector on an out-dialing call failing to obtain immediategaccess to a free junction, the sender will release without transmitting the numericals. When the operator, after the delayed search operation, eventually succeeds in obtaining a toll line, she will reset the numericals in the sender, using a dummy code combination whichv the sender will not retransmit. 7

Another object of the invention is to provide means to permit a both-way junction to be used in such a manner that the period of delay is maintained approximately equal for calls in each direction. It will be understood that where the number of junctions isrelatively small the device will control all the circuits but that in cases where the number of junctions is greater, arrangements can be made to divide the available junctions into three groups, the first operating only in one direction, the second operating in the reverse direction and thethird operating in either direction, according to the circumstances of. the traflic. In the past it has been the practice for this control to be exercised by the operators at the terminations of the junctions.

On long-distance circuits, for which delay working has to be introduced frequently, it is a common practice for the operators to pass a number of calls in one direction and then a number of calls in the other direction, without paying particular attention to the waiting load of traflic at either end. I

With more recent methods of toll switching it is becoming a practice to indicate to the operator one free junction in each group appearing on her position, and should all junctions be simultaneously in use, the particular one which becomes free first will be immediately indicated at both ends. Furthermore, no pro-vision is made to prevent the same junction being indicated at both ends even when more than one junction is free.

With C. L. R. working, a call is set up directly if a junction is available within, say, thirty seconds, but if a junction is not available in that time, the calling party is asked to hang up and a ticket is made out and passed to a delayed call position. In the systems employing call storage, however, it is the practice to encourage the operators to await a circuit becoming free for a longer time, and it will be understood that if there'are a number of calls waiting at each end of the junction there is a considerable danger that the junction will be seized at both ends simultaneously and the calls mutilated.

If toll dialing is employed it is important that such collisions should be avoided, and the present invention also provides means to control the direction from which calls should be accepted at the time of congestion. To accomplish this a recording device is associated with each end of a group of junctions and a record is maintained of the product of the number of calls and the delay.

It may happen that if there is a preponderance of calls in one direction, a single call in the reverse direction will have difliculty in being handled in its correct turn. To compensate for this possibility a further feature of this invention provides means whereby after a number of calls in one direction preference is given to a call waiting in the reverse direction, and as the number of successive calls in one direction increases the preference is also increased, tending to reverse direction.

In the accompanying drawings;

Fig. 1 shows the circuit of a non-numerical junction selector adapted for delayed calls;

Fig. 2 shows the circuit of a two-motion junction selector;

Fig. 3 represents, in schematic form, the circuits associated with both ends of a both-way junction group arranged to allot a junction falling idle to the end at which congestion is worse;

Fig. 4 shows the relevant portion of a non-numerical trunk selector, of the kind shown in full in Fig. 1;

Fig. 5 shows a direction delay recorder; associated in multiple with all non-numerical trunk selectors of a group;

Fig. 6 represents a delay counter circuit, associated with all the direction delay recorders;

Fig. 7 represents a both-way trunk line circuit accessible from the trunk selector;

Fig. 8 is an association circuit for connecting together a direction delay recorder and a trunk line circuit as the latter becomes free;

Fig. 9 is a direction compensator and is individual to the direction delay recorder of Fig. 5.

Fig. 1 shows a non-numerical switch, the searching operation of which is in part controlled by an operator. The circuit is taken into use from the bank contacts of a selector level 'fills a level or uses only part of a level.

a and b are looped causing the operation of relay A. Relay A closes a possible circuit for the relay P leading to a wiper, the bank contact of which, in the home position, is connected to a source of battery potential if any of the outlets fromthe switch are available. This source of potential is 'sufiicient to cause the operation of relay P which is a relay of the two-winding type and which is adapted to short-circuit one winding on its operation in order to reduce the potential on the bank contact after operation. Relay A also closes a circuit for relay C which also has two windings, one of which is normally shortcircuited, in which circumstances the relay C is slow to operate. If the relay P does operate it will open the circuit of relay C and close the circuit of relay L, which will look over its own make-before-break contacts. Relay L closes the driving circuit for the switch from ground connected to the bank contacts and the switch will continue to run through its interrupter contacts until it reaches an outlet not marked busy. At this point the relay K operates in series with the rotary magnet and switches the incoming leads through to the outlet. The relay K is maintained operated on the third wire. If all the outlets are engaged the relay P fails to operate and the relay C operates, connecting a flashing signal from lead FL to the fourth wire d which will cause a supervisory lamp at the operators position to flash intermittently. Relay C also I connects the high resistance relay HR in series with relay P to the group control wiper so that when source of potential is connected, indicating that one of the outlets has become free, the relay I-IR only will'operaten Relay HR in operating removes the flash. from the (2 wire which is now connected to a flicker signal in series with the second winding of relay C back to the operator. The original operating circuit of relay C is now switched over to an interrupted battery which is so timed in relation to the flicker signal that the relay is alternately maintained operated over one winding and then the other. When the operator wishes to commence the searching operation, the circuit over the fourth wire is opened, causing relay C to release.

The low resistance circuit for relay P is reconnected and when the relay P operates the switch hunts as already described. If two operators attempt to take a free outlet simultaneously only one P relay will operate, but in the other circuit relay HR will release, relay C will reoperate and flashing signal will be reconnected to the cl wire. When a further outlet becomes free the relay HR will operate again and the operator can make a further attempt in response to flicker.

Fig. 2 shows the circuit of a two-motion se lector which is arranged to be set by either one or two digits according as the group required Relay C, not shown, is arranged in the normal manner to operate with each impulse. This relay is slow to release and controls the release relay CC which is also slow to release. When relay C releases at the end of the first (or second) digit a circuit is closed through the operating contacts of relay CC to the congestion relay P and if the relay P operates to battery via the group congestion circuit GCC, the drive circuit of the rotary magnet RM, in series with left-hand winding of relay and on seizure the negative and. positive wires 'manner." When the switching relay H '(not shown) operates its contacts hI switch through lead d. If the relay P fails to operate before the relay CC releases, the circuit will be completed.

jing lead FLA to the relay FL which in turn conmeets the relay SC intermittently to the fourth wire, thereby giving a flashing signal to the operator. When the operator restores her listening key, relayv SC operates and locks, releasing BF so that busy flash is removed. Relay CC, in its normal position, also closes the circuit for the high resistance relay HR to the group control contact in series with P. When an outlet becomes free relay HR alone operates and switches over the circuit FL at hrl to the flicker ground via FLI thereby causing av quicker train of impulses to be sent back over the fourth wire to flicker the operators lamp. During these interruptions the circuit for the relay SC is maintained operated over its locking circuit. When the operator wishes the switch to attempt a search, the circiiit of the relay SC is opened or high resistance isinserted therein by throwing the listening key and the relay SC recloses the circuit for the relay BF. With both BF and HR operated, the relay CC reoperates via hT5, M3 and allows a further test to be made by the relay P; The circuit of the relay HR is opened by the relay CC and if relay P fails to operate before CC also releases, the flashing signal is reintroduced as already described.

Referring now to Fig. 3, which represents the equipment at both ends of a both-way junction group, an operator setting up a call in a wanted direction, is connected via a group selector GS to a non-numerical trunk selector TS, which is of the kind shown in Fig. 1 and is adapted to give access to an idle both-way junction circuit J C.

If all the outlets from TS are busy, connection is made to a direction delay recorder DR associated in multiple with all TS circuits giving access to the same group of toll junctions or trunks. Associated with all the DR circuits is a delay counter circuit DLC comprising a switch RI which is stepped round at a given speed whenever congestion conditions exist and has a'position individual to each TS circuit. During each revolution of switch RI, a switch R2 of each DR is given at least one step for each of its associated TS circuits awaiting a free outlet. The number of steps taken by R2 in this way is determined by a relay DP individual to DR. 'The compensator DRC comprises a switch R5 which records the number of times those junctions of the group in question, on becoming free, are taken into use consecutively at the far end, and accordingly varies the rate of stepping of a second switch R3 of DR for a purpose which will be explained shortly. The circuits JC of a group are adapted to be individually connected to the corresponding DR by an associated circuit AC. This connection is automatically made each time a junction falls free irrespective of the existence of congestion conditions in the group. Each JC comprises a switch R4.

When a junction falls free, the JC circuits at both ends are connected to their DR circuits and the switch R4 at the outgoing end for the call just terminated is stepped, causing pulses of two different frequencies X, Y to be sent consecutively. On receipt of this signal R4, at the incoming end, sends back a pulse of the Y frequency and the outgoing R4 returnsa further Y pulse.

a trunk line is available.

The incoming and outgoing circuits are now ready to signal the amount of congestion recorded to each other. "If calls are waiting at the incoming end, a first congestion pulse of 'Y frequency will be sent, and at the same time, the switch R3 of the incoming DR will be stepped forward atleast one step. At the outgoing end, on receipt of this pulse, a Y pulse is sent back and the corresponding R3 is also stepped, Originally, whenno congestion existed, R2 and R3 of DR were both at normal. R2 has been stepped forward over a number of contacts determined by the number of TS circuits of the group awaiting a free junction, and by the length of time these TS circuits have been in the waiting condition. RI takes one step per half-second and is a fiftypoint switch, and. therefore R2 has taken one step per waiting TS every twenty-five seconds- R3, when stepped as JC sends a Y congestion pulse, takes at least one step to catch up with R2.

R3 takes four steps per Y congestion pulse'normally, but is controlled by DRC to take only two stepsor one step if the other exchange has taken the last two, or three, junctions falling free respectively.

The incoming and outgoing ends continue to exchange Y pulses until switch R3 at one end catches up with its-R2, when no more Y pulses Will be sent from that end, and the "other end .still having congestion recorded, and receiving no further Y pulse, allows the TS circuits to flicker the operators to inform them that a junction' is available.

Congestion records at both ends willthen be built up again.

It will be seen that the end which has not taken the last two or more junctions, counts off its congestion record by means of switch R3 at a much slower rate than the other end, and therefore is more likely to get an available junction. DRC of course allows switch R3 to resume its normal stepping rate after a junction has been taken,

circuits are engaged. Relay C remains operated during the waiting period. Relay HR is connected to a wiper of the switch by C and will operate as soon as a trunk becomes available. "The operation of the relay HR will release 0. Relay HR removes the flashing signal and substitutes a flicker thereby indicating to the operator that The fact that relay C is operated in any one trunk selector circuit indicates that an. operator is waiting for a trunk line.

-It follows that an indication of the traflic waiting in any direction can be obtained by measuring the number of C relays which are operated simultaneously and the time period during which they remain operated. This measurement must be made independently for each direction and the direction delay recorder DR is, therefore, associated only with a group of TS circuits giving,

access to junctions in one direction only.

The actual measurement is controlled by the delay counter Fig. 6 whichmay be common to a number of directions. place as follows:

Relay C in the non-numerical trunk selector Fig. 4 connects ground through a decoupling resistance to relay ST of the direction delay recorder, Fig. 5, which in operating closes the obvious circuit for a congestion meter CM indicating the number of occasions on which all trunk lines are engaged. It also closes the obvious circuit for the relay CST of the delay counter Fig. 6.

Relay CST in operating connects the magnet RMI of the switch Rl to a half-second pulse supply causing the wipers of the switch to step forward one step every half second.

Two wipers Tm] I, Tml2 are connected together, one set of bank contacts being connected individually to C contacts of the trunk selectors, the other set of bank contacts being strapped together according to direction and connected to relays DP in the corresponding direction delay recorders, Fig. 5.

Every time the wipers of the switch RI pass over contacts corresponding to a trunk selector TS of the group associated with DR, Fig. 5, in the waiting condition, a ground connection will be passed to the relay DP in the delay recorder. Relay DP in operating closes the obvious circuit for magnet RM2 of the switch R2, which advances its wipers accordingly.

The switch R2 has only one level of contacts which are connected to a corresponding set of contacts in the switch R3, which also forms a part of the direction delay recorder. The switch R3 is advanced only when a trunk circuit becomes free and it is the function of the switches R2 and R3 to count off between them the amount of delay which has been storedsince the last trunk circuit became free. 7

Relay PC which is connected to the wiper rm3l is arranged to operate when the switches R3 and R2 are approximately in phase.

The wipers of the switch R3 are advanced in stages until the relay PC eventually operates indicating that the switch R3 has caught up the switch R2. The number of steps of the switch R3 comprising the stage may be varied by the compensator, Fig. 9, as described subsequently according to the circumstances.

When a trunk circuit is about to fall free because the call for which it has been used is ended, the release is made dependent upon the direction delay recorder and for this reason the both-way trunk line circuit Fig. 7 must be associated with the recorder. This association is performed by a group of relays K shown in Fig. 8, the connecting function of one of the K relays being shown in Fig. 7.

It will be appreciated that due to the releasing times of relays and the possible differences in exchange voltages the both-way circuit may not tend to become free simultaneously at both ends, and should it happen that two junctions of a group become free at approximately the same time, the associating relays may be caused to operate in such a way that the direction delay recorders at opposite ends become individually connected to different junctions and are unable to signal to one another. In order toavoid confusion arising in this way, one of the two terminations acts slightly diiferent from the other, it being adapted to cancel the first association and make a second association when the conditions indicate that the direction delay recorders have been associated with different trunk lines.

The relays KI, K2, K3, etc., are provided one Detailed operation takes per trunk line circuit and one of these relays and v its contacts are shown on Fig. 7.

The pairs of terminals AKI, AK2; AK3, AK4, Figs. 7 and 8, are particular to different junction circuits JC. A potential is connected to terminal AKI, for instance, when the correspond ing trunk line is about to release after completing an outgoing call, and a similar potential is placed on the terminal AK2 when the same circuit JC is about to release after receiving an incoming call. At one end of the trunk linethe terminals AK! and AK2 are connected together, but at the other end they are wired separately in order to avoid cross connections.

When a ground potential is connected to: a point such as AK3, Fig. 8, at the end of an outgoing call, the relay K2 will operate through contacts MI, 1092, k22,kw| to battery potential through relay KY. Relay K2 in operating closes its make-before-break contacts making itself independent of the break contact 71:22. Ground potential now being placed on terminals AKI or AK at the termination of other outgoing calls will not cause the operation of the relay KI or K3 because the operating circuit is opened at the contacts 7022.

When the pairs of terminals AKI and AK2, AK3 and AK4, etc. are connected together, and the K relays, Fig. 8, need have no right-hand windings, only one K relay can be operated at a time and this relay will remain operated until the trunk line circuit removes the ground potential.

When the corresponding terminals are not wired together but wired separately, the second terminal is Wired through a second Winding of the K relay and through a relay KW tothe battery potential through relay KY. With this arrangement a K relay can become operated on its second winding even if another K relay is already operated on its first winding. Furthermore, the operation of the relay KW in series with said K relay will open the circuits of the first windings of all K relays so that any K relay, which was previously operated via an outgoing terminal, is caused to release.

The K relay at the incoming end of a-junction about to come free cannot operate until a signal has been received from the outgoing end after the latter has been connected to its DR. It will be seen that with this arrangement if two trunk lines which have been used in different directions are released simultaneously and both outgoing ends make association with their corresponding direction delay recorders and, in consequence, initiate the releasing signals, a second K relay will be operated over its second winding at the one end to disassociate the delay. recorder at that end from the toll line to which it is connected and reassociate it with the toll line which has received an incoming signal.

Turning now to Fig. 7, the relay A is bridged across the conversational leads from the local subscriber and is designedv to operate so long as the callingsubscribers receiver is off the hook. The outgoing conversational leads are not shown. Relay A operates B, which is of the slow to release type. Relay C then operates and locks up so that the toll line circuit is not. automatically released when the calling subscriber clears.

Considering first the case in which the trunk line circuit is used for an outgoing call. The operation of relay B closes at contacts b-l the circuit for the magnet RM4 of switch R4 through its interrupter springs, the first bank QQntact and wiperrmfl causing the switch to advance to position 2. The. relay SC isoperated .(YlfljCOIltflCl; a2 of relay A) on all outgoing calls and the contact 30! closes a circuit for magnet RlVI4;"via its interrupter springs, sol, bank contacts, wiper rm43 to ground. This circuit is maintained until wiper rm44 reaches its first contacts, which is the twenty-sixth position of the switch. The switch remains in this position during the course of conversation but at the completion of conversation when the relay B releases the circuit for the magnet RM4 is completed through wiper rm42, the break contact b2, the contacts gl and the wiper rm44 to ground. The switch advances its wipers one step to position 21 in which position ground is connected to the terminal AKI through contacts b3, ro l, 302 and wiper rm48. If the direction delay recorder is not already associated with a trunk line circuit, the relay K will operate and. close at contact kl the circuit through the wiper rm42 for the magnet RM4, which advances the switch to position 28. In this position the toll. line circuit sends the initial release signal to the distant end. It will be understood that the signaling over the toll line may be vcarried out in a number of difierent ways, e. g. by the use of two or more voice frequencies placed on the line or by the use of a single frequency of various duration or by means of direct current signals. In this description it has been assumed that signaling is undertaken by means of two voice frequencies, but the sources of frequencies and their connections to the outgoing junction leads are not shown as they may be of any known type. When the switch R4 reaches position 28, that is, the third position in banks rm42, 44, 46 and 48, the circuit is closed for the relay FX through wiper rm46 contacts kl I, 302, rcl, b3. FX in operating connects the X frequency to the outgoing line. In position "the magnet RM4 is connected through its interrupter springs and rm42 to a half-second pulse supply causing the switch to advance one step per pulse to positions 29, 30, 3| and then 32. In positions 28, 29, 30 and 3| relay FX is maintained operated so that as a result the X frequency remains on the line the whole of this period: In positions 32 and 33 the circuit for the relay FX is open, but the circuit for the relay FXY is closed so that in these two positions the Y frequency is connected over the lines. The interrupter circuit for the magnet RM4 is completed wiper rm42 and the wipers are advanced to position 34. The toll line circuit now awaits a signal from the distant end of Y frequency and when this arrives, frequency-responsive relay Y not shown connects ground through contacts b3, rcl, s02, Icll, wiper rm46, contact yl to the terminal XZO, which is connected .to the direction delay recorder shown in Fig. 5, through one winding of relay KB and the relay Z, which both operate. 7

Relay Z at 2| opens a possible circuit for the magnet RM3, and contacts :cbl close the obvious circuit of the relay X. When the Y pulse terminates, the relays KB and Z are both released. The relay 163 is gauged with a heavy spring pressure so that it operates relatively slowly and releases quickly. The relay Z on the other hand has relatively light-pressure and operates quickly and releases relatively slowly. During the period between relays KB and Z releasing, a circuit is closed from ground, e2, :rl, :rb2, to the terminal MAG, which is connected via the corresponding terminal of the both-way trunk circuit, through k2, and rm42 to magnet RM4; This signal causes the switch R4 to advance a step and in the following position a circuit is reestablished for the relay FXY which again applied Y pulse over the trunk line. Switch R4 does not remain for any length of time .in this position because the circuit is at once closed through the wiper rm42 which causes the wipers to advance a further step.

In the next position of the switch, the circuit for the relay FXY is maintained until relay X releases and connects ground at X2 to terminal ZG which is extended through contact 103 through the bank contact and wiper rm42 to the magnet RM4 causing the wipers to advance to position 31. In this position the circuit awaits for a further Y pulse from the distant end which, as already described, causes the operation of the relay KB and Z and, at the termination of the Y pulse, ground is connected over the terminal MAG which advances the wipers of the switch R4 to position 38. In this position ground is extended through rm 46, contacts pol, and terminal X132 to the second winding of relay XB, Fig. 5, which is operated thereby, and in parallel through the metal rectifier, terminal X80 and contacts k4 to relay FXY. The operation of the relay FXY reconnects the Y frequency to the trunk line. The operation of relay XB, which looks up through contacts $113 and 22 to ground, causes the operation of the magnet RM3 through contacts :23, 2| and :rb4. Relay XB also closes at xbl, the circuit for relay X which in operating opens the short circuit across the interrupters ofRM3at m3 and causes the switch to take a step. The switch R3 continues stepping until the circuit is closed for the relay Z through the bank contact and wiper rm32 and the contacts 1'4.

Relay Z in operating opens the circuit of the magnet RM3, opens at 22 the holding circuit of the relay KB and closes through the contacts xl,a:b2 the circuit for RM4, which is therefore caused to advance through both positions 38 and 39 into position 40.

If the relayPC had been operated when the switch reached position 38; via stl, rm3 I, rm2l .to earth, because the switches R2 and R3 were in phase, relays KB and FXY would not have operated, Y pulse would not have been connected to the trunk line and relays CA, Fig. 9, and RC would have been operated via Jxyl, k5, pcl energized, rm46 to earth.

Relay RC is arranged to look over contacts b2. Switch R4 returns home through contacts 102 and rm to ground. Relay RC indicates that the toll line circuit should receive an incoming call and in consequence does not permit the condition ofthe group .test terminal to be altered. I

Assuming that the relay PC is not operated and that the switch R4 was advanced to position 40, the circuit would again await the receipt of Y pulse which again causes the operation of relays X8 and Z, and again at the termination of the Y pulse the wipers advance to position 4|. If the relay PC is still not operated the relays KB and FXY will be again operated in positions 4| and 42 and the wipers step forward to position 43 Assuming now that the distant end does not reconnect the Y pulse, the relays X3 and Z will not operate but-the circuit will be completed from the magnet RM4 through the wiper rm42, contact k2, terminal MAG, 152, Fig. 5, .rl, makebefore-break contacts mbl, left-hand winding of the relay MA to ground.

Relay MA being of relatively high resistance, the magnet RM4 will not be operated but the relay MA will operate and close the contacts mal and the half-second pulse supply to the second winding of relay MA and the relay MB. When this supply is connected the relay MB operates and. the relay MA remains operated for the duration of the pulse. On the completion of the pulse, relay MB remains operated on its upper winding through contacts ml)! in series with the magnet RM4, but MA is released. When ground is again connected to the pulse supply the circuit is completed through the contacts mal, 717122 for the relay MC and if by this time Y pulse has not been received, relay MC operates and connects ground via mcl, st4 to the MCG terminal through contacts 106, Fig. 7, to the lower winding of relay SC, which operates. Relay SC closes at $03 a locking circuit through b2, rm to ground. Contacts s04 open the locking circuit of relay C which in releasing closes a homing circuit; RM4, interrupter, sci, cl, rm44, ground. When the switch reaches home, ground is removed from the terminal AKI, and relay K is released together with the direction delay recorder.

It will be understood that the operation of relay SC, indicating that the trunk line should be used for an outgoing call, may take place at position 40, 43, 46, etc. and similarly the operation of the relay RC may take place at position 38, 4|, 44, etc.

If the trunk line circuit is associated with the direction delay recorder on an outgoing connection and the relay KW becomes operated because the distant end recorder is associated with the different trunk line, a circuit is completed through contacts k! and g2 for the relay G, which is arranged to lock up. The contacts gl and subsequently the contacts 93 and g4 advance the wipers of the switch R4 through normal to position 26 in which position the circuit for the relay G is opened. Relay G in releasing closes the circuit for the magnet RM4 through 1'm42, 112, Q], rm44 causing the switch to advance to position El when reassociation with the direction delay recorder will take place when the latter circuit becomes available.

Considering now the case of an incoming call, relays B and C of the trunk line circuit are operated and switch RM4 is advanced to position 2 but no further since SC is not energized. It remains in this position throughout the conversation but on release a Y pulse is received from the distant end.

Relay Y closes at 1 2 the circuit for the magnet RM4 and switch R4 is advanced to position 3. In position 3 ground is connected through wiper rm4l to terminal AKZ to cause the association with the direction delay recorder to take place. When the Y pulse is completed and the relay K operated, groundis connected through 1/3, Icl and rm ll to advance the switch to position 4.

In this position the relay FXY is operated and the return Y pulse is sent to the distant trunk exchange. The wipers are advanced by direct earth on 111241 to position 6 where a. further Y pulse signal is expected from the other exchange and when it is received causes the operation of relay X13 and Z, Fig. 5, in the manner already described.

In positions I and 8 the operation of relay X5 is made dependent on the condition of contacts pol as before so that, in this and subsequent sen-ding positions, the controlling switch R3 is advanced, and as soon as the switch R3 is in phase with the switch R2, no further congestion Y pulses are sent.

If no further Y pulse is received from the distant exchange, relays MA, MB and MC are operated as already described. The subsequent operation of relay SC results in the trunk line being made available for an outgoing call. If, on the other hand, relay PC is operated resulting in the operation of relay RC, the trunk line is prepared to receive a call from the distant end.

It may be arranged that if the outgoing end has no calls waiting the second signal sent in positions 35 and 36 will be of X pulse rather than of Y pulse; such an arrangement can be accepted at the incoming end by wiring position 6 to position 9 through the back contact of a relay RX (not shown) responding to the X pulse. It will be arranged that should the X pulse be received in position 6 the relay SC can be operated immediately.

During the period when the trunk line is associated with the direction delay recorder and relay KY is operated, the possible circuit for the switch R2 is opened at contact kyl and on this account the circuit for the relay PC cannot be caused to open instantaneously.

Reference has already been made to the fact that in certain circumstances there may be a preponderance of trafiic in one direction and in consequence over a relatively long period there will be a large number of Waiting callsin one direction. Under these conditions it may be difiicult for a call in the reverse direction to get access. In order to eliminate this possibility a compensator circuit is proposed as shown in Fig. 9. It is the purpose of this circuit to vary the connection via the bank contacts associated with the wiper rm32 so that the size of the stages of movement of said wipers, when sending congestion pulses, is in part dependent upon the direction in which the majority of the traffic is flowing.

As an example, the contacts associated with the wiper rm32 are divided up into three groups. Contacts I, 3, 5, I, 9 etc., are connected together and wired to terminal CX. Contacts 2, 6, l0, l4, etc. are connected together and; wired to terminal CY, contacts 4, 8, l2, etc. are likewise connected to terminal CZ, and also direct to the right-hand winding of relay Z.

Relay CA, Fig. 9, is connected in series with the operating winding of relays RC of the various trunk line circuits and every time that a trunk line is released and assigned for an incoming call relay CA will operate. Relay CA closes the obvious circuit for the switch R5 which is caused to take one step for each successive junction assigned for incoming use.

Contacts 3, 4, 5, 6, I, B, 9, I associated with wiper rml are commoned together and connected to the terminal CZ. Corresponding contacts associated with the wiper rm52 are connected to terminal CY and contacts 4, 5, 6, 1, 8, 9, l0 associated with wiper rm53 are connected to the terminal CX.

On the second successive incoming call switch R5 reaches position No. 3 and the terminals CY and CZ are commoned together and because of this the relay Z in the direction delay recorder is operated after only two steps instead of four steps of R3.

If a further incomingcall is received, R5 advances another step and in this .position terminals CX, CY and CZ are all commoned together. Relay Z operates after every one step of R3. On the use of any junction in' the route for an outgoing call a relay MC (not shown) will operate and complete the circuit through wiper rm54 to drive the switch to a further home position, from whence the process will be repeated.

What is claimed is:

1. In a toll switching system, the combination with a plurality of operators positions of a plurality of link circuits each-comprising a finder, an incoming line group available for connection with all of said link circuits, an allotter for operatively associating any link with any position, means responsive to the existence of a calling condition on any line of said incoming line group for operating any idle link to connect its associated finder with said calling line, and means responsive to an operation at anyone of said positions for operating said allotter to associate the link extended to the calling line with the position at which said operation has taken place.

2. In a toll switching system, the combination of two offices connected by a plurality of two-way trunk lines, a selector circuit at each ofiice having access to said trunk lines, means at each oflice operatively associated with each selector for determining and recording the time interval during which all of said trunk lines are busy, means at each ofiice operatively associated with each selector for determining and recording the time interval during which each of said selectors has been 'waiting for a free trunk line to establish a call in its own direction, means responsive to a line becoming free for signaling over said line the selector delay at each oflice, and means for allotting said free line to the ofiice which had the longest selector delay.

3. In a telephone system, two ofiices, a group of two-way trunk circuits extending between said ofiices, switching means at each office for seizing idle trunk circuits,'and means at each ofiice controllable in accordance with the number of calls awaiting completion at each oilice and the aggregate waiting period of such calls for allocating an idle trunk circuit for the use of the oflice in which the trafiic congestion is greater.

4. In a telephone system, two oflices, a group of two-way trunk circuits extending between said ofiices, switching means at each ofiice for seizing idle trunk circuits, means at each oflice for recording during periods when no idle trunk circuits are available the aggregate waiting time of calls awaiting an idle trunk circuit, and means at each oflice controllable jointly by the recording means at both oflices for determining whichfoffice may use an idle trunk circuit for an outgoing call when it becomes free.

5. In a telephone system, two ofiices a group of two-way trunk circuits extending between said o'fiices, switching means at each ofiicev for seizing idle trunk circuits, means at each oflice for recording during periods when no idle trunk circuits are available the aggregate waiting time of calls awaiting an idle trunk circuit, and means at each office controllable jointly by the recording' means at both oflices for allocating a trunk circuit when it becomes idle to the use of the ofiice whose recording means indicates the greater trai'fic congestion.

.6. In a telephone system, two oflices, a group of two-way trunk circuits extending between said ofiices, switching means at each'ofiice for seizing idle trunk circuits, means at each office for, recording during periods when no idle trunk circuits are available the aggregate waiting time.

of calls awaiting an idle trunk circuit, and means at each ofiice controllable jointly by the recording means at both ofiices responsive to a trunk circuit becoming free for indicating at the oifice wherethe greater traffic congestion exists that the free trunk circuit is to be used on an outgoing call .and :for indicating at the other ofiice that the free trunk circuit is to be reserved for an incoming call.

7. In a telephone system, two oflices, a group of two-way trunk circuits extending between said offices, switching means at each ofiice for seizing idle trunk circuits, means at each oflice for recording during periods when no idle trunk circuit is available the aggregate Waiting time of calls awaiting an idle trunk circuit, means at each ofiice operative when a trunk circuit becomes available for transmitting signal impulses to the other ofiice, and means at each ofiice jointly responsive to the recording means of that office and to the impulses received from the other oflice for allocating said idle trunk circuit for an outgoing call to the use of the office in which the traffic congestion is greater.

8. In a telephone system, two ofiices, a group of two-way trunk circuits extending between said ofiices, switching means at each oflice for seizing idle trunk circuits, means at each ofiice for recording during periods when no idle trunk circuits are available the aggregate waiting time of calls awaiting an idle trunk circuit, means at each ofiice operative when a trunk circuit becomes available for transmitting signal impulses in alternation over said idle trunk circuit to the other ofiice, and means at each office jointly responsive to the recording means of that oflice and to the impulses received from the other ofiice for allocating said idle trunk circuit for an outgoing call from the ofiice in which the trafiic congestion is greater and for an incoming call at'the office in which the trafiic congestion is less.

9, In a telephone system, two ofiices, a group of two-way trunk circuits extending between said ofiices, switching means at each oflice for seizing idle trunk circuits, a first recording switch at each ofiice, means at each office operable during periods when no idle trunk circuits are available for setting the associated recording switch in accordance with the aggregate waiting time of calls awaiting an idle trunk circuit, a second recording switch at each office, means at each ofiice operativewhen a trunk circuit becomes free for transmitting signal impulses to the other office for setting the second v recording switch at the other ofiice, and means operative when the recording switches of either ofiice are in substantial phase relationship for transmitting a signal to the other ofiice indicative that the free trunk circuit may be used at such ofiice for an outgoing call.

10. In a telephone system, two oflices, a group of two-way trunk circuits extending between said offices, switching means at each ofiice for seizing idle trunk circuits, a first recording switch at each ofiice, means at each ofiice operable during periods when no idle trunk circuits are available for setting the associated recording switch in accordance with the aggregate waiting time of calls awaiting an idle trunk circuit, a second recording switch at each office, means at each ofiice operative when atrunk circuit becomes free for transmitting signal impulses to the other ofiice for advancing the second recording switch at the other ofiice a predetermined amount in response to each impulse, means operative when the recording switches of either office are in substantial phase relationship for transmitting a signal to the other ofiice indicative that the free trunk circuit may be used at said other office for an outgoing call, and means at each office effective when the other ofiice has been given precedence for a predetermined number of successive outgoing calls for reducing the amount of advancement of the second recording switch thereof in response to impulses from the other oifice whereby said ofiice is given precedence for completing an outgoing call.

11. In a telephone system, two oflices, a group of two-way trunk circuits extending between said ofiices, switching means at each oifice for seizing idle trunk circuits, a first recording switch at each ofiice, means at each oflice operable during periods when no idle trunk circuits are available for setting the associated recording switch in accordance with the aggregate waiting time of calls awaiting an idle trunk circuit, a second recording switch at each oifice, means at each ofiice operative when a trunk circuit becomes free for transmitting signal impulses to the other office for advancing the second recording switch at the other ofiice a predetermined amount in response to each impulse, means operative when the recording switches of either office are in substantial phase relationship for transmitting a signal to the other office indicative that the free trunk circuit may be used at said other office for an outgoing call, and means at each office efiective in response to the allotment in succession of difierent predetermined numbers of available trunk circuits to the other oilice for outgoing calls for successively reducing the amount of advancement of the second recording switch thereof in response to the impulses from the other office whereby said office is given precedence for completing an outgoing call.

12. In a telephone system, two oflices, a group of two-way trunk circuits extending between said ofifices, switching means at each omce for seizing idle trunk circuits, trafiic congestion recording means in each office, and means in each office operative in response to a trunk circuit becoming available for associating the recording means of each of said ofiices with the opposite ends of said available trunk circuit,

13. In a telephone system, two ofiices, a group of two-way trunk circuits extending between said ofiices, switching means at each omce for seizing idle trunk circuits, traffic congestion recording means in each office, and means in each office operative in response to two trunk circuits becoming available substantially simultaneously for associating the recording means of each of said oflices with the opposite ends of one of said available trunk circuits.

14. In a telephone system, two oflices, a group of two-way trunk circuits extending between said ofiices, switching means at each office for seizing idle trunk circuits, means "at each office for recording during periods when no idle trunk circuit is available the aggregate waiting time of calls awaiting an idle trunk circuit, means at each end of each trunk circuit individual thereto operative when a trunk circuit becomes available for transmitting signal impulses over said trunk circuit to the other office, and means at each office jointly responsive to the recording means of that office and to the impulses received from the other ofiice for allocating said idle trunk circuit for an outgoing call to the use of the office in which the traffic congestion is greater.

15. In a telephone system, two ofiices, a group of two-way trunk circuits extending between said offices, switching means at each oflice for seizing idle trunk circuits, a trafic congestion recorder in each office, said recorders each comprising a first recording switch operable during periods when no idle trunk circuits are available for recording the aggregate waiting time of calls awaiting an idle trunk circuit, and a second recording switch, means at each end of each trunk circuit individual theretoand operative when a trunk circuit becomes available for associating the end of said trunk circuit at each oflice with the trafiic congestion recorder thereat and for transmitting signal impulses to the other oifice for setting the second recording switch at the other ofiice, and means operative when the recording switches of either ofiice are in substantial phase relationship for transmitting a signal to the other office indicative that the free trunk circuit may be used at said other office for an outgoing call.

ESMOND P. G. WRIGHT. GEOR

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