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`Motorola Solutions, Inc., Ex1016, p. 1
`
`

`

`United States Patent Office
`
`3,133,995
`Patented May 19, 1964
`
`1
`
`2
`iliary line circuit auxiliary line appearance in the cen(cid:173)
`tral office.
`In this specific illustrative embodiment the
`other line terminals may then be seized by another call(cid:173)
`ing party, the called subscriber again alerted, and the
`5 above procedures followed if the called party desires to
`terminate the present call, over the second set of line
`terminals, and receive the call waiting on his basic line
`circuit.
`If the new calling party tired of waiting for the sub(cid:173)
`scriber to terminate his present call and then answer, he
`would hang up before the called party returned to an
`on-hook condition in which case the circuit would be
`restored to normal and the called party not rung when
`he did hang up.
`A feature of my invention relates to the multiple-line
`appearances or sets of switching terminals or line ter(cid:173)
`minals in the switching equipment at an automatic dial
`control telephone switching center. The line terminals
`are arranged so that both sets of terminals may be pre(cid:173)
`ferred line terminals with the other set the second choice
`line terminals. The multiple-line terminals are thus ar-
`ranged so that if the first choice is busy the automatic
`switching equipment will automatically switch calls to
`the second choice or line appearance.
`As tJhis switching to the second set of line terminals
`is automatically done by the central office equipment,
`no special signaling is required from the calling party.
`Further by providing a second line appearance in the
`central office, no modifications need be made in the
`major components of the central office, such as in the
`markers and registers in a crossbar telephone office.
`Instead the sleeves of both line appearances are extended
`to the number group, in the crossbar office, so that the
`central office can hunt to the alternate line appearance
`if the first line appearance is busy. Such a procedure
`is presently followed in central offices for different pur-
`poses, such as PBX line hunting, and accordingly the
`present day central offices are currently equipped to op(cid:173)
`erate in this manner.
`Another feature of the invention relates to preventing
`the tone applied to the subscriber's line from being trans(cid:173)
`mitted to the other party of the first or previously es(cid:173)
`tablished connection.
`In this manner a calling party,
`who is also provided with this service, would not errone(cid:173)
`ously believe that a call was waiting for him too, as could
`be the case if both parties on the prior connection heard
`the alerting tone.
`It is a further feature of my invention to provide cir(cid:173)
`cuits for automatically interconnecting the subscriber's
`line with the second set of line terminals when a call
`is waiting on them and the subscriber finishes or termi-
`nates the first or previously established connection.
`A still further feature of my invention relates to circuit
`arrangements wherein either set of line terminals may be
`considered the regular line appearance for receiving calls
`and the other line appearance as the auxiliary line termi-
`nals, which line treminals are at the automatic switching
`center or central office. Thus, if a third call should arrive
`when the subscriber is busy with the second, it is directed
`to the first set of line terminals and the momentary spurt
`of call waiting tone sent to the subscriber, thereafter
`permitting the subscriber either to continue the second
`call or to terminate the second call and accept the third
`call. This series of operations will be repeated indefinitely
`so that as the subscriber is talking on a connection utilizing
`one set of line terminals, the next call may be held waiting
`at the other set of line terminals while the subscriber is
`alerted.
`It is a still further feature of this invention that the
`operation of the system is independent of whether the
`called subscriber originally initiated the prior call or mere(cid:173)
`ly received the prior call.
`
`25
`
`3,133,995
`CALlL AWAITING SIGNAL TELEPHONE CIRCUITS
`Alfred Zarmmj, l3rooklyn, N.Y., assignor to Beil Tele•
`phm1e lLaboratodes, Incorporated, New York, N.Y., a
`corporation ol' New York
`Filed §ept 18, 1961, Ser. No. 138,640
`2 Claims. (Cl. 179-84)
`This invention relates to telephone switching systems
`and more particularly to automatic telephone switching 10
`systems wherein it is desired to indicate to a busy called
`subscriber that another party is attempting to place a call
`to him.
`In usual telephone systems when a subscriber is en(cid:173)
`gaged on a telephone call, any other party attempting 15
`to reach his call receives a busy tone indicating the fact
`that the subscriber is priorly connected. The subscriber
`himself, however, is unaware of the attempt being made
`to reach him. In some instances the telephone subscriber
`may be engaged on a call of little importance while the 20
`incoming blocked call is one of considerable importance
`and one which he is anxious to receive. Accordingly,
`a number of arrangements have been suggested in the
`past to advise the called subscriber of the presence of
`this second call.
`Such prior arrangements, however, have generally in(cid:173)
`volved considerable modification of the existing telephone
`plant. Such modifications, including special signaling
`arrangements at each calling telephone, may prove ac(cid:173)
`ceptable in certain small installations, such as private 30
`branch exchanges, but would prevent any system de(cid:173)
`pendent thereon from having applicability in the gen(cid:173)
`eral telephone systems wherein each subscriber is con(cid:173)
`nected to a central office and connectable therethrough
`to the millions of telephones of our present day tele- 35
`phone network. Additionally, it is obvious that any
`major modifications in the existing telephone plant would
`render such a system prohibitively expensive.
`Accordingly, an object of this invention is to improve
`the telephone service supplied to a telephone subscriber 40
`by advising him of the presence of another call when
`his telephone is in use.
`Another object of this invention is to provide such
`service without the necessity of special signaling on the
`part of the calling party and without major modifica- 45
`tion of the equipment in the central office to which the
`subscriber is com1ected. Specifically it is an object of
`this invention to provide such service without modify-
`ing the markers or registers of the common control equip-
`ment in the central office.
`These and ovher objects of this invention are attained
`in accordance with one illustrative embodiment thereof
`by transmitting a tone to a telephone subscriber when
`the telephone is in use indicating that there is another
`call waiting. Specifically in accordance with my in- 55
`vention each subscriber to whom this service is extended
`is provided with an auxiliary line circuit which includes
`a second set of line terminals to which the second call(cid:173)
`ing party is connected by the central office equipment.
`The new calling party hears regular ringing induction 60
`tone just as though the line he called were idle. At
`the same time as seizure of the second set of line termi(cid:173)
`nals the auxiliary line circuit causes a short burst of tone
`to be applied to the called subscriber's line indicating
`to him that a second party is attempting to reach him. 65
`If the busy subscriber upon being advised of the pres(cid:173)
`ence of the second call wishes to receive it, he may ter(cid:173)
`minate his present call. Upon hanging up on his prior
`connection, ringing is applied to his line. When the
`called subscriber picks up his phone in response to this 70
`ringing he is, in accordance with my invention, auto(cid:173)
`matically connected to the new called party by the aux-
`
`50
`
`Motorola Solutions, Inc., Ex1016, p. 2
`
`

`

`3,133,995
`
`3
`A complete understanding of this invention and of
`these and various other features thereof may be gained
`from consideration of the following detailed description
`and the accompanying drawing, the sole figure of which is
`a schematic representation of one specific illustrative 5
`embodiment 'of my invention.
`Turning now to the drawing, the sole figure thereof
`shows the circuit details of an auxiliary line circuit in ac(cid:173)
`cordance with my invention for providing call waiting
`notification and call waiting holding for a subscriber to 10
`whom this service is available. The circuitry of my in(cid:173)
`vention depicted in the drawing is arranged for coopera(cid:173)
`tion with a No. 5 crossbar switching system, such as dis(cid:173)
`closed in Patent 2,585,904, granted to A. J. Busch,
`February 19, 1952, when modified in accordance with the 15
`article entitled, "Dual Voltage Operation of Relays and
`Crossbar Switches," by A. C. Mehring and E. L. Irwin,
`published in the Bell System Technical Journal for No(cid:173)
`vember 1955, vol. 34, No. 6, pages 1225 through 1240.
`The line appearance or line contacts are similar to the 20
`line terminations of the subscriber's line as described in
`thte above-identified Busch patent. The normal or regu-
`lar subscriber's line appearance or line link appearance
`is provided with the line relay and the cut-off relay of the
`type disclosed in the above-identified Busch patent. The 25
`auxiliary line link appearance may be similarly equipped
`with the line relay, and a cut-off relay, but it also need
`not be so equipped since during normal operation such
`calls will not be originated over the above-described
`auxiliary line terminals. Lines 100 represent the regular 30
`line terminals or line appearance of a subscriber's line.
`Originating calls from the given subscriber station such
`as 150 are transmitted over the line conductors to the
`telephone switching system 50. The telephone switching
`system, as well as the auxiliary telephone subscriber's line 35
`circuits and the associated equipment operate in the usual
`manner as described in the above-identified patent of
`It is noted that all of the contacts of both
`A. J. Busch.
`the T relay 32 and the B relay 28 are normal and un(cid:173)
`operated at this time. Thus contacts T-14, B-16, B-17, 40
`B-18, T-15 and T-19 are all open and remain in their
`normal condition and thus do not interfere wtih the use
`of this line circuit at this time. Likewise, the break
`contacts T-10, T-11, B-12 and B-13 are also normal
`and do not effect the operation of the subscriber's line 45
`at this time.
`Consequently, if the subscriber's station 150 originates
`a call, the central office equipment will respond thereto
`in the usual manner and the equipment in accordance
`with this invention will remain in its idle or normal 50
`condition.
`Likewise, if a call is directed to the subscriber's sta(cid:173)
`tion 150 it will be directed over the first choice set of
`terminals or line appearance 100 and cause the sub(cid:173)
`scriber's bell to ring. A subscriber may answer the call 55
`and later terminate the call whereupon the circuits of
`the Busch application as well as the subset 150 and the
`lines connecting the subset with the central station oper-
`If a call is directed to the
`ate in their usual manner.
`subscriber station 150 during the time this station is 60
`busy due either to having been called or having originated
`a call the regular line terminals or line appearance 100
`Inasmuch as
`will be busy in the switching system .50.
`the switching system is arranged to hunt over the in(cid:173)
`dividual terminals or appearances of a group of line 65
`terminals or appearances including the regular line ap(cid:173)
`pearance 100 and at least one auxiliary set of line ter(cid:173)
`minals or appearance 200, the equipment will test the
`auxiliary line terminals 200 and finding them idle will
`set up a connection to these terminals in the normal 70
`manner. The condenser 41 and resistor 42 simulate the
`ringing circuit in. the usual subscriber station set so that
`marker in the switching system 50 satisfactorily com(cid:173)
`pletes the subscriber's line continuity test and thus sets
`up a connection to these terminals.
`
`4
`The switching equipment or system 50 is in accord(cid:173)
`ance with the system disclosed in the above-identified
`patent to A. J. Busch when modified as described above.
`When a system of this type sets up a connection to a
`set of line terminals such as the auxiliary line terminals
`or appearance 200, a positive 130 volts is momentarily
`applied to the sleeve conductor S which causes the hold(cid:173)
`ing magnet 37 to operate and complete the connection
`through -the associated crossbar switch of the switching
`system 50 to the idle set of line terminals 200 designated
`T, RandS.
`The momentary application of the positive 130 volts
`to the sleeve conductor S to operate the hold magnet 37
`at this time is from a charged condenser as described in
`the above-identified article. This voltage is sufficient to
`momentarily operate the B relay 23 through the normal
`contacts 0-27 of the O relay 25 and diode 29. This
`voltage, however, does not cause the operation of the
`T relay 32 at this time due to the action of the inductor
`31 connected in series with the relay. At this time the
`make contacts 0-26 of the O relay 25 are open because
`relay 25 is not operated at this time.
`The operation of the B relay 28 closes contacts B-22
`which complete a circuit for the operation of the A relay
`23 from ground on the sleeve of the busy regular line
`terminals or appearance 100. As a result, the A relay 23
`operates and in turn closes contacts A-21 thus completing
`a holding path for A relay 23 from the sleeve conductor
`S of terminals 100 through the break contacts T-20 of the
`T relay 32 and the operated contacts A-21 of A relay 23.
`In addition, A relay 23 in operating also closes contacts
`A-34 which shunt the 48 volts through resistor 33 applied
`to the terminal of the T relay 32 thus preventing the
`operation of this relay from ground connected to the
`sl~eve terminal S of the auxiliary line appearance of ter(cid:173)
`mmal 200. The ground is applied to this terminal after
`the condenser has discharged terminating the application
`of a positive 130 volts. As a result T relay 32 does not
`operate at this time.
`As described above, the B relay 28 is operated due to
`the momentary application of the positive 130 volts to
`the sleeve conductor S of the auxiliary line terminals of
`appearance 200. Upon the termination of this positive
`voltage from the sleeve, the diode 29 prevents the negative
`48 volts through the hold magnet 37 from holding the
`B relay 28 operated. Relay 28 is a slow-release relay so
`that it will be operated and remain operated for an appre(cid:173)
`ciable interval of time due to the momentary application
`of the positive 130 volts to the sleeve conductor.
`During this momentary operation of relay 28 in addi(cid:173)
`tion to closing the contacts B-22 and causing the opera(cid:173)
`tion of the A relay 23 as described above, the momentary
`operation of relay 28 closes contacts B-18 which connect
`the resistor 43 across the T and R conductors of the first
`line appearance 100, thus maintaining the connection
`through the automatic switching equipment. In addition,
`the momentary operation of relay 28 opens the contacts
`of B-12 and B-13 and closes the contacts B-16 and B-17.
`As a result, the call waiting tone supply 35 is connected to
`the subscriber's station 150 or subset and at the same time
`the connection extending back through the switching sys-
`tem to the other subscriber of the first or busy call is inter(cid:173)
`rupted. Thus, the subscriber station 150 receives a spurt
`of call waiting tone from the tone supply 35, while the
`other subscriber to this call receives no such tone. These
`conditions prevail as long as relay 28 remains operated.
`Upon the release of relay 28 contacts B-18 open, con(cid:173)
`tacts B-12 and B-13 reclose and contacts B-16 and B-17
`open thus restoring the circuit of the first connection to
`the subscriber station 150 to its original condition where(cid:173)
`upon this subscriber can again converse with the sub-
`scriber who either called him or whom he called.
`During this time, the subscriber calling the subscriber
`station 150 who is connected to the auxiliary line terminal
`75 or appearance 200 will receive ringing indication tones
`
`Motorola Solutions, Inc., Ex1016, p. 3
`
`

`

`'d ;_)
`thus indicating that the subscriber station set is being rung.
`So long as all of the subscribers maintain their instru(cid:173)
`ments off normal the above-described set of conditions
`continue.
`If at this time still another subscriber calls
`the station 150 both the regular and the auxiliary line ter(cid:173)
`minals 100 and 200 will test busy. If there are no other
`sets of terminals, busy tone will be returned to this sub(cid:173)
`scriber.
`If additional sets of line terminals or appear(cid:173)
`ances are provided and interconnected in a manner sim(cid:173)
`ilar to the manner in which the sets 100 and 200 are con(cid:173)
`nected, then this call will be directed to such additional
`auxiliary line terminals or appearance.
`In case the calling party on the second call hangs up,
`first the hold magnet 37 will release and the connection
`from his line to the second or auxiliary set of line ter(cid:173)
`minals or appearances will be interrupted and the corre(cid:173)
`sponding circuits in the switching system 50 restored to
`normal. Thereafter, when the first call is terminated the
`switching system 50 will restore the circuits to normal and
`the A relay 23 will likewise release due to removal of
`ground from the sleeve conductor S of the first set of line
`terminals or appearance 100.
`If, however, the first call is terminated first then the
`connections through the switching system 50 to the regular
`set of line terminals or appearance 100 will be interrupted
`with the result that ground is removed from the sleeve
`conductor S of this set of line terminals and, as a result,
`the hold magnet 38 and the relay 23 both release. If the
`calling subscriber of the second call has not terminated
`the call at this time ground will still be connected to the
`sleeve terminal conductor S of the auxiliary set of line
`terminals or line appearance 200 by the switching system
`50. As a result, upon the release of relay 23 contacts
`A-34 will open and remove the shunt from around the
`resistor 33. Consequently, the T relay 32 will operate
`at this time in a circuit extending from battery through
`resistor 33, winding of relay 32, inductor 31 to ground
`connected on the S conductor of the auxiliary set of line
`terminals or line appearance 200 in the switching system
`50.
`Relay 32 in operating causes contacts T-10 and T-11 to
`open disconnecting the subscriber's line conductors from
`the regular set of line terminals or appearance 100 and
`contacts T-14 and T-15 will close connecting the line con(cid:173)
`ductors of the subscriber's station 150 to the T and R
`conductors of the auxiliary set of line terminals or appear(cid:173)
`ance 200. The operation of relay 32 also causes contacts
`T-19 to close and contacts T-36 to open. The operation
`of contacts T-36 removes the resistor 42 and the con(cid:173)
`denser 41 from across the T and R conductors of the aux(cid:173)
`iliary set of line terminals. The contacts 19 in closing
`connect a condenser 44 and resistor 45 across the T and
`R conductors of the regular set of line terminals or ap(cid:173)
`pearance 100 which will simulate a ringer in a subscriber
`station set so that should another call be directed to the
`subscriber's station set 150 during the time it is busy due
`to the above-described call over the auxiliary set of line
`terminals or appearance 200, the marker circuit in the
`switching system 50 can satisfactorily complete a con(cid:173)
`tinuity test to the then called subscriber's line.
`The connection of the T and R terminals or conductors
`of the auxiliary set of line terminals or appearance 200
`to the subscriber's line conductors extending to the sub(cid:173)
`scriber's station 150 will now cause ringing current to
`be applied to these line conductors and cause the sub(cid:173)
`scriber's bell to ring and the subscriber in answering a
`call will actuate the switching equipment in the switching
`system 50 in the usual manner. Thereafter, the call may
`be terminated in the usual manner at which time the hold
`maonet 37 and relay 32 will both release and restore
`the
`circuits to their initial or idle condition.
`If before the call over the auxiliary line terminals or
`appearance 200 is terminated another call shoul~ be di(cid:173)
`rected to the station set 150, the regular set of hne ter(cid:173)
`minals or appearance HIO will now test idle so that the
`
`O
`
`3,133,995
`
`6
`marker of the switching system 50 will establish a path
`from this new calling subscriber to these set of line ter(cid:173)
`minals. As pointed out above, the condenser 44 and
`resistor 45 and closed contacts T-19 provide a path for
`5 permitting the marker to satisfactorily complete a con(cid:173)
`tinuity test over the conductors T and R of the regular
`set of line terminals 100.
`In addition, the hold magnet
`38 is operated and since the T relay 32 is operated con(cid:173)
`tacts T-24 are closed and as a result the O relay 25
`10 operates.
`As described herein, the switching system 50 will apply
`positive 130 volts for a brief interval of time to the S
`conductor of the regular line appearance at this time to
`cause the hold magnet 3!l to operate in a very short
`15 interval of time. This high voltage will also cause the
`0 relay 25 to operate in a very brief interval of time
`and open contacts 0-27 and close contacts 0-26 thus dis(cid:173)
`connecting the winding of relay 23 from the sleeve or S
`terminal or conductor of the auxiliary set of line ter-
`20 minals or appearance 200 and connect the winding of
`relay 28 through the diode 29, resistor 30 and operated
`contacts 0-26 to the sleeve or S conductor of the regular
`set of line terminals or appearance 100. The operation
`of relay 25 is sufficiently fast so that the B relay 28 will
`25 operate in response to the positive 130 volts momentarily
`applied to the S or sleeve conductor of the regular set
`of line terminals 100 and in substantially the same man(cid:173)
`ner as described above in response to the momentary
`application of the positive 130 volts to the S or sleeve
`30 conductor of the auxiliary set of line terminals or appear(cid:173)
`ance 200. As before, the operation of relay 28 causes
`the contacts B-12 and B-13 to open and disconnect the
`calling subscriber connected to the line conductors over
`the auxiliary set of line terminals 200 and also causes
`35 contacts B-18 to close thus maintaining the path through
`the switching system 50 to this subscriber.
`Also, the operation of relay 28 causes contacts B-16
`and B-17 to close and connect the call waiting tone
`signal to the line conductors of the subscriber's station
`40 150, thus indicating that another call is waiting. Relay
`28 is only momentarily operated as described above so
`that this tone is applied for a short interval of time after
`which the connection is between the subscriber's station
`set 150 and the calling subscriber connected through the
`45 switching system 50 to the auxiliary set of line terminals
`or appearance 200 is reestablished whernupon the sub(cid:173)
`scribers can again communicate with each other.
`As before, if the subscriber connected to the regular
`set of line terminals disconnects first hold magnet 38
`50 and relay 25 will release and the circuits in the switching
`equipment 50 likewise will be restored to normal. There(cid:173)
`after, when the subscriber connected through the switch(cid:173)
`ing equipment to the auxiliary set of line terminals 200
`terminates a call, these circuits will be restored to their
`55 initial or idle condition in the usual way .
`If, either the subscriber con,,ected to the auxiliary set
`of line terminals or appearance 200 through the switch(cid:173)
`ing equipment or the subscriber at the subscriber's sta(cid:173)
`tion set 150 terminate the call before the subscriber
`60 connected to the regular set of line terminals or ap(cid:173)
`pearance 100 terminates a call then ground will be re(cid:173)
`moved from the sleeve or S conductor of the auxiliary
`line terminals or appearance 200 with the result that the
`hold magnet 37 and relay 32 will release. As a result,
`65 the connection between the T and R conductors of the
`auxiliary set of line terminals or appearance 200 is in(cid:173)
`terrupted and the subscriber's line terminals connected
`to the T and R conductors of the regular set of line ter-
`70 minals or appearance 100. Thereupon, the subscriber's
`bell at station 150 will ring and the subscriber may
`answer the call in the usual manner whereupon both
`in the switching system 50 and the auxiliary line circuits
`shown in the drawing respond in the manner described
`75 above.
`
`Motorola Solutions, Inc., Ex1016, p. 4
`
`

`

`3,133,995
`
`8
`
`7
`In the foregoing descriptions, it has been assumed that
`a regular set of line terminals or appearance 100 and
`one auxiliary set of line terminals or appearance 200 has
`been provided for each subscriber line desiring the fea(cid:173)
`ture of being notified of a call waiting and being per- 5
`milted to receive the new call if the existing call is ter(cid:173)
`minated sufficiently soon. More than one set of auxiliary
`line terminals or appearances may be provided if traffic
`conditions warrant and these additional auxiliary termi(cid:173)
`nals may be interconnected with the regular set of line 10
`terminals or appearance and the auxiliary set of line
`terminals or appearance shown in the drawing in a simi-
`lar manner.
`Other modifications may be made by those skilled in
`the art without departing from my invention. Thus in 15
`the arrangement described herein wherein the alerting
`tone is prevented from reaching the other party on the
`prior conversation by opening the talking path for the
`duration of the tone interval while maintaining super(cid:173)
`vision of the trunk circuit by a suitable resistance across 20
`the tip and ring conductors, clicks may be heard at both
`ends of the connection when the connection is broken
`and again when the connection is reestablished by the
`B relay. Furthermore, conversation is interrupted for
`If this should prove undesirable, 25
`the short tone interval.
`the alerting tone may be applied to the tip and ring con(cid:173)
`ductors of the called subscriber through a pair of repeat
`coils. At the same time, an inductor and capacitor, con(cid:173)
`nected in series, are cut into the circuit across the tip and
`ring conductors to the other side of the repeat coils than 30
`the called subscriber with the L and C combination de(cid:173)
`signed to be at series resonance at the tone frequency.
`In this manner the tone may be applied to the called
`subscriber without interrupting the direct-current path of 35
`the prior connection.
`It is, therefore, to be understood that the above de(cid:173)
`scribed atTangements are illustrative of the application of
`the principles of the invention and that numerous other
`arrangements may be devised by those skilled in the art 40
`without departing from the spirit and scope of the inven(cid:173)
`tion. Specifically, while the invention has been de(cid:173)
`scribed with reference to connection to a crossbar system
`of the type described in the above-mentioned Busch
`patent, the invention is not limited in applicability to any 45
`particular central office switching systems and may be
`equally utilized with other central office switching
`systems.
`
`What is claimed is:
`1. In combination, in a telephone switching system a
`telephone subscriber's line, two sets of selectable line
`terminal appearances therefor, means for selecting either
`of said line terminal appearances when they are not busy,
`means responsive to the selection of either of said line
`terminal appearances when the other of said line terminal
`appearances and said line are busy for transmitting a
`call-awaiting tone to the subscriber's line, and means
`responsive to the termination of the busy call for inter(cid:173)
`connecting the subscriber's line with the said other ter(cid:173)
`minal appearance, and means for thereafter applying
`ringing current to the subscriber's line for calling the
`subscriber.
`2. In a telephone system, a telephone subscriber's line,
`two sets of selectable line terminal appearances therefor
`each set including a sleeve terminal appearance, means
`for connecting said line to one of said line terminal ap(cid:173)
`pearances, means for simulating a subscriber's line con(cid:173)
`nectable to each of said line terminal appearances, means
`responsive to the selection of either of said line terminal
`appearances when the other of said line terminal appear(cid:173)
`ances and said line are busy for transmitting a call-await(cid:173)
`ing tone to the subscriber's line, said tone transmitting
`means including a tone source, a first relay having a
`winding, means for selectively connecting said first relay
`winding to said sleeve terminal appearances, and means
`including contacts of said first relay for connecting said
`tone source to the subscriber's line and for preventing
`transmission of said tone to the other subscriber inter(cid:173)
`connected with the subscriber's line, means responsive to
`the termination of the busy call for interconnecting the
`subscriber's line with the other of said line terminal ap(cid:173)
`pearances, said interconnecting means including a trans(cid:173)
`fer relay having contacts .and a winding connected to one
`of sleeve terminal appearances and means for changing
`the condition of said transfer relay on termination of
`said prior busy call including a contact of a relay con(cid:173)
`nected to the other of said sleeve terminal appearances,
`and means for preventing energization of said transfer
`relay on energization of said first relay.
`References Cited in the file of this patent
`UNITED STATES PATENTS
`West et al. _____________ Apr. 7, 1942
`Lomax _______________ Feb. 14, 1950
`Corbett _______________ May 30, 1950
`Lomax _________________ Nov. 3, 1959
`
`2,278,752
`2,497,782
`2,510,011
`2,911,478
`
`Motorola Solutions, Inc., Ex1016, p. 5
`
`