CA1072697A - Method and apparatus for automatically identifying an individual calling party on a multiparty telephone line - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
After description of a number of prior art automatic telephone number identification systems and certain problems associated therewith, a new method and apparatus for use in such systems which overcomes the pro-blems of the prior art is described. In its preferred form, the method includes the steps of applying to the telephone line at a central office a voltage which has a magnitude sufficient to produce a first predetermined value of loop current in the telephone line. At each party station, the loop current is caused to change between the first predetermined value and a second predetermined value in a manner unique to that party station, with the second predetermined value being smaller than the first predeter-mined value but greater than a value of loop current that would signify to the central office that an on-hook condition exists on the telephone line. At the central office, the loop current change is detected and com-pared with a plurality of stored loop current changes to provide party station identification, with each stored loop current change being unique to each party station. In a preferred embodiment, these steps occur in a predetermined time sequence, with the loop current changes also occurring at predetermined but distinct time intervals each of which is unique to a party station. The apparatus for practicing this method includes an automatic party identifier for location at the central office and a subscriber module adapted to be located in circuit with a party station and the telephone line.

Description

il~72~9~7 This invention generally relates to automatic telephone number identification apparatus, and, more particularly, to a method and apparatus, for automatically identifying an individual calling party on a multiparty telephone line, which is particularly useful as a component part of and in conjunction with such au~omatic telephone number identification apparatus.
Automatic telephone number identification apparatus is in widespread use in the United States and elsewhere or determining which individual telephone subscriber, or party, has placed a long-distance telephone call on a multipar~y telephone line, in order that the party may be appropriately billed for the cost of the call. Such appara~us is also being increasingly used for determining the party that has placed a local telephone call. Typic-ally, automatic telephone number id ntiication apparatus is divided into two portionsJ the first being an apparatus which identifies which party on a line has made the long-distance call, and the second being an apparatus for forwarding to a toll or other central office the telephone number of the thus-identified calling party.
The present invention deals particularly with that portion of automatic telephone number identification apparatus which is used to identify the calling party. By far the most widespread identification method and apparatus known to the prior art is that commonly referred to as resistance ground automatic number identifica~ion which is particularly adaptable to ~hose situations in which two parties share a common telephone line. Typically one of the parties, kno~n in the art as "party 2", has located with each telephone instrument at its station a ground mark circuit, usually comprising the series connection of a resistance and an inductor which is connected to ground. For example, the ground mark circuit may comprise a portion of a coil for a ringer or bell in each telephone instrument. The telephone instruments of the other party, known in the art as "party 1", either do not .

1~7Z~i97 have such a ground mark circuit or have the ground mark circuit therein dis-connected. To provide detection of the calling party, a central office associated with the common telephone line applies a DC signal to the co~on telephone line upon detection of a long-distance call having been initiated on that line, usually shortly after the calling par~y has dialed a number for which a toll charge is to he made. If the long-distance call has been initiated by party 2, a DC imbalance bet~een the tip ~T) and ring ~R) con-ductors of the telephone line resulting from the presence of the ground mark circuit is detected at the central office. If the call has been initiated by party 1, then no such DC imbalance is detected. The equipment at the central office then forwards the calling party's telephone number to a toll office for billing purposes.
Although simple in concept~ construction, and operation, resistance ground automatic number identification presents significant problems to telephone companies in actual application. For exampleJ each telephone instru-ment at each ~&rtystation must have its ground mark circuiit connected or dis-connected in accordance with that the party's designation as party 1 or party 2.
It is sometimes inconvenient for a telephone company to connect or disconnect the ground mark circuit at the time of installatlon of each telephone instru-2Q ment. Additionally, when a group of existing ~elephones are being converted from operator number identification to automatic number identification, burden-some p~cblems of arranging-for home visits to ;.nstall ground mark circuits are ; presented. Furthermore, with the decline of telephone leasing, and with a corresponding increase in the number of telephones!which are purchased and installed by subscribers, the control of a telephone company over the indi-vidual telephones in its system has slgnificantly decreased to a point where the telephone company cannot ~assure that the telephone instruments of an~ given subscriber either have or do not have the ground mark circuit

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lQ7;~:6~7 cormected in ~ccordance with that subscrib~r~s party identification. Not surprisingly, these problems of installation and control have caused numerous err~rs in proper identification of and billing of subscribers placing long-distance telephon~ calls. Finally, the ground mark circuit itself and i~s connection to the telephone instrument must be carefully designed to minimize noise that may be present on the telephone line due to the ground connection in the ground mark circuit.
A solution to the afore~entioned problems of installation, con~
and design of ground mark circuits is provided by the invention disclosed and claimed in United States patent 4,001,512 issued January 4, 1977, entitled "AUTOMATIC TELEPHONE NUMBER IDENTIFICATION CIRCUIT", by Darryl F. Proctor and Peter T. Ske~lly, which is assigned to the assignee of the present invention.
However, resistance ground number identification still cannot be used where more than two pa~ti~s share a common telephone line.
Another two-party identification method and apparatus known to the prior art includes a pair of reverse-parallel diodes which are located at the party 2 staticn and in series circuit with the telephone instruments thereof and the portion of the telephone line "downstream" of the co~mon connection of the party 1 and party 2 stations with that portion of the telephone line going to the central office. No such reverse-parallel diodes are provided in circuit with the instruments of the party 1 station. A
controllable voltage source is connected to one side of the telephone line at the central ofice, and a voltage detector is connected to the other side of the telephone line at the central office. Upon detection of the place-ment of a long-distance call, the central office supplies a short across the telephone line to discharge any distributed capacitance therein. Shortly thereafter, a very small DC voltage pulse is applied by the controllable vol-~age~sou~cei T~ the t~lephGne ~nsb~ment going off-hook is in the party 1 , .

1C97;Z69~7 station, this pulse will be reflected on the other side of the telephone line in the central office and will be detected by the voltage detector to signify that party 1 has placed a call. If the telephone instrument going off-hook is in the party 2 station, however, the voltage drop across the reverse-parallel connected diode pair will absorb the DC voltage pulse so that the -voltage appearing on the other side of the telephone line at the central office has a value insufficient to trigger the voltage detectorJ therefore signifying that party 2 has placed a call.
Although avoiding many of the problems associated with resistance ground number identification, systems of this type encounter much difficulty in application in the situation where diode bridges used for polarity guards, bridge taps, line lifters and loop extenders have been installed in the line, all of which provide voltage drops which can absorb the DC voltage pulse.
In addition, such systems are not applicable to part~ lines for more than two parties.
There are known to the prior ar~ various methdd and apparatus for providing identification of a calling party ~or those party lines having more than two parties connected thereto. In one system utilizing such a method and apparatus~ a circuit is connected to each telephone instrument in each subscriber station. Each Cil'CUit includes a diode and a resistor connected to ground, with the polarity of the diode connection and the resistance value of the resistor being unique for each subscriber station.
In response to application to the line at the central office of a DC voltage having a predetermined polarity, a predetermined value and direction of curren~
unique to the calling party exists on the line so that the calling party can be detected at the central office to provide party identification. Typic-ally, a combination of polar and marginal relays is used to effect current polarity and current value detection. In systems of this type, only four .

' ' 1~2~g7 parties can be detected, the diodes cause noise on ~he line, and all the other pr~lems and limitations of the resistance ground number identification systems are encountered.
In yet another multiple party identification method and apparatus, a network is placed in circuit with each telephone instrument at the party 2, party 3, and so forth stations, with no such network be ng provided at the party 1 station. All the network~ for each station are designed to conduct current upon the application of a predetermined voltage value thereto, usually with reference to ground, with the predetermined voltage values differing among the stations. For example, the net~ork may include a neon tube in series-parallel connection with an adjustable resistor) with the resistor establishing a network breakdown voltage, or, the network may include a PNPN voltage breakdown diode, or its electrical equivalent in-cluding~a zener diode and a switching network responsive thereto, with sel-ection of the brea~down voltages of the neon tubes, PNPN diodes or the ~ener diodes being chosen to correspond to the aforementioned pre~etermined voltage values. A step voltage source is provided at the central office for apply~
ing, in sequence, increasing voltage values to the common telephone line.
A detector is also provided at the central office for detecting when, in the sequence of voltage ~pplicationg current flows th~ough the common telephone line in order to provide party identification. Systems ~u~ilizing this method and apparatus are ~isadvantageous, however, in that again, each telephone instrument must include a proper network, and in that a constant reference or ground potential must be provided;lat all of the instruments at all of the stations.
Still another approach in the ~rior art to multiple party identifi-cati~n is the provision of separate conductors for each telephone instrument interconnected with contacts which are actuated upon that telephone instrument .' ::.. '.. ., :. , . ., :' ,.... :,:,, ,.. . .. : . :, . .... - . . ., : . :

~72~7 going off-hook, with the conductors being brought back to the central of~ice or to some other detection point. In ~his situat~-on, the number of conductors required for mul~iple parties make such systems ilnpractical for any widespread application.
Finally, the prior art also teaches a method and apparatus in which each telephone instrument is e~uipped with a tone gcnerator which is enabled upon that telephone ins~rum~nt going off-hook ~o apply a tone signal to the telephone line. If the tone generators are designed so that each generator emits a tone distinctive of the subscriber station at which it is located, then a receiver at the central office can pro~ide party detection in response to the actual tone ~hat appears on the line at the central office.
As with the resistance groudd and other methods and apparatus described ;~
above, each telephone instrument must be modified to include a proper ident-ification circuit, or, tone generator. Further, the existence of tones upon the lines is likely to interfere, at some point in the *elephone system, with conventional apparatus for detecting tones corresponding to the number that has been dialed and to other tones utili~ed in the system for interconnection purposes. The tones on the line are also quite audible to the calling party.
It is there~ore an object o~ this invention ~o provide, for use as part of and in conjunction with an automatic telephone number identification apparatus, a method and apparatus or automatically identifying an individual calling party on a multiparty telephone line, whi`Gh method and apparatus avoidsthe disadvantages of the prior art previously referred to.
It is another object of this invention to lprovide such a method and apparatus which can be used with substantially all multiparty telephone lines~ including those telephone lines which have more than two parties connected thereto.

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~72697 It is still another object of this invention to provide such a method and apparatus which do not require each telephone instrument at each party station to be modified, but only require that a modification be made to that portion of the telephone line extending between the telephone instru-ments at a subscriber station and a common junction of all the subscriber stations wi~h the portion of the telephone line going to the central of~ice~
thereby allowing the modification to be made without access to the telephone instruments and without access to the premises in which the telephone instru-ments are located.
lQ It is a further object of this invention to provide such a method and apparatus which does not require an earth ground reference at any point, thereby avoiding the problem of noise injection into the telephone line.
It is ~et a further object of this invention to provide such a method a~d apparatus which will furnish reliable party identifica~ion even though diode bridges, bridge taps, line lifters or most types of loop extend-ers are installed in conjunction with the telephone line.
Many of these objects, and other objects and advantages that will be recognized by those skilled in the art, are achievedl briefly, by a method for automatically identifying at a central office that one of a 2Q plurality of party sta~ions interconnected with the talephone line from which a telephone call has been placed.
The method comprises a first step of, at the central office, applying to the telephone l~ne a voltage having a magnitude sufficient ~o establish a first predeterntined valtte of loop current in the telephone line. This loop current value is greater than a value that would signify to the central offlce that an on-hook condition exists on the telephone line.
The method comprises a second step of, a~ that one party station, cattsing the loop current to change from the firs~ predetermined value in a , ,, . ~ ., .. . ......... , . . :: .......... . - - : .: .
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1~7Z6~7 manner which is unique to that one party station.
The method also comprises a third s-tep of 9 at the central office detecting the change in loop current and comp~ring the detected change in loop current with a plurality of stored loop curren~ changes to provide identification of that one part~ s~ation, with each stored loop current change being unique to each party station interconnected with the telephone line.
The uni~ue manner of loop current change may ~e time-related, that is, the change ma~ occur at a time ~hic~ is unique to the calling part~
ln stat~on, and part~ identification ma~ be made at the central office comparing ~he time of occurrence tof loop current change with a pluralit~
of predetermined time intervals, each predetermined time interval also 6eing unique to each part~ station.
Alte*nately, the loop current may ~e caused to c~ange bet~een the first predetermined value and a second predete~mined value, smaller than the first predetermined value but still not low enough to signif~
an on-hook condition, in a manner unique to the each party station.
In a preferred em~odiment, the loop current is regulated at the first predetermined value from a first t-ime which is substantially 2cL co~ncident ~i~h detection of placement o the telephone call toaa second time.
At the second tlme ~ and thereafter, the vol~age applied to the telephone line is regulated at the magnitude sufficient to produce the first pre~--determined value of loop current. At ~hat one party station, the loop current is *egulated at the second predetermined ~alue at a third time which i is subsequent to the second timej which current regulation is terminated at a fourth time ~hich is subsequent to the third time and w~ich is unique to that one party station. The central office ~egins monitoring the telephone line at a fifth time, su~sequentlt-oco the th~rd time~ to detect a rise in the .

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7Z~97 loop current toward the first predetermined value, and compares the tlme of the detected rise in loop current wi~ a pluralit~ of predetermined time intervals, eac~ unique to a part~ station, to provide identification of that one part~ station.
rn one embodim~nt of the invention, no such subscriber module is located in circuit with a particular one of the party stations, and de-tection of the placement of a long-distance call from that particular one of the party stations is made when the de~ected loop current a~ the central office does not change from the first predetermined value thereof.
lQ The objects of the invention are also achieved, at the central office, by an automatic party identifier which is selectively interconnected with the telephone line, and, at each party station by a subscriber module adapted to be located in circuit with th~ telephone line and the party station.
According to the present invention there is provided a subscriber module useful in conjunction with and forming part of an apparatus for detecting which party on a multiparty telephone line has placed a call thereon, said subscriber module including: a) first and second terminals adapted ~o -tbe connected in series circuit with the telephone line; b) first 2Q means connected between said first a~d second terminals for shunting current therebetween in a first predetermined direction of saidcaurrent; c) second means connected between said first and second terminals for controlling current therebetween in a second direction of said current which is opposite to said first direction, said second means including: i~ timing means responsive to the detection of ~urrent in said second direction for provid~
~ng a plurality of successive timing signals, ii) current regulating means for regulating the magnitude of said current in said second direction at a predetermined value which is greater than the magnitude of said currcnt -9~

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that ~ould signify an on-hook condition on the telephone line, said current regulating means initiating said currenk regulati~n in response to a first one of said plurality of timing signals and terminating said current regu-lation in response to a second, subsequent one of said plurality of timing signals, and iii) means selectively shunting current between said first and said second terminals in said second direction in response to said seeond one of said plurality of timing signals.
~ ccording to another aspect of the present invention there is provided a subscriber module useful in conjunction with and ~orming part of an apparatus for detecting which party on a multiparty telephone line has placed a call thereon, said subscriber module including: a) first and second terminals adapted to be connected in series circuit with the telephone line; and b~ means connected between said first and second term-inals for controlling current therebetween in a predetermined direction of said current, said means including i) timing means responsive to the de~ection of current in said predetermined direction for providing a plurality of successive timing signals, ii~ current regulating means for regulating the magnitude of said current in said predetermined direction at a predetermined value which is greater than the magnitude of said current that would signify an on-hook condition on the.telephone line, said current regulating means initiating said current regulation in response to a first one of said plurality of timing signals and terminating said current re-gulation in response to a second, subsequent one of said plurality of timing signals, and iii) means selectively shunting current between said ~ .
first and said sscond terminals in said prcdetermined direction in response to said second one of said plurality of timing signals. `:
In a preferred embodiment, the automatic party identifier includes a voltage source and means for selectively interconnecting the voltage source , . .. , . , , . - -... : .
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~L~7Z697 with the ~elephone line when party identification is to be made to thereby apply to the telephone line a voltage having a magnitude sufficient to pro-duce the first predetermined value of loop current therein. Means is provid-ed for regulating loop current in the telephone line at the first predeter-mined value, and for alternately regulating the magnitude of the voltage ap-plied to the telephone line by the voltage source at the magnitude sufficient to produce the first predetermined value of loop current ~herein. Timing means is provided for producing a plurality of timing signals, a first one of the plurality of timing signals controlling the regulating means so that the regulating means regulates the loop current for a predetermined period of time sufficient to stahilize the loop current at the first predetermined value, and so that the regulating means therea~ter regulates the magnitude of the voltage applied to the telephone line. A current le~e~ detector pro-vides a current level signal representative of loop current. Threshold means is responsive to a second one of the plurality of timing signals to com-pare9 at a time subsequent to the predetermined period of time, the current level signal with the threshold value of the loop current, the threshold value being lower than the` first predetermined value but higher than the second :
predetermined value, the threshold means providing an output signal when the loop current equals or exceeds the threshold value. Decoder means is responsive to a third one of the plurality of timing signals to provide a plurality of successive signals each existing during succeeding time intervals each succeeding time interval being unique to one of the parties on the multiparty telephone line. Finally, an output means is responsive to con~
currence of the output signal from the threshold means and one of the suc-cessive signals to provide a party identification signal.
In a preferred embodiment, the subscriber module includes first and second terminals adapted to be connected in series circuit with the ~
telephone line. First means is connected be~ween the first and second ter-' ' -11- ~, .: .
, minals for shunting curren~ th~rehetween in a first predetermined direction of current. Second means is connected between the first and second terminals for eontrolling current therebetween in a second direction o~ current which is opposite to the first direction. The second means includes timing means responsive to the detection of current in the second direction for provid-ing a plurality o~ successive timing signals. Current regulating means is also inc~ded for regula~ing the magnitude of ~he current in ~he second direct-ion at the second predetermined value, the current regulating means initiat-ing the current regulation in response to a first one of the plurality of timing signals and terminating the current regulation in response to a second, subsequent one of the plurality of timing signals. Finally, ailso included i5 means-lselectively shunting current ~etween the first and second terminals in the seond direction in response to the second one of the plurality of timing signalss The invention can perhaps best be understood by the reference to the following portion of the specification, taken in conjunction with the accompanying drawings in which:
FIGURE 1 is a block diagram illustrating a typical automatic number identification apparatus including the method and apparatus of the present invention;
FIGURE 2 is a block diagram of an automatic party identifier located at a central office as illustrated in FIGURE 1 and incorporating a portion of tha method and appara~us of the present invention;
FIGURE 3 is a combined schematic and block diagram of a subscriber module located at a subscriber station as illustrated in FIGURE l and also incorporating 'a portion of the present invention;
FrGURE 4 is a timing diagram for use with FIGURES 2 and 3; and FIGURE 5 is a schematic diagram illustrating a pref0rred embodiment of a portion of the automatic party identifier of FIGURE 2.
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~Ct7Z6~7 ~ ith referenc~ no~ to FIGURE 1, the invention will be described with reference to its applica~ion in conjunction wi~h a typical step-by- step central office, although i~ is to be clearly understood by those skilled in thc art that the invention finds equal applicability in central offices using other switching schemes, such as crossbar, ESS, or the like, and in fact is generally applicable wherever identification of a calling party on a multiple p~rty telephone line is desired.
A plurality of subscriber stations, identified as PARTY 1, PARTY 2, PARTY 3, PARTY 4, and PARTY 5 are interconnected wi~h a common telephone line Ll extending between those stations and a central office. The line Ll includes a single cable pair including tip ~T?~and ring ~R) conductors.
~t each station, one or more telephone instruments 10 are interconnected in parallel with the conductors, T, R, of line Ll. In addition, a single subscriber module 12 is placed at each subscriber station in circuit with the portion of the line Ll extending be~we0n the telephone instruments 10 at that station and a common junction of all the subscriber stations~with the exception that no such subscriber module 12 is placed in the aforementioned pdrtion of the line Ll associated with the PARTY 1 s~ation.
The line Ll extends to a central office and, in practice, may cover great distances and be passed ~hrough one or more loop extenders as is known to the prior art. At the central offj.ce, the line Ll terminates in a line circuit 14 which comprises one of a plurality of such line circuits located at the central office, with one such line circuit being provided for each telephone line, or cable pairl coming into the central office. It will be ; appreciated that some of these telephone lines will be private lines in which only a single subscriber station is connected thereto, and other tele-phone lines, such as the line Ll illustrated in FIGU~E l, may be multiple party telephone lines hauing a plurality of subscriber stations connected there-to.

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~l~7;~7 The line circuit 14 is int~rconnectcd by means of tip, ring and sleeve ~TRS) conductors o~ a line L2 to a line finder CLF) which has pernan-ently associated therewith a first selector ~FS), and by means of the ~ip, ring and sleeve conductors (TRS) of a line L3 to a connector CCONN~. The line finder LF has the line L2 and corresponding lines from ~he other line circuits in the central office connected to a bank of contacts thereof.
Similarly~ the first selector (FS) has connected to a bank of contacts thereof a plurality of outgoing trunk lines, including an outgoing dire~t distance dialing trunk line L4 having tip, ring and sleeve ~TRS) conductors.
A line splitting circuit 16 is interposed in the ~runk line L4 between the first selector ~FS) and a toll office which interconnects the central office with the long distance telephone network to which other cen~ral offices are similarly connected. The line spli~ting circuit 16 includes normally-closed contacts 16A in ~he line L4, and a pair of normally-open contacts 16BI 16C connected to opposite sides of contacts 16A, all of which are relay-operated. Normally-open contacts 16B connect the line L4 to the tip,~ring and sleeve ~TRS) conductors of a line L5 going to a first input of a register sender 18~ with the tip and ring conductors (TR~ of line L5 being co~upled through normally-open contacts 20A to an automatic party ; 20 identifier 20 forming part of the present invention. Contacts 20Ar~are controlled by a relay within automatic party identifier 20 as hereinaftex described.
The regis~er sender 18 has an output line L6 having tip and ring conductors (TR) which are connected to the line L4 through normally-open contacts 16C. The register sender 18 is also interconnected at the central ofice with an ANI matrix 22,~with regis~er sender 18 being capable of transmitting to ANI matrix 22 a PARTY CODE si-~al and receiving back there-from a CALLING STAION NUMB~R signal. The ANI matrix 22 also has connected . - ~ .

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~972697 thereto a plurali~y of sleeve ~SI) conductors from the connector CONN, with each sleeve conductor SI being respectively connected with a corresponding sleeve (S) conductor of the plurality of lines extending from the connector CONN (-~to the plurality of~.line circuits in the central office, including the S conductor in line L3 going to line circuit 14. In this manner, the ANI
matrix 22 is provided with a unique SI conduc~or corresponding to each telephone line coming into the central office.
The register sender 18 is also interconnected with the automatic party identifier 20, with register sender 18 being capable of providing thereto a START GROUND signal.when the identity of.a calling party is to be detected, and receiving back therefrom a PAKTY`CODE signal identifying the calling party as PART~ l, PARTY 2, andiso forth, which is transmi~ted to the ANI matrix 22 as aforesaid.
Assuming now.that a person at one of the subscriber stations interconnected with line Ll initiates the placing of a long-distance call, a resultant off-hook.condition of the telephone instrument 10 being utilized at that subscriber station ~resulting in a circuit being completed due to a corresponding termination of the conductors TR of line Ll~causes a relay within the line circuit 14 to be actuated to a) apply central office battery to line Ll, b) interconnect lines Ll and L2, L3, and c) actuate the line finder LF. As is conventional, the line finder LF steps through its bank of contacts until it comes to rest at the bank positon interconnected with line L2. At this time, dial tone is provided by the central office on line Ll~ by means not illustrated.
Thereafter, the calling subscriber dials the telephone number to be called, In response to recognition of a code representing a long-dist-ance call, such as the commonly used "l" code, the first selector FS steps through its bank of contacts to the bahk position to which line L4 .
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.: . . -~7Z~i97 is connected, ~hereby completing a circuit from the telephone instrument 10 at the calling station to the toll of~ice through line Ll, line circuit 1~, line L2, line finder LF, first selector FS, and line L4 (including normally-closed contacts 16A). Subsequent digits of the called telephone number, including the area code, and the called station number, are then received by and stored in a register within the toll office. Thereafter, the *oll office transmits a signal back along line L4 which is detected, by means not illustrated, and used to cause the~lre~ay within line splitting circuit 16 to operate, thereby opening contacts 16A and closing contac~s 16B, 16C. Accord-ingly, a circuit is then completed from the calling subscriber to the input of the register sender 18 through contacts 16B and line L5. At this time, the register sender 18 causes the central office battery to be removed from line Ll and applies a START GROUND signal to the automatic party identifier 20.
In response to the START GROUND signal, the automatic party ident-ifier 20 closes contacts 20A, therby providing a direct connection between automatic party identifier 20 and the calling station via line L5, contacts 16B1l line L4, the first selector FS, the line finder LF, line L2, the line circuit 14, and line Ll. The automatic party identifier 20 thereafter inter-rogates the line Ll to ascertain the party identification of the calling party, whether it be PARTY 1, PARTY a, or the like, as hereinafter described.
After detecting this party identification, the automatic party identifier 20 transmits a corresponding PARTY C~DE signal to register sender 18 which is retransmi.tted to the ANI matrix 22.
Concurrently with the investigation by au~omatic party identifier 20, register sender 18 transmits a unique signal on the S conductor of line L5 connected thereto. This unique signal will be coupled throu~h contacts 16B, line L4, the first seleçtor FS, the line finder LF, line L2, line c~rcuit 14, ~ -.
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and line L3 to appear at the position of ~he connector CONN ~hat is ~niquely associated with the calling line, such as linc Ll. Accordingly, a correspond-ing unique signal will be transmitted on the associated conductor Sl to the ANI matrix 22 to signify thereto that the call has been placed on line Ll.
Stored within the ANI matrix 22 are a plurality of calling station numbers which are grouped in a fi~rst direction according to line identit~ and a second direction according to the designations of stations as PARTY 1, PARTY 2, e~c. Therefore, the signal on conductor SI will ~mark~ ~he positions within ANI matrix 22 associated with line Ll, those posi~ions being the PARTY 1, PARTY 2, PARTY 3, PARTY 4, and PARTY 5 positions. The PARTY CODE signal suppli~d by register sender 18 accordingly gates on that por~ion of ANI mat-rix 22 which has been marked by the signal on conductor SI and which cor-responds to ~he party identification of the calling party. In response, ANI
matrix 22 supplies the CALLING STATION NUMBER output signal representing the calling station number to the register sender 18, which number is stored therein.
Register sender 18 then outpulses the stored calling number to the toll office via line L6, contacts 16C, and line L4. After this action, the regist0r sender 18 a) removes the START GROUND signal from automatic party identifier 20, causing contacts 20A~\thereof to be opened, b) causes the relay within line splitting circuit 16 to be deactuated, accordingly opening contacts 16B, 16C and closing contacts 16A, and c) causes the central office to reapply the central office battery to line Ll. At this time, a direct connection is again afforded between the calling party and the toll ofice so that the long'~distance call may proceed.
In a preferred embodiment, the present invention functions to provide party identification in the following manner. At a first t;me and in tresponse to the START GROUND signal from register sender 18, the au~omatic party identifler 20 begins to establish a irst prede~ermined value of loop current '~

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-~L~7Z69~7 ~in line L5, and in line Ll~, and, in doing so, interrogates line Ll~ Pre-ferably, this interrogation is initiated by the application of a predetermined voltage to the conductors TR of line L5, which pred~termined voltage is coupled through the central office circuits previously described to line Ll and appears ~hereon as a voltage which is opposite ln pplarity to the central office battery which has just been removed from line Ll. In response to this interroga~ion, that one of the subscriber modules 12 that is interconnected with the telephone instrument 10 that has gone off-hook begins a timing period.
At a second time sufficient to allow the first predetermined value of loop current to be established in line Ll, the automatic party identifier 20 terminates its control of the loop current in line ~l but continues to re-gulate the voltage thereacross at a level requ~r~d~oproduce the first predetermined value of loop current. At a subsequent, third time, the sub-scriber module 12 associated with the calling station initiates regulation of loop current in line Ll at a second predetermined value which is lower than the first predetermined value. At a fourth time and ater the passage of a predetermined time in~erval from the first time which is unique to the calling station, the subscriber module 12 associated therewith responds to the interrogation by terminating its regulation of loop current in line Ll and 2Q therefore allowing the loop current to rise toward the first predetermined value thereof. At successive fif~h times subsequent to the fourth time, the automatic party identi~ier 20 is successively enabled to monitor the line L5 ' Cand thus Ll) to detect acchange in the signal conditions thereon. Each successive fith'time is unique to each party station and establishes a "window" subsequent to the fourth time :for each party station in which identi- ' fication of that party station can be made. ~hen the loop current rises above a threshold value intermediate the first and second predetermined values thereof, the automatic party identifier 20 compares the time of such detection , .
........

~:17;~697 with the "window" then under investigation and provides a PARTY CODE signal identifying the calling party. Since the time interval between interrogation and response is unique to a given party station, this detection by the auto-matic party identifier 20 within a predetermined time "window" provides identification of the calling station, if the call has originated from any of the PARTY 2 - PARTY 5 stations. If the call has originated from~the PARTY 1 station, the absence of the subscriber mo~ule 12 therein causes the first predetermined value of loop current to remain in the line Ll (and ~hus L5) so that detection is made by the automatic party identifier 20 shortly after the first of the successive fifty times at which i~ is enabled.
~ith reference now to FIGURES 2-4, the detailed structure and operation of a preferred embodiment of the present invention will be described.
FIGURE 2 illustrates the automa~ic party identifier 30J FIGURE 3 illustrates a typical subscriber module 12, and FIGURE 4 is a timing diagram relating to the operation of the automatic party identifier 20 and the subscriber module 12.
In FIGURE 2, the conductors TR of the line L5 are connected through normally-open contacts KIA, KIB of a relay KI ~o first and second terminals of a constant current voltage source 30~ which is also connected to a reference ground potential ~isolated from earth ground) and which receives potentials of~VB and Vg from a power supply, not illustrated. Typically, VB
, may have a relatively high DC potential with reference to ground, e.~., 150 volts, whereas Vs has a relatively low potential with respect to ground, e.g., 12 volts. Contacts KlA, KlB correspond to contacts 20A in FIGURE 1.
~ Constan~ current and voltag~ source 30 provides a first output on : lead 30A to a clock enable and reset logic circuit 32, which has an ouput lead 32A going to an enable input of an output driver circuit 40, and output leads 32B, 32C going to respective disable and reset inputs of a counter and :

: :. - , . . , :
, ,-. .

~72~7 decoder circuit 36. Both the clock enable and reset logic circuit 32 and a disconnect timer 34 receive the STARr GROUND signal rom register sender 18.
In addition, the disconnect timer 34 includes the coil of relay Kl and has an output lead 34A~going to a DISCONNECT ou~put from the automatic party identifier 20 and forming party of the PARlY CODE signal coupled to regis~er sender 18.
Counter and decoder circuit 36 has a first output lead 36A going to clock enable and reset logic circuit 32, a second output lead 36B goi~ng to constant current and vol~age source 30, and a plurality of third output leads 36Cl, 36C2, 36C3, 36C4~ 36C5 and 36C6 going to the output driver circuit 40. In addition, output lead 36C6 is conn~cted back to the disable input of counter and decoder circuit 36 along with output lead 32C from clock enable and reset logic circuit 32, and is connected to the enable input of the output driver circuit 40 along with output lead 32A from clock enable and reset logic circuit 32. A clock 38 is also provided which has an output lead 38A connected to a clock input of counter and decod~r circuit 36.
The output driver circuit 40 has respective outputs identi~ied as PARTY lj PARTY 2, PARTY 3, PARTY 4, PARrrY 5 and DISCONNECT w~ich comprise the PARTY CODE signal from automatic par~y identifier 20.
As illustrated in FIGURE 2, the disconnect timer 3~, the clock enable ; and reset logic circuit 32, the counter and decoder circuit 36, the clock 38j and the output driver circuit 40 are each provided with the potentials Ys and a reference ground potential ~which is isolated from earth gro~d).
Additionally, clock enable and reset logic circuit 32 is provided with a potential VcO which may be obtaine~ from the cen~ral office battery.
In each subscriber station CFIGURE ~, the conductor T in the por-; tion of line Ll going to that station is connected to one side of the tele-phone instrument 10 therein. The subscriber module 12 is placed in series 3L~726~7 circuit with the conductor R of linc Ll and a conductor R' going to the other side of the telephone instrument 10, with additional telephone instruments at that su~scriber station being connected in parallel with telephone instru-ment 10. In subscriber module 12, the conductor R is connec~ed to a first terminal of a constant current source 50, with a second terminal of the constant current source 50 being connected to the conductor R'. A diode Dl and a silicon controlled rectifier SCRl are connected in rev~rse-parallel configuration across the first and second terminals of source 50, with the gate elect~ode of silicon controlled rec~ifier SCRl being connected to à first output lead 52A from a timing circui~ 52 which has a second output lead 52B going to constant cuTrent source 50~ A 7ener diode ZDl couples the conductor R' to voltage source inputs of both ~he timing circuit 52 and the cQnstant current source 50 via leads 50A and 52D. The tim-~ng circuit 52 also has a reference lead 52C connected directly to conductor R' and has con-nected thereto a plurality of strap connections identified as PARTY 2, PARTY 3, PARTY 4 and PARTY 5.
Referring now back to FIGURE 2, the constant current and voltage source 30, which is described in more de~ail hereinafter with reference to FIGURE 5, applies A voltag~ with the polarity indicated in FIGURE 2 to the conductors TR of line L5 ~and accordingly, line Ll) when relay Kl is energized and contacts KlA, KlB thereof are closed. Preferably, this voltage is opposite in polarity to that normally applied by the central office bat-tery. The source 30 also functions to regulate the loop current in line L5 ~and accordinglyl the loop current in line Ll) at a first, predetermined value, e.g.~ 30 milliamps ~ma). However, in response to a signal on lead 36B, source 30 functions to apply a constant voltage across thP conductors TR of line L5 with the polarity indicated in FIGURE 2 and with a voltage value which is `l equal to that required to produce the fi~st, ~redetermined value of loop ~ ' . : - , . -, : . . . : .

.

3L~7Z~97 curren~ at the time the signal on lead 36B is supplied thereto. Finally,source 30 also supplies a signal on lead 30A which is related to the magnitude of the loop current in line LS .
The clock enable and reset logic circuit 32, which is also des-cribed in more detail hereinafter with respect to FIGURE 5, functions as ~ol-lows. In response to ~he reception of a START GROUND signal from register sender l8, circuit 32 provides an output signal on lead 32C to reset the counters within counter and decoder circuit 36. As indicated in FIGURE 2, circuit 32 includes a current level de~ector 32' which is responsive to the signal on lead 30A to detect when the loop current exceeds predetermined thres-hold values thereof. After the reception of a START GROUND signal, and when the value of the loop current in line L5 has risen to a first minimum thres-hold value, e.g. J 13 ma, as detected by the current level detector 32', cir-cuit 32 removes the o~tput signal on line 32C, thereby enabling counter and decoder circuit 36. The minimum threshold value is smaller than the first predetermined value of loop current and represents a condition signiy-ing that the line 1,5 is not "dead", i.e., the sQUrce 30 has been connected th~eko and is operative. Finally, upon the reception of a signal on line 36A from counter and decoder circuit 36, and when the level of the loop current in line L5, represented by the sig~al on lead 30A, has risen to a level greater than a second threshold value, e.g., 25 ma, as detected by current level detector 32', circuit 32 provides an ou~put signal on lead 32B
to disable t~e counter and decoder circuit 36, and an output signal on lead 32A to enable the output d~iver circuit 40.
The disconnect timer 34 may comprise a simple timer circuit which is enabled by the START GROUND signal from register sender 18 for a predeter- ;
mined time interval. During actuation of disconnect timer 34, relay Kl is energized. At ~he end of this predetermined timer interval, relay Kl is de-.
~ . . . . , , , , . . . - .
' . . . ~ ! . , 269~

energized and an outpu~ signal is provided on lead 34A. As an cxample, the predetermined interval may be 800 milliseconds ~ms).
The clock 38 may comprise a conventional clock source providing a series of clock pulses on lead 38A at a predetermined frequency~ e.g., lKHz.
The co~nter and decoder circuit 36 may comprise conventional counter c:ircuits and a decoding output ~logic which function as follows. In response to an output s~gnal on lead 32C, the counters within circuit 36, are reset.
Upon removal of the signal o~ lead 32C, the counters within circuit 36 begin to count the clock pulses on lead 38A from clock 38. Thereafter, output signals are successively provided on leads 36B, 36A and 36C1-36C6 in the following manner and at the times illustrated in FIGURE 4. At time Tl, a momentary output signal is provided on lead 36B. At time T3, an output signal is providèd on lead 36A and an output signal is provided on lead 36Cl. At time T4, an output signal is provided on lead 36C2 and the output signal is removed from lead 36Cl. At time T6, an output signal is provided on lead 36C3 and the output signal is removed from lead 36C2. At time T8, an output signal is provided on lead 36C4 and the output signal is removed from lead 36C3. At time T~0, an output signal is provi.ded on lead 36C5 and ~he output signal is removed from lead 36C4. At time T12, an output signal is provided on 36C6 and the output signal is removed from lead 36C5.
~inally~ the provision of a signal to the disable input of circuit 36 on either lead 32A or lead 36C6 inhibits the counters therein from being stepped by the clock pulses on lead 38A so that the output signal being provided on the leads 36Cl-36C6 is retained.
The output driver circuit 40 may ccmprise a plurality of conventional gates and driver circuits which function as follows. In resp~nse to ~he con-~urrence o output signals on leads 36Cl, 36C2, 36C3, 36C4~ or 36C5 from counter and decoder circuit 36, and, an output signal on lead 32A from clock .

, - : : .

~7~6~

enable and reset logic circuit 32~ the output driver circuit 40 provid~s respectively, the PARTY 1, PARTY 2, PARTY 3, PARTY A, or PARTY 5 output signals.In response to an output signal on lead 36C6 from counter and decoder circuit 36, output driver circuit 40 provide the DISCONNECT output signal.
In each subscriber module 12 ~FIGURE 3~ the constant current source 50 may comprise a conventional constant current source for regulating the loop current in line Ll `~or, that in conductors R and R' connected to source 50) at the second predetermined value and at a third predet~mined value.
Normally, the third predetermined value ~e.g., 40 ma) is grea~er than the first predetermined current value established by constant current and voltage source 30, and the second predetermined value ~e.g., 18 ma) is less than the second threshold value sensed by clock enable and reset logic circuit 32.
~; Normally, source 50 functions to regulate the loop current at the third predetermined value, and unctions to regulate the loop current at the second predetermined value in response to a signal on lead 52B from timing circuit $2.
Timing circuit 52 may comprise a conventional monostablei multivibrator chain which functions to provide a plurality of successive output signals, as follows. In response to loop current in line Ll flowing as a result of the application of the constant current and voltage source 30 thereto, tim-2Q ing circuit 52 begins timing a~ time T0. Thereafter, timing circuit 52 pro-vides: an output signal on lead 52B at time T2; and an output signal on lead 52A at time T5, if the strap connection is for PAR~Y 2, at time T7 if the strap connection is or PARTY 3, at time T9 if the strap connection is for PARTY 4, and at time Tll if the strap connection is or PARTY 5.
1- As examples~ the follo~ing times from time T0 may be established:
Tl-40ms; T2-50ms;
T3~61ms; T4-66ms;
T5-73ms; T6-81ms;
.
-2~-~7~:6~7 T7-90ms; T~-99ms;
T9-lllms; T10-120ms;
T11-135ms; T12-150ms.
Assumi~ng now that a long-distance call has been initiated ~t one of the PARTY 1 - PARTY 5 stations interconnec~ed with line Ll, the provision of a START GROUND signal by register sender 18 actuates both disconnect timer 34 and the clock enable and reset logic circuit 32. The resul*ant energization of relay Kl causes the normally-open contacts KlA, KlB thereof to close, there-by coupling the constan~ currcnt and ~oltage source 30 to the conductors TR
of line L5 ~and accordingly, to line Ll~. Substantially simultaneously, clock enable and reset logic circuit 32 provides an output s~gnal on lead 32C to rese~ the counters within circuit 36. When the loop current in line L5 ~and line Ll) has risen to a level greater than the firstminimu~ threshold value established by clock enable and reset logic circuit 32, e.g., 13 ma, clock enable and reset logic circuit 32 removes the signal from lead 32C, thereby allowing the counters within 36 to be stepped by the clock pulses on lead 38A. This time is substantially coincident wi~h time T0 in FIGURE 4.
Thereafter, th~ loop current in line L5 ~and Ll) is regulated at the first predetermined value ~e.g., 30n~ma) for a time sufficient to allow all reactances associated with the lines interconnecting ~he calling station and the automatic par~y identifier 20 to become fully charged so that a reference set of signal conditions is therefore established on those lines for the later detection of a response from the calling station. As seen in FIGUI~ 4, the loop current starts at some arbitrary value at time T0 and eventually stabilizes at the first predetermined value at a time before time Tl.
Assuming now that the call has been initiated from the PAR~Y 1 sta-tion, which has no subscriber module l2 in circuit therewith~ an output signal ~O~Z~7 is provided at the automa~ic party identifier 20 by circuit ~ on lead 36B at ti~e Tl which causes the constan~ current and voltage source 30 to switch to its second state wherein it thereafter main~ains across the line L5 (and therefore across line Ll~ a constant voltage whose level is equal to that required to maintain the first, predetermined value of loop curr~nt at - the time of switc}ling. At this time, and thereafter, the loop current will remain at the first predetermined value ~.g., 30 ma) inasmuch as only the tele~hone instrument 10 is in circuit with the line Ll at the PARTY 1 station and inasmuch as the lines have been fully charged at time Tl.
lQ At time T3, circuit 36 provides an output signal on lead 36A which causes clock enable and reset logic circuit 32 to be~in monitoring for loop current greater than the second threshold value, e.g., 25 ma. Simultaneously an output signal is provided on lead 36Cl to output driver circuit 40. Since the loop current is at the first predetermined value, which is greater than the second threshold value, clock enable and reset logic circuit 32 provides an output signal on lead 32B to gate on output driver circuit 40 which there-by provides the PARTY 1 output signal therefrom. Since the output signal on lead 36Cl persists until timeT4~,,a"window" is established between times T3 and T4 for detecting loop curren~ in excess of the second threshold value, 2Q with the location of the window being unique to the PARTY 1 station.
Assuming now that the long-distance call has been placed from one of the PARTY 2 - PARTY 5 stations, the application of the reverse polarity voltage from the constant current and voltage source 30 to line L5 ~and to line Ll) at time T0 causes the diode Dl in that one of the subscriber modules 12 in circuit with the telephone instrument 10 that has gone off-hook to become reverse-biased and therefore non-conductive. Normally, diode Dl is conductivc with the application of normal polariky, central office battery ; and provides a low impedance shunt around the subscriber module 12 so that dial pulsing and voice transmission from the telephone instrument 10 are not ~ .

: : :: . : : .:::.: :. : . :: ,, :. . - . . ~ .: . - . ~ :
,: , . , - : .~',. . : : , :, :~ '' ' . .. ::'.' ' ' ~7Z~7 affected.
When diode Dl is not conductive~ however, the voltage therefore applied to the remainder of the subscriber module 12 causes timing circuit 52 to begin its ~iming function and constant current source 50 seeks to regulate the loop current in line Ll and thus L5 at the third predetermined value~Ce.g., 40 m~, with the voltage across the subscriber module 12 being substantially regulated at the voltage established by zener diode ZDl, which, for example, may be 6.2 volts. As has been previously described, the loop current at this time is being regulated a~ the first predetermined value by the constant current and voltage source 30 and thus the con~tant current source 50 is essentially a short circuit so that the subscriber module 12 appears to the line Ll as a low impedance, constant voltage load ~that provided by ~ener diode ZDl) to help establish the loop current at the first, predetermined value.
At time T2, or, after the time Tl at which the constant current and voltage source 30 is switched to its constant voltage mode, the timing circuit 52 provides an output on lead 52B so that the constant current source 50 switches to regulating the loop current at the second predetermined value, e.g., 18 ma. This second predetermined value must be chosen below the second 2~ threshold value of loop current established as a detection level for current level detector 32'. Preferablyj the second predetermined value must not be low enough to signify to the central ofice than an on-hook condition exists and that the calling station should be disconnected, but yet must be sufflciently below the second threshold value bo provide an acceptable signal-to-noise ratio for the response of the subscriber modulell2.
At time T3, the circuit 36 provides an output on lead 36Cl. Since the loop current is at this time being regulated at the second predetermined value, e.g., 18 maJ no output is provided by clock enable and reset logic , , :
; -27-~ :, . : - . . ,. . . : . -~726~7 circuit 32 on lead 32A and accordingly output driver circui~ 40 does not provide the PARTY 1 output. At time T4, circuit 36 provîdes an outpu* signal on lead 36C2 and removes the signal on lead 36Cl. If the calling station is strapped for PARTY 2 identificationl timing circuit 52 thereafter pro~ides an output signal on lead 52A at time T5~ thereby placing SCRI in a conductive state ~to provide a shunt across the remainder of the subscriber module 12 and, particularly, the constant current source 50. As a resultl the loop current begins to rise to the first predetermined value, e.g., 30 ma, due to ; the voltage established by constant current and voltage source 30. When the loop current exceeds the second threshold value~ e.g., 25 ma, clock enable and reset logic circuit 32 provides an output signal on lead 32A which, in conjunction with the still-existing output signal on lead 36C2, causes output driver circuit 40 to provide the PARTY 2 output signal. At time T6 circuit 36 provides an output signal on lead 36C3 and removes the output signal from lead 36C2.
It will therefore be appreciated that a window is established ; from times T4 to T6, for detection of a rise in loop current signifying that the calling party has a PARTY 2 station identification. As will also be appreciated by those skilled in the art, successive outputs on leads 36C3, 36C4, 36C5 and 36C6 respectively establish PARTY 3, PARTY 4 and PARTY 5 windows, during time T6-T8, T8-T10, and T10-T12, for detection of responses comprising a rise in loop current above the second predetermined value as a result of the operation of the timing circuit 52 in the subscriber module 12 associated with the station at which the call IS placed at times T7, T9 or Tll. Therefore, the PARTY 3 - PARTY 5 output signals from output driver cir-cuit 40 can also be provided.
At the same time ~hat the party identification is provided by Pn-abling the output driver circuit 40 with ~he signal on lead 32A, the signal on lead 32B disables the counters within counter and decoder circuit 36 .. , . .. .. . , ... ~ : .

~LCI 7269~7 ~rom being stepped by the clock pulses on lead 38A. l~ere~ore, the PARTY 1 - PA~TY 5 output signals are ~aintained until the removal of the START GROVND signal.
If the loop current does not at any time exceed the second threshold value after clock enable and reset ~logic circuit 32 removes its outpu~ signal from lead 32CI which could occur if the source 30 failed, if the subscriber module 12 in the calling station failed~ or if the telphone instrument 10 ~herein went to an on-hook condition as a result of the subscriber hanging up, then the output signal on lead 36C6 from circuit 3O at time T12 causes the output driver circuit 40 to provide the DISC~NNECT autput signal. Like-wise, if the loop current does not at any time exceed the first, minimum threshold value, e.g., 13 ma, established by clock enable and reset logic circuit 32, then the output signal on lead 34A from the disconnect timer 34 at the end of its predeter~ined time interval also serves as a DIS-CONNECT output signal. In responsel regis~er sender 18 returns the line splitting circuit 16 to its normal condi~ion by opening contacts 16B and 16C
and closing con~acts 16A, whereupon the disconnected status of the ~tations can be sensed by the central office to open the line circuit 14, or, if such disconnect status does not exist, to provids an alarm indication o~
- subscriber module failure.
Upon provision of any of the PARTY 1 - PARTY 5 or DISCONNECT output signals to the regis~er sender 18J the register sender 18 renloVes the START
GROUND signal from the automatic party identifier 20. In response thereto, the disconnect timer 34 is deactuatedJ thereby deenergi~ing relay Kl to open the contacts KlAJ KIB thereto *o disconnect the automatic party identifier 20 from the line L5.
It will be appreciated by those skilled in the art that a subscriber module 12 can also be placed in circuit with the telephone instrument 10 at .
.. , . .. . . , . . ~ .. . :
--: : :. : : : :................ :

~7Z697 the PARTY 1 station to provide a posi~ive indica~ion of PARTY 1 statusJ and that parties additional to PARTY 5 can also be identified by providing success-ive ~windows~ for the responses of the subscriber modules therein.
The choice of the first, sècond and third predetermined values of loop current, and the first and second thr~shold values thereof, is governed by ~any factors, of which the following are important. A first design consideration is that the system u~ilize a set of signal conditions unique to that sys~em so that known central office equipment will not respond to that set of signal conditions in any manner. A second design consideration is that the system have a signal-to-noise ratio in the set of signal conditions that is as high as possible to pe~mit reliable detection of calling parties As can be appreciated by those skilled in the art, the interrogat-; ion in the system is achieved by establishing the first predetermined value of loop current, and a response is achiev0d by thereafter limiting the loop - current to the lower, second predetermined value thereof and allowing the loop current to return to the first predetermined value at a predetermined time unique to the calling station.
Therefore, the signal-to-noise ratio can be increased by increas-ing the difference between the first and second predetermined values of 2Q loop current. For example, the second predeter~ined value of loop current could be lowered from the 18 ma ~alue previously discussed to zero. In such :
a case, a loop current sensing relay monitoring the line at the central of-fice would release when the called par~y answered ~he telephone call, which release would erroneously indicate that the calling party has placed its tele-phone instrument on-hook. The release of the loop current sensing relay will in many central offices cause the line relay to disconnect, thereby ~:
terminating the connection of the calling party to the called party even though in fact the calling party has not gone on-hook.
,:

:
,~ . . . . .. . .

.: . , :, - : : :, . . . .. :. ..
- ~ , . . . , :

1al7Z6~7 At the present time, loop curren~ sensing relays commonly used in central offices have a minimum or drop out current of approxi~ately 11 ma.
As a practical matter, many of these loop current sensing relays are out of adjustment and therefore may release for loop currents up to 16 ma. According-ly, 18 ma was chosen as the second predetermined value so as to be sufficient-ly above 16 ma to account for normal circuit tolerances and to insure that the worst case loop current sensing relays will not release. It should also ~e apparent that current regulation at the second predeter~ined value~ such as provided by the constant current source 50, is desirable to insure that ~ the current remains at that value rather than possibly dropping to a value which would release a loop current sensing relay.
As another exam~le, the first predetermined value of loop current could be significantly raised above the 30 ma value previously described.
However, for very long lines, including those with loop extenders, diode bridges, and the likel the impedance of the line may be such that the voltage applied to the line by the automatic party iden~ifier 20 (by the source 30) must be in excess of lOO VDC to achieve a loop current of 30 ma. Therefore, substantially higher voltages would be re~uired to achieve even higher loop currents, which higher voltages would not be compatible with those typically available and used in central offices.
It will also be appreciated by those skilled in the art that current regulation at the first predetermined value is desirable. If cur-rent regulation were not so provided, the application to the line of a vol-tage having a magnitude necessary to produce an acceptable loop current value on very long lines, e.g. 30 ma, would result in substantially higher currents being encountered upon the application of such a voltage to short lines.
It also should be noted that the constant current source S~ in each subscriber module 12 is normally inoperative, inasmuch as it seeks to regulate the loop current at the third predetermined value, e,-g., 40 ma, which ,. , .,...., . : .. ~ ,. . ..
, , . . . . . . . . :. . , ,' . ::

.

, ~L~7Z697 is higher than the first pr~dctcrmincd value established during that time by the constant current and voltage source 30 in thc automatic party identifier 20. However, during the initial period from time TO to time Tl during which the loop current is settl~ng to th~ first pred~termined value, exeessive loop currents may occur at the subscriber module 12 which should be limited to avoid any problems resulting there~rom.
As prsviously discussed, the first, minimum threshold value of loop current detected by current level detector 32' is simply chosen to reflect the fact that the constant current and voltage source 30 has applied a voltage to the line.
The second threshold value detected by current level detector 321 ideally should b~ just below the first predetermined value of loop current to achieve a high signal-to-noise ratio. Because of normal circuit to~crances which may result in the loop current actually being regulated~at some value below the first predetermined value during times TO-T2, the second threshold value was chosen to be 2S ma.
The specific times Tl, T2J etc. previously described are also arrived at to achieve reliable party identification for all lines with which the present invention may be utilized while yet achieving that identification in as~short a time as possible. If the times are significantly extended beyond those previously stated, the s~bscriber migh~ notice and object to the timer interval that i~ took for his long distance call to be placed inasmuch as the actual voice transmission on the ~all cannot start until the automatic party identiier 20 provides the PARTY CODE signal to register sender 18 which t~ereafter releases the line splitting circuit 16. & the other hand, the times cannot be sign~ficantly reduced since telephone lines are highly reactive and therefore a certain amount of time is necess~ary to establish the initial set of signal conditions on the line, e.g., the first , , , . . . . , . ~ ~; , . . . .
.. ..
: -. . - .. . :

.. ' ~CI1726~7 predetermined value o~ loop current, so that a responsc back from the sub-scriber module 12 is precise bo~h in value and in time, espc~ially for tele-phone lines of medium to long length. However, it is presently anticipated that the times previousl~r stated could be cut in half and still achieve acceptable results ~.r most telephone lines.
As previously discussed, and as discussed in more detail hereinafter with respect to the specific circuitry illustrated in FIGURE 5, the constant cuxrent and voltage source 30 applies a vol~age to the line which is isolated from earth ground. If the constant and current voltage source 30 were not so isolated, the current level de~ector 32' would be ~uscep~ible to ~ longitudinal currents in the conductors TR.of line L5. Typically, longitudinal : currents are those induced from adjacent power conductors and are picked up in phase in both.the conductors TR. Loop.current, on the other hand, is ~ out of phase on the conductors TR. Accordingly, the current level detector 32', in the case where a non-isolated supply were used, would have to include circuitry for differentiating between out of phase signals ~loop currents) and in-phase signals (longitudinal currents), with a consequent increase in the complexity and criticality of its circuitry. .:
It should.also be noted that the constant current and voltage source 30,.at time Tl, switches to regulating the voltage across the line so as to allow the subscriber module.l2.to thereafter regulate loop current but to maintain.on the line a set of signal conditions that permits the ~oop current to return to.the first predetermined value at ~he time ~TS, T7.~
T9, or Tll) that the subscrlber module 12 terminates its current regulation to signify a response to the interrogation.
Finally, the low.impedance of the subscriber module 12 during times T0-Tl is desirable to allow fast charging ~ the line by the constant current : and voltage source.30 so that the first predetermined value of loop current may . - ~ : ~ . : , . . .

. .
~ . , -. ., . - : - .~ : . : . , Z~97 be achieve~ as 500n as possiblc. As previously desGribed, this low impedance is afforded by the fact that substantially only the zener diode ZDI is in circuit with the line during the times T0-Tl, except for the instance where the loop current goes above the third predetermined value established by constant current source 50. The impedance of the subscriber module 12 afforded by zener diode ZDl is also low enough to avoid significant reductions in ringing signals applied to the line when ~he subscriber station in which the subscriber module 12 is located is being called ~inasmuch as ringing signals are AC and accordingly half cycles ~hereof will pass through zener diode ZDI and constant current source 50, with the other half-cycles passing through diode Dl).
From this discussion, those skilled in the art will acordingly .
recognize that the me~hod of the.present.invention, in its simplest form, may be practiced by applying at the central office a voltage to the telephone line which has a magnitude sufficient to establish the first pre-détermined value of loop current which of course is greater than the value of .
loop current signifying an on-hook condition on the telephone line, and by causing the loop current to cha~ge from this firs~ predetermin0d value in a manner unique to the calling party station. Although the change preferably is time-related~ and in fact may comprise a single "pulse" in which loop current is limited to the second predetermined valu0 for a time unique to the calling party station, the change may also comprise a sense of pulses which are asynchronously caused to occur and which contain within information suffi- i~
cient to identify the calling party station.
In all cases, the central office provides party identification by comparing the loop current change that occurs ~or, the absence of any loop current change) with a.plurality of stored loop current changes each uni~ue-to one party station~

. . , - ; . .

. .

~72~

Referring now ~o the specific embodiment in FIGURE 5, a connection is made from the conductor R of line L5 through normally-open contacts KlB, capacitor Cl, a resistor R2, and normally-open contacts KlA to the conductor T thereof. Potential VB is connected to the common junction of contact KlB and capacitor Cl, with the conductor T being referenced to an isolated ground potential through the circuitry illus*rated by connections to the common junction of capacitor Cl and resistor R2. The common junction of capacitor Cl and resistor R2 is connected to a curren~ and voltage regulating circui~ comprising the collector-to-emitter paths of a pair of Darlington-connected transistors Tl, T2 and parallel-connected resistor R14 and cap-acitor C3 which are in turn connected to isolated ground potential. The common junction of capacitor Cl and resistor R2 is also connected to a volt-age sensing circuit comprising resistors Rl9 and R20 which are connected in series to isolated ground potential.
The common junction of resistors Rl9 and R20 has appearing thereon a signal proportional to line voltage and is connected through a resistor R23 to the input of a normally-open gate circuit Gl and through a resistor R22 to the inverting input of an operational amplifier A4. A signal output of gate circuit Gl is connected to the,non-inverting input of operational amplifier A4 and through a capacitor C4 to isolated ground potential. The lead 36B from the counter and decoder circuit 36 is connected to the gating signal input of gate circuit Gl.
Operational amplifier A4 is connected as a comparator~ with a resistor R26 providing positive feedback between the output and inverting input thereof. The output of operational amplifier A4 is connected via a diode D5 to the common junction of a diode D3 and a resistor R10, and via a diode D6 to the inverting input of an opèrational amplifier A2, with resistor R18 being connected from the inverting input of operational ampliier A2 to .

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~(~'7Z6~'7 isola~ed ground potential. A resistor R13 connects the common junction of I diode D3 and resistor R10 to lsolated ground potential.
The non-inverting input of ope~ational amplifier A2 is supplied with a signal from the common junction of resistors R4 and R5 connected in series between the supply potential Vs and isolated ground potential, with the signal thereby being provided to the non-inverting input being repres~nt-ative of the first, minimum threshold value at which it is desired to start the operation of the ~u~omatic party identifier 20, e.g., 13 ma. The out-put of operational amplifier A2 is connected via a resistor Rll to the common junction of series-connected resistors R16, and R17, with resistor R16 being connected through a resistor R15 to the supply potential Vs and with resistor R17 being connected to isolated ground potential.
The potential VCO (which may be obtained from the central office battery~ is coùpled through a light emitting diode LED forming a first part of an optical isolat~r and a resistor Rl to the terminal upon which the START GROUND signal from the register sender 18 app~ars. A photo-transistor PT forming a second part of the optical isolator has its collector-to-emitter path connected from the common junction of resistors R15 and R16 to isolated ground potential. A common junction of resistors R16 and R17 is connected to the base o a transistor T3 whose emitter is connected to ground potential and whose collec~or is connected through a resistor R21 to the base of a transistor T4 and through series-connected diode D4 and resistor R24 to the common junction of capacitor C4 and the non-inverting input of operational amplifier A4. The supply potential Vs is connected to the base of transistor T4 through a resistor R25 and directly to the emitter of transistor T4. The collector of transistor T4 is connected to the output lead 32C going to the counter and decoder cirCU~t 36, with a resistor R27 coupling lead 32C to isolated ground potential.

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The common junction of capacitor C3, resistor R14, and the emitter of the Darlington-connected transistor pair Tl, T2) has appearing thereon a signal proportional to the loop current and is connected through series-connected diode D3 and resistor R10 ~o the inverting input of an operational amplifier A3. Parallel-connected capaci~or C2 and resistor R9 providc nega-tive feedback from the output of operational amplifier A3 to the inverting input thereof~ with the ou~put of operational amplifier A3 being coupled through a resis~or R12 to the base of the Darlington-connected transistor pair Tl, T2. The non-inverting input o~ operational amplifier A3 is connected to the common junction of series-connected resistors R7 and R9, with the resistor R7 being connected to the supply potential Vs and ~` resistor R8 being connected to isolated ground potential. Resistor R7 is adjustable to set the first predetGrmined value of loop current, e.g., 30 ma.
The inverting input of operational amplifier Al is connected to the common junction of resistors R3 and R6, with resistor R3 being connected ~o the supply potential Vs and resistor R6 being connect~d to isolated ground potential. Resistor R3 is adjustable to set the s~cond threshold value detected by current level detector 32', e.g., 25 ma. The output lead 36A
from the counter and decoder circuit 36 is also connected to the inverting input of operational amplifier Al. The output of operational amplifier Al has connected thereto the output lead 32B going to the counter and decoder circuit 36,~ and the ou~put lead 32A going to the output driver circuit 40.
In operati~n, the provision o~ the START GROUND signal by the register sender 18 at time T0 causes energization of relay Kl in disconnect timer 34, thereby closing contacts KlA and KlB9 and accordingly applying the potential VB to the line L5. Simultaneously, the START GRO~ND signal completes a circuit from VCO through the ligh~ emitting diode LED of the optical iso-lator, thereby turning on the phototransistor PT thereof to shunt resistors R16 .

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~L~t7;~ 37 and R17 to isolated ground potential. At this time, however, transistor T3 is maintained on by a signal supplied from operational amplifier A2 through resistor Rll, thereby providing a shunt discharge path to isolated ground potential through resistor R24 and diode D4 for any charge remaining on capacitor C4. When transistor T3 is on, ~ransistor T4 is also on which accordingly applies the supply potential Vs across resistor R27, thereby providing a signal ~n lead 32C to counter and decoder circuit 36 to reset the counters therein.
Upon application of the potential VB to line L5, loop current flows in line L5 and the magnitude thereof is represented by the loop current signal appearing at the common junction of the capaci~or C3, resistor Rl~, and the emitter of Darlington-connected transistor pair 11, T2. When the loop current signal, as coupled to the inverting input of operational amplifier A2, through diode D2, exceeds the first, minimum threshold value appearing at the common junction of the resistors R~ and R5 and coupled to the non-inverting input of operational amplifier A2, amplifier A2 ramoves its signal from transistor T3 to turn off transistor T3 and accordingly turn off transistor T4. When transistor T4 turns off, the reset signal provided thereby on lead 32C is removed, thereby allowing the counters within co~nters and decoder circuit 36 to begin counting the clock pulses from clock 38.
The loop current signal also flows through diode D3 and resistor R13 to develop a-signal proportional thereto which is applied through resistor R10 to the inverting input of operational ampliier A3. The regulation of loop current at the first predetermined value, e.g. 30 ma, is then achieved by operational amplifier A3 controlling the conduction of the Darlington-connected transistor pair Tl, T2 by comparing the actual loop current value with the ~irst predetermined value established at the common junction of re-sistors R7 and R8 and coupled to the non-inverting input of operational amplifier A3.

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~C~7Z697 At time Tl J cou~t~r and d~coder circuit 36 provid~s the mome~tary output signal on lead 36B which closes gate Gl for the duration thereof. The voltage signal appearing at the common junction of resistors Rl9 and R20 is then coupled through resistor R23 and gate Gl to charge capacitor C4 to a voltage representative of the voltage across line L5 at the time Tl, which of course is that voltage requir~d to produce the first predetermined value of loop current therein. Since transistor T3 is tu~ned of~, capacitor C4 cannot discharge and thereater stores therein this voltage value. When the momentary output signal on lead 36B is.~removed, gate Gl is again lQ opened and operational amplifier A4 thereafter compares the ac~ual voltage on line Ll, as represented by the signal coupled to its inverting input .
through resistor R22, with the stored voltage value contained in capcitor C4 and provides an outpu~ signal which is coupled through diode D5 to develop a control signal across resistor R13. The control signal across resistor R13 reverse-biases diode D3 so that the loop current signal appear-ing at the common junction of capacitor C3, resistor R14 and khe emitter of the Darlington-.connected transistor pair Tl, T2 can no.longer be provided to operational amplifier A3. The control signal is coupled through resistor R10 to the inverting input of operational amplifier A3 which functions to 20- control the conduction of the Darlingtion-connected transistor pair Tl, T2.
Since the sin~ai applied to the non-inverting.input of operational ampliier A3 from the common junction of resistors R7 and R8 is constant, it will be appreciated that the Darlington-connected transistor paIr Tl, T2 is thereafter controlled to maintain the voltage in the line ~1 at the value storet in capacitor C4. The output signal from operational amplifier A4 ~. .
also is coupled through dlode~D6 to the inverting input of operational amplifier A2 to maintnin the non-conduction of transistors T3 and T4.
At time T2, the timing circuit 52B provides an output signal on lead '..
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3~7;~6~7 52B to cause the cons~ant current source S~ to regulate the loop current at the second predetermined value, e.g.~ 18 ma.
At ~ime T3> the coun~er and decoder circuit 36 provides an out-put signal on lead 36A which thereafter permits the signal present at the common junction ~f resistors R3 and R6, and coupled to the in~erting input o operational amplifier Al, to be representative of the second threshold value, e.g.g 25 ma. When the loop current signal coupled to the inverting input of operational amplifier Al rises to a value equal to or greater than the second threshold value, operational amplifier Al provides an ou~put signal which is coupled through lead 32B ~o inhibit the counters within counter and decoder circuit 36 and which is coupled through lead 32A to enable one of the drivers within output driver circuit 40. As previously discussed, the time at which operational amplifier Al provides its output signal is indicative of the party identification of the party making the long~distance telephone call.
When the START GROUND signal is removed by register sender 18 the phototransistor PT becomes non-conductive to remove the shunt across resistors R16 and R17, thereby turning on transistors T3 and T4 ~since the loop current has dropped below the first threshold value due to opening of ¢~ntacts KlA, KlB).
While the invention has been described with respect to a preferred embodiment, it is to be clearly understood ,by those skilled in the art that the invention is not limited thereto, but rather is intended to be interpreted only in accordance with the following claims.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A subscriber module useful in conjunction with and forming part of an apparatus for detecting which party on a multiparty telephone line has placed a call thereon, said subscriber module including: a) first and second terminals adapted to be connected in series circuit with the telephone line; b) first means connected between said first and second terminals for shunting current therebetween in a first predetermined direction of said current; c) second means connected between said first and second terminals for controlling current therebetween in a second direction of said current which is opposite to said first direction, said second means including: i) timing means responsive to the detection of current in said second direction for providing a plurality of successive timing signals, ii) current regulat-ing means for regulating the magnitude of said current in said second direction at a predetermined value which is greater than the magnitude of said current that would signify an on-hook condition on the telephone line, said current regulating means initiating said current regulation in response to a first one of said plurality of timing signals and terminating said current regulation in response to a second, subsequent one of said plurality of timing signals, and iii) means selectively shunting current between said first and said second terminals in said second direction in response to said second one of said plurality of timing signals.

2. A subscriber module as recited in claim 1, wherein said first one of said plurality of timing signals is provided at a predetermined time after detection of said current in said second direction.

3. A subscriber module as recited in claim 1, wherein said timing means includes means for selecting the time at which said timing means provides said second one of said plurality of timing signals.

4. A subscriber module as recited in claim 1, wherein said first means comprises a diode, wherein said means selectively shunting current in said second direction comprises a controllable semiconductor device having first and second current-conducting terminals respectively connected to said first and second terminals, and also having a gating terminal having said second one of said plurality of timing signals applied thereto, and further comprising a zener diode in series circuit with said current regulat-ing means across said first and said second terminals, and means coupling a common junction of said zener diode and said current regulating means to said timing means to provide a signal, upon the flow of current in said second direction, to said timing means to initiate the operation thereof.

5. A subscriber module useful in conjunction with and forming part of an apparatus for detecting which party on a multiparty telephone line has placed a call thereon, said subscriber module including: a) first and second terminals adapted to be connected in series circuit with the telephone line; and b) means connected between said first and second terminals for controlling current therebetween in a a predetermined direction of said cur-rent, said means including: i) timing means responsive to the detection of current in said predetermined direction for providing a plurality of successive timing signals, ii) current regulating means for regulating the magnitude of said current in said predetermined direction at a predetermined value which is greater than the magnitude of said current that would signify an on-hook condition on the telephone line, said current regulating means initiating said current regulating in response to a first one of said plur-ality of timing signals and terminating said current regulation in response to a second, subsequent one of said plurality of timing signals, and iii) means selectively shunting current between said first and said second ter-minals in said predetermined direction in response to said second one of said plurality of timing signals.

6. A subscriber module as recited in claim 5, wherein said first one of said plurality of timing signals is provided at a predetermined time after detection of said current is said predetermined direction.

7. A subscriber module as recited in claim 5, wherein said timing means includes means for selecting the time at which said timing means pro-vides said second one of said plurality of timing signals.

8. A subscriber module as recited in claim 5, wherein said means selectively shunting current in said predetermined direction comprises a controllable semiconductor device having first and second current-conducting terminals respectively connected to said first and second terminals, and also having a gating terminal having applied thereto said second one of said plurality of timing signals, and further comprising a zener diode in series circuit with said current regulating means across said first and said second terminals, and means coupling a common junction of said zener diode and said current regulating means to said timing means to provide a signal, upon the flow of current in said predetermined direction, to said timing means to initiate the operation thereof.