METHOD AND APPARATUS FOR AUTOMATICALLY IDENTIFYING AN INDIVIDUAL CALLING PARTY ON A MULTIPARTY TELEPHONE LINE

METHODE ET DISPOSITIF D'IDENTIFICATION AUTOMATIQUE DU DEMANDEUR SUR UNE LIGNE TELEPHONIQUE PARTAGEE

English 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.

Claims

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


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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)


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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.


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Description

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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




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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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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

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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




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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

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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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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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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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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




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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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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-

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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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~ 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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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
. - ~ .
14
~.




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

~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


.
-15-=

:. :



- . ~

.: . . -

~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, ~ -




-16-

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


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

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

~ 7~69~

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
'~
-17-


- . : , . , :

.


., ,:
.
-


~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
,
-18-


.
........

~: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

-19
:




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

~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




-20-

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-



-22-

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~ . . . . , , , , . . . - .
' . . . ~ ! . ,

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

.
-23-



, - : : .

~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

-25 -

~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
~ .
-2S-




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

~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

-28-




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

~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




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~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.
,:
-30-

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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


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~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




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~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

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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~

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~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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~L~7Z~9~

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.

-38-

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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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