U.S. patent application number 09/966488 was filed with the patent office on 2002-02-21 for method and apparatus for detecting and locating a fault in a telecommunications environment.
This patent application is currently assigned to Turnstone Systems, Inc.. Invention is credited to Chea, Ramon C.W. JR..
Application Number | 20020021787 09/966488 |
Document ID | / |
Family ID | 23891014 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020021787 |
Kind Code |
A1 |
Chea, Ramon C.W. JR. |
February 21, 2002 |
Method and apparatus for detecting and locating a fault in a
telecommunications environment
Abstract
The invention presented herein is directed to a remotely
addressable maintenance unit (RAMU) working in conjunction with a
test head at the central office for detecting and locating faults
in digital subscriber loop (DSL) and/or plain old telephone system
(POTS) environments. The RAMU includes circuitry for setting and
resetting one or more relays for either normal or
testing/maintenance mode. The present invention provides a system
and method for addressing the RAMU by applying either positive or
negative voltages from the tip to ground, from ring to ground, and
from tip and ring to ground. In this manner, individual RAMUs can
be defined/designed to respond in certain voltage levels and
polarities. Accurate fault detection and sectionalization is
achieved by the combination of the addressing capabilities
enumerated herein, and the impedance signature designed into the
RAMU, working in concert with a test head in the central
office.
Inventors: |
Chea, Ramon C.W. JR.; (San
Jose, CA) |
Correspondence
Address: |
Pillsbury Winthrop LLP
Intellectual Property Group
1600 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Turnstone Systems, Inc.
|
Family ID: |
23891014 |
Appl. No.: |
09/966488 |
Filed: |
September 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09966488 |
Sep 27, 2001 |
|
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09476226 |
Dec 30, 1999 |
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Current U.S.
Class: |
379/29.01 ;
379/1.01; 379/18; 379/22.02; 379/29.03 |
Current CPC
Class: |
H04M 3/2209 20130101;
H04M 3/301 20130101 |
Class at
Publication: |
379/29.01 ;
379/1.01; 379/18; 379/22.02; 379/29.03 |
International
Class: |
H04M 001/24; H04M
003/08; H04M 003/22 |
Claims
I claim:
1. A method of addressing a remotely addressable maintenance unit
(RAMU), the method comprising the steps of: (1) applying a voltage
to a tip, ring, or tip and ring with respect to a ground; (2)
detecting a polarity of a signal and the voltage at the tip, ring,
or tip and ring with respect to the ground; (3) selecting a
polarity of a reference voltage based on the polarity of the
signal; (4) comparing the voltage at the tip, ring, or tip and ring
with the reference voltage having the selected polarity from step
(3); and (5) addressing the RAMU to a reset mode or a set mode
based on the voltages at the tip, ring, or tip and ring, and the
reference voltage.
2. A method according to claim 1, wherein the reset mode comprises
a normal mode and the set mode comprises a testing or maintenance
mode.
3. A method according to claim 1, wherein the addressing step
comprises the step of addressing the RAMU when the voltage at the
tip, ring, or tip and ring is greater than the reference
voltage.
4. A method according to claim 3, wherein the reset mode is
actuated when the polarity at the tip, ring, or tip and ring
includes a negative polarity.
5. A method according to claim 3, wherein the set mode is actuated
when the polarity at the tip, ring, or tip and ring includes a
positive polarity.
6. A method according to claim 1, wherein the addressing step
further comprises the step of actuating a relay.
7. A method according to claim 6, wherein the relay comprises one
of a latching or solid state relay.
8. A method according to claim 1, wherein the reference voltage is
adjustable.
9. A remotely addressable maintenance unit (RAMU) for detecting a
fault on a copper loop having a tip and a ring, comprising: means
for detecting a polarity of a signal and a voltage at the tip, the
ring, or the ring and tip with respect to a ground; means for
selecting a polarity of a reference voltage based on the polarity
of the signal; means for comparing the voltage at the tip, ring, or
tip and ring with the reference voltage; and means for addressing
the RAMU to a reset mode or a set mode based on the voltages at the
tip, ring, or tip and ring, and the reference voltage.
10. A RAMU according to claim 9, wherein the detecting means
comprises a signal detector.
11. A RAMU according to claim 10, wherein the signal detector
comprises a plurality of diodes and transistors.
12. A RAMU according to claim 9, wherein the reference voltage is
determined from voltages associated with a plurality of zener
diodes.
13. A RAMU according to claim 9, wherein the comparing means
comprises a level comparator.
14. A RAMU according to claim 13, wherein the level comparator
compares the reference voltage with voltages associated with a
plurality of zener diodes.
15. A RAMU according to claim 9, wherein the addressing means
comprises a relay.
16. A RAMU according to claim 15, wherein the relay comprises one
of a latching or solid state relay.
17. A RAMU according to claim 15, wherein the relay addresses when
the voltage at the tip, ring, or tip and ring is greater than the
reference voltage.
18. A RAMU according to claim 9, wherein the reset mode is actuated
when the polarity at the tip, ring, or tip and ring includes a
negative polarity.
19. A RAMU according to claim 9, wherein the set mode is actuated
when the polarity at the tip, ring, or tip and ring includes a
positive polarity.
20. A RAMU according to claim 9, wherein the reset mode comprises a
normal mode and the set mode comprises a testing or maintenance
mode.
21. A method of addressing a maintenance unit from a plurality of
maintenance units that are placed at a plurality of locations on a
copper loop, the method comprising the steps of: applying a
particular voltage having a positive or negative polarity to a tip,
ring, or tip and ring, with respect to a ground; comparing the
applied voltage to a plurality of reference voltages, wherein each
maintenance unit includes one reference voltage; and addressing a
particular maintenance unit where the corresponding applied voltage
to the particular maintenance unit is larger than the reference
voltage for the particular maintenance unit.
22. A method according to claim 21, wherein the applying step
comprises applying a voltage from a central office.
23. A method according to claim 21, wherein the addressing step
comprises addressing the maintenance unit to a reset mode or a set
mode.
24. A method according to claim 21, wherein the reset mode
comprises a normal mode and the set mode comprises a testing or
maintenance mode.
25. A method according to claim 21, wherein the reset mode is
actuated when the polarity at the tip, ring, or tip and ring
includes a negative polarity.
26. A method according to claim 21, wherein the set mode is
actuated when the polarity at the tip, ring, or tip and ring
includes a positive polarity.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a maintenance unit, and
more particularly, to a remotely addressable maintenance unit
(RAMU) for detecting and locating faults in digital subscriber loop
(DSL) and/or plain old telephone system (POTS) environments. The
RAMU of the present invention includes circuitry for setting and
resetting one or more relays for either normal or
testing/maintenance mode.
BACKGROUND OF THE INVENTION
[0002] Recently, there have been dramatic changes in the
telecommunications industry. For example, the Telecom Act of 1996
deregulated the local markets, which, in part, brought on the
emergence of new technologies to this industry. These changes are
also sparked by the growing demand for Internet access and for new
technologies that deliver higher speed connections over existing
infrastructure.
[0003] As is well known in the industry, Digital Subscriber Loop,
or DSL, is one of the most promising new technologies for
delivering superior service and higher speed connections over
existing infrastructure. In general, DSL uses the existing copper
loop that is used for conventional telephony, but delivers much
higher bandwidth. However, to achieve such high data rates, DSL
operates at a higher frequency and is thus more sensitive to the
length and quality of the copper loop. As a result, more
sophisticated levels of testing, monitoring, and maintenance are
required for successful DSL deployment.
[0004] Currently, the transmission rates for DSL technologies are
very much dependant on the distance between a telephone company and
a customer. Moreover, depending on the type of DSL technology, the
transmission rate downstream to the customer and upstream to a
telephone company may vary. For example, for asymmetric DSL, the
transmission rate is faster downstream to the customer than
upstream to the telephone company. Asymmetric DSL is well suited
for Internet usage and video on demand. For symmetric DSL, the
transmission rate is about the same for both downstream and
upstream.
[0005] DSL uses packet switching technology that operates
independently of voice telephone system, allowing telephone
companies to provide the service and not lock up circuits for long
distance calls. In addition, DSL can carry both voice and data
signals simultaneously, in both directions, allowing the customer
to log onto the Internet and make a telephone call at the same
time.
[0006] One major issue for those in this industry is the testing
and maintenance of such systems. Currently, there exists a
two-terminal testing device that is applied in the POTS (plane old
telephone system) environment, which, in general, has been
unsuccessful in the DSL environment.
[0007] FIG. 1 illustrates a simplified diagram of a POTS
environment having a conventional maintenance test unit (MTU). In
the conventional POTS environment, a central office (CO) 2 is
connected to a customer's telephone 8 using a pair of copper wires
4. The CO 2 includes a testing instrument such as a test head 3 for
performing the testing and maintenance functions. In between the CO
2 and the telephone 8, there lies a network interface device (NID)
such as the MTU 6. There may be multiple telephones 8 and a single
MTU 6 connected to one pair of wires 4 in the conventional POTS
environment. In additional, other conventional devices (i.e.,
switches), which are not illustrated herein, may also be
implemented in this environment.
[0008] The MTU 6 illustrated herein is generally intended for a
single party, loop-start line, voice frequency band POTS
environment implementation. This is intended to be compatible with
conventional test systems such as Local Test Disk (LTD), Mechanized
Loop Testing (MLT), CK08555 (KS-8455) voltmeter, Automatic Line
Insulation Test (ALIT), and the like.
[0009] FIG. 2 illustrates a diagram of an existing circuit used in
the POTS environment as shown in FIG. 1. In the CO 2, the test head
3 (i.e., LTD, MLT) typically includes a power source 10 such as DC
voltage V.sub.dc, current limiting resistor 12, and two terminals
14, 16, which are further connected to relay(s) 18. The relay(s) 18
allows the two terminals 14, 16 to connect to a tip wire 20 (tip)
and/or a ring wire 22 (ring). As is well known, tip and ring are
terms used for describing the two wires that are needed to set up a
telephony connection.
[0010] The MTU 6 includes a pair of voltage sensitive switches
(V.sub.ss), where one V.sub.ss 24 is coupled to the tip 20 and the
other V.sub.ss 26 is coupled to the ring 22. In addition, a
termination impedance Z.sub.t 28 is placed in between the two
V.sub.ss 24, 26, at a location near the customer's telephone 8. The
termination impedance Z.sub.t 28 is a signature impedance that
works in conjunction with the CO 2 test systems for fault
identification and localization.
[0011] Testing in the conventional POTS environment is generally
performed using only two terminals, tip 20 and ring 22. The
conventional testing method is generally acceptable in the POTS
environment, but as will be described hereinafter, in the DSL
environment, a more improved system and method is needed.
[0012] The conventional testing system and method used in the POTS
environment have many shortcomings and disadvantages. For example,
one major disadvantage with the conventional system and method is
that many fault conditions cannot be detected or located with exact
precision, thereby requiring truck rolls. As a result, the
conventional testing system and method require a great deal of time
and resources to locate and determine the type of faults, which
generally results in lost revenues and a more than desirable fix
time for the operating company and the customer. An additional
disadvantage using the conventional system and method is that
phones are required to be connected to the tip and ring for testing
for some type of fault identification and localization, which in
many cases, can be quite burdensome.
[0013] FIG. 3 illustrates a chart showing how the conventional MTU
responds to different voltage levels as measured from tip to ring.
For example, when the voltage difference from tip to ring is
between +35 to +65 volts, this is indicative of normal or talk mode
(ON mode), where the MTU is in a low impedance state. Conversely,
the same behavior can be achieved when the voltage difference is
reversed, as between -35 to -65 volts from tip to ring.
[0014] When the voltage difference is dropped between -28 to +28
volts, the MTU 6 is turned off and it is in a high impedance state.
Further, when the voltage difference from tip to ring is between
+70 to +120 volts or between -70 to -120 volts, the voltage
sensitive switches V.sub.ss 24, 26 are turned on, placing them in
low impedance states. Furthermore, these voltages activate
impedance signature Z.sub.t 28, providing the so-called distinctive
terminations to be detected by the test systems at the CO 2. The
impedance readings should be between 150K to 450K ohms when
measured with +70 to +120 volts, and be equal or greater than 100 M
ohms when the voltage is between -70 to -120 volts.
[0015] As DSL technology continues to evolve, the conventional
system and method using the MTU 6 is generally inadequate for
testing/maintenance in the DSL environment. Most DSL circuits do
not have batteries connected thereto ("dry circuit"), and thus the
MTU 6 will typically not function properly under this
environment.
[0016] Another disadvantage of the conventional system and method
is that the MTU 6 is typically implemented only with ILECs
(Incumbent Local Exchange Carriers), which utilize their customized
test systems to control and inter-work with the MTU 6. The CLECs
(Competitive Local Exchange Carrier), which are in direct
competition with the ILECs in the marketplace, currently do not
have such testing/maintenance systems to work with the MTUs.
Installing such test systems is a very costly proposition for the
CLECs.
[0017] Thus, there is a need for a system and method for providing
a remotely addressable maintenance unit for the DSL and POTS/DSL
environments for both CLECs and ILECs. There is also a need for
implementing a remotely addressable maintenance unit in existing
infrastructures in current POTS environment for improved
performance.
SUMMARY OF THE INVENTION
[0018] It is an object of the present invention to provide a
remotely addressable maintenance unit for the POTS, DSL, and
POTS/DSL environments.
[0019] It is another object of the present invention to provide a
system and method for verifying connections between the central
office and the remotely addressable maintenance units.
[0020] It is yet another object of the present invention to provide
a system and method for locating and determining faults between the
central office and the customer's house/building.
[0021] It is a further object of the present invention to provide a
system and method for identifying the tip and ring wires using a
"Signature."
[0022] It is yet another object of the present invention to provide
galvanic isolation of in-house wiring from an outside plant.
[0023] It is another object of the present invention to provide a
system and method for detecting loop faults, including open and
short circuits.
[0024] It is another object of the present invention to provide
sealing currents to the copper wires used between the central
office and the customer's house/building using the remotely
addressable maintenance unit.
[0025] It is still a further object of the present invention to
provide a system and method for remotely terminating service with a
predetermined impedance to a particular customer using the remotely
addressable maintenance unit for a loop only noise measurement.
[0026] It is yet another object of the present invention to provide
a system and method for determining loop resistance in existing
copper loops.
[0027] These and other objects of the present invention are
obtained by providing a remotely addressable maintenance unit
(RAMU) that can be used in the POTS, DSL, and POTS/DSL
environments. The RAMU of the present invention includes circuitry,
working in conjunction with test systems located in the CO, for
detecting and locating (sectionalizing between in-house and
out-house) faults in the POTS, DSL, and POTS/DSL environments. The
RAMU further includes circuitry for setting and resetting one or
more relays for normal or test/maintenance mode. A test head is
placed at the CO, which works in conjunction with a "Signature" in
the RAMU for performing testing and maintenance tasks on the copper
loop. The RAMU of the present invention can also be used to provide
a sealing current to the wires in the DSL environment. Furthermore,
the RAMU eliminates/reduces truck rolls through a more thorough and
accurate diagnosis of fault types and localizations, thereby saving
valuable time and resources for both the ILECs and the CLECs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] These and other objects and advantages of the present
invention will become apparent and more readily appreciated from
the following detailed description of the presently preferred
exemplary embodiments of the invention taken in conjunction with
the accompanying drawings, of which:
[0029] FIG. 1 illustrates a simplified diagram of a POTS
environment having a conventional maintenance test unit;
[0030] FIG. 2 illustrates a diagram of an existing circuit used in
the POTS environment as shown in FIG. 1;
[0031] FIG. 3 illustrates a chart showing how the conventional MTU
responds to different voltage levels as measured from tip to
ring;
[0032] FIG. 4 illustrates block diagrams of various environments
implementing the RAMU in accordance with the present invention;
[0033] FIG. 5A illustrates a functional block diagram of the RAMU
in accordance with the present invention;
[0034] FIG. 5B illustrates a flow diagram showing the steps
performed by the RAMU in accordance with the present invention;
[0035] FIG. 6 illustrates an example of the RAMU signaling
definition of the present invention;
[0036] FIG. 7 illustrates a detailed circuit diagram in accordance
with the present invention; and
[0037] FIG. 8 illustrates a specific example of the RAMU signaling
definition used in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The present invention will now be described in greater
detail, which will serve to further the understanding of the
preferred embodiments of the present invention. As described
elsewhere herein, various refinements and substitutions of the
various embodiments are possible based on the principles and
teachings herein.
[0039] The preferred embodiments of the present invention will be
described with reference to FIGS. 4-8, wherein like components and
steps are designated by like reference numerals throughout the
various figures. Further, specific parameters such as potential
differences, voltage values, circuit layouts, and the like are
provided herein, and are intended to be explanatory rather than
limiting.
[0040] FIG. 4 illustrates block diagrams of various environments
implementing the RAMU in accordance with the present invention. In
the first environment, DSL, a test head 100a with a conventional
processor board such as a P150 processor (e.g., CX100 Copper
CrossConnect system of Turnstone Systems, Inc.) in the central
office (CO) is connected to a loop (copper pair) 102a in the
outside plant. The loop 102a is further connected to a RAMU 104a,
which in turn is connected to the in-house wiring 106a. An ATU-R
(ADSL transceiver remote unit) 108a or a similar end unit is
further connected to the in-house wiring 106a, generally in the
customer's house/building. Unlike the conventional system and
method, the RAMU 104a is implemented instead of the MTU, where the
RAMU 104a is used for testing and maintenance.
[0041] In a similar manner, the RAMU can be implemented in a second
POTS environment, again using a test head 100b having a processor
such as a P150 processor, which is connected to a loop 102b. The
RAMU 104b is connected to both the loop 102b and the in-house
wiring 106b, which terminates with a conventional analog phone
109a. The system in the second POTS environment is similar to the
first DSL environment except that the phone 109a, instead of the
ATU-R 108a, is the end unit. These examples illustrate that the
RAMU of the present invention can be easily implemented in both DSL
and POTS environments.
[0042] In yet another embodiment of the present invention, the RAMU
can be implemented in an environment using both DSL and POTS
concurrently. For example, in a third DSL/POTS environment, a test
head 100c is again connected to a loop 102c, which in turn is
connected to a first RAMU 104c. The first RAMU 104c is further
connected to a POTS splitter 110, which is used to split the wires
for connection to a second RAMU 104d and a third RAMU 104e. As
shown, the POTS splitter 100 can be implemented in a star topology,
or in the alternative, other topologies such as a ring. The second
and third RAMUs 104d, 104e are further connected to the in-house
wiring 106c, which terminate at the ATU-R 108b and phone 109b,
respectively. The RAMUs 104a, 104b, 104c, 104d, 104e, are
preferably placed at the network interface on the outside of the
customer's house/building in which the outside plant copper wires
for the access network terminate. In the alternative, the RAMUs
104a, 104b, 104c, 104d, 104e, can be placed inside the
house/building structure.
[0043] FIG. 5A illustrates a functional block diagram of the RAMU
and FIG. 5B illustrates a flow chart of the steps performed by the
RAMU in accordance with the present invention. Referring first to
the RAMU 520 in FIG. 5A, two switches 502a, 502b are used to
indicate "reset" and "set" modes, which depends on the magnitude,
polarity, and duration of an electric signal. For example, when a
contact point a is connected to a contact point b via switch 502a
and a contact point a' is connected to a contact point b' via
switch 502b (as explicitly shown in FIG. 5A), the RAMU is in the
"reset" or normal mode. In the alternative, when the contact point
a is connected to the contact point c via switch 502a, and the
contact point a' is connected to the contact point c' via switch
502b, the RAMU is in "set" or testing/maintenance mode. Thus, when
the RAMU is subjected to an electrical impulse representing either
the "reset" or "set" control signal of proper magnitude, polarity,
and duration, the RAMU will switch to either the "reset" or "set"
mode and will remain in that mode even upon removal or cessation of
the control signal. The magnitude, polarity, and duration of the
"reset" and "set" control signals for the RAMU are dependent on the
specific application environment, and is generally defined/design
into the RAMU and the CO 510 before deployment of the RAMU outside
the CO 510. A more detailed description regarding the specific
circuit diagram and the conditions for the "reset" and "set" modes
are disclosed later herein.
[0044] In the CO 510, there exists a power source V.sub.b 512 and
two terminals 514, 516, which can be connected to the tip (T), ring
(R) and/or ground wires. One important feature of the present
invention is that the two terminals 514, 516 can now be connected
to the ground 518. In this manner, the functional capabilities of
the system is expanded as follows: (1) increases the addressing
capabilities of the system, allowing multiple devices to be
connected to the same copper pair; (2) de-couples the address
signals (i.e., DC voltage levels that are used to control the RAMU)
from voltages that are used for applications, such as for
measurements and sealing current, and hence significantly minimizes
interference between voltages representing control/addressing and
applications; and (3) address or control bi-stable devices that can
be used in the physical implementation of the RAMU.
[0045] Thus, in the preferred embodiment, using appropriate voltage
magnitude and duration, "set" mode is indicative when there is a
positive polarity from tip to ground, ring to ground, or tip and
ring to ground. Conversely, again using appropriate voltage
magnitude and duration, "reset" mode is indicative when there is a
negative polarity from tip to ground, ring to ground, or tip and
ring to ground. In addition, signals that have an amplitude equal
to at least twice or greater than the amplitude of the "set" or
"reset" control signals, applied between the tip and ring, will not
have any effect on the "present" state of the RAMU.
[0046] FIG. 6 illustrates an example of a RAMU signaling definition
of the present invention. In greater detail, FIG. 6 shows eight
different conditions/quadrants for addressing the RAMU: (1)
V.sub.tg (voltage from tip to ground) with positive polarity; (2)
V.sub.tg (voltage from tip to ground) with negative polarity; (3)
V.sub.rg (voltage from ring to ground) with positive polarity; (4)
V.sub.rg (voltage from ring to ground) with negative polarity; (5)
V.sub.trg (voltage from tip and ring to ground) with positive
polarity; (6) V.sub.trg (voltage from tip and ring to ground) with
negative polarity; (7) V.sub.tr (voltage from tip to ring) with
positive polarity; and (8) V.sub.rg (voltage from tip to ring) with
negative polarity. Certain conditions/quadrants (e.g., 1, 2, 3, 4,
5, 6) can be used for addressing and other conditions/quadrants
(e.g., 7, 8) can be used for applications. Voltage range between
-50V to +50 for all combination of tip, ring, and ground
configurations (V.sub.tg, V.sub.rg, V.sub.trg, V.sub.tr) have been
reserved for measurements and other industry applications such as
parameter measurements and telephonic functions.
[0047] The "reset" mode can be actuated with a negative polarity
using a V.sub.tg, V.sub.rg, or V.sub.trg condition, using arbitrary
voltages range (i.e., preferably, at a range less than -50V but
greater than -120V), which ranges are pre-defined/pre-designed.
Conversely, the "set" mode can be actuated with a positive polarity
using a V.sub.tg, V.sub.rg, or V.sub.trg condition, using arbitrary
voltage ranges (i.e., preferably, at a range less than +120V but
greater than +50V), which ranges are pre-defined/pre-designed. In
additional, a particular voltage range that actuates the "set" mode
should include a reciprocal voltage range to actuate the "reset"
mode (i.e., 55.8V to 68.2 V for "set" mode and -68.2V to -55.8V for
"reset" mode).
[0048] Each individual RAMU can be defined/designed to only respond
to a certain voltage range. For example, one can "set" one
particular RAMU to respond in the +55.8 to +68.2 voltage range, and
"reset" in the -55.8 to -68.2 voltage range. In the same manner,
another RAMU can be "set" and "reset" to respond in the +73.8 to
+90.2 voltage range, and -73.8 to -90.2 voltage range,
respectively. In this manner, multiple RAMUs can be remotely
addressable from the CO 510 by providing different voltages and
polarities to the tip and/or ring to ground. Further, installing
multiple RAMUs at different locations between the CO 510 and the
customer's house/building provides a way to determine the exact
location and type of fault in any environment.
[0049] Additionally, a sealing current can be provided to the wires
using the V.sub.tr condition and in conjunction with a properly
designed signature impedance. Thus, voltage between 0 to +65 volts
can be applied from tip to ring using the RAMU to provide a sealing
current to the copper wires. Other applications such as loop
powered tone generation can be performed by providing other
voltages to the ring and tip in the V.sub.tr configuration. It is
also noted that in FIG. 6, the voltage ranges are for illustrative
purposes only and other practical voltages ranges can be
substituted for those illustrated therein.
[0050] Referring back to FIG. 5A and as mentioned earlier herein,
the RAMU can be placed at the network interface outside of the
customer's house/building in which the outside plant copper wires
for the access network terminate, which wires are connected to
contact points a and a'. In the DSL or POTS environment, there is
typically a DTU (Digital Termination Unit)/phone set 540 connected
to the contact points b and b' through a pair of copper wires. When
the DTU/phone set 540 is connected to the contact points a and a',
via the contact points b and b', this represents the "reset" or
normal mode. Conversely, when the RAMU is in the "set" or
testing/maintenance mode, the DTU/phone set 540 is disconnected
from the contact points a and a', and such contact points are
connected to a Signature 532 via the contact points c and c'.
[0051] The Signature 532 is preferably a passive network or active
circuit elements that perform a specific function, as described in
more detail hereinafter. The Signature 532 contains specific
circuitry designed to identify the presence of the RAMU. The
Signature 532 can also perform the function of a resistance, which
is used to detect fault conditions in the tip and ring, loop length
measurements, and a DC path for a sealing current to "wet" the
loop.
[0052] The RAMU 520 further includes the following functional
blocks: Signal Detector 522, Level Comparator 524, "Adjustable"
Fixed Voltage Driver 526, Reference Voltage 528, and Relay 530. As
shown, the RAMU 520 can be connected to the CO 510 at the T and R
wires, and to the customer's house/building via the T' and R'
wires.
[0053] Reference will now be made to both FIGS. 5A and 5B
concurrently for a more complete understanding of the present
system and method. First, in step 602, a voltage is applied to T
and/or R. In step 604, the Signal Detector 522 coupled to the T and
R detects the polarity of the signal and voltage level at the T
and/or R with respect to ground. The polarity of the detected
signal is then fed into the Reference Voltage 528 to select a
polarity for the reference voltage in step 606. The Reference
Voltage 528 contains pre-defined voltage amplitude whose polarity
selections are controlled by a signal from the Signal detector 522.
The Reference Voltage 528 can also be adjustable depending on the
type and values of the hardware components used in a particular
circuitry.
[0054] The voltage with the proper polarity from the Reference
Voltage 528 is then inputted into the Level Comparator 524, which
is also coupled to the Signal Detector 522 and the Reference
Voltage 528. The Level Comparator 524 compares the T and/or R
voltages with the reference voltage from the Reference Voltage 528
in step 608. In step 610, when the value of the voltage from the T
and/or R is greater than the reference voltage, an enable signal is
generated by the Level Comparator 524 and inputted into the Fixed
Voltage Driver 526, for enabling the same.
[0055] The Fixed Voltage Driver 526 consists of a switching
function and a fixed voltage circuitry. The switching function
controls the application of a fixed voltage to drive the Relay 530.
The combination of the fixed voltage with a coil resistance of the
Relay 530, which is generally fixed for a given relay type, forms a
"constant current source." The current flowing through the Relay
530 is not affected by further increases in the voltage at the T
and/or R. In other words, once the circuitry detects a voltage at
the T and/or R, which exceeds a pre-defined value, the Fixed
Voltage Driver 526 applies a constant voltage and actuates the
Relay 530. The resultant current flowing through the Relay 530 is
also unaffected by further increase in voltages at the T and R.
This is an essential feature of the present invention to provide
optimum operations. In addition, the fixed voltage driver value can
be further adjusted to accommodate a different voltage rating of a
particular relay.
[0056] The Relay 530 is preferably a latching-type relay (includes
memory), which could be either electromechanical or semiconductor
solid state. The latching-type feature is essential in that once
the applied voltage exceeds a pre-defined reference voltage, a
constant voltage is applied to actuate the Relay 530. Once the
Relay 530 is actuated, the "set" or "reset" control voltage can be
subsequently removed, resulting in minimum or no power dissipation.
The latching-type feature is also essential because it can then
allow application of a voltage across the T and R to perform other
functions without affecting the Relay 530.
[0057] FIG. 7 illustrates an example of a detailed circuit diagram
that can be used in the present invention. Functionally, the Signal
Detector 522 includes the diodes D1 730, D2 732, D3 734, D4 736,
and transistors Q1 740, Q2 742, Q3 744, Q4 746. The Level
Comparator 524 uses the voltages associated with zener diodes Z1
712, Z3 718 or Z2 714, Z4 716, in conjunction the voltages
associated with zener diodes Z5 722, Z6 724. Next, the Reference
Voltage 528 is set by choosing a combination of voltages associated
with zener diodes Z1 712, Z3 718 or Z2 714, Z4 716, with voltages
associated with zener diodes Z5 722 or Z6 724. The zener diodes Z1
712, Z2 714, Z3 718, Z4 716, Z5 722, Z6 724 perform dual functions
for the Level Comparator 524 and the Reference Voltage 528.
[0058] The Fixed Voltage Driver 526 includes zener diodes Z5 722,
Z6 724. Adjustments/modifications to the Fixed Voltage Driver 526
can be made by selecting the voltages associated with zener diodes
Z5 722, Z6 724. For symmetrical operation, zener diodes Z5 722, Z6
724 can have identical values such as approximately 20V. Once the
zener diode voltages are known, the voltage required to drive the
Relay 530 is also known (i.e., 20V).
[0059] The Relay 530 is defined by K1 760, which can have the
following characteristics: 24V rated, single coil, two form-c
contacts, and latching-type. In other embodiments, a different
rated voltage relay can be used in the circuitry of FIG. 7. Note
that since the Relay K1 760 is rated at 24V, the actual voltage to
drive/actuate it is about 19.8V as defined by Z5 722 (20.0V), in
conjunction with forward drop of Z6 724 (0.7V), plus the V.sub.be
(base to emitter voltage drop) of Q4 746 (0.7V), minus the V.sub.be
of Q2 742 (0.7V), minus the V.sub.ce (collector to emitter)
saturation voltage of Q4 746 (0.2V), minus the forward drop
(V.sub.be) of D4 736 (0.7V).
[0060] The Signature 532 includes resistors R5 750, R6 752,
capacitor C2 770, and zener diodes Z7 780, Z8 782. Voltages for the
zener diodes Z7 780 and Z8 782 are selected to be different from
each other to enable identification of either the tip or ring.
Resistors R5 750, R6 752 and capacitor C2 770 together provide the
proper AC termination impedance for testing operations. This also
allows a DC current path to be present for the "wetting or sealing
current" of the loop.
[0061] The circuitry also includes a capacitor C3 772 for lightning
surge suppression and resistors R1 710, R2 708 for limiting a surge
current. The capacitor C1 774 is used to filter out ringing signals
that may be present, and for preventing erroneous circuit
operations due to transient voltages that may be present. The
resistor R7 754 is used to dissipate charges stored in the
capacitor C1 774.
[0062] During operation, when a positive voltage with respect to
the ground is applied to the T 704 while the R 706 is left open,
and the applied voltage is greater than the combined voltages set
by zener diodes Z2 714, Z5 722 and the forward diode voltage drops
for zener diodes Z4 716, Z6 724 (i.e., typically 0.7 volts),
current will begin to flow through the resistor R2 708, zener
diodes Z2 714, Z4 716, resistor R3 720, zener diodes Z5 722, Z6
724, and resistor R4 726. As the voltage from T 704 continues to
increase, so does the voltage at resistor R4 726. When the voltage
level increases to a value of V.sub.be (which is approximately
0.7V) for the transistor Q4 746, a base current is injected, which
turns on transistors Q4 746, Q2 742. Current then begins to flow
through relay K1 760, actuating the relay K1 760 in the "set" mode.
The relay current path is through resistor R2 708, zener diodes Z2
714, Z4 716, diode D2 732, transistor Q2 742, relay K1 760, diode
D4 736, and transistor Q4 746. The voltage across the relay K1 760
is defined by the voltage of zener diode Z5 722, V.sub.be drops for
zener diode Z6 724, transistors Q2 742, Q4 746 and diode D4 736.
Since the voltage of the zener diode Z5 722 is usually much greater
than the combined V.sub.be's, the voltage across the relay K1 760
is essentially the voltage of zener diode Z5 722. The voltage is
"impressed" across the relay K1 760 with a coil fixed resistance
and produces a fixed current through the relay K1 760, which is
independent of the voltage. Another key feature of the present
invention is the combined effect of a fixed voltage across the
relay K1 760, which is turned on only when the T and/or R voltage
reaches a pre-defined voltage, and thus results in an "interlock"
mechanism. This interlock mechanism applies to all subsequent
operations that are discussed hereinafter.
[0063] When a negative voltage with respect to ground is applied to
the T, while the R is left open, and the applied voltage is greater
than the combined voltages set by zener diodes Z6 724, Z4 716 and
the forward diode voltage drops for zener diodes Z5 722, Z2 714,
current will begin to flow through resistor R4 726, zener diodes Z6
724, Z5 722, resistor R3 720, zener diodes Z4 716, Z2 714, and
resistor R2 708. As the applied voltage continues to increase
across the T, so does the voltage at resistor R4 726. When the
voltage level increases to a value of V.sub.be for the transistor
Q3 744, current is injected, turning on transistors Q3 744, Q1 740.
Current then begins to flow through relay K1 760, actuating the
relay K1 760 to the "reset" mode.
[0064] When a positive voltage with respect to ground is applied to
the R, while the T lead is left open, and the applied voltage is
greater than the combined voltages set by zener diodes Z1 712, Z5
722 and the forward diode voltage drops for zener diodes Z3 718, Z6
724, current will begin to flow through resistor R1 710, zener
diodes Z1 712, Z3 718, resistor R3 720, zener diodes Z5 722, Z6
724, and resistor R4 726. As the voltage increases at R, the
voltage at the resistor R4 726 also increases. When the voltage
increases to the V.sub.be value for the transistor Q4 746, base
current is injected, turning on transistors Q4 746, Q2 742. Current
then begins to flow through relay K1 760, actuating the relay K1
760 in the "set" mode. The relay current path is through resistor
R1 710, zener diodes Z1 712, Z3 718, diode D2 732, transistor Q2
742, relay K1 760, diode D4 736, and transistor Q4 746. The voltage
across the relay K1 760 is defined by the voltage of zener diode Z5
722, V.sub.be drops for zener diode Z6 724, transistors Q2 742, Q4
746, and diode D4 736. Again, since the voltage associated with the
zener diode Z5 722 is usually greater than the V.sub.be's, the
voltage across the relay K1 760 is essentially the voltage of zener
diode Z5 722.
[0065] When a negative voltage with respect to ground is applied at
the R 706, while the T lead 704 is left open, and the applied
voltage is greater than the combined voltages set by zener diodes
Z6 746, Z3 718 and the forward diode voltage drops for zener diodes
Z5 722, Z1 712, current will begin to flow through resistor R4 726,
zener diodes Z6 724, Z5 722, resistor R3 720, zener diodes Z3 718,
Z1 712, and resistor R1 710. As the applied voltage increases, the
voltage across the resistor R4 726 will also increase. When it
reaches the V.sub.be drop of transistor Q3 744, current is
injected, turning on transistors Q3 744, Q1 740. Current then
begins to flow through relay K1 760, actuating the relay to "reset"
mode.
[0066] When a positive voltage is applied to both the T and R
concurrently with respect to ground, current will begin to flow
when the voltage is at the combined value set by either (1) zener
diodes Z2 714, Z5 722 and the forward diode voltage drops for zener
diodes Z4 716, Z6 724, and/or (2) zener diodes Z1 712, Z5 722 and
the forward diode voltage drops for zener diodes Z3 718 and Z6 724.
As the applied voltage increases, the voltage across resistor R4
726 also increases and when it reaches the V.sub.be of transistor
Q4 746, transistors Q4 746, Q2 742 turn on, allowing a current to
flow through relay K1 760, thereby actuating the relay K1 760 in
the "set" mode. The current path through the relay K1 760 is via
(1) resistor R1 710, zener diodes Z1 712, Z3 718, diode D2 732,
transistor Q2 742, relay K1 760, diode D4 736, and transistor Q4
746, and/or (2) resistor R2 708, zener diodes Z2 714, Z4 716, diode
D2 732, transistor Q2 742, relay K1 760, diode D4 736, and
transistor Q4 746.
[0067] When a negative voltage is applied to both the T and R
concurrently with respect to ground, current will begin to flow
when the voltage is at the combined value set by either (1) zener
diodes Z4 716, Z6 724 and the forward diode voltage drops for zener
diodes Z2 714, Z5 722, and/or (2) zener diodes Z3 718, Z6 724 and
the forward diode voltage drops for zener diodes Z1 712 and Z5 722.
As the applied voltage increases, the voltage across the resistor
R4 716 also increases and when it reaches the V.sub.be of
transistor Q3 744, transistors Q3 744, Q1 740 turn on, allowing a
current to flow through relay K1 760, thereby actuating relay K1
760 in the "reset" mode. The current path through the relay K1 760
is via (1) resistor R1 710, zener diodes Z1 712, Z3 718, diode D1
730, transistor Q1 740, relay K1 760, diode D3 734, and transistor
Q3 744, and/or (2) resistor R2 708, zener diodes Z2 714, Z4 716,
diode D1 730, transistor Q1 740, relay K1 760, diode D3 734 and
transistor Q3 744.
[0068] As described above, when relay K1 760 is in the "reset"
mode, the T and R are connected to the DUT/phone set 540, which
represents the normal operation mode. In the alternative, when
relay K1 760 is in the "set" mode, the T and R are connected to the
Signature 532, which represents the testing/maintenance mode.
[0069] FIG. 8 illustrates a specific RAMU Signaling Definition for
the circuit as shown in FIG. 7, which represents one RAMU and one
specific voltage level that the RAMU can be signaled/addressed.
[0070] From the previous discussion, it is easy to understand that
multiple RAMUs can be connected on the same line functioning at
different addressing voltage levels in order to locate and
determine the type of fault. By having a sequence of RAMUs, one can
determine the exact location of a fault, by invoking consecutive
RAMUs. In addition, by changing the level of the voltage values of
the zener diodes, a particular RAMU can be actuated by providing a
particular voltage. In other words, each RAMU can be
defined/designed with different levels of voltage sensitivity. In
other embodiments, other components can be substituted for the
specific components described herein so long as these components
perform essentially identical functions as described herein.
[0071] In the previous descriptions, numerous specific details are
set forth, such as specific functions, components, etc., to provide
a thorough understanding of the present invention. However, as one
having ordinary skill in the art would recognize, the present
invention can be practiced without resorting to the details
specifically set forth.
[0072] Although only the above embodiments have been described in
detail above, those skilled in the art will readily appreciate that
many modifications of the exemplary embodiments are possible
without materially departing from the novel teachings and
advantages of this invention.
* * * * *