Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Reexamination Certificate
1999-12-30
2002-01-29
Tieu, Binh (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S009060, C379S012000, C379S018000, C379S022070, C379S026010, C379S029030
Reexamination Certificate
active
06343114
ABSTRACT:
FIELD OF THE INVENTION
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
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.
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.
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.
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.
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.
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.
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.
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
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.
The MTU
6
includes a pair of voltage sensitive switches (V
ss
), where one V
ss
24
is coupled to the tip
20
and the other V
ss
26
is coupled to the ring
22
. In addition, a termination impedance Z
t
28
is placed in between the two V
ss
24
,
26
, at a location near the customer's telephone
8
. The termination impedance Z
t
28
is a signature impedance that works in conjunction with the CO
2
test systems for fault identification and localization.
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.
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.
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.
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
ss
24
,
26
are turned on, placing them in low impedance states. Furthermore, these voltages activate impedance signature Z
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.
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.
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.
Thus, there is a need for a system and method for providing a remotely addressable maintenance unit for the DSL and POTS/DSL environments f
Pillsbury & Winthrop LLP
Tieu Binh
Turnstone Systems, Inc.
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