Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of data transmission
Reexamination Certificate
2002-02-12
2004-03-16
Kuntz, Curtis (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of data transmission
C379S001010, C379S001030, C379S027010, C379S027020, C379S028000, C379S029010, C379S031000, C379S022000
Reexamination Certificate
active
06707886
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to determining suitability of an existing subscriber loop for supporting broadband services (i.e., DSL). It specifically concerns remote testing of such a subscriber loop and in particular performing tests without access to the subscriber loop and without requiring equipment and/or craft personal to be present at a customer end of the subscriber loop. In a specific embodiment, it involves using existing voiceband and touchtone keys of a standard telephone to determine suitability of an access line to provide broadband/DSL service.
BACKGROUND OF THE INVENTION
To provide broadband service over conventional subscriber loops (i.e., herein that circuitry connecting a network's central office to a subscriber premises; commonly a pair of wires) conventionally requires access to the subscriber premises to perform tests that assure that the loop is capable of providing broadband (i.e. DSL) service. The effects of loop network components such as loading coils, bridge taps, loop distance, and digital loop carriers (DLCs) severely adversely impact the ability to provide broadband service to an unacceptable extent.
Testing of subscriber loops (physical circuitry connecting a customer's premises to a central office) has become an important process for broadband service providers. All loop lines are not capable of providing broadband DSL service. These lines were never originally designed for this purpose. Unfortunately, the lines that are incapable of supplying broadband service are not known ahead of time; so, the lines must be tested for their ability to send/receive broadband signals. Several methods exist to perform this function. If you are the service provider who owns the loop (Incumbent Local Exchange Carrier or ILEC who runs the CO, typically), then you can test the wire directly, over any frequency band, from the CO to the customer premises. However, if you are a Competitive Local Exchange Carrier (CLEC), then the digitization of received signals that occurs at the CO limits an ability to test the loop to the voice band of the line, typically 300 to 3300 Hz. This limitation is due to a digital signal sampling property (Nyquist Criterion) of 4000 Hz maximum since the signal is typically sampled at 8000 Hz with 8 bit precision.
It would be advantageous to be able to test the subscriber loop using data obtained only from the voice band and extrapolate the results to the broader DSL frequency band (typically to 1 MHz). Such a system has been disclosed in U.S. Pat. No. 6,091,713, but the technique described therein requires a subscriber to be connected to test equipment through a voice band modem located at the customer premises. Their process uses data stored in registers that provide data obtained during the handshake or negotiation process; this voice band information is extrapolated for use over the greater DSL band. There may be times, however, where it is necessary or desirable to test the line without the use of a modem or computer (logic device) at the customer premises. One particular situation is where the test provider does not have direct access to the subscriber loop. In this instance, sending a craft person to the premise or providing special equipment at a customer site is prohibitively expensive.
It is desirable to test a subscriber loop for broadband service suitability without access to the customer premises and without the use of modems, personal computers and special logic devices on the customer premises.
A SUMMARY OF THE INVENTION
A subscriber loop test apparatus relates to the testing of a subscriber loop by the use of a touchtone telephone. The touchtones on a telephone provide Dual-Tone, Multiple Frequencies for each key pressed. For example, referring to
FIG. 1
, pressing the ‘3’ key causes tones at 697 and 1477 Hz to be sent across the telephone line. Pressing a sequence of keys provides discrete coverage of the frequency band from 697 to 1477 Hz, through the use of the touchtone telephone. The frequency band from 697 to 1477 Hz can be characterized in this fashion. Information about the line: loop loss (loop length), presence of bridge taps (i.e., excessively long bridge taps in particular) or loading coils, and the presence of Digital Loop Carriers (DLCs), et cetera. The use of the switch-hook flash provides the ability to determine the channel (impulse) response of the loop, including any noise and hum that may be on the loop due to imbalance or coupled interference. Both of these techniques shall be termed ‘user telephony input (UTI).’
In one specific embodiment, the testing technique uses existing voiceband and touchtone keys on a standard telephone to determine the suitability of a subscriber loop to provide broadband (DSL) service. The technique is advantageously integrated with an interactive voice response (IVR) system that provides inquiring subscribers instructions as to how to proceed and interact with a test server to determine broadband service suitability. With this arrangement a potential DSL user can be tested, prequalified and provisioned using a single automated process. This allows prompt and inexpensive service to the customer.
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Erving Richard Henry
Marcus Maura Elizabeth
Miller II Robert Raymond
Rice Christopher W.
AT&T Corp.
Kuntz Curtis
Tran Quoc D
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