Single-ended subscriber loop qualification for xDSL service

Details Single-ended subscriber loop qualification for xDSL service Single-ended subscriber loop qualification for xDSL service

1999-09-03

2001-07-24

Kuntz, Curtis (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Testing of subscriber loop or terminal

C379S024000, C379S030000, C379S032010, C370S248000, C324S533000, C324S534000

Reexamination Certificate

active

06266395

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to the provision of data services over subscriber loops in the Public Switched Telephone Network and, in particular, to a method and apparatus for the single ended qualification of subscriber loops to determine the suitability of such loops for the provision of high-speed data services.
BACKGROUND OF THE INVENTION
The exponential increase in the popularity of the Internet and related data services has prompted service providers in the Public Switched Telephone Network (PSTN) to seek new technologies for delivering high-speed data services to their customers. One solution is provided by Digital Subscriber Line (DSL) technologies. Several DSL technologies offer high-speed services over existing copper facilities, commonly referred to as “subscriber loops”. Such technologies include Asymmetrical Digital Subscriber Line (ADSL); High-bit-rate Digital Subscriber Line (HDSL); Rate Adaptive Digital Subscriber Line (RDSL); Symmetric Digital Subscriber Line (SDSL); and, very High-speed Digital Subscriber Line (VDSL). These digital subscriber line technologies are known collectively as “xDSL” services.
A problem encountered in the provision of xDSL services is that the subscriber loops have been largely neglected from a technology upgrade perspective. Existing subscriber loops were designed for voice telephony as opposed to high-speed data services. Consequently, many subscriber loops include wire gage changes and bridged taps (unused extension lines) which limit the available bandwidth. Other equipment installed on subscriber loops may also render the loop unsuitable for the provision of xDSL service. For example, load coils, voice frequency repeaters, loop extenders, Private Branch Exchanges (PBXs), line intercepts and incompatible data services all render subscriber loops unsuitable for the provision of xDSL service.
Testing apparatus for determining the physical and/or electrical characteristics of subscriber loops is known. Such apparatus is taught, for example, in U.S. Pat. No. 4,105,995 which issued Aug. 8, 1978 to Bothof et al.; U.S. Pat. No. 4,870,675 which issued Sep. 26, 1989 to Fuller et al.; and, U.S. Pat. No. 5,881,130 which issued Mar. 9, 1999 to Zhang. While such apparatus enables the determination of certain physical and/or electrical characteristics of the subscriber loop, none enable single ended determination of the bandwidth capacity of the subscriber loop for the provision of xDSL service.
Consequently, it has been the practice of service providers in the PSTN to dispatch a skilled technician to the premises of a customer who has requested, or expressed an interest in an xDSL service. The technician coordinates testing with another technician at the service provider's Central Office (CO). The dispatch of the skilled technician contributes significantly to the service provider's operating overhead and delays service provision due to the scheduling of subscriber loop qualification.
In order to reduce the cost and improve the efficiency of subscriber loop qualification, several solutions have been tried without success. For example, basic metallic measurements of electrical characteristics such as voltage, resistance and capacitance readings of the subscriber loop have been tried. However, these metallic measurements do not assess the high bandwidth range of the subscriber loop and consequently fail to provide a consistently accurate assessment of bandwidth available for xDSL service. Time Domain Reflectrometry (TDR) readings have also been tried without success. The problem is that TDR readings do not take physical properties of the cable or network topology information into account. The prior art methods have attempted to use measurements alone to generate rate predictions. Consequently, those prior art methods have failed because they do not correct for the physical properties of the subscriber loop, or equipment on the subscriber loop.
In order to screen customer inquiries and limit the number of requests for subscriber loop qualification for xDSL service, many service providers in the PSTN have implemented postal code maps which permit a subscriber to retrieve an indication of whether their subscriber loop is suitable for xDSL. The indication is retrieved, for example, by inputting a ZIP code or a postal code into a query screen available on the Internet. While such tools effectively limit the requests for subscriber loop qualification, in many ways they work against both the subscriber and the service provider. The postal code maps are based solely on an approximation of a distance between the subscriber premises and a serving CO in the PSTN. Because of this limitation, they cannot take into account the factors which may affect the suitability of the subscriber loop for xDSL service. Besides, because of the granularity of the postal code system, many subscriber loops suitable for the provision of xDSL service may be disqualified even though they are capable of providing some level of service.
There therefore exists a need to significantly reduce the costs of qualifying subscriber loops for xDSL service.
There also exists a need for a method and apparatus to permit the single ended qualification of subscriber loops.
There further exists a need to provide a method and apparatus for the single-ended qualification of subscriber loops which reduces the skill level required by operators performing the qualification.
There further exists a need for a method and apparatus for single ended qualification of subscriber loops which enables the pre-qualification of subscriber loops to permit a service provider to inform any service subscriber of the qualification of their subscriber loop on request.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a simple and economical method and apparatus for the single ended qualification of subscriber loops for xDSL service.
Accordingly, an aspect of the invention provides a method of qualifying a subscriber loop for xDSL services. The subscriber loop is connected to a public switched telephone network (PSTN) via a switch at a central office (CO). The method comprises the steps of: determining, from a CO end of the subscriber loop, one or more electrical characteristics of the subscriber loop; and estimating, based on the determined electrical characteristics, an xDSL bandwidth available on the subscriber loop.
A further aspect of the present invention provides a system for qualifying a subscriber loop for xDSL services. The subscriber loop is connected to a public switched telephone network (PSTN) via a switch at a central office (CO). The system comprises a processor adapted to determine, from a CO end of the subscriber loop, one or more electrical characteristics of the subscriber loop, and to estimate an xDSL bandwidth of the subscriber loop based on the determined electrical characteristics.
Thus the present invention provides a method and apparatus for single ended qualification of subscriber loops for xDSL services. Electrical characteristics of the subscriber loop preferably include values for: resistance (R); capacitance (C); inductance (L); and conductance (G) for each cable segment forming the subscriber loop. Additional electrical characteristics can, for example, include a wide band noise (WBN) value on the subscriber loop, and the presence of any one or more of: bridged taps; load coils; loop extenders; and other devices in the subscriber loop. The electrical characteristics of the subscriber loop can be determined by any one or more of; probing the subscriber loop from the CO end; estimation based on physical characteristics of the subscriber loop, and use of default values. In an embodiment of the invention, values of R, L, G, and C are contained in a cable properties database and may be accessed on the basis of the physical characteristics of the subscriber loop.
The physical characteristics of the subscriber loop preferably include information of: length; conductor size; cable insulation type; and cable installation type of each cab

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