Telephonic communications – Subscriber line or transmission line interface – Power supply
Reexamination Certificate
1999-08-16
2003-11-11
Tieu, Binh (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Power supply
C379S001030, C379S395010
Reexamination Certificate
active
06647117
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to telecommunications, and in particular to a method and apparatus for facilitating continuity of Voice over Digital Subscriber Loop (VoDSL) service to a subscriber during power failure and restoration at the customer premises, and a system incorporating the same.
BACKGROUND TO THE INVENTION
Digital Subscriber Une (DSL) modem technology has enabled the transmission of digital information at duplex rates from 144Kbits/s to over 1 Mbts/s over the subscriber loop. The demand for additional, telephone lines and integrated telephony and data services has given rise to Voice over DSL (VoDSL) solutions. For example a VoDSL system may provide 4 voice channels carried within the digital data over a single twisted pair subscriber loop from a Une Terminating Equipment (LTE) located in the Central Office to a Customer Premises equipment (CPE). In one implementation a VoDSL system carries the voice channel(s) in band as encoded data within the data stream and therefore there is no baseband POTS (Plain Old Telephony Service) as would be the case with for example ADSL or G.Lite. Unlike normal telephony the derived voice method of VoDSL requires local power at the CPE to perform the modulation and demodulation.
Conventional, analogue. POTS telephony over a twisted pair to the LTE has the benefit that during power failure at the customer premises emergency calls can still be placed since the line and the handset at the customer premises are powered from the central office. A disadvantage of existing VoDSL modems is that the amount of power required for normal operation could severely limit the operational loop length and not provide a service able to reach the majority of consumers. This has limited deployment of VoDSL systems to subscribers having an additional conventional POTS line which can be used In the event of power failure. Absence of support for lifeline services has therefore severely hindered deployment into the small business and especially the residential market.
Power feed from LTE has been tried for ISDN but it requires very high battery voltages and severely limits the operational loop length.
Use of batteries at the CPE to provide backup power in the event of power failure presents other problems: batteries may be bulky and therefore unattractive to subscribers; batteries require periodic maintenance to ensure reliability; and battery faults may not be detected until a local power failure occurs and they fail to provide power to the CPE and hence provide lifeline support, which defeats the object of their presence in the system.
OBJECT OF THE INVENTION
The invention seeks to provide an improved method and apparatus for Digital Subscriber Loop services in general and provision of improved lifeline capabilities during customer premises power failure in particular.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of operating a digital subscriber loop modem arrangement under a fault condition so as to provide at least a voice over DSL service, the method comprising the steps of: switching from a full-power digital subscriber loop functionality to a reduced-power digital subscriber loop functionality responsive to detection of loss of power to said arrangement.
According to another aspect of the invention, there is provided a method of operating a digital subscriber loop modem arrangement under a fault condition so as to provide at least a voice over DSL service on a digital subscriber line in which data and voice traffic are transported on a plurality of carriers, the method comprising the steps of: replacing the data with random data, disabling those data carriers on which the random data is transported, and maintaining transmission of those carriers transporting the voice traffic. According to a further aspect of the invention, there is provided a method of providing continuity of service at a subscriber premises In a digital subscriber loop system the, method comprising the steps of:
detecting power loss at said premises; and
switching customer premises equipment to a low-power mode capable of being powered from a local exchange connected to said customer premises equipment.
According to another aspect of the Invention, there is provided a digital subscriber loop modem arrangement comprising, a local power supply port, a circuit arranged to detect a loss of power at said electrical power input port; and arranged upon detection of failure of a power supply connected to said power supply port to switch from a full-power digital subscriber loop functionality to a reduced-power digital subscriber loop functionality.
Advantageously, the system avoids the need to provide battery backed up equipment at the customer premises, and the attendant need to keep the batteries in good condition, and yet, still allows a “lifeline” voice-over-DSL service to be provided In the presence of power loss at the CPE.
Advantageously, providing a viable strategy for provision of lifeline service during a power outage at the customer premises facilitates the carriage of POTS traffic in-band in ADSL.
Advantageously, a complete modem retrain is avoided thereby achieving continuity of service over the power outage.
Advantageously, a seamless transition is achieved during power-down.
The invention is also directed to a method by which the described apparatus operates and including method steps for carrying out every function of the apparatus.
The Invention also provides for a system for the purposes of digital signal processing which comprises one or more instances of apparatus embodying the present invention, together with other additional apparatus.
The invention is also directed to software for a computer, comprising software components arranged to perform each of the method steps.
The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.
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Bridger Mark
Tate Christopher
Wallace Andrew D
Barnes & Thornburg
Nortel Networks Limited
Tieu Binh
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