Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
2000-06-21
2004-02-10
Phu, Phoung (Department: 2631)
Pulse or digital communications
Transceivers
Modems
C375S257000, C370S252000
Reexamination Certificate
active
06690721
ABSTRACT:
FIELD OF INVENTION
The present invention relates to communications in digital subscriber lines. More specifically, it relates to a method for a splitterless asymmetric digital subscriber line modem to recover from insufficient transmit power.
BACKGROUND OF THE INVENTION
Digital Subscriber Line (“DSL”) is a developing modem technology that allows existing copper telephone lines to carry high bandwidth information. Familiar twisted-pair telephone lines are then able to carry high speed data communication to and from a customer site in addition to retaining a plain old telephone service (“POTS”) channel for voice communication. At the customer site, a DSL modem receives the downstream signal representing data for a customer from a central office for a telephone company and transmits upstream signal representing data from the customer to the central office.
One configuration of DSL is generally termed Asymmetric Digital Subscriber Line (“ADSL”). ADSL allows high-speed data transport to the customer site but only medium-speed data transfer from the customer site, whence the asymmetry. ADSL also allows the simultaneous use of the ADSL modem and POTS on the same telephone line. In this configuration, at a point where the twisted-pair telephone line enters the customer site, the POTS channel is split off from the ADSL modem by filters. One problem with this ADSL, however, is that a technician from the telephone company has to visit the customer site and install the splitter, referred to as “the truck roll.”
To overcome this problem, another configuration of ADSL forgoes the requirement of a splitter at the customer site. This configuration is generally called “splitterless ADSL” and also goes under the name of “G.Lite.” Splitterless ADSL is described in the International Telecommunications Union-Telecommunication Standardization Sector (“ITU-T”, formerly known as the CCITT) Recommendation G.992.2, which is incorporated herein by reference. ITU-T standards can be found on the World Wide Web at the Universal Resource Locator (“URL”) “www.itu.ch.” Splitterless ADSL modems include those manufactured by 3Com Corporation of Santa Clara, Calif., Lucent Technologies of Murray Hill, N.J., Texas Instruments of Dallas, Tex., and others.
In splitterless ADSL, an ADSL modem directly shares the same twisted-pair telephone line as a POTS telephone without the intervention of a splitter. Sharing the same twisted-pair telephone line, however, may result in some of the ADSL signal bleeding over into the audible frequency range of the POTS telephone. Audible noise effects, such as a buzzing in the earpiece or speaker, are heard on the POTS telephone when off-hook. The noise effect is the response of the internal circuitry of the telephone to the ADSL signal. The noise may be reduced by cutting back on the transmitted power of the ADSL modem. A method for reducing noise from an ADSL modem is described in U.S. patent application Ser. No. 09/458,568, assigned to the 3Com Corporation of Santa Clara, Calif., which is fully incorporated herein by reference.
The power cutback for reducing audible noise, however, may result in insufficient power for data transfer. It is desirable, therefore, to provide a method for an ADSL modem to recover from a power cutback that is too large to support data transfer. This may allow customers to continue using the ADSL modem to transfer data while they are also using the telephone, albeit with possibly degraded audio quality.
SUMMARY OF THE INVENTION
In accordance with preferred embodiments of the present invention, some of the problems associated with imposing a power cutback in a splitterless ADSL modem are overcome. The modem implements the power cutback to enable simultaneous use of a telephone and the modem. One aspect of the invention includes a method for recovering from a power cutback that limits transmitted power from the modem and prevents communication between the modem and a central office. The method includes determining whether the transmitted power from the modem after a previous power cutback is sufficient to establish communication between the modem and the central office. If the transmitted power from the modem is not sufficient to establish communication, the modem reduces the previous power cutback by a step value to obtain a new power cutback. The new power cutback is applied to the modem to obtain a new transmitted power. The modem repeats the above steps until the new transmitted power after the new power cutback is sufficient to establish communication between the modem and the central office.
For example, the method of the present invention may provide for a reduction of audible noise in the telephone from a G.Lite modem while, at the same time, maintaining communication between the modem and the central office. The method described herein may allow customers to use their telephones while the G.Lite modem is simultaneously transferring data.
REFERENCES:
patent: 6111936 (2000-08-01), Bremer
patent: 6154524 (2000-11-01), Bremer
patent: 6266348 (2001-07-01), Gross et al.
patent: 6356585 (2002-03-01), Ko et al.
patent: 6456650 (2002-09-01), Cheng et al.
patent: 6549568 (2003-04-01), Bingel
patent: 2001/0031048 (2001-10-01), Payne et al.
ITU-Telecommunication Standardization Sector, Jan. 18-22, 1999, Draft Recommendation G.992.2, pp. 1-152.
ITU-Telecommunication Standardization Sector, Oct. 12-23, 1998, G.994.1 Draft Document, pp. 1-35.
Tampere University of Technology Telecommunication Laboratory, Feb. 17, 1995, ADSL, pp. 1-20.
ITU-T Recommendation G.992.2 (06/99)—Splitterless asymmetric digital subscriber line (ADSL) transceivers.
ITU-T Recommendation G.994.1 (06/99)—Handshake procedures for digital subscriber line (DSL) transceivers.
Murphy Tim
Staszak Martin
Williams Richard
3Com Corporation
McDonnell & Boehnen Hulbert & Berghoff
Phu Phoung
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