Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1999-02-12
2001-11-27
Pham, Chi (Department: 2731)
Pulse or digital communications
Transceivers
Modems
C375S219000, C370S465000, C370S468000, C370S494000, C370S495000, C379S093010, C379S093090
Reexamination Certificate
active
06324212
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus using low spectrum selectively for both Asymmetric Digital Subscriber Line (ADSL) and Plain Old Telephone Service (POTS) service over a single loop by adding predetermined control messages to allow rapid mode switching between just ADSL service and combined ADSL and POTS service based on central office or subscriber events indicating voice call initiation.
BACKGROUND OF THE INVENTION
Asymmetric Digital Subscriber Line (ADSL) is defined, and pertinent standards information thereto is provided, in the Standards Document T1E1.4/98-007R1 entitled “Standards Project for Interfaces Relating to Carrier to Customer Connection of Asymmetrical Digital Subscriber Line (ADSL) Equipment”, Sept. 26, 1997, and subsequent revisions edited by Bingham and Van der Putten. More particularly, Asymmetric Digital Subscriber Line (ADSL) has been defined as consisting of a pair of Discrete Multitone (DMT) modems, one at each end of a twisted pair subscriber loop, with band splitters at each end to provide isolation between a high frequency spectrum (above 24 KHz) used for data transmission and lower frequencies (0-4 KHz) used for Plain Old Telephone Service (POTS) or Integrated Services Digital Network (ISDN) used in some applications. These modems use DMT technology to provide high data bandwidth and the ability to adapt the data rate at startup to match the transmission and noise characteristics of each individual subscriber loop. Each 4.3125 KHz band of the frequency spectrum (referred to as a Tone Bin), with center frequencies from 25.875 KHz (Tone Bin #
6
) to 1.04 MHz, is populated with a signal which may be considered to be a tone whose amplitude and phase are modulated to encode data bits. Tone Bins below 24 KHz (e.g., Tone Bins #
1
-#
5
) are not used for data transmissions.
Proposals have been made by various companies to define an alternate spectral assignment for Asymmetric Digital Subscriber Line (ADSL) Discrete Multitone (DMT) modems that allow for the use of low frequencies (below 24 KHz) for additional data throughput. In existing classical ADSL systems, the lower frequencies including the 0-4 KHz voice band and approximately 20 KHz of guard band thereabove, are reserved for Plain Old Telephone Service (POTS) telephony voice and signaling transmissions in some applications. In these classical ADSL systems, the ADSL data transmissions are transmitted in frequency bands above 24 KHz (Tone Bin #
6
and above) with the different transmissions separated by filters in central office and Customer Premises Equipment (CPE) splitters.
Recent interest in “splitterless” ADSL has generated an activity in trying to provide a dual modality for transmissions wherein a subscriber's line could be used either in the classical ADSL mode as described above, or in a data only mode. In the data only mode, the lower frequencies (0-24 KHz) would be used to carry additional DMT “tones” (Tone Bins #
1
-#
5
) modulated with additional data. Since the lower frequencies are transmitted preferentially by most telephone loops, these lower frequencies can add substantial throughput capability to the subscriber's line.
The recent focus has been on eliminating the band splitter, at least at the subscriber premises. This necessitates some reduction in data throughput, since data carrier amplitudes must be reduced to avoid interference to POTS voice generated by nonlinearities. Since the POTS phone impedance loads the subscriber loop, it reduces input amplitude and available spectral bandwidth to the data receivers. Alternatively, POTS filters may be installed on each POTS telephone to prevent the ADSL signal from reaching, or being adversely affected by, the telephone, whether on-hook or off-hook. Unfortunately, while these POTS filters will reduce, or substantially eliminate, the POTS signal interference and the need to reduce the ADSL signal amplitude, the filters may render one or two of the tones below Tone #
6
unusable. This reduction in data bandwidth is viewed as an acceptable tradeoff to reduce the complexity of installation of the service by eliminating equipment rewiring to accommodate the splitters. Coincidentally, complexity of the modem is reduced due to the narrower bandwidth and the attendant reduced signal processing bandwidth.
It is desirable to provide dual modality for transmissions wherein a subscriber's line can be used either in the classical ADSL mode as described above, or in a data only mode while providing rapid mode switching between just ADSL service and combined ADSL and POTS service based on central office or subscriber events indicating voice call initiation.
SUMMARY OF THE INVENTION
The present invention is directed to apparatus using low spectrum selectively for both Asymmetric Digital Subscriber Line (ADSL) and Plain Old Telephone Service (POTS) service over a single subscriber loop by adding predetermined control messages to allow rapid mode switching between just ADSL service and combined ADSL and POTS service based on central office or subscriber events indicating voice call initiation.
Viewed from one aspect, the present invention is directed to apparatus for providing both Plain Old Telephone Service (POTS) and Asymmetric Digital Subscriber Line (ADSL) data service over a common subscriber loop providing a predetermined frequency spectrum for transmission purposes. The ADSL data service makes use of a multiplicity of quadrature modulated tones separated in frequency from one another across the predetermined frequency spectrum, and POTS makes use of only a portion of said predetermined frequency spectrum. The apparatus comprises means for using said portion of the predetermined frequency spectrum for POTS while a POTS call is in progress, and means for excluding ADSL data service from at least said portion of the predetermined frequency spectrum and reducing the number of tones while a POTS call is in progress, and expanding ADSL data service into said portion of the predetermined frequency spectrum and increasing the number of tones while a POTS call is not in progress.
Viewed from another aspect, the present invention is directed to apparatus for providing bidirectional Asymmetric Digital Subscriber Line (ADSL) data service and Plain Old Telephone Service (POTS) over a subscriber loop. The apparatus comprises an ADSL transceiver and a control processor located in a local communication center. The ADSL transceiver receives ADSL data in a first direction from a remote source and loads the received ADSL data into predetermined tone bins for transmission over the subscriber loop to subscriber data equipment. The ADSL transceiver receives also ADSL data in a second direction in the predetermined tone bins from the subscriber loop for processing the ADSL data for transmission to the remote source. The control processor is responsive to a detection of an origination of a POTS call for generating a first control signal that causes the ADSL transceiver to load ADSL data into tone bins which are only in a frequency band above a predetermined frequency band used for a POTS call for data transmissions over the subscriber loop. The control processor is responsive to a detection of a termination of a POTS call for generating a second control signal that causes the ADSL transceiver to load ADSL data into tone bins which are in both the predetermined frequency band used for a POTS call and the frequency band thereabove for data transmissions over the subscriber loop.
Viewed from still another aspect, the present invention is directed to apparatus for implementing bidirectional Asymmetric Digital Subscriber Line (ADSL) data service and Plain Old Telephone Service (POTS) over a subscriber loop. The apparatus comprises an integrated line circuit which comprises detecting and processing circuitry, an ADSL transceiver, and a control processor. The detecting and processing circuitry detects an origination or termination of a POTS call directed to or from a subscriber coupled to the subscriber l
Nguyen Dung X.
Pham Chi
Siemens Information and Communication Networks Inc.
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