Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-01-25
2003-09-30
Pham, Chi (Department: 2631)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C375S222000
Reexamination Certificate
active
06628664
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to telephony in general, and in particular to apparatus and methods for transferring a high-speed voice-band data modem signal over telephone networks that incorporate equipment such as multiplexers and pair gain apparatus between the central office and the subscriber.
BACKGROUND OF THE INVENTION
Digital data is typically transmitted between the central office (CO) and the subscriber by converting the data to analog form suitable for band-pass transmission over POTS lines. Since all modern CO switches are digital, they perform a digital to analog (D/A) conversion on downstream data transmitted to the subscriber and analog to digital (A/D) conversion on upstream data received from the subscriber.
Transmission equipment such as multiplexers or pair gain devices installed between the CO and the subscriber usually require at least two additional conversions per one-way transmission. In a downstream transmission an A/D conversion is performed on transmissions received from the CO, typically at a central office terminal (COT), and a D/A conversion is performed on transmissions to the subscriber, typically at a remote terminal (RT). Upstream transmissions likewise usually require at least two additional conversions.
These additional conversions often degrade the transmission line quality thereby interfering with the operation of high-speed modems such as 56k pulse amplitude modulation modems such that it is often impossible to transmit data above 28,800 Kbps where such transmission equipment is used.
SUMMARY OF THE INVENTION
The present invention seeks to provide novel apparatus and methods for transferring a high-speed voice-band data modem signal over telephone networks that incorporate equipment such as multiplexers and pair gain apparatus between the central office and the subscriber, or other DAML-type systems. The present invention provides an improved system which overcomes the known disadvantages of the prior art as discussed above and provides transmission throughput substantially at the rated symbol rates of 56k pulse amplitude modulation modems.
There is thus provided in accordance with a preferred embodiment of the present invention a telecommunications system including an at least partially digital telephone link having an analog end portion, first and second modems disposed along the link, and analog/digital devices disposed along the link intermediate the modems which are operative to support communications between the first and second modems substantially at bit rates in excess of 28.8 Kbps.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, the analog signal having been prepared at a first codec, a clock interface operative to receive clock timing information of the first codec, a second codec operative to convert the analog signal for digital transmission, digital transmission apparatus operative to digitally transmit the converted signal and the clock timing information, a digital signal interface operative to receive the converted signal and the clock timing information, and a third codec operative to reconvert the converted signal to an analog form, characterized in that the third codec is operative to reconvert in clock-synchronicity with the first codec in accordance with the clock timing information.
Still further in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform &mgr;-Law companding.
Moreover in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform a-Law companding.
Further in accordance with a preferred embodiment of the present invention the second and third codecs are operative to perform sampling at a clock rate greater than the clock rate used by the first codec.
Still further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, a first codec operative to convert the analog signal for digital transmission, digital transmission apparatus operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a second codec operative to reconvert the converted signal to an analog form, characterized in that the first codec is operative to convert using linear conversion at a bit resolution greater than the bit resolution of the analog signal, and the second codec is operative to reconvert using linear conversion.
Additionally in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, the analog signal having been prepared at a first codec, and a second codec operative to convert the analog signal for digital transmission, characterized in that the second codec is operative to sample the analog signal at a clock rate greater than the clock rate used by the first codec.
Moreover in accordance with a preferred embodiment of the present invention the system further includes digital transmission apparatus operative to digitally transmit the converted signal, a digital signal interface operative to receive the converted signal, and a third codec operative to reconvert the converted signal to an analog form.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the first and second modems, a codec and a third modem, both arranged to receive the analog signal in parallel, a processor operative to receive digitized data from the third modem and provide the digitized data to a fourth modem, a selector operative to receive digitized data from either of the codec and the fourth modem, and digital transmission apparatus operative to digitally transmit the digitized data received from the selector, the selector selectively provides the digitized data to the digital transmission apparatus based on at least one predefined selection criterion.
Still further in accordance with a preferred embodiment of the present invention the selector is operative to selectively provide either of the digitized data received from the codec based on the absence of a modem training signal received at the third modem, and the digitized data received from the fourth modem based on the detection of a modem training signal received at the third modem.
Additionally in accordance with a preferred embodiment of the present invention the system further includes a buffer operative to buffer the digital data received from the third modem.
Moreover in accordance with a preferred embodiment of the present invention the processor is operative to operate both of the third and fourth modems at the same connection speed.
Further in accordance with a preferred embodiment of the present invention the system further includes an analog signal interface operative to receive an analog signal representation of digital data from a transmission source associated with one of the modems, a first codec operative to convert the analog signal to digital data form, a DSP filter operative to filter the digital data, digital transmission apparatus operative to digitally transmit the filtered signal, a digital signal interface operative to receive the filtered signal, and a second codec operative to reconvert the filtered signal to an analog form, charac
Guzikevits Zuri
Piasecki Joshua
Berkowitz Marvin C.
ECI Telecom Ltd.
Kumar Pankaj
Nath & Associates PLLC
Novick Harold L.
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