| 摘要 |
An integrated line-card terminates an asymmetric digital-subscriber line (ADSL) copper-pair at a single point in a central office. The line card contains analog line circuitry such as a ring generator, off-hook detector, D.C. current feed, and a single analog-digital (A/D) converter. The phone line carries a composite signal of both the high-frequency ADSL data and the low-frequency voice or plain-old-telephone-service (POTS) signal. Instead of using an analog frequency-splitter with bulky, expensive inductor coils, a digital splitter is used. A digital-signal processor (DSP) can be used to perform the digital splitting of ADSL and POTS. The waveforms from the analog phone line are first converted to digital values by the A/D converter, and then a digital splitter separates the low-frequency POTS from the high-frequency ADSL. The ADSL data is formatted by the DSP for a data pathway to the Internet, while the POTS data is converted by the DSP to A-Law or C-Law for transmission over the telephone network's PCM highway. The DSP can perform all decoding, encoding, compression, and formatting needed by both ADSL and POTS. The quality of the phone line is improved by having a single termination point at the central office, rather than separate termination points for POTS and ADSL data from the phone line.
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