| 摘要 |
A dual-mode filter network for an Asymmetric Digital Subscriber Line (ADSL) has a first frequency response when the Plain Old Telephone Service (POTS) telephone is on-hook and has a second frequency response when the POTS telephone is off-hook. A detector is used to determine the on-hook/off-hook status. The dual-mode filter network may be situated at the central unit and connected to a Public Switched Telephone Network (PSTN) while the detector at the remote unit connected between the POTS low pass filter and the POTS telephone. In such case, the detector outputs a signal which is transmitter via the twisted pair on an overhead channel. Alternatively, the dual-mode filter and the detector may be co-located at either the central unit or at the remote unit. Regardless of where it, or the detector are located, the dual-mode filter network has at least different combinations of components which are activated, depending on the on-hook/off-hook status of the POTS phone. In addition, a single-mode filter instead of the dual-mode filter can be used at the remote unit.
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