| 摘要 |
With a plug-in tone responsive unit at each extension, a central answering unit responds to a caller initiated, telephone company generated, ring signal on the telephone line and establishes a connection with the calling phone. Each of the remote units responds to a different predetermined tone frequency. When the caller pushes a key on a standard Touch Tone phone key pad to select a specific extension, the responding remote unit generates a ringing signal for that extension.
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