Telephonic communications – Telephone line or system combined with diverse electrical... – Having transmission of a digital message signal over a...
Patent
1993-11-15
1996-07-09
Kuntz, Curtis
Telephonic communications
Telephone line or system combined with diverse electrical...
Having transmission of a digital message signal over a...
379 98, 379199, 379114, 379140, H04M 1100
Patent
active
055352650
ABSTRACT:
A telephone line monitoring circuit for a MODEM monitors the TIP and RING lines of the telephone line. A first circuit of the monitoring circuit detects when a local phone goes off-hook while the MODEM is on-hook by sensing a decrease in a differential voltage between the TIP and RING lines. A second circuit detects the pick up of a local phone while the MODEM is off-hook by detecting a change in the impedance between the TIP and RING lines. A third circuit detects the hang up of a remote phone connected with the MODEM while the MODEM is off-hook by detecting a temporary break in the DC loop between the central office and MODEM. A snoop circuit monitors the telephone line for DTMF signals while the MODEM is on-hook. The snoop circuit becomes AC coupled to the telephone line when enabled, and does not apply a significant load to the telephone line. The monitoring circuit permits a processor to control a variety of call-related functions, including the recording of incoming voice mail messages, the logging of incoming and outgoing calls, and the blocking of outgoing calls to specified telephone numbers.
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AST Research Inc.
Kuntz Curtis
Woo Stella L.
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