through E&M signal.
3) Reversal polarity (analog signal)
：
For switch of PSTN, it will send the line reversal
polarity signal to the user of near end, if the user of far end answer or release the
call.
由
PSTN.
4) Line busy tone detection (analog signal): Detecting the line signal through the
equipment of FXO port, product can know the user of far end answering or
releasing the call according to the voice signal and type of signal.
For FXO port, only 3) and 4) are available. Detecting line voice signal is not reliable. For
example, if far end is unreachable, PSTN switch may provide IVR to caller, which will cause
the wrong judgment that the user of far end has answered.
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Disconnect Supervision function means you can monitor call release situation of far end
of PSTN remotely, and process accordingly through FXO, E1/T1 of PSTN Switch and PBX.
Just like remote Answer Supervision, Disconnect Supervision can be achieved through four
ways:
For FXO port, only 3) and 4) ways are available. For ordinary PSTN line, when one side
releases the call, it will send busy signal to opposite side and prompt him to hang up. So
normally line busy tone detection method is adopted to monitor the call release situation of
remote site. If line busy tone can not be provided or detected, we can also get the call
release information of far end through monitoring the polarity of line voltage during the call. If
the polarity reverses again, then the call is released in the far end.
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FXO, FXS, and E&M are all analog signal interfaces.
FXS (Foreign Exchange Station), a voice interface, is used to connect digital telephone
switch and POTS telephone. It simulates as PABX extension interface ( or user interface of
Central Office), and can realize the connection between an ordinary telephone and a
multiplexer. In simple words, FXS port is used to connect POTS ordinary telephone, and FAX
machine. FXS port can provide remote feed.
FXO (Foreign Exchange Office), also a voice interface, is used to connect central switch
and digital telephone exchange system. For Central Office, it simulates as PABX extension,
which can realize the connection between an ordinary telephone and a multiplexer. In simple
words, FXO is used to connect PSTN line, and it needs remote feed.
