[top]CPC (Calling Party Control) or Open Loop Disconnect
CPC (Calling Party Control) is a signal sent by a FXS device and received by a FXO device, to indicate that the calling party has hung up.
The CPC is normally signalled by a short circuit (0 volts) and ranges from 250 to 500 milliseconds in length.
Most FXO devices (telephones, answering machines, PBX ports, etc.) have a timer setting for CPC. Setting the time too large, at 800ms for example, when the CPC is only 500ms, will result in the device missing the disconnect signal and holding the line open. Conversely, setting the CPC too small, at 50ms, for example, could result in cut-offs. 20ms-50ms short circuits can occur after going off-hook or dialing, too small of a CPC value could cause the FXO device to misinterpret the off-hook or dialing as a hang-up.
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CPC
Linear Mode
