Calling Party Control is a line disconnect signal sent by a central office to customer equipment. It briefly drops the direct current on the telephone line to zero volts, typically for a few hundred milliseconds. This tells automated answering equipment like PBX systems and voicemail machines to release the line and reset for the next call.
Heard on the job
The answering machine keeps recording dead air because the PBX isn't passing the CPC signal down to the analog ports.
Insider tip
Without a proper CPC signal, automated systems will often record the fast busy signal or silence until their maximum recording time is reached.
Also heard as
- Calling Party Control
- open loop disconnect