How to get Disconnect Supervision on your BT Telephone Line
23rd Dec 2008, 20:42:58
Disconnect Supervision is a brief interruption of your telephone line's usual 48V signal. This voltage drop tells your device that the remote party has cleared the line and it is time to hang up. Disconnect supervision is also sometimes called "calling party control (CPC)," "open loop disconnect", "cutoff on disconnect" or "disconnect clear time (DCT)". Phew.
Anyway, by default, the timing of this voltage drop seems to be only 100ms or so which is too short for the FXO card in my Asterisk box.
Like most BT related problems, this can be resolved by speaking to the right person, using the right BT terminology and asking the right questions.
After about two hours of explaining the ins and outs of a cat's arsehole to several bemused and disinterested offshore call centre employees, I finally found the following procedure to be efficacious:
- Call 0800 800154.
- Unless your telephone line is a business line, do not enter any number or make any selection when prompted by the IVR, eventually you will fall through to a human being.
- When the nice lady or gentlemen answers, politely explain that you have a residential telephone line, but that you have been advised to contact them because you are using a PABX. Ask them to set the "Disconnect Clear Time" to 800ms.
- Thirty seconds later, your line will be working.
If anybody reading this knows how to get Virgin Media to do this, please tell me and I will award you one million points!*
*Cash value 0.000001p.