Disconnect Clear Time / Calling Party Clear

[electronicsuk]

Hello all. I'm a virgin media customer and have two lines installed to my house, both of which now run into an Asterisk PBX connected to SIP phones around my house. Trouble is, the voice modems installed in the computer running the PBX are having trouble detecting when the calling party on the other end of the line has hung up. This results in 10 seconds or so of silence at the end of any voicemail messages left on the PBX, and also causes my SIP phones to ring for an extra 5 seconds or so after the caller has hung up.

I have read this is a common problem when using voice modems on UK lines, often because of the Disconnect Clear Time (CPC) set at the exchange. Apparently most lines have a CPC time of about 100mS, although the voice modem requires more time than this to detect a hangup. BT can change the CPC/Disconnect Clear time for customers to anything up t0 900mS, can any NTL engineers tell me if it would be possible for me to alter the CPC of my two incoming lines to 800mS? I haven't even bothered ringing customer services as I'd be wasting my time even asking.

Thanks again.

Matthew