In the UK the serving telephone exchange sends a line break disconnect of approx 500mS when the calling party (who controls the call) hangs-up. The CO Trunk Circuit Descriptor “Disconnect Timer” should be programmed accordingly i.e. lower than this value.
Whilst some public telephone exchanges use “line reversal” disconnect supervision “busy tone” disconnect is by far the most common form of disconnect supervision elsewhere. This is easy enough to identify, connect a regular phone to the phone line, answer an incoming call, hang up at the far end and listen for tone(s).
If you’re lucky the phone company will confirm the tone(s) otherwise you will need to record and analyse the tone to establish the tone(s) frequency and on/off cadence. One way is to set-a voicemail box, ftp the message and use a freeware program to analyse. Once you know the tone you need to configure and enable CO Tone Detection.
There are some examples in the MCD Software Product_Support\COTonesDet directory
Note CO Tone Detection is only supported on embedded and or ASU trunks and NOT on the LS/GS Trunk Card. You need to be reasonably accurate when measuring the tones, when configured correctly it WILL resolve hang-up issues.