Disconnect Supervision

Situation: You have a connection to the PSTN. A caller from the Out There calls in to your PBX. They go into Voicemail, MusicOnHold, or enter a Conference. They hang up. But Asterisk does not notice, and continues recording voicemail messages/playing music/annoying other conference members by relaying a dialtone from the disconnected line. What's happening?

And what about when you have a SIP provider over an IP connection, NOT a PSTN connection? Any clues on that? (PHSchmidt)

Since I (JazEzork) don't have a clue, let me quote a few other people. If someone knows more than me, kindly edit this page.

Rich Adamsonsaid:

"Disconnect supervision refers to opening/closing the 2-wire circuit (as in hanging up a telephone), and in some cases, reversing tip/ring (48 volt polarity change)."

Mark Spencersaid:

"[FXO analog ports] don't detect busy signals. If you have "disconnect supervision" from your phone company (which is easy to test — just plug in a phone with a lighted keypad and watch to see if the keypad blinks off when the other end hangs up — if it does, you have the disconnect supervision), then your FXO should always be able to detect hangup."

and:

"Generally, loopstart does not include hang-up notification unless specifically done through forward-disconnect. Groundstart does include hangup notification as do the E&M based protocols. E&M also provides answer supervision, which neither Groundstart nor Loopstart do."

Steven Critchfieldsaid:
"Under Asterisk, Remote Disconnect Supervision is known as Kewlstart. In the Adtran it may be known just as disconnect supervision. Unless it is provided by the PSTN provider it doesn't help really."

Mike Holloway said:

"CPC (Calling Party Control) is a signal sent from most modern electronic COs to indicate that the "Calling Party" has hung up. It's usually called "Open Loop Disconnect" when you're programming telephone equipment. http://www.sandman.com/cpcbull.html"

and:

"I am betting you have a X100P card. I'm betting you have not enabled progress detection. I'm betting you do not have disconnect supervision. All this combines to give you a simple problem that asterisk doesn't know when the line was hungup and continues to try and service it. You can fix the problem by either getting the correct service, configuring your system to fake disconnect functions, or set a timeout on the call as you enter the section that leaves voicemail so the time allowed in this section is appropriately short and asterisk will hang up afterwards. ...