In any PBX phone system, it is important to accurately detect when an outside caller has "hung up" the phone. This capability allows the PBX to also hang up, completing the disconnection. Once the call is fully terminated, not only is the phone line available for other calls, but more importantly the phone company's billing charge for that call ends. One common way in which a phone or PBX manages call termination is positive disconnect supervision.
In a typical external call scenario (where a call is placed through a CO, not between extensions of the PBX), the CO detects when the caller hangs up and then sends a disconnect signal (loop current drop) to the PBX. The PBX is responsible for detecting and handling the disconnect signal from the CO.
After receiving a disconnect signal from the CO, the PBX may:
In both cases, a disconnect message, not a loop current drop, is sent to the called extension. Standard analog voice boards cannot interpret disconnect messages because these messages are usually digital. PBX Integration boards can, however, detect disconnect messages and send a disconnect event to an application where it is used by the Dialogic standard voice programming mechanisms for handling call termination.
When a call is placed between extensions of the PBX, a disconnect message, not a loop current drop, is also used to indicate when a caller hangs up. In this scenario, the application has no way of knowing when the caller has hung up so it can receive another call. PBX Integration boards can detect the disconnect message and send a disconnect event to an application.
Not all PBXs have positive disconnect supervision. Refer to the documentation for your PBX to determine if your PBX provides positive disconnect supervision.
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