PBX Integration Board User's Guide

2. Introduction to PBXs and KTSs
2.5. Positive Disconnect Supervision
PBX phone systems 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
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:
• terminate the outside call immediately and send a disconnect message to the
called extension
• send a disconnect message to the called extension and wait for the called
extension to hang up before formally terminating the call
In both cases, a disconnect message, not a loop current drop, is sent to the called
extension. Standard analog voice boards do not interpret disconnect messages
because these messages are usually digital. Dialogic
®
PBX Integration Boards
can, however, detect disconnect messages and send a disconnect event to an
application where it can be used by 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 does not know when the caller has hung up and can
receive another call. Dialogic
®
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 this feature.
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