Events that happen on the telephone network must be detected so that the voice-mail system
intelligently can communicate with the phone system. The MIU detects, recognizes, and
notifies interested parties of such events. When a call forwards to voice mail or a subscriber
calls to retrieve messages, the telephone system signals one of Unity’s ports that an incom-
ing call is happening. The MIU detects the incoming call and signals to the arbiter that a
call has arrived on a given port. Likewise, after the call has been answered and the caller
hangs up, the telephone system signals Unity ...
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