a user is alerted to an expected occurrence of an event and automatically provided with a predetermined notice period of the expected occurrence of the event by identifying an event having an unreliable start time , but a start time that can be predicted more accurately as the time of the event approaches by monitoring a precursor parameter to the event . by monitoring the precursor parameter , a prediction is made of when the event is likely to occur . advance notice that the event is expected to take place is automatically issued during a predetermined notice period before the expected time of the event . session initiation protocol communicates the advance notice .