This event is fired on Session Timer dialogs that have the role of
refresher, when a session refresh is required to test if the session
is still active. This event will be fired on a dialogs that have session
timers enabled, and have been selected as the refresher, when half of the
session expiry interval has passed since the last session refresh.
The application should immediately send a re-INVITE or UPDATE on the dialog to refresh the session
and reset the session timer.