The text in Internet Draft 05 Calendar Availability seems ambiguous in part.
First, the VavailabiityType object indicates a bound interval in which everything "defaults to" "busy-unavailable" whether or not busytype is present.
Then busyness is not indicated "...for any time periods corresponding to "AVAILABLE" subcomponents."
What is busyType used for then, if the Vavailability "defaults" to busy-unavailable? There's no clear semantics of any other busyType value.