Should we register each individual MIME type or a family?

[Rosen, Brian]

I work with NENA, the North American Number Association.  We're engaged
in a standards effort for "Next Generation 9-1-1", moving the emergency
call system to an IP network.  Our work is based on IETF work, and uses
SIP Event Notification (RFC3265).  We need to define event packages for
use within private IP networks connecting public safety agencies, and we
do not expect use of these packages to escape into the wild.

As a practical matter, defining an event package means defining one or
more XML structures that are passed in the event subscription and/or
notification.  These structures are passed in SIP bodies, and thus need
MIME types, typically within the application tree.  We will request
registration using a prefix of vnd.nena.

My question is whether to register each of these MIME types individually
with IANA, or register a subtree (vnd.nena.ng911) and create a registry
in NENA for the subtree (vnd.nena.ng911.queuestate).  I would appreciate
advise on that subject.  We would expect a dozen or so event packages. 

We will also need some other MIME types for other SIP related use, for
which similar issues apply.  NENA is creating a registry management
service not unlike a very small IANA, that could manage the subname
space if that was deemed appropriate.

Brian