[MEDIACTRL] An implementation question about BYE and <unjoin>

[Victor Paulsamy <vpaulsamy at ditechnetworks.com>]

An AS sends a <join> toward a MS to create media stream between two RTP sessions terminated on the MS.

At the time of <join>, the two SIP dialogs, referenced in id1 and id2 attributes are available.

Suppose, if one of the parties hung up by emitting a BYE toward the AS,
what is envisioned as an acceptable behavior for the controlling AS
from MEDIACTRL perspective (this is one of the loose ends that wasn't
specified):

1. the AS sends a BYE to cleanup the session; but never sends
<unjoin>, forcing MS to remove the media stream between the two
entities -- implicitly -- as the SIP session is cleaned up upon receiving
BYE?

or 

2. the AS sends <unjoin> first to the MS to remove the established media stream and then BYE to cleanup the session?

Thanks in advance.

--victor