[MMUSIC] Question to MIKEY embedding with kmgmt-ext.

Hi Elisabetta,

recently a question came up in the usage of the key management extentions
for SIP to use MIKEY:

Section 3.1.2 of draft-ietf-mmusic-kmgmt-ext-14 contains the following
statement: 

"If the key management rejects the offer and the session needs to be
aborted, the answerer SHOULD return a "488 Not Acceptable Here" message,
optionally also including one or more Warning headers (a 306 "Attribute not
understood" when one of the parameters is not supported, and a 399
"Miscellaneous warning" with arbitrary information to be presented to a
human user or logged, see Section 20.43 in [SIP]). Further details about the
cause of failure MAY be described in an included message from the key
management protocol. The session is then aborted (and it is up to local
policy or end user to decide how to continue)."

Concerning the sentence in bold (The sentence before the last sentence in
quotes), how does it do that in the following scenario?:
A UA receives an INVITE request containing an SDP offer with a MIKEY
I_MESSAGE that is for some reason unacceptable. The receiving UA will return
a 488 response, which does not contain an SDP answer. Therefore there is no
way of embedding a MIKEY R_MESSAGE to indicate the error. Is there any way
to signla the MIKEY error in this case?

Regards
	Steffen

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