[secdir] Secdir review of draft-ietf-sipcore-refer-clarifications-04

[Radia Perlman <[e-mail]>]

I have reviewed this document as part of the security directorate's ongoing
effort to review all IETF documents being processed by the IESG.  These
comments were written primarily for the benefit of the security area
directors.  Document editors and WG chairs should treat these comments just
like any other last call comments.

This is a clarifications document describing the changes to RFC3515 that
were implied by the publication of RFC6665. The document is fairly opaque to
readers not familiar with those two RFCs (including me), but its claim that
it does not change the security considerations for RFC3515 beyond those
already stated in RFC6665 seem highly plausible. It's a little surprising
that the contentof this document wasn't folded into RFC6665, but assuming
that document was adequately reviewed, this one should be fine.

Radia