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 documents lists set of requirements for the optimizations for
SIP/SIMPLE when used in large inter-domain environments. As such it
does not really have security considerations as it does not specify
any protocol, but it does have some security requirements. Most of
those security requirements are in type of "MUST NOT change security
requirements of existing RFCs".

I think the current document is good enough for security
considerations / requirements area.

One thing that do require more work is the abstract section. Now it is
very short (single sentence) and it mostly says same thing as title of
the document. It should give more information what is meant with
"inter-domain" and give references to the "SIP/SIMPLE" already there,
not just use those acronyms there withing expanding them or providing
references.

Taking few more sentenses from the "Introduction" section would fix
that problem.

Nits:

Section "4.  Considerations for Possible Optimizations":

"Some initial work to address= these issues can be found in:"
			    ^^^^
Extra '='-character.
-- 
kivinen at iki.fi