Last Call Review of draft-ietf-sipcore-originating-cdiv-parameter-05
review-ietf-sipcore-originating-cdiv-parameter-05-secdir-lc-rose-2018-10-22-00

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.

Background: SIP currently provides no standard way to indicate that an invite
via diversion from the original terminating user (e.g., via busy response or an
unconditional call forward) is the result of diversion rather than a new
origination, making it impossible in the absence of proprietary signaling to
distinguish between the two cases. This draft adds an orig-cdiv signal to the
P-Served-User header to indicate an invite resulting from a diversion, allowing
an application server to take different actions in the two cases.

Security evaluation: The addition of a new actionable signal is properly noted
as the main security consideration of this change, along with a reminder that
the P-Served-User header must be implemented as a privileged channel within a
single trust domain and not transited into a domain from an untrusted entity.

Other comments: As a reviewer new to SIP, I found the document very easy to
follow. The introduction contained basic background about the use case, a clear
explanation of the problem, and a high-level overview of the proposed solution.
The normative section of the document was very clearly illustrated by the later
examples section, containing two typical use-cases with clear diagrams. This is
a model internet draft.