Subject: [Sip] Asserted-Identity: A P- Header?

From: "Peterson, Jon" <[email-masked]>
Date: Fri, 17 May 2002 17:03:25 -0500

There has been some substantial discussion in this working group about the
naming of the new header for the short-term network asserted identity work.
Although it took us some time to arrive on an agreeable name, I'd like to
suggest a slight modification to 'Asserted-Identity' - namely that it become
a P- header.

P- headers are defined in the 'sipchange' draft that discusses how
extensions to SIP should be created. The P- is short for 'preliminary',
'private', or 'proprietary' - and in fact, I think the Asserted-Identity
header for the short-term work is in fact compatible with all three of those
adjectives. More substantially, there are also specific criteria for P-
headers provided in the sipchange draft (in section 6.1) and I believe
Asserted-Identity is a good match for nearly all of those criteria.

sipchange says that P- headers may be appropriate when extensions "are
private or proprietary in nature, because a characteristic motivating them
is usage that is known not to fit the Internet architecture for SIP." As an
extension, short-term asserted identity does not define new methods,
responses codes, or option tags (criterion 2). The header is purely
informational in nature (criterion 4). Asserted-Identity also bears a
significant applicability statement (criterion 7). The current draft also
meets the constraints identified by criteria 2 and 3. I'm sure we could get
Expert Review as specified in criterion 1, and that the document could be
passed as described by criterion 6. 

What do we gain by making Asserted-Identity a P- header? Really only
political leeway; this doesn't entail any changes to how the header works.
But the underlying Trust Domain model of the short-term identity work is not
very compatible with the Internet model, and this may very well cause us
some consternation moving forward this document (some discomfiture along
these lines was previously expressed over sip-privacy-04). By making this
header a P- header we can deflect this sort of criticism by identifying this
as work that is known to be specific to private networks that do not adhere
to the Internet model as such. sipchange introduced this concept
specifically so that we could get this sort of header passed. If we aren't
using the P- header for this, I'm not sure what we'd use it for.

One thing that I know we lose by making Asserted-Identity a P- header is
that the long-term identity story would no longer use the same header name
as the short-term identity work. However, since the interface between
long-term, certificate-based identity and short-term, trust-based identity
will be defined as a gatewaying process, we really don't incur any cost from
using different headers. Personally, I still feel there is something to be
gained by using 'From' as the header in the long-term story (specifically,
this jibes in certain ways with existing S/MIME behavior in rfc3261). So I
suppose I don't find this loss to be troubling.

Thoughts?

Jon Peterson
NeuStar, Inc.

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