Re: [sipcore] Reason as a parameter rather than an escaped header

Paul Kyzivat <pkyzivat@cisco.com> Wed, 24 November 2010 00:05 UTC

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Date: Tue, 23 Nov 2010 19:06:37 -0500
From: Paul Kyzivat <pkyzivat@cisco.com>
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To: Mary Barnes <mary.ietf.barnes@gmail.com>
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Cc: "Worley, Dale R \(Dale\)" <dworley@avaya.com>, "sipcore@ietf.org" <sipcore@ietf.org>
Subject: Re: [sipcore] Reason as a parameter rather than an escaped header
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On 11/23/2010 3:00 PM, Mary Barnes wrote:
> I think we are somewhat ratholing here.  A few responses inline below [MB].

Yes, I agree on that.

> The intent of the Reason in the HI entries is to capture the reason a
> request was retargeted.  The current normative text is the Reason
> (escaped header, header field, whatever) in the HI-entry is populated
> based on SIP Response codes and any other Reason header (e.g., Q.850)
> that might be associated with the request.  The Reason is included in
> the hi-entry with the hi-targeted-to-uri that was retargeted (i.e., the
> old) versus the hi-targeted-to-uri in the hi-entry to which the Request
> is being sent.  We should not change this due to backwards compatibility
> AND I think any new Reason values that we want to add to the hi-entries
> need to be added consistently.

> Thus IF there is agreement to add new Reason header field values for
> applications, then if those are used to populate the hi-entry, they
> should also be interpreted in the hi-entries to correspond to the
> hi-targeted-to-uri that was retargeted (i.e., the old URI that is lost)
> based on a decision that the request be associated with a specific
> application RATHER than the Reason being the application associated with
> the hi-entry with the hi-targeted-to-uri to which the request is being
> sent (i.e, the new URI).

In the interests of making progress rather than rat hole'ing, I already 
agreed (reluctantly) to acknowledge that the Reason headers in H-I 
entries need to continue to be assigned to the entries they have been, 
even though IMO this is nonsensical. We established that the URIs in H-I 
entries come from R-URIs that have no embedded headers, so that the 
embedded header in the H-I entry is only there as a result of explicit 
addition during the construction of the H-I entry. We just have to 
consider that the semantics of its presence there are unique.

I'm no longer arguing that point.

But my remaining concern is about the rules in 4244bis regarding how and 
when Reason headers are included in the H-I entries. It still seems to 
me that the text only talks about including them due to a response 
having been received. Where is the language that discusses adding a 
reason when retargeting is performed for some reason unrelated to a 
response?

While I think one can argue that a server doing such retargeting can 
imagine having sent the request to a virtual redirect server and then 
processing the response from it, ISTM that would then call for adding 
H-I entries for those steps.

> I would suggest that the best way forward is that we keep the current
> text as is and note that any additional Reason headers that are defined
> in the future MUST be interpreted in the same manner.  However, I do NOT
> think we should hold up 4244bis until we get full agreement on adding
> new Reason header values for applications as I firmly believe it is
> orthogonal - it can work based upon the current normative approach and
> interpretation of the Reason in the hi-entries.  We can debate till the
> end of time (or the end of SIPCORE WG as we did with other broken things
> in SIP) that this wasn't the right approach, but it is what it is and I
> think it's time to move forward.

I agree that 4244bis should not be held up because of the new reason 
values draft(s?).

At this point I would just like some clarity whether the *way* reasons 
are used in the examples in 
draft-mohali-sipcore-reason-extension-application-00 - reasons without 
responses - is thought to be *valid* in the context of 4244bis. If the 
answer is NO, then I'll shut up, and let Marianne or somebody else from 
3gpp complain if they think it should be.

If the answer is YES - that usage is considered valid according to 
4244bis, then I still want to know why, and perhaps see some additional 
text to make it clear.

	Thanks,
	Paul