Subject: [Sip] Open Issue #266: The Heterogeneous Error Response Forking Problem

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 6 Dec 2001 16:58:55 -0500

Issue:

A sends an INVITE to proxy P, which forks to UAS's B and C. B responds with
415, 
C with 401. 401 is passed upstream. A retries the INVITE, which goes to C,
which 
is ok with it and sends a 183. B still rejects with a 415. B will not ring.
C 
eventually results in an answering machine, even though the user was
actually at 
B.

The problem is a generalization of the problem that motivated the merging of

challenges in 401/407. However, here we have headers that "ask for more
info" 
that span different response codes. 

Furthermore, with the current mechanism, a proxy waits for all final
responses before passing one upstream. So, as long as SOME UA was happy with
the request, others that needed something different, and sent a 4xx of some
sort, will not get a resubmitted request.

Discussion points:

Robert has written a proposal on this:
http://www.nostrum.com/~rjsparks/draft-sparks-sip-fu-00.txt

More thinking is needed. Certainly, one potential solution is to simply
ignore this problem. Of the error-responses-that-ask-for-retry, and that can
be retried automatically - 401/407 (authentication), 415 (unknown media
type), 420 (Bad Extension), 484 (Address Incomplete), its not clear that any
of these will be common cases except for 401/407. In that case, things,
oddly enough, work if everyone challenges, otherwise, the most forgiving
phone will be the one that rings.

I have no specific proposal at this time, but am working on it. I believe
its closely related to the early media problem, with similar solutions being
needed.

-Jonathan R.

---
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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