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Re: [Sip] Error reporting in caller prefs



inline.

Adam Roach wrote:
"Jonathan Rosenberg" <jdrosen@dynamicsoft.com> writes:

I am inclined to go with approach 3, adding the appropriate discussions on the privacy considerations. The specific algorithm I would propose is this. If the caller prefs selection process results in zero contact, the proxy re-runs the algorithms without the implicit preferences. If now, there are contacts remaining, it concludes that the implicit preferences caused the problem. It then checks to see if the problem was methods or event packages, and generates a 405 or 489 accordingly.

Two comments; one con, one "interesting":

1. It seems to me that this approach adds a substantial burden
   to the proxy.
Well, its definitely more than zero. Caller prefs as it stands is, by definition, something a proxy spends cycles doing. How much more it will take to add this piece of processing, I am not certain.

2. This has the interesting effect of forcing the proxy to
   aggregate the methods and the event-packages
   available for an address-of-record. (e.g. if I have
   a client registered that supports MESSAGE,
   and one that supports INVITE, the proxy-generated
   405 will ostensibly indicate both INVITE and MESSAGE
   as acceptable methods.) Of course, this may well exacerbate
   the security problems you discuss -- but it also might
   be a useful feature. It also has the odd consequence that
   I can get a more accurate picture of your capabilities
   by intentionally sending an invalid method than
   I can by sending an OPTIONS...
Interesting indeed.

I would rather not reveal information which would otherwise not be revealed. I'd propose that the proxy reveal only the supported methods of the UA that would have otherwise received the request.

-Jonathan R.


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

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