Re: [Sip] Changes in caller prefs -09
Rohan Mahy <rohan@cisco.com> Wed, 13 August 2003 21:58 UTC
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Date: Wed, 13 Aug 2003 14:59:49 -0700
Subject: Re: [Sip] Changes in caller prefs -09
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Cc: sip@ietf.org, Ted Hardie <hardie@qualcomm.com>
To: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
From: Rohan Mahy <rohan@cisco.com>
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Hi, I already privately replied to Jonathan about this and spoke up at the meeting, but since there has been a significant lack of discussion... <as a chair> If you feel Jonathan's proposal is reasonable, please send him a private ping. If not, please raise your issues. </as a chair> On Tuesday, July 8, 2003, at 12:15 AM, Jonathan Rosenberg wrote: > Folks, > > You may have noticed that caller prefs -09 was posted: > > http://www.jdrosen.net/papers/draft-ietf-sip-callerprefs-09.txt > http://www.jdrosen.net/papers/draft-ietf-sip-callerprefs-09.html > http://www.ietf.org/internet-drafts/draft-ietf-sip-callerprefs-09.txt > > This document is substantially different from -08. > > First, the capabilities stuff has been yanked into a separate I-D > (http://www.ietf.org/internet-drafts/draft-ietf-sip-callee-caps- > 00.txt). That includes REGISTER and OPTIONS processing, and all of the > media feature tag definitions and registrations. > > The reason for the split, as I indicated in another note, was that we > believed there were going to continue to be problems with the caller > preferences piece of callerprefs (i.e., the Accept-Contact and > Reject-Contact header fields). A big issue we encountered with -08 > based on excellent input from Ted Hardie, was that q-value arithmetic > is a no-no. Q-values as defined are ordinal, and you can't perform > arithmetic on them, or compare them between different sources. We had > been doing a lot of that in -08. > > So, in -09, the algorithm has changed. THe proxy computes the score > for each Accept-Contact rule against each Contact, as before. The > overall caller preference for a contact is then computed as the > average of the scores across all Accept-Contacts for that contact. > Previously, we had a really complex function instead of arithmetic > average. The reason had a lot to do with quirks that arise when you > try to do q-value arithmetic. Anyway, once the average (the caller > preference) is computed, it is used in a specific way. For those > contacts with EQUAL Q-VALUES AS SET BY THE CALLEE, the caller > preference is used to order them. We never combine the caller and > callee preferences; we merely use the caller preference to provide an > order when the callee provides none. > > This algorithm is a lot simpler, and it never tries to do arithmetic > on q-values. However, there is some loss of functionality. I tested > the algorithm on all of the use cases, and found that a few failed. > For example, Section 3.5 of > http://www.jdrosen.net/papers/draft-ietf-sipping-callerprefs-usecases- > 00.txt describes a case. There, the caller wants the call to go to a > videophone, but will take an audio-only device as a second choice. The > callee prefers the audio-only phone. Because the caller preferences > can't ever reorder callee contacts with differing q-values, there is > no way to "override" the callee preference for the audio phone, and > still fall back to it in the case where the videophone doesnt work or > can't be reached. > Section 3.12 describes a similar case, where a user wants to go right > to voicemail, but will take a call with the user if there is no > voicemail. We can't do that anymore. <as an individual> I'm not losing any sleep over this use case, as the user can still do this in two-steps (use Reject-Contact first, get back a 404 response and then retry). Simple things should be easy. More complicated things can be harder. </as an individual> thanks, -rohan > I welcome comments on whether this loss of functionality is > substantial enough that we need to investigate ways of getting it > back. I personally would prefer to just declare victory with what > works and move on. > > Some of the other changes: > > * elimination of the q-values in the Accept-Contact; they were never > needed in any of the use cases, so I removed them > > * Clarification on the purpose of Proxy-Require, based on comments by > Mary and others during wglc. > > * A lot more discussion on how to set the require and explicit > parameters. These can be confusing, and its hard to tell which of them > you need. > > * when a proxy is redirecting, it sets the q-values for the contacts > to anything which orders them based on the results of the above > algorithm > > > Comments and questions welcome. > > Thanks, > Jonathan R. > -- > Jonathan D. Rosenberg, Ph.D. 600 Lanidex Plaza > Chief Technology Officer Parsippany, NJ 07054-2711 > dynamicsoft > jdrosen@dynamicsoft.com FAX: (973) 952-5050 > http://www.jdrosen.net PHONE: (973) 952-5000 > http://www.dynamicsoft.com > > > > _______________________________________________ > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip > This list is for NEW development of the core SIP Protocol > Use sip-implementors@cs.columbia.edu for questions on current sip > Use sipping@ietf.org for new developments on the application of sip _______________________________________________ Sip mailing list https://www1.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use sip-implementors@cs.columbia.edu for questions on current sip Use sipping@ietf.org for new developments on the application of sip
- [Sip] Changes in caller prefs -09 Jonathan Rosenberg
- Re: [Sip] Changes in caller prefs -09 Rohan Mahy