[Sip] Changes in caller prefs -09
Jonathan Rosenberg <jdrosen@dynamicsoft.com> Tue, 08 July 2003 07:17 UTC
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Date: Tue, 08 Jul 2003 03:15:31 -0400
From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Organization: dynamicsoft
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Subject: [Sip] Changes in caller prefs -09
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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. 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] Changes in caller prefs -09 Jonathan Rosenberg
- Re: [Sip] Changes in caller prefs -09 Rohan Mahy