Subject: [Sip] Re: Question Caller Preferences 08 draft

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 02 Jul 2003 03:40:29 -0400

I dont think I ever answered this.

George Foti (LMC) wrote:

> Quoting the 08 draft  section 7.4 (Matching):
> 
> Next, the proxy applies the predicates associated with the 
> Accept-Contact header field. For each contact that remains in the target 
> set, the proxy constructs a matching set, Ms. Initially, this set 
> contains all of the Accept-Contact predicates. Each of those predicates 
> is examined. It is matched to the contact predicate using the matching 
> operation of RFC 2533 [2]. If the result is not a match, and the 
> Accept-Contact predicate had its require flag set, the URI corresponding 
> to that contact predicate is discarded from the contact set. If the 
> result is not a match, but the Accept-Contact predicate removed from the 
> target set.

The above text is not actually whats in -08. The actual text is:

> Next, the proxy applies the predicates associated with the Accept-
>    Contact header field. For each contact that remains in the target
>    set, the proxy constructs a matching set, Ms. Initially, this set
>    contains all of the Accept-Contact predicates. Each of those
>    predicates is examined. It is matched to the contact predicate using
>    the matching operation of RFC 2533 [2]. If the result is not a match,
>    and the Accept-Contact predicate had its require flag set, the URI
>    corresponding to that contact predicate is discarded from the contact
>    set. If the result is not a match, but the Accept-Contact predicate
>    did not have its require flag set, that contact URI is not discarded
>    from the contact set, however, the Accept-Contact predicate is
>    removed from the matching set for that contact.

but your question is still relevant:

> 
> My question relates to the last statement in the above paragraph.
> The objective of that step, as I understand it, is to remove from the 
> set all predicates, that don't have an equivalent in the contact.
> 
> This step seems to be redundant, as it would not have an impact on the 
> score, since it would not change the score anyway (based on the way the 
> score is calculated)
> 
> Is my understanding correct?

In -08, I believe you are right. Setting the score to 0 is equivalent 
to removing the Accept-Contact predicate from the matching set. This 
algorithm has changed in -09, and with the new algorithm, it is not 
the case any longer.

> 
> My next question relates to the usage of the cancel-directive.
> Quoting the Draft :
> 
> cancel-directive: This type of directive indicates whether the
>              caller would like each proxy server to send a CANCEL
>              request downstream ("cancel") in response to a 200 OK from
>              the downstream server (which is the normal mode of
>              operation, making it somewhat redundant), or whether this
>              function should be left to the caller ("no-cancel"). If a
>              proxy receives a request with this parameter set to "no-
>              cancel", it SHOULD NOT CANCEL any outstanding branches on
>              receipt of a 2xx. However, it would still send CANCEL on
>              any outstanding branches on receipt of a 6xx.
> 
> The strength SHOULD NOT makes it unclear as to how the UAC can decide on 
> what to do, even if the proxy understands caller preferences.

The caller will end up seeing more 2xx than it normally would. It can 
then do what it wants - BYE some of them, keep some of them, as desired.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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