Re: [Gen-art] Gen-ART LC review of draft-hanes-dispatch-fax-capability-06.txt

[Gonzalo Camarillo <[e-mail]>]

Hi Paul,

[I am adding Paul to this thread since he was a coauthor of RFC 3840]

please, see below the exchange between Brian and Kevin regarding
draft-hanes-dispatch-fax-capability-06.txt.

This was Brian's original comment:

> Minor issue:
> ------------
> 
>    ... A UA
>    preferring the reception of fax calls MUST include the "sip.fax"
>    media feature tag in the Contact header field of REGISTER messages.
>    To confirm the registration of this preference, a SIP [RFC3261]
>    Registrar MUST then include this tag in the Contact header field of
>    its 200 OK response.
> 
> If the Registrar does not do this (e.g. because it hasn't been updated
> to support the new tag), what does the UA do when it receives the
> 200 OK response that doesn't include the tag?

Paul, can you share your views on this issue?

Thanks,

Gonzalo


On 05/12/2012 6:02 PM, Brian E Carpenter wrote:
> On 05/12/2012 14:12, Kevin Fleming wrote:
>> I suppose it could choose to unregister and re-register in some other way
>> in order to achieve its goals of receiving FAX calls, if it was configured
>> with enough network information to do so.
>>
>> Now that I think about it some more, is a registrar even allowed to return
>> a Contact header that differs from the one the UA supplied in its REGISTER
>> request? I suspect this is *not* allowed, and so if the registrar supports
>> Caller-Pref but the specific tag(s) in question fail some sort of
>> validation process, its only recourse would be to fail the REGISTER request
>> with a suitable error response.
> 
> If that's the standard behaviour, it would of course answer my question.
> 
>    Brian
> 
>>
>>
>> On Wed, Dec 5, 2012 at 6:35 AM, Brian E Carpenter <
>> [e-mail]> wrote:
>>
>>> On 05/12/2012 11:01, Kevin Fleming wrote:
>>>> The language in RFC 3840 doesn't appear to contemplate the situation
>>> you've
>>>> proposed. In its world, registrars can either support prefs (and will
>>>> accept "Require: pref") or they don't, and they don't have knowledge of
>>>> which feature tags are registered with IANA and which are not. Of course,
>>>> they *coud* attempt to validate the tags expressed by the UA, but I don't
>>>> see an explicit way for the registrar to indicate that the UA included
>>>> disallowed tags in its request.
>>> Understood, but in that case I don't see what good the confirmation
>>> of the tag from the registrar to the UA achieves - the UA is not going
>>> to be able to do anything with it (except maybe log whether it was
>>> received).
>>>
>>>     Brian
>>>
>>