Re: [sipcore] Syntax of Feature-Caps header

Yehoshua Gev <yoshigev@gmail.com> Wed, 06 March 2019 14:59 UTC

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From: Yehoshua Gev <yoshigev@gmail.com>
Date: Wed, 06 Mar 2019 16:59:16 +0200
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To: Christer Holmberg <christer.holmberg@ericsson.com>
Cc: "sipcore@ietf.org" <sipcore@ietf.org>
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Subject: Re: [sipcore] Syntax of Feature-Caps header
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Hi Christer,

Thanks for the additional examples.

The last fix you made in the example made me re-read RFC 6809.
I noticed that the RFC indicates that:

   The Feature-Caps header field can be used within a SIP REGISTER
   request and within the 200 (OK) response associated with such a
   request.


Although not explicitly forbidden, a Feature-Caps header is not expected to
be included in non-200 responses.
In the draft, there are cases that do include Feature-Caps header in such
responses (like 555).

I believe that the draft makes a correct use of the header, but it might be
worth thinking why RFC 6809 has not
thought of this use case.

Best,
Yehoshua


On Fri, Mar 1, 2019 at 1:22 PM Christer Holmberg <
christer.holmberg@ericsson.com> wrote:

> Hi,
>
>
>
> I also noted that adding the ‘+’ is not enough. Note that the Feature-Caps
> header field syntax also mandates the ‘*’.
>
>
>
> So, the correct way is:
>
>
>
> Feature-Caps: *;+sip.608
>
>
>
> Regards,
>
>
>
> Christer
>
>
>
>
>
> *From: *sipcore <sipcore-bounces@ietf.org> on behalf of Christer Holmberg
> <christer.holmberg@ericsson.com>
> *Date: *Thursday, 28 February 2019 at 16.50
> *To: *Yehoshua Gev <yoshigev@gmail.com>
> *Cc: *"sipcore@ietf.org" <sipcore@ietf.org>
> *Subject: *Re: [sipcore] Syntax of Feature-Caps header
>
>
>
> HI Yehoshua,
>
>
>
> Please see inline.
>
>
>
> >I have a question regarding the syntax of the Feature-Caps header since
> I've not managed to find any real examples of its usage.
>
> >
>
> >The ABNF in RFC 6809 is defined as:
>
> >   Feature-Caps = "Feature-Caps" HCOLON fc-value
> >                   *(COMMA fc-value)
> >   fc-value     = "*" *(SEMI feature-cap)
>
> >   feature-cap       =  "+" fcap-name [EQUAL LDQUOT (fcap-value-list
>
> >                            / fcap-string-value ) RDQUOT]
>
> >
>
> > Following this syntax, I guess that for sip-push the header will look
> like:
> *>   Feature-Caps: *;+sip.pns="webpush"*
>
> >
>
> >
>
> >One example I could find is on
> https://tools.ietf.org/html/draft-ietf-sipcore-rejected-03:
>
> *>   Feature-Caps: sip.608*
>
> >Without the asterisk and the plus sign.
>
> >
>
> > Which one is correct?
>
>
>
> The sip.pns example is correct. The sip.608 example needs to be corrected.
>
>
>
> (I THINK I had previously commented on this when reading sipcore-rejected,
> but I may be wrong…)
>
>
>
> >Due to the lack of examples, would it be possible to add an example to
> the sip-push draft that includes feature capabilities
>
> >and media tags (especially that sip.pnsreg is used for both)?
>
>
>
> I will look into it. I guess that could be done when addressing Ben’s
> comments.
>
>
>
> Regards,
>
>
>
> Christer
>
>
>