Re: [sipcore] RFC 4028 UAS behavior requirement of Require header

Hi Holi

The RFC says UAS should add a Require: timer in response when UAC is the
refresher to indicate to UAC that it is the refresher. But I think this is
redundant as UAC anyway knows it is the refresher and does not need a
reminder from UAS.

On Fri, May 28, 2021 at 3:18 PM Hoil Choi <hoil.choi@hotmail.com> wrote:

> Hi Ranjit, thanks for taking a look.
>
> However, I'm more interested in case where UAS is responding to UAC's
> request with refresher as itself (uac).  Consider this case -
>
> UAC ---- INVITE (Session-Expires: 1800;refresher=uac, Supported: timer)
> ----> UAS
> UAC <---- 200 OK (Session-Expires: 1800;refresher=uac)
> --------------------- UAS
>
> In this case, the statement in question seems to convey that UAS should
> also add "Require: timer" in its 200 response.  Why would this be, when
> it's clear that UAC declared itself as the refresher and that timer is
> supported?
>
> For reference, RFC 4028 Section 9 UAS Behavior (or page 16)
> If the refresher parameter in the Session-Expires header field in the 2xx
> response has a value of 'uac', the UAS MUST place a Require header field
> into the response with the value 'timer'.
>
> Thanks,
> Hoil
>
> ------------------------------
> *From:* Ranjit Avasarala <ranjitkav12@gmail.com>
> *Sent:* Friday, May 28, 2021 12:38 PM
> *To:* Hoil Choi <hoil.choi@hotmail.com>;
> Sip-implementors@lists.cs.columbia.edu <
> Sip-implementors@lists.cs.columbia.edu>
> *Cc:* sipcore@ietf.org <sipcore@ietf.org>
> *Subject:* Re: [sipcore] RFC 4028 UAS behavior requirement of Require
> header
>
> Hi Holi
> the presence of the "Require" header with value "timer" from UAS indicates
> to UAC that it (UAC) is performing the refreshing operation. but if the UAS
> is the refresher, then if Require header with value "timer" is present in
> response from UAS, then UAC should send BYE if it does not receive a
> session refresh request from UAS.
>
> Regards
> Ranjit
>
>
>
> On Fri, May 28, 2021 at 10:02 AM Hoil Choi <hoil.choi@hotmail.com> wrote:
>
> Hello,
>
> I hope this mail finds appropriate person or team for an answer to my
> question on RFC 4028.
> I am a SIP enthusiast and always learning a lot about it, but by no means
> am I an expert; so please excuse my ignorance.
>
> I came across an interesting statement In Section 9 UAS Behavior (or page
> 16).
>
>
> If the refresher parameter in the Session-Expires header field in the
>    2xx response has a value of 'uac', the UAS MUST place a Require
>    header field into the response with the value 'timer'.
>
>
> Statement seems to convey that UAS must place a Require header with value
> 'timer' when UAC requests itself to be the refresher.
>
> However, this statement should only be true, if UAC did not put
> Session-Expire with value of 'uac'.
>
> If UAC, in INVITE request, put Session-Expire with value of 'uac'
> (itself), UAS should not bother putting Require header field in the
> response.  Or to be more accurate, UAC should include 'timer' in Supported
> header, so that UAS doesn't have to bother putting Require header field.
>
> What is the reason behind the requirement of Require header, from UAS in
> this case?
>
> Thanks!
> Hoil Choi
> 253-273-5442
>
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