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

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<mailto: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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