B.Dutta,
Regarding "a change in SDP is not acceptable", this is
impossible to enforce with a re-INVITE. Even if B sends
the offer, A can change it's answer. From RFC 3264, section 8,
However, the answerer MUST generate a valid answer
(which MAY be the same as the previous SDP from the
answerer, or MAY be different), according to the
procedures defined in Section 6.
If a change is SDP is truely not acceptable and if you must
interoperate with UAs that don't enforce that policy,
you'd be better of using UPDATE for your session refreshes
or not using session timers at all.
-troy
Banibrata Dutta wrote:
Thanks for the excellent explanation of the "why" aspect.
Now I can imagine as to why in my case (where a change in
SDP is not acceptable), "B" must include "SDP" (as a matter
of policy).
regards,
B.Dutta
-----Original Message-----
From: Troy Cauble [mailto:[EMAIL PROTECTED]
Sent: Tuesday, August 23, 2005 8:51 PM
To: [email protected]; [EMAIL PROTECTED]
Subject: Re: [Sip-implementors] session refresh, but without SDP ?
From: "Neeraj Jain" <[EMAIL PROTECTED]>
Hi,
As per sec 14.1 of RFC3261, both of these are valid scenarios. This
says, in context of re-INVITE SDP, that - "It is important to note
that the full description of the session, not just the change, is sent."
Absence of SDP in re-INVITE means that it's a re-INVITE without an
offer, in which case first reliable response to it will contain an
offer and usual offer/answer process will follow.
Regards,
Neeraj Jain
BayPackets Technologies
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Banibrata Dutta
Sent: Tuesday, August 23, 2005 5:30 PM
To: 'Banibrata Dutta'; [email protected]
Subject: RE: [Sip-implementors] session refresh, but without SDP ?
Additional info:
NOTE: Here the "UAS" is the refresher.
A B
---INVITE(sdp)---> : M1
<--200 OK--------- : M2
---ACK-----------> : M3
...
<--INVITE()------- : M4
case1:
---200 OK(sdp)---> : M5
case2:
---200 OK--------> : M5'
Is the case1 the valid scenario in case of session refresh, i.e. M5
contains same "sdp" as M1 ?
or, is the case2 a valid scenarios ?
- bdutta
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Banibrata Dutta
Sent: Tuesday, August 23, 2005 4:42 PM
To: [email protected]
Subject: [Sip-implementors] session refresh, but without SDP ?
Hi,
Does absence of body (SDP) in the re-INVITE used to do session-refresh
(in case of Session-Timers), signify that media properties remain
unchanged from the previously negotiated ones, or does it mean, no
media, i.e. any established RTP sessions are to be torn down, if
re-INVITE doesn't contain body ?
thanks & regards,
bdutta
Bdutta,
It does not mean "no media". It means UA "A" should make an offer in a
response.
And while a re-INVITE is a session-refresh, UA "A" can't know that that's
the primary purpose of the re-INVITE. A re-INVITE without offer could
indicate a 3PCC-like flow where "A" is about to be connected to another UA.
So should the SDP offered remain unchanged from the previous negotiation?
That's up to UA "A"; if "B" needs it to be the same, it should have sent the
offer.
In my opinion, "A" should send an offer with all supported coders, not the
possibly reduced set from the previous negotiation, because it may be
opening negotiations with a new peer. But that's not a SIP requirement,
that's a policy.
-troy
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