Subject: [Sip] Invite without offer

From: "Aditya Sehgal" <[email-masked]>
Date: Tue, 15 Apr 2008 20:19:33 +0530

Hi all,
Is there any practical situation where in an Invite will contain no SDP.
Lets say A calls B.
My understanding (albeit limited) of the RFC makes me believe that 200 OK is
sent out when B will pick up the phone. Now assuming, the Initial Invite
contained no offer (and 100 rel is not supported),the first offer is then
sent out at 200 OK .If the return ACK is either dropped in the IP cloud or
is delayed, with no media established, the call is essentially useless.

So, is there any situation where it makes sense for a UE to send an Invite
without an Offer.

Please correct me if my assumptions are wrong.

Thanks & Regards,
Aditya Sehgal

-- 
Don't take life too seriously....Nobody comes out alive anyway
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---

From: "Manpreet Singh" <[email-masked]>
Date: Tue, 15 Apr 2008 11:01:04 -0400

usually clients would do this to know the far end full list of
capabilities before they send their own offer. although this can be done
via OPTIONS, but not everyone supports it and this is the other way of
doing it. the media might be delayed but the 200OK is re-transmitted so
it should connect fairly quickly. for this reason clients which do this,
end up doing 100rel to avoid these kind of situations
 
M

________________________________

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Aditya Sehgal
Sent: Tuesday, April 15, 2008 10:50 AM
To: [email-masked]
Subject: [Sip] Invite without offer

Hi all,

Lets say A calls B. 
My understanding (albeit limited) of the RFC makes me believe that 200
OK is sent out when B will pick up the phone. Now assuming, the Initial
Invite contained no offer (and 100 rel is not supported),the first offer
is then sent out at 200 OK .If the return ACK is either dropped in the
IP cloud or is delayed, with no media established, the call is
essentially useless.

So, is there any situation where it makes sense for a UE to send an
Invite without an Offer.

Thanks & Regards,
Aditya Sehgal

---

From: Hadriel Kaplan <[email-masked]>
Date: Tue, 15 Apr 2008 11:05:59 -0400

Your question is more appropriate for the SIP Implementers list methinks: [email-masked]
(see https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors)

But anyway, yes there are situations where an Invite will contain no SDP, and you MUST support receiving such - many systems send such offerless Invites.  But when you send Invites, I would strongly recommend you send it with an SDP offer unless it is actually technically impossible for you to do so, because many systems can't handle receiving one without it and will simply fail your request.

-hadriel

________________________________
From: [email-masked] [mailto:[email-masked]] On Behalf Of Aditya Sehgal
Sent: Tuesday, April 15, 2008 10:50 AM
To: [email-masked]
Subject: [Sip] Invite without offer

Hi all,
Is there any practical situation where in an Invite will contain no SDP.
Lets say A calls B.
My understanding (albeit limited) of the RFC makes me believe that 200 OK is sent out when B will pick up the phone. Now assuming, the Initial Invite contained no offer (and 100 rel is not supported),the first offer is then sent out at 200 OK .If the return ACK is either dropped in the IP cloud or is delayed, with no media established, the call is essentially useless.

So, is there any situation where it makes sense for a UE to send an Invite without an Offer.

Thanks & Regards,
Aditya Sehgal