Kasammiya Patil wrote:
Hi,
I have couple of questions regarding the use of UPDATE method.
1. Can UPDATE be used to send an answer SDP ?
Consider the following scenario:
- INVITE was sent without SDP
- 18x is received with Offer SDP
- There is no PRACK exchange because 18x does not contain a Require:100rel header
Now can UPDATE be used to send answer SDP??
I don't think so. If the 18x is not sent reliably, then SDP in it is just a courtesy, it isn't the real offer. The real offer is in the 2xx. So it isn't until the 2xx is received with the offer than an answer may be sent - in the ACK.
2. As per RFC 3311, UPDATE method should be used only if dialog is established.
If INVITE/18x exchange happened without PRACK, can both ends treat this as early dialog and feel free to use UPDATE ?
Again, I don't think so.
3. Is 18x send/recv over TCP considered reliable ?
In the following scenario:
- INVITE with offer sdp sent
- 18x over TCP with answer sdp recvd (No PRACK exchange happened)
Now can the caller/calleee use UPDATE ?
No. Provisionals are only considered reliable if sent with 100rel and confirmed with PRACK.
Paul
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