Once we get beyond 3261, adding 3262 and 3311, it no longer makes sense to talk about relating offers and answers to particular transactions, because a single offer/answer pair can be split across multiple transactions. It really only makes sense to think about the offers and answers in the context of dialog and independent of transactions.
What is it that make you think you can't send multiple offers and/or answers within a single transaction?
If anybody shares this belief with you I would like to get it resolved.
It is my understanding that *in the presence of 100rel*, INVITE, reliable provisional responses to invite, PRACKs, responses to PRACK, UPDATEs, responses to UPDATES, and ACK all provide opportunities to send offers and answers, subject only obeying the offer/answer protocol and the rule that the first offer must be in INVITE or in first reliable response to it. (Of course UPDATE can only be used if it is also supported.)
Paul
Christer Holmberg (JO/LMF) wrote:
Hi,
Comments inline ([CHH])
[CHH] My understanding is that only the first reliable provisoinal response may contain an offer, and only in the case that the initial INVITE didn't contain one (in which the answer is sent in the first PRACK).
I think that there can only be one offer/answer exchange per transaction, so once a SDP (offer or answer) has been sent in a provisional response no more can be sent for that transaction (INVITE). Or?
IF we were allowed to send more offers in provisional responses, how would we handle race conditions if the UAC at the same time sends a new offer (we can't send 491 to a provisional response)?
Well, RFC 3312 certainly calls for multiple offer/answer cycles per INVITE. (It isn't really one transaction, since it requires PRACK and the prack is a separate transaction.)
[CHH] Yes, but every 18x provisional response is part of the INVITE transaction, and within that single transaction I don't think you can send multiple offers and/or answers.
It is my understanding that once you take account of 3361, 3362, 3364 and 3311, offer/answer has been decoupled from specific messages. Within an invite dialog you may have a sequence of offer/answer exchanges. The main limitations are that each offer must be answered and that you can't send another offer until the prior one has been answered.
[CHH] I agree on that, but I still think you can't send multiple offers and/or answers within a single transaction.
Regards,
Christer Holmberg Ericsson Finland _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
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