Hi, I'm reporting a common error in some transparent B2BUA I'm testing. The
error is:
- The B2BUA receives a request from leg_A and generates a request in leg_B.
- leg_B arrives to a proxy that does parallel forking.
- The B2BUA receives various provisional responses (183) with different To_tag
due to parallel forking.
- The B2BUA generates a 183 response in leg_A for each 183 in leg_B, but it
uses an *unique and same* To_tag in both 183 responses in leg_A (but they
have different SDP).
I'm trying to demostrate that the above behaviour is incorrect since:
- There are two different early-dialogs between B2BUA and leg_B.
- There are just *one* early-dialog between caller (leg_A) and B2BUA (since
all the replies from B2BUA in leg_A have the same To_tag).
- The caller (UAC) will ignore any SDP after the first 183 containing a SDP,
even if a 200 OK arrives with a different SDP (since the To_tag would be the
same, so just the first SDP would be considered).
I think it's clearly specified in RFC 3261 (well, not so clearly):
-------------------------------------------------------
13.2.1 Creating the Initial INVITE
o If the initial offer is in an INVITE, the answer MUST be in a
reliable non-failure message from UAS back to UAC which is
correlated to that INVITE. For this specification, that is
only the final 2xx response to that INVITE. That same exact
answer MAY also be placed in any provisional responses sent
prior to the answer. The UAC MUST treat the first session
description it receives as the answer, and MUST ignore any
session descriptions in subsequent responses to the initial
INVITE.
[...]
Concretely, the above rules specify two exchanges for UAs compliant
to this specification alone - the offer is in the INVITE, and the
answer in the 2xx (and possibly in a 1xx as well, with the *same*
value), or the offer is in the 2xx [...]
-------------------------------------------------------
Could you please help me by confirming, detailing and explaining it?
Reall thanks a lot.
--
Iñaki Baz Castillo
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