Iñaki Baz Castillo wrote:
> El Lunes 06 Abril 2009, Brett Tate escribió:
>> The following was one of the threads:
>> https://lists.cs.columbia.edu/pipermail/sip-implementors/2008-August/020062
>> .html
>>
>> Read sections 12.1 and 12.1.1:
>>
>> "Within this specification, only 2xx and 101-199 responses with a To tag,
>> where the request was INVITE, will establish a dialog."
>>
>> "When a UAS responds to a request with a response that establishes a dialog
>> (such as a 2xx to INVITE), the UAS MUST copy all Record-Route header field
>> values from the request into the response (including the URIs, URI
>> parameters, and any Record-Route header field parameters, whether they are
>> known or unknown to the UAS) and MUST maintain the order of those values.
>> The UAS MUST add a Contact header field to the response."
>
> Yes, that was the conclusion. But I think that RFC 3261 doesn't define it
> clearly, and due to this, there are many implementors not adding Contact and
> RR in 1XX responses, so any other mechanism relying on it (as BYE on an early-
> dialog) could fail :(
I know people who attempt to cope with that by using the R-URI of the
initial INVITE to attempt an in-dialog request if they haven't yet
received a Contact. (Seems to be grasping at straws if you ask me, but I
suppose its better than nothing.)
It seems to be pretty common to want to do DTMF prior to the 200. If you
want to do that in signaling, with KPML or INFO, you need a Contact address.
Thanks,
Paul
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