[SR-Users] 100rel without direct reachability

[Iñaki Baz Castillo]

2011/6/19 Alex Balashov <abalashov at evaristesys.com>:
> Well, here's what 3261 12.1.1 ("UAS Behavior") says on the subject:
>
>   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.
>
> Since a 183 does not establish a dialog, I suppose that means there's no
> need for the UAS to copy the RR headers.

Wrong, 183 *does* establish a dialog. An early-dialog in fact, but
that doesn't matter. As said above, 1XX response with require 100rel
is a reliable response so it requires Contact header and mirroring
Record-Route headers.


> On the other hand, take a look at page 7 of RFC 3262:
>
>   http://www.ietf.org/rfc/rfc3262.txt
>
> It seems to say that Record-Route goes into "2xx,18x", although offers no
> elaboration on this point.  Whether this constitutes an amendment to the
> 3261 view I do not know.

It says:


            Header field              where      PRACK
            __________________________________________
            Record-Route                R          o
            Record-Route             2xx,18x       o


Of course Record-Route is optional in request (INVITE) and 18X or 2XX
responses, as the proxy could decide not to do record-routing.

-- 
Iñaki Baz Castillo
<ibc at aliax.net>