Take a look at the port-latching option for the port change.

-ovidiu

On Mon, Mar 9, 2026 at 3:25 PM Pavel Sindelka <[email protected]> wrote:
>
> Hello Andrea,
>
> which particular aspect are you interested in?
>
> The behavior can be demonstrated using just this simple route:
>
> route {
>     if (is_method("INVITE") && !has_totag()) {
>         t_newtran();
>         rtpengine_use_set(1);
>         rtpengine_offer( , , $var(sdp-offer), $rb(application/sdp));
>
> #       ... forward the SDP offer as modified by rtpengine using another 
> protocol
>
> #       ... receive the SDP answer from the other protocol and store it into 
> $var(orig-sdp-answer)
>
> ####    rtpengine_answer("to-tag=$sig_local_totag", , $var(new-sdp-answer), 
> $var(orig-sdp-answer));
>         rtpengine_offer("force-answer to-tag=$sig_local_totag", , 
> $var(new-sdp-answer), $var(orig-sdp-answer));
>
>         $var(contact) = "<sip:" + $socket_in(ip) + ":" + $socket_in(port) + 
> ">";
>         append_to_reply("Contact: $var(contact)\r\n");
>         append_to_reply("Content-Type: application/sdp\r\n");
>         t_reply_with_body(200, "OK", $var(new-sdp-answer));
>         exit;
>     }
>
>     #### handle other methods & reINVITEs ####
> }
>
> I am currently trying to understand why, upon receiving the answer command, 
> rtpengine changes the port it has indicated in its modified SDP offer and 
> chooses another one for actually forwarding the media received from the 
> calling party, but that's off-topic here.
>
> Pavel
>
>
> Dne 09.03.2026 v 13:00 [email protected] napsal(a):
>
> Date: Sun, 8 Mar 2026 08:14:09 -0500
> From: Andrea Sannucci <[email protected]>
> To: OpenSIPS users mailling list <[email protected]>, Pavel
> Sindelka <[email protected]>
> Subject: Re: [OpenSIPS-Users] rtpengine_answer() is silently ignored
> on request route handling the initial INVITE when acting as an UAS -
> what am I missing?
> Message-ID: <[email protected]>
> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
> Hello,
>
> can you show your configuration?
>
> Regards
>
> -----
> Andrea Sannucci - @AS
>
> El 8/03/2026 a las 8:01 a. m., Pavel Sindelka escribió:
>
> Hello,
>
> https://opensips.org/docs/modules/3.6.x/rtpengine.html#func_rtpengine_answer
> doesn't mention any restrictions on use of this function, but in
> reality opensips does not send anything to rtpengine if
> |rtpengine_answer()| is called on a request route handling the INVITE.
> Nothing in the log, no UDP exchange on the rtpengine control port,
> regardless whether |rtpengine_offer()| is called earlier on that route
> or not. If it is, the information exchange with rtpengine related to
> |rtpengine_offer()| can be seen both in the log and on the rtpengine
> control port.
>
> The intended overall workflow is to call |rtpengine_offer()|, handle
> the mangled SDP offer internally and generate the SDP answer, and get
> it "mangled back" using |rtpengine_answer()| before using it as the
> body of a locally generated 200 response to the INVITE. Could it be
> that as of now, |rtpengine_manage()| not only "combines the
> functionality ... based on message type and method ..." but the three
> individual methods have actually become just aliases of
> |rtpengine_manage()| for backward compatibility? Or is the actual
> execution of |rtpengine_answer()| suppressed thanks to some
> undocumented plausibility check?
>
> Is there any way to enforce execution of |rtpengine_answer()| on a
> request route handling the INVITE?
>
> Thank you for advice.
>
> Pavel
>
>
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