[SR-Users] Changing SDP with subst after rtpproxy_answer corrupts SDP

[Daniel Tryba]

On Thursday 15 January 2015 13:38:00 Matthias van der Vlies wrote:
> I have an on-reply route that needs to change the SDP version for the
> reply coming in. The use case is that I have a mobile originated call
> and there is some Ericsson switch that doesn't like it when the SDP
> version is updated (in this case by asterisk) although nothing has
> changed to the actual SDP (183 session progress and then OK.)  Funny
> thing is that Asterisk will actually drop a call if it receives a
> re-INVITE with same version... That's why they invented
> ignoresdpversion, but now it's the other way around.... :)
> 
> Mobile phone -> Ericsson MSC -> ACME packet -> (18X.4X.XXX.XX) Kamailio
> (10.41.0.21) -> Asterisk

Sounds familiar (the Ericsson is the troublemaker), my solution was to upgrade 
to asterisk 11.x. But since patching is not possible, I assume upgrading is 
neither. A workaround was to drop the 183 message in kamailio to Ericsson:

onreply_route[MANAGE_REPLY] {
        xlog("incoming reply\n");
        if(status=~"[12][0-9][0-9]")
                route(NATMANAGE);

        if(status=="183")
        {
                drop;
        }

...

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