[OpenSIPS-Users] Mediaproxy ver 2.3.4 - Conntrack meets Music on Hold

Dan Pascu dan at ag-projects.com
Wed Jul 1 05:09:30 CEST 2009


On 30 Jun 2009, at 19:11, Ruud Klaver wrote:

>> 3) detect this special case and change existing conntrack to point to
>> the MoH sever, putting it back later
>
> We actually considered implementing this, but not for this particular
> scenario. Some modems seem to switch IP address every X hours. If this
> change is during a relayed call, the RTP from one end will suddenly
> come from a new IP address, like in your scenario. What could be done
> is that the relay keeps listening on the allocated ports in userspace
> for traffic from a different host and switch the conntrack rule to the
> new IP if there is no traffic coming in anymore from the old IP.

This will not work in this case. The case you mention was possible  
because the media relay could detect if the stream coming from the new  
IP:port was actually the same stream by looking to the serial number  
present in the RTP. Since that was the same, it could assume that it's  
the same sender that just happened to have his IP changed during the  
call. In Stuart's case, since it's a new SIP dialog, with a new RTP  
stream sent by a different device it will have a different serial  
number. The only way to work would be to accept any stream which is  
opening Pandora's box for official media hijacking.

--
Dan






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