[SR-Users] NAT problem with recvonly calls

Daniel-Constantin Mierla miconda at gmail.com
Tue Dec 8 09:56:13 CET 2020


if the endpoint is not behind a port forwarding nat/firewall (when one
can instruct the rtp relay to use signaling address), then probably you
can try to remove the sendonly from the INVITE SDP. That will enable rtp
from endpoint to doorbell, which may rise additional concerns (e.g.,
privacy) if its is explicitly not wanted to happen. But as Alex said in
another response, the only way to get it work is to make the endpoint
behind nat to send a RTP packet. Usually the doorbells I encountered so
far were accepting incoming traffic as well, to discuss/interact with
the person ringing on it.


On 08.12.20 05:01, David Cunningham wrote:
> Hello,
> We have a problem with a SIP doorbell device which sends media one way
> only, and NAT at the receiving device.
> When the doorbell button is pressed it makes a call to a configured
> destination. Since the doorbell only sends and doesn't receive it
> sends the INVITE with sendonly in the SDP, and the destination then
> replies with a 200 OK with recvonly in the SDP. The problem is that
> the destination is behind NAT, and its reply contains a private
> network IP in the SDP.
> Normally Asterisk when nat=yes works around that by adjusting the
> destination for RTP to be the address it actually receives audio from,
> however because this device is recvonly Asterisk never receives audio
> from it. This means Asterisk keeps trying to send the doorbell's RTP
> to the private network IP which of course fails, and the destination
> never gets the RTP from the doorbell.
> We haven't found a solution in Asterisk to this, so are now looking to
> Kamailio which acts as a load-balancing proxy in front of Asterisk for
> one. For example, maybe we could use fix_nated_sdp, but only on 200
> OK's with recvonly.
> Has anyone else encountered this, and are there any recommended solutions?
> Thank you in advance!
> -- 
> David Cunningham, Voisonics Limited
> http://voisonics.com/ <http://voisonics.com/>
> USA: +1 213 221 1092
> New Zealand: +64 (0)28 2558 3782
> _______________________________________________
> Kamailio (SER) - Users Mailing List
> sr-users at lists.kamailio.org
> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

Daniel-Constantin Mierla -- www.asipto.com
www.twitter.com/miconda -- www.linkedin.com/in/miconda
Funding: https://www.paypal.me/dcmierla

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