Hi Daniel,

Removing the sendonly from the INVITE SDP sounds like the most workable solution in our case. We'd only want to do it for a new INVITE though, not a re-INVITE in a situation where a call is put on hold. Would you be able to give an example of such a configuration?

Thanks very much for your help!


On Tue, 8 Dec 2020 at 21:56, Daniel-Constantin Mierla <miconda@gmail.com> wrote:

Hello,

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.

Cheers,
Daniel

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/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782

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Daniel-Constantin Mierla -- www.asipto.com
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--
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782