[asterisk-users] NAT problem with recvonly calls

David Cunningham
Wed, 02 Dec 2020 21:29:06 -0000

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.

Does anyone know how to work around this issue?

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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