Symmetric RTP when one side only sends keep-alive RTP Packets

Hallo Asterisk-Experts,

I’ve got following situation:
UAC1 is behind NAT, Asterisk is not behind NAT.
UAC1 sends and receives Audio data -> Audio works in both directions
UAC1 shall receive also Video Data from UAC2, but sends only RTP keep-alive packets from the Video port. The keep-alive packets are simply a binary 0 which is sent from the video port of UAC1.

The RTP keep-alive packets can be seen on asterisk (as unknown RTP, from the right public IP/Port), but Asterisk doesn’t seem to be able to use these packets for symmetric RTP. Thus the Asterisk doesn’t send video data from UAC2 to the public IP/port, but to the private IP which is set in the SDP.

Does anyone know what kind of RTP packets are required so that Asterisk will be able to use them to establish symmetric RTP?


I imagine it requires valid ones. The answer may depending on the channel technology driver as well.

I don’t believe there is any standard that says that a single byte UDP frames on an RTP session is anything but invalid.

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