I have following setup use sip for screen share:
Client A <--> NAT-A box -- > sip-proxy/rtp-proxy --> NAT-B--> Client B
of course they are in ipv4 network.
A want to screen-share to B: currently Jitsi uses one-way video (A to B ) to achieve that.
The sip-proxy detect both A/B are behind NAT boxes, so it will manipulate the sdp inside the invite/200-OK, and use rtp-proxy to do the trick,
which means A/B will send/receive the rtp stream from rtp-proxy.
In order for this to work, the rtp proxy assumes the NAT boxes (most of them on the market?) to support symmetric rtp
Now since it is a one-way video, B never send out video stream, so the rtp-proxy will not get the correct ip/port to send the video stream to B.
The final result is that B can not show the A's screen.
To solve the issue, Is it possible that Jitsi send some dummy/emtpy rtp pkt from the B's video port? Essential it become a two-way video, but A send the main video stream, B just occasionally send out some dummy/empty rtp in order to keep the NAT punch hole.
some more detail about the rtp proxy etc could be found at: