Have to return to websocket implementation as there are seems more issues with p2p than were expected.
When my android tablet is LTE connected sometimes I see lags in transmitting UDP packets for UDP hole punching technique and sometimes connection cannot be established. Or may be I dont know how to cook it right.
So websocket seems to be better solution for now. And easier to use as it works in any modern browser on all major platforms. And no extra software installations are required. Next step could be WebRTC but there is much more work to make it run on microcontroller.