Bitchat – A decentralized messaging app that works over Bluetooth mesh networks

Interesting try but Bluetooth LE is a non-starter when talking about building a truly decentralized mesh network at scale. The range isn’t there to build a network unless its very tight (in distance). You need sub MHz and eventually cubesats to build something robust, everything else is a toy.

The big problem with BLE is the insane amounts of packet loss with extended advertising, even with perfect SNR many devices seem to just kind of not have the receive windows lined up right and drop 10% of packets.

The range is perfectly good for a lot of applications where one might actually want to not use the internet, just not all of them.

Dropping 10% of packets sounds like a trivial problem to solve. That's not a range that requires fancy things like erasure coding or even SACK; it's easily handled by just retransmitting packets that don't get acknowledged.

You need to track individual subscribers at that point, which uses lots of ram and could use lots of airtime, heuristics like resending until you get 1 reply like Meshtastic don't work well.

If there's receive window timing issues you can't assume two nodes right next two each other will get the same subset of packets most of the time.

My solution is just to resend every message four times, and not bother with protocol layer reliability for BLE at all, the packet rate is low and all the acknowledgements use airtime anyway.