Some systems for serialising data that may be useful for sending messages over LoRa.

• Custom format. Most efficient on space but least flexible and most work to reimplement.
• Protobufs - used by Meshtastic.
• BSON - Binary JSON. “BSON can be com­pared to bin­ary inter­change for­mats, like Proto­col Buf­fers. BSON is more “schema-less” than Proto­col Buf­fers, which can give it an ad­vant­age in flex­ib­il­ity but also a slight dis­ad­vant­age in space ef­fi­ciency (BSON has over­head for field names with­in the seri­al­ized data).”
• FlatBuffers - https://flatbuffers.dev/
• https://en.wikipedia.org/wiki/Cap%27n_Proto
• https://msgpack.org/index.html - used by LXMF / Reticulum
• Direct use of NMEA2000 PGNs?
• NMEA0183 strings?
• BSON SignalK? Probably way too verbose I guess.

I was tempted to go for a custom protocol because of very limited space, but after talking to someone about it last night I think I have been convinced protobufs or similar is the way to go. He said he worked with protobufs, as used by meshtastic, and with Reticulum, which uses a semi-custom protocol, and found meshtastic more pleasant to work with. Also, he is reïmplementing Reticulum in Rust, and such things are much easier where a protobuf library is already available. Also, it maybe possible to define the messages with protobufs, and still use that definition to serialise to a custom protocol.

Protobufs could also maintain compatibility with Meshtastic which could be useful if meshtastic becomes popular enough that nodes maybe encountered that can relay messages for us.