Frames are sent as datagrams. Fragmentation is not supported, so 1 frame = 1 datagram.
Responses are supported, but because UDP is not reliable, it is best suited for notifications.
Set rpc.udp.listen_addr to udp://0.0.0.0:1234 to listen on port 1234.
To use UDP for outbound RPC, set rpc.udp.dst_addr to the address of the server / peer, e.g. udp://192.168.1.23:1234.
mos supports UDP transport via the udp:// port scheme, e.g.:
$ mos call --port udp://192.168.11.5:1234/ Sys.GetInfo