Hi Stuart, On Sun, 20 Jan 2019, at 2:32 PM, Stuart Longland (VK4MSL) wrote: > A group name, which may not necessarily be a call-sign, could be > encoded as lower-case. > > I have no idea how existing AX.25 stacks (Linux kernel, G8BPQ, > AGWPE, TheNet, TNCs, etc) would react to such frames, whether they'd > discard them, strip the lower-case bits in the SSIDs, or pass the > SSIDs through as-is.
libax25's ax25_aton_entry (and by extension the widely used ax25_aton) uses toupper(), which might frustrate your attempts depending how exactly you're constructing and sending the frames. I think that working contrary to the spec would create doubt observing traffic with existing tooling as to whether a callsign is "really" capitalised or not. > 1. Using the reserved bits. There's two bits in the last octet of each > SSID, which are normally set to '1'. I could use one of those to > indicate this is a "unicast" address; setting that to 0 would mean > the message is being "multicasted" or "broadcasted". > > Interfaces like AGWPE's TCP socket protocol abstract these bits. No > idea if those would be preserved when passed through other AX.25 > stacks. Perhaps more so than the other ideas, this type of usage is blessed in the spec for "Destination Subfield Encoding": > The bits marked "R" are reserved bits. They may be used in an agreed-upon > manner in individual networks. When not implemented, they should be set to > one. I can't speak to how well this is exposed by the various AX.25 stacks but on a theoretical level I agree with this option being at the top of your list. Sounds like a cool project. Cheers, Tom VK7NTK