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.



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