[aprssig] Error checking within APRS packets

[Lynn W. Deffenbaugh (Mr)]

On 6/25/2011 11:42 AM, Guido Trentalancia wrote:
>
> I can only add in some way that it's still risky to do that. Have you 
> checked all possible TNCs being used nowadays ? Is there a standard 
> for TNCs ?

Unfortunately those answers would have to be "not possible" and "not 
even".  There is some level of apparent standardization across some 
TNCs, but when you get down to the details, there's no one standard.

KISS comes close, but then there's SMACK (KISS with a CRC, 
http://www.symek.com/g/smack.html).  SMACK is supposed to be 
backward-compatible with KISS implementations, but in my experience not 
all SMACK implementations quite make it.

And as for find out what TNCs are still in use, it might have been 
possible if TNCs actually put some sort of identifier in their 
transmissions, but many don't.  My APRSISCE/32 client uses every trick 
and signature that I've been able to discover to figure out what the 
software or hardware is that is generating the packets for a station, 
but it still comes up with 8,352 (43%) "Generic" and 442 (2.2%) 
"Unrecognized" out of the 36,700 stations that have been active in the 
past 2 hours (including CWOP and firenet.us).

Just like Microsoft, we're constrained by backward compatibility 
until/unless we're ready to take the hit of a total disconnect and even 
then, I think substantial research needs to be done to determine and 
document the effects on the "obsolete" platforms.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

PS.  This message is not intended to state my position on change, 
neither for nor against, but simply to answer the questions within the 
realm of my personal experience.