[aprssig] APRS Top-level parser

[Scott Miller]

What I'd REALLY like to see is a formal BNF description of the APRS 
formats.  As annoying as it can be, it does provide an unambiguous way 
to define a complex grammar.

Scott
N1VG

Robert Bruninga wrote:
> While discussing the basic APRS parsing technique this weekend,
> I realized that it did not exist on paper anywhere other than in
> code.  So I thought it would be a good idea to put it in pseudo
> English and in a document so everyone could have a common sheet
> of music.
> 
> APRS only has 4 basic packet types.  It is not what we do with
> POSITIONS, STATUS, MESSAGEs and QUERY packets that is bothering
> me, it is what we do with the other packets that fall out the
> bottom of the parser (as none-of-the-above) that have been
> inconsistently implemented and therefor gives different users,
> different perspectives on what they see on the APRS network.
> 
> APRS was designed to give the user a VIEW of everything in ham
> radio going on around him that is making itself known via AX.25.
> So how we handle the non-APRS packets was always fundamentally
> included in APRS.  This document explains:
> 
> http://www.ew.usna.edu/~bruninga/aprs/APRSparser.txt
> 
> Basically, it describes how every station is supposed to get a
> "vicinity position" until his real APRS posit is received.  This
> at least gets him into the system while we wait for a posit.
> 
> If I have not done an adequate job of capturing the
> top-level-parser in the above document, let me know how I can
> improve it.  Also, it would be nice to collect a summary of how
> various APRS clones did or did not implement these techniques.
> 
> Bob, WB4APR
> 
> 
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