[aprssig] BEACON - APRS or Not?

[Lynn W. Deffenbaugh (Mr)]

Shawn Stoddard wrote:
> The two stations in question are W4LAW-5 and W4LAW-6. You can see the 
> packets on the beacons at http://aprs.fi/?c=beacon&call=W4l*&limit=50.
>
> Steve responded back with good advice: be prepared for the unexpected. 
> As my understanding of APRS improves I have a much better idea of 
> right and wrong. So should my parser.
>
> The question becomes do you agree or disagree with Steve's response. 
> If you disagree, why?
I completely agree with Steve's response.  In my experience with my own 
parser (adopted from the Open Source T2-135 source code), not only do 
you have to ignore anything that may not be in the spec, but you also 
have to be ready for some truly bizarre packets that DO have an expected 
datatype.  There are still some Digi's out in the wild that seem to be 
running with PASSALL (or whatever the equivalent is).  In this mode, the 
digi/IGate doesn't care about the checksum on the original packet, but 
rebroadcasts the corrupted contents with a new checksum so later 
recipients can't even tell it's been mangled.

You'll see fixed coordinates that are not even in the range of 0-90 or 
0-180.  So far I haven't seen one (that I know of) with the NESW messed 
up, but I'm sure it's happened.

For my parser, I actually log packets received from APRS-IS to one of 
several directories.  GOOD gets the ones I'm currently handling, BAD 
gets the ones that I'm not handling, and NOPOS gets the ones that I 
handle, but do not have a position (like weather, messages, status, ...).

May I ask what you'll be doing with the parsed data?

Lynn (D) - KJ4ERJ - (No, I haven't check out the W4LAW-* stations yet)