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[aprssig] Mystery packet

Curt, WE7U archer at eskimo.com
Thu Dec 10 16:38:41 UTC 2009


On Thu, 10 Dec 2009, Lynn W. Deffenbaugh (Mr) wrote:

> The only thing not mentioned in this thread so far is that the AX.25 packets 
> on the air actually HAVE the "Used" bits set on ALL of the leading stations 
> in the path.  It is only the humanly-readable format that sometimes (most of 
> the time) suppresses the earlier ones and only puts the * on the last packet 
> in the path to have been marked "used".  This drove me nuts the first time I 
> tried to interpret raw KISS packets (barely wrappered AX.25)  and thought my 
> program was buggy due to all of the *s I was seeing.

Correct.  Plus you sometimes see AEA format monitor strings which
have a different order for the SRC/DST/Digipeat callsigns plus
different separator character between some of them as compared to
TNC-2 format monitor strings.  Fun eh?

The only reliable way of knowing what you're going to get each time
is to deal with KISS packets, not human-readable monitor-mode
packets.

Then again there are minor differences in KISS packets framing too
but they do leave the over-the-air bits alone at least: It's just
the extra KISS envelope that differs.

-- 
Curt, WE7U.                         <http://www.eskimo.com/~archer>
    APRS:  Where it's at!                    <http://www.xastir.org>
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Windows:  Microsoft's tax on computer illiterates. - WE7U.
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