[aprssig] Error checking within APRS packets

[Bob Bruninga]

>     What type of error checking does APRS have to
>     prevent corrupt data?

None.  The AX.25 packet is assumed to be error free (unless someone has PASSALL turned on, and then the result is totally error vulnerable).

But callsign-only errors can happen.

It happens all the time that a packet  is heard and then right in the middle of it, another packet steps on top. 
The combination of the two looks just like one long packet.

However the CRC Error check will fail........ (most of the time)......  Statistically, the CRC of the combined packet might just get lucky enough rarely to generate  the same CRC as the original packet. 

In this case, the parser sees the original callsign.  Then usually most of a path , and then the beginning of the next packet which just looks like a continuation of the address field of the header of the first.  This doesnt mater much, because the only thing the parser is looking for next is the : that begins the pacekt.

So, it can happen...