[aprssig] Error checking within APRS packets
Ian Wade G3NRW
g3nrw-radio at ntlworld.com
Tue Jun 21 18:09:27 EDT 2011
From: Guido Trentalancia <iz6rdb at trentalancia.com>
Date: Tue, 21 Jun 2011 Time: 22:40:17
>So, at this point my question is why did APRS forbid to use that
>bit-pattern (you like it that way, I call it that way) if the bottom
>layer could accommodate in some way through a trick (called
>First hypothesis: APRS names that "TNC Stream Switch".
This hypothesis is correct.
>From this I might suspect that the same bit-pattern is also used
>elsewhere (that is not as clever) than in AX.25 start/end flag.
Even though the bit patterns look the same, don't confuse the tilde
character with the AX.25 start/end flag. Because of bit stuffing, the
tilde is always converted to something else *before transmission* (so
that it can never look like a flag in the transmitted signal), then *on
reception* the bit stuffing is reversed, so you get the original tilde
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