[aprssig] Error checking within APRS packets
iz6rdb at trentalancia.com
Thu Jun 23 20:13:42 EDT 2011
On 23/06/2011 23:26, Lynn W. Deffenbaugh (Mr) wrote:
> On 6/22/2011 12:43 PM, Bill V WA7NWP wrote:
>> The APRS spec says to never use a tilde in the text field? If it's
>> true, that's silly. It's just another ASCI character. The
>> bit-stuffing magic happens at the hardware packet level and is totally
>> independent of what we put in the packet data -- for APRS or any other
>> packet application.
> The issue isn't with AX.25, but I believe there are some TNCs out
> there that use the tilde character as a way to switch sessions or
> streams or something. Given that, if the tilde character appears
> anywhere in a packet that needed to be transmitted by that TNC, most
> likely in some sort of CONVerse mode, not KISS, then really bad things
> would happen.
It is used also by HDLC/SDLC (along with the same bit-stuffing
technique) as the start/end flag similarly to AX.25 (which actually took
it from the former).
However in the original context (it was called "TNC stream switch"), it
should mean a control character used in TNCs to switch between (data)
streams of different connections (some other times 0x7c which is the
pipe "|" is used instead).
> Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
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