[aprssig] AX25 / KISS questions

Fred Hillhouse fmhillhouse at comcast.net
Fri Jun 9 09:20:09 CDT 2017



As I read through the specs I have a couple of mysteries.




The first byte is 'C0'.

The second byte-high nibble is a port byte - useful if talking to a
multi-port device I presume.

The second byte-low nibble is to flag to define the rest of the frame.
Should be 00 unless actually controlling the TNC in some fashion.


The last byte of the Destination Address Subfield, A7, is CRRSSID0. The C is
the mystery. If A1-A6 contains a TOCALL, should C be a '1' or '0'. My first
inclination is to believe it should be a '0' (Response V.2.X) if the packet
is not a TNC command. But then, a '1' could be signaling a command for a
distant TNC. Or does it really matter the packet is being applied to APRS?


Regarding bit (un)stuffing, this appears to not apply to the KISS packet but
is an action taken at the point of transmission/reception.


Please comment.


Best regards,

Fred N7FMH

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