On 30-Sep-99 Tomi Manninen wrote:
> Later came other layer 1 schemes like G3RUH/K9NG 9600bps, WA4DSY 56kbps,
> HAPN-1 4800bps etc. These all share the HDLC framing (bit stuffing, flags
> etc) but I still don't think even that is an integral part of AX.25. Tim
> you said HDLC bit stuffing etc is a layer 2 issue, where does one actually
> draw the line between physical layer and link layer?
>
Not where he did. Since the bit stuffing is an integral part of HDLC (and is
implemented by the SCC chip together with flag detection and CRC checking), I
declare it to be part of layer 1, ax25 is layer 2, the two netrom layers 3
and 4 respectively.
You cannot have HDLC without bit stuffing, bits are stuffed to make sure that
a flag cannot appear inside an HDLC frame, the fact this also is handy
because you are using NRZI and you mustn't have too many 1s in a row
otherwise you lose sync is just a happy accident (and of course nothing
whatever to do with the design of HDLC :-)
There are several that reckon ax25 is actually layer 3 with hdlc layer 2, but
they also believe that Linus rules the universe as opposed to merely being
immortal.
Dirk G1TLH
--
Dirk-Jan Koopman, Tobit Computer Co Ltd
At the source of every error which is blamed on the computer you will find
at least two human errors, including the error of blaming it on the computer.
