Linux-Hams archive - October 1999: Re: AX.25 Layer 1

Re: AX.25 Layer 1

Hamish Moffatt (ztzxeln.soxbiaq@inverdigm.com)
Fri, 1 Oct 1999 08:58:24 +1000

On Thu, Sep 30, 1999 at 07:25:10PM +0100, Dirk Koopman wrote:
> 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

For exactly the same reasons, I conclude that it is part of layer 1!
HDLC must be layer 2; it is the H(something, I forgot) Data Link Control,
and layer 2 is the Data Link layer. Bit stuffing is a transparency
mechanism used by HDLC. It is part of the HDLC protocol. It must be layer 2.

The fact that it performs scrambling for you is convenient.
Actually, I'm not too sure that it does do scrambling for you unless
your payload happens to be all 01111110; if it's all 0s, it does nothing
for you.

The physical layer is the bell tones, the carrier detect mechanism
and scheduling algorithms for transmitting.

Hamish VK3SB

-- 
Hamish Moffatt       Mobile: +61 412 011 176     mwlz@genuity.net
Rising Software Australia Pty. Ltd.    http://www.risingsoftware.com/
Phone: +61 3 9894 4788    Fax: +61 3 9894 3362    USA: 1 888 667 7839