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[ax25-layer2] 7-byte address proposal

Samuel A. Falvo II sam.falvo at gmail.com
Thu Aug 3 07:14:45 UTC 2006

On 8/3/06, scott at opentrac.org <scott at opentrac.org> wrote:
> Which TNCs?  I don't think any of the ones I've ever looked at have had any
> HDLC stuff in hardware - they all pipe data straight into the CPU.

Nearly all of them.  TNCs that employ KISS strip the FCS field from
the frame they send to the host PC.  Frames it receives from the host
PC are bridged to the RF medium after the TNC computes the FCS field
for the frame.

> I've been wanting to experiment with a Reed-Solomon concatenated ECC
> extension to AX.25.  I'm thinking a standard AX.25 frame could be followed
> by the ECC frame, which would have the compliment of the data frame's FCS.
> That'd cause old TNCs to ignore it completely, and would let supported TNCs
> be sure that the ECC block belongs to a particular data frame.

Hey, now that's an idea!  One of the reasons why I started thinking
about AFR was precisely because I wanted higher layers to be able to
include their own error correction mechanisms.  But, I never
considered the possibility of sending ECC information as a follow-up
frame instead of embedded within the frame.

Of course, the TNC will need to learn to keep frames around even if
its FCS doesn't match.  How does one control the lifetime of such

Samuel A. Falvo II

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