[drats_users] AX.25 Support

[Dan Smith]

Hi Craig,

> However, if you stick to KISS mode and only support Unnumbered
> Information frames (UI), you could greatly simplify the command mode
> structure.  You could provide a simple form for configuring the
> initial TNC parameters and the rest would operate as D-RATS does
> today on D-STAR.

Yeah, I understand that stuffing the D-RATS packets into the AX.25 UI
frames would be a simple way to enable digipeaters.  However, it opens
a can of worms that is likely to get out of control.  I really don't
want to get too far into the packet realm, and I don't want to end up
bringing in more of an antiquated protocol.  I *certainly* don't want
to end up with AX.25 data flowing through the D-STAR system.  I can
see the pressure for this increasing the closer we get to AX.25
support.

Right now, D-RATS wouldn't be a reasonable substitute for the packet
message-forwarding network.  Anyone replacing such a thing with D-RATS
in its current form would be losing a huge amount of automatic routing
functionality, contrary to the "use the right tool for the job"
comments others have posted here.  Further, I think that some work
needs to be done to D-RATS' file transfer algorithm to make it
tolerate working properly through a digipeater anyhow.  If we can't
digipeat, route, etc, then I don't think the added overhead of
stuffing it in an AX.25 packet makes much sense until we can.

So, I haven't ruled it out entirely, but I think I've shelved it for
the time being.  There is a lot of stuff I still need to do for the
0.3 release and beyond.

> A few initial TNC terminal commands to enter KISS mode and you are
> done.

Terminal mode TNCs were designed for a different era indeed.  Adding
support for all the various command sets seems rather unproductive at
this point.  I think that some documentation on how to put the various
models into KISS mode should be sufficient :)

FWIW, I've used the TNC-X for some testing and it works great.  Being
in KISS mode natively makes it easy.

> To send data to a KISS TNC, you only have to frame the data with the
> Frame End (FEND) character xC0.  There are escape charater sequences
> for data that contains the FEND character.  FEND in the data is
> replaced by FESC TFEND (xDB xDC).  FESC in the data is replaced by
> FESC TFESC (xDB xDD).  No CRC or checksum is provided and no RS-232C
> handshaking signals employed.

Yep, this is the work I've already done in the TNC mode.

Although the above sounds completely negative, I definitely appreciate
the discussion and comments on the usefulness of AX.25 support.  It's
an important part of deciding what to do.

Thanks Craig!

-- 
Dan Smith
dsmith#danplanet.com, s/#/@/
www.danplanet.com
KK7DS