[drats_users] AX.25 Support
Dan Smith
Tue Jun 2 07:05:02 PDT 2009
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
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