In article ,
Bill Horne wrote:

Gary,

AX.25 is the protocol that was used for packet transmission on ham radio
when I was using packet: I assume it's still the standard, since Linux
still has the option.

Yes, it is. It's showing its age but is still in use.

It might help you to think of it as TCP/IP with
ham calls signs added.

I think it's more proper to think of it as a lower-level protocol...
more like Ethernet, with callsigns taking the place of Ethernet MAC
addresses.

AX.25 can transmit its own style of datagrams, or data streams
(analogous to UDP and TCP respectively), and it can also carry IP
packets (and thus TCP and UDP).

If the Windows-based software is free, reliable, and meets your needs,
and you already have a Windows-based PC you're willing to dedicate to an
Igate, then you can certainly use that. However, I find Linux to be an
excellent substitute for Windows, especially for "single function"
machines such as a BBS or packet gateway. Linux is also able to run on
much older hardware than Windows, and (most importantly) offers native
support for the AX.25 protocol stack, allowing full use of higher-level
applications without modification: to Linux, AX.25 and TCP/IP are just
two different MAC layers.

Yup. 'Tis a definite advantage.

Once you've cut your teeth on handling a single AX.25 hookup on a
Linux system, you can (if desired) expand to running a whole stack of
AX.25 ports on the same system, with the same applications... doing
AX.25 routing, running a BBS, and so forth.

There are at least four ways to run ham packet on Linux:

- A full-powered TNC (like a PackRatt or a TAPR or MFJ TNC-2 or clone),
connected via a serial port - just like Windows. In this
arrangement, the TNC itself handles the full AX.25 protocol, and
you talk to it (via Linux) using a terminal emulator.

- With a TNC (full-featured or limited function) in "KISS" mode.
In this mode, the TNC handles the over-the-air transmission and
reception of packets, the Linux kernel handles all of the higher-
level AX.25 protocol support, and Linux applications provide the
connection management, BBS capability, etc.

- With a sound-card interface and a "soft modem" application. There's
no separate TNC - Linux uses the CPU (as a DSP, in effect) and sound
card to implement a modem, which then registers itself with the Linux
kernel as a "KISS" TNC... everything above this point is just like
the previous approach.

- Linux kernel AX.25, encapsulated into Ethernet (and then into
IP if you want). Good for connecting together multiple packet
nodes into a network via the Internet.

You can run two or more of these approaches on the same Linux system
at the same time, if you wish.

Not to mention that Linux is free-as-in-speech, and the license says so.

And also very close to free-as-in-beer, if you're already paying for a
broadband connection through which you can download it. With Linux
you can also see the source code to the full software stack (which can
be very good at times, and can also cause you the screaming horrors
occasionally) and make changes if you wish.

In fairness, Windows also supports at least three of these modes (full
TNC, KISS TNC, and sound-card "softmodem TNC"). I don't know about
Ethernet/IP encapsulation of AX.25.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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