[amsat-bb] Re: ax.25

[Paul Williamson]

At 12:35 PM +0200 9/26/06, Davide Vosti wrote:
>I'm part of a student team delevoping ax.25 for a cubesat.
>I want to ask you if you advice to you this protocol or not,

AX.25 is still current, but before going too far into implementation 
you will want to consider the needs of your application. Connected 
mode in AX.25 doesn't scale very well for multiple user access to 
spacecraft, but it's reasonably appropriate for a single station 
uploading critical data.

Depending on what you're trying to do in your CubeSat, you might want 
to consider using the PACSAT Protocol Suite, which builds on AX.25. 
See http://www.amsat.org/amsat/sats/nk6k/msatpro.html for protocol 
documentation. There are several groundstation implementations 
available. This has been the standard for amateur store-and-forward 
digital satellites since AO-16 in 1990.

If your needs are more modest, you may be able to simply ignore most 
of AX.25 and use only AX.25 UI frames as datagrams. The APRS standard 
may or may not be relevant to your application.

Regardless of what you implement on top of AX.25, I would call your 
attention to the FX.25 protocol extension for FEC that was proposed 
by Jim McGuire KB3MPL of the StenSat group. It's still just a 
proposal, but it seems to have promise. 
http://eludium.stensat.org/mcguire/FX-25_01_06.pdf

>We are developing ax.25 based on this document
>(http://www.nj7p.org/AX25.2.2-Jul%2098-3.pdf) but we have found that
>some information are missing... Do you have some others document?

That looks like the document, though I'm not sure of the status of 
the 2006 changes. I would assume that 
http://www.tapr.org/pub_ax25.html is the authoritative source for 
AX.25.

There's a TAPR mailing list for AX.25 discussions. That would 
probably be the best place to ask technical questions about AX.25 
issues. https://lists.tapr.org/cgi-bin/mailman/listinfo/ax25-layer2

73  -Paul
kb5mu at amsat.org