[aprssig] APRS message-handling algorithms / libraries

[John Goerzen]

Thanks John.  I've browsed the source and it looks helpful. Much 
appreciated.

-- John

On 04/08/2012 03:47 PM, John Gorkos wrote:
> Please review the code found here:
> https://github.com/ab0oo/javAPRSlib
> The multi-part message capability isn't in there, but the ability to 
> encode and decode messages is.
> Let me know if you'd like any help implementing or testing.
>
> John Gorkos
> AB0OO
>
> From: John Goerzen <jgoerzen at complete.org <mailto:jgoerzen at complete.org>>
> Reply-To: TAPR APRS Mailing List <aprssig at tapr.org 
> <mailto:aprssig at tapr.org>>
> Date: Sun, 08 Apr 2012 12:24:29 -0500
> To: <aprssig at tapr.org <mailto:aprssig at tapr.org>>
> Subject: [aprssig] APRS message-handling algorithms / libraries
>
> Hi folks,
>
> I am looking to write some APRS software, and I'm hoping to avoid 
> re-inventing the wheel.  I am particularly interested in libraries in 
> any cross-platform language (C, Perl, Python, Java, etc.) that can be 
> used to receive and generate APRS messages.
>
> In my research, there are quite a few libraries that receive APRS 
> messages, but I have found none that are helpful with generating 
> them.  This seems to be something with some complexity; such as:
>
>     * Splitting data up into packets of the appropriate size (APRSLink
>       for Winlink appears to somehow detect the type of device in use
>       and generates shorter messages for TH-D7A.  Anyone know how to
>       do this, and what are the appropriate sizes for the D7A, D72A,
>       710, and VX-8GR?)
>     * Processing/generating ACKs, REJs, etc.
>     * Proper timing for retransmit of packets that weren't ACKed.
>
> None of this is hugely complicated, and the APRS spec is fairly clear 
> on the ACK, REJ, etc. process.  The maximum message sizes appear to be 
> undocumented and I'm hoping someone can help me out there.
>
> My project, incidentally, is to build a bidirectional APRS-XMPP 
> bridge.  XMPP is the protocol behind the instant messaging tools such 
> as Jabber and Google Talk, and is available for free on every modern 
> platform.  In the spirit of both amateur radio and the Free Software 
> communities I'm a part of, full source code to this project will be 
> available.  I actually already wrote a much simpler piece of related 
> software, letting someone take a connected AX.25 session and bridge it 
> to XMPP, [1] so I do have some experience under my belt.  This is 
> obviously a more complex project, but XMPP looks like an excellent way 
> to bridge APRS to other systems.  I think it is a better fit than the 
> email gateways out there, and in fact, XMPP already has fields for 
> carrying presence information and location information with presence 
> packets.
>
> Are there any particular notes available to those implementing 
> gateways between APRS and non-APRS sources?  I have taken note of what 
> sites such as OpenAPRS or Winlink do to validate people for access, 
> and plan to do something similar here.
>
> Thanks,
>
> -- John
> KR0L
>
> [1] source code at https://github.com/jgoerzen/ax25xmpp
>
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