[aprssig] APRS message-handling algorithms / libraries
jgoerzen at complete.org
Sun Apr 8 15:09:44 CDT 2012
On the one hand, you raise good points; on the other hand, what I'm
proposing is nothing particularly new. We already have:
* PC keyboard to RF bidirectional messaging (Xastir, whatever is out
there for Windows)
* Bidirectional email to APRS messaging (APRSLink, other gateways)
So I guess I don't understand why XMPP is a concern whereas the others
aren't. Honestly I think it's LESS of a concern than email, as XMPP is
more strongly authenticated than SMTP is, etc. What does the iGate
operator do about someone on Winlink sending messages that they shouldn't?
On 04/08/2012 02:27 PM, Lynn W. Deffenbaugh (Mr) wrote:
> Please consider that the APRS channel is 1200 baud and shared in any
> given area. I considered a Skype chat IM to APRS gateway early on,
> but it is trivially easy to completely overwhelm the APRS channel with
> just a simple 2 or 3 person keyboard chat.
> Going from APRS to IM is easy, the RF side is initiating and providing
> the throttle. Going from IM to APRS is my concern, in additional to
> the authentication that "friend B" may not be a licensed amateur, even
> though approved by "friend A" who may be. Friend B is still not
> entitled to transmit on amateur frequencies, and it's not "friend A"
> taking the license risk, it's the IGate operator in "Friend A"'s
> Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
> On 4/8/2012 1:24 PM, John Goerzen wrote:
>> 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,  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.
>> -- John
>>  source code at https://github.com/jgoerzen/ax25xmpp
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