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Hi Lynn,<br>
<br>
On the one hand, you raise good points; on the other hand, what I'm
proposing is nothing particularly new. We already have:<br>
<ul>
<li>PC keyboard to RF bidirectional messaging (Xastir, whatever is
out there for Windows)</li>
<li>Bidirectional email to APRS messaging (APRSLink, other
gateways)</li>
</ul>
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?<br>
<br>
-- John<br>
KR0L<br>
<br>
<br>
<br>
On 04/08/2012 02:27 PM, Lynn W. Deffenbaugh (Mr) wrote:
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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.<br>
<br>
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 neighborhood.<br>
<br>
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and
Win32<br>
<br>
On 4/8/2012 1:24 PM, John Goerzen wrote:
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Hi folks,<br>
<br>
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.<br>
<br>
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:<br>
<ul>
<li>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?)</li>
<li>Processing/generating ACKs, REJs, etc.</li>
<li>Proper timing for retransmit of packets that weren't
ACKed.</li>
</ul>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Thanks,<br>
<br>
-- John<br>
KR0L<br>
<br>
[1] source code at <a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="https://github.com/jgoerzen/ax25xmpp">https://github.com/jgoerzen/ax25xmpp</a><br>
<br>
<br>
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