[aprssig] APRS-IS and I-gating

Jim Alles kb3tbx at gmail.com
Sat Nov 5 15:17:27 EDT 2016


Thanks for the 'sequence of operation'.​ some in-line comments in-line for

> The APRS-IS server will typically provide a LOT more packets than the
> criteria above.  Most interesting is the fact that an IGate will receive
> all packets for stations that were "recently" (typically 30 minutes) gated
> from RF to the APRS-IS.  This means that if your IGate copies a single
> packet station that is transmitting on RF and the APRS-IS, then you will
> receive ALL packets generated by that station for the next 30 minutes.

​And this is where things have diverged between the java code and the C
code.​ I have observed that in a side-by side comparison, Aprsc is a lot
more conservative from the get-go. This should make no difference to what a
well-crafted Igate client transmits on RF. However, it certainly can make a
difference on the local map display of that I-gate client instance. And as
an Igate operator, I prefer to see only what my station has heard on RF,
though I will tolerate a little fluff from messaging.

But then, when you combine JavAPRSSrvr's interpretation of the spec, with
some I-gate clients that are arguably broken in a default configuration (as
you know, Direwolf not being the first) hooking one of these things to a
transceiver would flood the local RF channel* (I don't like the word
network here). And I believe that has been a factor in APRS messaging not
catching on.

The following story is partly anecdotal, but it is *the take-away message*:
Years before I became licensed, some smart people with some real commercial
radio resources put quite a bit of effort into establishing an APRS network
in the Centre region. And they made the decision that they could not do a
TX I-gate, because when they did, the already very busy RF channel became
flooded. So for many years this community had a RX-only I-gate. Then I
arrived on the scene, following the lead of the Elmers, and would activate
a receive-only Igate when the other one went down, or to supplement the
network in an RF hole for special events. I had Xastir tethered to a Nextel
IDEN phone at one point; just to get the dots on the map.

So, recently, when the local I-gate went down hard with a dead computer, I
filled that role again, but this time I have some PSARC resources to
transmit with, and connect to the Interwebs, and a fill-in digi sure would
help my lowly HT. So I started researching - surely we can transmit
messages from here??? Then I stumbled upon Pete Lovell's conclusion that a
receive-only I gate is the death of many a message packet, under certain
circumstances. So we have been running a huge black hole for messaging here
in Centre County - hearing from hundreds of miles away and gating them to
the internet, but transmitting nothing.

"Crap!" I said as I shut my RX-only I-gate down.

And so I refreshed my setup with new versions of good software, and tried
out a 'new kid on the block' TNC app that has an elegant algorithm for
demodulating unbalanced tone levels, and started testing.

And so, here we are. Can anyone else see why APRS messaging has fizzled, if
this happened in other places? I hope Bob's baby can survive a re-boot. I
am certainly ready to give it a try!!!

But for some reason, I can't seem to get that IDEN modem software to work

Again, "good" (whatever that means to you) IGate software won't forward all
> of these packets to RF, but only enough to be relatively certain that the
> message recipient received the information.
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

​And to me, 'gud' means configurable.​

​And, that makes Direwolf GREAT!​ - don't get the idea I am bashing it. It
is still in my test suite because it is configurable. More on that later.

Thanks for being there!

Jim A. (KB3TBX)
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