[aprssig] local messaging

Jim Alles kb3tbx at gmail.com
Mon Nov 21 04:44:04 CST 2016


So, back to Bob's collision with reality:

APRS-IS behavior that does not recognize an APRS station (in the
IGate/APRS-IS system) unless and ONLY IF it sends a valid position report.
This is not how APRS messaging is supposed to work.  There should not be
any dependence on a position report for 2-way messaging to work.

And my dilemma, where Canada is two hops away on occasion:
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What do we have to work with to improve messaging, without saturating some
RF channel territories?

We have been discussing situational awareness, from two perspectives:

   - The mobile operator, expecting to exchange messages
   - The TX-IGate operator, wanting to minimize RF transmissions.

I am going to focus on me, the confused IGate operator to start. This is to
discuss the theoretical, not suggesting change or imply that it can be done.

Ok what happens to my map, if I hear a message from across the lake, and I
don't consider distance when I try to send a message back to him? I may
have to send 4-5 copies across two hops because He can't get the message
reliably - or get the acks back to me, lighting up digis for hundreds of
miles, for a hopeless cause.

But wait, (I presently am trying figure this one out - help -really!)

   1. My IGate transmits direct, no path. and can cover most of Happy
   Valley (maybe - not tested). It can't reach Interstate-80 to the north.
   2. My IGate transmits with PATH WIDE2-1 and I hit 4-5 High Profile Digis
   (HPDs) all at once, reaching I-80 and more, but being in earshot of all of
   them, we get collisions in the valley - wasted bandwidth locally w/ no
   benefit.
   3. My IGate transmits with PATH W3YA-1 <http://aprs.fi/info/a/W3YA-1>
   our closest high-profile digi @ 650' HAAT The packet hits I-80, and we get
   a second clean, strong copy in the valley

To me, it looks like #3 is The Right Thing To Do.

What do I limit my transmit decision to? It has to be no more distance than
what W3YA-1 can reach. I figure 50-60 miles in my case. I would reduce that
to 40 if I can realize a plan for a second IGate 50 miles south, in
farmland.

That means I need to ignore anything that wants to be transmitted beyond
that transmit coverage..

How do I decide that, without waiting to get a station's position beacon?
Number of hops (1) isn't helpful, because I can hear the other HPDs.

Can I know if it was Digi-peated once from direct to W3YA-1, from the path?
does that help? is it reliable? I still might not know that the station is
in transmit range of W3YA-1?

In my work, I might look for more sensors.to use. Many TX-Igates might have
fairly decent Internet Bandwidth. So this is a hypothetical tool for them:

IGates are store and forward mechanisms. Could we ask something else if it
knows where a station is, if we heard it, got a message for it, but don't
yet know whether it is worth chewing up the channel slot?

.ja.
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