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Messages via PCsat to Travelers

Another PCsat first:

An RF message somewhere on the planet sent on an APRS channel and
delivered via the internet to somewhere else on the planet where it was
gated via PCsat to the end user.  This is one more of the underutilized
features of PCSAT as integrated into the worldwide APRS system.  Here was
the original packet within range of DIGI-1.......

  W2KQ>APW251,DIGI-1*/1::WB4APR   :good show bob  73 Joe{003

That message was picked up by an Igate within range of DIGI-1 (Like all
APRS messages worldwide on any frequency) and sent to the internet to all
other IGates worldwide within seconds.  One of those IGates was AHUB-4
which has a port on PCSAT's channel.  It in turn had seen WB4APR last via
PCsat.  So like all Igates, it pulled the live packet off the internet and
sent if up via PCsat where it was digipeated back to WB4APR in Maryland

  AHUB-4>APW251,PCSAT-1*/1:}W2KQ>APRS,TCPIP,AHUB-4*::WB4APR   :good show
                           bob  73 Joe{003

This was an unplanned serendipitous packet, but since it demosntrated
where we are going with this, I thought I would share it.  Now for the
preverbial details:

1) In this case, the original packet was via PCSAT-1 (DIGI-1) but then
went back into the internet to come back out via another IGate (AHUB-4)
and then back up to the satellite.  But if anyone anywhere on the planet
had transmitted a packet to me during that 10 minute pass on their local
RF APRS network, it also would have been gated just as well.

2) This capability can IMPLODE the PCsat system unless we get everything
set up properly.  Here is the problem... By default, any IGate assumes
anyone it hears on RF is a local station (so Igates listening to PCsat
will rightfully assume then that they have an RF path to that person (they
do, but only for 5 minutes or so)...  But we cannot let ALL igates then
try to all transmit at once to send an internet packet back to someone via

Possible solutions:

1) Only one Satgate per footprint.  One on East coast and one on west
coast.  (but they will still collide enough to make this painful)

2) Travelers REGISTER with the SATGATE nearest where they will be
traveling.  No other packets are gated to PCsat.  Thus, only one IGate
will be watching for their traffic.

3) If there is only one satgate on your continent, then there is no
problem, but since ANY copy of APRS running on anyone's home station can
be  an IGate transparently, you see that we can have a BIG problem.

Problem is, I dont even konw who the SATGATES are other than a few.. and
they come and go.  But managing this worldwide amateur radio LIVE
messaging via satellites linked to the internet will need some committment
and planning.

But this was part of the PCsat design, and remember that we can deliver
these messages to MOBILES driving though Mississippi who dont even know
there is a satellite, because these messages can come down on 144.39
anywhere in the USA.

But that is why all along, PCsat operations assume that travelers with
the need to use the higher level features of PCsat will need to file a
travel plan so that the network can be managed.

There are other un-used features of PCsat for remote travelers, but so
far no such travelers (who will be out of range of the worldwide APRS
system) have applied other than VE3RRY who will be on a cruise ship in the
Carribean the week of 27 Jan.

de WB4APR@amsat.org, Bob

PCsat WEB  page     http://www.ew.usna.edu/~bruninga/pcsat.html
ISS-APRS FAQ:       http://www.ew.usna.edu/~bruninga/iss-faq.html
CUBESAT Designs     http://www.ew.usna.edu/~bruninga/cubesat.html
APRS LIVE pages     http://www.ew.usna.edu/~bruninga/aprs.html
APRS SATELLITES     http://www.ew.usna.edu/~bruninga/astars.html

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