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UI digipeating via AO16/LO19



Maybe to help the Satellite community understand what we are trying to do
with APRS via satellites and these early tests on AO16/LO19 with UI
packets, it might be useful to think of it as "worldwide two-way LIVE
amateur message paging".  Several things underlie this interest:

1)  The Kenwood THD7 HT is capable of sending text messages from its
keyboard and receiving and displaying them on its LCD display.  With the
MIR digipeater, we thus found that we could send and receive messages from
our SHirt pockets with rubber ducks.   Thus we HAVE the handheld amateur
satellite radio!  Now, without MIR, we need another satellite.

2)  We have a worldwide APRS informally linked Internet network that
distributes any packet heard ANYWHERE to EVERYWHERE.  Kind of like
cellular phone systems.  The internet links all the cells on the planet
together, while the users are all using their radios within their cell. 
But with out any knowledge of how, they can communicate with anyone
anywhere simply by knowing their CALLsign.

3)   The IGates that link every cell into the internet are nothing
special!  They  are nothing more than ANYONE who happens to be running
APRS while he is Logged on to his ISP (Even if he is doing something
else!).  THus, there are no special nodes, software, or Gateways.
Anyone and everyone can be a gateway at any time.  Thus, as long as anyone
can be heard anywhere, he can communicate anywhere.  Thus, as long as we
have at least ONE station on each continent listening to AO16/LO19, then
any messages via that satelite can go ANYWHERE on the planet within the
APRS infrastructure in real time.

4) Thus, the desire for a Satelite Digipeater to allow remote users who
are not near any of the terrestrial network, to send and receive messages
during a pass.  Remember, in APRS, a MESSAGE is typically ONE LINE or so.
You can say a LOT in one line if you want to...  As a UI packet, there is
NO connection, NO acks, NO timeouts, NO Queues.  As long as you see your
one or two packets digipeated, then you can assume they got there...

5) Since APRS is a live two-way system, All of the above, assumes that the
recepient of a message has his radio on.  In APRS there is no store-and-
forward.  Messages are deliverd LIVE or not at all.  With one exception.
A message can be addressed to "EMAIL" and a server written by WU2Z will
ACK the message and wrap it into an Email message for the internet.

Thus, today I received the following:

---------- Forwarded message ----------
Date: Sat, 11 Sep 1999 14:32:32 -0400 (EDT)
From: KB2WQM-1@unknown.net
To: wb4apr@amsat.org
Subject: APRS Message from KB2WQM-1

hello via pacsat

--------------------------
Message received by MacAPRS IGate station WU2Z
Located in NO BRUNSWICK, NJ
APRS path = KB2WQM-1>APS199,INTERNET TCP/IP
-----------------------------------------------------

As you can see, Jeff, KB2WQM sent this from his boat using a conventional
2 meter FM radio, and OMNI mobile antenna, and a manchester or modified
TAPR-2 TNC.  It was digipeated by AO16.  It was monitored by an IGate
somewhere and injected into the worldwide APRS stream (TELNET to
199.227.86.221 port 23) There it would normally pop back out to RF at any
IGate that had heard me locally.  But since he sent it to EMAIL, the WU2Z
server picked it up and Emailed it to me...

This is only an unusual example of APRS messaging.  Normally he would have
just sent the message directly to my station (most APRS operators leave
their station on the air at all times).  But here he decided to demo how
APRS messages can also be delivered via Email.

Unfortunately, without MIR, the only other digipeaters in space that
welcome APRS UI packets are AO16 and LO19.  For now, this prevents the
Kenwood HT from being used since it does not have a manchester TNC.
But anyone with a TAPR-2 clone TNC and 2m FM mobile radio can make a $3 
mod and transmit.  We want to demonstrate this capability to encourage
more digipeaters in space for mobile/handheld two-way brief messaging.

I hope this paints the larger picture and helps explain where we are
trying to go.  And despite what *used to be* very special hardware
requirements to operate the 1200 baud pacsats, Remember that NOW anyone
can transmit up to AO16/LO19 relatively simply and we only need a few
listening...

de WB4APR, Bob

For more info see http://web.usna.navy.mil/~bruninga/traknet.html

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