by Arte Booten, N2ZRC

     As with any packet  networking,  path selection depends on what can
be heard by you  and those that can actually  hear you.  You can get the
equivalent of an MHEARD command, showing you the paths stations near you
are using and which stations you hear direct by pressing the  D(igipeat)
key.  See who these are.  Hopefully, one of them will be a WIDE.

     Any  APRS  network relies on the majority of fixed stations  having
their TNC's  DIGIpeat function turned on and their MYAlias set to RELAY.
Since APRS is an unconnected protocol,  packet nodes  (with a few excep-
tions), which rely on connections  and error-checking for data transfer,
are counterproductive.  APRS utilizes that  DIGIpeat function by the use
of GENERIC callsigns as a TNC's alias(es), most commonly RELAY and WIDE.

     There are various  flavors of WIDE,  all represented differently on
the screens of different APRS  versions.   But first let me describe the
function of  RELAY in the APRS network,  as this is a useful,  but often
misused,  generic callsign.   RELAY stations  generally consist of  your
average  "Joe Aperze"  in order to allow low-power,  low gain mobile and
portable stations into the network.  In many areas, most of these RELAYs
are able to hit the nearest WIDE directly.

     This means that if you can hear and get digi'd by the nearest  WIDE
from a fixed location with reasonable consistency,  you should AVOID THE
USE OF RELAY because if a WIDE hears you,  others probably can as well..
and they're probably also using the alias RELAY.  This causes collisions
as each of the RELAYs that hear you try to digipeat your packet at about
the same instant.  And your packet will probably die then and there.

     Now back to the  various flavors of WIDE.   The first is just that.
It'll digipeat  anything that specifically goes via its callsign as well
as to the generic callsign WIDE, shown as a small green star in APRSDos.
Sometimes, there's also a weather station associated with this  DIGI, in
which case APRSDos shows them as a green circle.  Next comes WIDE-RELAY.
These are TNC's that can have two aliases and digi packets addressed via
RELAY, WIDE or its own callsign and show on APRSDos as big green stars.

     We also use WIDEs that use an alias of TRACE.   Their firmware sup-
ports the  DIGI-SWAP  function.   When it DIGIs something  addressed via
one of its generic callsigns it changes that GENERIC callsign to that of
its own in the VIA: field of that packet.  This allows people to see how
the network is  propagating and makes  selection of paths  a bit easier.
Those of us running APRSDos, WinMacAPRS and pocketAPRS see these as that
large star with a T in the middle.

     The next type uses something the inventor of APRS (The Great Oracle
of Glen Burnie)  Bob Bruninga, WB4APR,  first proposed several years ago
to enhance unconnected networking  via amateur packet radio and  Kantro-
nics recently picked up on.  It uses a scheme Bob calls WIDEn-n.  "N" is
a number between 1 & 6.   The first of these would represent  the number
of "hops" you want to take.

     The second of these numbers  depends on how many times  that packet
has been digipeated  by the time the last digi retransmitted  it.   It's
set by the firmware in current  Kantronics TNC's  (but I understand that
others *MAY* be coming out with it in the "near" future)  and decrements
one  from that number on the packet  it's heard, but hasn't yet  DIGI'd.
WIDEn-n TNC's  can also be set for callsign substitution, as I described
above.  They have an N in the middle of the green star.

     The  beauty of  WIDEn-n  is seen best  in a network in which  most,
if not all, WIDEs in a given area have such firmware.   In others, users
of callsign substitution might consider shutting that feature off.   Un-
fortunately,  not everybody that has a digi is  USING Kantronics' stuff.
And some of those that are  aren't willing or able  to change the  chip.
This pretty much  describes the  APRS  network in my part of  the woods.

     What's the best path?   Look around.   Who hears you.   Who do they
hear.   And where do you  want the packets to go?   I suppose you'd like
a nice, stable path from  Montauk to  Albany and  Newark to Binghampton.
Good luck.   The path you need is there, if you can see  anybody else on
your screen.   If a Green Star  can hear you,  then that's gonna be your
starting point.  From there, just follow the bouncing green stars.  73

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|Arte Booten  (n2zrc@arrl.net) AEC for Digital Services, NYC ARES/RACES|
|Riverdale, New York    [FN30bu]    !4052.71N/07354.06WNPHG5370/A=00240|
|PGP Key Fingerprint: D73E B889 C630 6F4A F31F 3083 56BD 0AAD 9996 3B03|
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