WORLDWIDE APRS MESSAGING                   WB4APR (draft 8 Sep 2001)
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Inherent in PCsat is the ability to deliver short one-line APRS type
messages to a handheld anywhere.  THis can be done live by anyone 
within the footprint of the recepient for delivery on the 145.825 
downlink.  In addition, there is the potential for delivery of such
messages to anyone anywhere via the existing national terrestrial
144.39 frequency as well.

But since each such message will add to the channel load in each of
the almost 1000 local 144.39 LAN's nationwide, this capability must
be used sparingly.  To limit usage of this system, it is reserved
only for special events, or remote travelers who make a reservation
for such service in advance.  Users will submit a travel plan which
will include the following data:

  CALL
  Email address
  phone numbers
  description of event, travel, or need
  List of authorized sending stations (HAM calls)
  beginning date
  duration in number of days
  LAT/LONG (in whole degrees) of center of travel area
  frequency (144.39 or 145.825)

An automatic centralized server system will accept such trip plans and
will assign a priority to each reservation.  During the travel period,
any APRS messages addressed to those individuals from the authorized
sending stations will be held until PCsat is over that location.  The
packets will be transmitted once a minute during the pass.

It is easy to see that such a delivery system can quickly become
saturated with only a few lines for only a few people.  Thus the need
for very careful management of the message load.

CENTRAL PCsat SERVER:

A central PCsat server will perform the following functions:

1) Accept and prioritize all Travel Plans
2) Respond with priorities and limitations
3) Accept and queue up authorized messages
4) Respond to each with a copy of the sorted queue of messages for
   that persons intended recepient so he can eliminate prior
   OBE messages and or delete old traffic, or note the
   messages that are above or below the load threshold.
   
5) Maintain a load threshold to limit the downlink to only say a dozen
   or so of the highest priority messages.  Some messages may be
   below the threshold.  Inform senders of status of all messages

6) At the predicted time for the LAT/LONG of the location of the
   target traveler, inject live messages into the APRS internet 
   system marked for RF delivery for THE specific PCsat SATGATE
   for that area.  ALL timing is done at the central server
   although the SATGATES will have a built-in 30 second delay to
   allow several packets to be bundled into a single uplink.

The only other packets on the 144.39 downlink will be a single once a
minute PCsat position report.  The purpose of this packet is to 
alert mobile and portable statiosn that PCsat is in view and that a
QSY to 145.825 will allow them to work the bird live if they desire.

de WB4APR
Bob Bruninga