APRS.TXT AUTOMATIC PACKET/POSITION

APRS.TXT AUTOMATIC PACKET/POSITION REPORTING SYSTEM (APRS)
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Document version: 8.5.3 (10 year anniversary update)
Document dated: 18 Sept 2002 (Previous version was 1 Mar 2000)
Author(s): Bob Bruninga, WB4APR@amsat.org
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Home page: www.aprs.org or www.ew.usna.edu/~bruninga/aprs.html

APRS is a real-time tactical digital communicatons protocol for exchanging
information between a large number of stations covering a large (local)
area. As a multi-user data network, it is quite different from
conventional packet radio.

APRS is different from regular packet in four ways. First by the
integration of maps and other data displays to organize and display
data, second, by using a one-to-many protocol to update everyone in real
time, third, by using generic digipeating so that prior knowledge of the
network is not required, AND FORTH, since 1997, a worldwide transparent
internet backbone, linking everyone worldwide. APRS turns packet radio
into a real-time tactical communications and display system for emergencies
and public service applications (and global communications). Normal
packet radio is useful in passing bulk message traffic (Email) from point-
to-point, but it does not do well at real time events where information
has a very short life time and needs to get to everyone quickly.

APRS is a LOCAL RF network. Although the Internet monitors APRS worldwide,
this is not the primary objective. But like all of our other radios, how
we use APRS in an emergency of special event is what drives the design of
the APRS protocol. Although APRS is used 99% of the time over great
distances, and benign conditions, the protocol is designed to be optimized
for short distance real-time crisis operations on RF.

APRS provides universal connectivity to all stations in the net by avoiding
the complexity and limitations of a connected network. It permits
any number of stations to exchange data just like voice users would on a
voice net. Any station that has information to contribute simply sends
it, and all stations receive it and log it. Secondly, APRS recognizes
that one of the greatest real-time needs at any special event or emergency
is the tracking of key assets. Where is the Event Leader? Where are the
emergency vehicles? Whats the Weather at various points in the County?

To answer these questions, APRS transmits and captures the location and
status of all stations. It can be used over any 2-way radio system
including HAM, CB, Marine Band, etc. See CB.txt, Boats.txt, Aircraft.txt.

APRS is on 144.39 throughout the North American Continent. Other
countries may use other frequencies. Check locally.

Included on the original APRSdos distribution disk (and this web site), are
several README text files on applications of APRS such as for weather nets,
direction finding, plotting satellite contacts, and monitoring DX clusters.
You must read at least the README.1st, DEMOS.txt, NewNotes.txt and HELP.txt
files. APRS uses UI frame broadcasts and map displays. There are three
major display subsystems and a number of other minor displays as follows:

LIST-STATUS - This display maintains a list of the latest UI status
packet from each station. In effect, this is a multi-station one-line
broadcast status system. On a DX cluster freq, this display accumulates a
list of all users and what was their latest command to the cluster.

POSITIONS - This display maintains a separate list of the positions of
each station often including a brief comment. They can also contain DF
and or WX info.

MAPS - Maps from 300 yards up to 4000 miles can be displayed. All
other APRS stations will be plotted. Stations reporting a course and
speed are dead-reckoned to their present position. Overlay databases of
the locations of all APRS DIGIpeaters, National WX Service sites and
even HAM stores are built in. You can zoom in to any point on the globe!

MESSAGES - In addition to the one-line STATUS packets, two-way
messages with acknowledgment are supported. All incoming messages alert
the user on arrival and are held on the MESSAGE screen until Killed.

BULLETINS - This screen maintains a list of active BULLETINS. These
are important multi-line BULLETINS addressed to everyone.

TRAFFIC - Shows the last 42 messages monitored between other stations
on the net. The MAPS-PLOTS-TRAFFIC command will connect these stations
with lines on the map.

LIST-LOG - This display is a time sequenced log of every new
status or message received. This is in contrast to the LATEST display
which only shows the most recent status packet per station.

HEARD LOG - Displays the total number of packets per station per hour. These statistics show the connectivity of the network over varying paths, such as H