APRSnet.txt  ver .007                                       2 Nov 1997
Bob Bruninga, WB4APR

     APRSnet is based on the pioneering work of Steve Dimse, K4HG, who 
wrote APRServ as a system for linking together APRS internet "worm holes" 
so that APRS traffic nationwide could be distributed among such sites 
via the very high bandwidth of the internet.  APRSnet is an extension 
to his original plan, to not only provide nationwide connectivity between
such APRS internet users, but to also provide on-the-air nationwide
connectivity to mobiles and other stations without direct internet 
access.  This also provdes the mechanism for extending the APRSnet into 
disaster areas or areas that have lost internet connectivity!  APRSnet 
is completely compatible with the existing nationwide APRS tracking 
network on two meters and just provides for the long haul of data 
nation/worldwide.  The system exchanges all of the standard APRS type 
packets, Position, Status, Objects, and Message\Bulletins.  See Steve's 
paper in the DCC proceedings or on http://aprs.miamisci.org/usa.html.

     Simply said, any APRS station that connects to one of Steve's 
APRServe sites has access to all packets nationwide for tracking,
weather monitoring, and messaging.  The network is distributive in 
that each such station not only receives packets from the internet, 
but also FEEDS any packets he hears into the same network for everyone
else.  This way the network is very flexible and not dependent on a fixed
system of sites.   MacAPRS already does this because it has a built in 
TCP-IP communications interface.  APRSnet.EXE is a version of APRSdos 
that was modified for greater tracking capacity and for this application.
The WinAPRS version is also underway by the Sproul Bros.

At this writing (Nov 97) there are 12 permanent nodes, and dozens of 
temporary dial in nodes all over the country.  These nodes do nothing 
more than FEED every packet heard on VHF/HF/Satellite to each other. 
(Currently, everything is FED to Steve's APRServ in Miami for further 
distribution.  Anyone telnetting to his site at www.aprs.net:10151 
will see all of these packets and they may also FEED their own local 
monitored packets into the APRServ network.

     The APRSnet concept extends this worldwide internet connectivity to 
local users on dedicated local APRSnet channels.  Whereas Steve's 
APRServe software serves all of the internet sites, APRSnet PC's take 
this data and STREAM it on a local APRSnet channel for local listeners.
Some of these ideas about APRSnet evolved from the paper presented by 
John Hansen, WA0PTV at the DCC, HamWeb:  Rethinking Packet Radio.  
ALthough his application was serving up WEB pages to the local Ham 
community, I have extended this idea to serve up the worldwide APRSnet.


DEFINITIONS:

NATIONWIDE APRS CHANNEL:  This is the single nationwide tracking
channel currently in use.  All mobiles report their positions and 
status on the nationwide APRS frequency in their local area.  As more 
and more APRSnet sites come on line, mobiles and fixed stations need 
only a minimum path length to cover their local area and make sure 
their packets at least get to a nearby APRSnet site.

APRSnet Channel:  This is an optional local channel wherever there is 
an APRSnet PC.  It is preferably different in each area, needing a clear 
channel coordination.  The APRServer transmits a continuous stream of 
packets of everything heard via the internet on this channel.  This is 
similar to the PACSAT protocol that assumes that everyone is listening 
and will collect what he needs just by monitoring the channel.  This 
continuous distribution of packets is called streaming.  Any user 
desiring to see the national APRS picture, tunes into this channel.

IGATE:  This was initially Steve's generic term for any Internet Gateway 
station that was feeding APRS data into his APRServer system.  Now we
can extend this to include the reverse path as well for streaming APRS 
data back out to a local APRSnet channel.

APRServe:  This is the software written by K4HG to do the internet
packet serving to everyone connected to his site.

APRSnet.EXE:  My simple DOS program to do the IGATE functions.  It has
several capabilities. as follows:

    INTERNET PORT:  Use this comm port to telnet to www.aprs.net:10151

    TNC PORT:       Your TNC can either stay on 145.79 or be a server

    FEEDING:        In this mode, everything heard by your TNC is feed
                    into APRServe via the telnet connection.

    STREAMING:      This streams all of your stations heard on the P
                    and L -lists to your community on your APRSnet channel

    USER:           This is standard APRS mode with only the TNC port 
                    active.  You use APRSnet.exe since it has more rooom
                    for the hundreds of stations than normal APRSdos.

CAUTION!!!          You must not activate STREAMING if your TNC is 
                    listening on the same channel it is serving.  
                    Otherwise you will form an infinite loop of packets!

TALKBACK CHANNEL:  To allow for increased capacity IN THE FUTURE and 
to avoid cluttering the National APRS channel with keyboard messages 
between FIXED stations, each APRSnet node can add a "talkback" channel 
where it listens for incomming traffic.  In many instances, it may be 
advantageous to use +/- 600 KHz offsets so that normal offset
transceivers can be used.  These talkback channels are again, only
a local coordination issue.  For now, user talkback is simply transmitted
on 145.79 and the IGATE gets it there...

ZIP-LAN:  THis is not related to the internet, but the unique features
of APRSNet allow it to also be connected to up to 5 or more local other
PCs usig only 2 conductor ZIP cord to all PC's.  All of these PC's can
communicate fully with each other and see everything off the air 
from a TNC also connected to the ZIP-LAN.  Only ONE station (the master)
can connect to the TNC SEND side.  This is very useful in EOC's or other
places where many APRS terminals are needed for local operations, but
only one station has SEND authority.  ALso useful for your kids PC's
to watch, track and communicate with DAD who is always on APRS.
See ZIP-LAN.txt.

APRSNET DIFFERENCES AND COMMANDS:

To facilitate the specific application of APRSnet.exe, many features were
eliminated from APRSdos, such as DX, Mscatter, DF, and SPACE modes.  The
D page is truncated to 40 bytes and several new commands have been added:

F1-TELNET        - Help pages about APRSnet

OPS-COM-INTERNET - Use this dumb terminal mode to access your TELNET

alt-S-NET-FEED   - Activates feeding packets from your TNC port to TELNET
         -SERVE  - Activates serving status/posits out your TNC port
         -TRANS  - Sets the transmit cycle time on your server channel
         -IGNORE - Toggles IGNORE filter on/off.  When ON, only posits
                   on the current screen will be saved.  This is so you
                   can zoom into an area, and your PLIST will only fill
                   with local packets to that area.
         -DIAL   - Save a DIAL string for your modem access.*  Invoke it
                   on the OPS-COM-INET screen with alt-D
         -LOGGON - Save your LOGGON string.*  Invoke it on the OPS-COM-
                   INET screen with alt-L.
         -CONNCT - Save your CONNECT string (open www.aprs.net:10151).*
                   Invoket it on the OPS-COM-INET screen with alt-C.
                   
                   * Note, these strings are viewable with OPS-DIGI-LIST

CONTROLS-XMT     - Toggles ON/OFF your TNC transmit 

JUST-TELNET      - Displays a list of other TELNET stations that are 
                   in your P-list.  The first hit sorts them so that
                   the TELNET guys are near the end of the list and
                   wont get bumped off.  Hit the command again for the
                   real list.

CAPACITY CONSIDERATIONS:  Even with 1200 stations showing on APRServe,
the overall througput is still only abou 700 baud.  This means for a 
while anyway, that you can STREAM this data locally on a 1200 Baud
channel.  As loading increases (now 2 weeks after introducing APRSnet 
its up to 1200 from 600 a month ago), we need algorithms to kick in, to 
filter redundant transmissions such as from FIXED station positions to 
allow mobile position reports to be reported more often.  

Beyond that level, 9600 baud or additional streaming channels will
be necessary.  In fact, other usefull APRS data can be distributed
in the same stream, such as EMWIN WX data, and DGPS signals.

Just like with the cellular phone industry, there is no limit to the
capacity of the system.  As more and more users come on board, the
APRSnet "cells" just get smaller and more focused.  One channel may
become the weather channel.  Another may be the EAST coast channel,
another may be the WEST coast channel or another may become the special
event channel....  The user just tunes in the streaming channel of
his current interest.  As more and more users join the internet,
less on-air bandwidth is required.

With the drastic demise of packet BBS systems, there should be plenty 
of VHF bandwidth available for these applications.  It is important to
note that these APRSnet channels are in fixed areas and are not even
preferred to be shared.  Therefore coordination is a local issue and
even other bands than 2 meters are quite usable.  Travelers or visitiors 
would be alerted to the local APRSnet channels by clicking on any IGATE
symbols he sees on his APRS map.

MESSAGING:  As sophistication grows, the APRSnet software will not only 
transmit all packets on the APRSnet channel, but will also split off 
message packets and send them over to the local APRS channel if it 
knows that the receipient is local.

USER SOFTWARE:  There is no distinction at the user end in APRSnet
traffic or conventional traffic except for the frequency separation.
Home stations simply monitor the APRSnet channel if they want to 
watch nationwide activity.  They still transmit their traffic on the 
normal APRS national channel, or later, on an alternate APRSnet 
talkback channel.  Mobiles will also operate as normal on the national 
channel, and will be able to see all local activity.  Stations with
internet access will join the network that way, thus freeing up
valuable RF spectrum for the mobiles and users without internet
access.  

NOTE:  The APRSnet channel uses a  slightly different protocol to 
handle the fact that the FROM CALL on the APRSnet will always be the 
call of the LOCAL IGATE TNC, so newer versions of all user software, 
Mac/Win/DOS will be needed to monitor the APRSnet channel.
This capability is in APRS8.0.


OPERATIONS:  When you start APRSnet.EXE you will see several pages of
description.  You may return to these later with the F1-TELNET command.
Next you log on to APRS and give the COM port (1 or 2) of your TELNET
connection and TNC. 

Next you alt-S-SAVE your config file so you wont have to do all that again.
Finally, you go to OPS-COM-INTERNET and do what ever you have to do to
connect to www.aprs.net:10151.  If you use a dial up line, you will need
to tell your modem to dial the phone.  This is simply the command:

ATDT #########  (AuTo Dial, Tone )

(Save this string and others using the alt-S-NET-DIAL, etc commands.)
Once you are logged in, you will need to open a TELNET connection.  Of the 
three systems where I work, there are three different formats!  THey are

   OPEN www.aprs.net:10151
   C www.aprs.net @10151
   www.aprs.net 10151

once you know this works, you will usually hit ESC to escape back into
APRS IMMEDIATELY so that APRS will plot the initial dump of stations.
If you dont hit ESC almost immediately, you will be stuck in O-C-I
screen and probably get overflows and maybe even lockup...  There is a
packet counter displayed during the initial dump.  I am seeing 1200 to
2600 packets in the 12 hour buffer.  APRSnet only keeps the last 380
for now..

Once you are back into APRSnet you should be able to do everything you
normally do.  THere is ONE new command, JUST-TELNET.  This will display
a list of only the other APRServe and APRSnet users.  If you do an OPS-
QUERY 4096 miles, then all other APRServe stations should respond within 
a few minutes.

If you plan on operating an APRSnet site, you should begin frequency
planning now.  Your site is probably not a good VHF site, so you will
need to transmit your APRSnet stream on one channel and then maybe
have digipeater sites to the north, south, east and west of town.
There are several possibilities:

SPEED DIALING:  Once you figure out your modem dial string and your
required LOGGON and CONNECT string, you may use the alt-S-NET-DIAL, 
LOGGON and CONNECT commands to save these strings (alt-S-SAVE).  Then 
when you are on the OPS-COM-INTERNET screen, you can just do alt-D to 
dial, alt-L to loggon, and alt-C to connect... (c www.aprs.net 10151 on 
my system)

INITIAL TRIALS:  You can transmit at a 50% duty cycle on channel A
and then have the outlying DIGIS all digipeat those packets back onto
channel A.  Crude, and people that can hear 2 digis will have problems
and if APRSnet catches on, your 50% duty cycle may not handle the load

DUAL FREQUENCY:  Same as above, but have each of the other digis 
listen on A but transmit on their own channels.  Still 50%, but
everyone gets a clear channel.  Also harder to find 4 channels.
OR, if you can get enough frequency separation, all of these digis
and your site can operate 100%, just tell the digis to operate full 
duplex.

DUAL BAND:  THis is probably the best.  Transmit on BAND A and then
have the outlying digis transmit on band B (multiple freqs)

9600 BAUD:  Do all this at 9600 baud!  Remember, 5 watt 9600 baud data 
radios are less than $150...


FREQUENCY PLANNING:  The need for a single nationwide APRS mobile
channel is as important as ever.  But, in addition, the APRSnet system 
will need a minimum of one other local APRSnet channel for the internet
streaming channel.  Notice that this channel does not need anything 
other than local coordination, since it is for a fixed site application
for fixed users.  As activity grows, an additional talkback channel
may be required.  Careful planning early on could arrange for the
talkback channel to be +/- 600 KHz from the streaming channel so that
normal T/R offsets can be used.  For example, if 145.63 is the APRSnet 
channel in an area, then 145.03 could possibly be used as the low 
duty cycle "talkback" channel to APRSnet.  Probably the 440 band is
ideal for this kind of expansion...

TRANSITION:  Unfortunately the APRSnet concept required a new on-air
protocol.  THis means that only new software (after APRSdos 796, Mac
2.0.7 and WinAPRS x.x.x is required to see these new packets.  This
APRSnet.EXE should work fine too...

For now, these are all just ideas to spur further thought.

de WB4APR

