MIR-TEST.TXT      APRS/MIR Test 11 March 1998
Document version: 8.3.8   7 Mar 99
Author(s):        Bob Bruninga, WB4APR <bruninga@nadn.navy.mil>
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On 11 March 1998 a special APRS/MIR test was conducted via the packet
system on the Space Station MIR.  The test was to show possible methods
for improving the visibility of MIREX communications to students and
schools:

   1) Demonstrate the use of a one-to-all protocol using UI frames for
   more effective use of the MIR downlink to multiple ground stations.

   2) Demonstrate the usefullness of spacecraft beaconing their
   GPS position a few times per footprint to identify their position.

   3) Use APRS map displays to display the moving position of the
   spacecraft and to display the locations of all participating
   ground stations.

   4) Demostrate the use of linked internet groundstations to
   distribute the live downlink collected from ground stations all
   over the US to users worldwide in real time.

BACKGROUND:  APRS is a connectionless protocol using UI frames to
communicate information effeciently among a large group of stations
in real time.  Each station transmits, and all stations capture, sort
and accumulate the information on a variety of display pages, including
maps.  The primary advantage of APRS is sharing information between 
the largest possible number of  users effeciently over a single shared 
channel.

MIR BULLETINS:  The MIR packet radio link is ideal for a one-to-all
protocol for distributing BULLETINS, ANNOUNCEMENTS and other information
to all users in the footprint.  Although MIR currently transmits a
few single line bulletins, these are sometimes lost among the
hundreds of other ACKS, REJECTS, and BUSY packets in the downlink
that sometime overshadow any transfer of information.  By using a
protocol like APRS to receive the MIR downlink, monitoring stations
can capture such properly formatted BULLETINS and ANNOUNCEMENTS of
interest to everyone and display them in a user friendly manner.


MAP DISPLAYS:  Since the MIR PBBS is a single user
system and therefore its uplink channel is jammed with dozens if not 
hundreds of users sending useless and competing CONNECT-REQUESTs.
The constant stream of DISCONNECT-BUSY packets in the downlink carries
no useful information other than an observation of the numbers trying.
Conversly, APRS transmits a single short position report which not only 
shows who is participating, but also the distribution of these stations 
within the map footprint.  The flavor conveyed to the users in this case 
is a feeling of participating camaraderie instead of individuals 
fiercely competing for the single user access.  This is a better
attitude to convey to students and the map display is certainly more
visually appealing than a scrolling display of disjoint packets.


INTERNET INTERLINKED GROUNDSTATIONS:  With the worldwide connectivity
of the internet, the downlink packets from MIR can be received by
groundstations anywhere and made available to all users everywhere
via the Worldwide linked APRServe system.  
For schools, it gives easy access even to individuals and classes 
with no amateur radio equipment.

THE APRS/MIR TEST:  Dr. Larson of the MIREX group suggested the APRS
Mir test be conducted for two orbits on the 10th of March.  Unfortunately 
the MIR packet system went off the air on these two orbits, so the test 
was extended to the next few orbits over the USA between 0230 AM and 
0400 AM local time.  Due to this poor timing, the test was extended for 
a full 5 orbits but not all schools got the news.

To keep things simple, APRS SPACE mode was not used and APRS users 
were told to operate normally on the MIR frequency and a transmit rate
of about one packet every 3 to 4 minutes.

Although MIR was not programmed to transmit any special Bulletins,
several ground stations transmitted such BULLETIN, STATUS and
MESSAGE packets.  Over 65 separate such packets were successfuly captured
during the test.  On average these packets were transmitted
successfully twice (110 times).  The advantage of using the few
specially authorized uplink sites to digipeat bulletins instead of
MIR means that the bulletins may be updated instantly on the ground
and then digipeated to ALL users at once without requiring an upload
to the BBS nor hundreds of individual downloads. Further, the crew was
not involved.

   In additon to the BULLETINS, each stations POSITION packet, if
successfuly digipeated by MIR, showed up colorfully on everyones maps. 
During the test 202 station position reports were displayed averaging 
about 40 per pass.

To inject the downlink from Mir into the Internet, a few of the normal
APRS I-Gates tuned their radios from the normal APRS frequency to the
Mir downlink frequency.  These Mir packets were intermingled with the
normal stream of APRS packets into the APRServe Internet
system.  Although they would be seen on the main www.aprs.net maps
they would be hard to distinguish from the usual 1000 to 1200 or more
APRS stations on the air.  To provide a unique display of the APRS/Mir
packets alone, a special WEB page was designated to filter out only
the APRS/MIR packets and display them spearately to users.  During
the day of the event there were over 11,000 hits on the server system
representing a peak load of 150 simultaneous users and as many as
1000 users on the special MIREX page.

STATISTICS:  In raw numbers, the following table compares the APRS
packets during the test to the other packets observed on the downlink.
These statistics were mostly derived from observations on the
east coast (Maryland) plus the APRS packets logged elsewhere.

PASS  TOTAL   PBBS  PBBS  BUSY  R0MIR  R0MIR  APRS  APRS
      PKTS    PKTS  USERS REJ   PKTS   USERS  PKTS  USERS
----- ------- ----- ----- ----  -----  -----  ----  -----
0740z  229      88    3   18    30     1       89   44
0910z  153      46    3    7    14     0      102   41
1050z  122      47    3    5    11     0       75   51
1220z  170      96    3   15    35     4       72   39
1400z  188      94    5   12    41     3       53   27

Of the 202 APRS stations, 6 were associated with schools and 5 were
mobiles inclusing one Naval Academy boat, and one railroad car.
Individual APRS packets were also reported by one station
in each of Tiawan, South Africa, Australia, Japan and Hawaii.
Although APRS  users were encouraged to only send their position
report until the total load on the channel could be assessed, there
were still 65 Bulletins and Messages that were successfully relayed.
Since the test was conducted over multiple passes, the 202 successful
stations actually represent 104 different stations.

SUCCESS RATE:  Of these 104 different stations, all were running 10
watts or more, but two were successful at 5 and 7 watts.  Of the
ten stations reporting a lack of success, 3 were running only
1 watt, and two were running 4 and 9 watts.  One was only transmitting
once an hour, and one was transmitting once every 5 minutes.  Another
was using an inside antenna.  Two were running 10 watts and 50 watts
but beacon rate was unreported.  If you consider a 10 watt baseline
and proper setup with a 3 to 4 miunte rate, then the success rate
appears to be near 98%.  Although there may be many more stations that
did not report their lack of success, these numbers clearly show that
the channel was not saturated nor congestion limited.  In fact, during
this test a nominal 3 Mir PBBS users logged onto the BBS per pass, but
typically only one was successful at uploading and downloading any
traffic.  Actually this is rather typical on most passes during user
hours, but in the middle of the night, as in this test, these BBS
users would have expected a less congested channel.


LESSONS LEARNED:

1)  Many stations did not try to reduce the length of their terrestrial
position reports.  Thus, there were many verbose packets.
A 30% improvement could be expected here.

2)  Similarly, the SPACE mode was not used.  It has the advantage of not
only being very short, but it automaticlly stops transmitting when it 
sees its own success.  This higher effeciency could support probably
double the number of stations and packets.

3)  Non APRS stations were recommended to use the very efficient
grid square method of reporting position by placing their gridsquare
in the UNPROTO TOCALL or their packets.  Unfortunately, this does
not work on Kantronics TNC's which always send their BText UI frames
to the callsign of BEACON.  THus their packets conveyed no position
information.

4)  For the pseudo moving MIR-6, MIR-8, and MIR-3 uplinked posits, these
should have all used the same ICON name of just MIR.  Although the
numbered MIR Icons made it possible to easily see which uplink station
was responsible for the ICON, the changing calls meant that as the
MIR-6 and Mir-8 uplink stations passed out of range, these posits
were stuck on the map at their last uplinked position and stopped
moving.  By using the same Icon name of Mir, then the single Icon
would have continued to move as long as there was at least one
uplink station in range.

6)  The uplinked MIR positions were more static than dynamic since
only about 20 were recorded on all 5 passes.  At one per minute,
this shows only a 20 % success rate for the possible 100 pass minutes.
Higher power or tracking antennas may be required.

CONCLUSIONS:   The test was successful in meeting all of the original
objectives.  The short notice and early morning hours helped to reduce
the number of participants to about 104 stations.  We think this number
is representative of the nominal number of schools that could be
authorized to simultaneously participate in future such Mir experiments.
A total of 12 stations associated with schools and students were
reported.  One station even displayed 5 APRS stations while operating
with a whip antenna inside a motel room on travel.

     The test demonstrated the value of using a UI frame one-to-all
packet protocol to improve the delivery of information to all ground
stations.  Further, the test demonstrated the value of a few special
MIREX ground stations to uplink the moving Mir position reports and
to relay real-time MIREX bulletins and announcements that can be
received by all stations in the footprint including receive-only
school stations.  Finally, the test showed the value of multiply
internet connected ground stations for not only providing a continuum
of data from the downlink across the whole country, but also for
providing WEB access to students and schools outside of the footprint
or without amateur radio equipment.  You may see a replay of the event
by using APRS to replay the file MIRTEST.HST or by visiting
www.aprs.net/mirex.html.

