Ham Radio 2000 #2/Ham Radio 2000 - Volume 2.iso/HAMV2/PACKET/APRS805/README/OPS.TXT

Text File | 1997-11-24 | 23KB | 391 lines

OPS.txt 8.0                APRS OPERATIONS NOTES

FOR a general APRS overview see APRS.txt.
FOR MOBILE Operations, see MOBILE.txt
FOR HF Operations, see HF.txt
FOR an APRS command summary see HELP.txt
FOR multi-PC operations on a piece of ZIP cord, see ZIP-LAN.txt

OVERVIEW:  This OPERATIONS file may help you to understand the finer points
of operating an APRS net both ROUTINE and SPECIAL EVENT.  Since APRS was
designed to facilitate real-time tactical communications, operating APRS
on a routine basis is sometimes like watching the grass grow!  The reason
for building a routine APRS net is primarily for operator training and
familiarity.  If your operators are not familiar with APRS in a benign
environment, then they will not be able to use it under stress!

Do NOT think that you need GPS for tracking special events.  It is so easy
to update your vehicle's position just by moving the cursor and hitting
the INPUT-MY command, that the only stations that need GPS are the ones
that are lost!

DIGIPEATER RULES:  The advantages of APRS are many, but there is a price.
Since APRS uses a fixed digipeater path sometimes different for different
stations depending on geographic location, there is a duplication of on the
air packets.  This assures that all stations in the net are maintained up
to date, but also proves to be less efficient during intense operator-to-
operator QSO's where this point-to-point traffic is also being unnecessarily
broadcast to all stations in the net.  In such cases ALWAYS CHOOSE THE
MINIMUM PATH TO THAT ONE STATION.  You will be amazed at the improvement
in throughput!  Watch the DIGI page, and if you can work him direct, DO SO!

WIDE-RELAYS AND MOBILES:  The greatest advantage of APRS is in the use of
generic alias callsigns for digipeaters so that mobiles do not have to
change their paths as they move from area to area.  Since WIDES are widely
separated and are made for WIDE area and LONGHAUL comms, many mobiles cannot
hit them reliably. For this reason, the favorite mobile path is RELAY,
WIDE,WIDE so that the mobile can be injected into the long haul WIDE
hops from any other APRS station (RELAY).  For this reason, however,
all WIDE area digipeaters must have the SECOND alias of RELAY for when
the mobile may be nearby the WIDE digipeater too.  This allows the WIDES
to remain WIDELY separated and local gap-filler digis (as RELAY only) to
be placed wherever needed to provide good mobile coverage everywhere.
See DIGIs.txt.  FIXED stations should NOT use RELAY generic paths except
under the unusual circumstances.  Or in brand new nets with no WIDES and
no one knows who is on the air or who has great coverage.


ROUTINE OPERATIONS:  The APRS default digipeater path of RELAY is ok for
a few users starting up an APRS net, but you will soon need to focus on a
few good stations to serve as WIDE area digipeaters.  The reason for this
is obvious.  As soon as you get 3 or more local stations on APRS, any
station living equi-distant (RF wise) from any two other stations will
ALWAYS hear a collision of EVERY packet digipeated by both of those
stations.  That is why, once your network begins to grow, you need to
designate your path by specific callsign and designate certain high
stations as permanent digipeaters.  If you put up a few good wide area
digipeaters with the generic ALIAS of WIDE, the coverage of the network
can be extended significantly.  It is important to keep generic
WIDEs well separated (40 miles or more over smooth terrain) to minimize
duplicate repeats (or you end up with the same collison problem but on a
larger scale).  Most users should be able to hit at least one of these
WIDEs.  Just like with the RELAY's, however, users should use the specific
digipeater call instead of the generic WIDE in routine cases to minimize
collisions.  You may store up to 12 different, frequently used DIGI paths
using the OPS-DIGI command for instant recall to tailor your DIGI path
for the exact calls and path for each QSO.  Proper use of this capability
can significantly improve APRS effeciency and reduce the use of the
WIDE,WIDE generic path!

The following paths are reasonable and are used under the circumstances
shown:

   RELAY,WIDE  - Default.  Good starting place to see whats out there
   WIDE,WIDE   - Gets you out 2 hops in all directions with minimal foldback

   WIDE,WIDE,W3XYZ,W4XYZ - Gets out 2 hops in all directions and 4 hops
                           in the direction towards W4XYZ

The following paths are NOT considered good practice and should not
normally be used... and if you do, some Do-gooder will fuss at you...

   RELAY,RELAY     - Some RELAY stations will never hear you due to colisions
                     but his may be ok if there are NO WIDES and no single
                     station has any better HAAT than any other
   .....WIDE,RELAY - NEVER do this.  EVERY home station for 50 miles will
                     key up on your every packet!
   WIDE,WIDE,WIDE  - Gets you out 3 hops in all directions but also results
                     in as many as 27 duplicate packets plus 30 seconds of
                     airtime.  Dont DO THIS!  No one will get through...
   WIDE,GATE       - You are QRMing the HF net which you cannot hear!
   WIDE,GATE,GATE,WIDE - You are QRMing every APRS net in the country!


TRACE DIGIS:  These are APRS unique digipeters that can digipeat based
only on the number of hops indicated in the digipeater SSID digit.
For example, a WIDE4-4 packet will be digipeated out 4 hops in all
directions with little or no duplication...  See DIGIS.TXT

ALTERNATE PATHS:  If you live in the middle of a network going both
   directions, then you should consider saving one or more paths using the
   OPS-DIGI-SAVE command.  Save one as WIDE,WIDE,NORTH1,NORTH2 and
   save the other as WIDE,WIDE,SOUTH1,SOUTH2.  Then use the OPS-DIGI-ALT
   command to specify them as alternate paths some percent of the time.
   These percentages subtract from your normal path and beacon rate, so
   understand that your main path will be used less often.


   All users must understand that they are responsible for setting their
outgoing VIA path so that their packets hit the intended area of interest.
Unlike normal CONNECTED protocols which automatically return ACKS via the
reverse path of incomming packets, APRS is an unconnected broadcast protocol
only and each station's packets will only go via the outgoing path set up by
that station.  If your station receives a duplicate APRS MSG packet more than
twice, it gives you a beep and an alert that your ACK's are probably not being
heard by the other station and that you should check your outgoing VIA path.


    APRS has a very useful feature for determining the best path between
stations.  The Power-Height-Gain reporting capability lets APRS plot range
contours around all stations that have included the P-H-G data in their
position reports.  For maximum effectiveness, every station should use the
INPUT-PWR command to enter his transmitter power, antenna Height Above
Average Terrain (HAAT), and antenna gain.  Also APRS permanent digipeaters
should include this info in their position beacons.  Do NOT use height
above sealevel or tower height!  You may live at 1000 feet above sea level
and have a 100 foot tower, but if the land around you is 100 feet higher
than you, then your HAAT is ZERO or NEGATIVE!  See DIGIs.txt and
PROTOCOL.txt for the exact formats.

    Those stations between WIDE area digipeaters only need to use the single
hop of WIDE and their packets will go in both directions.  Stations that can
only hit one WIDE area station may set the path of WIDE,WIDE without any
conflicts.  Paths of WIDE,WIDE,WIDE should be avoided because it folds back
on itself.  The same area can be covered by using WIDE,WIDE,W3XYZ where the
unique call of the third digipeater is specifically specified.  If you think
about it, stations at the end of an area can specify a pretty long string of
digipeaters since the path is linear.  Stations in the middle can only
specify a symetrical double hop with WIDE,WIDE before they have to begin
favoring one direction or another with unique calls.

CAUTIONS ABOUT APRS MESSAGES:  Remember that the general condemnation of
multiple digipeater hops in the packet community applies only to connected
protocols.  This is because the probability of success goes down drastically
because all ACKS must be successfully returned or all packets are repeated.
This is generally NOT a problem with most APRS operations which use UI
frames without acks.  HOWEVER, APRS one-line MSGS are ACKED, and the
inefficiency of digipeaters DOES APPLY!  If you do a lot of one-line
messages between operators, you will experience the same hopeless
probabilities of success as with conventional packet.  (As noted above,
APRS doubles up on ACKS on a poor channel and helps this situation
somewhat.)  But, in general, NEVER expect an APRS MSG to be successful
beyond 2 digi's except if everyone else is DEAD.  Operator messages are
a secondary function of APRS, and should not be used as a primary means
of passing traffic!  One further caution, since APRS suspends all packet
processing while waiting for the operator with a BOXED prompt, never
linger in a prompt.  The SEND command is a BOXED prompt and should not be
left un-completed!

ACKS THAT DONT MAKE IT:  Just like connected packet, the chance of a message
packet getting through is usually the same as the chance that the ACK will
get back.  If the radio path is only 50%, that means that the receiver will
probably get the message by the second transmission, but that the sender may
not get an ACK until after his 4th!  This is because the sender had to send 4
packets to get two through and the receiver then ACKed twice in order to get
one through.  You see this effect frequently on APRS, when you are talking
with a station over a long poor path.  You will notice that the person at
the other end has already responded to your message even before you get an
ack from your outgoing message.  BUT your next line will never go out UNTIL
it gets that ACK.  The reason that you will probably get his response message
before your ack, is because his response message is being repeated over and
over in the usual APRS decayed algorithm, but his ACK is ONLY transmitted
once each time he gets a dupe of your message line to him.

    What this means is that whenever it is obvious that the other station has
responded to your message line, you should ERASE it so that APRS will move on
to the next line.  Sometimes if you know that the other station is probably
hearing the digi better than the digi is hearing him, and you are not getting
ACKS, then simply send him messages in the blind.  Let each line will be
transmitted for 6 minutes and then you can erase it.  APRS will then move on
to the next line.  Remember that APRS will have transmitted 6 times in the
first 6 minutes, but that it will then be over 3 minutes, then 6 and then
12 minutes for further transmissions.

    To improve on this effect of lost ACK responses (which I see a lot on
HF), APRS recognizes a duplicate message, and not only sends out the usual
ACK, but stores a copy for transmisssion in the blind 30 seconds later.
The 30 second delay is to avoid cluttering up the frequency if the path is
good, since the sending station will have sent the message at least twice
in the first 30 seconds.  After the third transmission, it is clear that
the ACKs are getting lost and it is time to double up.  This algorithm has
the potential of doubling throughput on a poor channel!


SHORT MESSAGES:  As with any packet, especially on HF, the shorter the packet
the better the chance of getting through.  With 25 characters of overhead,
however, there is not much sense in making the message part much shorter
than a half line (40 characters).  The chance of a 40 character line getting
clobbered compared to a 75 character line is 65%.  On HF keep 'em short.
A trick that I frequently use whenever I know that a station is not currently
on the air, or the path is not currently good, is to send the first message
line with only the word "test" followed by additional lines with the body
of the message.  This way, only the very short "test" line is transmitted
(often for hours on HF) until the band opens, and then once the station ACKs
that line, the remaining lines are transmitted.

BULLETINS:  To send a bulletin to all stations, simply SEND a message to
BLN# where # is a line number from 1 to 9.  Like any other message, these
BULLETIN lines will be transmitted on the decaying time period and will
soon fade out of the system.  If you want the bulletin to remain at about
a 15 minute rate, then instead of using numerals in the BLN# mesage, use
a LETTER.  This way, new stations joining the net will quickly pick up
the BULLETINS.  Since lines are sorted onto the receiver's BULLETIN page,
a new BLNx line will overwrite any previous BLNx at all stations making
changes and corrections easy.  If your bulletin is time sensitive, be
sure to include the TIME in the text, since BULLETINS are not time-
stamped.  When your BULLETIN is no longer needed, simply ERASE your
outgoing BLN#.  This will stop your transmission of the BULLETIN lines.
Receiving stations can erase all old bulletins by using the ALT-E command.


GATEWAY RULES:  I have interjected this paragraph because of the large
number of APRS HF to VHF gateways now in operation.  First, it is very
important that users understand that GATEWAYS ARE ONLY INTENDED TO LINK
HF ACTIVITY INTO LOCAL VHF NETS.  IT IS INNEFFICIENT, DISCOURTEOUS, AND
MAYBE ILLEGAL TO LINK from VHF to HF.  Linking HF operations into every
local VHF APRS net in the country is not a problem, because the slow 300
baud data rate could never saturate ANY 1200 baud local net.  HOWEVER,
linking just ONE active VHF net ANYWHERE in the country out onto HF
WOULD CERTAINLY BLOCK ALL HF OPERATIONS NATIONWIDE!  The capability is
there for linking special events or cross country travelers on VHF out
for the entertainment of all HF listeners, but DO NOT ABUSE IT, OR WE
WILL LOOSE IT!  See HF.txt.

GATE SUMMARY:  On HF, use the path of GATE,WIDE and everyone in the
country within one WIDE hop of a GATE will likely see you.  *Never*
use GATE,WIDE,WIDE because your packets will now go 2 hops on VHF and
be seen MULTIPLE times from multiple gates!  No one can tell where the
GATE is and it is just a BIG MESS.  Believe me!

Second, never routinely go through a GATE on VHF.


USING THE OPS-COMM-TNC dumb terminal mode.  This mode works OK for using
your TNC normally, but it doesnt have any file transfer capabilities.  You
might try to find a small .EXE comm program that you can FILES-SHELL out
of APRS, do your COMM thing, and then EXIT back into APRS....  YAPP and
PACCTERM both work, but be careful of how these programs change your
TNC parameters...

OBJECTS:  As noted previously, anyone may place an object on the map and all
other stations will see it.  On their P-list, the object will be marked
with the last three letters of the originating station.  Any other station
that has more current information on that object can also update its
position by hooking, moving the cursor, and then hitting the insert key.
His station will begin uplinking the new posit, and all stations, will
update their P-list entry for that object INCLUDING THE ORIGINAL UPLINK
STATION!  Since the new position overwrites the old one, the original
originating station will now no longer uplink it.  This comes in handy during
hurricane tracking.  Who ever has information on the latest HURICANE posit
uplinks it and everyone then always sees the latest storm track without
anyone in the net being dependent on any one station for updates!

    Once objects are transmitted on to other station map screens, they will
remain there until that operator deletes them, even if the originator stops
transmitting them.  It will, however, fade to dark gray after 2 hours to
show it as an old report.  You can use the CONTROLS-FADE command to bring
them back to bright colors, or use the J command to see JUST-the-LATEST
symbols.  The KILL function permits the originator of an OBJECT KILL it
from all displays on the net.  His station will continue to uplink the
object, but tagged with a special KILL flag to suppress its display on all
screens.  It remains in everyone's P-lists, though, so they can refer back
to it if needed.  They must still manually DELete it from their P-list as
needed.  Once the originator has KILLED an object, he should let it remain
on his P-list for at least 6 minutes to be sure everyone has received the
KILL indicator; then he can delete it from his list.


NEAT OPERATOR FEATURES:

There are several  menus and commands you can use to set up your operating
envrionment.  Here are some highlights:

CONTROLS MENU:  You can set filters and how you want packets displayed.
MAPS:           Turn on or off most map features plus overlay data files
                on the maps such as DIGIS, Radio Shacks, etc
RADAR ALARMS:   Use OPS-SETradar to alarm if anyone enters your"airspace".
POSIT ALARMS:   Set ALARMS on any mobile which will alarm if he moves.
WX ALARMS:      Set Weather alarms on temps, winds or rain...
TRACK MODE:     Lock on to one station and keep map centered


SPECIAL EVENT OPERATIONS:

    The alt-SETUP-MODES-SPECIAL command sets up an APRS station to send
TO the UNPROTO address of SPCL... vice APRS...  and to ignore all other
packets NOT addressed to SPCL.  This allows the event participants to
keep their screens (P/L lists, etc) clear of unwanted other APRS stations
on frequency, while tracking the event normally.  All other stations
watching the event will still receive all SPCL event posits on their
screens, and they will be automatically marked with the # for special
display using the JUST-SPECIAL command or SPACE bar.

SPECIAL EVENTS:  The Cycle Across Maryland (CAM) bike tour is a good example
of a special event using APRS.  We had two of three relief vehicles with
GPS trackers.  These were assembled in cake pan enclosures duct-taped to
the roof with a small power cable extended down the windshield and clipped
directly to the battery.  These packages could be moved among vehicles in
about five minutes.  Some other packet mobiles ran APRS without GPS units
by just using the INPUT-MyPOS command to update their positions.  In this
manner, my normal APRS/GPS combo can be split into TWO separate tracked
vehicles for an event.  The GPS/TNC combo acts as a stand-alone tracker,
and my laptop and another TNC keep my vehicle on the map manually.

    Since we only have two WIDE-RELAY APRS digipeaters in the state, and
the CAM tour never went near them, we were dependent on home stations all
across the state to serve as digipeaters for the event.  The GPS packages
were set to digipeat via the RELAY,WIDE path.  Even without lots of APRS
stations (RELAYs) we got as many conventional packeteers to tune to our
frequency for the event and set their TNC aliases to RELAY for that day.
This way, the mobiles were never beyond range of at least one RELAY
station.  Due to the short range of our simple 1 watt units, we needed
home stations about every 5 to 10 miles.

     We also set up both GPS units with the alias of RELAY so that they
would also help digipreat each other along the trail.  The disdavantage
of this technique however, was evident as both vehicles returned to
the evenings command post (also RELAY) and you had three RELAYS in 100
yards of each other!  It was noisy within local simplex range of that site,
but stations all over the state still saw the packets via the permanent
WIDE digipeaters.

SYMBOLS:  Recent changes now permit HUNDREDS of different mobile symbols
by using the NUMERIC OVERLAY capability.  This makes it easy to distinguish
mobiles even with CALLSIGNS off to reduce clutter!

EMISSION CONTROL:  If there are only a few APRS stations involved in an
event but there are lots of APRS observers on frequency, then the observers
can set their transmitter off using the CONTROLS-X command to minimize QRM
on channel.  They can still transmit under manual control by using the
X key.


LOAD SHARING:  Since any station can take over reporting of any objects, one
approach is to let only one station hook every symbol that comes in and then
he becomes the reporting repsonsibility.  The original station that uplinked
the report in the first place will fall silent when it sees the report
comming from the designated Net Control station.  This way all positions are
reported by only one station on frequency, although all other stations can
still update the positions as needed.  Remember that the last station to
report the position of an object will be the one that continues to report it!


MARINE CORPS MARATHON:  See MARATHON.txt for the lessons learned using
APRS at the Marine Corps Marathon for the last 3 years in Washington DC.


ZIP_LAN MODE AND EMERGENCY OPERATIONS CENTERS:  Dont overlook, that a
handful of separate PC computers can ALL BE CONNECTED TO A SINGLE TNC AND
RADIO!  This fact can be used to create quite an impressive multi-station
tactcal communications system that will rival some 911 consoles! No
special LAN hardware is required other than a serial port and as much
two conductor zip cord as you need.  See ZIP-LAN.txt

This capability obsolete's the previous APRS MASTER/SLAVE mode that
had many limitations.  ZIP-LAN, on the other hand allows all stations
to have independent callsigns and to send and receive all traffic.

CAUTION:  This ZIP-LAN capability is not backwards compatible to any
software prior to APRS800, Mac/Win prior to 2.09 and APRSa4 ver 0408.

   This way ALL consoles see the tactical picture, and these ZIP-LAN PC's
are at the individual operator's disposal to zoom in, and hop from screen
to screen to give them access to what ever info they need!  Do not think
that a big screen display is better.  A single big screen is impressive,
but actually useless.  Only the person at the KEYBOARD of an APRS system
can actually get useful info from APRS.  In our county, you need to be below
the 8 mile scale to get an idea of what is going on at a crisis, and
while you are zoomed in there, others need to be focusing on other parts
of the county, or different screens.

  You can wire every PC in the building using cheap 2 conductor speaker
ZIP cord!  You can carry hundreds of feet of this stuff in your briefcase
with your portable laptop!

This is a TREMENDOUS capability, since these days PC's are much more
plentiful than TNC's and all available assets can be brought into the
picture.  Every SLAVE operator has his own INDEPENDENT access to all
of the APRS info without bothering the APRS operator.