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

Text File | 1997-09-07 | 18KB | 316 lines

DIGIS.TXT 7.9.7     AUTOMATIC PACKET REPORTING SYSTEM DIGIPEATERS

As of version 787, your maximum reporting period is dependent on the length
of your digipath.  This is so that at a special event or local area, using
direct or one hop, then your net-cycle time is 10 minutes.  Two hops is
20 minutes, 3 hops is 30 minutes etc up to the maximum value in your
CFIGxxx.APR file.  Currently the MaxTime defaults to 30 minutes.

WHERE ARE THE DIGIS?   Use the MAPS-OVERLAY-DIGIS command to see the
location and range of all APRS digis no matter where you are.  Please
send me data on any new digis so we can keep this DIGIS.POS file
up to date.

PACCOMM CALL-REPLACEMENT:  At Dayton 97, PacComm has introduced their new
digipeater ROM for all of their TNC's including any TAPR-2 clone which
will substitute its callsign in place of WIDE when a multiple WIDE,WIDE
packet is digipeated.  It will also IGNORE the packet from then on
completely eliminating looping duplicate packets.  This is the greatest
new capability in four years since APRS itself was introduced.  See the
section below on TRACE DIGIS.


BACKGROUND:  The range of any AX.25 packet may be extended by specifying
one or more digipeater callsigns.  The packet will be relayed by each
such digipeater in turn.  After each such digipeat, that callsign is
marked as used up so that at any instant, only the "next" digipeater
in the list has the potential to digipeat the packet.  Normally this
requires users to know the complete intended path for their packets.

   APRS, however, satisfies its real-time, emergency tactical needs
without prior knowledge by using generic callsigns.  ALL APRS stations
are given the generic digipeater callsign of RELAY.   This way any
station can use any other station as a digipeater by simply addressing
the packet VIA RELAY.  With this form of generic digipeating (RELAY),
a mobile, or new station does not have to know anything about the network
in advance in order to be seen by adjacent nodes.  After 10 minutes and
his map begins to show the location of all stations and digipeaters on
frequency, he can  then customize his outgoing Unproto path to specific
digipeater callsigns to cover his intended area without as much QRM.
Similarly all wide area digipeaters have the generic digipeater alias
of WIDE.

CAUTION:  Since the preferred APRS frequency of 145.79 is adjacent to the
SATELLITE band at 145.8, all APRS users should run minimum power.  High
and WIDE digipeaters in residential areas or near other satellite ops
should probably operate at 10 watts or less to minimimze QRM.  The purpose
of APRS digipeaters is to HEAR mobiles, NOT to be an aligator!

ROUTES: It is important that as APRS networks mature with fixed, known
digipeaters, that users at FIXED stations should avoid using the generic
RELAY or WIDE addressing.  Although it still makes sense for mobiles to
use the path of RELAY,WIDE, the path of RELAY should rarely be used after
the first hop by ANYONE, and never after a WIDE.  Remember, every packet
addressed via RELAY will key up EVERY APRS station that hears it.  In
any but the sparsest areas, the result is total congestion and collisions
which block anyone from copying the packet.  The D-list command lets
you see what digipeater paths other stations are using and it also marks
stations that you can hear direct.  Also under the OPS-DIGI command, users
can save up to 12 different DIGIpeater paths.  Users can select any given
path that is optimum for their present application with a single key
stroke.  The MAPS-PLOTS-POWER command will display a range circle around
all stations proportional to their power, and antenna.  Users can use
these plots to estimate what paths, through what stations, might be useful.

     Although digipeating is generally not good practice for AX.25 level 2
connections, it is ideal for APRS operation using UI frames only.  The low
duty cycle of APRS allows everyone to share the channel without anyone able
to totally hog the frequency.  Even Personal mail boxes are acceptible on
the APRS frequency, since mail is posted at keyboard rates and is NOT read
back by radio.  Users are NOT welcome to READ PBBS mail on the frequency.
Other CONNECTED mode operation of BBS's, mail forwarding, file transfers,
TCP-IP and DX clusters are discouraged.

APRS DIGIPEATERS:  Wide area APRS digipeaters should be widely separated to
provide long distance coverage with the minimum of hops.  But this does not
preclude the need for many interim RELAY digipeaters to fill in weak signal
areas or valleys.  These sites provide the first hop (via RELAY) for all
mobiles, which inturn then relay the packets to the main WIDE digipeater.
These WIDE sites link to other cities and provide a backbone for wide area
coverage.

WIDE DIGIPEATING:  Since these WIDE area digipeaters are located at
excellent locations, they should not only provide the WIDE backbone
function for the long-haul, but should also have the RELAY alias as well
for nearby mobiles and new stations.  The new PacComm 4.0 and Kantronics
8.2 Roms can be set up to digipeat up to FOUR generic aliases!  These
WIDE-RELAY backbone Digi's should be spaced 50 miles or more apart
depending on topology so that they are as widely separated while still
being able to hit each other.  All mobiles typically use the RELAY,WIDE
path so it does not matter whether they are near a DIGI or someone's
home station to be digipeated.

TRACE DIGIPEATERS:  Since the new PacComm ROMS can support 4 aliases and
have the Callsign-substitution algorithm, these new digipeaters should
be given the aliases of RELAY,WIDE,TRACE, and SS where SS is your state
abbreviation.  Although all 4 aliases are treated equally, using the
TRACE call has some important advantages:

  1)  The callsign substitution algorithm not only solves the looping
      duplication of packets, but it also provides a "TRACE" capability
      since packets arrive showing the actual path of all the digis
      that were used to propogate the packet.

  2)  It allows stations to use long generic paths such as TRACE,TRACE,
      TRACE... without dupes.  This is because only the new TRACE digis
      will respond and not the old WIDES.  YOu may mix TRACES and WIDES
      in a path if you know the locations of the WIDES.  The TRACE digis
      will still work on this path too.

  3)  DIGI operators should use the Numeric Overlay symbol "T" for their
      new TRACE digis so that users know where they are.



    Even if these WIDE/RELAY backbone nodes are 30 to 50 miles apart, as
long as every home station and local RELAY digipeater can hit at least
one WIDE, then the mobile path of RELAY,WIDE can cover as far as 100
miles!  Wider ranging mobiles can use the RELAY,WIDE,WIDE path without
causing too much QRM because of their low antennas.  BUT CONVERSLY,
RELAY,WIDE,WIDE should NEVER be used by a home station since he will
undoubtly hit many home RELAYS all at the same time and therefore generate
numerous dupes with every packet.

CAUTION: Fixed stations that can hit 2 or more WIDES should NEVER use
three generic RELAY/WIDE callsigns in a row, and RELAY should NEVER be
anywhere except the FIRST in the list.   Multiple TRACE hops are fine
but you shouldnt plan on QRMING beyond your immediate area except as
needed.  Although generic paths for mobiles are the normal, special
consideration must be given whenever there will be a great convergence
of generic mobiles using RELAY,WIDE paths, since each of them will repeat
each other!  In this case, they should change the path to not begin with
RELAY.  Here are the typical recommended settings for ALIASES and PATHS:

   MOBILE  (1-5 watts):  UN APRS V RELAY,WIDE,WIDE  MYAlias = RELAY
           (25-50 w  ):  UN APRS V WIDE,WIDE        MYAlias = RELAY


DEDICATED WIDE AREA APRS DIGIPEATER SET UP

   To set up a WIDE area APRS digi, you should only use a TNC that has
multiple aliases and preferably the PacComm TRACE algorithm.  ALso it
hould be installed as high as you can get it.  Set the following minimum
commands:

   MYCall W3XYZ-x                 (the digipeater call and SSID)
   MYAlias WIDE                   (this makes it digipeat WIDE packets)
           RELAY,TRACE,SS         (Other aliases.  SS may be your state)
   UNPROTO APRS VIA WIDE,TRACE,WIDE,TRACE   (you want its own BText posit
                                  (to go as far as reasonable.  THis
                                  (requires creativity where TRACE is not
                                  (yet fully used.  Do not use W,W,W if
                                  (this digi can hit more than one other
   B E 90                         (Sets Beacon to once every 15 minutes)
                                  (or B E 15 for Kantronics = 15 mins)

   BText                          (This is very important!
   BT !DDMM.mmN/DDDMM.mmW#PHG5360/W-R.... (identifying comments)
        |      |  |      | | ||||
       LAT     | LONG    | | ||||________ Omni (Direction of max gain)
               |         | | |||_________ Ant gain in dB
               |         | | ||__________ Height = log2(HAAT/10)
               |         | | |___________ Power = SQR(P)
               |         | |_____________ Power-Height-Gain PHG indicator
               |         |_______________ # is symbol for digipeater
               |_________________________ / for WIDE, \ for WIDE-RELAYS
                                          OR put the characters W-R
                                          in the comment field.  Use T
                                          for TRACE digis
 you can see by the integers in the POWER-HEIGHT-GAIN (PHG) string, there
are only 9 plus 0 possible values for each of these fields as follows:

  DIGITS   0  1  2   3   4   5   6    7    8    9  as used in the Pwr field
  -------------------------------------------------------------------------
  POWER    0, 1, 4,  9, 16, 25, 36,  49,  64,  81  watts  SQR(P)
  HEIGHT  10,20,40, 80,160,320,640,1280,2560,5120  feet   LOG2(H/10)
  GAIN     0, 1, 2,  3,  4,  5,  6,   7,   8,   9  dB
  DIR      0,45,90,135,180,225,270, 315, 360,   .  deg    D/45  This offsets
           *                                       the range circle in the
           * 0 means OMNI                          indicated direction

HEIGHT ABOVE AVERAGE TERRAIN:  Going out 10 miles in all directions, write
down the elevation every mile or so.  Average all of these points and
compare your elevation to the average.  You may be at 2000 feet above
sea level and have a 150 foot tower, but if the ground around you is at
2200 feet, then your HAAT is -50 feet!!!  Be honest!  Your circle should
go no further than the distance to which you can reliably copy an HT!
Even though you have an OMNI antenna, if the terrain favors a certain
dierction, then put that in for your directivity.


OPERATIONS WITH RELAY AND WIDE:

     Although the GENERIC WIDE/RELAY digipeating works well to get an APRS
net going, once you have more than two WIDES, the generic calls should be
avoided by all fixed stations to minimize unnecessary duplicates and
collisions.  Or use TRACE.  Using SPECIFIC callsigns significantly reduces
QRM.  A path of WIDE,WIDE,DIGI3,DIGI4 will get you out 2 hops in all
directions and 4 more hops in the direction of DIGI3 and DIGI4.  If you
want to go long distance in two directions, save another long path in the
other direction using the OPS-DIGi-SAVE comamnd and then activate it 50%
of the time usign the OPS-DIGI-ALT command.

     While building a new network, some well situated home stations may
need to operate as WIDEs temporarily.  To do this, simply manually
configure one of your TNC's other calls to WIDE.  MYAlias will not work,
because APRS will always reset that to RELAY.  You should not set yourself
to WIDE unless you have local agreement to do so.  Too many WIDE's, too
close together causes too much QRM.  If you are operating as a WIDE-RELAY,
be sure to put the BACKSLASH character between the LAT\LONG so you will
show up as green digi or select the DIGI# on the  symbols menu.

SEE README.HF for setting up your UNPROTO path for HF and HF/VHF gateways..



**********     WIDEn-n ALL DIRECTION GENERIC DIGIPEATING!     ****************
          THE ULTIMATE SOLUTION FOR MOBILE POSITION REPORTING

    For four years, we have been asking for someone to develop the WIDEn-n
digipeater code.  The WIDEn-n digi simply repeats ANY packet with the VIA
address of WIDEn-n; but ONLY ONCE.  It keeps a copy (or checksum) of the
last 30 seconds of packets, and compares each new packet that it hears
with these last ones to avoid dupes.  This completely eliminates the
multiple looping of packets caused by multiple generic paths such as
WIDE,WIDE,WIDE.  Without WIDEn-n, such a 3 hop path launched in the
middle of 3 WIDE digipeaters that all hear each other can generate as many
as 21 dupes!  In a WIDEn-n network, there would only be three
packets outward bound 3 hops.

NUMBER OF HOPS:  The "n" in the WIDEn-n path indicates the number of hops.
Each DIGI that repeats the packet decrements the WIDE-SSID by one.  So the
-n decrmenets to zero but the WIDEn portion indicates the original number
of hops so that recepients know how far it traveled.  A long distance
traveler or special event of wide interest may use up to WIDE7-7 but a
local commuter may only want to use WIDE2-2 to limit QRM.

SHORT PACKETS!  THe biggest advantage of the WIDEn-n routing is that
every packet still only has one DIGIpeater call.  THis means only 7 bytes
of overhead no matter how far the packet goes...

TRACEn-n.  Notice, however, that WIDEn-n packets arrive as WIDEn-0, showing
that it took n hops, but the receiver has no idea how it got to him.  If
the WIDEn-n digis also support TRACEn-n, however, then at each hop, not
only does the digi decrement the n, but it also INSERTS its MYCALL.  This
way a TRACEn-n packet arrives as DIGIa,DIGIb,DIGIc,DIGId etc.  Although
this is very powerful, it also makes the packets grow significanly in
length as they propogate and should only be used when messaging or when
you need to know the return path.

NEW TNC COMMANDS REQUIRED:  To make this work, there are three new TNC
commands needed:

     MYFlood:  Similar to MYAlias, sets up the callsigns to be used
     for WIDEn-n routing.  Usually WIDE

     MYTRACE:  Similar to MYFlood but does callsign insertion.

     HOPLimit:  This is a SYSOP parameter that can be used to limit the
     maximum number of HOPS permitted in a network.  Already the maximum
     number of hops is limited to 7, since the upper bit of the SSID is
     reserved for future use.  However, some SYSOPS may feel empowered
     to limit the maximum number of hops to some smaller number.

     AGELimit:  The WIDEn-n digi has to keep a copy of all digipeated
     packets (or a unique checksum) for a brief period for comparison
     with new packets heard to assure that it does not repeat a packet
     more than once.   This age limit determines how long packets must be
     kept for comaprison.  If the time is too long, then the list is big,
     If it is too short, then packets may propogate in a circle and get
     repeated again.  30 seconds seems like a good starting value for
     1200 baud channels.

This WIDEn-n capability would give us the ULTIMATE GENERIC MOBILE GPS
NETWORK!  It can handle both short and long hops with no dupes.  This
WIDEn-n algorithm is so powerful, there is no reason that it should not
be added to ALL TNC's as a FLOODn-n mode.  It would only work on UI
frames and MUST ONLY Be used at WIDE sites.  If it is enabled at any
home stations, this will SEVERLY QRM the network...


LEVEL FOUR NETWORK CONSIDERATIONS:

     Since NODES are so much smarter than digipeating, the ultimate
solutionis to have the NODES do all UI frame routing via high speed
backbones.  The APRS station simply sends his UI frame TO APRS VIA HOME;
Any NODE hearing that transmission that has knowledge of the route to
HOME, will send the single packet via the NODE network (level 4) to the
HOME node!  When it arrives at the HOME node, it is transmitted once as
a UI frame.  With this arrangement, a mobile only has to specify his one
intended destination, no matter where he travels!


DIGI/NODE COMPATIBILITY:  Mobiles should be able to specify a path that is
compatible with both nodes and digipeaters.  The nodes should only look at
the LAST digi field in an UNPROTO list for the final NODE destination.
Any preceeding fields are assumed to be DIGI's only.  This way a path of
APRS VIA WIDE,HOME would be repeated by any WIDE that heard it, but any
level 4 node that heard it would forward it to the HOME NODE.  If only one
field is included in the digipeater string, it would be interpreted as
both a digi and a HOME destination without any difficulty.  Digi's and
NODEs would digipeat it, and nodes (hearing it direct) would forward it at
level-4.

EXAMPLE:  A typical mobile just wanting to keep his spouse informed of his
whereabouts might want to just use the UNPROTO path of APRS VIA HOME.  Then
his UI frames will be digipeated by the local HOME node or digi and will
also be routed back to HOME by all NET-NODES along his travels.  If he also
wants to be seen by most HAMS in the areas of his travels, then he sets
his path to APRS VIA WIDE,HOME.  If he travels through a region that has
both DIGIs and NODES, he might choose APRS VIA WIDE,WIDE,HOME.  This way any
areas with digis would digipeat via WIDE,WIDE and if he gets to an area with
nodes which are aware of the path to HOME, then they will forward his packet
there.