Hi all,
I've sent this to the UKAPRS and UI-View lists as well as uk.radio.amateur
Why?
So that all those using 144.800 have an understanding of how digipeating
works with APRS/UI-View at the moment. There is obviously more than one way
to skin a cat, but this is what the US has come up with in all the years
that APRS has been used there. Seems a good a system as any to start with!
It's an extract from digis.txt, one of the readme files in APRSDos written
by WB4APR. I realise its a bit long winded, but it's INVALUABLE.
73...Ciemon G0TRT
BACKGROUND: The range of any AX.25 packet may be extended by
specifying one or more digipeater callsigns in the UNPROTO PATH. 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 and all digipeaters
are aliased as WIDE. This way any station can use any digpeater by
using an UNPROTO path of WIDE or he can use any other station as a
digipeater by simply addressing the packet VIA RELAY. With this
generic digipeating, 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.
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.
APRS DIGIPEATERS: Wide area APRS digipeaters should be widely
separated to provide long distance coverage with the minimum of hops.
If there is a need for interim digipeaters to fill in weak signal
areas or valleys, then they should be installed as needed but ONLY
with the RELAY alias.
MODERN APRS DIGIPEATING: At Dayton 97, PacComm introduced their new
TNC ROMs which will substitute their callsigns in place of their
generic Aliases whenever a packet is digipeated. The big advantage
besides tracebility is that they will also IGNORE the packet from then
on completely eliminating looping duplicate packets. This was a great
advance for APRS! This was followed in 1998 with Kantronics
implementing the APRS WIDEn-n algorithm which further improves
multi-hop efficiency.
WIDE DIGIPEATING: Although in start-up areas any TNC can be used as a
WIDE digi simply by setting its MYALIAS to WIDE and its BText to
include its APRS position, this is NOT recommended today in areas
within a mature APRS environment. Today, only TNC's with the new
PacComm 4.0 and Kantronics 8.2 Roms or later should be used. They
should be set up with the four generic calls of RELAY, WIDE, TRACE and
your state abbreviation. The functions of each of these generic
aliases are as follows:
RELAY - The universal default for all APRS stations
WIDE - Provides WIDE area digipeating
TRACE - Identical to WIDE, but helps identify only the new
digipeaters capable of these advanced routing capabilities
SS - Useful for state wide only digipeating
HOME STATIONS should never use any alias other than RELAY without the
full consent of the surrounding users and network planners.
TRACE DIGIPEATERS: Although all 4 aliases are treated equally, using
the TRACE call has some important advantages. Most important, it
allows for usage of the new anti-duping features in advance of waiting
until all WIDEs are converted to the new ROMS. As long as there are
any old WIDE only digipeaters, anything beyond WIDE,WIDE cannot be
used or it will result in bad duplications. But by using the
equivalent TRACE,TRACE,TRACE, the packet takes advantage of the new
digis without triggering the old ones.
MOBILES: Mobiles typically use the path of RELAY,WIDE because they
may be out of range of a WIDE digipeater but be near someone's home
station acting as a RELAY. Even if WIDE digipeaters 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 undoubtedly 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 should not 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.
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.
BACKGROUND: The range of any AX.25 packet may be extended by
specifying one or more digipeater callsigns in the UNPROTO PATH. 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 and all digipeaters
are aliased as WIDE. This way any station can use any digpeater by
using an UNPROTO path of WIDE or he can use any other station as a
digipeater by simply addressing the packet VIA RELAY. With this
generic digipeating, 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.
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.
APRS DIGIPEATERS: Wide area APRS digipeaters should be widely
separated to provide long distance coverage with the minimum of hops.
If there is a need for interim digipeaters to fill in weak signal
areas or valleys, then they should be installed as needed but ONLY
with the RELAY alias.
MODERN APRS DIGIPEATING: At Dayton 97, PacComm introduced their new
TNC ROMs which will substitute their callsigns in place of their
generic Aliases whenever a packet is digipeated. The big advantage
besides tracebility is that they will also IGNORE the packet from then
on completely eliminating looping duplicate packets. This was a great
advance for APRS! This was followed in 1998 with Kantronics
implementing the APRS WIDEn-n algorithm which further improves
multi-hop efficiency.
WIDE DIGIPEATING: Although in start-up areas any TNC can be used as a
WIDE digi simply by setting its MYALIAS to WIDE and its BText to
include its APRS position, this is NOT recommended today in areas
within a mature APRS environment. Today, only TNC's with the new
PacComm 4.0 and Kantronics 8.2 Roms or later should be used. They
should be set up with the four generic calls of RELAY, WIDE, TRACE and
your state abbreviation. The functions of each of these generic
aliases are as follows:
RELAY - The universal default for all APRS stations
WIDE - Provides WIDE area digipeating
TRACE - Identical to WIDE, but helps identify only the new
digipeaters capable of these advanced routing capabilities
SS - Useful for state wide only digipeating
HOME STATIONS should never use any alias other than RELAY without the
full consent of the surrounding users and network planners.
TRACE DIGIPEATERS: Although all 4 aliases are treated equally, using
the TRACE call has some important advantages. Most important, it
allows for usage of the new anti-duping features in advance of waiting
until all WIDEs are converted to the new ROMS. As long as there are
any old WIDE only digipeaters, anything beyond WIDE,WIDE cannot be
used or it will result in bad duplications. But by using the
equivalent TRACE,TRACE,TRACE, the packet takes advantage of the new
digis without triggering the old ones.
MOBILES: Mobiles typically use the path of RELAY,WIDE because they
may be out of range of a WIDE digipeater but be near someone's home
station acting as a RELAY. Even if WIDE digipeaters 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 undoubtedly 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 should not 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.
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.
