[aprssig] Aprx 2 beta - multi-receiver digi and igate

[Matti Aarnio]

A few systems are now running Aprx 2 series beta systems.
  - Ordinary digipeaters
  - Digipeater + Rx-iGate
  - Digipeater + Rx/Tx-iGate (Tx msgs only)
  - Rx-only iGates

( http://ham.zmailer.org/oh2mqk/aprx/ )

It is in beta because Tx-iGate rules are not yet completely
implemented, and there can be strange bugs in this system anyway.

However it can be configured with a filtering rule that allows only
messages to be relayed from APRSIS to RF, which greatly limits the
spurious traffic that usually flows from APRSIS to igates.
(I mean that when an rx-igate heard N0CALL-1 from radio, and gated it
to APRSIS, the javAPRSSrvr begins to send all observations of that
particular station to the igate.  Yes, it is semi-necessary for message
traffic igateing, but it also makes it necessary to have additional
filter rules at igate of when (not) to gate something... )


Simplest possible digipeater configuration would be:

mycall N0CALL-2
<interface>
   serial-device  /dev/ttyS0  19200 8n1 KISS
   tx-ok          true    # Enable transmitter
 # callsign     $mycall   # defaults to $mycall
</interface>
<digipeater>
   transmit     $mycall   # 2m transmitter
   <source>
       source   $mycall   # 2m receiver
   </source>
</digipeater>

Adding  <aprsis>  block will add Rx-iGate on this system, and adding
Tx-iGate on top of that is also quite simple.


Following is how we are now running an in-band + cross-band + tx-igate
that transmits on 144.800 MHz and 432.500 MHz at downtown Helsinki.

Content filters can be defined at all sources so that only selected
traffic will be digipeated.  Chosen filter processing language is copied
from javARPSSrvr's Filter Adjunct with a few "this is meaningless in
between radio interfaces" omissions.   Documentation is yet to catch
up with the implementation...

Anyway,  configuring this kind of complex digipeater is as "simple" as:

## omitting all <interface> definitions ...

<digipeater>
    transmit     OH2RDK-5     # 2m out
	# Digipeater duplicate checking is per transmitter

    <trace>
       maxreq     2		# Serving at most 2 hops on requests
       maxdone    2		# and at most 2 hops done
       keys       TRACE,WIDE
    </trace>
    # <wide> settings are overridden by the <trace> above

    <source>
        source         OH2RDK-5 # 2m in, main rx/tx interface
    #   #relay-type    digipeated # default mode is "digipeated"
    #   viscous-delay  0     # no viscous delay for RF->RF digipeating
        filter         t/m			# All messages
        filter         a/60.0/24.5/60.5/25.5	# and all positions within this area
    </source>
    <source>
        source         OH2RDK-2  # 70cm in, cross-band digi to 2m
        filter         t/m			# All messages
        filter         a/60.0/24.5/60.5/25.5	# and all positions within this area
    </source>
    <source>
        source         OH2RDK-R2 # 2m diversity rx1
        filter         t/m			# All messages
        filter         a/60.0/24.5/60.5/25.5	# and all positions within this area
    </source>
    <source>
        source         OH2RDK-R3 # 2m diversity rx2
        filter         t/m			# All messages
        filter         a/60.0/24.5/60.5/25.5	# and all positions within this area
    </source>
    #### NOTE: Some APRSIS / Tx-iGate processing rules are not yet implemented
    ####       Incomplete filtering limitation is achieved with  filter  t/m
    <source>                  # Adding APRSIS source makes this tx-igate
        source        APRSIS
        relay-type    third-party  # Must define this for APRSIS source!
        viscous-delay  5      # Recommendation: 5 seconds delay to give
                              # RF delivery time make itself known, and
			      # give dupefilter time to see them.
        filter         "t/m"  # See JavAPRSSrvr filter adjunct rules
    </source>
</digipeater>


If one wants to make  2m->70cm  and 70cm->2m  digipeaters on same server,
it is simply a matter of laying out two <digipeater> sets with appropriate
transmitters at each frequency.  Duplicate blockers are specific to
each transmitter.

Actually this system does not know of the frequencies, and could do
cross-channel digipeating as easily as cross-band.

Doing different WIDE/TRACE keywords per source is even possible.
A 6meter APRS digipeater with 2m/70cm cross-digipeater could be
something like this (with Bob's "6MTRS" keyword added in):

<digipeater>
   transmit   N0CALL-6   # 6m transmitter

   <trace>	# Applied on all sources, unless source has its own
       maxreq  3
       maxdone 3
       keys    WIDE,TRACE
   </trace>
   <source>
       source    N0CALL-6   # 6m receiver
       <trace>
            maxreq  3
            maxdone 3
            keys    6MTRS,WIDE,TRACE
       </trace>
   </source>
   <source>
       source   N0CALL-2    # 2m receiver
   </source>
</digipeater>