[aprssig] Smart TX igate message routing?

Robert Bruninga bruninga at usna.edu
Mon Mar 6 17:16:21 EST 2017

It does not matter how you address it, even if a digi does not digipeat it,
the channel is still busy during your packet period.  And if any digi hears
it at all, and digipeates it, then ALL the other digis are still blocked
during that time too.  So nothing is gained by limiting your packet to only
be digipeated by one, since all will be blocked for the same two packet
periods whether they digipeat it or not.

So APRS is designed to have all digieaters respond, and all respond at the
same time, so that again, only the same two slots are used.  So nothing is
gained by targeting the first hop of a packet.

Conversely an order of magnitude is gained by targeting the 2nd hop (if
any).  Because then only the SECOND digi in the direction you choose is
going to use up that 3rd slot time, instead of many.

This is why the DWAIT must be 0 in all APRS digis so they all transmit at
the same time and do not wait for the others.  That would drag out a single
packet over multiple slots (not desired in APRS).

This built-in fratricide is intentional.

Little is lost, since anyone that is 10 dB closer to any one digi than all
the rest will decode the packet no matter how many digis step on each
other.  Just the one that is 10 dB stronger to you will capture your FM
receiver and will decode it.

Bob, WB4aPR

*From:* jess at jesshaas.com [mailto:jess at jesshaas.com] *On Behalf Of *Jess
*Sent:* Monday, March 06, 2017 3:01 PM
*To:* Robert Bruninga
*Cc:* TAPR APRS Mailing List
*Subject:* Re: [aprssig] Smart TX igate message routing?

Maybe it is a stupid idea but I do think we could do a bit better than a
wide path. If we know a more specific path can't we decrease channel
congestion and QRM while increasing range without needing any modification
to the digipeater infrastructure?

Wouldn't the target station be more likely to receive the message if it is
only hearing it from the closest digipeater instead of a bunch of them
transmitting at the same time creating QRM?

When a mobile station is right next to an igate and they can hear each
other directly why should we spam the whole region with the traffic via

Also it allows for using other stations not just digipeaters to extend your
range for receiving messages not just transmitting. So if im in a valley
and cant hit/hear a digipeater I can set the first hop in my path to
another station i can hit and then when an igate tries to get a message
back to me it will route it through that station.


On Mon, Mar 6, 2017 at 10:11 AM, Robert Bruninga <bruninga at usna.edu> wrote:

APRS by design will be digipeated by EVERY digipeater that hears it.  So if
the one farther south hears it, it is already going to digipeat it anyway.
Nothing you need to do to make that happen…

And in SoCal, there are so many digis, that your path should be just one
hop and it will still hit every digi that hears it that first hop.


*From:* aprssig [mailto:aprssig-bounces at tapr.org] *On Behalf Of *Jess Haas
*Sent:* Monday, March 06, 2017 1:08 PM
*To:* TAPR APRS Mailing List
*Subject:* [aprssig] Smart TX igate message routing?

Where I am located in Southern California I can hit many digipeaters. For
home station beaconing setting a single one of them as my route seems to be
the way to go but for tx message igating I was thinking it may make more
sense if the outgoing path was the one that the station was last heard on.
Has anyone implemented anything like this?

For example the digipeater I have the strongest path to may not be able to
get a message to a station farther south but I can hear and hit a
digipeater rather far south that the station can hear easily. Also if I
have heard a station directly recently than I should have no problem
getting a message to them directly even if they have moved some with my
basestation antenna and possibly higher power so digipeating to the whole
area may be unnecessary.

Another advantage of this would be that a station that is in an RF hole
such as a valley that can't hear or hit a digipeater but has a path to
another station that can could set that station as a path and messages
would automatically be routed back to them.



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