[aprssig] Impossible to be digi+something else? (DWAIT=0)

Frank Knobbe k4fhk at knobbe.us
Wed May 18 16:37:13 CDT 2016

On Wed, 2016-05-18 at 13:42 -0400, Greg Trasuk via aprssig wrote:
> Our club just put up a new digipeater this past weekend (VE3RSB) running APRX as the IGate, but with the TinyTrak4 running as the digipeater.  One interesting thing I found was that it would digipeat perfectly, but then if I hit the internet services, like WHOIS or EMAIL-2, it would be inconsistent if I got a response.  Rare, actually.
> Turns out, we had APRX set up to do the “viscous digipeating” mentioned below for APRS-IS packets.  So if it heard the IS return packet first from a different IGate, it didn’t send the packet.  And since the digipeater is up on a hill overlooking Lake Ontario, it has a pretty good chance of picking up a packet from somewhere else along the lake that probably also heard the original weak station’s digipeated request.  When it heard the packet on RF from somewhere else, it didn’t send it out to RF locally. So the net result was that you had almost zero chance of getting a response from the “good” digipeater, basically because the digi has a far better vantage point than the handheld on my dining room table.
> So the moral of the story - viscous delay is good for fill-in, bad for a wide-area IGate.  Thinking about it now, though, I kind of wonder if it even makes sense for a fill-in.  Assuming there isn’t too much difference in latency between stations receiving IS packets for retransmission, it might be best to just let them all send simultaneously, same as local RF digis.  I’m not sure how good that assumption is, though.

For my scenario (multiple TX I-gates in the same area and earshot of two
high-digis) it works well. It will gate anything to IS. If there a
message from IS to RF, it will put it on the RF *if* it didn't hear it
on RF from a different gateway, as designed.

But you are correct. Viscosity is not for everyone and should only be
employed when the conditions on RF, and the impact viscosity would have
on it, are fully understood.


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