[aprssig] Airborne Digis

[Gregory A. Carter]

Hi Steve,

That's what I was afraid of with the preempting concept.

I believe the hardware we're using supports alternative or proportional
pathing so I'll give that a shot and set the airborne digi to only use
SAR1-1 and see where that gets me.

Thank you for the reply!

Greg

NV6G
OpenAPRS.Net

On Mon, Sep 14, 2009 at 9:52 AM, Stephen H. Smith <wa8lmf2 at aol.com> wrote:

>
> What do you mean by " if the airborne digi preempts, hitting on SAR1-1"  ?
>
> Path hops are processed SEQUENTIALLY from left to right.    Assuming you
> mean some kind of modified firmware that will let the airborne digi respond
> to "SAR1-1" out of sequence, even if the first two hops are not yet "used
> up",  it will depend on how the path is retransmitted.   If it comes out of
> the digi as:
>   WIDE1-1,WIDE2-1,SAR1-1*
> then potentially dozens and dozens of digis on the ground over a radius of
> hundreds of miles will simultaneously respond to the "WIDE1-1" hop.  [Both
> low-level home fill-ins AND true high-level WIDES respond to WIDE1-1.]
> Then all these retransmissions over a huge area will trigger all the real
> WIDEs again on the second (WIDE2-1) hop.
> If the airborne firmware traps and modifies the path string to output
> something like:
>
>  WIDE1-1*,WIDE2-1*,SAR1-1*
> or chops off the first two hops entirely to output just
>
>  SAR1-1*
> the airborne digi will, at least, not re-trigger the ground-based digis.
> However this STILL won't prevent ground-based digis from responding
> independently and simultaneously to the first two hops while the airborne
> digi is responding to the last hop.
> Further, on each digipeat by a ground-based digi, the airborne one will
> hear yet another "un-used"  SAR1-1 and act on it again if the dupe table
> isn't big enough and dupe time isn't long enough.   You will be creating
> huge numbers of simultaneous packets that will "step on each other" over a
> very large area.
> The disruption caused by "WIDE1-1,WIDE2-1" paths on balloons at altitude
> has been discussed many times on this list.   The impact on the 144.39
> network of a digipeater at altitude, rather than just a originating
> transmitter, will be at least an order of magnitude worse.
>
>
>
> If your user's devices could be set to alternately beacon on two different
> paths (i.e. the "proportional pathing" of the D710),  and you set the
> airborne digi to respond exclusively to SAR1-1 only, the impact on 144.39
> would be VASTLY reduced.    The users would alternately beacon
> "WIDE1-1,WIDE2-1" (to utilize the terrestrial digipeater network only), and
> SAR1-1 (to utilize the airborne digi with a guaranteed single hop only).
>
>
> ------------------------------------------------------------------------
>
> --
>
> Stephen H. Smith    wa8lmf (at) aol.com
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