[aprssig] WIDEs

[Robert Bruninga]

Curt, you dont understand callsign-substitution.
Once a digi's own call shows up anywhere in the path,
it will not ever digipeat that packet again.  Period.
Thus, it will not ping-pong.

But it will digi other copies that went via other 
digis before it got to it.  Yes, those are dupes, but
the only radiate outward.  They cannot come back
through this digi in "ping-pong" fashion.  Bob

>>> "Curt, WE7U" <archer at eskimo.com> 1/5/05 3:46:29 PM >>>
On Wed, 5 Jan 2005, Robert Bruninga wrote:

> >>> "Curt, WE7U" <archer at eskimo.com> 1/5/05 11:54:37 AM >>>
> >If you had wide,wide,wide,wide,wide,wide,wide,wide
> >as the path, and two digipeaters near each other responded
> >to wide, it'd go back and forth between them just like a pong
> >game.  Really sucks, but that's the way it is.
>
> That was true back before 1996 when there was no callsign
> substitution.  There shouldbe very few if any WIDE-only
> digis left.  All digis except a WIDE-only digi will do callsign
> substitution and so there cannot be any "ping-pong".

Depends on your definition of ping-pong.  If you mean that it won't
go on forever, you're absolutely correct.  If you mean that each
wide digi (of a set of two) that heard it won't pass it back and
forth between them a few times, then you'll need to rethink it.

As each wide gets used, the "digipeated" bit gets set (most TNC's
represent this as an asterisk in the serial output you see).  The
other wide will then digipeat it and set the next field's bit.  And
so on, and so on, until the eight digipeater bit gets set.  Then the
packet will die.  If more digipeaters are in the mix, the situation
is even worse than the below:

Two digipeaters, A and B.  Original digipeater fields in the packet:
"wide,wide,wide,wide,wide,wide,wide,wide"

    A*,wide,wide,wide,wide,wide,wide,wide
    A*,B*,wide,wide,wide,wide,wide,wide
    A*,B*,A*,wide,wide,wide,wide
    A*,B*,A*,B*,wide,wide,wide,wide
    A*,B*,A*,B*,A*,wide,wide,wide
    A*,B*,A*,B*,A*,B*,wide,wide
    A*,B*,A*,B*,A*,B*,A*,wide
    A*,B*,A*,B*,A*,B*,A*,B*



> But there are dupes.  Because even a callsign substitution
> digi only makes sure it will not digipeat THAT packet again.
> But if it gets another copy via another path from another
> WIDE, then it has not seen "that" packet before and will
> digipeat it again.

Ok, but I see it as the same packet with one more bit set, perhaps
with a callsign substitution as well.


> Yes, lots of dupes, but none of the dupes go "backwards"
> they all go forwards...

Still dupes.  Still trashing the network.

--
Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer 
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