[OZAPRS] Help with digi paths

[Tony Hunt]

David I very much disagree .. The networks are setup all wrong then
acording
to you.. We should configure them so that they all transmit at once ..
Preferably all at the exactly the same time .. Makes heaps of sense Hmmmmm
!! That should all decode fine allways..

> With improper ('polite') values, people receive (in your case) three
> times as many packets as they need (i.e. unneeded duplicates clogging
> up the channel).

Ah now this following problem is easy fixed .. Disconnect the DCD line on
the TNC Micro and lock it in a allways clear state .. It will tranmit
without waiting to see if the channel is clear if you want that to be a
feature ..

> With APRS, the values should be such that digis transmit immediately so
> that in your particular case, when you beacon, the three digis should
> immediately retransmit your beacon without waiting a few milliseconds to
> see if they might collide and probably wait for the other digis to

You seem to have found a good way to do it with software though..

> The proper values for UIDIGI are Persistance=255 and SlotTime=1 but the
> config files up to maybe a year ago (plus or minus) have "normal packet"
> polite default values unfortunately, e.g. Persistance=64  :-(

Lets see from the TNC manuals

SLOTTIME 'n'
                'n' = 0 to 250   specifies the time interval during which
                                 the TNC waits between generating random
                                 numbers, to see if it can transmit.

 PERSIST 'n'
                'n' = 0 to 255 specifies the threshold value for a random
                      number attempt to transmit.
                'n' = 0 Signifies a 1/256th chance of transmitting erery
                        SLOTTIME.
                'n' = 255 Signifies 'transmit right away without delay'

So your generating the Random number for the Persist check every 100mS and
deciding to transmit straight away with no delays .. This will clear the
channel traffic quickly or appear to. But you have increased the chances
of
frame collisions in the network which dont seem to be an issue to you
anyway.. Sorry Ive got a problem with that David .. How does increasing
frame collisions in a network help the effieciency on a CSMA network ?
Capture effect !! Does not compute .. Perhaps you were having a lend of us
..

Not sure if I am going to race off and  reprograme the digis just yet
though
!!

Tony Hunt VK5AH

----- Original Message ----- 
From: "David and Ann Fraser" <zl3ai at nzart.org.nz>
To: <ozaprs at marconi.ics.mq.edu.au>
Sent: Saturday, March 12, 2005 1:52 PM
Subject: Re: [OZAPRS] Help with digi paths


> Hi Andrew,
>
> On Sat, 12 Mar 2005 05:24:01 +1000, Andrew Rich wrote:
>
> > I can hear three digis direct
>
> > My path is WIDE
>
> > Three digis running UI-DIGI
>
> > Why does this happen ?
>
> > VK4TEC>APRS,WIDE <UI>
> > VK4TEC>APRS,DIGI1 <UI>
> > VK4TEC>APRS,DIGI2 <UI>
> > VK4TEC>APRS,DIGI3 <UI>
>
> > I would have thought UI-DIGI would have
>
> > VK4TEC>APRS,WIDE <UI>
> > VK4TEC>APRS,DIGI1 <UI>
>
> > VK4TEC>APRS,DIGI2 <UI> ignore
> > VK4TEC>APRS,DIGI3 <UI> ignore
>
> > Cheers Andy VK4TEC
>
> It looks like two or all three of the digis are set up with nice polite
> Persistance and SlotTime values as per the values normally used on
> connected mode packet channels, so that everybody shares the channel.
>
> With APRS, the values should be such that digis transmit immediately so
> that in your particular case, when you beacon, the three digis should
> immediately retransmit your beacon without waiting a few milliseconds to
> see if they might collide and probably wait for the other digis to
> finish sending your beacon.  Thus you're seeing three digis individually
> sending your beacon, instead of all three simultaneously.
>
> Due to FM Capture Effect, you should only see one digi repeating your
> beacon: the strongest one into your receiver.
>
> The proper values for UIDIGI are Persistance=255 and SlotTime=1 but the
> config files up to maybe a year ago (plus or minus) have "normal packet"
> polite default values unfortunately, e.g. Persistance=64  :-(
>
> With improper ('polite') values, people receive (in your case) three
> times as many packets as they need (i.e. unneeded duplicates clogging
> up the channel).
>
> 73 David.
>
> _______________________________________________
> ozaprs mailing list
> ozaprs at marconi.ics.mq.edu.au
> http://marconi.ics.mq.edu.au/cgi-bin/mailman/listinfo/ozaprs
>

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