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[aprssig] APRS low-power-local ALT input channel

nc8q-1 nc8q-1 at gelm.net
Wed Sep 29 12:38:47 UTC 2004


Ooopps, my bad!

PERSIST= 255/(N-1) 
 
 Where 'N' = number of stations sharing channel.

Thanks for noticing my error.

3s, Chuck

Henk de Groot wrote:
> 
> At 19:21 27-9-2004 -0400, nc8q wrote:
> >  When I did BBS<>BBS forwarding on a non-user channel. I used
> >(256/n)-1 where 'n' is the number of BBSs and nodes sharing the channel.
> >If there are only 2 BBSs/nodes they can each use 255 as identical keyup
> >collisions would be taken care of by the numbered "I" frames & SLOTTIME.
> >3 stations = 127 PERSIST, 4 stations = 84, 5 stations use 63, ...
> 
> Looks good to me if the amount of stations includes yourself. I assume the
> 2 BBSses talk to eachother in this case, the transmission will nicely
> switch between the two in that case.

Yes.

> Note that your equations do not match what you states before; (256/n)-1. In
> that case 4 would yield (256/4)-1 = 63. I assume "n" in this formula is the
> number of other stations.
> 
> >However, IMHO, APRS stations have such little data to send
> >and such infrequent transmissions,
> >that a PERSISTance of 1 should be adequate.
> 
> You mean a setting of the PERSIST parameter to 255 I guess so the
> probability of transmission P is always "1" regardless of the random
> number. Be carefull however, the TH-D7 and TMD-700, which default to a
> persist value of 128 (P = 0.5), have the PERSIST parameter upside down;
> setting PERSIST to 255 will block transmission, setting it to 0 will give a
> probability P = 1.
> 
> >However, this may not work with APRS's "UI" frames.  I am not familiar
> 
> The PERSIST and SLOTTIME values are channel access parameters, they apply
> to any transmission to access the shared medium, including UI frame
> transmission. Some stations may however still use the depricated DWAIT
> method. Other HDLC parameters like FRACK and RESP do not apply, since they
> only make sense for connection-oriented links. APRS is a connection-less
> protocol, none of the connection-oriented link parameters make any
> difference to the stations behaviour on the RF channel.
> 
> Kind regards,
> 
> Henk.





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