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[aprssig] ALOHA Circle Calculation

Alex Carver kf4lvz at yahoo.com
Tue Aug 3 20:07:09 UTC 2010

> From: "Bob Bruninga "
> > ... [the ALOHA circle] is the circle that contians 
> > a FULL [APRS channel].
> Ah, now the fun begins.  You want to know how many
> packets each of those stations puts on the network per 30
> minutes.  So we assume 2 for a home station, 6 for WX,
> 3 per digi and so on (this is from memory so I may not have
> exact numbers here).  
> Then we need to know how many copies each of those
> generates.  So we start at own-station and go
> outward.  Multiply each station's number by 1 until you
> get to the first digi.  From then on, multiply each
> stations numbers by 2, and so on until the third digi,
> multiply by 3 and so on.  Once  this total number
> reaches 1800, (30 minutes of seconds), then the channel is
> 100% saturated.
> That range defines the aloha circle.

How did you ever come up with the 1800 number?  Are you assuming a packet fits in a one-second window or are you using some other metric?

I always had a problem calling APRS an ALOHA network because the real ALOHANet used two frequencies rather than one.  Acknowledgments came back to the sender over a second channel which kept the first channel free for the next transmission.


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