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[aprssig] ALOHA Circle Calculation

Robert Bruninga bruninga at usna.edu
Wed Aug 4 14:14:41 UTC 2010


> How did you ever come up with the 1800 number? 
> Are you assuming a packet fits in a one-second 
> window..

Yes.  Seemed like a good approximation.

> 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. 

To my knowledge that may be true, and that is the obvious first
improvement to make to an ALOHA.  But I thought the definition
of the "ALOHA" net was simplex.  THen the next improvement to
ALOHA is CSMA (carrier sense) then the next improvement is full
duplex, etc..

My definition of an ALOHA circle is an arbitrary calculation not
based on any original ALOHA documents, but is just an attempt to
come up with a metric that gives a bound to the size of the
network based on channel load.

Bob, WB4APR

> -----Original Message-----
> From: aprssig-bounces at tapr.org 
> [mailto:aprssig-bounces at tapr.org] On Behalf Of Alex Carver
> Sent: Tuesday, August 03, 2010 4:07 PM
> To: aprssig at tapr.org
> Subject: Re: [aprssig] ALOHA Circle Calculation
> 
> > 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.
> 
> 
> 
> 
>       
> 
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