I'll pass this on to the list as that may been what John intended.as I had
my "reply to" address set to me again.
(Seems to have a mind of it's own (or of Bill's?)).

RM

_______________________________


From: "John Dammeyer" <johnd@autoartisans.com>

Hi,

I haven't heard about Aloha since my U days.  I remember studying that.
8-)

> A significant improvement is obtained by backing off for a
> random period
> AFTER the end of the packet being sent and then sending if
> still free. This

The alternative is what CAN does and that's arbitrate on the identifier
so if a collision occurs the highest priority device gets to keep the
channel and the others turn into receivers.

<snip>

> Random backoff to allow multi station competition is a
> standard feature of
> most collision detection schemes. Note that it should be as
> truly random as
> you can reasonably get to prevent some stations hogging the
> circuit. If you
> all drop into lockstep and compete together repeatedly you
> can also be in
> trouble.

The biggest program can occur if all the nodes are running the same
software using the same random initial key and for some reason they all
start up at the same time. In and RF system that's not so likely but in
a physical network hardwired with a common power supply that could be an
issue.

One thing I've done that appears to work fairly well is to use one of
the PIC A/D channels that measures battery voltage.  Since no battery is
exactly the same I get a sort of random number there.

Cheers,

John Dammeyer

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