From: Asbjorn Hojmark (Asbjorn@xxxxxxxxxxx)
Date: Mon Mar 13 2000 - 19:50:53 GMT-3
> What if all 24 ports were operating at full duplex? A
> backplane of 2.4Gbps wouldnt be enough, right? Or am I
> wrong?
I would argue, you're wrong.
> 24 x 200Mbps = 4.8 Gbps ?
Don't take this the wrong way but I think you've been listening
to much to marketing. A fast ethernet link is *not* 200 Mbps,
it's 100 Mbps full duplex (Luckily, nobody calls an E1 'a 4 Mbps
link').
Two hosts talking to each other on the same switch could poten-
tially transfer 200 Mbps (2 x 100 Mbps), not 400 Mbps (2 x 200
Mbps).
So if all traffic on the switch were unicast, you'd need 'ports
times 100 Mbps' (24 x 100 Mbps in your case) backplane capacity.
The problem is, of course, that marketing has also had its say on
backplane capacity as stated in data sheets so what you'll often
see is full duplex numbers (even if the backplane can't really
run full duplex, sigh).
And then there's the question of broad- and multicast traffic...
-A
-- Heroes: Vint Cerf & Bob Kahn, Leonard Kleinrock, Robert Metcalfe Links : http://www.hojmark.org/networking/
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