On Sun, Sep 24, 2000 at 08:44:18PM +1100, DaZZa wrote:
> On Sat, 23 Sep 2000 [EMAIL PROTECTED] wrote:
>
> > Present ethernets, from what I understand, transmit on demand and
> > perform a random timeout in the event of collision. This means
> > throughput drops at around 60-70% utilisation (can't remember the
> > exact figure).
>
> 60% is close enough. Any csma-cd based network running higher utilisation
> than that is in deep kimchee.
It actually depends on the number of (transmitting) hosts on the network -
the more hosts, the lower the max utilisation.
A network with one main transmitting host can easily get 90% plus
utilisation (hook-up two machines and do an ftp from one to the other).
At the upper end ethernet maxes out at about 30% utilisation!
Token ring on the other hand will happily handle 70-80% utilisation, even
with several hundred active nodes on the network. The main problem with
TR is that it's a much more complex protocol that ethernet (well, that and
the fact that IBM owned it, and thus it was very expensive).
> What you need for this is either.
>
> a CSMA-CA based network
>
> or
>
> A switched network
>
> In this case, the CA stands for collision avoidance - as opposed to the CD
> used in ethernet, which stands for collision detection.
CSMA-CD _is_ a collision avoiding algorithm, it's just not a very good one
(it will not transmit if it can see something already on the wire. The
collision detection is only there for when two hosts start transmitting at
around the same time).
Thing is, CSMA-CD use is dropping. As more and more people move to full
duplex ethernet the whole concept of collisions goes out the window - one
of the reason token ring is a dying standard.
Scott.
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