Re: Half-duplex and Full-duplex

Henrik Olsen (henrik@iaeste.dk)
Sun, 20 Jun 1999 18:18:00 +0000 (GMT)


On Tue, 15 Jun 1999, yenjet wrote:
> GReeting all,
>
> I remember not long ago, this mailing list was discussing about the
> different between half-duplex and full duplex on a network card setting.
> There is also come to a conclusion that half-duplex is suitable to be used
> in hub environment while full-duplex is more suitable to be used in switch
> environment. (Correct me if I'm wrong)
>
> So, is ther any resource/URL that I can refer to about this ? As I have to
> proof this to my company system administrator.
>
> In Linux, how do I specify that I wish to use half-duplex (as I know the
> NIC is default to full-duplex)? And where should I put in the
> configuration ? Is anyone know how to tune this half-duplex and full
> duplex in Windows NT server as this can improve our whole network
> performance ?
>
> Thanks in advanced.
Full duples is impossible with hubs, so shouldn't even be concidered.

With switches you will want to make sure both your switches and your nic's
support Flow Control packets, if not, you'll be a lot better off with half
duplex, since without Flow Control, ressource starvation in the switches
(buffers, not bandwidth) will result in dropped packets instead of the
collisions used to report it with half duplex.

Since dropped packets takes a lot longer than collisions to resend, (end
to end protocol rather than nic hardware) overall performance drops a lot
more with full duplex than with half duplex in high-use situations, which
is why half duplex is often the best choice in real life engineering, as
opposed to benchmarks to impres management.

-- 
Henrik Olsen,  Dawn Solutions I/S       URL=http://www.iaeste.dk/~henrik/
  Animal behaviour is best described by the four F's
  Feed, Fight, Flee and Reproduce

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