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SubjectRe: Linux 2.2.2 TCP delays every 41st small packet by 10-20 ms
Date
Donald Becker <becker@cesdis.gsfc.nasa.gov> wrote:

> Full duplex mode never has collisions.
> You were likely trying to use full duplex mode on a CSMA/CD Ethernet.
> Full duplex can only be used on host-to-host and host-to-switch links, and
> only when both endpoints are configured or negotiate full duplex.
>
> Full duplex can never be used when there is a repeater (aka hub) in the
> network. Spank yourself if you configured FDX in that case.

Actually, 3Com's muddied this a bit with their Hub 1000 SX Gigabit Ethernet
full-duplex repeater. They pull this off by using some sort of round-robin
internal negotiation instead of CSMA/CD to give ports access to the internal
bus; but all traffic still goes out all ports. I don't know much more about
it than that. So you can't do full-duplex with CSMA/CD Ethernet (which was
your point, of course), but weird repeaters exist that avoid collisions and
can do full-duplex.

It's a fine point though; in most cases that spanking is well deserved. :)

-- Steve Bonneville


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