Intel EtherExpress - full duplex?

Neil Hoggarth njh at kernighan.demon.co.uk
Sat Mar 11 12:31:22 GMT 2000


On Sat, 11 Mar 2000, jon wrote:

> This seems to suggest that my ethernet card is not running full-duplex.
> Is this the case?  Is there any reason why it isn't?
> 
> All my machines are conncted to a 3COM OfficeConnect 4*100BaseT hub,
> could this be the problem?  There's nothing in the manual regarding
> full- or half- duplex operation.

If you are connected to a hub then half-duplex is the correct mode of
operation. Full-duplex should only be used where you have a direct
connection to an Ethernet switch, or a direct connection between two
hosts.

Background: When you connect through a hub you share bandwidth with
all the other devices connected to that hub. Only one station on the
network can transmit at any one time. If two stations send overlapping
transmittions then a "collision" has occured. The stations involved
realize that their transmissions overlapped and got garbled, and wait a
random period before trying to resend. Full-duplex basically means "turn
off collision detection", and if you enable it in an environment where
collisions can occur then Bad Things will happen.

Regards,

Neil.







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