CJT said:
Are you sure about that? I haven't researched it carefully, but my
understanding was a little different -- that the appropriate duplex
setting had more to do with whether the port was operating at 10Mbps
or 100 than whether a hub or switch was in use.
Quite sure.
10 or 100Mbps can both operate either in full or half duplex modes.
Full duplex can only be used when there are only two devices directly
connected by a single cable, either PC to PC or PC to switch port or
PC to router or switch to switch etc. In full duplex mode both devices
can transmit and receive at the same time without having to listen
first. This works with a switch because each port is independent of
the others (i.e. each port is treated as a separate segment) and on
many switches ports can be different speeds, some at 10, some at 100
and even gigabit. You can, of course use half duplex in this scenario
but it's not making the best use of the available bandwidth.
A hub on the other hand is little more than a line spltter allowing a
number of devices to share the same medium (i.e. all devices are
effectively on the same piece of cable). Each port is directly
connected to the others and data from one port is transmitted on all
ports. Because of this each device has to listen before transmitting
otherwise collisions occur. This is why devices connected to a hub are
configured as half duplex and hub ports are always the same speed as
each other.
The most common problem occurs when using auto-detect as some nic's
detect the speed ok but not the duplex setting. In this case devices
can configure full duplex even if they are on shared media or if a
directly connected device is set for half duplex. If this happens, as
in the case of the OP, the device configured as full duplex happily
transmits without listening causing continual collisions with the
other devices and thus severly degrading the overall network
throughput.
BH
