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Full duplex is a point-to-point, collision-free Ethernet* connection
over twisted pair or fiber cabling. It allows independent, simultaneous
two-way transmissions in both directions.
Full duplex is primarily useful to extend the distance of an Ethernet
where the limitation on length is due to propagation delay, not
attenuation. For example, when using a single-mode fiber connection, the
media is capable of supporting distances of up to 100 km. However, due
to propagation delay, a maximum of 500 meters is allowed for Ethernet,
since the round-trip delay time must be less than 5.12 (seconds. Full
duplex removes the restriction on length due to propagation delay, since
a collision cannot occur in full duplex.
Full duplex switching is a very simple way to improve server
performance. Bandwidth is improved to the server since both
transmission and reception can occur simultaneously. If server reads and
writes are symmetric, 200 Mbps bandwidth can be realized. In actual
usage, bandwidth improvements are more modest.
There is one caveat to having a full duplex server connection, however.
Since all clients will be communicating with the server, there may be
times during peak usage when there is more traffic destined for the
server than the server port has bandwidth to accommodate. In this
situation, it is critical that the client ports have flow control. If
too many of the clients' packets are lost, the machines could lose their
connection to the server. Flow control can manage the traffic destined
for the server port and prevent users from experiencing unnecessary
interruptions in their work.
Thus you must be very cautious in installing a full duplex connection.
It is extremely important to keep in mind that flow control is not
generally possible over a full duplex link. Therefore, if a station on
a full duplex link tries to send more traffic onto another link across a
bridge or switch than that link can handle, frames will be lost.
Note: The Express Switch does not support NWAY. You must force the
duplex setting.
This applies to:
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