Specifications

Optimizing Performance
82
EIO0000000051 6/2010
Transmission Speed, Duplex and Auto-Negotiation
Introduction
Most Ethernet switches support multiple transmission speeds, full- and half-duplex
communication, and offer auto-negotiation capability. Hubs, by contrast, do not
support full duplex transmissions.
Duplex
Full duplex enables a switch port to both transmit and receive messages
simultaneously, over two dedicated communication channels. Half duplex, instead
only permits a port to transmit or receive messages at one time. Half duplex
communication presents the risk of signal collisions—as messages are both
received and transmitted over a single channel—and can result in poor performance
and message loss.
Auto-Negotiation
Auto-negotiation permits a switch port—connected to a remote device that also
supports auto-negotiation—to automatically configure itself for the maximum speed
and duplex configuration supported by both devices. However, it may be necessary
to manually configure the speed and duplex settings of the switch port, if its peer
device does not possess auto-negotiation capability.
Recommendation
Schneider Electric recommends that you employ only switches that support:
z both auto-negotiation and manual configuration of speed and duplex settings
z multiple speeds: 10/100/1000 Mbps
z both full duplex and half duplex