Allied Telesis AT-MC116XL - Manual (Page 15)

AT-MC115XL and AT-MC116XL Installation Guide
5
Duplex Mode
Duplex mode refers to the way an end-node sends and receives data on the
network. An end-node can operate in either half- or full-duplex mode,
depending on its capabilities. An end-node that is operating in half-duplex
mode can either send data or receive data, but it cannot do both at the same
time. An end-node that is operating in full-duplex mode can send and receive
data simultaneously. The best network performance is achieved when an end-
node can operate at full-duplex, since the end-node is able to send and receive
data simultaneously.
The twisted pair port and fiber optic port on the media converter can operate
in half-duplex, full-duplex, or auto-negotiate the duplex mode. The media
converter sets the duplex mode automatically through auto-negotiation. With
auto-negotiation, if the end-node is capable of full-duplex, the port is set
automatically to full-duplex mode. If the end-node is capable of half-duplex,
the port is set automatically to half-duplex mode.
The AT-MC115XL and AT-MC116XL media converters can operate in full-
duplex, half-duplex, or auto-negotiate the duplex mode. However, the end-
nodes connected to these media converters must operate in the same duplex
mode to avoid a duplex mode mismatch, which can result in poor network
performance.
Figure 3 shows an example of a duplex mode mismatch. A repeater (Unit 1),
capable of operating in half-duplex mode only, is connected to the 100Base-SX
port on the media converter, while a switch (Unit 2), capable of either half- or
full-duplex mode, is connected to the 10Base-T/100Base-TX port on the media
converter.
Figure 3 Example of a Duplex Mode Mismatch
In attempting to auto-negotiate with Unit 1, the media converter will
determine that the repeater is capable of half-duplex only and will set the port
connected to the unit appropriately. In auto-negotiating with Unit 2, the
media converter will determine that the switch can manage full-duplex and
will set the port connected to the switch to full-duplex. The result is a duplex
mode mismatch, with one unit operating in half-duplex and the other unit
operating in full-duplex. You could resolve this duplex mode mismatch by
manually configuring Unit 2, if possible, so that the port connected to the
media converter is set to half-duplex.
Unit 1
Unit 2
10/100Base-TX Repeater Media Converter 10/100Base-TX Switch