Allied Telesis AT-MC104LH - Manual (Page 19)

AT-MC10x Series Media Converters Installation Guide
9
In most configurations, you will want to leave the Auto-Negotiation button
activated so the unit can determine the appropriate duplex mode, based
on the capabilities of the end-nodes. For example, the Auto-Negotiation
feature on the media converter should be left activated in situations where
both end-nodes are also capable of Auto-Negotiation, or where both end-
nodes have been pre-set to the same mode or are capable of operating in
only one duplex mode, such as half-duplex.
There is one situation where it may be necessary to disable the Auto-
Negotiation feature, and that is to prevent a mismatch from occurring
between the duplex modes of the end-nodes. For example, Figure 8
shows two units that have been connected with a media converter. Unit 1
is a repeater that is capable of operating in half-duplex mode only. Unit 2
is a switch that can operate in either half- or full-duplex mode, and will
Auto-Negotiation the duplex mode.
In attempting to Auto-Negotiate with Unit 1, the media converter will
determine that the unit 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 unit can manage full-duplex and
will set the port connected to the unit to full-duplex. The result is a
mismatch, with one unit operating in half-duplex and the other unit
operating in full-duplex. This is referred to as a classic duplex mode
mismatch and will result in poor network performance between the end-
nodes.
Figure 8. Example of a Duplex Mode Mismatch
You can resolve the mismatch in one of two ways:
ˆ Manually configure Unit 2, if possible, so that the port connected to
the media converter is set to half-duplex.
ˆ Disable Auto-Negotiation on the media converter using the Auto-
Negotiation button. With Auto-Negotiation on the media converter
disabled, Unit 2 will assume that the converter is capable of only half-
duplex operation, thus eliminating the mismatch in duplex modes
between the end-nodes.
LINK TST
M/L ON
4 100Base-FX
LINK
ACT A/N OFF
A/N ON
100Base-TX FDX
LINK
ACT M/L ON
PWR
TX RX
CLASS 1 LASER PRODUCT
AT-MC103XL SINGLE MODE FIBER FAST ETHERNET MEDIA CONVERTER
750
Unit 1 Unit 2
100Base-FX Repeater
Media Converter
100Base-TX Switch