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Overview
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 2 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.
Unit 1
100Base-TX Repeater
You can resolve the mismatch in one of two ways:
Manually configure Unit 2, if possible, so that the port connected to
the media converter is set to half-duplex.
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.
External AC/DC Power Adapter
An external AC/DC power adapter is included with the media converter for
standalone operation. The power adapter supplies 12V DC to the media
converter. Allied Telesyn supplies an approved safety compliant AC power
adapter for the 120 and 240V AC versions with an unregulated output of 12V
DC at 1 A. The power required for the media converter is 12V DC, 500 mA.
6
CLASS 1
M/L
LASER PRODUCT
DO NOT STARE
ON
INTO BEAM
LNK TST
MC103SC/FS3 FAST ETHERNET MEDIA CONVERTER
Media Converter
Figure 2 Example of a Duplex Mode Mismatch
TX
RX
100Base-FX 100Base-TX
FDX
A/N ON
MDI
LNK
LNK
PWR
ACT
A/N OFF
MDI-X
ACT
M/L ON
SINGLE MODE
Unit 2
100Base-TX Switch
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