3Com ETHERLINK III User Manual

5-10 CHAPTER 5: TROUBLESHOOTING
Troubleshooting Hubs with Crossover Cable
When there is doubt whether a hub is performing
correctly, or if the impedance settings are in question, a
crossover cable can help you isolate the failing component.
1 Connect a file server and a client PC back to back
with a crossover cable to verify that the NIC and
network operating system are properly configured.
2 To make a crossover cable, simply connect TD+ to
RD+ and TD– to RD–.
The cable performs the crossover that is usually performed
by the hub. Figure 5-2 shows the pinouts for the
crossover cable:
.
Figure 5-2 Straight-through and Crossover Cable Pinouts
If the file server and client PC function together as a
small network, then either the existing cabling or the hub
is the problem.
■ If there is a proper crossover, the LED lights.
■ If there is a straight-through connection, the LED
does not light.
■ A blinking LED indicates that there is a polarity
mismatch (that is, TD+ to RD– instead of TD+ to RD+).
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Straight-through
10BASE-T cable
Crossover
10BASE-T cable
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TD+
RD+
TD
RD
TD+
RD+
TD
RD

3Com ETHERLINK III Specifications

General

Brand	3Com
Model	ETHERLINK III
Category	Adapter
Language	English