4-14 CHAPTER 4: TROUBLESHOOTING
Using wires from opposing pairs can cause signals to
be lost. For a 100BASE-TX cable, pins #1 and #2, and #3
and #6 must be on the same twisted strand.
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. Make sure that two twisted-pair wires are
used. Figure 4-7 shows the pinouts for the crossover cable.
On the straight-through cable, make sure that the wires are
from the same twisted pair.
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 appropriate LED
comes on.
■ 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+).
Book Page 14 Thursday, April 2, 1998 9:28 AM
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