3Com 3C509B - Troubleshooting Hubs with Crossover Cable

112 APPENDIX B: CROSSOVER CABLE TROUBLESHOOTING TIPS
Troubleshooting Hubs with Crossover Cable
A crossover cable can be used to isolate failures in these
components when hub performance or impedance settings
are in question.
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, connect TD+ to RD+ and
TD– to RD–.
The cable performs the crossover that is usually performed
by the hub. Figure 62 shows the pinouts for the
crossover cable:
Figure 62 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 failing.
■ With a correct crossover connection, the LED lights.
■ With a straight-through connection, the LED does
not light.
■ With a polarity mismatch (that is, TD+ to RD– instead of
TD+ to RD+), the LED blinks.
1
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8
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8
Straight-through
10BASE-T cable
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1
2
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8
1
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Crossover
10BASE-T cable
TD+
RD+ RD+
TD+
TD– TD–
RD– RD–
Book Page 112 Monday, June 7, 1999 8:55 AM