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B-14 APPENDIX B: TECHNICAL SUPPORT
Crossover Cable Troubleshooting Tips
When you work with network cabling, concentrators, and
adapters from different vendors, it is possible to connect
everything and still have no communication between
file servers and workstations.
When there are several unknown variables, it is difficult to
determine which component is broken. Use these tips to
isolate the problem.
1 Determine whether your equipment complies with
the 10BASE-T or 100BASE-TX standard.
This is particularly important for concentrators (hubs or
repeaters).
2 Connect a straight-through cable from the PC to
the hub.
The hub performs an internal crossover so that the signal
can go from TD+ to RD+ and TD– to RD–. When you look
at an RJ-45 connector from the front, pin 1 is identified on
the left-hand side when the metal contacts are facing up.
3 Make sure that the TD+ and TD– wires are twisted
together, and that the RD+ and RD– wires are twisted
together. The example in Figure B-5 shows 10BASE-T
cabling.
.
Figure B-5 Straight-through and Crossover Cable Pinouts
1
2
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4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
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8
1
2
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5
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8
Straight-through
10BASE-T cable
Crossover
10BASE-T cable
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TD+
RD+
TD
RD
TD+
RD+
TD
RD