Crossover Cable Troubleshooting Tips - 3Com Fast EtherLink XL PCI 10/100BASE-TX User Manual

Crossover Cable Troubleshooting Tips

When you work with network cabling, concentrators, and
NICs 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
cabling.
.
1
2
3
4
5
6
7
8
Figure 4-7 Straight-through and Crossover Cable Pinouts
Straight-through
10BASE-T cable
1
2
3
4
5
6
7
8
Crossover Cable Troubleshooting Tips
Figure 4-7
1 2 3 4 5 6 7 8
10BASE-T cable
TD+ 1
TD 2
3
RD+
4
5
RD 6
7
8
shows 10BASE-T
Crossover
1 TD+
2 TD
3
RD+
4
5
6 RD
7
8
4-13