Troubleshooting Hubs With Crossover Cable; Straight-Through And Crossover Cable Pinouts - 3Com EtherLink III User Manual

5-10 C
HAPTER

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:
.
1
2
3
4
5
6
7
8
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.
5: T
ROUBLESHOOTING
Straight-through
10BASE-T cable
1
2
3
4
5
6
7
8
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+).
1 2 3 4 5 6 7 8
10BASE-T cable
TD+
1
TD
2
3
RD+
4
5
RD 6
7
8
Crossover
TD+
1
TD
2
3
RD+
4
5
6 RD
7
8