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

Crossover Cable Troubleshooting Tips 4-13

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.

1Determine whether your equipment complies with the 10BASE-T or 100BASE-TX standard.

This is particularly important for concentrators (hubs or repeaters).

2Connect 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.

3Make sure that the TD+ and TD– wires are twisted together, and that the RD+ and RD– wires are twisted together. The example in Figure 4-7 shows 10BASE-T

cabling.

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

Figure 4-7Straight-through and Crossover Cable Pinouts