Allied Telesis AT-3012SL Installation Manual page 34

Data Cabling Connections
22
In both the crossover and straight-through instances, the wire is twisted pair.
Figure 16 demonstrates usable and unusable cable configurations for the
straight-through wire pairing in the UTP environment.
RJ45 Pin
TD+
TD-
RD+
Not Used
Not Used
RD-
Not Used
Not Used
RJ45 Pin
TD+
TD-
RD+
Not Used
Not Used
RD-
Not Used
Not Used
Figure 16: Hub-to-MAU Wiring (A) Usable and (B) Unusable
Diagram A of Figure 16 is correct because the proper pairs are twisted
together. Diagram B is incorrect because the wires for the receive pair, pins 3
and 6, are not twisted together. This could result in excessive common mode
noise and an unacceptably high data error rate.
If you pair pins incorrectly, as shown in Figure 16, Diagram B, your network
may have a high data error rate. In a straight-through cable, the transmit
pins, 1 and 2, are paired, as are the receive pins, 3 and 6. In a crossover cable
(Figure 16), pins 1 and 2, TD+ and TD-, are paired, as are pins 3 and 6, RD+
and RD-. When pins 1 and 2 are crossed over, they connect to pins 3 and 6
respectively, and pins 3 and 6, when crossed over, connect to pins 1 and 2
respectively.
A
1
Pair twisted as per Level 3, 4 or 5 cable.
1
2
3
1
4
5
6
7
8
B
This cable will not work for 10BASE-T.
Note that 3 and 6 are twisted, but are not a pair.
1
2
3
4
5
6
7
8
RJ45 Pin
1
1
TD+
2
TD-
3
RD+
4
Not Used
5
Not Used
6
RD-
7
Not Used
8
Not Used
RJ45 Pin
1
TD+
2
TD-
3
RD+
4
Not Used
5
Not Used
6
RD-
7
Not Used
8
Not Used