SMC Networks SMC7904WBRA - Manual (Page 129)

C
ABLES
B-4
Crossover Wiring
If the port on the attached device has straight-through wiring (MDI), use
crossover cable.
Crossover Cable Pin Assignments
End 1 End 2
1 (Tx+) 3 (Rx+)
2 (Tx-) 6 (Rx-)
3 (Rx+) 1 (Tx+)
6 (Rx-) 2 (Tx-)