#ethernet #IEEE #Table #MDIX #signal #names #wrong
IEEE 802.3 Clause 40.8 specifies the 1000BASE-T MDI and MDI-X connector pinouts as:
Below, in §40.8.2, it says
For a PHY that does not implement the crossover function, the MDI labels in the middle column of Table 40–12 refer to its own internal circuits. For PHYs that do implement the internal crossover, the MDI labels in the last column of Table 40–12 refer to the internal circuits of the remote PHY of the link segment.
Assuming a link composed of one MDI PHY and one MDI-X PHY connected with a straight-through cable, this paragraph leads to a contradiction: if the MDI and MDI-X signal names both refer to the PHY that does not implement the crossover function (i.e., the MDI PHY), then contact 1 cannot be both BI_DA+ and BI_DB+.
To avoid contradiction, both columns of Table 40-12 must refer to the PHY’s own internal circuits, implying that §40.8.2 is wrong. Alternatively, Table 40-12 should simply contain a single MDI column, as in §14.5.1 for 10BASE-T: