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Appendix D Connectors and pin assignments 203
Using the BayStack 380 10/100/1000 Switch
MDI and MDI-X devices
Media dependent interface (MDI) is the IEEE standard for the interface to
unshielded twisted pair (UTP) cable.
For two devices to communicate, the transmitter of one device must connect to the
receiver of the other device. The connection is established through a crossover
function, which can be a crossover cable or a port that implements the crossover
function internally.
Ports that implement the crossover function internally are known as MDI-X ports,
where X refers to the crossover function.
The following sections describe the use of straight-through and crossover cables
for connecting MDI and MDI-X devices.
MDI-X to MDI cable connections
The BayStack 380 Switch features Auto-MDI/MDI-X detection. With
auto-negotiation enabled, you can use straight Category 5 cables for MDI to
MDI-X connections.
Auto-polarity
The BayStack 380 Switch features auto-polarity. With autonegotiation enabled,
auto-polarity automatically reverses the polarity of a pair of pins from positive to
negative or negative to positive. This corrects the polarity of the received data if
the port detects that the polarity of the data has been reversed due to a wiring error.
Note: For the transmitter of one device to connect to the receiver of
another device, the total number of crossovers must always be an odd
number.