Auto Mdi/Mdi-X Connection - Moxa Technologies EtherDevice User Manual

Auto MDI/MDI-X Connection

The Auto MDI/MDI-X function allows users to connect MOXA EtherDevice Server's
10/100BaseTX ports to any kind of Ethernet device, without paying attention to the type of
Ethernet cable being used for the connection. To understand the meaning of this statement,
you simply need to remember that there are two types of Ethernet ports, and two types of
Ethernet cables. See the 10/100BaseTX Ethernet Port Connection section from Chapter 3
for detailed Pinout and Cable Wiring diagrams. In this section, we give a short primer of
the terminology, and indicate which cable should be used to connect which types of ports.
There are two types of Ethernet port in use. The first type is called an MDI (Medium
Dependant Interface) port, and is what you find on your PC's NIC (Network Interface
Card). The second type is called an MDI-X (Medium Dependant Interface, Crossover) port,
and is the type of port found in a standard HUB or switch. For this reason, we often refer to
an MDI port as being NIC-type, and an MDI-X port as being HUB/Switch-type.
There are also two types of Ethernet cable in use. The first type is a straight-through cable,
and the second type is a cross-over cable. The general connection rules are:
A straight-through cable is used to connect dislike ports:
MDI ↔ MDI-X.
A cross-over cable is used to connect like ports:
MDI ↔ MDI or MDI-X ↔ MDI-X.
For example, you should use a straight-through cable to connect your computer's Ethernet
NIC to a HUB or switch, but use a cross-over cable to connect your computer's Ethernet
NIC to another computer's Ethernet NIC.
4-4 MOXA EtherDevice Server User's Manual