A medium dependent interface (MDI) describes the interface (both physical and electrical/optical) in a computer network from a physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also defines a medium dependent interface crossover (MDI-X) interface. Auto MDI-X ports on newer network interfaces detect if the connection would require a crossover, and automatically chooses the MDI or MDI-X configuration to properly match the other end of the link. Ethernet The popular Ethernet family defines common medium-dependent interfaces. For 10BASE5, connection to the coaxial cable was made with either a vampire tap or a pair of N connectors. For 10BASE2, the connection to the coaxial cable was typically made with a single BNC connector to which a T-piece was attached. For twisted-pair cabling 8P8C, modular connectors are used (often incorrectly called "RJ45" in this context). For fiber, a variety of connectors are used depending on manufacturer and physical space availability. With 10BASE-T and 100BASE-TX, separate twisted pairs are used for the two directions of communication. Since twisted pair cables are conventionally wired pin to pin (straight-through) there are two different pinouts used for the medium-dependent interface. These are referred to as MDI and MDI-X (medium-dependent interface crossover). When connecting an MDI port to an MDI-X port, a straight-through cable is used, while to connect two MDI ports or two MDI-X ports, a crossover cable must be used. Conventionally, MDI is used on end devices and routers while MDI-X is used on hubs and switches. Some hubs and switches have an MDI uplink port (often switchable) to connect to other hubs or switches without a crossover cable. MDI vs. MDI-X The terminology generally refers to variants of the Ethernet over twisted pair technology that use a female 8P8C port connection on a computer, or other network device. The X refers to the fact that transmit wires on an MDI device must be connected to receive wires on an MDI-X device. Straight through cables connect pins 1 and 2 (transmit) on an MDI device to pins 1 and 2 (receive) on an MDI-X device. Similarly, pins 3 and 6 are receive pins on an MDI device and transmit pins on an MDI-X device. The general convention is for network hubs, bridges and switches to use the MDI-X configuration, while all other nodes such as personal computers, workstations, servers and routers use an MDI interface. Some routers