The interdependent interface ( MDI ) describes the interface (both physical and electrical/optical) within the computer network from the physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also defines interfaces of interfaces that depend on medium (MDI-X). The Auto MDI-X port on the newer network interface detects if the connection will require crossovers, and automatically selects MDI or MDI-X configurations to actually match the other end of the link.
Video Medium-dependent interface
Ethernet
The popular Ethernet family defines interfaces that depend on common media. For 10BASE5, the connection to the coaxial cable is made by tapping a vampire or a pair of N connectors. For 10BASE2, the connection to a coaxial cable is usually made with a single BNC connector attached to a T-piece. For 8P8C twisted pair cabling, modular connectors are used (often incorrectly termed "RJ45" in this context). For fiber, various connectors are used depending on the manufacturer and the availability of physical space.
With 10BASE-T and 100BASE-TX, separate twisted plugs are used for two-way communication. Because conventional cable twisted conventionally pin cable to pin there are two different pinouts used for interfaces that depend on the media. 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 when connecting two MDI ports or two MDI-X ports, a crossover cable should be used. Conventionally, MDI is used on end devices while MDI-X is used on hubs and switches. Some hubs and switches have an MDI port (often moveable) to connect to other hubs or switches without crossover cables.
Maps Medium-dependent interface
MDI vs. MDI-X
Terminology generally refers to a variant of Ethernet via twisted pair technology that uses a female 8P8C port connection on a computer, or other network device.
X refers to the fact that sending cables on MDI devices must be connected to receive cables on MDI-X devices. Straight through cable connects pins 1 and 2 (transmit) on MDI devices to pins 1 and 2 (received) on MDI-X devices. Similarly, pins 3 and 6 receive pins on MDI devices and send pins on MDI-X devices. The common convention is for network hubs and switches to use MDI-X configuration, while all other nodes such as personal computers, workstations, servers and routers use the MDI interface. Some routers and other devices have an uplink/normal switch to back and forth between MDI and MDI-X on a particular port.
The need to connect the transmitter from one side to the receiver on the other and vice versa makes it necessary to always have the odd number of cross between two devices, with an MDI-X port containing internal crossover. Thus, connecting MDI to MDI-X requires a straight-through cable (one total crossover). Connecting MDI to MDI (without crossover) or MDI-X to MDI-X (two crossovers) requires crossover (nother) on cable to get odd number. When using more complex settings through multiple patch panels in structured cabling, connections can use multiple patches and build cable segments. It is a good idea to have all the necessary crossovers on one side, namely the central hub/switch or on any secondary hub/switch.
Auto MDI-X
To connect two ports of the same configuration (MDI to MDI or MDI-X to MDI-X) with 10 or 100 Mbit/s (10BASE-T or 100BASE-TX) connections, an Ethernet crossover cable is required to cross send and receive signals at cable, so they are matched at the connector level. Confusion requires two types of cables for anything but the hierarchical star network topologies encouraging more automated solutions.
Auto MDI-X automatically detects the required cable connection types and configures the connections appropriately, eliminating the need for crossover cables for connecting switches or connecting peer-to-peer PCs. As long as it is enabled at one end of the link, both types of cables can be used. For auto MDI-X to operate correctly, data rates on the interface and duplex settings must be set to "automatic". Auto MDI-X was developed by Hewlett-Packard engineers Daniel Joseph Dove and Bruce W. Melvin. A pseudo-random number generator decides whether the network port will connect its transmitter, or its recipient to each of the twisted pairs used to automatically negotiate links.
When two MDI-X ports automatically connect together, which is normal for modern products, the algorithm resolution time is usually & lt; 500 ms. However, the asynchronous timer ~ 1.4 seconds is used to solve very rare cases (with probabilities less than 1 in 5ÃÆ'â € "10 21 ) from the loop where each end keeps changing.
Furthermore, Dove promotes auto MDI-X in the 1000BASE-T standard and also develops a patented algorithm for "MDI-X automatic forced mode" that allows links to be automatically created even if ports are not negotiated automatically. It may or may not be implemented on a particular device, so sometimes crossover cables may still be required when connecting auto MDI-X to MDI-X (hub or switch), especially when autonegotiation is disabled.
Newer routers, hubs and switches (including some 10/100 devices, and all 1 gigabit or 10 gigabit in practice) use auto MDI-X for 10/100 Mbit connections to automatically switch to the proper configuration after the cable is connected.
Gigabit and Ethernet links are faster using the twisted pair cable of the four cable pairs for simultaneous transmission in both directions. For this reason, there is no special transmission and receive pairing, and consequently, crossover cables are never required for 1000BASE-T communications. The physical medium attachment sublayer (PMA) provides the identification of each pair and usually continues to work even over the wires in which the exceptional pair exchanges or crossed.
See also
- Free media interface (MII)
References
External links
- "Apple products that require Ethernet crossover cable". Apple support website . October 22, 2008 . Retrieved June 17, 2011 .
- Non-automated connection diagram between MDI and MDIX devices
Source of the article : Wikipedia
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