An Ethernet crossover cable is a network cable used to connect two Ethernet network devices directly, such as two computers without a switch or router in between. They are used to send and receive data by enabling complex data transfers between computers, routers, and networks. Ethernet crossover cables are similar to straight-through cable except that they have pairs of wires that crisscross. Their internal wiring reverses the incoming and outgoing signals. It uses a design that allows the data output pins on one end of the cable to be connected directly to the data input pins on the other end of the cable.
Ethernet Crossover Cables vs. Straight-through Cables
These two types of ethernet cable are commonly used in most computer networking transmissions. A straight-through cable is used in local area networks to connect different devices like a computer to a network hub such as a router, router and switch, PC and switch, and so on. It is an alternative to wireless connections where one or more computers access a router through a wireless signal. A crossover cable is only required when interconnecting two devices with the same functionality.
Another significant difference between crossover cables and standard patch cables is that each type will have different wire arrangement in the cable for serving different purposes. If you hold up both ends of the cable and compare the pin-outs, you will note that the straight-through cable has matching wired pins while a crossover cable has pins that are typically reversed.
There are two standards for wiring Ethernet cables, as recognized by ANSI, TIA, and EIA. One is the T568A wiring standard, and the other is T568B. The difference between the two is the position of the orange and green wire pairs. Straight-through cables have a one wiring standard where both ends use the T568A wiring standard, or both ends use the T568B wiring standard. Unlike straight-through cables, crossover cables use two different wiring standards. One end uses the T568A wiring standard while the other end uses the T568B wiring standard.
Usually, the crossover cable has the words Crossover or Xover printed on it to distinguish it from straight-through ones.
Functionality Difference between Straight Cable and Cross Cable
Crossover cables are used when:
- Connecting a computer to a computer
- Connecting a router to a router
- Connecting a switch to a switch
- Connecting a hub to a hub and
- Connecting a router to a PC because both devices have the same components
- Connecting a router to a hub
- Connecting a computer to a switch
- Connecting a LAN Port to a switch or computer
- Connecting other dissimilar networking equipment
While in the past a crossover cable was required to connect two host devices directly, it is no longer necessary. Many modern network devices support Auto MDI-X, which automatically detects the proper connection type no matter which cable you use. For example, a computer with Auto MDI-X can use either a straight-through or crossover cable for any application.
Each answer lists two types of devices used in a 100BASE-T network. If these devices were connected with UTP Ethernet cables, which pairs of devices would require a straight-through cable? [Choose three answers.]
An Ethernet crossover cable is a crossover cable for Ethernet used to connect computing devices together directly. It is most often used to connect two devices of the same type, e.g. two computers [via their network interface controllers] or two switches to each other. By contrast, straight through patch cables are used to connect devices of different types, such as a computer to a network switch.
Intentionally crossed wiring in the crossover cable connects the transmit signals at one end to the receive signals at the other end.
Many network devices today support auto MDI-X [aka "auto crossover"] capability, wherein a patch cable can be used in place of a crossover cable, or vice versa, and the receive and transmit signals are reconfigured automatically within the device to yield a working connection.
Motivation[edit]
8P8C modular crossover adapter
The 10BASE-T and 100BASE-TX Ethernet standards use one wire pair for transmission in each direction. This requires that the transmit pair of each device be connected to the receive pair of the device on the other end. The 10BASE-T standard was devised to be used with existing twisted pair cable installations with straight-through connections.
When a terminal device [with an MDI port] is connected to a switch or hub, this crossover is done internally in the switch or hub [MDI-X port]. A standard straight-through cable is used for this purpose where each pin of the connector on one end is connected to the corresponding pin on the other connector.
One terminal may be connected directly to another without the use of a switch or hub, but in that case, the crossover must be done in the cabling. Since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. This wiring scheme constitutes a crossover cable. A crossover cable may also be used to connect two hubs or two switches on their upstream ports.
Because the only difference between the T568A and T568B pin and pair assignments are that pairs 2 and 3 are swapped, a crossover cable may be envisioned as a cable with one modular connector following T568A and the other T568B [see TIA/EIA-568 wiring]. Such a cable will work for 10BASE-T or 100BASE-TX.
The polarity of each pair is not swapped, but the pairs crossed as a unit: the two wires within each pair are not crossed.[1]
Cable requirement for Ethernet linkMDIMDI-XAuto MDI-XMDIcrossoverstraightanyMDI-XstraightcrossoveranyAuto MDI-XanyanyanyAutomatic crossover[edit]
Introduced in 1998, this made the distinction between uplink and normal ports and manual selector switches on older hubs and switches obsolete.[2] If one or both of two connected devices has the automatic MDI/MDI-X configuration feature, there is no need for crossover cables.
Although Auto MDI-X was specified as an optional feature in the 1000BASE-T standard,[3] in practice it is implemented widely on most interfaces.
Besides the eventually agreed upon Automatic MDI/MDI-X, this feature may also be referred to by various vendor-specific terms including: Auto uplink and trade, Universal Cable Recognition and Auto Sensing.
1000BASE-T and faster[edit]
In a departure from both 10BASE-T and 100BASE-TX, 1000BASE-T and faster use all four cable pairs for simultaneous transmission in both directions through the use of telephone hybrid-like signal handling. For this reason, there are no dedicated transmit and receive pairs. 1000BASE-T and faster require either a straight or one of the crossover variants only for the autonegotiation phase. The physical medium attachment [PMA] sublayer provides identification of each pair and usually continues to work even over cable where the pairs are unusually swapped or crossed.[4]
For most optical fiber variants of Ethernet, fibers are used in pairs with one fiber for each direction. The transmitter on one end of the connection needs to be connected to the receiver on the other and vice versa. For this, fiber patch cables with duplex connectors are normally configured as crossover as is the on-premises wiring.[citation needed] Thus, a simple connection with two patch cables at each end and a section of fixed cable in the middle has three crossovers in total, resulting in a working connection. Patch cable crossovers can usually be reconfigured very easily by swapping the connectors within a duplex bracket if required.
Pinouts[edit]
In practice, it does not matter if non-crossover Ethernet cables are wired as T568A or T568B, just so long as both ends follow the same wiring format. Typical commercially available pre-wired cables can follow either format depending on the manufacturer. What this means is that one manufacturer's cables are wired one way and another's the other way, yet both are correct and will work. In either case, T568A or T568B, a normal [un-crossed] cable will have both ends wired identically according to the layout in either the Connection 1 column or the Connection 2 column.
Half crossed[edit]
Crossover cable connecting two MDI ports
Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 [pins 4, 5, 7 and 8] remain un-crossed. This is the most common kind of crossover cable.