An
Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly where they would normally be connected via a
network switchA network switch is a computer networking device that connects network segments.The term commonly refers to a Network bridge that processes and routes data at the Data link layer of the OSI model...
, hub or
routerA router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers....
, such as directly connecting two
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator...
s via their
networkComputer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs...
adapters.
The
10BASE-TEthernet over twisted pair refers to the use of cables that contain insulated copper wires twisted together in pairs for the physical layer of an Ethernet network—that is, a network in which the Ethernet protocol provides the data link layer...
and
100BASE-TXIn computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the 100 megabit Ethernet standards 100baseTX is by far the most common and is supported by the...
EthernetEthernet is a family of frame-based computer networking technologies for local area networks . The name comes from the physical concept of the ether...
standards use one wire pair for transmission in each direction. The Tx+ line from each device connects to the tip conductor, and the Tx- line is connected to the ring.
An
Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly where they would normally be connected via a
network switchA network switch is a computer networking device that connects network segments.The term commonly refers to a Network bridge that processes and routes data at the Data link layer of the OSI model...
, hub or
routerA router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers....
, such as directly connecting two
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator...
s via their
networkComputer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs...
adapters.
Overview
The
10BASE-TEthernet over twisted pair refers to the use of cables that contain insulated copper wires twisted together in pairs for the physical layer of an Ethernet network—that is, a network in which the Ethernet protocol provides the data link layer...
and
100BASE-TXIn computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the 100 megabit Ethernet standards 100baseTX is by far the most common and is supported by the...
EthernetEthernet is a family of frame-based computer networking technologies for local area networks . The name comes from the physical concept of the ether...
standards use one wire pair for transmission in each direction. The Tx+ line from each device connects to the tip conductor, and the Tx- line is connected to the ring. This requires that the transmit pair of each device be connected to the receive pair of the device on the other end. When a
terminalIn the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers, work stations, routers in a VoIP network....
device is connected to a
switchA network switch is a computer networking device that connects network segments.The term commonly refers to a Network bridge that processes and routes data at the Data link layer of the OSI model...
or hub, this crossover is done internally in the switch or hub. 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 device may be connected directly to another without the use of a switch or hub, but in that case the crossover must be done externally in the cable. Since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. This is a
crossover cable. A crossover cable must also be used to connect two internally crossed devices (e.g., two hubs) as the internal crossovers cancel each other out. This can also be accomplished by using a straight through cable in series with a modular crossover adapter.
Because the only difference between the T568A and T568B pin/pair assignments are that pairs 2 and 3 are swapped, a crossover cable may be envisioned as a cable with one
connectorAn electrical connector is a conductive device for joining electrical circuits together. The connection may be temporary, as for portable equipment, or may require a tool for assembly and removal, or may be a permanent electrical joint between two wires or devices. There are hundreds of types of...
following T568A and the other T568B. Such a cable will work for 10BASE-T or 100BASE-TX.
1000BASE-T4Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2008 standard...
(Gigabit crossover), which uses all four pairs, requires the other two pairs (1 and 4) to be swapped and also requires the solid/striped within each of those two pairs to be swapped.
Crossover cable pinouts
Two pairs crossed, two pairs uncrossed
10baseT/100baseTX crossover
Pin |
Connection 1: T568A |
Connection 2: T568B |
Pins on plug face |
| signal |
pair |
color |
signal |
pair |
color |
| 1 |
BI_DA+ |
3 |
white/green stripe |
BI_DB+ |
2 |
white/orange stripe |
 |
| 2 |
BI_DA- |
3 |
green solid |
BI_DB- |
2 |
orange solid |
| 3 |
BI_DB+ |
2 |
white/orange stripe |
BI_DA+ |
3 |
white/green stripe |
| 4 |
|
1 |
blue solid |
|
1 |
blue solid |
| 5 |
|
1 |
white/blue stripe |
|
1 |
white/blue stripe |
| 6 |
BI_DB- |
2 |
orange solid |
BI_DA- |
3 |
green solid |
| 7 |
|
4 |
white/brown stripe |
|
4 |
white/brown stripe |
| 8 |
|
4 |
brown solid |
|
4 |
brown solid |
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.
Gigabit T568A crossover
All four pairs crossed
10base-T/100base-TX/1000base-TX/T4 crossover (shown as T568A)
Pin |
Connection 1: T568A |
Connection 2: T568A Crossed |
Pins on plug face |
| signal |
pair |
color |
signal |
pair |
color |
| 1 |
BI_DA+ |
3 |
white/green stripe |
BI_DB+ |
2 |
white/orange stripe |
|
| 2 |
BI_DA- |
3 |
green solid |
BI_DB- |
2 |
orange solid |
| 3 |
BI_DB+ |
2 |
white/orange stripe |
BI_DA+ |
3 |
white/green stripe |
| 4 |
BI_DC+ |
1 |
blue solid |
BI_DD+ |
4 |
white/brown stripe |
| 5 |
BI_DC- |
1 |
white/blue stripe |
BI_DD- |
4 |
brown solid |
| 6 |
BI_DB- |
2 |
orange solid |
BI_DA- |
3 |
green solid |
| 7 |
BI_DD+ |
4 |
white/brown stripe |
BI_DC+ |
1 |
blue solid |
| 8 |
BI_DD- |
4 |
brown solid |
BI_DC- |
1 |
white/blue stripe |
Gigabit T568B crossover
All four pairs crossed
10base-T/100base-TX/1000base-TX/T4 crossover (shown as T568B)
Pin |
Connection 1: T568B |
Connection 2: T568B Crossed |
Pins on plug face |
| signal |
pair |
color |
signal |
pair |
color |
| 1 |
BI_DA+ |
2 |
white/orange stripe |
BI_DB+ |
3 |
white/green stripe |
|
| 2 |
BI_DA- |
2 |
orange solid |
BI_DB- |
3 |
green solid |
| 3 |
BI_DB+ |
3 |
white/green stripe |
BI_DA+ |
2 |
white/orange stripe |
| 4 |
BI_DC+ |
1 |
blue solid |
BI_DD+ |
4 |
white/brown stripe |
| 5 |
BI_DC- |
1 |
white/blue stripe |
BI_DD- |
4 |
brown solid |
| 6 |
BI_DB- |
3 |
green solid |
BI_DA- |
2 |
orange solid |
| 7 |
BI_DD+ |
4 |
white/brown stripe |
BI_DC+ |
1 |
blue solid |
| 8 |
BI_DD- |
4 |
brown solid |
BI_DC- |
1 |
white/blue stripe |
In practice, it does not matter if your 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 who made them. What this means is that you may discover 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 according to the layout in the
Connection 1 column.
Automatic crossover
Automatic MDI/MDI-X ConfigurationAuto-MDIX is a computer networking technology that automatically detects the required cable connection type and configures the connection appropriately, thereby removing the need for crossover cables to interconnect switches or connecting PCs peer-to-peer...
is specified as an optional feature in the
1000BASE-T standardGigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2008 standard...
, meaning that straight-through cables will often work between Gigabit capable interfaces. This feature eliminates the need for crossover cables, making obsolete the uplink/normal ports and manual selector switches found on many older hubs and switches and greatly reducing installation errors. Note that although Automatic MDI/MDI-X is generally implemented, a crossover cable would still be required in the occasional situation that neither of the connected devices has the feature implemented and enabled. Prior to the 1000Base-T standard, using a crossover cable to connect a device to a network accidentally, usually meant wasted time troubleshooting the resulting lack of connection, but with this standard in place, that is no longer a concern.
Modern switches automatically apply an internal crossover when necessary. 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.
See also
- Crossover cable
The term crossover cable means a practical interconnecting solution of two devices of the same type, DTE-DTE or DCE-DCE, by modified version of a cable called a crosslink, as these devices are usually connected asymetrically: DTE-DCE...
- Registered jack
A registered jack is a standardized physical network interface — both jack construction and wiring pattern — for connecting telecommunications or data equipment to a service provided by a local exchange carrier or long distance carrier. The standard designs for these connectors and their wiring...
, which expands on the introduction and evolution of these connectors.
- Ethernet over twisted pair
- Guide to creating a crossover network