cross cable

Two pairs crossed, two pairs uncrossed
10BASE-T or 100BASE-TX 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, 100BASE-T4 or 1000BASE-T 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, 100BASE-T4 or 1000BASE-T 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 the manufacturer. 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.

[edit] Automatic crossover
Automatic MDI/MDI-X Configuration is specified as an optional feature in the 1000BASE-T standard[1], 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.

[edit] See also
The Wikibook The World of Peer-to-Peer (P2P) has a page on the topic of
Ethernet crossover cable network
Crossover cable
Registered jack, which expands on the introduction and evolution of these connectors.
Ethernet over twisted pair
[edit] References
^ Clause 40.4.4 in IEEE 802.3-2008