Crossover Cables vs Straight Through Cables

Ethernet patch cables can be wired in three different ways, the two main ways are called straight through and crossover. The third type is called rolled and has only specialized applications.

Generally speaking, straight through cables are used to patch between different types of equipment; for example, PCs to a hub.
Conversely, crossover cables are generally used to patch between similar types of equipment; a PC to another PC for example.
Some modern hubs don't care if you use crossover cables or straight through cables, they work out what you're using and configure themselves accordingly.

As stated at the outset, the actual difference is in the wiring. Inside the UTP patch cable there are 8 physical wires although the network only uses 4 of them (the other 4 are simply wasted). The 8 wires are arranged in what's known as pairs and one pair is used to send information whilst the other pair is used to receive information.

On a PC, the pair on pins 1 and 2 of the connector send information, whilst the pair on pins 3 and 6 receive the information. To make PCs talk to each we therefore need to connect the send pair of one PC to the receive pair of the other PC (and vice-a-versa). That means we need a crossover cable. If we used a straight through cable the both be listening on the one pair - and hearing nothing, and sending on the one pair - achieving nothing.

Electrically, the straight through and crossover cables look like the diagram below: The most common cable is the straight through cable. In a home or small office network you might only have one crossover cable used - perhaps from the cable or DSL modem to the distribution hub. How do you tell what sort of cable you have in your hand? You can tell by looking at the connectors, identifying the wiring from its colors, and comparing the ends. See the next question on color codes.

Color Codes

The standards say that Ethernet connectors should be cabled with specific colors on specific pins. There are two standard layouts - if a cable has the same layout on both ends it's a straight through cable. If a cable has one layout on one end and the other layout on the other end then it's a crossover cable. Whilst not universal, the color codes shown below are generally used on professional cables.

cross cable color code

straight through cable

In fact, while the colors are standardized and usually followed, that's not the important part. What's more important is that one "pair" (wires that are twisted together inside the cable sheath) is used for the transmit side and another pair for the receive side. If pairs aren't used then it's likely your cable will not work. Pairs are identified by the colors. The orange wire and the orange with white stripe (or sometimes white with orange stripe) wire are a pair. The brown wire and the brown with white stripe wire are a pair. Etc.

source: discountcablesusa

straight through cable

cross cable color code