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Ethernet Cheatsheet

Terminology

Cat 5/6/7 - The "Cat" is short for "category".

Crosstalk is where a signal transmitted in one circuit or channel creates an undesired effect in another circuit or channel. This could be from the multiple wires inside the Ethernet cable effecting each other, or from electronic equipment outside the wires having an impact (sometimes referred to as alien crosstalk). This is why Ethernet cables always appear to be getting a thicker outside sheath in order to improve potential speeds, but this also makes them less flexible.

Crossover - One used to have to buy different cables if one wanted to plug two computers directly into each other, or if they wanted to plug the computer into a router instead. The former required a crossover cable. Standard cables have an identical sequence of colored wires on each end, whereas crossover cables have the first and third wires (counting from left to right) crossed, as well as the second and sixth. However, the need for this ended with gigabit Ethernet as MDI-X became part of the standard, meaning any gigabit device will automatically work with your cables whether they be crossover or straight-through cables.

UTP stands for unshielded twisted pair, but also refers to all the Ethernet cables you generally buy which have a plastic sheath to protect them. UTP cabling does not offer as high bandwidth or as good protection from interference as coaxial or fiber optic cables, but it is less expensive and easier to work with.

Patch Cables - Most standard copper Ethernet cables are referred to as patch cables. However, ordinary phone cords can be considered patch cables, as well as the RCA and HDMI cables that connect a home TV and stereo system together.

Creating Custom Cables

The great thing about copper Ethernet cables is that it is easy to get a long roll of the stuff and cut it to the length you need, before sticking an RJ45 head on each end. You could even just cut your long cables up into shorter ones.

There are many different combinations you can use to wire a category 6 Ethernet cable. However, I like to follow this video which has a diagram at 1:44. It wouldn't matter if you got the head the wrong way round when crimping, as long as you were consistent on both sides of the cable.

Below is the wiring diagram from the video:

Categories

The different categories of cable vary in two key areas, the frequency they operate and the amount of shielding they have. By having better shielding, cables suffer less from crosstalk, and can operate at higher frequencies. However, more shielding also reduce how flexible the cable can be. E.g. you can have very flexible flat category 5 cables, but that is not possible with category 6 cables.

Speeds

  • 5 - up to 100 megabits per second (up to 100 meters).
  • 5e - 1 Gbps up to 50 meters
  • 6 - 1 Gbps up to 100 meters or 10 Gbps up to 55 meters.
  • 6a - 10 Gbps up to 100 meters.
  • 7 - 10 Gbps up to 50 meters using the usual RJ45 socket ends, but up to 100 meters if you use a newer TERA socket which shields the ends..

Whilst it is possible to get 10Gbps on category 6 or higher cables, your biggest problem will be getting the network switches and computer NICs that support such speed. The price difference is huge right now. You may be better off buying used SFP+ fibre-optic cables and NICs on ebay.

Frequencies

  • Category 5 - 100 Mhz
  • Category 5e - 100 Mhz
  • Category 6 - 250 MHz
  • Category 6a - 500 MHz
  • Category 7 - 600 Mhz

References