Eight wires in the right order
An RJ-45 plug has eight wires. Put them in the wrong order and the cable still fits the socket. The link may not work. It may work slowly with many errors.
Two colour orders are allowed. Pick one, keep to it, and every installer after you will understand your work.
Key words
| Word | What it means |
|---|---|
| Pin-out | the order of the wires on the pins of a plug or socket |
| 568A | one of two TIA/EIA colour orders for eight wires |
| 568B | the other TIA/EIA colour order, the most used in UK offices |
| Straight-through | a cable with the same order at both ends |
| Crossover | a cable with 568A at one end and 568B at the other |
| Pair | two wires twisted together, such as green and white-green |
| Wire map | a test that shows which wire reaches which pin |
| Ethernet | the common way to join wired devices in an office |
| Bidirectional | sending both ways at once on the same pairs |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can write the 568A and 568B orders, say when to use crossover or straight-through, and say which pairs each Ethernet standard uses.
Starter: copper and plugs
Have a go
Starter: copper and plugs
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
The two colour orders
| Pin | 568A | 568B |
|---|---|---|
| 1 | White-green | White-orange |
| 2 | Green | Orange |
| 3 | White-orange | White-green |
| 4 | Blue | Blue |
| 5 | White-blue | White-blue |
| 6 | Orange | Green |
| 7 | White-brown | White-brown |
| 8 | Brown | Brown |
The cells students fill in are left blank in this preview.
A or B: pick one
The two orders differ only by swapping the green and orange pairs. Both are allowed by TIA/EIA. Both are used in the UK and the USA. Some courses call A the American order and B the British one, but sites follow whichever the building already uses.
The rule that matters: use the same one at both ends and at every outlet and panel.
Straight-through and crossover
A straight-through cable has the same order at both ends. It joins different kinds of device, such as a computer to a switch.
A crossover cable has 568A at one end and 568B at the other. It joined two like devices, such as one computer to another. Today most ports sense the cable and adjust, so you seldom need one.
How Ethernet uses the pairs
| Ethernet name | Pairs used | How |
|---|---|---|
| 100BASE-T and 100BASE-TX | 2 of the 4 pairs | One pair sends, one pair receives |
| 1000BASE-T | All 4 pairs | Bidirectional: every pair sends and receives |
| 10GBASE-T | All 4 pairs | Bidirectional, on cable rated for 10 Gbit/s |
| 1000BASE-T1 | One pair | Ethernet over a single twisted pair, for short runs such as in vehicles |
| 1000BASE-SX and LX | Fibre | SX on multi-mode fibre. LX on single mode or multi-mode fibre |
The cells students fill in are left blank in this preview.