Three metres short
An electrician measures the straight line from a switch to an office wall socket. It is 30 metres. He buys 30 metres of cable.
The cable has to go up the wall, across the ceiling and down again. He is three metres short. The whole roll is wasted.
Planning a cable starts with two questions: what is it for, and how long must it be?
Key words
| Word | What it means |
|---|---|
| UTP | unshielded twisted pair, a cable of four pairs of copper wires with no metal screen |
| Patch cable | a short cable that joins a device to a wall socket or a patch panel |
| Permanent link | the fixed cable inside the walls between a socket and a patch panel |
| Run | the route the cable takes from one end to the other |
| Slack | a little extra cable kept at each end for mistakes and moves |
| Straight-through | a cable with the same wire order at both ends, to join different kinds of device |
| Crossover | a cable with the pairs swapped at one end, to join two similar devices |
| Category | the grade of a cable, such as Cat 5e or Cat 6 |
| Network | computers and devices joined together so they can share data |
| Router | a device that passes data between networks |
| Ethernet | the common wired way to join devices in a network |
| Channel | the whole path from one device to the other, including patch cables |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can decide what a cable is for and work out how much cable to cut, in whole metres.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
First decide the purpose
Ask three things. What two devices does the cable join? How fast must the link be? Is the cable fixed in a wall or does it move?
The answers choose the category (Cat 5e or Cat 6) and the type (straight-through or crossover). A fixed cable in a wall is a permanent link. A short moving cable is a patch cable.
Purpose chooses the cable
| What you join | Cable type | Why |
|---|---|---|
| Computer to a wall socket | Straight-through patch cable | Different kinds of device |
| Wall socket to a switch | Straight-through patch cable | A switch port expects a device |
| Switch to a router | Straight-through | Different kinds of device |
| Switch to switch, older ports | Crossover | Two similar devices |
| Computer to computer, direct | Crossover | Two similar devices |
| Inside the walls | Solid-core permanent link | It stays still and lasts longer |
The cells students fill in are left blank in this preview.
Modern ports often sort this out
Note
Most modern switches and computers detect the wire order and swap it themselves. Older equipment cannot. You still need to know both types, because the exam asks and old equipment exists.
Quick check
Have a go
Quick check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.