Copper Twisted Pair

You're going to see a lot of twisted pair out there, so let's talk about some of the components of twisted pair and get really familiar with it.

Jacket and shielding

First of all, it does have a jacket, just like coaxial does. We see that it has a shielding that goes around it. But not all twisted pair has shielding. You have essentially two different categories: you've got shielded twisted pair, or STP, and you've got unshielded twisted pair, or UTP. The more common out of the two actually is UTP. So we see a shielding on this particular example, but that doesn't necessarily mean that it's on all cables.

If you have the shielding, it also has this extra little cable that runs through it. It's a conductor. It's not insulated at all, it is just running along that shielding, and it helps ground that out. That's actually what you would run out to your rack or something else that's grounded, and you would ground it out, so that's what would protect these conductors so that way you have less interference.

The rip cord

One other thing that you'll see every once in a while — a lot of the cables will have this rip cord. It's an extra little thread that comes out of the jacket, and what it's used for is to take off a big chunk of that jacket. Meaning that you can grab hold of that and pull on it, and it will slice down the jacket lengthwise, and then you can peel that back and cut it off. So it's a quick and easy way to take the jacket off of a large section of this cable.

The core

The other thing that we see here is we've got this center little core to this. Not all of your twisted pair is going to have that either. The core right there looks like a little plus sign inside of this cable, and it's separating out our four pairs. We can see our four pairs here. That will be inside of some of your cables, but not necessarily all of your cables.

The pairs

Let's get into the pairs. As we see right here, we actually have eight different conductors — in the middle of each one of these lines is a conductor. And we break those conductors into pairs, so they're grouped into four pairs.

Each one of those pairs, one of them is essentially a ground for the pair, and then one actually transfers the data of the pair. We can see that they're also color-coded. Each one of these has a jacket in itself, or an insulator in itself, so it's not all grounding itself out against the other ones. They all have these insulators to it, and the conductor is in the middle.

We see here that this is a white cable with an orange stripe that's running down it, and this is an orange cable. So this is the orange pair, and it consists of a white orange and an orange. Then the green: we have a white green and a green. And the blue: we have a white blue and a blue. And the brown: we have a white brown and a brown. So for each of the conductors, that's how we identify which one is the data and which one is the ground, and which ones are paired together.

Those are the different pairs of this, and it's going to transfer the data. So we have four different pairs on this line.

Connectors

Typically with twisted pair we're not running it directly from device to device, where we have to go and wire these things up. We usually have connectors on the end of these, and the connectors are usually the same connector.

There are a lot of different types of connectors that we can put on the end of twisted pair, but the one that we're most concerned with, and that you'll see on the majority of the equipment out there, is the RJ45. This is a registered jack 45, and it defines what the dimensions of this end is, and the conductors, and the pinouts of these conductors. So the RJ45 is the connector here at the end.