Copper Termination Standards – CompTIA Network+ N10-007 – 2.1

Copper Termination Standards – CompTIA Network+ N10-007 – 2.1


The type of copper cables
you use on your network is important. But also the termination of
those cables is important. That’s why before
implementing a new network, it’s always good to
grab a cable tester and make sure that
all of your cables have been terminated correctly. These cable testers are
relatively inexpensive and they can quickly
show you exactly the way the cable is mapped from
one end of the connector to the other end. And if you’re not familiar with
running cables and terminating the ends, you may want to look
into getting a professional who really knows the nuances of
making your cable installation work perfectly. Like most things in
networking, there is a standard for
terminating cables. You can, of course, look at
the EIA/TIA-568-B standard that shows you exactly how to
terminate eight conductor 100-ohm balanced
twisted pair cabling, which is exactly the cabling
we use on today’s networks. You have the choice of two
different standards when you’re terminating copper cables. One is the T568A and
the other is the T568B. These are two different
termination standards. So you would
usually pick the one that you’d like to use and stay
with that termination standard throughout the installation
of your cables. Some people will use
certain types of pin outs depending on how they’re
running these cables. For example, if you’re running
cables on a single floor, some people prefer to
use T568A as the pin out for all your
horizontal cabling. But some organizations
prefer using 568B. It really doesn’t matter
which one you use, as long as you stay consistent. You do not want to terminate
one end of the cable with 568A and the other end with 568B. You will run into
problems, especially on a gigabit network. If we were to look at
all of the different pins inside of an RJ45
connector, and if we look at this from the
bottom of the connector, those pins are
numbered 1 through 8. Each one of these standards uses
slightly different pin outs. You can see on
the 568A standard, pin one is white and green
and pin two is green. You can see in
the 568B standard, it’s white and orange, and
orange for pins one and two. So notice the green
and the orange are different between
the 568A and the 568B. Fortunately, pins
four and five, which are blue and white and blue
and pins seven and eight, which are white and brown
and brown, are identical between 568A and 568B. You should be able to look at
the bottom of an RJ45 connector and see exactly how it
happens to be terminated. You can see we’ve got white,
orange, orange, white, green, a blue, a white blue, a green,
a white brown, and a brown. So this would be a
568B termination. And on the other end of
a straight through cable, we want to be sure that we’re
also terminating it with 568B. If we’re connecting a
workstation to a switch, then we’re usually using
a straight through cable. This is where pin one
is connected to pin one. Pin two is connected to pin
two, pin three to pin three, and so on, all the
way through pin eight. This is also called
a patch cable. And it’s one of the most common
ethernet cables you run into. If you have ethernet cables
connecting your equipment and you disconnect those
and look at the ends, you’ll see that
all of the pins are connecting straight through
from one side to the other. If we need a straight through
cable for 10BASE-T, which is a 10 megabit ethernet
network, or a 100BASE-T, which a hundred megabit
ethernet network, this straight through
cable only needs two pairs. So there’s four wires
inside of the cable that are used for these
specific ethernet standards. You can see pins one and two
on a network interface card are your transmit pairs. And if you’re looking
at a network switch, pins one and two are
the receive pairs. And we’re running straight
through from transmit to receive for
those two devices. The straight through cable
is a little different when you look at
gigabit ethernet, which has 1000BASE-T. This
straight through cable is going to use all four
pairs inside of the cable. And you’ll also notice
there’s no dedicated transmit and receive pairs. Instead, you’re able to both
send and receive traffic through a 1000BASE-T
connection on the same wires at the same time. This is a lot different
than dedicating a transmit and receive. And instead, we’re able to
send traffic in both directions simultaneously. If you need to connect
like devices to each other, you would not use a
straight through cable. In those cases, you’d
use a crossover cable. So if you’re connecting a
workstation to a workstation, you need a crossover. If you’re connecting
a switch to a switch, you need a crossover cable. You can see the pin outs
on a crossover cable are a lot different
than a straight through. We’re no longer going
from pin one to pin one. We’ll go from pin one to
pin three, and pin two to pin six, and so on. If you are connecting like
equipment to each other, you may find that you don’t
need to perform the crossover inside of the cable. Instead, you can perform the
crossover inside of the device that you happen to be using. This is called auto-MDI-X. And
this is something very common on the internet cards
inside of your workstations, your servers, your routers,
and all other ethernet devices. The device will examine
the incoming signal and make a determination
on whether it should act as a straight through
signal or as a crossover, and will make that change
in the ethernet card itself. One thing you’ll notice
with this crossover cable is that one side of this is
not 568A and the other side of this 568B. Ethernet crossover does not deal
with 568B or 568A standards. The ethernet
crossover is something very specific to
the way ethernet connects to each other. And it’s not related to
a termination standard. Visually, for a 10 megabit
and 100 megabit ethernet where we’re using two
pair, this is the way the crossover cable would look
when we’re going from pin one to pin three and
pin two to pin six. If we look at an ethernet
crossover cable for 1000BASE-T, or gigabit ethernet, you can
see that we maintain the pin one to pin three and pin
two to pin six so that we have backwards compatibility. But you can see
we’re also crossing over pins four and five
and pins seven and eight.

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