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Cisco CCNA Certification Exam Tutorial: The OSI Model's Physical Layer |
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To pass your CCNA exam and earn this coveted certification,
you've got to master the seven layers of the OSI model and
what each layer does. For those of you taking the two-exam
path, you can expect quite a few OSI model questions on the
Intro exam. In this seven-part series, we'll spend some time
taking a look at each of the OSI model layers, starting with
the Physical layer.
Often, CCNA candidates ask if the OSI model has any practical
uses for network administrators. I used to wonder the same
thing, and I can now tell you that the answer is definitely
yes!
The OSI model isn't something you want to memorize and then
forget about, as using the OSI model gives you a structured
approach for troubleshooting. Whenever a network device isn't
working properly, I always say to "start at the physical
layer". The Physical layer is Layer One of the OSI model,
and this is where troubleshooting should always start. Is
the device on? Is it properly connected? If everything is
fine at Layer One, you just move up to Layer Two, and continue
in this structured fashion until the problem is identified.
The Physical layer is the layer at which bits are transmitted
over the physical media. There is no routing or switching
going on at this layer. The data has been broken down into
more manageable pieces until the data takes the form of ones
and zeroes at the Physical layer.
Even though there's no routing or switching at the Physical
layer, CCNA candidates should be familiar with a couple of
network devices that work at Layer One. A repeater is a device
that regenerates an electrical signal, allowing the signal
to travel longer distances without fading. (The process of
an electrical signal gradually fading in strength over distance
is "attenuation".) A hub is basically a multiport
repeater, and both of these devices are considered Physical
layer devices. Ethernet and Token Ring both operate at the
Physical layer as well.
Learning the OSI model's Physical layer isn't just important
in your CCNA exam studies, it's the first step in any network
troubleshooting. After all, your network's end users are going
to have a tough time sending print jobs to a printer that's
turned off!
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNP and CCNA tutorials, The Ultimate CCNA Study
Package, and Ultimate CCNP Study Packages. For a FREE copy
of his latest e-books, “How To Pass The CCNA” and
“How To Pass The CCNP”, just visit the website!
You can also get FREE CCNA and CCNP exam questions every day!
Pass the CCNP exam with The Bryant Advantage!
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