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Cisco CCNA Certification The Many Different Kinds Of Switching |
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When you're studying for your CCNA exam, whether you're taking
the Intro-ICND path or the single-exam path, you're quickly
introduced to the fact that switching occurs at Layer 2 of
the OSI model. No problem there, but then other terms involving
switching are thrown in, and some of them can be more than
a little confusing. What is "cell switching"? What
is "circuit switching"? Most confusing of all, how
can you have "packet switching"? Packets are found
at Layer 3, but switching occurs at Layer 2. How can packets
be switched?
Relax! As you'll see in this article, the terms aren't that
hard to keep straight. Packet switching, for example, describes
a protocol that divides a message into packets before they're
sent. The packets are then sent individually, and may take
different paths to the same destination. Once the packets
arrive at the final destination, they are reassembled.
Frame switching follows the same process, but at a different
layer of the OSI model. When the protocol runs at Layer 2
rather than Layer 3, the process is referred to as frame switching.
Cell switching also does much the same thing, but as the
name implies, the device in use is a cell switch. Cell-switched
packets are fixed in length. ATM is a popular cell-switching
technology.
The process of circuit switching is just a bit different,
in that the process of setting up the circuit itself is part
of the process. The channel is set up between two parties,
data is transmitted, and the channel is then torn down. The
circuit-switching technology most familiar to CCNA candidates
is ISDN.
Don't let these terms confuse you. The four different terms
are describing much the same process. The main difference
is that they are occurring at different levels of the OSI
model, and using a different transport method to get the data
where it needs to go.
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNA and CCNP 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”, visit the website and download
your free copies. You can also get FREE CCNA and CCNP exam
questions every day! Pass the CCNA exam with The Bryant Advantage!
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