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Cisco CCNA Certification: The (Many) Different Kinds Of
Switching |
By:
Chris Bryant, CCIE #12933 |
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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.
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Article Source: http://www.powerdirectory.net/articles/article51521.html |
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