Learning by Doing: CISCO Certified Network ... - SCN Research

Paper Lab: OSI Model and Encapsulation
Objective:
To be able to learn more about the OSI model, its layers, and their descriptions.
Tools and Materials:
Paper and pencil
Background:
In your textbook you have learned about the layers of the OSI model, what happens on
each layer, and descriptions of each layer. You probably took the time to memorize
exactly the definitions of each layer. I got news for you…on “the” test the definitions are
completely different from the ones in the book. Wouldn’t it be nice if they did something
consistent for once? Actually the definitions are similar, just completely worded
differently. So here we will look at the definitions you were told and try to create some
alternate wordings. Your test will probably have something like a drag and drop scenario
for it so we will just use simple matching exercises here.
The OSI Model
There are seven layers in the OSI model. From bottom to top we number them from
layer 1 to layer 7. They are the: physical, data link, network, transport, session,
presentation, and application layers.
The reason we need to understand which layer is which number is to be able to decipher
sales brochures. Sometimes they refer to layer 2 devices, of which we could think
“bridges.”
As a memory device we can remember from the top down that All Presidents Seem To
Need Data Processors or “All People Seem To Need Domino’s Pizza.” There are other
mnemonic memory devices like something about taking spinach pizza always, but these
seems to work best for most people
Let’s take a brief look at each layer:
Application
Presentation
Session
Transport
identifies and establishes the availability of intended communication
partners, synchronizes cooperating applications, and establishes agreement
on procedures for error recovery and control of data integrity. “browsers”
translates multiple data representation formats by using a common data
representation format. “concerned with data structures and negotiation data
transfer syntax” “encoding, representation of data, ASCII”
synchronizes dialogue between presentation layer entities and manages their
data exchange. Information is encapsulated into data blocks here.
Responsible for reliable network communication between end nodes and
provides transport mechanisms for the est., maintenance, and termination of
virtual circuits, transport fault detection and recovery and information flow
control.
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