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Video - Introducing the OSI Model

Transcript + My Comments

This video by Kevin Wallace introduces the OSI networking model. Keven's videos teach networking in a light conversational way, with emphasis on retaining the information for the purpose of passing the CompTIA Network+ certification exam.

A fundamental concept in the study of networking is the OSI model. OSI stands for Open Systems Interconnect and it's a model of networks that was put together by the ISO (International Standards Organization).

The OSI model is made up of seven different layers and there are different memory aids to help you memorize these layers, and you would certainly want to memorize these for certification.

If we start at the bottom, down at the physical layer, that's layer 1, the physical layer is followed by the data link layer, layer 2, and then we have the network layer at layer 3, the transport layer at layer 4, the session layer at layer at layer 5, the presentation layer at layer 6, and finally the application layer at layer 7.

The trick to memorizing the names of the layers is to memorize the acrostic "Please Do Not Throw Sausage Pizza Away".

Note: In case you didn't know the meaning of the word acrostic (neither did I) from the American Heritage Dictionary: acrostic - a poem or series of lines in which the certain letters, usually the first in each line, form a name, motto, or message when when read in sequence. I guess when studying for the CompTIA Network+ certification exam (or any other exam) it is wise to use lots of acrostics.

The first letters of the acrostic reminding us of:

WordLayer
PleasePhysical
DoData Link
NotNetwork
ThrowTransport
SausageSession
PizzaPresentation
AwayApplication

Of course, this starts at the bottom of the OSI model and goes up. If we prefer to start at the top and go down, we can remember the acrostic "All People Seem To Need Data Processing".

There are a lot of metaphors to explain what goes on at the different layers of the OSI model. The metaphor Kevin prefers is to compare the OSI model to a bookshelf. Kevin points out, that on the bookshelf behind him in the video, he doesn't use one of the shelves, it contains no books.

His point is; you don't have to populate every layer of the OSI model. The OSI model is a REFERENCE model, it doesn't have to apply to every single networking scenario. It's just a general guideline. It was made to apply not just to IP based networks, but also to IPX networks, and Apple-talk network. Kind of a one-size-fits-all model.

More Networking Protocols and Standards:
• X.25 and Frame Relay Overview
• The OSI Application Layer
• IP version 6 (IPv6) Advantages and Implementation
• Comparison of the Layers of the OSI and TCP/IP Models
• Understanding IP Routing
• IPv4 Address Classes
• Classless IP Addressing
• Free eBook: IPv6 Addressing
• Integration of IPv6 with IPv4
• IPv6 Address Auto Configuration

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