CCNA - OSI Introduction

To understand the Data Communication Process, one has to understand the OSI Layer very clearly. And believe me it helps life time to troubleshoot or understand when there is a problem in Data Communication..

OSI is the acronym for Open System Interconnection. Before networks came into existence, computers could only communicate from the same manufacturers. So the companies either ran a full IBM or DECnet solution. 

OSI was designed by ISO (International Organization for Standardization) in late 1970’s, to break this barrier so that Computers from different manufacturer could communicate with each other.

OSI is a “Layered Approach”, which is a logical representation of how Data Communication should occur.

OSI reference model:

OSI has 7 different layers, divided into two groups, the top 3 layers defines how application within end stations will communicate with each other and with the user. And the bottom 4 layers defines how actually data is transferred.

·         Application Layer (Layer 7)

·         Presentation Layer (Layer 6)

·         Session Layer (Layer 5)

·         Transport Layer (Layer 4)

·         Network Layer (Layer 3)

·         Data Link Layer (Layer 2)

·         Physical Layer (Layer 1)

Well, I know it is difficult to learn the OSI layer in sequence for starters. But there is a very interesting way to remember this. I learnt in this way “Please Do Not Take Sales Person Advice” from Layer 1 to Layer 7

Note: For a Network Admin, the most important part is from Layer 4 to Layer 1, to check when there is a problem in network.

Well, this is the Basic of OSI model, I will describe in greater detail about each layer in my next post.

Thank You.

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