Saturday, 31 March 2018

osi model layers explanation

OSI Model Layers Explanation

Today our topic is important and interesting OSI Model layers explanation. Why this is important and interesting ? because of this is era of internet, The working principle of internet is based upon this OSI Model layers explanation.
Whenever we transfer any data like text, picture,video from one computer to the other computer this OSI Model layers is used. Nothing is seen but all the OSI model layers work in the system, So to Know about this is interesting.
Now lets start to understand OSI model layers and its working principles. 

What is OSI Model Layers ?

OSI (open system interconnection) is a reference model for how applications communicate over a network.

The purpose of the OSI model reference model is to guide hardware making vendors and software developers so the digital communication products and software program can inter operate, And provide a clear facility framework, Which describe the function of networking or telecommunication system.
See the below OSI model different layers, We will discuss one by one each layers functionality.
osi model layers explanation,osi reference model

                                                   OSI Model Layers Explanation  

You may be learn before this OSI model layer, may be also forget forever because your concept not cleared . But today we will learn OSI model layer such that, You will never forget. Hence we will learn OSI model layers with the help of a story.

OSI Reference Model story  

Well this is a reference model of seven different layers. This model is not implemented but we have taken OSI model reference to implement TCP/IP.
As told seven layers, Then question arises that which layers is consider as first layer, So for this it depend upon the Sender and Receiver.
If you are on sender side then your first layer will be Application layer because you will first touch the application layer.
If you are on receiver side then first layer will be Physical layer because to receive information first Physical layer is touched as shown in above figure.

To remember easily OSI reference seven layers model ,You can remember this phrase.
" All people seems to need data processing " .

Now we will try to understand OSI reference seven layers model by story, So suppose we have company of seven employee description as below.


Now some more details about all person work responsibilities, just read the story. 

osi model layers explanation,osi reference model

1 Andrew is CEO of the company, He know French language, Now he told Parwez i have 400 pages has to send other company xyz CEO need to deliver by today evening try best to deliver by evening and ensure.

2 Parwez told CEO ok will send and taken 400 pages, Then Parwez saw that all 400 pages are written in French language, But the other company xyz CEO is Indian and know English language only, Then Parwez translated this pages into English language, And now handed over 400 pages to Suresh and told this is important document need to deliver today urgent make sure no any mistake otherwise we will lost our job it is instruction of boss CEO.

3 Suresh  Now Suresh taken 400 pages and seen, where to go this document ok coming from Delhi and to go Mumbai. Now Suresh first called other company xyz same level Employee and asked today your company is open, Other company Employee told yes open, Then Suresh told ok i am sending some document to you after received, Please call me to inform, You have got the document ( In figure you can see dotted line shown ), Then other company xyz Employee says ok will inform you no problem.Then Suresh handed over document to Tanveer.

4 Tanveer  Received 400 pages and think that 400 pages are very important if i will send in a single bundle and by any means if bundle is lost then all document will lost this is danger, So he make four bundle of 100 pages each and given number 1,2,3,4 serially, And thought if by any means one bundle is lost, At least 3 bundle will deliver. Now handed over to Naveen.

5 Naveen Received 4 bundle and attached address From and To on each bundle and suggested  to driver the free route short distance to go fast and deliver timely, and finally handed over to Dinesh.

6 Dinesh  Received 4 bundle and checked all envelop are good address is also there, But envelop is open anyone can read this confidential document. Then Suresh fixed all four bundle with feviquick and sealed the enveloped with confidential documents round sealed such that if anyone try to open the document it will be recognize someone has open document and handed over to Pawan as saying that Naveen has informed you through  which route you have to go, you will follow that route and deliver this document fast.

7 Pawan  Received document and carrying this document and reaches to same level employee in other company xyz and handed over document.
Other company next level employee received and checked that document ok it is sealed means data is ok. Now this employee handed to next level now this checked four bundle and combined together and handed over to next level. 
Now next level employee received document and called to Suresh hi i have received your document now you not need to take tension, Then Suresh OK thank you now dotted line connection is break. Now document is delivered either other company xyz CEO read the document or not read the document, But data has been delivered work completed.

How OSI model work ?    

Application Layer

All software and app work, gmail, yahoo, facebook work on Application layer, its work is to provide user interface like when you open word, excel, note pad with the help of MS word, Hence user work at Application layer.

Presentation Layer

Encryption and decryption for example take two files Physics.mp3, Physics.doc, Physics.jpge, Now i ask you when we will open the Physics.mp3 it will open in vlc media where as when we open physics.doc it will open in ms word . So it is work of Presentation layer to how data will be represented.

Session layer

This is called end to end layer unless data is not delivered it will be in touch with receiver session layer. If data is lost it will display message data is not sent for example. 
When you send mail and if mail is not delivered the you get a message mail is failed and if mail is delivered then you get message mail is sent .
Hence session layer work end to end this is work of session layer.

Transport Layer

Segmentation is done by transport layer. here it is also important at this layer two protocol work TCP/UDP .
TCP is transmission control protocol and UDP is user data protocol.

Network Layer  

Routers work on this layers, find the route to deliver data work on IP addresses, Route is decided at this layer through which route data will be sent.

Data Link layer 

Added error detection and correction capability and also flow control work done by data link layer.

Physical Layer 

At Physical layer data is converted into bits binary and transmitted through medium wire copper , fiber or wireless and data delivered at receiver end.

Top three layers Application, Presentation, Session work on software where as bottom three layers Physical, Data link , Network work on hardware. 
And most important Transport combine these two software and hardware together.

Now we will continue next topic in next post .I hope you have enjoyed learning OSI Model Layers Explanation by story. If you like comment and share, Thanks for reading and sharing, keep reading more and more.       

Dated 28th Oct 2018              

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