Computer Networks: Chapter 3

COMPUTER NETWORKS :CHAPTER 3- Understanding the OSI model

Hello guys, here we are on chapter 3 0f computer networks.Sorry i was
out of town so i coudnt post , anyways in this post i will be
discussing about THE OSI MODEL.
some of you might have heard OSI model.Or you may have heard "this
is a layer 4 function or this layer deals with data packets etc etc".
Anyway its a model and it has layers , each of the layer do things.

m gonna walk you through what OSI model is and wats the concept behind
this and how it is usefull to us in this chapter and next few chapter .

LAYERS

Ok here is the mythical OSI model :

1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data link
7. Physical

(I RECOMMEND YOU TO MEMORIZE THESE LAYERS)

FUNCTION :
suppose you building a house, you just dont get everything and try messing with it.
You have to do it in a ordered way or in phases, and you have specialized people , specialized
equipment to complete it,
in same way OSI model helps us to break down network functions , it helps to understand how network
works.
creates standard for equipment manufacturing.Like in physical layer we deal with hardwares,hubs,
switches,routers,cables.. so manufacturer have to concentrate on physical layer and works according to
standard, dont worry u will understand :)

LAYERS INDIVIDUALLY

• Application layer

ok this is the top layer of the OSI model, now this layer is the most familiar layer becoz this is wat you see.
Any application you use which communicate through ur network like browser , e-mail client or COUNTER STRIKE ..these
all application deals with application layer .
AS SOON AS it starts sending data it passes through presentation layer

• Presentation layer

Accd. to cbt "presentation layer generi-fies the data", this means it formats ur data such that any server you are communicating
with understands your request.
Also this layer has encryption services, more precisely generic encryption services.
then data get passed to session layer

• Session layer

As name suggests , it starts and ends sessions and it keeps sessions separate like you using more than one application which is using your network then which data sud go to which app. this will b decided by session layer

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