OSI Model

What is OSI Model? 

According to Wikipedia, Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.

Why OSI? 

Let's imagine a situation where you have a bunch of Network equipment from Brand A (It's a top brand and expensive) for your company. After few years you have decided to expand your business and need to set up another office and when you conduct a market research you find that there is another brand Brand B which is cheaper than Brand A.

Things to note
1. Brand B is cheaper than Brand A
2. Brand B is new in the market and Brand A is the leader in the Market.

However you want to try using Brand B. As a consumer, you have the right to choose which brand you want to use. At this point, you find that you cannot use Brand B as Brand A does not support any other brand in the network. Hence, you are forced to buy Brand A for your new branch so that you can connect both the branches.

To avoid this kind of situation, ISO (International Standardization organization) came up with OSI Model which standardizes the communication function of a device irrespective of its technology. This helps in achieving interoperability between two different Brands.

DIfferent Layers of OSI Model:

OSI Model Consists of Seven different Layers. They are
7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Data Link
1 - Physical

OSI Layer is divided into 2 portions namely Hot layers and Media Layers.
Hot Layers consists of layer 7,6,5,4
Media Layers consists of layer 3,2,1