Have you ever heard of The OSI Model or The Open Systems Interconnection ? Maybe if you've ever heard of that but still have no idea about its meaning or if you've never heard of that but want to learn more about it, then you are in the right place . WELCOME!! We are here to discuss about The OSI Model, where it originates from and how it works.

WHAT IS OSI MODEL ?

According to Mr.Wikipedia OSI Model is...

The Open Systems Interconnection model (OSI model) is a conceptual model that characterises and standardises the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard communication protocols.

OSI is basically a standard used to systematize on how data is transferred from a computer to another computer through a network using the same protocols. Picture above shown The OSI Model in burger layers .

THE 7 LAYERS OF OSI MODELS

OSI Model Layer	Description
7 - Application	The application layer contains protocols used for process-to-process communications.
6 - Presentation	The presentation layer provides for common representation of the data transferred between application layer services.
5 - Session	The session layer provides services to the presentation layer to organize its dialogue and to manage data exchange.
4 - Transport	The transport layer defines services to segment, transfer, and reassemble the data for individual communications between the end devices.
3 - Network	The network layer provides services to exchange the individual pieces of data over the network between identified end devices.
2 - Data Link	The data link layer protocols describe methods for exchanging data frames between devices over a common media
1 - Physical	The physical layer protocols describe the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical connections for a bit transmission to and from a network device.

Source:Cisco

Easy explanation about 7 Layers of The OSI Model

APPLICATION

PRESENTATION

SESSION

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

PROTOCOLS

According to CISCO ...

Sending a message, whether by face-to-face communication or over a network, is governed by rules called protocols. These protocols are specific to the type of communication method being used. In our day-to-day personal communication, the rules we use to communicate over one medium, like a telephone call, are not necessarily the same as the rules for using another medium, such as sending a letter.

Meanings , every layer of OSI model must have protocols . It can be many protocols in one layer of OSI model .Examples are shown below .

PDU

Stands for "Protocol Data Unit." A PDU is a specific block of information transferred over a network. It is often used in reference to the OSI model, since it describes the different types of data that are transferred from each layer. The PDU for each layer of the OSI model is listed below.

Layer Name	Protocol Data Unit (PDU)
Physical	raw bits (1s or 0s) transmitted physically via the hardware
Data Link	a frame (or series of bits)
Network	a packet that contains the source and destination address
Transport	a segment that includes a TCP header and data
Session	the data passed to the network connection
Presentation	the data formatted for presentation
Application	the data received or transmitted by a software application

ENCAPSULATION/DE-ENCAPSULATION

This tutorial explains data encapsulation and de-encapsulation in detail with examples. Learn how data is encapsulated and de-encapsulated when it passes through the layers of OSI and TCP/IP models.