The OSI model
Tags: networking
Published: 2023-05-04 07:42:45

### Introduction

The Open Systems Interconnection (OSI) model is a conceptual framework used to describe the functions of a computer network.

![OSI Meme](https://img-9gag-fun.9cache.com/photo/aNg16Lr_460s.jpg)

The Open Systems Interconnection (OSI) model has `seven` layers, each of which serves a specific function in the communication process. A common way to remember the seven layers and their purposes is with the acronym "**All People Seem To Need Data Processing**." The first letter of each word corresponds to a different layer, starting with the bottommost layer and working up:

A: Application

P: Presentation

S: Session

T: Transport

N: Network

D: Data Link

P: Physical

Another way to remember the layers and their purposes is with the phrase "**Please Do Not Throw Sausage Pizza Away,**" which follows the same pattern as the first acronym. The layers are often referred to by their corresponding numbers, with the physical layer being layer 1 and the application layer being layer 7. Or you can come up with your acronym. Here's another one - **Please Do Not Teach Stupid People Acronym.**

### Application Layer - #7

The application layer is used by end-user software such as web browsers and email clients. It represents the level at which applications access **network services**. This layer represents the services that directly support applications such as software for file transfers, database access, and electronic mail.


### Presentation Layer - #6

The Presentation layer translates data from the Application layer into an **intermediary format**. This layer also manages security issues by providing services such as data encryption and compresses data so that fewer bits need to be transferred on the network.

### Session layer - #5

The Session layer allows two applications on different computers to **establish, use, and end a session**. This layer establishes dialog control between the two computers in a session, regulating which side transmits, plus when and how long it transmits.

### Transport layer - #4

The Transport layer handles **error recognition and recovery**. It also repackages long messages when necessary into small packets for transmission and, at the receiving end, rebuilds packets into the original message. The receiving Transport layer also sends receipt acknowledgments.

### Network Layer - #3

The Network layer addresses messages and **translates logical addresses and names into physical addresses**. It also determines the route from the source to the destination computer and manages traffic problems, such as switching, routing, and controlling the congestion of data packets.

### Data link layer - #2

The Data Link layer **packages raw bits** from the Physical layer **into frames** (logical, structured packets for data). This layer is responsible for transferring frames from one computer to another, without errors. After sending a frame, it waits for an acknowledgment from the receiving computer.

### Physical Layer - #1

The Physical layer **transmits** bits from one computer to another and **regulates** the transmission of a stream of bits over a physical medium. This layer defines how the cable is attached to the network adapter and what transmission technique is used to send data over the cable.

### Conclusion

This partition into ‘lower’ and ‘upper’ layers is a widely used way to distinguish between the communications-oriented layers and the applications-oriented layers. Layers 5 and 6 are often ignored in practical applications (the Internet protocol hierarchy has no equivalents to layers 5 and 6). The OSI model is a critical framework providing a standardized approach for computer networks to communicate.

I hope you have learned something new. If you have any funny acronyms, share them in the comment. Thank you for giving my article a read.