,OSI MODEL
Open Systems Interconnection Model
1. What is the OSI Model?
The OSI Model stands for Open Systems Interconnection Model.
It is a 7-layer conceptual model that explains how data travels from one computer to another
over a network.
In simple words:
The OSI Model divides network communication into 7 different layers, and
each layer has a specific job.
For example, when you send a message to your friend on WhatsApp, many things happen
between your phone and your friend's phone. The OSI model helps us understand those
networking processes step by step.
Why was the OSI Model created?
Different companies used to develop networking systems in different ways. This could make
communication between different systems difficult.
The OSI model provides a common framework for understanding and designing network
communication.
It helps students, network engineers, and developers understand:
● How data travels through a network
● What happens to data at each stage
● Where a network problem might occur
● How different networking protocols work
● How different network devices communicate
The 7 Layers of the OSI Model
The OSI model has 7 layers.
From top to bottom:
, Layer Name Main Function
7 Application Provides network services to applications
6 Presentatio Translates, encrypts, and compresses data
n
5 Session Establishes and manages communication
sessions
4 Transport Provides end-to-end data delivery
3 Network Handles logical addressing and routing
2 Data Link Handles frames and MAC addresses
1 Physical Transmits raw bits through the medium
Easy way to remember the order
From Layer 7 → Layer 1:
APSTNDP
You can remember:
All People Seem To Need Data Processing
Or simply remember:
Application → Presentation → Session → Transport → Network → Data Link → Physical
LAYER 7 — APPLICATION LAYER
What is the Application Layer?
The Application Layer is Layer 7, the highest layer of the OSI model.
It is closest to the user and network applications.
Its job is to provide network-related services that applications can use.
Simple example
Open Systems Interconnection Model
1. What is the OSI Model?
The OSI Model stands for Open Systems Interconnection Model.
It is a 7-layer conceptual model that explains how data travels from one computer to another
over a network.
In simple words:
The OSI Model divides network communication into 7 different layers, and
each layer has a specific job.
For example, when you send a message to your friend on WhatsApp, many things happen
between your phone and your friend's phone. The OSI model helps us understand those
networking processes step by step.
Why was the OSI Model created?
Different companies used to develop networking systems in different ways. This could make
communication between different systems difficult.
The OSI model provides a common framework for understanding and designing network
communication.
It helps students, network engineers, and developers understand:
● How data travels through a network
● What happens to data at each stage
● Where a network problem might occur
● How different networking protocols work
● How different network devices communicate
The 7 Layers of the OSI Model
The OSI model has 7 layers.
From top to bottom:
, Layer Name Main Function
7 Application Provides network services to applications
6 Presentatio Translates, encrypts, and compresses data
n
5 Session Establishes and manages communication
sessions
4 Transport Provides end-to-end data delivery
3 Network Handles logical addressing and routing
2 Data Link Handles frames and MAC addresses
1 Physical Transmits raw bits through the medium
Easy way to remember the order
From Layer 7 → Layer 1:
APSTNDP
You can remember:
All People Seem To Need Data Processing
Or simply remember:
Application → Presentation → Session → Transport → Network → Data Link → Physical
LAYER 7 — APPLICATION LAYER
What is the Application Layer?
The Application Layer is Layer 7, the highest layer of the OSI model.
It is closest to the user and network applications.
Its job is to provide network-related services that applications can use.
Simple example
