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Understanding the OSI Model: The 7 Layers of Network Communication Explained

Introduction:

The OSI Model (Open Systems Interconnection Model) is a fundamental framework that helps us understand how data travels across a network — from one device to another. It divides network communication into seven distinct layers, each with specific functions and responsibilities. Whether you're studying for the CCNA, starting your networking career, or simply trying to understand how data moves through a network, learning the OSI model is essential.


1) OSI Layer?

• OSI model called as Open Systems Interconnections models.

• OSI provides a standard for different computer systems to be able to communicate with each other.

• Network functions are divided into 7 Layers.


2) List of the OSI Layer?

🔹 Layer 7 >> Application Layer

🔹 Layer 6 >> Presentation Layer

🔹 Layer 5 >> Session Layer

🔹 Layer 4 >> Transport Layer

🔹 Layer 3 >> Network Layer

🔹 Layer 2 >> Data Link Layer

🔹 Layer 1 >> Physical Layer


3) Function of each Layer?

VII) Application Layer - The application layer is used by end-user software such as web browsers and email clients. It allows software send and receive the information and present meaningful data to user.

A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS)

VI) Presentation Layer - The presentation layer's job is to translate between application and network formats (encode, encrypt, and compress).

Example: sender has transferred the data as encryption format and receiver will receive the data as decryption format.

V) Session Layer - Session layers controls dialogues (session) between communicating hosts.

It establishes, manages, and terminates connections between the local application. (Example: web browser) and the remote application (example: YouTube).

Example: YouTube's servers are being used by countless people at every moment and there must be a way to manage all these sessions. That's the purpose of session layer of the OSI model.

IV) Transport Layer - The Transport layer provides host-to-host, end-to-end or process-to-process communication for applications.

It Breaks large piece of data into smaller segments which can be more easily sent over the network and are less likely to cause transmission problems if errors occur.

Example:

➤ if you're watching the video on online and this data was not segmented means if any error occurred in the video data, you wouldn't be able to continue to watch the video.

➤ If the Video data is segmented into many small units and if any error occurred in one unit means the video might skip for a second and then you can be able to watch continuously.

iii) Network Layer - Network Layer provides connectivity between end hosts on different networks. It provides logical addressing (IP Addresses) to route packets to a destination node.

Example - Routers are working in Layer 3

ii) Data Link Layer - Data Link Layer provides node-to-node connectivity and data transfer. Switches operate in Layer 2.

Example: direct connections between PC to Switch or switch to router or router to router.

i) Physical Layer - The physical layer is responsible for the physical cable or wireless connection between network nodes.

Digital bits are converted into electrical for wired connections or radio for wireless connections.


Conclusion:

The OSI model provides a clear structure for understanding how networks operate — from the physical transmission of bits to the presentation of data to users. Each layer plays a critical role in ensuring communication is efficient, secure, and reliable.

By mastering these seven layers, network engineers can troubleshoot issues faster, design efficient networks, and understand data flow from end to end.

> Remember: OSI may be theoretical, but its principles are the foundation of every modern networking device and protocol used today.

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