What is the OSI Model?: A Comprehensive Guide to OSI Network Layers

Do you know What is OSI model? This blog post will give you all information about OSI Model and 7 Layers that are physical, data link, network, transport, session, presentation, and application.

Updated: 06 Feb, 24 by Susith Nonis 18 Min

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The OSI (Open Systems Interconnection) model operates as a multi-layered framework, serving as a guide for facilitating communication among different systems without any changes to the underlying network. If you want to know what is OSI Model and everything about it, keep along with us!

The Open Systems Interconnection (OSI Full Form ) model is a conceptual framework used to understand and standardize the functions of a telecommunications or computing system without regard to its underlying internal structure and technology. Its purpose is to facilitate communication between different systems by segregating the communication process into seven distinct layers, each responsible for a specific aspect of networking. This layered architecture ensures organized and seamless communication across diverse and complex networks, making it an essential tool in network technologies such as the Internet Protocol (IP). Whether you're involved in cybersecurity, networking, or simply a curious internet user, understanding the OSI model can provide valuable insights into how data is transmitted and managed over networks. In this article, we delve into the intricacies of the OSI model, offering insight into its layers, significance, characteristics, and historical development. Join us as we explore the foundational blueprint that enables interoperability and efficient communication in the digital world.

In the late 1970s and early 1980s, as the world of networking started to evolve, there was a pressing need for a universally accepted model to aid the development and interoperability of diverse systems. Responding to this demand, the International Organization for Standardization (ISO) introduced the OSI in 1984 as a reference model to standardize the functions of a telecommunication or computing system into seven distinct layers. This development aimed to promote interoperability and standard communication protocols among different systems and networks. Its primary aim was to provide an everyday basis for the coordination of standards development for the purpose of systems interconnection.

  • Standardization: 

It allows different networks and systems to understand each other, enabling standardized communication without altering the internal workings of individual designs.

  • Interoperability: 

Hardware and software from different vendors can work together, paving the way for heterogeneous network environments.

  • Modular Development: 

Developers can modify or develop layers independently without disrupting the entire system.

  • Troubleshooting: 

The layered approach simplifies the process of troubleshooting network issues, as problems can be isolated to specific layers.

- Layered Architecture: 

The OSI model is divided into seven distinct layers, each responsible for specific functions.

- Hierarchical: 

The layers have a hierarchical order, with each layer serving the layer above it and being served by the layer below.

- Uniform Interfaces: 

Each layer of the model provides an interface to the layer above and below it.

- Functional Distribution: 

Functions in each layer are clearly defined, ensuring no overlaps in functionalities.

The Open Systems Interconnection (OSI) model operates as a multi-layered framework, serving as a guide for facilitating communication among different systems without any changes to the underlying network. 

The model is compartmentalized into seven distinct layers, each responsible for a specific aspect of networking. 

Beginning at the bottom, the Physical Layer handles the transmission of raw bits over physical mediums like cables. The Data Link Layer creates a reliable link between two connected nodes, managing error detection and flow control. 

The Network Layer is responsible for routing data packets to their destinations across potentially multiple networks. 

As packets move upward, the Transport Layer ensures end-to-end communication, data integrity, and packet sequencing. 

The Session Layer manages the initiation, maintenance, and termination of communication sessions. The Presentation Layer, often dubbed the "translator," deals with data encryption, compression, and conversion to a format understandable by receiving systems. 

Lastly, at the top, the Application Layer interfaces directly with end-users and applications, facilitating communication initiation and user services. This tiered structure ensures organized, seamless communication across diverse and complex networks.

1. Physical Layer: 

Ethernet, USB, Bluetooth, IEEE 802.11 (varieties of Wi-Fi)


This is the most basic OSI layer, concerned with the physical connection between devices. It defines the hardware elements involved, such as cables, switches, and network interface cards.


Data transmission is in the form of electrical impulses or light signals.

Real-life example: 

When you hit 'Enter' after typing the website's URL, the data (in the form of electrical signals) physically travels through the Ethernet cable or as radio waves in Wi-Fi. The components like cables, switches, and your laptop's network card operate at this layer.

2. Data Link Layer: 

ARP, MAC, PPP, Switching


Responsible for creating a reliable link between two directly connected nodes, it handles error detection and controls the flow of data.


MAC addresses (Media Access Control).

Real-life example: 

Your laptop has a MAC address—a unique identifier. The Data Link layer ensures that the data is correctly sent to and received from the router's MAC address using protocols like Ethernet.

3. Network Layer: 

IP (IPv4, IPv6), ICMP, OSPF, RIP, BGP   


This layer decides the best path for data transmission, commonly referred to as routing. It is concerned with data packet forwarding.


IP address.

Real-life example: 

Your data packet is directed to the appropriate destination IP address, which, in this case, would be the IP address of "example.com." This routing, often done by routers using protocols like IP, determines the best path for the data.

4. Transport Layer: 



It ensures end-to-end communication, error recovery, and data flow control. The layer ensures that messages are delivered in the sequence they were sent.


TCP (Transmission Control Protocol).

To gain further insights into how data is reliably transmitted over the internet, enhancing your understanding of the OSI model, delve into our comprehensive article on the TCP protocol, a cornerstone of network communication.

Real-life example: 

You want the website to load smoothly and correctly. The Transport Layer, using protocols like TCP or UDP, ensures data integrity, sequencing, and flow control. For instance, if you're accessing a webpage, TCP ensures all parts of the website reach your laptop for successful assembly and display.

5. Session Layer: 



This layer establishes, maintains, and terminates user connections in a network.



Real-life example: 

This layer establishes, maintains, and terminates the connection to the server hosting "example.com." Think of it as making a phone call (setting), talking (supporting), and then hanging up (terminating).

6. Presentation Layer: 



It translates data between the application and transport layers. It's responsible for data encryption, compression, and translation services.


JPEG, TIFF, and GIF for graphics formats.

Real-life example: 

"example.com" might send data in a particular format (e.g., compressed images). The Presentation Layer manages this data translation, encryption, and compression. It ensures that the data looks presentable (hence the name) and meaningful for the Application Layer.

7. Application Layer: 



This is the layer that directly interacts with end-users. It provides a set of utilities for application programs to access the network.



Real-life example: 

This is the layer at which you directly interact. When you use a web browser to visit "example.com," you're operating at the Application Layer. The browser requests the web page using protocols like HTTP or HTTPS, and the server responds, allowing you to view the content.

In this journey from your laptop to the website's server and back, data moves through each of the OSI model's layers, ensuring a smooth and effective communication process.

What is the OSI Model (Open Systems Interconnection Model)?

1. Modularity: 

Each layer is dedicated to a specific function. This clear division allows each layer to evolve independently without affecting others.

2. Interoperability: 

The standardized nature of the OSI layers ensures that products from different vendors can work together, promoting multi-vendor environments.

3. Troubleshooting Ease: 

By segregating the networking process into distinct layers, it becomes simpler to diagnose and rectify problems. Issues can be isolated to specific layers, streamlining the troubleshooting process.

4. Scalability: 

The clear division into layers means that changes or additions can be made to one layer without needing to alter others. This flexibility ensures that the model can adapt to technological advancements.

5. Uniform Standards: 

Each layer of the OSI model has its own defined protocols and standards, ensuring consistency and compatibility across the networking industry.

1. Complexity: 

The seven-layer structure, while thorough, can be considered complex. This complexity can make the model challenging to understand and implement in certain scenarios.

2. Performance Overhead: 

Handling the functionalities of each layer independently might introduce latency. Data encapsulation and de-encapsulation at each level can result in delays.

3. Not Always Practical: 

Not all networking tasks or protocols fit neatly into the OSI's seven layers. In some cases, particular layers are skipped or combined, making the model less practical for those instances.

4. Historical Redundancy: 

Some argue that certain layers of the OSI model, due to the evolution of networking technologies, are now redundant or can be combined. This leads to debates about its continued relevance in its current form.

5. Competition with TCP/IP: 

The more streamlined TCP/IP model, which combines certain layers of the OSI model, is widely used in real-world applications. This widespread adoption of TCP/IP sometimes puts the relevancy of the seven-layered OSI model into question.

While the OSI model's seven-layered structure offers clarity, flexibility, and standardization, it is not without its criticisms and challenges. However, its conceptual framework remains invaluable for understanding and designing complex network systems.

The Open Systems Interconnection (OSI) model and the TCP/IP (Transmission Control Protocol/Internet Protocol) model are both conceptual frameworks used to understand and standardize the functions of networking systems. However, they differ in various aspects, including their origin, structure, and real-world application. Here's a brief explanation of their differences:

1. Origin and Development:

   - OSI Model: 

Developed by the International Organization for Standardization (ISO) to provide a comprehensive standard for network communications across heterogeneous systems.

   - TCP/IP Model: 

Originated from protocols used in the ARPANET (precursor to the modern internet) and was developed by the Department of Defense. It's based on standard protocols used on the internet.

2. Number of Layers:

   - OSI Model: 

Consists of seven layers — Physical, Data Link, Network, Transport, Session, Presentation, and Application.

   - TCP/IP Model: 

Typically comprises four layers — Network Interface (or Link), Internet, Transport, and Application.

3. Layer Functions:

   - OSI Model: 

Has distinct Session and Presentation layers, separate from the Application layer.

   - TCP/IP Model: 

The functions of the OSI's Session, Presentation, and Application layers are all combined into the TCP/IP Application layer.

4. Adoption and Use:

   - OSI Model: 

More theoretical and comprehensive, used primarily as a reference model.

   - TCP/IP Model: 

More practical and based on real-world usage. It is the model upon which the entire internet is built and operates.

5. Flexibility and Evolution:

   - OSI Model: 

Being a general model, it can adapt to both connection-oriented and connectionless protocols in the Network layer.

   - TCP/IP Model: 

Initially designed around its namesake protocols (TCP and IP), it's more rigid in its layer definitions.

6. Standardization and Implementation:

   - OSI Model: 

Despite its thorough approach, not all layers of the OSI model have been implemented widely or have well-established universal protocols.

   - TCP/IP Model: 

Because it was derived from absolute protocol standards and practices, it's more widely implemented, especially given the growth and dominance of the internet.

In summary, while the OSI model serves as a detailed, theoretical framework for understanding the intricacies of network communication, the TCP/IP model offers a more practical, real-world approach closely aligned with the realities of internet communication.

While the OSI (Open Systems Interconnection) model serves as a foundational framework for understanding network communication, it's essential to explore how it aligns with or differs from modern networking protocols and technologies. In today's dynamic networking landscape, several key developments have shaped the way data is transmitted and managed across the internet. One such example is the emergence of the QUIC (Quick UDP Internet Connections) protocol, which has implications for layers 4 and above of the OSI model.

The Role of QUIC

QUIC, developed by Google and now widely adopted, is a protocol designed to enhance the speed and security of web communication. It operates primarily at the Transport layer (Layer 4) and above, impacting the Application, Presentation, and Session layers. Here's how QUIC relates to the OSI model:

  1. Transport Layer (Layer 4): QUIC's most significant impact is felt at this layer. Unlike traditional protocols like TCP (Transmission Control Protocol), which operates over the Internet Protocol (IP) at the Network layer, QUIC combines transport and encryption, offering a streamlined and secure alternative. This consolidation challenges the traditional separation of concerns between the OSI layers but contributes to improved performance and security.

  2. Session Layer (Layer 5): In the OSI model, the Session layer is responsible for establishing, maintaining, and terminating communication sessions. While QUIC does not directly map to this layer, its efficient connection establishment and management contribute to session-related functionality by reducing latency and enhancing user experience.

  3. Presentation Layer (Layer 6): The Presentation layer deals with data encryption, compression, and format translation. QUIC incorporates encryption as a fundamental component, ensuring data security and privacy. It encrypts both the header and payload, aligning with the OSI model's principles of securing data at this layer.

Contemporary Networking Realities

In contemporary networking, the OSI model's relevance remains strong as a conceptual framework, providing a structured way to understand network communication. However, it's important to acknowledge that modern protocols like QUIC, as well as other innovations in cloud computing, edge computing, and content delivery networks (CDNs), have introduced complexities and optimizations beyond the OSI model's original scope.

These developments underscore the need for a nuanced approach to network architecture and protocol design. While the OSI model remains a valuable tool for understanding the fundamentals of networking, it coexists with evolving technologies that may not neatly align with its seven-layer structure. As such, network professionals must adapt to these changes and consider the model's principles alongside modern realities to design efficient and secure network systems.

In summary, the OSI model offers a foundational understanding of network communication, but the ever-evolving landscape of modern networking protocols, such as QUIC, highlights the need for flexibility and adaptability in addressing contemporary networking challenges.

The OSI model serves as a foundational blueprint for understanding the intricate layers and processes involved in network communication. By compartmentalizing network functions into seven distinct layers, from physical hardware operations to high-level application interactions, its framework demystifies the complexities of data transmission. Although real-world networking primarily operates on the TCP/IP model, the conceptual clarity and systematic approach of the OSI model remain indispensable for network professionals and enthusiasts alike, offering a structured lens through which to view and analyze the multifaceted world of networking.

Deepen your understanding of networking by exploring the intricacies of the OSI model. Apply this knowledge to optimize your network operations and troubleshoot with precision. For additional information please contact us.

The OSI (Open Systems Interconnection) model is a conceptual framework that divides the functions of a telecommunication system into seven distinct layers. It's used to understand and standardize how different networking protocols interact.

The OSI Model consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

The OSI Model provides a standard structure that helps in understanding, designing, and troubleshooting network architectures. It ensures interoperability between products from different vendors and helps in diagnosing network problems.

Typically, yes. Data starts at the Application Layer and travels down to the Physical Layer on the sender's side. It's then transmitted over the network and travels from the Physical Layer up to the Application Layer on the receiver's side.

No, they are distinct models. The OSI Model has seven layers, while the TCP/IP model typically has four. However, both models serve the same purpose: to standardize networking protocols and improve communication between different network devices.

While many modern networks primarily use the TCP/IP model, the OSI Model remains an important conceptual tool for understanding and teaching network interactions.

The Network Layer (Layer 3) is responsible for determining the best path for data to travel across the network, a process known as routing.

HTTP operates at the Application Layer, TCP at the Transport Layer, and IP at the Network Layer.

The Presentation Layer is responsible for data translation, compression, and encryption. It ensures that data is in a readable format for the Application Layer.

Not directly. Devices using different Data Link Layer protocols (e.g., Ethernet and PPP) would typically need a translator or converter (like a bridge or gateway) to communicate.

Susith Nonis

Susith Nonis

I'm fascinated by the IT world and how the 1's and 0's work. While I venture into the world of Technology, I try to share what I know in the simplest way with you. Not a fan of coffee, a travel addict, and a self-accredited 'master chef'.