Mastering the OSI Model: 7 Layers & How It Compares to TCP/IP
Oct 8, 2025
How do things like computers, mobile phones, or servers communicate over a network? It seems big and hard at first, but the OSI model breaks down this entire process into simplistic layers. The OSI model is a means of understanding how data gets transferred from one device to another. It is an essential term for anyone wanting to learn networking or seeking to start a career in IT. In this particular blog, we will try to explain the OSI model in some simple terms, layer by layer, with concrete examples.
In this blog, we’ll walk you through each layer of the OSI model, explain what each one does to make these concepts easy to understand.
What is the OSI Model?
The OSI model, closely tethered to the Open Systems Interconnection model, was developed by the International Organization for Standardization (ISO) and serves as a guide to enable effective communication among diverse computer systems. It breaks down the communication process into seven layers, where each is responsible for a certain task during the data transmission.
The 7 Layers of the OSI Model
Now, on the technical side, we will discuss each of the seven layers, starting from the bottom:
1. Physical Layer
The Physical Layer is the lowest layer in the OSI. It is responsible for the physical connection between two devices and the transmission of raw bits (0s and 1s) through wire cables, wireless, or any other type of medium. The layer converts bits to electrical or optical signals when sending data. When receiving data, signals would also be converted back to bits and passed on to the next layer.
Common devices: Hub, Repeater, Modem, Network Cables (Ethernet, Fiber Optics).
Key functions include:
Bit Synchronization: Providing a clock that synchronizes send to receive bits.
Bit Rate Control: The nominal speed of the actual data sending in bits per second.
Physical Topology: The actual physical arrangement of the participating devices, such as star, bus, or mesh.
Transmission Mode: Type of data flow controls for simplex, half-duplex, and full-duplex classes.
2. Data Link Layer
Data Link Layer controls the transfer of data between devices on the same local area network. This layer converts bits coming from the Physical Layer into frames and adds hardware addresses (usually MAC addresses) to identify the recipient devices.
Common devices: Switches, Bridges.
Key functions:
Framing: The conversion of bits into frames for user-level convenience.
Error Detection: Check for errors in transmitted frames and take corrective actions.
Flow Control: Control the flow of data so the recipient does not get overwhelmed.
MAC Addressing: Use of hardware addresses to direct data within the network.
Access Control: Control when devices are able to send data, especially for network sharing.
3. Network Layer
The Network Layer routes data across the networks. The Network Layer uses logical addressing, such as IP addresses, to determine the optimal path for data packets from the source to the destination.
Common devices: Routers.
Key functions:
Logical Addressing: Issuing IP addresses.
Routing: Finding an optimal route to transmit data.
Forwarding: Forwarding packets from one network to another.
Fragmentation: Breaking up large packets so that they may be transmitted, and then reassembling them once they arrive.
4. Transport Layer
The Transfer Layer guarantees the reliable transfer of data between two devices. It is responsible for segmentation, error-checking, and flow control of data.
Common protocols: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
Key functions:
Segmentation: The Process of dividing the data into segments for transferring.
Error Recovery: Detect transmission errors, such as data loss and corruption, and recover the data.
Flow Control: Controlling the flow of data to prevent congestion.
Connection Management: Setting up and tearing down a connection, meaning it opens and closes communication sessions.
5. Session Layer
The Session Layer is responsible for managing the connections or sessions of computers. It keeps communication sessions open and synchronized to ensure that data is exchanged in proper order.
Key functions:
Session Management: Starts and maintains a record of a communication session.
Synchronization: Places checkpoints for recovering from failure.
Session Termination: Ending the session after completion of the communication.
6. Presentation Layer
The Presentation Layer is responsible for translating different data formats so that the receiving systems understand what information is transferred. Encryption and/or compression mechanisms may be applied here.
Key functions:
Data Translation: Converts data from one format to another (e.g., ASCII to binary).
Encryption: Protecting the data before transmission and decrypting it at reception.
Compression: Decreases the size of the information for quicker transmission.
7. Application Layer
The Application Layer is the layer that interacts directly with the users. It provides end-user services like email, web browsing, and file transfer over various protocols.
Common protocols: HTTP, FTP, SMTP, and DNS.
Key functions:
Network Services: Application support for the web browser and email clients.
Resource Sharing: For shared files and printers.
Remote Access: Users are allowed to connect to computers or services from any remote location.
How Layers Work Together
The transmission of data across the network starts with the Application Layer and traverses through all the other layers until it reaches the Physical Layer. Following this series of layers, the data is then transmitted through the network. The layers that will filter information relative to their respective protocols receive the data on the other end, and finally, the Application Layer returns it to them.
The OSI Model and TCP/IP Model: Key Differences
Indeed, the two frameworks, the OSI model and TCP/IP model, are popular models that explain data traveling across a communication network, but with different structural frameworks and real-world usage.
The OSI model comprises seven layers, namely Physical, Data Link, Network, Transport, Session, Presentation, and Application. This model was meant to be theoretical in nature so has standardized the communication within networks so that any layer would not perform a certain well-defined duty.
On the other hand, there are 4 layers in the TCP/IP model: Link, Internet, Transport, and Application. TCP/IP was devised on the basis of practically laid protocols on the internet and further merges some layers of the OSI model into broader categories. For example, TCP/IP groups OSI's Session and Presentation layers into the Application layer.
OSI Model Layers | TCP/IP Model Layers |
|---|---|
Application, Presentation, Session | Application |
Transport | Transport |
Network | Internet |
Data Link, Physical | Network access |
TCP/IP, on which the modern-day internet is based, is widely used in present-day real networks, while OSI remains a model that can be used by people to teach themselves the theoretical concepts involved in network connectivity.
A good knowledge of both models provides the user with excellent grounding in networking concepts and applies these concepts to real-world systems.
Real-Life Examples
Sending e-mails goes through three different levels of the TCP model: SMTP in the Application Layer, TCP in the Transport Layer, and IP in the Network Layer.
Accessing a website mainly relies on HTTP (Application Layer) and TCP (Transport Layer).
Video conferencing depends on the Session Layer to keep sessions alive and the Transport Layer for reliable transport of data.
Conclusion
Mastering the OSI model is the key to succeeding in networking, whether you are a beginner to networking or you are an aspiring network engineer. The OSI model is great for understanding how networks work. It divides network communication into seven layers, thereby providing a good framework for troubleshooting, designing, and managing networks.
