OSI Model Explained: 7 Layers, Functions, and Importance in Networking

 The   OSI   reference   model

Introduction:

The OSI (Open Systems Interconnection) Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. Developed by the International Organization for Standardization (ISO), the OSI model helps different systems communicate with each other across a network.

Whether you're a beginner in computer networking or preparing for exams, understanding the OSI model is essential. Each layer of the model plays a specific role, from handling physical connections to ensuring data reaches its destination reliably.

The OSI (open system interconnection) model has seven layers.

Order	Layer
1.	Physical layer It is concerned with transmitting raw bit. To define the type of encoding i.e., how 0’s and 1’s are changed to signals. To define the transmission rate. To decide whether the transmission is simplex, half duplex or full duplex. To define voltages and data rates needed for transmission.
2.	Data link layer It is concerned with frame The main function of data link layer are; data transfer, frame synchronization, flow control, error control, addressing, link management
3.	Network layer The network layer act as a network controller to routing data. It is concerned with packet of data It is concerned with circuit, message or packet switching. Router and gateways operate in the network layer.
4.	Transport layer Ensures that packets are delivered error free, in sequence and no loss or duplication. It provides error free transmission of data from one computer to another computer. Transport layer guarantee transmission of data from one end to other end. It does the function such as multiplexing, splitting or segmenting of the data.
5.	Session layer It controls logging on and off, user identification, billing and session management.
6.	Presentation layer The presentation layer is concerned with the syntax and semantics of the information transmitted. The form and syntax (language) of the two communicating systems can be different e.g. one system is using the ASCII code for file transfer and the other one uses IBM’s EBCDIC. The presentation layer provides the translation from ASCII to EBCDIC and vice versa.
7.	Application layer       o   The application layer contains       a variety of protocol that is         commonly needed by users such         as HTTP, file transfer,               electronic mail, and network           news. The functions of such as LOGIN, or password checking are also performed by the application layer.

Importance of the OSI Model

• Provides a universal language for networking
• Helps troubleshoot network issues efficiently
• Allows interoperability between different hardware and software systems

To better understand how networks work in real life, check out our post on the TCP/IP Model.