OSI Model Explained. The Open Systems Interconnection (OSI) model is a conceptual model that describes how data is communicated over a network. It is divided into seven layers, each of which performs a specific function. The seven layers are:
Physical layer: The physical layer is responsible for transmitting raw data bits over the physical network medium, such as copper wire, fiber optic cable, or radio waves.
Data link layer: The data link layer is responsible for framing the data into packets and transmitting them over the physical layer. It also detects and corrects errors that may occur during transmission.
Network layer: The network layer is responsible for routing packets between different networks. It also provides addressing and fragmentation/defragmentation services.
Transport layer: The transport layer is responsible for providing reliable end-to-end communication between applications. It also provides services such as flow control and congestion control.
Session layer: The session layer is responsible for managing and controlling communication sessions between applications. It also provides services such as authentication and authorization.
Presentation layer: The presentation layer is responsible for translating data into a format that can be understood by the receiving application. It also provides services such as encryption and compression.
Application layer: The application layer is responsible for providing network services to applications. It includes protocols such as HTTP, FTP, and SMTP.
The OSI model is a conceptual model, and not all networks implement all seven layers. However, it is a useful framework for understanding how data is communicated over a network.
A user opens a web browser and enters a URL.
The application layer of the web browser sends an HTTP request to the URL.
The transport layer of the web browser segments the HTTP request into packets and adds TCP headers to each packet.
The network layer of the web browser routes the packets to the web server hosting the URL.
The transport layer of the web server reassembles the packets into the original HTTP request.
The application layer of the web server retrieves the requested web page and sends it back to the user's web browser.
The application layer of the web browser displays the web page to the user.
The OSI model is a valuable tool for understanding and troubleshooting network problems. It can also be used to design and implement new network protocols and applications. Checkout full article on OSI Model