The Open Systems Interconnection (OSI) Model

This is the layer closest to the end-user. It provides network services directly to applications, such as web browsers or email clients. Protocols like HTTP, FTP, SMTP, and DNS operate here.

Often referred to as the "translator" of the network, this layer ensures that data from the application layer is in a format that the receiving system can understand. It handles encryption, decryption, and data compression.

This layer establishes, manages, and terminates connections between applications. It coordinates the "dialogue" between two devices, ensuring that data exchange is synchronized and resumed if a connection is interrupted.

The transport layer is responsible for end-to-end communication and error recovery. It segments data from the upper layers and manages flow control. Major protocols at this layer include TCP (which ensures reliable delivery) and UDP (which prioritizes speed).

This layer determines the best path for data to travel across different networks. It handles logical addressing (IP addresses) and routing, ensuring that packets arrive at the correct destination.

The data link layer provides node-to-node data transfer. It is responsible for physical addressing (MAC addresses) and detecting errors that may have occurred in the physical layer. Switches operate primarily at this level.

The foundation of the model, this layer defines the physical specifications of the network. This includes cables, hubs, repeaters, and the transmission of raw bit streams over a physical medium, such as copper wires, fiber optics, or radio waves.