CompTIA Network+ (N10-008) - Network Infrastructure & Security

The OSI model provides a conceptual framework for how network communications should function, dividing network communication into seven distinct layers to standardize protocols and facilitate interoperability between different systems.

The Application Layer is the closest to the end user, providing network services directly to end-user applications. Examples include HTTP, FTP, SMTP, and DNS.

The Presentation Layer handles data formatting, encryption, and compression to ensure data is presented in a format that the receiving application can understand. It translates data between the application layer and the network format.

The Session Layer establishes, manages, and terminates communication sessions between applications. It handles dialogue control and synchronization, ensuring that data streams are properly ordered and managed.

The Transport Layer provides reliable end-to-end data delivery between hosts. It handles segmentation, reassembly, error checking, and flow control. Key protocols are TCP (connection-oriented) and UDP (connectionless).

The Network Layer is responsible for logical addressing (IP addresses) and routing data packets across different networks. Routers operate at this layer. The primary protocol is IP (Internet Protocol).

The Data Link Layer provides reliable data transfer across a physical link. It handles physical addressing (MAC addresses), error detection, and flow control within a local network segment. Switches operate at this layer.

The Physical Layer defines the electrical and physical specifications for devices. It deals with the transmission and reception of raw bit streams over a physical medium (e.g., cables, wireless signals). Hubs and repeaters operate at this layer.