OSI Model

Layer 7 - Application | The layer closest to the end user that provides network services directly to applications (e.g., HTTP, HTTPS, FTP, SMTP, DNS).

Layer 6 - Presentation | Responsible for data formatting, translation, encryption, and compression so the application layer can understand it (e.g., SSL/TLS, JPEG, ASCII).

Layer 5 - Session | Establishes, manages, maintains, and terminates communication sessions between local and remote applications (e.g., NetBIOS, RPC).

Layer 4 - Transport | Handles end-to-end communication, segmentation, flow control, and error recovery; uses Protocol Data Unit (PDU): Segments (TCP) or Datagrams (UDP).

Layer 3 - Network | Controls packet routing, logical IP addressing, and path selection across different networks; PDU: Packets (e.g., IPv4, IPv6, ICMP, IPsec).

Layer 2 - Data Link | Handles physical node-to-node transfer, MAC hardware addressing, and framing; PDU: Frames (e.g., Ethernet, Switches, Switches/VLANs).

Layer 1 - Physical | Transmits raw binary bits over physical media like copper wire, fiber optics, or radio waves; PDU: Bits (e.g., Cables, Hubs, Repeaters).