OSI Model

The Open Systems Interconnection (OSI) model is a conceptual 7-layer framework developed by the ISO to standardize networking functions, allowing diverse systems to communicate. It maps the flow of data from software applications down to physical hardware, aiding in troubleshooting, security, and interoperability.

 

A	Layer	Protocols / Data	Data Unit	Functions	Hardware / Examples
A	Application	HTTP, HTTPS, FTP, TELNET, SMTP, DNS	Message	Provides services to end-users, interface for apps	Browsers (Chrome/Firefox), Email clients, Servers
P	Presentation	JPEG, PNG, GIF, MOV, SSL/TLS	Message	Data translation, encryption/decryption, compression	Handled by software, libraries (e.g., OpenSSL)
S	Session	RPC, NetBIOS, APIs	Message	Session establishment, management, termination, authentication	Software (API managers, session controllers)
T	Transport	TCP, UDP	Segment	Flow control, error detection/correction, sequencing, port addressing	Firewalls (stateful), load balancers
N	Network	IP, ICMP	Packet	Logical addressing, routing, packet forwarding	Routers, Layer 3 switches
D	Data Link	Ethernet, PPP, ARP	Frame	Physical addressing (MAC), error detection, frame delimiting	Switches, bridges, NICs
P	Physical	Ethernet, DSL, USB	Bit	Transmission of raw bits over medium	Cables, hubs, repeaters, NICs