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The Open Systems Interconnection (OSI) model is a conceptual framework created by the International Organization for Standardization (ISO) in 1984. It divides network communication into seven layers, each with a specific responsibility. Understanding the OSI model is essential for troubleshooting, designing, and discussing networks.
| Layer | Number | Name | Key Function | Example Protocols / Technologies |
|---|---|---|---|---|
| 7 | Application | Application | Provides network services to end-user applications | HTTP, FTP, SMTP, DNS, SSH |
| 6 | Presentation | Presentation | Data formatting, encryption, compression | SSL/TLS, JPEG, ASCII, UTF-8 |
| 5 | Session | Session | Manages sessions and connections | NetBIOS, RPC, PPTP |
| 4 | Transport | Transport | Reliable (or unreliable) end-to-end data delivery | TCP, UDP |
| 3 | Network | Network | Logical addressing and routing | IP, ICMP, ARP |
| 2 | Data Link | Data Link | Physical addressing and error detection | Ethernet, Wi-Fi (802.11), MAC addresses |
| 1 | Physical | Physical | Transmission of raw bits over a medium | Cables, fibre optics, radio waves |
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