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OSI Model Deep Dive
Map every network problem to a layer — the mental model used by every network engineer.
## The OSI Model Deep Dive
The OSI (Open Systems Interconnection) model isn't just exam content — it is the mental map professionals use to diagnose any network problem.
### The 7 Layers
| Layer | Name | Protocol Examples |
|-------|------|-----------------|
| 7 | Application | HTTP, DNS, SMTP |
| 6 | Presentation | TLS/SSL, JPEG |
| 5 | Session | NetBIOS, RPC |
| 4 | Transport | TCP, UDP |
| 3 | Network | IP, ICMP, BGP |
| 2 | Data Link | Ethernet, ARP |
| 1 | Physical | Cables, Wi-Fi radio |
**Mnemonic:** "All People Seem To Need Data Processing" (layers 7→1)