OSI & TCP/IP Models
Layered models split networking into responsibilities so each layer serves the one above it.
Cheat sheet
- ▸OSI (7): Physical, Data Link, Network, Transport, Session, Presentation, Application.
- ▸Mnemonic: Please Do Not Throw Sausage Pizza Away.
- ▸TCP/IP (4): Link, Internet, Transport, Application.
- ▸PDU: Bits → Frames → Packets → Segments → Data.
- ▸Devices: Hub/Repeater (L1), Switch/Bridge (L2), Router (L3).
- ▸Encapsulation adds headers going down; decapsulation removes them going up.
Layer mapping
| OSI layer | Protocols | Device | PDU |
|---|---|---|---|
| 7 Application | HTTP, DNS, SMTP, FTP | — | Data |
| 4 Transport | TCP, UDP | — | Segment |
| 3 Network | IP, ICMP, ARP* | Router | Packet |
| 2 Data Link | Ethernet, Wi-Fi MAC | Switch | Frame |
| 1 Physical | Cables, signals | Hub | Bits |
Top 10 campus interview questions
Quick quiz
1. Router works at layer:
2. PDU at transport layer:
3. How many layers in TCP/IP model?
4. MAC addresses are used at:
5. ARP maps: