OSI Model and TCP/IP
The OSI model (Open Systems Interconnection) was defined by ISO. It splits network communication into seven layers.
| No. | Layer | Job | Data unit |
|---|---|---|---|
| 7 | Application | Services to the user (HTTP, FTP, SMTP) | Data |
| 6 | Presentation | Translation, encryption, compression | Data |
| 5 | Session | Opens, manages and closes sessions | Data |
| 4 | Transport | End-to-end delivery, error recovery (TCP, UDP) | Segment |
| 3 | Network | Routing and IP addressing | Packet |
| 2 | Data Link | Framing, MAC addressing, error detection | Frame |
| 1 | Physical | Bits on the cable or air | Bit |
TCP/IP model (4 layers)
| Layer | Matches OSI | Protocols |
|---|---|---|
| Application | Application, Presentation, Session | HTTP, HTTPS, FTP, SMTP, DNS, DHCP |
| Transport | Transport | TCP, UDP |
| Internet | Network | IP, ICMP, ARP |
| Network Access (Link) | Data Link, Physical | Ethernet, Wi-Fi |
| TCP | UDP |
|---|---|
| Connection-oriented, reliable, ordered | Connectionless, faster, no guarantee |
| Web, email, file transfer | Video calls, live streaming, online games, DNS queries |
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from standard computer textbooks, Microsoft documentation and official sources. Features differ between Excel and Word versions (2016, 2019, 2021, 365) so check which version your exam follows. Found a mistake? Tell us.