01.03 · Cheat sheet
Computer Networks
The networking facts that come up in every CS-fundamentals round.
OSI model (top to bottom)
| # | Layer | Examples | Unit |
|---|---|---|---|
| 7 | Application | HTTP, DNS, SMTP, FTP | Data |
| 6 | Presentation | TLS, encoding, compression | Data |
| 5 | Session | Sessions, sync | Data |
| 4 | Transport | TCP, UDP, ports | Segment |
| 3 | Network | IP, ICMP, routers | Packet |
| 2 | Data link | Ethernet, MAC, switches | Frame |
| 1 | Physical | Cables, signals, hubs | Bits |
Remember 7 → 1: All People Seem To Need Data Processing. TCP/IP model: Application, Transport, Internet, Network access.
TCP vs UDP
| TCP | UDP | |
|---|---|---|
| Connection | Yes (3-way handshake) | No |
| Reliable, ordered | Yes | No |
| Speed | Slower | Faster |
| Header | 20 bytes or more | 8 bytes |
| Used for | Web, email, files | DNS, video, games, calls |
Handshake: SYN → SYN-ACK → ACK. Close: FIN and ACK in each direction.
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Inside: 8 sections.
- OSI model (top to bottom)
- TCP vs UDP
- Common ports
- IP addressing
- What happens when you open a URL
- Devices
- +2 more
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Item 3 of 12 · updated 2026-10-13