Table of contents

1. The scenario: one click and the people and devices involved
2. The mental model: seven layers, encapsulation, and the honest truth
3. Layer 1: Physical. Turning bits into radio, light, and voltage
4. Layer 2: Data Link. Getting a frame to the next box
5. Layer 3: Network. Getting a packet across the planet
6. Layer 4: Transport. Turning packets into reliable conversations
7. Layer 5: Session. Keeping a conversation going
8. Layer 6: Presentation. Agreeing on what the bytes mean
9. Layer 7: Application. What you actually asked for
10. The full replay: a millisecond timeline of the click
11. X-ray of one packet: byte budget and hop-by-hop rewrites
12. Inside the server: from the NIC to your handler
13. The return trip and the goodbye
14. Debugging by layer: the incident playbook
15. Architecture decisions by layer: the senior and manager view
16. Cheat sheet
17. Self-check questions (with answers)