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CN · written course

How a message crosses the world

How a message crosses the world and arrives intact.

Start reading32 pages · about 167 minutes

By the end of this course

You type an address and a page appears. Between those two moments a message is named, addressed, split, routed, acknowledged and reassembled by half a dozen independent systems that have never met. By the end you can explain every step, subnet a network on paper, and say why a video call drops frames instead of pausing.

All 32 pages

  1. 1What happens when you press Enter5 min read
  2. 2Why it is built in layers5 min read
  3. 3Wires, and how they are arranged4 min read
  4. 4Turning bits into a signal5 min read
  5. 5Frames, MAC addresses and switches5 min read
  6. 6Noticing that a frame arrived wrong5 min read
  7. 7Sharing one channel5 min read
  8. 8The frame everything local travels in5 min read
  9. 9Hubs, switches and how a frame finds its port5 min read
  10. 10Finding the hardware address5 min read
  11. 11IP addresses and what a mask means5 min read
  12. 12What travels in front of every packet5 min read
  13. 13Subnetting, worked properly6 min read
  14. 14Many devices, one public address5 min read
  15. 15The address space that does not run out5 min read
  16. 16How a router decides5 min read
  17. 17How a router learns the way6 min read
  18. 18The protocols that actually run5 min read
  19. 19The protocol that reports problems5 min read
  20. 20TCP: making an unreliable network look reliable6 min read
  21. 21Opening and closing a connection6 min read
  22. 22Not overwhelming the receiver5 min read
  23. 23Not overwhelming the network6 min read
  24. 24When you do not want reliability4 min read
  25. 25Names, and the protocol on top5 min read
  26. 26How a name becomes an address6 min read
  27. 27Three versions of the same protocol6 min read
  28. 28Why the padlock is there5 min read
  29. 29What the padlock actually promises6 min read
  30. 30Networking without a cable5 min read
  31. 31Getting content close, and spreading the load6 min read
  32. 32Wi-Fi, mobile and what changed5 min read

Then what

Reading is the first half. When you finish, the questions for this subject test whether it went in, and every wrong option tells you why it was wrong rather than just that it was.

See the questions for CN