MEPX
Chapter 4 of 10All chapters
  1. 1Layers
  2. 2Addresses
  3. 3DNS
  4. 4TCP and UDP
  5. 5Routing
  6. 6HTTP
  7. 7Wifi and local networks
  8. 8Latency and bandwidth
  9. 9Diagnosing problems
  10. 10How the internet fits together

Chapter 4 of 10

TCP and UDP

Two ways to send data.

The trade

TCP sets up a connection, numbers the packets, resends what is lost and delivers in order. UDP just sends, with no guarantees and far less overhead.

  • Web pages, email and file transfer use TCP because completeness matters.
  • Video calls and games prefer UDP, because a late packet is worse than a missing one.

Ports

A port number says which program on the machine the traffic belongs to. HTTPS is 443, HTTP is 80, SSH is 22, and a firewall usually works by allowing or blocking these.