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← Latency - Intro to Computer Science

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Showing Revision 5 created 05/24/2016 by Udacity Robot.

  1. I want to talk about the two main ways to
  2. measure a network. Those are called Latency and Bandwidth.
  3. What they mean is very different. They're often confused.
  4. Often people say bandwidth when they mean latency, or
  5. say latency when they mean bandwidth. They're quite different
  6. things. So let me explain what they are. So
  7. latency is the time that it takes for a
  8. message to get from the source to the destination.
  9. And that's for the start of the message. So, we can measure latency by timing
  10. when you start sending to the time
  11. that the receiver starts receiving. So this is
  12. the unit of time. It will be measured in something like seconds. For a fast
  13. network today, it's more often measured in milliseconds
  14. and there are 1000 milliseconds in one second.
  15. So now, you understand about latency. And when I
  16. go back to the Greek signaling network. So, suppose now
  17. that Zeus, who is all powerful, wanted to send a
  18. message from Rhodes to Sparta. And he thought that the
  19. latency of the smoke signal network as it was
  20. currently set up was too high, that it takes too
  21. long for the message that he sends starting from Rhodes
  22. to reach Sparta. So the question is, how could Zeus,
  23. and remember that in ancient Greece, Zeus was all
  24. powerful, reduce the latency between Rhodes and Sparta. So
  25. here are the choices. It makes the signalling nodes
  26. further apart. So instead of going from Rhodes to
  27. Naxos to Millios to Sparta, maybe it would have
  28. to go one hop. There would be a new
  29. island in the middle here, and it could go
  30. from Rhodes to the new island and then to Sparta.
  31. He could threaten the soldiers at all the signalling points and
  32. scare them into working harder, so they start the fires more quickly,
  33. when they need to send a message. He could find a way
  34. to make it so instead of just sending one color smoke, you
  35. could send different colors smoke. That would mean that with the same
  36. amount of smoke, you could send more different messages. Or he could
  37. increase the speed of light. That would mean that the the soldiers
  38. at each signaling point would see the previous smoke signal more quickly
  39. than they do now.