4 Matching Annotations
  1. Jul 2023
  2. May 2022
  3. Aug 2021
    1. Let’s say I’m the client, and you’re the server. First, I send you a packet, but before I do I write down a timestamp. When you receive that packet, you write down a timestamp. Then, you send me a reply, and before you do you write down a timestamp. Finally, when I receive that reply, I write down a timestamp. It may not seem that groundbreaking, but with just those four timestamps I can compute two important numbers, the offset, and the delay. The offset is how far my clock is off from yours, so if you think it’s 12 pm and I think it’s 12:05 pm then the offset would be five minutes. The delay is how long it took those packets to traverse the network. To compute those numbers you basically take a system of equations, and for me, an important aspect was actually writing down, with a piece of paper and a pencil, and solving these equations myself, was understanding that there’s a sort of huge assumption in this protocol, that the delay for that first packet, where I timestamped then you did, and the delay for the second packet, where you timestamped and then I did, the assumption is that those times are the same and if they’re not the same they introduce what’s called error, and that is a sort of very important aspect. That is an assumption that is made so that you can actually solve those equations to get the offset and the delay.

      Good laymen’s description of NTP algorithm

  4. Nov 2018
    1. 在配置时,NTP可以利用冗余服务器和多条网络路径来获得时间的高准确性和高可靠性。即使客户机在长时间无法与某一时间服务器相联系的情况下,仍可提供高准确度时间。

      难怪客户端配置里有很多个 server