time - 我期望来自以太网同一子网上的 0 层 NTP 服务器的时间有多准确？

Question

我有一个应用程序，它依赖 gpsd 和 ntpd 来准确地设置 linux 机器上的系统时间。

gpsd 由 NMEA + PPS 提供

该应用程序每秒通过网络传输约 25MB，我认为系统上的负载以某种方式导致时间抖动。 (加载的 PCI express 总线导致不规则的中断延迟)

我有另一台根本没有加载的机器，我可以设置它来读取 GPS 并充当已加载机器的 NTP 服务器。 (加载的机器将获得 startum 1 ？？？)

我期望来自以太网同一子网上的 0 层 NTP 服务器的时间有多准确？

我希望这不会太离题，我相信有时其他人会很高兴答案记录在此处。 ;-)

Answer 1

我能在 NTP accuracy 上找到的最佳信息，似乎在 LAN 设置中指向 1-2 毫秒:

NTP v4 with kernel mods to support it, is capable of much better than 1ms accuracy, possibly as good as 1ns. According to [Dave Mills] article, NTP v3 is accurate to 1-2ms in a LAN and 10s of ms in WAN nets. http://www.cis.udel.edu/~mills/ntp.html

Other articles suggest that with an accurate time source, such as a GPS time source, NTP is accurate to 50us, but the links on the Linux kernel support say that accuracy of a few ms are possible. http://www.atomic-clock.galleon.eu.com/support/ntp-time-server-accuracy.html

Another article says that it is dependent on the predictability of network delays (i.e. a low jitter network). http://www.postel.org/pipermail/end2end-interest/2003-April/002925.html