{"id":84016,"date":"2017-05-12T17:32:10","date_gmt":"2017-05-12T21:32:10","guid":{"rendered":"http:\/\/rbachnet.wwwmi3-ss40.a2hosted.com\/index.php\/"},"modified":"2022-01-13T17:09:22","modified_gmt":"2022-01-13T22:09:22","slug":"whose-time-is-it","status":"publish","type":"post","link":"https:\/\/rbach.net\/index.php\/whose-time-is-it\/","title":{"rendered":"Whose Time Is It?"},"content":{"rendered":"

\"Whose<\/a>What time is it? If you looked at the lower right corner of your Windows PC screen, you know what time it is. That is good enough for most people, but followers of the Bach Seat<\/em><\/a> want to know more. How does Microsoft know that time it is? Microsoft and everybody else uses Internet Engineering Task Force<\/a> (IETF) RFC 7822<\/a> standard protocol called Network Time Protocol<\/a><\/strong> (NTP).<\/p>\n

Network Time Protocol (NTP)<\/h3>\n

\"NetworkNTP<\/strong><\/a> is one of the oldest Internet protocols<\/a><\/strong> still in use. NTP was designed by UMich<\/a> alum David Mills<\/a> at the University of Delaware<\/a>. NTP can maintain time<\/strong> to within tens of milliseconds over the public Internet, and better than one-millisecond accuracy on a LAN. Like many other things in the network world, NTP is set up as a hierarchy. At the top of the tree are \u201cAtomic Clocks<\/a><\/strong>\u201d (Stratum 0). Corporations<\/a>, governments<\/a>, and the military<\/a> run atomic clocks.<\/p>\n

\"USNO<\/a>Atomic clocks are high-precision timekeeping devices<\/strong> that use the element cesium<\/a><\/strong>, which has a frequency of 9,192,631,770 Hertz. That means it “oscillates” a little over nine billion times a second. Knowing the oscillation frequency and then measuring it in a device creates an incredibly accurate timekeeping mechanism. Atomic clocks generate a very accurate interrupt and timestamp on a connected Stratum 1 computer. Stratum 0 devices are also known as reference clocks. The other stratum levels are:<\/p>\n

1<\/strong> – These are computers attached to stratum 0 devices. Stratum 1 servers are also called “primary time-servers”.<\/p>\n

2<\/strong> – These are computers that synchronize over a network with stratum 1 servers. Stratum 2 computers may also peer with other stratum 2<\/a> computers to offer more stable and robust time for all devices in the peer group.<\/p>\n

3<\/strong> computers synchronize with stratum 2 servers. They use the same rules as stratum 2, and can themselves act as servers for stratum 4 computers, and so on.<\/p>\n

\"First<\/a>Once synchronized, with a stratum 1, 2, or 3 server, the client updates the clock about once every 10 minutes, usually requiring only a single message exchange. The NTP process uses User Datagram Protocol<\/a> port 123<\/a>. The NTP timestamp message is 64-bits and consists of a 32-bit part for seconds and a 32-bit part for the fractional second. 64-bits gives NTP a time scale of 232 seconds (136 years) and a theoretical resolution of 232 seconds (233 picoseconds). NTP uses an epoch<\/a> of January 1, 1900, so the first rollover will be on February 7, 2036.<\/p>\n

Microsoft Windows Time Service<\/h3>\n

Microsoft<\/a><\/strong> (MSFT<\/a>) has a mixed history of complying with NTP. All Microsoft Windows versions since Windows 2000 include the Windows Time service<\/strong><\/a> (“W32Time”) which was originally implemented to support the Kerberos version 5 authentication protocol. It required time to be within 5 minutes of the correct value to prevent replay attacks. The NTP version in Windows 2000 and XP violates several aspects of the NTP standard. Beginning with Windows Server 2003 and Vista, MSFT\u2019s NTP was reliable to 2 seconds. Windows Server 2016 can now support 1ms time accuracy.<\/p>\n

In 2014 a new NTP client, ntimed<\/strong>, was started. As of May 2017, no official release was done yet, but ntimed can synchronize clocks reliably under Debian<\/a><\/strong> and FreeBSD<\/a><\/strong>, but has not been ported to Windows or\u00a0Apple<\/a> (AAPL<\/a>) macOS.<\/p>\n

Accurate time across a network is important<\/strong> for many reasons; discrepancies of even fractions of a second can cause problems. For example:<\/p>\n