Windows Time gets accuracy improvements and leap second support

Microsoft plans to integrate improvements in  the upcoming Windows 10 version 1809 and Windows Server 2019 operating systems that improve the accuracy of time.

The upcoming versions of Windows include compliant leap second support, a new time synchronization protocol called Precision Time Protocol (PTP), software timestamping, clock source stability improvements, and traceability support.

Leap seconds are needed to keep UTC in-sync with mean solar time. Current regulation makes it necessary to adjust the time accordingly but also make sure to maintain accuracy during a leap second.

Leap seconds get added in a very specific way. A clock runs the seconds from 0 to 59 usually for a total of 60 seconds. Leap seconds add an extra second and this has to be reflected somehow. When a leap second occurs, it is added to the last minute of the UTC day; the clock goes from 0 to 60 which results in a total of 61 seconds being counted at the time.

Microsoft did even add support for negative leap seconds. While they never occurred before, Windows is prepared for the event that this is going to happen.

Negative leap seconds are counted in similar fashion, only that a second is removed and not added so that only 59 seconds are counted and not 60 as usually.

Microsoft made the decision to not use leap second smearing as an option. Leap second smearing refers to a technique in which the extra second is split into much smaller units and added to the time throughout the day.

The reason why the technique is not added is that it has an error of order +/- 0.5 seconds with respect to the definition of UTC.

Precision Time Protocol

The coming versions of Windows will include time accuracy improvements next to that. Microsoft plans to include the Precision Time Protocol in Windows Server 2019 (Windows 10 also? Microsoft does not say) which won't replace the current standard Network Time Protocol (NTP) but will be an option for industries that require more accurate time syncing between network devices.

The main issue with NTP is that it assumes that the round-trip delay is symmetric in the network. PTP on the other hand supports latency per device which is more accurate.

Enter Precision Time Protocol (IEEE 1588v2). PTP enables network devices to add the latency introduced by each network device into the timing measurements thereby providing a far more accurate time sample to the endpoint (Windows Server 2019 or Windows 10, host or virtual machine).

Software Timestamping

Another new concept that Microsoft will introduce in the coming versions of Windows is Software Timestamping.

Since timing packets need to be processed by the operating system's networking stack prior to being used by the time service, latency that is added by these processes need to be accounted for as well.

Latency introduced by the networking stack may add up to 200µs in extreme scenarios which alone is higher than the sub-100µs target of some government regulations.

Microsoft records the timestamp of packets before and after they have been processed by Windows Networking Components to make time more accurate.

Other improvements

Microsoft revealed one additional accuracy-based improvement and options to better trace accuracy:

Clock Source Stability 

Attempts to make the clock source more stable by changing how time samples are processed.

It’s important to understand that a host system receives time “samples” from its time server, however it does not immediately apply these samples to the clock.

[..] we take multiple time samples, eliminate the outliers, and discipline the clock with the goal of bringing the system closer and closer to synchronization with the time server.

Traceability

Microsoft will add options to prove and trace the accuracy of time sources. Windows Server 2019 will include "additional logging capabilities  that can be used to audit the actions taken by the Windows Time service".

The logs may answer the following questions among others:

• What is the chosen time server and synchronization frequency
• When was the last synchronization and results of that synchronization
• What actions were taken after the synchronization (did we discipline the clock?)

The operating system supports new performance counters and admins may use a SCOM management pack to get notifications when NTP Offset thresholds are exceeded. (via Deskmodder)

Advertisement