When you set the value to a value other than MAX 0xFFFFFFFF , you can prevent computers from adopting time that is very inaccurate in the scenarios where the computer is restarted or the connectivity to external time sources is disrupted. For example, consider the case in which you have the MaxPosPhaseCorrection and MaxNegPhaseCorrection registry entries set for 48 hours on all domain controllers in the forest.

If any single domain controller experiences an unusual time jump of more than 48 hours, the value that you set for the MaxPosPhaseCorrection and MaxNegPhaseCorrection registry entries will prevent other computers from making the same time jump. Therefore, computers that are out of sync can be kept apart from the other computers until the administrator can investigate and take corrective action. Time accuracy is especially important on the forest root primary domain controller PDC.

Because the PDC is the root time source for the domain, inaccurate time changes on the PDC can potentially cause a domain-wide time jump. If you impose phase correction restrictions on the PDC, you can prevent other domain controllers in the forest from accepting the new time.

The default value of 48 hours instead of a default value of 5 minutes or 15 minutes is based on the following reasons:. These errors have a low correlation to the time skew because the cause may prevent Windows-based computers from adopting an accurate time value. So 48 hours was the next obvious time offset after 25 or 36 hours.

Administrators can also reduce the value with correct tools that report infrastructure and testing. Specific recommendations according to operating system version and computer role are described in the following sections. When you configure the authoritative time server to sync with an Internet time source, there's no authentication. You must reconfigure the following registry entries:. This default value means "Accept any time change.

It's represented in the registry as 2a hexadecimal or decimal. We recommend that you set the value of the MaxPollInterval registry entry to 10 or less or that you set the value of the SpecialPollInterval registry entry to 1 hour or less.

The 48 hours value can also be set on member servers that are running time sensitive-based applications. As a security best practice, we recommend that you reduce this default value. We also recommend that you set the value to 1 hour or an even smaller value, depending on time source, on network condition, on poll interval, and on security requirements. We recommend that you use the Global Policy object Editor to deploy these settings. The default Windows Time service parameter values that are defined in the Group Policy object GPO may not match the default values that are defined in the registry of Windows Server based domain controllers.

Other Windows Time service parameter values may also have to be changed in the GPO to match the default registry values in the domain controllers. When you configure the authoritative time server to sync with an Internet time source, there's no authentication in manual mode.

The default value is 43, The recommended value is 15 minutes or an even smaller value, depending on time source, on network conditions, and on security requirements. It also depends on the poll interval. We recommend that the poll interval value is set to one hour for every 24 hours. For more information about this registry entry, see Windows Server SP 4 registry entry section.

The synchronization type is NT5DS. The time service synchronizes from the domain hierarchy and the time service accepts all-time changes. Because NT5DS accepts any time change without considering the time offset, it's important to set up a reliable forest root time source in the time sync subnet. Privacy policy. Windows Time Service Architecture. Windows Time Service Time Protocols. Windows Time Service Processes and Interactions.

This topic explains only how the Windows Time service W32Time works. Although the Windows Time service is not an exact implementation of the Network Time Protocol NTP , it uses the complex suite of algorithms that is defined in the NTP specifications to ensure that clocks on computers throughout a network are as accurate as possible.

Ideally, all computer clocks in an AD DS domain are synchronized with the time of an authoritative computer. Many factors can affect time synchronization on a network. The following factors often affect the accuracy of synchronization in AD DS:.

Prior to Windows Server , the W32Time service was not designed to meet time-sensitive application needs. However, updates to Windows Server now allow you to implement a solution for 1ms accuracy in your domain. See Windows Accurate Time and Support boundary to configure the Windows Time service for high-accuracy environments for more information.

Computers that synchronize their time less frequently or are not joined to a domain are configured, by default, to synchronize with time. Therefore, it is impossible to guarantee time accuracy on computers that have intermittent or no network connections. An AD DS forest has a predetermined time synchronization hierarchy.

The Windows Time service synchronizes time between computers within the hierarchy, with the most accurate reference clocks at the top. If more than one time source is configured on a computer, Windows Time uses NTP algorithms to select the best time source from the configured sources based on the computer's ability to synchronize with that time source. The Windows Time service does not support network synchronization from broadcast or multicast peers.

Every computer that is running the Windows Time service uses the service to maintain the most accurate time. Computers that are members of a domain act as a time client by default, therefore, in most cases it is not necessary to configure the Windows Time Service.

However, the Windows Time Service can be configured to request time from a designated reference time source, and can also provide time to clients. The degree to which a computer's time is accurate is called a stratum.

The most accurate time source on a network such as a hardware clock occupies the lowest stratum level, or stratum one. This accurate time source is called a reference clock. An NTP server that acquires its time directly from a reference clock occupies a stratum that is one level higher than that of the reference clock. Resources that acquire time from the NTP server are two steps away from the reference clock, and therefore occupy a stratum that is two higher than the most accurate time source, and so on.

As a computer's stratum number increases, the time on its system clock may become less accurate. Therefore, the stratum level of any computer is an indicator of how closely that computer is synchronized with the most accurate time source.

When the W32Time Manager receives time samples, it uses special algorithms in NTP to determine which of the time samples is the most appropriate for use.

The time service also uses another set of algorithms to determine which of the configured time sources is the most accurate. When the time service has determined which time sample is best, based on the above criteria, it adjusts the local clock rate to allow it to converge toward the correct time.

If the time difference between the local clock and the selected accurate time sample also called the time skew is too large to correct by adjusting the local clock rate, the time service sets the local clock to the correct time.

This adjustment of clock rate or direct clock time change is known as clock discipline. The Windows Time Service Manager is responsible for initiating the action of the NTP time providers included with the operating system. The Windows Time Service Manager controls all functions of the Windows Time service and the coalescing of all time samples.

In addition to providing information about the current system state, such as the current time source or the last time the system clock was updated, the Windows Time Service Manager is also responsible for creating events in the event log.

These time samples are then passed to the Windows Time Service Manager, which collects all the samples and passes them to the clock discipline subcomponent. The clock discipline subcomponent applies the NTP algorithms which results in the selection of the best time sample. The clock discipline subcomponent adjusts the time of the system clock to the most accurate time by either adjusting the clock rate or directly changing the time.

If a computer has been designated as a time server, it can send the time on to any computer requesting time synchronization at any point in this process. Time protocols determine how closely two computers' clocks are synchronized. A time protocol is responsible for determining the best available time information and converging the clocks to ensure that a consistent time is maintained on separate systems. NTP is an Internet time protocol that includes the discipline algorithms necessary for synchronizing clocks.

NTP is a fault-tolerant, highly scalable time protocol and is the protocol used most often for synchronizing computer clocks by using a designated time reference. NTP time synchronization takes place over a period of time and involves the transfer of NTP packets over a network. NTP packets contain time stamps that include a time sample from both the client and the server participating in time synchronization. NTP relies on a reference clock to define the most accurate time to be used and synchronizes all clocks on a network to that reference clock.

UTC is independent of time zones and enables NTP to be used anywhere in the world regardless of time zone settings. NTP includes two algorithms, a clock-filtering algorithm and a clock-selection algorithm, to assist the Windows Time service in determining the best time sample.

The clock-filtering algorithm is designed to sift through time samples that are received from queried time sources and determine the best time samples from each source. The clock-selection algorithm then determines the most accurate time server on the network. This information is then passed to the clock discipline algorithm, which uses the information gathered to correct the local clock of the computer, while compensating for errors due to network latency and computer clock inaccuracy.

The NTP algorithms are most accurate under conditions of light-to-moderate network and server loads. As with any algorithm that takes network transit time into account, NTP algorithms might perform poorly under conditions of extreme network congestion. The Windows Time service is a complete time synchronization package that can support a variety of hardware devices and time protocols.

To enable this support, the service uses pluggable time providers. A time provider is responsible for either obtaining accurate time stamps from the network or from hardware or for providing those time stamps to other computers over the network. The NTP provider is the standard time provider included with the operating system. NtpServer output provider. This is a time server that responds to client time requests on the network.

Need more help? Expand your skills. Get new features first. Was this information helpful? Yes No. Thank you! Any more feedback? The more you tell us the more we can help. Can you help us improve? Resolved my issue. Clear instructions. Easy to follow. No jargon. Pictures helped. Didn't match my screen. Incorrect instructions. Too technical. Not enough information.