Windows Time Jitter Filtering Registry Key

This article identifies the specific Windows Registry keys and values responsible for configuring jitter filtering and time offset stabilization in the Windows Time (W32Time) service. It outlines the primary configuration paths in the Registry Editor (Regedit) and explains the essential parameters used to smooth out transient network delay variations and clock jitter.

Primary Registry Key for Jitter Filtering

The configuration parameters that govern jitter filtering, phase correction, and clock discipline algorithms are located in the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config

This key contains the internal algorithm settings that dictate how W32Time evaluates, filters, and applies clock adjustments based on network time samples.

Key Jitter and Stability Parameters

Within the Config subkey, several DWORD values directly manage jitter mitigation and phase offset filtering:

• SpikeWatchPeriod: Specifies the time period (in seconds) that an offset sample significantly larger than previous samples must persist before it is accepted as a genuine time shift rather than a temporary network spike or jitter anomaly.
• HoldPeriod: Defines the number of consecutive synchronization intervals that a time error must remain consistent before the client clock begins adjusting its rate to eliminate the phase error.
• PollAdjustFactor: Controls how dynamically the polling interval expands or contracts in response to clock stability and network dispersion. Higher values dampen reactions to short-term jitter.
• PhaseCorrectRate: Governs the rate at which the system clock corrects phase differences between the local clock and the target time source.
• MaxAllowedPhaseOffset: Establishes the threshold (in seconds) beyond which phase adjustments are filtered out as invalid or handled by step adjustments rather than continuous slewing.

Related NTP Client Settings

For settings that manage low-level network packet sampling and NTP provider behavior, refer to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient

• SpecialPollInterval: Determines the fixed polling frequency (in seconds) when specific peer flags are configured, affecting how frequently jitter samples are collected.
• CrossSiteSyncFlags: Governs synchronization behavior across domain and site boundaries, impacting packet routing and latency variation.

Applying Changes

After modifying any of these parameters in Regedit, apply the configuration without rebooting by executing the following commands in an elevated Command Prompt:

w32tm /config /update
net stop w32time && net start w32time