Managing User Profile Service slow link detection

This article describes how to optimize slow link detection to effectively balance the quality of the bandwidth estimate against the amount of time spent calculating the estimate.

Applies to:   Windows 11, Windows 10, Windows 8.1, Windows 8, Windows Server 2022, Windows Server 2019, Windows Server 2016, Windows Server 2012 R2, Windows Server 2012, Windows Server 2008 R2, Windows Server 2008


Windows User Profile Service can use slow link detection to determine whether to download a roaming user profile to the client computer when the user signs in. If the service determines that the connection to the client computer is slow, the client skips the download. Instead, it loads the local copy of the roaming user profile. The service also records an event that resembles the following:

Log Name: Application
Source: Microsoft-Windows-User Profiles Service
Event ID: 1543
Task Category: None
Level: Error
A slow network connection is detected for the roaming profile \\\profileshare$\USER\RWacker.V6. It will not be synchronized with the profile on this computer.

The user might also receive a message that resembles the following:

Your roaming profile isn't synchronized with the server because a slow network connection is detected. You've been signed in with a local profile.

The default configuration of the slow link detection settings should correctly identify slow links in most deployments. However, if Windows does not seem to identify slow links correctly, consider changing the slow link detection settings. For example, if the User Profile Service determines that a network connection is a fast link, but in reality the connection is slow, the user sign-in experience might be unusually slow. The user might see the "Waiting for the User Profile Service" message for an unacceptably long time.

More information

The following sections describe how the slow link detection algorithm works, and recommend a starting point and factors to consider in your own testing and tuning.

When slow link detection is enabled, the User Profile Service uses a temporary file on the server to do a set of file writes and reads. To calculate the link speed and delay during these operations, the service uses statistics that are measured by the Network Location Awareness (NLA) service.

The size of the temporary file is specified by the PingBufferSize registry entry. This entry is defined as follows:

  • Subkey: "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon"
  • Value: "PingBufferSize"
  • Type: REG_DWORD
  • Data: File transfer size in bytes
    • Default: 65,536
    • Minimum: 2,048
    • Maximum: 65,536 or 4,194,304


      The maximum value of PingBufferSize depends on the version of Windows, as described later in the article.

The quality of the estimate depends on the PingBufferSize value and how well the metrics of the algorithm match the actual transfer patterns and network topology.

For Windows Server 2016 and earlier versions, and Windows 10, version 1803 and earlier versions, the maximum value of PingBufferSize is 65536. During the link test, the service writes PingBufferSize + 200 bytes of data, and then measures the statistics.

This algorithm doesn't provide an estimate that's sufficiently refined to effectively identify slow links. It can produce false positives (a connection is labeled as a slow link despite being fast enough) or false negatives (a connection isn't labeled as a slow link despite being slow).

The slow link detection process has changed in Windows Server 2019 and Windows 10, version 1809 and later versions. Additionally, the maximum PingBufferSize value has increased to 4194304. The changes are available in the following updates:

The new algorithm uses a different file access pattern. Instead of writing data one time and then measuring, the new algorithm uses a combination of writing and reading, as follows:

  • Write (PingBufferSize + 8 KB) of data
  • Read the data four times (4 × (PingBufferSize + 8 KB))

This algorithm produces more accurate delay and throughput measurements. The new maximum PingBufferSize value provides more flexibility. However, if the link is very slow, a large PingBufferSize value might slow down the algorithm itself so that it delays the whole process of downloading the user profile.

Windows provides several Group Policy settings that control slow link detection. The following table describes some of the most important of these policies. For more information about how to use these policies, see Policy CSP - ADMX_UserProfiles: ADMX_UserProfiles/SlowLinkTimeOut.


If it's enabled, the Disable detection of slow network connections policy turns off slow link detection. In that case, the policies that are described in this article are ignored.

Policy Purpose
Control slow network connection timeout for user profiles If you enable this policy setting, you can change how long Windows waits for a response from the server before it considers the connection to be slow.

If you disable or don't configure this policy setting, Windows considers the network connection to be slow if the server returns less than 500 kilobits of data per second or takes 120 milliseconds to respond.
Wait for remote user profile If you enable this policy setting, the system waits for the remote copy of the roaming user profile to load, even if the download speed is slow.
Screenshot of a checkbox that appears on the sign-in page with Download my profile on a slow connection selected.
If you disable this policy setting or don't configure it, the system loads the local copy of the roaming user profile when a remote profile is slow to download.
Prompt user when a slow network connection is detected If you enable this policy setting, users will be allowed to define whether they want their roaming profile to be downloaded when a slow link with their roaming profile server is detected.

Testing the factors that affect profile download speed for your deployment

To optimize user profile downloads for your environment, you have to balance the following factors:

  • The Service Level Agreement (SLA) that governs the acceptable time allowed for the total sign-in and sign-out process for your users
  • The factors that affect profile download speed for your users
  • The policy and registry settings that optimize the slow link detection algorithm for your user's network connections

The following values are the defaults for the policy and registry settings.

  • Connection speed: 500 kbps
  • Time to wait: 120 milliseconds
  • PingBufferSize: 65,536 bytes

We've tested slow link detection by using < 10-Mbit/s broadband links plus VPN, Wi-Fi networks, and LAN connections. This testing shows that a PingBufferSize of 1,048,576 (1 MB) provides a balance between correctly identifying slow links and delaying the link detection process. We recommend that you use this value to start testing. Depending on your environment, the actual value that you should use might be lower or higher.

To make sure that slow link detection works reliably under various conditions, test several combinations of profiles (both full and incremental sync) and network conditions.

Network factors to consider

  • Slowest potential speeds. Account for the slowest network links that you expect your users to have. Typically, these include mobile carrier connections (such as LTE or UMTS) and home internet connections (such as DSL and cable).

    These networks tend to have asymmetric speeds. This design means that they download files at higher speeds than they upload files. Because it uses four times as many reads as writes of the same data, the new slow link detection algorithm is well-suited to analyzing asymmetric-speed networks.


    When a user signs out of Windows, Windows uploads any profile files that were updated during the user session. A link that has been identified as a fast link might still produce a slow sign-out experience.

  • Metering. These links may also be metered (priced according to the amount of data transmitted). Both the profile transfer and the slow link detection operations contribute to the data transmission total. Therefore, a larger PingBufferSize could increase network costs.

  • Encryption. VPN connections typically compress and encrypt data. Compression, encryption, and decryption add time to the network transfers, especially because some user profile data doesn't compress well.

User profile factors to consider

When the user signs in to Windows, the User Profile Service enumerates all the files in the user profile to determine what to update on the local copy. This update might involve downloading a few files that have changed (an incremental update) or downloading the entire user profile (full sync). When the user signs out, Windows uploads any profile files that have changed. This transaction resembles an incremental update.

For testing, consider the time that's required to download the entire user profile, especially the largest profile that you have. Because the User Profile Service enumerates the files, the "size" of a profile depends on both the number of files and the total amount of data in those files. Make sure that the user sign-in experience meets the SLA even when doing a full download of the largest profile.

Tuning the user profiles

You can improve the sign-in experience over slow links by configuring the user profiles as follows:

See also