Citrix Virtual Apps and Desktops



Editing the registry incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

Citrix HDX represents a broad set of technologies that deliver a high-definition experience to users of centralized applications and desktops, on any device and over any network.

Virtual channels

HDX is designed around three technical principles:

  • Intelligent redirection
  • Adaptive compression
  • Data de-duplication

Applied in different combinations, they optimize the IT and user experience, decrease bandwidth consumption, and increase user density per hosting server.

  • Intelligent redirection - Intelligent redirection examines screen activity, application commands, endpoint device, and network and server capabilities to instantly determine how and where to render an application or desktop activity. Rendering can occur on either the endpoint device or hosting server.
  • Adaptive compression - Adaptive compression allows rich multimedia displays to be delivered on thin network connections. HDX first evaluates several variables, such as the type of input, device, and display (text, video, voice, and multimedia). It chooses the optimal compression codec and the best proportion of CPU and GPU usage. It then intelligently adapts based on each unique user and basis. This intelligent adaptation is per user, or even per session.

    Adaptive compression

  • Data de-duplication - De-duplication of network traffic reduces the aggregate data sent between client and server. It does so by taking advantage of repeated patterns in commonly accessed data such as bitmap graphics, documents, print jobs, and streamed media. Caching these patterns allows only the changes to be transmitted across the network, eliminating duplicate traffic. HDX also supports multicasting of multimedia streams, where a single transmission from the source is viewed by multiple subscribers at one location, rather than a one-to-one connection for each user.

For more information, see Boost productivity with a high-definition user workspace.

At the device

HDX uses the computing capacity of user devices to enhance and optimize the user experience. HDX technology ensures that users receive a smooth, seamless experience with multimedia content in their virtual desktops or applications. Workspace control enables users to pause virtual desktops and applications and resume working from a different device at the point where they left off.

On the network

HDX incorporates advanced optimization and acceleration capabilities to deliver the best performance over any network, including low-bandwidth and high-latency WAN connections.

HDX features adapt to changes in the environment. The features balance performance and bandwidth. They apply the best technologies for each user scenario, whether the desktop or application is accessed locally on the corporate network or remotely from outside the corporate firewall.

In the data center

HDX uses the processing power and scalability of servers to deliver advanced graphical performance, regardless of the client device capabilities.

HDX channel monitoring provided by Citrix Director displays the status of connected HDX channels on user devices.

HDX Insight

HDX Insight is the integration of NetScaler Network Inspector and Performance Manager with Director. It captures data about ICA traffic and provides a dashboard view of real time and historical details. This data includes client-side and server-side ICA session latency, bandwidth use of ICA channels, and the ICA round-trip time value of each session.

You can enable NetScaler to use the HDX Insight virtual channel to move all the required data points in an uncompressed format. If you disable this feature, the NetScaler device decrypts and decompresses the ICA traffic spread across various virtual channels. Using the single virtual channel lessens complexity, enhances scalability, and is more cost effective.

Minimum requirements:

  • Citrix Virtual Apps and Desktops 7 v1808
  • XenApp and XenDesktop 7.17
  • NetScaler version 12.0 Build 57.x
  • Citrix Workspace app for Windows 1808
  • Citrix Receiver for Windows 4.10
  • Citrix Workspace app for Mac 1808
  • Citrix Receiver for Mac 12.8

Enable or disable HDX Insight virtual channel

To disable this feature, set the Citrix NetScaler Application Flow service properties to Disabled. To enable, set the service to Automatic. In either case, we recommend that you restart the server machine after changing these properties. By default, this service is enabled (Automatic).

Insight virtual channel image

Experience HDX capabilities from your virtual desktop

  • To see how browser content redirection, one of four HDX multimedia redirection technologies, accelerates delivery of HTML5 and WebRTC multimedia content:
    1. Download the Chrome browser extension and install it on the virtual desktop.
    2. To experience how browser content redirection accelerates the delivery of multimedia content to virtual desktops, view a video on your desktop from a website containing HTML5 videos, such as YouTube. Users don’t know when browser content redirection is running. To see whether browser content redirection is being used, drag the browser window quickly. You’ll see a delay or out of frame between the viewport and the user interface. You can also right-click on the webpage and look for About HDX Browser Redirection in the menu.
  • To see how HDX delivers high definition audio:
    1. Configure your Citrix client for maximum audio quality; see the Citrix Workspace app documentation for details.
    2. Play music files by using a digital audio player (such as iTunes) on your desktop.

HDX provides a superior graphics and video experience for most users by default, and configuration isn’t required. Citrix policy settings that provide the best experience for most use cases are enabled by default.

  • HDX automatically selects the best delivery method based on the client, platform, application, and network bandwidth, and then self-tunes based on changing conditions.
  • HDX optimizes the performance of 2D and 3D graphics and video.
  • HDX enables user devices to stream multimedia files directly from the source provider on the internet or intranet, rather than through the host server. If the requirements for this client-side content fetching are not met, media delivery falls back to server-side content fetching and multimedia redirection. Usually, adjustments to the multimedia redirection feature policies aren’t needed.
  • HDX delivers rich server-rendered video content to virtual desktops when multimedia redirection is not available: View a video on a website containing high definition videos, such as

Good to know:

  • For support and requirements information for HDX features, see the System requirements article. Except where otherwise noted, HDX features are available for supported Windows Multi-session OS and Windows Single-session OS machines, plus Remote PC Access desktops.
  • This content describes how to optimize the user experience, improve server scalability, or reduce bandwidth requirements. For information about using Citrix policies and policy settings, see the Citrix policies documentation for this release.
  • For instructions that include editing the registry, use caution: editing the registry incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

Auto client reconnect and session reliability

When accessing hosted applications or desktops, network interruption might occur. To experience a smoother reconnection, we offer auto client reconnect and session reliability. In a default configuration, session reliability starts and then auto client reconnect follows.

Auto client reconnect:

Auto client reconnect relaunches the client engine to reconnect to a disconnected session. Auto client reconnect closes (or disconnects) the user session after the time specified in the setting. If auto client reconnect is in progress, the system sends application and desktops network interruption notification to the user as follows:

  • Desktops. The session window is grayed out and a countdown timer shows the time until the reconnections occur.
  • Applications. The session window closes and a dialog appears to the user containing a countdown timer showing the time until the reconnections are attempted.

During auto client reconnect, sessions relaunch expecting network connectivity. User cannot interact with sessions while auto client reconnect is in progress.

On reconnection, the disconnected sessions reconnect using saved connection information. The user can interact with the applications and desktops normally.

Default auto client reconnect settings:

  • Auto client reconnect timeout: 120 seconds
  • Auto client reconnect: Enabled
  • Auto client reconnect authentication: Disabled
  • Auto client reconnect Logging: Disabled

For more information, see Auto client reconnect policy settings.

Session reliability:

Session reliability reconnects ICA sessions seamlessly across network interruptions. Session reliability closes (or disconnects) the user session after the time specified in the setting. After the session reliability timeout, the auto client reconnect settings take effect, attempting to reconnect the user to the disconnected session. When session reliability is in progress, application and desktops network interruption notification are sent to the user as follows:

  • Desktops. The session window becomes translucent and a countdown timer shows the time until the reconnections occur.
  • Applications. The window becomes translucent along with connection interrupted pop ups from the notification area.

While session reliability is active, the user cannot interact with the ICA sessions. However, user actions like keystrokes are buffered for few seconds immediately after the network interruption and retransmitted when the network is available.

On reconnection, the client and the server resume at the same point where they were in their exchange of protocol. The session windows lose translucency and appropriate notification area pop ups are shown for applications.

Default session reliability settings

  • Session reliability timeout: 180 seconds
  • Reconnection UI opacity level: 80%
  • Session reliability connection: Enabled
  • Session reliability port number: 2598

For more information, see Session reliability policy settings.

NetScaler with auto client reconnect and session reliability:

If Multistream and Multiport policies are enabled on the server and any or all these conditions are true, auto client reconnect does not work:

  • Session reliability is disabled on NetScaler Gateway.
  • A failover occurs on the NetScaler appliance.
  • NetScaler SD-WAN is used with NetScaler Gateway.

HDX adaptive throughput

HDX adaptive throughput intelligently fine-tunes the peak throughput of the ICA session by adjusting output buffers. The number of output buffers is initially set at a high value. This high value allows data to be transmitted to the client more quickly and efficiently, especially in high latency networks. Providing better interactivity, faster file transfers, smoother video playback, higher framerate and resolution results in an enhanced user experience.

Session interactivity is constantly measured to determine whether any data streams within the ICA session are adversely affecting interactivity. If that occurs, the throughput is decreased to reduce the impact of the large data stream on the session and allow interactivity to recover.


HDX adaptive throughput changes the way that output buffers are set by moving this mechanism from the client to the VDA, and no manual configuration is necessary.

This feature has the following requirements:

  • VDA version 1811 or later
  • Workspace app for Windows 1811 or later

Improve the image quality sent to user devices

The following visual display policy settings control the quality of images sent from virtual desktops to user devices.

  • Visual quality. Controls the visual quality of images displayed on the user device: medium, high, always lossless, build to lossless (default = medium). The actual video quality using the default setting of medium depends on available bandwidth.
  • Target frame rate. Specifies the maximum number of frames per second that are sent from the virtual desktop to the user device (default = 30). For devices that have slower CPUs, specifying a lower value can improve the user experience. The maximum supported frame rate per second is 60.
  • Display memory limit. Specifies the maximum video buffer size for the session in kilobytes (default = 65536 KB). For connections requiring more color depth and higher resolution, increase the limit. You can calculate the maximum memory required.

Improve video conference performance

Several popular video conferencing applications are optimized for delivery from Citrix Virtual Apps and Desktops through multimedia redirection (see, for example, HDX RealTime Optimization Pack). For applications that are not optimized, HDX webcam video compression improves bandwidth efficiency and latency tolerance for webcams during video conferencing in a session. This technology streams webcam traffic over a dedicated multimedia virtual channel. This technology uses less bandwidth compared to the isochronous HDX Plug-n-Play USB redirection support, and works well over WAN connections.

Citrix Workspace app users can override the default behavior by choosing the Desktop Viewer Mic & Webcam setting Don’t use my microphone or webcam. To prevent users from switching from HDX webcam video compression, disable USB device redirection by using the policy settings under ICA policy settings > USB Devices policy settings.

HDX webcam video compression requires that the following policy settings be enabled (all are enabled by default).

  • Client audio redirection
  • Client microphone redirection
  • Multimedia conferencing

If a webcam supports hardware encoding, HDX video compression uses the hardware encoding by default. Hardware encoding might consume more bandwidth than software encoding. To force software compression, add the following DWORD key value to the registry key: HKCU\Software\Citrix\HdxRealTime: DeepCompress_ForceSWEncode=1.

Network traffic priorities

Priorities are assigned to network traffic across multiple connections for a session using Quality of Service supported routers. Four TCP streams and two User Datagram Protocol (UDP) streams are available to carry ICA traffic between the user device and the server:

  • TCP streams - real time, interactive, background, and bulk
  • UDP streams - voice and Framehawk display remoting

Each virtual channel is associated with a specific priority and transported in the corresponding connection. You can set the channels independently, based on the TCP port number used for the connection.

Multiple channel streaming connections are supported for Virtual Delivery Agents (VDAs) installed on Windows 10, Windows 8, and Windows 7 machines. Work with your network administrator to ensure the Common Gateway Protocol (CGP) ports configured in the Multi-Port Policy setting are assigned correctly on the network routers.

Quality of Service is supported only when multiple session reliability ports, or the CGP ports, are configured.


Use transport security when using this feature. Citrix recommends using Internet Protocol Security (IPsec) or Transport Layer Security (TLS). TLS connections are supported only when the connections traverse a NetScaler Gateway that supports multi-stream ICA. On an internal corporate network, multi-stream connections with TLS are not supported.

To set Quality of Service for multiple streaming connections, add the following Citrix policy settings to a policy (see Multi-stream connections policy settings for details):

  • Multi-Port policy - This setting specifies ports for ICA traffic across multiple connections, and establishes network priorities.

    • Select a priority from the CGP default port priority list. By default, the primary port (2598) has a High priority.
    • Type more CGP ports in CGP port1, CGP port2, and CGP port3 as needed, and identify priorities for each. Each port must have a unique priority.

    Explicitly configure the firewalls on VDAs to allow the additional TCP traffic.

  • Multi-Stream computer setting - This setting is disabled by default. If you use Citrix NetScaler SD-WAN with Multi-Stream support in your environment, you do not need to configure this setting. Configure this policy setting when using third-party routers or legacy NetScaler SD-WAN to achieve the desired Quality of Service.

  • Multi-Stream user setting - This setting is disabled by default.

For policies containing these settings to take effect, users must log off and then log on to the network.

Show or hide the remote language bar

The language bar displays the preferred input language in an application session. If this feature is enabled (default), you can show or hide the language bar from the Advanced Preferences > Language bar UI in Citrix Workspace app for Windows. By using a registry setting on the VDA side, you can disable client control of the language bar feature. If this feature is disabled, the client UI setting doesn’t take effect, and the per user current setting determines the language bar state. For more information, see Improve the user experience.

To disable client control of the language bar feature from the VDA:

  1. In the registry editor, navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\wfshell\TWI.
  2. Create a DWORD value key, SeamlessFlags, and set it to 0x40000.

Unicode keyboard mapping

Non-Windows Citrix Receivers use the local keyboard layout (Unicode). If a user changes the local keyboard layout and the server keyboard layout (scan code), they might not be in sync and the output is incorrect. For example, User1 changes the local keyboard layout from English to German. User1 then changes the server-side keyboard to German. Even though both keyboard layouts are German, they might not be in sync causing incorrect character output.

Enable or disable Unicode keyboard layout mapping

By default, the feature is disabled on the VDA side. To enable the feature, toggle on the feature by using registry editor regedit on the VDA. Add the following registry key:


Name: EnableKlMap


Value: 1

To disable this feature, set EnableKlMap to 0 or delete the CtxKlMap key.

Enable Unicode keyboard layout mapping compatible mode

By default, Unicode keyboard layout mapping automatically hooks some windows API to reload the new Unicode keyboard layout map when you change the keyboard layout on the server side. A few applications cannot be hooked. To keep compatibility, you can change the feature to compatible mode to support these non-hooked applications. Add the following registry key:


Name: DisableWindowHook


Value: 1

To use normal Unicode keyboard layout mapping, set DisableWindowHook to 0.