Citrix Consulting: HDX 7.X: Do You Know Your Graphics Mode?

H.264 Enhanced SuperCodec

Initially part of HDX 3D Pro, the H.264 encoder is now part of the enhanced HDX SuperCodec graphics mode and allows for the delivery of Windows 8 and Server 2012 desktops. The encoder used in previous versions of XenApp and XenDesktop cannot be loaded in Windows 8 and is not optimized for Server 2012. Therefore this graphics mode is the default setting instead of the legacy mode in XenApp?? and XenDesktop 5.6. The codec runs completely on the server CPU (not in GPU) and allows for a desktop with desktop composition (Aero in Win7) to be delivered to any device although at the cost of additional server side CPU.

Compatibility Mode

When the endpoint Receiver does not support H.264 decoding or visual quality is set to “lossless” or “build to lossless”, the VDA will use an alternate JPEG based encoder. When this encoder is in use the graphics mode is called compatibility mode and should be avoided unless delivering a lossless session (no compression). The encoder can cause heavy bandwidth usage (3x or more) and can quickly saturate WAN connections. It is currently being rewritten although no release date has been set.
The following is?? an example of how Compatibility Mode may appear compared to the H.264 encoder with lossless text. On the left is compatibility mode which leaves artifacts and can result in blurry text. On the right, the H.264 encoder with lossless text is noticeably sharper.

The minimum Receiver versions to avoid Compatibility Mode are as follows.

• Windows – Receiver 3.4
• Mac – Receiver 11.8
• Linux – Receiver 13.0
• Mobile – Latest iOS or Android Receiver
• HTML5 Receiver 1.3
• Many thin client vendors are given access to the Receiver source code and create custom Receiver versions. At this time, there is no Receiver version on Dell’s Wyse ThinOS that supports the H.264 enhanced graphics mode.

Legacy Mode (Thinwire/Adaptive Display)

Legacy Mode in XenApp and XenDesktop 7.x enables the XenDesktop 5.x and XenApp 6.5 settings allowing for what was known as Adaptive Display. It is only applied through the Citrix Computer Policy of the same name. It is unavailable on Windows 8 and above due to Microsoft OS changes. It is available on Server 2012, but it cannot optimize the session due to Microsoft OS graphics changes and is not recommended unless Compatibility Mode is the alternative. There has been some reported customer?? success using Legacy Mode with Server 2012 when limiting the graphical experience (animations, wallpaper, and so on).

Enabling Legacy Mode does not disable DCR. If both are enabled, end points that can leverage DCR will continue to do so. Endpoints that cannot leverage DCR will revert to Legacy Mode instead of the?? H.264 enhanced codec.

Changes to Default HDX Behavior

The following list highlights some of the changes to default behavior introduced with XenApp and XenDesktop 7.x?? that can affect resource utilization and user experience.

• Desktop Composition Redirection (DCR) is on by default and requires significantly more bandwidth as of XenDesktop 7.5.
  • XenDesktop 7.6 introduces adaptive graphics within DCR similar to the behavior of the other graphics modes (Based on Receiver, versions mentioned in TechNote).
• The default frames per second (FPS) setting has increased from 24 (in XenApp 6.5) to 30. This may result in additional bandwidth and CPU utilization (Check if this was lowered additionally by policy if doing a migration to ensure there is not a large jump in resources).
• The H.264 graphics mode is used by default on XenApp 7.x and is unaffected by many adaptive display policies.
• It runs as process ctxgfx.exe on the VDA. You can look at its CPU usage in task manager.
  Note: In Legacy mode, the CPU cost was included in each application so this is not entirely a new CPU overhead.
• The H.264 graphics mode can deliver rich media and server rendered media more efficiently over the WAN. However many existing applications leverage GDI (Graphics Device Interface) and may be better optimized by the Thinwire adaptive display mode (Legacy Mode). (Does not apply on Server 2012/Windows8 and above)
• H.264 decoding requires a minimum receiver version. Older versions of Receiver will fall back to compatibility mode which suffers from additional bandwidth requirements and quality issues which may result in a poor user experience. Compatibility mode should be used as a last resort only.
• If VDA is running on Windows 7 or Server 2008 R2, the Thinwire adaptive display mode can be used to avoid compatibility mode issues. It is enabled by Citrix computer policy "Legacy Mode" only.
• Legacy mode is not supported on Windows 8 nor is it optimized to deliver the graphics stack in Server 2012. Under circumstances where only Legacy Mode and Compatibility Mode are an option, customers have had success with Legacy mode on Server 2012/R2 with a basic desktop experience.

Graphics Mode Selection Leading Practice

Although for first time Citrix deployments, the out of the box graphics settings may be sufficient, it will sometime be necessary to modify these through Citrix policies. The two main scenarios where the graphics modes settings will have a significant impact are:

1. Users are connecting over WAN connections - due to the large variation in bandwidth requirements of each mode.
2. Legacy and custom thin client Receivers versions are used - due to the lack of support for the H.264 encoder resulting in a “compatibility encoder”. This encoder suffers from very high bandwidth usage and is not recommended. It is currently being redeveloped.

Warning: There is currently a worst case scenario which, if encountered, should be noted and escalated. In this scenario, the deployment has a large number of Receivers which do not support H.264 decoding (Wyse ThinOS Receiver for example) and the OS deployed is Server 2012 or Windows 8. The compatibility mode encoder may result in high bandwidth and CPU utilization and poor performance. There have been cases where a single user in compatibility mode have saturated a WAN connection.

The following table details which graphics modes are supported and recommended based on the operating system and network connection used.

^1?? Should the end point use a Receiver which does not support H.264 decoding, the session will revert to the Compatibility Mode Encoder.
²?? Legacy Mode may require less CPU and bandwidth for delivering basic Windows 7 and Server 2008 R2 VDAs.
³?? Legacy Mode with Server 2012/R2 has seen success at customers who limit the visuals of the desktops (no animations, plain wallpaper no mouse shadows). Internal testing is ongoing.

Policy Table by HDX Graphics Mode

Many of the graphics policies in XenApp and XenDesktop 7.x only apply when a session is using a specific graphics mode. To help determine which policies will apply to a session see the policy table below adapted from a publicly available version in a highly recommended blog post by Gabriel Nguyen and Fedi Saidane.

Policy	User / Computer	Desktop Composition Redirection	H.264	Compatibility Mode	Legacy Graphics Mode	Default Setting / Comments
Desktop Composition graphics quality	User	X	??	??	??	Medium
Desktop Composition Redirection	User	X	??	??	??	Enabled
Display memory limit	Computer	??	X	X	X	65536 KB
Display mode degrade preference	Computer	??	??	??	X	Degrade color depth first
Dynamic window preview	Computer	??	X	X	X	Enabled
Image caching	Computer	??	??	??	X	Enabled??
Legacy graphics mode	Computer	??	??	??	X	Disabled This policy will enable Legacy Graphics Mode
Maximum allowed color depth	Computer	??	??	??	X	32 Bits Per Pixel
Notify user when experience is degraded	Computer	??	??	??	X	Disabled Only works on RDS. The UI Dialog for this didn’t get implemented in the Workstation VDA originally.
Persistent cache threshold	Computer	??	??	??	X	3000000 Kbps
Queuing and tossing	Computer	??	??	??	X	Enabled
Extra color compression	User	??	??	??	X	Disabled Extra Color Compression is an optimization that saves up to 20% on the size of lossy compressed images, but at the expense of quality. Turning it off makes some images, like text over a complex background appear sharper.
Extra color compression threshold	User	??	??	??	X	8192 Kbps
Heavyweight compression	User	??	??	??	X	Disabled
Lossy compression level	User	??	??	??	X	Medium
Lossy compression level threshold value	User	??	??	??	X	2147483647 Kbps
Minimum image quality	User	??	??	??	X	Normal
Moving image compression	User	??	??	??	X	Enabled Enables or disables Adaptive Display. Disabling Adaptive Display in Legacy Mode will revert to progressive display.
Progressive compression level	User	??	??	??	X	None If enabled in Legacy Mode, Adaptive Display is disabled and switched to Progressive Display.
Progressive compression threshold value	User	??	??	??	X	2147483647 Kbps
Target frame rate	User	??	X	X	X	30 fps
Target minimum frame rate	User	??	??	??	X	10 fps Valid for Legacy Adaptive Display ONLY: this setting is used to decide when to reduce quality for transient (moving) images.
Visual quality	User	??	X	X	??	Medium Setting the visual quality to ‘lossless’ or ‘build to lossless’ will use compatibility mode as it will not leverage compression. This is the only case when Compatibility Mode should be used.

Identifying HDX Graphics Mode Used

There are several ways to determine which graphics mode is used within a session for troubleshooting purposes. The best way to determine the graphics mode used depends on whether or not the session is accessible and if there are sufficient permissions to install HDX Monitor.
To remotely capture the graphics mode for all sessions in a site, you may run the script attached below on a delivery controller in the site or a machine with the PowerShell snapins installed. It will return a CSV with the username, desktop name, and graphics mode for active sessions along with additional information for troubleshooting. It is provided as-is and is not supported by Citrix. An example screenshot is provided below.
?? Site Graphics Modes Script

To check the graphics mode for a single session, use either HDX Monitor or WMI queries (via cmd or PowerShell equivalent). Below is a step by step guide to the graphics modes within HDX Monitor.
HDX Monitor can connect remotely to a VDA and specific sessions can be selected should the VDA be on a XenApp machine.

Screenshot	Details
??	When opening HDX Monitor in XenDesktop there are three tabs which display information about the graphics modes. Red – DCR Blue – H.264/Compatibility Green – Legacy (Thinwire)
?? ?? ?? ??	If using DCR the Direct 3D tab will show that Composition Redirection has started and is active. When using HDX Monitor to look at a session on a XenApp 7.x machine the Direct 3D tab will be unavailable as it is only supported on the Desktop VDA.
	In this case the graphics mode is using H.264 as noted by ‘DeepCompression’ Note that if Legacy mode is enabled, the same information will still be displayed however a warning message will appear at the bottom indicating that this graphics mode is not in use.
	The Thinwire tab which displays Legacy Mode information will also display a warning if it is not enabled. The warning message on either tab is the simplest way to distinguish whether Legacy Mode is in use. It is only used if explicitly enabled through policy.??
	Alternatively, the same information can be extracted directly through WMIC queries. The commands to the left can be run on a Desktop VDA to determine if DCR is currently in use. Through PowerShell the equivalent command is Get-WMIObject - Namespace root\citrix\hdx – Class citrix_virtualchannel_d3d
	The commands in this screenshot can be run on either a Desktop or Server VDA to determine if the H.264, Compatibility, or Legacy graphics modes are in use. “Component_Encoder” – will show whether H.264 or compatibility are in use should “Legacy Mode” be disabled. If Policy_LegacyGraphicsMode is ‘TRUE’ then Legacy mode is enabled and will be used unless the VDA is on a Windows 8 desktop. Note:?? AtomicFrameSupport is required for H.264 decoding. It is the default setting for Receiver 3.4 and above, however some customers have disabled this if using Presentation Server 4 due to a refresh issue. For XenApp Hosts: On a XenApp host only the first session information will be presented. If that session is for another user, the information may not be visible. To get information for all sessions append _enum to the command to retrieve all sessions on the host.

Additional Resources

There are several resources which you can use for additional information as well as public customer reference.

1. Virtual Desktop Handbook 7.x – Graphics modes design decisions are included under the Bandwidth Requirements section in the Design chapter.
2. HDX display with XenDesktop and XenApp 7.x – Detailed blog article covering graphics modes as well as policies. Also covers some recent field experience when Legacy Mode is the preferred mode. Contains the policy tables which have been adapted in this TechNote.
3. XenDesktop/XenApp 7.x Encoding Intro – Blog article which introduces the graphics modes and provides some design guidance and data.

Note: If blogging about the graphics modes, please tag blog posts with “HDX” and “HDX Graphics” so that PMs can track and distribute accordingly.
If you’d like to provide feedback and ideas on HDX policy templates in Citrix Studio please refer to the article by HDX PM Rachel Berry.