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VXC 6215 Citrix HDX Flash Redirection Overview

What is HDX MediaStream Flash Redirection

HDX MediaStream Flash Redirection allows you to move the processing  (flash rendering) of most Adobe Flash content from HVD VM to local  clients e.g 6215 thin client, or local computer with Citrix Receiver. By  moving the processing to the user end device, Flash Redirection helps  reduce server and network load, resulting in greater scalability while  ensuring a high definition user experience. With HDX MediaStream Flash  Redirection, users now have the ability to stream HDX Flash based  Web site content over ICA. This allows you to use the processing power  of the workstation of the user to run flash based streaming video  experience through Microsoft Internet Explorer, even with high  definition video content; reducing the need to use server side  resources.

In other words, without Flash Redirection, flash content is fetched  and rendered in server side (HVD), and the result video and audio stream  is sent down to the client for playback via the normal ICA connection  as normal graphic and voice objects, when there are heavy movement in  HVD, user may experience audio or video break up problems.

Two forms of flash redirection implementation:

1. Client side fetch and rendering:
Flash instance URL is  redirected to client, and client device will directly access to  Internet or the flash application hosting server to fetch the content,  then render the content locally,  and play back the audio and video with  the local sound device. This is the default flash redirection  behaviour, and it is also desired and recommended because fetch  and render Flash content on the endpoint is able to reduce server(HVD)  load, optimize the end-user experience, and be much more scalable for  large deployment. However this may not be always feasible if:

a. The content might be referenced by the Flash Player using a network address that is internal to an organization and such a URL can only be resolved on the server.
b. An  organization that restricts the network connectivity of their ICA  client devices so that they can communicate only with their XenApp or  XenDesktop servers

2. Server side fetch and client side rendering:
In above exceptional scenarios, we would the content to be firstly  fetched by the HVD, secondly the flash raw data is then retrieved by the  client from the HVD, and lastly the flash content is rendered in the  client to retain the user experience. This will help to maintain the  user experience and overcome the restriction of the end device  connectivity issue caused by e.g some security devices, firewall, proxy  server are blocking the direct internet access from the client devices. Server-side  content fetching is the exception option and can be configured on a  per-URL basis using a server-side configuration setting. In addition,  server-side content fetching must be enabled on the client. The Flash server-side content fetching URL list setting allows you to specify Web sites whose Flash content can be downloaded to the server then sent to the user device.

Flash redirection intelligent fallback behaviours:

There are some scenarios that the flash content is not possible or  suitable to be redirected to client device, HDX can intelligently  fallback to server rendering to ensure the flash content is loaded  successfully most of time to minimize the disruption to users.
1. If  you do not want all instances of Flash content to be redirected for  rendering on the user device. Typically, small Flash movies are  frequently used to play advertisements. Flash intelligent fallback  detects these instances and renders the content on the server. Using  this Citrix User Policy setting causes no interruption or failure in the  loading of the Web page or the Flash application.
2. If the client attempt to fetch the flash content for some reason failed.
3. The URL matched Flash Dynamic Blacklist

The HDX MediaStream for Flash feature Dynamic Blacklist Explained.

There are certain situations in which HDX MediaStream for  Flash failsfor certain Website URLs. This happens as a result of certain  Web pages that have been designed to work in a way that is not  compatible with our HDX architecture. These failures cannot be detected,  so HDX has been designed to create and use a Dynamic Blacklist to remember Websites that provoke these failures. In these situations,  the HDX feature falls back to server-side Flash rendering for the  current browser tab that provoked the failure. Additionally, it uses  server-side rendering for all future browser tabs that navigate to the  failing URL Website.

The Dynamic Blacklist URLs are stored in HVD windows registry table,

For Internet Explorer 7 and Internet Explorer 8 in non-protected mode:

For Internet Explorer 8 in protected mode, (Note: user SID specific path):

and if a URL is blacklist, the following occurs:

1. The current top-level URL of the offending browser  tab is refreshed, and HDX MediaStream for Flash is no longer used for  the reloaded page.
2. The current top-level URL of the offending  browser tab is added to the user's dynamic blacklist. If the user  browses to that URL for a period of time in the future (24 hours), then  the HDX MediaStream for Flash feature will not be used.
3. The appropriate event log is generated on the XenApp server (If the HDX GPO for server side event logging is enabled).
e.g "A Flash Player instance matched the HDX MediaStream for Flash  dynamic blacklist.  Server-side Flash rendering will be used if  available."

The URL by default is blocked from being client rendering for 24  hours on a per user basis, and the blocking period can be adjusted by  registry key "DynamicBlacklistAgingPeriod"

Flash Redirection interact with USB Redirection

For Flash Redirection client rendering, the local Flash player on  thin client (vxc 6215) or end device will use the default local audio  device on the thin client. If the connected USB headset is redirected to  the virtual desktop, then the local thin client SLE OS no longer owns  the USB device, and the Linux/client audio system has no knowledge of  the redirected USB headset. then the default audio device will be the  internal speaker. If the customer wants to use the USB headset for thin  client rendered Flash content then they will need to disable USB  redirection for that device. In another word, the redirected USB headset  is recognized and controlled by HVD WIN OS device manager, and if the  audio is played by the redirected USB device, it means the flash content  is actually rendered in the HVD and doing server rendering instead of   the client side rendering.

Components of HDX MediaStream flash redirection

Two types of Adobe Flash Players are required to use Flash  Redirection, and both types of Adobe Flash Players need to be on the  same major version (e.g Both are on 11.x) to be compatible, and if the  client detect the flash players are not compatible with each other, it  will fallback to server side rendering.
1. HVD adobe flash player:
This one is installed in HVD WIN OS and used with Windows Internet Explorer and is identified by Adobe as Flash Player for Windows Internet Explorer. This player is sometimes referred to as an ActiveX player

2. Thin client local adobe flash player
This is installed in thin client and is used with non-Internet Explorer browsers and is identified by Adobe as Flash Player for Windows - Other Browsers. This player is sometimes referred to as an NPAPI (Netscape Plugin Application Programming Interface) Flash Player.

For VXC 6215, a new ICA client (12.1) is required to be installed on  the thin client, and either the ICAsettings rpm or the new UC-addon  firmware rpm (8.6.639) is required to be installed on the thin client to  modify the ICA client connection configuration to support flash  redirection.

HIgh Level overview of Configuration for Flash Redirection

Flash redirection required both server side and client side configuration.

You can configure HDX MediaStream Flash Redirection settings on the  server side (HVD) through the HDX user Policies node of Citrix Desktop  Studio. These policies settings will be pushed to HVD VDA when the HVD  register with DDC. Or you can also use Active Directory GPO to push the  policies settings into HVD registry table. You control the Flash  Redirection features through the following Citrix User Policy settings:

  • Flash backwards compatibility
  • Flash default behavior
  • Flash intelligent fallback
  • Flash latency threshold
  • Flash server-side content fetching URL list
  • Flash URL compatibility list
  • Flash event logging
  • Flash acceleration
  • Flash background color list

You can change the default settings on the windows based user device  with the Group Policy Object Editor. For VXC 6215 thin client, the  client site configuration is done by the ICAsettings addon rpm or UC  addon rpm.

Detail Configuration Steps