XenDesktop Bandwidth: The Complete Set

Part 1 – The Prologue: Methodology and Infrastructure

Part 2 – By The Numbers: Take the time to optimize

Part 3 – Bringing It All Together: Daily User Average and General Recommendations

Part 4 – What about XenApp?

Part 5 – Do It Yourself: Starter Kit

Part 7 – Who needs a part 6 when we’re discussing XenDesktop 7.x (And XenApp 7.5!)

Bonus Customer Analysis!
Bonus HDX 3D Pro!

Part 7: XenDesktop 7.x (and XenApp 7.5)

Throughout this series, I have provided daily bandwidth requirements for XenDesktop 5.6 and XenApp 6.5, explained why seamless applications help to reduce bandwidth and provided optimizations that help you get the most out of your WAN.

Now with XenDesktop 7, everything has changed. This post also applies to the brand spanking new release of XenDesktop 7.1 so I’ll be referring to XenDesktop 7.x for the rest of the post.

UPDATE 4/24/14: Guess what, this also applies to XenDesktop and XenApp 7.5! I have made several changes throughout to reflect updates.

What’s New

In XenDesktop  and XenApp 7.x  there are three main delivery methods for the basic desktop (I am excluding HDX 3D Pro here).

  • The first is called Desktop Composition Redirection and is the improved version of what was known as Aero redirection from XenDesktop 5.x. It is available only in XenDesktop.
  • The second is the H.264 enhanced SuperCodec which is optimized for server rendered video and graphics delivery.
  • The third is called Legacy Mode, reverting to what was known as the original Adaptive Display in XenDesktop 5.x and XenApp 6.5.

Once again, I put these to the test and will share my results and recommendations regarding which delivery methods are best suited for the WAN.

Desktop Composition Redirection (DCR)

This is the default setting in XenDesktop 7.x for capable Windows end points. DCR is only available with Desktop OS VDAs.

In a LAN, a fully equipped Aero Windows desktop can be delivered with large CPU savings by using Desktop Composition Redirection (DCR). DCR allows for the offloading of CPU requirements to the end point at the cost of additional bandwidth. In a LAN or even a home office this is not much of an issue, however if necessary, it is possible to lower that bandwidth requirements through Citrix policies and Windows optimizations which have been provided in a previous blog post in this series.

As mentioned several times throughout the series, video delivery has an effect on bandwidth. Video is many times the biggest consumer of bandwidth. Most end points capable of DCR, will also be capable of Flash Redirection, which is highly recommended for reducing bandwidth and delivering a better user experience. This can now be done with Windows Media as well with the introduction of Windows Media client-side content fetching.

Now why is DCR the default setting for capable devices? If you are using Windows 7, Aero can be disabled by quite a few methods. Citrix policy, registry, Visual Settings GUI and more. In Windows 8 and above Aero is always on. You can either redirect its processing through DCR (hence the default setting) or process it in the datacenter at the cost of additional CPU (or GPU).

Now since DCR will not often be seen on the WAN let’s take a look at what we will be seeing – the H.264 SuperCodec.

H.264 Enhanced SuperCodec

This is the default setting in XenApp and XenDesktop 7.x for Server OS VDAs, mobile devices and devices which cannot support DCR.
It does however require Receiver 3.4 or above on Windows, 11.8 or above on Mac, 13.0 for Linux, or the latest Receiver through the iOS and Android app stores.

The H.264 SuperCodec has its roots in HDX 3D Pro although in this case does not have the associated requirements. It is processed completely on the CPU and can be used on almost all end points using the latest versions of Citrix Receiver.

In XenDesktop and XenApp 7.x, this codec also allows that fully equipped Aero desktop I would access from the LAN using DCR to look the same on my mobile, Mac, or Linux device with features like transparency and peek. As current users of XenDesktop 5.x are aware, Aero was not available on devices that did not support Aero redirection. This does come with an increase in CPU as everything is now rendered on the virtual desktop and sent compressed to the end point.

Since the H.264 SuperCodec is most relevant to the WAN, I decided to focus on testing configurations using this codec. What I found was that the codec adapts so well that there was not much tuning to be done in terms of optimizations. XenDesktop 7 will automatically disable some of the visual eye candy that I talked about earlier in the series and the rest can be disabled using the optimization kit I provided in the 5th post in the series.

Now how does the daily average compare to XenDesktop 5.x? Well that depends how you want to look at it. Running the Login VSI medium workload yields higher averages than those I ran with XenDesktop 5.6. This average was driven up mostly by the office applications which used very little bandwidth in XenDesktop 5.6. When it came to video XenDesktop 7 was the clear winner in terms of both bandwidth, and the amount of frames that were delivered to the end point with that bandwidth.

With that in mind, I decided to provide a formula based on the same Login VSI medium workload at the same 1.536Mbps network limit as previously provided for XenDesktop 5.6. For transparency sake, the numbers here are higher, based on the higher average seen in the workload. However when I completed manual tests and direct comparisons of server rendered video – the direct tests of user experience – I saw that comparing the two is like comparing apples and oranges.

Bandwidth (kbps) = 240H + 160D + 2000X + Z
= Number of concurrent users requiring video without flash redirection
D = Number of concurrent users who are not watching video
X = Number of concurrent users who require 3D applications  (2000kbps borrowed from other testing)
Z = Additional 1000 to 2000 kbps minimum capacity to support peaks in smaller environments (<10 users)

Note: This formula is for the  Windows 7 OS using the H.264 SuperCodec. It is based off of the Login VSI 4.0 Medium workload.  

For an updated formula based on additional customer analysis and testing see Bandwidth Update or refer to the Virtual Desktop Handbook.

The H.264 SuperCodec was designed with user experience in mind. It adapts better than the previous codec in XenDesktop 5.x and in the 1.536Mbps network, it utilized the available bandwidth more efficiently to deliver a better user experience, although it did use more bandwidth under the same conditions. To test the user experience out myself, I went back and performed the same manual testing that I discussed in blog post 2 of this series. What I saw was that even when delivering a full Aero enabled desktop, XenDesktop 7.x using the H.264 SuperCodec delivered a better user experience across the board in my manual tests.

The results for the manual testing can be downloaded via ShareFileHere.

Now why do I keep referring to the “SuperCodec”? Well as mentioned above, video delivery can be bandwidth intensive, but can be improved through HDX with features like Flash Redirection. When it comes to mobile devices, my iPhone for example, cannot leverage Flash Redirection and must rely mainly on server rendered video which means that adequate bandwidth is most important for a smooth experience. Furthermore, Aero features which have been unavailable on Mobile, Linux, or Mac devices can now all be delivered. The new H.264 codec is optimized for delivery of server rendered video and graphics and can deliver more frames per second to my iPhone (or any compatible mobile device) using less bandwidth. See the chart below comparing a Login VSI provided video at 480p fetched and rendered on the server side. The experience was very much improved with an almost doubling of frames per second delivered while still using less bandwidth!


Legacy Mode

Note: Legacy mode will not work with Windows 8 and above virtual desktops.  

Legacy mode is exactly what it sounds like. When enabled, the VDA will revert to the XenDesktop 5.x and XenApp 6.5 Adaptive Display settings which have been rigorously tested in the previous blog posts in this series. In the context of XenDesktop or XenApp 7.x, this delivery method should be considered when both bandwidth and CPU are constrained. The visual display policies to control Adaptive and Progressive Display are still available in XenDesktop and XenApp 7.x however they apply only when Legacy mode is enabled.

Note that when testing Legacy Mode using the Max Optimized configuration from the previous blog posts, the results were identical to those of using the XenDesktop 5.6 VDA. The bandwidth and CPU are lower in this scenario, however the user experience is not as rich in this case.

Legacy mode can still be leveraged in Server 2012 and Server 2012R2 to deliver applications and hosted shared desktops to a WAN when server scalability is more important than user experience. Legacy mode is enabled only through Citrix policy.

What to do with all these choices?

So now that there are three choices in delivering XenDesktop or two in the case of XenApp, you’re probably asking yourself, which one is best for me? Well of course the standard consulting answer is it depends, but here are a few things to think about when deciding.

  • In the LAN start off with DCR if you have the bandwidth and end points to support it. This will allow a rich user experience while minimizing CPU usage on the servers.
  • Now since DCR is only for the Desktop OS, use the H.264 codec if delivering XenApp in the LAN.
  • For remote home users with a broadband connection leverage DCR for a rich experience as most home connections have more than enough bandwidth.
  • In a WAN, use the H.264 SuperCodec, especially if using any server rendered video
  • If server scalability is a limiting factor due to CPU and bandwidth is constrained, leverage the Legacy mode feature and the benefits of XenDesktop 5.x Adaptive Display (Not available on Windows 8 and above)

To help summarize the three delivery methods, see the graphical cheat sheet below. Note, however that this is will help you get started, but it there is no substitute to testing so don’t forget to test, test, test!

Thanks For Reading,

Amit Ben-Chanoch
Worldwide Consulting
Desktop & Apps Team
Project Accelerator
Virtual Desktop Handbook