A Citrix secrets of success in providing graphics and 3D video on limited bandwidth connections is how we adjust dynamically to the network and end point to optimize the user experience. This is what we call Adaptive Display. HDX Our engineers are working on further improvements to Adaptive Display cases for mobile use in the output of Avalon Excalibur project, and the results are very impressive.
Adaptive Display has its roots in a technology called progressive display we introduced several years ago in Presentation Server 4.5. The concept was simple: When you move in 2D or 3D around the screen, the smooth movement is more important than image quality. There is no advantage to send each frame to full height on a low bandwidth connection if it results in hesitant, jerky movement or even a "slide show" worst. So Lossier compression used on progressive display moving images and a less lossy compression (compression may even lossless) for still images. The necessary level of compression will depend of course on the available network bandwidth to Progressive Display provided policy to treat different types of connections. In addition, the compression Heavyweight (arithmetic encoding) was presented as an option to provide even greater bandwidth savings for the same image quality at the expense of better use of CPU. And other technologies such Queuing & Tossing and Dynamic Frame Rate Shutter adjusted further delivery of graphics and video to squeeze the best possible user experience on a low bandwidth connection.
Progressive display was a bit difficult to set up properly. I often worried that some customers may not receive the full value of this feature due to incorrect or incomplete configuration. So with XenDesktop 5.5 and XenApp 6.5 HRP1 we introduced Adaptive Display. The basic principle remains the same as with progressive display, but Adaptive Display is self-tuning, even as network conditions change. Zero configuration.
With Excalibur, we will introduce the next generation of Adaptive Display. Our SuperCodec, which determines which compression algorithm to be used for different parts of the screen has been improved with Deep H.264-based compression XenDesktop HDX 3D Pro. Citrix VDI was the first provider to leverage H.264 codec technology with the introduction of XenDesktop HDX 3D Pro three years ago. We continued to improve our H.264 technology to offer higher rates framework, better image quality and best-in-class efficiency of bandwidth, as you saw in our XenDesktop 5.6 Feature Pack 1 HDX 3D Pro release, which came out in June. And now we have decided to expand our use of H.264 beyond 3D high-end graphics so that all users of XenDesktop and XenApp will benefit from the latest video codec technology. Our "secret sauce" is how we tune H.264 on the fly to dynamically adapt to changing network conditions.
The realization of 30 frames per second on a LAN is not a big challenge, but 3G is another story. With the start Excalibur code in the lab we see 18 frames per second on 3G 800 Kbps connections, more than double what was previously possible with such limited bandwidth. Scalability and WAN link has increased by over 100% with no reduction in video quality. Remarkably, our new technology can even provide a good experience to play HD video over low-speed connections by reducing the rate of a bit order of magnitude. For example, we can take a video of 8 Mbps and HD transrate down to 800 Kbps so that a user on a 3G connection will always get a good experience. And we can take advantage of the multimedia hardware decoding on mobile devices to offload the CPU and save battery power.
A glimpse of the future of Adaptive Display is possible with the release of Avalon Excalibur Tech Preview project and accompanying Citrix Receiver for Windows. Although we have not yet Adaptive Display integrated with desktop composition Redirection, which is the default out-of-the-box in the Tech Preview, you can enable Adaptive Display by changing your Windows 7 virtual desktop (configured with two vCPUs) from Aero mode in Basic mode. This will give you a glimpse of what is to come in mobile versions of Citrix Receiver.
With one fluid motion, the high rate video and graphics frame, on any device, over any network connection, HDX Adaptive Display is sure to play an increasing role to enable mobile workstyles.
Derek Thorslund
Director of product management, HDX
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