Using Windows Server 2008 Terminal Services? No DWM For You!
A cool feature introduced in Vista is the ability to remote the Aero Glass UI over RDP. One reason this feature is cool is that the remote computer need not be able to support Aero Glass on its own for this feature to work. Even systems that are not powerful enough to provide Aero Glass when accessed directly can support it when accessed remotely from a system that is powerful enough. This magic happens because RDP 6 is able to transmit the raw instructions from the Desktop Window Manager (DWM), rather than simply transmit the remote desktop as an image. It is the client device that then converts these instructions into the visual display.
I discussed this capability to transmit display instructions over RDP in my posts about WPF Remoting and expressed hope that Microsoft will provide this capability as part of Windows Server 2008 Terminal Services. Unfortunately the final word from Microsoft is that DWM is turned off in Windows Server 2008 when a Terminal Server session is started. This means that end-users will not get the Aero Glass experience when accessing remote desktops hosted on Terminal Servers.
How does this relate to Microsoft’s acquisition of Calista? The Calista technology, when integrated into RDP, will enable remoting of Aero Glass when the server has the ability to render it but the client does not. In other words it better utilizes server resources to create a high-end user experience, but ultimately it does stream down a sequence of (highly compressed), images. This is because the WPF instructions are executed on the server side.
So, as we can see, WPF Remoting and the Calista technology are sort of mirror images of each other, and in this way they compliment each other. When Microsoft does integrate these technologies into Windows Server Terminal Services the result will be a much improved experience for remote users using RDP regardless of client device capabilities, and optimal resource utilization.