The last couple of newsletters looked at some of the challenges associated with implementing virtualized servers. This newsletter will examine some of the challenges associated with implementing a virtualized desktop infrastructure (VDI).
As part of VDI, a virtual machine (VM) on a data center server hosts a complete user desktop including all its applications, configurations, and privileges. The client then accesses the applications via the network with the desktop and application objects delivered on demand over the network from the virtual desktop servers via a remote display protocol, such as Microsoft Remote Desktop Protocol (RDP) and/or Citrix’s ICA protocol. In some instances, the user’s desktop will contain two isolated environments. One environment is controlled by the IT organization and allows the user access to the corporate applications. The other environment contains whatever applications, data, music, photos, etc. the user has loaded onto their desktop.
Some of the primary benefits of virtualized desktops include simplified management, improved security, and increased reliability of desktop services. In addition, it allows users to access applications from a wide variety of devices, including fully functional PCs, stripped down PCs, or smartphones. The ability to use a smartphone to access corporate applications is very powerful. Unfortunately, it now introduces a wireless WAN link into the end-to-end information flow. That will present challenges that we will discuss some time in the future.
One of the primary challenges associated with VDI is the contention on the WAN link that connects the remote user with the VM in the data center. There is contention on this WAN link both among the various types of traffic (e.g., ICA/RDP, audio/video, other) that transit the WAN link, as well as among the various types of VDI traffic (e.g., screen refresh, file transfer/print, and keystrokes).
ICA and RDP are highly optimized protocols. For example, ICA has the ability to tune the TCP window size in order to improve performance. As such, optimizing TCP will have little impact on the VDI traffic stream. In addition, ICA and RDP incorporate a number of compression techniques including bitmap image compression, screen refresh compression, and general data compression. As a result, compression and caching will have little impact on the VDI traffic stream.
In contrast, QoS and bandwidth management can play a significant role in mitigating the WAN contention issues. Screen refresh, for example, is highly interactive and very sensitive to congestion. Video traffic is also very sensitive to congestion. QoS and bandwidth management can ensure that these applications perform well. While file transfer and print jobs are not very sensitive to congestion, they can induce congestion on the WAN and hence impact the other types of applications. QoS and bandwidth management can ensure that these applications do not interfere with applications that are sensitive to congestion.
This is our last newsletter for a while on the impact of virtualization. We will, however, be coming back to this topic in the near future.