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Virtual desktop infrastructure (VDI) challenges over the WAN

Many virtual desktop infrastructure (VDI) challenges present themselves over wide area networks (WANs). Here is how you can prepare your WAN for VDI while the technology matures.

Networks have to constantly adapt to new demands placed by new applications. For network engineers scrambling to...

keep pace with those demands, these guidelines will help you prepare for the many virtual desktop infrastructure (VDI) challenges created by application virtualization over the enterprise WAN.

The history of IT teaches us that—for the most part—applications drive innovation in network technologies. This is particularly evident on systems that support the WAN. To show you what I mean, let's take a stroll down IT memory lane and rewind the clock 20 years.

In the early 1990s, enterprise users were exposed to online content that drove bandwidth demands beyond dial-up speeds for—ahem!—work-related Internet traffic. Before the turn of the millennium, Voice over IP (VoIP) provided the motivation to add network intelligence to prioritize traffic and protect application performance via Quality of Service (QoS). More recently, video streaming—which is now used in conferencing across the enterprise WAN—quickly advanced from low quality to HD quality. All the while, we could not ignore the need to protect the user experience, which is increasingly difficult to protect with the growing complexity and burdens of applications on the WAN.

The point of all this is that network engineers have had to keep pace with the demands of applications placed on their networks. Whether it is to apply intelligence to better handle traffic to improve quality, or to implement policies to prevent applications like Farmville or Netflix from wasting valuable corporate WAN resources, network engineers have to be responsive to the needs of the business. As we look back at IT history, we should then ask: What are the next applications on the network that will create new demands to drive changes in the WAN?

Prepare your WAN for virtual desktop infrastructure (VDI) challenges

One such application that network engineers should be prepared for is virtual desktop infrastructure (VDI)/application virtualization. Even with the looming release of HTML5 by the W3C, applications and desktops still need to be delivered over IP via a protocol—such as ICA, PC-over-IP or RDP—that will place new demands on the network. The intent of this two-part article is to outline some VDI challenges introduced on your network.

VDI is real time with less tolerance
Like a demanding executive that wants the latest and greatest tablet yesterday, VDI is not only demanding but also intolerant of poor performance. Like voice and video over IP, VDI needs to transfer packets across the network as close to real time as possible. This is because the user is actually communicating with a virtual system at the data center, which is likely at another location. The user experience will be greatly affected by the network performance—particularly by latency. Network engineers need to be prepared to treat VDI as a real-time application.

WAN optimization won't come to the rescue
Unlike CIFS (i.e., file transfer), SMTP (i.e., email) and HTTP (i.e., Web traffic), VDI traffic does not benefit greatly from WAN optimization. My experience has proved WAN optimization unlikely to reduce more than 20% of VDI traffic. While WAN optimization will certainly help to reduce other traffic on your network and may even reduce VDI bandwidth consumption by a small amount, it can do nothing with the real barrier: The speed of light.

Common images and multimedia streams can be reduced by WAN optimization through caching and compression, but interactive traffic—like mouse and keyboard inputs—is a poor candidate for compression due to the fact that it is already a small packet stream. Additionally, it cannot be cached and therefore must traverse the WAN. Any latency above 250 milliseconds—even if only for short bursts—is noticeable by the user and gives the perception of a slow system.

The limited improvements, if any, that WAN optimization can provide to VDI are likely not enough to justify its cost as a solution to improve VDI performance. However, its ability to help reduce other competing traffic would improve the performance of applications outside of the VDI environment and reduce total bandwidth consumption.

VDI challenges network monitoring
If you wish to empower your IT team members with a useful monitoring tool to protect the performance of the VDI environment, you need more than MRTG graphs and SNMP alerts of jitter and packet loss. You need monitoring solutions that allow your team to find root causes of performance issues. Below are some recommendations:

  • Implement flow analytics by enabling features on your gateways/routers such as IPFIX, NetFlow or sFlow.
  • Get a comprehensive collector and analysis tool like Scrutinizer from Plixer International.
  • Learn how to analyze the traffic in real time by first learning the analysis tool and then by watching your environment during known periods of concern—like in the morning when everyone logs in.
  • Keep historical data for trend analysis. Historical data will allow you to compare your network performance before and after you deploy VDI to see what the effects of VDI are and what traffic potentially could affect performance before you fully deploy it.

Give VDI a higher priority on your QoS design
What I'm about to state next will go against the mainstream thinking of network engineers but should be considered. Give VDI the highest priority in your network QoS design. This goes against most of the standard QoS practices that put voice and video traffic below only monitoring and systems management traffic. I state this because VDI, like voice and video, is a communication protocol not between two people but rather the users and their virtual system/application. A typical user will communicate more with his or her virtual system than talk on the phone with other employees.

There is a problem here. Typical ISPs (Internet service providers) today won't allow this because the highest Class-of-Service levels are reserved in their network for voice and video. Therefore, you might have to wait for network service providers to catch up in their understanding of VDI before you can apply this practice.

In part two of this article, I will outline specific ways to analyze your VDI traffic to look for root causes of performance issues and to optimize your network to improve the user experience. Read on to prepare for the performance problems posed by VDI over WAN.

This was last published in August 2011

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