USB and VDI, why it’s not so easy!

On my current project we are looking at various VDI (virtual desktop infrastructure) solutions, to meet some pretty stringent requirements. In past years the technology was just not there yet to provide a fully collaborative A/V experience to our users so we stuck with traditional fat clients.

The killer application for us is desktop 2-way video conferencing using USB web cams and headsets. Currently we are using a third-party conferencing application, but it is end of life and now other options such as OCS 2007 R2 Live Meeting are on the table. But I digress.

Today there are limited number of VDI solutions which can support robust 2-way A/V to the desktop. The key to understanding which solutions you can choose from is understanding the gory details of USB. A number of VDI solutions today support a variety of USB devices including smart card readers or scanners. So what about web cams and head sets? Shouldn’t they work just as well? Unfortunately not.

Nearly all web cams and head sets operate in ‘isosynchronous‘ mode meaning the device is sending a constant (and likely high bit rate) datastream to the client device at precise intervals. Why is this important? Very few VDI solutions support isosynchronous devices, because technically they require a lot more intelligence and processing logic due to the large amount of constant data the device is sending.

The bottom line is the two VDI leaders, Citrix XenDesktop and VMware View, today do not natively support isosynchronous USB devices with their ‘hosted’ VDI product. By hosted I mean a client OS VM running on a server, remoted to a client device via ICA (Citrix) or RDP (Microsoft). Plus, if you are using VDI over a WAN you need to consider the bandwidth required by such USB devices in addition to the multimedia stream the user is viewing.

In addition to a hosted VDI solution, Citrix has a streaming OS feature where the OS runs on the client end point device but PXE boots from the network so it acts just like a typical fat client and thus can use any USB device you wish. So today with Citrix XenDesktop OS streaming, full 2-way A/V conferencing is possible. However, this is just a LAN solution and will not work over a WAN. For WAN solutions, you are looking at a hosted VDI solution.

But back to the hosted VDI solutions, since that is a more common approach. If you have looked at all into thin clients, you will have heard of Wyse. They are one of the leaders, and have a variety of hardware devices at many price points. Wyse has a proprietary add-on to Citrix XenDesktop and VMware View which is called TCX. TCX has several components, one of which is isosynchronous USB support. Unfortunately, this proprietary software requires a Wyse end point device and an additional license for each device.

Wyse makes a variety of appliances which work for many customers, but they do not produce the most powerful thin client on the market. The most beefy thin client today is the HP GT7725. With Windows 7, Aero Glass, and future graphical intensive programs, lengthy refresh cycles, robust hardware is at the top of my list. Thus after careful consideration, I ruled out Wyse which also ruled out the TCX extensions for enhanced USB support.

So for now, the Citrix XenDesktop using the OS streaming model is the primary solution I am evaluating. There are enhancements to both XenDesktop and VMware View later this year which should add native isosynchronous support to hosted VDI solutions. If and when this happens, it will open up another deployment scenario which could be very useful since it would be WAN friendly unlike the OS streaming mode.

In my next blog I will cover some of the cool features of the HP GT7725 which make it a very appealing platform and might even replace a traditional thick client by adding local flash storage.

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February 1, 2012 4:33 pm

Has much change in this regard since this was posted? We are running in to issue with USB storage devices as it applies to the end user experience.