Virtual desktop infrastructure (VDI) projects could come unstuck if implementers treat them as just another flavour of server-based computing, a WAN acceleration expert has warned.

Ofer Bezalel, Expand Networks' services VP, said that although VDI - which gives each user their own virtual PC, hosted on a server in the datacentre - uses the same RDP and ICA remote access protocols as Terminal Services, its bandwidth demands are much higher because its usage profile is quite different.

Where Terminal Services is typically used to deploy task-specific applications or capabilities, VDI is all about providing the full capability of a desktop PC, he explained.

"We're talking about a significant hike in the bandwidth load on the network," he said. "An average of 20kbit/s per RDP session for Terminal Services can rise to 150kbit/s or even several Mbit/s with VDI because now you have a lot more information passing through.

"In server-based computing the applications tend to be tied down, and usage is less intensive and less graphical. With VDI, it's your own desktop, so the application load is different and more graphical. Sessions also tend to be longer and transmit a lot more information."

Bezalel said the problem will be particularly acute where branch office users are trying to connect to virtual desktops at the head office, over the WAN.

He added that while TCP acceleration and QoS optimisation can help, they cannot fix the problem completely because of the chatty and real-time nature of RDP and ICA. What's needed is specific optimisation software for those protocols, such as the RDP add-on Expand offers for its Compass WAN accelerator devices, he claimed.

One RDP user that has already experienced WAN congestion as a result of these issues is Reed Exhibitions. Duncan Carmichael, the company's global WAN manager, said he dealt with the problem by adding Expand's technology.

"By working with Expand we have experienced significant performance improvements in our RDP response times while eliminating any congestion issues, and the deployment was seamless," he added.