Moving up the stack, organizations also need to consider the type of VDI implementation being optimized. TCP-based VDI protocols, such as Citrix ICA, can be accelerated by a number of vendors, including Blue Coat, Riverbed and Silver Peak, but not all VDI implementations rely on TCP. Part of VMWare's PCoIP, for example, runs on User Datagram Protocol (UDP), as does Sun Ray ALP. The only WAN optimizer I've seen claim to accelerate IP and, by extension, UDP is Silver Peak.
You've also got the matter of packet flows to consider here. With a VDI implementation, every client must maintain at least one flow, and the average thin client can have 10 to 15 TCP flows at any one time. Organizations need to be sure that the data center appliance they're purchasing can support a huge volume of concurrent flow or risk scaling issues.
WAN optimizers will be challenged to identify the right application at the right time. Application classification is essential if WAN optimizers are going to know how to accelerate certain kinds of traffic. Yet many WAN optimizers continue to classify applications based on port numbers. I know this will come as a shock to those of you living in the 21st century, but classifying applications strictly based on port numbers is going to be problem when a bazillion different Web applications share port 80.
Instead, WAN optimizers need some kind of deep packet inspection (DPI) engine to look deeper into the packet to know what types of applications are being accelerated. Riverbed, for example, has long been able to differentiate between types of traffic and then prioritize user activities accordingly within the Citrix ICA environment, but that hasn't been the case with PCoIP. Riverbed claims to have addressed the issue with its AppFlow Classification Engine, which will be available in the first quarter of this year.
VDI offers organizations a number of operational benefits, and WAN optimizers can in theory help realize those benefits at the branch office. But this story will play out well for IT pros only when the WAN optimizers address all of the VDI's networking challenges.