Citrix's ICA protocol (and related acceleration technologies, like SpeedScreen) have been around for over a decade. Even though not too many people focus on the value of ICA anymore, its value becomes immediately apparent to anyone who switches back to RDP after using ICA for awhile. So when Citrix announced their XenDesktop product last May, a lot of us were excited because we could use ICA for a VDI product.
Unfortunately, we quickly learned that the capabilities of the ICA protocol implementation in XenDesktop were not as fully-featured as the capabilities in Presentation Server / XenApp. (I called this "Partial ICA") It was ironic, because moving to XenDesktop is kind of an all-or-nothing thing, yet the experience was worse than using XenApp, which could be used for just certain applications as needed.
Citrix announced XenDesktop 3 yesterday, and one of the big parts of the announcements was some additional capabilities of the ICA protocol that will bring ICA on XenDesktop more in line with ICA on XenApp. I asked Citrix's Calvin Hsu to clarify exactly what was and was not included with ICA in XenDesktop 3.
The first clarification that Calvin wanted to make was that ICA on XenDesktop 2 wasn't "limited" per se, it's just that Citrix didn't have time to implement all of the features that are in XenApp. In other words, ICA is ICA... it's all the same "version." But XenDesktop 2 didn't have all of the host side code written yet to do as much as XenApp 5.
That said, let's take a look at the specific limitations capabilities of ICA that were not included in the XenDesktop 2 product. (This list is pasted directly from Citrix's official XenDesktop 2 Technical FAQ.)
- Kerberos SSPI or SmartCard Virtual Channels
- SpeedScreen multimedia acceleration & zero latency
- PDA sync, TWAIN, shadowing and SmartAuditor
- Audio on Vista
- ICA perfmon counters (SMC) and end-user experience metrics
Let's break this down into two lists, to look at what's there and what's not.
New capabilities of ICA in XenDesktop 3
- SpeedScreen multimedia acceleration (which is now called HDX MediaStream)
- Smartcard virtual channels
- PDA sync and TWAIN (both covered by the new, broad support for USB devices called HDX Plug-n-Play, which actually supports more than devices than on XenApp now)
- ICA perfmon counters (SMC) and end-user experience metrics. Perfmon counters can be consumed by any software running on the Virtual Desktop Agent.
ICA limitations / missing features in XenDesktop 3
- Kerberos SSPI
- SpeedScreen local text echo. (Instant mouse click feedback is a client side feature and has always been available.)
- Audio on Vista (this is coming soon)
- EdgeSight agent to consume the Citrix-specific metrics, like SMC and end user experience. (Although EdgeSight can now track the other usual historical metrics for pooled / non-persistent desktops.
Thanks to Calvin for taking the time to make these clarifications!