Recently, Citrix announced and demoed their App Receiver for iPhone product, which will allow iPhone users working for a company with a Citrix XenApp implementation to run Windows applications on their iPhone remotely.
While this is not the first Windows Terminal Server (WTS)-type client for the iPhone, there are a few important differences I noted from the demos on Citrix's site. Citrix has put some time into making their implementation a good iPhone application: rather than making you push and pull the Windows Desktop and Explorer around to get to your files, Citrix has abstracted the Windows environment so that you can more effectively get to folders in My Documents and other locations in a way that is efficient using the iPhone UI.
The "normal" way of dragging and double-tapping repeatedly to access files and folders in WTS clients on the iPhone gets tiresome quickly. Citrix employs a columnar method that looks nicer. There's nothing that can be done about actually using Windows applications on an iPhone, but every little bit helps.
Performance optimizations and better scale
Based on the demos I saw, it also appears that Citrix has done a lot of work on optimizing the performance of applications running in XenApp, so that the languorous performance I occasionally run into with existing iPhone WTS clients, even on WiFi networks, should be minimized in the Citrix client. This is important if you're in a situation where you can't get Wi-Fi access.
With Citrix can you forget you're really running the application on a server miles, or hundreds of miles away, despite only being on a 56K dialup connection. While the iPhone UI is not going to make using Windows applications that transparent, for a limited use case, such as accessing documents and making minor changes, the speed and UI improvements in Citrix's application will be quite welcome.
One thing to keep in mind when talking about Citrix and WTS is that they are not the same as Virtual Network Computing (VNC) and Apple Remote Desktop (ARD). Those products are designed from a 1:1 use model—1 person talking to a computer at a time. While you can have multiple people log into a system via VNC, even on a fast network, the bandwidth requirements quickly become an issue. It's one reason why, even on a clean Gigabit Ethernet network, I run ARD in greyscale mode, just to keep the speed up.
Citrix's ICA protocol, and Windows' RDP protocols are far less bandwidth intensive, so you can have 10, 20, or even a hundred connections to a single server at the same time, and everyone is happily working away. (Seriously, try running an ARD session over dialup in full color mode sometime, then compare it to a WTS or Citrix session. The differences will become obvious in a hurry.)
Where VNC is useful for taking over a computer remotely, Citrix and WTS are designed to allow multiple separate logins. A good analogy for this is the X Window system used on other Unix flavors, only Citrix/WTS can actually be less bandwidth intensive than those.
Roamin' IT gnomes
Another handy feature of WTS/Citrix is their support for disconnected mode, aka "Easy Roaming" in Citrix-speak. This feature allows you to be working on something in one place, say the office, and instead of logging out to go somewhere, you simply disconnect. When you get to where you're going, you reconnect, and your session is preserved as it was, ready for you to continue with what you were doing.
For the iPhone, Citrix uses the accelerometer in the iPhone so that within the Citrix client, you can use Easy Roaming by just shaking the iPhone. Not a technical feature, but kind of fun, and considering how un-fun terminal services inherently are, I'm impressed that they were able to figure out a way to give us a little amusement with our new, improved electronic leash.
Now, without being able to actually test Citrix's iPhone client, there's no way to really say how much better it performs and how well the new features are implemented. It's also important to keep in mind that this is a client for Citrix's Terminal Services implementation, so if it works at all with say Windows Terminal Server, or Aqua Connect Terminal Server is not guaranteed, and if it does work with non-Citrix implementations, not every feature may be supported. But based on the demos I've seen, and past experience with Citrix, it's clear that this offering will raise the bar for remote access applications on the iPhone quite a bit.
[John C. Welch is a senior systems administrator for The Zimmerman Agency, and a long-time Mac IT pundit.]