Network administrators think about packets like car pools: if you stuff more into each “vehicle,” it’s more efficient, right?

Not when it comes to ICA packets. Let me explain.

The standard network maximum transmission unit (MTU) is 1500 bytes. The default maximum for ICA data is 1460 bytes, allowing for some overhead before the packet traverses the network.

Typically, ICA traffic is comprised of many small packets, as well as a some large packets. Large packets are commonly generated for initial session screen paints and printing jobs, whereas the ongoing user session is principally comprised of many small packets. For the most part, these small packets are the highest priority ICA data called Thinwire. Thinwire incorporates mouse movements and keystrokes. This ICA data is compiled based on activity and time as follows:
• Mouse movements: 50 milliseconds
• Keystrokes: 100 milliseconds

Let’s say that a packet of 60 bytes of data is generated for UserA based on these parameters during an ongoing XenApp or XenDesktop session. It’s important for these 60 bytes of data to traverse the network quickly and without delay. Otherwise, the user will perceive that the session is slow.

If you change these default values, let’s say by 10x, in order to make the packet larger (because fuller packets traverse the network more efficiently, right?), then UserA will experience approximately 10x delay (because it’s okay for the user to wait, right?). I’m being sarcastic here to stress a point: filling the Thinwire-based ICA packet isn’t more efficient because it has a negative impact on the user experience.

Although it may seem counterintuitive to keep the ICA packet size small in order for it to be more efficient, the user experience demands it. So, how can you optimize ICA?

By ensuring that ICA data traverses the network efficiently, the user experience is enhanced. Optimizing ICA is based on administrative configurations for ICA within XenApp and/or XenDesktop, as well as refining how ICA traffic at layer 4 and 6 traverses the WAN. But how do you go about doing that?

Join me on Wednesday, August 25th, for the Optimizing XenApp and/or XenDesktop Across the WAN TechTalk. Within that session, we’ll go deep into ICA, including specific settings that directly affect ICA traffic. We’ll even dissect some packets so that you can better understand what exactly is crossing the wire. No need to bring your own scalpel and forceps!

Jo Harder, Senior Architect