Thursday, April 6, 2023

Want to reduce your HDX bandwidth usage by up to 15%? Try this!

Usually when I write a blog post, I would introduce some new graphics optimization aimed at delivering the same great user experience but at lower cost. But this time, it’s a little different, and I need your help.

The Reducer

First, let’s talk about compression. If you’re reading this, you probably have some understanding of compression and why it’s useful when it comes to remoting protocols. Indeed, we use a variety of compression techniques, some suited to graphics, some to audio. But we also have a general purpose compressor designed to work across all virtual channels. Internally, we call this “The Reducer.” Sounds like a villain straight out of a movie, right? Actually, he’s one of the good guys and has been at the core of our protocol, compressing every byte of every packet that passes through our stack, for the past 20 years.

Actually, he’s so good, he’s been very difficult to replace. That was until a few years ago, when I had a breakthrough, and several others that have followed since. What initially started out as a bit of a side project has finally made it into our protocol!

Lower Costs and Better Performance

Here’s the best part: the new algorithm is so optimized that, based on our testing, server scalability does not appear to be affected! Or to put it another way, users should not see any degradation in the in-session experience. Actually they may even notice an improvement. How is this possible you might ask? Not only does lowering bandwidth reduce costs on pay-per-byte networks, it also means that packets take less time to transmit, resulting in faster response times. This is particularly true on constrained or shared links, for example, at a remote branch office.

With all that said, replacing something that has been battle tested for 20+ years is a decision that should not be taken lightly. So while the new version looks promising, it is currently disabled by default. This is where you come in.

How to Use the New Reducer

You can turn on the new Reducer with a single registry setting in VDA 2303. You’ll also need Citrix Workspace app 2303 for Windows, which you can get from our downloads page at The registry key is different depending on whether you’re using a single-session Workstation OS (Windows 10 or 11) or Server / multi-session OS (Windows Server / Windows 10 or 11 multi-user):


Windows 10 or 11 (the “WDSettings” key needs to be created if it doesn’t already exist):


Windows Server / Windows 10 or 11 multi-user:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\icawd

Create or modify the following value:

[REG_DWORD] ReducerOverrideMask = 23 (decimal)

Once you’ve set this, simply disconnect / reconnect (or logoff / logon), and the new Reducer should be selected if you’re using Citrix Workspace app 2303 for Windows. Don’t worry, you can still connect with other versions of Citrix Workspace app just fine: the older Reducer will be selected as it always has been.

One thing to note is that if you’re connecting via NetScaler Gateway (NGS is fine), HDX Insight will be disabled. An upgrade of NetScaler Gateway will be required once we switch defaults.

You’ll see the biggest improvements on typical productivity workloads, like Office-like apps or browsing web-pages. I last blogged about Trader workloads, and we’ve seen improvements there, as well. Remember, it works across all virtual channels, so bulk transfers of uncompressed files should also be quicker and use less bandwidth. Workloads consisting of a lot of audio, video or heavy graphical content may not show a significant improvement due to the other virtual channel specific compression being used.

Get in Touch

If you have the ability to measure bandwidth usage in your organization, then I would absolutely love to hear from you on whether you see any difference, good or bad! There is no replacement for real-world data, and perhaps knowing you had a small part to play in the development of new and innovative features within HDX may be a good enough reason to get in touch.

Thanks for reading and please do reach out by emailing me at: muhammad.dawood[at]


from Citrix Blogs

No comments:

Post a Comment