Citrix HDX marches on in release 1811

Citrix has made some updates to HDX in the latest release, and Jo Harder dissects the new features and explains the good and the not-so-good for admins and users.

When comparing virtualized apps and desktop solutions, HDX is often the key functionality that distinguishes Citrix from its competitors. So, what’s in the latest 1811 release? (And, for those that may have been afraid to ask, what’s exactly is HDX?)

Let’s delve into the bits and bytes of HDX.

What is exactly is Citrix HDX?

The true definition of HDX is High Definition eXperience, which can be construed as a follow-on to the Independent Computing Architecture (ICA) protocol. As you probably know, Citrix started thin-client computing back in the 1990s based on ICA and has progressively improved upon that technology.

HDX emerged as a marketing term that embodied not only the ICA protocol but also key features such as peripheral support, policies, and all things related to session bandwidth. Basically, the technologies that comprise the user session communications fall under the umbrella of HDX.

New features in Release 1811

Release 1811 included numerous Citrix HDX enhancements that feature some interesting technological advancements. Most of these new features operate quietly behind the scenes to improve the user experience.

Adaptive Throughput
Presenting virtualized apps and desktops to users has always been a challenge for WANs, especially where bandwidth availability fluctuates. ICA was built on technology that automatically compresses user traffic based on bandwidth availability, which is why bandwidth utilization tests differ so dramatically when comparing single-user access versus multiple-user access to the same Citrix server. Just when we thought the abundance of land-based bandwidth resolved those issues, the graphical nature of applications and more bandwidth-constrained use cases, such as cellular, have added new challenges.

From a technical standpoint, bandwidth compression only solves part of the problem, and Citrix’s new Adaptive Throughput is a dramatic improvement. Adaptive Throughput maximizes the data transfer rate that is pushed through to the client device, primarily evidenced by reduced video choppiness and better user interactivity.

In the Q3 release, the default ICA buffer packet count in Workspace App 1808 doubled, but this hard setting may not have been universally optimal. While administrators could manually adjust parameters based on environmental requirements, it’s unlikely that many did so.

This new release allows larger amounts of data to be sent and only reduces throughput if it affects interactivity. As a result, more data can flow based on the current state. For example, if a user is accessing a graphics-intensive application and transferring files as well, the screen is allotted the ample bandwidth and retains priority while the file transfer may be allocated less bandwidth based on availability.

Relevance: The goal of a Citrix session is to equate to a local computer experience; however, the network is a key and often unknown variable. Overall, this feature will improve the user experience because of more data throughput and prioritization.

Graphics: DPI Matching and Virtual Display Layout
Keeping in mind that ICA is a presentation-layer protocol, this means that the user screen is populated by a myriad of bitmaps, not the actual data. Because the display technology incorporated into user graphics has improved dramatically and provides a higher level of detail and quality, users expect that their Citrix sessions will likewise provide that same level of graphic richness as compared with local devices.

DPI support is about dealing with the latest high-resolution displays (4K+) and maintaining graphics and text size in the session to match the endpoint. As such, the client (Receiver / Citrix Workspace App) must be DPI aware. This can be done either though scaling (first released with Receiver for Windows 4.10 in early 2018) or DPI matching (new in 1811 for Citrix Workspace App for Windows). The main difference between these two options comes down to scalability and image quality considerations.

Virtual Display Layout is also about getting the most out of the newest high-resolution displays, and in particular, aimed at larger 40+ inch monitors. The main use case would be for customers to replace multi-monitor setups with a single large 4K+ monitor as is the case in the financial services sector.  

Relevance: If you’re using simple greenscreen apps, these display improvements won’t mean much to you, but if you are virtualizing corporate training materials, CAD applications, and similar highly graphical apps across a large monitor, these improvements will be most welcomed.

File transfers: Client Drive Mapping
Remember the early days of Client Drive Mapping (CDM) when it took what seemed an eternity to transfer a file to or from the local computer? While it will never be quite as fast as transferring a file from the local computer to a thumb drive, CDM has been re-architected, and file transfers are now much faster.

Previously, CDM data was being sent in 1 MB chunks and then would stop and wait for acknowledgements. As a result, file transfers were throttled at sub-optimal line speeds. Now, CDM is stream oriented, and the acknowledgement logic is handled by the Winstation driver, which is an underlying component that is the muscle of ICA. Winstation optimally controls the bandwidth estimation and queuing mechanisms.

Relevance: Previous clunkiness was definitely a pain point because file transfers were slow and sometimes failed. While many organizations disallow file transfers via policy for security reasons, those that do allow it will find that faster file transfers will be most welcomed by users.

Overall analysis

As competition heats up, enhancements to Citrix HDX continue to provide product differentiation. In particular, Adaptive Throughput should be welcomed for dramatic improvements to the overall user experience. DPI matching, virtual display, and client drive mapping will be appreciated based on niche requirements.

However, one HDX feature that still doesn’t have a good news story is Enlightened Data Transport (EDT), which is a subsequent generation of ICA. This awesome UDP-based user session transport protocol has been available for over a year, but it is still not available with the Gateway Service. Although this feature probably hasn’t blocked customers from moving to Citrix Cloud, some have been disappointed afterwards upon learning that EDT was not yet available. This highlights that better orchestration of features that are dependent on multiple product groups within Citrix require closer alignment.

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