Citrix's HDX technologies combine to form the company's remote display protocol, which includes capabilities that help IT deliver high-definition virtual desktops and applications to users on any device they work with.
Citrix HDX protocol is designed specifically for the XenDesktop and XenApp virtualization platforms. Citrix built its High Definition Experience (HDX) technologies on top of the Independent Computing Architecture remote display protocol the company developed at its outset over two decades ago. Citrix designed HDX to work well even on high-latency, low-bandwidth wide area network connections.
HDX protocol came on the end-user computing scene in February 2009 when the company released XenDesktop 3.0. HDX is in direct competition with Microsoft's Remote Desktop Protocol and RemoteFX technologies, and VMware's PC over IP protocol that it licenses from Teradici. VMware also came out with its own remote display protocol, Blast Extreme, in Horizon 7 in May 2016.
Dive into the following slides to learn about features such as data deduplication and 3D graphics optimization that differentiate Citrix HDX from the rest of the pack.
HDX has a few features that reduce network traffic in an effort to streamline performance. For example, data deduplication, prevents redundant files and images from clogging up network traffic and causing latency. Citrix HDX caches patterns of data that users access most frequently, including graphics and documents, to reduce network traffic between VDI clients and servers. In effect, only changes to users' virtual desktop take up network bandwidth.
Citrix HDX protocol also supports multicasting to minimize the amount of data in transit between endpoints and the servers. This allows multiple users to simultaneously view a single media stream, instead of accessing their own individual stream, which takes up more network resources.
Citrix HDX protocol renders DirectX graphics with CPU or a graphics processing unit by sending the graphics through a software rasterizer. The rasterizer takes vector graphics and turns them into the pixels users see on their screens, passing on the desktop composition from the server to the endpoint. This process works well because a lot of apps, including Microsoft's Office suite, are designed to work through graphics processors.
For users who need to use 3D graphics applications, Citrix offers HDX 3D Pro, which supports hardware-based GPU sharing for OpenGL and DirectX graphics applications. HDX 3D Pro includes deep compression, which improves the traffic throughput even in low-bandwidth networks. The 3D Pro version is ideal for users who work with computer-aided design apps, graphical information system software, or picture archiving and communication systems for medical images.
Citrix HDX Mobile strives to provide the most native experience possible for smartphone and tablet users working with Windows applications through Citrix Receiver. For starters, HDX Mobile allows IT to refactor Windows apps for mobile devices, which can include optimizing apps for touchscreens with multi-touch gestures and native menu controls. To make things even easier, many touch-based features, such as keyboard auto-display, are already included in XenApp and XenDesktop and do not require any changes to applications' source codes.
The Citrix HDX Mobile software developer's kit features more than 50 application programming interfaces developers can use to add even more mobile capabilities. Some of the features include switching to the device's local interface instead of using the Windows layout and an autosense tool that can identify the size of the client device's screen and whether or not to use a horizontal layout.
Like all remote display protocols, HDX relies on one of two Open Systems Interconnection stack Layer 4 protocols. HDX is based on the Transmission Control Protocol (TCP), but can also use the User Datagram Protocol (UDP).
TCP is the more reliable option of the two. It maintains the connection between the server and the endpoint until it receives confirmation of data delivery. If anything goes wrong, TCP resends data until successfully delivered. UDP does not wait for confirmation. It just sends the data. Because it skips the confirmation step, UDP is faster and particularly helpful for delivering media-heavy messages.
TCP also creates data packets and delivers them to the endpoints where they are reassembled in sequence. UDP does not take the time to sequence the data it sends.
HDX can use both UDP and TCP but is primarily based on TCP, whereas VMware's PC over IP protocol which is based on UDP.
