Demystifying desktop virtualization technology
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When it comes to virtual desktop infrastructure, administrators have a lot of choices. You may have wondered about the differences between VDI software options, remote display protocols or all the licenses out there. In this series, we tackle some of the biggest head-scratchers facing VDI admins to help you get things straight.
In VDI environments, the remote display protocol has a big responsibility: to transmit data from a data-center-hosted desktop to the endpoint.
Popular remote display protocols offer high-resolution sessions, multimedia stream remoting, multi-monitor support, dynamic object compression, USB redirection, drive mapping and more. Microsoft's Remote Desktop Protocol (RDP), VMware's PC-over-IP (PCoIP) and Citrix's HDX are the most commonly used, but there are other protocols from companies such as Ericom and Hewlett-Packard.
Each remote display protocol works differently depending on the network and which applications are being delivered, so you need to know how the major protocols diverge. Let's get this straight.
What's under the hood of a remote display protocol?
RemoteFX, HDX and PCoIP are Layer 7 protocols that are based on two Open Systems Interconnection (OSI) stack Layer 4 protocols: the User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). TCP divides data into packets and reassembles them at the endpoint, while UDP does not sequence the packets.
TCP is more reliable because it makes sure that a connection is maintained until all the data is delivered. Plus, if an error occurs, TCP sends the affected data again. UDP does not confirm that all packets are received at the endpoint, but that means it's faster for delivering media-heavy messages such as video.
Remote display protocols have their limitations, especially when it comes to delivering graphics-intensive applications. Great performance requires a lot of bandwidth, which can clog the network. Plus, if you want low CPU use, your protocol will hog bandwidth and weaken end user performance. As desktop virtualization expert Brian Madden says, you can have "low bandwidth, good experience, low CPU … pick any two."
RemoteFX, an enhancement to Microsoft's Remote Desktop Protocol, was released with Windows Server 2008 R2 to boost high-definition graphics rendering. RemoteFX works on Hyper-V only, although Citrix Systems Inc. does support the protocol for use in XenDesktop environments. Windows Server 2012 RemoteFX allows Remote Desktop Services to use UDP when necessary, while previous versions could only use TCP.
RemoteFX and Windows Server 2012
RDP was initially for LAN-only delivery, but the latest version adds WAN optimization. RemoteFX in Windows Server 2012 also comes with multitouch support and Adaptive Graphics, a feature that does visual element-rendering on the host rather than the client.
More on remote desktop protocols
Are you using RemoteFX?
Video: Comparing the major remote display protocols
RDP and RemoteFX in Windows 8
An overview of remote display protocol technology
Keep in mind that you'll have to upgrade to Windows 8 to get some of these enhancements. However, Microsoft also added RDP 8.0 support for client access devices running Windows 7 SP1 and Windows Server 2008 R2 (although not all new RemoteFX capabilities are included).
Microsoft RemoteFX vs. Citrix HDX
The differences between RemoteFX and HDX were more apparent before some of the changes to RemoteFX in Windows Server 2012. But HDX is still better known for performance over the WAN. Plus, Citrix historically provides more clients for HDX. While Microsoft provides RDP clients for Windows and Mac, Citrix provides HDX clients for Windows, Mac, Linux, Blackberry, iOS, Android, Sun and more.
Citrix's remote display protocol was originally called ICA, but the company evolved the offering into the HDX suite in 2009 with the release of XenDesktop 3.0. HDX refers to all the technologies Citrix offers that deliver the end-user experience, including multimedia redirection, browser acceleration, bandwidth control and other components. It's based on the TCP but can use UDP in certain situations.
Citrix also offers HDX 3D Pro for high-end graphics application delivery.
Improved WAN acceleration in XenDesktop 5.5
WAN connections tend to have high latency and low bandwidth, making it difficult for remote display protocols to deliver apps promptly. XenDesktop 5.5 added built-in WAN acceleration technology that accelerates HDX traffic through packet compression and decompression.
HDX MediaStream and RichGraphics step it up
XenDesktop 5.5 updated HDX MediaStream with better Flash redirection and a new end-to-end flow control and frame-dropping capability. Version 5.6 improved mobile application access with XenApp and boosted protocol support in Citrix Receiver.
VMware's remote display protocol PCoIP, developed by Teradici Corp., works with the vendor's View desktop virtualization product. While RemoteFX requires remote hosts to use a graphic processing unit for bitmap encoding, PCoIP uses the regular server CPU. PCoIP differs from the other protocols in that it's based mainly on the UDP.
PCoIP improvements in VMware View 5
WAN performance tends to be better with Citrix HDX than with VMware's remote display protocol. Still, VMware View 5 improved PCoIP by increasing network user density and reducing bandwidth consumption over the LAN and WAN. It also added more cache control settings.
PCoIP support for Microsoft RDS
PCoIP has traditionally been confined to VMware View VDI, but Teradici added support for PCoIP in Remote Desktop Services environments. That could allow View shops to eliminate XenApp for remote desktop delivery. Still, Teradici's Arch -- its session-hosted remote desktop offering -- comes with some limitations, one being that it doesn't run on Windows Server 2012.