Remote display protocols dictate virtual desktop experience

Citrix, VMware and Microsoft all offer remote display protocols with their VDI products. Each one brings a little something different to the table.

There are a plethora of remote display protocol options IT professionals can choose from to deliver the virtual desktop experience, each with varying degrees of capability and functionality.

The majority of VDI shops use Citrix's Independent Computing Architecture (ICA) or HDX, Microsoft's Remote Desktop Protocol (RDP) or RemoteFX, VMware's Blast Extreme, or Teradici Corp.'s PCoIP. Not to mention the third-party options on the market.

Microsoft RDP

Microsoft RDP is the ubiquitous access protocol for Windows servers and desktops. It has developed into a feature-rich protocol for delivering the virtual desktop experience. It includes:

  • 32-bit color;
  • 128-bit encryption;
  • audio redirection;
  • file system redirection;
  • printer redirection;
  • bandwidth tuning;
  • seamless Windows access with client-side file type associations; and
  • USB and legacy port redirection.

All Windows clients come with the Microsoft Terminal Services Client installed as a part of the base operating system. As a result, IT can easily deploy minimal remote access.

What are the biggest challenges to the user experience with desktop virtualization?

Further, Microsoft created connect over remote desktop to allow RDP to work on Apple macOS devices. FreeRDP enables RDP for Linux. Neither version is as rich as the official Microsoft version, but if IT pros need a simple and common access method for their users, these tools can get the job done.

One of the main RDP issues in terms of virtual desktop experience is connectivity. If RDP recognizes that there has been no activity for 10 seconds, the protocol throttles the connection to 50% by design. This can get old very quickly as the user waits for the session to fully reconnect every time he takes a quick break.

Even so, RDP works on almost any client, so if users can survive the constant timeouts, RDP is fully capable of providing sterling service in all but the harshest of deployments.

Microsoft RemoteFX

RemoteFX is effectively an enhancement to RDP based on Microsoft's acquisition of Calista Technologies in 2008. The company introduced RemoteFX with Server 2008 R2 SP1.

RemoteFX can pass a virtualized instance of a physical graphics processing unit (GPU) to a virtualized version of Windows 7, 8.1 and 10 when running on Hyper-V.

RemoteFX is particularly useful for delivering a virtual desktop experience that requires highly graphical programs, such as computer-aided design or real-time video, to users running on Hyper-V deployed desktops.

RemoteFX is only available in virtual deployments running on Hyper-V.

Citrix ICA

Like RDP, ICA features virtual channels that enhance the capabilities of the base protocol, allowing for local folder redirection, USB redirection, graphics offloading and use of the graphical capabilities of the local device to enhance graphical output.

ICA can also degrade the display to compensate for low bandwidth or higher latency connections.

ICA is, for the most part, hypervisor-agnostic, but IT must use XenServer as the underlying hypervisor to offload GPUs.

Citrix HDX

HDX is similar to RemoteFX in that it is all about enhancing the virtual desktop experience over lower bandwidth and higher latencies. Three technical principles underlay HDX.

Intelligent redirection examines the screen activity, application commands, endpoint device, and network and server capabilities to instantly determine how and where to render an application or desktop action. Redirection can occur at the local client or device levels.

Client redirection offloads tasks from the server and places them on the client. With device and peripheral redirection, webcams, printers and scanners can be terminated locally to allow users to interact with these devices at native USB speeds.

Adaptive compression sets the codecs the protocols use based on the network conditions, and it determines the intelligent utilization of CPU and GPU resources.

Deduplication of network traffic enables HDX to support multicasting of multimedia streams where delivery of a single transmission from the source to many users creates one-to-many communications. HDX caching deduplicates the data users access, including bitmap graphics, files, print jobs and streaming media.

HDX also recentralizes processing by utilizing x264 protocol enhancements that aid in GPU offloading to server-based GPUs. HDX deals with graphical elements at the source and deduplicates or compresses them before sending them to the client, which helps deliver a better experience to end users.

Like ICA, HDX can use almost any hypervisor except when it comes to offloading GPUs, where it requires XenServer.

Teradici PCoIP

Horizon View has a long-term relationship with Teradici and its PCoIP protocol. The first difference between PCoIP and RDP and ICA is that the protocol uses the User Datagram Protocol (UDP) to transfer data packets. UDP makes PCoIP faster than other protocols because it doesn't have to wait for the endpoint to confirm that it received a packet like it does with the Transmission Control Protocol.

In deployments where bandwidth is high and latency is low, PCoIP delivers a nearly native virtual desktop experience thanks to UDP. In networks that don't perform well, issues could arise.

At the end of the day, protocol choice is driven more by the VDI vendor choice.

Teradici attempts to address this by allowing PCoIP to lower the amount of traffic that passes across the network by using adaptive encoders. What's more, the encoders are intelligent enough to push the performance counter back up when the congestion clears.

VMware's PCoIP stack is not the full version, but a software emulated version. IT pros do not have to install a Teradici card on the endpoint because the ability to decode the PCoIP stream is built into the Horizon View client. Installing the card, however, will improve performance.

PCoIP only works with the ESXi hypervisor.

VMware Blast Extreme

If PCoIP continually throttles the performance of the UDP stream, users will notice performance fluctuations. VMware's answer to this problem is Blast Extreme.

Blast Extreme is based on the original HTML Access protocol called Blast. Blast was very feature-limited and was based on a JPG/PNG codec that does not do video or high-intensity graphics very well.

The new Blast Extreme protocol introduced with Horizon 7 and the version 4 client has feature parity with PCoIP and has been enhanced to utilize the H.264 codec for highly graphical content. Like PCoIP, Blast Extreme relies on the ESXi hypervisor.

At the end of the day, protocol choice is driven more by the VDI vendor choice than one feature over another because all of the protocols are fully capable.

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