Virtual desktop infrastructure: The big picture

VDI technologies vary from vendor to vendor, and all are quickly evolving with terms of performance and capabilities. It's important to consider all options before choosing a display protocol.

This is the first section in our desktop virtualization handbook on VDI vendors.

Virtual desktop infrastructure (VDI) is only as good as the client that allows it to communicate. In turn, that communications technology fully relies on efficient protocols. Virtualization vendors have come to realize that maximizing the performance of protocols is one of the most important factors in growing their market presence. A protocol's ability to deliver a virtual desktop that's indistinguishable to users from a physical desktop is critical for a successful VDI implementation.

Typically, VDI is heavily dependent on the network, especially when using the common configuration of a data center-based virtual server that communicates with a remote thin client or a rich client located on a user's desktop PC. For the user, a display protocol that is transmitted across the LAN or WAN handles all virtual machine (VM) activity. Because a "network" resides between the user's PC and the VM's server, it's crucial that a display protocol optimizes bitmap changes, user input and other activities across the pipe. Simply put, the more efficient the protocol is, the better the end user's experience will be.

Dozens of remote display protocols are associated with VDI, and most are proprietary designs from the major virtualization vendors. Many of these protocols are established and well known, but some are newcomers in the market or new designs that boast performance improvements. The key to remote display protocol performance comes from bandwidth, but that is a limited resource.

Bandwidth constraints are forcing companies that design remote display protocols to develop new ways to lower bandwidth while increasing performance -- a difficult task at best. All VDI vendors are focused on this conundrum, and many have turned their focus to Citrix as the company to beat.

Before deciding on a VDI technology for your data center, it's important to know where the market is headed and what the primary players are doing to address performance concerns and to keep VDI in the forefront of corporate technology.




Microsoft Remote Desktop Protocol 
HP Remote Graphics Software 
Sun Microsystems Appliance Link Protocol 
Red Hat Smart Protocol for Internet Cellular Exchange
Wyse TCX Suite
Teradici PC over IP 
Quest Experience Optimized Protocol

The primary display protocol that Citrix offers is the Independent Computing Architecture (ICA), which is somewhat platform-independent. Citrix has versions of ICA for Windows, Mac, Unix, Linux and some smartphones. ICA has been around for about 15 years, giving Citrix a significant lead over other companies that have display protocols for VDI implementations. ICA has also been known as a top-performing protocol because of its compression capabilities and the optional use of a rich client that offloads some of the video processing from the remote server to the local PC.

Citrix is banking on its HDX in XenDesktop 4 to breathe some fresh performance life into remote display protocol technology. HDX encompasses many technologies, such as HDX MediaStream, HDX RealTime, HDX 3D and other Citrix HDX sub-brands. Each of HDX's built-in technologies offers specific capabilities to remote display users. For example, HDX Plug and Play supports client USB devices, multiple monitors, client printers, client drive mapping, local port mapping, smart cards and scanners.

Microsoft Remote Desktop Protocol (RDP)
RDP came on the scene with Microsoft's introduction of Terminal Services, a technology that allows access to PC sessions running in the data center via a terminal client. RDP has evolved from its initial version (RDP 4.0), which was bundled with Windows NT 4.0 Server Terminal Services Edition to RDP 7.0, which is available with Windows Server 2008 R2. RDP 7.0 adds functionality such as Windows Media Player redirection, bidirectional audio, multimonitor support, Aero Glass support, enhanced bitmap acceleration and language bar docking.

The current version of RDP requires a Windows 7 client PC as well as a Windows Server 2008 R2 system on the back end. While that limits the applicability of RDP 7.0, Microsoft plans to add additional client support in the near future. Performance-wise, RDP 7.0 relies heavily on Microsoft technologies, possibly limiting its use in heterogeneous networks.

HP Remote Graphics Software (RGS)
Hewlett-Packard designed RGS to allow professionals to work together in real time with secure access to rich multimedia resources, applications and data. It's an independent protocol for remote graphics that uses the remote host's processing capabilities and turns the entire remote desktop into streamed video while still offering remote video and audio.

Essentially, RGS started out as a technology for collaboration, but the needs of real-time collaboration -- the ability to quickly share bandwidth-intensive data such as graphics over limited bandwidth without degrading the user experience -- closely matches the needs of VDI users. This capability makes RGS a viable remote display protocol for virtual desktops.

HP doesn't offer a complete "soup-to-nuts" VDI solution, but the company is licensing RGS to other vendors. Some vendors, such as VMware, are incorporating support for the protocol. RGS offers a lot of promise, but only if you are working with products that support RGS natively.

Sun Microsystems Appliance Link Protocol (ALP)
Sun has been offering a remote desktop experience for some time under the product banner of Sun Ray. The technology aimed to bring a remote terminal type of access to the data center while supporting a graphical user interface, operating system and streaming multimedia. The Sun Ray protocol (now called ALP) is at the heart of the company's solution. ALP has been recognized for its efficiency and ability to work in graphics-intensive environments.

While Sun Ray falls under the umbrella of niche products, ALP seems to have a broader appeal, with some VDI and connection broker vendors adding support for the protocol. Sun's upcoming Desktop Access Client will incorporate ALP and will fully move the company into the realm of VDI in the cloud. VMware fully supports ALP, delivering virtual desktops over the network with high latency. By combining VMware VDI with ALP, administrators will be able to deliver high-performance desktop environments in a WAN deployment.

Red Hat Smart Protocol for Internet Cellular Exchange (SPICE)
Red Hat jumped into the VDI market with its acquisition of Qumranet. With Qumranet the company got SolidICE and SPICE. Solid ICE is the VDI component running on KVM that consists of a virtual desktop server and controller front end. Solid ICE allows Red Hat to rapidly enter the VDI market without threatening its server OS business.

The SPICE protocol enables a standardized connection protocol alternative to RDP with enhancements for the VDI user experience. Through its SPICE remote rendering technology, Red Hat now offers a full-powered virtual desktop that can handle high-definition video and video conferencing.

Red Hat claims that SPICE has superior graphics performance, improved video quality (30 plus frames per second), bidirectional audio for soft phones and IP phones, and bidirectional video for video telephony and video conferencing. It requires no specialized hardware.

Wyse TCX Suite
Wyse Technology's TCX Multimedia 3.0 software streamlines the delivery of the multimedia stream to the local client for a rich user experience within a thin-computing architecture. Wyse TCX components support a variety of back-end infrastructure solutions such as Microsoft Terminal Services, Citrix XenApp, Citrix XenDesktop and VMware View or VDI.

Wyse TCX Multimedia software provides rich multimedia playback capabilities within an ICA or RDP connection. The software layer has both server and client components that redirect multimedia processing tasks dynamically between the client and server. The multimedia stream is decoded locally on the client using the local processing power of the device, thereby providing complete multimedia playback capabilities. Components in the TCX suite support multiple displays and USB peripherals and enable high-quality audio.

Teradici PC over IP (PCoIP)
Teradici originally took a different approach from other vendors. The company's display protocol was heavily integrated into a firmware/hardware solution that added hardware to a PC in the data center and then transmitted that PC's activity via IP to a thin-client device.

Recently, however, Teradici partnered with VMware to make its PCoIP available under VMware's View technology; this would make PC over IP compatible with VDI in the data center. Currently, PCoIP works with hardware-based zero-client products from OEMs and thin-client vendors including Amulet-Hotkey, ClearCube Technology, Dell, Devon IT, Elsa Technology, EVGA, Fujitsu, IBM, Leadtek Research, Samsung, Verari Systems and Wyse.

Quest Experience Optimized Protocol (EOP)
When Quest Software's Desktop Virtualization Group has introduced the EOP for remote desktops. EOP addresses common native protocol problems to ensure that a centralized desktop deployment delivers a viable virtualization environment as well as a true local-desktop user experience.

EOP was designed to support bidirectional audio for dictation, collaboration and Voice over Internet Protocol applications, and multimedia content such as recorded webcasts and Web-based training. It also provides the ability to render graphics and animation, including browser and flash animation with graphics acceleration. It can also deal with network latencies over 200 milliseconds, preventing applications from becoming unresponsive.

EOP is available as an optional add-on to Provision Networks Virtual Access Suite 5.10, a virtual desktop and application delivery solution for VMware Infrastructure and Windows Terminal Server and Hyper-V platforms. EOP is an extension of RDP that connects to Microsoft Terminal Services and uses several methods to improve the virtual desktop experience.>


The protocol puzzle
A wide mix of display protocols is available -- some are proprietary, others are tied to hardware, and others have already been licensed by VDI vendors. This can complicate the selection of which protocol to deploy.

For example, enterprises running a pure Microsoft environment may want to stick with RDP, while those supporting multiple desktop OSes may find Citrix a suitable choice. Some administrators may want to consider if they're going to deploy thin-client or zero-client devices as part of their VDI solution. In such cases, a technology like Teradici's PCoIP may be a better fit. Regardless of the protocol or technology selected, VDI and display protocols vendors are working hard to advance the performance of remote computing, incorporating virtualization capabilities into products that perform well, regardless of bandwidth or the end user's location.


Frank Ohlhorst is an IT journalist who has also served as a network administrator and applications programmer before forming his own computer consulting firm.

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