Application Virtualization -
A Citrix Overview

Application virtualization abstracts the application interface from the application logic

Virtualization allows Windows applications that run on a server in the data center and the user interface to be virtually delivered to the end user by passing only screen pixels, keystrokes and mouse actions between the client and server over the network. Virtual application technology, combined with both client and server components running together in the data center, results in lower bandwidth use and faster application performance. Since the application is not installed or executed on the end-point device, customers gain broad compatibility with client devices, networks, and operating systems, as well as eliminating the headaches of application compatibility and lockdown on the end point. Consequently, there is no dependence on the local operating system or device drivers, and hardware requirements are minimal.

This enables IT organizations to dramatically reduce the costs of delivering applications by centralizing management, security and control of applications and data. Application virtualization and application streaming are the principle technologies that enable this simplified and consolidated control; together, they provide a flexible application delivery system that can dynamically select the best method based on the user, application and network.

How It Works

To virtualize applications, it’s necessary to abstract the user interface (logical layer) from the application processing (physical layer) that occurs on a centralized, secured server. This technology is ideal for delivering client/server applications because it eliminates the complexities of deploying, managing, updating and securing a vast array of client software on each individual user’s access device. Instead, a single instance of the client application is installed on a server within the secure confines of the data center. The application is then virtually delivered to all the local, remote and mobile users, regardless of device, network or location.

Citrix Presentation Server delivers applications to users through the Independent Computing Architecture (ICA®), a communication protocol by which servers and client devices exchange data in a server environment to separate an application’s logic from its user interface. In addition to the ICA protocol, Presentation Server also supports the Microsoft Terminal Services Remote Desktop Protocol (RDP).

The ICA protocol encrypts and transports an application’s screens from the server it is running on to the user’s client device, and returns the user’s input to the application on the server. As an application runs on a server, Presentation Server intercepts the application’s display data and uses the ICA protocol to send this data to the ICA client software running on the user’s device, increasing application performance.

The application user interface (UI) is delivered to the end user virtually by passing only screen pixels, keystrokes and mouse actions between the client and server over the network without the need for pushing actual data or software, increases security – especially when using external networks like Web and wireless. This virtualization technology, combined with having both client and server components running together in the data center, typically results in less bandwidth use and faster application performance. During this process, 100% of the application’s logic (for both client and server components) executes on the server and, regardless of whether it is Windows, UNIX, Java™ or Web based, the application can now be accessed from any device or location over any network.

With Presentation Server application virtualization technology, users access applications running on the server the exact same way they would if the applications were running on the local device - through desktop icons or start menu as examples - making this process transparent. Meanwhile, IT administrators benefit from a far more cost-effective, easy-to-manage and secure method for deploying and managing business applications.

Application Streaming

There are times when a user requires applications to execute locally on the workstation, such as when they are disconnected from the network. Application streaming, a new feature in Citrix Presentation Server 4.5, extends the value of Citrix to applications running on desktops and laptops. Applications are cached locally in an “isolation environment,” rather than installed on the device. This eliminates application conflicts and the need for extensive regression testing. Users get all the flexibility they need, and IT administrators get all the benefits of centralized application management that they have come to expect from Citrix.

Application streaming enables IT to:

• Eliminate application conflicts and operating system instability resulting from desktop application installation
• Reduce the costs associated with regression testing, deployment, maintenance, updates and de-provisioning of applications being run locally on users’ machines
• Offer applications as an on-demand service
• Lower application support costs by automatically updating and repairing applications every time they are used
• Speed regulatory compliance by eliminating the need for extensive testing to certify applications
• Enhance security by giving IT administrators complete control over applications delivered to desktops, even those of unmanaged partners and users

An application virtualization architecture enables IT with centralized management and users with remote application access

Dual-Mode Streaming

Presentation Server 4.5 combines application virtualization and application streaming, giving IT the flexibility to dynamically define how to deliver applications under various scenarios. Because user needs change depending on the application, the device or the network, Presentation Server offers a policy-based virtual fallback for streamed applications. This feature enables applications to be streamed to the workstation by default, but allows them to be delivered virtually when certain conditions exist, such as unavailability of the Streaming Client, IP address or workstation operating system. With dual-mode streaming, users enjoy the best application experience, no matter the circumstances.