Citrix XenApp

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Citrix XenApp
Developer(s) Citrix Systems
Stable release 5.0 / 2008-09-08; 9 months ago[1]
Operating system Microsoft Windows Server
Supported by v4.0
HP-UX - Solaris - AIX
Type Application Delivery
License Proprietary
Website www.citrix.com

Citrix XenApp (formerly Citrix MetaFrame Server and Citrix Presentation Server) is an application virtualization/application delivery product that allows users to connect to their corporate applications. XenApp can either host applications on central servers and allow users to interact with them remotely or stream and deliver them to user devices for local execution.


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[edit] How XenApp works

Utilizing integrated application virtualization technology, XenApp isolates applications from the underlying operating system and from other applications to increase compatibility and manageability. Applications are streamed from a centralized location into an isolation environment on the target device where they will execute. The target device can be a user PC or a server in the data center.

Citrix XenApp is unique in that it is a complete application delivery system, offering both online and offline application access through a combination of application hosting and application streaming directly to user devices. When users request an application, XenApp determines if their device is compatible and capable of running the application in question. The minimum requirements of a target device are a compatible Windows operating system and appropriate Citrix client software. If the user device meets minimum requirements, then XenApp initiates local application delivery via application streaming directly into an isolated environment on the users device. In the event that the user device is not capable of running a particular application, XenApp initiates hosted application delivery.

Hosted application delivery uses application streaming to deliver applications to hosting servers in the data center. XenApp then connects the user to the server to which the application has been delivered. The application then executes entirely on the server. The user interacts with the application remotely by sending mouse-clicks and keystrokes to the server. The server then responds by sending screen updates back to the users device.

In both hosted and local application delivery, user interaction with the application is seamless. Printers, drives, peripherals and even the clipboard work in the exact same manner as if the application were installed. However, whereas local application delivery is limited to Windows-based operating systems at this time, hosted application delivery via XenApp allows any user on any operating system to access any application delivered by IT. XenApp enables Windows, Mac, Linux, UNIX, Thin clients, iPhone, Windows Mobile devices, and even Symbian and Java-enabled devices to run any Windows or UNIX-based applications using hosted application delivery. Another advantage of hosting applications using XenApp is that it lets users connect to these applications remotely, from their homes, airport Internet kiosks, smart phones, and other devices outside of their corporate networks. From an end-user perspective, users can log in to their corporate network from, for example, an airport kiosk, see all of the applications they would see everyday at work, including Outlook email and any internal applications, and access them from the kiosk in a secure environment. To the user, the application would appear as if it was installed and running on their computer (seamless desktop integration), whereas in reality, the application is running on a server in their corporate environment.

Local application delivery using application virtualization solutions like XenApp, is considered, by some, to be a improvement over traditional application deployment models. Hosted application delivery like that available in Citrix XenApp and Microsoft Terminal Services are reminiscent of the mainframe-terminal system, where a central powerful computer does most of the processing work and smaller, much less powerful machines provide the user interface.

Some academic institutions use XenApp to provide their students and faculty with remote access to applications running on campus servers. Similarly, because of the higher degree of security built-in to Citrix and other remote access platforms, various military branches extensively use these to offer their deployed and remote personnel, access to secure and sensitive military systems from a remote location. The same security argument is a driving factor behind Citrix's success in Healthcare and Financial Services which are regulated industries in which customer data security and protection is paramount.

More information on how XenApp works is available at the Citrix website.

[edit] Technical details and licensing

XenApp began life as an application hosting solution. Only since 2007 has XenApp included application virtualization and streaming technologies that enable application delivery to user devices. The core XenApp application hosting technology utilizes Citrix Systems' proprietary presentation layer protocol or thin client protocol called Independent Computing Architecture (ICA). The Microsoft Remote Desktop Protocol, part of Microsoft's Terminal Services, is based on Citrix technology and was licensed from Citrix in 1997. [2]

Unlike traditional framebuffered protocols like VNC, ICA transmits high-level window display information, much like the X11 protocol, as opposed to purely graphical information. This is possible because the Citrix Display Driver which is installed in Session Space is capable of capturing high level GDI draw commands, which can be replayed on GDI-capable clients, for example Windows-based clients. Clients are available for several operating systems, including Microsoft Windows (CE, 16-bit, 32-bit and 64-bit platforms), Mac OS, Linux, and other Unix-like systems.

Citrix MetaFrame version 3.x and 4.x servers listen for client connections on TCP port 2598, by default. [3] [4] If the Session Reliability feature is disabled, then the server will listen on port 1494. Older MetaFrame servers (those running MetaFrame version 2.x or earlier) do not have the Session Reliability feature, and therefore always default to port 1494.

Both local and hosted application delivery methods in XenApp leverage existing network transmission protocols including TCP, HTTP, HTTPS, SMB and CIFS.

The Citrix Developer Network contains a set of software development kits that enable custom development for XenApp. These SDKs include the following:

  • Citrix XenApp SDK
  • Citrix Virtual Channel SDK
  • Citrix ICA Client Object SDK
  • Citrix Web Interface SDK
  • Citrix Simulation API SDK

XenApp components, including application hosting servers, if any, reside on a Microsoft Windows computer, which can be either standalone or part of a larger cluster (farm) of Citrix servers. It is important to note that in addition to concurrent user Citrix licensing, there must exist a Terminal Server Client Access License (CAL) and a Windows Server CAL from Microsoft for each client connection. Both products must be adequately licensed for the environment to function correctly.

There is a web-based Citrix client, freely available under the name Web Interface for XenApp. The Web Interface may be used as a secure ICA proxy over HTTPS when combined with Citrix Secure Gateway, both of which are included in the base XenApp product. XenApp also supports three UNIX variants: HP-UX, Solaris, and AIX which are included in Enterprise and Platinum editions of XenApp.

[edit] UNIX version

Presentation Server for UNIX is available for Solaris (SPARC and x86), AIX, and HP-UX. Patches typically come out first for the Solaris version. The product started as MetaFrame for Solaris 1.0 which was released in March 2000.[5] MetaFrame for UNIX (MFU) 1.1 added support for AIX and HP-UX and came out in the fall of that year and Feature Release 1 came out about a year later. The next version came out in the first half of 2003. It was originally planned as MFU 1.1 Feature Release 2 but was rebranded MetaFrame Presentation Server for UNIX 1.2.[6] However, references to MFU 1.1. FR2 can still be found (e.g. in the license key). Presentation Server for UNIX (PSU) 4.0 was released in the first half of 2005 and was the first version to be bundled with the Presentation Server suite.[7] Existing customers paying for upgrades and new versions (known as Subscription Advantage) can however continue to get just the UNIX version. Existing MFU 1.x installs cannot be upgraded to PSU4; instead a clean install is required.

[edit] Competition

Traditionally Citrix XenApp has faced minimal or no competition in the thin client computing space. But with Microsoft's new Terminal Services for Windows Server 2008, Microsoft Terminal Services is emerging as a clear competitor to XenApp at least in the small and medium business market space. Other XenApp competitors include Quest Software vWorkspace and Ericom Software, and PowerTerm WebConnect. XenApp is built on top of the Windows Terminal Server platform which was originally developed by Citrix in the early-mid 90s. Win4Lin Virtual Desktop Server from Virtual Bridges provides similar functionality for serving sessions from Linux servers, while Sun's application virtualization offering, the Sun Secure Global Desktop, serves to provide a complete solution allowing for the delivery of both Windows and Unix applications on all major platforms.

[edit] See also

[edit] References

  1. ^ (2007-02-12). Introducing Citrix XenApp. Citrix Systems. Retrieved on 2008-04-12.
  2. ^ Microsoft and Citrix Sign Technology Cross-Licensing and Development Agreement: Microsoft Signs Agreements With Citrix and Prologue Software
  3. ^ CTX104147 - Explaining ICA Session Reliability, Common Gateway Protocol, on TCP Port 2598 - Citrix Knowledge Center
  4. ^ Goodbye 1494, Hello 2598! Citrix Enhances ICA and Changes its Default Port - From BrianMadden.com
  5. ^ C. Thi Nguyen (2000-03-22). "MetaFrame for UNIX Rises with Sun Solaris". WindowsITPro.com. http://www.windowsitpro.com/articles/print.cfm?articleid=8405. Retrieved on 2007-05-22. 
  6. ^ "MetaFrame(R) Presentation Server for UNIX(R) 1.1 and 1.2". Citrix. http://www.citrix.com/English/ps2/products/qa.asp?contentID=1449&faqID=20479&title=MetaFrame(R)+Presentation+Server+for+UNIX(R)+1.1+and+1.2. Retrieved on 2007-05-22. 
  7. ^ Chris Gilbert (2005-04-27). "Presentation Server for Unix 4.0 details". Citrix. http://support.citrix.com/forums/thread.jspa?forumID=4&threadID=62565&tstart=90. Retrieved on 2007-05-22. 

[edit] External links

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