XenApp Architecture

Citrix XenApp is a sophisticated system that has become the de facto standard for application delivery. It is one of the reasons why people in the same breath mention XenApp when they speak of Microsoft Terminal Services. They do so because they imply that XenApp successfully extends Microsoft’s Terminal Server by adding essential features to it that are still missing even in its latest release.



The solution formerly known as the Citrix Presentation Server has remarkably stepped forward in its current version by going beyond the scope of mere application delivery: according to the new concept applications get virtualised in the first place, to achieve best possible degree of performance and flexibility, and the actual application delivery is carried out thereafter. This is how Citrix combines the efficiency of the XenServer virtualisation and the time-tested power of reliable Application delivery known from the Presentation Server to form a totally new approach called XenApp.

With the help of the secured XenApp architecture each and every enterprise can now centralize and consolidate its application and data stock while providing its employees with a single but stable access facility which works independently of their current location. The major benefit of this solution is the difference between the two concepts: the legacy approach known from the Terminal Server delivers entire sessions to the user consuming a good portion of the overall bandwidth, whereas the XenApp approach concentrates on scalable and personalized applications to achieve high-performance conditions even with little bandwidth available.

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Citrix Xenapp 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.

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.

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.

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.

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Citrix XenServer

In the world of Xen paravirtualization, the hypervisor exists in several different forms. A few Xen platforms come with Linux distributions while others don't. Some Xen hypervisors even disguise themselves as different technologies (Microsoft Hyper-V, I'm looking at you.)

Then there is Citrix's Xen offering, XenServer. This article will explain how to install Citrix XenServer and then begin using Citrix's management console, XenCenter.

Choosing a Citrix Xen platform

Citrix offers four different versions of XenServer. The free version is called XenServer Express and can be downloaded from the Citrix website. XenServer Express is an excellent choice for those interested in testing Citrix's basic virtualization offering. You can install XenServer Express on a single server, but you can only manage that one server with it. However, you can install as many virtual machines as the hardware of your server can support.

Citrix deals with Citrix Xenserver. You can Buy Software of these kinds online on many websites e.g. http://www.softwareforless.com/. Delivery Center, composed of Citrix XenDesktop, Citrix XenApp, Citrix XenServer and NetScaler, virtualizes servers, desktops and applications, centralizes them in the data center and broadcasts them as an on-demand service.

Citrix Xenapp

Citrix XenApp 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.

Network Protocol

The core XenApp application hosting technology utilizes Citrix Systems' proprietary presentation layer protocol or thin client protocol called Independent Computing Architecture (ICA).

Unlike framebuffered protocols like VNC, ICA transmits high-level window display information, much like the X11 protocol, as opposed to purely graphical information. The Citrix Display Driver is installed in Session Space and captures 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. 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.

Server Components

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.

Client Components

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 Citrix Xenapp.

Citrix also deals with Citrix Xenserver. You can Buy Software of these kinds online on many websites e.g. http://www.softwareforless.com/. Delivery Center, composed of Citrix XenDesktop, Citrix XenApp, Citrix XenServer and NetScaler, virtualizes servers, desktops and applications, centralizes them in the data center and broadcasts them as an on-demand service.

About Citrix Systems

Citrix Systems, Inc. is an American multinational corporation that provides server and desktop virtualization, networking, software-as-a-service (SaaS) and cloud computing technologies for more than 230,000 organizations worldwide.

Citrix states that “A world where anyone can work and play from anywhere.” is its corporate vision.

Citrix is based in Fort Lauderdale, Florida, in the South Florida metropolitan area, and has subsidiary operations in California and Massachusetts, and additional development centers in Australia, India and the United Kingdom.

Customers include the world’s largest Internet companies, 99 percent of Fortune Global 500 enterprises, and hundreds of thousands of small businesses and consumers worldwide. Citrix partners with over 10,000 companies worldwide in more than 100 countries. Founded in 1989, annual revenue in 2008 was $1.6 billion.

Following the acquisition of XenSource, Inc in October 2007, Citrix shepherds the Xen open source hypervisor project.

The more focused products of Citrix are Citrix Xenapp and Citrix Xenserver. You can Buy Software of these kinds online on many websites e.g. http://www.softwareforless.com/.

Citrix Delivery Center, Citrix Cloud Center (C3) and Citrix Online Services product families simplify computing for millions of users, delivering applications as an on-demand service to any user, in any location on any device.

Citrix Delivery Center, composed of XenDesktop, Citrix XenApp, Citrix XenServer and NetScaler, virtualizes servers, desktops and applications, centralizes them in the data center and broadcasts them as an on-demand service.