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Windows Terminal Server/Citrix MetaFrame Demystified

Author: Ronald S. Wilner
Contributed by Progressive Network Solutions, Inc.



In the rapid pace of IT technologies today, the single most critical element is to provide services, support, and applications to the users. Information Technology Department�s entire infrastructure, manpower, and assets are committed to the timely deployment of applications and data to the users. Yet, when a new application is readied for deployment, the very infrastructure used to support the applications provides the greatest roadblock to its deployment. A new technology called Server Based Computing, has afforded IT managers a means to rapidly deploy applications without the need to upload applications to the desktop. This trend is evident in the levels of spending for thin client devices used to connect to server based computing applications. Wyse reports: From January 1999 through June 1999, Wyse's worldwide thin-client shipments rose 189 percent to more than 115,000 units. Other manufacturers report similar increases.

Challenges of Enterprise-Wide Application Deployment

IT professionals must leverage their existing computing infrastructure-hardware, applications, network and training; while attempting to keep costs of computing ownership low. In addition they must consider:

  1. Managing and supporting users in a timely and cost-effective manner.

  2. Extending access to business-critical applications to dispersed users-regardless of connection, location, or device.

  3. Ensuring exceptional application performance

  4. Providing tight security for enterprise-level computing.

Management. Traditional application deployment is time consuming, expensive and difficult to maintain. Administrators have to physically distribute applications to every client and deal with version control issues, remote support, multiple system configurations and data replication. When confronted with hundreds of users, the cost of application ownership can quickly spiral out of control.

Access. With a mixture or desktop devices, network connectivity and operating systems, access to vital Windows-based applications is difficult. In the case of Internet/ intranet computing, there may be no alternatives for non-Web enabled applications.

Performance. Most applications are designed for the high-bandwidth environment. These types of applications put a tremendous strain on congested corporate networks and reduce the response time for remote users. Many users simply avoid using the network during peak times. This reduces productivity, creates an atmosphere of ill will toward the network among the users.

Security. Security is a growing challenge. In the traditional client server environment, applications and data live on both the server and the client�s desktop. This could increase the risk of unauthorized access and it also may increase the risk of critical data being lost or stolen.

Server Based Computing.

This is a model whereby applications are deployed, managed, supported and executed 100% on a server. It uses a multi-user operating system and a method for distributing the presentation of an application�s interface to a client device. Not unlike a mainframe, all applications are centrally maintained and distributed from the server. Unlike a mainframe, these applications can be DOS based, Windows 16 bit, Windows 32 bit, or even Java based.

Server based computing can be used with the existing network infrastructure and current computer standards. It is designed to work with the existing and future family of Windows based product. Windows NT Terminal Server Version provides the core technology used to deliver server based computing.

How does it work?

There are three critical elements. The first involves the ability for multiple concurrent users to log on and run applications in a separate, protected session on a single server. The second is an efficient computing technology the separates the application�s logic from its users� interface, so only keystrokes, mouse clicks, and screen updates travel the network. This permits the application to perform independent of the bandwidth. The third element is centralized application and client management, enabling large computing environments to overcome the critical application deployment challenges of management, access, performance, and security.

Server based computing uses two Citrix technologies, Citrix client protocol called Independent Computing Architecture {ICA} and Citrix Multiwin. The ICA protocol shifts application processing from the client device to the server, Multiwin enables multiple users to simultaneously access applications running on a server.

Enterprise Scalability

Two challenges face Information Technology in the large enterprise. The first is: How does the IT professional give immediate access to only those groups of uses who need an application without touching each desktop?

The second: If the deployment is successful, how can the potential hundreds of users access the same application without clogging the network or bringing the server to its knees?

There are two critical elements at work. The first requires a way to iconize or publish an application giving permissions to only the groups of people who need access to the applications.

This is possible using the core elements of Windows Terminal Server and MetaFrame together. The MetaFrame product extends the reach of Windows Terminal server to include the ability to iconize an application and make it available to any client or user who an administrator wishes to give permissions.

By installing the application directly on the WTS/ MetaFrame server or in a three-tier environment, we can specify who has permissions to access the application. An applet called Published Application Manager, allows us to predefine what application a specific group of users has permissions to run. PAM, can then be used to broadcast the icon to the desktop of FAT client users. An administrator can also define a custom desktop to appear on a thin client device when a user logs in. This desktop can be customized to show only those application icons needed by that users.

When the user clicks on the icon, the client�s machine connects to the server. A session is started and only the mouse movements, keyboard clicks and net-changes are sent back to the client. The applications and data never leave the server. Packets going to and from the server or only 10Kps to 20 Kps. This affords a small footprint to the network and minimal impact to a congested network.

This simplification of application deployment can be future automated for each user. PAM allows us to broadcast the icon directly to a client�s desktop. When a user logs into the server, the server pushes the Icons to the client�s desktop. No additional installation is required by administration. New clients are easy to install. One or two diskettes worth of information contain client software. Once the client is loaded, all the icons are pushed to the desktop. If the client is ever deleted, it can simply be reinstalled and the icons will again be accessible on the server.

The second element targets the needs of the large Enterprise. For the large Enterprise, systems must be scalable to support the potential of hundreds of users. Addition functionality can be added to provide a scalable solution called Load Balancing. Servers can be grouped together, each having Windows Terminal Server, MetaFrame, Load Balancing, and shared Published Applications. These grouped servers form a server farm. By grouping servers within a server farm, users logins can be directed to the least busy server. A server farm can each host multiple published applications. These applications can be run on more than one machine at a time. If more than one application is accessed at a time, the server that already is hosting the client�s session will permit additional applications. When considering the requirements for sizing and selection of computer server hardware, administration may use several general rules of thumb. A single quad processor server with 1 GB of memory could potentially host 50 or 60 concurrent sessions. An enterprise with 200 users may consider 4 quad processors grouped in a server farm. It is common knowledge that smaller servers are better than larger servers when distributing the load for many concurrent connections. In our example above, administration may want to consider 8 dual processor systems. When using this combination, response times on each server tend to be faster and there is less of a chance for service outage if one machine becomes unavailable.

As the needs of the Enterprise change, clients can access applications via direct LAN connection, via WAN connection, via remote node, direct async modem connection, or via the intranet / Intranet.

WEB / intranet Connectivity

A particularly large challenge is providing access to application or data via the WEB. Since many of the current Win-Intel based applications are not WEB enabled, the question can be asked, how does an administrator provide access?

Server Based Computing uses the Published Application Manager to publish and iconize an application. Once the application is published, two files must be transferred to the WEB server. PAM is used to create an ICA file that contains the definitions of the application, its location, colors and resolutions. The ICA file acts as a client on the WEB server. There is a procedure to change the MIME type on the WEB server so the ICA file can be recognized and launch a session directly to the WTS/MetaFrame server.

The second element for WEB computing is the HTML file. A file is created that contains a hyperlink to the ICA file. When this link is selected, the ICA file starts a session and the published application is launched. Using a combination ICA file and HTML file enables a non-Web enabled application to be launched via the intranet or Internet. This method permits access to most Dos, Windows 16 bit, or Windows 32 bit software application that would not normally be enabled for WEB access.

Accessing the Latest 32-bit applications on Legacy Desktops.

One of the most significant functions of server based computing is using older none Y2K compliant desktops to act as clients to the server based computing environment. Since the only software needed on the client�s device is ICA and a communications protocol, even some of the oldest devices can be used to connect to a server based computing device. In this manner, every client device can access and run the most demanding software on their personal machines without the need to upgrade the client�s device. Most client devices can access the central server. A partial list of clients include, 286, 386, 486, Pentium based Win Tell machines, Apple Mac, Unix, Windows CE, Network Computers, Dos based machines, X.11 clients, etc. In this manner, non Win-Intel machines can access the latest in 32-bit software.

Administration of these devices is centralized. Should a remote user require help, the central administrator can shadow the device and assist with instruction and training.


Network Productivity can be improved in the Enterprise with the use of Windows Terminal Server and MetaFrame. Application deployment, control, and administration are central. This reduces the costs associated with touching and loading software on each client device. WTS/ MetaFrame provide a complete solution for Management, Access, Performance, Enterprise Scalability and Security � all of which is required for successful deployment of applications. 

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