Overview of Terminal Services

by [Published on 24 Feb. 2005 / Last Updated on 24 Feb. 2005]

This article presents a high-level overview of Terminal Services technologies on Microsoft Windows platforms. Topics covered include a brief history of Terminal Services, its usefulness in enterprise environments, solutions from Microsoft and Citrix, and some special challenges for deploying and using Terminal Services.

Check out MSTerminalServices.org, a new resource for Windows Terminal Services and Citrix focusing on all aspects of server based computing and thin client computing.

Terminal Services has been a part of the Windows server OS since NT 4.0, but its history as a technology goes back further to the late 80s when Ed Iacobucci founded Citrix. Ed had been working with IBM trying to develop a multi-user version of OS/2, but IBM wasn't much interested so Ed left to start his own company (good move). In the early 90s Microsoft came out with Windows NT 3.51, their first really solid 32-bit Windows server platform, but Microsoft too wasn't much interested in developing a multi-user version of their OS at the time, so in 1994 Microsoft granted Citrix access to their NT source code so Citrix could develop this technology as a third-party vendor. Soon afterward Citrix released their revolutionary WinFrame product, and its immediate success soon led Microsoft to shift gears and in 1997 Microsoft licensed Citrix technology so they could incorporate it into NT 4.0. The result was the release in 1998 of Hydra, Microsoft's code name for Windows NT 4.0 Terminal Server Edition. Hydra of course has since been superceded by the built-in Terminal Services feature of Windows 2000 Server and more recently in Windows Server 2003.

And there we are today. But why all the fuss? What good is Terminal Services technology anyway?

The Terminal Services Advantage

From the operations side of running a business, there are really only two things that are important: time and money. The great thing about Terminal Services is that it can save you both.

From a time-saving perspective, Terminal Services lets administrators install, configure, manage and maintain applications centrally on a few servers. This is usually much faster and easier to do than deploying applications on hundreds or thousands of desktop machines at different sites across an enterprise. And by making the job of the administrator easier, companies also save money on IT support costs for their information systems infrastructure. Furthermore, centrally-deployed applications are usually easier to maintain (for example, patching and upgrading) and simpler to troubleshoot when things go wrong. As a result, downtime is reduced, users are more productive, and business booms along.

Another cost-saving perspective is that since in a terminal server environment all application logic runs on the server, the processing and storage requirements for client machines are minimal. This means you can save money by keeping in service older desktop computers running legacy versions of Windows, and focus your limited IT budget on a few high-powered systems to run as your terminal servers. Or you can toss your old desktop PCs and buy thin clients like Windows-Based Terminals (WBTs) instead, such as those from Neoware, Wyse, and other vendors. The options are almost limitless since terminal servers let you run almost any DOS, Win32, or Web-based application from almost any client platform as we'll see in a moment.

So what are the options for running terminal servers in today's enterprise environment? There are two major players in the landscape, Microsoft and Citrix, and we'll start by looking at Microsoft's latest offering, the built-in Terminal Services component of Windows Server 2003.

Windows Terminal Services

First off, let's take note that Terminal Services in Windows Server 2003 is light-years ahead of its predecessor in Windows 2000 Server. Key enhancements over that older platform include the following:

  • Remote administration mode no longer requires the installation of additional components, you just select a checkbox on the Remote tab of the System tool in Control Panel and presto, up to two users can simultaneously connect to your server to remotely administer it. Not only that, you can even connect to the actual console session on the remote server, something you couldn't do in Windows 2000.
  • Remote Desktop Protocol (RDP) has been enhanced to improve display and device redirection and enhance security through powerful encryption algorithms, making Terminal Services so secure you don't need a VPN tunnel when you're connecting to it over a public network like the Internet.
  • The optional Session Directory component now lets you scale Terminal Services upwards to meet the demands of even large enterprises by letting you build a load-balanced terminal server farm that lets users reconnect to the same terminal server they were connected to should they somehow become disconnected. This maintaining of session state lets you run mission-critical business applications on terminal server farms.
  • And perhaps best of all, Terminal Services can now be configured, managed and locked-down using dozens of Group Policy settings new to Windows Server 2003, allowing administrators to take advantage of the flexibility and power of Group Policy to simplify the configuration and management of Windows Terminal servers.

So it would seem that if you want to deploy terminal servers in the enterprise that Windows Server 2003 is a no-brainer as far as choice is concerned, right? After all, it's got the horsepower, it's got the scalability, it's even got the clients for different Windows platforms ranging from Windows 95 to Windows XP to Windows CE on Pocket PC devices. There is even a client for the Macintosh platform, and also an ActiveX client that runs within the Internet Explorer web browser so you can connect to Terminal Services over the Internet. For more details on Windows Terminal Services and how to set it up and configure it, you can take a look at the articles Windows 2003 Terminal Services (Part 1) and Windows 2003 Terminal Services (Part 2), both by Andrew Z. Tabona right here on WindowsNetworking.com

Anyway, even from our brief discussion here it might seem that Windows Server 2003 Terminal Services has got everything, and it's all you need, right? Not so fast!

Citrix Access Infrastructure

Citrix, the company that actually developed the underlying technology behind Windows Terminal Services, wisely chose not to rest on its laurels but to continue refining and enhancing their product line until today they have a compelling suite of applications called Citrix MetaFrame Access Suite. This package consists of a handful of key products that run on Windows Server 2003 and go beyond what Windows Terminal Services itself can do. Here's the lineup:

  • Citrix MetaFrame XP Presentation Server. This is Citrix's own version of Terminal Services and lets you connect any client device to any application running on the presentation server (terminal server). And by "any" I really mean any. While Microsoft clients for Terminal Services are currently limited to Windows and Mac platforms, Citrix clients are available for Windows, Mac, various flavors of UNIX, and even EPOC handheld devices. Not only that, there's even a UNIX version of Presentation Server so you can run UNIX and Java applications on a terminal server while accessing them from Windows clients. This flexibility is key in large enterprises where the operating system environment is a heterogeneous mixture of Windows and UNIX, and if you want anyone to run any application from anywhere in your enterprise then Presentation Server is definitely something you should look at.
  • Citrix MetaFrame Secure Access Manager. This complementary product for Presentation Server provides for role-based control over who can access applications and documents running on Presentation Server. With its built-in standards-based encryption, you can provide access anywhere even over the Internet without the need of additional security such as deploying a VPN.
  • Citrix MetaFrame Password Manager. This add-on provides single sign on (SSO) authentication so your Presentation Server users only need a single password to gain access to a wide range of services and resources on Windows and UNIX servers.
  • Citrix MetaFrame Conferencing Manager. This add-on allows sharing of Presentation Server application sessions so workers can collaborate using the same applications and work on documents together. It's also a great tool for conducting online training in your enterprise.

What gives Presentation Server a lot of its power is its ICA (Independent Computing Architecture) protocol, the presentation protocol used on the Citrix platform for transmitting keystrokes, mouse movements, and screen updates between thin clients and the presentation server. ICA is the Citrix counterpart of Microsoft's Remote Desktop Protocol (RDP) used by Terminal Services, and it's illuminating to compare their capabilities:

Client Support

ICA

RDP

Windows 95/98/NT/2000/XP

X

X

Windows for Workgroups 3.11

X

X

Windows 3.1

X

DOS

X

Windows CE

X

X

Macintosh

X

UNIX

X

Linux

X

Java

X

Web browser

X

X

Conclusion

So do you need the Citrix MetaFrame Access Suite, or will Windows Server 2003 Terminal Services be enough? Time and money--weigh the benefits of each solution and consider the costs, then decide. Don't just jump on the bandwagon by thinking you can deploy a terminal server, keep your old desktop PCs, save desktop licensing costs and walk away a winner. Both Terminal Services and Presentation Server have their own licensing requirements and they're complex, so you really need to do your research to see which one gives you the most bang for your buck (or whether you'll even be saving any money at all moving your business from a client/server to a terminal server computing environment). Another factor to consider is that the hardware you use to run a terminal server on generally has to be top quality and pretty beefy, and such machines come with their own hefty price tag as well. In fact, sizing the underlying hardware you need to meet your current and projected requirements is one of the key steps in planning a move to Terminal Services, and Microsoft has provided a helpful whitepaper that can help your planning in this regard.

Once all is said and done, Terminal Services (or Presentation Server) may be just for you or it may not. But it's just a tool anyway to help you get the real job done, namely, whatever business your company is in.

Check out MSTerminalServices.org, a new resource for Windows Terminal Services and Citrix focusing on all aspects of server based computing and thin client computing.

The Author — Mitch Tulloch

Mitch Tulloch avatar

Mitch Tulloch is a widely recognized expert on Windows administration, networking, and security. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy and use Microsoft platforms, products and solutions.

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