Thin Client/Server Computing Works

I come from an AS/400 background, so I'm comfortable with the terminal concept. The idea of installing a terminal and not touching it for years appeals to me. But does this technology work in the real Windows NT enterprise world? Can you use thin client/server computing (TCSC) with hundreds, even thousands of users?

The answer to both questions is yes. To give you the information you need to decide whether thin client/server solutions will be useful in your enterprise, I've interviewed representatives of nine organizations with thin-client technology in production. These people represent a wide variety of industries: retail, military, hospitality, education, banking, shipping, distribution, manufacturing, and health care. I'll set the stage by giving you a brief background on TCSC and an overview of some current market trends. Next, I'll take a look at the future of thin-client technology. Finally, I'll present the nine case studies and let you judge how effective a solution TCSC can be.

Thin Client/Server Technology
A thin client is a network-dependent terminal capable of displaying remote applications that run entirely on an attached server. A thin-client device can be a PC, network computer (NC), or terminal. The key to thin-client computing is that applications run on the server—not on the client. An NC or PC that runs all or part of an application is not a thin client.

A thin-client device uses one of three protocols to communicate with the server: Independent Computing Architecture (ICA), Remote Desktop Protocol (RDP), or X. These protocols transfer display information from the server to the client, and keyboard and mouse input from the client to the server. Although these protocols serve a technical purpose, they also have a significant effect on the thin client/server market. Citrix owns ICA, which runs on a wide range of devices: PCs, NCs, Windows-based terminals, and non-Windows-based terminals. ICA can adapt its performance characteristics by running compressed for remote devices and uncompressed for locally attached devices. ICA also supports shadowing, which lets an administrator take control of a thin-client device. Shadowing is useful for end-user support and training.

Microsoft owns RDP, which runs on Windows CE-based terminals and Windows-based PCs. A licensing agreement between Citrix and Microsoft limits device support in RDP. The 1997 agreement states that for 2 years, RDP will support Windows-based terminals and ICA will also support Windows-based terminals—and all other thin-client devices. As Citrix is doing with ICA, Microsoft is optimizing RDP to work well in both remote and locally attached conditions. RDP does not currently support shadowing.

X is an open-standard protocol that X terminals use. X is optimized for locally attached devices and does not perform well in remote-computing situations.

The magic in TCSC is on the server side. Several years ago, Citrix modified NT Server 3.51 to let multiple user sessions run on one server: A properly equipped server can run as many as 60 to 100 NT sessions. In 1997, Microsoft licensed this technology from Citrix and, in 1998, released a new version of NT called Microsoft Windows NT Server 4.0, Terminal Server Edition.

Here's how Terminal Server works. Suppose you have 50 users running Microsoft Word on terminals attached to a server running Terminal Server. A portion of Terminal Server's disk and RAM are allocated to each user. Terminal Server must keep track of each user's activity separately. Terminal Server transmits screen output using a thin-client protocol. As a user types on the keyboard, the keystrokes travel via the protocol to Terminal Server, which processes the requests. Word thinks it's running on one dedicated workstation and is unaware of other users. From Terminal Server's point of view, a portion of Word is loaded for each user, and another portion is shared among all users. For a detailed explanation of how Terminal Server works, see Mark Russinovich, "Inside Microsoft Terminal Server," July 1998.

If Microsoft licensed Citrix's technology to come up with Terminal Server, does Citrix provide any additional functionality? Citrix supplements Terminal Server with a product called MetaFrame. MetaFrame provides support for ICA, shadowing, load balancing, and other administrative features. All of the administrators I interviewed chose the ICA protocol because of its superior remote support over RDP. If you want ICA, you need MetaFrame.

Where Thin Client/Server Technology Fits
Adding thin clients to your existing environment doesn't mean you must rip out your PCs and replace them with thin-client devices. The traditional PC environment and the thin-client environment coexist well (to learn more about mixing PCs and thin clients, see Christa Anderson, "Can a Hybrid Network Work for Your Enterprise?" October 1998). However, most of the organizations I profile in this article replaced existing dumb terminals. These organizations discovered that replacing older terminals with newer terminals is easy, and that doing so lets you run your legacy applications and provide users with access to the latest NT applications.

The technical aspects of replacing existing systems are easy to handle—the difficulty comes from political considerations. Let me explain. Suppose you determine that your users need peripheral devices, whether a 3.5" drive, CD-ROM drive, scanner, or printer. Users can share these devices on the network, which is not a technical challenge. However, when users are comfortable being the masters of their machines, they don't want administrators to take total control of those machines. It's the "personal" in PC that users crave. Yet from an administrator's point of view, every time a user saves a file on a PC, that machine becomes a different PC from all the other PCs the company is supporting, thus complicating the computing environment. Some of the administrators I interviewed have braved the political challenge and replaced PCs. Others don't want to tackle that challenge—yet.