| Enterprise Computing for the Office - Using Thin Clients |
by Michael C. Barnes (Jun. 3, 2003)
Using Thin Clients
A thin client is a device that does not have a disk drive. They can range from stateless, which means that they act as only a keyboard, mouse, and display with all the graphics, processing and data input being controlled on the server.
There are thin clients that run a display protocol such as Win Terminals or X Terminals. There are also diskless workstations – sometimes called lean clients because all the processing is done locally.
The illustration below demonstrates a configuration using the DFC as the main server for diskless clients.
The server is running an operating system that is LTSP enabled. It is possible to add this capability to virtually any Linux distribution. When the thin clients are turned on, they download the kernel over the network but run it locally. All applications run on the local computer. This solution is ideal for schools. Any user can long into their home directory from any client. This solution also offers the advantage that the processes are running on the local client and not on the server.
The drawback of this solution is that all clients share the same configuration file for X Windows. This means that you will either have to create a very generic configuration or all clients will have to use the same video card and mouse.
Note: It is possible to use the VESA graphics standard with most video cards.
Microsoft has a protocol, RDP that allows the use of Win Terminals. In the past, it was quite expensive to support thin clients off of Microsoft Servers because you would need server software that communicated between the Win Terminals and Microsoft's advance server.
There are now Open Source and commercial solutions that allow you to connect to Microsoft Advance Server as if you were a Win Terminal. To the user, it looks as if they have booted directly into Microsoft Windows 2000. As of this writing, RDP 4.0 is supported with Open Source and commercial solutions are available that support RDP 5.2. RDP 5.2 requires Microsoft XP and above. RDP 5.2 supports 24-bit color while RDP 4.0 supports only 8-bit color. RDP 5.2 supports sound on the local client while RDP 4.0 does not.
In the previous configuration, the thin clients emulate a Microsoft protocol called RDP. RDP allows users to support a remote screen on a local device. RDP has different versions. RDP 4.0 allows for 8-bit color and does not support local sound. RDP 5.2 allows 24-bit color and support for local sound. RDP 5.2 is only available for Microsoft XP or above.
In the above illustration, the thin clients are configured to act like Win Terminals. Our proposed solution uses an embedded Linux that does this emulation and doesn't require additional software such as Citrix’s MetaFrame. It is also possible to implement a Win Terminal using Microsoft’s Windows CE.NET.
This solution is ideal for point of sale (POS), reservation systems, security stations, banking, airline reservation, and dispatching.
Many companies sell dedicated Windows Terminals. These are often the same price or more expensive to purchase than personal computers. Some solutions require expensive third party solutions to connect the Windows Terminals to the Microsoft Windows 2000 Advance Server.
One of the challenges facing companies is that often their core business systems run on both Unix and Microsoft Windows systems. Windows Terminals must network directly to a Microsoft Windows based server. It can become complicated and require additional third party software if users have to access critical applications running on legacy mainframes or Unix servers.
Unix and Linux servers require a different protocol from Microsoft Windows 2000. The protocol Unix requires is X11. The current version is X11R6. There are terminals that emulate X11 and these are called X terminals. The way that X terminals connect to the Unix server is essentially the same as the way that Windows Terminals connect to Microsoft Windows based servers.
X terminals are often as expensive as PCs. They also require a server to operate. It can become complex to use X terminals to interface to core business solutions running on Microsoft Windows. There are third party software packages that make this possible but they are expensive.
An inexpensive approach would be to set up a diskless client server. The diskless workstations would boot into Linux. This would be set up the same as our first illustration. In this case, the user would be using Linux to run a program that emulated a Windows Terminal. The user would simple click on an ICON that runs a program that will run RDP. There are Open Source and commercial solutions.
The photo below is taken off of a screen of a diskless client connecting into a Microsoft Advance server using an Open Source RDP protocol. To the user, it looks exactly as if they are using a PC and running their applications locally.
The above solution uses an embedded Linux that has both X terminal and RDP support. This solution eliminates the need to boot off of a Linux server. The clients can be plugged directly into a network supporting RDP or into a network supporting X Terminal protocol. In the configuration above, we use an intermediate server. This server provides local storage, provides local applications – such as office automation, e-mail and browser. The local server also acts as a local traffic cop implementing a zone of control for added security.
It is possible to add printers and other devices to the Local Area Network Server. The LAN Server can then be a printer server, file server, applications server, firewall and gateway.
The LAN server becomes the gateway to the corporate Wide Area Network (WAN). In the illustration, we show the WAN supporting a Microsoft Advance Server 2000 and a Unix file server. Each client can support applications on either platform. It is also possible to support additional protocols such as 3270 via the LAN server.
For additional information, please check the following websites and resources:- http://www.norhtec.com
- http://www.citrix.com
- http://www.rdesktop.org
- http://www.ltsp.org
- http://www.samba.org
- http://linas.org/linux/raid.html
Also by Michael C. Barnes:
 About the author: Michael C. Barnes is currently president of NorhTec. Mr. Barnes has over 20 years experience with computers and another 10 years experience with more primitive networks, to include paper tape and morse code. Mr. Barnes has 18 years of experience with various Unix systems and spent 13 years with Sun Microsystems.
Mr. Barnes became fascinated with GNU/Linux turned the common PC into a Unix like workstation. By 1998, GNU/Linux surpassed the desktop environments offered on traditional Unix workstations.
When GNU/Linux is combined with low-cost x86 platforms, organizations now have the power to create enterprise computing for the small organization.
Mr. Barnes, born in Kentucky, now lives in Bangkok, Thailand with his wife, Linda Kubota-Barnes and his daughter Karen Barnes.
Copyright © 2003 by Michael C. Barnes. Reproduced by DesktopLinux.com with permission.
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