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Choosing the right thin client is secondary in light of the many decisions that must be made about infrastructure. Because thin clients run their Windows applications on remote servers, the network infrastructure must be fast and reliable, while server architecture needs to be beefy.

Most thin clients use about 30 Kbps of bandwidth. This does not include the bandwidth for large print jobs or for downloading or uploading files. The backbone should use a switched 100-Mbps or 1-Gbps Ethernet, FDDI or ATM topology. For remote-office links, a frame relay circuit is fast and reliable, though enterprises are increasingly using VPNs and the Internet. Bandwidth-management tools from Cisco Systems or Packeteer police the network and prioritize thin-client traffic over print jobs and downloads.

At a minimum, application servers need processing power and RAM. Microsoft planning documents suggest scaling the number of processors according to the number of users and the types of applications (click here for more information). Also, plan for about 10 MB of RAM per concurrent user above the minimum RAM to run the OS and applications. Application servers should be dedicated to the task and connect to other servers over the backbone for file, print and database services. And maintain a dedicated backup system, preferably on a separate network.

Although we are setting up a single source of failure, clustering application servers can provide high availability while load-balancing software, such as Citrix MetaFrame, will ensure high accessibility to resources. Fault-tolerant solutions can also be applied to file, print and database servers depending on SLA (service-level agreement). For additional insurance, you can use multiple, redundant data centers with failover functionality or contract with an off-site facility for complete disaster recovery.

Once you have the back-end server farm set up, turn your attention to presenting applications to users on thin clients. Which thin-client device you choose will depend on application support and manageability.

Sizing Up Thin Clients

Base your choice of a protocol for remote display and input capabilities on the types of applications you plan to support. Unix hosts support the X11 protocol for X Window and ship with X terminal client software. X11 has wide support in the Unix community and is optimized for high-bandwidth conditions. If you have big pipes and Unix applications to share, X11 is your protocol. But if you're serious about providing access to Windows-based applications, you'll need Citrix's ICA (Independent Computing Architecture) protocol or Microsoft's RDP (Remote Display Protocol).

Thin-Client Protocols Click here to enlarge

RDP supports 16- and 32-bit Windows, including Windows CE. Under NT 4 Terminal Server Edition, RDP 4 was designed for high-bandwidth enterprise environments. Under Win2000 Terminal Services, RDP 5 conserves bandwidth with data compression and bitmap caching, and provides an easy way to monitor and control client sessions. Although RDP is closing in on ICA functionality, RDP client support still lags. Also, ICA allows for rapid application deployment through "publishing," in which an application is published to client desktops without additional client-side configuration. ICA and Citrix MetaFrame, however, add considerable costs to thin-client computing.

A license for MetaFrame on NT 4 Terminal Server or Win2000 Terminal Services is $4,995 for 15 concurrent users. With or without ICA, each thin client initiating a session under Windows must be licensed with a Windows 2000 Professional license or a Windows 2000 TS-CAL (Terminal Services Client Access License) and a Windows 2000 Server CAL or Microsoft BackOffice family CAL. Although a Microsoft-only solution is less costly, it may not be the most cost-effective, in light of Citrix's wide client support and RAD (rapid-application-deployment) tools. Either way, for a cost-effective thin solution, look for devices that support both ICA and RDP.

Most thin clients are billed as WBTs (Windows-based terminals). WBTs support a compact ROM-loadable Windows OS with built-in support for RDP and ICA. Host emulation may be resident in ROM, downloaded from the server, and run locally or displayed remotely from server-based emulation. These thin clients may also support a local browser. Other thin clients use X Window with a local Web browsers and a built-in JVM (Java Virtual Machine) on Linux. Most of these devices support ICA and RDP and access Windows applications using MetaFrame or NeTraverse's Win4Lin. Other thin clients don't even register on the scale.

Sun's Sun Ray follows the JavaStation. It is a stateless device with only a mouse, keyboard and display. The Sun Ray has no OS but includes a SPARC processor and small piece of client code (Hot Desk) that manages remote display and connectivity with Solaris servers running back-end applications. Among Web-based offerings, Citrix NFuse and SCO Tarantella Enterprise 3 enable PCs and thin clients to launch authorized applications from within browsers. And Win2000 Terminal Services offers a Web-based RDP client with ActiveX control through its TSAC (Terminal Services Advanced Client). Click here for more on Web-based thin clients.

The number of local applications on thin clients directly affects distributed management tasks. All thin clients require updates to ROM and the local OS. But local browsers and JVMs require version control with periodic updates, bug fixes and security patches. Although local applications can reduce the number of applications and TCP sessions on the server, they increase the need for local management. Vendors should offer remote-management platforms to flash update the BIOS and upgrade the OSes and local applications. But don't take these offerings at face value -- they must be tested. For added manageability, look for a thin client that supports SNMP.

Thin-client RAM and flash memory make a difference, especially if you're using local applications. Thin clients with local browsers and JVMs need at least 64 MB of RAM to execute Java applets and other applications. If you prefer Intel processors onboard, you may be limited to thin clients from Network Computing Devices' ThinStar line (Intel MMX). Other options include VIA Technologies Cyrix Media and Advanced Micro Devices' K6-2. Processor speeds range from 233 MHz to 266 MHz, but faster processors don't translate to better thin-client performance. In server-based computing, it's the server that matters.

Typical display devices should have no moving parts. If you need a fatter thin client, vendors offer optional hard disks, CD-ROMs and floppy disks, but additional hardware will increase your house calls. Although PC manufacturers like IBM and Compaq Computer Corp. make thin clients, compare their products with the offerings of Boundless Technologies and Wyse Technology, which specialize in thin clients. Also, investigate the offerings of value-added resellers for system integration and support. If you're concerned that your investment will be obsolete before its time, look at leasing options.

Thin Future

Thin clients today satisfy the demand for single-purpose clients and for multipurpose access to Microsoft Office products like Word, Excel and PowerPoint. Tomorrow, thin clients will get thinner. We should see smaller hardware designs with stripped-down code, solely dedicated to remote input, display and connectivity. And when network bandwidth improves for wireless devices, we'll likely see mobile thin clients accessing e-mail, calendars and groupware from remote servers in real time.