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January 17, 2000
Web posted at: 10:10 a.m. EST (1510 GMT)

by Kevin Tolly

(IDG) -- With Y2K worries over, you can finally turn up the heat on long-neglected projects. If industry analysts are correct, renting applications from application service providers (ASP) will be a focus of activity. But as you draw up your plan and rough out your budget, don't forget about including WAN bandwidth.

It's tough to find information about how much bandwidth one should allot each user when implementing thin-client networking to deliver rented applications. In fact, neither thin-client giant Citrix nor its major licensee, Microsoft, spend much time addressing the issue. Scouring through various technical and marketing offerings reveals that the vendors believe 20K bit/sec per user is a good rule of thumb.

So let's consider our options for deploying applications to a contingent of 50 simultaneous users. Accepting 20K bit/sec as valid would allow a single T-1 to support some 75 users (20K bit/sec x 75 = 1.5M bit/sec). Supporting our hypothetical group of 50 would require only 1M bit/sec of capacity.

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But what would happen if the 20K bit/sec rule of thumb were wrong? The Tolly Group conducts ongoing research in the area of thin-client networking and, according to our research, that number is rarely accurate.

In fact, our studies of Microsoft Office applications accessed via thin clients across a T-1 showed moderately paced typing with several applications open triggering streams that, for example, averaged 97K bit/sec with peaks of 122K bit/sec. With this average, the T-1 link would fill up with just 15 simultaneous users. Allowing for the peak would knock that number down to 12 users.

Imagine now that the T-1 you thought was overkill for 50 users could, in reality, only support a dozen Microsoft Office users. What does that added WAN expense do for the bottom-line benefits you thought server-based computing would deliver?

Where did the 20K bit/sec number come from? That is a question I cannot answer. Is it possible for applications to run within the 20K bit/sec window? For average consumption, the answer is yes. Some client scenarios we ran clocked in at 9K and 18K bit/sec. Still, these applications were troublesome because their runs showed peaks of 90K and 122K bit/sec, respectively.

If you are a bit bewildered by this situation, take a moment to consider the heritage of thin-client computing. Some 10 years ago, Citrix developed its Independent Computing Architecture (ICA) protocol to off-load processing - not bandwidth - from low-end machines. Early on, Citrix allowed Windows 3.1 applications to run on DOS machines.

Today, the ICA protocol enjoys a well-deserved renaissance courtesy of the ASP movement. With that in mind, however, one thing is clear - no plan is complete until the WAN bandwidth budget for rented applications is figured in.