ASP Use Of Thin-Client Model May Cause Stormy Weather

Given the booming application service provider marketplace, it’s clear network professionals are finding compelling reasons to outsource their IT headaches. But with the ASP model often comes dependence on thin-client network protocols such as Citrix Systems Inc.’s Independent Computing Architecture and the Internet. Recent studies show that when the weather gets stormy on the Internet – and packets get lost – the impact on ASP client performance can be significant.

Before you get too worried, remember that not every ASP offering requires a thin-client data stream such as ICA or Microsoft Corp.’s Remote Desktop Protocol. Many, such as, simply run normal or Secure Sockets Layer sessions via a standard browser. Others, such as an ASP that delivers Windows 2000 applications, will need to do so via a thin-client mechanism. This usually means implementing a Citrix server or a Microsoft Terminal Server (the basic code of which is licensed from Citrix.)

With thin client, instead of the application residing and executing on a local PC, it resides and executes on the server. The server can be sitting on your internal high-speed net or, as with the ASP model, at an Internet site. The work is performed on the presumably high-end server, and only the screen updates are delivered to your station – hence the “remote desktop” designation Microsoft uses. The benefits are manifold.

Besides the advantage of eliminating software maintenance issues, the data access architecture of most legacy applications meshes nicely with the server-based approach. For example, while it is possible to run applications such as traditional accounting or database packages across a low-speed network, the clients typically are written so they issue reads for each and every record they need to scan. While these reads are instantaneous in a high-speed server, they take forever across a LAN. Thin client eliminates this problem and makes virtually every program a candidate for remote access.

But we often need to pull batches of data down for further analysis or to take on the road. The thin-client software accommodates this by creating “virtual drives” on the remote desktop. These drives represent the physical drives on local PCs. And by using a drag-and-drop interface, chunks of data can be moved from the server to the thin-client machine, and back again.

However, a recent Tolly Research study has shown that when the storm clouds appear on the network and packet loss starts to occur, these file transfers can bog down considerably.

With Citrix ICA, for example, a packet loss of 3 per cent causes file-transfer time to increase by 100 per cent. This is not a surprise, as a single lost frame has a ripple effect up and down the stack. And while 3 per cent is above what you’d expect on the Internet, such situations do occur.

If nothing else, this research shows what really counts is not how your system works in perfect conditions, but how well it holds up in a storm.

Tolly is president of The Tolly Group, a strategic consulting and independent testing company in Manasquan, N.J. He can be reached at or www.tolly. com.

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