Performance Testing of Communication Protocols For Three-Tier Computing: Results for ICA and X Windo - Computer Communications and Networks, 1997. Proceedings., Sixth International Conference on

We present the results of performance tests to compare two protocols for three-tier computing using the Windows NT operating system. Three-tier computing features a data server for stored databases (Tier I) , an application server that runs applications (Tier 2), and a simple client program that runs on desktop machines that presents the user interface (Tier 3). Three protocols are available to communicate between Tier 2 and 3: Intelligence Computer Architecture (ICA) with and without data compression, and X Window. We measured the performance of the three protocols in a multi-user environment in which we simulated the workload imposed by typical users. We found that, for Microsoji Office 97 and Lotus Notes applications, the X Window protocol uses approximately twice the network bandwidth of ICA, without compression. We also found that compressed ICA generates roughly one third less network traffic than uncompressed ICA at a cost of 20% of additional processor utilization. Introduction Three-tier computing is a computing architecture widely promoted as offering important cost benefits. 1,223 The three-tier approach is not new; it was developed at the Massachusetts Institute of Technology in 1984 based on use of the X Window protocol to allow a smart terminal to display the user interface &om a program running at a server m a ~ h i n e . ~ . ~ The X Window protocol is widely used today; the X Window industry produces revenue estimated at $2 billion annually;6 a paper forecasting computing trends for the 90s discussed the growing use of X Window pr~tocol .~ More recently, as the memory requirements and complexity of Windows applications has grown, the three-tier computing approach has been introduced for use with Windows systems. The advantages claimed for the three-tier approach are the reduction of desktop machine cost because the desk machine does not have to run Windows applications, but runs a relatively simple user interface program instead. Because the hnction of the desktop machine is more limited than that of a personal computer, the expectation is that the regular upgrades to desktop machines that are a feature of the PC environment will be less frequent with the three-tier approach. There are news reports that Fortune 500 companies are adopting this approach for thousands of desktops, and are reducing their costs by millions of dollars. Another advantage is reduced support and administration costs because the applications all fun in a single environment that can be controlled. Recently, products that use operating system extensions so that standard Windows client programs can run on a Windows NT application server have been introduced and have enjoyed market success, presently selling at the rate of approximately 2 1,000 new desktop installations per month.8 These products use a modified version of the Windows NT operating system to run an unmodified Windows application program at the sever, and they transmit the user interface to the desktop over a communications connection, that may be a LAN or a low-speed connection. One vendor, Citrix, extends the Windows NT system fiom Microsoft so that it can be used as an application server, running application programs, capturing the user interface, and transmitting it to desktop clients using the ICA protocol.’ Several other companies, including Insignia, Tektronix and NCD, extend the Citrix product by also adding the X Window protocol.9310 Thus, all of the three-tier server products in the Windows NT environment employ either the ICA or X Window protocols to communicate displays from Tier 2 to Tier 3 and keyboard and mouse actions from Tier 3 to Tier 2. As ICA can be used with or without data compression, there are actually three protocol choices: ICA compressed, ICA uncompressed, and X Window. To plan an installation of three-tier computing in the Windows NT environment, relative performance information these three alternatives is needed, in terms of network bandwidth used and processing resources 45