Computer clients offer a good computing experience. As network quality degrades, interactive performance suffers. It is latency-not bandwidth-that is the greater challenge. Tightly coupled tasks such as graphics editing suffer more than loosely coupled tasks such as Web browsing. The combination of worst anticipated network quality and most tightly coupled tasks will determine whether a thin-client approach is satisfactory for an organization. Stateless thick clients, an alternative to thin-client computing, preserve many of the benefits of thin-client computing but eliminate its acute sensitivity to network latency. This alternative approach achieves this improvement by asynchronously transferring more runtime state to a client and executing from that state on a local processor. In his 1983 classic, "Hints for Computer System Design," 2 Butler Lampson offered the following quote from Jim Morris: "The nicest thing about the Alto is that it doesn't run faster at night." This quote succinctly captures the joy of a time-sharing user who has just discovered the crisp, unvarying performance of a personal computer on highly interactive tasks. Gone is the pain of sluggish interactive response during periods of peak load. By colocating a processor with each user, personal computing offers a computing experience that is unaffected by the actions of other users. The adequacy of thin-client computing is highly variable and depends on both the application and the available network quality. For intensely interactive applications, a crisp user experience may be hard to guarantee. An alternative-stateless thick clientspreserves many of the benefits of thin-client computing but eliminates its acute sensitivity to network latency. Carnegie Mellon University A fter a few false starts in the past decade, thinclient computing is finally gaining serious attention and acceptance among large and medium-size companies. For example, recent Wall Street Journal articles (17 Jan. 2005, 3 Feb. 2005) predicted that more than 3 million enterprise desktops, amounting to 10 percent of the market, will be thin clients by 2008. These articles also mention Time-Warner, Wal-Mart, and the Pentagon as examples of enterprises that are adopting thin clients in significant numbers. Microsoft is also reported to be close to releasing a stripped-down version of Windows XP that transforms an old PC into a thin client (www. brianmadden.com; 18 April 2005). A thin client consists of a display, keyboard, and mouse combined with sufficient processing power and memory for graphical rendering and network communication with a compute server using a specialized protocol. All application and operating system code is executed on the server. The client has no long-term user state and needs no disk. A standard PC can be made to function as a thin client through software such as Virtual Network Computing (VNC). 1 We describe an approach to quantifying the impact of network latency on interactive response and show that the adequacy of thin-client computing is highly variable and depends on both the application and available network quality. If near ideal network conditions (low latency and high bandwidth) can be guaranteed, thin
Tolia et al. REF investigates interactive user experience on thin clients and reports that "thin-client computing is highly variable and depends on both the application and available network quality." The study used both measurements and simulations and stresses that latency is the key limiting factor and not bandwidth.
Quantifying Interactive User Experience on Thin Clients
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Computer Science