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Java in combination with Web browsers' abilities to load and execute untrusted Java applets in a secure fashion has made computing over the Web a possibility. Now the challenge is to fully utilize this potential, given the limitations imposed by browsers. This paper presents Knitting-Factory, an infrastructure to facilitate Web-based computing, which addresses this challenge. It supports building distributed applications, specifically those consisting of Java applets executing in browsers. It is composed of (1) a distributed name service to assist users in locating other participants of a distributed computation via standard browsers, (2) an embedded class server to eliminate the need for external HTTP servers for serving applet code, and (3) a technique for direct applet-to-applet communication.In this paper, we describe the design and implementation of KnittingFactory and demonstrate its benefits by applying it to three distinct areas of Web-based computing. First, we apply our distributed name service to a client/server architecture to enable RMI clients to locate servers on unknown hosts. Second, we use the embedded class server to extend the capability of Charlotte, a parallel computing environment. And finally, we build a collaborative application using our direct applet-to-applet communication technique which does not require a forwarding agent. Metacomputing on theWeb: The projects which focus on Java-based parallel computing include ATLAS [1], Charlotte [3], JPVM [11], JavaParty [22], Javelin [8], ParaWeb [6], and WebFlow [5]. Similarly, there have been proposals for Web-enabled virtual machines as a base for High Performance Computing and Communication (HPCC) platform [14], to use Java in an SPMD programming model [17], and to extend Java with global pointers and remote service request mechanisms from the Nexus communication library [13]. Unfortunately, all but Charlotte and Javelin fail to take advantage of Web browsers in bringing distributed computing to every-day users.JPVM provides a message passing interface to Java stand-alone applications, but not applets. Projects such as JavaParty and [17] require running a Java process to server

Many popular Web sites employ a set geographically dispersed, replicated servers to address the issue of overloaded servers and network congestion. Such distributed Web sites require allocation mechanisms to dispatch request in a way such that any desired load distribution can be enforced. Unlike most traditional approadms, we propose a technique which pushes the allocation functionality onto the client. We argue that this approach scales well aud may rsuit in increased performance in many cases. Building on theoretical work based on game theory, we show that the usage of individual replicas cau be ef.-fatively controlled with cost functions even when the clients are noncooperative.We present the design aud implementation of WehSeAl, our prototype system rerdiz-bg these techniques.WebSeAl does not require any changes to exist-mg client and server code, cotiorma to HTTP standards, and does not generate any control messages.Experiment results indicate that WebSeAl improves periiorrnance while imposing little overhead.

While Java and applets have created a new perspective for Web applications, some problems are still unsolved. Among these are the question of how Java applets can find other members of the collaboration session, how to deal with the restrictions imposed by the Java security model, and how to overcome the inability of applets to communicate directly, even if they belong to the same distributed application. KnittingFactory addresses the problem of finding other members of a collaboration session by providing a distributed registry system where the search is performed within a Web browser without violating its security model; the problem of arbitrary placement of applications by providing the core functionality for downloading applets from an arbitrary node; and finally the problem of direct applet-applet communication by using the Java Remote Method Invocation mechanisms to give applets information on how their fellow applets can be reached. Two example applications validate this concept and demonstrate the ease of use of KnittingFactory. 1 Report Documentation Page Form Approved OMB No. 0704-0188Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.