\section{Conclusion}
\label{sec:conclusion}

In this paper, we have proposed a global computing architecture.  It
allows any machine connected to the Internet to make a portion of
their computing resources available to remote clients and also utilize
resources offered by other machines. A broker is used to register and
claim resources, and to take care of accounting.  We also presented a
rudimentary Netscape-based broker architecture using Java.  We
discussed economic aspects of our proposal and gave scenarios of
possible developments and various uses of the proposed infrastructure,
from coarse-grained supercomputing applications running on thousands
of nodes, to Internet stations.

We anticipate several challenging technical problems when implementing
a complete version of the proposed broker architecture. In particular,
we examined the high interpretation overhead of Java byte code, and
solutions like just-in-time compilation and dynamic compilation. We
also examined security and correctness problems arising when executing
untrusted code.
% <ADA> Jan 18, 1997
% the problem of optimizing fast user level communication
% within a confined environment like Java,
% fault-tolerance and
% correctness problems
%
Finally, we raised the problem of encrypted computing, a technique to
hide programs or data from the remote hosts executing them.  Although
we currently are unaware of any attempt to give a precise definition
of algorithm encryption, we believe encrypted computing to be a major
issue in large-scale implementation of SuperWeb-like architectures.

While the presented infrastructure is primarily intended to work
across the whole Internet, it is also usable on a smaller scale. In
fact, we anticipate that its initial implementations will be inside
large organizations administering their own Intranets. This would
allow such organizations to use their complete hardware base more
efficiently.  At the same time this simplifies several of the
technical problems that are not yet solved completely, in particular,
the security and privacy issues.
% <ADA> Jan 17, 1997
% Within a single organization, security and
% encryption, while still a concern, become a less important issue.
% In addition, intranets provide
% larger bandwidth and lower latency of communication allowing for
%wider range of communication intensive parallel applications to be solved.

In our further research, we
plan to make our rudimentary broker architecture more usable and
user-friendly, improve its performance, and include security,
accounting, and authentication mechanisms.
% We also intend to  of the current prototype and to run
% a few large test cases such as breaking a large RSA key \cite{cracking} 
% and performing a large QCD simulation.

\section{Acknowledgments}
This work was supported by the National Science Foundation under
NSF CAREER Award CCR-9502661 and
NSF Postdoctoral Award ASC-9504291.
Computational resources were provided by
NSF Instrumentation Grant  CDA-9216202,
NSF Infrastructure Grant CDA-9529418 and Sun Microsystems. 
We would like to thank  Peter Cappello, Bernd Christiansen, Mihai Ionescu, 
and Michael Neary for their work on Javelin and Bjorn Birnir for insightful
discussions on encrypted computing.
%
% <ADA> Jan 27, 1997. We didn't get any comments, did we?
%
% We also thank the anonymous
%reviewers for their valuable feedback on this paper.


