Introduction

 

Almost any user of the World Wide Web will be familiar with the following problems:

• Frequently, the file server mentioned in a particular URL is down, unreachable, or busy.
• While additional copies of the file named by that URL may exist (on so-called mirror sites), there is no mechanism for finding them, no way to know whether such copies are current, and no means of ensuring that the mirrored copy has not been altered.
• URLs become stale, that is, a URL which once pointed to a particular file no longer points to any version of that file.
• Search services are often out-of-date due to the sheer size of the net and the necessity to periodically poll each server to see whether its files have changed.
• Search services that return URLs often return duplicate hits because the same file is accessible by multiple URLs. Search services do attempt to eliminate duplicates, but often with the result of eliminating the more desirable URLs from the point of view of proximity.
• There is a need to be able to label resources according to certain criteria, and for the user to be able to examine such labels before attempting to access the resource.
• Given the ease by which many file servers (whether primary servers or mirror sites) may be compromised, there is a need for a service that allows the integrity and authenticity of a file to be checked.

The Internet Architecture Board (IAB) held a workshop on Internet Information Infrastructure in October of 1994 which led to the following recommendations [7]:

• increased focus on a general caching and replication architecture,
• rapid deployment of name resolution services,
• articulation of a common security architecture for information applications.

The workshop report pointed out performance, reliability, and scaling problems with current Internet information services similar to those we have listed above. In general, the report recommended inclusion of a ``wholesale'', or ``middleware'' layer in the information architecture that would sit between the lower ``raw materials'' layer and upper ``retail'' layer, with standard interfaces between the layers.

We propose an architecture for a system, called the Resource Cataloging and Distribution System (RCDS) which addresses the problems described above. We hope that our work will constitute a substantial contribution toward realization of the middleware layer described in the IAB report and toward solving the scaling problems described in [3].

 
• Design Goals
• Issues