X.500 Index DSAs and scaling issues for an indexed white pages directory service

Abstract

This paper introduces the notion of X.500 Index DSAs. These are DSAs which hold indexes to entries held in the distributed X.500 directory. An Index DSA provides a similar enhancement to distributed X.500 to the one that archie provides for FTP. Index DSAs are created to provide specific services that are hard to provide in a fully distributed directory. An Index DSA is not technically different from an ordinary DSA, except that it does not provide references to parts of the DIT it does not hold. A pragmatic difference is that Index DSAs effectively hold pointers to entries, rather than the entries themselves. The paper then examines whether Index DSAs really can solve a critical white pages search problem, which is that if a user is unable to restrict the scope of a query to one organisation, then there is no systematic way of restricting the scope of the query to a small number of servers. The analysis is based on using a sample of past queries made within the UK DIT. The paper examines whether Index DSAs allow us to prune the search space sufficiently to allow efficient country-wide searches. The paper also examines whether there are substantial differences in query resolution effectiveness between using a single Index DSA and using a small set of hierarchically organised Index DSAs.