Network Working Group                                    S.E. Kille
INTERNET--DRAFT                           University College London
                                                         March 1991








  Replication Requirements to provide an Internet Directory using
                               X.500









Status of this Memo

A companion document discussed an overall framework for deploying
X.500 on the Internet [Kil90].  This document considers certain
deficiencies of the 1988 standard, which need to be addressed
before an effective open Internet Directory can be established
[CCI88].  The only areas considered are primary problems, to which
solutions must be found before a pilot can be deployed.  This
INTERNET--DRAFT concerns itself with deficiencies which can only be
addressed by use of additional protocol or procedures for
distributed operation.

This draft document will be submitted to the RFC editor as an
informational document.  Distribution of this memo is unlimited.
Please send comments to the author or to the discussion group
<osi-ds@CS.UCL.AC.UK>.



INTERNET--DRAFT         Replication Requirements         March 1991


1  Distributed Operation Extensions

The Internet Directory will operate DSAs over TCP/IP using RFC 1006
[RC87], and DSAs over the an ISO Network Service.  Distributed
operation procedures should not require full connectivity.


2  Knowledge Replication

Knowledge information is critical to resolution of names, and
performing searches.  Knowledge information high up the tree needs
to be widely available.  Consider resolving a name below
``Country=US''. To do this, a DSA needs to have full knowledge at
this point.  Many DSAs need to be able to do this, in order to give
reasonable response and availability.  It would be an unacceptable
bottleneck to force such resolution to a single or small number of
DSAs.  To replicate this knowledge widely, a systematic approach to
replication is needed.


3  Data Replication

Searches are often made at the root and country level, and this is
a vital service (e.g., an approximate match of an organisation
name).  Data needs to be collected in such a way that this sort of
searching is reasonably efficient.  The usual X.500 approach of
subordinate references militates against this.  At a node in the
DIT, subordinate references to the entries below are held.  These
entries will be in many DSAs, each of which needs to be accessed in
order to perform the single level search.  It is suggested that
replication of data is necessary to achieve this.

The major requirement for this replication is high up the DIT,
where information must be replicated between different
implementations.  At lower levels of the DIT, it is reasonable for
DSAs to be of the same implementation and to use implementation
specific techniques in order to achieve performance and
availability.


4  Alternate DSAs

When a DSA Referral is returned, only the master DSA is indicated.
This will lead to a single point of failure.  It seems important to
allow for additional references to slave copies, in order to get
better availability.  This needs to be solved in conjunction with
the problem described in the previous section.


Kille                                                        Page 1



INTERNET--DRAFT         Replication Requirements         March 1991


5  Guidelines for use of Replication

To be effective, the replication specification needs to provide
guidelines for deployment in the pilot, in order to meet the
desired service criteria.


6  Some scaling targets

Most techniques for replication have scaling limits.  It is
important that mechanisms used do not stress the limits of the
mechanism.  The order of magnitude envisioned in the pilot is
100 000 non-leaf entries and several million leaf entries.


References

[CCI88] The directory - overview of concepts, models and services,
        December 1988. CCITT X.500 Series Recommendations.
[Kil90] S.E. Kille. Building and internet directory using X.500,
        November 1990. Internet Draft:
        draft-ietf-osix500-directories-00.txt.

[RC87]  Marshall T. Rose and Dwight E. Cass. ISO Transport
        Services on top of the TCP. Request for Comments 1006, DDN
        Network Information Center, SRI International, May 1987.



7  Security Considerations

Security considerations are not discussed in this INTERNET--DRAFT .


8  Author's Address

    Steve Kille
    Department of Computer Science
    University College London
    Gower Street
    WC1E 6BT
    England


    Phone:  +44-71-380-7294




Kille                                                        Page 2



INTERNET--DRAFT         Replication Requirements         March 1991


    EMail:  S.Kille@CS.UCL.AC.UK
















































Kille                                                        Page 3