rfc1684.txt

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Network Working Group                                            P. Jurg
Request for Comments: 1684                                    SURFnet bv
Category: Informational                                      August 1994


          Introduction to White Pages Services based on X.500

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This document aims at organisations who are using local and global
   electronic communication on a day to day basis and for whom using an
   electronic White Pages Service is therefore indispensable.

   The document provides an introduction to the international ITU-T
   (formerly CCITT) X.500 and ISO 9594 standard, which is particularly
   suited for providing an integrated local and global electronic White
   Pages Service.

   In addition a short overview of the experience gained from the
   Paradise X.500 pilot is given. References to more detailed
   information are included.

   The document should be useful for managers of the above mentioned
   organisations who need to get the necessary executive commitment for
   making the address information of their organisation available by
   means of X.500.

Table Of Contents

   1. Introduction ................................................  2
   2. Concept of X.500 ............................................  3
     2.1  Directory Model .........................................  3
     2.2  Information Model .......................................  4
   3.  Benefits of X.500 ..........................................  5
   4.  Organisational aspects of X.500(experience from Paradise) ..  6
   5.  Applications of X.500 ......................................  8
   6.  References .................................................  9
   7.  Security Considerations .................................... 10
   8.  Author's Address ........................................... 10






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RFC 1684       Introduction to X.500 White Pages Services    August 1994


1. Introduction

   Due to the tremendous growth and development of international
   computer networks we have nowadays the possibility to overcome -
   without having to travel - geographical distances when working
   together with other people. Besides the possibility of using the
   telephone we may use electronic data exchange to discuss working
   documents, new ideas, plans or whatsoever. One of the most popular
   means for this is electronic mail, which can be used to exchange
   all kinds of electronic data: from informal pure text messages to
   formatted and multi-media documents.

   As the number of people connected to computer networks grows (and
   it does continuously, it is at least doubling each year!), it
   becomes more difficult to track down people's electronic (mail)
   addresses. Hence, in order to make global communication over
   computer networks work, a global White Pages service is
   indispensable. Such a service should of course provide people's
   electronic mail addresses, but could also easily contain telephone
   and fax numbers and postal addresses.

   Currently, one technical solution for a globally distributed
   White Pages service is X.500 and there exists an international
   infrastructure based on X.500 technology called 'Paradise'
   (Piloting An inteRnationAl DIrectory SErvice), which contains about
   1.5 million entries belonging to persons and 3,000 belonging to
   organisations. Worldwide 35 countries are involved. Paradise is
   also a project of the EC. The project continues until September
   1994. Afterwards its operational tasks will be taken over by a
   European service provider for the R&D community (DANTE).

   The goal of Paradise and related national initiatives is to
   stimulate and extend the use of the X.500 White Pages service.
   Within the pilot attention is paid to technical and organisational
   aspects. The Paradise infrastructure is mainly based on the
   Internet Protocol. The specific issues that are related to the use
   of the Internet Protocol for X.500 can be found in [5].

   In the decision process of joining the international X.500
   infrastructure and opening (part) of the local (address)
   information to the outside world, it is important that an
   organisation fully understands the technical and organisational
   issues that are involved.

   This document tries to be of help in this matter first by
   explaining the main concepts of X.500 (section 2) and subsequently
   by pointing out its benefits (section 3), the organisational
   aspects that are involved (section 4), and for which other



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RFC 1684       Introduction to X.500 White Pages Services    August 1994


   applications the X.500 infrastructure may be used in the near
   future (section 5).

2. Concept of X.500

   The X.500 standard describes a so-called 'Directory Service', which
   can be used for all types of electronic directories. This document
   focusses on the use of X.500 for a global White Pages Directory.
   The concept of X.500 may roughly be divided in the 'Directory
   model' and the 'Information model'.

   2.1  Directory model

   X.500 uses a distributed approach to achieve the goal of a global
   Directory Service. The idea is that local (communication oriented)
   information of an organisation is maintained locally in one or more
   so called Directory System Agents (DSA's). 'Locally' is a flexible
   expression here: it is possible that one DSA keeps information of
   more than one organisation. A DSA essentially is a database:

      - in which the information is stored according to the X.500
        standard (see section 2.2),

      - that has the ability, where necessary, to exchange data
        with other DSA's.

   Through the communication among each other the DSA's form the
   Directory Information Tree (DIT). The DIT is a virtual hierarchical
   datastructure consisting of a 'root', below which 'countries' are
   defined. Below the countries (usually) 'organisations' are defined,
   and below an organisation 'persons', or first additional
   'organisational units', are defined (see the simplified illustration
   below where only three countries and no organisational units are
   presented). The DIT is a representation of the global Directory.

             root                      o
                                      /|\
                                     / | \
                                    /  |  \
             countries            uk   de  fr
                                 / |   /\   |\
                                /  |  /  \  | \
             organisations     a   b c    d e  f
                               |   | |    | |  |
             persons          ..  .. ...  .... ...






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RFC 1684       Introduction to X.500 White Pages Services    August 1994


   Each DSA holds a part of the global Directory and is able to find
   out, through the hierarchical DIT structure, which DSA holds which
   parts of the Directory.

   The standard does not describe how to distribute different part of
   the Directory among DSA's. However, the information corresponding to
   a single node of the DIT (i.e., a country, organisation, person)
   cannot be distributed over several DSA's. In practice a large
   organisation will maintain one or more DSA's that hold its part of
   the Directory. Smaller organisations may share a DSA with other
   organisations.The distribution among the DSA's is totally transparent
   to the users of the Directory.

   A user of the Directory can be a person or a computer. A user
   accesses the Directory through a so-called Directory User Agent
   (DUA). The DUA automatically contacts a nearby DSA by means of which
   the user may search or browse through the DIT and retrieve
   corresponding information. A DUA can be implemented in all sorts of
   user interfaces. Therefore users may access the Directory through
   dedicated DUA interfaces or for example e-mail applications.
   Currently most DUA nterfaces to be used by persons are dedicated, but
   it is expected that in the near future a lot of DUA interfaces will
   be integrated with other applications.

2.2 Information Model

   Besides the Directory model, the X.500 standard also defines the
   information model used in the Directory Service.

   All information in the Directory is stored in 'entries', each of
   which belongs to at least one so-called 'object class'. In the White
   Pages application of X.500, on which we focus here, object classes
   are defined such as 'country', 'organisation', 'organisational unit'
   and 'person'.

   The actual information in an entry is determined by so-called
   'attributes' which are contained in that entry. The object classes to
   which an entry belongs define what types of attributes an entry may
   use and hence what information is specific for entries belonging to
   that object class. The object class 'person' for example allows
   attribute types like 'common name', 'telephone number', and 'e-mail
   address' to be used and the object class 'organisation' allows for
   attribute types like 'organisation name' and 'business category'.
   Dependent on its type an attribute can take one or more values.

   To specify the name of an entry in the DIT, at least one attribute
   value of the entry is used. The entry of a person is usually named
   after the value of the attribute type 'common name'. The name of an



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RFC 1684       Introduction to X.500 White Pages Services    August 1994


   entry must be unique on the same level in the subtree of the DIT to
   which the entry belongs.

   An example of an entry belonging to the object class 'person' is:

       Attribute type              Attribute value
       --------------              --------------

       Object Class:               top
                                   person
       Common Name:                Thomas Lenggenhager
                                   T. Lenggenhager
       Surname:                    Lenggenhager
       Postal Address:             SWITCH
                                   Limmatquai 138
                                   CH-8001 Zuerich
       Telephone Number:           [phone]
       Facsimile Telephone Number: [phone]
       Mail:                       [e-mail]

   This entry corresponds to the node in the DIT that occurs below the
   node of the organisation 'SWITCH' and is named after the first value
   of the attribute type 'common name': 'Thomas Lenggenhager'.

3.  Benefits of X.500

   Why should one use X.500 for a local White Pages service? Here are
   some good arguments:

      - The distributed character of the service. A large
        organisation may distribute the responsibility for the
        management of the information it presents through X.500 by
        distributing this information over several DSA's (without
        losing the overall structure)

      - The flexibility of the service. Besides for public purposes,
        X.500 may also be used for specific private Directory Service
        applications. Whereas the definitions of the DIT, object
        classes and attribute types of the public White Pages
        information within an organisation have to conform to those
        of the rest of world, the internal applications may use their
        own DIT structure and their own definitions of object classes
        and attributes (the values being only visible within (a part)
        of the organisation). Nevertheless one local infrastructure
        can be used for both the public and private computers.






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