The X.500 Directory Service
There are many networks around today that provide an infrastructure for
communication - postal network, phone network, internet. However to make use
of these networks it is usually assumed that the prospective user can supply
some sort of information about the underlying structure of the network in
question. In most cases this takes the form of an address for the party you
wish to contact.
Remembering this information for your inner circle of friends (those you
frequently with) is not a large problem. An address book can be kept to
record any details that you might forget. The problem arises when you wish
to make contact with someone for the first time - presumably you know their
name but you may not know their address or even the best communication
network to contact them on. Indeed even if you have contacted someone in
the past, they may have changed addresses in the meantime and not informed
you. Again the address book mechainsm is defunct.
The solution to this problem in the telephone world is to publish a phone
number directory which is updated reasonably regularly ( once a year, which
suffices if you live in a country where it takes months to get a phone
connected). However even in the telephone world this system is begining to
show its age. Several directories are required for a large city. Also,
more and more people are communicating with people outside their local
With the electronic network expected to grow at an even faster rate than the
phone network, the motivation for some type of electronic directory is
obvious. Some phone companies, notably France Telecom, have already produced
electronic directories. In the future it would be particularly useful if
the directories for all the networks could be combined. Then we could
find someone`s telephone number and internet address in the same place, and
that person could direct people as to the best way to reach him at a
Having a centralised database for this electronic directory is a non
starter for at least two reasons
For these and other reasons a distributed, locally administered, worldwide
directory service is the best solution. Each local element will look after
its own updates, maintenance, security policy and requsts for information
from local users. It will also service requests from other elements who's
users require information which is not available at their sites.
For all the elements of this directory to be able to communicate
information, some sort of protocol is necessary. This is where the
X.500 standard comes from.
A directory covering all the communications networks on the planet would
be very large and consequently slow to access any individual entry.
Who would maintain such a database? Even if some organistaion bore the cost
of the physical storage required, the bureaucracy needed to handle
the updates and the maintenance would be a nightmare.
For a WWW interface to the X.500 service click
This will start you off at the 'top of the world' in terms of
countries. Take your pick!.
This WEB page is supposed to be act as an overview of the X.500
standard for the novice. It is not meant to be definitive nor does it
go into detail about any of the implementations of the standard. It should
give you a feel for the flexibility of the standard and the usefulness of the
service that could be provided if this standard gained wide acceptance.
This overview has been split into the following sections
The Structure and Model of the Directory
The Components and Protocols of the X500 Directory
How the Directory deals with Security Issues
At this moment in time, the Directory has yet to really take off with
the implementors or the business community. Obviously for a global directory,
adoption by a large range of users will be the only real guide to its
success. Its no good having the best directory standards or software if
the world at large it can't communicate with the world at large. By reading
this page you
will certainly get a feel for the complexity of the standard. The reason
the standard is complex is that it must be very flexible if it is to
acheive its grand aim - a single tree structured directory covering all the
communications networks in the world. The next decade will decide if the
standards people have been over ambitious or very far sighted.
The Current and Future Applications of the Directory