The X.500 Directory Service

Introduction

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 communicate 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 domains.

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 particular time.

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.

For a WWW interface to the X.500 service click here . 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

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.