RFC 1309 (rfc1309) - Page 2 of 16

Technical Overview of Directory Services Using the X

RFC 1309              Technical Overview of X.500             March 1992


   communicate with another person, PROVIDED THAT YOU KNOW HOW TO REACH
   THEM.

   Thus, along with the expansion of the telecommunications
   infrastructure came the development of Directory Services. In this
   paper, we will discuss various models of directory services, the
   limitations of current models, and some solutions provided by the
   X.500 standard to these limitations.

2  MODELS OF DIRECTORY SERVICES

2.1  The telephone company's directory services.

   A model many people think of when they hear the words "Directory
   Services" is the directory service provided by the local telephone
   company. A local telephone company keeps an on-line list of the names
   of people with phone service, along with their phone numbers and
   their address. This information is available by calling up Directory
   Assistance, giving the name and address of the party whose number you
   are seeking, and waiting for the operator to search his database. It
   is additionally available by looking in a phone book published yearly
   on paper.

   The phone companies are able to offer this invaluable service because
   they administer the pool of phone numbers. However, this service has
   some limitations. For instance, you can find someone's number only if
   you know their name and the city or location in which they live. If
   two or more people have listings for the same name in the same
   locality, there is no additional information which with to select the
   correct number. In addition, the printed phone book can have
   information which is as much as a year out of date, and the phone
   company's internal directory can be as much as two weeks out of date.
   A third problem is that one actually has to call Directory assistance
   in a given area code to get information for that area; one cannot
   call a single number consistently.

   For businesses which advertise in the Yellow Pages, there is some
   additional information stored for each business; unfortunately, that
   information is unavailable through Directory Assistance and must be
   gleaned from the phone book.

2.2 Some currently available directory services on the Internet.

   As the Internet is comprised of a vast conglomeration of different
   people, computers, and computer networks, with none of the hierarchy
   imposed by the phone system on the area codes and exchange prefixes,
   any directory service must be able to deal with the fact that the
   Internet is not structured; for example, the hosts foo.com and



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