RFC 1202 (rfc1202) - Page 2 of 11

Directory Assistance service

RFC 1202              Directory Assistance Service         February 1991


   The Directory service is provided to applications through the
   Directory Access Protocol (DAP), which binds a Directory User Agent
   (DUA) to a Directory System Agent (DSA).

                                        | Directory Service
                                        |    provided via DAP
                                        |
               +-----------+            |            +-----------+
               |           |            |            |           |
               |    DUA    |  |    DSA    |
               |           |            |            |           |
               +-----------+            |            +-----------+
                                        |
                         Directory User |

   The DAP is an OSI application layer protocol which uses the rich OSI
   upper-layer infrastructure.  Unfortunately, the coding investment to
   implement the DAP is significant.  As such, it is difficult to host
   applications using the Directory on smaller workstations and personal
   computers.

   This memo details a local mechanism which has been successfully used
   to separate the functionality of the DAP from the complexity of
   implementing the DAP.  That is, a split-DUA model is used: the DAP is
   implemented on an entity (the "Directory Assistant"), which resides
   on a capable workstation or mainframe and exports a simpler
   interface, the "Directory Assistance" (DA) protocol, to other end-
   systems where the user-interface resides, termed the DA-client.

   Since this mechanism provides assistance to applications wishing to
   access the Directory, it is termed the "Directory Assistance" (DA)
   service:



















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