Directory System Agent

A Directory System Agent (DSA) is the element of an X.500 directory service that provides User Agents with access to a portion of the directory (usually the portion associated with a single Organizational Unit).^[1]^[2]^[3] X.500 is an international standard developed by the International Organization for Standardization (ISO), and the International Telecommunication Union (ITU-T). The model and function of a directory system agent are specified in ITU-T Recommendation X.501.

Active Directory

In Microsoft's Active Directory the DSA is a collection of servers and daemon processes that run on Windows Server systems that provide various means for clients to access the Active Directory data store.^[4]^[5]

Clients connect to an Active Directory DSA using various communications protocols:

LDAP version 3.0—used by Windows 2000 and Windows XP clients^[4]^[5]
LDAP version 2.0^[4]^[5]
Security Account Manager (SAM) interface—used by Windows NT clients^[4]^[5]
MAPI RPC interface—used by Microsoft Exchange Server and other MAPI clients^[4]^[5]
A proprietary RPC interface—used by Active Directory DSAs to communicate with one another and replicate data amongst themselves^[4]^[5]

^ Daniel Blum (1989-10-30). "Details of X.500 architecture". Network World. 6 (43). IDG Network World Inc: 58. ISSN 0887-7661.
^ Zahir Tari and Omran Bukhres (2001). Fundamentals of distributed object systems: the CORBA perspective. Parallel and distributed computing. Vol. 8. John Wiley and Sons. p. 219. ISBN 978-0-471-35198-6.
^ "X.500: Directory Access Protocol (DAP)". Javvin Technologies, Inc. Archived from the original on 2005-11-23. Retrieved 2005-09-22.
^ ^a ^b ^c ^d ^e ^f "Platform SDK: Active Directory: Directory System Agent". MSDN. Microsoft. Archived from the original on 2005-05-27. Retrieved 2005-09-22.
^ ^a ^b ^c ^d ^e ^f "Active Directory: Active Directory Diagnostics, Troubleshooting, and Recovery: Summary of Active Directory Architecture: Directory System Agent". Windows 2000 Server Resource Kit. Microsoft. Retrieved 2010-10-02.