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]
References
RFCs
- RFC 2148 — Deployment of the Internet White Pages Service