Using the Best of X.500

The X.500 family of standards were developed jointly by the International Standards Organization (ISO) and the International Telecommunications Union (ITU) to promote the development of an international white pages directory service made of up of large numbers of Directory System Agents (DSAs) connected in an Open Systems Interconnection (OSI) network using protocols defined in the standard. There have been several significant barriers to the deployment of X.500 directories:

• TCP/IP has become the de facto network protocol, not the OSI protocol suite.
• X.500 assumes a global directory structure and requires some defined authority to manage the top of the tree internationally and in each country.
• X.500 names are complex in structure and difficult to use. For example, a typical X.500 name might be "C=US,O=Myco,OU=Platforms,OU=Division,CN=JamesSmith, which many users find cumbersome when compared to the Internet form, "JamesSmith@Myco.COM".
• X.500 defines only protocols, not APIs. This has obstructed the development of tools that can work with X.500 directories.

The X.500 family of standards is most useful for providing interoperability among directories. The communications protocols can be carried over a TCP/IP network, eliminating the dependence on OSI. The existence of well-defined protocols and formats makes interoperation among different directory services practical.

The next generation Windows NT Directory Services, as was earlier noted, provide subsets of the 1993 X.500 protocols necessary to enable participation in an existing X.500 directory as well as to interoperate with directories and tools that support the X.500 protocols. The relevant X.500 protocols are:

• DAP: the Directory Access Protocol
• DSP: the Directory System Protocol
• DISP: the Directory Information Shadowing Protocol

Figure 4: LDAP, HTTP and X.500 Protocol s mean Interoperability.

Support for these protocols allows next generation Windows NT Directory Services to participate fully in mixed Internet and X.500 environments. The end user benefits from the implementation features of next generation Windows NT Directory Services without the burdensome overhead of X.500.

Providing a Rich Set of Application
Programming
Interfaces (APIs)

The next generation Windows NT Directory Services provide powerful, flexible, and easy-to-use APIs. The availability of a rich set of APIs to the directory encourages the development of applications and tools that make use of the directory's services. The next generation Windows NT Directory Services provide three major API sets:

• Active Directory components, a set of COM objects for manipulating and querying multiple directory services
• MAPI, the Windows® Open Services Architecture (WOSA) Messaging API
• LDAP C API (RFC1823), an informational RFC that is the de facto standard in C programming for LDAP applications.