Q. What are the protocols used by AD?

Because Active Directory is based on standard directory access protocols, such as Lightweight Directory Access Protocol (LDAP) version 3, and the Name Service Provider Interface (NSPI), it can interoperate with other directory services employing these protocols.
LDAP is the directory access protocol used to query and retrieve information from Active Directory. Because it is an industry-standard directory service protocol, programs can be developed using LDAP to share Active Directory information with other directory services that also support LDAP.
The NSPI protocol, which is used by Microsoft Exchange 4.0 and 5.x clients, is supported by Active Directory to provide compatibility with the Exchange directory.