Specifies the Directory Access Protocol, the Directory System Protocol, the Directory Information Shadowing Protocol and the Directory Operational Binding Management Protocol which fulfil the abstract services specified in Recommendation ITU-T X.501 | ISO/IEC 9594-2, Recommendation ITU T X.511 | ISO/IEC 9594-3, Recommendation ITU-T X.518 | ISO/IEC 9594-4 and Recommendation ITU-T X.525 | ISO/IEC 9594 9. It includes specifications for supporting underlying protocols to reduce the dependency on external specifications. The protocols may be encoded using all standard ASN.1 encoding rules.