ITU-T Recommendation X.519 | ISO/IEC 9594-5 specifies the Directory Access Protocol, the Directory System Protocol, the Directory Information Shadowing Protocol and the Directory Operational Binding Management Protocol fulfilling the abstract services specified in ITU-T Recommendation X.501 | ISO/IEC 9594-2, ITU-T Recommendation X.511 | ISO/IEC 9594-3, ITU-T Recommendation X.518 | ISO/IEC 9594-4 and ITU-T Recommendation X.525 | ISO/IEC 9594-9. It includes specifications for supporting underlying protocols to reduce the dependency on external specifications.