ITU-T M.495-1989 Transmission Restoration and Transmission Route Diversity: Terminology and General Principles - General Maintenance Principles - Maintenance of International Transmission Systems and Telephone Circuits (Study Group IV) 10 pp
This may include the verification of switching operations, re-synchronization of digital transmission, etc.
ITU-T M.495-1989 history
1989ITU-T M.495-1989 Transmission Restoration and Transmission Route Diversity: Terminology and General Principles - General Maintenance Principles - Maintenance of International Transmission Systems and Telephone Circuits (Study Group IV) 10 pp