The Recommendations covering the maintenance of groups and supergroups will apply as far as possible but there will be a number of new maintenance problems which are peculiar to multiple destination links. In particular, arrangements will be needed to check the performance of the MU main section of such links. In order to simplify the procedures and minimize interference to other users of the common path, it is recommended that the send reference station (see Figure1/M.460) for the MU main section should act as a focal point for reports and inquiries concerning the MU main section. The group, supergroup, etc., control stations will still be responsible for localizing a fault to a particular section of a link in accordance with Recommendation M.130.
ITU-T M.535-1988 Referenced Document
ITU-T M.130 Operational Procedures in Locating and Clearing Transmission Faults - General Maintenance Principles - Maintenance of International Transmission Systems and Telephone Circuits (Study Group IV) 9 pp*， 1989-01-01 Update
ITU-T M.535-1988 history
0000 NF P18-310-13:2015
1988ITU-T M.535-1988 SPECIAL MAINTENANCE PROCEDURES FOR MULTIPLE DESTINATION, UNDIRECTIONAL (MU) GROUP AND SUPERGROUP LINKS