Synchronous Digital Hierarchy (SDH) - Unidirectional performance monitoring for the network element view (Endorsement of the English version EN 301155 V 1.1.1 (1998-05) as German Standard)
同步数字体系(SDH).网元视图的单向性能监测(认可英文版EN 301155 V 1.1.1(1998-05)为德国标准)