Note SONET由ANSI制定； SDH由TU-T制定. SONET(Synchronous Optical Network,同步光纤网络) SDH(Synchronous Digital Hierarchy,同步数字体系) 17.217.2 SONET由ANSI制定; SDH由ITU-T制定. Note SONET (Synchronous Optical Network,同步光纤网络) SDH (Synchronous Digital Hierarchy,同步数字体系)