国家重点实验室 Conclusion √AS the representatives of synchronous- and asynchronous-transmission switching,SDH and Ethernet are significantly important,and have been using widely and extensively in Access,Metropolitan, Core networks. It is mandatory that students have the firm basic knowledge about the both. More details in Data and computer communication authored by William Stallings,and Chapters three and five of Access network techniques PPT.Conclusion  As the representatives of synchronous- and asynchronous-transmission & switching, SDH and Ethernet are significantly important, and have been using widely and extensively in Access, Metropolitan, Core networks.  It is mandatory that students have the firm basic knowledge about the both. More details in Data and computer communication authored by William Stallings, and Chapters three and five of Access network techniques PPT