国家重点 Comments (continued): As its name suggests,SDH has following advantages: a)In SDH network,all network elements are synchronous; b)The transmission rate at each level is four times to that of its adjacent lower level,and N=1,4,16,64,256,which explains the “hierarchy'”; c) It is suitable for optical transmission of high speed with up to 40Gbps; d The powerful network management makes it easy for network operators to configure and maintain,which satisfies partly the requirements of NGN#(New/Next Generation Network) with reprogrammable,reconfigurable and reconstruction- enabled features e) It has the pointer adjustment mechanism that allows the "load to vary within some limited ranges,which means the "load"may be faster or lower than the standard rate. More details in Chapter three of Access network techniques PPT.Comments (continued): As its name suggests, SDH has following advantages: a) In SDH network, all network elements are synchronous; b) The transmission rate at each level is four times to that of its adjacent lower level, and N=1,4,16,64,256, which explains the “hierarchy”; c) It is suitable for optical transmission of high speed with up to 40Gbps; d) The powerful network management makes it easy for network operators to configure and maintain, which satisfies partly the requirements of NGN# (New/Next Generation Network) with reprogrammable, reconfigurable and reconstruction￾enabled features ; e) It has the pointer adjustment mechanism that allows the “load ” to vary within some limited ranges, which means the “load” may be faster or lower than the standard rate. More details in Chapter three of Access network techniques PPT