三、ATM信元组成 1.信元格式 GFC VPI VPI VPI VCI VPI VCI VCI VCI VCI PT CLP VCI PT CLP HEC HEC (a)UNI (b)NNI UNI:User Network Interface NNI:Network Node Interface 10 2023/6/262023/6/26 10 三、ATM信元组成 1．信元格式 GFC VPI VPI VCI VCI VCI PT CLP HEC VPI VPI VCI VCI VCI PT CLP HEC (a) UNI (b) NNI UNI： User Network Interface NNI： Network Node Interface