DXI is an ATM (and SMDS) interface that converts variable-length network frames to fixed-length ATM cells. ATM DXI converts LAN frames to the variable-length DXI frame format. An ATM DSU/CSU then converts DXI frames to fixed-length ATM cells. This two-step conversion simplifies processing on the ATM DSU/ CSU, because it only needs to convert one type of frame.