V.35 DTE and V.35 DCE interfaces Automatic dial backup capability via V.35 DCE interface Dial backup requires external DTE DSU IV ESPT for single SW56 circuit ISU 128r and ISU 512T for one to four BRI ISDN circuits at 128 to 512 kbps TSU DSU/CSU for 1.536 T1 bandwidth Does not accommodate plug-on modules