isdnBasicRateIfType 1.3.6.1.2.1.10.20.1.1.1.1.1

The physical interface type. For 'S/T' interfaces, also called 'Four-wire Basic Access Interface', the value of this object is isdns(75). For 'U' interfaces, also called 'Two-wire Basic Access Interface', the value of this object is isdnu(76).