This first part of EN 300 324 specifies the electrical, physical, procedural and protocol requirements for the V5.1 interface between an Access Network (AN) and the Local Exchange (LE) for the support of the following access types: - analogue telephone access; - ISDN basic access with a line transmission system conforming to ETS 300 297 [8] for the case with a NT1 separate from the AN; - ISDN basic access with a user network interface according to ETS 300 012 [4] at the user side of the AN (i.e. the interface at the T reference point); - other analogue or digital accesses for semi-permanent connections without associated outband signalling information.