This Recommendation 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 ITU-T G.960 [4] for the case with a NT1 separate from the AN; ISDN basic access with a user-network interface according to ITU-T I.430 [3] 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.