Q3 interface at the Local Exchange (LE) for line and circuit testing of analogue and Integrated Services Digital Network (ISDN) subscriber lines - Part 1: Q3 interface specification
Signalling Protocols and Switching (SPS) - V interfaces at the digital Local Exchange (LE); V5.1 interface for the support of Access Network (AN) - Part 1: V5.1 interface specification; English version ETS 300324-1:1994
