Gives requirements for private exchanges for correct interworking with the networks run by British Telecommunications or Kingston upon Hull City Council. Describes requirements for simple call routing mode operation for a PBX connected at the users' premises directly to analogue interfaces and where the terminating stations and cabling are treated as an entirety. Direct dialling in ports to which private circuits or other voice or data stations are connected are not specified in this Section but in other Parts. Does not apply to exchanges for connection to shared lines or 1 + 1 carrier systems or PBXs in parallel with other apparatus whose ringer equivalence number exceeds 0.3.