scope:

The present standard defines requirements to support the Narrowband Multi-service Delivery System (NMDS) which provides interfaces connected via a Network Termination Node (NTN) to a Local Exchange (LE), in order to support existing PSTN and ISDN services over an existing ISDN-Basic Access digital subscriber line (DSL). The Narrowband Multi-Service Delivery System (NMDS) may also be connected via a V5 interface Access Network (AN) to a Local Exchange (LE) in order to provide existing PSTN and ISDN services. This optional arrangement is described in annex D which identifies two alternative methods to provide the same overall functionality.