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.
The present document also contains requirements which relate to the functionality of a (new) Network Termination
Node (NTN) for supporting both Public Switched Telephone Network (PSTN) access and Integrated Services Digital
Network - Basic Access (ISDN-BA) S/T reference point interfaces over a single (digital section) transmission system as
used for existing ISDN-BA. The NTN encompasses NT2-like (noted NT2*) functionality, physical PSTN user port(s)
and PSTN protocol functionality.
An NMDS implementation may contain one ISDN-BA port and/or a limited number of PSTN ports. Typically one or
two PSTN ports would be supported.
In order to maintain an evolutionary path for PSTN services, the national V5 PSTN protocol mapping is assumed to
exist and forms an integral part of this specification.
NOTE: It is an underlying principle of the present document that, wherever practicable, steps may be taken to
minimize the cost of the NTN, subject to maintaining the required functionality.