This TS identifies the Mobile services Switching Centre/Interworking Functions (MSC/IWFs) and requirements to support interworking between:
PLMN and PSTN
PLMN and ISDN
It is not possible to treat ISDN and PSTN as one type of network, even when both ISDN and PSTN subscribers are served by the same exchange because of the limitations of the PSTN subscribers access i.e. analogue connection without D channel signalling.
Within this TS, the requirements for voice and non voice (data) calls are considered separately.