This TS identifies the Mobile-services Switching Centre/Interworking Functions (MSC/IWFs) and
requirements to support interworking between:
PLMN and PSTN;
PLMN and ISDN;
for circuit switched services in the PLMN. 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 the present document, the requirements for voice and non-voice (data) calls are considered separately.