General requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)
The present document identifies the Mobile-services Switching Centre/Interworking Functions(MSC/IWFs)and requirements to support interworking between:
a)PLMN and PSTN;
b)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 becauese 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.
From GSM R99 onwards the following services are no more required to be provided by a GSM PLMN:
-the dual Bearer Services"alternate speech/data"(BS 61)and "speech followed by data"(BS 81);
-the dedicated services for PAD (BS 4x)and Packet access (BS 5x);
-the single asynchronous and synchronous Bearer Services (BS 21..26,BS 31...34).
If a PlMN network still provides these services it shall fulfil the specification of GSM R98.
The present document is valid for a 2nd generation PLMN (GSM)as well as for a 3nd generation PLMN (UMTS).If text applies only for one of these systems it is explicitly mentioned by using the terms"GSM"and "UMTS".If text applies to both of the system,but a distinction between the ISDN/PSTN and the PlMN is necessary,the term "PLMN"is used.
Descriptions related to facsimile are not applied to UMTS but to GSM.
