09.073GPPGeneral Requirements on Interworking between the Public Land Mobile Network (PLMN) and the Intergrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)TS
Compatibility checking is carried out on the following items:
a) Low layer compatibility ‑ utilizing low layer compatibility and bearer capability information elements.
b) High layer compatibility ‑ utilizing high layer compatibility information element.
The use of the progress indicator for compatibility checking is outside the scope of this ETS.
Indication of compatibility requirements is carried out as described in subclause 9.2.2 under "a) Functional operation" or "b) Mobile subscriber indicates requirement in call confirmation message" and subclause 10.2.2 "Network interworking mobile terminated".
For subscription checking, relevant for the interworking described in clauses 9 and 10 of this ETS, refer to GSM 02.01.