C.4 SDP Offer-Answer considerations

29.0073GPPGeneral requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)Release 17TS

The "network-initiated-service-change" is a declarative parameter. If an "vnd.3gpp.clearmode" RTP payload type with an associated "network-initiated-service-change" parameter is included in an SDP "m="-line in an SDP offer, this RTP payload type shall either be rejected by excluding it from the "m="-line in the SDP answer, or the RTP payload type shall be included in the answer and the associated "network-initiated-service-change" parameter shall then be supplied in the answer.