Section: 5.2.2.4 Notification of interworking in connection with mobile terminating call establishment
Content: In this subclause, the term "interworking" is used only in the meaning of interworking with a network other than PLMN or ISDN, not as interworking between PLMN and ISDN since this is the normal case. In this sense, PLMN and ISDN are seen within the same environment, called the PLMN/ISDN environment. During call establishment the call may enter an PLMN/ISDN environment, e.g., because of interworking with another network, with a non-PLMN/ISDN user, or with non-PLMN/ISDN equipment within the calling or called user's premises. When this occurs, the network may include a progress indicator information element to be included in the SETUP message to be sent to the called mobile station specifying progress description value: a) #1 "call is not end-to-end PLMN/ISDN; further call progress information may be available in-band" or b) #3 "origination address is non-PLMN/ISDN". See also subclause 5.5.1 for further reactions of the mobile station.