If the calling user and the network operator allow fallback to occur to an alternative bearer capability, then the destination network shall indicate this to the destination user by means of repeated Bearer capability information elements within the SETUP message sent to indicate the presence of a call request.
The order of the information elements shall indicate the priority of the bearer capabilities. Bearer capability information elements shall be in ascending order of priority, i.e. a subsequent Bearer capability information element shall indicate a bearer capability with higher priority.
If fallback allowed is indicated in the SETUP message as described above, and the user wishes to accept the call without having fallback occur, the user shall include in the CONNECT message sent to the network the Bearer capability information element of the requested bearer service or teleservice.
If fallback allowed is indicated in the SETUP message as described above, and the user wishes to accept the call with having fallback occur to the lowest priority alternative bearer capability, the user may, but need not, include in the CONNECT message sent to the network the Bearer capability information element of the alternative bearer service or teleservice.
If no Bearer capability information element is indicated by the called user, the network shall assume that the lowest priority bearer capability is selected.
If fallback allowed is indicated in the call request, and no interworking has been encountered (i.e. a progress description No.1, call is not end-to-end ISDN, further call progress information may be available in-band or progress description No. 2, destination address is non-ISDN has not been sent), the destination network shall indicate the resultant bearer capability and connection type to the originating network at the time the bearer is established, even if no Bearer capability information element is received from the destination user.