The procedures of 5.8 shall apply, with the addition that:
a) If the calling user receives no High layer compatibility information element in the CONNECT message, or prior to the CONNECT message in some other call control message, the user shall assume that the high layer compatibility is unknown.
Note - It may be possible to subsequently identify the high layer compatibility from any in-band protocol within the B-channel.
b) If the calling user receives a Progress indicator information element with 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 subsequent to a Progress indicator information element with a progress description No. 5 interworking has occurred and has resulted in a telecommunication service change, then the last received Progress indicator information element shall be taken account of. Where the progress description is No. 1 call is not end-to-end ISDN, further call progress information maybe available in-band or progress description is No. 2 destination address is non-ISDN the user shall assume a bearer service category of circuit-mode 64 kbit/s 8 kHz structured usable for 3.1 kHz audio information transfer.