Recommendation ITU-T Q.1912.5 defines the signalling interworking between the Bearer Independent Call Control (BICC) or ISDN User Part (ISUP) protocols and SIP in order to support services that can be commonly supported by BICC or ISUP and SIP-based network domains. It includes assured early dialogue, end-to-end support for ISDN user equipment, support of number portability and support interworking of supplementary services.