This ITU-T Recommendation specifies procedures in order to provide interaction between N-ISDN and INAP CS-2/CS-3, i.e. to support IN services in an ISDN environment. This ITU-T Recommendation only considers the case where the SSP is located at a transit level. As a consequence, this could lead to limitations for ISDN supplementary services. The interaction between other signalling systems and INAP can be found by consulting the relevant interworking Recommendation to the N-ISDN in combination with the N-ISDN/INAP interaction Recommendation.