The Recommendation specifies procedures in order to provide interaction between ISUP and INAP CS-1, i.e. to support IN services in an ISDN environment. This 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 ISUP in combination with the ISUP/INAP interaction Recommendation.