scope:

This European Telecommunication Standard (ETS) specifies the interworking between the Signalling System No.7 Integrated Services Digital Network (ISDN) User Part (ISUP) version 2 (as specified in ETS 300 356-1 [2]) and the Signalling Systems No.5 (as specified in CCITT Recommendations Q.140 to Q.164 [7]), R2 (as specified in CCITT Recommendations Q.400 to Q.490 [8]), Telephone User Part (TUP) (as specified in CCITT Recommendations Q.721 to Q.725 [17]), and TUP+ (as specified in CEPT Recommendation T/S 43-02 E [18]).

ISUP version 2 (as specified in ETS 300 356-1 [2]) has been designed to allow peer-to-peer operation to a version 1 exchange (as specified in ETS 300 121 [1]) without requiring any knowledge of that situation. This means that different ISUP versions (like version 1 and version 2) cannot be considered as different signalling systems in an exchange. A specific interworking specification is not required, relevant information is contained in ETS 300 356-1 [2].

This specification is applicable to international transit exchanges, but may be used as a basis for the interworking in international gateway exchanges, because ISUP at the national side may also be based on ISUP version 2.