This Recommendation is part of the set of Specification and description language Recommendations for SDL-2008. It defines how Abstract Syntax Notation One (ASN.1) modules can be used in combination with SDL-2008. The combined use of SDL and ASN.1 permits a coherent way to specify the structure and behaviour of telecommunication systems, together with data, messages and encoding of messages that these systems use. This Recommendation is revised to be consistent with the rest of the ITU-T Z.100 series for SDL-2008, because it references the syntax and semantics of the language in other Recommendations in the series. There are some refinements of this Recommendation based on its use and usefulness, and changes to ASN.1.