Recommendation ITU-T Z.105 defines how Abstract Syntax Notation One (ASN.1) modules are usable in combination with Specification and Description Language 2010 (SDL-2010). This text replaces Recommendation ITU-T Z.105 (2003) to align with Recommendations ITU-T Z.100, ITU T Z.101, ITU-T Z.102, ITU-T Z.103, ITU-T Z.104, and ITU -T Z.106 and ITU T Z.107 for SDL -2010. Recommendation ITU-T Z.105 (2003) replaced the semantic mappings from ASN.1 to SDL -2000 defined in Recommendation ITU-T Z.105 (1999). The use of ASN.1 notation embedded in the Specification and Description Language previously defined in Recommendation ITU-T Z.107 (1999) is not defined by this Recommendation. The main area of application of this Recommendation is the specification of telecommunication systems. The combined use of SDL-2010 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 version of Recommendation ITU-T Z.105 include necessary alignments with ASN.1:2002 Recommendations, mapping of XML values, improved mapping of bit string values and mapping of relevant ASN.1 constructs for extensions.