Abstract Syntax Notation One is a platform-independent “language” that can be used to define data structures. It is a common standard of the ITU-T (International Telecommunication Union) and the ISO (International Organization for Standardization). ASN.1 is used to uniquely describe the message elements of protocols of the OSI model. It is used by OSI-compliant techniques such as X.500 and X.509, but also by Internet protocols such as SNMP or LDAP. ASN.1 is also used in the telecommunications sector, for example in GSM for the billing of roaming calls.