(Abstract Syntax Notation.One) An international standard since 1984 for classifying data structures. There are 27 data types with tag values starting with 1; for example, Boolean (1), integer (2), and bit string (3). ASN.1 is widely used in ground and cellular telecommunications as well as aviation. BERs, DERs, CERs and PERs ASN.1 uses additional rules to lay out the physical data, the primary set being the Basic Encoding Rules (BERs), which are often considered synonymous with ASN.1. Distinguished Encoding Rules (DER) are used for encrypted applications, and Canonical Encoding Rules (CER) is a DER derivative that is not widely used. Packed Encoding Rules (PER) result in the fewest number of bytes. For more information, visit www.asn1.org.