An International Organization for Standardization (ISO) standard that provides a mechanism for encoding human-readable symbols into condensed binary form. Abstract Syntax Notation One (ASN.1), which is part of the X.400 and X.500 specifications, provides a standard way of formatting and encoding X.400-based e-mail messages for transmission over a network. More generally, ASN.1 is a method of specifying abstract objects that are intended for any form of serial transmission. ASN.1 is also used for defining objects in Management Information Base (MIB) files for Simple Network Management Protocol (SNMP).
ASN.1 is similar in syntax to a programming language, and it allows the definition of different data types, data structures, arrays, classes, and other structures similar to those found in the C++ programming language. The presentation layer (layer 6) of the Open Systems Interconnection (OSI) reference model uses ASN.1 as the standard for specifying the syntax of information exchanged between applications at this layer. ASN.1 data types can be either simple or structured.
ASN.1 data structures are encoded as octets in hexadecimal notation. These structures are then transmitted over the network as binary information.
The Octet Encoding Rules (OER) were designed to be easy to implement and to produce encodings more compact than those produced by the Basic Encoding Rules (BER). In addition to reducing the effort of developing encoder/decoders, the use of OER can decrease bandwidth utilization (though not as much as the Packed Encoding Rules), save CPU cycles, and lower encoding/decoding latency.