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ASN.1 is a computer language designed by the CCITT/ITU for the specification of data types and values, especially in communication protocols. Although it has been designed for the OSI presentation layer, it can be used for many other purposes, e. g. the lower OSI layer protocols and many other protocol architectures.
ASN.1 is typically used to define the protocol data units (PDUs) of communication protocols. To map a PDU into a concrete sequence of octets, the ASN.1 standard offers several encoding rules. There are two main encoding rules:
-
Basic encoding rules (BER): The basic encoding rules
prefixes each component of the PDU by an identifying tag and the data length.
These encoding rules are very simple but space consuming and are mostly
used for the encoding in old standards.
- Packed encoding rules (PER): The packed encoding rules encode the values in a very compact format and are often using the minimum number of bits required. These encoding rules are very complex and are mostly used in recent standards.