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ASN.1 (Abstract Syntax Notation 1) - an explanation

A language used for defining datatypes. ASN.1 is used in OSI standards and TCP/IP network management specifications.ASN.1 is a formal notation used for describing data transmitted by telecommunications protocols, regardless of language implementation and physical representation of these data, whatever the application, whether complex or very simple.

The notation provides a certain number of pre-defined basic types such as:
  • integers (INTEGER)
  • booleans (BOOLEAN)
  • Character strings (IA5String, UniversalString...)
  • Bit strings (BIT STRING)
  • and many more...

and makes it possible to define constructed types such as:
  • structures (SEQUENCE)
  • lists (SEQUENCE OF)
  • choice between types (CHOICE)

Subtyping constraints can be also applied on any ASN.1 type in order to restrict its set of values.

Unlike many other syntaxes which claim to be extensible, ASN.1 offers extensibility which addresses the problem of, and provides support for, the interworking between previously deployed systems and newer, updated versions designed years apart.

ASN.1 sends information in any form (audio, video, data, etc.) anywhere it needs to be communicated digitally. ASN.1 only covers the structural aspects of information (there are no operators to handle the values once these are defined or to make calculations with). Therefore it is not a programming language.

ASN.1 definition can be contrasted to the concept in ABNF of "valid syntax", or in XSD of a "valid document", where the focus is entirely on what are valid encodings of data, without concern with any meaning that might be attached to such encodings. That is, without any of the necessary semantic linkages.

One of the main reasons for the success of ASN.1 is that this notation is associated with several standardized encoding rules such as the BER (Basic Encoding Rules), or more recently the PER (Packed Encoding Rules), which prove useful for applications that undergo restrictions in terms of bandwidth. These encoding rules describe how the values defined in ASN.1 should be encoded for transmission (i.e., how they can be translated into the bytes 'over the wire' and reverse), regardless of machine, programming language, or how it is represented in an application program. ASN.1's encodings are more streamlined than many competing notations, enabling rapid and reliable transmission of extensible messages -- an advantage for wireless broadband. Because ASN.1 has been an international standard since 1984, its encoding rules are mature and have a long track record of reliability and interoperability.

An ASN.1 definition can be readily mapped (by a pre-run-time processor) into a C or C++ or Java data structure that can be used by application code, and supported by run-time libraries providing encoding and decoding of representations in either an XML or a TLV format, or a very compact packed encoding format.

Tools on almost all operating systems support ASN.1. ASN.1 also supports popular programming languages such as Java, C and C++, as well as older ones including COBOL. As an example of ASN.1's universality, there are tools that have been ported to over 150 different computing platforms.

There are a lot of well-tested ASN.1 tools that have been used for a long time. Using such tools, there are less likely to be costly delays in bringing new products to market or, even worse, recalling products based on new code that hasn't been sufficiently tested for flaws.

ASN.1 is widely used in industry sectors where efficient (low-bandwidth, low-transaction-cost) computer communications are needed, but is also being used in sectors where XML-encoded data is required (for example, transfer of biometric information).