• ASN.1 (Abstract Syntax Notation One) is a standard way to describe a message (a unit of application data) that can be sent or received in a network.
• ASN.1 is divided into two parts: (1) the rules of syntax for describing the contents of a message in terms of data type and content sequence or structure and (2) how you actually encode each data item in a message.
• ASN.1 is defined in two ISO standards for applications intended for the Open Systems Interconnection (OSI) framework:
ISO 8824/ITU X.208 specifies the syntax (for example, which data item comes first in the message and what its data type is)
ISO 8825/ITU X.209 specifies the basicencoding rules for ASN.1 (for example, how to state how long a data item is)
• 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),etc..
and makes it possible to define constructed types such as:
structures (SEQUENCE),
lists (SEQUENCE OF),
choice between types (CHOICE),etc..
• 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.
• 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.
• ASN.1's encodings are more streamlined than many competing notations, enabling rapid and reliable transmission of extensible messages -- an advantage for wireless broadband.
• 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).
• Here's an example of a message definition specified with ASN.1 notation:
Report ::= SEQUENCE { author OCTET STRING, title OCTET STRING, body OCTET STRING, biblio Bibliography }
In this very simple example, "Report" is the name of this type of message. SEQUENCE indicates that the message is a sequence of data items. The first four data items have the data type of OCTET STRING, meaning each is a string of eight-bit bytes.
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i. ASN.1 is more than just syntax. It is a formal language developed for use with application layers for data transfer between systems.
ii. It is also applicable within the system for clearly separating the abstract syntax and the transfer syntax at the presentation layer.
iii. We define abstract syntax as the set of rules used to specify data types and structures for storage of information. Transfer syntax represents the set of rules for communicating information between systems.
iv. Thus, abstract syntax would be applicable to the information model and transfer syntax to the communication model. The abstract syntax can be used with any presentation syntax, depending on the medium of presentation.
v. The abstract syntax in ASN.I makes it independent of the lower-layer protocols. The algorithm to convert the textual ASN.I syntax to machine-readable code is called bask encoding rides (BER).
vi. The relationship between ASN.1 and BER parallels that of source code and machine code.
vii. ASN.1 (Abstract Syntax Notation One) Used to define the format of SNMP messages and managed objects (MIB modules) using an unambiguous data description format
ASN.1 Data Types Basic Types: Boolean, Integer, Bitstring, Octet string, Null, Object identifier Real, Enumerated, NumericString, PrintableString, IA5String, UTCTime, GeneralizedTime, CharacterString
Constructed Types: (a) CHOICE (b) SEQUENCE, SEQUENCE OF (c) SET, SET OF