ASN.1

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ASN.1

• Abstract Syntax Notation One

ASN.1 is a standard way to describe a message(a
unit 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. 2. How you
actually encode each data item in a message.
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Why Care about Technical Architecture Standards?

• If you want You must standardize
• Application APIs
• Portability
• Implementation
• Interoperability Protocols
• Implementation
• Replaceability All

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ASN.1 Encoding

• Given any ASN.1 description of a message, a
  representation can be derived mechanically by
  applying a set of encoding rules.
• Initially only a single set, the Basic Encoding
  Rules(BER), were standardized.
• Later Canonical and Distinguished Encoding Rules
  were standardized

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Encoding Abstract Values

• When any (correct) set of encoding rules are
  applied to the abstract values in any given ASN.1
  type, they will produce bit-patterns (actually
  octet strings) for each value such that any given
  octet string corresponds to precisely one
  abstract value.
• The reverse is not necessarily true.

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ASN.1 data types

• ASN.1 notation is recognizable as a high level
  definition language.
• It is constructed in modules with unique
  identifiers.
• There are over 20 built-in identifiers e.g.
  BOOLEAN, INTEGER, ENUMERATED, REAL, BIT STRING,
  UTCTime, EXTERNAL, OCTET STRING, NULL etc.

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• Arbitrarily complex structures can be built up
  from these data types using constructors such as
  
• SET - order not significant
• SEQUENCE -fixed order
• one example,
• WeatherReport SEQUENCE
• stationNumber INTEGER(1..99999)
• timeOfReport UTCTime
• pressure INTEGER(850..1100)
• temperature INTEGER(-100..60)
• humidity INTEGER(0..100)
• windVelocity INTEGER(0..500)
• windDirection INTEGER(0..48)

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TLV(type-length-value), ILC(identifier - length -
contents)

• BER generate encodings which are of a class known
  as type - length - value.
• Now in ASN.1 they are called as identifier -
  length - contents.
• The structure is therefore recursive such that
  the contents can be a series of ILCs
• This bottoms out with genuine contents such as a
  text string or an integer.

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Basic Encoding Rules

• A Schematic Representation

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The use of ASN.1 Compilers