ASN.1 - Abstract Syntax Notation One

ASN.1 is the language for structured information describtion. That is why, it is typically used for information that has to be conveyed acros some interfaces or communication medium. It is internationally standardised by CCITT (ITU-T) standard X.409. The name (ASN.1) comes from ISO later.

The big effort of ASN.1 is that any ASN.1 message can be mechanicaly derived by aplying a set of rules, ones of them - Basic Encoding Rules - are standardised.

ASN.1 Basics

BER - Basic Encoding Rules

The original CCITT Recommendation X.409, which first standardised the notation known today as ASN.1, included also a set of encoding rules. The intent of designers (it was in 1983) was to define a universal set of encoding rules which could be built into every system. Encoding would simply become a protocol. It was proposed to be used in all the RM OSI layers, but it failed for a number of non-technical reasons.

The BER generate encoding of class known as type - length - value (TLV), because the basis of encoding is a structure made up of those three parts. Many encoding schemes employ this structure, however only few of them apply this scheme as consistently as BER. That three parts are termed as Identifier, Length and Contents. Each part of encoding has an integral number of octets.

BER Basics