Identifier Classes

4 classes of types are distinguished. The class is encoded in bits 8 and 7 of the first octet of the identifier.

Table: Identifier Classes

Two forms of Identifier are distinguished by bit 6 of the First Identifier Octet: verbatim58 The construction of extension octets is by the following rules:
  1. Bits 5-1 of Octet 1 are all set to 1.
  2. Each extension Octet encodes the remaining binary value, the last Octet having bit 8 clear.
  3. Thus bits 7-1 of all extension octets plus bits 7-1 of the last octet are concatenated to form one bitfield encoding the unsigned binary integer ID code.
  4. The ID code is formed from the shortest number of Octets possible: no leading extension octets can have bit 8 clear.
Valid ID Code octets will take the form: verbatim59 The Length specifies the length in octets of the contents of the element. It is itself variable in length, taking 3 forms shown in table #tbt71#1609>.

Table: Length encodings

The Interpretation of the contents field depends upon the ID Code and any context dependency implied by the ASN.1 specification. Octets are sequenced exactly as the ASN.1 order implies: linear order of items in a specification occupy successive Octets of the contents.