30.7 Formal Definitions Using ASN.1
The SMI standard specifies that all MIB variables must be defined and referenced using ISO's Abstract Syntax Notation 1 (ASN.13). ASN.1 is a formal language that has two main features: a notation used in documents that humans read and a compact encoded representation of the same information used in communication protocols. In both cases, the precise, formal notation removes any possible ambiguities from both the representation and meaning. For example, instead of saying that a variable contains an integer value, a protocol designer who uses ASN.l must state the exact form and range of numeric values. Such precision is especially important when implementations include heterogeneous computers that do not all use the same representations for data items.
Besides keeping standards documents unambiguous, ASN.l also helps simplify the implementation of network management protocols and guarantees interoperability. It defines precisely how to encode both names and data items in a message. Thus, once the documentation of a MIB has been expressed using ASN. 1, the human readable form can be translated directly and mechanically into the encoded foml used in messages. In summary:
The TCP/IP network management protocols use a formal notation called ASN.1 to define names and types for variables in the management information base. The precise notation makes the form and contents of variables unambiguous.
Abstract from Internetworking With TCP/IP Vol I: Principles, Protocols, and Architecture Fourth Edition,
DOUGLAS E. COMER,
Department of Computer Sciences Purdue University, West Lafayette, IN 47907,
PRENTICE HALL,
Upper Saddle River, New Jersey 07458