ASN.1

ASN.1 - An introduction

ASN.1 is the acronym for Abstract Syntax Notation One, a language for describing structured information; typically, information intended to be conveyed across some interface or communication medium. ASN.1 has been standardised internationally. It is widely used in the specification of communication protocols.

• ASN.1 is a data definition language defined by ISO 8824
• Represents data in machine independent way
• Presentation Layer (OSI Layer 6) codes/decodes ASN.1 from/to internal data format
• Used by CMIP and SNMP to represent MIB information
• Basic encoding rules (BER)
• Rules to encode ASN.1 definitions into transfer syntax
• Represents ASN.1 in bit patterns
• ASN.1 Modules are registered using the ISO Registration Hierarchy
• ASN.1 data types are referenced by GDMO
• All Network Elements convert their internal data to ASN.1 for transmission

Figure 1 - ASN.1 Conversion Principles

The big advantage using ASN.1 is that a network entity or computer has to know only one coding rule for transferred data and that`s ASN.1. The coded data is machine independent. There are ASN.1 compilers which generate C or C++ code from these ASN.1 definitions. The compiler generated encode/decode functions are then compiled and linked on the different computers and can be used by the client software. The machine independency is achieved through the portability of the generated C or C++ code.

C Language Structs vs. ASN.1 Definitions

Figure 2 - ASN.1 Coding Example

ASN.1 Module Example