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Introduction
The Abstract Syntax Notation One (ASN.1) is a notation language that is used for describing structured information that is intended to be transferred across some type of interface or communication medium. It is especially used for defining communication protocols.
As ASN.1 is widely popular, the SDL Suite allows you to translate ASN.1 data types to SDL and to encode/decode ASN.1 data types.
By using ASN.1 data types in the implementation of your application, you will optimize your development process. The following list displays some of the advantages of ASN.1:
- ASN.1 is a standardized, vendor-, platform- and language independent notation.
- A vast number of telecommunication protocols and services are defined using ASN.1. This means that pre-defined ASN.1 packages and modules are available and can be obtained from standardization organizations, RFCs, etc. For instance, the ASN.1 data types defining SNMP are available in RFC 1157.
- When ASN.1 data types are transmitted over computer networks, their values must be represented in bit-patterns. Encoding and decoding rules determining the bit-patterns are already defined for ASN.1. The SDL Suite supports BER and PER encoding.
- ASN.1 enables extensibility. This means that it simplifies compatibility of systems that have been designed and implemented large time frames apart.
- The SDL Suite and the TTCN Suite can share common data types by specifying these in a separate ASN.1 module.
Implementation of ASN.1
When importing ASN.1 data types to your SDL system, you need to translate the ASN.1 definitions to SDL. The SDL Suite does this for you using a tool called ASN.1 Utilities. This tool is automatically invoked when you analyze your SDL system.
However, having the ASN.1 data types translated to SDL is not enough to include them in your application. If you are going to transfer application-generated information on computer networks, the values of the data types must be encoded. When transferring signals in or out of your SDL system, you must also create the interface between the environment and the system.
Thus, the process of implementing ASN.1 data types can be divided into three separate steps:
The definitions of the abstract syntax and the transfer syntax is presented below.
Abstract Syntax
The basic idea is to transport some type of information between two nodes using protocol messages. The abstract syntax is defined as the set of all possible messages that can be transported. To create the abstract syntax you must:
- design some form of data structure defined in a high-level programming language, for instance ASN.1.
- define the possible set of values that the data structure can take.
Transfer Syntax
The transfer syntax is the set of bit patterns that represents the abstract syntax messages with each bit pattern representing just one value. The rules determining the bit-patterns are called the encoding rules.
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