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ASN.1
ASN.1, described in [23], stands for Abstract Syntax Notation One. ASN.1 is a language for the specification of data types and values. ASN.1 is very popular for the specification of data in telecommunication protocols and services, especially in higher (i.e. application oriented) layers. Many telecommunication standards are based on ASN.1. Also TTCN is based on ASN.1. An example of an ASN.1 module is shown below.
Example 645 : An example of an ASN.1 module
ProtocolData DEFINITIONS ::=BEGIN- - contains data definitions for an example protocolCheckSum ::= INTEGER (0..65535)DataField ::= OCTET STRING (SIZE (0..56))PDU ::= SEQUENCE {sequenceNr INTEGER (0..255),dataField DataField,checksum CheckSum OPTIONAL }ENDA strong point of ASN.1 is that there are encoding rules that define how an ASN.1 data value is encoded to bits, the most well-known being the Basic Encoding Rules. From an ASN.1 data type definition, functions can be automatically generated that take care of the coding and decoding.
An ASN.1 definition can be imported into SDL as if it was a package. When an ASN.1 data type is imported into SDL, automatically a set of operators that is defined in Z.105 [25] is available for that type.
It is recommended to use ASN.1 for the specification of parameters of signals to/from the environment of the SDL system, especially when encoding rules are to be applied on such signals, or when a TTCN test suite is to be developed. In the latter case the ASN.1 definitions can be directly reused in the TTCN test suite.
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