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The TTCN Notation
As the use of standards within the world of Information Technology and Telecommunications has increased tremendously during the last decade, so has the need for methods and tools that support the verification and validation of both the standards and their actual implementations.
This need has been addressed by ISO and ITU in the "Framework and Methodology for Conformance Testing of Implementations of OSI and ITU Protocols". The framework has for some time had the status of an international standard as ISO/IEC 9646 (or X.290).
The standard introduces the concept of abstract test suites (consisting of abstract test cases). This is a description of a set of tests that should be executed for a system. The tests should be described using a black-box model, i.e. only control and observation using the available interfaces.
The abstract tests are to be described using a formal language rather than using informal natural language. As part of the standard the language TTCN is defined in order to describe the abstract tests.
TTCN - Tree and Tabular Combined Notation
With TTCN a test suite is specified. This is a collection of various test cases together with all the declarations and components it needs.
Each test case is described as an event tree. In this tree behaviors like "First we send A, then either B or C will be received, if it was B we will send D..." are described. The new version of TTCN allows several event trees to be running concurrently.
TTCN is abstract in the sense of being independent of the actual test systems. This means that a test suite in TTCN for one application (protocol, system...) can be used in any test environment for that application.
The use of TTCN has increased tremendously during the last years. This has been augmented by the significant amount of TTCN test suites released by various standardization bodies. TTCN is however not only used in standardization work. The language is very suitable for all kinds of functional testing for communicating systems. This has led to a wide usage also within the industry.
The specifications of the messages being sent and received can be defined using either the built-in form of TTCN or by using ASN.1.
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