The TTCN language is part of the ISO/IEC 9646 conformance testing framework and is specially designed for the specification of tests of communication systems.

The standard introduces the concept of abstract test suites. This is a description of a set of tests (test cases) that should be executed for testing an IUT together with the relevant data declarations. The tests are described using a black box model (where the internal behavior of the IUT is not relevant). Each test case is an event tree in which external behavior such as: "If we send the message 'connect request,' either 'connect confirm' or 'disconnect indication' will be received" is described. The messages can be defined using either the TTCN–type notation or ASN.1.

A TTCN test suite consists of the following four major parts, each substructure organizing the different components of the language (see Figure 2):

1. suite overview part
2. declarations part
3. constraints part
4. dynamic part

Figure 2. The Basic Structure of a TTCN Test