TTCN is a programming language for the testing of communication protocols . A TTCN test suite consists of a large number of test scenarios written in TTCN.

Until version 2, the language is written unconventionally in tables and called t ree and t abular c ombined n otation (“combined tree and tabular notation”). Reading and writing in this language required editors specific to TTCN. With version 3, TTCN was renamed t esting and t is c ontrol n otation ( “scoring tests and control tests”). It is closer to modern programming languages ​​and can be written in a traditional text editor. TTCN-3 is even more flexible than TTCN-2, because it can be used to test traditional software,

For their execution, all versions require dedicated compilers or interpreters.

TTCN is widely used, for example, by ETSI and ITU to test telecommunication protocols. Compliance tests for ETSI standards such as ISDN , DECT , GSM , EDGE or 3G were carried out in TTCN. In recent years, it has been used to test other standard protocols such as Bluetooth and IP .

The execution of these tests on products (for example, fixed or mobile telephones or network elements) makes it possible to verify that the implementation of the protocol for these products meets the requirements defined by the telecommunication standards.

TTCN is often used in tandem with ASN.1 .