Originally Timo Noko SDL. Set of telecommunication solftware programming tools created by Timo Noko in 1978-1990 while mostly employed by Nokia using programming language Nokolisp.
Firstly there was the TNGRAPH, a graphical tool to create the SDL-language spefication. Then there was the TNANAL to test the overall validity of the specs. And thirdly there was the TNCODE macro processor to produce the actual code to be used in Nokia DX 200 telephone exchange.
Later (from 1990 onwards) TNSDL was totally revised by more qualified authors to implement the SDL-88 specification which automatized the code generation phase.
(Wikipedia now claims that TNSDL means Tele-Nokia-SDL from 1990. Really it does not. This paper was written in 1982, two years before I was employed by Nokia.)