Acknowledgements

iAbstract This thesis deals with two important topics: The use of the best possible technology in the development of telecommunications systems in a world of rapid change and in-creasing competition. The word \best " implies a technology that satises the requirements of the application and a tech-nology that enables high design eÆciency in bringing projects to rapid and successful results. The introduction and exploitation of functional programming in industry. Functional programming is a long established dis-cipline within academia where its advantages are well known. The thesis is built around the actual case of the concurrent func-tional programming language Erlang which was developed at the Computer Science Laboratory at Ericsson and which is now avail-able as open source. Erlang is now used in about 20 systems, notably the ATM switching system AXD 301 where Ericsson in two years moved from having no system to having a veritable agship. Starting as a purely technical project the progress of Erlang came to touch upon many other topics such asManagement of Technology and Open Source. i