ch. In line with this it focuses on success factors in the user network and user-business interface, especially services including implementation, charging, quality and security. Services and the service layer are described in detail because of their increasing importance from a business point of view. Fundamental technical plans are the most important tool used to explain the technical context, that is, when vertical networks turn into a horizontal network. Such plans offer a layered end-to-end approach. The book focuses on the core network rather than on the access network. The reasons are the following: The paradigm shift is faster in the core network parts than in the access parts. At the same time the core converges whereas the number of access alternatives increases as new technologies are developed for existing media (new mobile systems, xDSL (a family of digital subscriber lines), power-line systems, WLAN (wireless local area networks) etc.). It is not possible to cover all access alternatives with any depth within the frame of this book. An access system overview is provided in Chapter 13. The goal is to enable connection of all different accesses including WLAN to the evolving new core, the 'all-access network'. The all-access network becomes a dis- tributed gateway between the different accesses. People with a telecentric background may possibly regard the new core networks as huge group switches. Introduction On the other hand the access chapter is closer to standardized systems than other chapters in the book. It could therefore be useful to have an early look at this chapter when reading the book. The overall management of the paradigm shift implementation is a challenging task, and different approaches are possible. Leading telecom operator managers recommend much more business-oriented thinking at the expense of focusing on the very latest hyped services. When appropriate, the book applies a business-oriented view in line with this statement. Can the shift be measured? Of course not, but a way to 