4.1 Introduction

IN was once heralded as a network re-arrangement that would provide any telecommunications service need that any user could conceivably want. In practice, over the years, commercial priorities, financial constraints and inter-working limitations have inevitably limited the vision's potential. Whilst in the early days the IN concept had high aspirations, reality had to intervene sooner or later to remind us what might be feasible and what might not be. For example, call routing decisions based on the time of day are perfectly feasible, whereas a routing decision based on the colour of a user's shirt may be less feasible!

As already discussed, AT&T and then Bellcore, in the USA, made the running on early exploratory work on IN specifications and the European operators watched the results carefully. In the early 1990s there was a lot of activity in the USA on IN specification production, although these standards being formulated by Bellcore were obviously designed to meet US needs and US switching system requirements, some of which were less relevant outside the US.

In the early 1990s, the CCITT (now the ITU-T) set up a study group hierarchy for intelligent network standards, and the first result was the CCITT IN CS-1 (Capability Set 1) in 1993. CS-1 was planned to be the first of several steps towards the introduction of intelligent network concepts into telephony networks. It...