The design and engineering of new network intelligence platforms to accommodate the ever-changing and growing demands of customers, presents rich market opportunities and challenges tempered by concerns arising from the problematic experiences of similar system and network developments. As the telecommunications industry evolves, customers are increasingly coming to expect the perception of instantaneous access to service providers together with transparency to network failures. System performance dictates that response times need to be minimised, sufficient redundant capacity installed in case of failure and controls embedded within the design to manage the exceptional situations (such as media stimulated events) that continually threaten network integrity. Network design based on a 'top-down,' 'end-to-end' methodology plays a fundamental role in delivering solutions that meet customers' performance needs. It is necessary to consider service scenario mixes, service demand, physical network topology, signalling message flows, the mapping of functional entities to physical components, and routing as part of the network design process to ensure that performance requirements are met. The use of 'what-if' design tools is particularly relevant as part of this process. A challenging task faces the System Designer with the often conflicting goals of good performance and provision of service flexibility.