Communication methods are essential to enable the continual expansion of the technological society in which we live. They enable people to exchange ideas, opinions and synchronise all interactions between themselves and others. Telephony is still the predominant method of communication although new techniques, such as electronic mail and mobile communications are becoming more and more popular. Network users are requesting increasingly complex services which cannot be effectively supported by existing network architectures. Also, there is a desire to share data, distribute application processing among network elements and an increasing demand for more sophisticated telecommunications services. All of these factors have led to the evolution of new networking architectures.
A particular architecture which has evolved is the Intelligent Network (IN), in which services are provided independently of the bearer networks or equipment vendors. The IN is essentially an architecture which separates the service logic from the telephone exchanges, enabling the establishment of an open platform for uniform service creation, implementation and management. It enables advanced customer orientated services to be rapidly and cost effectively introduced.
In the traditional Plain Old Telephone Service (POTS), the switching systems (known as ‘switches’) perform the basic call processing. Each supplementary service is a non-reusable software entity that modifies this basic process in the switches. The switching network typically consists of a hierarchy of switches, e.g. a local exchange level, an intermediate exchange level and a transit exchange level, as shown in figure 1.
In these systems, if the switch based services are situated at the transient (top) level, there is a large overhead for their use. This is because of the number of switches and related trunks that need to be accessed in order to use a service. For this reason, services have been ‘migrating’ to lower levels of the hierarchy, reducing the overhead for service use. In the extreme case, each local exchange level switch contains the service data, meaning that every service must be loaded into every switch’s software before it can be used (see figure 2).