TABLE OF CONTENTS The original idea of an intelligent network (IN) was to be able to define a system capability that would support the rapid building and deployment of a large range of new services into a telephony network. Services include those with advanced call distribution features, such as call queueing. The ITU specifies a series of recommendations that define such a capability, incorporating the intelligent network application protocol (INAP) [1]. Abernethy and Munday [2] provide a useful overview of IN standards and services.
Although overloads can occur simply because insufficient capacity has been provided for the demand expected, it is more common for them to be caused by some quickly arising event, which may be unanticipated. These include network or system failures, tariff changes, and network system processes that have been scheduled to occur synchronously. They also include the types of service often deployed on an IN, such as media stimulated events or natural emergencies (e.g. bad weather), when the traffic can be very volatile. To make matters worse, traffic is usually magnified by calling customer or system repeat attempt behaviour. Such overload causes are discussed further in section 7.2 of Chapter 7. Any system needs effective overload controls in order to avoid excessive response times and reduced throughput, or even failure (see Chapter 7 for more details). In the case of an IN, there are architectural reasons why it may be especially...
