Analysing SCP congestion control strategies: a study of control dynamics

Bellcore is responsible for developing and maintaining requirements for the telecommunications protocols and network elements (NEs) that are supported by our owner companies, the Regional Bell Operating Companies (RBOCs) in the North American market. The requirements, when deployed, allow interoperability between NEs built by different suppliers, which is essential in a multi-supplier network. The major intelligent network (IN) service deployed worldwide is the "freephone" or "toll free" service, known in North America as the "800 service". The nature of this service, in that the service subscriber (rather than the person dialling the number) pays for each call, makes it a prime candidate for congestion/overload particularly in respect to various media stimulated events or natural disaster scenarios. The congestion control developed to combat this is known as automatic code gapping (ACG), a rate based control that places an upper bound on the rate at which end-offices may send IN queries to a service control point (SCP). Although the focus of the article is on the advanced intelligent network (AIN), currently being deployed in North America, the performance characteristics of ACG and our subsequent conclusions apply equally to the international deployment of IN.