ABSTRACT
In such an environment it is becoming increasingly difficult to specify, develop, test, and interconnect these complex, heterogeneous, distributed telecommunications systems. Moreover, it is becoming almost impossible to guarantee that the highly in egral operation of such systems will be preserved. A classical example of things going wrong is reflected in the events of the January 1990 brownout [6-1] [6-2] of the AT&T American network. A control mutation originating in the switching system propagated through the signalling network causing degradation of operation and ending in a total shutdown. The whole eastern seaboard of the U.S. lost telephone connections for several hours, the financial loss amounting to 1 billion dollars. After such an experience, the established operators rightfully fear opening their networks to less experienced network operators whose actions might jeopardise operation of their networks.
