Performance improvement by a ring network for overflow from first choice routes

A network is considered having two hierarchical levels, namely first choice routes and a star-type last choice network. The principle of alternate routing offers an economic utilization of the channels, a high probability that calls can be served in failure states even though with diminished GOS, and finally a certain capability to handle local traffic overload. The performance of such a network can be improved by an overlaid ring network connecting a number of switching nodes and taking over the overflowing traffics from these nodes. The ring can be operated with a central or a distributed switching system.