DISTRIBUTED TYPE SWITCHING NETWORKS BASED ON THROUGH TRANSIT SWITCHING.

In through transit switching the routes in distributed type switching networks are standardized and, while idle trunks on the standard routes are held in the connected state, these idle trunk lines are utilized to simplify trunk switching in the network. The degree of the resulting simplification of trunk switching can be measured by the ratio of the number of switching offices where control is needed to complete a route under consideration by connecting the idle trunk lines to the number of switching offices on the same route. Experiments with a simulated model of the system showed that this ratio can be kept below about 1/5 even under very severe conditions. It is also shown that the blocking probability due to the multistage switching can be improved to a great extent by increasing the degree of freedom of route selection in the form of alternative routing. It turns out that even if alternative routing is allowed, the merit of simplification of trunk switching is still preserved.