Channel allocation system for distributed digital switching network

DETAILED DESCRIPTION OF THE DRAWINGS A.
System Layout FIG.
1 illustrates a switching network for interconnecting various types of voice or data equipment and telephone lines, indicated generally as units 11-15 in accordance with the instant invention.
In the preferred embodiment, the switching network generally includes four stages.
The first two stages, referred to as interface (I/F) switches 22 and access switches (AS) 24, are in terminal units (Tu's) 20 which provide an entry point to the switching network for telephone lines and terminal equipment.
The third and fourth stages, referred to as the section switches 26 and the reflection switches 28, respectively, are located on individual switch planes 30.
Each of the terminal units 20 includes fourteen interface switches 22 and three access switches 24.
Each of the interface switches in a terminal unit is coupled by a communications link to each of the three associated access switches.
In the preferred embodiment, there are six switching planes 30 in the switching network.
Each of the 3 access switches of a terminal unit is coupled to a different set of four out of the six switching planes via its corresponding communications link.
A section switch on a switching plane is linked to two out of the three access switches from each terminal unit and, therefore, since there are nineteen section switches on a switching plane in a maximum system of this configuration, there can be as many as ninety-five terminal units coupled to each plane.
In the maximum system of this configuration each switching plane also includes nine reflection switches 28, each of which is linked to all of the other section switches.
With this arrangement, a communication path can be established from a key station to a line termination via an interface switch and any one of three access switches and an interface switch at the key station end, appropriate section switches and reflection switches on any one of six switching planes, and any one of three access switches and the interface switch at the line end