Q. What is Bens Network?

It's a non-blocking network. It's a special type of Clos network where first and last stage consists of  2×2 switches (for n input  and m output network it will have n/2 switches of 2 ×2 order and the last stage will have m/2 switch of 2×2 order the  middle stage will have  two n/2 Χ m/2 switches. Numbers n and m are should be the power of 2.

Thus, for 16×16 3-stage Bens network first stage and third stage will consist of 8 (2×2) switches and middle stage will consist of 2 switches of size (8×8).  The association of crossbar would be as follows:

Figure: 16X16 3-stage Benz network

The switches of several phases present complete connectivity. So by appropriately configuring the switch any input can be passed to any output. Think about a Clos network with 3 stages and 3×3 switches in every phase.