Full-Fan-In Matrix

This topology (shown below) allows for multiple simultaneous paths, and allows inputs to share outputs (input signals are combined into a shared output).  Full-Fan-In matrices are the complement to the Full-Fan-Out topologies, and are typically used at Uplink or Transmission sites.

In this example: Input 2 is routed to Output 4, and Input 1 is also routed to Output 4.  At this point, Output 1 (or any other output) can be routed to other available inputs.