what are multistage interconnection networks ?

Answer 1

Multistage interconnection networks (MINs) are used in multiprocessing systems to provide cost-effective, high-bandwidth communication between processors and/or
memory modules.

The networks can be unbuffered or buffered. In unbuffered networks with circuit switching, physical path must be established before the actual data transfer. Buffered networks
with packet switching are more flexible in that packets are routed through the network without establishing a physical path.