Switching  via an interconnection network

The switching  techniques  overcome the bandwidth  limitation of a single  shared bus. This technique use a more sophisticated interconnection network such as  those  that have  been  used in the past  to inter connect  processor in a  multiprocessor computer architecture.

A crossbar switch  is an interconnection network consisting of  2 N buses that connect N input ports  to N output  ports as shown  in figure. A packet  arriving at an input  port travels  along the horizontal bus  attached to the input port until it intersects  with the  vertical bus leading to the desired output  port. If the vertical bus leading to the  bus output  port is free the packet is transferred to the output port. If the  vertical bus is being  is used  to transfer a packet  from  another  port to this same  output  port. The arriving  packet is blocked and  must be  queued  at the input port.