Crossbar switch is a versatile switching network. It is basically a network of switches. Any module can be connected to any other module by closing the appropriate switch. Such networks, where there is a direct link between all pairs of nodes are called fully connected networks.
In a fully connected network, many simultaneous transfers are possible. If n sources need to send data to n distinct destinations then all of these transfers can take place concurrently. Since no transfer is prevented by the lack of a communication path, the crossbar is called a nonblocking switch.
In the Figure 10.5 of crossbar interconnection network, a single switch is shown at each cross point. In actual multiprocessor system, the paths through the crossbar network are much wider.
can be connected to any other module 
by closing the appropriate switch. Such networks, where there is a direct link between all pairs of nodes are called fully connected networks. 