What is Crossbar Switches and Multistage switch in Space Division Switch?

Answer 1

BOTH CROSSBAR AND MULTISTAGE SWITCHES COMES UNDER CIRCUIT SWITCH(USE IN SWITCHING AT DATALINK LAYER OF WIDE AREA NETWORK(WAN)).AGAIN CIRCUIT SWITCH IS DIVIDED INTO TWO TYPES:1.SPACE DIVISION

2.TIME DIVISION

SPACE DIVISION has two parts i:e crossbar and multistage switches.crossbar switch-A crossbar switch connects n inputs to m outputs in a grid,using electronic micro switches(transistors) at each crosspoint.To connect n inputs to m outputs using a crossbar switch requires n*m crosspoints.The major limitation of this design is the no of crosspoints required.for example:To connect 1000 inputs to 1000 outputs requires a switch with 1.000,000 crosspoints.A crossbar switch with this no of crossspoints is impractical.such a switch is also inefficient because statistics show that,in practice,fewer than 25% of the crosspoints are in use at any given time. The rest are idle.multistage switch-The solution to limitation of the crossbar switch is the multistage switch,which combines crossbar switches in several(normally three)stages.In a single crossbar switch,only one row and one coloumn is active for any connection.so we need n*n crosspoints.If we can allow multiple paths inside the switch ,we can decrease the no of crosspoints.Each crosspoints in the middle stage can be accessed by multiple crosspoints in the first or third stage.The multistage switch has one drawback-blocking during periods of heavy traffic.The whole idea of multistage switching is to share the crosspoints in the middle stage crossbars.