Explain crossbar exchange, with all call processing steps and diagrams.

The fundamental idea of crossbar switching is to give a matrix of n x m sets of contacts with only n + m activators or less to choose one of the n x m sets of contacts. It form of switching is also termed as coordinate switching as the switching contacts are arranged into a x-y-plane. The diagrammatic representation of a cross point switching matrix is demonstrated in figure. Now here is an array of horizontal and vertical wires demonstrated by solid lines. A set of horizontal and vertical contact points are connected to all these wires. The contact points form pairs, all pairs having a bank of three or four horizontal and a equivalent bank of vertical contact points. A contact point pair functions as a cross point switch and keeps separated or open when not in utilize. The contact points are mechanically mounted and also electrically insulated upon a set of vertical and horizontal bars demonstrated as dotted lines. The bars are attached, in turn to a set of electromagnets.

FIG - 3 X 3 Crossbar Switching

If an electromagnetic energized, so the bar attached to this slightly rotates in a way which the contact points attached to the bar move closer to its facing contact points but don't in fact make any contact. At this time if an electromagnet in the vertical direction is energized, the matching bar rotates causing the contact points at the intersection of the two bars to close. It happens since the contact point move towards each other. For illustration if electromagnets M2 and M3' are energized, a contact is set-up at the cross point 6 as the subscriber B is connected to the subscriber C.