What is CrossBar switching and how it works?

Answer 1

A crossbar switch is one of the principal architectures used to construct switches of many types. Originally the term was used literally, for a matrix switch controlled by a grid of crossing metal bars, and later was broadened to matrix switches in general. Crossbar switches are sometimes referred to as "cross-point switches," "crosspoint switches," or "matrix switches." The other principal switch architectures are that of a memory switch or a crossover switch. A banyan switch is an important type of crossover switch.
The crossbar switch is the principle line and trunk switching device used in crossbar system talking paths and may be described as a selective multi-unit two stage relay. It consists of a rectangular field of contact springs arranged in ten horizontal rows and either ten or twenty vertical rows. It is operated by horizontal and vertical bars.

The horizontal bars and attached flexible wire fingers are known as the selecting elements of the crossbar switch .Each selecting bar, of which there are five on each switch, can be partially rotated on its axis in either direction by one of two select magnets associated with that selecting bar. Each of the five selecting bars on a switch may thereby either raise or lower its selecting fingers to select one of the ten horizontal rows of contacts.

The vertical unit has ten sets of relay like contact springs and a holding bar. Each set of contacts consists of three to six pairs of normally open or "make" contact springs.

The operating springs have bifurcated (two forked) ends equipped with precious metal contacts. The holding bar is part of a long vertical armature pivoted so as to rotate under control of a holding magnet and a restoring spring.

Each spring assembly is equipped with an actuating card which is constructed to act as a stop limiting the vertical travel of the selecting finger. With the switch normal, one selecting finger is at rest in a horizontal position midway between each pair of spring assembly and in a vertical position midway between the actuating card and holding bar.

It requires a two stage operation to close the contacts at any crosspoint. First a selecting magnet must be operated. This moves a selecting finger either up or down as . Second the holding magnet of the desired vertical is operated. The selecting finger is trapped between the holding bar and the actuating card and operates the selected contacts. The selecting magnet must remain operated until after the holding magnet operates.

Upon the release of the selecting magnet the selecting finger remains held between the holding bar and actuating card, and due to the flexible nature of the finger the selecting bar will return to normal. It may operate again to select crosspoints on other vertical units which are under control of the same selecting bar. The switch may also be equipped with "off normal" spring assemblies which are associated with the selecting and holding magnet and operate when the magnet is energized. They are individual to each magnet and are not dependent upon the two-stage operating cycle described. "Off normal" spring assemblies are provided when it is necessary to give an electrical signal that a selecting or holding magnet has fully operated its associated bar.



Crossbar switching technology opens up the opportunity to use computational resources in achieving automatic switching!
Please visit:
http://people.deas.harvard.edu/~jones/cscie129/nu_lectures/lecture11/switching/xbar/xbar.html

Answer 2

OK, But this is going to be really simplified.
Place in a line, 10 vertical copper bars, all separated from each other. Number them 1,2,3,4, etc.
Now in front of them but separated from them, place 10 horizontal copper bars. Number them a,b,c,d, etc.
Now connect your telephone to number 2 and your friend Bob will connect his telephone to C.
If you were able to move vertical bar 2 forward and horizontal bar C backward such that they touched each other, you will have established a conversation between yourself and Bob.
The actual movement of the bars, both horizontal and vertical is accomplished by electrical magnets.
I hope that helps.

Answer 3

Given a circuit with many connections from the outside, a cross bar switch allows any input to be connected to any combination of the other connections.