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Principle of CBS

Basic idea is to provide a matrix of nm sets of contacts with only

n+m activities or less to select one of nm sets of contacts

Figure

There is an array of horizontal and vertical wires shown by solid

lines

A set of vertical and horizontal contact points are connected to these wires

The contact points form a pair

Each pair consisting of a bank of three or four horizontal and corresponding

bank of vertical oints

A contact point pair act as a Cross Point (CP) switch, and remain

separated or open when not in use

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T e contact points are mec anica y mounte an e ectronica y

insulated on a set of horizontal and vertical bars (HB & VB)

shown b dotted lines

These bars are attached to a set of electromagnet

The corresponding bar rotates & make the connection

ons er t e examp e o as s own n gure.

It shows 6 subscribers with HB representing inlet and VB the outlet

Try for establishing the following connection in sequence:

A to C and B to E

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T e CP AC atc es y energizing first y HB A an t en VB C

Now for BE, when HB B energizes, BC may latch

-

This can be prevented by introducing an energizing sequence

for latchin

A CP latches only if the HB is energized first, and then the VB

In this way, BC will not latch.

Then for completing BE connection, the VB E needs to be

energized

energized

This should also be avoided, and is done by providing the de-energizing

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T us after e-energizing A, t e energizing of E wi atc t e

CP BE

Thus, the following procedure should be followed for theestablishing a connection in a CBS:

nerg ze nerg ze

Energize VB OR Energize HB

- -

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w tc on gurat on:

In a nonblocking CB configuration, there are N2 SE for N users

,

connection establishment

two given subscribers

It depends upon who initiates the call

e.g., when A wishes to call B, it uses CP AB

while, when B wishes to call A, it uses CP BA

Thus, by designing a suitable control mechanism, only one switchmay be used to establish a connection between two subscriber

.

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,with N2/2 switches

We can also eliminate the diagonal CP as it connect the same node

The call establishment procedure still follows the same pattern

i.e. HB ener izes first then VB but irres ective of who calls

Thus the number of CP then reduces to N(N-1)/2 s num er a so represen u y connec e ne wor

But, this number is still very large to be practical

t can e re uce s gn cant y y proper es gn ng

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The CB hardware ma be reduced b connectin two subscribersto a single bar

and letting the bar turn in both direction i.e., clockwise and anticlockwise

With such an arrangements, the number of CB reduces, but the

In the blocking CBS, the number of VB is less than the number of

. , ,

Energize HB A

Energize VB P

De-energize HB A

Energize HB B

Ener ize VB P

De-energize HB B

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T