8/7/2019 TSS-S4
1/11
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
8/7/2019 TSS-S4
2/11
8/7/2019 TSS-S4
3/11
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
8/7/2019 TSS-S4
4/11
8/7/2019 TSS-S4
5/11
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
8/7/2019 TSS-S4
6/11
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
- -
8/7/2019 TSS-S4
7/11
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
.
8/7/2019 TSS-S4
8/11
,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
8/7/2019 TSS-S4
9/11
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
8/7/2019 TSS-S4
10/11
8/7/2019 TSS-S4
11/11
T