CROSS-BAR SWITCHING
ELC 524E
Monday, 20th February 2012
HISTORY OF CROSS-BAR EXCHANGES
• 1915: Bell company Western Electric's
"coordinate selector"
• 1919: Swedish governmental agency
designs Gotthilf Betulander design
• 1938: AT&T's 1XB crossbar exchanges
developed by Bell Telephone Labs
GENERAL DEFINITION
• A switch connecting multiple inputs to multiple
outputs in a matrix manner.
N-Inputs
M-Inputs
• Other Types of Switches:
– Rotating Switch
– Memory Switch
3X3 CROSSBAR SWITCH(1)
3X3 CROSSBAR SWITCH(2)
3X3 CROSSBAR SWITCH(3)
3X3 CROSSBAR SWITCH(4)
6X6 CROSSBAR SWITCH
Activation Sequence:
1. Energize Horizontal Bar
2. Energize Vertical Bar
3. De-Energize Horizontal Bar
NON-BLOCKING X-BAR
N
Inputs
N - Outputs
Number of Switches - N2
Number of Connections – N/2
COST -CAPACITY
Number of
Subscribers
4
Switches
16
S/Capacity
2
16
256
8
64
4,096
32
128
16,384
64
EUF
(Capacity/Sw)
0.125
0.03125
0.0078125
0.00390625
DIAGONAL CONNECTION X-BAR(1)
DIAGONAL CONNECTION X-BAR(2)
Number of Cross-points = N(N-1)/2
N
4
16
SW-XBAR
16
256
64
128
4,096
16,384
SW-DIAGONAL X-BAR
6
120
2,016
8,128
DOUBLE-SWING HORIZONTAL SWITCH
BARS
Double-Swing
X-bars
Vertical Hold X-bars
BLOCKING CROSS-BAR (1)
P
A
B
C
D
E
F
G
Q R
P’ Q’ R’
BLOCKING CROSS-BAR (2)
P
Q R
R’ Q’ P’
A
B
C
D
E
F
G
No. Switches = 2NK
•N = Number Subscriber
•K = Max No. of Connections
BLOCKING CROSS-BAR WITH
TRANSFER LINES
P Q R
R’ Q’ P’
A
B
C
D
E
F
G
No. Switches = N2(K+L)
•N = Number Subscriber
OGT1
•K = Max No. of Local Connections
OGT 2
•L = Max No. of Outgoing Lines
TYPES OF X-BAR SWITCHES: MINI-SWITCH
TYPES OF X-BAR SWITCHES: REED SWITCH
CROSS-BAR EXCHANGE ORGANIZATION
(1)
Dial Tone Marker
Links
DT REG1 - N
Subscriber
Lines
IOT 1 - N
ICT 1 - N
1-N
OGT 1 - N
Primary Switch
Secondary Switch
Establishment/Completing
Marker
Trunk Frame
CROSS-BAR EXCHANGE ORGANIZATION
(2)
SUBSCRIBER LOOP
SIGNALLING
ELC 523 E
Monday 20 February 2012
TYPES OF SIGNALLING
1. Subscriber loop
signalling
2. Inter-exchange
signalling
3. Intra-exchange or
register signalling.
FIVE SIGNALLING FUNCTIONS BY
OPERATOR
1. Respond to the calling
subscriber to obtain the
identification of the called
party.
2. Inform the calling subscriber
that the call is being
established.
3. Ring the bell of the called party.
4. Inform the calling subscriber, if
the called party is busy.
5. Inform the calling subscriber, if
the called party line is not
obtainable for some reason.
DIAL TONE
1. Indicates that the exchange is ready to accept dialled
digits from the subscriber.
2. The subscriber should start dialling only after hearing
the dial tone.
3. Else, initial dial pulses may be missed by the exchange
which may result in the call landing on a wrong number
or exchange timing out
RINGING CURRENT
• When the called party line is obtained, the
exchange control equipment sends out the
ringing current to the telephone set of the called
party
BUSY TONE
NUMBER UNOBTAINABLE
ROUTING TONE OR CALL-IN-PROGRESS
TONE
RINGING TONE
• As the ringing current is transmitted to the called
subscribe, the control equipment sends out a
ringing tone to the calling subscriber