1. ELC 524E Monday, 20th February 2012
CROSS-BAR SWITCHING
ELC 524E
Monday, 20th February 2012

2. 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

4. GENERAL DEFINITION
A switch connecting multiple inputs to multiple outputs in a matrix manner.
Other Types of Switches:
Rotating Switch
Memory Switch
N-Inputs
M-Inputs

5. 3X3 CROSSBAR SWITCH(1)

6. 3X3 CROSSBAR SWITCH(2)

7. 3X3 CROSSBAR SWITCH(3)

8. 3X3 CROSSBAR SWITCH(4)

9. 6X6 CROSSBAR SWITCH Activation Sequence: Energize Horizontal Bar
Energize Vertical Bar
De-Energize Horizontal Bar

10. NON-BLOCKING X-BAR N Inputs N - Outputs Number of Switches - N2
Number of Connections – N/2

11. COST -CAPACITY Number of Subscribers Switches S/Capacity EUF
(Capacity/Sw) 4 16 2
0.125
256 8 64
4,096 32
128
16,384

12. DIAGONAL CONNECTION X-BAR(1)

13. DIAGONAL CONNECTION X-BAR(2)
Number of Cross-points = N(N-1)/2 N
SW-XBAR
SW-DIAGONAL X-BAR 4 16 6
256
120 64
4,096
2,016
128
16,384
8,128

14. DOUBLE-SWING HORIZONTAL SWITCH BARS
Double-Swing X-bars
Vertical Hold X-bars

15. BLOCKING CROSS-BAR (1) P Q R P’ Q’ R’ A B C D E F G

16. 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

17. BLOCKING CROSS-BAR WITH TRANSFER LINESP Q R R’ Q’ P’ A B C D E F G
No. Switches = N2(K+L)
N = Number Subscriber
K = Max No. of Local Connections
L = Max No. of Outgoing Lines
OGT1
OGT 2

18. TYPES OF X-BAR SWITCHES: MINI-SWITCH

19. TYPES OF X-BAR SWITCHES: REED -SWITCH

20. CROSS-BAR EXCHANGE ORGANIZATION (1)
Dial Tone Marker
Links
DT REG1 - N
Subscriber Lines
1 - N
IOT 1 - N
ICT 1 - N
OGT 1 - N
Secondary Switch
Primary Switch
Trunk Frame
Establishment/Completing Marker

21. CROSS-BAR EXCHANGE ORGANIZATION (2)

23. SUBSCRIBER LOOP SIGNALLING
ELC 523 E
Monday 20 February 2012

24. TYPES OF SIGNALLING Subscriber loop signalling
2. Inter-exchange signalling
3. Intra-exchange or register signalling.

25. 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.

26. DIAL TONE
Indicates that the exchange is ready to accept dialled digits from the subscriber.
The subscriber should start dialling only after hearing the dial tone.
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

27. 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

28. BUSY TONE

29. NUMBER UNOBTAINABLE

30. ROUTING TONE OR CALL-IN-PROGRESS TONE

31. RINGING TONE
As the ringing current is transmitted to the called subscribe, the control equipment sends out a ringing tone to the calling subscriber