CROSS-BAR SWITCHING

ELC 524E Monday, 20 th 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 - N 2 Number of Connections – N/2

COST -CAPACITY

Number of Subscribers 4 16 64 128 Switches 16 256 4,096 16,384 S/Capacity 2 8 32 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 64 128 SW-XBAR 16 256 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

A B C D E F G

BLOCKING CROSS-BAR (1)

P Q R P’ Q’ R’

A B C D E F G

BLOCKING CROSS-BAR (2)

P Q R R’ Q’ P’

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 •K = Max No. of Local Connections •L = Max No. of Outgoing Lines OGT1 OGT 2

TYPES OF X-BAR SWITCHES: MINI-SWITCH

TYPES OF X-BAR SWITCHES: REED SWITCH

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