CROSSBAR SWITCHING ELC 524 E Monday 20 th

CROSS-BAR SWITCHING ELC 524 E 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 1 XB 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

3 X 3 CROSSBAR SWITCH(1)

3 X 3 CROSSBAR SWITCH(2)

3 X 3 CROSSBAR SWITCH(3)

3 X 3 CROSSBAR SWITCH(4)

6 X 6 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 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 64 SW-XBAR 16 256 4, 096 128 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 = 2 NK • 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 = N 2(K+L) • N = Number Subscriber OGT 1 • 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 REG 1 - N Subscriber Lines IOT 1 - N ICT 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