Telephony9-1 Chapter 9 Telephony Communication Networks P. Demeester.

Telephony 9-1

Chapter 9Telephony

Communication NetworksP. Demeester

Telephony 9-2

Chapter 9 outline

9.1 Introduction

9.2 Analog Telephony

9.3 Digital Telephony

References

Table of Contents

Telephony 9-3

Introduction

EVOLUTION in the TELEPHONE NETWORK : basic service still telephony analog ==> digital transmission/switching in core analog ==> digital transmission in access (limited) advanced control and signalling introduction of optical fiber in core service integration (ISDN)

• PSTN• POTS• IDN• ISDN

Telephony 9-4

Analog Telephony

9.1 Introduction

9.2 Analog Telephony9.2.1 Architecture

9.2.2 Transmission

9.2.3 Switching

9.2.4 Control

9.3 Digital TelephonyReferencesTable of Contents

Telephony 9-5

General Architecture

LEX

LEX

LEX

TEX

TEX

TEX TEX

term

inals te

rmin

als

transmissionlinks

LEX

twisted pair

corenetwork(mesh)

accessnetwork

(star)

accessnetwork

(star)

localnetwork

localnetwork

Telephony 9-6

Photo of the first electric telephone (circa March 10, 1876). Note: the transmitter on the left consisted of a small container of acid in which a wire moved up and down in response to the acoustic pattern of speech (sound waves).

INVENTION: March 10, 1876

transmitter receiver

produces varyingresistance

WATSON’S RECEIVER:

metallicdiaphragm

BELL’s TRANSMITTER:

EQUIVALENT ELECTRICAL CIRCUIT:

wire movesup and down

in acid

tunnel toconcentrate

sound

diaphragm movesup and down

Resistance acrossterminalsvaries with soundacid

Key Feature: variable resistance transmitter

varyingresistance receiver

constant dcvoltage

The Telephone

Telephony 9-7

Microphone Earphone

Telephoneline

(pair of wires)

soundwave Recreatedsoundwave

DiaphragmDiaphragm

Electrical currentwave form

Carbongranules

battery

The Telephone

Telephony 9-8

Talk

Dial : pulses

Push : tones

Technology improved but the basic concepts remained the same

TRANSFER THE TELEPHONE NUMBER and TALK

The Telephone

Telephony 9-9

Cost

No. of exchanges (S)

Exchange cost

Junction line cost

Subscribers’ line cost

Total network cost

Optimum no.of exchanges

S

1 e

xch

an

ge

SS

SS

4 e

xch

an

ge

Mesh-Star Topology

Telephony 9-10

Analog Telephony

9.1 Introduction

9.2 Analog Telephony9.2.1 Architecture

9.2.2 Transmission

9.2.3 Switching

9.2.4 Control

9.3 Digital TelephonyReferencesTable of Contents

Telephony 9-11

LEX TEX

amplifier

Transmission over coax(FDM)

... ... ... ...

...

...

...

tootherexchanges

LEX TEX

amplifiers

Transmission over wires(SDM)

cable

FDM-multiplexers FDM-demultiplexers

Frequency Division Multiplexing (FDM)

Telephony 9-12

Bandwidth Consists of Bandwidth Usual Number ofname baseband channels

Channel (1 24 telegraph 4 kHz 0-4 kHz 1telephone channel) subchannel

120 Hz spacingGroup 12 channels 48 kHz 60-108 kHz 12Supergroup 5 groups 240 kHz 312-552 kHz 60Basic hypergroup 15 supergroups 3.7 MHz (3.6 MHz used) 312-4028 kHz 900(also called a ‘super (3 mastergroups)(240 kHz per supergroup (4 MHz line)mastergroup) with 8 kHz spacing

normally between each)Basic hypergroup 16 supergroups 4 MHz 60-4028 kHz 960(alternative)Mastergroup 5 supergroups 1.2 MHz 312-1548 kHz 300Hypergroup 9 mastergroups 12 MHz 312-12336 kHz 2700(12 MHz)Hypergroup 36 mastergroups 60 MHz 4404-59580 kHz 10800(60 MHz)

Frequency Division Multiplexing (FDM)

Telephony 9-13

Analog Telephony

9.1 Introduction

9.2 Analog Telephony9.2.1 Architecture

9.2.2 Transmission

9.2.3 Switching

9.2.4 Control

9.3 Digital TelephonyReferencesTable of Contents

Telephony 9-14

frequency

division

multiplexing

Circuit Switching

LEX

LEX

TEX

cabletwisted pair

flexibleconnection

circuit switched networkfixed bandwidthlow delayguarantee to finish call

space division

multiplexing

Telephony 9-15

Switch Evolution

Switch

• manual switches (patch panel)• electromechanical switches

- rotary switches- cross-bar switches (relay based)

• semiconductor switches

Telephony 9-16

Strowger switch

Single motion selector (Strowger)

electro-magnet

pivot

pawl

ratchetwheel

wiperarm

outlet 1outlet 2

outlet 3

outlet 4

outlet 5

outlet 6

outlet 7

outlet 8

outlet 9outlet 10

HandsetLifted

Digit 4Dialed

DialReleased

Digit 4Pulse Sequence

NextDigit

Dialed

Next DigitPulse Sequence

Loopdisconnect(10 pps)signaling

66mS

33mS

Minimum 400mSinter digit pause

0

123

4

5

6

78 9

Telephony 9-17

Multistage Switching

4 xx

5 xx

45 x

49 x

55 x

495

stage 1 stage 2 stage 3

Telephony 9-18

Multistage Switching

Principle of Strowger automatic switching

Telephony 9-19

Crossbar Switch

cross-bar switch

cable

twistedpair

cross-point : relay, transistor

more cables

Telephony 9-22

Concentration, distribution,expansion

1

100

901

1000

1

100

901

1000

100 x10

100 x10

100 x10

100 x10100

x100

1

10

91

100

1

10

91

100

expander

LOCALLINES

1

100 1000

1

1001000

11

30

.00

0 c

ross-p

oin

tsim

pro

ved

fu

ncti

on

ality

concentrator distributor

Telephony 9-23

Analog Telephony

9.1 Introduction

9.2 Analog Telephony9.2.1 Architecture

9.2.2 Transmission

9.2.3 Switching

9.2.4 Control

9.3 Digital TelephonyReferencesTable of Contents

Telephony 9-24

User and Control Plane

LEX

LEX LEX

TEX

TEX

LEX

TEX TEX

user

pla

ne

switch hardware

cont

rol p

lane

overlay network• U / C -plane• UNI / NNI• Call set-up• Signaling• Routing

UNI

NNI

UNI : LD, DMTF NNI : SS7

Telephony 9-25

Call Setuptim

e

calling party called partyexchange A exchange B

off-hook (seize)

dial tone

address digits

seize signal

proceed-to-send signal

address digits

ringing currentringing toneringing tone

answer signal (off-hook)answer signal (off-hook)

CONVERSATION

forward clear (on-hook) forward clear (on-hook) backward clear (on-hook)

Telephony 9-26

Signaling : UNI

Example Digit 2 will causetone pair 697Hz

and 1336Hz1209 1336 1447 1633

All frequencies shown in Hertz (Hz)

697

770

852

941

Low-freq. band

High-freq. band

calling party local exchange

• LD• DTMF

UNI

2 697

1336

Telephony 9-27

Routing : network hierarchy

Satellitelinks

Submarinecables

Internationalnetwork

Trunknetwork

Junction network

Local network

International gatewayexchange

National tandem exchanges

Regional tandem exchanges

Local tandem exchanges

Local exchangesCustomer lines

Note : today telecom operators are reducing the number of layers in the hierarchyby the use of consolidation (larger and fewer telephone switches)

• routing table set-up• call forwarding

Telephony 9-28

Digital Telephony

9.1 Introduction

9.2 Analog Telephony

9.3 Digital Telephony9.3.1 From A to D

9.3.2 Architecture

9.3.3 Transmission

9.3.4 Switching

ReferencesTable of Contents

Telephony 9-29

t

z(t)

analog/digitalconverter

TIME : sampling period T = 1/sampling frequency (=1/f)T T T

sampling in time +sampling in amplitude

AMPLITUDE :number of discrete levels(number ofbits used)

000

001

010

011

100

101

110

111

100 100 011 001 001 011 101 110 110 011 001 001 011 100

Analog to Digital Conversion

Telephony 9-30

Analog telephony : bandwidth 300 - 3400 Hz

Sampling frequency : f = 8 kHz (T=125 sec period)

Digitization : 8 bits (256 levels)

==> 8 bits at 8 kHz sampling gives : 64 kbit/s

or : 8 bits every 125 sec

Digital telephony : 64 kbit/sWhy sampling at 8 kHz ?

Analog to Digital Conversion

Telephony 9-31

How fast should we sample in order to be able to reproduce the original analog signal ?

if the bandwidth of the signal is B, we should sample at least with a

frequency f = 2B(Nyquist criterium)

Telephony: 8000 Hz sampling >2x3100 Hz bandwidth => OK

Sampling in time : Nyquist criterium

Telephony 9-32

Digital Telephony

9.1 Introduction

9.2 Analog Telephony

9.3 Digital Telephony9.3.1 From A to D

9.3.2 Architecture

9.3.3 Transmission

9.3.4 Switching

ReferencesTable of Contents

Telephony 9-33

General Architecture

LEX

LEX LEX

TEX

TEX

LEX

TEX TEX

accessnetwork

(star)

accessnetwork

(star)

corenetwork(mesh)

term

inals te

rmin

als

transmissionlinks

twisted pair

localnetwork

localnetwork

• local and core network : digital transmission and switching• access network : analog transmission• evolution from analog to digital network (1 single network!)• IDN : Integrated Digital Network

DIGITAL ANALOGANALOG

Telephony 9-34

Digital Telephony

9.1 Introduction

9.2 Analog Telephony

9.3 Digital Telephony9.3.1 From A to D

9.3.2 Architecture

9.3.3 Transmission

9.3.4 Switching

ReferencesTable of Contents

Telephony 9-35

Twisted pair

Coaxial cable

Optical fiber

twistlength

Outer sheathOuter conductor

Insulation

Innerconductor

Light at less thancritical angle isabsorbed in jacket

Angle ofincidence

Angle ofreflection

CoreJacket

Cladding

• separately insulated• twisted together• often “bundled” into cables

• outer conductor is braided shield• inner conductor is solid metal• separated by insulating material• covered by padding

• glass or plastic core• laser or light emitting diode• specially designed jacket• small size and weight

Guided Transmission Media:twisted pair, coax, fiber

Telephony 9-36

bit-TDM multiplexer

GATE A

GATE B

GATE C

GATE D

OUTPUT

4 bits

1 bit

TRIB A

TRIB B

TRIB C

TRIB D

1 bitA

B

C

D

gate

OUTPUTINPUT

4 bits

BIT INTERLEAVED

Time Division Multiplexing (TDM)

Telephony 9-37

BYTE INTERLEAVEDcompress and add

125 sec8 bits64 kbit/s

125 sec32 bits256 kbit/s

MUX

inputsignals

outputsignal

byte-TDMmultiplexer

1 byteA

B

C

D

4 bytes

frame frame

Time Division Multiplexing (TDM)

Telephony 9-38

CLOCK(synchronization)

BYTE

BIT

FAS

FRAME

Timing in TDM

Telephony 9-39

Europe USA Japan

bitrate multiplex bitrate multiplex bitrate multiplex

kbit/s factor kbit/s factor kbit/s factor

64 64 64

2048 30/31 1544 24 1544 24

8448 4 6312 4 6312 4

34368 4 44736 7 32064 5

139264 4 139264 3 97728 3

higher bitrates are proprietary

• from 64 kbit/s to 2.048 Mbit/s : byte interleaved• higher multiplex levels : bit interleaved

PDH: Plesiochronous Digital Hierarchy

Telephony 9-40

SynchronousTransport

Module(SDH)

STM - 1

STM - 4

STM - 16

STM - 64

Line RateMbit/s

155.52

622.08

2488.32

9953.28

SynchronousTransport

Signal(SONET)

STS - 1

STS - 3

STS - 12

STS - 48

STS - 192

SDH : Synchronous Digital Hierarchy (Europe)

51.84

SONET : Synchronous Optical Network (USA)

SDH: Synchronous Digital Hierarchy

Telephony 9-41

Digital Telephony

9.1 Introduction

9.2 Analog Telephony

9.3 Digital Telephony9.3.1 From A to D

9.3.2 Architecture

9.3.3 Transmission

9.3.4 Switching

ReferencesTable of Contents

Telephony 9-42

TIME-switching

SPACE-switching

64 kbit/s circuits

...

...

Mb/s

TRANSIT EXCHANGE (TEX)TEX

TEX

LEX

TEX

PDHtransmission

links

1

2

3

4

8

34

1

2

3

4

2

1

2

3

4

2

DEMUX (PDH)

...

1

2

3

4

8

34

1

2

3

4

2

1

2

3

4

2

2 1

2

3

4

8

34

2 1

2

3

4

1

.

.

.

N

INPUT OUTPUT

1

.

.

.

N

2 1

2

3

4

8

34

2 1

2

3

4

...

DIGITAL SWITCH BLOCK MUX (PDH)

e.g.: TS8 from input (2, 3, 15)

to

TS20 from output (N, 1, 3)

34 Mb/sport

8 Mb/sport

2 Mb/sport

Concept

Telephony 9-43

3

3

3

3

2

2

2

2

1

1

1

1

1 1 1 12 2 2 23 3 3 3

INLETS

OUTLETS

Space Switching

Telephony 9-44

TSITime Slot Interchange

1234frame

1234frame

1234frame

1234frame

1234

1234TSI

TS1

TS2

TS3

TS4

Time Switching

Telephony 9-45

LEX

TEX

LEX

8 bit125 sec

frame32 bit

125 sec

Switch &Multiplex

circuit : a timeslot (8 bits) in every frame (125 sec)

is allocated between two phones during a callexchange : multiplex calls, switch calls

Summary

Telephony 9-46

Connection 1 :A2/TS10 -> B1/TS20

time switches

space switches

TSI

TSI

TSI

A1

A2

A3

B1

B2

B3

Connection 2 :A2/TS11 -> B2/TS20

TS20TS10TS20TS11 ?

Time-Space Switching

Telephony 9-47

Connection 1 :A2/TS10 -> B1/TS20

time switches

space switches

TSI

TSI

TSI

A1

A2

A3

B1

B2

B3

Connection 2 :A2/TS11 -> B2/TS20

TS14TS10TS15TS11

TSI

TSI

TSI

TS20TS15

TS20TS14

time switches

Time-Space-Time Switching

Telephony 9-48

# Switches installed perYear

1950 1960 1970 1980 1990 2000 2010 2020

Panel

Step-by-step

Crossbar

AnalogSPC

DigitalSPC

Broadband(electronic)

Broadband(photonic)

SPC = Stored Program Control

Switch technology over the years for a typical industrialized country

Evolution

Telephony 9-49

1980 84 88 92 96 2000 Year

Percentageof Total

Access Linesin US

100

90

80

70

60

50

40

30

20

10

0

Analog SPC

Digital SPC

Electro-mechanical

0 3 105 1 7 2 0

16

2319

363338

424852

5859 6056

5044

62

80

9297

99

Evolution

Telephony 9-50

References

“Networks and Telecommunications, Design and Operation” by Martin P. Clark (1997,Second Edition, John Wiley & Sons Ltd., ISBN 0-471-97346-7)

“Telecommunications switching, traffic and networks”, by J.E. Flood (1994, Prentice Hall, ISBN-0-13-033309-3)

“SPC Digital Telephone Exchanges”, F.J. Redmill & A.R. Valdar, Peter Peregrinus Ltd, 1990, ISBN 0 86341 298 x

“Integrated Digital Networks”, L.S. Lawton, Sigma Press, 1993, ISBN 1-85058-181-9

Telephony 9-51

Table of Contents

9.1 Introduction 2

9.2 Analog Telephony

9.2.1 Architecture 4

9.2.2 Transmission 10

9.2.3 Switching 13

9.2.4 Control 23

9.3 Digital Telephony

9.3.1 From A to D 28

9.3.2 Architecture 32

9.3.3 Transmission 34

9.3.4 Switching 41References 50Table of Contents 51