telephony9-1 chapter 9 telephony communication networks p. demeester
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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 9-19
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 9-39
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 9-44
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
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