1 introduction to telecommunications lecture 1 paul flynn
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1
Introduction to Telecommunications
� Lecture 1
� Paul Flynn
2
The Public Switch Telephone Network(PSTN)
Composed of the following major network elements:
lines
trunks
repeater
transmission equipment (e.g. repeaters, multiplexers, DCS)
switch switch
switch
switches
PBX
SS7 & IN
network signaling and control (e.g. SS7 and IN)
PCMODEM
station equipment (e.g. telephone sets, MODEMs, FAX machines, …)
3
Telephony Equipment
� Telephone set
� PBX (Private Branch Exchange)Advanced features and call routing
10s to 100s of telephone sets
� Telephone Exchange
4
Basic Call Progress: On-Hook
TelephoneExchange
Local Loop2 wires
LocalLoop
-48 DC Voltage-48 DC VoltageDC Open CircuitDC Open CircuitNo Current FlowNo Current Flow
5
TelephoneExchange
LocalLoop
LocalLoop
Basic Call Progress: Off-Hook
DC CurrentDC CurrentDial ToneDial Tone
Off-HookOff-HookClosed Closed CircuitCircuit
6
Basic Call Progress: Dialing
Dialed DigitsDialed DigitsPulses or Pulses or
TonesTones
DC CurrentDC Current
TelephoneExchange
LocalLoop
Off-HookOff-HookClosed Closed CircuitCircuit
7
DC CurrentDC Current
TelephoneExchange
LocalLoop
Basic Call Progress: Switching
AddressAddresstoto
PortPortTranslationTranslationLocal
Loop
Off-HookOff-HookClosed Closed CircuitCircuit
8
Basic Call Progress: Ringing
Ring BackRing BackToneTone
DC CurrentDC CurrentDC Open Cct.DC Open Cct.Ringing ToneRinging Tone
TelephoneExchange
LocalLoop
LocalLoop
Off-HookOff-HookClosed Closed CircuitCircuit
9
Basic Call Progress: Talking
Voice EnergyVoice EnergyDC CurrentDC Current
Voice EnergyVoice EnergyDC CurrentDC Current
TelephoneExchange
LocalLoop
LocalLoop
Off-HookOff-HookClosed Closed CircuitCircuit
10
Analog Telephony—Signaling
� Supervisory
� Addressing
� Call progress
11
Off-Hook Signaling
� Loop Start (almost all telephones)
Seizure is detected when current flows through local loop, due to off-hook
12
Analog Telephony— Supervisory Signaling
� Loop startCurrent flow sensed
SwitchSwitch SwitchSwitch
13
Loop StartLoop
(Local or Station)
+–
+–
AC
+–
Station PBX or Central Office
DC Current
Ringing
SwitchSwitch
SwitchSwitch
SwitchSwitch
14
Signaling and Addressing
Analog Transmission“In-Band” Signaling0–9, *, # (12 Digits)
Digital Transmission“Out-of-Band”
Message-BasedSignaling
ISDNDial Pulse DTMF
15
Pulse Dialing
Make(Circuit Closed)
Break(Circuit Open)
Off-Hook Dialing Inter-Digit Next Digit
Pulse Period(100 ms)
US:60/40 Break/Make
700 ms
16
Tone Dialing
1 2 3 A
4 5 6 B
7 8 9 C
* 0 # D
Dual Tone Multifrequency (DTMF)
1209 1336 1477 1633
697
770
852
941
Timing:Timing:60 ms Break60 ms Break40 ms Make40 ms Make
17
Network Call Progress Tones
ToneTone Frequency (Hz)Frequency (Hz) On TimeOn Time Off TimeOff Time
DialDial
BusyBusy
Ringback, NormalRingback, Normal
Ringback, PBXRingback, PBX
Congestion (Toll)Congestion (Toll)
Reorder (local)Reorder (local)
Receiver Off-hookReceiver Off-hook
No Such NumberNo Such Number
350 + 440350 + 440
480 + 620480 + 620
440 + 480440 + 480
440 + 480440 + 480
480 + 620480 + 620
480 + 620480 + 620
1400 + 2060 + 2450 +26001400 + 2060 + 2450 +2600
200 to 400200 to 400
ContinuousContinuous
0.50.5 O.5O.5
22 44
11 33
0.20.2 0.30.3
0.30.3 0.20.2
0.10.1 0.10.1
Continuous, Freq. Mod 1HzContinuous, Freq. Mod 1Hz
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Voice Channel Bandwidth
OutputVoltage
orEnergy
Frequency(K-Hertz)
1 2 3 4.2
Voice SignalVoice Signal
Voice ChannelVoice Channel
Tone DialingSignals
Systems ControlSignals
19
Local Access Network
Telephone Exchange
Feeder Route Boundary
40,000 to 50,000 Lines
Serving AreaBoundary
20
Summary
� Analog voice technology dates back to the 1900’s
� Information exchange based on voltage, current flow, grounding, etc.
21
Digital Telephony
Digital Trunking
ExchangeExchangeExchangeExchange
Analog Loop Digital Network
POTSExchangeExchange
L.E.L.E.
Digital Loop Digital Network
ISDNSwitchSwitch
22
Digital Telephony
= Sample
8 kHz (8,000 Samples/Sec)Codec Technique
Sampling StageAnalog Audio Source
Pulse Code Modulation—Nyquist Theorem
Voice Bandwidth = Voice Bandwidth = 300 Hz to 3400 Hz300 Hz to 3400 Hz
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Pulse Code Modulation—Analog to Digital Conversion
Stage 1
Quantizing Stage
Quantizing Noise
100100111011001
A—Law (Europe)A—Law (Europe)A—Law (Europe)A—Law (Europe)
µ—Law (USA–Japan)µ—Law (USA–Japan)µ—Law (USA–Japan)µ—Law (USA–Japan)
24
Digital Telephony Summary
� Analog telephony emulation
Voice encoding
Limited signaling
Loop consolidation
25
Voice Coding and Compression
� Speech coding schemes
� Digitizing voice
� Voice compression
26
Voice Compression Technologies
Bandwidth(Kbps)
Quality
UnacceptableUnacceptable BusinessQuality
BusinessQuality
TollQuality
TollQuality
8
16
32
24
64
0
*PCM (G.711)
*PCM (G.711)
*ADPCM 32 (G.726)
*ADPCM 32 (G.726)
*ADPCM 24 (G.726)
*ADPCM 24 (G.726)
*ADPCM 16 (G.726)
*ADPCM 16 (G.726) *
LDCELP 16 (G.728)*
LDCELP 16 (G.728)
*CS-ACELP 8 (G.729)
*CS-ACELP 8 (G.729)*
LPC 4.8*
LPC 4.8
(Cellular)(Cellular)
27
Digitizing Voice: PCM Waveform Encoding� Nyquist Theorem: sample at twice the
highest frequency Voice frequency range: 300-3400 Hz
Sampling frequency = 8000/sec (every 125us)
Bit rate: (2 x 4 Khz) x 8 bits per sample
= 64,000 bits per second (DS-0)
� By far the most commonly used methodCODEC
PCM64 Kbps
= DS-0
28
Waveform Coders
Sam
pli
ng
Sam
pli
ng
Fil
teri
ng
Fil
teri
ng
En
cod
ing
En
cod
ing
Qu
anti
zin
gQ
uan
tizi
ng
1110010010010110
WaveformENCODER
WaveformDECODER
29
Voice Compression
� Objective: reduce bandwidth consumption
Compression algorithms are optimized for voice
Unlike data compression: these are “loose”
� Drawbacks/tradeoffsQuantization distortion
Tandem switching degradation
Delay (echo)
30
Digital Speech Interpolation (DSI)
� Voice Activity Detection (VAD)
� Removal of voice silence
� Examines voice for power, change of power, frequency and change of frequency
� All factors must indicate voice “fits into the window” before cells are constructed
� Automatically disabled for fax/modem
31
Voice Activity Detection
Voice “Spurt” Silence
Pink Noise
Time
Voice Activity(PowerLevel) SID Buffer SID
Hang Timer No Voice Traffic Sent
B/W Saved
- 54 dbm
- 31 dbm
Voice “Spurt”
32
Bandwidth Requirements
Voice Band Traffic
Encoding/Encoding/CompressionCompression
ResultResultBit RateBit Rate
G.711 PCMG.711 PCMA-Law/A-Law/uu-Law-Law
64 kbps (DS0)64 kbps (DS0)
G.726 ADPCMG.726 ADPCM 16, 24, 32, 40 kbps16, 24, 32, 40 kbps
G.729 CS-ACELPG.729 CS-ACELP 8 kbps8 kbps
G.728 LD-CELPG.728 LD-CELP 16 kbps16 kbps
G.723.1 CELPG.723.1 CELP 6.3/5.3 kbps6.3/5.3 kbpsVariableVariable
33
Voice Quality
Compression MethodCompression Method MOS ScoreMOS Score DelayDelay(msec)(msec)
64K PCM (G.711)64K PCM (G.711) 4.44.4 0.750.75
32K ADPCM (G.726)32K ADPCM (G.726) 4.24.2 11
16K LD-CELP (G.728)16K LD-CELP (G.728)
8K CS-ACELP (G.729)8K CS-ACELP (G.729) 4.24.2 1515
8K CS-ACELP (G.729a)8K CS-ACELP (G.729a) 1515
3–53–54.24.2
3.63.6
Anything Above an MOS of 4.0 Is “Toll” Quality
34
Voice Network Transport
� Voice Network Transport is typically TDM circuit-based:
T1/E1
DS3/E3
SONET (OC3, OC12, etc.)
� But can also be packet-based:ATM
Frame Relay
IP
35
Voice Transport and Delay
Time (msec)
0 100 200 300 400
CB ZoneCB ZoneCB ZoneCB Zone
Cumulative Transmission Path Delay
Satellite QualitySatellite QualitySatellite QualitySatellite Quality
Fax Relay, BroadcastFax Relay, BroadcastFax Relay, BroadcastFax Relay, BroadcastHigh QualityHigh QualityHigh QualityHigh Quality
Delay Target
500 600 700 800
36
The Public Switch Telephone Network(PSTN)
Composed of the following major network elements:
lines
trunks
repeater
transmission equipment (e.g. repeaters, multiplexers, DCS)
switch switch
switch
switches
PBX
SS7 & IN
network signaling and control (e.g. SS7 and IN)
PCMODEM
station equipment (e.g. telephone sets, MODEMs, FAX machines, …)
Structure of the tel. network
Telephone networks
Telephone networks
Fiber to the curb (FTTC)
40
European Numbering Plan defines format for dialed numbers in Europe As of 1/95
00 + 353 + 71 - 91 - 55363
(N digits are 2-9, X digits are 0-9)
international calls are initiated by dialing 00, followed by country and city code (if any)
phone number shortage crisis – Why?
International preliminary code
Station number
Exchange code
Area code (geographic region)
International Country Code
41
Network Architecture
� ISDN is an access specification to a network
ISDNPBX
PRANT1BRA
Common ChannelCommon ChannelSignalling Network andSignalling Network and
DatabaseDatabase
Circuit Switched Services
Dedicated Circuit Services
Public PacketPublic PacketNetworkNetwork
TelcoTelcoSwitchSwitch
TelcoTelcoSwitchSwitch
42
Public ISDN and SS7
TransmissionNetwork
PBXPBX22PBXPBX11
Signaling System 7DSS1 DSS1
SwitchSwitchSwitchSwitch
SignalingNetwork
BRI BRI
PRI PRI
DSS1 is a Public ISDN Protocol
43
ISDN and SS7 “The Bridge Between the Islands”
ExchangeExchange
Exchange
ISDN—PRI
SS7Signaling Network
Voice Transmission
Voice Transmission
PBX1
Voiceand
Signaling
SCP
SSPSSP
SSP
SCP
STP
STP
STP
STPSTP
STP
44
Convergence
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