Transcript Lecture 1 - IT, Sligo

Introduction to
Telecommunications
• Lecture 1
• Paul Flynn
1
The Public Switch Telephone Network
(PSTN)
Composed of the following major network elements:
switches
trunks
lines
station equipment (e.g. telephone sets, MODEMs, FAX machines, …)
transmission equipment (e.g. repeaters, multiplexers, DCS)
network signaling and control (e.g. SS7 and IN)
SS7 & IN
switch
switch
PBX
repeater
switch
MODEM
PC
2
Telephony Equipment
• Telephone set
• PBX (Private Branch Exchange)
Advanced features and call routing
10s to 100s of telephone sets
• Telephone Exchange
3
Basic Call Progress: On-Hook
Telephone
Exchange
Local Loop
2 wires
Local
Loop
-48 DC Voltage
DC Open Circuit
No Current Flow
4
Basic Call Progress: Off-Hook
Off-Hook
Closed
Circuit
Telephone
Exchange
DC Current
Dial Tone
Local
Loop
Local
Loop
5
Basic Call Progress: Dialing
Off-Hook
Closed
Circuit Dialed Digits
Pulses or
Tones
Telephone
Exchange
DC Current
Local
Loop
6
Basic Call Progress: Switching
Off-Hook
Closed
Circuit
Telephone
Exchange
DC Current
Local
Loop
Address
to
Port
Translation
Local
Loop
7
Basic Call Progress: Ringing
Off-Hook
Closed
Circuit
Ring Back
Tone
DC Current
Local
Loop
Telephone
Exchange
DC Open Cct.
Ringing Tone
Local
Loop
8
Basic Call Progress: Talking
Off-Hook
Closed
Circuit
Telephone
Exchange
Voice Energy
DC Current
Voice Energy
DC Current
Local
Loop
Local
Loop
9
Analog Telephony—Signaling
• Supervisory
• Addressing
• Call progress
10
Off-Hook Signaling
• Loop Start (almost all telephones)
Seizure is detected when current flows
through local loop, due to off-hook
11
Analog Telephony—
Supervisory Signaling
• Loop start
Current flow
sensed
Switch
Switch
12
Loop Start
Station
PBX or Central Office
Loop
(Local or Station)
Switch
DC Current
Ringing
+
–
Switch
+
–
Switch
+
–
AC
13
Signaling and Addressing
Dial Pulse
DTMF
Analog Transmission
“In-Band” Signaling
0–9, *, # (12 Digits)
ISDN
Digital Transmission
“Out-of-Band”
Message-Based
Signaling
14
Pulse Dialing
Off-Hook
Dialing
Inter-Digit Next Digit
Make
(Circuit Closed)
Break
(Circuit Open)
700 ms
US:60/40 Break/Make
Pulse Period
(100 ms)
15
Tone Dialing
Dual Tone Multifrequency (DTMF)
1209
1336
1477
1633
697
1
2
3
A
770
4
5
6
B
852
7
8
9
C
941
*
0
#
D
Timing:
60 ms Break
40 ms Make
16
Network Call Progress Tones
Tone
Frequency (Hz)
On Time
Off Time
Dial
350 + 440
Continuous
Busy
480 + 620
0.5
O.5
Ringback, Normal
440 + 480
2
4
Ringback, PBX
440 + 480
1
3
Congestion (Toll)
480 + 620
0.2
0.3
Reorder (local)
480 + 620
0.3
0.2
Receiver Off-hook
1400 + 2060 + 2450 +2600 0.1
0.1
No Such Number
200 to 400
Continuous, Freq. Mod 1Hz
17
Voice Channel Bandwidth
Voice Channel
Output
Voltage
or
Energy
Voice Signal
.2
1
Tone Dialing
Signals
2
3
4
Frequency
(K-Hertz)
Systems Control
Signals
18
Local Access Network
Feeder Route Boundary
Telephone
Exchange
40,000 to
50,000 Lines
Serving
Area
Boundary
19
Summary
• Analog voice technology dates
back to the 1900’s
• Information exchange based on
voltage, current flow, grounding, etc.
20
Digital Telephony
Digital Trunking
Exchange
Exchange
Analog Loop
POTS
Digital Network
Exchange
L.E.
Digital Loop Digital Network
ISDN
Switch
21
Digital Telephony
Pulse Code Modulation—Nyquist Theorem
Voice Bandwidth =
300 Hz to 3400 Hz
Analog Audio Source
Codec Technique
Sampling Stage
= Sample
8 kHz (8,000 Samples/Sec)
22
Pulse Code Modulation—
Analog to Digital Conversion
A—Law (Europe)
Quantizing Noise
100100111011001
Stage 1
µ—Law (USA–Japan)
Quantizing Stage
23
Digital Telephony Summary
• Analog telephony emulation
Voice encoding
Limited signaling
Loop consolidation
24
Voice Coding and Compression
• Speech coding schemes
• Digitizing voice
• Voice compression
25
Voice Compression
Technologies
Unacceptable
Business
Quality
Toll
Quality
*
64
PCM (G.711)
(Cellular)
Bandwidth
(Kbps)
*
32
ADPCM 32 (G.726)
*
24
16
8
0
ADPCM 24 (G.726)
*
ADPCM 16 (G.726)
*
LPC 4.8
*
LDCELP 16 (G.728)
*
CS-ACELP 8 (G.729)
Quality
26
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 method
CODEC
PCM
= DS-0
64 Kbps
27
Encoding
Quantizing
Sampling
Filtering
Waveform Coders
Waveform
ENCODER
1110010010010110
Waveform
DECODER
28
Voice Compression
• Objective: reduce bandwidth
consumption
Compression algorithms are optimized for voice
Unlike data compression: these are “loose”
• Drawbacks/tradeoffs
Quantization distortion
Tandem switching degradation
Delay (echo)
29
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
30
Voice Activity Detection
- 31 dbm
B/W Saved
Voice
Activity
(Power
Level)
Hang Timer
No Voice
Traffic Sent
SID Buffer
SID
- 54 dbm
Pink Noise
Voice “Spurt”
Silence
Voice “Spurt”
Time
31
Bandwidth Requirements
Voice Band Traffic
Encoding/
Compression
G.711 PCM
A-Law/u-Law
G.726 ADPCM
Result
Bit Rate
64 kbps (DS0)
16, 24, 32, 40 kbps
G.729 CS-ACELP
8 kbps
G.728 LD-CELP
16 kbps
G.723.1 CELP
6.3/5.3 kbps
Variable
32
Voice Quality
Anything Above an MOS of 4.0 Is “Toll” Quality
Compression Method
MOS Score
Delay
(msec)
64K PCM (G.711)
4.4
0.75
32K ADPCM (G.726)
4.2
1
16K LD-CELP (G.728)
4.2
3–5
8K CS-ACELP (G.729)
4.2
15
8K CS-ACELP (G.729a)
3.6
15
33
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
34
Voice Transport and Delay
Cumulative Transmission Path Delay
CB Zone
Satellite Quality
Fax Relay, Broadcast
High Quality
0
100
200
300
400
500
600
700
800
Time (msec)
Delay Target
35
The Public Switch Telephone Network
(PSTN)
Composed of the following major network elements:

switches

trunks

lines

station equipment (e.g. telephone sets, MODEMs, FAX machines, …)

transmission equipment (e.g. repeaters, multiplexers, DCS)

network signaling and control (e.g. SS7 and IN)
SS7 & IN
switch
switch
PBX
repeater
switch
MODEM
PC
36
Structure of the tel. network
Telephone networks
Fiber to the curb
(FTTC)
Telephone networks
European Numbering Plan


defines format for dialed numbers in Europe
As of 1/95
00 + 353 + 71 -
91 -
55363
Station number
Exchange code
Area code (geographic region)
International Country Code
International preliminary code
(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?
40
Network Architecture
• ISDN is an access specification
to a network
Common Channel
Signalling Network and
Database
ISDN
PBX
PRA
Telco
Circuit Switched Services
Switch
Telco
Switch
BRA
NT1
Dedicated Circuit Services
Public Packet
Network
41
Public ISDN and SS7
Signaling
Network
BRI
PBX1
PRI
DSS1
BRI
Switch
Transmission
Network
Switch
Signaling System 7
PRI
PBX2
DSS1
DSS1 is a Public ISDN Protocol
42
ISDN and SS7 “The Bridge
Between the Islands”
Voice Transmission
STP
Exchange
SSP
Exchange
SSP
SS7
SCP
Signaling Network
Voice
Transmission
STP
STP
Voice
and
ISDN—
Signaling
PRI
STP
Exchange
STP
PBX1
SSP
STP
SCP
43
Convergence
44