Introduction to Telecommunications

1
Introduction to Telecommunications

• Lecture 1
• Paul Flynn

2
The Public Switch Telephone Network(PSTN)

• Composed of the following major network elements

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
Telephone Exchange
Local Loop 2 wires
Local Loop
-48 DC Voltage DC Open Circuit No Current Flow
5
Basic Call Progress Off-Hook
Off-Hook Closed Circuit
Telephone Exchange
DC Current Dial Tone
Local Loop
Local Loop
6
Basic Call Progress Dialing
Off-Hook Closed Circuit
Telephone Exchange
Dialed Digits Pulses or Tones
DC Current
Local Loop
7
Basic Call Progress Switching
Off-Hook Closed Circuit
Telephone Exchange
Address to Port Translation
DC Current
Local Loop
Local Loop
8
Basic Call Progress Ringing
Off-Hook Closed Circuit
Telephone Exchange
Ring BackTone DC Current
DC Open Cct. Ringing Tone
Local Loop
Local Loop
9
Basic Call Progress Talking
Off-Hook Closed Circuit
Telephone Exchange
Voice Energy DC Current
Voice Energy DC Current
Local Loop
Local Loop
10
Analog TelephonySignaling

• 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 start
• Current flow sensed

Switch
Switch
13
Loop Start
Station
PBX or Central Office
Loop (Local or Station)

Switch


DC Current
Switch

AC
Ringing

Switch

14
Signaling and Addressing
Dial Pulse
DTMF
ISDN
Analog Transmission In-Band Signaling 09, ,
(12 Digits)
Digital Transmission Out-of-Band Message-Based S
ignaling
15
Pulse Dialing
Off-Hook
Dialing
Inter-Digit
Next Digit
Make (Circuit Closed)
Break (Circuit Open)
700 ms
US60/40 Break/Make
Pulse Period (100 ms)
16
Tone Dialing
Dual Tone Multifrequency (DTMF)
1209
1336
1477
1633
697
1
2
3
A
Timing 60 ms Break 40 ms Make
4
5
6
B
770
852
7
8
9
C
941

0

D
17
Network Call Progress Tones
Tone
Frequency (Hz)
On Time
Off Time
Dial Busy Ringback, Normal Ringback,
PBX Congestion (Toll) Reorder (local) Receiver
Off-hook No Such Number
350 440 480 620 440 480 440 480 480
620 480 620 1400 2060 2450 2600 200 to 400
Continuous 0.5 O.5 2 4 1 3 0.2 0.3 0.3 0.2 0.
1 0.1 Continuous, Freq. Mod 1Hz
18
Voice Channel Bandwidth
Voice Channel
Output Voltage or Energy
Voice Signal
Frequency (K-Hertz)
1
2
3
4
.2
Tone Dialing Signals
Systems Control Signals
19
Local Access Network
Feeder Route Boundary
Telephone Exchange
40,000 to 50,000 Lines
Serving Area Boundary
20
Summary

• Analog voice technology dates back to the 1900s
• Information exchange based on voltage, current
  flow, grounding, etc.

21
Digital Telephony
Digital Trunking
Exchange
Exchange
Analog Loop
Digital Network
Exchange
POTS
L.E.
Digital Loop Digital Network
Switch
ISDN
22
Digital Telephony
Pulse Code ModulationNyquist Theorem
Voice Bandwidth 300 Hz to 3400 Hz
Sampling Stage
Analog Audio Source
Codec Technique
23
Pulse Code ModulationAnalog to Digital
Conversion
ALaw (Europe)
Quantizing Noise
100100111011001
Stage 1
Quantizing Stage
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
Unacceptable
Business Quality
Toll Quality
64
PCM (G.711)
(Cellular)
Bandwidth (Kbps)
32
ADPCM 32 (G.726)
24
ADPCM 24 (G.726)
16
ADPCM 16 (G.726)
LDCELP 16 (G.728)
8
CS-ACELP 8 (G.729)
LPC 4.8
0
Quality
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 method

CODEC
PCM 64 Kbps
DS-0
28
Waveform Coders
1110010010010110
Filtering
Sampling
Encoding
Quantizing
Waveform ENCODER
Waveform DECODER
29
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)

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
- 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
32
Bandwidth Requirements
Voice Band Traffic
Encoding/ Compression
Result Bit Rate
G.711 PCM A-Law/u-Law
64 kbps (DS0)
G.726 ADPCM
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
33
Voice Quality
Anything Above an MOS of 4.0 Is Toll Quality
Delay(msec)
Compression Method
MOS Score
64K PCM (G.711)
4.4
0.75
32K ADPCM (G.726)
4.2
1
16K LD-CELP (G.728)
35
4.2
8K CS-ACELP (G.729)
4.2
15
3.6
8K CS-ACELP (G.729a)
15
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
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
36
The Public Switch Telephone Network(PSTN)

• Composed of the following major network elements

37
Structure of the tel. network
Telephone networks
38
(No Transcript)
39
Fiber to the curb (FTTC)
Telephone networks
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
41
Network Architecture

• ISDN is an access specification to a network

Common Channel Signalling Network and Database
Telco Switch
PRA
Circuit Switched Services
Telco Switch
ISDN PBX
BRA
NT1
Dedicated Circuit Services
Public Packet Network
42
Public ISDN and SS7
SignalingNetwork
BRI
BRI
Transmission Network
Switch
Switch
PBX2
PBX1
PRI
PRI
Signaling System 7
DSS1
DSS1
DSS1 is a Public ISDN Protocol
43
ISDN and SS7 The Bridge Between the Islands
Voice Transmission
STP
Exchange
Exchange
SSP
SSP
SS7 Signaling Network
SCP
Voice and Signaling
Voice Transmission
ISDN PRI
STP
STP
STP
STP
Exchange
PBX1
SSP
SCP
STP
44
Convergence