Introduction to Telephony

1
Introduction to Telephony
2
Agenda

• Basic Analog Telephony
• Basic Digital Telephony
• Consolidated Transport Networking

3
Telephony Equipment

• Telephone set
• Key system
• Optimizes use of telephone sets to lines
• Mechanical to electronic
• 2 to 10 sets typically
• PBX (Private Branch Exchange)
• Advanced features and call routing
• 10s to 100s of telephone sets
• Central office switch

4
Analog TelephonyPOTS Basics
Tip
Ring
Sleeve
5
Basic Call Progress On-Hook
Telephone Switch
Local Loop
Local Loop
-48 DC Voltage DC Open Circuit No Current Flow
6
Basic Call Progress Off-Hook
Off-Hook Closed Circuit
Telephone Switch
DC Current Dial Tone
Local Loop
Local Loop
7
Basic Call Progress Dialing
Off-Hook Closed Circuit
Telephone Switch
Dialed Digits Pulses or Tones
DC Current
Local Loop
8
Basic Call Progress Switching
Off-Hook Closed Circuit
Telephone Switch
Address to Port Translation
DC Current
Local Loop
Local Loop
9
Basic Call Progress Ringing
Off-Hook Closed Circuit
Telephone Switch
Ring BackTone DC Current
DC Open Cct. Ringing Tone
Local Loop
Local Loop
10
Basic Call Progress Talking
Off-Hook Closed Circuit
Telephone Switch
Voice Energy DC Current
Voice Energy DC Current
Local Loop
Local Loop
11
Analog TelephonySignaling

• Supervisory
• Addressing
• Call progress

12
Off-Hook Signaling

• Loop Start (almost all telephones)
• Seizure is detected when current flows through
  local loop, due to off-hook
• Ground Start (PBXs)
• Seizure is detected when one wire is grounded
• Seizure can be initiated in both directions

13
Analog Telephony Supervisory Signaling

• Loop start
• Current flow sensed

• Ground start
• Momentary ground ring lead

Switch
Switch
14
Loop Start
Station
PBX or Central Office
Loop (Local or Station)

Switch


DC Current
Switch

AC
Ringing

Switch

15
EM Signaling

• PBXs, switches
• Separate signaling leads for each direction
• E-Lead (inbound direction)
• M-Lead (outbound direction)
• Allows independent signaling

State On-Hook Off-Hook
E-Lead Open Ground
M-Lead Ground Battery Voltage
16
Signaling and Addressing
Dial Pulse
DTMF
ISDN
Analog Transmission In-Band Signaling 09, ,
(12 Digits)
Digital Transmission Out-of-Band Message-Based S
ignaling
17
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)
18
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
19
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
20
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
21
Local Access Network
Feeder Route Boundary
Central Office
40,000 to 50,000 Lines
Serving Area Boundary
22
Switching Systems

• Manual controlSwitch/cord boards

Off-Hook Indicator
Tip Ring
Patch Cord Pairs
Manual Ring
23
PSTN Network Hierarchy
1
1
1
Class Name 1 Regional Center 2 Sectional
Center 3 Primary Center 4C Toll Center 4P Toll
Point 4X Interm. Point 5 End Office 5R EO w/
RSU R Remote Sw. Unit
3
4C
5
2
4P
4P
3
4C
5
5
4X
5R
4P
4C
5
5
4X
5R
R
24
Types of Voice Circuits
Serving Area 415-NXX-XXX
Serving Area 510-NXX-XXX
Class 5
Class 5
415-577-3800
415-655-1400
OPX Off-Premises Ext.
FX Foreign Exchange
415-577-3801
ARD Auto Ring Down
25
Echo in Voice Networks
Listener
Talker
Delay
Talker Echo
Listener Echo
26
Normal Signal Flow
Receive Direction
Central Office
2-Wire Local Loop
2w-4w Hybrid
Transmit Direction

• 2- to 4-wire hybrid combines receive and transmit
  signals over the same pair
• 2-wire impedance must match 4-wire impedance

27
How Does Echo Happen?

• Echo is due to a reflection

Central Office
Receive Direction
2-Wire Local Loop
2w-4w Hybrid
Rx and Tx superimposed
Transmit Direction
Impedance Mismatch at the 2w-4w Hybrid Is the
Most Common Reason for Echo
28
Echo Is Always Present

• Echo as a problem is a function of the echo
  delay, and the magnitude of the echo

Echo Is Unnoticeable
(dB) Echo Path Loss
Echo Is a Problem
Echo Path Delay (ms)
29
Ways to Defeat Echo

• Increase the loss in the echo path
• Can often be the solution
• Disadvantage Static setting, reduces the signal
  strength of the speaker
• Echo suppresser
• Acts like a noise gate, effectively making
  communications half-duplex

30
Echo Canceller

• Most effective means for removing echo

Central Office
E/C

Echo Canceller Block Diagram
Adaptive Filter
31
Summary

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

32
Agenda

• Basic Analog Telephony
• Basic Digital Telephony
• Consolidated Transport Networking

33
Digital Telephony
Digital Trunking
Switch
Switch
Analog Loop
Digital Network
Switch
POTS
CB
Digital Loop Digital Network
Switch
ISDN
34
Digital Telephony
Pulse Code ModulationNyquist Theorem
Voice Bandwidth 300 Hz to 3400 Hz
Sampling Stage
Analog Audio Source
Codec Technique
35
Pulse Code ModulationAnalog to Digital
Conversion
ALaw (Europe)
Quantizing Noise
100100111011001
Stage 1
Quantizing Stage
36
Digital TelephonyT1 and E1/J1
T1 ITU-T G.733
E1/J1 ITU-T G.732
Sampling Frequency
8 kHz
8 kHz
Channel Bit Rate
DS064 kbps
DS064 kbps
Time Slots per Frame
24
32
Channels per Frame
24
30
Bits per Frame
24 x 8 1 193
32 x 8 256
Framing
D4/Super Frame (12) Extended Super Frame (24)
E1 Multiframe (16) J1 CRV in Bit 1 of frame
Framing Indicator
193rd Bit of Frame
2.048 kbps Word of 7 Bits in the 0 Channel of
Odd Frames
System Bit Rate
8,000 x 193 1.544 Mbps
8,000 x 256 2.048 Mbps
Signaling
E1 CCS in TS 16 CAS in TS 162 Ch Every Other
Frame J1 TS0
Robbed Bit Channel Associated
Signaling D4/Super Frame Extended Super
Frame LSB/Channel LSB/Channel Frame 6 and
12 Frames 6, 12, 18, 24
37
DS1 Framing Format
193rd Bit of each frame used for frame
synchronization. D4 Framing is 12 frames D4
framing pattern is 100011011100 ESF is 24
frames, with framing, CRC and an FDL channel ESF
Framing pattern is 001011, in frames 4, 8, 12,
16, 20 and 24 Channel Associated Signaling robs
the LSB of every byte in frames 6, 12, 18 and 24
for ABCD bits Common Channel Signaling (ISDN)
uses TS 24
24 Frames per Extended SuperFrame
24 Time Slots125m sec
38
Extended Super-Frame Format
S Bits
Bit Use in Each Channel Time Slot
SignalingBit Use Options
FrameNumber
Fe
DL
BC
Traffic
Signaling
T
2
4
16
1

m

2


C1
3

m

4
0


5

m

6


C2
Bits 17
Bit 8
A
A
A

7

m

8
0


9

m

10


C3
11

m

B
12
1


Bits 17
Bit 8
A
B

13

m

14


C4
15

m

16
0


17

m

18


C5
Bits 17
Bit 8
A
A
C

19

m

20
1


21

m

22


C6
23

m

24
1


Bits 17
Bit 8
A
B
D

39
E1 Frame Format
16th Time Slot Contains Multiframe Alignment
Signal
ABCD Signaling Bits for Time Slots 1 and 17
Time Slot 0 Synchronization 0011011 Bits 2 to 8
16 Frames per Multiframe
ABCD Signaling Bits for Time Slots 15 and 31
32 Time Slots125usec
40
Digital Signaling Schemes
Channel Associated Signaling
Extended Super Frame
Bit Frame A 6th B 12th C
18th D 24th
Audio Address Signaling (DTMF)
Supervision On/Off Hook
Address Signaling (Dial Pulse)
41
Digital Signaling Schemes
Common Channel Signaling
E-1
Time Slot 16
Time Slot 0
Supervision On/Off Hook
Address Signaling (Dial Pulse)
Audio Address Signaling (DTMF)
42
Digital TelephonySynchronization

• Bit synchronization
• Primary reference source
• Ones density (except for J1/CMI)
• Time slot synchronization
• Bits/byte/channel
• Frame alignment
• Basic rule
• 193rd bit pattern

43
Digital Telephony Synchronization
One Multiframe (ESF)
3 ms
12
1
24
1 Frame, 125us, 193bits 24 Time Slots
1
24
12
1 Channel Time Slot, 5.18us
648ns
44
SynchronizationTraditional Network Clocking
Strata
Master Clock
Stratum
1
.00001ppm
Timing
Toll Office
Timing
Timing
One per LATA
2
Timing
End Office
End Office
Bits Distribution
DCS
3
PBX
PBX
4
45
Digital TelephonyAnalog Emulation and Pair Gain

• Backbone to largest interoperable network in the
  world
• Signaling information exchange based on 30 year
  old concepts
• Twiddling bits based on 100-year old signaling

46
Digital Telephony Summary

• Analog telephony emulation
• Voice encoding
• Limited signaling
• Loop consolidation

47
Agenda

• Basic Analog Telephony
• Basic Digital Telephony
• Consolidated Transport Networking

48
Consolidated Transport Networking
Consolidated Transport Networking
CALL PRO CESSIN G
Frame, Packet, Cell,CES, DS0
Remote/Branch Access
Gateway/Integrated Switching
Cell, CES
Trunking
Gateway
Campus/Desktop
Packet
49
Consolidated Transport Network Solutions

• PBX trunking
• PBX trunk pathing
• Intelligent voice network switching
• Branch/remote office access
• Virtual switch access
• Tie line and OPX transport
• Alternate packet routes

50
PBX Trunk Pathing
PSTN
PBX2
PBX2
PSTN
PSTN
PBX1
PBX4
CES/IWF
PVCs
PBX4
CES/IWF
CES/IWF
51
Network SynchronizationAdaptive Clocking
Transmit Clock
Outbound Frames
In-Bound Cells
Reassembly FIFO Queue
PBX1
PBX2
ATM Network
IWF 1
IWF 2
52
Network SynchronizationSynchronous Residual
Time Stamp
Transmit Clock
PBX1
PBX2
ATM Network
Receive Clock
IWF 1
IWF 2
53
Network SynchronizationSynchronous Clocking
Traceable to a Single Reference Source
PRS
PBX1
PBX2
ATM Network
IWF 1
IWF 2
54
PBX Trunk Pathing
PSTN
PBX2
PBX2
PSTN
PSTN
PBX1
PBX4
Network Synchronization
PBX2
PSTN
PSTN
PVCs
PBX1
PBX4
CES/IWF
PBX3
55
PBX Trunking
PBX Trunk PathingConsiderations

• N2 connections
• Tandem hops dependent on topology
• Dedicated point-to-point circuits
• Point-to-point signaling
• Platform availability

56
PBX Trunking Intelligent Voice Switching
PSTN
PBX2
PBX2
PSTN
PSTN
PBX1
PBX4
PBX2
PBX1
PBX4
Dynamic VCs
VNS

• PBX signaling
• DPNSS
• ETSI-QSIG
• ISO-QSIG

PBX3
57
PBX TrunkingIntelligent Voice Network Switching

• Efficient trunk groups
• Efficient WAN utilization
• PBX to network signaling
• Tandem switch replacement
• Dynamic setup of virtual circuits
• Compression
• Voice activity detection

58
Consolidated TransportBranch/Remote Office
Access

• Explosive branch office data networking
• Similar voice and data traffic patterns
• Technology advancements

59
Satellite AccessConsolidated Transport
PBX Trunk Network
PBX4
PBX1
Access WAN
H-PBX1
H-PBX2
60
Branch/Remote Office Virtual Switch Access
Access WAN
KTS/ PBX
61
Branch/Remote Office AccessTie Line and OPX
Transport
KTS/ PBX
Access WAN
KTS/ PBX
KTS/ PBX
62
Consolidated TransportAlternate Routes
Access WAN
PBX
PBX
Backbone Network
PSTN
63
Fixed vs. Usage Billed Service
CTN Bandwidth
Tie Trunk
DDD
A Plan
Billing Cycle Cost ()
Z
5
10
15
20
25
30
35
Usage/Billing Cycle (Hours/Month)
64
Consolidated Transport - FAX Services
PBX Trunk Network
PSTN
Internet
F
Access WAN
F
F
F
F
H-PBX2
H-PBX1
65
Agenda

• Basic Analog Telephony
• Basic Digital Telephony
• Consolidated Transport Networking

66
Thank You!
QA
67
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